Local chemical environment and Na-ion diffusion behavior of O3-type NaNi1/3Mn1/3Fe1/3O2 cathode for Na-ion batteries from first-principles study

The O3-type NaNi1/3Fe1/3Mn1/3O2 (NNFM) is considered one of the most promising layered cathode candidates for sodium-ion batteries (SIBs). However, non-equilibrium structural evolution during charging induces detrimental local chemical environment alterations. These include transition metal octahedral (TMO6) distortion and kinetic barriers that impede Na+ migration. Herein, Through first-principles density functional theory (DFT) calculations, this work systematically investigates the correlation between local chemical environments and Na+ diffusion kinetics in NNFM. Moreover, Mn3+ ions in the transition metal (TM) layer are strategically replaced by Ta5+ cations with strong oxygen affinity, enabling modulation of the local coordination chemistry. Specifically, Ta ions enlarges the Na+ ion transport channels and enhances the bonding capability between TM and O atoms. The spacing between metal layers shrinks to 2.125 & Aring;, and the spacing between sodium layers grows to 3.306 & Aring;. At the same time, changes in the material's electronic structure show downward shifts of 1.1 eV (for non-bonding oxygen) and 0.74 eV (for bonded metal-oxygen states), making the bandgap smaller (0.406 eV). These effects work together to reduce oxygen loss and keep the battery reactions stable during charging. Therefore, local chemical environment modulation can provide technical direction for the development of high-performance SIBs.