Self‐Discharge Behaviors in Aqueous Batteries

Abstract 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.