Towards High-Energy-Density Aqueous Zn-Ion Batteries: From Fundamental Challenges to Integrated Design Strategies

Abstract

Aqueous Zn-ion batteries (AZIBs) are regarded as promising candidates for safe, low-cost, and sustainable electrochemical energy storage. However, their practical application remains constrained by insufficient energy density, which originates from the interrelated challenges of cathode chemistry, Zn anode reversibility, electrolyte stability, and interfacial side reactions. This review systematically examines the fundamental challenges that impede the development of high-energy-density AZIBs and summarizes recent progress in material and system-level design strategies. Special attentions are devoted to: (i) high-voltage, high-capacity cathode materials; (ii) Zn anode stabilization strategies based on structural and interfacial regulation; and (iii) electrolyte engineering, including water-in-salt electrolytes, gel electrolytes, and functional additives. The analysis highlights that energy-density enhancement cannot be achieved through isolated optimization of a single component; instead, it requires synergistic coordination among the cathode, electrolyte, anode, and their interfaces. Recent advances demonstrate that integrated design strategies can efficiently inhibit cathode dissolution, Zn dendrite growth, corrosion, hydrogen evolution, and other parasitic reactions while improving voltage output, reversible capacity, and cycling durability. This review further outlines key future directions, including mechanistic studies, intelligent materials design, engineering-scale validation, and standardized evaluation protocols. Overall, this review offers a comprehensive framework and practical guidance for the rational development of next-generation high-energy-density AZIBs.