Highly Thermally Stable, Highly Electrolyte Wettable Hydroxyapatite/Cellulose Nanofibers Hybrid Separators for Lithium-Ion Batteries

Separators have an important influence on the safety and performance of lithium-ion batteries (LIBs). However, traditional polyolefin-based separators suffer from poor thermal stability and weak electrolyte wettability. Here, by using hydroxyapatite (HAP) and cellulose nanofibers (CNFs) as raw materials, we fabricated a unique HAP/CNF hybrid separator. The separators exhibit excellent thermal properties, with high thermal stability (up to 250 degrees C) and outstanding flame retardancy. The separators also demonstrate excellent electrolyte wettability. Compared to polypropylene (PP) separators, the HAP/CNF separators show a smaller contact angle with electrolytes, 17.2 degrees for HAP/CNF and 45.5 degrees for PP. Meanwhile, the HAP/ CNF separators illustrate an excellent smoothness of 68.0 nm. In addition, the batteries assembled with the hybrid separators display a better performance compared with the batteries assembled with commercial PP separators. The raw materials are green, and the fabrication processes are free of organic solvents. We envision that the HAP/CNF hybrid separator could be a promising separator candidate for next-generation high-safety and high-performance LIBs.