Synthesis And Electrochemical Performance Of Li₂FeSiO₄Materials For Lithium-ion Batteries

With the advantages of high theoretical capacity, abundant raw materials, low cost and environmentally benign, Li2FeSi04has been considered as an attractive material for lithium-ion batteries. However, the application of this material is greatly limited by its low electronic conductivity and slow diffusion of lithium ions. Based on the problems above, the synthesis condition, carbon coating, electrochemical properties and the kinetics of lithium ion insertion-extraction process of Li2FeSi04as cathode materials were investigated here. Moreover, we explored Li2FeSiO4as a new anode materials for lithium-ion batteries. The main contents can be summarized as follows:Nano-Li2FeSiO4/C composite were synthesized by sol-gel method using citric acid as chelant and carbon source. The effects of Li source, Fe source and synthesis temperature on the structure and electrochemical properties of materials were investigated. The results showed that the composite calcined at600℃for10h, using CH3COOLi·2H2O as Li source, Fe(NO3)3·9H2O as Fe source has a monoclinic structure with good crystallinity and little impurities, the average size of Li2FeSi04/C particles is approximately20-40nm, the carbon content of the material is10.06%. The initial discharge capacity of Li2FeSiO4/C composite is156.6mAh g-1at C/16, the discharge capacity retains143.3mAh g-1after30cycles. At0.1C,0.2C,0.5C,1C and2C rate, the Li2FeSi04/C electrode delivered a discharge capacity of152.8,128.1,102,81.2and60.1mAh g-1, respectively.The electrode process kinetics of Li2FeSiO4/C was studied by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). CV analysis indicated that the electrode had good reversible and Li-ion diffusion coefficients (Do) in oxidation and reduction process were7.15×10-12and7.05×10-12cm2s-1respectively. The EIS showed that the charge transfer resistance (Rct) had a minimum at2.8V. The Li-ion diffusion coefficients calculated by EIS range from1.25×10-14to1.69×10-14cm2s-1at2.6to3.0V. Nano-Li2FeSiO4was researched as anode materials for lithium-ion batteries. The electrochemical test showed that the Li2FeSi04anode delievered an initial discharge capacity of880mAh g-1at50mA g-1, and the discharge capacity was498mAh g-1after30cycles, even at the current density of500mA g-1, the discharge capacity was235mAh g-1. The electrochemical procedures of the Li2FeSiO4anode were emphasized by ex-situ XRD and cyclic voltammograms.