Flame-retarding battery cathode materials based on reversible multi-electron redox chemistry of phenothiazine-based polymer

ABSTRACT Polymeric organic battery materials are promising alternatives to the transition-metal-based ones owing to their enriched chemistries. However, the flammability of organic compounds brings in serious concern on battery safety. In addition to use flame-retarding electrolyte/electrolyte additives or battery separators, flame retardancy can readily be achieved through the integration of flame-retarding unit into the polymer backbone, imparting the flame retardancy permanently. The as-designed polymer based on phenothiazine shows significantly shortened self-extinguished time without deteriorating its intrinsic thermodynamic and electrochemical properties. Moreover, two electron per phenothiazine molecule is realized for the first time in a highly reversible manner with discharge voltages of 3.52 V and 4.16 V versus Li+/Li and an average capacity of ca. 120 mAh g−1 at a current rate of 2 C. The origin of the reversibility is investigated through density functional theory (DFT) calculations. These findings address the importance of molecular design for safer and more stable organic materials for batteries.