Experimental investigation of the influence of venting gases on thermal runaway propagation in lithium-ion batteries with enclosed packaging

Thermal runaway (TR) of lithium-ion batteries (LIBs) involves venting high-temperature combustible gases. Common enclosure-style battery packs without specialized venting can constrain these gases, potentially promoting thermal runaway propagation (TRP) within the module. To clarify the impact of unignited TR venting gases on TRP, this study conducted comparative experiments on LiFePO4 modules with normal packaging (NP) and isolated venting packaging (IVP). In NP, the module's top includes baffles allowing venting to spread, whereas IVP uses dedicated airflow channels to isolate venting. Quantitative analyses of TRP behavior, temperature, and mass loss rates were conducted under varying heating positions and states of charge (SOCs). Results indicated that NP modules exhibited faster TRP in all tests due to heat accumulation from venting gases in the semi-enclosed space between cell surfaces and packaging, compared to IVP. In the side heating scenario, TR behavior of SOC 100 % NP modules was more severe, with an average heat contribution from TR venting gases of front-end cells just before safety valve activation in back-end cells being 27.3 %, while not all cells underwent TR under IVP. Under intermediate heating, lower SOCs caused TR venting gas heat contribution to decrease from 27.4 % at SOC 100 %-8 % at SOC 50 %. These findings demonstrate that venting gases from TR cells significantly accelerate TRP in enclosed structures, highlighting the critical importance of packaging design for safety. Consequently, venting gases should be directed away from the module and effective thermal insulation measures implemented to reduce TRP risk.