Insights into the storage mechanism of novel mesoporous hollow TiO2-x/C nanofibers as a high-performance anode material for sodium-ion batteries

Titanium oxide (TiO2) is one of the promising anode materials for sodium-ion batteries (SIBs) owing to its high theoretical capacity (335 mA h g−1), reasonable operation voltage (0.7 V), low cost, and low toxicity, but suffers from its low electronic conductivity and ionic diffusion coefficient. Here, the novel mesoporous hollow TiO2-x/C nanofibers were designed and synthesized by the simple coaxial electrospinning with the annealing treatment in H2/Ar atmosphere (H–TiO2-x/C). Benefitting from the oxygen vacancies (OVs), mesoporous hollow nanofibers, and conductive carbon framework, the electronic conductivity and ionic diffusion coefficient of H–TiO2-x/C are remarkably enhanced. The as-synthesized H–TiO2-x/C demonstrates an excellent reversible capacity of 262.4 mA h g−1 at 33.5 mA g−1, superior rate performance of 142.6 mA h g−1 at 1.675 A g−1, and prominent capacity retention of almost 100% with a capacity of 131.3 mA h g−1 over 7000 cycles under a current density of 3.35 A g−1. Moreover, the in-situ X-ray diffraction analysis and density functional theory calculation reveal that the H–TiO2-x/C possesses stable structure and low energy barriers. Furthermore, Na-ion full-cell of Na0.67Ni0.33Mn0.37Ti0.3O2//H–TiO2-x/C delivers an energy density of 398.2 Wh kg−1 with a retention of 95.1% after 100 cycles at 0.335 A g−1. This work indicates the great promise of the novel mesoporous hollow H–TiO2-x/C nanofibers as high-performance anode materials for SIBs.