Multielement-Doped Fe_xSe_y/Carbon Nanotube Composites for High Performance Sodium-Ion Storage

Fe x Se y -based composites have become very attractive anode materials for sodium-ion batteries due to their excellent electrochemical reversibility and the low price of iron resources. However, the unsatisfactory rate capacities and cycling stabilities continue to stimulate modification studies on synthetic strategies, crystal structure, morphologies, and composition structures. Here, we presented a straightforward synthetic route to a series of multielement-doped Fe x Se y /carbon nanotube (Fe x Se y /CNT) composites containing different ion selenide phases (Fe 3 Se 4, FeSe 2, and FeSe) from a single priceless stainless-steel powder. Among them, Fe 3 Se 4 /CNT exhibits the best rate capability and cycling stability with micron-scale sizing (250.0 mAh g –1 at 50 A g –1 and 338.6 mAh g –1 after 1600 cycles at 10 A g –1 ). The excellent sodium-ion storage properties of the Fe 3 Se 4 /CNT electrode could be attributed to the small subgrain size, abundant crystal boundaries, and amorphous regions in the composite structures caused by high-content multielement doping. The performance differences among the as-prepared composites containing various iron selenides lie in their intrinsic crystal structure characteristics. The practical application prospects of the Fe 3 Se 4 /CNT electrodes are also proved. The full cell assembled with Fe 3 Se 4 /CNT and Na 3 V 2 (PO 4 ) 2 F 3 /C displayed a high-rate capability of 368 mAh g –1 at 5 A g –1 and good capacity retention (about 100%) after 150 cycles.