Wearable and portable mobile phones play a critical role in the market, and one of the key technologies is the flexible electrode with high specific capacity and excellent mechanical flexibility. Herein, a wire-in-wire TiO₂/C nanofibers (TiO₂ ww/CN) film is synthesized via electrospinning with selenium as a structural inducer. The interconnected carbon network and unique wire-in-wire nanostructure cannot only improve electronic conductivity and induce effective charge transports, but also bring a superior mechanic flexibility. Ultimately, TiO₂ ww/CN film shows outstanding electrochemical performance as free-standing electrodes in Li/K ion batteries. It shows a discharge capacity as high as 303 mAh g⁻¹ at 5 A g⁻¹ after 6000 cycles in Li half-cells, and the unique structure is well-reserved after long-term cycling. Moreover, even TiO₂ has a large diffusion barrier of K⁺, TiO₂ ww/CN film demonstrates excellent performance (259 mAh g⁻¹ at 0.05 A g⁻¹ after 1000 cycles) in K half-cells owing to extraordinary pseudocapacitive contribution. The Li/K full cells consisted of TiO₂ ww/CN film anode and LiFePO₄/Perylene-3,4,9,10-tetracarboxylic dianhydride cathode possess outstanding cycling stability and demonstrate practical application from lighting at least 19 LEDs. It is, therefore, expected that this material will find broad applications in portable and wearable Li/K-ion batteries.

Ta-doped TiO₂/C nanofibers can enhance the electrical conductivity, shorten the ion transport distance. Thus it shows outstanding electrochemical performance in both Li/K-metal half cells and Li/K full cells..