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1、Exploration research of new cathode materials with high capacity for Li-ion battery,Yong Yang State Key Lab of Physical Chemistry of Solid Surface, Xiamen University China,Whatare the major players of the cathode materials,Electrode materials,High energy density,High power density,Layered oxide cath
2、ode materials,Polyanion: LFePO4,Spinel, LiMn2O4,High energy density,Li2FeMnSiO4; Organic-type Fluorides,Further improvement of layered oxide-based cathode materials,1) Nickel-based layered cathode materials: Lattice-doping Surface coating 1) H. S. Liu, et al ; Electrochimica Acta, 2004, 49:1151-1159
3、; Solid State Ionics, 2004, 166:317-325 2) 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 su
4、itable anode systems.,High-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.,Layered Oxide-type Cathode Materials,High energy density batteries,Layered oxide cathode materi
5、als Li2MnO3. LiNixCoyMn1-x-y O2 : 270mAh/g or even higher,Gas evolution, e.g. O2, CO2,High capacity cathode materials,Charging 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 hi
6、gh activity combine together to form O2 molecules with low oxidation capability to electrolytes.,1/4,5 times,Advantages: Low cost excellent thermal stability no oxygen evolved at low amount Li+ intercalated Disadvantages: Lower capacity and low electronic conductivity,Phosphate should be developed a
7、s High Power Density and Safe Cathode Materials,Polyanion compounds(i.e. LiFePO4) with stable framework is one of the excellent candidate as new generation cathode materials in lithium-ion batteries,Olivine type: LiMPO4 (PO4)3- Orthosilicates: Li2MSiO4 (SiO4)4- The redox potential of Mn+/n+1 can be
8、modulated by the coordinated polyanion group Lower inductive effects of silicate anions compared with phosphate anion, but higher inductive effects than oxide anion is expected.,Why do we choose Silicates ? orthosilicate materials (Li2MSiO4): Two lithium ions should be reversible extracted or insert
9、ed in principle without distinctively changes of the crystal structure.,A novel cathode materials with more than one electron exchange: Li2MnSiO4,Rietveld plot of Li2MnSiO4/C composite.,Y. X. Li, Z.L.Gong, Y. Yang; J. Power Sources, 174(2), 528-532, 2007 Y.Yang, Y.X.Li, Z.L.Gong; Chinese Patent CN 2
10、00610005329,Li2MnSiO4正极材料循环性能的研究,Cyclic stability of Li2MnSiO4 material is poor!,The 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, Electrochem. Solid-State Lett. 9 (2006) A542.,Li2Mn1-xFexSiO4/C,Cyclic performance of improved
11、Li2Mn0.5Fe0.5SiO4,Current density： 10mA/g (C/16)， Temperature：30 oC,Evidence for fading mechanism of Li2MnSiO4,870cm-1,SiO44-,SiO44-,SiO44-,SiO32-,Solid MAS 7Li NMR of Li2MnSiO4 at different charged states,From ex-situ NMR spectra, it is proposed that the rate of deintercalation of Li+ at different
12、sites are different, and some Li2SiO3 are newly formed,Questions,Can we get 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 me
13、chanism for mixed system, i.e. Li2Fe1-xMnxSiO4 (0 x1) In-situ or ex-situ XAS, Solid MAS NMR, Mossbauer ,XRD pattern of Li2Fe0.5MnSiO4,SEM images of Li2Fe0.5Mn0.5SiO4,Structure and morphology of Li2Fe0.5Mn0.5SiO4/C,Electrochemical performances of Li2 Fe0.5Mn0.5SiO4,The initial two cycles at 5 mA/g be
14、tween 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 Li2Fe0.5Mn0.5SiO4 at 5, 10 and 150 mA/g, and Li2MnSiO4 at 5 mA/g,i=20 mA/g, 1.5-4.8 V,Electrode Reaction Mechanism Study- In-situ XANES,The f
15、irst charge-discharge curves of Li2Fe0.5Mn0.5SiO4 during in-situ measurement,SSRF Shanghai, China 上海同步辐射光源,In-situ Fe K-edge XANES spectra during the first charging process,In-situ Mn K-edge XANES spectra during the first charging process,Evolution of absorption edge of Fe and Mn of Li2Mn0.5Fe0.5SiO
16、4 in the first charging and discharging processes.,Nano-structured Li2FeSiO4 with excellent rate capabilities and cyclic stability,Space group: Orthorhombic Pmn21,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. Y
17、ang* Electrochem. Solid State Lett., 11, A60-63 (2008).,Structure, Morphology and Microstructure of Carbon-coated Li2FeSiO4,Nanostructured characteristic of the Li2FeSiO4 make it as high-rate cathode materials feasible,Electrochemical performance of the Li2FeSiO4 cathodes at different cycles,1.54.8
18、V versus Li+/Li; 1/16 C,Z. L. Gong, Y. X. Li, G. N. He, J. Li, Y. Yang* Electrochem. Solid State Lett., 11, A60-63 (2008).,Z. 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 ca
19、rbon connection.,Excellent cyclic stability of Li2FeSiO4,Excellent thermal stability,No extra heat give off during heating process!,At our synthesis conditions, two modifications of Li2CoSiO4 (, and ) which are derivatives of low temperature Li3PO4 were obtained. a: ; Oorthorhombic and space-group P
20、mn21. 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. Appl. Phys. 2007, 7, 611,The temperature dependence of the
21、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,Galvanostatic chargedischarge curves for Li2CoSiO4-based cathodes at current rate 16 mA/g.,Electrochemical performance,spa
22、ce-group: Pmn21,Corrugated layer,First-principles investigations on the structural and electronic properties,Structure of Li2MSiO4,Reference: S.Q.Wu, et al; Computational Materials Science, 2009, 44, 1243-1251,O Co - O,O Si - O,Conclusions,A series of silicates cathode materials such as Li2FeSiO4, L
23、iFexMn1-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 carbon-coated nanostructured Li2FeSiO4 material with excellent rate performance,
24、 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.,Some comments,We have made some promising progress about silicates in the last few years,
25、 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. Silicates system is quite complex than we imagine, we need to more techniques to charac
26、terize 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,