Electrochemical Mechanism Analysis of Dual-Site Doped on P2-Na2/3Ni1/3Mn2/3O2 Enabling Anionic and Cationic Redox with Excellent Electrochemical Performance

In recent years, P2-layered manganese-based cathodes have garnered considerable attention because of their exceptional capacity, high energy density, and facile synthesis. Nevertheless, the poor rate capability and inferior capacity retention at high discharge rates have limited their application in commercial batteries. In this work, we report a stable P2-type Na0.62K0.05Mn0.67Ni0.17Mg0.11Zn0.05O2 layered oxide cathode material with both alkali metal site doping and transition metal site doping and confirm that the synergistic effect of the K–Mg–Zn system suppresses the phase transition of P2–O2 and reduces the activation energy of interfacial charge transfer. Furthermore, the introduction of the K–Mg–Zn system results in favorable cycling stability rate performance of the sample. Specifically, the initial discharge capacity at 0.1C is measured to 140.9 mAh g–1, with a capacity retention of 95.1% after 100 cycles at 1C. Remarkably, even after 2000 cycles at 20C, the capacity retention remains at 82.8%. Ex situ X-ray photoelectron spectroscopy (XPS) analysis and the density functional theory (DFT) calculation reveal that the charge compensation during the KNMMZ charging and discharging process can be interpreted as the cooperative action of Mn3+/Mn4+ and Ni2+/Ni3+/Ni4+ redox couples in the voltage range of 2–4 V, while peaks around 4.2 V are attributed to the anionic redox action. Ex situ X-ray diffraction (XRD) analysis reveals the pronounced capability of KNMMZ to effectively suppress the P2–O2 phase transition. The complex impedance measurements and the galvanostatic intermittent titration technique validate that the K–Mg–Zn system enhances the diffusion of sodium ions. Furthermore, the full cell demonstrates outstanding cyclic electrochemical performance, underscoring its exceptional stability and durability throughout multiple charge–discharge cycles. Consequently, the P2-type Na0.62K0.05Mn0.67Ni0.17Mg0.11Zn0.05O2 system presents promising prospects for the advancement of high-energy SIBs in practical applications.