Regulating bond structure and local electronic state optimizes the cycling stability of layered sodium-ion cathode materials

Layered transition metal oxides are considered ideal cathode materials for sodium-ion batteries. However, the layered structure irreversibly degenerates during the charging and discharging process, which directly results in a significant reduction of the battery’s capacity and service life. In this work, potassium ions have been incorporated into the alkali metal layer to improve the comprehensive electrochemical properties of layered transition metal oxide materials. The insertion of K⁺ ions alters the local electronic state, thereby improving the bond energy between transition metals (TM) and oxygen, enhancing the structural stability of the material. Additionally, the Na-O bond is elongated, widening the diffusion pathway for Na⁺ ions, and lowering the migration barrier of Na⁺. The designed compound Na_0.6K_0.012Mn_0.67Ni_0.22Fe_0.11O₂ delivers an initial discharge-specific capacity of 131 mAh g^− 1 at 0.5 C and maintains a reversible specific capacity of 89 mAh g^− 1 at 2 C. Moreover, it exhibits impressive cycle stability, maintaining 80% of its capacity after 100 cycles at 2 C.