Wearable and portable mobile phones play a critical role in the market,and one of the key technologies is the flexible electrode with high spe-cific 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.Ulti-mately,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 perfor-mance(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.