Anion‐Mediated Solvation Enables Robust Interphases for High‐Performance Sodium‐Organic Batteries

Sodium‐organic batteries (SOBs), which leverage abundant and low‐cost materials, are a promising energy storage technology. However, their practical viability is largely hinged on the instability of the reactive sodium metal anode and the degradation of organic cathodes in conventional electrolytes. Herein, a weakly solvating electrolyte is designed, comprising 2 M sodium bis(fluorosulfonyl)imide in a non‐fluorinated co‐solvent of 1,2‐dimethoxypropane and cyclopentyl methyl ether. This unique formulation promotes an anion‐reinforced Na⁺ solvation sheath, which generates a robust, inorganic‐rich solid‐electrolyte interphase (SEI). This tailored interphase stabilizes the anode by promoting uniform sodium deposition and mitigates cathode degradation by forming a protective cathode‐electrolyte interphase (CEI). As a result, the electrolyte enables highly reversible Na plating/stripping, achieving a Coulombic efficiency of 98.6% over 800 cycles at 0.5 mA cm−2. When coupled with a perylene‐3,4,9,10‐tetracarboxylic dianhydride cathode, the SOB demonstrates exceptional stability, retaining 97.8% of its capacity after 300 cycles at 1 C (100 mA g−1). This work demonstrates that engineering an anion‐mediated solvation structure through targeted solvent‐solvent interactions is a promising strategy for developing cost‐effective and long‐lasting SOBs.