Self‐Discharge Behaviors in Aqueous Batteries

Aqueous batteries (ABs) are considered emerging candidates for grid-scale energy storage due to their inherent safety, cost-effectiveness, and environmental compatibility. In recent years, major advances have been made in ABs toward improving their energy density and cycling stability, and progressing their prospects for real application. However, self-discharge, a critical parameter for practical applications, remains largely underexplored. Many studies either overlook this aspect entirely or employ inconsistent testing protocols, making cross-system comparisons difficult and diminishing the reliability of reported data. To date, no comprehensive review that systematically addresses self-discharge in ABs is available. In this review, we aim to fill this gap by providing an in-depth analysis of self-discharge phenomena in state-of-the-art ABs. We first summarize the underlying mechanisms responsible for self-discharge and then critically evaluate current measurement approaches, offering recommendations for practical and standardized testing protocols. Furthermore, we highlight mitigation strategies from both electrolyte and electrode perspectives, providing a materials-oriented overview of self-discharge suppression. This review not only offers a theoretical framework for understanding self-discharge behaviors in ABs, but also proposes clear guidelines for future experimental assessment, thereby enhancing their practical relevance and accelerating their development toward commercialization.