From insulator to semiconductor: carbon nanotubes enhancing the electrochemical performance of Na 2.5 Fe 1.75 (SO 4 ) 3 cathode materials for sodium ion batteries

Sodium iron sulfate (Na 2+2 x Fe 2− x (SO 4 ) 3 , NFS) is a promising cathode material for sodium-ion batteries (SIBs) for large-scale energy storage systems due to its low cost and long life.