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

Abstract

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 LiPF₆ 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 | LiCoO₂ (≈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 | LiCoO₂ pouch cell at 4.5 V and aggressive Li | LiNi_0.5Mn_1.5O₄ 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.