Challenges and design opportunities for high-energy-density aqueous zinc-ion batteries: from electrochemically active to functional components

Abstract

Aqueous zinc-ion batteries (AZIBs) have garnered increasing attention as next-generation rechargeable batteries owing to their inherent safety, environmental friendliness, and cost-effectiveness, which was not fully provided by conventional lithium-ion batteries (LIBs). However, establishing AZIBs as viable alternatives to LIBs requires substantial improvements in energy density. While cathode design has traditionally been regarded as a primary factor, system-level enhancement requires not only increased operating voltage and charge storage capacity but also a reduction in electrochemically inactive components. In this review, we provide a comprehensive discussion of multi-faceted strategies for maximizing the energy density of AZIBs. From the cathode perspective, increasing areal capacity through high-mass-loading electrodes and developing cathode materials with both high voltage and large capacity are essential. Unfortunately, aqueous electrolytes remain constrained by the narrow electrochemical stability window, which prompts strategies to suppress water decomposition and enable high-voltage operation. On the anode side, metallic zinc (Zn) foil is typically employed and excess Zn is often required to ensure long-term stability, which further reduces practical energy density. Separators, despite being less emphasized, also play a significant role because conventional glass fiber separators are thick and heavy, impeding energy density optimization. Accordingly, developing advanced separators with reduced thickness and improved electrochemical properties becomes increasingly important. This review identifies key limitations that constrain the energy density of AZIBs and explores viable strategies and future design directions toward high-energy-density realization. We anticipate that a system-level perspective will offer valuable insight into the development of next-generation AZIBs and support their positioning as competitive alternatives to LIBs.