Lithium-Ion Intercalation Behavior of LiFePO[sub 4] in Aqueous and Nonaqueous Electrolyte Solutions

Abstract

Lithium-ion intercalation behavior of LiFePO4LiFePO4 in both aqueous and nonaqueous electrolyte solutions was extensively investigated. LiFePO4LiFePO4 showed a much better rate capability in the Li2SO4Li2SO4 aqueous electrolyte than in the 1M1M LiFP6-PCLiFP6-PC nonaqueous electrolyte. Kinetic properties of LiFePO4LiFePO4 particles were studied by cyclic voltammetry (CV) using a powder microelectrode. The apparent Li+Li+ diffusion coefficients were evaluated from CV data, ranging from 7.23×10−11cm2∕s7.23×10−11cm2∕s in 0.05M0.05M Li2SO4Li2SO4 to 2.05×10−10cm2∕s2.05×10−10cm2∕s in 1M1M Li2SO4Li2SO4 , and 4.06×10−11cm2∕s4.06×10−11cm2∕s in 1MLiFP6-PC1MLiFP6-PC nonaqueous electrolyte. Electrochemical impedance spectroscopy demonstrated that the differences in the evaluated value of Li+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.