The stability of electrode materials in aqueous environments presents a significant challenge for the long-term performance of energy storage systems, particularly when operating at potentials that promote water electrolysis. Many electrode materials undergo spontaneous self-discharge, resulting in a gradual loss of stored charge. While previous studies have shown that metallic and inorganic electrodes in aqueous solutions can experience significant self-discharge, much less is known about this phenomenon in organic electrodes. To bridge this gap, this study investigates the self-discharge behavior of polyimide (PI)-based electrodes, focusing on 1,4,5,8-naphthalenetetracarboxylic dianhydride-derived polyimide (PNTCDA) in aqueous electrolyte solutions. Through a systematic evaluation of charge loss, we demonstrate that while water reduction primarily drives reversible self-discharge, it also indirectly contributes to irreversible capacity loss by generating reactive species and conditions that accelerate the hydrolytic degradation of the polymeric structure. These processes are particularly pronounced when the anode material is in its electrochemically reduced state at low potentials. Comparisons with nonaqueous systems reveal that even small amounts of water can significantly accelerate capacity loss, underscoring the susceptibility of organic-based electrodes to instability when operating within potential windows where water is reduced. These findings highlight the critical need for strategies to mitigate both reversible self-discharge and irreversible degradation processes in aqueous battery systems.

Aqueous batteries with metal anodes exhibit robust anodic capacities, but their energy densities are low because of the limited potential stabilities of aqueous electrolyte solutions. Current metal options, such as Zn and Al, pose a dilemma: Zn lacks a sufficiently low redox potential, whereas Al tends to be strongly oxidized in aqueous environments. Our investigation introduces a novel rechargeable aqueous battery system based on Mn as the anode. We examine the effects of anions, electrolyte concentration, and diverse cathode chemistries. Notably, the ClO4-based electrolyte solution exhibits improved deposition and dissolution efficiencies. Although stainless steel (SS 316 L) and Ni are stable current collectors for cathodes, they display limitations as anodes. However, using Ti as the anode resulted in increased Mn deposition and dissolution efficiencies. Moreover, we evaluate this system using various cathode materials, including Mn-intercalation-based inorganic (Ag0.33V2O5) and organic (perylenetetracarboxylic dianhydride) cathodes and an anion-intercalation-chemistry (coronene)-based cathode. These configurations yield markedly higher output potentials compared to those of Zn metal batteries, highlighting the potential for an augmented energy density when using an Mn anode. This study outlines a systematic approach for use in optimizing metal anodes in Mn metal batteries, unlocking novel prospects for Mn-based batteries with diverse cathode chemistries.