Safety and cycling stability enhancement of cellulose paper-based lithium-ion battery separator by aramid nanofibers

Commercial polyolefin separators suffer from poor electrolyte wettability and low thermal stability, which give rise to unsatisfied electrochemical performance and severe safety hazards for lithium-ion batteries (LIBs). Herein, a novel paper-based composite separator composed of electrolyte-affinitive cellulose fibers (CFs) and thermally stable aramid nanofibers (ANFs) was successfully fabricated through the traditional papermaking method. The ANFs as a functional nanofiller played crucial roles in improving the defects of pure CF separator including large-sized pores, low mechanical strength and high flammability. Specifically, the CF/ANF composite separator with 20 wt% ANFs (CF/ANF-20) possessed narrow micropores, satisfied tensile strength (33 MPa), excellent thermal resistance (without dimensional shrinkage up to 200 °C) and flame retardancy, which greatly enhanced the safe operation of battery. Moreover, inheriting from the highly porous structure and exceptional electrolyte affinity of CF separator, the CF/ANF-20 composite separator exhibited appropriate porosity and superior electrolyte wettability, which brought about a high electrolyte uptake (157%), thus endowing it with better ionic conductivity (0.75 mS cm−1) and lower interfacial resistance compared to commercial polypropylene separator. Accordingly, the LiFePO4/Li half cells using CF/ANF-20 separator delivered outstanding rate capability and stable cycling performance. All results indicate that the CF/ANF-20 separator shown great balance between the electrochemical performance and safety is an intriguing candidate for advanced LIBs.