Insights into the non-uniform electrochemical and thermal mechanisms of pouch-type lithium-ion battery

Thermal safety concerns regarding lithium-ion batteries necessitate an in-depth understanding of the self-heating mechanism. While extensive models have been proposed to determine battery heat generation, the real-time performance is directly affected by the multidimensional distributions of electrochemical reactions and temperature, with the underlying action deserving thorough investigation. To clarify the unevenness of lithium-ion batteries, a multiphysics-based model that integrates a three-dimensional electrochemical model and a three-dimensional thermal model is built and validated in this work. Since overpotential and local current density show dynamic and inhomogeneous distribution caused by the ion concentration gradient, electrochemical reaction in turn affects the variations in heat generation and temperature distribution. Positive electrode causes higher proportion of heat at the beginning of discharge, while negative electrode contributes to more heat at the end, thus affecting the heat generation trend. The location of maximum heat generation and temperature gradually shifts from near-tab region to central region. Additionally, lithium-ion battery is also characterized by a large thermal gradient along cross-plane direction. Polarization heat generated by negative electrode accounts for the largest proportion of self-heating, especially at low temperatures, which leads to reduced ion diffusion. Besides, the discharging energy efficiency also reduces correspondingly at low temperature and high discharge rate, which indicates the energy underutilization due to the increase of irreversible heat. These findings not only unveil the intrinsic mechanisms of lithium-ion batteries but also provide a potential framework for mitigating inhomogeneous temperature.