Deciphering the electrochemical behavior of Mn-based electrode-electrolyte coupling system toward advanced electrochemical energy storage devices

Mn-based aqueous electrochemical energy storage devices (AEESDs) are promising candidates for sustainable and flexible energy applications due to their environmental benignity, high theoretical capacity and versatile architecture. One of the effective strategies to boost their electrochemical performance is to introduce Mn2+ ions into the electrolyte, which can trigger a reversible solid/liquid reaction process of Mn2+/MnO2 deposition/dissolution with a high capacity and an ideal electrochemical kinetics. However, the complex energy storage mechanism that involves the Mn2+/MnO2 deposition/dissolution and the intrinsic insertion/extraction of proton and metal ions remains elusive and poses a great challenge for the rational design of Mn-based AEESDs. Moreover, the insufficient dissolution of MnO2 can lead to the deterioration of performance, which hinders their practical applications. To address these issues, we systematically investigate the Mn2+ ions added Mn-based AEESDs by employing a novel quasi-steady electrochemical measurement technique, and establish a kinetic evolution model to elucidate the solid/liquid reaction at different interface conditions. Furthermore, a full cell is assembled and measured to explore the real electrochemical process of Mn-based electrode with additive Mn2+ ions, which is influenced by the potential windows and charge-discharge rate. This study may provide new insights for the development of advanced AEESDs. •The kinetics evolution model has been established by using MPSM, which visually illustrates the kinetics of Mn-based AEESDs.•The dissolution of MnO2 is insufficient due to low concentration of protons and leading to lower coulombic efficiency.•The insertion/extraction of metal cations will be eliminated as the wide potential window and fast electrochemical process.