Coaxial electrospinning synthesis free-standing Sn/TiO2 flexible carbon fibers with sheath/core structure for advanced flexible lithium/potassium-ion batteries

•A new three-dimensional conductive network composed of the sheath (TiO2) / core structure (Sn) was fabricated successfully.•The sheath/core structure improves the electronic conductivity and provides a buffer for volumetric strain.•The fiber core Sn and sheath TiO2 form a heterojunction interface, accelerating electron transport. Flexible Sn/TiO2 carbon nanofiber (ST-NCF) composites were constructed by doping TiO2 into tin-based carbon nanofibers via coaxial electrospinning. Sn/TiO2 carbon nanofiber was directly used as an anode for Lithium-ion Batteries (LIBs) and Potassium-ion Batteries (PIBs), which show exceptional electrochemical performances. The layered sheath/core structure of the material lead to its good electrochemical properties, where the core Sn carbon nanofiber was encapsulated by the sheath layer of TiO2 nanoparticles. In addition to enhancing its electrical conductivity, the outer TiO2 and N-doped carbon fiber matrix also provide a buffer zone for volumetric strain during charging and discharging. The fiber core Sn and sheath TiO2 form a heterojunction interface on the two-dimensional tube surface, which increases the diffusion rate of ions and electrons. After 100 cycles, TiO2-NCF and ST-NCF-40%TBT (40% TBT indicates the percentage of TiO2 in shell solution to the total composition of shell spinning solution) show capacities of 386.6 mAh g−1 and 1336 mAh g-1, respectively, at 0.5A g-1. After 2000 cycles, ST-NCF-40%TBT in LIBs displayed a high capacity of 299 mAh g-1 at 10 A g-1. After 350 cycles at 1A g-1, the capacity of ST-NCF-40%TBT in PIBs is reserved at 307 mA h g-1. Due to the superior mechanical flexibility of ST-NCF-40%TBT films, it will be a promising anode candidate for flexible LIBs and PIBs. [Display omitted]