Abstract
Despite their intrinsic safety and cost-effectiveness, aqueous zinc (Zn)-organic batteries have been struggling with the rapid performance degradation arising from the poor reversibility of Zn anodes and the dissolution of cathodes. Here, we present a new aqueous eutectic electrolyte by coupling a hydrated Zn salt (Zn(ClO4)2·6H2O) exclusively with a neutral ligand (succinonitrile) to mitigate these issues. The unique aqua Zn2+ solvates with a succinonitrile-assisted solvation shell enable an unusual Zn/Zn2+ reversibility of 98.4% Coulombic efficiency along with smooth Zn deposition. Moreover, all water molecules contribute to the formation of the eutectic network, resulting in a delayed oxidation and suppressed solvating ability. When a quinone-based polymer material (38 wt % sulfur content) is utilized as a cathode, the Zn-organic battery with this aqueous eutectic electrolyte exhibits an unprecedented cyclability with a low capacity decay rate (0.004% per cycle over 3,500 cycles) and superior low-temperature performance.
[Display omitted]
•Mixing a hydrated Zn salt with a ligand leads to a new aqueous eutectic Zn electrolyte•A ligand-assisted solvation structure enables the reversible Zn plating/stripping•The absence of free water suppresses the dissolution of organic cathodes•The commonly accepted nonideal perchlorate anion is stabilized in the eutectic network
Aqueous Zn batteries in conjunction with organic cathodes are attractive owning to their safe, green, and low-cost characteristics. However, their rechargeability has been plagued by the lack of suitable electrolytes that can support both the reactive Zn and the soluble organic materials. This work represents our new finding in aqueous Zn electrolytes with the hydrated eutectic nature, which involves a simple formulation based on mixing a hydrated Zn salt with a neutral ligand. The participation of the ligand in the primary Zn2+ solvation shell plays a pivotal role in stabilizing Zn plating/stripping with smooth deposits and suppressed side reactions. Importantly, all water molecules are isolated from each other due to the eutectic network and remain bound in the metal coordination sphere (outer shell), significantly inhibiting the dissolution of organic cathodes, and thus achieving a minimal capacity decay (0.004% per cycle) for Zn-organic batteries, even if the Zn excess is limited.
Zn-organic batteries are unstable in conventional aqueous electrolytes from both anode and cathode aspects. We demonstrated a new hydrated eutectic electrolyte based on a simple formulation of a hydrated Zn salt and a neutral ligand, in which the reorganized solvation shell of Zn2+ and low activity of water molecules allow high-efficient Zn plating/stripping and suppress the dissolution of organic cathodes.