Fig. 1. Schematic of the “smart” electrospun separator with thermal-triggered flame-retardant properties for lithium-ion batteries.

(A) The free-standing separator is composed of microfibers with a core-shell structure, where the flame retardant is the core and the polymer is the shell. The encapsulation of the flame retardant inside the protective polymer shell has prevented direct exposure and dissolution of the flame retardant into the electrolyte, preventing their negative effects on the electrochemical performance of the battery. (B) Upon thermal triggering, the polymer shell would melt and then the encapsulated flame retardant would be released into the electrolyte, thus effectively suppressing the ignition and burning of the electrolytes.