SnCo Nanoparticles Loaded in Hollow Carbon Spheres Interlinked by N-Doped Carbon Fibers for High-Performance Sodium-Ion Batteries.

The development of Sn-based materials with electrochemically inactive matrices is a novel strategy to alleviate the volume expansion and giant structure strain/stress during the sodiation/desodiation process. In this work, a freestanding membrane based on the unique bean pod-like host composed by nitrogen-doped carbon fibers and hollow carbon spheres (HCSs) encapsulated with SnCo nanoparticles is synthesized by electrospinning (B-SnCo/NCFs). In this unique bean pod-like structure, Sn acts as a host for Na + storage, while the Co plays the important role of an electrochemically inactive matrix that can not only buffer the volume variations but also inhibit aggregation and particle growth of the Sn phase during the electrochemical Na-Sn alloying process. Meanwhile, the introduction of hollow carbon spheres can not only provide enough sufficient void space to withstand the volume expansion during the (de)sodiation processes but also improve the conductivity of the anode along the carbon fibers. Furthermore, the B-SnCo/NCF freestanding membrane can increase the contact area between the active material and the electrolyte, which can provide more active sites during the cycling process. When used as an anode material for Na-ion batteries, the freestanding B-SnCo/NCF anode exhibits an outstanding rate capacity of 243.5 mA h g -1 at 1.6 A g -1 and an excellent specific capacity of 351 mA h g -1 at 0.1 A g -1 for 300 cycles.