Preparation of Fe-doped Na₂Mn₃O₇ and its Application as a Cathode Material for Sodium-ion Batteries

Rechargeable sodium-ion batteries are considered an alternative to Li-ion batteries in terms of large-scale grid storage applications. Finding a cathode material with excellent performance plays a vital role in batteries. Cation doping is one of the methods to stabilize the crystal structure of layered cathode materials for sodium-ion batteries (SIBs) and enhance their electrochemical performance. In this work, we studied the effect of Fe doping on the properties of the Na₂Fe_xMn_2-xO₇ (x=0.0, 0.5) layered material, which was synthesized via a conventional solid-state method at 600 °C. The X-ray diffraction (XRD) analysis showed that the as-synthesized material was crystallized in a pure P2-type structure, except for the nondoped sample. The Fe-doped cathode samples delivered more stable cycle performance than a nondoped cathode material. An initial charge capacity of over 200 mAh g^-1 was achieved for the Fe-doped electrode. Meanwhile, the nondoped electrode delivered approximately 90 mAh g^-1 of initial charge capacity. After 25 continuous charge-discharge cycles at a constant current (20 mA g^-1), approximately 70% and 60% of the initial capacity remained for Fe-doped and nondoped electrodes, respectively.