A comparative analysis of lithium-ion batteries with different cathodes under overheating and nail penetration conditions

This work compares the thermal runaway characteristics and heat generation of LiCoO2(LCO), Li(Ni0·6Mn0·2Co0.2)O2 (NMC622) and LiFePO4 (LFP) batteries with the same capacity under thermal abuse, and provides an in-depth study of the electro-thermal behaviour and internal physical-chemical changes under mechanical abuse, forming basis for understanding thermal runaway and safe use of batteries. The overheating test shows that the LCO battery is the most dangerous during thermal runaway because of higher heat generation, followed by the NMC622 and LFP batteries. However, the LFP battery is more prone to thermal runaway than the NMC622 and LCO batteries under adiabatic environment due to the shortest time to trigger thermal runaway. The nail penetration test shows the NMC622 battery has the worst internal short circuit tolerance, followed by the LCO and LFP batteries. The LFP material is less affected by nail penetration and extrusion, and the LFP battery at 50% state of charge (SOC) has the lowest risk of thermal runaway. The particles and crystal structures of the LCO and NMC622 materials are obviously damaged due to nail penetration, especially the LCO, which produces a new phase LiAlCo0·8O2. The risk of thermal runaway of the battery increases with the increase of SOC.