A sustainable green strategy: Flame-retardant cellulose-based separators for enhancing the safety and cycle stability of lithium-ion batteries

Lithium-ion battery (LIB) separators act an essential role on maintaining electrochemical properties and safety, while polyolefin-based separators exhibit poor thermal stability, resulting in potential safety concerns. In this work, based on 4-aminopyridine (4-AP) and hexachlorocyclotriphosphazene (HCCP), cellulose-based separator modified by HCCP cross-linked 4-AP, named CBS@H-AP, is fabricated to improve the safety and electrochemical stability of LIB. CBS@H-AP is synthesized through the crosslinking reaction of H-AP on the cellulose surface. CBS@H-AP demonstrates low flammability (self-extinguishing) and high thermal-dimensional stability (no apparent heat shrinkage at 240 °C for 5 min). Furthermore, CBS@H-AP discloses high porosity (68.4 %) and wettability (a contact angle of electrolyte of 15.1°). LIB utilizing CBS@H-AP separator unfolds excellent cycle stability, maintaining a capacity retention of 97.2 % and an average coulombic efficiency of 99.2 % at 0.5C over 100 cycles. This work opens up new possibilities for the application of cellulose-based separators in enhancing the safety and cycle stability of LIBs.