Exceptionally highly stable cycling performance and facile oxygen-redox of manganese-based cathode materials for rechargeable sodium batteries

In this study, the effect of Zn doping on the electrochemical properties of P2-Na-2/3[Mn1-xZnx]O-2 (x = 0.0, 0.1, 0.2, 0.3) is investigated for the first time. The P2-Na-2/3[Mn0.7Zn0.3]O-2 electrode deliveres a specific discharge capacity of approximately 190 mAh g(-1) based on the oxygen-redox reaction (O2-/O1-), after which the Mn-4/Mn3+ redox reaction contributes to the capacity. The cycling performance of the P2-Na-2/3[Mn0.7Zn0.3]O-2 electrode is also greatly enhanced compared with that of the P2-Na2/3MnO2 electrode (capacity retention of 80% vs. 30% after 200 cycles). This improved cyclability is due to the suppression of cooperative Jahn-Teller distortion as well as stabilization of the structure by the electrochemically inactive Zn2+ ions. First-principle calculations and experimental analysis, including X-ray photoelectron spectroscopy and X-ray absorption near edge structure spectroscopy, clearly confirms that the Zn2+ substitution in P2-Na2/3MnO2 enables the O2-/O1- redox reaction. In addition, time-of-flight secondary ion mass spectroscopy analysis reveals that no sodium carbonates forms on the electrode surface. Our findings provide a potential new path to utilize cost-effective Mn-rich cathode materials for sodium-ion batteries via not only cationic redox but also anodic redox.