The early warning for overcharge thermal runaway of lithium-ion batteries based on a composite parameter

The wider application of lithium-ion batteries(LIBs)is restricted by electric abuse. Moreover, overcharging is an important reason for thermal runaway. In order to prevent the occurrence of overcharge thermal runaway (OTR) events, a new three-level warning method is presented. By comparing Fiber Bragg Grating (FBG) and thermocouple real-time thermal monitoring, FBG shows a better temperature response. The OTR experiment is carried out, and the whole process of lithium battery thermal runaway under different overcharge rates (1 C, 1.5 C, and 2 C) is divided into three stages. Based on the cross-sensitivity of strain and temperature for FBG, a composite parameter (virtual temperature) affected by temperature and strain is proposed as an early warning index. Combining with the changes in virtual temperature, surface temperature, and the early voltage variation of thermal runaway, a three-level early warning model for thermal runaway is proposed. The first-level warning: the temperature difference between virtual temperature and surface temperature reaches 5 °C. The second-level warning: the virtual temperature reaches 70 °C. The third-level warning: the surface temperature reaches 80 °C. This method can provide a reference for monitoring and early warning of LIBs in energy storage power stations.