Dual Flame‐Retardant Mechanism‐Assisted Suppression of Thermal Runaway in Lithium Metal Batteries with Improved Electrochemical Performances

Abstract Despite considerable research efforts of lithium metal batteries (LMBs) in various aspects are performed, however the application as the power sources for transport vehicles remains challenging from the safety concerns and durability of LMBs. Therefore, to improve the safety and electrochemical performance of LMBs, a sophisticated separator composed of decabromodiphenyl ethane (DBDPE) and a CaO nanocomposite is engineered to concurrently impart the flame‐retardant properties and enhance Li‐ion transport. During normal operation, the coated CaO particles enhance the Li‐ion transport, and the cycle performance of the LMB improves as the Li‐metal cycling efficiency is enhanced without any side reactions. In contrast, under abnormal conditions, particularly at high temperatures, the coated CaO and DBDPE chemically react and act as fire extinguishers in the LMB. DBDPE exhibits gas‐phase flame‐retardant characteristics and forms HBr at high temperatures, which then subsequently reacts with CaO nanocrystals, forming CaBr 2 with liquid‐phase flame‐retardant characteristics. Hence, both liquid‐ and gas‐phase flame‐retardant characteristics are observed in the DBDPE–CaO‐coated polyethylene separator (DCPE) in the pouch‐level LMB. The formation of the in situ halogen‐based material in the LMB is attributed to a spontaneous chemical mechanism‐based flame‐retardant strategy. Consequently, the distinctive features of the DCPE separator improves the electrochemical performance and safety of LMBs.