Fe doping mechanism of NaMnO tunnel phase cathode electrode in sodium-ion batteries.

Due to its stability and low cost, the tunnel-style sodium-manganese oxide (NaMnO) material is deemed a popular cathode choice for sodium-ion rechargeable batteries. However, the Jahn-Teller effect caused by Mn in the material results in poor capacity and cycling stability. The purpose of this experimental study is to partially replace Mn with Fe, in order to reduce the Jahn-Teller effect of the material during charging and discharging process. The results of Raman spectroscopy and X-ray photoelectron spectroscopy confirmed that the content of Mn decreased after Fe doping. Electrochemical studies show that the NaMnFeO cathode has better rate performance (exhibits a reversible capacity of 87.9 mAh/g at 2 C) and cycle stability in sodium-ion batteries. The diffusion coefficient of sodium ions increases by Fe doping. The excellent rate performance and capacity improvement are verified by density functional theory (DFT) calculation. After doping, the band gap decreases significantly, and the results show that the state density of O 2p increases near the Fermi level, which promotes the oxidation-reduction of oxygen. This work provides a straightforward approach to enhance the performance of NaMnO nanorods, and this performance improvement has guiding significance for the design of other materials in the energy storage domain.