yanpeng guo, huiqiao li,* and tianyou zhai*download.xuebalib.com/xuebalib.com.30274.pdfy. guo, prof....

REVIEW

1700007 (1 of 25) © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advmat.de

Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries

Yanpeng Guo, Huiqiao Li,* and Tianyou Zhai*

DOI: 10.1002/adma.201700007

reactions upon cycling. Whether layered LiCoO2, Li-rich or Ni-rich LiMO2 (M = Ni, Co, Mn, etc.), doped spinel LiMxMn2−xO4 (M = Ni, Cu, Cr, V, etc.) or olivine LiFePO4, none of them is able to achieve a capacity larger than 250 mA h g−1.[4] This unsat-isfying situation thus triggers the devel-opment of cathodes based on multi-ion reactions, such as S and O2 that possess an extremely high theoretical capacity of 1672 mA h g−1.[5]

It is worth mentioning that these lithium-free cathodes can be put into practical use only when paired with lithium-containing anodes.[6] From this viewpoint, metallic lithium itself can serve as the ideal anode for S and O2 cathodes due to its highest theoretical capacity (3860 mA h g−1), lowest density (0.59 g cm−3) and most negative elec-trochemical potential (−3.04 V).[5] Com-pared to present LIBs (e.g., 387 W h kg−1 in theory for commercialized graphite/LiCoO2 system), the utilization of metallic lithium as the anode further promotes

the energy density of lithium-metal batteries (LMBs), as shown in Figure 1. For instance, Li–O2 and Li–S battery sys-tems demonstrate exceptional high theoretical energy densities up to 3505 W h kg−1 and 2567 W h kg−1, respectively.[5] These lithium-metal battery systems show great potential to meet the rigid requirements of newly emerged industries and fully exploit the advantages of metallic lithium. However, directly using metallic lithium as the anode was once deemed as an insurmountable obstacle, especially in liquid organic electrolyte (LOE) systems.[7] Firstly, the heterogeneous deposition caused by large polarization and strong electric field tends to induce dendrite nucleation. The following unrestrained growth could result in terrible short circuit, fire, or explosion in the pre-sence of flammable LOEs. Secondly, the hyperactive metallic lithium could spontaneously react with the electrolytes, cathode materials, and resultants shuttled from the cathode. These irreversi ble reactions imply speedy loss of active materials and rapid increase in cell impedance, leading to fast capacity fading. Moreover, the infinite hostless volume changes within the lithium-metal anode upon cycling could cause severe lithium corrosion and complete anode pulverization, as well as large amount of dead-lithium formation.

Fortunately, various celebrated research groups in the bat-tery field have intensively explored the failure mechanism of lithium-metal anodes and put forward effective strategies

Lithium-metal batteries (LMBs), as one of the most promising next-genera-tion high-energy-density storage devices, are able to meet the rigid demands of new industries. However, the direct utilization of metallic lithium can induce harsh safety issues, inferior rate and cycle performance, or anode pulverization inside the cells. These drawbacks severely hinder the commer-cialization of LMBs. Here, an up-to-date review of the behavior of lithium ions upon deposition/dissolution, and the failure mechanisms of lithium-metal anodes is presented. It has been shown that the primary causes consist of the growth of lithium dendrites due to large polarization and a strong electric field at the vicinity of the anode, the hyperactivity of metallic lithium, and hostless infinite volume changes upon cycling. The recent advances in liquid organic electrolyte (LOE) systems through modulating the local current density, anion depletion, lithium flux, the anode–electrolyte interface, or the mechanical strength of the interlayers are highlighted. Concrete strategies including tailoring the anode structures, optimizing the electrolytes, building artificial anode–electrolyte interfaces, and functionalizing the protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future perspectives of introducing solid-state electrolytes to radically address safety issues are presented.

Lithium-Metal Batteries

Y. Guo, Prof. H. Li, Prof. T. ZhaiState Key Laboratory of Material Processing and Die & Mould TechnologySchool of Materials Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074, P. R. ChinaE-mail: [email protected]; [email protected]

1. Introduction

High-energy-density storage has already become an urgent issue on account of the rapid growth in new industries, such as high-end communication terminals, electric vehicles (EV), aerospace, large-scale energy storage stations, etc.[1] Prevailing “rocking-chair-based” lithium-ion batteries (LIBs) or sodium-ion batteries (NIBs) have once been regarded as suitable candidates in view of their long lifespan and fine safety.[2] Unfortunately, even though the energy density of insertion-type LIB systems has been optimized close to their theoretical value via modu-lating each component of the battery (electrode materials, sepa-rators, electrolytes, current collector (CC), etc.), it is still far below the expected energy level of, for example, EV diesels.[3] A major reason for this embarrassment lies in the severely lim-ited capacity of cathodes owing to their single-ion-intercalation

Adv. Mater. 2017, 1700007

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim1700007 (2 of 25)

www.advmat.dewww.advancedsciencenews.com

to address the aforementioned harsh issues in the past three years. The deposition behaviors of lithium ions, dendrite nucle-ation and growth mechanism, the effect of anode-electrolyte interface, etc., have been substantially investigated and further characterized by advanced techniques. Based on the date from Web of Science, more than 500 papers dealing with the above puzzles have been published from 2014 to 2016. More astound-ingly, an average of 15 articles have come out per month since 2016, indicating a roaring expansion in this field.[11] This research contributes a lot to the revival of the lithium anode for next-generation high-energy-density LMBs.

Here, a comprehensive review of recent advances that facili-tate the use of lithium-metal anodes is provided. The deposi-tion behaviors of lithium ions and failure mechanisms of lith-ium-metal anodes, plus the guiding principles are thoroughly reviewed. According to those mathematical, electrochemical, and thermodynamic models, it is accepted that lowering the cur-rent density, reducing anion depletion, smoothing the anode–electrolyte interface, reshaping the lithium-ion flux, as well as mechanically blocking the dendrites are effective to promote the safety or electrochemical performances of lithium-metal anodes. Recently developed strategies to control the behaviors of lithium-metal anodes, including tailoring anode structures, optimizing electrolytes, building artificial solid electrolyte inter-face (SEI) layers, and functionalizing protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future prospects of intro-ducing solid-state electrolytes to radically address the safety issues are given.

2. The Failure Mechanisms of Lithium-Metal Anodes

The direct utilization of metallic lithium as the anode is prone to neutralize LMBs, especially under LOE systems. This unsat-isfying condition has a close relationship to the uncontrollable deposition behavior of lithium ions, hyperactivity of metallic lithium, and infinite volume-change upon cycling. Concretely, battery failures rooted in lithium-metal anodes can be divided into three categories: i) catastrophic short-circuit induced by unrestrained dendrite growth; ii) inferior cycle-performance caused by continuous side-reactions toward metallic lithium and considerable dead-lithium formation; iii) complete anode pulver-ization and electrical disconnection evoked by infinite volume change. Here the detailed failure mechanisms are reviewed.

2.1. Dendrite Formation and Short Circuit

The behavior of lithium ions in LMBs is totally different from the intercalation/extraction behavior in LIBs. Typically, during charging, lithium ions get electrons from the external circuits and then directly deposit on the anode surface or beneath in the form of metallic-lithium particles. Similar to other metal ions like Zn2+ or Cu2+, of which the electrodeposition behaviors have been thoroughly investigated,[12] it has been confirmed that dendrite-like patterns will form on the top of the lithium anode if no modification is done to the system. To unravel the behavior of lithium deposition and evolution of the anode

morphology and interface, considerable models from different aspects have been put forward via calculations or advanced characterization techniques.

A fundamental mechanism to explain the dendrite nuclea-tion and growth has been proposed via in situ observations

Yanpeng Guo received her B.S. degree from Nanjing University of Aeronautics and Astronautics in 2015. She is now a Ph.D. candidate in the School of Materials Science and Engineering, Huazhong University of Science and Technology (HUST). Her research is focused on pro-moting lithium-metal anodes for high-energy batteries.

Huiqiao Li received her B.S. degree in chemistry from Zhengzhou University in 2003, and then received her Ph.D. degree in physical chemistry from Fudan University in 2008. Afterward, she worked as a postdoctoral fellow for 4 years at the Energy Technology Research Institute, National Institute of Advanced Industrial Science and

Technology (AIST), Japan. Currently, she is a full Professor at the School of Materials Science and Engineering, HUST. Her research interests include energy-storage materials and electrochemical power sources, such as lithium-ion bat-teries, sodium-ion batteries, and supercapacitors.

Tianyou Zhai received his B.S. degree in chemistry from Zhengzhou University in 2003, and his Ph.D. degree in physical chemistry from the Institute of Chemistry, Chinese Academy of Sciences (ICCAS) in 2008. Afterward, he joined the National Institute for Materials Science (NIMS) as a JSPS postdoctoral fellow, and then as an ICYS-MANA

researcher within NIMS. Currently, he is a Chief Professor in the School of Materials Science and Engineering, HUST. His research interests include the controlled synthesis and exploration of fundamental physical properties of inorganic functional nanomaterials, as well as their promising appli-cations in energy science, electronics, and optoelectronics.

Adv. Mater. 2017, 1700007



in symmetrical lithium/polymer cells. A simple ambipolar diffusion equation at the electrodes is adopted to detect the evo-lution of ionic concentrations, as follows:[13]

µµ µ( )

∂∂

=+

C

xx

J

eD( ) a

a Li+

(1)

where J is the effective electrode current density, D is the ambi-polar diffusion coefficient, e is the electronic charge, μa and µLi+ are the anion and Li+ mobilities. If dC/dx < 2C0/L (L and C0 refer to the inner electrode distance and initial concentration, respectively), the ionic concentration at the negative electrode maintains a steady state with constant concentration gradient and electrostatic potential value. In this case, lithium ions deposit smoothly. Once dC/dx > 2C0/L, as shown in Figure 2a, the ionic concentration at the electrode drops to zero and the potential will eventually diverge at a time called “Sand’s time” τ:

τ πµ µ

µ( )

=+

De C

J4

202

a Li2

a2

2+

(2)

µµ µ

≈ − =+

t t1a Lia

a Li

+

+

(3)

where ta and tLi+ represent the anionic and Li+ transference number, respectively. Clearly, dC/dx is in proportion to the effec-tive current density. In the high current density regime, anion and Li+ concentrations exhibit different behaviors, and thus lead to excessive positive charge at the negative electrode. This induces a large electric field and results in dendrite formation, which will

grow at the velocity of anion departure from the anode (ν = − μaE). Here, E is the electric field and τ refers to the time when lithium dendrites start to grow. Actually, this model has laid a solid foun-dation for future investigations and considerable impressive work has been done, inspired by this model. Grey’s group later used 7Li magnetic resonance imaging (MRI) to monitor the dendrite growth.[14] It was observed that the onset of dendrite growth at current densities higher than the critical value was in accordance with the model above. Bai et al. also developed novel capillary cells and sandwich cells to straightforwardly monitor the lithium-deposition behaviors.[15] It was shown that lithium deposition was a two-step process, as presented in Figure 2b (inset). An initial reaction-limited root-growth with mossy-like morphology is fol-lowed with a second dendrite-like tip-growth. Voltage responses of capillary cells at various deposition current densities demon-strates that higher current density could lead to an earlier start of dendrite formation. Therefore, it is highly challenging to obtain LMBs with decent rate performance. Besides, the starting time of dendrite nucleation is inversely proportional to the total depo-sition capacity. The certain threshold value is defined as “Sand’s capacity” (Csand = Jτsand). Above this critical value, dendrite-like morphology will form and penetrate through the nanoporous ceramic membrane. This result explains why the battery per-formance deteriorates if the total lithium-deposition capacity is increased. According to these equations, one can anticipate that the local effective current density, anion mobility and depletion, electrolytes concentration, and total deposition capacity can be carefully modulated to delay dendrite nucleation.

A solid electrolyte interphase (SEI) layer is another crit-ical factor that relates to dendrite formation.[17] An SEI

Adv. Mater. 2017, 1700007

Figure 1. Schematic diagrams of: a) lithium-ion batteries and b) lithium-metal batteries. c) Comparison of typical electrode materials in terms of voltage and capacity, and the energy densities of LMBs are much larger than LIBs. However, the utilization of lithium-metal anodes is severely hindered by: d) Safety issues induced by lithium dendrite. Reproduced with permission.[8] Copyright 2015, Wiley-VCH. e) Inferior cyclability caused by continuous side reactions. Reproduced with permission.[9] Copyright 2015, Wiley-VCH. f) Anode pulverization incurred by infinite volume change inside the anode. Reproduced with permission.[10] Copyright 2015, National Academy of Sciences.



layer is formed at the LOE/anode interface due to electrolyte decomposition and parasitic reaction between electrolytes and metallic lithium. Generally, a SEI layer is electronically insu-lating but ionically conductive, and thus prevents further side reactions toward the lithium anode, while the transport of lithium ions is not blocked. During deposition, solvated lithium ions in the electrolyte cast off solvent molecules at the interface, and thus are small enough to pass through between vacan-cies in the SEI layer. Finally, lithium ions reach the surface of the anode and accept electrons from the external circuit, and deposit as metallic lithium particles. In view of this transpor-tation mechanism, rationally designing the internal electronic structures and chemical compositions of the SEI layer can help

to manipulate the migration path of ions and the final deposi-tion sites. Besides, the mechanical properties of the SEI layer also affect the deposition behavior. Common SEI layers made up with inorganic salts demonstrate poor elasticity and are vul-nerable to crack under stress.[18] Once a pinhole forms within the SEI layer, the fresh lithium surface presents higher conduc-tivity and surface area, and thus acts as preferential deposition sites. Lithium ions then diffuse toward these “hot spots” and concentrate in the vicinity. Ultimately, lithium dendrite grows and the process will be accelerated at the absence of mechanical restrains (Figure 2c). In this sense, it is imperative to main-tain the integrity and homogeneity of the SEI layer to mitigate locally enhanced deposition.

Adv. Mater. 2017, 1700007

Figure 2. Failure mechanisms of the lithium-metal anode are explained by different models. a) Classical mathematical model for time-dependent lithium deposition. It is observed that the morphology undergoes a transformation from mossy to dendritic near “Sand’s time”. Reproduced with permission.[13] Copyright 1999, Elsevier. b) Voltage responses of capillary cells at various deposition current-densities (inset: representative optical images of lithium deposits) are in accordance with the previous mathematical model. Reproduced with permission.[15] Copyright 2016, Royal Chemical Society. c) SEI model dealing with the effect of mechanical properties of the SEI layer on lithium deposition behavior. Once a pinhole forms inside the brittle SEI layer, lithium deposition will be locally enhanced, followed by dendrite nucleation and growth. d) Dead-lithium formation. During dissolution, some of the active lithium particles underneath lose electrons and dissolute into the electrolytes, leading to detachment of lithium whiskers above. Reproduced with permission.[16] Copyright 1998, Elsevier. e) Anode pulverization owing to the fast inward movement of the interface between dead lithium and active lithium. Reproduced with permission.[9] Copyright 2015, Wiley-VCH.



2.2. Hyperactivity and Inferior Cycle Performance

The long-term cycle performance is one of the key perfor-mances of batteries. The undesired cycle performance in pre-sent LMBs is closely associated with the hyperactivity of metallic lithium. Owing to the high chemical/electrochemical activity, metallic lithium is apt to spontaneously react with most atmos-pheric gases, polar-aprotic electrolyte solvents, salt anions, etc., particularly under electrochemical conditions. For example, the repeated breakage and repair of the brittle SEI layer upon cycling induced by volume change are common, which could cause long-lasting irreversible lithium depletion. In addition to these electrochemical reactions, the self-generated chemical reaction is much more uncontrollable. For example, the imme-diate chemical reaction toward dissolved lithium polysulfides or O2 from the cathode could deteriorate the performance even further if unprotected lithium foil is utilized in Li–S/O2 batteries. Besides, typical resultants like Li2S/Li2S2 in Li–S batteries are insoluble, which will deposit over the top. These electrical insulating products could not be reused due to the deprivation of ability to gain or give electrons, leading to both anode and cathode consumption. Besides, the thickness of these undesired products deposited on the anode surface will increase upon prolonged cycles, and thus cause large interfa-cial impedance, which could greatly limit the fast ion transport. Therefore, it is of great essence to prebuild a protective layer or passivation layer before the full-cell assembly.

Dead-lithium formation inside the cell as well paralyzes the battery.[19] As shown in Figure 2d, tiny lithium particles or fila-ments could detach from the substrate and then are compactly wrapped by an electronically insulating SEI layer, leading to the formation of dead-lithium.[16] Although dead-lithium par-ticles lose their electrochemical reactivity, they still maintain their chemical reactivity in consideration of their relatively high specific surface area (SSA), and thus act as potential threats to the security of the batteries. Generally, it is of high chance to trigger dead-lithium formation when the effective current density of dissolution is larger than that of deposition.[16] Once the dead-lithium forms, it could not be reversed back to active lithium and participates in the deposition/dissolution proce-dures, leading to a loss of lithium source and gradually intensi-fied capacity-fading.

2.3. Infinite Volume Changes and Electrical Disconnection

The appearance of electrical disconnection is always overlooked and devoid of enough investigations. But in reality, it often occurs before the dendrite formation and short circuits. This kind of battery failure always correlates to the large internal impedance and infinite volume expansion inside the anode upon cycling. The endless reaction between the electrolyte and metallic lithium can cause a fast inward interphase shift. Specif-ically, the upper surface of the anode is covered by an SEI layer and the lithium beneath dissolves into the electrolyte. During the subsequent cycling, the anode structure becomes loose and porous to allow for electrolytes penetration, especially after the SEI layer breaks down. The interphase between active and inac-tive lithium hence displays an inward movement, accompanied

by unrecoverable corrosion inside the whole lithium anode (Figure 2e). Recent work strongly supports the aforementioned mechanism.[9] It was revealed that the loss of capacity, thick-ness of the SEI layer, and internal resistance increased steeply with applied current density, and the battery ended up with a broken circuit rather than a short circuit. The whole anode was filled up with electroinactive dead-lithium, and liquid electro-lytes inside were literally depleted. Additionally, lithium ions were deposited in the form of individual particles within the anode. Without a specific host to trap and connect these active lithium depositions, the whole electrode suffers from a floating electrode/separator interface, internal stress fluctuation, and electrical disconnection between lithium depositions.

Based on the above failure mechanisms, it can be inferred that efforts should be made to rationally control the deposi-tion behavior of lithium ions, the properties of SEI layers, the activity of metallic lithium, and the volume changes in order to obtain desirable electrochemical and safety performance. Generally, uniform lithium-ion flux, integral SEI layers with mechanical rigidity and flexibility, lithium foil with a protective layer, etc., are expected, and to date, tremendous impressive achievements guided by equations and principles above have been made. Especially in the past three years, both liquid- and solid-electrolyte systems have witnessed booming develop-ments. The dendrite can be effectively suppressed for a long period of time together with remarkably improved cycle and rate performance.

3. Strategies to Revive Lithium-Metal Anode in LOEs

3.1. Tailoring Anode Structures

So far, various advanced characterization techniques have been adopted to investigate the dynamic process inside the planar lithium foil during lithium deposition/dissolution.[20] It has been visualized that the fresh lithium in the interior rather than previous surface-deposited lithium microstructures will dissolve and preferentially deposit in the subsequent cycles, indicating an inward growth of the porous lithium interface. LMBs with conventional flat lithium foil and planar CCs fail to confine and reuse these microstructures, and thus the prefer-ential deposition is intensified, leading to dendrite formation upon cycling.[21] Besides, these randomly distributed structures severely damage the continuity and electron transport path-ways inside the lithium anode, and thus exacerbate the capacity fading. It is believed that special anode structures should be introduced to suppress dendrites and to activate or eliminate these unwanted lithium microstructures.

Lithium powder and mechanically surface-modified lithium foil have been put forward as substitutes for planar lithium foil to delay the onset of dendrites.[22] The surface area of the anode is largely enhanced to provide considerable depositing sites, and thus dendrite growth is suppressed for a period time. However, neither the surface state of the lithium foil nor boundaries between powders can last a very long time, and the whole foil turns into aggregates of randomly scattered lithium microstructures upon prolonged cycles. In comparison, strate-gies concentrated on CCs have achieved better performances

Adv. Mater. 2017, 1700007



since Stucky’s group utilized spatially heterogeneous carbon cloth as the CC in 2012.[23] CC is an essential part in the bat-teries and is able to collect the microcurrent of lithium particles and transport it to the external circuit. Traditional copper foil with a surface area of ca. 0.089 m2 g−1 is replaced by nanostruc-tured ones to further reduce the current density, to manipulate the lithium deposition sites, and to provide continuous hosts for lithium microstructures (Figure 3a). Three critical factors, including conductivity, surface area, and morphology, should be thoroughly considered and carefully designed. So far, a 3D copper array with a sub-micrometer skeleton,[24] a self-standing copper nanowire network,[25] a 3D bicontinuous porous copper foil,[26] etc., have been fabricated for subsequent lithium depo-sition, and all of them demonstrate dendrite-proof morpholo-gies. However, more endeavors should be made to facilitate the processability and reduce the fabrication cost for further commercialization. Besides, nanostructured copper is easy to be oxidized and thus loses its electrical conductivity. To avoid drawbacks of nanostructured copper, carbon-coated copper foils are developed (Figure 3b). Carbon-based materials show dis-tinct advantages over nanostructured copper. On the one hand, carbon can be easy processed into nanostructures with different morphologies and versatile structures (e.g., 1D nanofibers, 2D graphene film) together with well-retained conductivity for fast electron transfer. On the other hand, carbon-based materials possess better flexibility to accommodate volume changes than rigid copper. The slurries made of certain carbon-based mate-rials, organic binders (e.g., poly(vinylidene fluoride) (PVDF),

poly(tetrafluoroethylene) (PTFE) and liquid solvent (e.g., N-methylpyrrolidone (NMP), deionized water (DI) are cast onto the planar copper foil and act as functional layers. Carbon-based materials with different structures and morphologies have been adopted such as super P,[27] mechanically or ther-mally exfoliated graphene,[28] hydrothermally reduced graphene framework,[29] unstacked graphene,[30] etc. These carbon coat-ings all contribute to a better electrochemical performance. The fundamental reasons have a close relationship to their excellent conductivity, high specific surface area, and suitable pore size/volume. In particular, Zhang’s group successfully prepared a special kind of unstacked graphene, which delivered an ultra-high SSA of ca. 1666 m2 g−1, pore volume of ca. 1.65 cm3 g−1 and superior electrical conductivity of ca. 435 S cm−1. The copper coated with this graphene coating exhibited a much enhanced performance with a total lithium capacity of 5 mA h cm−2 at a current density of 2 mA cm−2. And it is observed that if cur-rent density is lowered to 4 × 10−5 mA cm−2, lithium deposi-tion on a planar copper could as well present a homogeneous morphology. This result further proved the correctness of Sand’s time equation. Compared to those nanostructured or carbon-coated copper foils, self-standing carbon films, them-selves directly as CCs, are able to avoid adverse impacts on electrical conductivity originated from organic binders or carbon abscission. Besides, carbon-based film can be shaped to become ultrathin, to further reduce the thickness and weight of the CC (Figure 3c). Therefore, these carbon CCs are able to deliver much higher energy densities. Some pioneering studies

Adv. Mater. 2017, 1700007

Figure 3. The schematic diagrams, merits (black) and demerits (red) of three typical anode structures before lithium deposition. a) Nanostructure copper CCs. Reproduced with permission.[24] Copyright 2015, Nature Publishing Group. b) Carbon-coated copper foil. Reproduced with permission.[30] Copyright 2016, Wiley-VCH. c) Self-standing carbon framework. Reproduced with permission.[32] Copyright 2016, Wiley-VCH.



using carbon-fiber papers,[23] porous graphene networks,[31] CNT-decorated ultrathin graphite foam,[32] etc., have been con-ducted, which give insightful guidance for further study on construction of nanostructures, preparation, and characteriza-tion. Basically, 3D porous carbon scaffolds with superior con-ductivity, conformity, and wettability toward LOEs are desired. Despite their merits, carbon-based materials still possess some demerits adverse to the battery performance. Taking graphite as an example, most of the alkyl carbonate solvents and salt anions are reduced on graphite surfaces around 1.0 V in the presence of Li+, leading to the formation of insulating surface film or gas release. In addition, the co-intercalation of Li+ and solvent mole cules at potentials below 1.0 V could result in exfoliation of graphite. More severely, the gas evolution between graphene planes and inner pressure can easily split the graphite par-ticles, especially when the surface film is relativity weak. The cracking of graphite allows further surface reaction on those newly cracked particles, leading to their absolute electrical iso-lation and increased electrode impedance.[33] To mitigate these problems, careful selection of the electrolytes and design of nanostructures is of great significance for these self-standing carbon frameworks. Fast precipitation of strong, cohesive, and complete highly passivating surface films is needed, particularly

for carbon-based CCs with ultrahigh SSA. Among present elec-trolytes, mixtures of ethylene carbonate (EC) and linear-alkyl carbonate solvents including dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc., have been widely used and proved beneficial to the formation of stable surface films.[28,31] Dual salts or electrolyte additives also plays an important role in film forming process.[29,30] However, the electrical conductivity of carbon-based materials is about four orders of magnitude lower than that of copper, and thus their high-rate performances are inferior to copper.

It is apparent that aforementioned three types of CCs (i.e., nanostructured copper, carbon-coated copper, self-standing carbon framework) could not be directly utilized in LMBs owing to the absence of a lithium source. Additional pre-electrodeposition of lithium into these CCs and a subsequent cell disassembly process are required for further performance evaluation in LMBs (Figure 4a). Apart from the complexities, such assembly/disassembly processes may introduce impu-rities, induce side reactions toward lithium, and destroy the integrity of the anode. Fortunately, lithium-containing alloys, like Li–Mg,[19b] Li–B,[34] Li–Sn,[35] etc., have been fabricated and enable dendrite-free morphologies when used in LMBs. The reasons underneath are related to the difference in deposition

Adv. Mater. 2017, 1700007

Figure 4. Approaches to load lithium source into the present anode structures. a) Electro-deposition in assembled cells, followed by a cell disassembly to take out the lithium-deposited electrodes. SEM images. Reproduced with permission.[29] Copyright 2015, American Chemical Society. b) Prestore lithium source during alloy preparation. The Li7B6·7.6Li framework. Reproduced with permission.[34a] Copyright 2014, Wiley-VCH. c) Molten-lithium infusion. Reproduced with permission.[36] Copyright 2016, Nature Publishing Group.



kinetics over different media, and their 3D nanostructures that effectively confine the lithium depositions. For instance, the fibrous Li7B6·7.6Li framework has been proposed as a prom-ising anode material for LMBs (Figure 4b).[34a] Herein, the metallic lithium embedded in a fibrous Li7B6 matrix undergoes repeated dissolution/deposition, while the 3D Li7B6 framework helps to decrease the growth velocity of lithium deposits and minimize their final size. It is worth mentioning that to main-tain the integrity of the framework the charging voltage is set below 0.8 V to avoid lithium de-alloying. However, high-quality lithium alloys are difficult to prepare, especially those with spe-cific nanostructures. Molten lithium infusion has been recently developed as a novel technique to load lithium. This approach transfers the conventional loading process from hidden inside to the outside of cells, demonstrating advantages in control-lability, loading mass, and choice of CCs. Generally, the CCs (or host) should possess superior lithiophilicity and thermal stability over the melting point of lithium (180 °C). Functional groups or surface coatings that are able to react with molten lithium have been introduced to endow the CC (or host) with lithiophilicity. Graphene oxide (GO) film that contains residual water and surface OH groups are easy to be infused with molten lithium.[36] As shown in Figure 4c, when partially put into contact with molten lithium, GO film immediately expands into an extremely porous structure with desired nanogaps and nanopores, which are beneficial for following lithium infusion and deposition. Then, fast and uniform lithium intake into the films can be realized simply via edge contact with molten lithium. Surface coatings (e.g., Si, ZnO) are able to react or alloy with metallic lithium, and thus vastly increase the lithi-ophilicity. Upon infusing, molten lithium would firstly react with the coatings and then infuse into the depth of the matrix due to a capillarity force. Si-coated carbon-fiber network,[10] ZnO-coated PI matrix,[37] ZnO-coated porous garnet-based solid electrolytes,[38] etc. are successfully infused with molten lithium and serve as self-supported lithium composite anodes, exhib-iting both high ionic and electrical conductivity. It is known that predeposition via an electrochemical method only applies to conductive CCs. Apparently, this newly developed approach has widened the choice of host, for example, non-conducting poly mer matrix and solid-state electrolytes. However, an addi-tional coating process is required for most hosts. The coating layers inevitably lead to extra consumption of molten lithium and increase in internal resistance. More importantly, their morphologies and compositions will affect the deposition behaviors of lithium ions. Besides, rigid operation conditions, especially at the absence of air, moisture, etc. are required, owing to hyperactivity of molten lithium. The amount of molten lithium sticking to the upper surface should be mini-mized to fulfill a perfect confinement.

In conclusion, the introduction of nanostructured anodes mainly provide the following three functions: i) significantly reduce the current density and thus delay the potential dendrite onset; ii) effectively weaken the charge center caused by pre-viously deposited lithium bulges via defects or protuberances, and hence the lithium deposition sites are manipulated; iii) pro-vide adequate space to entrap lithium deposition interior via nano- or micropores inside the structure. Taking the batteries energy density, electrochemical performance, fabrication cost,

and complexity into consideration, a self-standing 3D nano-structured carbon-based framework encapsulated with lithium via molten lithium infusion shows distinct advantages. Not-withstanding the present laudable results, future researchers are still confronted with some harsh problems, such as enhanced side reactions owing to high surface area and sur-face deposition on the upper surface of these conductive CCs (hosts), which may lead to intensified electrolytes consumption and potential dendrite growth. How to drive the lithium ions into the depth of the host is critical and essential. Although some studies have mentioned that defects,[31] differences in electrical conductivity,[23,25] and hierarchical structures[32] could contribute to the interior deposition, these methods are not that radical according to their SEM images. Cui’s group thoroughly investigated the nucleation over-potential on various hosts, and unraveled a host-dependent growth phenomenon that enabled selective deposition of lithium.[39] Results show that lithium ions will preferentially deposit on Au, Ag, Zn, and Mg rather than Cu, Ni, C, Sn, and Si substrates. Based on the theoretical investigations, hollow carbon spheres with Au NPs inside were prepared. Owing to a lower over-potential on Au seeds than carbon spheres (Figure 5a,b), lithium ions indeed selectively nucleated on the Au seeds, as expected, and deposited within the interior of carbon spheres, according to in situ TEM char-acterization results (Figure 5c,d). Besides, it was observed that lithium deposited on pure carbon nanospheres presented obvious dendrite formation on the outer walls (Figure 5e). Guided by these instructive studies, it is believed that these tai-lored anode structures will usher better applications in LMBs.

3.2. Optimizing Electrolytes for Better Lithium-Anode Performance

The LOE, composed of polar organic solvents and lithium salts, is a dispensable part of the battery. Electrolyte regulation is one of the most effective and convenient routes to promote long-term performance and suppress dendrites growth. Owing to their prominent impacts and low cost, electrolyte regula-tion is suitable for commercialization. Compositions, addi-tives, and concentration of the electrolytes vastly influence the properties of the SEI layer and lithium-deposition behaviors. As mentioned above, repeated breakage/repair, heterogeneity in chemical composition, morphologies, physical properties, and the partial dissolution of the SEI layer could induce locally enhanced deposition and endless lithium/electrolytes con-sumption. Hence, high-quality SEI layers with well-maintained integrity, stability, and homogeneity could effectively suppress potential dendrite formation and extend the lifespan of bat-teries. In addition to form a desirable SEI layer, some recent advances even provide a possibility for modulating the deposi-tion behaviors of lithium ions.

3.2.1. Forming Integral Intrinsic SEI Layer

Generally, intrinsic SEI layers consist of various organic (oligomer and polymer) and inorganic products, where the organic part endows the SEI layer with flexibility to accommo-date lithium depositions, while the inorganic part enables swift

Adv. Mater. 2017, 1700007



lithium-ion transport. However, inorganic lithium carbonate (Li2CO3) and lithium ethylene dicarbonate (LEDC), as two main SEI components, are thermodynamically unstable near the lithium deposition potential and permit reactions upon cycling, while lithium oxide (Li2O) is the only thermodynami-cally and kinetically stable component, and a thin layer of Li2O in the innermost SEI layer is of great essence to avoid breakage in the absence of a fluoride source.[40] Besides, chemical and physical anisotropy are common inside the SEI layer, as well leading to heterogeneous lithium flux and uneven deposition. Taking ionic conductivity, for example, lithium ions tend to pass through where presents higher ionic conductivity owing to a lower migration barrier. This process is subsequently acceler-ated and results in dendrite formation. So far, selected solvents, lithium salts, and additives are introduced to effectively and efficiently modulate the properties of SEI layers.[41]

The SEI layers formed in electrolytes with solvents like ethylene (EC), polycarbonate (PC), diethyl carbonate (DEC), 1-3 dioxolane (DOL), 1,2-dimethoxyethane (DME), tetrahydro-furan (THF), etc., and lithium salts like lithium hexafluoro-phosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium triflate (LiSO3CF3), etc. have been thoroughly characterized.[42] As for solvents, a brief comparison of typical components within the SEI layer in alkyl carbonates and in DOL solutions is presented in Figure 6. The SEI layer formed in alkyl carbonate electrolytes is full of brittle ionic species, while insoluble oligomers of polydioxolane

are found on the external surface in DOL-containing electro-lytes, owing to the partial polymerization of DOL. The corres-ponding SEI layer of DOL solution thus possesses much enhanced flexi bility to resist the huge internal stress induced by volume changes. For practical applications, DOL is usu-ally used with another famed low viscous solvent, DME. DME enables a high lithium transference number that increases the number of lithium ions near the anode surface, contributing to spatially uniform deposition.[42c] Lithium ions prefer to bind with oxygen atoms in the solvent molecules, and thus promotes the ring opening reaction of the DOL solvent and accelerates its decomposition, while DME maintains certain stability.[43] Other novel solvents, like fluorinated ether and 1,4-dioxane (DX), were investigated as well.[44] Specifically, these two solvents both improve the densification, mechanical strength, and ionic con-ductivity of the SEI layer with higher inorganic components. Additio nally, due to its low reactivity toward lithium and anti-oxidation capability, DX is able to elevate the electrochemical stability window up to ca. 4.87 V, which is the highest value for present neat ether-based electrolyte systems. In addition to solvents, the utilization of lithium salts like LiFSI, LiTFSI, and LiFNFSI as well greatly enhances the cycle stability of LMBs.[45] FSI− anion is even described as a magic anion for electrochem-istry due to its promotion for the formation of a robust SEI layer. The reductive breakdown of FSI− yields a large amount of inor-ganic salts like LiF, LiOH, and LiSO2F, which enhance the ionic conductivity and mechanical strength inside the SEI layer. The

Adv. Mater. 2017, 1700007

Figure 5. A powerful strategy to inhibit lithium deposition upon the anode surface. a,b) Voltage profile during lithium deposition on hollow carbon shells without (a) and with (b) Au NPs at 0.5 mA cm−2. The inset shows the SEM image after deposition as well as the corresponding schematic. c–e) TEM images of nanocapsules with Au NPs after lithium deposition (c), after in situ electron-beam heating (d), and carbon shell without Au NPs after lithium deposition (e). Reproduced with permission.[39] Copyright 2016, Nature Publishing Group.



FNFSI− anion shows a preferred reduction process at the anode that facilitates stable SEI formation. Besides, these salts possess intensified chemical stability toward various kinds of reactive intermediates when used in Li–S batteries. Furthermore, as indicated by the Chazalviel model, dendrite grows at the velocity of anion departure from the anode. Special emphasis should be placed on the anion part from composition or space structure. Taking these salts for example, the large anion structure inside markedly impedes their diffusion speed, and thus slows down dendrite formation at the anode. Room-temperature ionic liq-uids (RTILs) are also introduced to produce integral, intrinsic SEI layers.[46] The flexible combination of different anions and cations provides the potential to exert a significant amount of control over the decomposition of the SEI. However, RTIL suf-fers from dendrite formation when practical current densities are applied, owing to a relatively low lithium-ion transference number in both electrolytes and SEI layers. A typical modifica-tion is to use zwitterionic compounds, which are able to tether the anion and cation making up the ionic liquids.[47] One of their function is to prevent immigration of component ions under the electric field, and hence delay the onset of dendrite formation. The other one is to increase the dissociation via shielding ion–ion interactions, and thus the lithium ion trans-portation is enhanced with additional anion paths for migra-tion through the electrolyte. In view of their excellent thermal

stability, zero volatility and flammability, and a wide electro-chemical window, it is assumed that ionic liquids can be better used if the above problems are addressed. Guo’s group hybrid-ized the ionic liquids (Py13TFSI) with high concentrated ether electrolytes.[48] The synergetic effect between Py13TFSI-modified SEI layer and reduced free anions contributes to an exceptional reversibility upon lithium deposition/dissolution.

Additives also contribute a lot during the formation of the SEI layer, which are directly added into the present commercialized electrolytes. Inorganic additives, such as HF,[49] trace-amounts of water,[50] LiF,[51] LiBr,[52] LiNO3,[53] lithium oxalyldifluoro-borate (LiODFB),[54] lithium polysulfide (Li2Sn),[29,55] copper acetate,[56] etc. are conducive to stabilize and strengthen the SEI layer, due to their modulation of components in the SEI layer, for example, LiF. These additives significantly facilitate the lithium-ion transportation within the SEI layers and enhance mechanical strength to bear the internal stress originated from volume changes upon cycling. Thereinto, the combination of LiNO3 and Li2Sn is the most widely used in Li–S batteries. It has been confirmed that the favorable effect of single LiNO3 or Li2Sn cannot be maintained upon prolonged cycles, as shown in Figure 7.[55a,57] In particular, the SEI layer formed with the dual additives contains a bottom layer of LiNxOy and lithium sulfides, and a top layer of lithium sulfates, owing to oxidation of polysulfides by LiNO3. However, the high content of Li2Sn in

Adv. Mater. 2017, 1700007

Figure 6. Regulated electrolytes enable the formation of integral SEI layer. Upon deposition and dissolution, the surface comprised of inorganic ionic spices cannot accommodate the morphological change and thus may break down, leading to highly non-uniform lithium deposition, which can form dendrites. Here, the substitution of DOL for conventional alkyl carbonates significantly improves the flexibility due to the partial polymerization of DOL, and thus helps to maintain the integrity of SEI layer. Reproduced with permission.[42b] Copyright 2000, Elsevier.



this dual-additive system could etch the present SEI layer and cause severe anode corrosion as well.[55b] As for LiNO3, the only prominent drawback is the repeated active reaction toward the lithium anode. Hybrid additives like VC–LiNO3 (VC is vinylene carbonate),[53b] DOL–LiNO3,[58] or using LiNO3 as a co-solvent like Li2S5–LiNO3–LiTFSI ternary salts,[55a] are proposed to address the above problem. Compared to those inorganic addi-tives, organic species mainly help to improve the flexibility of the surface layer owing to the formation of insoluble polymeric products, which always promote speedy stabilization of the interface. Typical organic additives include polymer,[59] VC,[53b,60] fluoroethylene carbonate (FEC),[61] toluene,[62] pyrrole,[63] etc. Thereinto, FEC is one of the most effective, owing to its com-bination of functions coming from organic and inorganic addi-tives. The decomposition products of FEC contain C–F polymer (i.e., the polymer derived from the C–F molecule) and LiF, and hence the protective film formed on the lithium anode pre-sents superior flexibility to withstand volume changes and fast lithium-ion diffusion, even at high current densities.

In summary, the quality of the SEI layer is closely related to performance, particularly the long-term cycle performance. The present optimization in electrolyte components and additives truly exert salutary effects on performances of laboratory-based cells. In consideration of existing commercialized electrolytes with specific solvents and lithium salts, adding some additives may be a better choice. Additives have a much wider scope of applications in different types of electrolytes for different kinds of cathodes, like LiFePO4, oxygen, or sulfur. The regulation in electrolyte components is always only suitable for a particular cathode, while additives like FEC have been proved to be effec-tive for the above three. However, the development of additives still needs more endeavor. First of all, the main function of aforementioned additives is to stabilize the SEI layer, while the deposition behavior of lithium ions remains unchanged. Since the mechanical flexibility and strength of the SEI layer is not able to be modulated in a wide range, it may fail to maintain its integrity now or later. Secondly, upon long-cycling, continuous consumption of additives is evitable, but the amount of addi-tion is limited by the solubility and cell impedance. Thirdly, the effect of additives tends to decay with time. Tiny changes in

the electronic structures of the SEI layer are happening, which affect the final performance, even though it maintains in an integral state.

3.2.2. Regulating Lithium Deposition Behavior

The above research mainly focuses on intrinsic SEI-layer modu-lation, while the deposition behavior or deposition sites are not radically tuned. Herein, some powerful strategies are discussed in detail. What differs from the aforementioned strategies is that there always exist some chemical or physical interactions between the additives and lithium flux. In other words, the modulation of the intrinsic SEI layer can be regarded as a “pro-tective strategy”, while the manipulation of deposition behavior ought to be a “fundamental method”. So far two major strate-gies have been confirmed to possess the above functions, that is, adding special metal ions or solid functional particles and increasing the electrolyte concentration.

As mentioned before, metallic-ion deposition is common during the electrochemical process. When metallic ions are introduced into the LOEs, both alien metal ions and lithium ions show tendency to deposit during discharging. It can be inferred that the sequence of deposition and the applied poten-tial play important roles in the lithium deposition behavior and morphology. Basically, the electrochemical potential determines the order. According to the Nernst equation as follows:[64]

αα

= −φE ERT

zFlnRed Red

Red

Ox (4)

where the local reduction potential (ERed) depends on the standard reduction potential φE( )Red , the ratio of the reductant’s chemical activity (αRed) to oxidant’s chemical activity (αOx), the number of electrons transferred (z), and the absolute tempera-ture (T). Among these metal-ion additives, the Group I alkali metals have extremely strong reducibility. Previous research has shown that their reducing powers in [C4mpyrr][NTf2] and propylene carbonate follow the trend: Na > Li > K ≈ Rb > Cs,[65] but their local reduction potential can be modulated to activate

Adv. Mater. 2017, 1700007

Figure 7. Illustration of the surface film behavior on lithium-anode cycling in the same LiTFSI-DOL electrolytes with different electrolytes. Reproduced with permission.[57b] Copyright 2014, Elsevier.



different deposition mechanisms. In one respect, Li-metal alloy could form after alien ion deposition. The co-deposition mechanism is proposed exactly in this case,[66] which is also suitable for some other metal ions such as Sn2+,[67] Al3+,[63] Mg2+,[68] etc. Taking the Li–Na co-deposition for example, the deposition behavior in a Na+-containing electrolyte is pre-sented in Figure 8a. SEI layer is instantaneously formed on the initially deposited lithium and then breaks down owing to the large internal stress. Afterward, fresh lithium exposes to the electrolytes, meanwhile, sodium ions deposit on the active lithium surface along with Li–Na alloy formation. The sequential lithium ions will deposit elsewhere, where there is a lower energy barrier. Ultimately, the surface of the lithium foil displays a dimpled rather than dendrite-like morphology. However, this co-deposition mechanism is not always condu-cive to better performances. There is a competition between a newly formed alloy surface and a primary lithium surface for deposition due to their different chemical and physical proper-ties.[63,67] For example, excellent performances are obtained in the presence of the Li–Al alloy interface with high conductivity, while adverse results are achieved in the Li–Sn alloy. Further-more, the concentration of alien ions and potential applied can be carefully altered to enable co-deposition. Alkaline-earth-metal ions at 0.05 M concentration significantly reduced den-drite growth, and a sphere-like morphology without dendrites was achieved when the concentration was increased to 0.1 M.[69] Accordingly it can be assumed that the co-deposition mechanism greatly depends on the electrodeposition potential of foreign metal ions, which is determined by the ion itself, concentration, and chemical interaction toward the electrolyte solvent. Another is the self-healing electrostatic shield (SHES) mechanism, which is proper for alien metal ions that would absorb instead of deposit onto the active lithium surface before

the next deposition.[64,70] Cs+ (or Rb+) is deliberately chosen and added into the LOE. As presented in Figure 8b, Li+ and Cs+ both absorb on the surface of the electrode at the initial stage of deposition. Lithium ions start to deposit as soon as the poten-tial drops down to the critical value for lithium deposition. The electrons from the external circuit then gather at the lithium tip and thus attract those positively charged Cs+ in the vicinity until the entire exposed surface is occupied. The large electric repulsion force between the positively charged tip and lithium ions retards following deposition in the vicinity of preformed protrusions, leading to their smooth deposition at adjacent regions until full coverage is achieved. Moreover, in contrast to traditional thinking that the SEI layer forms at a potential of about 0.9–1.2 V, here, a thin LiF-rich SEI layer is found at about 2.05 V with the addition of Cs+. It is proved that the synergetic effects of SEHS and this preformed, stable SEI layer together contribute to the final vertically grown, self-aligned, and highly compacted nanorod-like morphology.[71] Afterward, the pure adsorption behavior instead of deposition, and the state of posi-tive charge is confirmed via surface analysis and in situ Li-7 and Cs-133 nuclear magnetic resonance investigations; the results of which further support the aforementioned mechanism.[72] Ionic-liquid-tethered nanoparticles are also introduced to reg-ulate the deposition behavior of lithium ions.[73] For instance, SiO2-IL-TFSI nanoparticles are well distributed in a PC matrix and are able to provide two major functions: i) act as a reservoir to release anions when necessary, to reduce the space charge electric field near the electrodes. Actually, an immobilization of as little as 10% of the anion can evidently reduce ion concentra-tion gradients during polarization, and hence promote uniform lithium deposition; ii) offer mechanically strong and highly tortuous pathways that are adverse to dendrite growth. How-ever, the introduction of solid particles undoubtedly increases the internal impedance of the cell and scatters lithium-ion transportation.

Highly concentrated electrolytes with a reduced anion transference number help to minimize the polarization and electric field intensity, and thus delay dendrite nucleation at the anode surface. Besides, the anion transport is severely hindered, and hence the velocity of potential dendrite growth will be slowed down. The decreased amount of free solvent also suppresses the continuous parasitic reaction between the electrolyte and the lithium anode. In this sense, increasing the concentration of electrolytes is a multieffective strategy for high energy LMBs. The concentration exerts significant effects on the amount of lithium-complex pairs, ion transference number, and ionic conductivity. Lithium-ion transference (tLi+

) is defined as the ratio of a partial amount of charge trans-port by Li+ to the total charge transport. Ionic conductivity (σi) is determined by its concentration (ci) and mobility (σi) (σi = nciμi). The ion mobility depends on the viscosity (η) and the radius (ri) (μi = 1/6 πηri). For those highly concentrated elec-trolytes, tLi+ increases to a higher value, while ionic conductivity decreases at the same time. But, more importantly, the amount of mobile anions greatly reduced due to the coordination with Li+. Based on these theoretical principles, Chen’s group deve-loped a new class of “solvent in salt” (LiTFSI in DOL/DME (v/v = 1)) electrolyte for high-energy LMBs.[74] This electrolyte with ultrahigh salt concentration displays a tLi+ value up to 0.73.

Adv. Mater. 2017, 1700007

Figure 8. Illustration of electrolytes with metal ion additives that enable the manipulation of lithium deposition. a) Co-deposition mechanism. Na+ could block dendrite growth by depositing on electrochemically active lithium surface. Reproduced with permission.[66b] Copyright 2013, Electrochemical Society. b) Self-healing electrostatic shield mechanism. Cs+ or Rb+ will accumulate in the vicinity of the tip to form an electro-static shield, repelling Li+ to deposit at adjacent regions of the anode.[64] Copyright 2013, American Chemical Society.



Meanwhile, considerable amount of anions are tethered to lithium ions, and solvent molecules are trapped by these large lithium-complex pairs. During deposition, the space charge created by anion depletion is minimized, and thus den-drite nucleation is inhibited. Additionally, the dissolution of unfavo rable intermediate products such as lithium polysulfides is reduced when used in Li–S batteries. Similarly, a highly concentrated electrolyte with 4 M LiFSI in DME is designed as well, and DME is selected owing to its lowest reduction potential that benefits formation of the SEI layer.[75] The poten-tial states of each component in the 1 M and 4 M electrolytes are visualized via molecular dynamic simulations and pre-sented in Figure 9a,b. 60% of FSI− and Li+ are uncoordinated and fully solvated respectively in 1 M electrolyte, respectively, while only about 3% of FSI− are uncoordinated, and 6% of Li+ are fully solvated in 4 M electrolyte. Clearly, anions are almost tightly immobilized by lithium ions, while another large por-tion of lithium ions transport more swiftly owing to incomplete solvation. Besides, the significant decrease in ionic conductivity will harm the high-rate performance if the concentration is fur-ther increased up to 5 M, which is determined by specific elec-trolyte solvent and salt. The final optimized 4 M electrolyte has

been later adopted to construct anode-free rechargeable lithium batteries and demonstrates an unprecedented high Coulombic efficiency over 99.8%.[76] These encouraging results stimulate more work that focuses on this efficient and effective strategy. Various concentrated electrolytes with novel solvents or salts were utilized and demonstrated enhanced anode stability and electrochemical performance.[77] Additionally, operating con-ditions like high-rate discharging also produce a transient high-concentration electrolyte layer around the anode surface, while a low-rate discharging process can result in numerous dead-lithium particles (Figure 9c,d).[78] With a slow release of lithium ions, an immediate reaction between the newly exposed lithium and free solvent will follow. Upon cycling, cat-astrophic corrosion of the lithium anode is bound to happen. Contrarily, substantial lithium ions dissolute from the anode and accumulate at the vicinity of the anode, with the formation of a transient high-concentration electrolyte layer during a fast-discharging process. These uncoordinated lithium ions show high propensity for pairing with the anions. Similar to those effects in highly concentrated electrolytes, the depletion of salt anions, solvents, and metallic lithium is substantially reduced together with a smoothened SEI layer.

Adv. Mater. 2017, 1700007

Figure 9. Illustration of highly concentrated electrolytes that enable the manipulation of lithium deposition. Snapshots of the MD simulation boxes of a) 1 M LiFSI-DME electrolyte and b) 4 M LiFSI-DME electrolyte (Li, purple; uncoordinated DME solvent molecules, light gray; O, red; N, blue; S, yellow; F, green). It is observed that a considerable number of anions are tethered to lithium ions, and solvent is trapped by these large lithium–complex pairs in highly concentrated electrolytes. During deposition, the space charge created by anion depletion is minimized, and thus dendrite nucleation is inhibited. Reproduced with permission.[75] Copyright 2015, Nature Publishing Group. The SEI evolution on a lithium-metal anode in a cell when discharged at c) low rate and d) high rate. Transient high-concentration electrolyte layer formed during high C-rate discharging also contributes to a stable SEI layer with uniform lithium deposition, while low C-rate discharging leads to serious anode corrosion. Reproduced with permission.[78] Copyright 2016, Wiley-VCH.



Generally, the development of new kinds or a novel combina-tion of additives may be the future trend in view of their multi-functions, low addition, and low cost. Though some existing additives like LiNO3, VC, FEC, etc. have already been commer-cialized in LIBs, there are challenges for them to be extended to LMBs, especially high-energy-density Li–S or Li–O2 bat-teries. The interactions between the cathode materials or reac-tion products and the lithium anode set higher requirements to the functions of additives. For example, in the laboratory, cells like asymmetric Li/electrolytes (with additives)/Li, the SEI layers are proved to be stable and integral for hundreds of cycles. But the lithium polysulfides in Li–S batteries may gradu-ally etch them off, or oxygen in Li–O2 batteries may oxidize the additives or further react with the SEI components, leading to the formation of thermodynamically and kinetically unstable spices. Therefore, there still need many experiments, character-izations, or simulations and calculations to develop ideal addi-tives for high-energy LMBs.

3.3. Building Artificial Anode/Electrolyte Interface to Protect Lithium-Metal Anodes

The artificial anode–electrolyte interface is constructed outside of the batteries with favorable properties to protect the lithium underneath. The direct contact between metallic lithium and organic liquid electrolytes is blocked by this artificial interface before cell assembly. Therefore, consumption of the electrolytes and electrode materials, heterogeneous deposition, and den-drite formation caused by intrinsic SEI layers can be success-fully averted. With the help of this artificial interface, planar copper foil with electrodeposited lithium or flat lithium foil can be used as anodes. Artificial interfaces, by contrast, own many advantages. First of all, it is quite convenient to modulate their properties in the absence of effects originating from uncon-trollable electrochemical processes, such as applied current density, voltage range, cathode materials, etc., all of which will influence the formation of intrinsic SEI layers. Secondly, the properties can be tailored more extensively. For example, some organic solvents may not be suitable as electrolyte solvents due to unmatchable reduction potential or physical properties (e.g., boiling point, vapor pressure), but these solvents may have the potential to chemically react with metallic lithium to form a stable, artificial interface with high quality. At present, the fab-rication of such artificial interfacial layers outside of batteries involves two major strategies: chemically reacting with metallic lithium foil and directly surface coating. Since the interfaces built via reactions toward metallic lithium possess similar fea-tures (i.e., electronically insulating but ionically conductive) to those intrinsic SEI layers, they are widely described as “artificial SEI”. While, for interfaces built via coating, they in some sense play similar roles as conventional SEIs when working, and thus are also called “artificial SEIs” in our following discuss.

3.3.1. Artificial SEI Layer via Reactions Toward Metallic Lithium

This kind of strategy is based on the hyperactivity of metallic lithium and native film on the surface. In the early stages,

solid-state electrolytes, such as Li3N and lithium phosphorous oxy nitride (LiPON), were directly formed on the surface and protected the lithium anode from corrosion by the LOE.[79] How-ever, the downside of these two kinds of material is their long and rigid fabrication process. For example, LiPON electrolyte were chemically deposited on lithium-metal anodes by magne-tron sputtering from a Li3PO4 target in a N2 process gas, accom-panied by an in situ reaction with metallic lithium. Besides, in order to achieve a continuous thin film, a fairly smooth lithium surface without micrometer-size pores or crevices is required. To avoid these disadvantages, tetraethoxysilane (TEOS) is adopted to react with the hydroxyl groups on the surface of active metallic lithium.[80] The lithium surface after TEOS treatment is covered by a 1-micron-thick silicate film with interconnected pores for ion transportation. This technique is compatible with large-scale production and is less expensive. However, the sol–gel-derived film is porous with uncontrollable porosity and pore size. Once the electrolyte penetrates through the pores and directly touches the metallic Li, the electrolyte and Li react. Liu et al. developed a facile but effective ex situ electrochemical strategy, as shown in Figure 10a.[61b] Symmetric Li/electrolyte/Li cells are initially charged from 0 to 0.7 V with a scan rate 1 mV s−1 for two cycles in 1 M lithium triflate (LiCF3SO3) in tetraethylene glycol dime-thyl ether (TEGDME)-FEC (5:1 w/w). Afterward, the anodes of the cells are unpacked and reassembled into Li–O2 batteries with 1 M TEGDME-LiCF3SO3 as the electrolyte. Here, the voltage and scan rate are selected to only allow FEC decompo-sition into C–F polymer and LiF over the anode surface, ena-bling a stable preformed artificial interface before Li–O2 battery assembly. Besides, the potential reaction with the O2 cathode is eliminated. To further simplify the procedure, Basile et al. directly immersed the lithium anode into the RTILs for a period of time, thus creating a durable and lithium-ion conducting layer.[81] This kind of pretreatment shows profound applications for the future, but the decomposition products consist of some unstable compounds, which tend to partially dissolute in highly polar, organic electrolytes. If it happens, the lithium-ion flux will be locally enhanced and further evolve into dendrite formation. The reaction agents and solvent should be elaborately selected in consideration of the chemical and physical stability of the resultant film, and a single component is desired with homoge-neous properties. Guided by these principles, a pure Li3PO4 layer has been designed and prepared via an in situ reaction between poly(phosphoric acid) (PAA) and lithium foil with a native film (Figure 10b).[82] This uniform Li3PO4 layer with a thickness of ca. 50 nm remarkably eliminates the uneven lithium-ion flux resulting from heterogeneity in composition and conductivity. Despite its excellent chemical and electrochemical stability in LOEs, a high modulus of ca. 11 GPa is also presented to effec-tively restrain dendrite growth.

Generally, the aforementioned approaches based on reac-tions toward metallic lithium are able to obtain compact protec-tive layers on the lithium surface. These layers always contain certain kinds of lithium-containing inorganic species profiting from the in situ reactions. Thus, such kinds of artificial SEI pos-sess not only fast ion-conducting properties to smooth the dep-osition process, but also superior mechanical strength to block the dendrite growth. However, it is hard to obtain an integral film with homogeneous properties and compositions, which

Adv. Mater. 2017, 1700007



may result in an uneven lithium-ion flux or locally enhanced deposition. Another chief drawback is that these layers lack the flexibility to accommodate interior volume changes. It is known that bulk lithium undergoes a transformation from dense to loose structures upon cycling, and the floating interface and volume changes may crack these relatively weak layers upon prolonged battery testing.

3.3.2. Artificial SEI Layer via Coating

Compared to reactions toward metallic lithium, coating shows advantages in controlling the composition, morphology, mechanical strength, and flexibility. The materials are always coated on planar lithium or copper foil. Relatively speaking, directly coating on lithium foil is better, owing to the elimina-tion of the predeposition process for full-cell characterization.

Polymers have been considered as suitable coatings in view of their superior electronically insulating properties and flex-ibility to accommodate volume changes, such as a poly(vinylene carbonate-co-acrylonitrile) (P(VC-co-AN)) layer,[83] thin porous polyacetylene (PA) film,[84] HF-assisted etched nanoporous poly(dimethylsiloxane) (PDMS) film,[85] etc. For instance, PDMS is selected owing to its chemical inertness and process conveni-ence. As shown in Figure 11a, lithium ions pass through the

nanopores within the film and then deposit beneath. Besides, the PDMS film buffers the volume changes well, by going up and down. However, these polymers are mechanically weak to resisting the dendrite growth, especially at high current densi-ties. Generally, the modulus shall be on the order of 1 GPa in order to suppress dendrites.[86] To solve these problems, two strategies have been developed. One is to introduce high-mod-ulus layers or additives as substitutions. The other strategy is to leave extra space for depositions via specially designed nano-structures, to reduce the stress exerted on the artificial inter-face. 2D atomic crystal layer materials, such as graphene flakes and h-BN nanosheets, are famous for their chemically inert and ultrahigh mechanical strength approaching 1 TPa, which have been utilized as suitable high-modulus coatings.[87] Addition-ally, the pore diameters within the hexagonal rings are about 1.4 and 1.2 Å for graphene and h-BN, respectively. Therefore, no chemical species can pass through the layers, while those relatively smaller lithium ions can penetrate through the local points and line defects induced by a chemically grown pro-cess. Their high flexibility and tensile modulus are conducive to accommodate a volume change upon deposition. However, the complicated preparation process significantly hinders their scalability. Comparatively, atomic layer deposition (ALD) is more facile to fabricate artificial interfaces directly upon the surface of lithium foil.[88] The self-limiting reactions in the

Adv. Mater. 2017, 1700007

Figure 10. Artificial SEI layer via reaction toward metallic lithium. a) Electrochemical formation of protective film on lithium anode in 1 M LiF3SO3 in TEGDME-FEC (5:1 v/v) electrolytes before Li–O2 battery assembly. Reproduced with permission.[61b] Copyright 2015, Wiley-VCH. b) The morphology evolution on untreated lithium foil (upper) and Li3PO4-modified lithium foil (lower). Here Li3PO4 layer is formed via chemical reaction between poly(phosphoric acid) (PAA) and the surface layer of lithium foil. Reproduced with permission.[82] Copyright 2016, Wiley-VCH.



ALD process contribute to conformal films and allow for pre-cise control of atomic thickness. Al2O3 layer with a thickness of ca. 14 nm was coated on lithium foil via ALD for the first time. Inorganic Al2O3 layer is chosen for its high mechanical strength and the ionically conductive LixAl2O3 product after lithiation, both of which are beneficial to the promotion of per-formance. Al2O3 particles are also used with a polymer matrix, in which Al2O3 particles provide sufficient mechanical strength to inhibit dendrite formation, while the polymer matrix renders fast lithium-ion transport.[89] A porous Al2O3 layer covered with a reinforced FEC-induced skin layer has also been developed.[90] Coatings, like interconnected hollow carbon nanospheres,[91] ion exchange induced multilayer nanomembrane,[92] etc., have been adopted to provide additional interspace to accom-modate lithium depositions. As presented in Figure 11b, the hollow carbon nanospheres layer exhibits an ultrahigh Young’s modulus of ≈200 GPa to suppress potential dendrite growth. The coating is weakly bonded to the substrate and able to float up and down upon cycling without any cracks forming.

Despite the aforementioned advantages, coatings still show disadvantages, such as selectivity toward the substrates, limited lithium-ion conductivity, etc. It can be inferred that the adhe-sion strength between substrates and coating layers may deter-mine the final structure design and battery performances. For instance, if the adhesion is relatively weak, a certain quantity of lithium deposition is able to separate the coating from the copper substrate, and thus the floating layer is able to accom-modate the volume change. In this case, the coating only needs to introduce nanopores for ion transportation. On the other hand, if the adhesion is strong, lithium ions tend to only deposit on the electrically conducting locations, which could accelerate the dendrite nucleation and growth. In this case, adequate room should be introduced in the internal structure.

To conclude, coatings and reactions are two major approaches to build artificial interfaces over the anode surface

and have been proved to be effective. However, both possess some merits and demerits, as discussed above. More recently, Cui’s group skillfully combined lithium-ion conducting, inor-ganic nanoparticles (Li3N) and a polymer matrix (polymerized styrene butadiene rubber) as the protective layer via an in situ reaction between Cu3N and metallic lithium (Figure 12).[53e] Thus, the final artificial SEI layer exhibits high lithium-ion con-ductivity, mechanical strength, and flexibility, simultaneously. Inspired by this instructive work, principles for designing an artificial interface are presented. Primarily, the interfacial layer should be homogeneous in all aspects to suppress locally enhanced deposition. Secondly, it has to be endowed with enough flexibility to accommodate volume changes and inter-facial fluctuations. Thirdly, it shall possess a compact structure and high elastic modulus to block potential dendrite growth. Furthermore, high ionic conductivity is also required for fast and uniform transport of lithium ions over the whole electrode surface; and, for the sake of energy density and internal impedance of the whole cell, the thickness and weight should be minimized as much as possible.

3.4. Functionalizing Interlayers to Suppress Lithium Dendrites

Conventional nonwoven polymeric or microporous separators, such as polyethylene (PE) or polypropylene (PP), are too fragile to resist dendrites, and have no significant effect on the lithium deposition behaviors. Modified interlayers are herein developed to further guarantee the battery performance, mainly through introducing interactions towardthe dendrites or lithium-ion flux. Herein, the interlayers are endowed with different func-tions, including specially designed separators or additional pro-tective layers, to compensate for the separator weaknesses.

Coating is one of the most useful techniques to modulate the properties of commercial separators. Relevant materials,

Adv. Mater. 2017, 1700007

Figure 11. Artificial SEI layer via coating. a) Lithium deposition on Cu substrate coated with porous PDMS thin film. Reproduced with permission.[85] Copyright 2016, Wiley-VCH. b) Lithium deposition on Cu substrate coated with a hollow carbon nanosphere layer. Here the hollow structures create extra space for lithium depositions, and thus the stress exerted on artificial interface is reduced. Reproduced with permission.[91] Copyright 2014, Nature Publishing Group.



such as mussel-inspired polydopamine,[93] boron-nitride (BN) nanosheets,[94] ultrathin nitrogen/sulfur co-doped graphene nanosheets (NSG),[95] ZrO2/POSS multilayer,[96] Al2O3/poly(phenyl-co-methacryloxypropyl)silsesquioxane compos-ites,[97] etc., have been adopted with different functions. Spe-cifically, the polydopamine coating increases the wettability between the PE separators and electrolytes, and thus enables a well-distributed lithium-ion flux over the whole lithium sur-face. Besides, catechol moieties of polydopamine or NSG coatings present a kind of electrostatic attraction toward the lithium anode, and thus release the surface tension of the lithium metal and suppress the initiation of dendrite growth. As for BN coatings in Figure 13a, the defects and junctions inside the BN layer change the amount of nuclei, and hence the once sharp dendrites turn into much thinker ones, which can’t penetrate through the mechanically strong BN layer. In terms of those ceramic or ceramic–polymer composites, which are mainly designed to improve the mechanical properties of the separators, they show some distinct drawbacks, including: i) the direct contact between lithium and ceramics could induce immediate reactions; ii) the insufficient wettability between ceramic materials and liquid electrolytes may blemish the ion transport; and iii) ceramic particles are easy to detach from polymeric separators owing to poor adhesion. More recently, a novel silica-nanoparticle-sandwiched separator (PE/SiO2/PE) has been put forward, which effectively avoids some aforemen-tioned drawbacks.[98] Moreover, the working mechanism under-neath for the markedly extended life is exactly based on the spontaneous reaction between metallic lithium and SiO2 nano-particles. Specifically, the dendrites that already puncture the bottom layer will react with the SiO2 nanoparticles, and thus the further advance of dendrites is cut off. However, it can be inferred that, firstly, the cell impedance in this tri-layer sepa-rator may be quite large, and thus increase the barrier for ion transportation. Secondly, continuous consumptions of lithium and SiO2 nanoparticles happens during the long-time deposi-tion test. Thirdly, the reaction between metallic lithium and SiO2 nanoparticles needs time, and it is hard to match the cur-rent density and reaction rate. From this viewpoint, this novel mechanism to suppress dendrites still has a long way to go.

Similar sandwich-like separators with a conductive Cu layer between can form an intelligence-security monitoring system to monitor dendrite growth before a battery catastrophe.[99] An additional external circuit is connected between the copper layer and the lithium anode. Once the dendrite grows and already punctures the lower separator, a steep decline in the voltage of this circuit will be observed, and the whole cell is not shorted at that time. In addition to coatings, novel separators with desired structures or compositions are also used. Generally, separators with precisely ordered/well-reticulated nanoporous structures are able to create uniform lithium flux over the anode surface, and thus contribute to homogeneously deposition, such as ano-dized aluminum oxide (AAO) membranes (Figure 13b) and inverse opal-inspired nanoscaffolds.[100] High modulus cellulose nanofibers,[101] aramid nanofibers,[102] polyoxyzole nanofiber (PBO-NM),[103] etc., have been utilized as dendrite-proof sepa-rators in LMBs. For instance, as shown in Figure 13c, the thin PBO-NM membrane made via simple blade-casting can achieve impressive mechanical properties with a Young’s moduli of ca. 20 GPa and an ultimate strength of ca. 525 MPa.

With regard to additional protective layers, they were designed to function as pure physical barriers in the early stages, such as flexible lithium-ion conducting membranes.[8] Afterward, they have been endowed with new functions. Dif-ferent from separators, these additional interlayers are not required to be electronically insulating. Therefore, a conduc-tive carbon nanotube buffer layer,[105] 3D fibrous metal felt (FMF),[106] carbon nanofiber network,[107] etc., are introduced and achieve dendrite-free morphologies, together with good cycle and rate capability. Taking the FMF for example, it not only helps to confine lithium depositions within the 3D frame-work, but also impart electron transport pathways to activate those isolated lithium particles. Besides, the relatively rigid fibers could cut off potential dendrites. Lately, the chemical force between polar functional groups (e.g., OH, CO, and CN groups in 3D, partially oxidized, polyacrylonitrile nanofiber networks; SiO, OH, and OB groups in glass fiber) and lithium ions is also proved to be able to change the lithium-ion flux, and thus manipulate lithium deposition sites, as shown in Figure 13d.[104] In particular, the movement of

Adv. Mater. 2017, 1700007

Figure 12. Illustration of a potential ultimate strategy to build ideal artificial SEI layers. Here the Cu3N + SBR composite artificial SEI layer enables high lithium-ion conductivity, mechanical strength, and flexibility for stable lithium-metal anodes. Reproduced with permission.[53e] Copyright 2016, Wiley-VCH.



lithium ions toward the “hot spots” created by initially deposited lithium is retarded by the chemical force from polar functional groups, and thus the preferential deposition is mitigated. This close interaction has been later confirmed via simulations and computations. Lithium ions display the highest binding energy toward those polar functional groups instead of copper or the deposited lithium particles. Besides, the polymer network or glass fiber could act as a buffer layer to entrap lithium deposi-tions inside and contribute to less electrolyte consumption.

Generally, an ideal separator for LMBs are expected to pos-sess good wettability, fast ion conductivity, strong mechanical strength, and the ability to manipulate the lithium deposition behaviors. In view of cell impedance, weight, and volume, directly functionalizing the separators may be a better strategy than inserting additional protective layers, although the latter has more choices in terms of compositions, structures, and properties (mechanical strength, conductivity, etc.). The pre-sent approaches can already modify the separators in a wide

range, in which ceramic coating is the most common, but the drawbacks are also distinct, as summarized above. In this sense, it might be a right choice to develop a novel separator due to the earth-abundant sources, wide variety, and good pro-cessability of polymers.

4. Challenges and Outlook

LOEs are widely used due to their incomparable ionic conduc-tivity and excellent interfacial wettability toward lithium anodes. However, they show negligible mechanical strength to block the dendrite growth and volume expansion upon repeated deposi-tion/dissolution. Besides, the hyperactivity between metallic lithium and liquid electrolytes cause severe lithium corrosion. The consequential SEI layer makes matters even worse, of which the breakage and heterogeneity could accelerate the den-drite growth and electrolyte/lithium consumption. Guided by

Adv. Mater. 2017, 1700007

Figure 13. Illustrations of functionalized interlayers to suppress the dendrites. a) Separator with high modulus BN coatings. Reproduced with permis-sion.[94] Copyright 2015, American Chemical Society. b) Separator with specially designed internal structures. Reproduced with permission.[100a] Copy-right 2014, Royal Chemical Society. c) Separator with high modulus compositions. The polyoxyzole nanofiber membranes (PBO-NM) via blade casting method (left) enable ultimate strengths of ca. 525 MPa and Young’s moduli of ca. 20 GPa. Reproduced with permission.[103] Copyright 2016, American Chemical Society. d) Functionalized additional layer with chemical force toward lithium ions. It can be observed that the lithium ions are uniformly distributed over the surface with GF, leading to a smooth deposition. Reproduced with permission.[104b] Copyright 2016, Wiley-VCH.



the failure mechanisms of the lithium-metal anode, consider-able efforts have been conducted and proved to be workable in laboratory coin cells. However, there are still challenges to over-come, especially for further practical applications. For the sake of energy density, cell performance, and safety, the introduction of solid-state electrolytes seems to be a fundamental strategy for next-generation, high-energy LMBs.

4.1. Challenges

The aforementioned strategies, including tailoring anode struc-tures, optimizing electrolytes, building artificial interfaces, and functionalizing interlayers, indeed mitigate the safety hazards of lithium-metal anode, and significantly improve the electrochemical performance of LMBs. However, at the same time, these strategies suffer from certain shortcomings, as follows: i) strategies like tailoring the anode structures need an additional predeposition process to load the lithium source for each slice of electrode, which is not practical in industrial applications; ii) the dilemma between dendrite suppression and electrochemical performance is still hard to resolve (e.g., the utilization of 3D anode nanostructures would increase the contact area between electrolytes and lithium depositions, and thus intensify the side reactions); iii) the introduction of spe-cially designed anode structures, artificial SEI layers, protec-tive interlayers, etc., inevitably increase the cell impedance and decrease the energy density of the whole cell; iv) strategies like adding additives are not sustainable due to continuous con-sumption upon prolonged cycles in view of their low amount addition; v) most effectual approaches only apply to conditions such as low current density, small lithium deposition capacity, specific electrolyte compositions, high addition of electrolytes, etc. In fact, there is large gap between the laboratory coin cells and commercial pouch cells.[19c] Taking the current density for example, the current applied in a pouch cell is several dozen to one hundred times larger than that in coin cells, indicating that there is still a high chance of dendrite growth, even though the present strategies are utilized. Besides, in consideration of the hyperactivity and huge volume expansion, the proposal of

building a “house” with a 3D host as the frame and an artificial SEI layer as the roof seems to be a powerful method, as dis-played in Figure 14. And in order to avoid surface deposition, preferential nucleation sites need to be added to drive lithium ions into the depth of the 3D conductive host. Nevertheless, how to build this integrated anode structure needs special con-sideration and remains a challenge.

In addition, these LOE systems also make it harder to uti-lize the present in situ or operando characterization techniques due to their relatively low boiling point, flowability, and insta-bility toward water or atmospheric gases. Most of the present characterization are either based on solid electrolytes (e.g., Li2O,[39] polymers,[13,108]) or specially designed artificial cells,[109] each exhibiting differences from realistic cells, with respect to electrode size or thickness. To date, the fundamental mecha-nisms and dynamics process of dendrite nucleation/growth and interfacial evolution are still not sufficiently characterized and explained. Therefore, the development of advanced char-acterization techniques, theoretical calculation, and simulation is extremely urgent for clear, comprehensive, noninvasive, and versatile investigations of the deposition process and related variables in the liquid phase.

4.2. Outlook

The introduction of solid-state electrolytes (SSEs) seems to be a fundamental tool to resolve the safety hazards caused by lithium dendrites once for all, in view of their mechanical rigidity, and features like nonflammable, non-explosive, and zero-leakage further enhance the safety of LMBs. Besides, SSEs prevent unwanted chemical interactions between the electrodes owing to their inhabitation of soluble electrode components from the cathode. More importantly, solid inorganic electro-lytes only allow the transfer of lithium ions, and thus eliminate the severe concentration gradient that always happen in liquid electrolytes, which is proved to be a chief cause that leads to dendrite nucleation.[13,110] Furthermore, SSEs exhibit relatively weak selectivity toward the cathodes while the LOEs used in batteries with LiCoO2, S, and O2 is totally different. Therefore,

Adv. Mater. 2017, 1700007

Figure 14. The proposal of building a “house” for hyperactive and hostless lithium by employing a 3D conductive host as the frame and artificial SEI layer as the roof.



Adv. Mater. 2017, 1700007

SSEs possess great potential for application in next-generation high-energy LMBs, while both solid polymer and inorganic electrolytes have already been used and achieved substantial success in LMBs.[111]

Typical solid polymer electrolyte (SPE) consists of a rationally selected polymer matrix and lithium salts. The development of SPEs toward the lithium anode is greatly hampered by two harsh issues: i) the dilemma between mechanical rigidity and ionic conductivity; ii) a relatively low lithium-ion transference number, owing to strong interactions between lithium ions and the polymer matrix, which will cause polarization and a strong electric field in the vicinity of the electrode. Hopefully, various approaches have been put forward to resolve these two problems. Firstly, effective additives with different mor-phology and compositions have been introduced. Thereinto, liquid plasticizers are added to give the polymer liquid-like ion conductivity, but at the expense of mechanical strength.[112] To further improve their mechanical strength and ion con-ductivity at the same time, rigid inorganic nano particles,[113] lithium-ion conducting nanowires or networks,[114] oxide-ion conducting nanowires,[115] etc., have been added via ex situ or in situ strategies. Techniques like thermal or UV curing and in situ polymerization also enable the transformation from gel-like to solid-like morphologies.[116] Secondly, the internal molecular structures of the polymer matrix have been modu-lated to release more free lithium ions. Cross-linked poly-mers,[117] block copolymers,[118] single-ion conducting lithiated nafion membrane,[119] super-delocalized polyanion,[120] aromatic poly(arylene ether)s,[121] interpenetrating poly(ether-acrylate) networks,[122] covalent organic frameworks (COFs),[123] poly-merized ionic networks,[124] poly(poly(propylene carbonate) membranes,[125] etc., have been synthesized and utilized as solid electrolytes. Notably, the development of single-ion conducting polymer electrolyte is the most promising, owing to a lithium-ion transference number close to one. This kind of electrolyte eliminates potential at the concentration gradient, polarization,

and a strong electric field at the electrode surface, and thus sup-presses dendrite formation and polymer decomposition.

Compared to SPEs, solid inorganic electrolytes (SIEs) are single-ion conductive, with exceptional high mechanical strength. However, in consideration of their relatively low lith-ium-ion conductivity, and poor wettability and stability toward solid lithium foil, most efforts in SIEs have been made to inves-tigate the ion transport mechanisms and develop new fast ion-conductive SIEs, or ameliorate the knotty interfacial issues. The several types of currently developed SIEs are summarized in Table 1. Among them, thio-LISICON-type (e.g., Li10GeP2S12) has already reached an ionic conductivity over 10−2 S cm−1, which is comparable to those LOEs.[126] In addition, the con-ducting mechanisms underneath and design principles have been thoroughly investigated.[127] Despite their superior con-ductivity, these kinds of electrolytes are not stable with lithium anodes and the oxide cathodes. In terms of interfacial problems, advanced characterization techniques have been adopted to investigate the evolution process of the solid–solid interface.[128] Three types of interfaces have been elucidated, including a stable interface without any reactions, a mixed electronically and ionically conductive interface, and electronically insulating but ionically conductive interface. Among the three, the second type is disastrous and needs to be avoided. One approach is to introduce stable coatings, such as glass-ceramic electrolytes and amorphous electrolytes, which exhibit superior wettability and stability toward lithium (Figure 15a).[129] In addition to coat-ings based on SSEs, Au and Si coatings are also introduced to stabilize the interface and increase the wettability, owing to their ability to form alloys with metallic lithium at room tem-perature.[130] Taking the Si coating for example, in Figure 15b, the original lithiophobic interface is transformed into super-lithiophilic with an ultrathin Li–Si alloy layer, leading to a steep decline in interfacial resistance from 925 Ω cm2 (bare garnet) to 127 Ω cm2 (Si-coated garnet). Additionally, the once heteroge-neous ion flux is smoothed over the anode surface. Metal oxide

Table 1. Summary of representative solid inorganic electrolytes and their advantages and disadvantages.

Crystal structure

Representatives Ionic conductivity (R.T.)

Advantages Disadvantages Ref.

Perovskite Li0.33La0.56TiO3 10−3 S cm−1 Air-stable; High bulk conductivity Low total conductivity; Uncontrollable

products; Ti4+ reduction toward Li

[132]

Antiperovskite Li3OX, Li3−n(OHn)X (X = Cl, Br) 10−3 S cm−1 Stable toward metallic Li; Ultrahigh energy window Uncontrollable preparation [133]

Garnet Li7La3Zr2O12 10−4 S cm−1 Thermal and chemical stability; Environmental

benignity; Low cost; Ease of preparation

Huge interfacial resistance; Dendrites

penetrating via grain boundaries

[134]

LISICON Li4SiO4−Li3PO4 10−3 S cm−1 Exceptional stability; Easy to synthesize and handle Relatively low ionic conductivity [135]

Thio-LISICON Li10GeP2S12 Li10SnP2S12 10−1–10−2 S cm−1 High bulk conductivity Not stable with lithium anode and

oxide cathodes; Ta5+ reduction toward Li

[126,136]

Argyrodite Li6PS5X (X = Cl, Br, I) 10−2–10−3 S cm−1 Cheap precursors; Wide electrochemical window Unstable to polar organic solvents [137]

NASICON Li1+xAlxTi2−x(PO4)3 10−4 S cm−1 Abundant reserves; Low cost; Atmospheric

stabilityTi4+ reduction toward Li; Huge interfacial

resistance; Large grain boundaries

[138]

Layered Li3N 10−3 S cm−1 Stable toward metallic Li Low electrochemical decomposition

potential

[139]

Amorphous LiPON 10−6 S cm−1 Low electronic conductivity; High stability

window; Stable toward metallic Li

Relatively low ionic conductivity [140]

Glass–ceramic Li7P3S11 10−2 S cm−1 High conductivity; Low grain boundary resistance Hygroscopic; Limited voltage windows [141]



Adv. Mater. 2017, 1700007

coatings like ZnO and Al2O3 also dramatically improve the interfacial performance between garnets and lithium foil via a lithiation process.[38,131] Comparatively, the lithiated metal–oxide interface possess higher lithium ion conductivity com-pared to those Li-alloys, facilitating easy and uniform ion trans-port within the interface. Furthermore, elemental substitution or doping (e.g., Al, Ta, Nb, Ca) also contribute to stabilization of the interface via in situ formation of Li-alloys or replacement of unstable elements.[128a]

In addition to SPEs or SIEs, solid or solid-like hybrid elec-trolytes (SHEs) have recently ignited intensive attention owing to their ability to combine the advantages and avoid the dis-advantages of each component. So far, several groups have made some successful attempts that shed insightful light for future researches. One type of SHE is the careful combina-tion of two kinds of existing electrolyte (e.g., LOEs, ionic liq-uids (ILs), solid polymer electrolytes (SPEs) and solid inor-ganic electrolytes (SIEs)). Representative combinations include ILs–SIEs,[142] LOEs–SPEs,[143] SIEs–SPEs,[144] etc.; for example, as shown in Figure 16a, the sandwich-like solid hybrid elec-trolyte comprehensively utilizes the superior wettability and strong adhesion strength of the SPE to increase the contact area toward bulk lithium anode. Besides, the single-ion con-ductive LATP layer blocks anions from vacating the anode/electrolyte interface, and thus prohibits the decomposition of the polymer, owing to a much reduced electric-double-layer field. Another type of SHE is the combination of low-modulus

electrolytes and high-modulus materials. Herein, the high-modulus material is to form a rigid framework to nanoconfine or support the low-modulus electrolytes, which is different from those additives. Thereinto, high modulus SiO2 and Al2O3 have been widely used due to their stability and com-patibility toward metallic lithium. Layered polymer/ceramic/polymer electrolytes,[145] liquid-electrolyte-confined AAO/glass fiber/AAO framework,[146] liquid-electrolyte-con-fined hollow SiO2 spheres,[147] etc., have been developed to obtain solid-like mechanical rigidity but liquid-like ion conductivity. For example, as shown in Figure 16b, the pow-ders of hollow nanospheres with a diameter of ca. 25 nm and shell thickness of ca. 5 nm are processed into tablets and then soaked into the liquid electrolytes. Due to the enor-mous absorption for liquid electrolytes and nanoconfining effect of the hollow nano-spheres, the final solid-like hybrid electrolyte possesses an ionic conductivity about 2.5 × 10−3 S cm−1. Besides, a novel SHE made up with nanoporous graphene-analogue boron nitride (g-BN) nanosheets and ionic liquids is also prepared, and demonstrates an ionic conductivity up to 3.85 × 10−3 S cm−1.[148]

It is believed that the high-energy LMBs will usher a bright, solid future with the help of these novel approaches. In particular, the ionic conductivity of some solid electro-

lytes is able to reach the same level as liquid ones. Besides, their intrinsic, inferior interfacial wettability and stability are also well solved via coating or hybridizing. In this sense, the introduction of solid electrolytes will undoubtedly endow high-energy-density LMBs with better electrochemical performance and, more importantly, the safety performance.

5. Conclusion

Here, we have highlighted recent advances to revive lithium metal as the anode for next-generation, high-energy batteries. The harsh issues toward lithium-metal anodes and their fun-damental formation mechanism are thoroughly discussed, together with instructive guiding principles to manipulate the deposition behavior of lithium ions and suppress the for-mation/growth of lithium dendrite, to inhibit parasitic reac-tions associated with hyperactive lithium, and to minimize the volume changes upon cycling. The developments and representative work on lithium-metal anodes in the past three years under liquid organic electrolyte systems are reviewed, including the tailoring the anode structure, optimizing electro-lytes, building artificial anode–electrolyte interfaces, and func-tionalizing interlayers. Finally, the remained challenges in LOE systems are presented and future perspectives of introducing solid-state electrolytes to radically address the safety issues are given.

Figure 15. Illustrations of ameliorating the solid–solid interface between the solid inorganic electrolytes and lithium foil via coating different stable materials. a) Glass–ceramic electro-lyte coating. Reproduced with permission.[129b] Copyright 2016, American Chemical Society. b) Si coating based on alloy reaction with metallic lithium. It is shown that the once super-lithiophobic interface with an internal impedance of ca. 925 Ω cm2 turns into superlithiophilic interface with a relatively low impedance of ca. 127 Ω cm2. Reproduced with permission.[130b] Copyright 2016, American Chemical Society.



Adv. Mater. 2017, 1700007

AcknowledgementsThe authors acknowledge the National Natural Science Foundation of China (21571073, 21673090, 51551205), Hubei Provincial Natural Science Foundation of China (2016CFA031), National Key Research and Development Program of “Strategic Advanced Electronic Materials” (2016YFB0401100), National Basic Research Program of China (2015CB932600), the Program for HUST Interdisplinary Innovation Team (2015ZDTD038) and the Fundamental Research Funds for the Central University. The authors also thank the Analytical and Testing Center of HUST for the measurements.

Keywordslithium anodes, lithium dendrites, lithium-metal batteries, solid electrolytes

Received: January 1, 2017Revised: February 18, 2017

Published online:

[1] a) S. Chu, A. Majumdar, Nature 2012, 488, 294; b) K. Amine, R. Kanno, Y. Tzeng, MRS Bull. 2014, 39, 395; c) B. Dunn, H. Kamath, J.-M. Tarascon, Science 2011, 334, 928.

[2] a) J. B. Goodenough, K.-S. Park, J. Am. Chem. Soc. 2013, 135, 1167; b) G. Jeong, Y.-U. Kim, H. Kim, Y.-J. Kim, H.-J. Sohn, Energy Environ. Sci. 2011, 4, 1986; c) Z. Yan, L. Liu, J. Tan, Q. Zhou, Z. Huang, D. Xia, H. Shu, X. Yang, X. Wang, J. Power Sources

2014, 269, 37; d) Z. Yan, L. Liu, H. Shu, X. Yang, H. Wang, J. Tan, Q. Zhou, Z. Huang, X. Wang, J. Power Sources 2015, 274, 8.

[3] a) J. M. Tarascon, M. Armand, Nature 2001, 414, 359; b) Y. X. Yin, S. Xin, Y. G. Guo, L. J. Wan, Angew. Chem., Int. Ed. 2013, 52, 13186; c) L. Grande, E. Paillard, J. Hassoun, J. B. Park, Y. J. Lee, Y. K. Sun, S. Passerini, B. Scrosati, Adv. Mater. 2015, 27, 784.

[4] N. Nitta, F. Wu, J. T. Lee, G. Yushin, Mater. Today 2015, 18, 252.[5] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon,

Nat. Mater. 2012, 11, 19.[6] R. Cao, W. Xu, D. Lv, J. Xiao, J.-G. Zhang, Adv. Energy Mater. 2015,

5, 1402273.[7] M. S. Whittingham, Science 1976, 192, 1126.[8] N. B. Aetukuri, S. Kitajima, E. Jung, L. E. Thompson, K. Virwani,

M. L. Reich, M. Kunze, M. Schneider, W. Schmidbauer, W. W. Wilcke, D. S. Bethune, J. C. Scott, R. D. Miller, H. C. Kim, Adv. Energy Mater. 2015, 5, 1500265.

[9] D. Lu, Y. Shao, T. Lozano, W. D. Bennett, G. L. Graff, B. Polzin, J. Zhang, M. H. Engelhard, N. T. Saenz, W. A. Henderson, P. Bhattacharya, J. Liu, J. Xiao, Adv. Energy Mater. 2015, 5, 1400993.

[10] Z. Liang, D. Lin, J. Zhao, Z. Lu, Y. Liu, C. Liu, Y. Lu, H. Wang, K. Yan, X. Tao, Y. Cui, Proc. Natl. Acad. Sci. USA 2016, 113, 2862.

[11] Web of science, http://apps.webofknowledge.com/Search. do?product=UA&SID=3EM2tkHrDyFCfvspJi1&search_mode= GeneralSearch&prID=578cabaf-7fc1-4620-9eae-73ee51139083, accessed: December 2016.

[12] Y. Sawada, A. Dougherty, J. P. Gollub, Phys. Rev. Lett. 1986, 56, 1260.

[13] C. Brissot, M. Rosso, J. N. Chazalviel, S. Lascaud, J. Power Sources 1999, 81–82, 925.

Figure 16. Illustrations of solid hybrid electrolytes that combine the advantages of each component. a) Polymer/ceramic/polymer-sandwich elec-trolytes (left). The curves inside are electric potential profiles of the solid hybrid electrolytes and individual solid polymer electrolyte (right). A much reduced double-layer electric field is observed inside the sandwich electrolyte due to the suppressed anion transfer in LATP, and thus the potential polymer decomposition at the anode surface is inhibited. Reproduced with permission.[144b] Copyright 2016, American Chemical Society. b) Liquid electrolytes with confined hollow SiO2 spheres as the electrolyte. Due to the enormous absorption for liquid electrolytes and nanoconfining effect of the hollow nanospheres, the final electrolytes deliver a solid-like robust mechanical rigidity with a liquid-like superior ionic conductivity. Reproduced with permission.[147a] Copyright 2015, American Chemical Society.

http://apps.webofknowledge.com/Search.do?product=UA&SID=3EM2tkHrDyFCfvspJi1&search_mode=GeneralSearch&prID=578cabaf-7fc1-4620-9eae-73ee51139083





Adv. Mater. 2017, 1700007

[14] H. J. Chang, A. J. Ilott, N. M. Trease, M. Mohammadi, A. Jerschow, C. P. Grey, J. Am. Chem. Soc. 2015, 137, 15209.

[15] P. Bai, J. Li, F. R. Brushett, M. Z. Bazant, Energy Environ. Sci. 2016, 9, 3221.

[16] J.-i. Yamaki, S.-i. Tobishima, K. Hayashi, S. Keiichi, Y. Nemoto, M. Arakawa, J. Power Sources 1998, 74, 219.

[17] a) E. Peled, J. Electrochem. Soc. 1979, 126, 2047; b) X.-B. Cheng, R. Zhang, C.-Z. Zhao, F. Wei, J.-G. Zhang, Q. Zhang, Adv. Sci. 2016, 3, 1500213.

[18] Y. S. Cohen, Y. Cohen, D. Aurbach, J. Phys. Chem. B 2000, 104, 12282.

[19] a) D. Aurbach, E. Zinigrad, H. Teller, P. Dan, J. Electrochem. Soc. 2000, 147, 1274; b) T. J. Richardson, G. Chen, J. Power Sources 2007, 174, 810; c) X.-B. Cheng, C. Yan, J.-Q. Huang, P. Li, L. Zhu, L. Zhao, Y. Zhang, W. Zhu, S.-T. Yang, Q. Zhang, Energy Storage Mater. 2017, 6, 18.

[20] a) F. Sun, L. Zielke, H. Markotter, A. Hilger, D. Zhou, R. Moroni, R. Zengerle, S. Thiele, J. Banhart, I. Manke, ACS Nano 2016, 10, 7990; b) K. J. Harry, D. T. Hallinan, D. Y. Parkinson, A. A. MacDowell, N. P. Balsara, Nat. Mater. 2014, 13, 69; c) J. Wandt, C. Marino, H. A. Gasteiger, P. Jakes, R. A. Eichel, J. Granwehr, Energy Environ. Sci. 2015, 8, 1358; d) S. Chandrashekar, N. M. Trease, H. J. Chang, L. S. Du, C. P. Grey, A. Jerschow, Nat. Mater. 2012, 11, 311.

[21] R. L. Sacci, J. M. Black, N. Balke, N. J. Dudney, K. L. More, R. R. Unocic, Nano Lett. 2015, 15, 2011.

[22] a) J. Heine, S. Krüger, C. Hartnig, U. Wietelmann, M. Winter, P. Bieker, Adv. Energy Mater. 2014, 4, 1300815; b) M. H. Ryou, Y. M. Lee, Y. J. Lee, M. Winter, P. Bieker, Adv. Funct. Mater. 2015, 25, 834; c) J. Park, J. Jeong, Y. Lee, M. Oh, M.-H. Ryou, Y. M. Lee, Adv. Mater. Interfaces 2016, 3, 1600140.

[23] X. L. Ji, D. Y. Liu, D. G. Prendiville, Y. C. Zhang, X. N. Liu, G. D. Stucky, Nano Today 2012, 7, 10.

[24] C. P. Yang, Y. X. Yin, S. F. Zhang, N. W. Li, Y. G. Guo, Nat. Commun. 2015, 6, 8058.

[25] L. L. Lu, J. Ge, J. N. Yang, S. M. Chen, H. B. Yao, F. Zhou, S. H. Yu, Nano Lett. 2016, 16, 4431.

[26] Q. Yun, Y. B. He, W. Lv, Y. Zhao, B. Li, F. Kang, Q. H. Yang, Adv. Mater. 2016, 28, 6932.

[27] H.-K. Kang, S.-G. Woo, J.-H. Kim, S.-R. Lee, Y.-J. Kim, Electrochim. Acta 2015, 176, 172.

[28] A. Zhamu, G. R. Chen, C. G. Liu, D. Neff, Q. Fang, Z. N. Yu, W. Xiong, Y. B. Wang, X. Q. Wang, B. Z. Jang, Energy Environ. Sci. 2012, 5, 5701.

[29] X.-B. Cheng, H.-J. Peng, J.-Q. Huang, R. Zhang, C.-Z. Zhao, Q. Zhang, ACS Nano 2015, 9, 6373.

[30] R. Zhang, X.-B. Cheng, C.-Z. Zhao, H.-J. Peng, J.-L. Shi, J.-Q. Huang, J. Wang, F. Wei, Q. Zhang, Adv. Mater. 2016, 28, 2155.

[31] R. Mukherjee, A. V. Thomas, D. Datta, E. Singh, J. Li, O. Eksik, V. B. Shenoy, N. Koratkar, Nat. Commun. 2014, 5, 3710.

[32] S. Jin, S. Xin, L. Wang, Z. Du, L. Cao, J. Chen, X. Kong, M. Gong, J. Lu, Y. Zhu, H. Ji, R. S. Ruoff, Adv. Mater. 2016, 28, 9094.

[33] D. Aurbach, E. Zinigrad, Y. Cohen, H. Teller, Solid State Ionics 2002, 148, 405.

[34] a) X. B. Cheng, H. J. Peng, J. Q. Huang, F. Wei, Q. Zhang, Small 2014, 10, 4257; b) X. Zhang, W. Wang, A. Wang, Y. Huang, K. Yuan, Z. Yu, J. Qiu, Y. Yang, J. Mater. Chem. A 2014, 2, 11660.

[35] Q. Xu, Y. F. Yang, H. X. Shao, Phys. Chem. Chem. Phys. 2015, 17, 20398.

[36] D. Lin, Y. Liu, Z. Liang, H. W. Lee, J. Sun, H. Wang, K. Yan, J. Xie, Y. Cui, Nat. Nanotechnol. 2016, 11, 626.

[37] Y. Y. Liu, D. C. Lin, Z. Liang, J. Zhao, K. Yan, Y. Cui, Nat. Commun. 2016, 7, 10992.

[38] C. Wang, Y. Gong, B. Liu, K. Fu, Y. Yao, E. Hitz, Y. Li, J. Dai, S. Xu, W. Luo, E. D. Wachsman, L. Hu, Nano Lett. 2017, 17, 565.

[39] K. Yan, Z. Lu, H.-W. Lee, F. Xiong, P.-C. Hsu, Y. Li, J. Zhao, S. Chu, Y. Cui, Nat. Energy 2016, 1, 16010.

[40] K. Leung, F. Soto, K. Hankins, P. B. Balbuena, K. L. Harrison, J. Phys. Chem. C 2016, 120, 6302.

[41] O. Crowther, A. C. West, J. Electrochem. Soc. 2008, 155, A806.[42] a) D. Aurbach, A. Zaban, A. Schechter, Y. Ein-Eli, E. Zinigrad,

B. Markovsky, J. Electrochem. Soc. 1995, 142, 2873; b) D. Aurbach, J. Power Sources 2000, 89, 206; c) M. S. Park, S. B. Ma, D. J. Lee, D. Im, S. G. Doo, O. Yamamoto, Sci. Rep. 2014, 4, 3815.

[43] X. Chen, T.-Z. Hou, B. Li, C. Yan, L. Zhu, C. Guan, X.-B. Cheng, H.-J. Peng, J.-Q. Huang, Q. Zhang, Energy Storage Mater. 2017, DOI: 10.1016/j.ensm.2017.01.003.

[44] a) C. Zu, N. Azimi, Z. Zhang, A. Manthiram, J. Mater. Chem. A 2015, 3, 14864; b) R. R. Miao, J. Yang, Z. X. Xu, J. L. Wang, Y. Nuli, L. M. Sun, Sci. Rep. 2016, 6, 21771.

[45] a) H. B. Han, S. S. Zhou, D. J. Zhang, S. W. Feng, L. F. Li, K. Liu, W. F. Feng, J. Nie, H. Li, X. J. Huang, M. Armand, Z. B. Zhou, J. Power Sources 2011, 196, 3623; b) J. J. Hu, G. K. Long, S. Liu, G. R. Li, X. P. Gao, Chem. Commun. 2014, 50, 14647; c) R. Miao, J. Yang, X. Feng, H. Jia, J. Wang, Y. Nuli, J. Power Sources 2014, 271, 291; d) I. A. Shkrob, T. W. Marin, Y. Zhu, D. P. Abraham, J. Phys. Chem. C 2014, 118, 19661; e) Q. Ma, B. Tong, Z. Fang, X. Qi, W. Feng, J. Nie, Y.-S. Hu, H. Li, X. Huang, L. Chen, Z. Zhou, J. Electrochem. Soc. 2016, 163, A1776.

[46] a) N. Schweikert, A. Hofmann, M. Schulz, M. Scheuermann, S. T. Boles, T. Hanemann, H. Hahn, S. Indris, J. Power Sources 2013, 228, 237; b) Y. Jin, J. Zhang, J. Song, Z. Zhang, S. Fang, L. Yang, S.-i. Hirano, J. Power Sources 2014, 254, 137; c) D. R. MacFarlane, N. Tachikawa, M. Forsyth, J. M. Pringle, P. C. Howlett, G. D. Elliott, J. H. Davis, M. Watanabe, P. Simon, C. A. Angell, Energy Environ. Sci. 2014, 7, 232; d) L. Grande, J. von Zamory, S. L. Koch, J. Kalhoff, E. Paillard, S. Passerini, ACS Appl. Mater. Interfaces 2015, 7, 5950.

[47] N. Byrne, P. C. Howlett, D. R. MacFarlane, M. Forsyth, Adv. Mater. 2005, 17, 2497.

[48] N.-W. Li, Y.-X. Yin, J.-Y. Li, C.-H. Zhang, Y.-G. Guo, Adv. Sci. 2016, 4, 1600400.

[49] a) K. Kanamura, S. Shiraishi, Z. I. Takehara, J. Electrochem. Soc. 1996, 143, 2187; b) Y. Lu, Z. Tu, L. A. Archer, Nat. Mater. 2014, 13, 961.

[50] J. F. Qian, W. Xu, P. Bhattacharya, M. Engelhard, W. A. Henderson, Y. H. Zhang, J. G. Zhang, Nano Energy 2015, 15, 135.

[51] S. Choudhury, L. A. Archer, Adv. Electron. Mater. 2016, 2, 1500246.[52] Y. Lu, Z. Tu, J. Shu, L. A. Archer, J. Power Sources 2015, 279, 413.[53] a) S. S. Zhang, Electrochim. Acta 2012, 70, 344; b) J. Guo,

Z. Y. Wen, M. F. Wu, J. Jin, Y. Liu, Electrochem. Commun. 2015, 51, 59; c) D. Aurbach, E. Pollak, R. Elazari, G. Salitra, C. S. Kelley, J. Affinito, J. Electrochem. Soc. 2009, 156, A694; d) S. S. Zhang, J. Power Sources 2016, 322, 99; e) Y. Liu, D. Lin, P. Y. Yuen, K. Liu, J. Xie, R. H. Dauskardt, Y. Cui, Adv. Mater. 2016, 29, 1605531.

[54] F. Wu, J. Qian, R. Chen, J. Lu, L. Li, H. Wu, J. Chen, T. Zhao, Y. Ye, K. Amine, ACS Appl. Mater. Interfaces 2014, 6, 15542.

[55] a) C.-Z. Zhao, X.-B. Cheng, R. Zhang, H.-J. Peng, J.-Q. Huang, R. Ran, Z.-H. Huang, F. Wei, Q. Zhang, Energy Storage Mater. 2016, 3, 77; b) C. Yan, X.-B. Cheng, C.-Z. Zhao, J.-Q. Huang, S.-T. Yang, Q. Zhang, J. Power Sources 2016, 327, 212.

[56] C. Zu, A. Dolocan, P. Xiao, S. Stauffer, G. Henkelman, A. Manthiram, Adv. Energy Mater. 2016, 6, 1501933.

[57] a) W. Li, H. Yao, K. Yan, G. Zheng, Z. Liang, Y.-M. Chiang, Y. Cui, Nat. Commun. 2015, 6, 7436; b) S. Xiong, K. Xie, Y. Diao, X. Hong, J. Power Sources 2014, 246, 840.

[58] T. Jaumann, J. Balach, M. Klose, S. Oswald, J. Eckert, L. Giebeler, J. Electrochem. Soc. 2016, 163, A557.

[59] Y. Matsuda, M. Sekiya, J. Power Sources 1999, 81–82, 759.[60] H. Ota, K. Shima, M. Ue, J. I. Yamaki, Electrochim. Acta 2004, 49,

565.

https://doi.org/10.1016/j.ensm.2017.01.003



Adv. Mater. 2017, 1700007

[61] a) J. Heine, P. Hilbig, X. Qi, P. Niehoff, M. Winter, P. Bieker, J. Electrochem. Soc. 2015, 162, A1094; b) Q. C. Liu, J. J. Xu, S. Yuan, Z. W. Chang, D. Xu, Y. B. Yin, L. Li, H. X. Zhong, Y. S. Jiang, J. M. Yan, X. B. Zhang, Adv. Mater. 2015, 27, 5241; c) X.-Q. Zhang, X.-B. Cheng, X. Chen, C. Yan, Q. Zhang, Adv. Funct. Mater. 2017, 27, 1605989.

[62] J. W. Choi, G. Cheruvally, D. S. Kim, J. H. Ahn, K. W. Kim, H. J. Ahn, J. Power Sources 2008, 183, 441.

[63] M. Wu, Z. Wen, J. Jin, Y. Cui, Electrochim. Acta 2013, 103, 199.[64] F. Ding, W. Xu, G. L. Graff, J. Zhang, M. L. Sushko, X. Chen,

Y. Shao, M. H. Engelhard, Z. Nie, J. Xiao, X. Liu, P. V. Sushko, J. Liu, J.-G. Zhang, J. Am. Chem. Soc. 2013, 135, 4450.

[65] R. Wibowo, L. Aldous, S. E. W. Jones, R. G. Compton, Chem. Phys. Lett. 2010, 492, 276.

[66] a) K. P. Doyle, C. M. Lang, K. Kim, P. A. Kohl, J. Electrochem. Soc. 2006, 153, A1353; b) J. K. Stark, Y. Ding, P. A. Kohl, J. Electrochem. Soc. 2013, 160, D337.

[67] M. Ishikawa, M. Morita, Y. Matsuda, J. Power Sources 1997, 68, 501.[68] S. Yoon, J. Lee, S. O. Kim, H. J. Sohn, Electrochim. Acta 2008, 53, 2501.[69] J. K. S. Goodman, P. A. Kohl, J. Electrochem. Soc. 2014, 161, D418.[70] W. Jia, C. Fan, L. Wang, Q. Wang, M. Zhao, A. Zhou, J. Li, ACS

Appl. Mater. Interfaces 2016, 8, 15399.[71] Y. H. Zhang, J. F. Qian, W. Xu, S. M. Russell, X. L. Chen,

E. Nasybulin, P. Bhattacharya, M. H. Engelhard, D. H. Mei, R. G. Cao, F. Ding, A. V. Cresce, K. Xu, J. G. Zhang, Nano Lett. 2014, 14, 6889.

[72] a) F. Ding, W. Xu, X. L. Chen, J. Zhang, Y. Y. Shao, M. H. Engelhard, Y. H. Zhang, T. A. Blake, G. L. Graff, X. J. Liu, J. G. Zhang, J. Phys. Chem. C 2014, 118, 4043; b) J. Z. Hu, Z. C. Zhao, M. Y. Hu, J. Feng, X. C. Deng, X. L. Chen, W. Xu, J. Liu, J. G. Zhang, J. Power Sources 2016, 304, 51.

[73] a) S. S. Moganty, N. Jayaprakash, J. L. Nugent, J. Shen, L. A. Archer, Angew. Chem., Int. Ed. 2010, 122, 9344; b) Y. Lu, S. K. Das, S. S. Moganty, L. A. Archer, Adv. Mater. 2012, 24, 4430; c) Y. Lu, K. Korf, Y. Kambe, Z. Tu, L. A. Archer, Angew. Chem., Int. Ed. 2014, 53, 488.

[74] L. M. Suo, Y. S. Hu, H. Li, M. Armand, L. Q. Chen, Nat. Commun. 2013, 4, 1481.

[75] J. Qian, W. A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin, J. G. Zhang, Nat. Commun. 2015, 6, 6362.

[76] J. Qian, B. D. Adams, J. Zheng, W. Xu, W. A. Henderson, J. Wang, M. E. Bowden, S. Xu, J. Hu, J.-G. Zhang, Adv. Funct. Mater. 2016, 26, 7094.

[77] a) Z. Fang, Q. Ma, P. Liu, J. Ma, Y. S. Hu, Z. Zhou, H. Li, X. Huang, L. Chen, ACS Appl. Mater. Interfaces 2017, 9, 4282; b) N. Togasaki, T. Momma, T. Osaka, J. Power Sources 2016, 307, 98.

[78] J. M. Zheng, P. F. Yan, D. H. Mei, M. H. Engelhard, S. S. Cartmell, B. J. Polzin, C. M. Wang, J. G. Zhang, W. Xu, Adv. Energy Mater. 2016, 6, 1502151.

[79] a) N. J. Dudney, J. Power Sources 2000, 89, 176; b) G. Ma, Z. Wen, M. Wu, C. Shen, Q. Wang, J. Jin, X. Wu, Chem. Commun. 2014, 50, 14209.

[80] G. A. Umeda, E. Menke, M. Richard, K. L. Stamm, F. Wudl, B. Dunn, J. Mater. Chem. 2011, 21, 1593.

[81] A. Basile, A. I. Bhatt, A. P. O’Mullane, Nat. Commun. 2016, 7, 11794.

[82] N. W. Li, Y. X. Yin, C. P. Yang, Y. G. Guo, Adv. Mater. 2016, 28, 1853.[83] S. M. Choi, I. S. Kang, Y.-K. Sun, J.-H. Song, S.-M. Chung,

D.-W. Kim, J. Power Sources 2013, 244, 363.[84] D. G. Belov, O. V. Yarmolenko, A. Peng, O. N. Efimov, Synth. Met.

2006, 156, 745.[85] B. Zhu, Y. Jin, X. Hu, Q. Zheng, S. Zhang, Q. Wang, J. Zhu,

Adv. Mater. 2017, 29, 1603755.[86] a) C. Monroe, J. Newman, J. Electrochem. Soc. 2005, 152, A396;

b) G. M. Stone, S. A. Mullin, A. A. Teran, D. T. Hallinan,

A. M. Minor, A. Hexemer, N. P. Balsara, J. Electrochem. Soc. 2012, 159, A222.

[87] K. Yan, H. W. Lee, T. Gao, G. Zheng, H. Yao, H. Wang, Z. Lu, Y. Zhou, Z. Liang, Z. Liu, S. Chu, Y. Cui, Nano Lett. 2014, 14, 6016.

[88] a) E. Kazyak, K. N. Wood, N. P. Dasgupta, Chem. Mater. 2015, 27, 6457; b) A. C. Kozen, C.-F. Lin, A. J. Pearse, M. A. Schroeder, X. Han, L. Hu, S.-B. Lee, G. W. Rubloff, M. Noked, ACS Nano 2015, 9, 5884.

[89] a) H. Lee, D. J. Lee, Y. J. Kim, J. K. Park, H. T. Kim, J. Power Sources 2015, 284, 103; b) D. J. Lee, H. Lee, Y. J. Kim, J. K. Park, H. T. Kim, Adv. Mater. 2016, 28, 857.

[90] Z. Peng, S. W. Wang, J. J. Zhou, Y. Jin, Y. Liu, Y. P. Qin, C. Shen, W. Q. Han, D. Y. Wang, J. Mater. Chem. A 2016, 4, 2427.

[91] G. Zheng, S. W. Lee, Z. Liang, H. W. Lee, K. Yan, H. Yao, H. Wang, W. Li, S. Chu, Y. Cui, Nat. Nanotechnol. 2014, 9, 618.

[92] C. B. Bucur, A. Lita, N. Osada, J. Muldoon, Energy Environ. Sci. 2016, 9, 112.

[93] M. H. Ryou, D. J. Lee, J. N. Lee, Y. M. Lee, J. K. Park, J. W. Choi, Adv. Energy Mater. 2012, 2, 645.

[94] W. Luo, L. H. Zhou, K. Fu, Z. Yang, J. Y. Wan, M. Manno, Y. G. Yao, H. L. Zhu, B. Yang, L. B. Hu, Nano Lett. 2015, 15, 6149.

[95] W. K. Shin, A. G. Kannan, D. W. Kim, ACS Appl. Mater. Interfaces 2015, 7, 23700.

[96] M. Chi, L. Shi, Z. Wang, J. Zhu, X. Mao, Y. Zhao, M. Zhang, L. Sun, S. Yuan, Nano Energy 2016, 28, 1.

[97] W. Na, A. S. Lee, J. H. Lee, S. S. Hwang, E. Kim, S. M. Hong, C. M. Koo, ACS Appl. Mater. Interfaces 2016, 8, 12852.

[98] K. Liu, D. Zhuo, H. W. Lee, W. Liu, D. Lin, Y. Lu, Y. Cui, Adv. Mater. 2017, 29, 1603987.

[99] a) D. Lin, D. Zhuo, Y. Liu, Y. Cui, J. Am. Chem. Soc. 2016, 138, 11044; b) H. Wu, D. Zhuo, D. Kong, Y. Cui, Nat. Commun. 2014, 5, 5193.

[100] a) S. J. Kang, T. Mori, J. Suk, D. W. Kim, Y. K. Kang, W. Wilcke, H. C. Kim, J. Mater. Chem. A 2014, 2, 9970; b) J. H. Kim, J. H. Kim, K. H. Choi, H. K. Yu, J. H. Kim, J. S. Lee, S. Y. Lee, Nano Lett. 2014, 14, 4438.

[101] K.-H. Choi, S.-J. Cho, S.-J. Chun, J. T. Yoo, C. K. Lee, W. Kim, Q. Wu, S.-B. Park, D.-H. Choi, S.-Y. Lee, S.-Y. Lee, Nano Lett. 2014, 14, 5677.

[102] G. Nystrom, A. Marais, E. Karabulut, L. Wagberg, Y. Cui, M. M. Hamedi, Nat. Commun. 2015, 6, 7259.

[103] X. M. Hao, J. Zhu, X. Jiang, H. T. Wu, J. S. Qiao, W. Sun, Z. H. Wang, K. N. Sun, Nano Lett. 2016, 16, 2981.

[104] a) Z. Liang, G. Zheng, C. Liu, N. Liu, W. Li, K. Yan, H. Yao, P. C. Hsu, S. Chu, Y. Cui, Nano Lett. 2015, 15, 2910; b) X. B. Cheng, T. Z. Hou, R. Zhang, H. J. Peng, C. Z. Zhao, J. Q. Huang, Q. Zhang, Adv. Mater. 2016, 28, 2888.

[105] D. Zhang, Y. Zhou, C. Liu, S. Fan, Nanoscale 2016, 8, 11161.[106] H. Lee, J. Song, Y. J. Kim, J. K. Park, H. T. Kim, Sci. Rep. 2016, 6,

30830.[107] A. Zhang, X. Fang, C. Shen, Y. Liu, C. Zhou, Nano. Res. 2016, 9, 3428.[108] a) M. Rosso, T. Gobron, C. Brissot, J. N. Chazalviel, S. Lascaud,

J. Power Sources 2001, 97–98, 804; b) C. Monroe, J. Newman, J. Electrochem. Soc. 2003, 150, A1377.

[109] a) G. Rong, X. Zhang, W. Zhao, Y. Qiu, M. Liu, F. Ye, Y. Xu, J. Chen, Y. Hou, W. Li, W. Duan, Y. Zhang, Adv. Mater. 2017, 29, 1606187; b) K. N. Wood, E. Kazyak, A. F. Chadwick, K. H. Chen, J. G. Zhang, K. Thornton, N. P. Dasgupta, ACS Cent. Sci. 2016, 2, 790; c) A. J. Leenheer, K. L. Jungjohann, K. R. Zavadil, J. P. Sullivan, C. T. Harris, ACS Nano 2015, 9, 4379; d) Z. Zeng, W. I. Liang, H. G. Liao, H. L. Xin, Y. H. Chu, H. Zheng, Nano Lett. 2014, 14, 1745.

[110] J. Janek, W. G. Zeier, Nature Energy 2016, 1, 16141.[111] F. J. Li, H. Kitaura, H. S. Zhou, Energy Environ. Sci. 2013, 6, 2302.[112] a) K. M. Abraham, M. Alamgir, J. Electrochem. Soc. 1990, 137,

1657; b) W. Huang, Z. Zhu, L. Wang, S. Wang, H. Li, Z. Tao,



Adv. Mater. 2017, 1700007

J. Shi, L. Guan, J. Chen, Angew. Chem., Int. Ed. 2013, 52, 9162; c) H. Zhao, Z. Jia, W. Yuan, H. Hu, Y. Fu, G. L. Baker, G. Liu, ACS Appl. Mater. Interfaces 2015, 7, 19335; d) G. Tan, F. Wu, C. Zhan, J. Wang, D. Mu, J. Lu, K. Amine, Nano Lett. 2016, 16, 1960.

[113] a) J. E. Weston, B. C. H. Steele, Solid State Ionics 1982, 7, 75; b) F. Capuano, F. Croce, B. Scrosati, J. Electrochem. Soc. 1991, 138, 1918; c) F. Croce, G. B. Appetecchi, L. Persi, B. Scrosati, Nature 1998, 394, 456; d) Y. S. Lee, J. H. Lee, J. A. Choi, W. Y. Yoon, D. W. Kim, Adv. Funct. Mater. 2013, 23, 1019; e) Z. Zhu, M. Hong, D. Guo, J. Shi, Z. Tao, J. Chen, J. Am. Chem. Soc. 2014, 136, 16461; f) J. Shim, D. G. Kim, H. J. Kim, J. H. Lee, J. C. Lee, ACS Appl. Mater. Interfaces 2015, 7, 7690; g) D. Lin, W. Liu, Y. Liu, H. R. Lee, P. C. Hsu, K. Liu, Y. Cui, Nano Lett. 2016, 16, 459.

[114] a) W. Liu, N. Liu, J. Sun, P. C. Hsu, Y. Li, H. W. Lee, Y. Cui, Nano Lett. 2015, 15, 2740; b) K. Fu, Y. H. Gong, J. Q. Dai, A. Gong, X. G. Han, Y. G. Yao, C. W. Wang, Y. B. Wang, Y. N. Chen, C. Y. Yan, Y. J. Li, E. D. Wachsman, L. B. Hu, Proc. Natl. Acad. Sci. USA 2016, 113, 7094.

[115] W. Liu, D. Lin, J. Sun, G. Zhou, Y. Cui, ACS Nano 2016, 10, 11407.[116] a) L. Porcarelli, C. Gerbaldi, F. Bella, J. R. Nair, Sci. Rep. 2016, 6,

19892; b) S.-H. Kim, K.-H. Choi, S.-J. Cho, E.-H. Kil, S.-Y. Lee, J. Mater. Chem. A 2013, 1, 4949.

[117] a) R. Khurana, J. L. Schaefer, L. A. Archer, G. W. Coates, J. Am. Chem. Soc. 2014, 136, 7395; b) Q. Pan, D. M. Smith, H. Qi, S. Wang, C. Y. Li, Adv. Mater. 2015, 27, 5995.

[118] a) R. Bouchet, S. Maria, R. Meziane, A. Aboulaich, L. Lienafa, J.-P. Bonnet, T. N. T. Phan, D. Bertin, D. Gigmes, D. Devaux, R. Denoyel, M. Armand, Nat. Mater. 2013, 12, 452; b) S. Inceoglu, A. A. Rojas, D. Devaux, X. C. Chen, G. M. Stone, N. P. Balsara, ACS Macro Lett. 2014, 3, 510; c) M. W. Schulze, L. D. McIntosh, M. A. Hillmyer, T. P. Lodge, Nano Lett. 2014, 14, 122; d) J.-C. Daigle, A. Vijh, P. Hovington, C. Gagnon, J. Hamel-Paquet, S. Verreault, N. Turcotte, D. Clement, A. Guerfi, K. Zaghib, J. Power Sources 2015, 279, 372; e) D. Devaux, D. Gle, T. N. T. Phan, D. Gigmes, E. Giroud, M. Deschamps, R. Denoyel, R. Bouchet, Chem. Mater. 2015, 27, 4682; f) O. Kim, S. Y. Kim, J. Lee, M. J. Park, Chem. Mater. 2016, 28, 318.

[119] Y. Lu, M. Tikekar, R. Mohanty, K. Hendrickson, L. Ma, L. A. Archer, Adv. Energy Mater. 2015, 5, 1402073.

[120] Q. Ma, H. Zhang, C. Zhou, L. Zheng, P. Cheng, J. Nie, W. Feng, Y.-S. Hu, H. Li, X. Huang, L. Chen, M. Armand, Z. Zhou, Angew. Chem., Int. Ed. 2016, 55, 2521.

[121] H. Oh, K. Xu, H. D. Yoo, D. S. Kim, C. Chanthad, G. Yang, J. Jin, I. A. Ayhan, S. M. Oh, Q. Wang, Chem. Mater. 2016, 28, 188.

[122] X.-X. Zeng, Y.-X. Yin, N.-W. Li, W.-C. Du, Y.-G. Guo, L.-J. Wan, J. Am. Chem. Soc. 2016, 138, 15825.

[123] D. A. Vazquez-Molina, G. S. Mohammad-Pour, C. Lee, M. W. Logan, X. F. Duan, J. K. Harper, F. J. Uribe-Romo, J. Am. Chem. Soc. 2016, 138, 9767.

[124] a) K. Yin, Z. X. Zhang, X. W. Li, L. Yang, K. Tachibana, S. I. Hirano, J. Mater. Chem. A 2015, 3, 170; b) P. Zhang, M. Li, B. Yang, Y. Fang, X. Jiang, G. M. Veith, X. G. Sun, S. Dai, Adv. Mater. 2015, 27, 8088.

[125] J. J. Zhang, J. H. Zhao, L. P. Yue, Q. F. Wang, J. C. Chai, Z. H. Liu, X. H. Zhou, H. Li, Y. G. Guo, G. L. Cui, L. Q. Chen, Adv. Energy Mater. 2015, 5, 1501082.

[126] N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto, A. Mitsui, Nat. Mater. 2011, 10, 682.

[127] Y. Wang, W. D. Richards, S. P. Ong, L. J. Miara, J. C. Kim, Y. F. Mo, G. Ceder, Nat. Mater. 2015, 14, 1026.

[128] a) W. D. Richards, L. J. Miara, Y. Wang, J. C. Kim, G. Ceder, Chem. Mater. 2016, 28, 266; b) S. Wenzel, S. Randau, T. Leichtweiss, D. A. Weber, J. Sann, W. G. Zeier, J. Janek, Chem. Mater. 2016, 28, 2400; c) C. Ma, Y. Cheng, K. Yin, J. Luo, A. Sharafi, J. Sakamoto, J. Li, K. L. More, N. J. Dudney, M. Chi, Nano Lett. 2016, 16, 7030.

[129] a) K. H. Park, D. Y. Oh, Y. E. Choi, Y. J. Nam, L. L. Han, J. Y. Kim, H. L. Xin, F. Lin, S. M. Oh, Y. S. Jung, Adv. Mater. 2016, 28, 1874; b) X. Yao, D. Liu, C. Wang, P. Long, G. Peng, Y.-S. Hu, H. Li, L. Chen, X. Xu, Nano Lett. 2016, 16, 7148; c) H. T. T. Le, D. T. Ngo, V. C. Ho, G. Z. Cao, C. N. Park, C. J. Park, J. Mater. Chem. A 2016, 4, 11124.

[130] a) H. Kitaura, A. Hayashi, T. Ohtomo, S. Hama, M. Tatsumisago, J. Mater. Chem. 2011, 21, 118; b) W. Luo, Y. Gong, Y. Zhu, K. K. Fu, J. Dai, S. D. Lacey, C. Wang, B. Liu, X. Han, Y. Mo, E. D. Wachsman, L. Hu, J. Am. Chem. Soc. 2016, 138, 12258; c) C. L. Tsai, V. Roddatis, C. V. Chandran, Q. L. Ma, S. Uhlenbruck, M. Bram, P. Heitjans, O. Guillon, ACS Appl. Mater. Interfaces 2016, 8, 10617.

[131] X. Han, Y. Gong, K. Fu, X. He, G. T. Hitz, J. Dai, A. Pearse, B. Liu, H. Wang, G. Rubloff, Y. Mo, V. Thangadurai, E. D. Wachsman, L. Hu, Nat. Mater. 2017, 16, 572.

[132] a) C. Ma, K. Chen, C. Liang, C.-W. Nan, R. Ishikawa, K. More, M. Chi, Energy Environ. Sci. 2014, 7, 1638; b) T. Ohnishi, K. Mitsuishi, K. Nishio, K. Takada, Chem. Mater. 2015, 27, 1233.

[133] a) Z. D. Hood, H. Wang, A. S. Pandian, J. K. Keum, C. D. Liang, J. Am. Chem. Soc. 2016, 138, 1768; b) Y. T. Li, W. D. Zhou, S. Xin, S. Li, J. L. Zhu, X. J. Lu, Z. M. Cui, Q. X. Jia, J. S. Zhou, Y. S. Zhao, J. B. Goodenough, Angew. Chem., Int. Ed. 2016, 55, 9965.

[134] a) R. Murugan, V. Thangadurai, W. Weppner, Angew. Chem., Int. Ed. 2007, 46, 7778; b) P. Bottke, D. Rettenwander, W. Schmidt, G. Amthauer, M. Wilkening, Chem. Mater. 2015, 27, 6571.

[135] Y. Deng, C. Eames, J. N. Chotard, F. Lalere, V. Seznec, S. Emge, O. Pecher, C. P. Grey, C. Masquelier, M. S. Islam, J. Am. Chem. Soc. 2015, 137, 9136.

[136] P. Bron, S. Johansson, K. Zick, J. S. auf der Gunne, S. Dehnen, B. Roling, J. Am. Chem. Soc. 2013, 135, 15694.

[137] a) H. J. Deiseroth, S. T. Kong, H. Eckert, J. Vannahme, C. Reiner, T. Zaiss, M. Schlosser, Angew. Chem., Int. Ed. 2008, 47, 755; b) E. Rangasamy, Z. Liu, M. Gobet, K. Pilar, G. Sahu, W. Zhou, H. Wu, S. Greenbaum, C. Liang, J. Am. Chem. Soc. 2015, 137, 1384; c) C. Yu, S. Ganapathy, N. J. J. de Klerk, I. Roslon, E. R. H. van Eck, A. P. M. Kentgens, M. Wagemaker, J. Am. Chem. Soc. 2016, 138, 11192.

[138] a) H. Kitaura, H. S. Zhou, Energy Environ. Sci. 2012, 5, 9077; b) B. Lang, B. Ziebarth, C. Elsasser, Chem. Mater. 2015, 27, 5040.

[139] a) U. v. Alpen, A. Rabenau, G. H. Talat, Appl. Phys. Lett. 1977, 30, 621; b) T. Lapp, S. Skaarup, Solid State Ionics 1983, 11, 97.

[140] a) J. Li, C. Ma, M. Chi, C. Liang, N. J. Dudney, Adv. Energy Mater. 2015, 5, 1401408; b) M. Nisula, Y. Shindo, H. Koga, M. Karppinen, Chem. Mater. 2015, 27, 6987.

[141] Y. Seino, T. Ota, K. Takada, A. Hayashi, M. Tatsumisago, Energy Environ. Sci. 2014, 7, 627.

[142] D. Y. Oh, Y. J. Nam, K. H. Park, S. H. Jung, S.-J. Cho, Y. K. Kim, Y.-G. Lee, S.-Y. Lee, Y. S. Jung, Adv. Energy Mater. 2015, 5, 1500865.

[143] Y. Wang, B. Li, J. Ji, A. Eyler, W.-H. Zhong, Adv. Energy Mater. 2013, 3, 1557.

[144] a) J. Zheng, M. Tang, Y. Y. Hu, Angew. Chem., Int. Ed. 2016, 55, 12538; b) W. Zhou, S. Wang, Y. Li, S. Xin, A. Manthiram, J. B. Goodenough, J. Am. Chem. Soc. 2016, 138, 9385; c) X. Wang, Y. Hou, Y. Zhu, Y. Wu, R. Holze, Sci. Rep. 2013, 3, 1401.

[145] Z. Y. Tu, Y. Y. Lu, L. Archer, Small 2015, 11, 2631.[146] Z. Tu, M. J. Zachman, S. Choudhury, S. Wei, L. Ma, Y. Yang,

L. F. Kourkoutis, L. A. Archer, Adv. Energy Mater. 2017, 7, 1602367.[147] a) J. S. Zhang, Y. Bai, X. G. Sun, Y. C. Li, B. K. Guo, J. H. Chen,

G. M. Veith, D. K. Hensley, M. P. Paranthaman, J. B. Goodenough, S. Dai, Nano Lett. 2015, 15, 3398; b) D. Zhou, R. Liu, Y.-B. He, F. Li, M. Liu, B. Li, Q.-H. Yang, Q. Cai, F. Kang, Adv. Energy Mater. 2016, 6, 1502214.

[148] M. Li, W. Zhu, P. Zhang, Y. Chao, Q. He, B. Yang, H. Li, A. Borisevich, S. Dai, Small 2016, 12, 3535.

本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具

http://www.xuebalib.com/cloud/

http://www.xuebalib.com/

http://www.xuebalib.com/cloud/


http://www.xuebalib.com/vip.html

http://www.xuebalib.com/db.php

http://www.xuebalib.com/zixun/2014-08-15/44.html


yanpeng guo, huiqiao li,* and tianyou zhai*download.xuebalib.com/xuebalib.com.30274.pdfy. guo, prof....

Documents