Research on Thermal Runaway Features of Lithium-Ion Batteries with Different Aging Histories for Energy Storage Under Conditions of Overcharging

In this study, we investigate the effect of aging on the thermal runaway characteristics of 314 Ah lithium iron phosphate batteries with different cycles (0, 400, and 1000 cycles), with the batteries being overcharged to thermal runaway with a 0.5 C charging rate. The results indicate that aging significantly reduces the severity of thermal runaway for a battery. Fresh batteries exhibited intense jet fires with a peak temperature of 501.4 °C, while aged batteries produced only heavy smoke without obvious flames, with peak temperatures dropping to 401.2 °C. Aging leads to the thickening of the SEI film, increased internal resistance, and an unstable voltage response, extending the thermal runaway trigger time from 1979 s to 4039 s, but with a lower trigger temperature. The negative tab consistently remained the core heat accumulation point, with temperature differences of 10–30 °C compared to other wall surfaces, and the core temperature during thermal runaway exceeded 500 °C. The transition from casing rupture to jet fire occurred within only 2 s, indicating an extremely short safety response window. Through this research, we provide critical insights for the aging assessment and thermal safety management of energy storage batteries.