Interphase Synergy Achieving Stable Cycling Performance for Aqueous Zn-MnO2 Battery

The lattice distortion resulting from the Jahn–Teller effect (JTE) at the Mn redox center typically induces irreversible phase transitions and structural degradation, which in turn diminishes the reversible capacity and long-term cycling performance. Here, N-doped carbon quantum dots (N-CDs) grafted to the surface of 3 × 3 tunnel todorokite-type MnO₂ (TMO) nanosheet (abbreviated to TMO@N-CDs) are designed. The adsorption of N-CDs promoted the charge transfer and redistribution between Mn and O and promoted the closer electron cloud overlap between Mn and O, thus enhancing the bonding strength of Mn–O bonds, stabilizing the lattice structure, inhibiting JTE, and realizing reversible H⁺/Zn²⁺ storage. Meanwhile, a significant amount of N-CDs can increase active sites of TMO nanosheet, enhance the binding ability with metal ions, and accelerate the ion diffusion kinetics, thus realizing stable electrochemical performances. The density functional theory (DFT) calculation shows that there is obvious orbital overlap between Mn and O in [MnO6] octahedron, which further quantifies the strong interaction between Mn and O through interphase synergy between N-CDs and TMO. The reversible (de)insertion behavior dominated by H⁺ during charging and discharging was proved by operando XRD and ex-situ SEM. As expected, the obtained TMO@N-CDs cathode exhibits remarkable electrochemical properties in terms of high reversible capacity, good rate performance, and satisfactory cycling stability (after 1000 cycles, the specific capacity remains 96.02%).