A strong/weak solvents co-solvation electrolyte for fast-charging lithium metal batteries

Electrolyte engineering has improved the cycling life and energy density of lithium metal batteries (LMBs) by simultaneously stabilizing Li anodes and high voltage cathodes (such as LiNi_0.6Co_0.2Mn_0.2O₂, NCM622). However, these electrolytes often compromise the fast-charging performance due to relatively low Li⁺ transport kinetics and sluggish interfacial dynamics. Herein, we introduce a strong/weak solvents co-solvation strategy designed to construct an electrolyte with anion-rich clusters and rapid Li⁺ transport kinetics for fast-charging and energy-dense LMBs. In this approach, N,N-dimethylsulfamoyl fluoride (FSN) serves as the weak solvent, co-coordinating Li⁺ together with the strong solvent 1,2-dimethoxyethane (DME) to form an anion-rich first solvation sheath, while the remaining DME molecules distribute externally to facilitate Li⁺ transport. The resulting FSN-DME electrolyte exhibits an impressive ionic conductivity of 7.43 mS cm⁻¹ and an exceptional Li metal efficiency of 99.6 %. When applied in 1-Ah NCM622||Li pouch cells, the FSN-DME electrolyte enables stable operation of 300 cycles at 0.2/0.5 C and 100 cycles at 1 C charge/discharge rates under stringent conditions (cathode areal loading: 3.75 mAh cm⁻², electrolyte: 3.0 g Ah⁻¹). This breakthrough in strong/weak solvents co-solvation electrolytes, along with the development of Li₂O-rich SEI interfacial layers, provides a robust foundation for designing next-generation electrolyte materials that support both fast-charging and long-life LMBs.