Analyzing and mitigating battery ageing by self-heating through a coupled thermal-electrochemical model of cylindrical Li-ion cells

An integrated battery model is constructed by coupling a three-dimensional electrochemical model with a two-dimensional axisymmetric heat transfer model, and implemented for simulation of the thermal behavior in a 21,700-type cylindrical cell, comprising a graphite/LiNi0.8Co0.15Al0.05O2 chemistry. The electrochemical model is based on the disassembled battery structure and considers the temperature-dependent ageing kinetics induced by solid electrolyte interphase (SEI) formation and metallic Li plating. Compared with a classic pseudo-2D (P2D) model, the proposed model provides better fitting results for both battery electrochemical and thermal properties. The simulation results show battery surface temperatures can reach up to 80 °C and 110 °C for discharge rates of 3C and 4C, respectively. By applying appropriate cooling liquids, this surface temperature increase can be efficiently controlled and the core temperature will be correspondingly reduced, while the internal temperature gradient remains the same. It is primarily the improvement of thermal conductivity in radial direction which can reduce differences between core and surface temperature. Moreover, the model is able to characterize accelerated ageing kinetics caused by battery self-heating during operation. The results show that the capacity of the investigated battery decreases to 80% after 500 cycles, which is in good agreement with commercial specifications.