Effect of Ni Doping Content on Phase Transition and Electrochemical Performance of TiO2 Nanofibers Prepared by Electrospinning Applied for Lithium-Ion Battery Anodes

Abstract

Titanium dioxide (TiO₂), as a potential anode material applied for lithium-ion batteries (LIBs), is constrained due to its poor theoretical specific capacity (335 mAh·g⁻¹) and low conductivity (10⁻⁷-10⁻⁹ S·cm⁻¹). When compared to TiO₂, NiO with a higher theoretical specific capacity (718 mAh·g⁻¹) is regarded as an alternative dopant for improving the specific capacity of TiO₂. The present investigations usually assemble TiO₂ and NiO with a simple bilayer structure and without NiO that is immersed into the inner of TiO₂, which cannot fully take advantage of NiO. Therefore, a new strategy was put forward to utilize the synergistic effect of TiO₂ and NiO, namely doping NiO into the inner of TiO₂. NiO-TiO₂ was fabricated into the nanofibers with a higher specific surface area to further improve their electrochemical performance due to the transportation path being greatly shortened. NiO-TiO₂ nanofibers are expected to replace of the commercialized anode material (graphite). In this work, a facile one-step electrospinning method, followed by annealing, was applied to synthesize the Ni-doped TiO₂ nanofibers. The Ni doping content was proven to be a crucial factor affecting phase constituents, which further determined the electrochemical performance. When the Ni doping content was less than 3 wt.%, the contents of anatase and NiO were both increased, while the rutile content was decreased in the nanofibers. When the Ni doping content exceeded 3 wt.%, the opposite changes were observed. Hence, the optimum Ni doping content was determined as 3 wt.%, at which the highest weight fractions of anatase and NiO were obtained. Correspondingly, the obtained electronic conductivity of 4.92 × 10⁻⁵ S⋅cm⁻¹ was also the highest, which was approximately 1.7 times that of pristine TiO₂. The optimal electrochemical performance was also obtained. The initial discharge and charge specific capacity was 576 and 264 mAh·g⁻¹ at a current density of 100 mA·g⁻¹. The capacity retention reached 48% after 100 cycles, and the coulombic efficiency was about 100%. The average discharge specific capacity was 48 mAh·g⁻¹ at a current density of 1000 mA·g⁻¹. Approximately 65.8% of the initial discharge specific capacity was retained when the current density was recovered to 40 mA·g⁻¹. These excellent electrochemical results revealed that Ni-doped TiO₂ nanofibers could be considered to be promising anode materials for LIBs.