Synthesis of yolk-shell Bi2O3@TiO2 submicrospheres with enhanced potassium storage

Due to their enormous potential for large-scale energy storage, rechargeable potassium-ion batteries have been widely researched and developed. However, the drastic volume change of electrode materials induced by the huge size of potassium ions during cycling remains a challenge for the construction of stable anodes. Herein, we propose a novel weak acid etching strategy to design and fabricate robust yolk-shell spheres with enough internal void space, in which the Bi2O3 nanospheres are well confined in the compartments of TiO2 submicrospheres (y-Bi2O3@TiO2). In situ transmission electron microscopy (TEM) and ex situ X-ray diffraction (XRD) are conducted to elucidate the structural evolution of y-Bi2O3@TiO2 and the interaction between K+ and Bi2O3 during cycling. Thanks to the yolk-shell nanoarchitecture and the superior buffering property of outer TiO2 covering, the as-obtained composite shows a high specific capacity of 383.5 mAh g(-1) at 100 mA g(-1), a considerable rate capacity of 134.1 mAh g(-1) at 2 A g(-1) and a stable cycling performance of 216.8 mAh g(-1) at 500 mA g(-1) over 500 cycles when used for potassium storage. Subsequently, the potassium-ion full battery, constructed by pairing y-Bi2O3@TiO2 anode with the thermally annealed 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) cathode, exhibits an outstanding cycling stability. Hopefully, this carefully-designed strategy can inspire the further development of superior energy storage materials in the near future.