Synthesis of One-Dimensional Mesoporous Ag Nanoparticles-Modified TiO2 Nanofibers by Electrospinning for Lithium Ion Batteries

Abstract

TiO₂ is regarded as a prospective electrode material owing to its excellent electrochemical properties such as the excellent cycling stability and the high safety. However, its low capacity and low electronic conductivity greatly restrict the further improvement in electrochemical performance. A new strategy was put forward to solve the above defects involved in TiO₂ in which the low capacity was enhanced by nanomerization and porosity of TiO₂, and the low electronic conductivity was improved by introducing Ag with a high conductivity. One-dimensional mesoporous Ag nanoparticles-embedded TiO₂ nanofibers (Ag@TiO₂ nanofibers) were successfully synthesized via a one-step electrospinning process combined with subsequent annealing treatment in this study. The microstructure and morphology of mesoporous TiO₂@Ag nanofibers were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption. TiO₂ nanofibers mainly consisted of a large amount of anatase TiO₂, accompanied with traces of rutile TiO₂. Ag nanoparticles were uniformly distributed throughout TiO₂ nanofibers and promoted the transformation of TiO₂ from the anatase to the rutile. The corresponding electrochemical performances are measured by galvanostatic charge-discharge, cycle stability, rate performance, cycle voltammetry, and electrochemical impedance spectroscopy measurements in this research, with pristine TiO₂ nanofibers as the reference. The results indicated that the introduction of Ag nanoparticles into TiO₂ nanofibers significantly improved the diffusion coefficient of Li ions (5.42 × 10^-9 cm²⋅s^-1 for pristine TiO₂, 1.96 × 10^-8 cm²⋅s^-1 for Ag@TiO₂), and the electronic conductivity of TiO₂ (1.69 × 10^-5 S⋅cm^-1 for pristine TiO₂, and 1.99 × 10^-5 S⋅cm^-1 for Ag@TiO₂), based on which the comprehensive electrochemical performance were greatly enhanced. The coulombic efficiency of the Ag@TiO₂ nanofibers electrode at the first three cycles was about 56%, 93%, and 96%, which was higher than that without Ag (48%, 66%, and 79%). The Ag@TiO₂ nanofibers electrode exhibited a higher specific discharge capacity of about 128.23 mAh⋅g^-1 when compared with that without Ag (72.76 mAh·g^-1) after 100 cycles at 100 mA·g^-1. With the current density sharply increased from 40 mA·g^-1 to 1000 mA·g^-1, the higher average discharge capacity of 56.35 mAh·g^-1 was remained in the electrode with Ag, when compared with the electrode without Ag (average discharge capacity of about 12.14 mAh·g^-1). When the current density was returned to 40 mA·g^-1, 80.36% of the initial value was returned (about 162.25 mAh·g^-1) in the electrode with Ag, which was evidently superior to that without Ag (about 86.50 mAh·g^-1, only 55.42% of the initial value). One-dimensional mesoporous Ag@TiO₂ nanofibers can be regarded as a potential and promising candidate as anode materials for lithium ion batteries.

Keywords: electrospinning; lithium ion battery; mesoporous nanofibers; sliver; titanium oxide.

Figure 1

Schematic illustration of the electrospinning process.

Figure 2

XRD patterns of (a) TiO₂ nanofibers; (b) Ag nanoparticles-embedded TiO₂ (Ag@TiO₂) nanofibers.

Figure 3

XPS survey spectra of (a) TiO₂ nanofibers and (b) Ag@TiO₂ nanofibers, and high-resolution XPS spectra of Ti 2p, O 1s, Ag 3d.

Figure 4

N₂ adsorption–desorption isotherms of (a) TiO₂ nanofibers and (b) Ag@TiO₂ nanofibers.

Figure 5

FE-SEM images of (a) TiO₂ nanofibers, (b) Ag@TiO₂ nanofibers. TEM images of (c) TiO₂ nanofibers, (d) Ag@TiO₂ nanofibers. (e) HRTEM image of a section of Ag@TiO₂ nanofiber. (f) Selected-area electronic diffraction (SAED) pattern of Ag@TiO₂ nanofibers.

Figure 6

TEM image of (a) a single Ag@TiO₂ nanofiber for elemental mapping. Mapping of (b) O, (c) Ag, and (d) Ti.

Figure 7

Electrochemical performances of TiO₂ and Ag@TiO₂ nanofibers electrodes. Cyclic voltammograms of (a) TiO₂ nanofibers electrode and (b) Ag@TiO₂ nanofibers electrode from the first to third cycle at a scanning rate of 0.1 mV/s between 0–3 V. First three charge and discharge cycles of (c) TiO₂ nanofibers electrode and (d) Ag@TiO₂ nanofibers electrode. (e) Cycling performance at 100 mA⋅g⁻¹. (f) Rate capability of TiO₂ and Ag@TiO₂ nanofibers electrodes at different current densities.

Figure 8

Schematic illustration of the distribution of Ag nanoparticles in Ag@TiO₂ nanofibers.

Figure 9

Nyquist plots of pristine TiO₂ nanofibers electrode and Ag@TiO₂ nanofibers electrode at room temperature.