The disassembly analysis and thermal runaway characteristics of NCM811 family battery cells

Lithium-ion batteries are susceptible to thermal runaway during thermal abuse, potentially resulting in safety hazards such as fire and explosion. Therefore, it is crucial to investigate the internal thermal stability and characteristics of thermal runaway in battery pouch cells. This study focuses on dismantling a power lithium-ion battery, identified as Ni-rich LiNi_xCo_yMn_1-x-yO₂ (NCM811, LiNi_0.83Co_0.12Mn_0.05O₂) lithium-ion battery pouch cell through material characterization methods. The authors delve into the stability of the main component materials of lithium-ion cells and the mechanism of the thermal runaway induced by the cells. In addition, thermal runaway experiments are conducted under overheating conditions to analyze the effect of different states of charge (SOC) levels on battery cell temperature and gas changes. This information can serve as an active safety warning signal and allow for an extended window for passive safety measures. In conclusion, (i) uniform internal porosity facilitates efficient Li-ion diffusion. (ii) Thermal stability hierarchy: cathode > anode > separator. (iii) The elevated SOC levels expand risks, necessitating integrated monitoring of temperature, thermal ramp rate, and CO evolution for precise hazard alerts.