Quasi‐Localized High‐Concentration Electrolytes for High‐Voltage Lithium Metal Batteries

The poor compatibility with Li metal and electrolyte oxidation stability preclude the utilization of commercial ester‐based electrolytes for high‐voltage lithium metal batteries. This work proposes a quasi‐localized high‐concentration electrolyte ( q‐ LHCE) by partially replacing solvents in conventional LiPF 6 based carbonated electrolyte with fluorinated analogs (fluoroethylene carbonate (FEC), 2,2,2‐trifluoroethyl methyl carbonate (FEMC)) with weakly‐solvating ability. The q‐ LHCE enables the formation of an anion‐rich solvation sheath, which functions like LHCE but differs in the partial participation of weakly‐solvating cosolvent in the solvation structure. With this optimized electrolyte, inorganic‐dominated solid electrolyte interphases are achieved on both the cathode and anode, leading to uniform Li deposition, suppressed electrolyte decomposition and cathode deterioration. Consequently, q‐ LHCE supports stable cycling of Li | LiCoO 2 (≈3.5 mAh cm −2 ) cells at 4.5 V under the whole climate range (from −20 to 45 °C) with limited Li consumption. A practical ampere‐hour level graphite | LiCoO 2 pouch cell at 4.5 V and aggressive Li | LiNi 0.5 Mn 1.5 O 4 cell at 5.0 V with excellent capacity retention further reveals the effectiveness of q‐ LHCE. The refinement of old‐fashioned carbonate electrolytes provides new perspectives toward practical high‐voltage battery systems.