Composite phase change material for preventing battery thermal runaway propagation: Critical condition and inhibition strategy

The use of phase change material (PCM) is a promising strategy to prevent the thermal runaway propagation (TRP) of electrochemical energy storage system due to its endothermic phase change. However, the thermophysical properties of typical composite PCM are various, and the mechanism by which PCM can inhibit TRP with respect to the corresponding critical conditions has not yet been revealed. In this work, under the critical property distribution, the detailed TRP inhibition characteristics of composite PCM with or without coupling additional strategy are investigated. First, a two-dimensional battery TRP model is developed. By determining the critical condition of no TRP, the distribution function of thermal conductivity and phase change enthalpy is fitted. This splits PCM into two zones: TRP zone and TRP inhibition zone, which can be used to determine whether various PCM match the inhibition criterion. There are two clear classes of favorable composite PCM that result in TRP inhibition: a high thermal conductivity class and a low thermal conductivity class. On the basis of critical property distribution, the heat transfer process of composite PCM with some representative proportions is compared. The results reveal that the TRP inhibition mechanism of composite PCM with different thermal conductivity is significantly related to the anisotropic heat conduction in the battery. Furthermore, for the PCM that falls within the TRP zone, defining the "uneconomical parts" is a crucial precondition for the design of an additional strategy (e.g., conventional air or liquid medium). Then the safe-by-design principle of the TRP inhibition based on PCM can be achieved in three ways: enhancing the heat conduction, heat insulation, or heat dissipation based on the critical condition.