Nb-doped NaNi1/3Fe1/3Mn1/3O2 and its high-voltage performance as sodium-ion battery cathode

Abstract

O3-NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) becomes one of the primary cathode materials for sodium-ion batteries due to its low cost, high capacity, and easy preparation. However, its slow diffusion kinetics and severe lattice distortion at high voltage significantly affect its electrochemical performance. In this study, Nb doping is applied to NFM using the sol-gel method to enhance its electrochemical properties. Both the theoretical calculations and experimental results indicate that Nb doping not only reduces the migration energy barrier for Na ions but also stabilizes the crystal structure. The Nb-doped NFM material retains 83.7 % of its initial capacity after 100 cycles at a voltage range of 2–4.2V and a 1C current density. When the current density increases from 0.1C to 10C, the capacity retention rate reaches 48.25 %, significantly higher than the 27.76 % retention rate of the undoped sample. These findings provide new insights into the mechanism of Nb doping for improving the high-voltage stability of O3-type materials and hold valuable implications for further optimization of cathode materials in sodium-ion batteries.