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

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. © 2022 The Royal Society of Chemistry