A multi-level early warning strategy for the LiFePO4 battery thermal runaway induced by overcharge

The thermal runaway (TR) of lithium-ion batteries (LIBs) is difficult to control when it reaches the late stage, which results in disastrous accidents, while the current means of early warning are biased late or inaccurate. Therefore, an early monitoring and warning strategy is necessary for LIB to mitigate TR. In this study, overcharge tests on LiFeO4 batteries were conducted at various current rates (C-rates). The evolutions of voltage, gas, and temperature during overcharge were analyzed, and the TR process could be divided into four stages: Stage I (initial stage), Stage II (gas detected stage), Stage III (reaction accelerating stage), Stage IV (post-TR stage). The maximum surface temperature difference (ΔTmax) exceeded 5 °C in Stage II. Incremental capacity analysis (ICA) and differential voltage analysis (DVA) were used to reveal the internal mechanism when different gases were detected in Stage II, and the safety performance of the LIB was affected severely. To avoid TR of LIB, it was necessary to start early warning in Stage II. A Three-Level warning strategy was proposed based on the voltage turning point (VTP), temperature, and the appearance of various gases in Stage II. A reliable warning before the TR was achieved by setting the threshold effectively, and the TR event was mitigated successfully. These findings provide a critical basis to enhance the monitoring and warning capability of the battery management system as well as battery safety.