Nonflammable PVDF-based gel polymer electrolytes modified by dimethyl methylphosphate for wide temperature range, long cycle-life and high-safety lithium metal batteries

Gel polymer electrolytes (GPEs) has been considered as a promising candidate for the development of lithium metal batteries (LMBs) with high energy density and high safety, yet most reported GPEs is flammable, making the LMBs still facing great safety hazards. Herein, we used dimethyl methylphosphate (DMMP) as the functional flame retardant and plasticizer for poly(vinylidene fluoride) (PVDF) matrix to develop a novel nonflammable PVDF-DMMP GPEs for LMBs. The DMMP not only highly enhances the flame resistance of PVDF-DMMP GPEs, the efficient dissociation of lithium salt and the rapid transport of lithium ions, but also helps to form stable and robust CEI/SEI layers. As a result, the ultrathin PVDF-DMMP GPEs (∼20 µm) present superb flame resistance, high ionic conductivity (1.34 × 10⁻³ S cm⁻¹ at 30°C), fast lithium ion transport (\(t_{\text{Li}^{+}}=0.59\) at 30°C), high electrochemical stability voltage window (over 4 V) at 30–80°C and uniform lithium deposition. When used in Li∥Li symmetric cells, Li∥LiFePO₄ (LFP) and Li∥LiNi_0.8Co_0.1Mn_0.1O₂ full cells, the nonflammable PVDF-DMMP GPEs could endow these cells with long-term cycle stability, high rate capability, wide-temperature operation ranges (from −20 to 80°C) and high safety simultaneously. Even when suffering from harsh deconstructive tests, the Li∣PVDF-DMMP GPEs∣LFP pouch cells still work normally without any safety hazards. The actual energy density of the packed pouch cell is as high as 508 Wh kg⁻¹. Therefore, our work can provide a promising strategy for the design of high safety and high-energy-density LMBs.