An easily degradable composite separator with high affinity to ionic-liquid-based electrolytes for safe Li-ion batteries

Ionic-liquid-based electrolytes emerge as a viable alternative to commercial carbonate electrolytes due to their superior stability and safety, especially at high temperatures. However, their affinity to the currently widely used polyolefin-based separators is poor. Herein, an economical and environmentally friendly separator composed of hydroxyapatite and cellulose nanofibers is designed and fabricated. The composite separator possesses a fibrous network with a large surface area and rich polar groups, featuring high wettability and ionic conductivity based on carbonate and ionic-liquid-based electrolytes. The LiFePO4/Li half-cell with this separator exhibits superior cyclability with a high capacity of ∼130 mAh g−1 using an ionic-liquid electrolyte at room temperature. Moreover, the resulting composite separator is thermally stable, and the assembled batteries achieve outstanding cyclability at 80 °C. Furthermore, the universality of the separator is demonstrated by successful employment in sodium and zinc-ion batteries. The as-fabricated composite separator is easily degradable and promising as an environmental-benign substitute to conventional polyolefin-based separators for next-generation batteries.