Active and passive safety enhancement for batteries from force perspective

Thermal runaway (TR) has become a critical issue for Li-ion battery applications in electric vehicles and energy storage stations. To address this issue, early warning and thermal runaway propagation (TRP) mitigation are significant for the active and passive safety of the battery system, respectively. This study proposes the expansion force as a reliable warning signal, which is proven to provide more interval (>500 s) for escape and rescue compared with voltage and temperature signals. Besides, the TR expansion force changing mechanism due to thermal expansion, gas generation/accumulation, and venting is investigated. Furthermore, the TRP expansion force and deformation changing mechanism is explained from the perspective of expansion, squeeze, and venting. The TRP debris deformation trend is verified through mechanical modeling. The maximum TR expansion force increment (ΔFmax)-capacity (Q) equalization and ΔFmax-cell index equations are proposed based on the TR/TRP tests of three types of prismatic batteries. Moreover, a TRP mitigation structure is proposed to amplify the TR expansion force, which is validated to effectively amplify the force, causing the mechanical destruction of the in-line module holder. A TRP mitigation test proves that the first TR cell capsizes the module holder to hinder the heat transfer between the front/back surfaces of the prismatic batteries when the TR expansion force exceeds the preload. Without enough heat transfer, the TR of the following battery cells cannot be triggered even under jet fire impact. This study guides the active and passive safety design for the prismatic battery system.