What a role does the safety vent play in the safety of 18650-size lithium-ion batteries?

Abstract

Herein, a series of experiments were performed to illustrate the impact of safety vents on the evolution of thermal runaway behaviors of 18650-size lithium-ion batteries. Meanwhile, the effect of safety vents on the thermal safety of batteries with different states of charge (SOC), i.e. 0%, 50% and 100% and cathode chemistries, i.e. lithium nickel manganese cobalt oxide (NMC), lithium cobalt oxide (LCO) and lithium iron phosphate (LFP) was explored. Compared with the battery with a safety vent, the thermal runaway behaviors of the battery in the absence of a safety vent are greatly worsened with ignition and thermal runaway occurring far earlier. As the battery SOC increases, it is demonstrated that the effect of the safety vent on battery thermal safety is reduced to some extent, with the difference in the times to thermal runaway between the batteries with and without a safety vent decreasing gradually. Besides that, it is found that the effect of the safety vent on the thermal runaway features of LFP-based batteries is relatively minor than in NMC-based batteries and LCO-based batteries. There is a linear-increasing relationship between the thermal runaway time difference and the mass loss difference for batteries with and without a safety vent.