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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 UniversityChina1Whatare the major players of the cathode materialsElectrode materialsHigh energy densityHigh power densityLayered oxide cathode ma
2、terialsPolyanion: LFePO4, Spinel, LiMn2O4High energy densityLi2FeMnSiO4;Organic-typeFluorides2Further 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
3、Ionics, 2004, 166:317-3252) Z.R.Zhang, 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 sy
4、stems.3High-CapacityHigh-Capacity LiLi(1-x)/3Mn(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)324.5324.5314.0314.0Dischar
5、ge Discharge (mAh/g)(mAh/g)249249263.1263.1ICL (mAh/g)ICL (mAh/g)75.575.550.950.94Layered 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,
6、270mAh/g or even higher, Gas evolution, e.g. O2, CO2High capacity cathode materialsCharging to high voltage 5In-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 fo
7、rm O2 molecules with low oxidation capability to electrolytes.1/45 times6Advantages: 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
8、Materials Polyanion compounds(i.e. LiFePO4) with stable framework is one of the excellent candidate as new generation cathode materials in lithium-ion batteries7Olivine type: LiMPO4 (PO4)3- Orthosilicates: Li2MSiO4 (SiO4)4- The redox potential of Mn+/n+1 can be modulated by the coordinated polyanion
9、 group Lower inductive effects of silicate anions compared with phosphate anion, but higher inductive effects than oxide anion is expected.8Why do we choose Silicates ? orthosilicate materials (Li2MSiO4):Two lithium ionsTwo lithium ions should be reversible extracted or inserted in should be reversi
10、ble extracted or inserted in principle without distinctively changes of the crystal principle without distinctively changes of the crystal structurestructure.9A novel cathode materials with more than one electron exchange: Li2MnSiO4 Rietveld plot of Li2MnSiO4/C composite.Y. X. Li, Z.L.Gong, Y. Yang;
11、 J. Power Sources, 174(2), 528-532, 2007 Y.Yang, Y.X.Li, Z.L.Gong; Chinese Patent CN 210Li2MnSiO4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!11The first charge/discharge profiles of Li2Mn1-xFexSiO4/C at a current density of 10 mA g-1.* Z.L. Gong, Y.X. Li, Y. Yang, Electroche
12、m. 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/C12 Cyclic performance of improved Li2Mn0.5Fe0.5SiO4 Current density：10mA/g (C/16)， Temperature：30 oC13Evi
13、dence for fading mechanism of Li2MnSiO4870cm-1 SiO44-SiO44-SiO44-SiO32-14Solid 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 formed15QuestionsCan we get
14、 better cyclic performance in SiO44- framework with more than one electron for 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,
15、 Solid MAS NMR, Mossbauer 16XRD pattern of Li2Fe0.5MnSiO4SEM images of Li2Fe0.5Mn0.5SiO4Structure and morphology of Li2Fe0.5Mn0.5SiO4/C17Electrochemical 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.Th
16、e initial two cycles at 150 mA/g between 1.5 and 4.8 V.18Cyclic performances of Li2Fe0.5Mn0.5SiO4 at 5, 10 and 150 mA/g, and Li2MnSiO4 at 5 mA/g19i=20 mA/g, 1.5-4.8 VElectrode Reaction Mechanism Study- In-situ XANESThe first charge-discharge curves of Li2Fe0.5Mn0.5SiO4 during in-situ measurementSSRF
17、 Shanghai, China上海同步辐射光源上海同步辐射光源20In-situ Fe K-edge XANES spectra during the first charging process21In-situ Mn K-edge XANES spectra during the first charging process22Evolution of absorption edge of Fe and Mn of Li2Mn0.5Fe0.5SiO4 in the first charging and discharging processes.23Nano-structured Li2
18、FeSiO4 with excellent rate capabilities and cyclic stabilitySpace group:OrthorhombicPmn21 X-ray diffraction patterns 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). 24Structure, Morph
19、ology and Microstructure of Structure, Morphology and Microstructure of Carbon-coated LiCarbon-coated Li2 2FeSiOFeSiO4 4Nanostructured characteristic of the Li2FeSiO4 make it as high-rate cathode materials feasible25The inverse of the magnetic susceptibility with temperature agrees well with paramag
20、netism for pure sample. The arrow point out the anomalies characteristics of an antiferromagnetic ordering of Li2FeSiO4 below TN = 20 K. The curve agree well with Curie-Weiss law in the whole paramagnetic region.26Electrochemical performance of the Li2FeSiO4 cathodes at different cycles1.54.8 V vers
21、us 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). 27Excellent rate-performance of the silicate cathode materialsZ. L. Gong, Y. X. Li, G. N. He, J. Li, Y. Yang* Electrochem. Solid State Lett., 11, A60-63 (2008). Reasons: Porous nanostr
22、ucture, and improved electronic conductivity through carbon connection.28Excellent cyclic stability of Li2FeSiO429Excellent thermal stabilityNo extra heat give off during heating process!30 At our synthesis conditions, two modifications of Li2CoSiO4 (, and ) which are derivatives of low temperature
23、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 Power Sources, 2007, 174(2), 524-527, S. Q. Wu, J. H. Zhang, Z. Z. Zhu and Y. Yang, Curr. A
24、ppl. Phys. 2007, 7, 61131The 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 property32Galvanostatic chargedischarge curves for Li2CoSiO4-based catho
25、des at current rate 16 mA/g. Electrochemical performance33space-group: Pmn21SiO4 - MO4LiO4SiO4 - MO4Corrugated layerFirst-principles investigations on the structural and electronic propertiesStructure of Li2MSiO4Reference:1)S.Q.Wu, et al; Computational Materials Science, 2009, 44, 1243-1251 O Co - O
26、O Si - O34Conclusions 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 has been achieved.We have made a
27、 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 were characterized. 35Some c
28、ommentsnWe 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 electrochemical performance.nSili
29、cates 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, 36Acknowledgement National Natural Science Foundation of China (NNSFC, Grant No. 20873115 and no. 90606015) Ministry of Science and Technology,China (Grant No. 2007CB9702)Xiamen University3738
