Detailed measurements of thermal runaway propagation and fire spread for Li-ion battery multi-module setup

Fire incidents of lithium-ion battery (LIB) energy storage systems (BESS) have become more frequent with their large-scale deployment. Such fire hazards are attributed to the thermal runaway (TR) of LIBs, thermal runaway propagation (TRP) within a LIB module and between modules. Experimental assessment of such hazards is challenging due to the scale and complexity of BESS, and numerical modeling is a promising alternative. However, current LIB research has mostly focused on simple LIB stacks, thus lacking insights on the TRP process in a practical BESS system. The present study examines the TRP and flame generation of two stacked industrial modules, each partially populated with twelve 63Ah-capacity pouch cells at 100 % state-of-charge. Within each LIB module, the TRP rate is quasi-steady but accelerates due to the preheating of unreacted cells by the ejecta that is released during TR and transported along the module's internal space. The plastic scaffolding, a structural component that mounts cells, increases cell spacing and affects the TRP rate. However, the plastic also pyrolyzes due to the heating from cell TR. The flame generated by burning the TR vent gas and plastic pyrolysate is the primary mechanism for TRP between modules in the tested configuration. Therefore, the heat release from plastic components becomes important in inter-module propagation. On the other hand, inter-module heat transfer through the external metal casing plays a smaller role in the present configuration. These experimental findings reveal important TR and fire propagation physics and will facilitate the development of BESS fire spread modeling. • Ejected gas did not self-ignite, and module-to-module propagation did not occur without a flame. • The external flame was the primary mechanism for TRP to the between modules. • Preheating of cells by ejected materials caused acceleration of TRP within each module. • Plastic components contributed significantly to overall combustion heat release.