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: weighing a raw material X and a raw material Y, placing the raw materials in a container containing an alcohol solvent, mixing and stirring to obtain slurry A, and grinding the slurry A to obtain precursor slurry B; 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. Wherein the molecular formula of the anhydrous compound of the X raw material is M3 (PO4) 2 and / or MPO4, and the Y raw material is sodium salt. Through special design of the raw materials and the solvent and synergistic cooperation of mixing, spray drying and sintering, the positive electrode material with relatively high purity and relatively good electrochemical performance can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a cathode material and a preparation method thereof. Background Art

[0002] Compared with lithium batteries, sodium batteries have the advantages of rich resources, low cost, and high safety, and are currently a hot topic in the research of new energy materials. Among them, polyanion cathode materials have attracted much attention due to their low cost, good cycle stability, and high safety.

[0003] At present, the commonly used preparation methods for polyanion cathode materials of sodium-ion batteries are solid-phase ball milling process and liquid-phase process. However, due to the uneven mixing between Na, M (transition metal element), and PO4 3- among them, a large number of impurity phases are usually generated in the final product, affecting the electrochemical performance of the material.

[0004] Therefore, providing a new preparation method for the cathode material of sodium-ion batteries to solve the above defects is an urgent problem to be solved at present. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a cathode material and a preparation method thereof. Through the special design of raw materials and solvents, and the coordinated cooperation of mixing, spray drying, and sintering, the present application can prepare a cathode material with higher purity and better electrochemical performance.

[0006] To achieve the above purpose, the first aspect of the present application provides a preparation method for a cathode material, wherein the molecular formula of the cathode material is Na4M 3-3a N 6a / m (PO4)2P2O7 / C, where N is a doped metal element, the valence state of N is m, m is a natural number greater than 0, M is a transition metal element, and 0 ≤ a ≤ 0.3. The preparation method of the cathode material includes the following steps: Mixing step: Weigh X raw material and Y raw material, place them in a container containing an alcohol solvent, mix and stir to obtain slurry A, and grind slurry A to obtain precursor slurry B; Spray drying step: Place precursor slurry B in a spray drying device for spray drying treatment to obtain precursor powder C; Sintering step: Place precursor powder C in a sintering device for sintering treatment to obtain the cathode material; Among them, the anhydrous compound of X raw material has a molecular formula of M3(PO4)2 and / or MPO4, and Y raw material is a sodium salt.

[0007] In the above preparation method, the X raw material is almost insoluble in water and alcohol solvents such as ethanol. The Y raw material can be selected from sodium salts that are soluble or insoluble in water. Adding an alcohol solvent to the solvent can not only wash away the impurities adhering to the surfaces of the X raw material and the Y raw material, but also increase the solubility of the Y raw material in the solution, which helps the sodium ions in the Y raw material to adsorb on the surface of the X raw material particles. At the same time, since the alcohol solvent contains carbon atoms, the carbon atoms remaining in the mixing step can serve as a carbon source in the subsequent spray drying step and sintering step to form an irregular carbon coating layer. Through the special combination of the above raw materials and solvents, and by coordinating the mixing step, spray drying step, and sintering step, the obtained cathode material product has a high purity and good electrochemical performance.

[0008] In some embodiments, the molecular formula of the anhydrous compound of the X raw material is M3(PO4)2. Further, 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).

[0009] In some embodiments, the molecular formula of the anhydrous compound of the X raw material is MPO4. Further, the X raw material is selected from FePO4·z4H2O (0 ≤ z4 ≤ 8).

[0010] In some embodiments, in the mixing step, the mass percentage (m x ) of the X raw material ranges from 15% ≤ m x ≤ 80%.

[0011] In some embodiments, the Y raw material is selected from one or more of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, Na2HPO4, NaH2PO4, and Na3PO4.

[0012] Further, the Y raw material is selected from sodium salts containing phosphorus elements.

[0013] In some embodiments, in the mixing step, the mass percentage (m Y ) of the Y raw material ranges from 30% ≤ m Y ≤ 95%.

[0014] In some embodiments, in the mixing step, the alcohol solvent is one or more of methanol, ethanol, propanol, butanol, and pentanol.

[0015] Furthermore, the concentration of the alcohol solvent ≤ 30%; preferably, the concentration of the alcohol solvent ≤ 20%; more preferably, the concentration of the alcohol solvent ≤ 15%.

[0016] In some embodiments, in the mixing step, an antioxidant is further added and mixed with the raw material X and the raw material Y in a container containing an alcohol solvent and stirred to obtain the slurry A. Furthermore, the mass percentage of the antioxidant in the slurry A ≤ 30%.

[0017] In some embodiments, the antioxidant is selected from one or more of ascorbic acid, vitamin C, citric acid, and vanillin. Preferably, the antioxidant is vanillin.

[0018] In some embodiments, in the mixing step, by mass fraction, the ratio range of the mass of the raw material X to the mass of the antioxidant is (90~100):(5~20).

[0019] In some embodiments, in the mixing step, the slurry A is placed in a ball mill and ground to obtain a precursor slurry B, wherein the rotation speed of the ball mill is 100~400 r / min; preferably, 150~300 r / min.

[0020] The second aspect of the present application provides a positive electrode material prepared according to the preparation method of the positive electrode material described above.

[0021] The third aspect of the present application provides a sodium ion battery, which includes the positive electrode material provided in the second aspect of the present application.

[0022] The fourth aspect of the present application provides a battery module, which includes the sodium ion battery provided in the third aspect of the present application.

[0023] The fifth aspect of the present application provides an electrical device, which includes 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.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Through the special combination of raw materials and solvents, and in coordination with the mixing step, spray drying step, and sintering step, the positive electrode material product obtained in the present application has a high purity and good electrochemical performance; 2. The preparation method provided in the present application is simple to operate and has a low production cost, showing a prospect for large-scale production;

[0025] 3. For the sodium ion battery provided in the present application, due to the high purity of the positive electrode material, the discharge capacity and cycle performance of the battery can be significantly improved. Description of the Drawings

[0026] Figure 1 Process flow chart for the preparation of the cathode material of the present invention Figure 2 XRD pattern of the cathode material Na4Fe3(PO4)2P2O / C prepared in Example 1 of the present invention Detailed implementation manners

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0029] In the description of this application, unless otherwise specified, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0030] The weights of the relevant components mentioned in the description of the embodiments of this application not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between each component. Therefore, as long as the contents of the relevant components in the description of the embodiments of this application are scaled up or down in proportion, they are within the scope disclosed in the description of the embodiments of this application. Specifically, the weights described in the description of the embodiments of this application can be mass units well-known in the chemical engineering field such as μg, mg, g, kg, etc.

[0031] Without special instructions, all the implementation manners and optional implementation manners of this application can be combined with each other to form a new technical solution.

[0032] Without special instructions, all the technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] The following will detail the implementation manners of this application.

[0034] The first embodiment of the present application provides a cathode material. The molecular formula of the cathode material is Na4M 3-3a N 6a / m (PO4)2P2O7 / C (or expressed as Na4(M3(PO4)2) 1-a (N 6a / m m+ (PO4) 2a )P2O7 / C), where N is a doped metal element, the valence state of N is m, m is a natural number greater than 0, M is a transition metal element, and 0 ≤ a ≤ 0.3. Specifically, M can be selected from one or more of transition metal elements such as Fe, Mn, etc. N is a doped metal element. It can be understood that the doped metal element N is other metal elements different from the transition metal element M. Specifically, N can be selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, Cu.

[0035] In any embodiment of the present application, when a = 0, that is, the doped metal element N is not 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 cathode material is Na4Mn3(PO4)2P2O7 / C; when M is selected from Fe, the molecular formula of the cathode material is Na4Fe3(PO4)2P2O7 / C; when M is selected from Ni, the molecular formula of the cathode material is Na4Ni3(PO4)2P2O7 / C; when M is selected from Co, the molecular formula of the cathode material is Na4Co3(PO4)2P2O7 / C. When M is two or more selected from 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 / C, where 0 ≤ e ≤ 3, 0 ≤ f ≤ 3, 0 ≤ g ≤ 3, and 0 ≤ e + f + g ≤ 3.

[0036] It can be further understood that when the cathode material is doped with the metal element N, the doped metal element N is other metal elements different from the transition metal elements M (Mn, Fe, Ni, and Co). The doped metal element N can be one or more of Mg, Al, Ti, V, Zn, Zr, Cr, Cu.

[0037] The first aspect of the present application provides a preparation method of a cathode material, including the following steps: Mixing step: Weigh X raw material and Y raw material, place them in a container containing an alcohol solvent, mix and stir to obtain slurry A, and slurry A is ground to obtain precursor slurry B; Spray drying step: Place the precursor slurry B in a spray drying device for spray drying treatment to obtain precursor powder C; Sintering step: Place the precursor powder C in a sintering device for sintering treatment to obtain the cathode material; Among them, the anhydrous compound of the X raw material has a molecular formula of M3(PO4)2 and / or MPO4, and the Y raw material is a sodium salt.

[0038] In the above preparation method, the X raw material is almost insoluble in water, and the Y raw material can be selected from sodium salts that are soluble or insoluble in water. Adding an alcohol solvent to the solvent can not only clean the impurities attached to the surfaces of the X raw material and the Y raw material, but also increase the solubility of the Y raw material in the solution, which helps the sodium ions in the Y raw material to adsorb on the surface of the X raw material particles; at the same time, since the alcohol solvent contains carbon atoms, the carbon atoms remaining in the mixing step can serve as a carbon source in the subsequent spray drying step and sintering step to form an irregular carbon coating layer; through the special selection of the above raw materials and solvents, synergistically combining the mixing step, spray drying step and sintering step, the obtained cathode material product has a high purity and good electrochemical performance.

[0039] In addition, the above preparation method is simple to operate and has relatively low purity requirements for the X raw material and the Y raw material. Therefore, it can effectively reduce the cost of industrial production and has the prospect of large-scale production.

[0040] The applicant has found through in-depth research that when the raw materials and solvents of this application meet the aforementioned design conditions, if one or more of the following conditions can also be met, the purity of the cathode material can be further improved and the performance of the battery can be further improved.

[0041] In any embodiment of this application, the anhydrous compound of the X raw material has a molecular formula of M3(PO4)2. Further, 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), Co3(PO4)2.z3H2O (0≤z3≤8). Since Mn3(PO4)2.yH2O (0≤y≤7) and Fe3(PO4)2.z1H2O (0≤z1≤8), Ni3(PO4)2.z2H2O (0≤z2≤8), Co3(PO4)2.z3H2O (0≤z3≤8) are easy to produce industrially, it is beneficial to the industrial promotion and application of the cathode material provided by this application.

[0042] 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). The polyanionic sodium-ion battery cathode material is similar to the lithium-ion olivine material. The Fe-based material has good electrochemical performance, but the low plateau voltage results in a low energy density; the Mn-based material has a high plateau voltage and a high energy density, but the low electronic conductivity leads to poor electrochemical performance and poor cycle stability due to the Jahn-Teller effect; the Ni-based and Co-based materials have high voltage platforms, but the cost is relatively high. The mixture of two or more of Mn, Fe, Ni, and Co under the synergistic effect results in a material with better energy density, electrochemical performance, and cycle life, and a moderate cost, meeting the actual application requirements.

[0043] Further, Mn3(PO4)2.yH2O (0 ≤ y ≤ 7) is selected from Mn3(PO4)2·3H2O. Since Mn3(PO4)2·3H2O can be directly prepared by the coprecipitation of manganese salts and phosphates in solution, it is simple and easy to operate, which is beneficial to reducing the production difficulty, improving the efficiency of industrial production, and reducing the cost of purchasing raw materials externally.

[0044] Further, Fe3(PO4)2.z1H2O (0 ≤ z1 ≤ 8) is selected from Fe3(PO4)2·8H2O. Since Fe3(PO4)2·8H2O can be directly prepared by the coprecipitation of ferrous salts and phosphates in solution, it is simple and easy to operate, which is beneficial to reducing the production difficulty, improving the efficiency of industrial production, and reducing the cost of purchasing raw materials externally.

[0045] Further, Ni3(PO4)2.z2H2O (0 ≤ z2 ≤ 8) is selected from Ni3(PO4)2·8H2O. Since Ni3(PO4)2·8H2O can be directly prepared by the coprecipitation of nickel salts and phosphates in solution, it is simple and easy to operate, which is beneficial to reducing the production difficulty, improving the efficiency of industrial production, and reducing the cost of purchasing raw materials externally.

[0046] Further, Co3(PO4)2.z3H2O (0 ≤ z3 ≤ 8) is selected from Co3(PO4)2·8H2O. Since Co3(PO4)2·8H2O can be directly prepared by the coprecipitation of cobalt salts and phosphates in solution, it is simple and easy to operate, which is beneficial to reducing the production difficulty, improving the efficiency of industrial production, and reducing the cost of purchasing raw materials externally.

[0047] Further, 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.

[0048] Further, the X raw material is selected from Mn3(PO4)2·3H2O and Fe3(PO4)2·8H2O. Similar to lithium iron manganese phosphate, sodium manganese iron phosphate composite combines the low cost of iron and manganese and the high voltage platform of manganese to synergistically provide the cathode material with the best cost performance.

[0049] In any embodiment of the present application, the molecular formula of the anhydrous compound of the X raw material is MPO4. Further, the X raw material is selected from FePO4·z4H2O (0 ≤ z4 ≤ 8).

[0050] Further, the X raw material is selected from FePO4·2H2O, FePO4·3H2O, and FePO4·8H2O. The structure of ferric orthophosphate is relatively stable, and the storage and transportation requirements of raw materials are relatively low.

[0051] It can be understood that the X raw material may also simultaneously contain M3(PO4)2 and MPO4. For example, the X raw material is Mn3(PO4)2·yH2O (0 ≤ y ≤ 7) and FePO4·z4H2O (0 ≤ z4 ≤ 8).

[0052] Further, the X raw material is selected from Mn3(PO4)2·3H2O and FePO4·8H2O. Similar to lithium iron manganese phosphate, sodium manganese iron phosphate composite combines the low cost of iron and manganese and the high voltage platform of manganese to synergistically provide the cathode material with the best cost performance.

[0053] 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, Na2HPO4, NaH2PO4, and Na3PO4. It can be understood that the above compounds include both their corresponding anhydrous compounds and their compounds containing different crystal waters.

[0054] Further, the Y raw material is selected from sodium salts containing phosphorus elements. For example, the Y raw material is selected from one or more of Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, Na2HPO4, NaH2PO4, and Na3PO4. Since phosphorus elements are easily lost in the mixing step, when formulating the raw material ratio, sodium elements and transition metal elements are usually used as the calculation basis, and then phosphorus elements are supplemented through a phosphorus source supplement. Selecting the Y raw material from sodium salts containing phosphorus elements can reduce the addition amount of the phosphorus source supplement, or even eliminate the need for additional phosphorus source supplement.

[0055] In any embodiment of the present application, in the mixing step, the mass ratio (m x ) of the X raw material ranges from 15% ≤ mx ≤80%. The mass ratio of raw material X = mass of raw material X / mass of alcohol solvent.

[0056] The applicant found that when the mass ratio of raw material X is too low, more side reactants will be produced. When the mass ratio of raw material X is too high, serious agglomeration will occur during the mixing step. Therefore, it is recommended that the mass ratio of raw material X be preferably in the range of 15% - 80%.

[0057] In any embodiment of the present application, during the mixing step, the mass ratio of raw material Y (m Y ) ranges from 30% ≤ m Y ≤ 95%. The mass ratio of raw material Y = mass of raw material Y / mass of alcohol solvent.

[0058] Furthermore, the mass ratio of raw material Y ≥ 50%.

[0059] The applicant found that when the mass ratio of raw material Y is too low, it cannot be evenly dispersed on the surface of raw material X, resulting in the generation of more impurities. It is recommended that the mass ratio of raw material Y be preferably in the range of 50% - 95%.

[0060] In any embodiment of the present application, during the mixing step, the alcohol solvent is one or more of methanol, ethanol, propanol, butanol, and pentanol. Preferably, the alcohol solvent is ethanol.

[0061] The applicant found that when the transition metal element M in raw material X contains divalent transition metal ions (for example, ferrous ions), due to the presence of alcohol solvent in the mixing step, the oxidation of divalent transition metal ions to trivalent transition metal ions will be accelerated. Due to the change in the valence of transition metal ions, the elemental ratio of the primary product in the mixing step will be unbalanced, resulting in the generation of impurities in the final product after the sintering step.

[0062] The applicant further found that by reasonably controlling the volume fraction of the alcohol solvent, the oxidation of divalent transition metal ions can be effectively slowed down, and the generation of impurities can be reduced. Further, the concentration of the alcohol solvent ≤ 30%; preferably, the concentration of the alcohol solvent ≤ 20%; more preferably, the concentration of the alcohol solvent ≤ 15%.

[0063] Furthermore, the concentration of the alcohol solvent ≥ 2%.

[0064] Even further, the concentration range of the alcohol solvent is 5% - 10%.

[0065] If the concentration of the alcohol solvent is too high, the oxidation of divalent transition metal ions will be accelerated; if the concentration of the alcohol solvent is too low, the drying time required in the subsequent spray drying step will be longer. Reasonably controlling the volume fraction of the alcohol solvent helps to improve the preparation efficiency and reduce the generation of impurities.

[0066] Low-concentration alcohol solvents can be diluted by adding distilled water or other solvents to high-concentration alcohol solvents. For example, industrial ethanol with a concentration of 95% is diluted to an ethanol solvent with a concentration of 20% using distilled water.

[0067] In any embodiment of the present application, in the mixing step: the raw materials at least include X raw material and Y raw material. It can be understood that the raw materials also include other raw materials in addition to X raw material and Y raw material.

[0068] In any embodiment of the present application, in the mixing step, the raw materials further include: one or more of an antioxidant, a modification additive, a phosphorus source supplement, a carbon source, a dispersant, and a viscosity reducer.

[0069] In any embodiment of the present application, in the mixing step, the raw materials further include: an antioxidant. In the mixing step, an antioxidant is added and mixed and stirred with the X raw material and the Y raw material in a container containing an alcohol solvent to obtain the slurry A. It can be understood that adding an antioxidant can effectively inhibit the oxidation of divalent transition metal ions or reduce trivalent transition metal ions to divalent transition metal ions.

[0070] Furthermore, the mass percentage of the antioxidant ≤ 30%.

[0071] Even further, the mass percentage of the antioxidant ≥ 5%.

[0072] The mass percentage of the antioxidant = the mass of the antioxidant / the mass of the alcohol solvent.

[0073] Furthermore, by mass fraction, the ratio range of the mass of the X raw material to the mass of the antioxidant is (90~100):(5~20).

[0074] If the mass percentage of the antioxidant is too low, it cannot play an effective inhibitory role. If the mass percentage of the antioxidant is too high, redundant antioxidant adhering to the X raw material needs to be cleaned, increasing the complexity and difficulty of the preparation process. Therefore, reasonably controlling the content of the antioxidant, especially the ratio of the antioxidant to the X raw material, helps to improve the preparation efficiency.

[0075] Furthermore, the antioxidant is selected from ascorbic acid, vitamin C, citric acid, and vanillin.

[0076] Preferably, the antioxidant is vanillin. The applicant has found through experiments that the cathode material synthesized with vanillin as the antioxidant has better electrochemical performance.

[0077] In any embodiment of the present application, in the mixing step, the raw materials further include: a modification additive, and the modification additive contains a doped metal element N.

[0078] The main purpose of the modified additive is to perform cation doping on the synthesized cathode material. Generally, the ionic conductivity and electronic conductivity of polyanion materials are both low, while appropriate cation doping can greatly improve their ionic conductivity and electronic conductivity, thereby enhancing the electrochemical performance of the obtained cathode material.

[0079] Understandably, the molecular formula of the cathode material obtained by adding the modified additive is Na4(M3(PO4)2) 1-a (N 6a / m m+ (PO4) 2a )P2O7. The doped 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, Cu.

[0080] Furthermore, the modified additive can be selected from simple substances, compounds, solutions, etc. containing the above elements.

[0081] Furthermore, the modified additive can be soluble in water or insoluble in water.

[0082] Furthermore, the molecular formula of the modified additive is N 6 / m m+ (PO4)2, where N is selected from one or more of Mg, Al, Ti, V, Zn, Zr, Cr, Cu, and m + is the valence of N. This is because the N 6 / m m+ (PO4)2 in the molecular formula of N 1-a (N 6a / m m+ (PO4) 2a )P2O7 contains N in the a chemical bond 6 / m m+ (PO4)2. In the mixing step, the required modified doped 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 doped metal element N during the subsequent reaction process.

[0083] Furthermore, the mass ratio of the modified additive ≥ 1%.

[0084] Furthermore, the mass ratio of the modified additive ≤ 20%.

[0085] The mass ratio of the modified additive = the mass of the modified additive / the mass of the alcohol solvent.

[0086] In any embodiment of the present application, in the mixing step, the raw materials may further include: a phosphorus source supplement. Appropriately adding a phosphorus source supplement can increase the phosphorus element content of the raw materials, which helps to supplement the phosphorus element lost during the preparation process. For example, during the mixing process, due to a short mixing time or other factors, the phosphorus element is not fully attached to the X raw material. In particular, when the above-mentioned modification additive does not select N 6 / m m+ (PO4)2, but rather N in the form of a simple substance or other compounds (such as oxides, carbonates, oxalates, nitrates), a phosphorus source supplement is added to the raw materials, and the sum of the chemical stoichiometry of phosphorus in the phosphorus source supplement is 2:3 / m of the sum of the chemical stoichiometry of the added N. This can ensure that the chemical formula of the finally obtained substance conforms to Na4(M3(PO4)2) 1-a (N 6a / m m+ (PO4) 2a )P2O7, improving the purity of the prepared cathode material.

[0087] It can be understood that the phosphorus source supplement is a simple substance or compound containing phosphorus. The phosphorus source supplement can be soluble in water or insoluble in water.

[0088] Furthermore, the phosphorus source supplement is a solvent containing phosphorus. The solvent can be more easily mixed uniformly with other materials during stirring and grinding.

[0089] Furthermore, the phosphorus source supplement is selected from one or more of H3PO4, NH4H2PO4, (NH4)2HPO4. The above-mentioned phosphorus sources are soluble in water, are easily mixed uniformly with M3(PO4)2 and N compounds, and do not leave any impurities after high-temperature sintering.

[0090] Furthermore, the mass ratio of the phosphorus source supplement ≥ 1%.

[0091] Furthermore, the mass ratio of the phosphorus source supplement ≤ 20%.

[0092] The mass ratio of the phosphorus source supplement = the mass of the phosphorus source supplement / the mass of the alcohol solvent.

[0093] In any embodiment of the present application, in the mixing step, the raw materials further include: a carbon source.

[0094] Specifically, the carbon source can be selected from one or more of inorganic carbon materials and / or organic carbon materials.

[0095] Furthermore, the organic carbon materials are selected from one or more of citric acid, glucose, sucrose, polyethylene glycol, starch, lignin, and asphalt.

[0096] Furthermore, the inorganic carbon materials are selected from one or more of graphite, activated carbon, carbon nanotubes, and graphene.

[0097] In any embodiment of the present application, in the mixing step, the raw materials further include: a dispersant.

[0098] 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.

[0099] In a specific embodiment, in the mixing step, the raw materials further include: a viscosity reducer.

[0100] Furthermore, the viscosity reducer is selected from one or more of polyvinyl alcohol, polyethylene glycol, and polypropylene glycol.

[0101] In any embodiment of the present application, in the mixing step, slurry A is placed in a ball mill and ground to obtain precursor slurry B, where the rotation speed of the ball mill is 100 - 400 r / min. Preferably, the rotation speed of the ball mill is 150 - 300 r / min. Since high-speed grinding will accelerate the oxidation of divalent transition metal elements, reasonably controlling the rotation speed of the grinding machine at a relatively reduced rate can slow down the oxidation.

[0102] 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 precursor powder C, contribute to more complete reaction of precursor powder C in the sintering step; and can also reduce the occurrence of other side reactions that may generate impurities during the spray drying process, thereby improving the purity of the cathode material.

[0103] Furthermore, the inlet temperature of the spray drying equipment is 190 - 220 °C.

[0104] 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 precursor powder C, facilitate the sintering of precursor powder C in subsequent steps; and thereby improve the purity of the cathode material.

[0105] Furthermore, the outlet temperature of the spray drying equipment is 90 - 110 °C.

[0106] In any embodiment of the present application, it further includes a pretreatment step, the pretreatment step is located before the sintering step, and the pretreatment step includes: treating precursor powder C in an ammonia water solution.

[0107] Ammonia water can further undergo a complexation reaction with the precursor powder C, affecting the grain growth rate and morphological structure of the precursor powder C by controlling the concentration of free ions, and enabling corresponding ions such as Na + and P2O7 4- to diffuse to the correct sites to the greatest extent during the calcination step, reducing the occurrence of other side reactions that may generate impurities during the subsequent calcination process, avoiding the formation of impurity phases, promoting the reaction to produce pure-phase products, and thus improving the purity of the cathode material.

[0108] Furthermore, in the pretreatment step, the mass percentage concentration of the ammonia water solution is 2-10%.

[0109] Furthermore, in the pretreatment step, the treatment time of the pretreatment is 2-15h. Preferably, the treatment time of the pretreatment is 3-8h.

[0110] In any embodiment of the present application, in the pretreatment step, the treatment time for placing the precursor powder C in the ammonia water solution is 3-4h.

[0111] In any embodiment of the present application, in the sintering step, the atmosphere for the sintering treatment is an inert atmosphere or a reducing atmosphere.

[0112] Furthermore, preferably, the sintering can be carried out by single sintering or multiple sinterings.

[0113] Furthermore, preferably, when the sintering treatment is carried out in an inert atmosphere, nitrogen is preferred. The 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 concentration of free ions, thereby improving the purity of the cathode material.

[0114] In any embodiment of the present application, in the sintering step, the temperature range for the sintering treatment 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 and the specific surface area decreases, resulting in a reduction in the electrochemical performance of the battery made of the cathode material.

[0115] Furthermore, preferably, the temperature range for the sintering treatment is 450-800°C.

[0116] Furthermore, preferably, the temperature range for the sintering treatment is 450-750°C.

[0117] In any embodiment of the present application, in the sintering step, the time for the sintering treatment is 3-20h.

[0118] Furthermore, preferably, the time for the sintering treatment is 10-20h.

[0119] In any embodiment of the present application, in the sintering step, the heating rate of the sintering equipment is 5-10 °C / min.

[0120] The present application also provides a sodium-ion battery, including the positive electrode material described above or the positive electrode of the positive electrode material prepared by the above preparation method. Specifically, the positive electrode includes a current collector and a positive electrode active material provided on the current collector, and the positive electrode active material includes the positive electrode material of the present application or the positive electrode material prepared by the preparation method of the present application.

[0121] The present application also provides a battery module, including the above sodium-ion battery. Specifically, the battery module includes a housing, a cover plate, 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 plate is used to close the opening of the housing.

[0122] The present application also provides an electrical device, including the above sodium-ion battery. The electrical device can be a device with a sodium-ion battery as a power supply device. Exemplarily, the electrical device can be a small electronic device (such as a mobile phone, a tablet computer, a laptop computer, etc.), or a large transportation device such as a vehicle (such as a hybrid vehicle, an electric vehicle, etc.), or an electric tool (such as an electric drill, an electric saw, etc.). Examples

[0123] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those not specified in the examples in terms of specific technology or conditions, they shall be carried out according to the technology or conditions described in the literature in the art or according to the product specification. Those reagents or instruments not specified in terms of the manufacturer can be obtained as conventional products through commercial purchase. Example 1

[0124] 1. Preparation method of positive electrode material: Weigh 100.32 g of Fe3(PO4)2·8H2O as X raw material, 53.18 g of Na4P2O7 as Y raw material, 20 g of sucrose as carbon source, and 15.74 g of PEG (molecular weight 1675) as dispersant. Using 10% ethanol (ethanol is commercially available industrial ethanol with a concentration of 95%) and 90% distilled water as the medium, mix at 300 r / min for 50 min to obtain slurry A, and the obtained slurry A is ground by sanding to obtain slurry B. After spray drying slurry B, precursor powder C is obtained. Then, the precursor C is placed in a nitrogen atmosphere and calcined at 500 °C for 10 h to obtain Na4Fe3(PO4)2P2O7 / C (in this example, M is Fe and a = 0).

[0125] Figure 2XRD test of the synthesized Na4Fe3(PO4)2P2O7 / C shows that the obtained product is a pure phase with basically no impurity peaks.

[0126] 2. Preparation of Coin Cells Take 0.8 g of the above Na4Fe3(PO4)2P2O7 / C material, 0.1 g of conductive carbon black, and 0.1 g of PVDF, mix them by grinding with NMP as the medium, and coat the obtained slurry on 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 1 cm as the working electrode, and a sodium metal sheet is used as the counter electrode. 1 M NaPF6 dissolved in EC:DEC (50:50 vol / vol) is used as the electrolyte, and a coin cell (2032) is assembled under an inert atmosphere. Example 2

[0127] The preparation method of the positive electrode material is similar to that of Example 1, except that the weighed X raw material is 81.2 g of Mn3(PO4)2·3H2O; the Y raw material is 56.38 g of Na2HPO4. Example 3

[0128] The preparation method of the positive electrode material is similar to that of Example 1, except that in the mixing step, 20 g of vanillin is added. Example 4

[0129] The preparation method of the positive electrode material is similar to that of Example 1, except that 15% ethanol and 85% distilled water are used as the medium. Example 5

[0130] The preparation method of the positive electrode material is similar to that of Example 1, except that the mixture is mixed at 400 r / min for 50 min to obtain slurry A.

[0131] The positive electrode material products prepared in Examples 1-5 were subjected to charge-discharge tests, and the test results are shown in Table 1: Table 1. Charge-discharge test results of the positive electrode material products prepared in Examples 1-5 Initial discharge capacity Initial Coulombic efficiency Number of cycles Capacity retention rate Example 1 111mAh / g 91% 1000 86% Example 2 106mAh / g 87% 1000 86% Example 3 116mAh / g 92% 1000 90% Example 4 104mAh / g 87% 1000 87% Example 5 102mAh / g 86% 1000 82% It can be seen from the data in the table that the positive electrode materials synthesized by this method all exhibit high initial discharge capacities and Coulombic efficiencies, and also exhibit excellent cycling performance at high currents. This strongly proves that through the special design of raw materials and the synergistic cooperation of mixing, spray drying, and sintering, the present invention can prepare positive electrode materials with relatively high purity and good electrochemical performance.

[0132] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cathode material, the molecular formula of the cathode material being Na4M 3-3a N 6a / m (PO4)2P2O7 / C, where N is a doped metal element, the valence state of N is m, m is a natural number greater than 0, M is a transition metal element, and 0 ≤ a ≤ 0.3, and the method is characterized in that The preparation method includes the following steps: Mixing step: Weigh raw material X and raw material Y, place them in a container containing an alcohol solvent, mix and stir to obtain slurry A, and grind the slurry A to obtain precursor slurry B; Spray drying step: Place the precursor slurry B in a spray drying device for spray drying treatment to obtain precursor powder C; Sintering step: Place the precursor powder C in a sintering device for sintering treatment to obtain the positive electrode material; Wherein, the molecular formula of the anhydrous compound of the raw material X is M3(PO4)2 and / or MPO4, and the raw material Y is a sodium salt.

2. The preparation method of the cathode material according to claim 1, characterized in that The molecular formula of the anhydrous compound of the raw material X is M3(PO4)2, and 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), Co3(PO4)2·z3H2O (0≤z3≤8); and / or The molecular formula of the anhydrous compound of the raw material X is MPO4, and the raw material X is selected from FePO4·z4H2O (0≤z4≤8).

3. The preparation method of the positive electrode material according to claim 1, wherein the raw material Y is selected from one or more of NaOH, Na2C2O4, CH3COONa, Na2CO3, NaHCO3, Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7, Na2HPO4, NaH2PO4, and Na3PO4.

4. The method for preparing the cathode material according to claim 1, wherein In the mixing step, the alcohol solvent is one or more of methanol, ethanol, propanol, butanol, and pentanol.

5. The preparation method of the cathode material according to claim 4, characterized in that, The concentration of the alcohol solvent ≤ 30%; preferably, the concentration of the alcohol solvent ≤ 20%; further preferably, the concentration of the alcohol solvent ≤ 15%.

6. The preparation method of the cathode material according to claim 1, characterized in that, In the mixing step, an antioxidant is further added, and it is mixed and stirred with the raw material X and the raw material Y in a container containing an alcohol solvent to obtain the slurry A, and the mass percentage of the antioxidant in the slurry A ≤ 30%.

7. The preparation method of the positive electrode material according to claim 6, characterized in that, The antioxidant is selected from one or more of ascorbic acid, vitamin C, citric acid, and vanillin.

8. The method for preparing the cathode material according to claim 6 or 7, characterized in that, By mass fraction, the ratio range of the mass of the raw material X to the mass of the antioxidant is (90~100):(5~20).

9. The method for preparing the cathode material according to claim 1, wherein In the mixing step, the slurry A is placed in a ball mill and ground to obtain precursor slurry B, wherein the rotation speed of the ball mill is 100~400 r / min; preferably, 150~300 r / min.

10. A cathode material, characterized in that, Prepared by the preparation method of the positive electrode material according to any one of claims 1~9.

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