Thermal runaway is the main factor contributing to the unsafe behaviors of lithium-ion batteries(LIBs)in practical applications. The application of separators for the thermal shutdown has been proven as an effective approach to protecting LIBs from thermal runaway. In this work, we developed a thermal shutdown separator by coating a thin layer of low-density polyethylene microspheres(PM) onto a commercial porous polypropylene(PP) membrane and investigated the thermal response behaviors of the as-prepared PM/PP separator in LIBs. The structural and thermal analysis results revealed that the coated PM layer had a porous structure, which facilitated the occurrence of normal charge-discharge reactions at ambient temperature, although it could melt completely and fuse together within very short time periods: 3 s at 110 ℃ and 1 s at 120 ℃, to block off the pores of the PP substrate, thereby cutting off the ion transportation between the electrodes and interrupting the battery reaction. Consequently, the PM/PP separator exhibits very similar electrochemical performance to that of a conventional separator at ambient temperature. However, it performs a rapid thermal shutdown at an elevated temperature of ～110 ℃, thus controlling the temperature rise and maintaining the cell in a safe status. Due to its synthetic simplicity and low cost, this separator shows promise for possible application in building safe LIBs.
