Understanding the boundary and mechanism of gas-induced explosion for lithium-ion cells: Experimental and theoretical analysis

Thermal runaway (TR) of lithium-ion (Li-ion) batteries (LIBs) involves multiple forms of hazards, such as gas venting/jetting, fire, or even explosion. Explosion, as the most extreme case, is caused by the generated flammable gases, and a deflagration to detonation transition (DDT) may occur in this process. Here, overheat-to-TR tests and the corresponding outgas-induced explosion tests were conducted on 42 Ah Li-ion cells with Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode. The sum of CO₂, H₂, C₂H₄, CO, and CH₄ accounted for more than 90% of the gases. Lower/upper explosion limits (LEL/UEL), laminar flame speed, and ideal stable detonation pressure were calculated to interpret the explosion characteristics and boundary. It turned out that shockwave was easily to be compressed and accelerated under higher state of charge (SOC) conditions. Thus, Li-ion cells explosion may evolve into unstable detonation in encapsulated battery pack and its evolution mechanism was explained, which provides a new idea for explosion-proof design of LIBs system. Additionally, a comprehensive assessment method was developed to intuitively characterize TR hazards. Severity of explosion presented an upward trend with the increase of SOC while the sensitivity was not the same. This study provides a further anatomy of TR, which is instructive to the safety of power battery systems.