Robust and High-Wettability Pristine Poly(ether ether ketone) Nanofiber Separator for Heat-Resistant and Safe Lithium-Ion Battery

Separator is a pivotal component of lithium-ion batteries (LIBs) and determines the electrochemical performance and safety. However, with the increase in energy density and application scenarios, commercial polyolefin separators are increasingly unable to undertake heavy responsibility of battery safety protection. Herein, a new kind of nanofiber separator based on poly(ether ether ketone) (PEEK) with excellent thermal stability, self-extinguishing, and superior electrochemical properties is reported. Effective inheritance of intrinsic properties from raw PEEK materials and optimized hot-pressing operation endows the separator with high robustness and wettability, showing tensile strength of 15.8 MPa and a contact angle of 17.2°. The high thermal stability of PEEK can ensure the separator to preserve the structural integrity and microstructure at temperatures beyond 300 °C, and the excellent self-extinguishing peculiarity of PEEK capacitates the high safety of LIB. Notably, benefitting from high porosity and polar surface, the PEEK separator shows high electrolyte uptake of 245.5% and exhibits a wider electrochemical window and faster lithium-ion transport number than commercial polyolefin separators. Furthermore, cells assembled with PEEK separator display better performance than the ones with PE separator, and the PEEK LIB has been successfully used to light up a lamp at a high temperature of 150 °C.