Revealing the effect of conductive carbon materials on the sodium storage performance of sodium iron sulfate

Na2Fe2(SO4)3 (NFS), as a promising cathode for sodium-ion batteries, is still plagued by its poor intrinsic conductivity. In general, hybridization with carbon materials is an effective strategy to improve the sodium storage performance of NFS. However, the role of carbon materials in the electrochemical performance of NFS cathode materials has not been thoroughly investigated. Herein, the effect of carbon materials was revealed by employing various conductive carbon materials as carbon sources. Among these, the NFS coated with Ketjen Black (NFS@KB) shows the largest specific surface area, which is beneficial for electrolyte penetration and rapid ionic/electronic migration, leading to improved electrochemical performance. Therefore, NFS@KB shows a long cycle life (74.6 mA h g-1 after 1000 cycles), superior rate performance (61.5 mA h g-1 at a 5.0 A g-1), and good temperature tolerance (-10 degrees C to 60 degrees C). Besides, the practicality of the NFS@KB cathode was further demonstrated by assembling a NFS@KB//hard carbon full cell. Therefore, this research indicates that a suitable carbon material for the NFS cathode can greatly activate the sodium storage performance. The Na2Fe2(SO4)3@KB cathode shows excellent electrochemical performance, and the assembled Na2Fe2(SO4)3@KB//hard carbon full cell also exhibits a high operation voltage of 3.5 V and good capacity retention of 77.3% after 100 cycles.