Thermal-triggered fire-extinguishing separators by phase change materials for high-safety lithium-ion batteries

High-energy lithium-ion batteries face significant challenges at abuse conditions, where thermal runaway is easily triggered and always accompanied with fire and explosion. Here we report a novel separator design that simultaneously absorbs thermal energy within the cell and improves fire safety. A thermo-responsive composite separator is fabricated by coating the commercial polyolefin separator with ceramic silica microcapsules that are internally encapsulated with both a phase-change material (PCM) and a flame retardant. As a “smart gatekeeper”, the PCM can not only store heat within the cell to minimize the temperature rise, but control the thermal-stimuli release of the flame retardant. In particular, the electrochemical performance of batteries is not sacrificed, taking advantages of the elaborate encapsulation of flame retardant and PCM inside a protective silica microcapsule and avoiding the direct dissolution of them into the electrolyte. Upon thermal stimuli, the solid-liquid transition of PCM occurs to increase molecular mobility and release the flame retardant. The low melting point of PCM could facilitate the prompt release of flame retardant at the early stage of thermal runaway, avoiding short circuit caused by thermal inertia. The PCM-based heat-regulated release system for flame retardant effectively reduces the safety risks caused by thermal runaway, which holds great promise as multifunctional separators for high-safety lithium-ion batteries.