Synthesis and characterization of macroporous tin oxide composite as an anode material for Li-ion batteries

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Journal of power sources, 196, 22, pp. 9731-9736, 2011-11-15

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Synthesis and characterization of macroporous tin oxide composite as

an anode material for Li-ion batteries

Yim, Chae-Ho; Baranova, Elena A.; Courtel, Fabrice M.; Abu-Lebdeh, Yaser;

Davidson, Isobel J.

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ContentslistsavailableatScienceDirect

Journal

of

Power

Sources

j ou rn a l h o m e pa g e :w w w . e l s e v i e r . c o m / l o c a t e / j p o w s o u r

Synthesis

and

characterization

of

macroporous

tin

oxide

composite

as

an

anode

material

for

Li-ion

batteries

Chae-Ho

Yim

a

_,

_Elena

_A.

_Baranova

a

_,

_Fabrice

_M.

_Courtel

b

_,

_Yaser

_Abu-Lebdeh

b,∗

_,

_Isobel

_J.

_Davidson

b a_Department_of_Chemical_and_Biological_Engineering,_University_of_Ottawa,₁₆₁_rue_Louis_Pasteur,_Ottawa,_ON,_K1N_6N5,_Canada

b_National_Research_Council_Canada,₁₂₀₀_Montreal_Road,_Ottawa,_ON,_K1A_0R6,_Canada

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received7June2011

Receivedinrevisedform15July2011 Accepted16July2011

Available online 22 July 2011 Keywords:

MacroporousSnO2/Ccomposite SnO2

Li-ionbatteries

a

b

s

t

r

a

c

t

AmacroporousSnO2/Ccompositeanodematerialwassynthesizedusinganorganictemplate-assisted

method.Polystyrenespheresweresynthesizedandusedastemplateandleadtomacroporous

morphol-ogywithporesof300–500nmindiameterandasurfaceareaof54.7m2_g−1_._X-ray_diffraction_showed

thattheSnO2nanoparticlesarecrystallizedinarutileP42/mnmlatticewiththepresenceofSnmetal

traces.ThesynthesizedmacroporousSnO2/Ccompositeprovidedpromisingperformanceinlithiumhalf

cellsshowingadischargecapacityof607mAhg−1_after₅₅_cycles._It_was_found_that_the_macroporous

SnO2/Ccompositeisstableandresistanttopulverizationuponcycling.

1. Introduction

Carbongraphitehasbeenthemostpopularanodematerialin useforLi-ion batteriesdue toitsmoderatecost, longcyclelife and negligible volumechange duringbattery cycling [1]. How-ever, due to its limited theoretical capacity to 372mAhg−1 _or 833mAhmL−1_,_other_materials_are_being_sought_out;_among_them aremetalsthatcanreversiblyalloywithlithiumsuchassilicon (SiLi4.4,4200mAhg−1),tin(SnLi4.4,993mAhg−1),antimony(SbLi3, 660mAhg−1_),_and_aluminium_(LiAl,₉₉₄_mAh_g−1₎_[1]_._These_metal alloysarepromisinganodematerialsduetotheirlithiumuptakeat lowpotentialandthreetotenfoldhighertheoreticalcapacities thangraphite. However,themajor problemwiththese materi-alsistheextremely largevolumechange(250–400%) uponthe alloying/dealloyingreactionwithlithium[1].Itcauses mechani-calcracks,pulverizationandlossofelectronicconductivityamong theparticlesandthecurrentcollector.Itresultsinanextremely poorbatterycyclelife[1–3].

One approach to prevent pulverization during the battery cyclingistominimizetheparticlesizeinmultiphasealloymatrices

[4]alongwiththeuseofbindersthatcanaccommodatevolume changes,suchassodiumcarboxymethylcellulose(NaCMC)[5]or styrenebutadienerubber(SBR)[6].Anotherapproachwouldbeto useaninertmatrixsuchasLi2OasinthecaseofSnO2.Itreacts withlithiuminatwo-stepprocess,firstviaanirreversible reac-tionwhereSnO2 isreducedintoSnthatthenfurtherreactswith

∗ Correspondingauthor.Tel.:+16139494184;fax:+16139912384. E-mailaddress:Yaser.Abu-Lebdeh@nrc-cnrc.gc.ca(Y.Abu-Lebdeh).

lithium byformingatin–lithium alloy[7].Asaresult, theLi2O matrixpreventsseverevolumechangeandkeepstheSnin nano-sizedform.AsreportedbyBrousseetal.[8],thesizeoftheparticles playsacrucialroleinthecaseoftinoxide,assmaller(nano) par-ticlesareabletobetteraccommodatetheabsolutevolumechange thanlarger(micro)ones.PristineSnO2nanoparticlesorcomposites usuallyshowamediumcapacityaround350–450mAhg−1_at_a_rate ofC/5[9–13].Bymaking3Dflower-shapedSnO2nanostructures, acapacityof670mAhg−1_was_obtained_at_a_rate_of_C/8._However, buildinguptheLi2Onetworkcouldnotpreventcompletevolume changes ofSn,leading topulverization.Otheralternativeshave beenintroduced,suchascoatingNi–SnontoCunano-rods[14],and sphericallyporousmulti-deckcageSnO2 [15].Otherapproaches includedispersionofSnO2particlesontoacarbonmaterial[13,16], or carboncoating ofSnO2 particles [17].Using a layer-by-layer technique to obtain carbon nanotubes as a substrate for SnO2 nanotubes (50wt%),Yang et al.[18] obtaineda specific capac-ityof450mAhg−1_._Recently,_research_groups_started_working_on graphene/SnO2 compositesasawaytobetteraccommodatethe volume change;SnO2 nanoparticleswouldbetrapped between layersofgraphene,asshowninthefollowingRefs.[19–24].

Three-dimensionallyorderedmacroporous(3DOM)materials havebeenusedforavarietyofapplicationsinchemicaland bio-chemical sensors[26–28],photonicbandgapmaterials[29–31]

andnanofabrication[32].Thesynthesisofthistypeofmaterials involvestheuseofacolloidaltemplate[25].3DOMmaterial syn-thesiswasadaptedinthisworktoobtainanorderedcarbon-coated porousSnO2thatwouldpreventthesignificantvolumechangeand Snpulverization duringbattery cycling.In a battery,thehighly orderedmacroporousmaterialshouldhavegreatersurfacein

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9732 C.-H.Yimetal./JournalofPowerSources196 (2011) 9731–9736

tactwiththeelectrolyteandleadtobetterlithiumdiffusionintothe electrodematerial,andthusfastercharge/dischargerate.Porous SnO2templated-structureshaveimprovedalotofthereversible capacityandalsotheratecapabilityofSnO2electrodes,asshown byKimandCho[33];theyobtainedcapacitiesof775mAhg−1_at C,whichisalmostthetheoreticalreversiblecapacityofSnO2.At higherrates,acapacity upto730mAhg−1 _was_obtained_at_10C, which is 93% of thetheoretical reversible capacity. The use of polystyrene(PS)asanorganiccolloidaltemplatenotonlymade itpossibletomakeacarboncoatedmacroporousSnO2/C compos-itebutalsotoobtainahighcarboncontentduetothenatureofthe thermaldecompositionofPS.Highcarboncontentwillimprovethe electronicconductivityoftheelectrodeandthuscompensatefor theinsulatingnatureofLi2O.Poly(methylmethacrylate)(PMMA) colloidsareanothercommontemplatetosynthesize3DOM crys-tals.However,depolymerisationofPMMAduringsinteringsteps reducestheamountofcarbonspreadoverSnO2/C[34].Therefore thePScolloidscanbeconsideredbettercandidatetodisperseSnO2 particlesintothecarbonmacroporousmaterial.

Ingeneral,3DOMmaterialsaresynthesizedbyinfiltrationof precursorsolutionontoatemplate[35–37].Inthiswork,weused adifferentapproachbymakingaSnO2/PScompositebymeansof ahydrothermalreaction.Thiswasfollowedbyacalcinationstep at600◦_C_in_argon_in_order_to_decompose_the_PS_colloids_and_form aporouscarbonmatrixsurroundingtheSnO2nanoparticles.The performanceofthemacroporousSnO2/Ccompositeandpristine SnO2nanoparticleswascomparedinlithiumhalfcellbatteryusing sodiumcarboxymethylcellulose(NaCMC)asbinder.

2. Materialsandmethods 2.1. Syntheses

PScolloidsweresynthesizedbyemulsion polymerization,as describedbyHollandetal.[25].Thestyrenemonomerwasobtained from Sigma–Aldrich (≥99% Reagentplus) and waspurged with nitrogenpriortouse.Then,50mLofstyrenewasaddedto425mL ofde-ionizedwater,whichwasalsopurgedwithnitrogen.The mix-turewasheatedto70◦_C._To_initialize_the_{polymerization,}₂₅_mL_of nitrogenpurged0.1MK2S2O8(Sigma–Aldrich,99%)aqueous solu-tionwasaddedtothemixture.Thesolutionwaskeptat70◦_C_for 24hundernitrogen.ThePScolloids werewashedwithethanol (CommercialAlcoholsInc.,95%)andcentrifugedat10,000rpmfor 1htoobtaintheorderedorganictemplate.Thisstepwasrepeated threetimestoremovetheinorganicimpurities.

Tinoxidewassynthesizedbymeansofahydrothermalreaction. First,0.356gofSnCl2·2H2O(Fisher,98.4%)wasdissolvedin50mLof de-ionizedwaterand50mLofethanol.Then,0.240gofPScolloids wereaddedtothesolutionandmixedfor24husingmagnetic stir-ringtohomogenizeanddispersethePScolloidsinthesolution.The beakercontainingthesolutionwascoveredwithaparafilmto pre-ventwater/ethanolevaporation.Theresultantmilkysolutionwas putintoanautoclavereactor(Parr,BombNo.4744)for6hat120◦_C. Afterthesynthesis,theautoclavereactorcontainingthesolution waslefttocooltoroomtemperature.Theresultingsolutionwas centrifugedtoorderthePScolloidsandbuildtheSnO2/PS compos-ite.Theobtainedpowderwaswashedthreetimeswithethanol, andthencalcinatedunderargon.Thefirstsinteringstepwas con-ductedat260◦_C_for₃_h,_while_the_second_sintering_was_conducted at600◦_C_for_another₃_h._Since_the_melting_point_of_PS_is₂₄₀◦_C,_the firstsinteringat260◦_C_ensured_that_PS_melted_down_from_the crys-tallizedSnO2phase.Aslowheatingrateof2◦Cmin−1wasused.The calcinationwasperformedunderargoninordertoobtainacarbon coatingontotheSnO2nanocomposite(SnO2/C).Thesamesynthetic

procedurewasfollowedbutwithouttheadditionofthePStemplate topreparethenon-templatedpristineSnO2nanoparticles. 2.2. Characterizationofcompositematerials

PowderX-raydiffractionwascarriedoutbetween15◦_and₈₅◦ (2angles) usingaBrukerAXSD8diffractometerwitha CoK␣ sourcewith35kVand45mAofpower,adivergenceangleof0.3◦_, astepsizeof0.027◦_,_and_an_acquisition_time_of₁_s_per_step._The patternswereanalyzedbytheRietveldrefinementmethod[38]

usingthesoftwareTOPASv4.2fromBrukerAXS[39].Thecrystallite sizesweredeterminedusingthefundamentalparameterapproach methoddevelopedbyChearyandCoelho[40].Themorphologyof thematerialwascharacterizedbyscanningelectronmicroscopy (SEM)usingaJEOL840A.Thermalgravimetricanalysis(TGA)was performedtoquantifytheamountofcarbonpresentintheSnO2/C composite.ATGA2950TAinstrumentwasused.Thecompositewas heatedat10◦_C_min−1_up_to₁₁₀◦_C_for₃₀_min_to_remove_moisture containedinthematerialandthenheatedcontinuouslyupto800◦_C inairinordertooxidizethecarbonfromthecomposite.

Furtherelectrochemicalcharacterizationwasperformedusing a 2325-type coin cell. Because of the interest in SnO2/C com-posite,onlyhalf cellswithlithium asa counter electrodewere used.Theelectrode waspreparedfroma slurrymadeof75wt% activematerial,5wt%carbonSuperS(Timcalgraphiteand Car-bon,Switzerland),5wt%carbongraphiteE-KS4(KG,Lonza G+T, Switzerland)and15wt%sodiumcarboxymethylcellulose(NaCMC, Calbiochem)asabinder.NaCMCwasusedasa5wt%solution dis-solvedindoubledistilledH2O.Theslurrywascastontoacopper foilcurrentcollectorthatwascleanedusinga 2.5%HClsolution inwater.Thecastwaspreparedusinganautomateddoctorblade spreaderanddriedovernightinaconvectionovenat85◦_C,_and thenina vacuumovenovernightat80◦_C._Individual_electrodes (Ø=12.5mm)were punched out, dried at 80◦_C _under _vacuum overnight,pressedundera pressureof0.5metric ton,andwere usedaspositiveelectrodes.Alithiumdisk(Ø=16.5mm)wasused asanegativeelectrode(counterelectrodeandreferenceelectrode). 70␮Lof1MLiPF6inEC:DMC(1:1byvol.)wasusedaselectrolyte andspreadoveradoublelayerofthepolypropyleneseparators. Thebatterieswereassembledinanargon-filleddrybox.Thecells werecycledgalvanostaticallyatC/12usinganArbinbatterycycler andtestedusingcyclicvoltammetrytechniques.Cyclic voltamme-trywascarriedoutusingaBiologicVMP3potentiostatandswept at0.1mVs−1_between₅_mV_and_1.5_V_for_five_cycles.

3. Resultsanddiscussion

Atwo-stepsynthesiswasnecessarytoachieveamacroscopic porousstructureofcarbon-coatedSnO2andthecarbonnetworkin whichtheSnO2nanoparticlesaredispersed.PScolloidswereused toobtaintheporousmorphology.Thechallengeherewasto syn-thesizeSnO2withoutdestroyingthePScolloids.Toachievethis,a hydrothermalreactionwasused.First,thetinprecursor (SnCl2) hadtoundergooxidation reactionata temperaturelowerthan 240◦_C_to_prevent_the_melting_of_PS. _Moreover,_the_organic tem-platehadtobecalcinedunderoxygen-freeatmospheretoobtaina carboncoating.Thus,thehydrothermalreactionfollowedby calci-nationunderargonwastotallyadequate.Duringthecentrifugation step,thePScolloidswereorderedandthevoidsamongthe col-loidswerefilledwiththeSnO2nanoparticles.Fig.1showstheSEM micrographofthepreparedanddriedSnO2/PScomposite.ThePS colloidsareorderedandtheirintegrityispreserved.Fig.2shows theRietveldrefinementoftheXRDpatternoftheSnO2/PS com-posite.Thefirstbroadpeakaround23◦₂_corresponds_to_the_PS reflection.TheotherpeakscorrespondtotheSnO2rutileP42/mnm

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Fig.1.SEMmicrographsofthecentrifugedanddriedSnO2/PScomposite synthe-sizedviaahydrothermalreaction.Inset:SEMmicrographofthePScolloidsusedfor thesynthesis.

Fig.2.RietveldrefinementoftheX-raydiffractionpatternofthecentrifugedand driedSnO2/PScompositesynthesizedviaahydrothermalreaction.

Table1

LatticeparametersofSnO2beforeandafterremovaloforganictemplate.

a( ˚A) c( ˚A) SnO2/PS Synthesized 4.753(8) 3.249(6) Ref.[44] 4.73 3.18 Crystalsize(nm) 3.2(2) SnO2/C Synthesized 4.7424(8) 3.1873(6) Ref.[44] 4.73 3.18 Crystalsize(nm) 6.37(4) Sn Synthesized 5.831(9) 3.13(1) Ref.[45] 5.83 3.18

Crystalsize(nm) N/A

structure:31◦₍₁₁_0),₄₀◦₍₁₀₁₎_and₆₁◦₍₂₁_1)._The_lattice parame-tersandcrystallitesizeareshowninTable1.Thelatticeparameter valuesslightlydeviatefromthereferencevaluesduetothe amor-phousnaturefortheobtainedmaterial.Crystallitesizebelow5nm hasbeencalculated.Itisimportanttonotethatnootherphases wereobservedontheXRDpatterns.

Fig.3. SEMmicrographofthemacroporousSnO2/Ccompositeafterthecalcination ofthetemplateunderargonat260◦_C_for₃_h,_and₆₀₀◦_C_for₃_h.

Fig.4. RietveldrefinementoftheX-raydiffractionpatternofthemacroporous SnO2/Ccompositeaftercalcinationofthetemplateunderargonat260◦_C_for₃_h, and600◦_C_for₃_h.

TheresultingSnO2/PScompositeswerecalcinedunderargon in order toobtainporousand carbon-coated SnO2.The porous morphology wasachievedby a slowheating rateat 2◦_C_min−1 andsinteringattwodifferenttemperaturesinordertocontrolthe decompositionofPS.Fig.3showstheSEMmicrographafterthe cal-cinationofthePStemplate.ThefingerprintofthePScolloidscan beobservedasasphericalporousmorphology.Arandomlyordered butinterconnectedmacroporousopenstructurewasobtained,very differentthana3DOM.Mostofthepores’diameterrangesfrom300 to500nm,whichcorrespondstothesizeofthePScolloids. How-ever,somevoidsarebiggerthanthesizeofthePScolloidsthatcould beduetothevolatiledecompositionofPScolloidsortheabsence ofSnO2nanoparticlesbetweensomePScolloidsbeforethe calcina-tionstep.Thedarkareasoftheimageareduetotheunevensurface oftheSnO2/Ccomposite,wheretheSnO2isabsentpriortothe cal-cinations.AlsoduetothefactthatSnO2islessconductive,SnO2 comesoutasbrighterareaintheSEMimage.

Fig. 4 shows the Rietveld refinement of the pattern of the finalmacroporousSnO2/Ccomposite.Twocrystallinephasesare observed:SnO2andSn.TheappearanceofSnaftercalcinationis believedtobetheresultofthereducingatmosphere.This orig-inatesfromthecalcinationatelevatedtemperatureofPSunder

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Fig.5.ThermogravimetricanalysisofthemacroporousSnO2/Ccompositeafter calcinationofthetemplateunderargonat260◦_C_for₃_h,_and₆₀₀◦_C_for₃_h._The measurementwasdoneunderairat10◦_C_min−1_.

Fig.6. Cyclicvoltammogramsofahalf-cellmeasuredbetween0.005Vand1.5V at0.1mVs−1_of_the_macroporous_SnO2/C_composite_after_the_calcination_steps._Li metalwasusedascounterandreferenceelectrode.

argon,whichprovidesreducingconditions,leadingtothe reduc-tionofsomeSn4+_of_SnO

2toSn0.Asaresult,1.1wt%ofcrystalline Snwasestimatedviaacomputinganalysis(Topasv4.2).Table1

showsthelatticeparametersandthecrystallitesizeobtainedfrom theXRDpatternofthesinteredSnO2/Ccomposite.Lattice param-etersareinagreementwiththereferencedvalues(Table1).Due tothehighcalcinationtemperature,growthinthecrystallitesize wasobservedfromlessthan5nmupto6.37(4)nm.TheBET sur-faceareaofthecompositewas54.7m2_g−1_,_which_is_very_similar towhatisreportedbyLytleetal.(55m2_g−1₎_[35]_.

ToestimatetheamountofcarboninthesynthesizedSnO2/C composite,TGAwasconductedontheresultingmaterial.Asshown in Fig.5, continuousweight loss wasobserved when the tem-peraturewas raisedup to110◦_C;_it _corresponds _to_the_loss _of water.Thetemperaturewasmaintainedat110◦_C_for₃₀_min_in ordertoremoveanymoisture.Thetemperaturewasthenincreased to800◦_C_at₁₀◦_C_min−1_._The_second_weight_loss_(8.3%)_observed between350and 450◦_C _was_the_result_of_the_{decomposition}_of carbonfromtheSnO2/Ccomposite.Whenconsideringthatthere is1.1wt%ofSn,0.2%weightgainoccurredduetotheoxidationof

Fig.7. VoltageprofileofthefirstfivecyclesofthemacroporousSnO2/Ccomposite. ArateofC/12wasused.

Fig.8.DischargecapacityofthemacroporousSnO2/Ccompositeandthepristine SnO2nanoparticles.ThecolumbicefficiencyofthemacroporousSnO2/Ccomposite isalsorepresented.

Sn.Asaresult,0.2wt%shouldbeaddedtothe8.3%weightlossto moreaccuratelyestimatetheamountofcarboninthesynthesized SnO2/Ccomposite.ThetotalamountofcarbonresidueinSnO2/C compositeisthencanbeestimatedas8.5wt%.

Fig.6showsthecyclicvoltammograms(CVs)ofthe macrop-orousSnO2/Ccomposite.TheirreversiblereductionofSnO2toSn (blackline)isobservedonthefirstcycle.Thesmallcathodicpeak around1.25V(peakA)andthepeakat0.65V(peakB)vs.Li/Li+_are duetothepartialreductionofSnO2toelementSnandthesolid electrolyteinterface(SEI)formationduringthefirstdischarge[41]. SEIformationiscausedbythedecompositionoftheelectrolyteand thelithiumsaltatthesurfaceoftheelectrode,andbothpeaks dis-appearafterthefirstcycle.Thecathodicpeaksbelow0.3V(peakb) areduetotheformationoftheLixSnalloy(0≤x≤4.4).Thenoise inthesepeaksis duetothemulti-stagelithiumintercalationof LixSnalloys[42].Theanodicpeakat0.6V(peakb′)correspondsto

thede-alloyingreactionofLixSn(0≤x≤4.4).Thesetworeactions arefullyreversible.Anadditionalreversibleprocessisobservedat 1.25V(peaka′₎_and_1.0_V_(peak_a)._This_process_is_believed_to_be associatedwiththerecovery,tosomeextent,ofsometinoxides (SnO2orSnO)[42,43].

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UsingthecompositiondeterminedviaTGAandXRD,the the-oreticalcapacityvalueofthemacroporousSnO2/Ccompositewas estimatedat732mAhg−1_._A_reversible_capacity_of₁₅₀_mAh_g−1_was usedforthecarboncoating,assumingitisablackcarbon.In the-ory,SnO2 exhibitafirstdischargecapacityof1494mAhg−1 and areversibledischargecapacityof782mAhg−1_._There_were_many attemptstosynthesize3DOMSnO2,however,onlyLytleetal.[35] andWangetal.[36]performedelectrochemicalcharacterizations.

Fig.7shows thevoltageprofileofthefirstfive cyclesof ahalf cellmadeusingthemacroporousSnO2/Ccomposite;thecellwas cycledatC/12.Thefirstcycleshowsafirstdischargecapacityof 1705mAhg−1_._This_value_corresponds_to_the_irreversible_reduction ofSnO2 toSn,theformationofLi2O,andthepartiallithiationof thecarboncoating.Snthenfurtherreactedwithlithiumtoform a tin–lithiumalloy. Thesereactionsareshown in thefollowing equations:

SnO2+4Li++4e−→Sn+2Li2O (1) Sn+xLi++xe−↔ SnLix(0≤x≤4.4) (2) 6C+xLi++xe−↔C6Lix(0≤x≤1) (3) Thefirstdischargecurvecontainsseveralfluctuationsdueto noiseoriginatedfromtheequipment.Thechargeisrepresented byaslopingplateauaround0.5Vvs.Li/Li+_._The_irreversible capac-ityobservedinthefirstcycleis800mAhg−1_,_or_47%_of_the_first dischargecapacity[13].Afterwards,cyclesfourandfivearerather stable,suggestinggoodcapacityretention.

Fig.8showsthedischargecapacitiesofthemacroporousSnO2/C compositeandthepristineSnO2nanoparticlespreparedwithout PStemplate as wellas the columbicefficiency of the macrop-orousSnO2/Ccompositeelectrode.Aspreviouslydiscussed,alarge irreversiblecapacityisobservedforthefirstcycleduetothe irre-versiblereductionofSnO2toSnandtheformationoftheSEI.The macroporousSnO2/Ccomposite showedafirstdischarge capac-ity of 1705mAhg−1 _with _47% _of _irreversible _capacity _whereas theSnO2nanoparticlesshowsalowerfirstdischargecapacityof 1150mAhg−1_with_an_{irreversibility}_of_37%._The_larger_irreversible capacityobservedforthemacroporousSnO2/Ccompositeisdueto thecarboncoatingandalsoduetothelargersurfaceareathatleads tomoreSEIformation.Forthefirstsevencycles,astable capac-ityof900mAhg−1 _was_observed._After_a_12-h_rest,_the_capacity startedfading.Areversiblecapacity of607mAhg−1 _is_observed after55cycles.Thecolumbicefficiencyisquitestablearound98% startingatcycle8.ThemacroporousSnO2/Ccompositeshowed bet-tercapacityretentionthanthepristineSnO2nanoparticleswhich exhibitsacapacityofonly300mAhg−1_after₅₅_cycles._Wang_et_al. reportedfirstdischargecapacitiesaround1500–1600mAhg−1_and reversible capacities of 150mAhg−1 _and ₃₃₀_mAh_g−1 _after ₅₅ cyclesat current rates of50 and 100mAg−1_, _respectively _[36]_. Thesevaluesaremuchlowerthantheonesobtainedinthepresent studywhichwebelieveisduetothedifferenceintheamountof carbonpresentinthecomposite.Moreover,Wangetal.reported acarboncontentof62wt%whereasitisonly8.5wt%inourcase

[36].Itisimportanttohavecarboninthecompositetoprovide electronicconductivity,buttheblack carbonobtaineddoesnot providehighcapacitystorage,soitisimportanttokeepits con-tentlowinordertoobtainbetterperformance.3DOMSnO2from Wangetal.hadlesscapacityfadeduetothehighlyordered struc-ture,butlowercapacityduetothehighcarboncontentcompared toourmaterial.

4. Conclusions

Inthepresentwork,amacroporousSnO2/Ccompositeanode material was synthesized using an organic template-assisted

hydrothermalsynthesis.Acontentof8.5wt%ofcarbonwas deter-minedinthecomposite.AsverifiedbySEM,aftercalcinations,pores of300–500nmindiameterwereobserved.ArutileSnO2crystalline phasewasobtainedbyXRDwithtracesofSnmetal.Thematerial performance,characterizedinhalfcells,suggeststhatnano-sized porousSnO2matrixmaterialisstableandresistantto pulveriza-tionduringcycling.After55 cycles,themacroporouscomposite had a capacity of 607mAhg−1_, _whereas _the _SnO

2 nanoparti-clewithoutPStemplateshowedonlyhalfthecapacityreaching 300mAhg−1_.

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