Hexagonal Boron Nitride-Coated Polyimide Ion Track Etched Separator with Enhanced Thermal Conductivity and High-Temperature Stability for Lithium-Ion Batteries

The separator plays a vital role in preventing thermal runaway in lithium-ion batteries (LIBs). Herein, a PI/hBN (polyimide/hexagonal boron nitride) separator with excellent thermal stability and enhanced thermal conductivity is successfully prepared by ion track etching and doctor blade coating to achieve highly safe LIBs. The PI/hBN separator displays good electrolyte wettability, high mechanical strength, excellent thermal stability, and enhanced in-plane thermal conductivity, as well as good electrochemical performance when applied in LIBs. Specifically, PI track-etched membranes have been used to prepare separators with rigid structures and functional groups in polymer chains, thereby enabling the separators to be stable at temperatures as high as 500 °C. Moreover, hBN-coated nanoplates enhance the in-plane thermal conductivity of the separator to reduce the local heat accumulation in the battery while also promoting interfacial compatibility to facilitate the conduction of lithium ions. Lithium iron phosphate/lithium cells with the PI/hBN separator deliver better rate capability and superior capacity retention. The PI/hBN separator is a promising candidate for achieving highly safe LIBs, and this work paves the way for engineering roll-to-roll techniques to suppress thermal runaway and improve battery safety.