SOC-dependent venting behavior of thermal runaway in 18,650 LiFePO4 batteries

Gas eruption induced by thermal runaway (TR) of lithium-ion batteries (LIBs) is one of the critical issues restricting their safe application. Accurate measurement of eruption dynamic parameters is crucial for risk assessment and safety design. To investigate the State of Charge (SOC)-dependent venting behavior during TR, this study employed a three-axis force sensor to directly capture the recoil force ( ) and mass loss ( ) based on the principle of momentum conservation, deriving the mass flow rate ( ) and venting velocity ( ), which effectively overcomes the technical bottleneck of traditional methods. The results reveal a distinct two-stage characteristic of TR: In the safety valve opening stage, the peak recoil force is 0.16-0.29 N, independent of SOC; In the TR stage, dynamic parameters are SOC-dependent, with mild mass loss of 5.01-5.77 g under low SOC (≤75%). At 100% SOC, the maximum venting velocity reaches 497.6±38.46 m·s -1 , with total mass loss of 26.38±1.02 g and TR duration of 1017±167 ms, exhibiting intense energy release. This study uncovers the SOC-dependent differences between the two TR stages, providing key parameters for battery safety design.