Zn metal-free anodes for dendrite-free aqueous zinc-ion batteries: mechanisms, materials, and optimization strategies

Aqueous zinc-ion batteries (AZIBs) have emerged as promising alternatives for large-scale energy storage, due to their intrinsic safety, low cost, and abundant zinc reserves. Nevertheless, their practical application is greatly hindered by critical issues including dendrite formation and hydrogen evolution on metallic zinc anodes, making the development of Zn metal-free anodes a fundamental strategy to solve these bottlenecks. This review systematically summarizes recent advances in Zn metal-free anodes for AZIBs, with emphasis on energy storage mechanisms, material systems, and performance optimization strategies. Firstly, the Zn 2+ storage mechanisms, including intercalation, conversion, and alloying reactions, are discussed to clarify the fundamental electrochemical processes. Then, the key materials are systematically classified, such as transition metal oxides, transition metal sulfides/selenides, metals/alloys, and organic compounds, highlighting their distinct structural and electrochemical characteristics. Subsequently, the prevailing optimization strategies aimed at enhancing electrochemical performance are summarized, focusing on the governing principles of morphology regulation, heterostructure design, composite engineering, and vacancy engineering. Finally, the current challenges and future research directions are proposed. This review provides a comprehensive framework for understanding the structure-mechanism-performance relationships of Zn metal-free anodes and offers valuable guidance for the rational design of next-generation high-energy and long-lifespan AZIBs.