An oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material and a preparation method thereof

Abstract

The application discloses an oxygen vacancy and nitrogen doped TiO2(001) / Ti3C2 composite material which can be used as a negative electrode material of a sodium ion battery. The preparation of the composite material comprises the following steps: (1) preparing a TiO2(001) product; (2) preparing an oxygen vacancy and nitrogen doped TiO2(001) product through a hydrothermal method; and (3) preparing an oxygen vacancy and nitrogen doped TiO2(001) / Ti3C2 composite material through an ultrasonic dispersion method. The application aims to overcome the low electronic conductivity and slow sodium ion diffusion rate of TiO2, and proposes a hybrid point defect (HPD) engineering to synthesize an oxygen vacancy (OVs) and N doped (OVs-N-TiO2) strategy, introduces oxygen vacancies and nitrogen doping modification into TiO2(001), and simultaneously, with the performance advantages of Ti3C2, composites OVs-N-TiO2(001) and Ti3C2 to prepare an oxygen vacancy and nitrogen doped TiO2(001) / Ti3C2 composite material (OVs-N-TiO2(001) / Ti3C2), so as to overcome the poor conductivity and other problems, and thus improve the electrochemical performance of the material as a negative electrode material of a sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery anode material preparation technology, specifically relating to an oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material that can be used as a sodium-ion battery anode material and its preparation method. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used due to their superior electrochemical performance. However, numerous problems have also emerged in their applications, such as limited lithium resources and high costs, forcing the development of alternative energy storage systems. Sodium-ion batteries share similar working principles with lithium-ion batteries, and given the abundance and low cost of sodium resources, their research and application have become a hot topic. Studies have shown that sodium-ion batteries, as a novel secondary chemical power source, possess advantages such as abundant resources, low cost, high energy conversion efficiency, long cycle life, high safety, excellent high and low temperature performance, high rate charge and discharge performance, and low maintenance costs. They hold promise for complementing lithium-ion batteries in large-scale electrochemical energy storage.

[0003] Although sodium-ion batteries are considered a potential alternative to lithium-ion batteries, the slow reaction kinetics and low specific capacity of the anode materials are major challenges. Titanium dioxide (TiO2) is favored due to its low cost, good cycle stability, and high theoretical capacity (335 mAh·g). -1 Anatase, rutile, and TiO2(B) (bronze), whether in bulk or nanostructure form, have been extensively studied due to their advantages such as near-zero strain during charging and discharging. They are considered promising anode materials for sodium-ion batteries (SIBs). However, TiO2 has low electronic conductivity (~10⁻¹² S·cm). -1 ), and Na + The slow diffusion rate in TiO2 severely limits its practical applications.

[0004] Point defect engineering (vacancy and heteroatom doping) in compounds is a common method for modulating the electronic structure and chemical properties of compounds due to lattice distortion and electron redistribution, and has been widely used to improve the kinetic behavior and performance of electrode materials. Oxygen vacancies (OVs), as common crystal defects, can modulate the surface properties and electronic structure of titanium dioxide, thereby improving its photoelectric and catalytic properties. The presence of oxygen vacancies in titanium dioxide alters its electronic energy levels, leading to changes in its light absorption wavelength range. For example, introducing oxygen vacancies (OVs) into TiO2 can reduce the band gap and increase the density of states (DOS), thereby improving its conductivity and kinetics. Doping TiO2 with other heteroatoms (such as N, S, and F) has similar effects. For instance, a self-supporting nanotube array of sulfur-doped TiO2 based on metal was prepared using electrochemical anodic oxidation and sulfidation. This TiO2 nanotube array, used as an anode for sodium storage, exhibited ultra-stable cycling performance, maintaining 167 mAh·g after 4400 cycles. -1 The capacity retention rate is 91%. Although methods for regulating TiO2 through vacancy defects and heteroatom doping have been extensively studied, there are still some problems in controlling single-point defects of vacancy or heteroatom doping. Furthermore, the content of foreign heteroatom doping is usually low, making it difficult to integrate into a stable TiO2 crystal structure. This patent addresses the problems of low conductivity and slow Na+ diffusion rate in TiO2 by introducing oxygen vacancies, which, under oxygen vacancy induction, is more conducive to nitrogen atom doping. Simultaneously, it forms a mixed defect of oxygen vacancies and nitrogen atom doping to solve these problems. Then, by combining with the layered Ti3C2 structure, the electrochemical performance of TiO2 is further improved. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to overcome the shortcomings of low electronic conductivity and slow sodium ion diffusion rate of TiO2. A mixed point defect (HPD) engineering strategy is proposed to synthesize oxygen vacancies (OVs) and nitrogen doping (OVs-N-TiO2). Oxygen vacancies and nitrogen doping modification are introduced into TiO2(001). At the same time, taking advantage of the performance advantages of Ti3C2, OVs-N-TiO2(001) is combined with Ti3C2 to prepare oxygen vacancy nitrogen doped TiO2(001) / Ti3C2 composite material (OVs-N-TiO2(001) / Ti3C2) to overcome its poor conductivity and other problems, thereby improving its electrochemical performance as a sodium-ion battery anode material.

[0006] To achieve the above-mentioned objectives, the following technical solution is proposed:

[0007] An oxygen-vacancy-nitrogen-doped TiO2(001) / Ti3C2 composite material suitable as a negative electrode material for sodium-ion batteries is disclosed. This composite material consists of oxygen-vacancy-nitrogen-doped modified TiO2(001) and Ti3C2, and has a specific surface area of ​​69.421 m². 2 ·g -1 The average pore size is 15.585 nm.

[0008] A method for preparing an oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material that can be used as a negative electrode material for sodium-ion batteries includes the following steps:

[0009] 1. Preparation of TiO2(001)

[0010] 5 mL of tetrabutyl titanate (Ti(OBu)4) was placed in a 50 mL beaker, and 0.6 mL of 47% HF solution (a crystal facet control agent) was added. The resulting mixture was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180 °C for 24 h. After the reaction was completed, the apparatus was allowed to cool naturally to room temperature before being removed. The mixture was then subjected to a rotation speed of 4000 r·min. -1 Centrifuge for 6 min, remove the supernatant, add distilled water to wash, centrifuge, repeat 5-6 times until the supernatant is neutral (pH=6-7), transfer to a vacuum drying oven and dry at 60℃ for 12 h to obtain white powder TiO2(001) product.

[0011] 2. Preparation method of oxygen-vacancy nitrogen-doped TiO2(001)

[0012] 7.8 mL of tetrabutyl titanate (Ti(OBu)4) was placed in a 100 mL beaker, and 0.6 mL of HF solution (crystal facet control agent) was added. Then, 68 mL of ammonia water (oxygen vacancy generating reducing agent and nitrogen source) was added to the mixture. The mixture was magnetically stirred for 2 h. The mixture was then transferred to a polytetrafluoroethylene reactor and placed in an oven for hydrothermal reaction at 150 ℃ for 24 h. After the reaction was completed, the apparatus was allowed to cool naturally to room temperature and then removed. The solution was centrifuged at 4000 r·min⁻¹ for 6 min, and the supernatant was removed. Distilled water was added for washing, and the mixture was centrifuged. This process was repeated 5-6 times until the supernatant was neutral (pH=6-7). The supernatant was then placed in a vacuum drying oven and dried at 60 ℃ for 12 h to obtain a white powder oxygen vacancy nitrogen-doped TiO₂(001) product (denoted as OVs-N-TiO₂(001)).

[0013] 3. Preparation method of oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material

[0014] Weigh 0.4 g of OVs-N-TiO2(001) and 0.2 g of Ti3C2, and disperse them separately in 20 mL of ethanol solution. First, ultrasonically disperse for 1 h, then magnetically stir for 1 h. Finally, mix the two solutions and continue magnetically stirring for 5 h. After stirring, filter the resulting mixture and wash it 5-6 times with anhydrous ethanol. Place the resulting precipitate in a vacuum drying oven and dry it at 60 ℃ for 12 h to obtain a black powder sample (denoted as OVs-N-TiO2(001) / Ti3C2).

[0015] Compared with existing TiO2 modifications, this invention has the following features: (1) It proposes a mixed point defect (HPD) engineering method to synthesize oxygen vacancy (OVs) and N doping (OVs-N-TiO2) TiO2 materials, and introduces oxygen vacancy and N atom doping into TiO2 to alleviate the insufficiency of single-point defect control; oxygen vacancy can enhance the delocalization of Ti's 3d orbitals, reducing the band gap, while N atom doping can introduce N 2p states slightly above the valence band, forming a doping level, shifting the Fermi level to the conduction band, and improving electronic conductivity. (2) Ti3C2 has high conductivity comparable to metals, and Na + The diffusion barrier is very low, which means that the sodium ion diffusion rate is very high. In order to further improve the specific capacity, rate performance and cycle performance of oxygen vacancy (OVs) and N doping (OVs-N-TiO2) TiO2, the OVs-N-TiO2(001) is combined with Ti3C2 to prepare OVs-N-TiO2(001) / Ti3C2 composite material by taking advantage of the performance advantages of Ti3C2. Attached Figure Description

[0016] Figure 1(ac) and Figure 1(d) are TEM and HRTEM images of the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material in the embodiments of the present invention.

[0017] Figure 2 The adsorption-desorption curves are shown for the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material in the embodiments of the present invention.

[0018] Figure 3 (a) and Figure 3 (b) shows the cycling performance of the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material in the embodiments of the present invention under different current densities.

[0019] Figure 4 This is a rate performance diagram of the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material in an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] A method for preparing an oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material that can be used as a negative electrode material for sodium-ion batteries includes the following steps:

[0022] 1. Preparation of TiO2(001)

[0023] 5 mL of tetrabutyl titanate (Ti(OBu)4) was placed in a 50 mL beaker, and 0.6 mL of 47% HF solution was added. The resulting mixture was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180 °C for 24 h. After the reaction was completed, the apparatus was allowed to cool naturally to room temperature before being removed. The mixture was then subjected to a rotation speed of 4000 r·min. -1 Centrifuge for 6 min, remove the supernatant, add distilled water for washing, centrifuge, repeat 5 times until the supernatant is neutral (pH = 6), transfer to a vacuum drying oven and dry at 60℃ for 12 h to obtain white powder TiO2(001) product.

[0024] 2. Preparation method of oxygen-vacancy nitrogen-doped TiO2(001)

[0025] 7.8 mL of tetrabutyl titanate (Ti(OBu)4) was placed in a 100 mL beaker, and 0.6 mL of 47% HF solution was added. Then, 68 mL of 28% ammonia solution was added to the mixture. The mixture was magnetically stirred for 2 h. The mixture was then transferred to a polytetrafluoroethylene reactor and placed in an oven for hydrothermal reaction at 150 °C for 24 h. After the reaction was completed, the apparatus was allowed to cool naturally to room temperature (25 °C) before being removed. The solution was centrifuged at 4000 r·min⁻¹ for 6 min, and the supernatant was removed. Distilled water was added for washing, and the mixture was centrifuged. This process was repeated 5 times until the supernatant was neutral (pH=6). The supernatant was then dried in a vacuum drying oven at 60 °C for 12 h to obtain a white powder oxygen-vacancy nitrogen-doped TiO₂(001) product (denoted as OVs-N-TiO₂(001)).

[0026] 3. Preparation method of oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material

[0027] Weigh 0.4 g of OVs-N-TiO2(001) and 0.2 g of Ti3C2, and disperse them separately in 20 mL of ethanol solution. First, ultrasonically disperse for 1 h, then magnetically stir for 1 h, and finally mix the two solutions and continue to magnetically stir for 5 h. After stirring, filter the resulting mixture and wash it 5 times with anhydrous ethanol. Place the resulting precipitate in a vacuum drying oven and dry it at 60 ℃ for 12 h to obtain a black powder sample (denoted as OVs-N-TiO2(001) / Ti3C2).

[0028] The morphology characterization results of the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material are shown in Figures 1(a) and 1(b). Figure 1 (a) A large number of particles can be observed attached to the layered Ti3C2. After magnification, it can be observed that the attached particles are plate-like structures. Figure 1 (b) indicates that the particulate matter is OVs-N-TiO2(001) material. (See attached image) Figure 1 (c) is Ti3C2 material. HRTEM test can reveal clear and uniform lattice stripes with a spacing of 0.235 nm, proving that the material attached to the Ti3C2 surface is OVs-N-TiO2(001) material. This further confirms that the OVs-N-TiO2(001) / Ti3C2 composite material was successfully prepared.

[0029] The adsorption-desorption curve test results of the oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material are attached. Figure 2 From the appendix Figure 2 It can be seen that the specific surface area of ​​the OVs-N-TiO2(001) / Ti3C2 sample is 69.421 m². 2 g -1 The average pore size measured by the BJH method was 20.240 nm. Compared with OVs-N-TiO2(001), the specific surface area of ​​the composite was reduced, which may be because the titanium dioxide nanosheets adhered to the titanium carbide surface to form a layered structure. Although the specific surface area was slightly reduced, the formed layered structure is more conducive to cycling stability. The reduction in specific surface area, on the other hand, proves that the titanium dioxide nanosheets were successfully attached to the surface of titanium carbide, and the preparation of the composite material was successful.

[0030] The cycling test results of the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material are shown in the appendix. Figure 3 From the appendix Figure 3 (a) It can be seen that the initial discharge specific capacity of TiO2(001) material is 205 mAh·g. -1 , at 0.1 A·g -1After 100 cycles at the current density, the capacity retention rate was 35.6%, and the initial discharge specific capacity of the OVs-N-TiO2(001) material was 219 mAh·g. -1 At 0.1 A·g -1 After 100 cycles at current density, the capacity retention rate was 46%, and the initial discharge specific capacity of the OVs-N-TiO2(001) / Ti3C2 composite material was 230 mAh·g. -1 After 100 cycles, the capacity retention rate was 58%. (See attached image) Figure 3 (b) TiO2(001) material, OVs-N-TiO2(001) material and OVs-N-TiO2(001) / Ti3C2 composite material at 1 A·g -1 The cycling performance curves after 400 cycles at the current density are shown in the attached figure. As can be seen from the figure, compared with TiO2(001) and OVs-N-TiO2(001) materials, the discharge specific capacity, cycling stability and capacity retention of the OVs-N-TiO2(001) / Ti3C2 composite material are significantly improved. This may be because the introduction of N element and oxygen vacancies allows the 2p state of N atoms to mix with the 2p state of O atoms, which helps to narrow the band gap of TiO2(001) and increase the density of states (DOS), thereby improving electronic conductivity and charge transport. On the other hand, due to the addition of Ti3C2, OVs-N-TiO2(001) particles are adsorbed on the surface and interlayer of Ti3C2. Ti3C2 provides channels for ion transport and shortens the ion / electron path. Moreover, the Ti3C2 composite can promote the diffusion rate of sodium ions and alleviate the problem of OVs-N-TiO2(001) agglomeration to a certain extent, thereby improving the overall electrochemical performance.

[0031] The rate performance test results of the oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material are attached. Figure 4 From the appendix Figure 4 It can be seen that the capacity of the three materials gradually decreases with increasing discharge rate. However, the discharge specific capacity of the OVs-N-TiO2(001) / Ti3C2 composite material is significantly higher than that of TiO2(001) and OVs-N-TiO2(001) materials. (The data is presented at discharge rates of 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 A·g.) -1 At that time, the initial capacities of the OVs-N-TiO2(001) / Ti3C2 composite material were 240, 163, 145, 120, 102, and 89 mAh·g, respectively. -1 And the multiplier returned to 0.2 A·g -1 It can still maintain the initial discharge specific capacity (145 mAh·g) -1The OVs-N-TiO2(001) exhibited superior electrochemical performance. Further evidence confirmed that the appropriate addition of Ti3C2 improved the discharge specific capacity and cycle stability of OVs-N-TiO2(001).

Claims

1. A sodium-ion battery anode material, characterized in that: The negative electrode material is an oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material with a specific surface area of ​​69.421 m². 2 ·g -1 The average pore size is 15.585 nm; the oxygen-vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material is prepared by the following steps: (1) Preparation of oxygen vacancy nitrogen-doped TiO2(001): 7.8 mL of tetrabutyl titanate was placed in a 100 mL beaker, 0.6 mL of 47% HF solution was added, and 68 mL of 28% ammonia water was added to the mixture. The mixture was magnetically stirred for 2 h. The mixture was then transferred to a polytetrafluoroethylene reactor and placed in an oven. The mixture was hydrothermally reacted at 150 °C for 24 h. After the reaction was completed, the apparatus was allowed to cool naturally to room temperature and then removed. The solution was centrifuged at 4000 r·min-1 for 6 min. The supernatant was removed, and distilled water was added for washing. The mixture was centrifuged and repeated 5-6 times until the supernatant was pH=6-7. The mixture was then placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a white powder oxygen vacancy nitrogen-doped TiO2(001) product. (2) Preparation of oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material: Weigh 0.4 g of oxygen vacancy nitrogen-doped TiO2(001) and 0.2 g of Ti3C2, disperse them in 20 mL of ethanol solution respectively, first ultrasonically disperse for 1 h, then magnetically stir for 1 h, finally mix the two solutions, and continue to magnetically stir for 5 h. After stirring, filter the resulting mixture and wash it 5 times with anhydrous ethanol. Place the obtained precipitate in a vacuum drying oven and dry it at 60 ℃ for 12 h to obtain black powder sample oxygen vacancy nitrogen-doped TiO2(001) / Ti3C2 composite material product.

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