A rapidly calibratable mechanical model of pouch lithium-ion batteries for fast charging conditions

The stack pressure in lithium-ion battery system shows significant effect on the life span of batteries and stability of whole structure. A precise mechanic model which can predict the stress or strain evolution of the battery during operation is becoming more interested in multi-physics sensors estimation, control, and warning by battery management systems, especially in fast charging conditions. However, the construction and calibration of mechanical models is currently not as efficient and accurate as electrical ones. This paper proposes a rapidly calibratable mechanical model of pouch lithium-ion batteries, aiming at coping with a wide range of rate and temperature variations in fast charging scenarios. Free-swelling property of the battery at different charging rates are pre-discussed, and thermal expansion is decoupled at the same time. An in-process compression modulus' rapid identification method is then executed in multiple temperatures and preloading, providing comprehensive state of charge (SOC)-thermal-stress three-factor mechanical parameters. A Commercial LiNi_xCo_yMn_zO₂ pouch battery is chosen for modeling and validation. A typical multi-stage charging strategy is finally used to verify the accuracy of the proposed model. The results show that the proposed mechanical model has sufficient accuracy as well as strong adaptability in fast charging scenarios.