Thermally Conductive Enhanced Composite Phase Change Materials for Improving Thermal Safety of Lithium-Ion Batteries

Thermal runaway of lithium-ion batteries is a critical issue restricting their safe application. Efficient thermal management and flame-retardant protection are essential for improving the safety of battery systems. In this study, polyethylene glycol (PEG) was used as the phase change energy storage matrix, and expanded graphite (EG), flake copper, and MXene nanosheets were introduced to construct a three-dimensional thermally conductive enhancement network. Zinc hydroxystannate (ZHS) and ammonium polyphosphate (APP) were added as synergistic flame retardants to prepare thermally conductive enhanced composite phase change materials with efficient heat dissipation, leakage prevention, and flame retardancy. The structure and thermal properties of the materials were systematically characterized by XRD, SEM, DSC, TGA, and the steady-state heat flow method, with emphasis on evaluating their thermal safety regulation performance in lithium-ion battery cells and modules. The results show that the composite PCMs exhibit no leakage at 60 °C and 80 °C, and the thermal conductivity reaches 3.81 W/(m·K) at a metal filler mass fraction of 20%. In module tests at a 3C discharge rate, the CM2 material reduced the peak temperature by 25.2 °C compared with natural cooling and maintained the maximum temperature difference between cells within the safety threshold. In addition, the inherent flame retardancy of the material helps delay thermal runaway propagation, providing dual safety protection through heat dissipation and fire resistance for battery systems. This study offers a new approach for the design of high-safety thermal management materials for lithium-ion batteries.