Passive cooling of lithium-ion batteries based on flexible phase change materials: Molecular structure, interactions and mechanistic aspects

Abstract

The trend for electric vehicles to replace traditional fuel vehicles is becoming increasingly apparent with the global tendency towards carbon peaking and carbon neutrality. As the core of electric vehicles, the working safety of lithium-ion batteries is becoming more and more important. This review presents an overview of the battery thermal management system (BTMS) based on flexible composite phase change materials (FCPCM), which discusses the flexibility generation mechanism of FCPCM for BTMS in terms of molecular structure, interactions and mechanistic aspects. Before introducing FCPCM, this review summarizes the approaches of phase change materials (PCM) in enhancing thermal conductivity, anti-leakage performance and safety performance. However, there are still defects such as strong rigidity and poor mechanical strength. The inclusion of flexible matrix could effectively improve the flexibility. Microscopically, flexibility is enhanced by the creation of the flexible structure. At the contact interface, the enhanced flexibility increases the interfacial wettability, thus reducing the contact thermal resistance between the PCM and the cell, and enabling the heat transfer performance to be improved. Due to the different flexible materials added, the microscopic mechanisms vary, including flexible structural support, physical cross-linking of microscopic molecular chains and chemical bonding cross-linking between molecules. Thermal induced flexibility enhances the packaging performance of FCPCM. Furthermore, FCPCM offers considerable improvement in mechanical and shape memory properties due to inter-molecular interactions. This review provides a timely introduction to the emerging advantages of FCPCM over traditional composite PCMs for BTMS applications. Finally, the challenges and difficulties encountered in the application of FCPCM in batteries are pointed out, and an outlook on future research directions is given.