Constructing a high-performance cathode for aqueous zinc ion batteries via understanding the energy storage mechanism of MnO

MnO, a potential cathode for aqueous zinc ion batteries (AZIBs), has received extensive attention. Nevertheless, the hazy energy storage mechanism and sluggish Zn²⁺ kinetics pose a significant impediment to its future commercialization. In light of this, the electrochemical activation processes and reaction mechanism of pure MnO were investigated. Combining the Pourbaix diagram and phase diagram of Zn-Mn–O with experiment results, the essential energy storage behavior of MnO cathode can be explained as follows: (1) Zn²⁺ insertion/extraction into ZnMn₂O₄ derived from MnO-based active material, and (2) Zn²⁺ insertion/extraction into ZnMn₂O₄ (originated from the transition of Mn²⁺ → Zn₂Mn₃O₈ → ZnMn₂O₄ in the electrolyte). To further ulteriorly enhance the electrochemistry performance of MnO, N-doped carbon fiber surrounding MnO nanoparticles was constructed, which can provide a conductive matrix with a high specific surface area preventing the undue stack of as-formed ZnMn₂O₄. Additionally, it creates a conductive highway for Zn²⁺ penetration through the electrode/electrolyte interphase, thanks to the electron-rich N that facilitate the reduction of the desolvation penalty. Thus, the results from this study provide a new angle for designing high-performance MnO-based cathodes for AZIBs.

Graphical abstract