Metal‐Free Eutectic Electrolyte with Weak Hydrogen Bonds for High‐Rate and Ultra‐Stable Ammonium‐Ion Batteries

Abstract As the need for sustainable battery chemistry grows, non‐metallic ammonium ion (NH₄⁺) batteries are receiving considerable attention because of their unique properties, such as low cost, nontoxicity, and environmental sustainability. In this study, the solvation interactions between NH₄⁺ and solvents are elucidated and design principles for NH₄⁺ weakly solvated electrolytes are proposed. Given that hydrogen bond interactions dominate the solvation of NH₄⁺ and solvents, the strength of the solvent's electrostatic potential directly determines the strength of its solvating power. As a proof of concept, succinonitrile with relatively weak electronegativity is selected to construct a metal‐free eutectic electrolyte (MEE). As expected, this MEE is able to significantly broaden the electrochemical stability window and reduce the solvent binding energy in the solvation shell, which leads to a lower desolvation energy barrier and a fast charge transfer process. As a result, the as‐constructed NH₄‐ion batteries exhibit superior reversible rate capability (energy density of 65 Wh kg^–1_{total active mass} at 600 W kg^–1) and unprecedent long‐term cycling performance (retention of 90.2% after 1000 cycles at 1.0 A g^–1). The proposed methodology for constructing weakly hydrogen bonded electrolytes will provide guidelines for implementing high‐rate and ultra‐stable NH₄⁺‐based energy storage systems.