Hydrogen-nitrogen plasma assisted synthesis of titanium dioxide with enhanced performance as anode for sodium ion batteries

Sodium ion batteries are considered as one of the most promising energy storage devices as lithium ion batteries due to the natural abundance of sodium. TiO₂ is very popular as anode materials for both lithium and sodium ion batteries because of the nontoxicity, safety and great stabilities. However, the low electronic conductivities and inferior sodium ion diffusion make it becoming a great challenge to develop advanced TiO₂ anodes. Doping heteroatoms and incorporation of defects are believed to be great ways to improve the electrochemical performance of TiO₂ anodes. In this work, commercial TiO₂ (P25) nanoparticles was modified by hydrogen and nitrogen high-power plasma resulting in a disordered surface layer formation and nitrogen doping as well. The electrochemical performances of the samples as anode materials for sodium ion batteries was measured and the results indicated that after the hydrogen–nitrogen plasma treatment, H–N-TiO₂ electrode shows a 43.5% of capacity higher than the P-TiO₂ after 400 cycles long-term discharge/charge process, and the samples show a good long cycling stability as well, the Coulombic efficiencies of all samples are nearly 99% after 50 cycles which could be sustained to the end of long cycling. In addition, hydrogen–nitrogen plasma treated TiO₂ electrode reached the stable high Coulombic efficiency earlier than the pristine material. High resolution TEM images and XPS results indicate that there is a disordered surface layer formed after the plasma treatment, by which defects (oxygen vacancies) and N-doping are also introduced into the crystalline structure. All these contribute to the enhancement of the electrochemical performance.