锂离子电池阴极材料LiMn2O4研究进展

REVIEWA review of recent developments in the surface modificationof LiMn 2O4 as cathode material of power lithium-ion batteryTing-Feng Yi the AlPO 4-coated LMO only exhibited the capacity loss of2.6 and 7.6 at 30 C and 55 C,respectively. Theimprovement of cycleability is ascribed to the AlPO 4 film,minimizing the contact area of LiMn 2O4/electrolyte inter-face, thus, suppressingthe dissolution of Mn effectively [28].MetalIt is well known that gold and silver belong to the lowest-resistance metals; hence, they can be expected to enhanceelectron conduction of coated LMO and then improve itselectrochemical performance. Tu et al. [29] have reportedthat a nano-gold film-coated LMO by ion sputteringmethod shows better capacity retention at room temperaturethan that of uncoated LMO, which is attributed to reducecontact area of electrode/electrolyte interface and sup-pressed dissolution of manganese during electrochemicalcycling. Zhou et al. [30] reported that the initial dischargecapacity was decreased with increasing the amount of Agcoating, but Ag 0.1/LMO exhibits the highest dischargecapacity after 40 cycles 108 mAh g- 1 among all samples.Son et al. [31] also reported that the silver-coated nano-particle LMO 3.2 wt. Ag shows excellent cycleability at2 C galvanostatic conditions. It can be concluded that theimproved cycleability of metal coating LMO can beattributed to enhanced electron conduction between LMOparticles because of the low resistance of silver and gold.Electrode materialsThe LMO surface coated with other electrode materialscan probably be an effective way to improve theelectrochemical performance at room temperature andelevated temperature. The reason for the improvedelevated temperature properties of LMO coated by otherelectrode materials is that the surface coating reduces thedissolution of Mn, which results from the suppression ofthe electrolyte decomposition. The coated electrodematerials include LiCoO 2 performed by sol– gel methods[32– 34] and microemulsion method [35], LiNi 0.8 Co 0.2 O2[36], Li 4Ti 5 O12 [37, 38], LiNi 0.05 Mn 1.95 O4 [ 39], andLiCu xMn 2 - xO4 [ 40]. The synthesis methods and theelectrochemical performance of coating by other electrodematerials are plotted in Table 2.Carbon materialsCarbon coating has been known to be effective not only inenhancing the electrical conductivity of metal oxides butalso in increasing their absorbing ability against organicmolecules. In addition, a coated carbon layer would protectthe metal oxides from chemical corrosion. Han et al.reported that [41] the coated carbon layer composed ofdisordered amorphous carbon and polycyclic aromaticSpinelSpinel PVPMetaprecursorSpinelMn nSpinelSpinel PVPMetalprecursorSpinelMnnSpinelCoating layerFig.1 Schematic diagram of the metal oxide coating LMO procedurefrom [15]780 Ionics 2009 15779– 784Table1SynthesismethodsandtheelectrochemicalperformanceofLMOcoatedbymetaloxideCoatedoxidesandreferencesSynthesisElectrochemicalperformancesNano-SiO2[14]LMOpowderwaspreparedbythesol–gelmethodcalcinatedat850Cfor15h.SiO2-coatedLMOweresynthesizedbypolymericprocessatthecalculationof1.0,2.0,and3.0wt.byusingsilicicacidasthecoatingofrawmaterials.2.0wt.ofSiO2-coatedLMOhassignificantlyimprovedthecapacityretentionandexcellentcycleabilityfor30Cand60CcomparedwiththeuncoatedLMObecausetheformationofapassivelayerfilmduringelectrochemicalcyclingiscontrolled.MgO [16]LMOpowderwasobtainedfromMerckKGaAhighlypure,Libatterygrade.MgO-coatedLMOwassynthesizedasfollowsthemixedsolutionofLMOandCH3COO2Mg4H2Oisaddedwithaqueousammonia,thencentrifuged,andwashed.Theformedproductwasfurtherdriedat450Cunderairfor4h.ThecapacityfadingofMgO-coatedLMOelectrodesatelevatedtemperaturesismuchsmallercomparedtoregularLMOelectrodes.ZnO [17]LMOwassynthesizedbyasolid-statemethod.LMOwasaddedintothemixedsolutionofzincacetateandtriethanolamineandevaporatedat80Cuntilablackgelformed.Thegelwasdriedat100Cfor2handcalcinedfor6hat500CtoobtaintheZnO-coatedLMO.UncoatedLMOdeliveredanaveragecapacitylossof0.81percyclein50cycles;the1wt.,2wt.,and5wt.ZnO-coatedLMOonlyshowedtheaveragecapacitylossof0.54,0.19,and0.14percycle,respectively,underacurrentrateofC/2at55Cbetween3.4and4.3V.CeO2[21]LMOwassynthesizedbyasolid-statemethod.ForpreparingCeO2-coatedLMOpowderbyusingapolymericprecursorbasedonthePechinimethod.TheinitialdischargecapacitywasdecreasedwiththeincreasedamountofCeO2coating,and2CeO2-coatedLMOexhibitsaslightdecreaseinitsoriginalspecificcapacityof107mAhg-1andexcellentcapacityretentionmorethan82ofitsinitialcapacity.ZrO2 [22]LMOwasfromSedemaBelgium.FormakingtheZroxidecoatinglayer,Zrbutoxidewasmixedwith1-butanolinavolumeratioofalkoxide/alcohol14underultrasonicagitationfor30min.LMOpowderwasthendispersedintothecoatingsolution,followedbysettlingundervacuum.Thedispersionsolutionwasthenevaporated.Finally,thecoatedpowderwascalcinedat400C,ground,andsieved.5wtZrO2-coatedLMOshowstremendousenhancementincyclingstabilityatCDratesupto10C,andthecoatedspinelelectrodeexhibitsalowercubic-tetragonaltransitionpotential,asmallercharge-transferimpedanceby4-to5-fold,anditprofoundlyreduceslatticecontractionby66uponcharge.Al2O3[24]AsolprecursorforcoatingwaspreparedbymixingethylalcoholandAlCl36H2OJunsei,JapanandthenLiMn2-xMxO4Nikki,Japan,MZr,reversiblecapacity100mAhg-1wasimmersedinsolprecursor.Afterdryingat80C,thepowderobtainedwascalcinatedat500Cfor3h.TheinitialcapacityofAl2O3-coatedLMOishigherthanthatofthebareLMO,andthecellperformancewasenhancedwiththeAl 2O3coating.Al 2O3-coatedsampleshaveimprovedinterfacialpropertiesbetweentheelectrolyteandelectrode.Co–Almixedmetaloxide[25]LMOpowderwasprovidedbyShijiazhuangBestBatteryMaterialCo.,Ltd.China.ThemixedsolutionofLMO,CoNO326H2OandAlNO3 39H2OisaddedwithLiOHH2OsolutiontomaintainthemixtureatpH10.5withvigorousagitationfor3h,andthenfilteredanddriedat120Cfor12h,andsubsequentlyheat-treatedinafurnaceatdifferenttemperaturesfor5hinair.TheamountofCointhecoatingsolutionwasvariedfrom2to4wt.basedonLMOwhiletheamountofAlinthecoatingsolutionwasfixedat0.5wt.basedonLMO.TheCoAl-MMO-coated3wt.Coand0.5wt.AlbasedonLMOLMOafterheattreatmentat400Cshowsthebestcyclingstabilitywithaspecificdischargecapacityof100mAhg-1and92.2mAhg-1after50cyclesat25Cand55C,respectively.ThisismuchhigherthanthatofthepristineLMO97.4and73.7mAhg-1at25Cand55C,respectively.Ionics 2009 15779– 784 781Table2SynthesismethodsandtheelectrochemicalperformancecoatedbyotherelectrodematerialsOtherelectrodecoatingmaterials[references]SynthesisElectrochemicalperformancesLiCoO2[33]Stoichiometricamountsoflithiumacetateandcobaltacetateweredissolvedindistilledwater.Anaqueousglycolicacidwatersolutionwasthenaddedtothismixturesolutiontoproduceagel-typesolution,andthepHvaluewascontrolledat6.5–7.0.Theresultantsolutionwasevaporateduntilitsconcentrationreachedabout1mol/l.ThecommercialLMOpowderwasthenaddedtothisresultantcoatingsolutionwhilestirring,andthenscreenedwithacentrifuge.Thescreenedpowderwasdriedinavacuumovenandcalcinedfor6hat800C.LiCoO2-coatedLMOshowedahigherdischargecapacityof120mAh/gthanLiMn2O4115mAh/g.LMOmaintainedonly50ofitsmaximumcapacityata20-Crate2400mA/g;theLiCoO2-coatedLMOmaintainedmorethan80ofmaximumcapacity.LiCoO2-coatedLMOwith3wt.conductingagentacetyleneblackshowedthehigherratecapabilitythanas-receivedLMOwith20wt.conductingagent.LiNi0.8Co0.2O2[36]Stoichiometricamountsofacetateandglycolicacidweremixedindistilledwateraccordingtopriority,andthepHwascontrolled6.5–7.0.Theresultantsolutionconcentrationofwascontrolledat0.7–1mol/l.CommercialLMOwasthenaddedtothiscoatingsolutionwithaconstantstirring.Thepowderinthecoatingsolutionwasscreenedwithacentrifugetoremovetheremainingcoatingsolution.Thescreenedpowderwasdriedinavacuumovenandwascalcinedfor6hat750Cinoxygenatmosphere.ThecoatedLMOshowedanexcellentcapacityretentionat65CcomparedwithpureLMO.ThecapacityofpureLMOdecreaseddrasticallywithcyclingat65C,andLiNi0.8Co0.2O2-coatedLMOshowslower0.08percycleloss.LiNi 0.8Co0.2O2-coatingisaveryeffectiveinimprovingtheelevatedtemperatureproperties.Li4Ti 5O12[37]LMOwaspreparedbyacitricacid-assistedsol–gelmethod.Tetrabutyltitanate,lithiumacetate,andaceticacidweredissolvedinamixedsolutioncontainingethanolanddistilledwateraccordingtopriority.Andthen,theas-preparedLMOwasaddedtothepreviouslymentionedsolunderstirring.Thegelatinsoformedwasdriedat100Cfor1handfiredat800Cfor1htoobtainthefinalpowders.TheLMOdeliveredadischargecapacityof116mAhg-1atthefirstcycleandremainedonly71.4mAhg-1after45cycles.Thecapacitylosswasabout0.99at55C.However,0.62and0.45capacitylosspercyclewerefoundfor2and5molLTO-coatedLMO.TheimprovementofelectrochemicalperformanceisattributedtothesuppressionofelectrolytedecompositiononthesurfaceofLMO.LiNi0.05Mn1.95O4[39]ByatartaricacidgelmethodIncomparisonwiththeunmodifiedLMO,theLiNi0.05Mn1.95O4-modifiedLMOexhibitedexcellentelectrochemicalcharacteristics,thesameinitialdischargecapacityof125mAhg-1,highcharging–dischargingefficiency,andgoodcyclestability.LiCuxMn2-xO4[40]TheprecursorofLMOwascalcinedat600Cfor10handmixedwithCuCH3COO2indeionizedwater.Themixturepowderswerethencalcinedat870Cfor10htosynthesizeLiCuxMn2-xO4-coatedLMOcomposite.LiCuxMn2-xO4-coatedLMOcompositecathodematerialexhibitedbetterelectrochemicalperformancethanthebaseLMO,especiallyathighCrates.782 Ionics 2009 15779– 784hydrocarbons can modify the cubic spinel-type atomicarrangement of lithium manganate, and that the carboncoating can improve the electrode performance of spinellithium manganate because of the increase of grainconnectivity and/or the protection of manganese oxidefrom chemical corrosion. Patey et al. [42] reported thatLMO/carbon nanocomposites had a considerably higherspecific galvanostatic discharge capacity at a 5-C rate orgreater than the electrode with powder of pure LMO, andthe specific energy of a thin-layer lithium-ion batterycontaining the flame-made LMO/carbon nanocomposite aspositive electrode and LiC 6 as negative electrode78 Wh kg- 1 at 50-C rate.FluorideFluoride is also used to coat LMO to improve itscycleability because it is very stable even in HF. Li et al.[43] reported that the discharge capacity of LMO decreasesslightly with increasing the amount of the coated SrF2 to2.0, but the cycleability of LMO at elevated temperatureis improved obviously. LMO remains only 79 of its initialcapacity after 20 cycles, whereas the 2.0 molar fractioncoated LMO shows 97 of its initial capacity retentioncycle at 55 C.Lee et al. [44] reported that the BiOF-coatedspinel Li 1.1 Al 0.05 Mn 1.85 O4 electrode had excellent capacityretention at 55 C,maintaining its initial discharge capacityof 96.1 after 100 cycles while that of the pristine materialwas only 84.4 compared with the initial dischargecapacity.Novel materialsIt is well known that molten Li 2 O– 2B2 O3 LBO compo-sitions exhibit a combination of good wetting propertiesand relatively low viscosity in the molten state and alsoexhibit good ionic conductivity [45, 46]; LBO materialsalso are stable against the high oxidation potentials of the 4-V positive electrode materials used in Li-ion batteries. Theside reaction and Mn dissolution between the interface ofthe cathode electrode and electrolyte was reduced signifi-cantly by surface modification of LBO glass in the LMO.Chan et al. [ 47] have reported that LMO cathode materialscoated with LBO via solid-state method exhibited relativelygood cycling performance, but the capacity fade was still2.63 after 10 cycles at a current rate of 0.1 C. ahan et al.[48] reported that the capacity retention of LBO-coatedLMO via solid-state method is 7.5 after 30 cycles, andLBO-coated LMO electrode via solution method has anexcellent cycling behavior without any capacity loss evenafter 30 cycles at room temperature and a 1-C rate asplotted in Fig. 2. Chan et al. [49] have also reported thatLi 1.08 Mn 2O4 cathode materials coated with LBO have abetterhigh-temperature performancethan that of Li 1.08 Mn2O4.The LBO-coated cathode powder with the fading rate of only7 after 25 cycles showed better cycleability than the baseone with the fading rate of 17 after 25 cycles at highertemperature.The polymer possessesthe antioxidative capability, andslowly expands instead of dissolving while dipping it in theelectrolyte for a long time. As a result, the modified LMO-based cathode displays an improved stability duringrepeated charge/discharge in organic electrolyte at anelevated temperature [50, 51]. Hu et al. [50] reported thatthe electrochemical storage properties of the spinel at 55 Cbasedon the LMO film surface decoratedwith the functionalpolymer was improved, and the 45th discharge capacitywas improved at 55 C from 56.8 to 81.4 mAh g- 1 on theLMO electrode. Arbizzani et al. [51] reported that poly3,4-ethylenedioxy thiophene pEDOT can function as anelectronic conductor and substitute the carbon usually mixedwith the inorganic oxide-based electrodes to improve theelectronic conductivity of nonstoichiometric Li 1.03 Mn 1.97 O4spinel, and the reversible capacity and capacity retention areincreased.ProspectFrom the above illustrations, it can be concluded thatcoated LMO is one of the promising cathode materials forpower lithium-ion batteries for electric vehicles since theyshow excellent performances, such as high capacity, goodcycleability, high rate capability, high thermal stability, andhigh-temperature performance. Surface coatings such asmetal oxide and other compounds/composites on LMO canprevent the direct contact of electrolyte solutions withcathode materials, reduce the generation of acids like HF,0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 3080859095100105110115120DischargecapacitymAhg-1Cycle numberLiMn2O4LBO coated LiMn2O4solid state methodLBO coated LiMn2O4solution methodFig. 2 Cycleability of all LMO materials at1-C discharge rate at roomtemperature from [48]Ionics 2009 15779– 784 783improve structural stability, and suppress phase transitions.It is sure that the surface coating of LMO cathode materialswill play, more and more, an important role in improving itselectrochemical performance. Better and/or cheaper LMOcathode materials from surface modification will come upin the near future [52– 55]. At present, LMO is themainstreaming cathode material of power lithium-ionbattery, and, especially the modified LMO, is the trend ofdevelopment of power lithium-ion battery cathode materialin the long term.References1. Thackeray MM, Johnson PJ, de Picciotto LA, Bruce PG, Good-enough JB 1984 Mater Res Bull 191792. Amatucci GG, Schmutz CN, Blyr A, Sigala C, Gozdz AS, LarcherD, Tarascon JM 1997 J Power Sources 69113. Wohlfahrt-Mehrens M, Vogler C, Garche J 2004 J PowerSources 127584. Xia Y, Zhou Y, Yoshio M 1997 J Electrochem Soc 14425935. Xia Y, Zhang Q, Wang H, Nakamura H, Noguchi H, Yoshio M2007 Electrochim Acta 5247086. Jeong I-S, Kim J-U, Gu H-B 2001 J Power Sources 102557. Sun Y-K, Hong K-J, Prakash J, Amine K 2002 ElectrochemCommun 43448. Ein