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

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-1total 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. Hydrogen bonds dominate the solvation interaction of NH4+. Weakening the interactions between NH4+ and solvent molecules can significantly improve the rate capability and long-term cycling performance of NH4-ion batteries.image

Automated summary

Non-metallic ammonium ion (NH4+) batteries have attracted attention due to their low cost, non-toxicity, and environmental sustainability. This study elucidates the solvation interactions between NH4+ and solvents, and proposes design principles for weakly solvated electrolytes. By constructing a weak hydrogen bonded electrolyte, NH4+ ion batteries exhibit superior rate capability and long-term cycling performance.