Dual phase change separator combining cooling and thermal shutdown functions for Li-ion battery with enhanced safety

•EVBseparatorwithsuperiorelectrochemicalperformancewasfabricatedforLIB.•PEGcoremeltsat50°Ctostoreheattemporarilyforcoolingandperformanceenhancement.•PBSshellmeltsat110°Cwithoutshrinkageforthermalshutdownandsafetyenhancement. The rapid growth of electric vehicles raises an unmet need to enhance high-temperature performance and safety of Li-ion battery (LIB). Herein, polyethylene glycol/polyvinylidene fluoride (PEG/PVDF) core @ polybutylene succinate (PBS) shell separator with cooling and thermal shutdown functions was fabricated using a one-step coaxial electrospinning method. The separator exhibited superior electrochemical performance even at room temperature due to good wettability and high porosity. When battery temperature rises as discharging, PEG with 50 °C melting point (m.p.) will melt to store heat temporarily. Thus, the separator with cooling function can effectively enhance ion conductivity to alleviate specific capacity drop and polarization voltage increase. As temperature decreases after battery discharging, the separator will release thermal energy to prepare for the next working cycle. When thermal runaway happens and raises temperate above 100 °C rapidly, the PBS shell will melt at 110 °C without skeleton thermal shrinkage. Separator pores can be blocked by the melted PBS and Li+ ions transfer can be inhibited in time to prevent disastrous consequence. Thus, dual phase change of the separator provides a novel and effective strategy for synergistic performance and safety enhancement of high temperature LIB.