Numerical modeling and analysis of thermal behavior and Li+ transport characteristic in lithium-ion battery

Abstract

A lithium-ion battery is consist of numerous electrochemical cell units connected in parallel. The performance of lithium-ion battery is closely related to thermal and Li+ transport behavior in lithium-ion battery. It is essential to pay attention to the heat transfer and mass diffusion in the lithium-ion battery. The outside cooling condition and the geometrical structure will result in uneven thermal and electrochemical distribution on the cross section. A 2D (two-dimensional) electrochemical-thermal coupled model was developed for LiFePO4 battery to investigate the uneven thermal and electrochemical distribution. The potential distribution and electrochemical reaction rate were focused on both in spatial view and temporal view. The potential distribution both in cathode and anode, and the electrochemical reaction rate on the cross section showed an obvious non-uniformity in the spatial distribution. This non-uniformity was mainly determined by the geometrical structure of the battery. In the temporal view, non-uniformity index of current density was defined and presented a parabolic trend during the discharging process. Also, there was a heating effect of tab on the electrode material region of battery, due to the higher heat generation rate and lower heat capacity of tab during the discharge process. Discharging area on the tab directly determined and significant affected the current density and the temperature distribution on the tab respectively. In the design of battery cell and battery pack, the structure of tab and connecting method between batteries must be considered to avoid local higher current density or contact electric resistance and corresponding higher temperature region and to improve the performance of battery.