Toward high stability of O3‐type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode material with zirconium substitution for advanced sodium‐ion batteries

Abstract

We successfully synthesized a series of O3‐type NaNi 1/3 Fe 1/3 Mn 1/3− x Zr x O 2 ( x = 0, 0.01, 0.02, 0.04) cathode materials by the solid‐state reaction method. Energy dispersion spectroscopy, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy results confirmed the successful incorporation of Zr elements into the lattice to substitute Mn. Due to the introduction of Zr 4+ , the crystal structure modulation of O3‐NaNi 1/3 Fe 1/3 Mn 1/3 O 2 has been realized. By increasing the Zr 4+ content, the width of the sodium diffusion layer expands, thereby facilitating the diffusion of sodium ions. Consequently, the material exhibits a remarkable enhancement in high‐rate capability. At the same time, increasing the Zr 4+ content results in a notable decrease in both the average bond length of TM−O and the thickness of the TMO 6 octahedron in the transition metal layer, resulting in a significant improvement in the cycling performance and structural stability of the cathode material. Additionally, the in‐situ XRD results demonstrate that the optimized cathode composition of O3‐NaNi 1/3 Fe 1/3 Mn 1/3–0.02 Zr 0.02 O 2 (NFMZ2) undergoes a reversible phase transition of O3 → O3 + P3 → P3 → O3 + P3 → O3 during the charge–discharge process.