Facile and fast Na-ion intercalation employing amorphous black TiO2-x/C composite nanofiber anodes

• Published in: Electrochimica acta Vol. 263; pp. 417 - 425
• Main Authors: Lee, Na-Won, Jung, Ji-Won, Lee, Jun-Seo, Jang, Hye-Yeon, Kim, Il-Doo, Ryu, Won-Hee
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.02.2018
• Subjects: Amorphous structure; Anode material; Black TiO2-x; Electrospinning; Sodium-ion battery; Anode material; Electrospinning; Sodium-ion battery; Amorphous structure; Black TiO2-x
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2018.01.085

Structural and electronic modification of titanium oxide (TiO2) nanomaterials induced by the co-introduction of fully disordered glass phase and oxygen vacancies can lead to remarkable advances in the electrode performance in emerging energy storage systems. We report on the effective co-creation of fully amorphous nanofibers (NFs) composed of black TiO2-x and conductive carbons throughout the NF structure, and evaluate the materials as potential anodes in sodium-ion batteries. The black TiO2-x nanofiber is successfully fabricated by electrospinning a precursor solution followed by a two-step sequential thermal treatment in an air and reducing atmosphere. The NF electrode could deliver approximately two-fold higher 2nd discharge capacity and an excellent kinetic performance even under high rates compared to that delivered by anatase-structured white TiO2 NFs used as reference, because of (i) an inherent free volume in the glass phase corresponding to the enlarged Na+ sites, (ii) increased electrical conductivity (low bandgap) resulting from the presence of Ti3+, (iii) introduction of conductive carbon agents around the TiO2-x domain, and (iv) one-dimensional NF feature allowing numerous Na+ reaction sites at the electrochemical interface. We also elucidate the morphological and structural changes in the nanofibers after discharge and charge by ex-situ characterizations. [Display omitted] •We succeed in co-creating amorphous nanofiber structure composed of black TiO2-x and conductive carbons.•Black TiO2-x/carbon nanofibers are prepared by electrospinning followed by a two-step thermal treatment.•Black TiO2-x/carbon nanofiber delivers excellent electrochemical performance compared to those of anatase TiO2 nanofiber.•The benefits and reaction mechanism of the black TiO2-x/carbon nanofiber anode in the Na-ion cell operation is elucidated.