Advanced Poly (Ether Ether Ketone) Separator for Lithium Metal Battery

The development of high-performance separators is urgently needed to improve the safety and electrochemical performance of high-energy-density lithium metal batteries (LMB). Poly (ether ether ketone) (PEEK) is an ideal separator candidate due to its high chemical resistance and excellent thermal stability. However, the processing of PEEK for separators with proper porous structure is rather challenging. Beyond the conventional sulfonation process of PEEK, here, a reversible chemical modification strategy is exploited to fabricate heat-resistant PEEK separators with sophisticated hierarchical pore architecture. The lyophilic PEEK separators including dense surface layers, middle layers with horizontally aligned pore arrays, and honeycomb-structured bottom layers enable fast ion transport and uniform Li⁺ flux, realizing dendrite-free characteristics during the lithium deposition process. Hence, the PEEK separator assembled LiFePO₄||Li battery delivers a remarkable capacity of 103.6 mAh·g^-1 after 1000 cycles at 3 C, and offers more than two times longer cycle life than that of other PEEK-based separators. Even at 70 °C, a high capacity retention rate of 84.2% is achieved after 200 cycles, ensuring battery safety in high-temperature environments. Different from the commonly used surface modification strategy for functional separators, the approach reported herein exhibits a fundamental advance in separator manufacturing for future high-safety LMBs.