C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3

.sc iencedi rect .com

Avai lab le at www

ScienceDirect

journal homepage: www.elsev ier .com/ locate /carbon

Superior electrochemical propertiesof spherical-like Co2(OH)3Cl-reducedgraphene oxide composite powderswith ultrafine nanocrystals

http://dx.doi.org/10.1016/j.carbon.2014.11.0390008-6223/� 2014 Elsevier Ltd. All rights reserved.

* Corresponding author: Fax: +82 2 928 3584.E-mail address: yckang@korea.ac.kr (Y.C. Kang).

Gi Dae Park, Jong-Heun Lee, Yun Chan Kang *

Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136-713, Republic of Korea

A R T I C L E I N F O

Article history:

Received 22 August 2014

Accepted 19 November 2014

Available online 27 November 2014

A B S T R A C T

Co2(OH)3Cl/reduced graphene oxide (RGO) composite powders for use as anodes in lithium

ion batteries were prepared directly by spray pyrolysis from a colloidal solution of graphene

oxide sheets and cobalt chloride. Co2(OH)3Cl nanocrystals less than 10 nm in size were uni-

formly distributed throughout the spherical Co2(OH)3Cl/RGO composite powder. CoCl2Æ6H2-

O/RGO, CoCl2Æ6H2O/Co3O4/RGO, and Co3O4 powders were also prepared by post-treatment

of the Co2(OH)3Cl/RGO powders at 200, 300, and 400 �C, respectively, in air. The initial dis-

charge capacities of the Co2(OH)3Cl/RGO, CoCl2Æ6H2O/RGO, CoCl2Æ6H2O/Co3O4/RGO, and

Co3O4 powder electrodes at a current density of 1000 mA g�1 were 1685, 1518, 1655, and

1046 mA h g�1, respectively, and their discharge capacities after 200 cycles were 1186,

1030, 884, and 805 mA h g�1, respectively. The discharge capacities of the Co2(OH)3Cl/RGO

composite powder electrode for the 2nd and 600th cycles at a current density of

5000 mA g�1 were 1063 and 833 mA h g�1, respectively. The Co2(OH)3Cl/RGO powders had

smaller charge transfer resistance and faster lithium-ion diffusion rate than the other

materials.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Since the emergence of lithium ion batteries (LIBs), efforts to

develop improved electrode materials have continued [1–36].

Whereas the development of Li-bearing mixed-oxide cathode

materials has reached its limit, the development of anode

materials using a variety of components is ongoing [23–29].

In particular, novel reaction concepts involving the reversible

electrochemical reaction of Li with transition metal oxides

have produced anode materials incorporating metal hydrox-

ides, sulfides, chlorides, nitrides, fluorides, oxysulfides, and

so on [30–36]. The electrochemical properties of metal-oxide

materials with various compositions have been investigated

for their suitability in LIB anodes because of the easy synthe-

sis of these oxides. However, metal-oxide materials suffer

from poor electrochemical properties because of the large vol-

ume change they undergo during cycling. Therefore, the prob-

lems related to obtaining anode materials with high energy

density, long cycle life, high rate capability, and adequate

safety remain unresolved.

Recently, it was reported that metal hydroxychlorides

[Mx(OH)3Cl] had great potential for application as LIB anode

C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3 15

materials [37,38]. Kim et al. showed that copper hydroxychlo-

ride (Cu2(OH)3Cl) is a promising electrode material [37]. Cobalt

hydroxychloride (Co2(OH)3Cl) powders prepared by spray

pyrolysis also possess electrochemical properties beneficial

for anodes [38]. Bare Co2(OH)3Cl powders containing CoCl2(H2O)2 and CoO impurity phases possess a high capacity of

955 mA h g�1 at a current density of 1000 mA g�1, but bare

Co2(OH)3Cl powders prepared using a one-pot spray pyrolysis

process contained some impurities. The preparation of

phase-pure Co2(OH)3Cl powders for LIBs and their electro-

chemical properties has not been investigated.

Graphene is an impressive support material for active

nanomaterials because of its high electric and thermal con-

ductivity, flexibility, large surface area, and chemical stability

[39–45]. Recently, the preparation of metal oxide/reduced

graphene oxide (RGO) and metal sulfide/RGO composite pow-

ders by one-pot spray pyrolysis was reported [46,47]. In this

study, for the first time, we demonstrate that metal hydroxy-

chloride/RGO composites prepared by one-pot spray pyrolysis

are promising LIB anode materials. The formation mecha-

nism of Co2(OH)3Cl/RGO composite powders, selected as the

first target material system, was investigated. The electro-

chemical properties of the Co2(OH)3Cl/RGO composite

powders were compared with those of cobalt chloride hydrate

and cobalt oxide powders, which were obtained by post-

treatment of the Co2(OH)3Cl/RGO powders in air.

2. Experimental section

2.1. Synthesis of Co2(OH)3Cl/RGO composites

Graphene oxide (GO) was synthesized from graphite flakes

using a modified Hummers method, as described in our pre-

vious report [46]. The as-synthesized GO was re-dispersed in

distilled water and then exfoliated by ultrasonication to

obtain graphene oxide sheets. 0.15 M of CoCl2Æ6H2O (Junsei

Chemical Co., Ltd.) was dissolved into 500 mL of a 1 mg mL�1

exfoliated graphite oxide dispersion to fabricate the Co2(OH)3Cl/RGO composite precursor. The Co2(OH)3Cl/RGO composite

powders were prepared directly by spray pyrolysis from the

corresponding spray solutions. The schematic diagram of

Scheme 1 – Formation mechanism of the spherical Co2(OH)3Cl-RG

this figure can be viewed online.)

the spray pyrolysis process is shown in Fig. S1. Pyrolysis

was carried out in a quartz reactor 1200 mm in length and

50 mm in diameter; the reactor temperature was maintained

at 700 �C. Nitrogen at a flow rate of 10 L min�1 was used as the

carrier gas. Also, cobalt chloride hydrate and cobalt oxide

powders were obtained by post-treatment of the precursor

Co2(OH)3Cl/RGO powders in an air atmosphere for 3 h at a

heating rate of 10 �C min�1.

2.2. Characterizations

The crystal structures of the powders were investigated using

X-ray diffractometry (XRD, X’pert PRO MPD) with Cu-Ka radi-

ation (k = 1.5418 A)) at the Korea Basic Science Institute (Dae-

gu). The morphology of the powders was investigated using

field-emission scanning electron microscopy (FE-SEM, Hitachi

S-4800) and high-resolution transmission electron micros-

copy (HR-TEM, JEOL JEM-2100F) carried out at a working volt-

age of 200 kV. The specific surface areas of the powders before

and after post-treatment at various temperatures were

calculated by a Brunauer–Emmett–Teller (BET) analysis of

nitrogen adsorption measurements (TriStar 3000). The

decomposition characteristics of the precursor Co2(OH)3Cl/

RGO powders were determined using thermogravimetric

analysis (TGA, SDT Q600) performed in air at a heating rate

of 20 �C min�1.

2.3. Electrochemical measurements

The capacities and cycling properties of all the powder sam-

ples were determined using a 2032-type coin cell. The cell

electrode was prepared from a mixture containing 70 wt.%

active material, 20 wt.% Super P, and 10 wt.% sodium carboxy-

methyl cellulose (CMC) binder. Lithium metal and a micropo-

rous polypropylene film were used as the counter electrode

and separator, respectively. The electrolyte was a solution of

1 M LiPF6 in a 1:1 volume mixture of fluoroethylene carbon-

ate/dimethyl carbonate (FEC/DMC). The size of the electrode

was 1 cm · 1 cm. The thickness and mass loading of the elec-

trode were 15 lm and 1.4 mg cm�2, respectively. The charge/

discharge characteristics of the samples were determined by

O composite powder by spray pyrolysis. (A colour version of

16 C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3

cycling through a 0.001–3 V potential range at a fixed set of

current densities. Cyclic voltammetry measurements were

carried out at a scan rate of 0.07 mV s�1.

3. Results and discussion

The formation mechanism of the spherical Co2(OH)3Cl/RGO

composite powder by spray pyrolysis is shown in Scheme 1.

A droplet several microns in size containing GO sheets and

Fig. 1 – Morphologies of the Co2(OH)3Cl/RGO composite powders

(f) elemental mapping images. (A colour version of this figure c

cobalt chloride salt was formed by an ultrasonic nebulizer.

Drying of the droplet produced a crumpled cobalt chloride

hydrate/GO composite powder as an intermediate product

in the region near the reactor entrance. The thermal decom-

position of cobalt chloride hydrate in a nitrogen atmosphere

into Co2(OH)3Cl and HCl gas occurred at the middle part of

the reactor, maintained at 700 �C. The thermal reduction of

GO into RGO occurred simultaneously. The GO and/or RGO

inhibited the crystal growth of cobalt chloride and Co2(OH)3Cl

: (a) and (b) FE-SEM images, (c–e) TEM images, and

an be viewed online.)

Fig. 2 – XRD patterns of the powders before and after post-

treatment at various temperatures. (A colour version of this

figure can be viewed online.)

C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3 17

during development of the composite powders. Therefore,

Co2(OH)3Cl nanocrystals were uniformly distributed through-

out the spherical Co2(OH)3Cl/RGO composite powder.

The morphologies of the Co2(OH)3Cl/RGO composite pow-

ders prepared directly by spray pyrolysis are shown in Fig. 1.

FE-SEM images of the composite powders demonstrated that

Fig. 3 – Characteristics of the Co2(OH)3Cl/RGO composite powde

desorption isotherms, and (d) pore size distribution. (A colour v

the individual particles were crumpled spheres with a size of

�1.5 lm. A single composite powder particle was formed from

each droplet during the drying and decomposition stages. The

high-resolution TEM image shown in Fig. 1d and e depict

Co2(OH)3Cl nanocrystals with a size below 10 nm wrapped

in a few layers of RGO. The high-resolution TEM image shown

in Fig. 1e exhibits distinct lattice fringes with a spacing of

0.59 nm, indicating planes of cobalt hydroxychloride. The

elemental mapping images shown in Fig. 1f revealed uniform

distributions of Co, Cl, and C throughout the composite

powder.

XRD patterns of the powders before and after post-treat-

ment at various temperatures are shown in Fig. 2. The precur-

sor powders directly prepared by spray pyrolysis had the

phase-pure crystal structure of cobalt hydroxychloride. The

microscale conversion of cobalt chloride hydrate inside pow-

der with several microns in size resulted in the phase-pure

Co2(OH)3Cl/RGO composite powder. The mild reducing atmo-

sphere around the powders due to the RGO nanosheets also

contributed the formation of phase-pure Co2(OH)3Cl/RGO

composite powders by spray pyrolysis. The main crystal struc-

ture of the powders post-treated at 200 �C was CoCl2Æ6H2O.

Partial decomposition of CoCl2Æ6H2O into Co3O4 resulted in

powders with mixed crystal structures of CoCl2Æ6H2O and

Co3O4 at a post-treatment temperature of 300 �C. Complete

decomposition of Co2(OH)3Cl via the CoCl2Æ6H2O intermediate

rs: (a) Raman spectrum, (b) TG curve, (c) N2 adsorption and

ersion of this figure can be viewed online.)

Fig. 4 – Morphologies of the powders post-treated at 200 �C: (a) and (b) FE-SEM images, (c–e) TEM images, and (f) elemental

mapping images. (A colour version of this figure can be viewed online.)

18 C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3

into Co3O4 occurred at a post-treatment temperature of

400 �C. The composite powders post-treated at 200, 300, and

400 �C were designated as CoCl2Æ6H2O/RGO, CoCl2Æ6H2O/

Co3O4/RGO, and Co3O4, respectively.

Fig. 3 showed characteristics of the Co2(OH)3Cl/RGO com-

posite powders. The Raman spectrum of the Co2(OH)3Cl/

RGO composite powders directly prepared by spray pyrolysis

is shown in Fig. 3a. The D and G graphene bands in the Raman

spectrum were observed at 1326 and 1588 cm�1, respectively.

The higher signal peak intensity of the D band compared to

the G band revealed the reduction of GO into RGO during ther-

mal reduction. Fig. 3b shows the thermogravimetric (TG)

curve of the Co2(OH)3Cl/RGO composite powders. The first

weight loss event occurred below 150 �C and was caused by

the evaporation of adsorbed water molecules. The TG curve

exhibited three distinct weight loss events between 200 and

1200 �C. The reactions occurring at each weight decrease step

are outlined in Fig. 3b. The event at around 340 �C was the

result of the decomposition of Co2(OH)3Cl into CoCl2ÆxH2O

and the dehydration of CoCl2ÆxH2O into CoCl2. The complete

Fig. 5 – Cyclic voltammetry curves of the powders before and after post-treatment at various temperatures: (a) Co2(OH)3Cl/

RGO, (b) CoCl2Æ6H2O/RGO, (c) CoCl2Æ6H2O/Co3O4/RGO, and (d) Co3O4. (A colour version of this figure can be viewed online.)

C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3 19

decomposition of CoCl2 into Co3O4 occurred at temperatures

below 690 �C. The decomposition of RGO also occurred during

the decomposition of CoCl2 into Co3O4. The final weight loss

step observed at around 900 �C was due to the reduction of

Co3O4 into CoO. The RGO content in the Co2(OH)3Cl/RGO com-

posite powders calculated from the result of TG was

17.2 wt.%. The N2-adsorption and -desorption isotherms of

the Co2(OH)3Cl/RGO composite powders (Fig. 3c) exhibited

clear hysteresis, indicating the existence of mesopores. The

Co2(OH)3Cl/RGO composite powders possessed well-devel-

oped mesopores, as shown by the Barrett–Joyner–Halenda

(BJH) pore size distribution in Fig. 3d. The BET surface area

of the Co2(OH)3Cl/RGO composite powders was 17 m2 g�1.

The Raman spectrum shown in Fig. S2 revealed the exis-

tence of RGO in the composite powders post-treated at 200

and 300 �C. The composite powders post-treated at 200 and

300 �C had hysteresis loops in their N2-adsorption and -

desorption isotherms, as shown in Fig. S3. The BET surface

areas of the powders post-treated at 200, 300, and 400 �C were

15.8, 12.0, and 2.5 m2 g�1, respectively. Fig. S4 shows the BJH

pore size distributions of the powders post-treated at various

temperatures. The complete decomposition of the Co2(OH)3Cl/RGO composite at a post-treatment temperature of 400 �Cyielded pure Co3O4 powders with low pore volume and low

BET surface area.

The morphologies of the spherical CoCl2Æ6H2O/RGO pow-

ders post-treated at 200 �C are shown in Fig. 4. FE-SEM and

TEM images of the composite powders showed crumpled

spheres of layered RGO. The high-resolution TEM image

shown in Fig. 4e contains CoCl2Æ6H2O nanocrystals with sizes

larger than 10 nm. Compared to the Co2(OH)3Cl/RGO precur-

sor, crystal growth occurred at a post-treatment temperature

of 200 �C. The high-resolution TEM image in Fig. 4e shows dis-

tinct lattice fringes with a spacing of 0.68 nm, indicating

planes of cobalt chloride hexahydrate. The elemental maps

shown in Fig. 4f revealed uniform distributions of Co, Cl,

and C components throughout the composite powder.

Figs. S5 and S6 show the morphologies of the powders post-

treated at 300 and 400 �C. The FE-SEM images as shown in

Figs. 1 and S6 revealed the grain growth of the powders after

post-treatment. However, the micron-scale size and spherical

shape of the precursor powders persisted, even after post-

treatment at 400 �C. The schematic diagram for the formation

of the CoCl2Æ6H2O/RGO, CoCl2Æ6H2O/Co3O4/RGO, and Co3O4

powders are shown in Fig. S7.

The electrochemical properties of the Co2(OH)3Cl/RGO,

CoCl2Æ6H2O/RGO, CoCl2Æ6H2O/Co3O4/RGO, and Co3O4 powders

are shown in Figs. 5 and 6. The cyclic voltammograms (CVs)

of the four samples for the first 5 cycles obtained at a scan

rate of 0.07 mV s�1 are shown in Fig. 5. The main reduction

peaks in the Co2(OH)3Cl/RGO and CoCl2Æ6H2O/RGO composite

powders upon initial discharge were observed at 0.92 and

0.97 V, respectively. Compositionally, Co2(OH)3Cl is a solid

solution of Co(OH)2 and CoCl2 [38,48]. Therefore, the reduction

Fig. 6 – Electrochemical properties of the powders before and after post-treatment at various temperatures: (a) initial charge

and discharge curves, (b) cycling performances at a current density at 1000 mA g�1, (c) Nyquist plots after 100 cycles, (d)

relationship between Zre and x�1/2 in the low-frequency region after 100 cycles, (e) rate performance of the Co2(OH)3Cl/RGO

composite powders, and (f) long term cycling performance of the Co2(OH)3Cl/RGO composite powders at a current density of

5000 mA g�1. (A colour version of this figure can be viewed online.)

20 C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3

peaks correspond to the conversion of Co(OH)2 and CoCl2 into

Co nanocrystals, LiOH and LiCl, respectively [38,49,50]. The

new reduction peaks observed at around 1.78 V during the

second discharge originated from the conversion of amor-

phous Co(OH)2 and CoCl2 formed during the initial cycles

[38,49,50]. The voltammograms of the pure-Co3O4 powder

electrodes had a distinct reduction peak at 0.84 V during the

initial discharge due to the formation of Co nanoclusters

and amorphous Li2O [51]. The later CV profiles of the pure

Co3O4 powders overlapped those from the second cycle.

However, the CV profiles of the Co2(OH)3Cl/RGO and CoCl2-

Æ6H2O/RGO composite powder electrodes changed consider-

ably during the first 5 cycles because of the complex

reactions with Li. The CV profiles of the CoCl2Æ6H2O/Co3O4/

RGO composite powders shown in Fig. 5c exhibited mixed

characteristics of the CoCl2 and Co3O4 phases.

The initial discharge and charge voltage profiles of the four

samples at a constant current density of 1000 mA g�1 are

shown in Fig. 6a. The initial discharge voltage profiles of

the Co2(OH)3Cl/RGO, CoCl2Æ6H2O/RGO, and CoCl2Æ6H2O/Co3O4/

C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3 21

RGO composite electrodes had several plateaus. On the other

hand, the pure Co3O4 powder electrode possessed one plateau

at 0.98 V during the first discharging process. These results

coincided well with those of the CVs shown in Fig. 5. The ini-

tial discharge capacities of the Co2(OH)3Cl/RGO, CoCl2Æ6H2O/

RGO, CoCl2Æ6H2O/Co3O4/RGO, and Co3O4 powder electrodes

were found to be 1685, 1518, 1655, and 1046 mA h g�1, respec-

tively, and their initial Coulombic efficiencies were 76, 74, 75,

and 76%, respectively.

Fig. 6b shows the cycling performances of the four sam-

ples at a constant current density of 1000 mA g�1. The dis-

charge capacities of the Co2(OH)3Cl/RGO composite powder

electrodes were 1685 and 1102 mA h g�1 for the 2nd and 5th

cycles. The discharge capacities of the CoCl2Æ6H2O/RGO elec-

trodes also strictly decreased during the first 7 cycles. These

changes in the discharge capacities during the first few cycles

were related to the transformation of the crystalline structure

into a stable amorphous structure during cycling. The dis-

charge capacities of the Co2(OH)3Cl/RGO, CoCl2Æ6H2O/RGO,

CoCl2Æ6H2O/Co3O4/RGO, and Co3O4 electrodes after 200 cycles

were 1186, 1030, 884, and 805 mA h g�1, respectively. The vol-

umetric discharge capacity of the Co2(OH)3Cl/RGO electrode

after 200 cycles was 1409 mA h cm�3.

Fig. 6c shows the Nyquist impedance plots for the four

samples obtained after the 100th cycle in a fully charged

state. The medium-frequency semicircle is assigned to the

charge–transfer resistance (Rct), whereas the line inclined at

�45� to the real axis corresponds to lithium diffusion within

the electrodes [52–54]. The Co2(OH)3Cl/RGO powder electrode

had a smaller charge transfer resistance than the others.

The structural stability of the Co2(OH)3Cl/RGO powders with

ultrafine crystallite sizes resulted in the low charge transfer

resistance, even after 100 cycles. Fig. 6d shows the relation-

ship between the real part of the impedance spectra (Zre)

and x�1/2, where x is the angular frequency, in the low-

frequency region after 100 cycles. The low slope r, the Warburg

impedance coefficient, of the real part of the impedance

spectra (Zre) versus x�1/2 revealed a fast lithium-ion diffusion

rate in the Co2(OH)3Cl/RGO composite powders [55,56]. Fig. 6e

shows the rate performance of the Co2(OH)3Cl/RGO composite

powders; the current density increased from 500 to

6000 mA g�1 in a step-by-step manner, and then returned to

500 mA g�1. The stable reversible discharge capacities of the

Co2(OH)3Cl/RGO composite powders decreased slightly from

1040 to 805 mA h g�1 as the current density was increased

from 500 to 6000 mA g�1, and the discharge capacity recov-

ered at 1051 mA h g�1 when the current density was restored

to 500 mA g�1. The long-term cycling performance of the

Co2(OH)3Cl/RGO composite powders at a high current density

of 5000 mA g�1 are shown in Fig. 6f. The discharge capacities

of the composite powders for the 2nd and 600th cycles were

1063 and 833 mA h g�1, respectively. As shown in Fig. 6f, the

composite powders showed high Coulombic efficiencies of

above 99.1% from the 6th cycle onward.

Fig. S8 shows the TEM images of the Co2(OH)3Cl/RGO com-

posite powders obtained after 100 cycles at a current density

of 2000 mA g�1. The spherical morphology of the composite

powders persisted, even after cycling at a high current den-

sity. The good structural stability of the Co2(OH)3Cl/RGO com-

posite powders incorporating ultrafine nanocrystals improved

their electrochemical properties. The high electrical conduc-

tivity of the RGO also improved the electrochemical proper-

ties of the Co2(OH)3Cl/RGO composite powders. X-ray

photoelectron spectroscopy (XPS) analysis was also per-

formed to explain the superior electrochemical properties of

the Co2(OH)3Cl/RGO powders. XPS profile shown in Fig. S9a

revealed the presence of cobalt, oxygen, carbon, and chlorine.

The Cl 2p peak in the XPS profile shown in Fig. S9b could be

deconvoluted into four components i.e., C–Cl (2p3/2), C–Cl

(2p1/2), Co–Cl (2p3/2), and Co–Cl (2p1/2) bonds, which corre-

sponded to peaks at 201.0, 202.9, 198.5, and 199.7 eV, respec-

tively, and unequivocally indicating the covalent bond

formation between Cl and RGO. The binding between the

Co2(OH)3Cl and RGO also improved the electrochemical prop-

erties of the Co2(OH)3Cl/RGO powders [57,58].

4. Conclusions

In this study, spherical metal hydroxychloride/reduced graph-

ene oxide (RGO) composite powders were prepared using one-

pot spray pyrolysis from a colloidal solution of graphene

oxide (GO) sheets and metal salt for the first time. The forma-

tion mechanism of the Co2(OH)3Cl/RGO composite powders

during the spray pyrolysis process was identified. The simul-

taneous thermal decomposition of cobalt chloride hydrate

and thermal reduction of GO sheets inside the reactor at

700 �C produced the Co2(OH)3Cl/RGO composite powders dur-

ing spray pyrolysis. Ultrafine Co2(OH)3Cl nanocrystals were

uniformly distributed all over the spherical Co2(OH)3Cl/RGO

composite powder. The Co2(OH)3Cl/RGO composite powders

had superior electrochemical properties compared with those

of the associated CoCl2Æ6H2O/RGO, CoCl2Æ6H2O/Co3O4/RGO,

and Co3O4 powders. This novel process could be applied to

the preparation of metal hydroxychloride/RGO composite

with various compositions for a wide array of applications

in energy storage devices.

Acknowledgment

This work was supported by the National Research Founda-

tion of Korea (NRF) grant funded by the Korea government

(MEST) (No. 2012R1A2A2A02046367).

Appendix A. Supplementary data

Supplementary data associated with this article can be found,

in the online version, at http://dx.doi.org/10.1016/

j.carbon.2014.11.039.

R E F E R E N C E S

[1] Cabana J, Monconduit L, Larcher D, Palacın MR. Beyondintercalation-based Li-ion batteries: the state of the art andchallenges of electrode materials reacting throughconversion reactions. Adv Mater 2010;22(35):E170–92.

[2] Zhang L, Wu HB, Lou XW. Iron-oxide-based advanced anodematerials for lithium-ion batteries. Adv Energy Mater2014;4(4):1300958.

22 C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3

[3] Chen JS, Lou XW. SnO2-based nanomaterials: synthesis andapplication in lithium-ion batteries. Small 2013;9(11):1877–93.

[4] Xiong S, Chen JS, Lou XW, Zeng HC. Mesoporous Co3O4 andCoO@C topotactically transformed from chrysanthemum-like Co(CO3)0.5(OH) 0.11H2O and their lithium-storageproperties. Adv Funct Mater 2012;22(4):861–71.

[5] Gao G, Wu HB, Lou XW. Citrate-assisted growth of NiCo2O4

nanosheets on reduced graphene oxide for highly reversiblelithium storage. Adv Energy Mater 2014;4(14):1400422.

[6] Zhang L, Wu HB, Lou XW. Metal-organic-frameworks-derivedgeneral formation of hollow structures with high complexity.J Am Chem Soc 2013;135(29):10664–72.

[7] Cheng FY, Chen J. Transition metal vanadium oxides andvanadate materials for lithium batteries. J Mater Chem2011;7(21):9841–8.

[8] Zhu ZQ, Wang SW, Du J, Jin Q, Zhang TR, Cheng FY, et al.Ultrasmall Sn nanoparticles embedded in nitrogen-dopedporous carbon as high-performance anode for lithium-ionbatteries. Nano Lett 2014;14(1):153–7.

[9] Gao HY, Hu Z, Zhang K, Cheng FY, Chen J. IntergrownLi2FeSiO4ÆLiFePO4–C nanocomposites as high-capacitycathode materials for lithium-ion batteries. Chem Commun2013;49(29):3040–2.

[10] Zhu ZQ, Cheng FY, Chen J. Investigation of effects of carboncoating on the electrochemical performance of Li4Ti5O12/Cnanocomposites. J Mater Chem A 2013;7(1):9484–90.

[11] Zhang XL, Cheng FY, Yang J, Chen J. LiNi0.5Mn1.5O4 porousnanorods as high-rate and long-life cathodes for Li-ionbatteries. Nano Lett 2013;13(6):2822–5.

[12] Zhang Q, Chen H, Wang J, Xu D, Li X, Yang Y, et al. Growth ofhierarchical 3D mesoporous NiSix/NiCo2O4 core/shellheterostructures on nickel foam for lithium-ion batteries.ChemSusChem 2014;7(8):2325–34.

[13] Bai J, Li XG, Liu GZ, Qian Y, Xiong SL. Unusual formation ofZnCo2O4 3D hierarchical twin microspheres as a high-rateand ultralong-life lithium-ion battery anode material. AdvFunct Mater 2014;24(20):3012–20.

[14] Urban A, Lee JH, Ceder G. The configurational space ofrocksalt-type oxides for high-capacity lithium batteryelectrodes. Adv Energy Mater 2014 [1400478].

[15] Sakuda A, Takeuchi T, Okamura K, Kobayashi H, Sakaebe H,Tatsumi K, et al. Rock-salt-type lithium metal sulphides asnovel positive-electrode materials. Sci Rep 2014;4:4883.

[16] Chang JB, Huang XK, Zhou GH, Cui SM, Hallac PB, Jiang JW,et al. Multilayered Si nanoparticle/reduced graphene oxidehybrid as a high-performance lithium-ion battery anode. AdvMater 2014;26(5):758–64.

[17] Sun W, Wang Y. Graphene-based nanocomposite anodes forlithium-ion batteries. Nanoscale 2014;6(20):11528–52.

[18] Shi Y, Wang JZ, Chou SL, Wexler D, Li HJ, Ozawa K, et al.Hollow structured Li3VO4 wrapped with graphenenanosheets in situ prepared by a one-pot template-freemethod as an anode for lithium-ion batteries. Nano Lett2013;13(10):4715–20.

[19] Wei QL, An QY, Chen DD, Mai LQ, Chen SY, Zhao YL, et al.One-pot synthesized bicontinuous hierarchical Li3V2(PO4)3/Cmesoporous nanowires for high-rate and ultralong-lifelithium-ion batteries. Nano Lett 2014;14(2):1042–8.

[20] Rui X, Tan H, Yan Q. Nanostructured metal sulfides for energystorage. Nanoscale 2014;6(17):9889–924.

[21] Mani V, Babu G, Kalaiselvi N. Li2MnSnO4/C anode for highcapacity and high rate lithium battery applications.Electrochim Acta 2014;133(1):347–53.

[22] Sharma P, Damien D, Nagarajan K, Shaijumon MM,Hariharan M. Perylene-polyimide-based organic electrodematerials for rechargeable lithium batteries. J Phys Chem Lett2013;4(19):3192–7.

[23] Etacheri V, Marom R, Elazari R, Salitra G, Aurbach D.Challenges in the development of advanced Li-ion batteries:a review. Energy Environ Sci 2011;1(4):3243–62.

[24] Islam MS, Fisher CAJ. Lithium and sodium battery cathodematerials: computational insights into voltage, diffusion andnanostructural properties. Chem Soc Rev 2014;43(1):185–204.

[25] Scrosati B, Hassoun J, Sun YK. Lithium-ion batteries. A lookinto the future. Energy Environ Sci 2011;4(9):3287–95.

[26] Kim HS, Jeong GJ, Kim YU, Kim JH, Park CM, Sohn HJ. Metallicanodes for next generation secondary batteries. Chem SocRev 2013;42(23):9011–34.

[27] Roberts AD, Li X, Zhang HF. Porous carbon spheres andmonoliths: morphology control, pore size tuning and theirapplications as Li-ion battery anode materials. Chem Soc Rev2014;43(13):4341–56.

[28] Palacin MR. Recent advances in rechargeable batterymaterials: a chemist’s perspective. Chem Soc Rev2009;38(9):2565–75.

[29] Goriparti S, Miele E, Angelis FD, Fabrizio ED, Zaccaria RP,Capiglia C. Review on recent progress of nanostructuredanode materials for Li-ion batteries. J Power Sources2014;257(1):421–43.

[30] Poizot P, Laruelle S, Grugeon S, Dupont L, Tarascon JM. Nano-sized transition-metal oxides as negative-electrode materialsfor lithium-ion batteries. Nature 2000;407(6803):496–9.

[31] Reddy MV, Rao GVS, Chowdari BVR. Metal oxides andoxysalts as anode materials for Li ion batteries. Chem Rev2013;113(7):5364–457.

[32] Wessells CD, Huggins RA, Cui Y. Copper hexacyanoferratebattery electrodes with long cycle life and high power. NatCommun 2011;22:550.

[33] Stan MC, Klopsch R, Bhaskar A, Li J, Passerini S, Winter M.Cu3P binary phosphide: synthesis via a wetmechanochemical method and electrochemical behavior asnegative electrode material for lithium-ion batteries. AdvEnergy Mater 2013;3(2):231–8.

[34] Chen S, Zhu JW, Wang X. One-step synthesis of graphene-cobalt hydroxide nanocomposites and their electrochemicalproperties. J Phys Chem C 2010;114(27):11829–34.

[35] Nie P, Shen LF, Luo HF, Ding B, Xu G, Wang J, et al. Prussianblue analogues: a new class of anode materials for lithiumion batteries. J Mater Chem A 2014;2(16):5852–7.

[36] Ko JK, Wiaderek KM, Pereira N, Kinnibrugh TL, Kim JR,Chupas PJ, et al. Transport, phase reactions, and hysteresisof iron fluoride and oxyfluoride conversion electrodematerials for lithium batteries. ACS Appl Mater Interfaces2014;6(14):10858–69.

[37] Kim SW, Park KY, Ryu JK, Ko JW, Cho WS, Kim SM, et al.Energy storage in in vivo synthesizable biominerals. RSC Adv2012;2(13):5499–501.

[38] Park GD, Ko YN, Kang YC. Electrochemical properties ofcobalt hydroxychloride microspheres as a new anodematerial for Li-ion batteries. Sci Rep 2014;4:5785.

[39] Wang CY, Li D, Too CO, Wallace GG. Electrochemicalproperties of graphene paper electrodes used in lithiumbatteries. Chem Mater 2009;21(13):2604–6.

[40] Wu ZS, Ren WC, Wen L, Gao L, Zhao JP, Chen ZP, et al.Graphene anchored with Co3O4 nanoparticles as anode oflithium ion batteries with enhanced reversible capacity andcyclic performance. ACS Nano 2010;4(6):3187–94.

[41] Liang MH, Zhi LJ. Graphene-based electrode materials forrechargeable lithium batteries. J Mater Chem2009;19(45):5871–8.

[42] Zhou GM, Wang DW, Li F, Zhang L, Li N, Wu ZS, et al.Graphene-wrapped Fe3O4 anode material with improvedreversible capacity and cyclic stability for lithium ionbatteries. Chem Mater 2010;22(18):5306–13.

C A R B O N 8 4 ( 2 0 1 5 ) 1 4 – 2 3 23

[43] Yoo EJ, Kim JD, Hosono EJ, Zhou HS, Kudo T, Honma I. Largereversible Li storage of graphene nanosheet families for usein rechargeable lithium ion batteries. Nano Lett2008;8(8):2277–82.

[44] Chen Y, Guo F, Qiu Y, Hu H, Kulaots I, Walsh E, et al.Encapsulation of particle ensembles in graphene nanosacksas a new route to multifunctional materials. ACS Nano2013;7(5):3744–53.

[45] Chen Y, Guo F, Jachak A, Kim SP, Datta D, Liu J, et al. Aerosolsynthesis of cargo-filled graphene nanosacks. Nano Lett2012;12(4):1996–2002.

[46] Choi SH, Kang YC. Crumpled graphene-molybdenum oxidecomposite powders prepared by a continuous process and itsexcellent performance as anode for lithium-ion batteries.ChemSusChem 2014;7(2):523–8.

[47] Choi SH, Kang YC. Uniform decoration of vanadium oxidenanocrystals on reduced graphene-oxide ball by aerosolprocess for lithium-ion battery cathode material. Chem Eur J2014;20(21):6294–9.

[48] Zhao ZG, Geng FX, Bai JB, Cheng HM. Facile and controlledsynthesis of 3D nanorods-based urchin like and nanosheets-based flowerlike cobalt basic salt nanostructures. J PhysChem C 2007;111(10):3848–52.

[49] Liu JL, Cui WJ, Wang CX, Xia YY. Electrochemical reaction oflithium with CoCl2 in nonaqueous electrolyte. ElectrochemCommun 2011;13(3):269–71.

[50] He YS, Bai DW, Yang XW, Chen J, Liao XZ, Ma ZF. A Co(OH)2-graphene nanosheets composite as a high performanceanode material for rechargeable lithium batteries.Electrochem Commun 2010;12(4):570–3.

[51] Kim JH, Kang YC. Electrochemical properties of micron-sized,spherical, meso- and macro-porous Co3O4 and CoO–carboncomposite powders prepared by a two-step spray dryingprocess. Nanoscale 2014;6(9):4789–95.

[52] Ko YN, Park SB, Jung KY, Kang YC. One-pot facile synthesis ofant-cave-structured metal oxide – carbon microballs bycontinuous process for use as anode materials in Li-ionbatteries. Nano Lett 2013;13(11):5462–6.

[53] Li GD, Xu LQ, Hao Q, Wang M, Qian Y. Synthesis,characterization and application of carbon nanocages asanode materials for high-performance lithium-ion batteries.RSC Adv 2012;2(1):284–91.

[54] Du XY, He W, Zhang XD, Yue YZ, Liu H, Zhang XG, et al.Enhancing the electrochemical performance of lithium ionbatteries using mesoporous Li3V2(PO4)3/C microspheres. JMater Chem 2012;22(13):5960–9.

[55] Fu CC, Li GS, Luo D, Zhenga J, Li LP. Gel-combustion synthesisof Li1.2Mn0.4Co0.4O2 composites with a high capacity andsuperior rate capability for lithium-ion batteries. J MaterChem A 2014;2(5):1471–83.

[56] Srinivasan NR, Mitra S, Bandyopadhyaya R. Improvedelectrochemical performance of SnO2-mesoporous carbonhybrid as a negative electrode for lithium ion batteryapplications. Phys Chem Chem Phys 2014;16(14):6630–40.

[57] Zhou G, Wang DW, Yin LC, Li N, Li F, Cheng HM. Oxygenbridges between NiO nanosheets and graphene forimprovement of lithium storage. ACS Nano 2012;6(4):3214–23.

[58] Wu ZS, Zhou G, Yin LC, Ren W, Li F, Cheng HM. Graphene/metal oxide composite electrode materials for energystorage. Nano Energy 2012;1:107–31.