Unveiling solvation structure and desolvation dynamics of hybrid electrolytes for ultralong cyclability and facile kinetics of Zn–Al alloy anodes

Abstract

Despite the high theoretical capacity and natural abundance of Al metal anodes, the reversible and fast multivalent storage of Al³⁺ ions remains challenging because their large charge density leads to strong electrostatic interactions with other components and sluggish kinetics. Herein, we report the record-high plating/stripping time (>8000 h) and high rate capability of Zn–Al alloy anodes in Al³⁺-containing hybrid electrolytes. The more reversible Al deposition on Zn in nitrile-based hybrid electrolyte than carbonate- and amide-based hybrid and aqueous electrolytes is attributed to weak Al³⁺–solvent interactions and fast Al³⁺ transfer kinetics. In particular, these electrochemical behaviors of nitrile-based electrolyte originate from a unique solvation structure, the interrelation among H₂O, organic solvents, and Al³⁺, and the conformational change of bound/free solvents upon desolvation, as elaborated via theoretical simulations, two-dimensional infrared correlation spectroscopy, and other characterizations. The superiority of this hybrid electrolyte was confirmed by achieving a high specific capacity (183 mA h g⁻¹ and 1.08 mA h cm⁻²) and long cycling of >5000 cycles of full cells integrating Zn–Al alloy anodes (25 μm) with vanadium dioxide/carbon nanotubes (8 mg cm⁻²) and activated carbon (10 mg cm⁻²) cathodes, respectively, which considerably exceed those of Al-based full cells.