Unlocking high-rate O3 layered oxide cathode for Na-ion batteries via ion migration path modulation

Abstract

O3-NaNi1/3Fe1/3Mn1/3O2 is a promising layered cathode material with high specific capacity, low cost, and simple synthesis. However, sluggish kinetic hindrance is attributed to the size discrepancy between the large Na-ion and narrow tetrahedral interstitial positions, leading to inferior rate capacity and low reversible capacity. Herein, F− with light‐weight and strong electronegativity is introduced to substitute O atoms in the bulk structure, which intensifies the bond strength of transition metal and oxygen and enlarges the Na+ diffusion channel. In addition, density-functional theory (DFT) calculations demonstrate that the electrostatic interaction is weakened between Na+ in the tetrahedral site and the transition-metal cation directly below it, dramatically reducing the migration barriers of Na+ diffusion. Consequently, the as-obtained NaNi1/3Fe1/3Mn1/3O1.95F0.05 sample displays outstanding rate performance of 86.7 mA h g−1 at 10 C and excellent capacity retention of 84.1% after 100 cycles at 2 C. Moreover, a full cell configuration using a hard carbon anode reaches the energy density of 307.7 Wh kg−1. This strategy paves the way for novel means of modulating the Na-ion migration path for high-rate O3-type layered cathode materials.