Abstract: The square aluminum-shell lithium iron phosphate battery is prone to internal short circuit under overcharge and other conditions, which seriously threatens the safe operation of the energy storage power station. An in-situ testing platform for overcharge thermal runaway multi-parameter characteristics of battery was built. The battery was placed inside the module shell for testing to simulate the static closed environment of the actual battery. The designed in-situ gas monitoring system was used to monitor the concentration of CO, CO₂, and H₂, and the high-temperature resistance strain gauge was used to measure the overcharge expansion deformation of the battery. The overcharge thermal runaway phenomenon and the characteristics of voltage, temperature, gas production and deformation of batteries with different charging rates and capacities were studied. Aiming at the problem of battery thermal runaway suppression, we designed a self-triggering battery thermal runaway suppression device based on thermal sensitive insulating material. The results show that a small amount of CO and H₂ can be detected in the square aluminum-shell lithium iron phosphate battery in a few seconds before the explosion-proof valve is opened. The expansion deformation first appears in the middle of the battery, and the deformation is detected at least 243 s earlier than the gas is detected, and at least 248 s earlier than the battery short circuit. The surface deformation can be used as an effective indicator for early warning of battery overcharge thermal runaway. The designed self-triggering battery thermal runaway suppression device can reduce the maximum temperature of battery overcharge thermal runaway from 358.80 ℃ to 259.06 ℃. At the same time, the device has the advantages of small size, low cost, no power supply and does not affect other batteries after reaction, which can effectively realize the distributed thermal runaway suppression of the energy storage power station. The research results are of great significance for the safety warning of lithium iron phosphate energy storage power station.