Engineering Polyethylene Separators With Graphene Oxide‐Polyhedral Oligomeric Silsesquioxane Nanocomposites for Enhanced Thermal Resilience and Electrochemical Performance

Lithium (Li)‐ion batteries (LIBs) are indispensable for modern energy storage applications. However, Li dendrite formation poses serious challenges to their safety and long‐term stability. As a key component of LIBs, separators must simultaneously prevent internal short circuits while enabling efficient Li + transport. Enhancing their electrolyte wettability, thermal stability, and mechanical strength is critical to improving overall battery performance. In this study, we present a functional separator design incorporating polyhedral oligomeric silsesquioxane‐modified graphene oxide (GO‐POSS) nanofillers to enhance the thermal and electrochemical performance of commercial polyethylene (PE) separators. GO provides abundant oxygen‐containing functional groups that improve electrolyte wettability and facilitate Li + transport, whereas POSS forms a thermally stable ceramic char layer that reinforces thermal stability and interfacial adhesion. The resulting GO‐POSS‐coated separators exhibit improved ionic transport, excellent thermal resilience, enhanced rate capability, and extended cycle life. Notably, Li/NCM622 cells assembled with the GO‐POSS‐coated separator achieved 82.7% capacity retention after 300 cycles at 0.1 A g −1 , compared with 76.5% for cells using unmodified PE separators. Furthermore, the GO‐POSS coating suppressed Li dendrite formation, contributing to cycling stability and safety. These findings demonstrate the potential of GO‐POSS‐based separator designs in advancing high‐performance and safe next‐generation LIBs.