An Advanced Strategy for Enhancing the Structural Stability and Strength of P2-Type Layered Oxide Sodium Ion Battery Cathodes by Zn/F Dual-Site Doping

Abstract

Modifications through doping at both the anion site and the transition metal site within P2-type layered oxide cathodes for sodium-ion batteries typically exhibit a synergistic effect, which enhances the performance of these sodium-ion batteries. In this study, a prominent enhancement in the performance of P2-Na0.67Ni0.15Fe0.20Mn0.65O2 (NFM) was achieved through a Zn/F dual-site doping strategy. The doped material P2-Na0.67Zn0.05Ni0.15Fe0.20Mn0.60O1.95F0.05 (ZNFMF), prepared by co-precipitation followed by solid-state mixing and calcination method, exhibits superior cycling stability and rate performance in electrochemical tests. The doping of Zn/F optimizes the local electronic structure of the material, reduces the valence state of transition metal (TM) elements, enhances the binding energy between lattice oxygen and TM elements, shortens the TM-O bond length, effectively suppresses structural distortion, and improves the cycling performance and structural stability of the material. In-situ XRD and Raman also confirm the improved structural reversibility of the material during the cycling process. The nano-indentation test further confirms that the Young's modulus and hardness of the ZNFMF is significantly improved compared to NFM during the cycling process. This research successfully improves the structural stability, electrochemical performance, and air stability of the sodium-ion battery cathode material through Zn/F dual-site doping, providing new ideas and methods for the further research and development of sodium-ion battery cathode materials.

Keywords: P2-type layered cathode oxide, Dual-site doping, Local electronic structure, Structural stability, Air stability