Lithium-ion intercalation Behavior of LiFePO4 in aqueous and nonaqueous electrolyte solutions

Lithium-ion intercalation behavior of LiFePO4 in both aqueous and nonaqueous electrolyte solutions was extensively investigated. LiFePO4 showed a much better rate capability in the Li2SO4 aqueous electrolyte than in the 1 M LiFP6-PC nonaqueous electrolyte. Kinetic properties of LiFePO4 particles were studied by cyclic voltammetry (CV) using a powder microelectrode. The apparent Li+ diffusion coefficients were evaluated from CV data, ranging from 7.23 X 10(-11) cm(2)/s in 0.05 M Li2SO4 to 2.05 X 10(-10) cm(2)/s in 1 M Li2SO4, and 4.06 X 10(-11) cm(2)/s in 1 M LiFP6-PC nonaqueous electrolyte. Electrochemical impedance spectroscopy demonstrated that the differences in the evaluated value of Li+ diffusion coefficients and the rate capability between two electrolyte systems are mainly due to the different interfacial charge transfer. A theoretical calculation with density functional theory was also employed to study the process of charge transfer at interface. (c) 2007 The Electrochemical Society.