Phosphorus‐Structured Gel Electrolytes Enable Dual Protection for Thermal Runaway‐Resistant Lithium Metal Batteries

The development of safe lithium metal batteries (LMBs) is critical for practical applications with high‐energy density demanding. In this study, a phosphorus‐containing diethyl vinylphosphonate (DEVP)‐based gel polymer electrolyte (PD‐VI GPE) with high ionic conductivity of 6.38 mS cm −1 is prepared by in situ γ‐ray radiation polymerization. The PD‐VI GPE induces the formation of a uniform, dense fluorine‐, and phosphorus‐rich solid electrolyte interphase (SEI) in Li||Cu coin cells, effectively suppressing interfacial side reactions and enabling stable lithium deposition. Pouch cells assembled with the PD‐VI GPE (2 g Ah −1 ) exhibit a specific energy of 420 Wh kg −1 with 89% capacity retention over 80 cycles. A novel in situ separator thermal shrinkage assay reveals that the PD‐VI GPE‐coated Celgard separator maintains structural integrity at 129 °C. Phosphorus‐functional groups in the PD‐VI GPE act as oxygen radical scavengers, inhibiting cathode‐derived O 2 evolution in abusive conditions. Thus, LMBs assembled with the PD‐VI GPE demonstrate suppressed thermal runaway and mechanical abuse tolerance. This study establishes a material design paradigm that concurrently addresses interfacial stability and safety challenges, paving the way for the application of LMBs in energy systems with high‐safety requirements.