Solvation Regulation Reinforces Anion‐Derived Inorganic‐Rich Interphase for High‐Performance Quasi‐Solid‐State Li Metal Batteries

Abstract Solid‐state polymer lithium metal batteries are an important strategy for achieving high safety and high energy density. However, the issue of Li dendrites and inherent inferior interface greatly restricts practical application. Herein, this study introduces tris(2,2,2‐trifluoroethyl)phosphate solvent with moderate solvation ability, which can not only complex with Li ⁺ to promote the in‐situ ring‐opening polymerization of 1,3‐dioxolane (DOL), but also build solvated structure models to explore the effect of different solvation structures in the polymer electrolyte. Thereinto, it is dominated by the contact ion pair solvated structure with pDOL chain segments forming less lithium bonds, exhibiting faster kinetic process and constructing a robust anion‐derived inorganic‐rich interphase, which significantly improves the utilization rate of active Li and the high‐voltage resistance of pDOL. As a result, it exhibits stable cycling at ultra‐high areal capacity of 20 mAh cm ⁻² in half cells, and an ultra‐long lifetime of over 2000 h in symmetric cells can be realized. Furthermore, matched with LiNi _0.9 Co _0.05 Mn _0.05 O ₂ cathode, the capacity retention after 60 cycles is as high as 96.8% at N/P value of 3.33. Remarkably, 0.7 Ah Li||LiNi _0.9 Co _0.05 Mn _0.05 O ₂ pouch cell with an energy density of 461 Wh kg ⁻¹ can be stably cycled for five cycles at 100% depth of discharge.