Enhanced safety of lithium ion batteries through a novel functional separator with encapsulated flame retardant and hydroxide ceramics

The safety concerns associated with lithium-ion batteries (LiBs) pose a significant obstacle to the widespread practical use of high-energy–density batteries. To address this challenge, we developed a functional flame-retardant and ceramic-coated separator (F-CCS) that enhances safety features while maintaining optimal performance. The F-CCS incorporates an encapsulated flame retardant and a hydroxide ceramic, namely AlOOH, to achieve flame retardancy. We integrated a phosphorus-based flame retardant, triethyl phosphate (TEP), which formed a carbonized layer, effectively suppressing fire and creating a protective layer. To safeguard the TEP from the electrolyte and electrochemical reactions, it is encapsulated within a cross-linked polymer. By carefully optimizing the ratio of the encapsulated flame retardant to ceramic in the coating layer, the F-CCS attains a balance between thermal stability, flame retardancy, and ionic conductivity. Notably, the F-CCS formed a flame-retardant protective layer on the surface of the separator to maintain the area without catching fire, as shown in the video. Evaluation of the electrochemical performance revealed suitable power performance and cycle stability, comparable to those of conventional CCSs. These findings present a promising solution for enhancing the safety and reliability of LiBs, particularly in high-energy–density applications, thereby paving the way for their wider implementation.