Research on the Early Warning Mechanism for Thermal Runaway of Lithium-Ion Power Batteries in Electric Vehicles

Abstract

Lithium-ion power batteries are critical to the macrostrategy of new energy vehicles, and safety concerns such as thermal runaway remain a major bottleneck in the productization and industrialization of lithium batteries. Based on COMSOL Multiphasic, an electrochemical-thermal coupling model for lithium-ion power batteries is created, as well as a thermal model for thermal runaway. A comparative study on lithium-ion power batteries was conducted using this model under on-board conditions, high rate cyclic charging and discharging conditions, and thermal abuse conditions. The temperature rise rate, average temperature, current, and voltage of the lithium-ion power battery and their correlation with thermal runaway are investigated. The results show that the temperature rise rate can significantly characterize the occurrence of thermal runaway, and when the temperature rise rate exceeds 1°C/s, the lithium-ion power battery has a high probability of thermal runaway. In addition, when the average temperature exceeds 80°C, there is a potential risk of thermal runaway in Li-ion power batteries. The results of the study show that high temperatures take longer to trigger thermal runaway, and the battery is slower to warm up. The time it takes for thermal runaway to occur, the maximum temperature reached, and the maximum voltage are all strongly connected to the overcharge flow under overload abuse conditions. The shorter the time it takes for thermal runaway to occur and the greater the maximum temperature and voltage attained, the larger the overcharge current.