Ultrastrong and Heat-Resistant Poly(ether ether ketone) Separator for Dendrite-Proof and Heat-Resistant Lithium-Ion Batteries

Separators are a pivotal component of lithium-ion batteries (LIBs) due to their vital role in maintaining a good ionic flow and preventing internal short circuit. The separators with superior thermal stability, ultrahigh mechanical strength, and excellent electrolyte wettability are essential for ensuring the safety and energy density of LIBs. Herein, an ultrastrong poly(ether ether ketone) (PEEK) separator is fabricated via thermally induced phase separation using a binary diluent for the first time, which maintains the intrinsic outstanding properties of a PEEK resin. Computational simulation and experimental verification are performed to optimize fabrication conditions. The as-prepared PEEK separator with high porosity (70.3%) shows a tortuous and three-dimensional porous structure; furthermore, the abundant polar groups on PEEK endow the separator with excellent electrolyte wettability (contact angle of 19° and electrolyte uptake of 387%). Notably, the PEEK separator exhibits excellent thermal stability (almost no shrinkage at 300 °C), flame resistance, and ultrastrong mechanical strength (tensile strength of 124 MPa, Young’s modulus of 7.84 GPa, and puncture strength of 10.5 MPa), which can avoid short circuit and greatly guarantee the safety of LIBs. In particular, the PEEK separator presents excellent interfacial compatibility and both a higher ionic conductivity (1.57 mS cm–1) and lithium-ion transference number (0.55). Significantly, the PEEK-based LiFePO4/Li cell displays a very stable cycle performance and better rate capability. In addition, the PEEK-based lithium–sulfur cell also shows better battery performance than a commercial polyethylene-based cell. Consequently, the specially fabricated PEEK separator is a promising separator candidate for enhanced safety and electrical performance of lithium-ion and lithium–sulfur batteries.