Solvent Reorganization and Additives Synergistically Enable High-Performance Na-Ion Batteries

Electrolytes with high and localized salt concentrations have been successfully developed to mitigate parasitic reactions in rechargeable batteries, but at the expense of high cost, high viscosity, and slow kinetics. An alternative electrolyte design concept beyond the current strategies is crucial to reaching practical applications. From salt to solvent, herein, we demonstrate solvent reorganization to develop highly stable dilute phosphate electrolytes (0.16-0.85 M) for Na-ion batteries. This solvent reorganization is the result of optimal intermolecular interactions between the main solvent phosphate and charge-asymmetric trifluorotoluene (PhCF₃) as a solvent coordinator. Appropriate solvent reorganization induced by PhCF₃ can reinforce the solvation network of electrolytes without employing high concentrations of expensive salts, which enables a highly stable dilute phosphate electrolyte in combination with synergic additives. With the designed dilute electrolyte, NaCu_1/9Ni_2/9Fe_1/3Mn_1/3O₂ (CNFM)||HC Na-ion full cells demonstrate stable cycling for 400 cycles and a high Coulombic efficiency of >99.95% at 0.2 C. An Ah-level pouch cell is evidenced with highly safe cycling of over 100 cycles with 90.1% capacity retention and without inflation at 60 °C. This work opens an alternative avenue in designing electrolytes by manipulating solvent interactions instead of focusing on local solvation structure and high salt concentrations.