Template-free synthesis of hollow titanium dioxide microspheres and amorphous titanium dioxide microspheres with superior lithium and sodium storage performance

Abstract

Hierarchical hollow TiO₂ microspheres (H-TiO₂) and amorphous solid TiO₂ microspheres (A-TiO₂) were synthesized using a template-free method. Initially, quasi-monodisperse solid TiO₂ microspheres (A-TiO₂) were obtained by controlled thermal hydrolysis of titanium sulfate, forming aggregates of amorphous particles, followed by solvothermal treatment to convert the solid structure into a hollow and crystalline H-TiO₂ structure. SEM and TEM images revealed that the morphological evolution from A-TiO₂ to H-TiO₂ conforms precisely to the inside-out Ostwald ripening mechanism. The unique hollow layered structure endows H-TiO₂ with a large specific surface area of 93.3 m²/g and a rich porous structure. When used as an anode material for LIBs and SIBs, H-TiO₂ exhibits superior cycling stability and rate performance compared to A-TiO₂. For LIBs, H-TiO₂ achieves a reversible capacity of 342.2 mA h g⁻¹ at a 0.2C charge/discharge rate and retains unprecedented long-term stability at high current densities (258.5 mA h g⁻¹ after 1000 cycles at 5C and 220.4 mA h g⁻¹ after 1000 cycles at 10C). For SIBs, H-TiO₂ exhibits a reversible capacity of 271.7 mA h g⁻¹ at 0.2C, with specific capacities of 173.4 mA h g⁻¹ after 1000 cycles at 1C and 101.4 mA h g⁻¹ after 2000 cycles at 5C. Furthermore, kinetic calculations demonstrate that H-TiO₂ possesses higher Li⁺ and Na⁺ diffusion rates, adsorption capacities, and conductivity, further explaining its excellent electrochemical performance.