Thermal and stoichiometry inhomogeneity investigation of large-format lithium-ion batteries via a three-dimensional electrochemical-thermal coupling model

Large-format lithium-ion batteries (LIBs) have attracted extensive concern due to the advantages of increasing energy density and reducing manufacturing costs. However, inhomogeneity is widely present in large-format LIBs, which may lead to local degradation or edge lithium plating, thereby reducing the battery durability and safety. In this study, an electrochemical-thermal (ECT) coupling model for large-format LIBs is developed to quantitatively investigate the battery inhomogeneity during charging and discharging. First, two different sizes of batteries with the same electrode material are disassembled and tested to obtain the battery model parameters. Second, a novel method for determining the parameters of the ECT coupling model for large-format LIBs is proposed to solve the technical challenge of difficult model parameter calibration. Specifically, the ECT coupling model parameters of large-format batteries are determined using those of small-format batteries. The experimental results show that the three-dimensional ECT coupling model exhibits high accuracy, with the root mean square error of voltage and temperature within 17.8 mV and 1.27 ˚C, respectively, at 1C discharge rate and SOC greater than 2.5 %. Finally, the temperature and stoichiometry coefficient inhomogeneity of large-format LIBs during charging and discharging under different conditions are analyzed quantitatively. The results show that the inhomogeneity of large-format LIBs increases significantly with increasing discharge rate and battery length. A large-format battery with a length of 900 mm achieves a balance between inhomogeneity and length. This study contributes to a quantitative understanding of the inhomogeneity of large-format LIBs and provides a model-based perspective for designing and optimizing large-format LIBs.