A novel flexible composite phase change material applied to the thermal safety of lithium-ion batteries

Large deformation of lithium-ion batteries (LIBs) under mechanical load can cause internal short circuit of the battery. Further, the LIBs generate a large amount of heat during the rapid charging and discharging process. The internal short circuit and heat accumulation in the battery can lead to explosion or fire, so mechanical damage and thermal runaway are the two major safety issues that hinder the practical application of LIBs. To this end, we have designed a new type of flexible composite phase change material (FCPCM) with dual functions of anti-extrusion and heat absorption. Firstly, paraffin wax (PW) is adsorbed in the pores of expanded graphite (EG) to obtain EG/PW composite phase change material (CPCM). Then, the powdered PW/EG and flake copper powder (FCP) as the heat conductive filler are coated in a thermoplastic elastomer (TPE) for secondary encapsulation, and the FCPCM with a high latent heat (137 J/g) is obtained. TPE not only reduces the leakage rate of PW but also improves the deformation capacity of CPCM and absorbs extrusion energy. As a filler with high thermal conductivity, FCP can effectively improve the thermal conductivity of the FCPCM. When the FCP content is 5 wt%, the thermal conductivity is as high as 3.357 W/mK. In the battery extrusion experiment, when the loading displacement reaches 13 mm, the battery does not suffer mechanical damage and internal short circuit. Next, the prepared FCPCM is applied to the thermal management of a battery. Experiments and simulations were combined to investigate the heat dissipation capacity of the FCPCM for battery at different discharge rates and different ambient temperatures, and 3 cycles at the maximum discharge rate (5C) and an ambient temperature of 30 °C were able to meet the requirements for practical use. The results verify that FCPCM exhibits immense application potential in the thermal management of batteries. Overall, we provide a new method for the design of CPCMs with excellent mechanical extrusion energy absorption and heat dissipation performance.