Effects of temperature variation on Li_xFePO₄/C (0<x<1) electrode process

Abstract

LiFePO₄/C was prepared via solid state reaction and characterized with X-ray powder diffraction and charge–discharge test. As-prepared LiFePO₄/C has a triphylite structure and exhibits an excellent rate capability and capacity retention. Electrochemical impedance spectroscopy (EIS) was applied to investigate Li_xFePO₄/C (0<x<1) electrode on temperature variation. The valid equivalent circuit for EIS fitting was determined which contains an intercalation capacitance for Li+ ion accumulation and consumption in the electrode reaction. The surface layer impedance needs to be included in the equivalent circuit when LiFePO₄/C is deeply delithiated at a relatively high temperature. EIS examination indicates that a temperature rise leads to a better reversibility, lower charge transfer resistance, higher exchange current density J0 and greater Li+ ion diffusion coefficient for the Li_xFePO₄/C electrode process. The Li⁺ ion concentration in Li_xFePO₄/C is potential to impact the Li⁺ ion diffusion coefficient, and a decrease in the former results in an increase in the latter.

Keywords

lithium ion cell / LiFePO₄/C / electrode process / electrochemical impedance spectroscopy / equivalent circuit / Li⁺ ion diffusion coefficient

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