Dual thermal-response separator utilizing phase change materials with polysulfides chemisorption for safe and stable lithium–sulfur batteries

A novel thermoregulating separator (TS) for lithium–sulfur batteries (LSBs) utilizing phase change materials (PCMs) was fabricated by encapsulating the n -docosane (C22) in a polymethyl methacrylate (PMMA) shell, followed by co ating onto the surface of an electrospun poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane. Acting as a “smart gatekeeper”, this TS can promptly mitigate internal temperature increases, as the melting of C22 absorbs a significant amount of heat. As a result, the battery demonstrates excellent cycling stability and consistent coulombic efficiency. More importantly, C22 will be released from the ruptured microcapsules when the heating temperature exceeds 105 °C, effectively blocking the gaps of the separator. This action initiates a thermally induced shutdown mechanism of the battery, preventing the escalation of any accidents. Moreover, the ester groups of PMMA exhibit strong chemical adsorption effect on the polysulfides, which was proven by density functional theory calculations. The TS based on PCMs effectively mitigates the safety hazards associated with thermal runaway and suppresses the shuttling of polysulfides. It is expected to demonstrate vast potential for the development of stable and long-lasting Li S batteries.