Positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a positive electrode material and a preparation method thereof. The preparation method comprises the following steps: a mixing step: putting a raw material X and a raw material Y into a container filled with water, mixing and stirring to obtain slurry A, and then grinding the slurry A to obtain precursor slurry B; wherein the X raw material is a substance which contains an M element and is not easy to dissolve in water, the Y raw material is a sodium salt which is easy to dissolve in water, and at least one of the X raw material and the Y raw material contains a phosphorus element P; a spray drying step: placing the precursor slurry B in spray drying equipment for spray drying treatment to obtain precursor powder C; and a sintering step: putting the precursor powder C into sintering equipment for sintering treatment to obtain the positive electrode material. According to the preparation method, the raw materials are specially designed in the mixing step, and the spray drying step and the sintering step are cooperated, so that the obtained positive electrode material product is high in purity and relatively good in electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries are currently a hot topic in new energy materials research due to their advantages such as abundant resources, low cost, good low-temperature performance, and high safety. To alleviate the pressure of lithium resource shortages and reduce raw material costs, providing a method for preparing sodium-ion batteries that is highly efficient, easy to industrialize, and possesses excellent electrochemical performance has become one of the urgent problems to be solved in the battery industry.

[0003] However, existing methods for preparing sodium-ion battery cathode materials suffer from significant impurity generation in solid-phase ball milling and complex liquid-phase preparation processes. Therefore, the preparation methods for sodium-ion battery cathode materials still need improvement. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a cathode material and a method for preparing the same, which can produce a cathode material with high purity and good electrochemical performance by combining raw material design with mixing, spray drying and sintering steps.

[0005] The first aspect of this application provides a method for preparing a cathode material, wherein the cathode material has the molecular formula Na₄M₂ 3- 3a N 6a / m (PO4)2P2O7, wherein element M is selected from at least one of Mn, Fe, Ni, and Co, element N is a doped metal element different from element M, element N is in the valence state m, m is a natural number greater than 0, 0≤a≤0.3, characterized in that the preparation method includes the following steps: Mixing step: Place raw material X and raw material Y in a container filled with water and mix and stir to obtain slurry A. Then grind slurry A to obtain precursor slurry B. Among them, raw material X is a substance containing element M and is not easily soluble in water; raw material Y is a sodium salt that is easily soluble in water; at least one of raw material X and raw material Y contains phosphorus element P. Spray drying step: The precursor slurry B is placed in a spray drying device for spray drying to obtain precursor powder C; Sintering step: The precursor powder C is placed in a sintering device for sintering treatment to obtain the cathode material.

[0006] In any embodiment, the average particle size of raw material X ranges from 100 to 4000 nm.

[0007] In any embodiment, the particle size D50 of raw material X ranges from 100 to 4000 nm.

[0008] In any embodiment, the particle size D10 of raw material X ranges from 100 to 1500 nm.

[0009] In any embodiment, the particle size D90 of raw material X ranges from 300 to 10000 nm.

[0010] In any embodiment, the particle sizes D50, D10, and D90 of raw material X satisfy: D50 / D10 ≤ D90 / D10.

[0011] In any implementation, the polydispersity index of raw material X ranges from 0.1 to 0.7.

[0012] In any embodiment, during the mixing step, the mass ratio of raw material X to water in the container ranges from 15% to 80%; preferably from 15% to 75%; more preferably from 20% to 55%.

[0013] In any embodiment, the preparation method further includes a precursor preparation step, which includes: introducing solution S1 into the first inlet of a microreactor, wherein solution S1 contains element M; introducing solution S2 into the second inlet of the microreactor, wherein solution S2 contains phosphorus element P; mixing solution S1 and solution S2 through the microreactor to obtain a suspension, wherein the suspension is matured, centrifuged, filtered, and dried to obtain raw material X.

[0014] In any embodiment, the precursor preparation step further includes a pH adjuster, which is used to adjust the pH value of the solution S1 and / or the solution S2 and / or the suspension.

[0015] In any embodiment, the pH value of solution S1 is in the range of 2.5-3.5.

[0016] In any embodiment, when the pH adjuster is used to adjust solution S1, the pH adjuster is selected from at least one of hydrochloric acid, sulfuric acid, or glacial acetic acid (CH3COOH).

[0017] In any embodiment, the pH range of solution S2 is 7.0-11.0.

[0018] In any embodiment, when the pH adjuster is used to adjust solution S2, the pH adjuster is selected from at least one of NaOH or ammonia; preferably, the pH adjuster is ammonia.

[0019] In any embodiment, the pH range of the suspension is 3.0-7.0.

[0020] In any embodiment, when the pH adjuster is used to adjust the suspension, the pH adjuster is selected from at least one of H3PO4, NH4H2PO4, (NH4)2HPO4, NaH2PO4, or Na2HPO4.

[0021] A second aspect of this application provides a cathode material prepared according to the method for preparing the cathode material.

[0022] A third aspect of this application provides a sodium-ion battery comprising the positive electrode material provided in the second aspect of this application.

[0023] A fourth aspect of this application provides a battery module that includes the sodium-ion battery provided in the third aspect of this application.

[0024] The fifth aspect of this application provides an electrical device comprising at least one selected from the positive electrode material of the second aspect of this application, the sodium-ion battery of the third aspect of this application, or the battery module of the fourth aspect of this application.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This application achieves high purity and good electrochemical performance of cathode material products by specially designing the selection of raw materials in the mixing step and coordinating the spray drying and sintering steps; 2. The method for preparing the cathode material provided in this application is simple and conducive to industrial production; 3. The sodium-ion battery provided in this application can significantly improve the discharge capacity and cycle performance of the battery due to the high purity of the cathode material. Attached Figure Description

[0026] Figure 1 This is a process flow diagram for preparing the cathode material according to some embodiments of the present invention.

[0027] Figure 2 The image shows the XRD pattern of raw material Fe3(PO4)2·8H2O prepared in Example 1 of this invention.

[0028] Figure 3 The image shows the XRD pattern of the cathode material Na4Fe3(PO4)2P2O7 prepared in Example 1 of this invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] In the description of this application, the terms “(1)”, “(2)”, “first”, and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as “(1)”, “(2)”, “first”, or “second” may explicitly or implicitly include at least one of that feature. In the description of this application, “multiple” means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0032] In the description of this application, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0033] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the weights mentioned in the embodiments of this application can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0036] The embodiments of this application will be described in detail below.

[0037] The first aspect of this application provides a method for preparing a cathode material, wherein the cathode material has the molecular formula Na₄M₂ 3- 3a N 6a / m(PO4)2P2O7, wherein element M is selected from at least one of Mn, Fe, Ni, and Co, element N is a doped metal element different from element M, element N is in the valence state m, m is a natural number greater than 0, 0≤a≤0.3, characterized in that the preparation method includes the following steps: Mixing step: Place raw material X and raw material Y in a container filled with water and mix and stir to obtain slurry A. Then grind slurry A to obtain precursor slurry B. Among them, raw material X is a substance containing element M and is not easily soluble in water; raw material Y is a sodium salt that is easily soluble in water, and at least one of raw material X and raw material Y contains phosphorus element P. Spray drying step: The precursor slurry B is placed in a spray drying device for spray drying to obtain precursor powder C; Sintering step: The precursor powder C is placed in a sintering device for sintering treatment to obtain the cathode material.

[0038] In the above preparation method, water is used as a medium to mix and stir the raw materials in the mixing step. In terms of raw material design, raw material X is a substance that is not easily soluble in water. Therefore, when raw material X is added to the aqueous solution, it will form dispersed microparticles. Raw material Y is a sodium salt that is easily soluble in water. When raw material Y is added to the aqueous solution, it will form sodium ions. Under the action of external force (stirring and grinding), the uniform distribution of sodium ions on the surface of raw material X can be accelerated. After the mixing step, through the synergistic cooperation of the spray drying step and the sintering step, a cathode material product with high purity can be obtained.

[0039] Generally, "not easily soluble in water" can be understood as having a solubility of less than 0.01 g / 100 g of water at room temperature (20°C); "easily soluble in water" can be understood as having a solubility of more than 3 g / 100 g of water at room temperature.

[0040] Furthermore, the applicant discovered that by rationally controlling the particle size of raw material X, the electrochemical performance of the cathode material can be further improved. Since raw material X is a substance that is not easily soluble in water, the quality of raw material X plays a crucial role in the performance of the synthesized material; by using raw material X with a small particle size, the synthesized material has higher purity, and the sodium-ion battery made from it has good electrochemical performance.

[0041] Through in-depth research, the applicant has discovered that, in addition to meeting the aforementioned design conditions, if the X raw material of this application can also meet one or more of the following conditions, the electrochemical performance of the sodium-ion battery prepared by the cathode material can be further improved.

[0042] In any embodiment of this application, the average particle size of raw material X ranges from 100 to 4000 nm.

[0043] In any embodiment of this application, the particle size D50 of raw material X ranges from 100 to 4000 nm.

[0044] If the particle size of raw material X is too small, it is prone to agglomeration during the mixing step; if the particle size of raw material X is too large, fewer sodium ions are adsorbed on its surface, which can easily generate impurities during the synthesis process. When either the average particle size or the particle size D50 of raw material X meets the above-mentioned range, the prepared sodium-ion battery has good cycle performance.

[0045] Preferably, the average particle size of raw material X is in the range of 500-3000 nm; more preferably, it is in the range of 700-1500 nm.

[0046] Preferably, the particle size D50 of raw material X is in the range of 200-1500 nm; more preferably, it is in the range of 700-1500 nm.

[0047] Furthermore, the particle size D10 of raw material X ranges from 100 to 1500 nm. The particle size range of small particles in raw material X is within the above range, and within the range of average particle size and particle size D50, which can mitigate the agglomeration problem that may occur during the mixing step.

[0048] Furthermore, the particle size D90 of raw material X ranges from 300 to 10000 nm. Preferably, the particle size D90 ranges from 500 to 4000 nm. The particle size range of large particles in raw material X is within the above range, and its overlap with the average particle size range and particle size D50 range is relatively high, resulting in good particle size uniformity of the material.

[0049] Preferably, the particle size D10 of raw material X is in the range of 180-1200 nm.

[0050] Preferably, the particle size D90 of raw material X is in the range of 300-8000 nm, and more preferably 300-4000 nm.

[0051] Furthermore, the D50 / D10 ratio of raw material X is ≤ D90 / D10. This implies that the number of small particles in raw material X is greater than or equal to the number of large particles, and correspondingly, the proportion of particles with high specific surface area is the same or higher. Under the same mass of raw material X, raw material X with a high specific surface area adsorbs more sodium ions. In subsequent spray drying and sintering steps, raw material X with a high specific surface area exhibits stronger activity, which facilitates the combination of element M in raw material X with sodium ions, resulting in the preparation of a cathode material with superior performance.

[0052] In any embodiment of this application, the polydispersity index of raw material X ranges from 0.1 to 0.7. When the polydispersity index of raw material X is within the above range, its particle size distribution is narrow and the particle size is relatively uniform, which is beneficial to the uniform distribution of sodium ions on the surface of raw material X.

[0053] Preferably, the polydispersity index of raw material X is in the range of 0.2-0.6, more preferably 0.2-0.5, and even more preferably 0.2-0.42.

[0054] In any embodiment of this application, the mass ratio of raw material X to water in the container ranges from 15% to 80%. Because raw material X has low solubility in water, being almost insoluble, its mass ratio to water significantly affects the uniformity of the mixture during the mixing process. Too low a proportion of raw material X reduces production efficiency and hinders large-scale industrial production; too high a proportion of raw material X leads to severe agglomeration during the mixing process, placing higher demands on the mechanical properties of the mixing equipment and increasing production costs.

[0055] Further, preferably, the mass ratio of raw material X to water in the container is in the range of 15% to 75%.

[0056] Furthermore, preferably, the mass ratio of raw material X to water in the container ranges from 20% to 55%. Understandably, controlling the mass percentage of raw material X within a reasonable range can alleviate agglomeration, reduce water consumption, and improve production efficiency.

[0057] In any embodiment of this application, raw material X is a compound containing elements M and P. It is understood that the cathode material contains sodium (Na), M, P, and oxygen (O), with sodium (Na) obtained from raw material Y; raw material X is a compound containing elements M and P, requiring relatively fewer types of raw materials for synthesis, thus simplifying the production process and reducing production costs.

[0058] In any embodiment of this application, the solubility product Ksp of the anhydrous compound corresponding to raw material X is ≤1.0×10-25. The applicant has found that when the solubility product of raw material X is less than the above range, it has lower solubility than raw material X with a solubility of less than 0.01g / 100g water, which can mitigate the imbalance of elemental ratio caused by raw material X dissolving in water, thus reducing the generation of impurities.

[0059] In any embodiment of this application, the anhydrous compound of raw material X has the molecular formula M3(PO4)2 and / or MPO4. Furthermore, the applicant proposes that when the above-mentioned materials are selected for raw material X, the raw material formulation of the mixing step can be significantly simplified, and production efficiency can be improved.

[0060] In any embodiment of this application, the X raw material is selected from one or more of Mn3(PO4)2.z1H2O (0≤z1≤7), Fe3(PO4)2.z2H2O (0≤z2≤8), Ni3(PO4)2.z3H2O (0≤z3≤8), Co3(PO4)2.z4H2O (0≤z4≤8), and FePO4.z5H2O (0≤z5≤8).

[0061] The preparation method of cathode materials also includes a precursor preparation step.

[0062] In any embodiment of this application, raw material X is obtained through a precursor preparation step. The precursor preparation step includes: introducing solution S1 into the first inlet of a microreactor, solution S1 containing element M; introducing solution S2 into the second inlet of the microreactor, solution S2 containing phosphorus element P; mixing solutions S1 and S2 through the microreactor to obtain a suspension, which is then aged, centrifuged, filtered, and dried to obtain raw material X.

[0063] Understandably, solution S1 can be an aqueous solution or an organic solution. Solution S1 is an aqueous solution formed by dissolving a solute containing element M in water; solution S1 can also be an organic solution formed by dissolving a solute containing element M in an organic solvent. The organic solution can be an organic solvent dissolved in water; or it can be a mixed organic solution formed by mixing multiple organic solvents. For example, the organic solvent is 95% ethanol; or 20% ethanol (using 95% commercially available industrial ethanol diluted with distilled water).

[0064] Similarly, solution S2 can be an aqueous solution or an organic solution. Solution S2 is an aqueous solution formed by dissolving a solute containing phosphorus element P in water; it can also be an organic solution formed by dissolving in an organic solvent; or it can be a liquid substance containing phosphorus element P (such as phosphoric acid, ammonium phosphate, etc.).

[0065] In any embodiment of this application, the solute of solution S1 is selected from ferrous sulfate, ferrous chloride, ferric sulfate, ferric chloride, manganese sulfate, manganese chloride, cobalt sulfate, nickel sulfate, etc. The solvent of solution S1 is water or ethanol.

[0066] In any embodiment of this application, the solute of solution S2 is selected from one or more of Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, Na2HPO4, NaH2PO4, Na3PO4, H3PO4, NH4H2PO4, (NH4)2HPO4, and (NH4)3PO4. The solvent of solution S2 is water or ethanol.

[0067] Furthermore, the applicant discovered that the particle size of raw material X could also be controlled by controlling the pH value.

[0068] In any embodiment of this application, the precursor preparation step further includes a pH adjuster. The pH adjuster is used to adjust the pH value of solution S1, and / or solution S2, and / or suspension.

[0069] Furthermore, a pH adjuster is used to regulate the pH value of the suspension, ensuring it remains within the range of 3.0-7.0. Since element M readily forms M(OH)₂ or M(OH)₃ precipitates in an alkaline environment, it can introduce impurities such as M(OH)₂ or M(OH)₃ into the X raw material. Therefore, controlling the pH value of the suspension within a suitable range is beneficial for synthesizing X raw material with higher purity.

[0070] Furthermore, the pH range of the suspension is 3.0-5.5. Understandably, as the suspension matures, its pH value will gradually increase. Maintaining the pH value of the suspension in a relatively low range can inhibit the formation of impurities such as M(OH)2 or M(OH)3.

[0071] Furthermore, when element M contains ferrous iron, the pH range of the suspension is 3.0-4.5. When element M contains ferrous iron, the acidic environment can also inhibit the oxidation of ferrous iron to ferric iron, avoiding other side reactions caused by elemental imbalance and thus preventing the generation of impurities.

[0072] Furthermore, when a pH adjuster is used to adjust the pH value of a suspension, the pH adjuster is an acidic adjuster containing phosphorus (P). Specifically, the pH adjuster is selected from at least one of H3PO4, NH4H2PO4, (NH4)2HPO4, NaH2PO4, or Na2HPO4. Because the selected pH adjuster is an acidic adjuster containing phosphorus (P), it not only maintains the acidic environment of the suspension and prevents deterioration, but also serves to supplement the phosphorus source.

[0073] Furthermore, the applicant discovered that when the above method is scaled up for production, the volume of the suspension is relatively large. With a large volume of suspension, adjusting the pH value using a pH adjuster can lead to pH imbalances. Sudden increases or decreases in localized pH levels can result in impurity formation or localized dissolution of the suspension. Therefore, the applicant proposes an alternative solution: controlling the pH value of solution S1 or solution S2, thereby controlling the pH value of the suspension and reducing impurity formation caused by localized pH changes in the suspension.

[0074] In one embodiment of this application, a pH adjuster is used to adjust the pH value of solution S1, such that the pH value of solution S1 is in the range of 2.5-3.5; or a pH adjuster is used to adjust the pH value of solution S2, such that the pH value of solution S2 is in the range of 7.0-11.0. By controlling the pH values ​​of solutions S1 and S2 within the above ranges, the pH value of the suspension after mixing in the microreactor can be relatively maintained between 3.0 and 7.0.

[0075] Furthermore, when the pH adjuster is used to adjust solution S1, the pH adjuster is selected from at least one of hydrochloric acid, sulfuric acid, or glacial acetic acid (CH3COOH). Preferably, the pH adjuster is hydrochloric acid or glacial acetic acid. A weak acid as the pH adjuster not only places lower requirements on the corrosion resistance of the production equipment but also facilitates pH adjustment, preventing rapid changes in the pH of solution S1 that could lead to localized pH imbalances.

[0076] Furthermore, when the pH adjuster is used to adjust solution S2, the pH adjuster is selected from at least one of NaOH or ammonia. Preferably, the pH adjuster is ammonia. Ammonia gradually evaporates as the suspension matures, causing the pH of the suspension to decrease, which helps maintain a weakly acidic environment in the suspension.

[0077] In any embodiment of this application, the molar concentration S1 of element M in solution S1 is... mol The concentration is 0.05-10 mol / L. In solution S2, the molar concentration of phosphorus (P) is S2. mol The concentration is 0.05-10 mol / L.

[0078] In any embodiment of this application, the aging of the suspension is performed by placing the suspension in a container and stirring. The aging time is 0.2-40 hours.

[0079] In one specific embodiment, raw material X is Mn3(PO4)2.z1H2O (0≤z1≤7), Fe3(PO4)2.z2H2O (0≤z2≤8), Ni3(PO4)2.z3H2O (0≤z3≤8), Co3(PO4)2.z4H2O (0≤z4≤8), or FePO4.z5H2O (0≤z5≤8) prepared by the above-described precursor preparation steps.

[0080] The mixing step of this application also includes raw material Y, which is a sodium salt that is easily soluble in water. Raw material Y can be a single sodium salt or a mixture of multiple sodium salts.

[0081] In any embodiment of this application, the solubility of the corresponding anhydrous compound of raw material Y is ≥3g / 100g water.

[0082] In any embodiment of this application, raw material Y is one or more compounds containing sodium (Na) and phosphorus (P), and the solubility of its corresponding anhydrous compound is ≥3g / 100g water. Raw material Y with a solubility product ≥3g / 100g water has better solubility in aqueous solution, and it readily generates sodium ions, pyrophosphate ions, and phosphate ions (monohydrogen ions / dihydrogen ions), which helps to uniformly disperse sodium ions, pyrophosphate ions, and phosphate ions on the particle surface of raw material X.

[0083] In any embodiment of this application, raw material Y is two or more sodium salts. Raw material Y is selected from at least two of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, H4P2O7, Na2HPO4, NaH2PO4, Na3PO4, H3PO4, NH4H2PO4, (NH4)2HPO4, and (NH4)3PO4.

[0084] In any embodiment of this application, Y is a sodium salt. Y is selected from NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, Na2HPO4, NaH2PO4, or Na3PO4.

[0085] In any embodiment of this application, the stoichiometric ratio of sodium (Na) to phosphorus (P) in raw material Y is 2:1, that is, the sum of the stoichiometric ratios of sodium (Na) and phosphorus (P) in raw material Y is 2:1. It can be understood that as long as the stoichiometric ratio of sodium (Na) to phosphorus (P) in raw material Y meets the requirement of 2:1, it is acceptable.

[0086] When raw material Y is a variety of sodium salts, the stoichiometric ratio of sodium (Na) to phosphorus (P) is 2:1. This means that the ratio is 2:1 according to the molar ratio, not an absolute 2:1. For example, it could be 2:1.01 or 2:0.99, etc. As long as it is within a certain range of stoichiometric difference, it falls within the scope of protection claimed in this application.

[0087] Raw material Y can also be selected from one or more of Na4P2O7 and Na2HPO4. Raw material Y is Na4P2O7 or Na2HPO4. Raw material Y can also be a mixture of Na4P2O7 and Na2HPO4.

[0088] In any embodiment of this application, the mass ratio of raw material Y to water in the container ranges from 15% to 80%. Preferably, the mass ratio of raw material Y to water in the container ranges from 20% to 55%. Raw material Y is a water-soluble sodium salt, and a relatively high concentration of raw material Y can increase the adsorption of sodium ions, pyrophosphate ions, and phosphate ions in raw material Y on the surface of raw material X particles.

[0089] In any embodiment of this application, in the mixing step: the solvent is an aqueous solution.

[0090] In the mixing step: An alcohol solvent may also be added to the aqueous solution. The alcohol solvent is one or more of methanol, ethanol, propanol, butanol, and pentanol.

[0091] In any embodiment of this application, the mixing step further includes: excipient A. Excipient A is added to slurry A, and then slurry A is ground to obtain precursor slurry B; or raw material X, raw material Y, and excipient are placed together in a container filled with water, mixed and stirred to obtain slurry A, and then slurry A is ground to obtain precursor slurry B.

[0092] The excipients include at least one of an antioxidant, a phosphorus source supplement, a dispersant, and a viscosity reducer. The antioxidant is selected from at least one of ascorbic acid, vitamin C, citric acid, and vanillin. The phosphorus source supplement is selected from at least one of H3PO4, NH4H2PO4, and (NH4)2HPO4. The dispersant is selected from at least one of polyethylene oxide, polytetrafluoroethylene, polyacrylic acid, polymethyl acrylate, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and carboxyethyl methyl cellulose. The viscosity reducer is selected from at least one of polyvinyl alcohol, polyethylene glycol, and polypropylene glycol.

[0093] The ratio of the mass of the auxiliary material to the mass of water in the container is in the range of 0 to 20%.

[0094] The molecular formula of the cathode material provided in this application is Na₄M⁻. 3-3a N 6a / m (PO4)2P2O7 can also be expressed as Na4(M3(PO4)2) 1-a (N 6a / m m+ (PO4) 2a P2O7); wherein, element M is selected from at least one of Mn, Fe, Ni, and Co, element N is a doped metal element different from element M, element N is in the valence state m, m is a natural number greater than 0, and 0≤a≤0.3.

[0095] The element M is selected from at least one of Mn, Fe, Ni, and Co. Understandably, the element M can be selected from one of Mn, Fe, Ni, and Co, such as Mn; the element M can be selected from two or more of Mn, Fe, Ni, and Co, such as Mn and Fe, or Mn, Fe, and Co.

[0096] When element M is only one element; for example, if it is selected from Mn, the molecular formula of the cathode material is Na4Mn3(PO4)2P2O7; if M is selected from Fe, the molecular formula of the cathode material is Na4Fe3(PO4)2P2O7; if M is selected from Ni, the molecular formula of the cathode material is Na4Ni3(PO4)2P2O7; if M is selected from Co, the molecular formula of the cathode material is Na4Co3(PO4)2P2O7. When M is selected from two or more of Mn, Fe, Ni, and Co, the molecular formula of the cathode material is Na4Mn e Fe f Ni g Co 3-e-f-g (PO4)2P2O7, where 0≤e≤3, 0≤g≤3, 0≤g≤3, and 0≤e+f+g≤3.

[0097] When a = 0, no N element is added; when a > 0, the doping metal element N is added. The N element is a doping metal element different from the M element. The N element is selected from at least one of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

[0098] Nitrogen (N) is introduced through modifying additives. The introduction of these additives can significantly improve the ionic and electronic conductivity of the cathode material, thereby enhancing its electrochemical performance.

[0099] The modifying additive can be added in at least one of the mixing, spray drying, or sintering steps. In the mixing step, the modifying additive is added to slurry A, which is then ground to obtain precursor slurry B. In the spray drying step, precursor slurry B is mixed with the modifying additive and then processed in a spray drying apparatus to obtain precursor powder C. In the sintering step, precursor powder C is mixed with the modifying additive and then sintered in a sintering apparatus to obtain a cathode material containing nitrogen (N).

[0100] The solid content of the modified additive is 1%-20%. Solid content refers to the mass ratio of the modified additive to the added slurry or powder. For example, in the mixing step, the solid content of the modified additive refers to the mass ratio of the modified additive to slurry A; in the spray drying step, the solid content of the modified additive refers to the mass ratio of the modified additive to precursor slurry B; and in the sintering step, the solid content of the modified additive refers to the mass ratio of the modified additive to precursor powder C.

[0101] The modifying additive is selected from elements or compounds containing at least one of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu. It may also be a solution containing the above elements.

[0102] Preferably, the molecular formula of the modified additive is N 6 / m m+ (PO4)2. When the molecular formula of the modified additive is N... 6 / m m+ When (PO4)2 is used, the molecular formula of the modified additive is similar to that of N in the cathode material. 6a / m The (PO4)2 unit is the same. Due to the similar structure, it is beneficial for the insertion of N element in the modified additive, and no other impurity elements will be introduced.

[0103] Because the conductivity of cathode materials is low, a carbon source needs to be introduced to improve their conductivity. The molecular formula of a cathode material with an introduced carbon source can be expressed as Na₄M₂. 3-3a N 6a / m (PO4)2P2O7 / C, can also be expressed as Na4(M3(PO4)2) 1-a (N 6a / m m+ (PO4) 2a P₂O₇ / C. The carbon element (C) represents the carbon coating in the cathode material. The carbon element (C) is introduced into the cathode material through a carbon source.

[0104] Similar to modified additives, the carbon source is added in at least one of the mixing, spray drying, or sintering steps.

[0105] Furthermore, the carbon source can be selected from one or more inorganic carbon materials and / or organic carbon materials. Organic carbon materials are selected from one or more of citric acid, glucose, sucrose, polyethylene glycol, starch, lignin, and pitch. Inorganic carbon materials are selected from one or more of graphite, activated carbon, carbon nanotubes, and graphene.

[0106] In any embodiment of this application, during the spray drying step, the inlet temperature of the spray drying equipment is 180–300°C. Further, the inlet temperature of the spray drying equipment is 190–220°C.

[0107] In any embodiment of this application, during the spray drying step, the outlet temperature of the spray drying equipment is 80–130°C. Further, the outlet temperature of the spray drying equipment is 90–110°C.

[0108] In any embodiment of this application, a pretreatment step is further included, which is located between the spray drying step and the sintering step. The pretreatment step includes: placing the precursor powder C in an ammonia solution for ammoniation treatment.

[0109] In any embodiment of this application, the sintering atmosphere is air or an inert atmosphere during the sintering step.

[0110] In any embodiment of this application, the sintering temperature range during the sintering step is 300-800°C. Specifically, the temperature can be 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C.

[0111] In any embodiment of this application, the sintering process takes 3-20 hours.

[0112] In any embodiment of this application, the heating rate of the sintering equipment in the sintering step is 5-10°C / min.

[0113] This application also provides a sodium-ion battery, including the above-described positive electrode material or a positive electrode material prepared by the above-described preparation method. Specifically, the positive electrode includes a current collector and a positive electrode active material disposed on the current collector, wherein the positive electrode active material includes the positive electrode material of this application or a positive electrode material prepared by the preparation method of this application.

[0114] This application also provides a battery module including the aforementioned sodium-ion battery. Specifically, the battery module includes a housing, a cover, and a sodium-ion battery. The housing has a receiving cavity and an opening; the sodium-ion battery is received in the receiving cavity; the cover is used to close the opening of the housing.

[0115] This application also provides an electrical device including the aforementioned sodium-ion battery. The electrical device can be a device powered by a sodium-ion battery. Exemplarily, the electrical device can be a small electronic device (such as a mobile phone, tablet computer, laptop computer, etc.), a large transportation device such as a vehicle (such as a hybrid vehicle, electric vehicle, etc.), or a power tool (such as an electric drill, electric saw, etc.). Example

[0116] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Example 1

[0117] Preparation method of raw material X: According to the molar mass ratio, a 0.6 mol / L FeSO4·7H2O solution (solution S1) and a 0.4 mol / L (NH4)3PO4·3H2O solution (solution S2) were prepared. Solutions S1 and S2 were connected to the first and second inlets of a microreactor, respectively, for mixing. The suspension was collected at the outlet of the microreactor. After stirring and maturing the suspension for 1 hour, the pH value was measured to be 4.5. The stirred and matured suspension was washed using a centrifuge and dried in a vacuum oven to obtain a bluish-gray Fe3(PO4)2·8H2O X raw material (see attached). Figure 2 The average particle size was measured to be 781.8 nm, the particle size D50 was 820.6 nm, the particle size D10 was 446.2 nm, the particle size D90 was 1818.3 nm, and the polydispersity index was 0.302.

[0118] Methods for preparing cathode materials: Weigh out 100.32 g of Fe3(PO4)2·8H2O from raw material X, 53.18 g of Na4P2O7 from raw material Y, and 670 g of distilled water (the mass of raw material X accounts for approximately 15% of the mass of water); mix raw material X and raw material Y in an aqueous solution in a grinding tank to obtain slurry A.

[0119] Weigh 20 g of sucrose (carbon source) and 15.74 g of PEG (molecular weight 1675) as dispersant, and add them to the grinding jar containing slurry A. Place the grinding jar in a grinder and grind and mix at 300 r / min for 50 min to obtain precursor slurry B.

[0120] Precursor slurry B is placed in a spray dryer, with the inlet temperature set to 220°C and the outlet temperature to 100°C, to obtain precursor powder C.

[0121] Then, the precursor powder C was placed in a nitrogen atmosphere and calcined at 500℃ for 10h to obtain Na4Fe3(PO4)2P2O7 / C.

[0122] Figure 3 XRD analysis of the synthesized Na4Fe3(PO4)2P2O7 / C showed that it was a pure phase with virtually no impurity peaks.

[0123] 3. Preparation of button cells Take 0.8g of the above Na4Fe3(PO4)2P2O7 / C material, mix it with 0.1g of conductive carbon black and 0.1g of PVDF, grind it with NMP as the medium, and coat the resulting slurry onto an aluminum foil current collector. After drying, a positive electrode sheet is obtained. The obtained electrode sheet is cut into a square electrode with a side length of 1cm to be used as the working electrode, and a sodium metal sheet is used as the counter electrode. A coin cell (CR2032) is assembled under an inert atmosphere using 1M NaPF6 dissolved in EC:DEC (50:50 vol / vol) as the electrolyte.

[0124] 4. Particle size testing method for raw material X The particle size parameters (average particle size, D10, D50, D90) and polydispersity index of raw material X were obtained using a Zhenli Optical particle size analyzer. The particle size testing method was in accordance with GB / T 19077-2016.

[0125] 5. pH value testing method At room temperature, the pH value of a solution or suspension is measured using a pH meter.

[0126] 6. Battery charge / discharge test The prepared coin cell (CR2032) was subjected to charge-discharge tests at a charge-discharge current of 1C for 50 cycles. Example 2

[0127] The preparation method of raw material X is similar to that in Example 1, except that 0.01 mol / L sulfuric acid is added to the S1 solution to adjust the pH value of the S1 solution to 3.0, and the pH value of the suspension is tested to be 3.9 after the microreactor reaction.

[0128] The preparation method of the positive electrode material is the same as that in Example 1. Example 3

[0129] The preparation method of raw material X is similar to that in Example 1, except that 0.01 mol / L of NH4H2PO4 is added dropwise to the suspension to adjust the pH of the suspension to 5.5.

[0130] The preparation method of the positive electrode material is the same as that in Example 1. Example 4

[0131] The preparation method of raw material X is similar to that in Example 3, except that the amount of NH4H2PO4 added is increased and the pH value of the suspension is adjusted to 6.5. Example 5

[0132] The preparation method of raw material X is similar to that in Example 1, except that solution S1 is 0.6 mol / L MnSO4·H2O. The pH value of the suspension was measured to be 6.8. The suspension was then aged, centrifuged, filtered, and dried to obtain a light pink Mn3(PO4)2·3H2O raw material.

[0133] The preparation method of the cathode material is similar to that in Example 1, except that the weighed raw material X is 81.2 g Mn3(PO4)2·3H2O and the raw material Y is 56.38 g Na2HPO4. Example 6

[0134] The preparation method of raw material X is similar to that in Example 5, except that the suspension is placed on a constant temperature stirrer for maturation at 50°C for 10 hours.

[0135] The preparation method of the positive electrode material is the same as that in Example 5. Example 7

[0136] The preparation method of raw material X is similar to that in Example 5, except that the suspension is placed on a constant temperature stirrer for maturation at 65°C for 20 hours.

[0137] The preparation method of the positive electrode material is the same as that in Example 5. Example 8

[0138] The preparation method of raw material X is the same as in Example 1.

[0139] The preparation method of the positive electrode material is similar to that in Example 1, except that 335g of distilled water is weighed (the mass of raw material X accounts for about 30% of the mass of water). Example 9

[0140] The preparation method of raw material X is the same as in Example 1.

[0141] The preparation method of the positive electrode material is similar to that in Example 1, except that 183g of distilled water is weighed (the mass of raw material X accounts for about 55% of the mass of water). Example 10

[0142] The preparation method of raw material X is the same as in Example 1.

[0143] The preparation method of the positive electrode material is similar to that in Example 1, except that 125g of distilled water is weighed (the mass of raw material X accounts for about 80% of the mass of water). Example 11

[0144] There are two raw materials. The preparation method of raw material Fe3(PO4)2·8H2O is the same as that in Example 1, and the preparation method of raw material Mn3(PO4)2·3H2O is the same as that in Example 5.

[0145] The preparation method of the cathode material is similar to that in Example 1, except that raw material X (35.46g of Fe3(PO4)2·8H2O and 31.95g of Mn3(PO4)2·3H2O) and raw material Y (37.87g of Na2HPO4) are weighed.

[0146] The pH value, particle size of the X raw material, and polydispersity index of the suspensions in Examples 1-7 are shown in Table 1: Serial Number pH value of suspension Average particle size / nm D10 / nm D50 / nm D90 / nm Multi-dispersion index D50 / D10 D90 / D10 Example 1 4.5 781.8 446.2 820.6 1818.3 0.302 1.84 4.08 Example 2 3.9 543.9 205.9 310.6 537.1 0.317 1.51 2.61 Example 3 5.5 781.8 273.2 349.8 516.4 0.244 1.28 1.89 Example 4 6.5 993.7 395.1 608.4 1048.8 0.307 1.54 2.65 Example 5 6.8 993.7 593.4 1062.2 1949.8 0.307 1.79 3.29 Example 6 6.7 1256.2 451.5 674.6 1172.2 0.379 1.49 2.60 Example 7 6.4 2865.7 1185.3 3794.3 9473.5 0.419 3.20 7.99 The cathode material products prepared in Examples 1-11 were subjected to charge-discharge tests, and the test results are shown in Table 2: Serial Number Initial discharge capacity Initial Coulomb efficiency Capacity retention Example 1 114 94% 92% Example 2 119 94% 93% Example 3 116 92% 91% Example 4 116 92% 89% Example 5 108 93% 81% Example 6 106 90% 80% Example 7 106 91% 80% Example 8 113 92% 91% Example 9 109 92% 90% Example 10 103 90% 88% Example 11 105 91% 90% As shown in Table 2, the cathode material prepared using this method exhibits good cycle performance and capacity retention. Comparing Examples 5-7, it can be seen that the electrochemical performance of the prepared cathode material slightly decreases with increasing raw material particle size. Smaller raw material particle size results in better electrochemical performance. Comparing Examples 8-10, it can be seen that the cathode material prepared with a lower proportion of raw material X exhibits superior electrochemical performance.

[0147] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Here, without departing from the spirit of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A method for preparing a cathode material, wherein the cathode material has the molecular formula Na₄M₂ 3-3a N 6a / m (PO4)2P2O7, where, Element M is selected from at least one of Mn, Fe, Ni, and Co, and element N is a doped metal element different from element M. The valence state of element N is m, where m is a natural number greater than 0, and 0 ≤ a ≤ 0.

3. The preparation method is characterized by the following steps: Mixing step: Place raw material X and raw material Y in a container filled with water and mix and stir to obtain slurry A, then grind slurry A to obtain precursor slurry B; wherein, raw material X is a substance containing element M and not easily soluble in water, raw material Y is a sodium salt that is easily soluble in water, and at least one of raw material X and raw material Y contains phosphorus element P; Spray drying step: The precursor slurry B is placed in a spray drying device for spray drying to obtain precursor powder C; Sintering step: The precursor powder C is placed in a sintering device for sintering treatment to obtain the cathode material.

2. The method for preparing the cathode material according to claim 1, characterized in that, The average particle size range of the X raw material is 100-4000 nm; and / or The particle size D50 of the X raw material ranges from 100 to 4000 nm; and / or The particle size D10 of the X raw material is in the range of 100-1500 nm; and / or The particle size D90 of the X raw material ranges from 300 to 10000 nm.

3. The method for preparing the cathode material according to claim 1, characterized in that, The particle sizes D50, D10, and D90 of the X raw material satisfy the following condition: D50 / D10 ≤ D90 / D10.

4. The method for preparing the cathode material according to claim 1, wherein the polydispersity index of the X raw material is in the range of 0.1-0.

7.

5. The method for preparing the cathode material according to claim 1, wherein in the mixing step, the mass ratio of the X raw material to the water in the container ranges from 15% to 80%; preferably from 15% to 75%; more preferably from 20% to 55%.

6. The method for preparing the cathode material according to claim 1, characterized in that, The preparation method further includes a precursor preparation step, which includes: introducing solution S1 into the first inlet of a microreactor, wherein solution S1 contains element M; introducing solution S2 into the second inlet of a microreactor, wherein solution S2 contains phosphorus element P; mixing solution S1 and solution S2 through the microreactor to obtain a suspension, wherein the suspension is matured, centrifuged, filtered, and dried to obtain raw material X.

7. The method for preparing the cathode material according to claim 6, characterized in that, The precursor preparation step also includes a pH adjuster, which is used to adjust the pH value of the solution S1 and / or the solution S2 and / or the suspension.

8. The method for preparing the cathode material according to claim 7, characterized in that, The pH range of solution S1 is 2.5-3.5; and / or The pH range of solution S2 is 7.0-11.0; and / or The pH range of the suspension is 3.0-7.

0.

9. The method for preparing the cathode material according to claim 7 or 8, characterized in that, When the pH adjuster is used to adjust solution S1, the pH adjuster is selected from at least one of hydrochloric acid, sulfuric acid, or glacial acetic acid (CH3COOH); and / or When the pH adjuster is used to adjust solution S2, the pH adjuster is selected from at least one of NaOH or ammonia; preferably, the pH adjuster is ammonia; and / or When the pH adjuster is used to adjust the suspension, the pH adjuster is selected from at least one of H3PO4, NH4H2PO4, (NH4)2HPO4, NaH2PO4, or Na2HPO4.

10. A positive electrode material, characterized in that, The cathode material is prepared according to any one of claims 1 to 9.

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