Deciphering the Electrochemical Behaviors of the Electrode‐Electrolyte Coupling toward Advanced Electrochemical Energy Storage Device

Abstract Aqueous electrochemical energy storage devices (AEESDs) exhibit tremendous potential for grid‐scale energy storage due to their high ionic conductivity, high safety, and environmental friendliness. Nevertheless, the improvement of energy density is always accompanied by the loss of power density due to the sluggish ion migration in the bulk of the electrode. Redox electrolytes are proposed as one of the most promising strategies to expand from electrode materials to the whole device to improve the energy density and power density of AEESDs simultaneously. It is thus vital to understand the electrochemical behaviors and mechanism of the coupling system between the electrode and redox electrolyte during the electrochemical charge‐discharge process. In this study, the electrochemical kinetic evolution model of the redox electrolyte in the electrode is established via quasi‐steady electrochemical measurement and in situ Raman study, revealing the redox reaction of electrolyte originates from charge transfer between ions in electric double layer (EDL). Accordingly, the electrochemical performances are optimized by adjusting the electrolyte concentration. The decline of coulombic efficiency is systematically analyzed, which can be attributed to ionic drifting during a redox reaction. This study may pioneer designing the advanced electrochemical energy storage device by integrating electrode materials and electrolytes.