research article multishelled nio hollow spheres decorated ...rechargeable lithium-ion batteries...

Research ArticleMultishelled NiO Hollow Spheres Decorated byGraphene Nanosheets as Anodes for Lithium-Ion Batteries withImproved Reversible Capacity and Cycling Stability

Lihua Chu1 Meicheng Li12 Yu Wang1 Xiaodan Li1 Zipei Wan1

Shangyi Dou1 and Yue Chu1

1State Key Laboratory of Alternate Electrical Power System with Renewable Energy SourcesNorth China Electric Power University Beijing 102206 China2Chongqing Materials Research Institute Chongqing 400707 China

Correspondence should be addressed to Meicheng Li mclincepueducn

Received 15 December 2015 Revised 16 January 2016 Accepted 21 April 2016

Academic Editor Raul Arenal

Copyright copy 2016 Lihua Chu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Graphene-based nanocomposites attract many attentions because of holding promise for many applications In this workmultishelled NiO hollow spheres decorated by graphene nanosheets nanocomposite are successfully fabricated The multishelledNiO microspheres are uniformly distributed on the surface of graphene which is helpful for preventing aggregation of as-reduced graphene sheets Furthermore the NiOgraphene nanocomposite shows much higher electrochemical performance witha reversible capacity of 2615mAh gminus1 at a current density of 200mAgminus1 after 100 cycles tripled compared with that of pristinemultishelled NiO hollow spheres implying the potential application in modern science and technology

1 Introduction

With the rapid development of the global economy fastdepletion of nonrenewable energy and the increasing envi-ronmental problems it is urgent to develop new clean andsustainable sources and technologies for energy storage andconversion with high efficiency [1ndash3] Rechargeable lithium-ion batteries (LIBs) are a promising one for the upcomingdemand such as electric vehicles and grid storage systemsbecause of their high energy density long lifespan andenvironmental benignancy

As one of the special structures of carbon graphene hasinitiated enormous scientific activities with the honeycomblattice structure unique structural features of chemical sta-bility high surface area flexibility and superior electric andthermal conductivity It has been used as ideal building blocksfor energy storage systems with improved electrochemicalproperties compared with these host materials such asmetalmetal oxide and sulfide [4 5] To further explore the potentialapplication of graphene-based nanomaterials deriving from

the decoration of graphene nanosheets (GNS) with nano-materials attracts more and more interest So far severalgraphene-based nanocomposites have been successfully fab-ricated and show desirable combinations of properties thatare not found in individual components [6 7]

Nickel oxide (NiO) is one of prospective anode materialsin li-ion battery (LIB) which possesses the advantages of hightheoretical capacity (717mAh gminus1) high natural abundancenontoxicity low cost and environmental benignity [8ndash11]However the practical utilization of NiO is still limited owingto its poor cycling and rate performances of the NiO-basedLIBs Several strategies have been undertaken to enhancethe performance of NiO electrode materials One well-establishedmethod is constructing hybrid withGNS Variousstructures of NiOGNS such as porous NiO-wrapped GNS[12] 3D-hierarchical NiOGNS [13] and graphene anchoredwith nickel nanoparticles [14] have been prepared revealingthat the NiOGNS nanocomposite reinforces the propertiesof pristine NiO which favors their wide application in LIBs

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 4901847 6 pageshttpdxdoiorg10115520164901847

2 Journal of Nanomaterials

Aggregation of route

Graphite oxidenanosheets spheres on GO

nanosheets

Heat treatment

hollow spheres on

Hydrothermal

Multishelled NiO

Ni2+ ions

Ni(OH)2 hollow

graphene nanosheets

Figure 1 Illustration of the procedures for preparation of NiOgraphene hierarchical structure

In this work we report the solvothermal method for thesynthesis ofmultishelledNiOhollow spheresGNSnanocom-posite in which the multishelled NiO hollow spheres arewrapped by GNSThis hybrid architecture is found to displaymuch improved electrochemical properties by comparison tothat of pristine multishelled NiO hollow microspheres

2 Experimental

The composite was prepared by the solvothermal method3mL graphite oxide (6mol Lminus1) was ultrasonically dispersedin 30mL of deionized water and then 1 g of Ni(NO)

3

sdot6H2

Oand 1 g of D-glucose were added adjusting the pH to 1090with NH

3

sdotH2

O using a pH meter and magnetic stirrer toform a homogeneous solution at room temperature Thesolution was then transferred into a Teflon-lined stainlesssteel autoclave (50mL) sealed and heated at 150∘C for15 h The product was collected by centrifugation washedwith deionized water several times to remove impurity andthen dried at 60∘C in vacuum Finally the NiOgraphenewas obtained by calcining the precursor in N

2

at 300∘Cfor 2 h and then in air at 500∘C for 2 h For comparisonthe multishelled NiO spheres were prepared by a similarsolution-based method and subsequent calcination with theabsence of graphene oxide (GO)

The crystallographic structures morphology and micro-structure of the as-prepared products were characterized byBruker D8 Focus X-ray powder diffractometer with usingCu K

120572

(120582 = 15406 A) radiation over a range of 2120579 from20∘ to 90∘ FEI Quanta 200F microscope field emissionscanning electron microscope (FESEM) and Tecnai G2 F20Field emission transmission electronmicroscopy (TEM)withaccelerating voltage of 200 kV Raman measurements wererecorded on Laser Confocal Micro-Raman Spectroscopy(LabRAM Aramis)

Electrochemical measurements were conducted using aCR-2032-coin type cell configuration The electrode mate-rials are a slurry consisting of 80wt of electrode mate-rials 10 wt of acetylene black (Super-P) and 10wt ofpolyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidinoneThey were coated onto a copper foil and driedat 100∘C in vacuum for 12 h before pressing Lithium foilwas used as the counter and reference electrodes and thepolypropylene foil (Celgard 2400) was used as the separatorThe electrolyte was 1M LiPF

6

dissolved in a mixture ofethylene carbonate (EC) and dimethyl carbonate (DMC) (vv= 1 1) Galvanostatic discharge-charge (GDC) experimentswere carried out at different current densities in the voltage

range of 001ndash300V with a multichannel battery tester(Maccor Inc USA) Cycling and rate performances weremeasured by the electrochemical workstation (LANDbatterytest system)

3 Results and Discussion

A schematic illustration of the fabrication process of NiOgraphene composite is shown in Figure 1 Graphite oxide(GO) was sonicated in di-water to form a homogeneoussuspension Then the GO nanosheets absorb Ni2+ ionswhich react with OHminus to grow Ni(OH)

2

architectures on GOnanosheets Here OHminus were released by NH

3

sdotH2

O whichcan also control themorphology of theNi(OH)

2

architecturesThe formation of Ni(OH)

2

fromNi2+ ions and NH3

sdotH2

O canbe expressed by the following reactions

Ni2+ + 119909NH3

sdotH2

O 997888rarr [Ni (NH3

)

119909

]

2+

+ 6H2

O (1)

[Ni (NH3

)

119909

]

2+

997888rarr Ni2+ + 119909 (NH3

)(2)

NH3

sdotH2

O 997888rarr NH4

+

+OHminus (3)

Ni2+ + 2OHminus 997888rarr Ni (OH)2

(4)

During the calcination Ni(OH)2

decomposed to yieldmultishelled NiO hollow spheres following Ni(OH)

2

rarr

NiO + H2

O and GO nanosheets reduced to graphene bylosing oxygen-containing surface groups [15 16] So theNi(OH)

2

GO precursor converted to NiOGNS compositesafter annealingThe pristinemultishelledNiO hollow sphereswould be obtained without GO during the similar reactionprocess which were discussed in our previous paper [17]

The XRD patterns of NiO and NiOGNS composite areshown in Figure 2(a) All of the diffraction peaks of pure NiOsample can be ascribed to face centered cubic NiO (JCPDSnumber 071-1179) which correspond to (111) (200) (220)(311) and (222) planes respectively All the characteristicpeaks of pureNiO are also observed forNiOGNS composite(002) diffraction peak of GNS is typically located at about24∘ in the XRD pattern but it is not obvious in Figure 2(a)Because the content of graphene is low and the diffractionof disorderedly stacked GNS is quite weaker as comparedto the well-crystalline NiO the presence of graphene can beconfirmed in the Raman spectra of NiOGNS as shown inFigure 2(b) where the G characteristic peaks of graphene areobvious though the D peak located at sim1350 cmminus1 is invisible

The morphology of pristine NiO and NiOGNS compos-ite is compared by SEM and TEM Pure NiO is composed of

Journal of Nanomaterials 3

(111)

(200)

(220)

(311)(222)

NiO

NiOgraphene

Inte

nsity

(au

)

30 40 50 60 70 80 90202120579 (degree)

(a)

250 500 750 1000 1250 1500 1750 2000

G

DNiO

NiOgraphene

NiO

NiO

Inte

nsity

(au

)

Raman shift (cmminus1)

(b)

Figure 2 (a) X-ray diffraction patterns and (b) Raman spectra for pristine NiO and NiOgraphene composite

500nm

(a)

500nm

3120583m

(b)

100nm

(c)

(200)

(200)

(111)

2nm

15Aring

20Aring24Aring

(d)

Figure 3 SEM images of pristine multishelled NiO spheres (a) NiOgraphene (b) TEM images of NiOgraphene (c) and HRTEM patternof multishelled NiO spheres (d)

multishelled spheres as shown in Figure 3(a) The NiOGNSare composed of typical rippled and crumpled GNS andmultishelled NiO spheres (Figure 3(b)) It can be clearlyseen that the multishelled NiO microspheres with diametervarying from 20 120583m to 35 120583m are uniformly distributed on

the surface of GNS The hybrid architecture can effectivelyprevent the agglomeration of as-reduced GNS The insetof Figure 3(b) is the multishelled NiO sphere on the GNSwhich demonstrates that the multishelled NiO spheres donot change after the addition of graphene Figure 3(c) shows


NiO charge capacity

NiO discharge capacityNiOgraphene charge capacityNiOgraphene discharge capacity

NiOgrapheneNiO

00

02

04

06

08

10

Cou

lom

bic e

ffici

ency

minus10 10 20 30 40 50 60 70 80 90 100 1100Cycle number

0

200

400

600

800

1000

1200Sp

ecifi

c cap

acity

(mA

hg)

(a)

NiOgrapheneNiO

100mAg

200mAg400mAg

800mAg 1Ag

100mAg

minus200

0

200

400

600

800

1000

1200

10 20 30 40 50 600Cycle number

Spec

ific c

apac

ity (m

Ah

gminus1 )

(b)

Figure 4 (a) Capacity retention and Coulombic efficiency at a current density of 200mAgminus1 (b) Rate performance at various currentdensities between 100mAgminus1 and 1A gminus1

the TEM image of NiOGNS which further confirms themultishelled sphere feature of NiO The HRTEM patternof multishelled NiO sphere is presented in Figure 3(d)The lattice spacing of 015 02 and 024 nm is observedcorresponding to the interspaces of (220) (200) and (111) and(200) planes of cubic NiO

The electrochemical properties of NiOGNS compositewere evaluated as anode for lithium-ion batteries (LIBs)Figure 4 displays the cycling and rate performances ofNiOGNS composite and pristine NiO The initial dischargecapacities are sim1100mAh gminus1 as shown in Figure 4(a) Itis much higher than the theoretical value (718mAh gminus1)mainly attributed to the solid electrolyte interphase (SEI)film formation and the additional Li+ storage in the spacebetween NiO spheres and GNS The reversible capacity ofNiO spheres decreases to 771mAh gminus1 after 100 cycles Whilethe reversible capacity of NiOGNS composite still can retain2615mAh gminus1 after 100 cycles which ismore than three timesof pristine NiO sphere The columbic efficiencies increase toand almost keep stable in the scale of 98-99 at successivecycles indicating that the formed SEI film is favorable andstable [18] The enhanced cycling performance of NiOGNScomposite should be ascribed to the addition of grapheneand the hybrid architecture Firstly the GNS have muchbetter conductivity due to the wider layer spacing comparedwith NiO The 119889-spacing of GNS was found to be 0365 nmand the maximum 119889-spacing of NiO is 024 nm ((111) latticeplane) [19] Therefore the GNS can offer additional sites foraccommodation of Li+ leading to the enhanced reversiblecapacity Secondly the flexible GNS can accommodate thevolume change and prevent the aggregation of active materi-als upon cycling Thirdly the hybrid architecture can also behelpful for preventing aggregating or restacking of as-reducedGNS

Moreover the NiOGNS composites also exhibitenhanced rate capacity compared with pristine NiO spheresas presented in Figure 4(b) The discharge capacitiesof NiOGNS at 100mAgminus1 200mAgminus1 400mAgminus1800mAgminus1 and 1 A gminus1 are 2923mAh gminus1 (10th cycle)2259mAh gminus1 (20th cycle) 1873mAh gminus1 (30th cycle)1693mAh gminus1 (40th cycle) and 1665mAh gminus1 (50th cycle)respectively In the initial 10 cycles with a small currentdensity (100mAgminus1) the capacities of pristine NiO andNiOGNS composite are comparable and the pristine NiOis even a little better than NiOGNS composite which maybe caused by the lower capacity of graphene as compared toNiO [18] However the situation reverses when the currentdensity increases The enhanced rate capacity could bereasonably attributed to advantageous combination of thehighly conductive GNS and the favorable multishelled NiOhollow spheres architecture with large specific surface areaand open inner cavity which can facilitate the rapid diffusionof lithium ions from electrolyte to active material

As shown in Figure 4(b) the capacity dropped dramati-cally from sim1100mAh gminus1 to a little more than 300mAh gminus1during the first five cycles with a small current density(100mAgminus1) Generally the capacity lost in the first severalcycles can be attributed to the irreversible reactions involvedin the formation of the SEI layer In addition the formationand stabilization of the SEI layer are a gradual processso that stable capacity also requires a process which hasbeen described in many works [20 21] It is also probablycaused by large theoretical capacity difference between NiO(717mAh gminus1) and graphene (372mAh gminus1) During the firstseveral cycles the synergy effect between NiO and graphenedoes not play well during the lithiation and delithiationprocess therefore the NiO and graphene do not serve well in


terms of improving and stabilizing capacity So the droppedcapacity is due to the formation of SEI layer and the capacitydifference in the first several cycles

The NiOGNS composite demonstrates improved elec-trochemical performance which could be due to severalreasons Firstly the wider GNS can offer additional sites forthe accommodation of Li+ compared with NiO Moreoverthe well-contact GNS and multishelled NiO hollow spherescan facilitate the continuous and rapid conducting pass wayof Li+ which are beneficial for enhancing specific capacityand rate performance of the active materials Secondly GNSare anticipated to prevent the collapse and aggregation of theactive materials upon cycling which brings about excellentcycling stability Vice versa the hybrid architecture can alsobe helpful for preventing aggregating ofGNS [12]Thirdly thelarge specific surface area and open inner cavity of GNS andthe favorable multishelled NiO hollow spheres architecturecan provide sufficient electrodeelectrolyte contact areas andfacilitate the continuous and rapid electron transport throughthe electrodes resulting in the improved rate performance

4 Conclusions

In summary we have successfully fabricated NiOGNS com-posite in which the multishelled NiO microspheres areuniformly distributed on the surface of GNS The compositeshows much enhanced cycling stability and capacity com-pared with the pristine multishelled NiO hollow sphereswhen evaluated as the anode materials in LIBs The superiorperformance in LIBs originates from the addition of GNSand the sandwich-like architecture which can facilitate thecontinuous and rapid electron transport and prevent thecollapse of nanostructures and aggregation of the activematerials The strategies described here could offer an effec-tive method to improve the electrochemical performance ofother electrode materials with large volume changes and lowelectrical conductivities

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This work is supported partially by National High-techRampD Program of China (863 Program no 2015AA034601)National Natural Science Foundation of China (Grantnos 91333122 51402106 51372082 51172069 61204064and 51202067) PhD Programs Foundation of Ministryof Education of China (Grant nos 20120036120006 and20130036110012) Par-Eu Scholars Program and the Funda-mental Research Funds for the Central Universities

References

[1] H Xia C Hong X Shi et al ldquoHierarchical heterostructuresof Ag nanoparticles decorated MnO

2

nanowires as promisingelectrodes for supercapacitorsrdquo Journal of Materials ChemistryA vol 3 no 3 pp 1216ndash1221 2015

[2] H Xia C Hong B Li et al ldquoFacile synthesis of hematitequantum dotfunctionalized graphene-sheet composites asadvanced anode materials for asymmetric supercapacitorsrdquoAdvanced Functional Materials vol 25 no 4 pp 627ndash635 2015

[3] H Xia D Zhu Z Luo et al ldquoHierarchically structuredCo3

O4

PtMnO2

nanowire arrays for high-performancesupercapacitorsrdquo Scientific Reports vol 3 article 2978 2013

[4] J Zhu D Yang Z Yin Q Yan and H Zhang ldquoGrapheneand graphene-based materials for energy storage applicationsrdquoSmall vol 10 no 17 pp 3480ndash3498 2014

[5] M Pumera ldquoGraphene-based nanomaterials for energy stor-agerdquo Energy and Environmental Science vol 4 no 3 pp 668ndash674 2011

[6] C Zhang X Peng ZGuo et al ldquoCarbon-coated SnO2

graphenenanosheets as highly reversible anode materials for lithium ionbatteriesrdquo Carbon vol 50 no 5 pp 1897ndash1903 2012

[7] D-H Lee J-C Kim H-W Shim and D-W Kim ldquoHighlyreversible li storage in hybrid NiONigraphene nanocompos-ites prepared by an electrical wire explosion processrdquo ACSApplied Materials amp Interfaces vol 6 no 1 pp 137ndash142 2014

[8] N S Spinner A Palmieri N Beauregard L Zhang J Cam-panella and W E Mustain ldquoInfluence of conductivity on thecapacity retention of NiO anodes in Li-ion batteriesrdquo Journal ofPower Sources vol 276 pp 46ndash53 2015

[9] X Yan X Tong J Wang C Gong M Zhang and L LiangldquoSynthesis of hollow nickel oxide nanotubes by electrospinningwith structurally enhanced lithium storage propertiesrdquoMateri-als Letters vol 136 pp 74ndash77 2014

[10] W Sun X Rui J Zhu et al ldquoUltrathin nickel oxide nanosheetsfor enhanced sodium and lithium storagerdquo Journal of PowerSources vol 274 pp 755ndash761 2015

[11] D Mao J Yao X Lai M Yang J Du and D Wang ldquoHierar-chicallymesoporous hematitemicrospheres and their enhancedformaldehyde-sensing propertiesrdquo Small vol 7 no 5 pp 578ndash582 2011

[12] D Xie Q Su W Yuan Z Dong J Zhang and G DuldquoSynthesis of porous NiO-wrapped graphene nanosheets andtheir improved lithium storage propertiesrdquo Journal of PhysicalChemistry C vol 117 no 46 pp 24121ndash24128 2013

[13] L Tao J Zai K Wang et al ldquo3D-hierarchical NiO-graphenenanosheet composites as anodes for lithium ion batteries withimproved reversible capacity and cycle stabilityrdquo RSC Advancesvol 2 no 8 pp 3410ndash3415 2012

[14] Y J Mai J P Tu C D Gu and X LWang ldquoGraphene anchoredwith nickel nanoparticles as a high-performance anodematerialfor lithium ion batteriesrdquo Journal of Power Sources vol 209 pp1ndash6 2012

[15] H Li L Pan C Nie Y Liu and Z Sun ldquoReduced grapheneoxide and activated carbon composites for capacitive deioniza-tionrdquo Journal of Materials Chemistry vol 22 no 31 pp 15556ndash15561 2012

[16] I R M Kottegoda N H Idris L Lu J-Z Wang and H-K Liu ldquoSynthesis and characterization of graphenendashnickeloxide nanostructures for fast chargendashdischarge applicationrdquoElectrochimica Acta vol 56 no 16 pp 5815ndash5822 2011

[17] L Chu M Li Z Wan et al ldquoMorphology control and fabrica-tion of multi-shelled NiO spheres by tuning the pH value viaa hydrothermal processrdquo CrystEngComm vol 16 no 48 pp11096ndash11101 2014

[18] Y Huang X-L Huang J-S Lian D Xu L-M Wangand X-B Zhang ldquoSelf-assembly of ultrathin porous NiO


nanosheetsgraphene hierarchical structure for high-capacityand high-rate lithium storagerdquo Journal of Materials Chemistryvol 22 no 7 pp 2844ndash2847 2012

[19] E J Yoo J Kim E Hosono H-S Zhou T Kudo and I HonmaldquoLarge reversible Li storage of graphene nanosheet families foruse in rechargeable lithium ion batteriesrdquo Nano Letters vol 8no 8 pp 2277ndash2282 2008

[20] X Huang H Yu J Chen Z Lu R Yazami and H H HngldquoUltrahigh rate capabilities of lithium-ion batteries from 3Dordered hierarchically porous electrodes with entrapped activenanoparticles configurationrdquoAdvancedMaterials vol 26 no 8pp 1296ndash1303 2014

[21] K Cao L Jiao H Liu et al ldquo3D hierarchical porous 120572-Fe2

O3

nanosheets for high-performance lithium-ion batteriesrdquoAdvanced Energy Materials vol 5 no 4 Article ID 14014212015

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Aggregation of route

Graphite oxidenanosheets spheres on GO

nanosheets

Heat treatment

hollow spheres on

Hydrothermal

Multishelled NiO

Ni2+ ions

Ni(OH)2 hollow

graphene nanosheets

Figure 1 Illustration of the procedures for preparation of NiOgraphene hierarchical structure

In this work we report the solvothermal method for thesynthesis ofmultishelledNiOhollow spheresGNSnanocom-posite in which the multishelled NiO hollow spheres arewrapped by GNSThis hybrid architecture is found to displaymuch improved electrochemical properties by comparison tothat of pristine multishelled NiO hollow microspheres

2 Experimental

The composite was prepared by the solvothermal method3mL graphite oxide (6mol Lminus1) was ultrasonically dispersedin 30mL of deionized water and then 1 g of Ni(NO)

3

sdot6H2

Oand 1 g of D-glucose were added adjusting the pH to 1090with NH

3

sdotH2

O using a pH meter and magnetic stirrer toform a homogeneous solution at room temperature Thesolution was then transferred into a Teflon-lined stainlesssteel autoclave (50mL) sealed and heated at 150∘C for15 h The product was collected by centrifugation washedwith deionized water several times to remove impurity andthen dried at 60∘C in vacuum Finally the NiOgraphenewas obtained by calcining the precursor in N

2

at 300∘Cfor 2 h and then in air at 500∘C for 2 h For comparisonthe multishelled NiO spheres were prepared by a similarsolution-based method and subsequent calcination with theabsence of graphene oxide (GO)

The crystallographic structures morphology and micro-structure of the as-prepared products were characterized byBruker D8 Focus X-ray powder diffractometer with usingCu K

120572

(120582 = 15406 A) radiation over a range of 2120579 from20∘ to 90∘ FEI Quanta 200F microscope field emissionscanning electron microscope (FESEM) and Tecnai G2 F20Field emission transmission electronmicroscopy (TEM)withaccelerating voltage of 200 kV Raman measurements wererecorded on Laser Confocal Micro-Raman Spectroscopy(LabRAM Aramis)

Electrochemical measurements were conducted using aCR-2032-coin type cell configuration The electrode mate-rials are a slurry consisting of 80wt of electrode mate-rials 10 wt of acetylene black (Super-P) and 10wt ofpolyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidinoneThey were coated onto a copper foil and driedat 100∘C in vacuum for 12 h before pressing Lithium foilwas used as the counter and reference electrodes and thepolypropylene foil (Celgard 2400) was used as the separatorThe electrolyte was 1M LiPF

6

dissolved in a mixture ofethylene carbonate (EC) and dimethyl carbonate (DMC) (vv= 1 1) Galvanostatic discharge-charge (GDC) experimentswere carried out at different current densities in the voltage

range of 001ndash300V with a multichannel battery tester(Maccor Inc USA) Cycling and rate performances weremeasured by the electrochemical workstation (LANDbatterytest system)

3 Results and Discussion

A schematic illustration of the fabrication process of NiOgraphene composite is shown in Figure 1 Graphite oxide(GO) was sonicated in di-water to form a homogeneoussuspension Then the GO nanosheets absorb Ni2+ ionswhich react with OHminus to grow Ni(OH)

2

architectures on GOnanosheets Here OHminus were released by NH

3

sdotH2

O whichcan also control themorphology of theNi(OH)

2

architecturesThe formation of Ni(OH)

2

fromNi2+ ions and NH3

sdotH2

O canbe expressed by the following reactions

Ni2+ + 119909NH3

sdotH2

O 997888rarr [Ni (NH3

)

119909

]

2+

+ 6H2

O (1)

[Ni (NH3

)

119909

]

2+

997888rarr Ni2+ + 119909 (NH3

)(2)

NH3

sdotH2

O 997888rarr NH4

+

+OHminus (3)

Ni2+ + 2OHminus 997888rarr Ni (OH)2

(4)

During the calcination Ni(OH)2

decomposed to yieldmultishelled NiO hollow spheres following Ni(OH)

2

rarr

NiO + H2

O and GO nanosheets reduced to graphene bylosing oxygen-containing surface groups [15 16] So theNi(OH)

2

GO precursor converted to NiOGNS compositesafter annealingThe pristinemultishelledNiO hollow sphereswould be obtained without GO during the similar reactionprocess which were discussed in our previous paper [17]

The XRD patterns of NiO and NiOGNS composite areshown in Figure 2(a) All of the diffraction peaks of pure NiOsample can be ascribed to face centered cubic NiO (JCPDSnumber 071-1179) which correspond to (111) (200) (220)(311) and (222) planes respectively All the characteristicpeaks of pureNiO are also observed forNiOGNS composite(002) diffraction peak of GNS is typically located at about24∘ in the XRD pattern but it is not obvious in Figure 2(a)Because the content of graphene is low and the diffractionof disorderedly stacked GNS is quite weaker as comparedto the well-crystalline NiO the presence of graphene can beconfirmed in the Raman spectra of NiOGNS as shown inFigure 2(b) where the G characteristic peaks of graphene areobvious though the D peak located at sim1350 cmminus1 is invisible

The morphology of pristine NiO and NiOGNS compos-ite is compared by SEM and TEM Pure NiO is composed of


(111)

(200)

(220)

(311)(222)

NiO

NiOgraphene

Inte

nsity

(au

)

30 40 50 60 70 80 90202120579 (degree)

(a)

250 500 750 1000 1250 1500 1750 2000

G

DNiO

NiOgraphene

NiO

NiO

Inte

nsity

(au

)


(b)


500nm

(a)

500nm

3120583m

(b)

100nm

(c)

(200)

(200)

(111)

2nm

15Aring

20Aring24Aring

(d)





NiO charge capacity


NiOgrapheneNiO

00

02

04

06

08

10

Cou

lom

bic e

ffici

ency


0

200

400

600

800

1000

1200Sp

ecifi

c cap

acity

(mA

hg)

(a)

NiOgrapheneNiO

100mAg

200mAg400mAg

800mAg 1Ag

100mAg

minus200

0

200

400

600

800

1000

1200

10 20 30 40 50 600Cycle number

Spec

ific c

apac

ity (m

Ah

gminus1 )

(b)









4 Conclusions


Competing Interests


Acknowledgments


References


2




O4

PtMnO2























O3









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(111)

(200)

(220)

(311)(222)

NiO

NiOgraphene

Inte

nsity

(au

)

30 40 50 60 70 80 90202120579 (degree)

(a)

250 500 750 1000 1250 1500 1750 2000

G

DNiO

NiOgraphene

NiO

NiO

Inte

nsity

(au

)


(b)


500nm

(a)

500nm

3120583m

(b)

100nm

(c)

(200)

(200)

(111)

2nm

15Aring

20Aring24Aring

(d)





NiO charge capacity


NiOgrapheneNiO

00

02

04

06

08

10

Cou

lom

bic e

ffici

ency


0

200

400

600

800

1000

1200Sp

ecifi

c cap

acity

(mA

hg)

(a)

NiOgrapheneNiO

100mAg

200mAg400mAg

800mAg 1Ag

100mAg

minus200

0

200

400

600

800

1000

1200

10 20 30 40 50 600Cycle number

Spec

ific c

apac

ity (m

Ah

gminus1 )

(b)









4 Conclusions


Competing Interests


Acknowledgments


References


2




O4

PtMnO2























O3









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




NiO charge capacity


NiOgrapheneNiO

00

02

04

06

08

10

Cou

lom

bic e

ffici

ency


0

200

400

600

800

1000

1200Sp

ecifi

c cap

acity

(mA

hg)

(a)

NiOgrapheneNiO

100mAg

200mAg400mAg

800mAg 1Ag

100mAg

minus200

0

200

400

600

800

1000

1200

10 20 30 40 50 600Cycle number

Spec

ific c

apac

ity (m

Ah

gminus1 )

(b)









4 Conclusions


Competing Interests


Acknowledgments


References


2




O4

PtMnO2























O3









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






4 Conclusions


Competing Interests


Acknowledgments


References


2




O4

PtMnO2























O3









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








O3









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article multishelled nio hollow spheres decorated ...rechargeable lithium-ion batteries...

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