Cooperative Solvation of Lithium Ion by Dual Strongly-Solvating Solvents for Reversible Lithium Metal Batteries

Optimizing the Li+ solvation structure is crucial for improving the electrochemical performance and long-term stability of lithium metal batteries (LMBs). This study presents a Li+ solvation structure in which hetero strongly solvating solvents are colocalized within the first solvation sheath. This structure was realized using nonfluorinated polar solvents, particularly ethylene carbonate (EC) and sulfolane (SL). In conventional electrolytes, solvent-solvent interactions are typically negligible during solvation, as the coordination environment is dominated by individual Li+-solvent binding energy. In contrast, our system revealed that EC and SL exhibit significant intermolecular interactions even within the solvation shell, forming a structurally cooperative solvation environment. This configuration, driving strong solvent-solvent interactions to effectively weaken Li+-solvent interactions, facilitated two critical processes: (1) enhanced Li+ desolvation, enabling more efficient lithium metal deposition, and (2) anion incorporation into the first solvation sheath, stabilizing the solid-electrolyte interphase (SEI). As a result, the optimized electrolyte based on dual strong solvents achieved high lithium metal reversibility (initially 98.24%, 99.35% on average for Coulombic efficiency), enabled stable cycling of lithium metal batteries with high-loading cathodes, and suppressed gas evolution and transition metal dissolution under high-voltage operation.