Negative active material, preparation method thereof and sodium ion battery

Abstract

The invention relates to the technical field of energy storage, in particular to a negative electrode active material, a preparation method thereof and a sodium ion battery, the negative electrode active material comprises titanium dioxide and a coating layer coating the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne, and the surface of the graphdiyne is provided with a wrinkle structure. Titanium dioxide is used as a sodium storage material and has a stable structure; by coating the surface of titanium dioxide with graphdiyne, more sodium storage sites can be increased, the sodium storage amount is increased, and the conductivity of titanium dioxide can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a negative electrode active material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] In the research and development of sodium ion batteries, hard carbon materials are widely used due to their internal crystal arrangement disorder, more pores and higher capacity. Currently, most commercialized sodium ion batteries use hard carbon materials as negative electrode materials; however, the "sodium insertion-hole filling" low platform reaction process of hard carbon materials is limited by the slow sodium ion diffusion process, resulting in poor rate performance, and the low reaction potential greatly increases the risk of sodium dendrite precipitation and growth.

[0003] Titanium dioxide is one of the candidate materials for application in sodium battery negative electrodes due to its structural stability, low price, abundant reserves and environmental friendliness. The theoretical specific capacity of titanium dioxide is 335 mAh g -1 However, due to its low first coulomb efficiency, small ion diffusion rate and low electronic conductivity, its development space is limited. Graphene has excellent electrical conductivity and is often used to coat electrode materials to increase electrical conductivity, but in sodium ion batteries, sodium ions are difficult to pass through graphene due to their large diameter, limiting ion transport.

[0004] Therefore, there is an urgent need in the art for a new negative electrode material that can improve sodium storage capacity while ensuring electrical conductivity. SUMMARY

[0005] Therefore, the present application is devoted to providing a negative electrode active material, a preparation method thereof and a sodium ion battery to solve the problems of insufficient fast charging capacity and insufficient sodium storage sites of titanium dioxide in the prior art.

[0006] To solve the above technical problems, the present application is implemented as follows: The first aspect of the present application provides a negative electrode active material, which comprises titanium dioxide and a coating layer coated on the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne, and the surface of the graphdiyne has a wrinkle structure.

[0007] Optionally, the mass ratio of the graphdiyne to the titanium dioxide is (3-8): 100.

[0008] Optionally, the surface of the graphdiyne is further doped with second period element atoms; the second period element atoms include boron atoms and / or beryllium atoms.

[0009] Optionally, the mass ratio of the second period element atoms to the graphdiyne is (1-5): 100.

[0010] The second aspect of the present application provides a preparation method of a negative active material, comprising the following steps: S1, mixing graphdiyne with a first acid solution and performing an oxidation reaction to obtain an oxidation reaction product; mixing the oxidation reaction product with water to obtain a first material; performing a first filtration and washing treatment on the first material to obtain a graphdiyne aqueous solution; S2, adding a titanium source in an aqueous solvent to obtain a solution containing titanium; mixing the solution containing titanium after a second heating treatment with a lye to obtain a mixed solution; performing a third heating treatment on the mixed solution to obtain a first product; mixing the first product with water to obtain a second material; performing a third filtration and washing treatment on the second material to obtain an intermediate product; mixing the intermediate product with a second acid solution and performing a pyrolysis reaction to obtain a slurry containing titanium dioxide; S3, mixing the graphdiyne aqueous solution with the slurry containing titanium dioxide to obtain a third material; performing a hydrothermal reaction on the third material to obtain a reaction product; performing a washing treatment and a drying treatment on the reaction product; Wherein, the pH of the first material is 6-7; the pH of the second material is 7-8.

[0011] Optionally, the first acid solution comprises nitric acid and / or sulfuric acid; the mass concentration of H + in the first acid solution is greater than 90%; the mass ratio of the graphdiyne mixed with the first acid solution is 1: (18-22); and / or, the titanium source comprises metatitanic acid; and / or, in the solution containing titanium, the mass of solute is 50-60wt%; and / or, the mass ratio of the product after the second heating treatment mixed with the lye is 1: 15-20; and / or, the second acid solution comprises hydrochloric acid, and the mass concentration of H + in the second acid solution is 1.8-2.0%; and / or, the lye comprises NaOH and / or KOH; the mass concentration of OH - in the lye is 35-38%; and / or, the mass ratio of the graphdiyne aqueous solution mixed with the slurry containing titanium dioxide is 1: 0.8-1.2.

[0012] Optionally, in step S1, the conditions of the oxidation reaction include: a temperature of 40-50℃ and a time of 60-80min; and / or, the conditions of the first heating treatment include: after the aqueous solution of graphdiyne is heated to boiling, stirring for 90-120min; and / or, in step S2, the conditions of the second heating treatment include: a temperature of 80-90℃ and a time of 20-30min; and / or, the third heating treatment includes: heating the mixed solution to 100-120℃ and holding for 50-60min; and / or, in step S3, the conditions of the hydrothermal reaction include: a temperature of 140-160℃ and a time of 7-9h.

[0013] Optionally, the preparation method further comprises: in step S1, after mixing the aqueous solution of graphdiyne with a doping source, performing a first heating treatment to obtain a doped aqueous solution of graphdiyne; in step S3, mixing the doped aqueous solution of graphdiyne with the slurry containing titanium dioxide to obtain the third material; wherein the doping source comprises at least one of NaBH4, BeH2, NaBeH3 and BH3.

[0014] The third aspect of the present application provides a sodium ion battery, which comprises a negative electrode material, and the negative electrode material comprises the above-mentioned negative electrode active material and / or the negative electrode active material prepared according to the above-mentioned preparation method.

[0015] Through the above technical solutions, the present application has the following beneficial technical effects: (1) The negative electrode active material of the present application comprises titanium dioxide and a coating layer coated on the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne. The present application uses titanium dioxide as a sodium storage material, which has a stable structure; by coating graphdiyne on the surface of titanium dioxide, more sodium storage sites can be increased, the sodium storage amount can be improved, and the conductivity of titanium dioxide can be effectively improved.

[0016] (2) In the preparation method of the negative electrode active material of the present application, an aqueous solution of graphdiyne and a slurry containing titanium dioxide are prepared respectively, then the aqueous solution of graphdiyne and the slurry containing titanium dioxide are mixed to obtain a third material; the third material is subjected to a hydrothermal reaction to obtain a reaction product; and the reaction product is subjected to washing treatment and drying treatment. The preparation method of the present application can uniformly coat the doped graphdiyne on the titanium dioxide, make the structure of the prepared negative electrode active material more regular, and avoid the introduction of impurities.

[0017] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the application, and together with the description serve to explain the principles of the application. Drawings in which:

[0019] Figure 1 The overall electron microscope image of the negative electrode active material prepared in Example 1.

[0020] Figure 2 The electron microscope image of the wrinkle structure of the negative electrode active material prepared in Example 1 is shown.

[0021] Figure 3 The schematic diagram of the graphdiyne two-dimensional material structure is shown. DETAILED DESCRIPTION

[0022] The present application discloses a kind of negative electrode active material and its preparation method and sodium ion battery, and the person skilled in the art can improve process parameters to realize by referring to the content herein. It is particularly pointed out that all similar substitutions and changes are obvious to the person skilled in the art, and they are all regarded as including in the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0023] In the description of the present application, the list of items connected by the term "at least one of" or other similar terms means any combination of the listed items. For example, if the items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if the items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0024] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be roughly about the ranges or values. For ranges, the endpoints are included in the ranges or values, and the ranges or values are inclusive of the individual points within the ranges. The disclosure of any range or value is intended as a disclosure of a new and distinct range or value.

[0025] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0026] If there is no special indication, all the technical features of the present application and optional technical features can be combined with each other to form new technical solutions.

[0027] If there is no special indication, the "includes" and "contains" mentioned in the present application represent open type, and can also be closed type. For example, the "includes" and "contains" can represent that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0028] In order to solve the problems of insufficient fast charging capacity and insufficient sodium storage sites of titanium dioxide in the prior art, the present application adopts the following technical solutions: The first aspect of the present application provides a negative electrode active material, which comprises titanium dioxide and a coating layer coated on the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne, and the surface of the graphdiyne has a corrugated structure.

[0029] The coating layer of the negative electrode active material of the present application comprises graphdiyne, wherein graphdiyne is one of two-dimensional carbon materials, has similar electronic structure with graphene, has large specific surface area and good electrical conductivity, and is different from graphene in that the layer spacing of graphdiyne is larger, and has larger pore site gap. Such structure can make ions pass through the pores more easily, that is, ions can migrate in three-dimensional direction in graphdiyne, thereby improving ion migration rate.

[0030] The negative electrode active material of the present application comprises titanium dioxide and a coating layer coated on the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne. The present application uses titanium dioxide as a sodium storage material, which has a stable structure; by coating graphdiyne on the surface of titanium dioxide, more sodium storage sites can be increased, the sodium storage amount can be improved, and the electrical conductivity of titanium dioxide can be effectively improved.

[0031] In the present application, the "graphdiyne surface has a corrugated structure" means that the surface of graphdiyne is wavy, that is, the surface of graphdiyne forms wave peaks and wave valleys. Figure 1 As shown in the figure, the corrugated structure of the present application can increase more sodium storage sites, the generation of wave peaks increases the gap between TiO2 and graphdiyne, so that Na can be stored between them, a pseudo-capacitance effect (referring to reversible electrochemical reaction occurring on the surface layer or near-surface layer of the electrode material, which makes ions stable on the surface layer of the electrode) is generated, and the sodium storage amount is improved; the reason for the occurrence of wave peaks is that not all acetylene bonds C in graphdiyne can form covalent bonds with O on the surface of titanium dioxide, so after some acetylene bonds C in graphdiyne form covalent bonds with O, the adjacent C will have a tendency to move upward in order to maintain the stability of the surface structure of graphdiyne, and this tendency is greater than the tendency to form covalent bonds with O atoms. When the interaction force is balanced, there is no displacement, thus causing the surface to fluctuate.

[0032] In an embodiment of the present application, the mass ratio of the graphdiyne and the titanium dioxide can be (3-8): 100. If the mass ratio of the graphdiyne and the titanium dioxide is too large, the graphdiyne covers too much titanium dioxide, which causes the graphdiyne to stack, resulting in a steric hindrance effect, reducing compaction and affecting the energy density. If the mass ratio of the graphdiyne and the titanium dioxide is too small, the graphdiyne is not completely coated, which reduces the conductivity and affects the fast-charging performance. Illustratively, the mass ratio of the graphdiyne and the titanium dioxide can be any value in 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, or any value within a range formed by any two of the above values.

[0033] In an embodiment of the present application, the surface of the graphdiyne can also be doped with second-period element atoms; the second-period element atoms include boron atoms and / or beryllium atoms. The second-period element atoms doped in the present application preferably have a smaller number of outermost electrons than carbon atoms. By doping these atoms, on the one hand, the conductivity can be improved, and on the other hand, when the atoms combine with carbon atoms, charge transfer occurs, which causes some regions to lack electrons, thereby forming holes, making it easier for Na atoms to transfer to the surface, reducing the potential energy of Na atoms moving to the surface of the graphdiyne, and reducing the internal resistance and sodium storage potential. In this embodiment, the mass ratio of the second-period element atoms to the graphdiyne can be (1-5): 100. If the mass ratio of the second-period element atoms to the graphdiyne is too large, the doping energy is too high, making it difficult to embed and the structure unstable; if the mass ratio of the second-period element atoms to the graphdiyne is too small, after doping, the number of holes formed is small, and the improvement in the performance of the graphdiyne is not obvious. Illustratively, the mass ratio of the second-period element atoms to the graphdiyne can be any value in 1:100, 2:100, 3:100, 4:100, 5:100, or any value within a range formed by any two of the above values.

[0034] As a preferred embodiment of the present application, the second periodic element atom of the graphdiyne surface doping simultaneously includes boron atoms and beryllium atoms, and compared with single doping, double doping is easier to change the physical and chemical properties of the original system, that is, to change the semiconductor properties of graphdiyne into conductor properties, because of the synergistic effect between the two doping elements, which can be more evenly distributed in the raw material, while single doping is difficult to achieve; and the first principle calculation (here the first principle calculation method: 1, the lattice size of graphdiyne is fixed as 2*2; 2, for easy calculation, when single doping Be or B, replace any position C on the benzene ring of graphdiyne; 3, when double doping Be and B, each doping different benzene ring C; 4, put the model into VASP software for first principle calculation to get the system energy of the final structure optimization model), the system energy of Be-B co-doping is lower than that of single doping, that is, Be-B double doping of graphdiyne can be more easily achieved; the single-layer graphdiyne belongs to hexagonal system, belongs to space group P6 / MMM, and after optimization, the lattice constant a is 6.89 Å, and α=β=90°, γ=120°. As shown in Figure 3 The sp hybrid acetylene bond length is 1.222 Å, the sp2 hybrid benzene ring bond length is 1.425 Å, and the bond length connecting the benzene ring and the acetylene bond is 1.409 Å. This two-dimensional material structure is mainly composed of triangular-like gaps and six-membered ring gaps, and the area of the triangular-like gap is 3.4 times that of the six-membered ring gap.

[0035] The second aspect of the present application provides a preparation method of a negative electrode active material, which comprises the following steps: S1, mixing graphdiyne with a first acid solution and performing an oxidation reaction to obtain an oxidation reaction product; mixing the oxidation reaction product with water to obtain a first material; performing a first filtration and washing treatment on the first material to obtain a graphdiyne aqueous solution; S2, adding a titanium source in an aqueous solvent to obtain a titanium-containing solution; mixing the titanium-containing solution with a lye after a second heating treatment to obtain a mixed solution; performing a third heating treatment on the mixed solution to obtain a first product; mixing the first product with water to obtain a second material; performing a third filtration and washing treatment on the second material to obtain an intermediate product; mixing the intermediate product with a second acid solution and performing a pyrolysis reaction to obtain a slurry containing titanium dioxide; S3, mixing the graphdiyne aqueous solution with the slurry containing titanium dioxide to obtain a third material; performing a hydrothermal reaction on the third material to obtain a reaction product; performing a washing treatment and a drying treatment on the reaction product; The pH of the first material is 6-7; and the pH of the second material is 7-8.

[0036] The preparation method of the negative active material in the application comprises the following steps: preparing a graphite diyne oxide aqueous solution and a slurry containing titanium dioxide respectively, mixing the graphite diyne aqueous solution and the slurry containing titanium dioxide to obtain a third material, performing a hydrothermal reaction on the third material to obtain a reaction product, and performing washing treatment and drying treatment on the reaction product. The preparation method can make the doped graphite diyne uniformly coated on the titanium dioxide, make the structure of the prepared negative active material more regular, and avoid the introduction of impurities.

[0037] In the application, the graphite diyne is mixed with a first acid solution to generate an oxidation reaction product with functional groups such as carboxylic acid and ketonic acid. Exemplarily, the first acid solution can comprise nitric acid and / or sulfuric acid; the mass concentration of H + in the first acid solution is greater than 90%.

[0038] According to the application, if the mass ratio of the graphite diyne to the first acid solution is too small, the graphite diyne may be excessively reacted, and multiple filtrations are required when the first acid solution is washed, which reduces the efficiency; if the mass ratio of the graphite diyne to the first acid solution is too large, the reaction may be insufficient, and part of the graphite diyne has not generated the oxidation product such as carboxylic acid and ketonic acid. In the application, the mass ratio of the graphite diyne to the first acid solution can be 1: (18-22). Exemplarily, the mass ratio of the graphite diyne to the first acid solution can be any value in 1:18, 1:19, 1:20, 1:21 and 1:22 or any value in the range formed by any two of the above values. In the application, since the concentration of the first acid solution is high, the oxidation reaction product needs to be mixed with water for dilution.

[0039] Exemplarily, the titanium source can comprise metatitanic acid. In the application, metatitanic acid is used as the titanium source, which is non-toxic and harmless, and does not have additional side reactions, and the final product obtained does not need to be treated too much.

[0040] According to the application, if the mass of the solute in the titanium-containing solution is too small, the conversion efficiency of the final product may be low; if the mass of the solute in the titanium-containing solution is too large, the titanium-containing solution may be too viscous, and the pyrolysis reaction may not be sufficient. In the application, the mass of the solute in the titanium-containing solution can be 50-60 wt%. Exemplarily, the mass of the solute in the titanium-containing solution can be any value in 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt% and 60 wt% or any value in the range formed by any two of the above values.

[0041] According to the present application, if the mass ratio of the product after the second heating treatment to the lye is too small, it can cause excessive heat during the reaction, generating other by-products; if the mass ratio of the product after the second heating treatment to the lye is too large, it can cause insufficient reaction and low conversion rate of titanium dioxide. In the present application, the mass ratio of the product after the second heating treatment to the lye can be 1:15-20. For example, the mass ratio of the product after the second heating treatment to the lye can be any value in 1:15, 1:16, 1:17, 1:18, 1:19 and 1:20 or any value in the range formed by any two of the above values.

[0042] For example, the second acid solution includes hydrochloric acid, wherein the hydrochloric acid can neutralize the lye and does not generate by-products. In the present application, the mass concentration of H + in the second acid solution can be 1.8-2.0%. For example, the mass concentration of H + in the second acid solution can be any value in 1.8%, 1.85%, 1.9% and 2.0% or any value in the range formed by any two of the above values.

[0043] For example, the lye can include NaOH and / or KOH. In the present application, the mass concentration of OH - in the lye can be 35-38%. For example, the mass concentration of OH - in the lye can be any value in 35%, 36%, 37% and 38% or any value in the range formed by any two of the above values.

[0044] In the present application, if the mass ratio of the aqueous solution of graphdiyne to the slurry containing titanium dioxide is too small, it can cause uneven coating of titanium dioxide on graphdiyne, reducing the sodium storage capacity; if the mass ratio of the aqueous solution of graphdiyne to the slurry containing titanium dioxide is too large, it can cause part of the graphdiyne not to be coated on the titanium dioxide, but to be locally stacked, losing the composite effect. The mass ratio of the aqueous solution of graphdiyne to the slurry containing titanium dioxide can be 1:0.8-1.2. For example, the mass ratio of the aqueous solution of graphdiyne to the slurry containing titanium dioxide can be any value in 1:0.8, 1:0.9, 1:1.0, 1:1.1 and 1:1.2 or any value in the range formed by any two of the above values.

[0045] In an embodiment of the present application, in step S1, the conditions of the oxidation reaction can include a temperature of 40-50°C and a time of 60-80 min; and / or, the conditions of the first heating treatment include heating the aqueous solution of oxidized graphdiyne to boiling and stirring for 90-120 min.

[0046] The second filtering and washing treatment in step S1 of the present application can include: filtering the oxidized graphdiyne aqueous solution after the first heating treatment using filter paper to separate the graphdiyne and water, then rinsing the filtrate on the filter paper with deionized water for multiple times to remove residual acid, and finally dissolving the filtrate in deionized water again.

[0047] In an embodiment of the present application, the second heating treatment in step S2 can include: a temperature of 80-90℃ and a time of 20-30min. The third heating treatment includes: heating the mixed solution to 100-120℃ and keeping the temperature for 50-60min.

[0048] In step S2 of the present application, the intermediate product is mixed with a second acid solution to generate TiOCl2, and heating is performed to make TiOCl2 undergo pyrolysis reaction to generate titanium dioxide, thereby obtaining a slurry containing titanium dioxide.

[0049] In an embodiment of the present application, the hydrothermal reaction in step S3 can include: a temperature of 140-160℃ and a time of 7-9h.

[0050] As a preferred embodiment of the present application, the preparation method can further include: in step S1, after mixing the graphdiyne aqueous solution with a doping source, performing a first heating treatment to obtain a doped graphdiyne aqueous solution; and in step S3, mixing the doped graphdiyne aqueous solution with the slurry containing titanium dioxide to obtain the third material.

[0051] Illustratively, the doping source can include at least one of NaBH4, BeH2, NaBeH3 and BH3.

[0052] In this embodiment, the first heating treatment can include: heating the oxidized graphdiyne aqueous solution to boiling, and then stirring for 90-120min.

[0053] The third aspect of the present application provides a sodium ion battery, which includes a negative electrode material, and the negative electrode material includes the above-mentioned negative electrode active material and / or the negative electrode active material prepared according to the above-mentioned preparation method.

[0054] The present application is further described in detail by the following examples. The raw materials used in the examples can be obtained by commercial channels.

[0055] Example 1 (1) Preparation of negative electrode active material The graphdiyne is mixed with a 90% mass concentration sulfuric acid solution and subjected to an oxidation reaction to obtain an oxidation reaction product; the oxidation reaction product is stirred and deionized water is added dropwise to dilute the solution to neutral pH to obtain a first material; the first material is subjected to a first filtration and washing treatment, and the filtered and washed product is dispersed in water to obtain an oxidized graphdiyne aqueous solution.

[0056] NaBH4 and NaBeH3 doping sources are added to the oxidized graphdiyne aqueous solution, the mass ratio of NaBH4, NaBeH3 and graphdiyne is 1.5:1.5:100, heating is performed to boil, after stirring and reaction, the supernatant is removed by filtration, the remaining filtrate is washed with clean water, and the washed filtrate is mixed with water to obtain a Be&B double-doped graphdiyne and water mixed system.

[0057] Titanium-containing solution is obtained by adding metatitanic acid to the aqueous solvent to obtain a solution with a mass of 50%; the titanium-containing solution is heated to 80°C and then NaOH solution is added to obtain a mixed solution; the mixed solution is heated to 110°C and incubated for 60 min, then diluted to neutral with water, and cooled to 55°C to obtain a second material; the second material is subjected to filtration and washing to obtain an intermediate product; the intermediate product is added to hydrochloric acid to generate TiOCl2, and heating is performed to obtain a slurry containing titanium dioxide.

[0058] The Be&B double-doped graphdiyne and water mixed system is mixed with the slurry containing titanium dioxide to obtain a third material; the mass ratio of Be&B double-doped graphdiyne and titanium dioxide is 5:100, the third material is subjected to a hydrothermal reaction to obtain a reaction product, and the reaction product is subjected to washing and drying treatment to obtain a Be&B double-doped graphdiyne / titanium dioxide composite material.

[0059] (2) Preparation of negative electrode sheet: The prepared negative electrode active material, carbon black, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) are uniformly mixed in a ratio of 96.0:1.0:1.1:1.9, and deionized water is added to make the solid content 50% and the viscosity 4000; the obtained slurry is coated on a copper foil with a coating density of 10.5 g / cm 2 ; after drying, the negative electrode sheet is obtained by rolling.

[0060] (3) Preparation of positive electrode sheet: Prussian blue, carbon black (SP), carbon nanotubes (CNT), polyvinylidene fluoride (PVDF), and N-methyl pyrrolidone (NMP) are uniformly mixed in a mass ratio of 96:1.5:0.5:2.0:45 to obtain a positive electrode slurry, which is uniformly coated on an aluminum foil current collector with a coating density of 22.5 g / cm 2 ; after drying, rolling, and die cutting, the positive electrode sheet is obtained.

[0061] (4) Preparation of the battery: The positive electrode sheet, the negative electrode sheet, and the separator (the intermediate film layer is PE of 9 μm, one side of the film is ceramic coating of 3 μm, and the other side is PVDF coating of 3 μm) are wound and assembled in the order of one positive electrode, one separator, and one negative electrode, the assembled electrode roll is then packaged into an aluminum plastic film, and electrolyte (solute is 1 mol / L LiPF6, and solvent is EC:EMC:DMC = 1:1:1) is injected into the aluminum plastic film, then formation, aging, and capacity distribution are performed, and finally the aluminum plastic film is sealed to obtain the battery.

[0062] Example 2 The preparation method of the negative electrode active material in this example is the same as that in Example 1, except that only NaBH4 doping source is added to the aqueous solution of oxidized graphdiyne, and the mass ratio of NaBH4 to graphdiyne is 3:100.

[0063] The preparation methods of the negative electrode sheet, the positive electrode sheet, and the battery in this example are the same as those in Example 1.

[0064] Example 3 The preparation method of the negative electrode active material in this example is the same as that in Example 1, except that only NaBeH3 doping source is added to the aqueous solution of oxidized graphdiyne, and the mass ratio of NaBeH3 to graphdiyne is 3:100.

[0065] The preparation methods of the negative electrode sheet, the positive electrode sheet, and the battery in this example are the same as those in Example 1.

[0066] Example 4 The preparation method of the negative electrode active material in this example is the same as that in Example 1, except that urea doping source is added to the aqueous solution of oxidized graphdiyne, and the mass ratio of urea to graphdiyne is 3:100.

[0067] The preparation methods of the negative electrode sheet, the positive electrode sheet, and the battery in this example are the same as those in Example 1.

[0068] Example 5 The preparation method of the negative electrode active material in this example is the same as that in Example 1, except that the aqueous solution of oxidized graphdiyne is not doped and is directly mixed with the slurry containing titanium dioxide.

[0069] The preparation methods of the negative electrode sheet, the positive electrode sheet, and the battery in this example are the same as those in Example 1.

[0070] Example 6 The preparation method of the negative electrode active material in this example is the same as that in Example 1, except that the mass ratio of graphdiyne to titanium dioxide is 3:100.

[0071] The preparation methods of the negative electrode sheet, the positive electrode sheet and the battery in this example are the same as those in Example 1.

[0072] Example 7 The preparation method of the negative active material in this example is the same as that in Example 1, except that the mass ratio of graphdiyne to titanium dioxide is 8:100.

[0073] The preparation methods of the negative electrode sheet, the positive electrode sheet and the battery in this example are the same as those in Example 1.

[0074] Comparative Example 1 In this comparative example, titanium dioxide is used as the negative electrode material.

[0075] The preparation methods of the negative electrode sheet, the positive electrode sheet and the battery in this example are the same as those in Example 1.

[0076] Comparative Example 2 The preparation method of the negative active material in this comparative example is the same as that in Example 5, except that equal mass of graphene is used to replace graphdiyne.

[0077] The preparation methods of the negative electrode sheet, the positive electrode sheet and the battery in this example are the same as those in Example 1.

[0078] Test Example 1 The batteries prepared in Examples 1-7 and Comparative Examples 1-2 are subjected to performance tests, and the test results are shown in Table 1.

[0079] The capacity test method is as follows: at room temperature, 0.01C constant current charging is performed to 2.7V, and the first circle charging capacity is recorded; after 30min, 0.33C discharging is performed to 1.0V, and the first circle discharging capacity is recorded, and the first efficiency is obtained by the first circle discharging capacity / the first circle charging capacity; 30min is allowed to stand; then 0.33C constant current charging is performed to 2.7V, and constant voltage charging is performed until the current is less than or equal to 0.05C, and 30min is allowed to stand, and 0.33C discharging is performed to 1.0V; the above steps are repeated twice, and the second 0.33C capacity is recorded as the battery discharging capacity.

[0080] The room temperature direct current resistance method is as follows: at room temperature, 0.33C constant current charging is performed to 2.7V, and constant voltage charging is performed until the current is less than or equal to 0.05C, so that the battery is fully charged, and the battery SOC is adjusted to 50% by discharging, and 2C discharging is performed for 30s, and the 10s data is extracted as the direct current resistance at 50% SOC.

[0081] The cycle number method is as follows: the battery is repeatedly charged and discharged in the mode of charging 1C and discharging 1C, and the cycle number is the cycle number when the capacity retention rate is 80%.

[0082] Table 1 As can be seen from the data in Table 1, by comparing Example 1, 6 and 7 with Example 2, 3 and 4, the double-doped graphdiyne / titanium dioxide composite system is more stable than the single-doped graphdiyne / titanium dioxide composite system; by comparing Example 1 with Example 5, the doped graphdiyne / titanium dioxide composite system is more stable than the undoped graphdiyne / titanium dioxide system; by comparing Example 5 with Comparative Example 2, the graphdiyne-coated titanium dioxide is more stable than the graphene-coated titanium dioxide system; and the graphene-coated titanium dioxide has a higher internal resistance, because graphene has only six-membered rings, and the gap is smaller than the diameter of sodium ions, and sodium ions cannot pass through, while the triangular gap in the structure of graphdiyne is larger than the sodium ions, and sodium ions can directly pass through the graphdiyne and be embedded in the titanium dioxide, so that the internal resistance is lower; by comparing the data of Examples 1-7 with Comparative Example 1, the capacity storage and initial efficiency of Examples 1-7 are higher, the internal resistance is also lower, and the cycle number is greatly increased.

[0083] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A negative electrode active material, characterized by, The negative electrode active material comprises titanium dioxide and a coating layer coated on the surface of the titanium dioxide; wherein the coating layer comprises graphdiyne, and the surface of the graphdiyne has a wrinkle structure.

2. The negative electrode active material according to claim 1, characterized by The mass ratio of the graphdiyne to the titanium dioxide is (3-8):

100.

3. The negative electrode active material according to claim 1, characterized by The surface of the graphdiyne is further doped with second-period element atoms; the second-period element atoms comprise boron atoms and / or beryllium atoms.

4. The negative electrode active material according to claim 3, characterized by The mass ratio of the second-period element atoms to the graphdiyne is (1-5):

100.

5. A method for producing a negative electrode active material, characterized by, The preparation method comprises the following steps: S1, mixing graphdiyne with a first acid solution and performing an oxidation reaction to obtain an oxidation reaction product; mixing the oxidation reaction product with water to obtain a first material; performing a first filtration and washing treatment on the first material to obtain a graphdiyne aqueous solution; S2, adding a titanium source in an aqueous solvent to obtain a titanium-containing solution; mixing the titanium-containing solution with an alkali solution after a second heating treatment to obtain a mixed solution; performing a third heating treatment on the mixed solution to obtain a first product; mixing the first product with water to obtain a second material; performing a third filtration and washing treatment on the second material to obtain an intermediate product; mixing the intermediate product with a second acid solution and performing a pyrolysis reaction to obtain a slurry containing titanium dioxide; S3, mixing the graphdiyne aqueous solution with the slurry containing titanium dioxide to obtain a third material; performing a hydrothermal reaction on the third material to obtain a reaction product; performing a washing treatment and a drying treatment on the reaction product; wherein the pH of the first material is 6-7; and the pH of the second material is 7-8.

6. The preparation method according to claim 5, characterized in that, The first acid solution comprises nitric acid and / or sulfuric acid; the mass concentration of H + in the first acid solution is greater than 90%; the mass ratio of the graphdiyne mixed with the first acid solution is 1: (18~22); and / or, The titanium source comprises metatitanic acid; and / or, The mass of the solute in the titanium-containing solution is 50-60 wt%; and / or, The mass ratio of the product after the second heating treatment to the alkali solution is 1:15-20; and / or, The second acid solution comprises hydrochloric acid, the mass concentration of H + 1.8-2.0%; and / or, The alkali liquor comprises NaOH and / or KOH; the mass concentration of OH - in the alkali liquor is 35-38%; and / or, The mass ratio of the graphdiyne aqueous solution to the slurry containing titanium dioxide is 1:0.8-1.2; and / or, In step S1, the conditions of the oxidation reaction comprise a temperature of 40-50℃ and a time of 60-80 min; and / or, In step S2, the conditions of the second heating treatment comprise a temperature of 80-90℃ and a time of 20-30 min; and / or, the third heating treatment comprises heating the mixed solution to 100-120℃ and maintaining the temperature for 50-60 min; and / or, In step S3, the conditions of the hydrothermal reaction comprise a temperature of 140-160℃ and a time of 7-9 h.

7. The preparation method according to claim 5, characterized in that, The preparation method further comprises: in step S1, mixing the graphdiyne aqueous solution with a doping source and performing a first heating treatment to obtain a doped graphdiyne aqueous solution; and in step S3, mixing the doped graphdiyne aqueous solution with the slurry containing titanium dioxide to obtain the third material. The doping source comprises at least one of NaBH4, BeH2, NaBeH3 and BH3.

8. A sodium-ion battery, characterized in that, The sodium-ion battery comprises a negative electrode material, wherein the negative electrode material comprises the negative electrode active material according to any one of claims 1-4 and / or the negative electrode active material prepared by the preparation method according to any one of claims 5-7.

Images