The Lithium-ion Battery Cathode Material For Li <sub> 2 </ Sub> FeSiO <sub> 4 </ Sub> / C Synthesis And Modification

Based on the review of cathode materials for lithium ion batteries, the paper focused on the Li2FeSiO4/C cathode materials. The Li2FeSiO4/C cathodes were prepared by wet chemistry and high temperature solid-state method. The preparation conditions were optimized and the modification of materials had been carried out. Moreover, we explored new methods by which Li2FeSiO4/C materials were made form general raw materials.The Li2FeSiO4/C was prepared by wet chemistry and high temperature solid-state method. The effects of circumfluence process, solvent in precursor preparation and calcining temperature on the properties of the Li2FeSiO4/C were investigated. The preparation conditions are optimized as using circumfluence process, using water as solvent in precursor preparation and calcining at 650℃. The initial discharge specific capacity reaches 165 mAh·g-1, and the discharge capacity remains 138 mAh·g-1 after 10 cycle.The Li2FeSi04 was modified by carbon coating and doping. The sample using the sucrose as carbon source shows less impurity and larger initial discharge specific capacity than the samples using other carbon source. With increasing the content of Mn and Ni in Li2Fe1-2xNixMnxSiO4/C (x=0,0.2,0.3), the initial discharge specific capacity are 165 mAh·g-1,201 mAh·g-1 and 72 mAh·g-1 respectively, and the Li2Fe0.6Ni0.2Mn0.2SiO4 material showed excellent electrochemical performance. With 10% Li2SiO3 (by molar ratio) doped in the Li2FeSiO4/C cathode, the initial discharge specific capacity reaches 149 mAh·g-1, and the capacity keep was about 84.6% after 10 cycles. With 20% LiFePO4 (by molar ratio) doped in the Li2FeSiO4/C material, the initial discharge specific capacity reaches 135 mAh·g-1, and the capacity keep was about 73.3% after 10 cycles.New methods synthesizing Li2FeSiO4/C materials were researched. Among the samples using ferrous dichloride as iron source, the sample with circumfluence process and Li:Fe:Si molar ratio of 2.1:1, using Li2CO3 as lithium source and calining at 650℃shows the best electrochemical performance. Among the samples using ferric chloride as iron source, the stirring time and mode during precursor preparation remarkably influences the electrochemical performance, and the electrochemical performance are improved with increasing the calcining temperature from 450℃to 650℃.Electrochemical impedance spectroscopy (EIS) measurements and potential step chronoamperometry methode (PSCA) were used in investigating the kinetics behaviors of the Li2FeSiO4/C cathodes. With carbon coating, the conductivity of samples increases, and the electrochemical impedance decreases. When the calcining heat increases from 600℃to 750℃, the electrochemical impedance decreases. Among the samples synthesized by the three different methods, the sample made from ferrous dichloride shows the largest diffusion coefficients, while that from ferric chloride shows the smallest diffusion coefficients.