A novel high voltage battery cathodes of Fe²⁺/Fe³⁺sodium fluoro sulfate lined with carbon nanotubes for stable sodium batteries

Current trends in battery research are promoting the development of feasible methods to prepare electrode materials with new architectures that can meet the requirements of high energy density associated with sodium ion batteries (SIB). It is logical to use solid-state processing techniques to fabricate SIB electrode materials due to its ease of handling and capability for large-scale production. From the SIB standpoint, the sulfate based polyanionic system is well known for its high operating voltage. The present study utilizes a hitherto-unknown solid-state process with an entirely new composition to develop an electrode comprising earth abundant carbon, sodium, sulfur, fluorine, and iron materials. This new NaFeSO4F-CNT system, where CNT is carbon nanotube, obtained by the solid-state technique, exhibits a highly stable Fe2+/Fe3+redox couple and achieves a capacity of ∼110 mAg−1at 0.1C with capacity retention of >91% after 200 cycles (1C). This is the best-ever reversible, high potential sulfate based cathode for sodium ion batteries reported to date. This study also provides an in-depth understanding of the outstanding electrochemical performance of this novel electrode. These findings can make it possible to achieve maximum performance from potential electrodes, when the operating temperature is limited to 350 °C or below.