Ion-concentration gradient electrolyte engineering in aqueous Zn-based batteries

Abstract

Aqueous Zn-based batteries (AZBs) have attracted considerable attention as promising energy storage systems because of their intrinsic safety, low cost, and environmental friendliness. However, their practical application is limited by the instability of the Zn electrode interface, including uneven Zn deposition, hydrogen evolution, and other parasitic side reactions. These issues are closely related to the heterogeneous distribution of Zn²⁺ ions and the resulting imbalance of interfacial reactions during cycling. Ion concentration gradient engineering has therefore emerged as an effective strategy to regulate Zn²⁺ transport behavior and stabilize the Zn electrode interface. This review systematically summarizes recent advances in the construction of Zn²⁺ concentration gradients in AZBs, covering both liquid and hydrogel electrolyte systems. Representative strategies, including functional electrolyte additives, ion-selective separators, asymmetric electrolyte configurations, gradient hydrogel networks, and additive-assisted hydrogel electrolytes, are discussed. These approaches demonstrate that spatial regulation of Zn²⁺ concentration fields can fundamentally influence ion transport pathways, solvation and desolvation processes, electric double layer structures, and interfacial reaction kinetics, thereby homogenizing Zn²⁺ flux, suppressing hydrogen evolution and dendrite growth, and improving the reversibility of Zn plating and stripping. In addition, recent progress in advanced characterization techniques, including electrochemically parameterized ion transport modelling, in situ ion concentration mapping, and fluorescence-based operando visualization, is needed to elucidate the dynamic evolution of Zn²⁺ concentration gradients and their correlation with interfacial stability. Finally, general design principles, key challenges, and future perspectives for ion concentration gradient engineering are discussed, guiding the rational development of high-performance and durable AZBs.

Keywords

Aqueous Zn-based batteries / quasi/all solid-state batteries / Zn electrode / gradient electrolyte / advanced characterization

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