Ordered alternating symbiotic crystal structure niobium tungsten oxide and its preparation method and application

Abstract

The present invention provides a method for preparing niobium-tungsten oxide with an ordered alternating intergrowth crystal structure. A niobium source and a tungsten source are dissolved in a mixed solution of ethanol and deionized water, and the pH is adjusted to 2-3. An organic polymer is added to form a gel solution, and then the gel-calcination method is used to prepare the niobium-tungsten oxide with an ordered alternating intergrowth crystal structure. Using niobium and tungsten as the metal source, the present invention prepares a unique ordered alternating intergrowth crystal structure of niobium-tungsten oxide through high-temperature gel calcination. This structure is stable and significantly improves the material's comprehensive electrochemical properties, including specific capacity, cycle rate, and long cycle life. The material demonstrates ultra-high-rate long-cycle performance of 20,000 cycles at a current density of 100C.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and in particular to a niobium-tungsten oxide with an ordered alternating symbiotic crystal structure, a preparation method thereof, and applications thereof. Background Art

[0002] The booming development of the new energy market has established the important market position of lithium-ion batteries. In order to better meet market needs and promote the upgrading of new energy storage equipment, energy storage efficiency must be further improved. However, the lithium ion transmission rate of graphite materials used as negative electrodes is low. Under high-rate conditions, the working potential of about 0.1V can easily lead to electrolyte decomposition, forming lithium dendrites and unstable solid electrolyte membranes, and even causing safety issues such as short circuits, fires, and thermal runaway. This greatly limits the application of graphite negative electrodes in the field of fast-charging lithium batteries. For this reason, fast-charging lithium batteries are one of the current research hotspots.

[0003] To achieve fast charging standards while maintaining the existing material system, optimizing process conditions and charging strategies can improve charging efficiency, performance, and effectively extend battery life. However, fundamentally, the essence of fast energy storage lies in the rapid transfer of ions and electrons within the electrodes. Therefore, improving ion diffusion and electron conductivity is key to successfully achieving the goal of fast battery charging.

[0004] Based on the intrinsic structural characteristics and physicochemical properties of negative electrode materials, various optimization strategies can be adopted to improve their fast charging capabilities. For example, nanostructures and porous frameworks can be constructed to shorten the ion migration path; array structures can be constructed to promote rapid contact between ions and the intercalation layer, leading to rapid lithium insertion; and composite conductive additives or the introduction of defects can compensate for the poor conductivity of the material itself. However, despite these modification strategies, most electrode materials lack substantial improvement in ionic / electronic conductivity, making it difficult to achieve good rapid lithium storage capabilities.

[0005] The study found that the crystal structure of materials with fast charging potential can all be attributed to deformation of the original ReO3 shear crystal structure, that is, the appropriate crystal structure is the essential reason for fast charging. At the same time, compared with non-phase change materials, phase change materials are not suitable for high current charging.

[0006] Therefore, there is an urgent need for a simple preparation method to construct a crystal structure that can achieve fast charging of lithium batteries, which is of great significance for the development of the next generation of new energy technologies. Summary of the Invention

[0007] In order to solve the problems existing in the background technology, the present invention provides an ordered alternating symbiotic crystal structure niobium tungsten oxide and a preparation method thereof. The method is simple and efficient. The prepared material has an ordered alternating symbiotic crystal structure, has fast charging potential, and has excellent electrochemical properties.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] In the first aspect, the present invention provides a method for preparing niobium tungsten oxide with an ordered alternating symbiotic crystal structure, comprising dissolving a niobium source and a tungsten source in a mixed solution of ethanol and deionized water, adjusting the pH value to 2-3, adding an organic polymer to form a gel solution, and then adopting a gel calcination method to prepare the niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0010] Furthermore, the specific steps of the gel calcination method are: drying the gel solution to obtain a gel, pre-calcining the gel to obtain a precursor, first keeping the precursor at 750-850°C for 6-8h, and then keeping it at 950-1050°C for 12-13h to obtain the ordered alternating symbiotic crystal structure niobium tungsten oxide.

[0011] The insulation condition of 750-850℃ can improve the diffusion coefficient of atoms, promote the diffusion of ions and defects and other material transfer processes, and the insulation condition of 950-1050℃ can ensure the generation of the required crystal structure.

[0012] Furthermore, during the high-temperature calcination process, the temperature is first increased to 750-850° C. at a heating rate of 4.5-5.5° C. / min, and then increased to 950-1050° C. at a heating rate of 1.5-2.5° C. / min.

[0013] A heating rate of 1.5 to 2.5°C / min can provide sufficient reaction time, which is beneficial to the growth of the crystal structure.

[0014] Furthermore, the pre-firing temperature is 340-360° C., and the pre-firing time is 3 h to 4 h.

[0015] Furthermore, the organic high molecular polymer is one of polyvinyl pyrrolidone, polyvinyl alcohol or polyacrylonitrile.

[0016] Furthermore, the mass ratio of the niobium source to the tungsten source is 3:0.3-0.4, the amount of the niobium source added to each mL of the ethanol-deionized water mixed solution is 0.06-0.15 g, the amount of the organic high molecular polymer added to each mL of the ethanol-deionized water mixed solution is 0.075-0.125 g, and the mass ratio of ethanol to deionized water is 1:0.2-5.

[0017] Furthermore, the niobium source is one of niobium oxalate, ammonium niobate or niobium pentachloride, and the tungsten source is ammonium metatungstate or tungsten hexachloride.

[0018] Furthermore, an organic monobasic acid is used to adjust the pH to 2-3.

[0019] Furthermore, the organic monobasic acid is oxalic acid, acetic acid or citric acid.

[0020] In a second aspect, the present invention provides niobium-tungsten oxide having an ordered alternating intergrown crystal structure prepared by the above method.

[0021] In a third aspect, the present invention provides the use of the above-mentioned ordered alternating symbiotic crystal structure niobium tungsten oxide in the preparation of lithium battery negative electrodes.

[0022] The beneficial effects of the present invention are:

[0023] 1) The present invention uses niobium tungsten as the metal source and prepares a unique ordered alternating symbiotic crystal structure of niobium tungsten oxide by high-temperature calcination of gel. This structure exists stably and is accompanied by an orderly distributed internal stress, which can alleviate the Li + The volume deformation during the insertion and removal process improves the battery life; the structure has a wider Li + Diffusion channel, lower Li + The diffusion barrier, stronger Li-O binding energy and smaller band gap construct a three-dimensional efficient ion / electron transmission path, improve the electrochemical reaction kinetics, and greatly enhance the comprehensive electrochemical performance of the material, such as specific capacity, cycle rate and long cycle life, demonstrating an ultra-high rate long cycle performance of 20,000 cycles at a current density of 100C.

[0024] 2) The sol-calcination method used in the present invention has simple process conditions, loose preparation conditions, and can be completed by heating under natural conditions such as air, avoiding harsh conditions such as inert atmosphere, high voltage, high current, and violent combustion. The single synthesis amount far exceeds the current existing technologies (such as combustion method, electrospinning, etc.), and has great economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is the XRD pattern of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0027] Figure 2 This is a PDF diagram of the ordered alternating intergrown crystal structure of niobium tungsten oxide prepared in Example 1 of the present invention;

[0028] Figure 3 This is a STEM image of the ordered alternating intergrown crystal structure of niobium tungsten oxide prepared in Example 1 of the present invention;

[0029] Figure 4SAED pattern of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0030] Figure 5 This is a GPA diagram of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0031] Figure 6 This is an EDS image of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0032] Figure 7 This is the GITT diagram of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0033] Figure 8 This is a UV-vis Tauc curve of the ordered alternating intergrown crystal structure niobium tungsten oxide prepared in Example 1 of the present invention;

[0034] Figure 9 This is the electrochemical long cycle diagram of the ordered alternating symbiotic crystal structure niobium tungsten oxide prepared in Example 1 of the present invention at a current density of 100C. DETAILED DESCRIPTION

[0035] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0036] Lithium-ion battery anode materials have poor fast-charging performance. Traditional niobium-tungsten oxide has a single, deformed original ReO3-type shear crystal structure, but has the potential to be used as a lithium-ion battery anode material for fast charging. The inventors used tungsten and niobium as metal sources and prepared niobium-tungsten oxide with an ordered alternating intergrowth crystal structure through high-temperature calcination. As a lithium-ion battery anode material, the electrochemical performance has been greatly improved. The technical solution is as follows:

[0037] The present invention provides a method for preparing niobium tungsten oxide with an ordered alternating intergrowth crystal structure. A niobium source and a tungsten source are dissolved in a mixed solution of ethanol and deionized water, and the pH value is adjusted to 2-3. An organic high molecular polymer is added to form a gel solution, and then a gel calcination method is used to prepare the niobium tungsten oxide with an ordered alternating intergrowth crystal structure.

[0038] Preferably, the specific steps of the gel calcination method are: drying the gel solution to obtain a gel, pre-calcining the gel to obtain a precursor, first keeping the precursor at 750-850°C for 6-8h, and then keeping it at 950-1050°C for 12-13h to obtain the ordered alternating symbiotic crystal structure niobium tungsten oxide.

[0039] Preferably, during the high-temperature calcination process, the temperature is first increased to 750-850° C. at a heating rate of 4.5-5.5° C. / min, and then increased to 950-1050° C. at a heating rate of 1.5-2.5° C. / min.

[0040] Preferably, the pre-calcination temperature is 340-360° C., and the pre-calcination time is 3-4 hours.

[0041] In some preferred embodiments, the heating rate of the pre-firing is 4.5-5.5° C. / min.

[0042] Preferably, the organic polymer can form a gel system using existing materials in the gel calcination method. In some preferred embodiments, the organic polymer is polyvinyl pyrrolidone, polyvinyl alcohol or polyacrylonitrile. After adding the organic polymer, stirring is continued until the organic polymer is completely dissolved to obtain a gel solution; in some preferred embodiments, the stirring speed is between 400 r / min and 500 r / min, and the stirring time is between 12 and 18 hours.

[0043] Preferably, the drying conditions are: drying temperature is 120° C. to 180° C., and drying time is 12 to 18 hours.

[0044] Preferably, the mass ratio of the niobium source to the tungsten source is 3:0.3-0.4.

[0045] Preferably, the amount of niobium source added to each mL of ethanol-deionized water mixed solution is 0.06-0.15 g, the amount of organic high molecular polymer added to each mL of ethanol-deionized water mixed solution is 0.075-0.125 g, and the mass ratio of ethanol to deionized water is 1:0.2-5.

[0046] In some preferred embodiments, the niobium source is one of niobium oxalate, ammonium niobate or niobium pentachloride, and the tungsten source is ammonium metatungstate or tungsten hexachloride.

[0047] An organic monoacid is used to adjust the pH value of the solution. In some preferred embodiments, the organic monoacid is oxalic acid, acetic acid or citric acid.

[0048] The following are specific examples.

[0049] Example 1

[0050] 1. Dissolve 3g of niobium pentachloride and 0.4g of ammonium metatungstate in 30ml of a mixed solution of ethanol and deionized water containing 1g of oxalic acid, with the ratio of ethanol to deionized water being 1:5. After complete dissolution, a colorless and transparent metal mixture is obtained;

[0051] 2. Add 2.5 g of polyvinylpyrrolidone (PVP) to the above metal mixture and stir at 400 r / min for 12 h to obtain a transparent gel solution;

[0052] 3. The gel solution was placed in an oven at 180°C for 12 hours and then transferred to a muffle furnace for pre-calcination for 3 hours. The muffle furnace was heated from room temperature to 350°C at a heating rate of 5°C / min to obtain a precursor;

[0053] 4. The cooled precursor was placed back into the muffle furnace, heated to 800°C at a heating rate of 5°C / min and kept at that temperature for 6 hours, then heated to 1000°C at a heating rate of 2°C / min and kept at that temperature for 12 hours, and then naturally cooled to room temperature to obtain niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0054] The ordered alternating intergrowth crystal structure niobium tungsten oxide prepared in Example 1 was characterized by X-ray diffraction (XRD), atomic pair distribution function (PDF), double spherical aberration transmission electron microscopy (STEM), selected area electron diffraction (SAED), geometric phase analysis (GPA), chromatograph (EDS), etc., and the following was obtained: Figure 1-6 The result graph shown.

[0055] Figure 1 The XRD pattern of niobium tungsten oxide with ordered alternating intergrowth crystal structure is shown in Figure 2. Figure 1 It can be seen that the Bragg diffraction peak of the ordered alternating symbiotic crystal structure of niobium tungsten oxide coincides exactly with the characteristic diffraction peak of the niobium tungsten oxide standard PDF card (PDF-01-073-1324), and can be attributed to a tetragonal phase I-4 structure. At the same time, there are no other impurity peaks, which proves the good crystallinity and pure phase characteristics of the material.

[0056] Figure 2 The PDF diagram of the ordered alternating intergrowth crystal structure of niobium tungsten oxide is shown in Figure 1. Figure 2 It can be seen that in The material shows a broad peak at , which indicates that the disorder of the material increases. The interatomic distance can be attributed to the distance between the niobium atom and the coordinated oxygen atoms on the adjacent niobium atom. This is because there are a large number of dislocation slip planes in the ordered alternating symbiotic crystal structure of niobium tungsten oxide, which may lead to different coordination situations of the oxygen atoms at this site, thus showing a large degree of disorder.

[0057] Figure 3 The STEM image of the ordered alternating symbiotic crystal structure of niobium tungsten oxide is shown in Figure 1. Figure 3It can be seen that the material contains two crystal structures, 4×4×∞ and 4×3×∞, arranged in an orderly alternating pattern, demonstrating the formation of an ordered alternating intergrowth crystal structure. When the (210) crystal plane slips, a dislocation defect is generated, which destroys the material's inherent stability. According to Pauling's rule, since the interior of a crystal tends to form the lowest energy stable structure, the two rows of atoms adjacent to the slip plane attract each other, forming a new coordination environment and crystal structure.

[0058] Figure 4 The SAED pattern of the ordered alternating intergrowth crystal structure of niobium tungsten oxide is shown in Figure 2. Figure 4 It can be seen that superlattice lattices appear in the ordered alternating symbiotic crystal structure niobium tungsten oxide, which once again proves the existence of the ordered alternating symbiotic crystal structure. At the same time, its diffraction spots are located in the same reciprocal space position as niobium tungsten oxide, proving its ReO3 type structure and belonging to a single crystal material.

[0059] Figure 5 The GPA diagram of the ordered alternating intergrowth crystal structure of niobium tungsten oxide is shown in Figure 1. Figure 5 It can be seen that the material forms compressive stress at the dark stripes, which simultaneously induces tensile stress at the adjacent bright stripes. The overall distribution of compressive and tensile stresses is alternating, and this stress distribution coincides precisely with the arrangement of the crystal structure. Further analysis based on elasticity theory shows that the linear tension exerted by dislocations at the nodes is the cause of dislocation relaxation. This tension also promotes the full extension of slip dislocations within a sufficiently wide space, thus creating dislocation slip planes that run throughout the material.

[0060] Figure 6 The EDS image of the ordered alternating intergrowth crystal structure of niobium tungsten oxide is shown in Figure 1. Figure 6 It can be seen that the material presents the morphology of nanorods. The nanoscale particle size gives the material a larger specific surface area, increases the contact sites of lithium ions on the surface of the material, is more conducive to the transport of lithium ions, and further improves the fast charging performance; at the same time, the three elements of niobium, tungsten and oxygen are evenly distributed along the nanorod morphology, further confirming the successful preparation of the material.

[0061] The ordered alternating symbiotic crystal structure niobium tungsten oxide prepared in Example 1 can be applied to the negative electrode of a lithium battery. The lithium battery includes a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte that impregnates the separator. The preparation method of the negative electrode sheet includes: using the ordered alternating symbiotic crystal structure niobium tungsten oxide as an active material, Super P as a conductive agent, and polyvinylidene fluoride as a binder, mixing and evenly coating the mixture on a carbon-coated aluminum foil, and forming the negative electrode sheet after drying. The mass ratio of the ordered alternating symbiotic crystal structure niobium tungsten oxide, the Super P, and the polyvinylidene fluoride is 7 to 8:1 to 2:1.

[0062] The ordered alternating intergrowth crystal structure niobium tungsten oxide prepared in Example 1 was characterized by constant current intermittent titration technique (GITT), ultraviolet visible absorption spectroscopy (UV-vis), electrochemical performance test, etc., and the following was obtained: Figure 7-9 The result graph shown.

[0063] Figure 7 The GITT diagram of the ordered alternating intergrowth crystal structure of niobium tungsten oxide is shown in Figure 1. Figure 7 It can be seen that the lithium ion diffusion coefficient of this material is on the order of 10 -9 , indicating that the ordered alternating symbiotic crystal structure can effectively reduce the diffusion barrier of lithium ions.

[0064] Figure 8 The UV-vis Tauc curve of ordered alternating symbiotic crystal structure niobium tungsten oxide is shown in Figure 2. Figure 8 It can be seen that the band gap of this material is about 2.86eV, which is smaller than the 2.92eV of traditional niobium tungsten oxide, indicating that the electron diffusion potential energy of the ordered alternating symbiotic crystal structure is lower and more conducive to the rapid transport of electrons.

[0065] Figure 9 The electrochemical long cycle diagram of ordered alternating intergrowth crystal structure niobium tungsten oxide, Figure 9 It can be seen that the maximum specific capacity of the material after stable cycling at a current density of 100C is 70.2mAh / g, which is 4.3 times that of traditional niobium tungsten oxide. After 20,000 cycles, calculated based on the highest specific capacity, it still has a capacity retention rate of 77%, proving the excellent ultra-fast charging performance of niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0066] Example 2

[0067] 1. Dissolve 3g of niobium pentachloride and 0.45g of ammonium metatungstate in 20ml of a mixed solution of ethanol and deionized water containing 1g of oxalic acid, with the ratio of ethanol to deionized water being 1:3. After complete dissolution, a colorless and transparent metal mixture is obtained;

[0068] 2. Add 2.5 g of polyacrylonitrile (PAN) to the above metal mixture and stir at 400 rpm for 12 h to obtain a transparent gel solution;

[0069] 3. The gel solution was placed in an oven at 180°C for 12 hours and then transferred to a muffle furnace for pre-calcination for 3 hours. The muffle furnace was heated from room temperature to 350°C at a heating rate of 5°C / min to obtain a precursor;

[0070] 4. The cooled precursor was placed back into the muffle furnace, heated to 850°C at a heating rate of 5°C / min and kept at that temperature for 6 hours, then heated to 950°C at a heating rate of 2°C / min and kept at that temperature for 12 hours, and then naturally cooled to room temperature to obtain niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0071] Example 3

[0072] 1. Dissolve 3g of niobium pentachloride and 0.5g of ammonium metatungstate in 50ml of a mixed solution of ethanol and deionized water containing 1g of oxalic acid, with the ratio of ethanol to deionized water being 1:0.5. After complete dissolution, a colorless and transparent metal mixture is obtained;

[0073] 2. Add 3.75 g of polyvinyl alcohol (PVA) to the above metal mixture and stir at 400 r / min for 12 h to obtain a transparent gel solution;

[0074] 3. The gel solution was placed in an oven at 180°C for 12 hours and then transferred to a muffle furnace for pre-calcination for 3 hours. The muffle furnace was heated from room temperature to 350°C at a heating rate of 5°C / min to obtain a precursor;

[0075] 4. The cooled precursor was placed back into the muffle furnace, heated to 750°C at a heating rate of 5°C / min and kept warm for 6 hours, then heated to 1050°C at a heating rate of 2°C / min and kept warm for 12 hours, and then naturally cooled to room temperature to obtain niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0076] Through performance characterization, both Example 2 and Example 3 prepared niobium tungsten oxide with an ordered alternating symbiotic crystal structure.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure, characterized in that: The niobium source and the tungsten source are dissolved in a mixed solution of ethanol and deionized water, and the pH value is adjusted to 2-3, an organic polymer is added to form a gel solution, and then the ordered alternating intergrowth crystal structure niobium tungsten oxide is prepared by a gel calcination method; The specific steps of the gel calcination method are: drying the gel solution to obtain a gel, pre-calcining the gel to obtain a precursor, and pre-heating the precursor at 750-850°C for 6-8 hours and then at 950-1050°C for 12-13 hours to obtain the ordered alternating symbiotic crystal structure niobium tungsten oxide.

2. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to claim 1, characterized in that: During the high-temperature calcination process, the temperature is first increased to 750~850°C at a heating rate of 4.5~5.5°C / min, and then increased to 950~1050°C at a heating rate of 1.5~2.5°C / min.

3. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to claim 1, characterized in that: The pre-firing temperature is 340~360℃ and the time is 3h~4h.

4. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to any one of claims 1 to 3, characterized in that: The organic high molecular polymer is one of polyvinyl pyrrolidone, polyvinyl alcohol or polyacrylonitrile.

5. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to any one of claims 1 to 3, characterized in that: The mass ratio of the niobium source to the tungsten source is 3:0.3-0.4, the amount of the niobium source added to each mL of the ethanol-deionized water mixed solution is 0.06-0.15 g, the amount of the organic high molecular polymer added to each mL of the ethanol-deionized water mixed solution is 0.075-0.125 g, and the mass ratio of ethanol to deionized water is 1:0.2-5.

6. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to claim 5, characterized in that: Use oxalic acid, acetic acid or citric acid to adjust the pH to 2~3.

7. The method for preparing niobium-tungsten oxide with an ordered alternating symbiotic crystal structure according to claim 5, characterized in that: The niobium source is one of niobium oxalate, ammonium niobate or niobium pentachloride, and the tungsten source is ammonium metatungstate or tungsten hexachloride.

8. A niobium-tungsten oxide with an ordered alternating symbiotic crystal structure, characterized in that: The method is prepared by any one of claims 1 to 7.

9. Use of the ordered alternating symbiotic crystal structure niobium tungsten oxide according to claim 8 in the preparation of a negative electrode for a lithium battery.

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