Flexible C-Mo₂C fiber film with self-fused junctions as a long cyclability anode material for sodium-ion battery

Electrospun carbon fiber films have high contact resistance at the fiber junctions, which causes poor cycling stability and limits their further improvement in energy storage performances. To eliminate the contact resistance of the film, we provide a new strategy to fuse the fiber junctions by introducing MoO₂ in the fibers, which replaces the C-C interface by a more active C-MoO₂-C interface at the fiber junction to promote mass transfer. MoO₂ reacts with C matrix to generate Mo₂C and form self-fused junctions during the carbonization process. Due to much lower charge transfer and sodium diffusion resistance, the C-Mo₂C fiber film with self-fused junctions shows much better cyclability with capacity retention of 90% after 2000 cycles at a constant current density of 1 A g^-1. Moreover, the Mo₂C particles provide many electrochemically active sites, leading to additional improvement in sodium storage. The C-Mo₂C fiber film has a capacity of 134 mA h g^-1 at 1 A g^-1 and a high capacity of 99 mA h g^-1 even at 5 A g^-1.