Titanium-based phosphate composite material and preparation method and application thereof

Abstract

The invention relates to a titanium-based phosphate composite material and a preparation method and application thereof, and belongs to the technical field of sodium ion batteries. The preparation method comprises the following steps: S1, mixing a surfactant and a solvent to obtain a surfactant solution; s2, uniformly stirring an M source, a titanium source, a phosphorus source, an organic carbon source and a surfactant solution to obtain a mixed solution; s3, adding a chelating agent and a pH regulator into the mixed solution, and regulating the pH to 3-5 to obtain a sol solution; and S4, the sol solution is subjected to gelation treatment, aging treatment, decarburization treatment and calcination treatment, and the titanium-based phosphate composite material is obtained. According to the preparation method, a sol-gel method is adopted, a surfactant is introduced in the preparation process, the pH value, the gelation temperature and the like are regulated and controlled, and the micron-level titanium-based phosphate composite material is successfully prepared. And the titanium-based phosphate composite materials with different voltages and different discharge specific capacities are prepared by adjusting the types and proportions of cations.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a titanium-based phosphate composite material and a preparation method and application thereof. Background Art

[0002] Sodium ion batteries often use sodium titanium phosphate as the negative electrode material. The high potential of sodium titanium phosphate comes from the fact that in this crystal structure, only Ti-OP bonds exist. 3- Polyanion to Ti 4+ It has a strong inductive effect, making Ti 4+ To Ti 3+ The electrochemical redox potential corresponding to the valence change is 2.1 V (vs Na / Na + For the titanium phosphate compound MTiOPO4, since the covalency of the titanium-oxygen-titanium bond is weaker than the oxygen-phosphorus bond, the redox potential can be significantly reduced to 1.2V-1.5V (vs Na / Na + Among various titanium-based phosphate anode materials, KTiOPO4 has a larger cross-cavity and the lowest potential of KTiOPO4, which is 1.23V, and has great potential in achieving faster ion dynamics and lower cycle strain in sodium-ion batteries.

[0003] However, there are few studies on MTiOPO4, especially on material preparation. CN 111029573A mentions the use of a titanium substrate as a current collector and a potassium titanyl phosphate (chemical formula KTiOPO4) film grown on a titanium substrate as an active material, but this preparation method requires a vacuum environment and is relatively complicated to prepare; at the same time, due to the influence of the preparation process and the intrinsic properties of the material, no carbon source is introduced during the preparation process, resulting in a low electronic conductivity of the material.

[0004] Sol-gel is a wet chemical synthesis method. It mainly forms a stable sol through the hydrolysis and polycondensation reaction of precursors such as metal organic compounds or inorganic salts in a solvent. The sol is then transformed into a gel after aging. It is widely used in the preparation of battery materials. However, the powder prepared by conventional sol-gel has an extremely high specific surface area, resulting in a very low loading amount of the material when it is coated to make electrodes, and it cannot be used in practice. Therefore, based on the sol-gel method, a new method is developed to prepare high-performance sodium-ion battery negative electrode materials, but there are great challenges. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a titanium-based phosphate composite material and a preparation method and application thereof.

[0006] The first object of the present invention is to provide a method for preparing a titanium-based phosphate composite material, comprising the following steps:

[0007] S1, mixing a surfactant and a solvent to obtain a surfactant solution;

[0008] S2, stirring the M source, titanium source, phosphorus source, organic carbon source and the surfactant solution described in S1 to obtain a mixed solution; the amount of the M source, titanium source, phosphorus source and organic carbon source satisfies the chemical formula MTiOPO4 / C, wherein the carbon content is 0.5wt%-5wt%;

[0009] S3, adding a chelating agent and a pH adjusting agent to the mixed solution described in S2, adjusting the pH to 3-5, and obtaining a sol solution;

[0010] S4, subjecting the sol solution described in S3 to gelation treatment, aging treatment, decarburization treatment and calcination treatment to obtain the titanium-based phosphate composite material.

[0011] In one embodiment of the present invention, in S1, the surfactant is selected from sodium dodecylbenzene sulfonate and / or sodium dodecyl sulfate; the addition of the surfactant can change the surface properties of the sol particles, promote the agglomeration of particles, and thus reduce the specific surface area;

[0012] and / or, the solvent is selected from one or more of water, ethanol and acetone;

[0013] And / or, the mass fraction of the surfactant in the surfactant solution is 0.2%-1%.

[0014] In one embodiment of the present invention, in S2, the M source is selected from one or more of a sodium source, a lithium source and a potassium source;

[0015] And / or, the titanium source is selected from one or more of titanium dioxide, tetrabutyl titanate and titanium tetrachloride;

[0016] and / or, the phosphorus source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus pentoxide, sodium dihydrogen phosphate, lithium dihydrogen phosphate and potassium dihydrogen phosphate;

[0017] And / or, the organic carbon source is selected from one or more of sucrose, glucose and polyacrylic acid;

[0018] And / or, the mass ratio of MTiOPO4 / C to surfactant is 99.95:0.05-99:1.

[0019] In one embodiment of the present invention, the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium acetate and sodium dihydrogen phosphate;

[0020] And / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate;

[0021] And / or, the potassium source is selected from one or more of potassium carbonate, potassium hydroxide, potassium acetate, potassium dihydrogen phosphate and dipotassium hydrogen phosphate.

[0022] In one embodiment of the present invention, in S2, the stirring temperature is 30°C-60°C, and the stirring time is 3h-5h.

[0023] In one embodiment of the present invention, in S3, the chelating agent is selected from citric acid and / or ethylenediaminetetraacetic acid;

[0024] And / or, the pH adjuster is selected from ammonia and / or phosphoric acid;

[0025] And / or, the mass ratio of MTiOPO4 / C to the chelating agent is 99:1-90:10.

[0026] In one embodiment of the present invention, in S4, the gelation treatment is performed at a temperature of 180°C-250°C and for a time of 2h-4h;

[0027] And / or, the aging treatment is performed at a temperature of 60°C-150°C and a time of 4h-6h;

[0028] And / or, the decarburization treatment temperature is 300°C-350°C, and the time is 3h-6h;

[0029] And / or, the heating rate of the calcination treatment is 2 / min-5°C / min, the temperature is 600°C-800°C, and the time is 6h-12h.

[0030] The second object of the present invention is to provide a titanium-based phosphate composite material prepared by the method described, wherein the titanium-based phosphate composite material includes a titanium-based phosphate and a carbon coating layer coated on the surface of the titanium-based phosphate, the particle size of the titanium-based phosphate composite material is 2μm-5μm, and the thickness of the carbon coating layer is 5nm-20nm; the chemical formula of the titanium-based phosphate composite material is MTiOPO4 / C, and M is selected from one or more of sodium, lithium and potassium.

[0031] In one embodiment of the present invention, the chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C and / or Li 1-y Na y TiOPO4 / C, 0≤x<1, 0≤y<1.

[0032] In one embodiment of the present invention, the chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C and / or Li1-y Na y TiOPO4 / C, 0≤x≤0.5, 0.5≤y≤1;

[0033] When the chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C, when 0≤x≤0.5, the specific capacity is 100mAh / g-135mAh / g;

[0034] When the chemical formula of the titanium-based phosphate composite material is Li 1-y Na y TiOPO4 / C, when 0.5≤y≤1, the specific capacity is 80mAh / g-110mAh / g.

[0035] In one embodiment of the present invention, the specific surface area of ​​the titanium-based phosphate composite material is 7 m 2 / g-10m 2 / g.

[0036] The third object of the present invention is to provide a sodium ion battery, wherein the negative electrode material of the sodium ion battery is the titanium-based phosphate composite material, and the positive electrode material is selected from a polyanion material and / or a Prussian blue material.

[0037] The technical solution of the present invention has the following advantages over the prior art:

[0038] (1) The preparation method described in the present invention adopts the sol-gel method, and successfully prepares a micron-level titanium-based phosphate composite material by introducing a surfactant, adjusting the pH value and the gelation temperature during the preparation process. Among them, the surfactant can effectively regulate the surface properties and interactions of the particles in the sol system and change the aggregation state of the particles; the pH value can optimize the reaction environment and affect the hydrolysis and polycondensation reaction rates of the precursor; and the gelation temperature plays a key role in the formation of the microstructure of the material. At different temperatures, the chemical bonding and crystallization processes inside the material are different. Under the combined effect of these three factors, the prepared titanium-based phosphate composite material presents an ideal microstructure, and the specific surface area is significantly reduced, meeting the needs of practical applications.

[0039] (2) The preparation method of the present invention prepares titanium-based phosphate composite materials with different voltages and different discharge specific capacities by adjusting the type and ratio of cations. Different cations have unique chemical properties and electronic structures, occupying different positions in the material lattice, thereby changing the crystal structure and electronic conduction properties of the material, changing the embedding and extraction capabilities of sodium ions in the material, and thus regulating the discharge specific capacity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0041] Figure 1 This is a TEM image of the titanium-based phosphate composite material of Example 1 in Test Example 2 of the present invention;

[0042] Figure 2 This is a SEM image of the titanium-based phosphate composite material of Example 2 in Test Example 2 of the present invention;

[0043] Figure 3 This is a SEM image of the titanium-based phosphate composite material No. 1 in Test Example 2 of the present invention;

[0044] Figure 4 This is a SEM image of the titanium-based phosphate composite material No. 5 in Test Example 2 of the present invention;

[0045] Figure 5 This is a charge and discharge curve diagram of a battery made of the titanium-based phosphate composite material of Example 1 in Test Example 3 of the present invention at a 1C rate. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0047] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0048] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0049] In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0050] Example 1

[0051] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0052] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0053] S2, adding potassium dihydrogen phosphate, tetrabutyl titanate and sucrose to the surfactant solution, stirring at 45° C. for 3 hours to obtain a mixed solution; wherein the amounts of potassium dihydrogen phosphate, tetrabutyl titanate and sucrose satisfy the chemical formula KTiOPO4 / C, and the carbon content is 0.5wt%; the mass ratio of KTiOPO4 / C to the surfactant is 99.5:0.5;

[0054] S3, adding citric acid and ammonia water to the mixed solution at the same time, adjusting the pH value to 4, stirring evenly, and obtaining a sol solution; wherein the mass ratio of KTiOPO4 / C to citric acid is 95:5;

[0055] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 100°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0056] Example 2

[0057] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0058] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0059] S2. Add potassium dihydrogen phosphate, sodium dihydrogen phosphate, titanium dioxide and glucose to the surfactant solution, and stir at 45° C. for 3 h to obtain a mixed solution; wherein the amounts of potassium dihydrogen phosphate, sodium dihydrogen phosphate, titanium dioxide and glucose satisfy the chemical formula K 0.8 Na 0.2 TiOPO4 / C, carbon content 0.5wt%; K 0.8 Na 0.2 The mass ratio of TiOPO4 / C and surfactant is 99.5:0.5;

[0060] S3, add citric acid and ammonia water to the mixed solution, adjust the pH value to 4, stir evenly, and obtain a sol solution; wherein, K 0.8 Na 0.2 The mass ratio of TiOPO4 / C and citric acid is 95:5;

[0061] S4. The sol solution was gelled at 200°C for 2.5 hours, and aged at 90°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0062] Example 3

[0063] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0064] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0065] S2. Add potassium carbonate, sodium carbonate, ammonium dihydrogen phosphate, titanium tetrachloride and sucrose to the surfactant solution, stir at 45° C. for 3 h to obtain a mixed solution; wherein the amounts of potassium carbonate, sodium carbonate, ammonium dihydrogen phosphate, titanium tetrachloride and sucrose satisfy the chemical formula K 0.7 Na 0.3 TiOPO4 / C, carbon content 1wt%; K 0.7 Na 0.3 The mass ratio of TiOPO4 / C and surfactant is 99.5:0.5;

[0066] S3, add citric acid and ammonia water to the mixed solution, adjust the pH value to 4, stir evenly, and obtain a sol solution; wherein, K 0.7 Na 0.3 The mass ratio of TiOPO4 / C and citric acid is 95:5;

[0067] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 110°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0068] Example 4

[0069] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0070] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0071] S2, adding sodium dihydrogen phosphate, tetrabutyl titanate and sucrose to the surfactant solution, stirring at 45° C. for 3 hours to obtain a mixed solution; wherein the amounts of sodium dihydrogen phosphate, tetrabutyl titanate and sucrose satisfy the chemical formula NaTiOPO4 / C, and the carbon content is 0.5wt%; the mass ratio of NaTiOPO4 / C to the surfactant is 99.5:0.5;

[0072] S3, adding citric acid and ammonia water to the mixed solution at the same time, adjusting the pH value to 4, stirring evenly, and obtaining a sol solution; wherein the mass ratio of NaTiOPO4 / C to citric acid is 95:5;

[0073] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 120°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0074] Example 5

[0075] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0076] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0077] S2. Add lithium carbonate, sodium carbonate, lithium dihydrogen phosphate, titanium tetrachloride and polyacrylic acid to the surfactant solution, and stir at 45° C. for 3 h to obtain a mixed solution; wherein the amounts of lithium carbonate, sodium carbonate, lithium dihydrogen phosphate, titanium tetrachloride and polyacrylic acid satisfy the chemical formula Li 0.2 Na 0.8 TiOPO4 / C, carbon content 5wt%; Li 0.2 Na 0.8 The mass ratio of TiOPO4 / C and surfactant is 99.5:0.5;

[0078] S3, add citric acid and ammonia water to the mixed solution, adjust the pH value to 4, stir evenly, and obtain a sol solution; wherein Li 0.2 Na 0.8 The mass ratio of TiOPO4 / C and citric acid is 95:5;

[0079] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 100°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0080] Embodiment 6 (basically the same as embodiment 3, except that the dosage of potassium carbonate and sodium carbonate is different)

[0081] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0082] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0083] S2. Add potassium carbonate, sodium carbonate, ammonium dihydrogen phosphate, titanium tetrachloride and sucrose to the surfactant solution, stir at 45° C. for 3 h to obtain a mixed solution; wherein the amounts of potassium carbonate, sodium carbonate, ammonium dihydrogen phosphate, titanium tetrachloride and sucrose satisfy the chemical formula K 0.3 Na 0.7 TiOPO4 / C, carbon content 1wt%; K 0.3 Na 0.7 The mass ratio of TiOPO4 / C and surfactant is 99.5:0.5;

[0084] S3, add citric acid and ammonia water to the mixed solution, adjust the pH value to 4, stir evenly, and obtain a sol solution; wherein, K 0.3 Na 0.7 The mass ratio of TiOPO4 / C and citric acid is 95:5;

[0085] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 110°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0086] Example 7 (basically the same as Example 5, except that the amounts of lithium carbonate and sodium carbonate are different)

[0087] The titanium-based phosphate composite material and the preparation method thereof of the present invention specifically comprise the following steps:

[0088] S1. Preparation of surfactant solution: using deionized water as solvent and sodium dodecyl sulfate as surfactant, prepare a surfactant solution with a mass fraction of 1%;

[0089] S2. Add lithium carbonate, sodium carbonate, lithium dihydrogen phosphate, titanium tetrachloride and polyacrylic acid to the surfactant solution, and stir at 45° C. for 3 h to obtain a mixed solution; wherein the amounts of lithium carbonate, sodium carbonate, lithium dihydrogen phosphate, titanium tetrachloride and polyacrylic acid satisfy the chemical formula Li 0.8 Na 0.2 TiOPO4 / C, carbon content 5wt%; Li 0.8 Na 0.2 The mass ratio of TiOPO4 / C and surfactant is 99.5:0.5;

[0090] S3, add citric acid and ammonia water to the mixed solution, adjust the pH value to 4, stir evenly, and obtain a sol solution; wherein Li 0.8 Na 0.2 The mass ratio of TiOPO4 / C and citric acid is 95:5;

[0091] S4. The sol solution was gelled at 200°C for 3 hours, and aged at 100°C for 5 hours after complete gelation. The material was ground and placed in a tubular atmosphere furnace, first decarburized at 350°C for 4 hours, then heated to 700°C at a rate of 2 / min and calcined for 8 hours. After cooling, it was crushed to obtain a titanium-based phosphate composite material.

[0092] Test Example 1

[0093] Based on Example 2, the effects of surfactant, pH value, gelation temperature and aging time on the particle size (μm) and specific surface area (m 2 / g), Table 1 shows the relevant variables and performance parameters:

[0094] Table 1

[0095] Sample Surfactants pH Gelation temperature Aging time Particle size Specific surface area Example 2 Sodium Lauryl Sulfate 4 200 5 2-5 8.4 No. 1 / 4 200 5 0.2-0.8 32.3 No. 2 Sodium Lauryl Sulfate 3 200 5 2-5 9.7 No. 3 Sodium Lauryl Sulfate 5 200 5 2-5 7.1 No. 4 Sodium Lauryl Sulfate 1 250 6 / / No. 5 Sodium Lauryl Sulfate 7 200 5 7-10 3.5 No. 6 Sodium Lauryl Sulfate 4 220 4 2-5 7.7 No. 7 Sodium Lauryl Sulfate 4 300 4 6-8 3.1 No. 8 Sodium Lauryl Sulfate 4 100 6 ＜1 19.4

[0096] As can be seen from Table 1, compared with Example 2, the particle size of the material finally obtained by No. 1 is nanometer-level and has a higher specific surface area. This is because sodium lauryl sulfate is an anionic surfactant, and its molecular structure is composed of a hydrophilic sulfate head and a hydrophobic hydrocarbon chain tail. This special structure enables sodium lauryl sulfate to self-assemble in an aqueous solution to form micelles, which can provide a hydrophobic environment for sol particles, prompting particles to migrate and aggregate inside the micelles, combined with a higher gelation temperature and a longer aging time, providing enough kinetic energy and time for the growth of the crystal nucleus in the micelle, which is conducive to the growth of single crystal particles, thereby reducing the specific surface area of ​​the entire system. However, since No. 1 does not add a surfactant, the nucleation rate is much greater than the crystal nucleus growth rate, resulting in the presence of a large number of sol ions, which in turn leads to a smaller particle size and a higher specific surface area of ​​the prepared material.

[0097] Combining Example 2 and No. 2-5, it can be seen that when the pH is less than 3 (No. 4), even after aging at 250°C for 6h, a gel state cannot be formed, indicating that the pH value of the sol solution cannot be too low. When the pH value is greater than 5 (No. 5), serious hard agglomeration is found, the particle size becomes larger, and the specific surface area decreases, indicating that the pH value of the sol solution cannot be too high. When the pH value of the sol solution is between 3-5, as the pH value increases, the particle size of the obtained material does not change much, and the specific surface area decreases slightly, which is mainly because the proportion of large-particle single crystals increases.

[0098] Combining Example 2 and No. 7-8, it can be seen that when the gelation temperature is too high (No. 7), the grains grow too fast and the particle size is relatively large; when the gelation temperature is too low (No. 8), the nucleation rate is much greater than the nucleus growth rate, resulting in the presence of a large number of sol ions. The particle size of the prepared material is nanometer-level and has a high specific surface area.

[0099] Test Example 2

[0100] The titanium-based phosphate composite materials prepared in Examples 1-2 and Nos. 1 and 5 were characterized. Figure 1-Figure 4 As shown. Figure 1 It can be seen that the surface of titanium-based phosphate KTiOPO4 is surrounded by a carbon coating layer (light-colored area), and the thickness of the carbon layer is about 10nm. Figure 2 It can be seen that the titanium-based phosphate composite material K 0.8 Na 0.2 The particle size of TiOPO4 / C is about 2μm-5μm, not nano-sized particles. Figure 3 It can be seen that without adding surfactant, the particle size of the prepared material is less than 0.5 μm (500 nm). Figure 4 It can be seen that when the pH value is greater than 5, the prepared material suffers from severe hard agglomeration.

[0101] Test Example 3

[0102] Battery Assembly:

[0103] Negative electrode sheet: titanium-based phosphate composite material, conductive agent is conductive carbon black (super P), adhesive is polyvinylidene fluoride (PVDF), and negative electrode current collector is 6μm aluminum foil; titanium-based phosphate composite material, conductive agent and adhesive are mixed according to the mass ratio of 8:1:1, and N-methylpyrrolidone is added to stir into a uniform and stable negative electrode slurry, and then the negative electrode slurry is evenly coated on the surface of the negative electrode current collector, and 200μm scraper coating is performed, and the negative electrode sheet is obtained after drying and cold pressing. The mass load of the titanium-based phosphate composite material is about 2.5mg / cm 2 .

[0104] Counter electrode: Sodium metal sheet.

[0105] Isolation film: The base film of the isolation film is a polyethylene film with a thickness of 9μm.

[0106] Electrolyte: Sodium hexafluorophosphate was dissolved in ethylene carbonate to prepare an electrolyte with a concentration of 1 mol / L.

[0107] Assembly of sodium ion battery: Arrange the negative electrode sheet, separator, counter electrode and separator in sequence, and use winding as the assembly method.

[0108] Performance Test:

[0109] The assembled sodium ion battery is subjected to discharge medium voltage, specific capacity and other tests:

[0110] (1) Charge / discharge test: The sodium ion battery is charged / discharged at a rate of 1C in the voltage range of 0-3V;

[0111] (2) Discharge medium voltage (V): refers to the potential difference between the positive and negative electrodes when the battery is in the intermediate state of charge (usually about half of the charge is discharged) during the continuous discharge process from the beginning to the end of the discharge. The lower this voltage is, the better. When paired with a fixed positive electrode material, the greater the voltage difference of the whole battery, the higher the specific energy.

[0112] (3) Specific capacity (mAh / g): The battery is tested for discharge using a battery charge and discharge test device, and the total amount of electricity released from the battery from full charge to full discharge is recorded, i.e., the discharge capacity (mAh); the mass (g) of the active material involved in the electrochemical reaction in the battery is accurately weighed. If the specific capacity of the battery as a whole is to be calculated, the total mass of the battery can also be used; then the actual specific capacity of the battery is calculated using the following formula: specific capacity = discharge capacity / mass of active material;

[0113] Table 2 and Figure 5 The following are the relevant performance parameters finally measured:

[0114] Table 2

[0115] Sample Chemical formula Discharge medium voltage Specific capacity Example 1 <![CDATA[KTiOPO4 / C]]> 1.24 134 Example 2 <![CDATA[K 0.8 That 0.2 TiOPO4 / C]]> 1.26 125 Example 3 <![CDATA[K 0.7 That 0.3 TiOPO4 / C]]> 1.30 119 Example 4 <![CDATA[NaTiOPO4 / C]]> 1.39 111 Example 5 <![CDATA[Li 0.2 That 0.8 TiOPO4 / C]]> 1.41 109 Example 6 <![CDATA[K 0.3 That 0.7 TiOPO4 / C]]> 1.49 75 Example 7 <![CDATA[Li 0.8 That 0.2 TiOPO4 / C]]> 1.51 39

[0116] From Table 2 and Figure 5 It can be seen that the discharge specific capacity of Example 1 is 134 mAh / g, and the discharge medium voltage is 1.24 V. When the chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C, as the K content in the titanium-based phosphate decreases, its discharge specific capacity shows a decreasing trend. When 0≤x≤0.5, the specific capacity is 100mAh / g-135mAh / g. Compared with Example 3, Example 6 has a specific capacity of only 75mAh / g because the potassium content is less than 0.5. This is mainly because potassium ions have a larger ionic radius and can provide a larger ion diffusion channel for the insertion of sodium ions, thereby having a higher electrochemical capacity. When the chemical formula of the titanium-based phosphate composite material is Li 1-y Na yTiOPO4 / C, when 0.5≤y≤1, has a specific capacity of 80mAh / g-110mAh / g; compared with Example 5, Example 7 has a specific capacity of only 39mAh / g because the lithium content is greater than 0.5. This is because the radius of lithium ions is too small to support the lattice structure, and the deintercalation of sodium ions is very difficult.

[0117] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a titanium-based phosphate composite material, characterized in that: The following steps are involved: S1, mixing a surfactant and a solvent to obtain a surfactant solution; S2, stirring the M source, titanium source, phosphorus source, organic carbon source and the surfactant solution described in S1 to obtain a mixed solution; the amount of the M source, titanium source, phosphorus source and organic carbon source satisfies the chemical formula MTiOPO4 / C, wherein the carbon content is 0.5wt%-5wt%; S3, adding a chelating agent and a pH adjusting agent to the mixed solution described in S2, adjusting the pH to 3-5, and obtaining a sol solution; S4, subjecting the sol solution described in S3 to gelation treatment, aging treatment, decarburization treatment and calcination treatment to obtain the titanium-based phosphate composite material.

2. The method for preparing the titanium-based phosphate composite material according to claim 1, characterized in that: In S1, the surfactant is selected from sodium dodecylbenzene sulfonate and / or sodium dodecyl sulfate; and / or, the solvent is selected from one or more of water, ethanol and acetone; And / or, the mass fraction of the surfactant in the surfactant solution is 0.2%-1%.

3. The method for preparing the titanium-based phosphate composite material according to claim 1, characterized in that: In S2, the M source is selected from one or more of a sodium source, a lithium source and a potassium source; And / or, the titanium source is selected from one or more of titanium dioxide, tetrabutyl titanate and titanium tetrachloride; and / or, the phosphorus source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus pentoxide, sodium dihydrogen phosphate, lithium dihydrogen phosphate and potassium dihydrogen phosphate; And / or, the organic carbon source is selected from one or more of sucrose, glucose and polyacrylic acid; And / or, the mass ratio of MTiOPO4 / C to surfactant is 99.95:0.05-99:

1.

4. The method for preparing the titanium-based phosphate composite material according to claim 3, characterized in that: The sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium acetate and sodium dihydrogen phosphate; And / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate; And / or, the potassium source is selected from one or more of potassium carbonate, potassium hydroxide, potassium acetate, potassium dihydrogen phosphate and dipotassium hydrogen phosphate.

5. The method for preparing the titanium-based phosphate composite material according to claim 1, characterized in that: In S3, the chelating agent is selected from citric acid and / or ethylenediaminetetraacetic acid; And / or, the pH adjuster is selected from ammonia and / or phosphoric acid; And / or, the mass ratio of MTiOPO4 / C to the chelating agent is 99:1-90:

10.

6. The method for preparing the titanium-based phosphate composite material according to claim 1, characterized in that: In S4, the gelation treatment is performed at a temperature of 180°C-250°C and for a time of 2h-4h; And / or, the aging treatment is performed at a temperature of 60°C-150°C and a time of 4h-6h; And / or, the decarburization treatment temperature is 300°C-350°C, and the time is 3h-6h; And / or, the heating rate of the calcination treatment is 2 / min-5°C / min, the temperature is 600°C-800°C, and the time is 6h-12h.

7. The titanium-based phosphate composite material prepared by the method according to any one of claims 1 to 6, characterized in that: The titanium-based phosphate composite material includes titanium-based phosphate and a carbon coating layer coated on the surface of the titanium-based phosphate. The particle size of the titanium-based phosphate composite material is 2μm-5μm, and the thickness of the carbon coating layer is 5nm-20nm. The chemical formula of the titanium-based phosphate composite material is MTiOPO4 / C, and M is selected from one or more of sodium, lithium and potassium.

8. The titanium-based phosphate composite material according to claim 7, characterized in that: The chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C and / or Li 1-y Na y TiOPO4 / C, 0≤x<1, 0≤y<1.

9. The titanium-based phosphate composite material according to claim 7, characterized in that: The chemical formula of the titanium-based phosphate composite material is K 1-x Na x TiOPO4 / C and / or Li 1-y Na y TiOPO4 / C, 0≤x≤0.5, 0.5≤y≤1.

10. A sodium ion battery, characterized in that: The negative electrode material of the sodium ion battery is the titanium-based phosphate composite material described in any one of items 1-6, and the positive electrode material is selected from polyanion materials and / or Prussian blue materials.

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