Hollow ball-flower type niobium pentoxide material as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a hollow ball-flower niobium pentoxide material. The preparation method comprises the following steps: dissolving a niobium source in a mixed solution of ethanol and deionized water; adding a certain amount of urea; carrying out heating reaction on the obtained mixed solution; and cooling, washing, drying and roasting to obtain the catalyst. The prepared hollow ball-flower-shaped niobium pentoxide material is composed of nanosheets with the thickness of about 15 nanometers and is hollow inside, the transmission distance of lithium ions and electrons is shortened, and the internal hollow structure plays a role in buffering the volume change of the niobium pentoxide material in the lithium intercalation and deintercalation process; meanwhile, N doping is realized at a reduction site in the synthesis process, and the conductivity of niobium pentoxide is improved by N doping, so that the niobium pentoxide has excellent electrochemical performance when being used as a lithium ion battery negative electrode material. In addition, the synthesis process is simple, the reaction controllability is high, and large-scale production is easy.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery materials, and specifically relates to a hollow flower ball type niobium pentoxide material for lithium ion battery negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density and working voltage, excellent cycle life and environmental friendliness, and are widely used in various fields of people's lives. The currently widely used graphite carbon materials have poor safety and fast charging performance, and there is an urgent need to develop new high-performance negative electrode materials to replace graphite carbon materials. Niobium pentoxide (Nb2O5) belongs to the shear plane ReO3 structure, which is conducive to the diffusion of lithium ions; its lithium insertion and extraction potential is high (1-2.0 V), which ensures the safety of the battery. Therefore, niobium pentoxide is a high-performance lithium-ion battery negative electrode material with great development prospects, but its defects of low electronic and ionic conductivity limit the performance of its electrochemical performance.

[0003] People improve the electrochemical properties of niobium pentoxide through various ways such as doping, compounding with conductive phase materials or reducing the particle size of materials. Among them, reducing the particle size of materials can shorten the transmission path of lithium ions and electrons, which is a common method to improve the electrochemical properties of niobium pentoxide. So far, people have synthesized nano-scale niobium pentoxide materials with various morphological structures, such as nanoparticles, nanowires, nanosheets, nanorods, etc. In recent years, people have found that the morphological structure of electrode materials has a great influence on their electrochemical properties, especially some electrode materials with special morphological structures show excellent electrochemical properties. Hollow structure electrode materials have a large surface area, which can increase contact with the electrolyte and shorten the transmission distance of lithium ions and electrons; and the hollow structure can also play a slow charging role for the volume change of electrode materials during the insertion / extraction of lithium, which is conducive to maintaining the structural stability of electrode materials. Patent (CN 200910243310.5) discloses a method for preparing hollow niobium pentoxide using niobium oxalate and phosphate as raw materials, and the obtained nano niobium pentoxide hollow spheres are obtained. Zhou et al. synthesized hollow niobium pentoxide microspheres using carbon spheres as templates (W. Zhou, L. Fang, L. Long, et al. Facile preparation of Nb2O5@carbon hollow microspheres as high-performance anode materials for lithium-ion batteries, Journal of Nanoscience and Nanotechnology 19 (2019) 268-217.). Kong et al. synthesized hollow Nb2O5 spheres using the polycondensate of resorcinol and formaldehyde as templates (L. Kong, C. Zhang, J. Wang, et al. Nanoarchitectured Nb2O5 hollow, Nb2O5@carbon and NbO2@carbon core-shell microspheres for ultrahigh-rate intercalation pseudocapacitors, Scientific Reports 6 (2016) 21177.). In the process of preparing the hollow niobium pentoxide material, carbon spheres or the polycondensate of resorcinol and formaldehyde are used as templates. The template needs to be prepared first and then removed. The whole preparation process is relatively complicated.

[0004] Based on this, this application was developed. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a one-step preparation method for hollow flower-ball-type niobium pentoxide material without the need for a template. The hollow flower-ball-type niobium pentoxide material prepared by the method exhibits a hollow flower-ball-type structure composed of a large number of nanosheets, and exhibits excellent electrochemical properties when used as a negative electrode material for lithium-ion batteries.

[0006] The present invention also provides the hollow flower ball type niobium pentoxide material and its application in lithium ion batteries, sodium ion batteries, supercapacitors and the like.

[0007] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a hollow flower ball type niobium pentoxide material, comprising the following steps: a) adding the niobium source to a mixture of ethanol and deionized water under stirring at room temperature, and stirring for 0.1-12 h (preferably 3-12 h); b) adding an appropriate amount of urea to the above solution and continuing stirring for 0.1-24 h (preferably 6-24 h); c) heating the mixed solution obtained in step b) at 60-300°C for reaction for 0.1-60 h. After the reaction is completed, washing and drying the obtained reaction precipitate, and then calcining at 300-900°C for 0.5-30 h to obtain the product.

[0008] Specifically, in step a), the niobium source may be one or both of niobium oxalate and ammonium niobate oxalate hydrate, and the concentration of niobium ions in the solution is 0.001-7 mol / L, preferably 0.2-4 mol / L.

[0009] Specifically, in step a), the volume ratio of ethanol to deionized water is 1:10-30:1.

[0010] Furthermore, in step b), the molar ratio of the niobium source to urea includes but is not limited to 1:1-100, preferably 1:1-70.

[0011] More preferably, in step c), the reaction may be heated at 120-250° C. for 5-60 h. In step c), the calcination may be performed at 400-800° C. for 2-30 h.

[0012] Furthermore, the reaction precipitate obtained in step c) can be washed several times with deionized water and ethanol respectively.

[0013] The present invention provides a hollow flower ball type niobium pentoxide material prepared by the above preparation method. Further, the hollow flower ball type niobium pentoxide material is composed of a large number of niobium pentoxide nanosheets and is hollow inside.

[0014] The present invention provides the application of the hollow flower ball type niobium pentoxide material in the fields of lithium ion batteries, sodium ion batteries, supercapacitors and other energy storage devices.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: 1) The present invention does not require a template and only requires one step of hydrothermal synthesis to prepare the hollow flower-shaped niobium pentoxide material. The synthesis process is simple and suitable for large-scale industrial production.

[0016] 2) The hollow flower-ball-shaped niobium pentoxide material obtained by the present invention is assembled from a large number of niobium pentoxide nanosheets, and the nanosheets can both increase the contact area with the electrolyte and shorten the transmission path of lithium ions and electrons. It has stronger electrochemical reaction kinetics than the hollow structure niobium pentoxide composed of nanoparticles.

[0017] 3) The present invention not only regulates the morphology of niobium pentoxide, but also realizes in-situ doping of N. N doping reduces the band gap of niobium pentoxide and improves its conductivity.

[0018] 4) The hollow flower-shaped niobium pentoxide material prepared by the present invention has excellent electrochemical performance as a negative electrode of a lithium-ion battery: the capacity at a high rate of 20C is 150 mAh / g, and the capacity after 2000 cycles at a rate of 20C is maintained at 125 mAh / g. In addition, the hollow flower-shaped niobium pentoxide material prepared by the present invention can also be used in the fields of supercapacitors and sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the X-ray diffraction pattern of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present application; Figure 2 This is a scanning electron microscope photograph of the hollow flower ball-shaped niobium pentoxide material prepared in Example 1 of the present application; Figure 3 This is a transmission electron microscope photo of the hollow flower ball-shaped niobium pentoxide material prepared in Example 1 of the present invention; Figure 4 The scanning electron microscope image of the hollow flower ball-shaped niobium pentoxide material prepared in Example 1 of the present invention and the corresponding Nb, N and O element distribution diagram; Figure 5 The photoelectron spectrum of the N element of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention; Figure 6 This is the Tauc plot of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention; Figure 7 This is the rate charge-discharge curve of the hollow flower-ball-shaped niobium pentoxide material prepared in Example 1 of the present invention; Figure 8 This is a high-rate long-cycle performance curve of the hollow flower-ball-shaped niobium pentoxide material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0021] In the following examples, all the raw materials used are common commercially available products that can be directly purchased.

[0022] Room temperature refers to 25±5°C.

[0023] Example 1 A method for preparing a hollow flower ball type niobium pentoxide material is as follows: 1) adding niobium oxalate to a mixture of ethanol and deionized water under stirring at room temperature and stirring for 12 hours, wherein the concentration of niobium ions in the solution is 1.35 mol / L, and the volume ratio of ethanol to deionized water is 1:3; 2) adding urea to the above solution, wherein the molar ratio of niobium oxalate to urea in the solution is 1:5, and continuing stirring for 24 hours; 3) heating the mixed solution obtained in step 2) in a constant temperature drying oven at 188° C. for 60 hours; 4) washing the reaction precipitate obtained in step 3) with deionized water and ethanol for several times, respectively, and then drying it in a vacuum drying oven; 5) The powder obtained in step 4) is placed in a muffle furnace and calcined at 700° C. for 10 hours to obtain a hollow flower ball type niobium pentoxide material.

[0024] Example 2 A method for preparing a hollow flower ball type niobium pentoxide material is as follows: 1) adding ammonium niobate oxalate hydrate to a mixture of ethanol and deionized water under stirring at room temperature for 6 hours, wherein the concentration of niobium ions in the solution is 0.86 mol / L, and the volume ratio of ethanol to deionized water is 1:6; 2) adding urea to the above solution, wherein the molar ratio of ammonium niobate oxalate hydrate to urea in the solution is 1:37, and continuing stirring for 18 hours; 3) heating the mixed solution obtained in step 2) in a constant temperature drying oven at 210° C. for 5 hours; 4) washing the reaction precipitate obtained in step 3) with deionized water and ethanol for several times, respectively, and then drying it in a vacuum drying oven; 5) The powder obtained in step 4) is placed in a muffle furnace and calcined at 550° C. for 30 hours to obtain a hollow flower ball type niobium pentoxide material.

[0025] Example 3 A method for preparing a hollow flower ball type niobium pentoxide material is as follows: 1) adding niobium oxalate and ammonium niobate oxalate hydrate in a mass ratio of 1:1 to a mixture of ethanol and deionized water under stirring at room temperature, and stirring for 12 hours, wherein the concentration of niobium ions in the solution is 2.02 mol / L, and the volume ratio of ethanol to deionized water is 2:1; 2) adding urea to the above solution, wherein the molar ratio of the niobium salt source to urea in the solution is 1:62, and continuing stirring for 6 hours; 3) heating the mixed solution obtained in step 2) in a constant temperature drying oven at 200° C. for 20 hours; 4) washing the reaction precipitate obtained in step 3) with deionized water and ethanol for several times, respectively, and then drying it in a vacuum drying oven; 5) The powder obtained in step 4) is placed in a muffle furnace and calcined at 680° C. for 20 hours to obtain a hollow flower ball type niobium pentoxide material.

[0026] Example 4 A method for preparing a hollow flower ball type niobium pentoxide material is as follows: 1) adding ammonium niobate oxalate hydrate to a mixture of ethanol and deionized water under stirring at room temperature and stirring for 10 hours, wherein the concentration of niobium ions in the solution is 3.52 mol / L, and the volume ratio of ethanol to deionized water is 3:1; 2) adding urea to the above solution, wherein the molar ratio of ammonium niobate oxalate hydrate to urea in the solution is 1:12, and continuing stirring for 6 hours; 3) heating the mixed solution obtained in step 2) in a constant temperature drying oven at 205° C. for 24 hours; 4) washing the reaction precipitate obtained in step 3) with deionized water and ethanol for several times, respectively, and then drying it in a vacuum drying oven; 5) The powder obtained in step 4) is placed in a muffle furnace and calcined at 500° C. for 30 hours to obtain a hollow flower ball type niobium pentoxide material.

[0027] Example 5 A method for preparing a hollow flower ball type niobium pentoxide material is as follows: 1) adding niobium oxalate to a mixture of ethanol and deionized water under stirring at room temperature for 3 hours, wherein the concentration of niobium ions in the solution is 0.26 mol / L, and the volume ratio of ethanol to deionized water is 1:10; 2) adding urea to the above solution, wherein the molar ratio of niobium oxalate to urea in the solution is 1:2, and continuing stirring for 6 hours; 3) heating the mixed solution obtained in step 2) in a constant temperature drying oven at 175° C. for 12 hours; 4) washing the reaction precipitate obtained in step 3) with deionized water and ethanol for several times respectively, and then drying it in a vacuum drying oven; 5) The powder obtained in step 4) is placed in a muffle furnace and calcined at 765° C. for 2 hours to obtain a hollow flower ball type niobium pentoxide material.

[0028] Related test data Figure 1 This is the X-ray diffraction pattern of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present application. Figure 1 As shown, the diffraction peaks of the sample are in good agreement with the standard diffraction peaks of orthorhombic phase Nb2O5 in the PDF card, indicating that the synthesized sample is a relatively pure orthorhombic phase niobium pentoxide material.

[0029] Figure 2 This is a scanning electron microscope photo of the hollow flower ball-shaped niobium pentoxide material prepared in Example 1 of the present application. Figure 2 As shown, the sample presents a regular flower-shaped structure composed of nanosheets and is hollow inside.

[0030] Figure 3 This is a transmission electron microscope photo of the hollow flower ball-shaped niobium pentoxide material prepared in Example 1 of the present invention. Figure 3 As shown, the transmission electron microscopy image further proves that the sample has a hollow flower ball morphology, and the thickness of the nanosheets that make up the hollow flower ball is about 15 nanometers.

[0031] Figure 4 The SEM image of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention and the corresponding distribution of Nb, N and O elements are shown. Figure 4 As shown, Nb, O and N elements are evenly distributed in the sample, further proving that the prepared material is N-doped hollow flower-ball type niobium pentoxide material.

[0032] Figure 5 This is the photoelectron spectrum of the N element of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention. Figure 5 The XPS graph of N shown in the figure shows that there is a N-Nb bond (395.08 eV) in the sample, indicating that N replaces part of the oxygen and is doped into the crystal lattice of the flower-shaped niobium pentoxide material.

[0033] Figure 6 This is the Tauc plot of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention. Figure 6As shown, the band gap value of the prepared hollow flower-shaped niobium pentoxide material (N-Nb2O5) is 2.92 eV, which is smaller than the band gap value of pure Nb2O5 (3.14 eV), indicating that N doping can enhance the electrical conductivity of Nb2O5.

[0034] The prepared hollow flower ball type niobium pentoxide material, carbon black and polyvinylidene fluoride were ground and mixed in a mass ratio of 7:2:1, and a certain amount of N-methylpyrrolidone was added and stirred for 6 hours to prepare a uniform slurry. The prepared slurry was evenly coated on the copper foil with a coater and baked in a vacuum drying oven at 120 °C for 12 hours. The baked pole piece was punched into a φ12 mm disc with a punching machine and compacted with a pressure of 6-8 MPa. In a glove box filled with argon, a CR2025 button cell was assembled with a metal lithium sheet as the counter electrode, a polypropylene fiber as the diaphragm, and 1 mol L-1 LiPF6 / EC+DMC (volume ratio 1:1) as the electrolyte. The assembled battery was first left to stand for 12 h, and then the electrochemical performance was tested on the battery test system.

[0035] Figure 7 This is the rate charge-discharge curve of the hollow flower-shaped niobium pentoxide material prepared in Example 1 of the present invention. Figure 7 As shown, the hollow flower ball-shaped niobium pentoxide material has excellent rate performance as a negative electrode material for lithium-ion batteries, with a capacity of 150 mAh / g at a high rate of 20C.

[0036] Figure 8 This is the high rate long cycle performance curve of the hollow flower ball type niobium pentoxide material prepared in Example 1 of the present invention. Figure 8 As shown, the capacity of the hollow flower ball-shaped niobium pentoxide material as a negative electrode material for lithium-ion batteries remains at 125 mAh / g after 2000 cycles at a 20C rate.

[0037] Under the same conditions, the electrochemical properties of the hollow flower ball type niobium pentoxide materials prepared in Examples 2 to 5 as negative electrode materials for lithium ion batteries were tested. The results showed that the prepared hollow flower ball type niobium pentoxide materials had electrochemical properties comparable to those of Example 1.

[0038] In summary, the hollow flower-ball-shaped niobium pentoxide material prepared by the present invention is composed of nanosheets with a thickness of about 15 nanometers and is hollow inside, which not only shortens the transmission distance of lithium ions and electrons, but also the internal hollow structure plays a buffering role in the volume change of the niobium pentoxide material during the lithium insertion and extraction process; at the same time, N doping is achieved at the reduction site during the synthesis process, and N doping greatly improves the conductivity of niobium pentoxide, and exhibits excellent electrochemical properties as a negative electrode material for lithium ion batteries.

[0039] Although the preferred embodiments of the present invention have been shown and described above, the applicant would like to emphasize and illustrate that: for those skilled in the art, it can be understood that various changes, modifications, substitutions and variations of these embodiments without departing from the principle and spirit of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow flower ball type niobium pentoxide material, characterized in that: The following steps are involved: a) adding the niobium source to a mixture of ethanol and deionized water under stirring at room temperature for 0.1-12 h; b) Add appropriate amount of urea to the above solution and continue stirring for 0.1-24 h; c) heating the mixed solution obtained in step b) at 60-300°C for reaction for 0.1-60 h. After the reaction is completed, washing and drying the obtained reaction precipitate, and then calcining at 300-900°C for 0.5-30 h to obtain the product.

2. The method for preparing the hollow flower ball type niobium pentoxide material according to claim 1, characterized in that: In the step a), the niobium source is one or both of niobium oxalate and ammonium niobate oxalate hydrate, and the concentration of niobium ions in the solution is 0.001-7 mol / L.

3. The method for preparing the hollow flower ball type niobium pentoxide material according to claim 1, characterized in that: In step a), the volume ratio of ethanol to deionized water is 1:10-30:

1.

4. The method for preparing the hollow flower ball type niobium pentoxide material according to claim 1, characterized in that: In the step b), the molar ratio of the niobium source to urea is 1:1-100.

5. The method for preparing the hollow flower ball type niobium pentoxide material as claimed in claim 1, characterized in that: In the step c), the reaction is heated at 120-250° C. for 5-60 h.

6. The method for preparing the hollow flower ball type niobium pentoxide material according to claim 1, characterized in that: In the step c), the calcination is carried out at 400-800° C. for 2-30 h.

7. The method for preparing the hollow flower ball type niobium pentoxide material as claimed in claim 1, characterized in that: The reaction precipitate obtained in step c) is washed several times with deionized water and ethanol respectively.

8. A hollow flower ball type niobium pentoxide material prepared by the preparation method according to any one of claims 1 to 7.

9. The hollow flower ball type niobium pentoxide material according to claim 8, characterized in that: The hollow flower ball type niobium pentoxide material is composed of a large number of Nb2O5 nanosheets and is hollow inside.

10. Application of the hollow flower ball type niobium pentoxide material according to claim 8 in lithium ion batteries, sodium ion batteries and supercapacitors.

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