Core-Double-Shell TiO2@Fe3O4@C Microspheres with Enhanced Cycling Performance as Anode Materials for Lithium-Ion Batteries

Abstract

Due to the volume expansion effect during charge and discharge processes, the application of transition metal oxide anode materials in lithium-ion batteries is limited. Composite materials and carbon coating are often considered feasible improvement methods. In this study, three types of TiO₂@Fe₃O₄@C microspheres with a core-double-shell structure, namely TFCS (TiO₂@Fe₃O₄@C with 0.0119 g PVP), TFCM (TiO₂@Fe₃O₄@C with 0.0238 g PVP), and TFCL (TiO₂@Fe₃O₄@C with 0.0476 g PVP), were prepared using PVP (polyvinylpyrrolidone) as the carbon source through homogeneous precipitation and high-temperature carbonization methods. After 500 cycles at a current density of 2 C, the specific capacities of these three microspheres are all higher than that of TiO₂@Fe₂O₃ with significantly improved cycling stability. Among them, TFCM exhibits the highest specific capacity of 328.3 mAh·g^-1, which was attributed to the amorphous carbon layer effectively mitigating the capacity decay caused by the volume expansion of iron oxide during charge and discharge processes. Additionally, the carbon coating layer enhances the electrical conductivity of the TiO₂@Fe₃O₄@C materials, thereby improving their rate performance. Within the range of 100 to 1600 mA·g^-1, the capacity retention rates for TiO₂@Fe₂O₃, TFCS, TFCM, and TFCL are 27.2%, 35.2%, 35.9%, and 36.9%, respectively. This study provides insights into the development of new lithium-ion battery anode materials based on Ti and Fe oxides with the abundance and environmental friendliness of iron, titanium, and carbon resources in TiO₂@Fe₃O₄@C microsphere anode materials, making this strategy potentially applicable.

Keywords: anode materials; carbon coating; core–double-shell structure; electrochemical properties; lithium-ion batteries.

Figure 1

(a) Preparation schematic of TiO₂@Fe₃O₄@C microspheres and digital images of (b) TFCS, (c) TFCM, (d) TFCL.

Figure 2

(a) XRD patterns of TiO₂, TiO₂@Fe₂O₃, TFCS, TFCM, TFCL (b) Raman spectra of TiO₂, TiO₂@Fe₂O₃, TFCS, TFCM, TFCL.

Figure 3

XPS spectra of TFCM (a) survey, (b) Fe 2p, (c) O 1s, (d) C 1s.

Figure 4

SEM images of the (a) TiO₂, (b) TiO₂@Fe₂O₃, (c,d) TFCS, (e,f) TFCM (g,h) TFCL; The EDX spectrum and EDS mapping images of the (i) TFCS, (j) TFCM, (k) TFCL.

Figure 5

CV curves of (a) TiO₂@Fe₂O₃ and (b) TFCS, (c) TFCM, and (d) TFCL microspheres at the scanning rate of 0.1 mV s⁻¹ in the range of 0.01~3.5 V.

Figure 6

Galvanostatic discharge/charge curves for the 1st, 2nd, 3rd, 10th, and 100th cycles at a current density of 0.2 C for (a) TiO₂@Fe₂O₃, (b) TFCS, (c) TFCM, and (d) TFCL microspheres.

Figure 7

Cycling performances of TiO₂@Fe₂O₃, TFCS, TFCM, TFCL, commercial graphite and coulombic efficiencies of TFCS, TFCM, TFCL at the current density of 2 C.

Figure 8

Rate performances of TiO₂@Fe₂O₃, TFCS, TFCM and TFCL at the current densities of 100, 200, 400, 800, and 1600 mA g⁻¹.

Figure 9

Nyquist plots of TiO₂@Fe₂O₃, TFCS, TFCM and TFCL in the frequency range from 1 × 10⁶ to 0.01 Hz. The inset shows the corresponding equivalent circuit.