Na0.67Mn(1-x)FexO2 Compounds as High-Capacity Cathode Materials for Rechargeable Sodium-Ion Batteries

Abstract

Herein, we report on electrochemical and structural properties of low-cost Na0.67Mn(1-x)FexO2 (NMFx) cathode materials synthesized through substitution of Mn with small amounts of Fe. The materials were fabricated using a simple solid-state synthesis method. Electrochemical performance of the cathodes was significantly improved when initial electrochemical activation had been performed. Activated Na0.67Mn0.9Fe0.1O2 material displayed a high capacity of 132 mAh/g after 100 cycles and delivered an exceptionally high rate capability of 116 mAh/g at 500 mA/g. Energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV) and ex situ X-ray photoelectron-spectroscopy (XPS) analyses suggested that Fe had played a structural as well as an electrochemical role in cathode performance. Ex situ and in situ X-ray diffraction (XRD) studies were used to analyze the associated structural variations during the capacity evolution.