Investigation on Thermal Characteristics of Lithium Battery Based on Electro‐Chemical Thermal Coupled Model

ABSTRACT Numerical simulation as a bridge between battery material properties and thermal safety behavior can quantify the thermo‐electrochemical coupling mechanisms and discover thermal characteristics under different operating conditions. Although earlier research has been conducted to investigate the relation between the discharge rate and heat generation in lithium‐ion batteries, most of them are limited to qualitative analyses under single‐rate conditions without quantitative understanding of the dynamic evolution of three‐dimensional thermal fields under multiple discharge rates. To fill this gap, this study examines the thermal behavior and the liquid‐phase lithium‐ion transport behavior during the discharge process of lithium‐ion batteries. Using an electrochemical‐thermal coupling model of NMC523 lithium batteries, this work reveals, for the first time, the spatial nonuniformity of lithium‐ion concentration, temperature and heat generation inside the cells under different discharge rates (1/3C‐4C) and depths of discharge (DOD). The results indicate that the highest temperature is always observed at the radial center of the cell and increases considerably with higher discharge rate up to 65.9°C at 4C, which is higher than the safety threshold of 60°C. Both the internal temperature difference and rate of temperature rise increase as discharge rate and DOD increase, reaching a maximum at the end of discharge. High‐rate discharge also results in high lithium‐ion enrichment at the negative electrode and severe depletion at the positive electrode, resulting in a high concentration gradient between the electrodes. In particular, the liquid‐phase lithium‐ion concentration at the end of discharge is 17%, 29%, and 47% of the initial concentration at 1C, 2C, and 4C, respectively. In addition, the heat generation mechanism that dominates changes from reversible heat at low discharge rates to irreversible heat (ohmic and polarization heat) at high rates. Further analysis indicates that improved surface heat dissipation can effectively suppress the concentration gradient and internal heat accumulation of lithium‐ions. This study gives a theoretical basis for the thermal management design and safety optimization for high‐rate lithium‐ion battery discharge from a multiphysics point of view.