Practical High‐Voltage Lithium Metal Batteries Enabled by Tuning the Solvation Structure in Weakly Solvating Electrolyte

Li metal batteries (LMBs) are ideal candidates for future high‐energy‐density battery systems. To date, high‐voltage LMBs suffer severe limitations because of electrolytes unstable against Li anodes and high‐voltage cathodes. Although ether‐based electrolytes exhibit good stability with Li metal, compared to carbonate‐based electrolytes, they have been used only in ≤4.0 V LMBs because of their limited oxidation stability. Here, a high concentration electrolyte (HCE) comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a weakly solvating solvent (1,2‐diethoxyethane, DEE) is designed, which can regulate unique solvation structures with only associated complexes at relatively lower concentration compared to the reported HCEs. This effectively suppresses dendrites on the anode side, and preserves the structural integrity of the cathode side under high voltages by the formation of stable interfacial layers on a Li metal anode and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode. Consequently, a 3.5 m LiFSI–DEE plays an important role in enhancing the stability of the Li||NMC811 cell with a capacity retention of ≈94% after 200 cycles under a high current density of 2.5 mA cm−2. In addition, the 3.5 m LiFSI–DEE electrolyte exhibits good performance with anode‐free batteries. This study offers a promising approach to enable ether‐based electrolytes for high‐voltage LMBs applications. By combining a weakly solvating solvent (1,2‐diethoxyethane) and high salt concentration (lithium bis(fluorosulfonyl)imide), the solvation structures can be tuned to consist of mainly associated species at a relatively lower concentration in comparison to superconcentrated electrolytes. This effectively can suppress dendrites on the Li metal anode and preserve the structural integrity of the LiNi0.8Mn0.1Co0.1O2 cathode side under high voltages (4.4 V).