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.