A positive electrode material and preparation method thereof

Abstract

The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode material and a preparation method thereof. The preparation method of the present application comprises: a mixing step: weighing a certain amount of raw material X and raw material Y, placing them in a container filled with water, mixing and stirring to obtain slurry A, and then grinding to obtain precursor slurry B; a spray drying step: placing the precursor slurry B in a spray drying device for spray drying treatment to obtain precursor powder C; a sintering step: placing the precursor powder C in a sintering device for sintering treatment to obtain the positive electrode material. The present application can prepare a positive electrode material with high purity and good electrochemical performance through the special design of raw materials, and the coordinated coordination of mixing, spray drying and sintering.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density and long cycle life, are widely used in both energy storage and power batteries. With the rapid development of these two sectors, lithium resources are becoming increasingly scarce, becoming a bottleneck in the development of lithium-ion batteries in my country. Sodium, with its high abundance (2.3%), belongs to the same main group as lithium and shares similar electrochemical properties, making sodium-ion batteries a viable alternative to lithium-ion batteries. With the soaring price of lithium and its increasing scarcity, the research and development and industrialization of sodium-ion batteries will have significant social and commercial value.

[0003] Sodium-ion batteries offer a low-cost advantage, giving them a strong competitive edge in certain market segments. Their industrialization could alleviate the shortage of lithium resources to a certain extent, leading to a focus on the research and development of sodium-ion battery electrode materials in new energy materials. Polyanion cathode materials, in particular, are attracting considerable attention due to their low cost, excellent cycle stability, and high safety.

[0004] Currently, the commonly used methods for preparing polyanion cathode materials for sodium-ion batteries include solid-phase ball milling and liquid-phase processes. However, the solid-phase ball milling process cannot ensure uniform mixing of Na, M, and PO₄, resulting in the formation of a large number of impurities in the final product, which affects the electrochemical performance of the material. The liquid-phase process also produces precipitates of various phosphate-based metal salts during the mixing process, which also causes uneven mixing of Na, M, and PO₄, leading to the formation of a large number of impurities in the final product, affecting the electrochemical performance of the material.

[0005] Therefore, providing a new method for preparing a positive electrode material for a sodium ion battery to solve the above-mentioned defects is an urgent problem to be solved. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a positive electrode material and a preparation method thereof. The present application can prepare a positive electrode material with higher purity and better electrochemical performance through special design of raw materials and coordinated coordination of mixing, spray drying and sintering.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a method for preparing a positive electrode material, wherein the molecular formula of the positive electrode material is Na4M 3-3δ N 6δ / m (PO4)2P2O7, where N is a doping metal element and the valence state of N is m +, M is a transition metal element, and 0≤δ≤0.3, the preparation method of the positive electrode material comprises the following steps:

[0008] Mixing step: Weigh a certain amount of raw material X and raw material Y, place them in a container filled with water, mix and stir to obtain slurry A, and then grind to obtain precursor slurry B;

[0009] Spray drying step: placing the precursor slurry B in a spray drying device for spray drying to obtain a precursor powder C;

[0010] Sintering step: placing the precursor powder C in a sintering device for sintering to obtain a positive electrode material;

[0011] The X raw material is a water-insoluble substance containing a transition metal element M, the Y raw material is a water-soluble substance containing the element Na, and at least one of the X raw material and the Y raw material contains the element P.

[0012] In the above preparation method, particularly in the mixing step, the raw materials are mixed and stirred using water as a medium. In terms of the design of the raw materials, the X raw material is a substance containing the transition metal element M that is not easily soluble in water. Therefore, when the X raw material is added to the aqueous solution, it will form dispersed small particles. The Y raw material is a substance containing the element Na that is easily soluble in water. When the Y raw material is added to the aqueous solution, sodium ions are formed. Under the action of external force, the uniform distribution of sodium ions on the surface of the X raw material can be accelerated. Furthermore, after the mixing step, the spray drying step, the pretreatment step, and the sintering step are coordinated to obtain a positive electrode material product with higher purity.

[0013] In some embodiments, the X raw material is one or more compounds containing transition metal M and element P, and the solubility product K of the corresponding anhydrous compound is sp ≤1.0×10 -25 .

[0014] In some embodiments, the Y raw material is a compound containing one or more of the elements Na and P, and the solubility of the Y raw material in the corresponding anhydrous compound is ≥3 g / 100 g water.

[0015] In some embodiments, both the X raw material and the Y raw material contain the element P.

[0016] In some embodiments, in the X raw material, the stoichiometric ratio of the transition metal element M to the element P is 3:2.

[0017] Furthermore, the molecular formula of the anhydrous compound of the X raw material is M3(PO4)2.

[0018] Further preferably, the X raw material is selected from one or more of Mn3(PO4)2.yH2O (0≤y≤7), Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8), and Co3(PO4)2.z3H2O (0≤z3≤8).

[0019] Further preferably, the X raw material is selected from Mn3(PO4)2.yH2O (0≤y≤7) and / or Fe3(PO4)2.z1H2O (0≤z1≤8).

[0020] Further preferably, the X raw material is selected from Mn3(PO4)2·3H2O and Fe3(PO4)2·8H2O.

[0021] In some embodiments, in the Y raw material, the stoichiometric ratio of element Na to element P is 2:1.

[0022] In some embodiments, the Y raw material is selected from one or more of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, H4P2O7, Na2HPO4, NaH2PO4, Na3PO4, H3PO4, NH4H2PO4, (NH4)2HPO4 and (NH4)3PO4.

[0023] Further preferably, the Y raw material is selected from Na4P2O7 and / or Na2HPO4.

[0024] In some embodiments, in the mixing step, the mass proportion of raw material X is ≥15%.

[0025] More preferably, the mass proportion of raw material X is ≤80%.

[0026] In some embodiments, in the mixing step, the mass proportion of raw material Y is ≥ 20%.

[0027] More preferably, the mass proportion of raw material Y is ≤70%.

[0028] In some embodiments, the mixing step further includes: one or more of a modifying additive, a phosphorus source supplement, a carbon source, a dispersant, and a viscosity reducer.

[0029] In some embodiments, the mixing step further includes adding a modifying additive, wherein the modifying additive includes the doping metal element N, wherein the doping metal element N is another metal element different from the transition metal element M.

[0030] Preferably, the doping metal element N is selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

[0031] More preferably, the molecular formula of the modifying additive is N 6 / m m+ (PO4)2.

[0032] More preferably, in the mixing step, the weight proportion of the modifying additive is ≥1%. Even more preferably, the weight proportion of the modifying additive is ≤20%.

[0033] In some embodiments, the mixing step further includes a phosphorus source supplement, which is one or more of a simple substance, a compound, or a solution containing element P.

[0034] Preferably, the phosphorus source supplement is selected from one or more of H3PO4, NH4H2PO4, and (NH4)2HPO4.

[0035] More preferably, in the mixing step, the mass proportion of the phosphorus source supplement is ≥1%. Even more preferably, the mass proportion of the phosphorus source supplement is ≤20%.

[0036] In some embodiments, the particle size D50 of the precursor slurry B after grinding is 300-800 nm.

[0037] Preferably, the particle size D50 of the precursor slurry B is 300-600 nm; more preferably 300-450 nm.

[0038] In some embodiments, a pretreatment step is further included. The pretreatment step is located before the sintering step, and the pretreatment step includes: placing the precursor powder C in an ammonia solution for treatment.

[0039] In some embodiments, in the pretreatment step, the mass percentage concentration of the ammonia solution is 2-10%.

[0040] In some embodiments, in the pretreatment step, the pretreatment time is 2-15 hours.

[0041] In some embodiments, in the spray drying step, the inlet temperature of the spray drying equipment is 180-300°C, preferably 190-220°C.

[0042] In some embodiments, in the spray drying step, the outlet temperature of the spray drying equipment is 80-130°C, preferably 90-110°C.

[0043] In some embodiments, in the sintering step, the sintering treatment temperature ranges from 300-800°C; preferably, the temperature ranges from 450-800°C; and more preferably, from 450-750°C.

[0044] In some embodiments, in the sintering step, the sintering treatment time is 3-20 hours, preferably 10-20 hours.

[0045] In some embodiments, during the sintering step, the heating rate of the sintering equipment is 5-10° C. / min.

[0046] The second aspect of the present application provides a positive electrode material, which is prepared according to the preparation method of the positive electrode material.

[0047] The third aspect of the present application provides a sodium ion battery, which includes the positive electrode material provided by the second aspect of the present application.

[0048] A fourth aspect of the present application provides a battery module, which includes the sodium ion battery provided by the third aspect of the present application.

[0049] The fifth aspect of the present application provides an electrical device comprising at least one selected from the positive electrode material of the second aspect of the present application, the sodium ion battery of the third aspect of the present application, or the battery module of the fourth aspect of the present application.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. This application uses special raw material design, as well as the coordinated combination of mixing, spray drying, and sintering, to produce a positive electrode material with high purity and good electrochemical performance;

[0052] 2. The preparation method provided in this application is simple to operate, has low production cost, and has prospects for large-scale production.

[0053] 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 positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart of the preparation process of the positive electrode material of the present invention;

[0055] Figure 2 This is the XRD pattern of the cathode material Na4Fe3(PO4)2P2O7 prepared in Example 1 of the present invention;

[0056] Figure 3 This is an SEM image of the positive electrode material Na4Fe3(PO4)2P2O7 prepared in Example 1 of the present invention;

[0057] Figure 4 Graph showing charge and discharge curves at different rates for the sodium ion battery prepared in Example 1 of the present invention;

[0058] Figure 5 This is a cycle curve diagram of the sodium ion battery prepared in Example 1 of the present invention at a current density of 10C. DETAILED DESCRIPTION

[0059] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0061] In the description of this application, the terms "(1)", "(2)", "first", and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, a feature specified as "(1)", "(2)", "first", and "second" may explicitly or implicitly include at least one of the features. In the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically specified.

[0062] In the description of this application, unless otherwise indicated, 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).

[0063] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the weights described in the examples of this application may be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0065] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0066] The following describes the implementation of the present application in detail.

[0067] The first embodiment of the present application provides a positive electrode material. The molecular formula of the positive electrode material is Na4M 3-3δ N 6δ / m (PO4)2P2O7 (or expressed as Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )P2O7), where N is a doping metal element and the valence state of N is m + , M is a transition metal element, and 0≤δ≤0.3. Specifically, M can be selected from one or more transition metal elements such as Fe and Mn. N is a doping metal element. It is understood that the doping metal element N is a metal element other than the transition metal element M. Specifically, N can be selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

[0068] In any embodiment of the present application, when δ=0, no doping metal element N is added. It can be understood that when M is only one element; for example, when it is selected from Mn, the molecular formula of the positive electrode material is Na4Mn3(PO4)2P2O7; when M is selected from Fe, the molecular formula of the positive electrode material is Na4Fe3(PO4)2P2O7; when M is selected from Ni, the molecular formula of the positive electrode material is Na4Ni3(PO4)2P2O7; when M is selected from Co, the molecular formula of the positive electrode material is Na4Co3(PO4)2P2O7. When M is two or more selected from Mn, Fe, Ni and Co, the molecular formula of the positive electrode material is Na4Mn α Fe β Ni γ Co 3-α-β-γ (PO4)2P2O7, where 0≤α≤3, 0≤β≤3, 0≤γ≤3, and 0≤α+β+γ≤3.

[0069] It is further understood that when the positive electrode material is doped with a metal element N, the doped metal element N is a metal element other than the transition metal element M (Mn, Fe, Ni, and Co). The doped metal element N may be one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

[0070] The first aspect of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0071] Mixing step: Weigh a certain amount of raw material X and raw material Y, place them in a container filled with water, mix and stir to obtain slurry A, and then grind to obtain precursor slurry B;

[0072] Spray drying step: placing the precursor slurry B in a spray drying device for spray drying to obtain a precursor powder C;

[0073] Sintering step: placing the precursor powder C in a sintering device for sintering to obtain a positive electrode material;

[0074] The X raw material is a water-insoluble substance containing a transition metal element M, the Y raw material is a water-soluble substance containing the element Na, and at least one of the X raw material and the Y raw material contains the element P.

[0075] In the above preparation method, first, in the mixing step, the raw materials are mixed and stirred using water as a medium. In terms of the design of the raw materials, the X raw material is a substance that is not easily soluble in water and contains the transition metal element M. Therefore, when the X raw material is added to the aqueous solution, it will form dispersed small particles. The Y raw material is a water-soluble substance containing the element Na. When the Y raw material is added to the aqueous solution, sodium ions are formed. Under the action of external force, the uniform distribution of sodium ions on the surface of the X raw material can be accelerated. Furthermore, after the mixing step, a high-purity positive electrode material product can be obtained through the coordinated cooperation between the spray drying step, the pretreatment step, and the sintering step.

[0076] In addition, the above preparation method is simple to operate, has low production cost, and has prospects for large-scale production.

[0077] After in-depth research, the applicant found that when the raw materials of the present application meet the aforementioned design conditions and can also meet one or more of the following conditions, the purity of the positive electrode material can be further improved and the performance of the battery can be further improved.

[0078] In any embodiment of the present application, the X raw material is one or more compounds containing transition metal M and element P, and the solubility product K of the corresponding anhydrous compound is sp ≤1.0×10 -25 It can be understood that the X raw material with a smaller solubility product can be stably present during the grinding process in the mixing step, which helps to prepare the precursor slurry B with higher purity.

[0079] In any embodiment of the present application, the Y raw material is a compound containing one or more of the elements Na and P, and its solubility in the corresponding anhydrous compound is ≥3 g / 100 g water. It is understood that a Y raw material with a solubility product ≥3 g / 100 g water has better solubility in an aqueous solution, and is more likely to produce sodium ions, pyrophosphate, phosphate (monohydrogen / dihydrogen), etc., which helps these ions to be evenly dispersed on the surface of the particles of the X raw material.

[0080] In any embodiment of the present application, both the X raw material and the Y raw material contain the element P. It is understandable that, since the positive electrode material is fitted to contain M3(PO4)2, in which the element P is an important component, the inventors of the present application have found that the element P will be lost during the synthesis and preparation of the material, resulting in the generation of various types of impurities. Therefore, increasing the content of the element P helps to reduce the generation of impurities. Therefore, the selected X raw material and Y raw material both contain the element P, which can increase the percentage of the element P in the synthesis environment and help reduce the generation of impurities.

[0081] In any embodiment of the present application, the X raw material further includes element P. In the X raw material, the stoichiometric ratio of the transition metal element M to the element P is 3:2, that is, in the X raw material, the sum of the stoichiometric ratios of the transition metal element M: the stoichiometric ratio of the element P = 3:2. It can be understood that the X raw material can be a compound or a mixture of multiple compounds. As long as the sum of the stoichiometric ratios of the transition metal element M and the stoichiometric ratio of the element P is 3:2, it falls within the scope of the X raw material. It can be understood that since it is fitted into the positive electrode material Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )P2O7, which contains (1-δ) stoichiometric M3(PO4)2. When the sum of the stoichiometric ratios of the transition metal elements and the sum of the stoichiometric ratios of element P meet the requirements of 3:2, the X raw material just provides the transition metal element M and element P in M3(PO4)2, which helps to synthesize a positive electrode material with higher purity.

[0082] In any embodiment of the present application, the molecular formula of the anhydrous compound of the X raw material is M3(PO4)2. The X raw material not only provides the synthetic positive electrode material Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ)P2O7 required M3(PO4)2; and M3(PO4)2 with a smaller solubility product is stable during the grinding process and is evenly mixed with the elemental Na and elemental P in the Y raw material; In addition, during the sintering step, the presence of M3(PO4)2 also helps to synthesize the higher purity positive electrode material Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )P2O7.

[0083] Since it is fitted into the positive electrode material Na4M 3-3δ N 6δ / m (PO4)2P2O7 (where the valence state of N is m + ), also written as Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )P2O7, which contains (1-δ) stoichiometric M3(PO4)2. When the sum of the stoichiometric ratios of the transition metal element M and the stoichiometric sum of the element P meet the requirements of 3:2, the X raw material just provides the transition metal element M and the element P in M3(PO4)2, which helps to synthesize a positive electrode material with higher purity.

[0084] In any embodiment of the present application, the raw material X is selected from one or more of Mn3(PO4)2.yH2O (0≤y≤7), Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8), and Co3(PO4)2.z3H2O (0≤z3≤8). Since Mn3(PO4)2.yH2O (0≤y≤7), Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8), and Co3(PO4)2.z3H2O (0≤z3≤8) are easy to industrialize, they are beneficial to the industrial promotion and application of the positive electrode materials provided by the present application.

[0085] Furthermore, the solubility product Ksp of Mn3(PO4)2 is 1.0×10 -27 , the solubility product Ksp of Fe3(PO4)2 is 1.0×10 -36 , the solubility product Ksp of Ni3(PO4)2 is 5.0×10 -31 , the solubility product Ksp of Co3(PO4)2 is 2.04×10 -35 .

[0086] In any embodiment of the present application, the X raw material is selected from at least two or more of Mn3(PO4)2.yH2O (0≤y≤7), Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8) and Co3(PO4)2.z3H2O (0≤z3≤8). Polyanion sodium cathode materials are similar to lithium ion olivine materials. Fe-based materials have good electrochemical properties, but the low platform voltage leads to low energy density; Mn-based materials have high platform voltage and high energy density, but low electronic conductivity leads to poor electrochemical performance, and are affected by the Jahn-Teller effect, resulting in poor cycle stability; Ni-based and Co-based materials have high voltage platforms, but high costs. When two or more of Mn, Fe, Ni, and Co are mixed together under the synergistic effect, a material with good energy density, electrochemical performance, cycle life, and moderate cost is obtained, which meets the needs of actual applications.

[0087] Furthermore, Mn3(PO4)2.yH2O (0≤y≤7) is selected from Mn3(PO4)2·3H2O. Mn3(PO4)2·3H2O can be directly prepared by co-precipitating a manganese salt and a phosphate in a solution, which is simple and easy to prepare. This helps reduce production difficulty, improve the efficiency of industrial production, and reduce the cost of purchasing raw materials.

[0088] Furthermore, Fe3(PO4)2.z1H2O (0≤z1≤8) is selected from Fe3(PO4)2·8H2O. Since Fe3(PO4)2·8H2O can be directly prepared by co-precipitation of ferrous salt and phosphate in solution, it is simple and easy to prepare, which helps to reduce production difficulty, improve the efficiency of industrial production, and reduce the cost of purchasing raw materials.

[0089] Furthermore, Ni3(PO4)2.z2H2O (0≤z2≤8) is selected from Ni3(PO4)2·8H2O. Since Ni3(PO4)2·8H2O can be directly prepared by co-precipitation of nickel salt and phosphate in solution, it is simple and easy to prepare, which helps to reduce production difficulty, improve the efficiency of industrial production, and reduce the cost of purchasing raw materials.

[0090] Furthermore, Co3(PO4)2.z3H2O (0≤z3≤8) is selected from Co3(PO4)2·8H2O. Co3(PO4)2·8H2O can be directly prepared by coprecipitating a cobalt salt and a phosphate in a solution, which is simple and easy to prepare. This helps reduce production difficulty, improve the efficiency of industrial production, and reduce the cost of purchasing raw materials.

[0091] Furthermore, the X raw material is selected from one or more of Mn3(PO4)2·3H2O, Fe3(PO4)2·8H2O, Ni3(PO4)2·8H2O, and Co3(PO4)2·8H2O.

[0092] Furthermore, the X raw material is selected from Mn3(PO4)2·3H2O and Fe3(PO4)2·8H2O. Similar to lithium iron manganese phosphate, composite sodium manganese phosphate combines the low cost of iron and manganese with the high voltage platform of manganese to synergistically provide the most cost-effective cathode material.

[0093] In any embodiment of the present application, in the Y raw material, the stoichiometric ratio of the element Na to the element P is 2:1, that is, the sum of the stoichiometric ratios of the element Na in the Y raw material: the sum of the stoichiometric ratios of the element P = 2:1. It can be understood that the Y raw material can be a compound or a mixture of multiple compounds. As long as it meets the ratio of the sum of the stoichiometric ratios of the element Na: the sum of the stoichiometric ratios of the element P = 2:1, it belongs to the category of the Y raw material. It can be understood that since it is fitted into the positive electrode material Na4M 3-3δ N 6δ / m (PO4)2P2O7 contains an equal stoichiometric amount of Na4P2O7. When the sum of the stoichiometric ratios of element Na: the sum of the stoichiometric ratios of element P = 2:1, the Y raw material just provides the sodium and phosphorus elements in Na4P2O7, which helps to synthesize a positive electrode material with higher purity.

[0094] In any embodiment of the present application, the Y raw material is selected from one or more of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, H4P2O7, Na2HPO4, NaH2PO4, Na3PO4, H3PO4, NH4H2PO4, (NH4)2HPO4 and (NH4)3PO4. It is understood that the above compounds include both their corresponding anhydrous compounds and their compounds containing different crystal waters.

[0095] Furthermore, the Y raw material is selected from one or more of Na4P2O7 and Na2HPO4. The applicant has discovered that Na4P2O7 and Na2HPO4 are not only soluble in water but also have strong complexing ability with transition metal elements, which facilitates uniform mixing with the X raw material in water, thereby helping to produce a higher-purity positive electrode material.

[0096] In any embodiment of the present application, in the mixing step, the mass proportion of raw material X is ≥15%.

[0097] Furthermore, the mass proportion of raw material X is ≤80%.

[0098] The applicant has found that a low weight percentage of raw material X will produce a large number of side reactions, while a high weight percentage of raw material X will cause severe agglomeration during the mixing step. Therefore, it is recommended that the weight percentage of raw material X be preferably between 15% and 80%.

[0099] In any embodiment of the present application, in the mixing step, the mass proportion of the Y raw material is ≥20%.

[0100] Furthermore, the mass proportion of Y raw material is ≤70%.

[0101] The applicant has found that when the weight percentage of raw material Y is too low, it cannot be evenly dispersed on the surface of raw material X, resulting in the formation of a large number of impurities. However, when the weight percentage of raw material Y is too high, the pH value of the solution is too high, requiring the addition of a pH adjuster and increasing the preparation difficulty. Therefore, it is recommended that the weight percentage of raw material Y be 20% to 70%.

[0102] In any embodiment of the present application, in the mixing step, the raw materials at least include raw material X and raw material Y. It can be understood that the raw materials also include other raw materials in addition to raw material X and raw material Y.

[0103] In any embodiment of the present application, in the mixing step, the raw materials further include: one or more of a modifying additive, a phosphorus source supplement, a carbon source, a dispersant, and a viscosity reducer.

[0104] In any embodiment of the present application, in the mixing step, the raw material further includes: a modifying additive, and the modifying additive includes a doping metal element N.

[0105] The main purpose of the modified additive is to dope the synthesized cathode material with cations. Generally, the ionic and electronic conductivities of polyanionic materials are relatively low, but appropriate cation doping can greatly improve their ionic and electronic conductivities, thereby enhancing the electrochemical performance of the resulting cathode material.

[0106] It can be understood that the molecular formula of the positive electrode material obtained by adding the modifying additive is Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ The doping metal element N is another metal element different from the transition metal element M. Specifically, N can be selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

[0107] Furthermore, the modifying additive may be selected from simple substances, compounds, solutions, and the like containing the above-mentioned elements.

[0108] Furthermore, the modifying additive may be soluble in water or insoluble in water.

[0109] Furthermore, the molecular formula of the modifying additive is N 6 / m m+ (PO4)2, wherein N is selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu, and m + is the valence of N. This is because the molecular formula N 6 / m m+ (PO4)2 and Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )N in the delta chemical bond contained in the P2O7 molecular formula 6 / m m+ (PO4)2, in the mixing step, the required modified doping metal element N is introduced, but no other new impurity elements are introduced, and due to the similar structure, it is easier to mix evenly during the mixing process, which is beneficial to the embedding of the doping metal element N in the subsequent reaction process.

[0110] Furthermore, the mass proportion of the modifying additive is ≥1%.

[0111] Furthermore, the mass proportion of the modifying additive is ≤20%.

[0112] In any embodiment of the present application, during the mixing step, the raw materials may further include: a phosphorus source supplement. The appropriate addition of a phosphorus source supplement can increase the phosphorus content of the raw materials and help replenish the phosphorus lost during the preparation process, for example, when the phosphorus is not fully attached to the X raw material due to a short mixing time or other factors during the mixing process. In particular, when the above-mentioned modifying additive is not selected as N 6 / m m+ (PO4)2, but rather N in the form of a single substance or other compound (such as oxides, carbonates, oxalates, nitrates), a phosphorus source supplement is added to the raw materials, and the stoichiometric sum of phosphorus in the phosphorus source supplement is 2:3 / m of the stoichiometric sum of the added N. This ensures that the chemical formula of the final material meets

[0113] Na4(M3(PO4)2) 1-δ (N 6δ / m m+ (PO4) 2δ )P2O7, thereby improving the purity of the prepared positive electrode material.

[0114] It is understood that the phosphorus source supplement is a simple substance or compound containing phosphorus element. The phosphorus source supplement can be soluble in water or insoluble in water.

[0115] Furthermore, the phosphorus source supplement is a solvent containing phosphorus element. The solvent can be more easily mixed with other materials during the stirring and grinding process.

[0116] Furthermore, the phosphorus source supplement is selected from one or more of H3PO4, NH4H2PO4, (NH4)2HPO4. The above phosphorus sources are soluble in water, easily mixed with M3(PO4)2 and N compounds, and are unlikely to retain any impurities after high-temperature sintering.

[0117] Furthermore, the mass proportion of phosphorus source supplements is ≥1%.

[0118] Furthermore, the mass proportion of phosphorus source supplements is ≤20%.

[0119] In any embodiment of the present application, in the mixing step, the raw material further includes: a carbon source.

[0120] Specifically, the carbon source can be selected from one or more of inorganic carbon materials and / or organic carbon materials.

[0121] Furthermore, the organic carbon material is selected from one or more of citric acid, glucose, sucrose, polyethylene glycol, starch, lignin, and asphalt.

[0122] Furthermore, the inorganic carbon material is selected from one or more of graphite, activated carbon, carbon nanotubes, and graphene.

[0123] In any embodiment of the present application, in the mixing step, the raw material further includes: a dispersant.

[0124] Furthermore, the dispersant is selected from one or more of polyethylene oxide, polytetrafluoroethylene, polyacrylic acid, polymethyl acrylate, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose and carboxyethyl methyl cellulose.

[0125] In a specific embodiment, in the mixing step, the raw materials further include: a viscosity reducer.

[0126] Furthermore, the viscosity reducing agent is selected from one or more of polyvinyl alcohol, polyethylene glycol, and polypropylene glycol.

[0127] In any embodiment of the present application, the particle size D50 of the precursor slurry B after grinding is 300-800nm. The particle size of the precursor slurry B is controlled within an appropriate range, which helps to mix the sodium and phosphorus elements in the X raw material and the Y raw material evenly, and is conducive to the preparation of a positive electrode material with higher purity. When the particle size of the precursor slurry B is less than 300nm, it is easy to agglomerate, which may lead to incomplete reaction in the spray drying step and the sintering step, so that the generated positive electrode material contains more impurities. When the particle size of the precursor slurry B is greater than 800nm, during the sintering process, Na + and P2O7 4- , especially P2O7 4-, it is difficult for all of them to diffuse to the correct site, which leads to the easy appearance of impurity phases, such as Na2MP2O7.

[0128] Furthermore, the particle size D50 of the precursor slurry B is 300-600 nm. Furthermore, the particle size D50 of the precursor slurry B is 300-450 nm.

[0129] In any embodiment of the present application, in the spray drying step, the inlet temperature of the spray drying equipment is 180-300° C. Controlling the inlet temperature of the spray drying equipment within an appropriate range can improve the average particle size and bulk density of the precursor powder C, thereby facilitating a more complete reaction of the precursor powder C during the sintering step. It can also reduce the occurrence of other side reactions that may generate impurities during the spray drying process, thereby improving the purity of the positive electrode material.

[0130] Furthermore, the inlet temperature of the spray drying equipment is 190-220°C.

[0131] In any embodiment of the present application, in the spray drying step, the outlet temperature of the spray drying equipment is 80-130° C. Controlling the outlet temperature of the spray drying equipment within an appropriate range can maintain the material activity of the precursor powder C, facilitate the sintering of the precursor powder C in the subsequent step, and thereby improve the purity of the positive electrode material.

[0132] Furthermore, the outlet temperature of the spray drying equipment is 90-110°C.

[0133] In any embodiment of the present application, a pretreatment step is further included. The pretreatment step is located before the sintering step. The pretreatment step includes: placing the precursor powder C in an ammonia solution for treatment.

[0134] Ammonia can further react with the precursor powder C to affect the grain growth rate and morphology of the precursor powder C by controlling the concentration of free ions, and make the corresponding ions such as Na + and P2O7 4- During the calcination step, it diffuses to the correct site to the greatest extent possible, reduces the occurrence of other side reactions that may generate impurities during the subsequent calcination process, avoids the generation of impurities, and promotes the reaction to produce pure phase products, thereby improving the purity of the positive electrode material.

[0135] Furthermore, in the pretreatment step, the mass percentage concentration of the ammonia solution is 2-10%.

[0136] Furthermore, in the pretreatment step, the pretreatment time is 2-15 hours. Preferably, the pretreatment time is 3-8 hours.

[0137] In any embodiment of the present application, in the pretreatment step, the precursor powder C is placed in the ammonia solution for a treatment time of 3-4 hours.

[0138] In any embodiment of the present application, in the sintering step, the atmosphere of the sintering treatment is air or an inert atmosphere.

[0139] Furthermore, preferably, the sintering can be performed once or multiple times.

[0140] Furthermore, preferably, when an inert atmosphere is used for the sintering treatment, nitrogen is preferred. An ammonia atmosphere can reduce the occurrence of other side reactions that may generate impurities during the calcination process, control the grain size of the precursor powder C, and the free ion concentration, thereby improving the purity of the positive electrode material.

[0141] In any embodiment of the present application, in the sintering step, the sintering temperature range 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. When the temperature is as high as 800° C., the particle size of the particles in the precursor powder C is too large, the specific surface area is reduced, and the electrochemical performance of the battery made of the positive electrode material is reduced.

[0142] Furthermore, preferably, the temperature range of the sintering treatment is 450-800°C.

[0143] Furthermore, preferably, the temperature range of the sintering treatment is 450-750°C.

[0144] In any embodiment of the present application, in the sintering step, the sintering treatment time is 3-20 hours.

[0145] Furthermore, preferably, the sintering treatment time is 10-20 hours.

[0146] In any embodiment of the present application, in the sintering step, the heating rate of the sintering equipment is 5-10° C. / min.

[0147] The present application also provides a sodium ion battery comprising a positive electrode of the positive electrode material or the positive electrode material prepared by the above-mentioned preparation method. Specifically, the positive electrode comprises a current collector and a positive electrode active material disposed on the current collector, wherein the positive electrode active material comprises the positive electrode material of the present application or the positive electrode material prepared by the preparation method of the present application.

[0148] The present application also provides a battery module including the aforementioned sodium-ion battery. Specifically, the battery module includes a housing, a cover plate, and the sodium-ion battery. The housing has a cavity and an opening; the sodium-ion battery is housed in the cavity; and the cover plate is used to seal the opening of the housing.

[0149] The present application also provides an electrical device comprising the aforementioned sodium-ion battery. The electrical device may be a device that uses a sodium-ion battery as a power supply. For example, the electrical device may 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.).

[0150] Example

[0151] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0152] Example 1

[0153] 1. Preparation method of positive electrode material:

[0154] 100.32g of Fe3(PO4)2·8H2O (X raw material), 53.18g of Na4P2O7 (Y raw material), 20g of sucrose (carbon source), and 15.74g of PEG (molecular weight 1675) (dispersant) were weighed separately. The mixture was mixed in an aqueous medium at 500 rpm for 30 minutes to obtain slurry A. The obtained slurry A was sand-milled to obtain slurry B, whose particle size D50 was measured to be 512nm. Slurry B was spray-dried to obtain precursor powder C. Precursor C was then placed in a nitrogen atmosphere and calcined at 500°C for 10 hours to obtain Na4Fe3(PO4)2P2O7 / C (in this example, M is Fe and d=0).

[0155] Figure 2-3 The synthesized Na4Fe3(PO4)2P2O7 / C was characterized and tested in detail. XRD showed that the obtained phase was pure and there was basically no impurity peak ( Figure 2 ). SEM shows that the particle size of the obtained material is 2-4mm ( Figure 3 ).

[0156] 2. Preparation of Button Cells

[0157] Take 0.8 grams of the above-mentioned Na4Fe3(PO4)2P2O7 / C material, mix it with 0.1 grams of conductive carbon black and 0.1 grams of PVDF, grind it with NMP as the medium, apply the obtained slurry to the aluminum foil current collector, and obtain the positive electrode after drying. The obtained electrode is cut into a square electrode with a side length of 1 cm as the working electrode, and the metal sodium sheet is used as the counter electrode. 1M NaPF6 is dissolved in EC:DEC (50:50vol / vol) as the electrolyte, and a button cell (2032) is assembled under an inert atmosphere. The button half-cell test results show that the discharge capacity of the material is 117mAh / g at 0.1C, 102mAh / g at 1C, and 90mAh / g at 10C ( Figure 4 ). 10C first cycle 88.6mAh / g, 2000 cycles 80.1mAh / g; capacity retention rate 90.4% ( Figure 5 ).

[0158] Example 2

[0159] The preparation method of the positive electrode material is similar to that of Example 1, except that a pretreatment step is provided before the sintering step. Specifically, the precursor C is placed in a 2% by mass ammonia solution for 3 hours and then calcined in a nitrogen atmosphere.

[0160] Example 3

[0161] The preparation method of the positive electrode material is similar to that of Example 1, except that, in the mixing step, the mixing is carried out at 800 r / min in the aqueous medium for 30 min.

[0162] Example 4

[0163] The preparation method of the positive electrode material is similar to that of Example 1, except that in the mixing step, the particle size of the slurry B is adjusted by adjusting the grinding parameters, and the particle size D50 of the slurry B is measured to be 400 nm.

[0164] Example 5

[0165] The preparation method of the positive electrode material is similar to that of Example 1, except that the X raw material weighed is 81.2 g Mn3(PO4)2·3H2O; and the Y raw material weighed is 56.38 g Na2HPO4.

[0166] Example 6

[0167] The preparation method of the positive electrode material is similar to that of Example 1, except that the X raw material weighed is 31.95g Mn3(PO4)2 and 35.46g Fe3(PO4)2·2H2O; the Y raw material is 37.87g Na2HPO4.

[0168] Example 7

[0169] The preparation method of the positive electrode material is similar to that of Example 1, except that the X raw material weighed is 97.01 g Fe3(PO4)2·8H2O; the Y raw material weighed is 53.18 g Na4P2O7 and 1.52 g NH4H2PO4.

[0170] Example 8

[0171] The preparation method of the positive electrode material is similar to that of Example 1, except that the weighed raw material X is 76.03 g Mn3(PO4)2·3H2O and the raw material Y is 53.18 g Na4P2O7.

[0172] Example 9

[0173] The preparation method of the positive electrode material is similar to that of Example 8, except that 2.62 g of Zn powder as a modifying additive is added in the mixing step.

[0174] Example 10

[0175] The preparation method of the positive electrode material is similar to that of Example 1, except that the X raw material weighed is 38.18g Mn3(PO4)2·3H2O, 46.85g Fe3(PO4)2·8H2O, 1.70g Ni3(PO4)2·8H2O, and 1.71g Co3(PO4)2·8H2O; the Y raw material is 53.18g Na4P2O7 and 1.50g NH4H2PO4.

[0176] Example 11

[0177] The preparation method of the positive electrode material is similar to that of Example 11, except that 37.88 g of a 10% solution of Zn(NO 3 ) 3 as a modifying additive is added in the mixing step.

[0178] The positive electrode material products prepared in Examples 1-11 were subjected to charge and discharge tests, and the test results are shown in Table 1:

[0179] Table 1. Charge and discharge test results of the positive electrode material products prepared in Examples 1-11

[0180]

[0181] The data in the table show that the positive electrode materials synthesized by this method all exhibit high initial discharge capacity and coulombic efficiency, and also show excellent cycle performance under high current. This strongly proves that the present invention can prepare positive electrode materials with high purity and good electrochemical performance through the special design of raw materials and the coordinated coordination of mixing, spray drying and sintering.

[0182] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a positive electrode material, wherein the molecular formula of the positive electrode material is , where N is a doping metal element and the valence state of N is , M is a transition metal element, and , characterized in that, The preparation method comprises the following steps: Mixing step: Weigh a certain amount of raw material X and raw material Y, place them in a container filled with water, mix and stir to obtain slurry A, and then grind to obtain precursor slurry B; Spray drying step: placing the precursor slurry B in a spray drying device for spray drying to obtain a precursor powder C; Sintering step: placing the precursor powder C in a sintering device for sintering treatment to obtain the positive electrode material; The X raw material is a water-insoluble substance containing a transition metal element M, the Y raw material is a water-soluble substance containing the element Na, and at least one of the X raw material and the Y raw material contains the element P; The X raw material is one or more compounds containing transition metal elements M and elements P, and the solubility product of the corresponding anhydrous compound is ; The Y raw material is a compound containing one or more of the elements Na and P, and the solubility of the corresponding anhydrous compound is ≥3g / 100g water; The X raw material is selected from one or more of Mn3(PO4)2.yH2O (0≤y≤7), Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8), and Co3(PO4)2.z3H2O (0≤z3≤8); The Y raw material is selected from one or more of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, H4P2O7, Na2HPO4, NaH2PO4, Na3PO4, H3PO4, NH4H2PO4, (NH4)2HPO4 and (NH4)3PO4.

2. The method for preparing the positive electrode material according to any one of claim 1, characterized in that: In the X raw material, the stoichiometric ratio of the transition metal element M to the element P is 3:2; in the Y raw material, the stoichiometric ratio of the element Na to the element P is 2:

1.

3. The method for preparing the positive electrode material according to claim 1, wherein: The mixing step further includes adding a modifying additive, wherein the modifying additive includes the doping metal element N, wherein N is selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, and Cu.

4. The method for preparing the positive electrode material according to claim 3, wherein: The molecular formula of the modifying additive is .

5. The method for preparing the positive electrode material according to claim 1, wherein: In the mixing step, a phosphorus source supplement is also included; the phosphorus source supplement is selected from one or more of H3PO4, NH4H2PO4, and (NH4)2HPO4.

6. The method for preparing the positive electrode material according to claim 1, wherein: The particle size D50 of the precursor slurry B is 300-800 nm.

7. The method for preparing the positive electrode material according to claim 6, wherein: The particle size D50 of the precursor slurry B is 300-450 nm.

8. The method for preparing the positive electrode material according to claim 1, wherein: The method further includes a pretreatment step, which is located before the sintering step. The pretreatment step includes placing the precursor powder C in an ammonia solution for treatment.

9. The method for preparing a positive electrode material according to claim 1, wherein In the spray drying step, the inlet temperature of the spray drying equipment is 180-300°C, and the outlet temperature of the spray drying equipment is 80-130°C; and / or In the sintering step, the sintering temperature range is 300-800° C., the sintering time is 3-20 hours, and the heating rate of the sintering equipment is 5-10° C. / min.

10. A positive electrode material, characterized in that Prepared according to the method for preparing the positive electrode material according to any one of claims 1 to 9.

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