Highly transient thermal runaway and gas emission dynamics of LiFePO4 batteries under extreme overcharge conditions

Abstract The large-scale application of lithium-ion batteries in new energy systems positions their fire safety under extreme environments as a primary focus. Overcharge-induced thermal runaway (TR), particularly under highly transient and irregular electrical conditions, serves as a critical safety bottleneck. This study systematically investigates the TR, pyrolysis, and gas emission dynamics of commercial 15 Ah LFP batteries driven by extreme high-rate overcharging (up to 12C). By employing multi-parameter synchronous monitoring—including temperature, voltage, gas release, infrared thermography, and particularly extreme mechanical impact—the coupled thermo-electrical-mechanical behaviors of battery TR in non-equilibrium states are comprehensively elucidated. The results indicate that as the charging rate increases, the battery is forced into a highly transient state where the TR triggering time significantly shortens and heat accumulation effects intensely accelerate. Notably, under these extreme conditions, more prominent destructive characteristics are manifested. Specifically, a highly rapid maximum surface temperature (Tmax) surge to 453°C and an accumulated heat of 140 kJ are generated at the 6C rate, while an extreme mechanical structural expansion force reaches 9300 N at 12C. This research uncovers the novel physical and chemical mechanisms governing battery TR under extreme thermo-electric coupled conditions, offering advanced diagnostic insights and a theoretical framework for the fire safety of next-generation energy systems.