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1、 Exploration research of new cathode materials with high capacity for Li-ion batteryYong YangState Key Lab of Physical Chemistry of Solid Surface,Xiamen UniversityChinaWhatare the major players of the cathode materialsElectrode materialsHigh energy densityHigh power densityLayered oxide cathode mate
2、rialsPolyanion:LFePO4,Spinel,LiMn2O4High energy densityLi2FeMnSiO4;Organic-typeFluoridesFurther improvement of layered oxide-based cathode materials1)Nickel-based layered cathode materials:Lattice-dopingSurface coating1)H.S.Liu,et al;Electrochimica Acta,2004,49:1151-1159;Solid State Ionics,2004,166:
3、317-3252),et al;J Power Sources,2004,129(1):101-106;J.Phys.Chem.B;2004,108,17546-17552 2)Li-rich Li-Ni-Co-Mn-O system;Very promising system,still more study are needed.E.g.first cycle efficiency,rate capability,safety issues,how choose suitable anode systems.High-CapacityHigh-Capacity LiLi(1-x)/3Mn(
4、2-x)/3Nix/3Co3/xO2 Cathode Charge/discharge at 18 mA/g,2.0 4.8 V The initial discharge capacity is 249 mAh/g,about 100 mAh/g higher than that of LiCoO2.0.1 C0.1 CBare Bare AlFAlF3 3-coated-coatedCharge Charge(mAh/g)(mAh/g)324.5324.5314.0314.0Discharge Discharge(mAh/g)(mAh/g)249249263.1263.1ICL(mAh/g
5、)ICL(mAh/g)75.575.550.950.9Layered Oxide-type Cathode MaterialsHigh energy density batteriesLayered oxide cathode materials Layered oxide cathode materials LiLi2 2MnOMnO3 3.LiNiLiNix xCoCoy yMnMn1-x-y1-x-y O O2 :2 :270mAh/g or even higher,270mAh/g or even higher,Gas evolution,e.g.O2,CO2High capacity
6、 cathode materialsCharging to high voltage In-situ Electrochemical Mass spectroscopic techniques and Its use in Li-ion batteries AlF3 coating layer provides a buffer layer to make oxygen atoms with high activity combine together to form O2 molecules with low oxidation capability to electrolytes.1/45
7、 timesAdvantages:Low cost excellent thermal stability no oxygen evolved at low amount Li+intercalatedDisadvantages:Lower capacity and low electronic conductivityPhosphate should be developed as High Power Density and Safe Cathode Materials Polyanion compounds(i.e.LiFePO4)with stable framework is one
8、 of the excellent candidate as new generation cathode materials in lithium-ion batteriesOlivine type:LiMPO4 (PO4)3-Orthosilicates:Li2MSiO4 (SiO4)4-The redox potential of Mn+/n+1 can be modulated by the coordinated polyanion group Lower inductive effects of silicate anions compared with phosphate ani
9、on,but higher inductive effects than oxide anion is expected.Why do we choose Silicates?orthosilicate materials(Li2MSiO4):Two lithium ionsTwo lithium ions should be reversible extracted or inserted in should be reversible extracted or inserted in principle without distinctively changes of the crysta
10、l principle without distinctively changes of the crystal structurestructure.Theo.(mAh g-1)Exp.(mAh g-1)LiCoO2274140LiNiO2275200LiNi1-xCoxO2275170180LiNi1/2Mn1/2O2280180190LiFePO4170150Li2FeSiO4331165 Li2MnSiO4333209(1st cycle)Li2MnxFe1-xSiO4332235(x=0.5)A novel cathode materials with more than one e
11、lectron exchange:Li2MnSiO4 Rietveld plot of Li2MnSiO4/C composite.Y.X.Li,Y.Yang;J.Power Sources,174(2),528-532,2007 Y.Yang,;Chinese Patent CN 200610005329Li2MnSiO4正极材料循环性能的研正极材料循环性能的研究究Cyclic stability of Li2MnSiO4 material is poor!The first charge/discharge profiles of Li2Mn1-xFexSiO4/C at a curren
12、t density of 10 mA g-1.*Z.L.Gong,Y.X.Li,Y.Yang,Electrochem.Solid-State Lett.9(2006)A542.A capacity of 214 mAh/g(86%of the theoretical capacity,1.29 electrons per unit formula)was achieved for Li2MnxFe1-xSiO4(x=0.5)sample.Li2Mn1-xFexSiO4/C Cyclic performance of improved Li2Mn0.5Fe0.5SiO4 Current dens
13、ity：10mA/g(C/16)，Temperature：30 oCCapacityCapacity（mAh/g)mAh/g)The changes in Valence The changes in Valence of Mn ions of Mn ionsLiLi2 2MnSiOMnSiO4 4209209+2+2 +3.25 +3.25LiLi2 2MnMn0.50.5FeFe0.50.5SiOSiO4 4235235+2+2 +3.84+3.84Evidence for fading mechanism of Li2MnSiO4870cm-1 SiO44-SiO44-SiO44-SiO
14、32-Solid MAS 7Li NMR of Li2MnSiO4 at different charged statesFrom ex-situ NMR spectra,it is proposed that the rate of deintercalation of Li+at different sites are different,and some Li2SiO3 are newly formedQuestionsCan we get better cyclic performance in SiO44-framework with more than one electron f
15、or transition metal ions?What are main factors control the capacity and cyclic stability of the silicates materials?Whats the reaction step and mechanism for mixed system,i.e.Li2Fe1-xMnxSiO4(0 x1)In-situ or ex-situ XAS,Solid MAS NMR,Mossbauer XRD pattern of Li2Fe0.5MnSiO4SEM images of Li2Fe0.5Mn0.5S
16、iO4Structure and morphology of Li2Fe0.5Mn0.5SiO4/CElectrochemical performances of Li2 Fe0.5Mn0.5SiO4The initial two cycles at 5 mA/g between 1.5 and 4.8 V.The initial two cycles at 10 mA/g between 1.5 and 4.8 V.The initial two cycles at 150 mA/g between 1.5 and 4.8 V.Cyclic performances of Li2Fe0.5M
17、n0.5SiO4 at 5,10 and 150 mA/g,and Li2MnSiO4 at 5 mA/gi=20 mA/g VElectrode Reaction Mechanism Study-In-situ XANESThe first charge-discharge curves of Li2Fe0.5Mn0.5SiO4 during in-situ measurementSSRF Shanghai,China上海同步辐射光源上海同步辐射光源In-situ Fe K-edge XANES spectra during the first charging processIn-situ
18、 Mn K-edge XANES spectra during the first charging processEvolution of absorption edge of Fe and Mn of Li2Mn0.5Fe0.5SiO4 in the first charging and discharging processes.Nano-structured Li2FeSiO4 with excellent rate capabilities and cyclic stabilitySpace group:OrthorhombicPmn21 X-ray diffraction patt
19、erns of the carbon coated Li2FeSiO4.Insert:TEM image of the material.Z.L.Gong,Y.X.Li,G.N.He,J.Li,Y.Yang*Electrochem.Solid State Lett.,11,A60-63(2008).Structure,Morphology and Microstructure of Structure,Morphology and Microstructure of Carbon-coated LiCarbon-coated Li2 2FeSiOFeSiO4 4Nanostructured c
20、haracteristic of the Li2FeSiO4 make it as high-rate cathode materials feasibleThe inverse of the magnetic susceptibility with temperature agrees well with paramagnetism for pure sample.The arrow point out the anomalies characteristics of an antiferromagnetic ordering of Li2FeSiO4 below TN=20 K.The c
21、urve agree well with Curie-Weiss law in the whole paramagnetic region.Electrochemical performance of the Li2FeSiO4 cathodes at different cycles1.54.8 V versus Li+/Li;1/16 CZ.L.Gong,Y.X.Li,G.N.He,J.Li,Y.Yang*Electrochem.Solid State Lett.,11,A60-63(2008).Excellent rate-performance of the silicate cath
22、ode materialsZ.L.Gong,Y.X.Li,G.N.He,J.Li,Y.Yang*Electrochem.Solid State Lett.,11,A60-63(2008).Reasons:Porous nanostructure,and improved electronic conductivity through carbon connection.Excellent cyclic stability of Li2FeSiO4Excellent thermal stabilityNo extra heat give off during heating process!At
23、 our synthesis conditions,two modifications of Li2CoSiO4(,and)which are derivatives of low temperature Li3PO4 were obtained.a:;Oorthorhombic and space-group Pmn21.b:orthorhombic The XRD profiles of the Li2CoSiO4 powers prepared at different conditions.Co-silicates-Li2CoSiO4 L.Gong,Y.X.Li,Y.Yang;J Po
24、wer Sources,2007,174(2),524-527,S.Q.Wu,J.H.Zhang,Z.Z.Zhu and Y.Yang,Curr.Appl.Phys.2007,7,611The temperature dependence of the inverse molar magnetic susceptibility 1/m for Li2CoSiO4 powers prepared at 873 K.The magnetization curves M(H)at 2 K for Li2CoSiO4 powers prepared at 873 K.Magnetic property
25、Galvanostatic chargedischarge curves for Li2CoSiO4-based cathodes at current rate 16 mA/g.Electrochemical performancespace-group:Pmn21SiO4-MO4LiO4SiO4-MO4Corrugated layerFirst-principles investigations on the structural and electronic propertiesStructure of Li2MSiO4Reference:1),et al;Computational M
26、aterials Science,2009,44,1243-1251 O Co-OO Si-OConclusions A series of silicates cathode materials such as Li2FeSiO4,LiFexMn1-xSiO4,Li2CoSiO4 with and without carbon coating have been synthesized,some of them could achieve more than 1-1.6 Li+reversible exchange.e.g.Li2Mn0.5Fe0.5SiO4 with 235 mAh/g h
27、as been achieved.We have made a carbon-coated nanostructured Li2FeSiO4 material with excellent rate performance,it shows a promise as cathode materials for high-power lithium-ion batteries.Phase-pure Li2CoSiO4 has been prepared successfully and its physical properties and electrochemical performance
28、 were characterized.Some commentsnWe have made some promising progress about silicates in the last few years,but due to several phases or even impurity may be formed during the synthesis,we need to refine our synthesis route and get well-controlled and phase-purifed products with satisfied electroch
29、emical performance.nSilicates system is quite complex than we imagine,we need to more techniques to characterize it,esp.in-situ techniques for characterization of intercalation/de-intercalation process including bulk and local crystal and electronic structure,Acknowledgement National Natural Science Foundation of China(NNSFC,Grant No.20873115 and no.90606015)Ministry of Science and Technology,China(Grant No.2007CB9702)Xiamen University