Research on overcharge thermal runaway behavior characteristics of explosion-proof LiFePO₄/C lithium battery power supply

As an important foundation for the electrification development of coal mine equipment, mine-used explosion-proof lithium battery power supplies have developed rapidly in recent years. However, in underground coal mines, although mine-used lithium batteries protected by flameproof enclosures effectively avoid mechanical abuse and thermal abuse risks, they still face the risk of thermal runaway caused by electrical abuse, especially overcharging. Once the high-temperature substances and hazardous gases generated by lithium battery thermal runaway couple with the external explosive environment, serious safety hazards will arise. To investigate the safety risks and prevention-control measures of mine-used explosion-proof lithium battery power supplies under the mainstream flameproof explosion-proof power supply structure, a dedicated test platform and test method were designed to simulate the overcharging process of the flameproof enclosure and series battery packs of mine-used explosion-proof lithium battery power supplies. The overcharge thermal runaway characteristics of mine-used lithium batteries with different capacity specifications show that as the lithium battery capacity increases, thermal runaway is triggered earlier and the maximum temperature rises. The overcharge thermal runaway characteristics under different charging rates indicate that the maximum temperature of lithium battery thermal runaway further increases with the increase of charging rate. For the large amount of overheated gas-liquid mixture (300-500 ℃) generated during the thermal runaway of large-capacity lithium batteries, there may be a risk of explosion-proof failure, i.e., igniting the gas environment in underground coal mines, if it is not sufficiently cooled when discharged from the power supply flameproof enclosure to the outside. During the overcharging process, mine-used lithium batteries first open the pressure relief valve before entering the thermal runaway process. Stopping charging when the valve opens can terminate the reaction process. Emergency measures such as power cut-off and cooling based on monitoring characteristic gases such as CO and H₂ generated when the valve opens can effectively prevent the occurrence of thermal runaway faults and improve the safety of mine-used explosion-proof lithium battery power supplies in explosive environments underground coal mines.