Carbon-Free TiO ₂ Microspheres as Anode Materials for Sodium Ion Batteries

In this study, we synthesize a carbon-free anatase/bronze TiO ₂ microsphere (TiO ₂ (A/B)-MS) via the solvothermal method and demonstrate its potential for use as a high-performance anode material for sodium-ion batteries. The highly compact structure of the microsphere constructed from nanoprimary particles not only enhances the structural stability and subsequently leads to good cycling performance but also enables the transport pathways for Na ⁺ ions and electrons to be shortened, ensuring fast Na-storage performance. In addition, an anatase/bronze interfacial structure of the material further improves fast Na ⁺ -ion diffusion kinetics. Benefiting from these merits, the proposed TiO ₂ (A/B)-MS demonstrates a high specific capacity of 221 mAh g ^-1 at 0.1 C, fast charge-discharge capability up to 50 C, and long-term cycling stability over 1000 cycles at 1 and 10 C without using a conductive carbon matrix. A combination of various experiments and theoretical studies is used to verify the outstanding Na-storage performance of TiO ₂ (A/B)-MS.