A comparative analysis on thermal runaway behavior of Li (Ni_xCo_yMn_z) O₂ battery with different nickel contents at cell and module level

The problem of thermal runaway (TR) propagation challenges the safety design of battery packs, because it aggravates the thermal hazards to accidents. There are many unsolved scientific questions in understanding the mechanisms of TR and its propagation behavior for large format lithium-ion batteries (LIBs). LiNi_xCo_yMn_zO₂(NCM) is considered as one of the most promising cathode materials for lithium-ion batteries LIBs, given its higher energy design and lower cost. However, higher Nickel (Ni) content of cathode material worsens the thermal stability of LIBs. This paper provides a comparative analysis on the TR propagation behavior of NCM battery with different Ni ratios. Results have shown that when the characteristic temperatures of TR {T₁, T₂, T₃}and the specific electrochemical energy of the cell are similar, TR propagation behavior will be similar, no matter what kinds of chemistry the cell has. Observation suggests that the average propagation time within a large format cell is 7-10 s in module tests. Besides, the internal temperature of the cell has an order of NCM622 ≥ NCM523 ≥ NCM111,whereas the mass is ordered by NCM622 > NCM523 > NCM111.This work firstly reports the TR feature in large format LIBs with different Ni ratios, both at cell and module level, providing the guidelines for engineering practice and further theoretical researches.