Electrolyte Engineering Towards Aqueous Zinc-Ion Batteries for Wide Temperature Applications

<p dir="ltr">Zinc-ion batteries (ZIBs) show promise for grid-scale energy storage but face challenges such as zinc dendrite growth, the hydrogen evolution reaction (HER), and passivation. Practical applications in places with harsh temperature conditions require ZIBs to operate reliably across a wide temperature range. However, the high freezing points of aqueous electrolytes cause salt precipitation and reduced ionic conductivity at low temperatures. Ion transport, including the diffusion of Zn²⁺ in the bulk electrolyte, the desolvation of Zn²⁺ at the electrolyte/electrode interface, and the migration of Zn²⁺ through the solid electrolyte interphase (SEI), is significantly slowed at subzero temperatures, leading to energy and power density loss. Electrolyte strategies such as "water-in-salt", co-solvent, additives, eutectic, and ionic liquids have been proposed to solve these challenges.</p><p dir="ltr">The co-solvent strategy is an effective approach. Co-solvents with good miscibility with water can destroy the hydrogen bonds (HBs) between water molecules, thereby lowering the freezing point of the electrolyte. This thesis presents three innovative electrolyte design strategies using co-solvent systems to suppress side reactions, enhance anti-freezing properties, and improve zinc-ion transport kinetics. The weak co-solvent G2 reduces solvated water molecules and increases anion in the solvation sheath, resulting in a weakly solvating electrolyte with accelerated desolvation and suppressed side reactions. The strong co-solvent/H₂O hybrid electrolyte suffers from sluggish desolvation kinetics. The coordination intervention strategy using urea and a halogen-mediated hybrid electrolyte strategy employing potassium iodide (KI) are proposed to weaken the coordination between Zn²⁺ and solvents. These approaches effectively inhibit water-related side reactions, accelerate Zn²⁺ diffusion and desolvation.</p><p dir="ltr">This thesis offers a comprehensive understanding of the relationships between solvation structures (solvent-solvent, solvent-ion, and ion-ion interactions) and battery performance, including enhanced anti-freezing properties, highly reversible Zn plating/stripping, and accelerated Zn²⁺ transport kinetics. These innovative approaches lay a solid foundation and provide valuable insights for designing electrolytes for next-generation ZIBs.</p>