Solvent Toughened Glass Gel Electrolyte for High‐Voltage Lithium Metal Batteries

In situ polymerization electrolytes hold great promise for high‐energy‐density lithium‐metal batteries but often require additional separators due to their limited mechanical strength. Here, inspired by “glassy gels”, we developed a free‐standing glass gel electrolyte by introducing tributylmethylphosphonium dimethyl phosphate ([P 4441 ] [DMP]) into a poly(acrylic acid) (PAA) matrix. Strong non‐covalent interactions between [P 4441 ] [DMP] and PAA chains generate a tough and homogeneous network while enabling efficient ion transport. The resulting glass gel electrolyte exhibits an ionic conductivity of 2.2 mS cm −1 , a Li + transference number of 0.59, a tensile strength of 30 MPa, and an elongation of up to 700%. The solvent‐toughened scaffold effectively confines the liquid electrolyte and mitigates parasitic reactions with Li metal. Consequently, Li||Li symmetric cells achieve stable cycling for 1900 h at 3 mA cm −2 with an areal capacity of 3 mAh cm −2 . Li//NCM811 cells retain 90% of their capacity after 420 cycles, while Li//LiCoO 2 cells exhibit stable cycling for over 290 cycles at 1 C with a cutoff voltage of 4.6 V. This work provides a robust strategy for designing free‐standing electrolytes for high‐energy‐density lithium‐metal batteries.