Layered Sodium-Rich Cathode Material Na_1.2Ni_0.2Mn_0.6O₂ with a High Rate and a Long Cycle Life

This study successfully designed and synthesized a sodium-rich layered material, P2-Na_1.2Ni_0.2Mn_0.6O₂ (referred to as NNMO), via a straightforward sol-gel method. Analysis confirms that NNMO possesses a P2 phase (P63/mmc) layered structure, featuring a significantly enlarged interlayer spacing, which is conducive to the rapid diffusion of sodium ions. Further investigations revealed that the introduction of nickel (Ni) effectively reduced the manganese (Mn³⁺) content, thereby mitigating the Jahn-Teller effect and enhancing the material's electrochemical stability. Electrochemical performance tests demonstrated that the NNMO electrode exhibited superior performance within a 2-4.0 V voltage range. At a current density of 0.2 C, the initial cycle reversible capacity reached 127.4 mAh g^-1, and after 100 cycles, the electrode maintained a high specific capacity of 114.9 mAh g^-1, indicating a 90.2% capacity retention rate. Notably, after cycling at a high current density of 1 C for 500 cycles, the NNMO material still achieved a capacity retention rate of 90.0%, showcasing its exceptional cycle stability. These results suggest that the developed NNMO material, due to its excellent electrochemical performance and stability, holds great promise as a potent candidate for next-generation sodium-ion batteries.