A Scalable Approach to Na2FeP2O7@Carbon/Expanded Graphite as a Low‐Cost and High‐Performance Cathode for Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) are the most promising candidates as alternatives to lithium‐ion batteries (LIBs), owing to the natural abundance of sodium salt and the low cost. However, the commercial application of SIBs is principally hampered by the absence of suitable cathode materials. Herein, a novel Na 2 FeP 2 O 7 @carbon/expanded graphite (NFPO@C/EG) composite with a unique microstructure was developed through a scalable sol‐gel process followed by a ball‐milling procedure with expanded graphite. Benefiting from the multiscale carbon‐modified structure, the NFPO@C/EG effectively improves the electronic conductivity and, at the same time, shortens the path of sodium ion transmission. As a consequence, the NFPO@C/EG cathode presents a much higher specific capacity and more stable cycling stability than NFPO@C and NFPO. The unique design of NFPO@C/EG endows a high ratio of pseudocapacitance contribution and a large Na + diffusion coefficient. As a consequence, the NFPO@C/EG cathode displays stable cycle performance (82 mAh g −1 over 400 cycles at 232 mA g −1 ) and superior rate capability (60 mAh g −1 at a high charge/discharge density of 2320 mA g −1 ). This multiscale carbon‐modified design concept builds an avenue for the practical application of polyanionic cathode materials and promotes the development of low‐cost SIBs.