Evaluation of the rate determining processes for LiFePO₄ as cathode material in lithium-ion-batteries

Lithium iron phosphate is a promising cathode material for the use in lithium-ion batteries meeting the demands of good stability during cycling and safe operation due to reduced risk of thermal runaway. However, slow solid state diffusion and poor electrical conductivity reduce power capability. For further improvement, all rate determining electrode processes have to be quantified. Electrochemical impedance spectroscopy (EIS) has proven to be a powerful tool for the characterization of electrochemical systems. In recent publications (1,2), a physical interpretation for the impedance response of LiFePO ₄/Li-cells was given and an equivalent circuit model was proposed. In this contribution, the proposed equivalent circuit is used to quantify the predominant electrode processes depending on temperature (0°C...30°C), SoC (10% ... 100%) and microstructure characteristics (porosity).