Numerical simulation of transport characteristics of Li-ion battery in different discharging modes

A three-dimensional electrochemical-thermal coupling model of LiFePO4 battery was developed based on the real multi-layer structure. The model was developed to describe the discharge process of the battery in four modes: the constant current, constant overpotential, constant voltage and maximum power discharge processes. The electric conductivity of the electrode, the electric conductivity of the current collector, the ionic conductivity of the electrolyte and the diffusion coefficient of the electrolyte were considered. The results show that: (1) In the constant current discharge mode, the core electrochemical reaction area of the positive electrode moved towards the separator while that of the negative electrode moved towards the current collector due to the change of the electrolyte concentration. (2) In the constant overpotential discharge process, the change of the average chemical reaction rate and the decreasing rate of the current density increased with increasing overpotential. (3) In the constant voltage discharge process, the current density and the temperature increased when the electrode thickness was increased. (4) In the maximum power discharge process, the output power increased with increasing electrode thickness but decreased with increasing contact resistance at the same current density.