Iron Oxychloride as the Cathode Material for Sodium Ion Batteries

Iron oxychloride (FeOCl) with a layered structure may be a potential cathode material for rechargeable sodium ion batteries, due to its large interlayer spacing and high theoretical capacity. Here, the FeOCl material is employed as the cathode material for sodium ion batteries for the first time. Its morphology, electrochemical sodium storage performance, and reaction mechanisms are systematically investigated. The as-prepared FeOCl cathode exhibits a high discharge capacity of 321 mAh g⁻¹ in the voltage range of 1.4–4.0 V (vs. Na/Na⁺) at 10 mA g⁻¹ during the first cycle; however, the discharge capacity fades to 69 mAh g⁻¹ after 30 cycles due to the large volume change of FeOCl and phase separation during cycling. The intercalation and conversion reaction mechanism of FeOCl during reversible sodium ion storage is demonstrated by the results of energy-dispersive spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy.