Hollow Rutile Cuboid Arrays Grown on Carbon Fiber Cloth as a Flexible Electrode for Sodium-Ion Batteries

Flexible electrodes with high charge storage capacity, low solid-state diffusion resistance toward charges, and excellent mechanical properties are needed for fabricating flexible energy storage devices. In this paper, an approach is described to synthesize a composite material with hollow rutile TiO 2 cuboid arrays supported on carbon fiber cloth (H-TiO 2 @CFC). This composite material is used as a self-supporting and binder-free anode for sodium-ion storage, delivering reversible charge capacities of 287.3 at 0.1 C and 103.3 mAh g −1 at 50 C, respectively. The observed excellent electrochemical performance of the H-TiO 2 @CFC electrode is mainly attributed to its unique architecture, which facilitates ion transport, improves electron conductivity, and enables active surface reactivity toward sodium ions. In situ X-ray diffraction characterization results reveal a nearly zero strain structure of the hollow rutile TiO 2 in H-TiO 2 @CFC against electrochemical cycling. An analysis of the charge storage mechanism reveals a significant pseudocapacitance contribution to the charge storage, accounting for the observed high-rate performance of the electrode. A flexible full cell fabricated with the H-TiO 2 @CFC as the anode and Na 3 V 2 (PO 4 ) 3 as the cathode exhibits both excellent electrochemical properties and flexibility against mechanical deformation, demonstrating the great promise of the H-TiO 2 @CFC composite material for flexible battery cells.