Achieving safe high-voltage lithium-metal batteries by tailoring electrolyte systems†

Lithium-metal batteries (LMBs) with a Ni-rich high-voltage cathode enable the delivery of a high energy density. However, a persistent challenge lies in the instability of the electrode–electrolyte interface leading to shortened cycling lifespans and heightened safety concerns. Herein, based on a non-flammable solvent, we designed a weakly solvating non-flammable electrolyte system, with high ionic conductivity, in which a safe high-voltage lithium battery has been achieved. By regulating the solvating structure of the electrolyte, a stable and robust electrode–electrolyte interface at both the lithium metal anode and high-voltage cathode can be built. In the designed electrolyte, the decomposition of anions and fluorinated ethylene carbonate (FEC) as film-formers is simultaneously facilitated at the electrode surface by employing a weakly coordinated co-solvent. The anion and FEC co-derived chemical interface enriched with lithium fluoride enables a high lithium deposition–stripping Coulombic efficiency of 99.06% and stable cycling of a 4.7 V LiNi_0.8Mn_0.1Co_0.1O₂ cathode. The composed LMBs achieve an energy density of 692 W h kg⁻¹ at the electrode level (based on the total mass of cathode and anode materials). The strategy reported in this work points out a promising way to develop safe and high energy density LMBs.