Thermal-Electrochemical simulation of electrochemical characteristics and temperature difference for a battery module under two-stage fast charging

The electrochemical characteristics and temperature difference are crucial for a battery module, but they are seldom taken into account in the previous works of multistage fast charging focusing on reducing charging time and temperature rise for a single battery. A multilayer electrochemical-thermal coupled model incorporating parallel connected cells inside each battery is developed for a serially connected battery module using two-stage fast charging patterns with different charging current rates (C-rates) in two charging stages to study the electrochemical characteristics, temperature difference and state of balance. Results show that the shift of C-rate causes a sudden change in the magnitude and spatial distribution of local current density, and in the magnitude of solid phase Li+ concentration gradient and electrolyte Li+ concentration. The non-uniformity of electrochemical performance inside a battery generally is more significant when the C-rate of the first stage is higher than that of the second stage. The charging pattern with lower C-rate in the first stage has potential in reducing the maximum local temperature difference in a battery while increasing the maximum temperature difference of module. The increase and decrease of the C-rate in the second stage easily aggravates the state of balance at the end of charging and leads to a sudden fluctuation of state of balance in the shift of C-rate, respectively. The charging strategy should be optimized with the consideration of electrochemical performance, cooling intensity, coolant temperature, battery initial temperature and state of balance.