A polyanion composite positive electrode material and its preparation method and application

Abstract

The present invention provides a polyanion composite cathode material and its preparation method and application. The preparation method comprises the following steps: (1) mixing a sodium source, a vanadium source, a phosphorus source, and a fluorine source and ball milling to obtain a polyanion material; (2) mixing the polyanion material, an organic acid, aniline, and water and dispersing the mixture to obtain a mixed solution; the mixed solution undergoes a polymerization reaction in the presence of an oxidant to obtain a primary product; (3) mixing the primary product with an organic solvent, performing solid-liquid separation, and obtaining a solid phase and a liquid phase; (4) sequentially mixing and drying the solid phase and the liquid phase to obtain the polyanion composite cathode material. The present invention forms a uniform polyaniline coating on the surface of the polyanion material through the design and synergistic effect of raw materials and process routes, so that the polyanion composite cathode material has excellent electrochemical performance. The preparation method has a simple process, mild conditions, low cost, is easy to implement large-scale production, and has a wide range of applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery materials, and specifically relates to a polyanion composite positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with rapid economic development and adjustments to energy strategies, the lithium-ion battery industry has faced unprecedented challenges. Furthermore, limited lithium reserves and uneven geographical distribution have led to high prices for lithium materials, significantly restricting the further development of lithium-ion batteries. Sodium, a member of the same element family as lithium, has similar properties. Sodium is abundant, widely distributed, and low-cost, making it a promising alternative to lithium. In recent years, sodium-ion batteries, with their similar operating principles and cost advantages to lithium-ion batteries, have shown promising market prospects in energy storage, low-power electric vehicles, and other fields.

[0003] Sodium ion batteries are usually assembled from positive electrode sheets, negative electrode sheets, separators and electrolytes. The performance of sodium ion batteries depends largely on the selection of positive and negative electrode materials. Currently known positive electrode materials include transition metal oxides, polyanionic compounds, Prussian blue analogs, etc. Polyanionic compounds are composed of polyanionic polyhedrons and transition metal ions connected by strong covalent bonds and have a three-dimensional network structure. The polyanions can support and stabilize the crystal structure of the compound, so they have good thermal stability and electrochemical stability. Polyanionic compounds usually contain 3 or 4 Na + , which can realize the transfer of multiple electrons; moreover, by changing the elements and transition metals that form the polyanions, the redox potential and charge and discharge voltage of the material can be adjusted; based on the above advantages, polyanionic compounds have always attracted much attention in the industry.

[0004] In the family of polyanionic sodium cathode materials, vanadium-based polyanionic compounds have the characteristics of stable unit cell structure and fast sodium diffusion, and are expected to obtain sodium-ion batteries with high specific energy, high specific power and high stability; however, the intrinsic conductivity of vanadium-based polyanionic compounds is relatively low, which seriously affects the electrochemical performance of the material.

[0005] Currently, the main method for improving vanadium-based polyanionic compounds is carbon coating. For example, CN108511711A discloses a sodium vanadium phosphate composite cathode material with a flaky structure. Its preparation method includes ball milling a sodium source, a phosphorus source, a vanadium source, and a carbon source in an organic solvent, followed by drying and high-temperature calcination to obtain the flaky sodium vanadium phosphate composite cathode material. The carbon source is a carbohydrate compound, added in an amount of 30-80 wt% of the sodium vanadium phosphate. CN110165183A discloses a method for preparing a sodium vanadium phosphate composite material, which comprises the following steps: first, mixing a sodium source, a vanadium source, and a phosphorus source, ball-milling the mixture, and drying the mixture to obtain a precursor powder; then, sintering the precursor powder in a non-oxidizing atmosphere to obtain sodium vanadium phosphate; then, dissolving an organic carbon source in a dispersant, adding sodium vanadium phosphate thereto, stirring, evaporating the mixture until a gel is formed, drying, and grinding the mixture to obtain a mixed powder; finally, mixing and grinding a Y-containing compound with the mixed powder, and sintering the mixture at 300-500°C for 0.5-3h to obtain a sodium vanadium phosphate composite material containing a co-doped carbon layer. CN111994889A discloses a method for preparing a sodium vanadium phosphate cathode material, which comprises first, wet-milling ammonium metavanadate, sodium dihydrogen phosphate dihydrate, and glucose using a planetary ball mill, drying, and obtaining a sodium vanadium phosphate precursor; then, reacting the mixtures by a hydrothermal method to form a sodium vanadium phosphate precursor; and finally, sintering the sodium vanadium phosphate precursor by a solid-phase method to prepare a sodium vanadium phosphate composite material powder. Although introducing a carbon coating layer into vanadium-based polyanionic compounds helps improve the electrical conductivity of the material, the existing carbon coating method has a long preparation cycle, requires high temperature sintering, and has high production costs. Moreover, the composite of carbon and vanadium-based polyanionic compounds is poor, resulting in poor stability of the positive electrode material, which in turn affects the cycle performance of sodium-ion batteries.

[0006] Therefore, developing vanadium-based polyanionic compounds with high conductivity, good stability and excellent electrochemical performance is an urgent problem to be solved in this field. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a polyanion composite positive electrode material and its preparation method and application. Through the design and coordination of raw materials and process routes, a uniform polyaniline coating layer is formed on the surface of the polyanion material. The obtained polyanion composite positive electrode material has excellent conductivity, charge and discharge specific capacity and stability, thereby improving the electrochemical performance of sodium ion batteries.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a polyanion composite positive electrode material, the preparation method comprising the following steps:

[0010] (1) mixing a sodium source, a vanadium source, a phosphorus source, and a fluorine source and ball milling the mixture to obtain a polyanion material;

[0011] (2) mixing the polyanionic material obtained in step (1), the organic acid, and the aniline with water and dispersing the mixture to obtain a mixed solution; and subjecting the mixed solution to a polymerization reaction in the presence of an oxidant to obtain a primary product;

[0012] (3) mixing the initial product obtained in step (2) with an organic solvent, and performing solid-liquid separation to obtain a solid phase and a liquid phase;

[0013] (4) The solid phase and the liquid phase obtained in step (3) are sequentially mixed and dried to obtain the polyanion composite positive electrode material.

[0014] In the preparation method provided by the present invention, a fluorine-doped vanadium-based polyanion compound is first obtained by ball milling. Compared with sodium vanadium phosphate, the introduction of a fluorine source in step (1) makes the obtained polyanion material (sodium vanadium fluorophosphate) have a higher charge-discharge specific capacity and a higher working potential (sodium vanadium fluorophosphate 3.8-3.9V, sodium vanadium phosphate 3.4V) due to the inductive effect of fluorine, which is conducive to improving the energy density of sodium ion batteries. At the same time, the higher voltage has higher requirements on the structure of the material, the electrolyte system, etc. Moreover, the intrinsic electronic conductivity of sodium vanadium fluorophosphate is low, resulting in slow sodium ion diffusion power, so it is more necessary to improve the electronic conductivity of the material. Through the design of the preparation method, the present invention in situ coats the polyanion material (sodium vanadium fluorophosphate) with a highly conductive polyaniline (PANI) polymer material. By in-situ chemical coating, the uniformity, thickness and strength of the coating layer are improved, effectively solving the problems of low electronic conductivity of the material and poor structural cycle stability. Moreover, by introducing a layer of polymer substance on the surface of the polyanion material, the interface stability is improved, which can effectively avoid side reactions between the material and the electrolyte; further, the F on the surface of the material combines with the coated PANI to form a PFANI-like substance. The introduction of F can also improve the polymer material's own antioxidant properties, water resistance, corrosion resistance, etc., further enhancing the protective effect between the active material and the electrolyte.

[0015] Specifically, in the preparation method provided by the present invention, step (1) synthesizes the polyanion material under the action of ball milling mechanical energy, without the need for high-temperature sintering, the required time is short, the process is simplified, the production efficiency is greatly improved, the production cost is reduced, and the obtained polyanion material has the characteristics of small particles and good uniformity. In step (2), the polyanion material is mixed with an organic acid, aniline, and water to obtain a mixed liquid (emulsion); in the presence of an oxidant, aniline (An) monomer is subjected to in-situ oxidative polymerization coating on the surface of the polyanion material to form a polyaniline coating layer to obtain the primary product; in step (3), the primary product is mixed with an organic solvent and demulsified, and the polyaniline not coated on the surface of the polyanion material in the system is extracted into the liquid phase (organic phase), and the polyanion material coated by in-situ oxidative polymerization is precipitated (solid phase), so that the system is divided into solid and liquid phases; after the solid and liquid are separated, in step (4), the obtained solid phase and liquid phase (organic phase) are mixed uniformly and then dried, so that the polyaniline in the liquid phase (organic phase) and the solid phase (polyanion material coated by polymerization) are deposited and interact with each other, so that the polyaniline coating layer on the surface of the polyanion material is more uniform and complete.

[0016] In summary, the present invention first prepares a polyanion material based on sodium vanadium fluorophosphate by ball milling, then introduces aniline monomer and designs a process route including two coating processes. Through the design and synergistic effect of raw materials and process routes, an in-situ polymerized, uniformly performing, and thickly thick polyaniline coating is formed on the surface of the polyanion material, resulting in a polyanion composite positive electrode material having excellent electrochemical properties, particularly significant improvements in electrical conductivity and structural stability. The preparation method is simple, mild, does not require complex and harsh reaction conditions such as high temperature / high pressure, is low-cost, is easy to implement in continuous large-scale production, and has a wide range of applications.

[0017] Preferably, the sodium source in step (1) comprises any one or a combination of at least two of sodium metavanadate, sodium vanadate, sodium fluoride, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium bromide, sodium chloride, sodium carbonate, and sodium hydroxide.

[0018] Preferably, the vanadium source in step (1) includes any one of sodium metavanadate, sodium vanadate (NaVO3), vanadium oxysulfate, ammonium metavanadate, ammonium vanadate, vanadium dioxide, vanadium trioxide, and vanadium chloride, or a combination of at least two thereof.

[0019] Preferably, the phosphorus source in step (1) includes any one of sodium phosphate, sodium dihydrogen phosphate (NaH2PO4), disodium hydrogen phosphate, and phosphoric acid, or a combination of at least two thereof.

[0020] Preferably, the fluorine source in step (1) comprises sodium fluoride (NaF) and / or ammonium fluoride.

[0021] It should be noted that, in the present invention, the sodium source, vanadium source, phosphorus source, and fluorine source can be different substances respectively; at least two of the sodium source, vanadium source, phosphorus source, and fluorine source can also be the same substance, for example, the sodium source and the vanadium source are the same substance, the sodium source and the phosphorus source are the same substance, and the sodium source and the fluorine source are the same substance.

[0022] Illustratively, the sodium metavanadate and / or sodium vanadate used in step (1) can serve as both a sodium source and a vanadium source; the sodium fluoride used in step (1) can serve as both a sodium source and a fluorine source; the sodium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate used in step (1) can serve as both a sodium source and a phosphorus source.

[0023] Based on this, among the sodium source, vanadium source, phosphorus source, and fluorine source in step (1), there is a substance that can serve as a precursor of two elements. In this case, only one can be selected. If the molar ratio of one substance does not meet the requirements of the polyanion material, other precursors containing a single required element can be added.

[0024] Preferably, the molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphorus in the phosphorus source, and fluorine in the fluorine source is (1-10):1:(1-8):(0.5-8); wherein, the 1-10 can be 2, 3, 4, 5, 6, 7, 8 or 9, etc.; the 1-8 can be 2, 3, 4, 5, 6 or 7, etc.; the 0.5-8 can be 0.6, 0.8, 1, 2, 3, 4, 5, 6 or 7, etc.; and the specific point values ​​between the above point values, due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0025] As a preferred technical solution of the present invention, the molar ratio of the sodium source, vanadium source, phosphorus source, and fluorine source is determined based on the configuration of the target polyanion material and the stoichiometric ratio of each atom. Since the raw material cost of the vanadium source is relatively high among the sodium source, vanadium source, phosphorus source, and fluorine source, the amount (molar amount) of the other raw materials used is based on the vanadium element in the vanadium source to ensure the most complete conversion of the vanadium source.

[0026] Preferably, the vanadium source in step (1) includes a pentavalent vanadium source (such as sodium vanadate, ammonium vanadate), and the mixed material further includes a reducing agent.

[0027] Preferably, the reducing agent includes any one of hydroxylamine hydrochloride (HONH2HCl), hydroxylamine (NH2OH), hydroxylamine sulfate (2NH2OH·H2SO4), oxalic acid, citric acid, and ascorbic acid, or a combination of at least two thereof.

[0028] Preferably, the molar ratio of the pentavalent vanadium source to the reducing agent is 1:(1-5), for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or 1:4.5.

[0029] Preferably, the mixed material in step (1) further includes a transition metal source; the transition metal source includes any one or a combination of at least two of a manganese source, an iron source, a nickel source, a cobalt source, a copper source, a titanium source, and a tin source, more preferably a manganese source and / or an iron source, and even more preferably a manganese source.

[0030] Preferably, the manganese source includes manganese oxide and / or manganese salt, more preferably any one or a combination of at least two of MnO, MnO2, Mn2O3, Mn3O4, manganese acetate, manganese carbonate, manganese sulfate, manganese chloride (MnCl2), and manganese nitrate.

[0031] Preferably, the iron source includes any one of iron oxide, iron salt (ferric salt), ferrous salt (ferrous salt) or a combination of at least two thereof, and further preferably any one of FeO, Fe2O3, Fe3O4, ferrous sulfate, ferrous oxalate, ferrous phosphate, ferrous nitrate, ferrous carbonate, ferrous acetate, ferric nitrate, ferric phosphate and ferric carbonate or a combination of at least two thereof.

[0032] Preferably, the molar ratio of the transition metal in the transition metal source to the vanadium in the vanadium source is (0.1-1):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 or 0.9:1, etc.

[0033] Preferably, the ball milling in step (1) is dry ball milling; thus, under the action of the mechanical energy of dry ball milling, each raw material reacts in one step to obtain the target product, without the need for high-temperature secondary sintering, and without the need to add solvent during the ball milling process, which significantly reduces the raw material cost, time cost and process cost of preparing the polyanion material, and the obtained polyanion material has small particles and good uniformity.

[0034] Preferably, the ball milling speed in step (1) is 400-800 rpm, for example, it can be 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm or 750 rpm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0035] Preferably, the ball milling time in step (1) is 0.5-8h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h or 7.5h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0036] Preferably, after the ball milling in step (1) is completed, washing and drying steps are also included.

[0037] Preferably, the washing detergent comprises water and / or an alcohol solvent.

[0038] Preferably, the alcohol solvent includes any one of ethanol, n-propanol, and isopropanol, or a combination of at least two of them.

[0039] Preferably, the product obtained by ball milling is washed alternately with water and alcohol solvents, and the number of washing times is 2-5 (eg, 3 or 4) times, more preferably 3 times.

[0040] Preferably, in step (2), the mass of the aniline is 0.05-8%, based on the mass of the polyanionic material as 100%, for example, it can be 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or 7.5%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0041] As a preferred technical solution of the present invention, based on the mass of the polyanion material being 100%, the mass of the aniline is 0.05-8%, and a polymerization reaction occurs in the presence of an organic acid and an oxidant to form an in-situ polymerization coating on the surface of the polyanion material. The treatment of steps (3) and (4) forms a secondary coating effect, so that the obtained polyanion composite positive electrode material has a polyaniline coating layer with uniform properties and thickness, complete structure and stability. The polyanion composite positive electrode material has excellent electrical conductivity, specific capacity and stability, and excellent electrochemical performance. If the amount of aniline monomer used is too small, a uniform polyaniline coating layer cannot be obtained, and the conductivity of sodium vanadium fluorophosphate cannot be effectively improved; if the amount of aniline monomer used is too large, the polyaniline layer coated on the surface of the sodium vanadium fluorophosphate will be too thick. Although the thick polyaniline layer can provide a good physical barrier between the positive electrode and the electrolyte, it will also hinder the diffusion of sodium during the insertion and extraction process, resulting in low capacity of the material; in addition, excessive monomer usage will also cause the overall cost of the material to increase.

[0042] Preferably, the organic acid in step (2) is dodecylbenzenesulfonic acid.

[0043] As a preferred technical solution of the present invention, the organic acid is dodecylbenzenesulfonic acid (DBSA), which is an organic protonic acid. Compared with inorganic protonic acids (such as hydrochloric acid, sulfuric acid and phosphoric acid), DBSA has good environmental stability, is not easy to migrate, and will not affect the polarity of the formed polyaniline (PANI) molecular chain after doping; moreover, as an organic sulfonic acid, DBSA contains both polar and non-polar groups in its molecular structure, has a large molecular weight, and greatly improves conductivity and solubility. It is used for the in-situ oxidative polymerization of aniline on the surface of the polyanion material, which helps to form a uniform polyaniline coating layer, so that the obtained polyanion composite positive electrode material has significantly improved electrochemical performance.

[0044] Preferably, the molar ratio of the organic acid to aniline in step (2) is (0.5-1.0):1, for example, it can be 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1 or 0.95:1, etc.

[0045] Preferably, in step (2), based on the mass of the organic acid (preferably DBSA) as 1 g, the volume of water is 100-500 mL, for example, 150 mL, 200 mL, 250 mL, 300 mL, 350 mL, 400 mL or 450 mL, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range, and 200-400 mL is further preferred.

[0046] Preferably, the oxidant in step (2) is persulfate, more preferably ammonium persulfate.

[0047] As a preferred technical solution of the present invention, the oxidant is ammonium persulfate (APS), which has strong oxidizing ability, does not contain metal ions, and is easy to handle.

[0048] Preferably, the molar ratio of the oxidant to aniline in step (2) is (0.5-2.0):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1 or 1.9:1, etc.

[0049] Preferably, in step (2), the polyanion material, the organic acid (dodecylbenzenesulfonic acid) and water are first mixed, and then mixed with aniline and dispersed uniformly to obtain a mixed solution; an oxidant is added to the mixed solution and a polymerization reaction is carried out to obtain a primary product.

[0050] Preferably, the oxidant is added to the mixed solution in the form of an aqueous solution.

[0051] Preferably, the oxidant is added dropwise.

[0052] Preferably, the temperature of the polymerization reaction in step (2) is 15-40°C, for example, it can be 16°C, 18°C, 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C or 38°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and room temperature is further preferred.

[0053] Preferably, the polymerization reaction time in step (2) is 5-8h, for example, it can be 5.5h, 6h, 6.5h, 7h or 7.5h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Preferably, the polymerization reaction in step (2) is carried out in a protective atmosphere.

[0055] Preferably, the protective atmosphere includes any one of nitrogen atmosphere, argon atmosphere, and helium atmosphere, or a combination of at least two of them.

[0056] Preferably, the organic solvent in step (3) comprises any one of dichloromethane, chloroform, tetrachloromethane, chlorobenzene, and dichlorobenzene, or a combination of at least two thereof, and chloroform is more preferred.

[0057] Preferably, the volume ratio of the primary product to the organic solvent in step (3) is 1:(0.1-2.0), for example, it can be 1:0.2, 1:0.3, 1:0.5, 1:0.6, 1:0.8, 1:1, 1:1.1, 1:1.3, 1:1.5, 1:1.7 or 1:1.9, and more preferably 1:(0.1-1.0).

[0058] Preferably, the solid phase obtained by the solid-liquid separation in step (3) is further subjected to a washing step.

[0059] In the present invention, the initial product is an aqueous emulsion system, which is mixed with an organic solvent to cause demulsification. Free polyaniline in the initial product that is not coated on the surface of the polyanion material is extracted into the liquid phase (organic phase), completing the precipitation of the polyanion material coated by in-situ oxidative polymerization (i.e., solid phase). After standing and stratification, the system is separated into solid and liquid phases. After solid-liquid separation, a solid phase (preliminary coated polyanion material) and a liquid phase (organic phase) are respectively obtained, and the liquid phase (organic phase) contains polyaniline.

[0060] Preferably, the liquid phase obtained by the solid-liquid separation in step (3) includes an organic phase and an aqueous phase. After oil-water separation, the organic phase is optionally washed and then enters step (4), that is, the liquid phase in step (4) is an organic phase, which includes a mixture of an organic solvent and polyaniline.

[0061] Preferably, the mixing in step (4) is carried out under stirring conditions.

[0062] Preferably, the mixing time in step (4) is 0.1-12h, for example, it can be 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.8h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or 11h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 0.1-1h is further preferred.

[0063] Preferably, the drying method in step (4) is vacuum drying.

[0064] Preferably, the drying temperature in step (4) is 80-170°C, for example, it can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0065] Preferably, the drying time in step (4) is 6-48 h, for example, it can be 8 h, 10 h, 12 h, 16 h, 20 h, 24 h, 28 h, 30 h, 32 h, 36 h, 40 h or 44 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0066] Preferably, step (3) further includes crushing and screening steps after drying.

[0067] Preferably, the screening screen is a 300-mesh screen.

[0068] Preferably, the preparation method specifically comprises the following steps:

[0069] (1) mixing a sodium source, a vanadium source, a phosphorus source, a fluorine source, an optional reducing agent, and an optional transition metal source and ball milling to obtain a polyanion material;

[0070] Wherein, the transition metal source is selected from any one of manganese source, iron source, nickel source, cobalt source, copper source, titanium source, and tin source, or a combination of at least two thereof; the ball milling is dry ball milling with a rotation speed of 400-800 rpm and a time of 0.5-8 h;

[0071] (2) mixing the polyanion material obtained in step (1), dodecylbenzenesulfonic acid, and aniline with water and dispersing the mixture to obtain a mixed solution; adding an oxidant to the mixed solution, causing the mixed solution to undergo a polymerization reaction in the presence of the oxidant to obtain a primary product;

[0072] The method comprises the following steps: based on the mass of the polyanion material being 100%, the mass of the aniline is 0.05-8%; the molar ratio of the dodecylbenzenesulfonic acid, the oxidant, and the aniline is (0.5-1.0):(0.5-2.0):1; and the polymerization reaction is carried out in a protective atmosphere at a temperature of 15-40° C. for 5-8 hours.

[0073] (3) mixing the primary product obtained in step (2) with an organic solvent to demulsify, and after layering, performing solid-liquid separation and oil-water separation to obtain a solid phase and an organic phase; the volume ratio of the primary product to the organic solvent is 1:(0.5-2.0);

[0074] (4) The solid phase and the organic phase obtained in step (3) are mixed evenly, and dried at 80-170° C. for 6-48 hours to obtain the polyanion composite positive electrode material.

[0075] In a second aspect, the present invention provides a polyanion composite positive electrode material, which is prepared by the preparation method described in the first aspect.

[0076] Preferably, the polyanion composite cathode material is a polyaniline-coated polyanion material, and the polyanion material is Na3(VO x ) 2-y M y (PO4)2F 3-2x .

[0077] Wherein, M is selected from any one of Ni, Co, Mn, Fe, Cu, Ti, and Sn, or a combination of at least two thereof.

[0078] 0≤x≤1, for example, x can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0079] 0≤y≤1, for example, y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0080] Preferably, the M is Mn or Fe, more preferably Mn.

[0081] Preferably, y is 0, and the polyanion composite cathode material is sodium vanadium fluorophosphate coated with polyaniline, and the chemical formula is Na3(VO x )2(PO4)2F 3-2x .

[0082] Preferably, the particle size of the polyanion composite positive electrode material is less than 60 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or 55 μm, etc., further preferably ≤50 μm, further preferably ≤20 μm, and most preferably ≤15 μm.

[0083] Preferably, the first-cycle discharge capacity of the polyanion composite cathode material at 1.0C is >105 mAh / g, more preferably ≥105.8 mAh / g, and can reach 105.81-114.37 mAh / g.

[0084] In a third aspect, the present invention provides an application of the polyanion composite cathode material as described in the second aspect, wherein the polyanion composite cathode material is applied to an electrochemical device.

[0085] Preferably, the electrochemical device comprises a sodium ion battery or a capacitor.

[0086] In a fourth aspect, the present invention provides a sodium ion battery, comprising the polyanion composite positive electrode material as described in the second aspect.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] (1) In the preparation method provided by the present invention, a polyanion material is first prepared by ball milling, and then an aniline monomer is introduced. A process route including two coating steps is designed. Through the design and synergistic effect of the raw materials and process route, a polyaniline coating layer with uniform performance and thickness is formed on the surface of the polyanion material. The resulting polyanion composite positive electrode material has excellent electrochemical properties, especially significant improvements in conductivity and structural stability. The preparation method has a simple process route, mild preparation conditions, does not require complex and harsh reaction conditions such as high temperature / high pressure, is low cost, is easy to achieve continuous large-scale production, and has a wide range of applications.

[0089] (2) The polyanion composite positive electrode material has enhanced conductivity, excellent structural stability and specific capacity, small particles, good uniformity, and can effectively improve the first-week discharge capacity and cycle performance of sodium ion batteries. The first-week discharge capacity at 1C is greater than 105mAh / g, and the capacity retention rate after 100 cycles is greater than 90%. The rate performance and cycle stability at 1C are excellent, and it can be used as an ideal positive electrode active material in the energy storage field. DETAILED DESCRIPTION

[0090] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0091] As used herein, the terms "comprises," "including," "having," "containing" or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0092] "Optionally" or "either" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0093] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0094] The terms "one embodiment," "some embodiments," "exemplarily," "specific examples," or "some examples" used in the present invention mean that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this document, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example.

[0095] Moreover, the technical features involved in various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0096] Example 1

[0097] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0098] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium fluorophosphate);

[0099] (2) preparing the polyanion material obtained in step (1) and aniline An in a mass ratio of 1:0.05; preparing the molar ratio of dodecylbenzenesulfonic acid DBSA to An in a ratio of 0.75:1, and the molar ratio of ammonium persulfate APS to An in a ratio of 1:1;

[0100] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0101] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0102] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0103] Example 2

[0104] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0105] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium fluorophosphate);

[0106] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.05; the molar ratio of DBSA to An was 0.55:1, and the molar ratio of APS to An was 1:1;

[0107] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0108] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0109] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0110] Example 3

[0111] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0112] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium fluorophosphate);

[0113] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.05; the molar ratio of DBSA to An was 0.9:1, and the molar ratio of APS to An was 1:1;

[0114] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0115] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0116] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0117] Example 4

[0118] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0119] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium fluorophosphate);

[0120] (2) preparing the polyanion material obtained in step (1) and An at a mass ratio of 1:0.05; preparing the molar ratio of DBSA to An at 0.55:1 and the molar ratio of APS to An at 0.5:1;

[0121] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0122] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0123] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0124] Example 5

[0125] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0126] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium fluorophosphate);

[0127] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.05; the molar ratio of DBSA to An was 0.55:1, and the molar ratio of APS to An was 1.5:1;

[0128] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0129] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0130] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0131] Example 6

[0132] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0133] (1) NaVO3, NaH2PO4, NaF, HONH2HCl and MnCl2 were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF, HONH2HCl and MnCl2 were added in a molar ratio of 1.92:3:3:6:0.08, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in alternating fashion, and then dried in an oven at 120° C. for 18 h to obtain a polyanionic material (sodium manganese vanadium fluorophosphate);

[0134] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.05; the molar ratio of DBSA to An was 0.75:1, and the molar ratio of APS to An was 1:1;

[0135] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0136] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0137] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0138] Example 7

[0139] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0140] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0141] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.01; the molar ratio of DBSA to An was 0.75:1, and the molar ratio of APS to An was 1:1;

[0142] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0143] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0144] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0145] Example 8

[0146] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0147] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0148] (2) preparing the polyanion material obtained in step (1) and An at a mass ratio of 1:0.03; preparing the molar ratio of DBSA to An at 0.75:1 and the molar ratio of APS to An at 1:1;

[0149] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0150] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0151] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0152] Example 9

[0153] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0154] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0155] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.07; the molar ratio of DBSA to An was 0.75:1, and the molar ratio of APS to An was 1:1;

[0156] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0157] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0158] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0159] Example 10

[0160] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0161] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0162] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.1; the molar ratio of DBSA to An was 0.75:1, and the molar ratio of APS to An was 1:1;

[0163] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0164] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0165] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0166] Example 11

[0167] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0168] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0169] (2) preparing the polyanion material obtained in step (1) and An in a mass ratio of 1:0.05; preparing the molar ratio of p-toluenesulfonic acid TSA to An in a ratio of 0.75:1, and the molar ratio of APS to An in a ratio of 1:1;

[0170] In a nitrogen atmosphere, the polyanion material, TSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0171] (3) adding 100 mL of chloroform to the primary product (400 mL) obtained in step (2) to demulsify and extract, and performing solid-liquid separation after standing for stratification. The obtained liquid phase is subjected to oil-water separation, and the organic phase (polyaniline extract) is retained. The organic phase and the solid phase are washed separately and set aside;

[0172] (4) The solid phase and the organic phase obtained in step (3) were mixed, magnetically stirred at room temperature for 15 minutes to fully mix them, and then transferred to a vacuum oven at 160° C. and dried for 24 hours. The product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0173] Comparative Example 1

[0174] A polyanion positive electrode material and a preparation method thereof. The preparation method comprises the following steps: performing a simple pre-grinding treatment on NaVO3, NaH2PO4, NaF and HONH2HCl for standby use; adding the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl in a molar ratio of 1:1.5:1.5:3, ball-milling at 700 rpm for 2 hours, and then ball-milling at 800 rpm for 1 hour to obtain a ball-milled mixture; taking out the ball-milled mixture, washing it with water / ethanol three times in an alternating manner, and drying it in an oven at 120°C for 18 hours. The product is ground and sieved with 300 mesh to obtain the polyanion positive electrode material (sodium vanadium fluorophosphate).

[0175] Comparative Example 2

[0176] A polyanion positive electrode material and a preparation method thereof. The preparation method comprises the following steps: performing a simple pre-grinding treatment on NaVO3, NaH2PO4, NaF, HONH2HCl and MnCl2 for standby use; adding the pre-treated NaVO3, NaH2PO4, NaF, HONH2HCl and MnCl2 in a molar ratio of 1.92:3:3:6:0.08, ball-milling at 700 rpm for 2 hours, and then ball-milling at 800 rpm for 1 hour to obtain a ball-milled mixture; taking out the ball-milled mixture, washing it with water / ethanol three times in an alternating manner, and drying it in an oven at 120°C for 18 hours. The product is ground and sieved with 300 mesh to obtain the polyanion positive electrode material (sodium manganese vanadium fluorophosphate).

[0177] Comparative Example 3

[0178] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0179] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0180] (2) The polyanion material obtained in step (1) and An were prepared in a mass ratio of 1:0.05; the molar ratio of DBSA to An was 0.75:1, and the molar ratio of APS to An was 1:1;

[0181] In a nitrogen atmosphere, the polyanion material, DBSA, and 300 mL of deionized water were mixed. An was added during stirring and rapidly stirred for 15 minutes to uniformly disperse the mixture to form a white emulsion. The APS solution was slowly added dropwise to the mixed emulsion. After the polymerization reaction at room temperature for 7 hours, stirring was stopped to obtain the primary product.

[0182] (3) Filtering the initial product obtained in step (2), collecting the solid phase, washing the solid phase with water / ethanol, and drying it in an oven at 120° C. for 18 h. The product is sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0183] Comparative Example 4

[0184] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0185] (1) obtaining a polyanionic material by the method of step (1) in Example 1;

[0186] (2) The polyanion material obtained in step (1) and polyaniline (purchased from Aladdin, 98%) were prepared in a mass ratio of 1:0.05; the polyaniline was mixed with chloroform to obtain a solution with a polyaniline concentration of 0.4 mol / L; the polyanion material was added to the solution, mixed under magnetic stirring for 15 minutes, transferred to a vacuum oven at 160°C and dried for 24 hours, and the product was sieved through 300 mesh to obtain the polyanion composite positive electrode material.

[0187] Comparative Example 5

[0188] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0189] (1) NaVO3, NaH2PO4 and HONH2·HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4 and HONH2·HCl were added in a molar ratio of 1:1.5:3, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in alternating fashion, and then dried in an oven at 120°C for 18 h to obtain a polyanionic material (sodium vanadium phosphate);

[0190] (2) The sodium vanadium phosphate material is subjected to an in-situ polyaniline coating treatment according to steps (2), (3) and (4) in Example 1 to obtain the polyanion composite positive electrode material.

[0191] Comparative Example 6

[0192] A polyanion composite positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0193] (1) NaVO3, NaH2PO4, NaF and HONH2HCl were subjected to a simple pre-grinding treatment and set aside; the pre-treated NaVO3, NaH2PO4, NaF and HONH2HCl were added in a molar ratio of 1:1.5:1.5:3, an amorphous carbon source was weighed according to 5 wt.% of the above-mentioned feed, and mixed and evenly mixed, and ball-milled at 700 rpm for 2 h, and then at 800 rpm for 1 h to obtain a ball-milled mixture; the ball-milled mixture was taken out, washed with water / ethanol three times in an alternating manner, and then dried in an oven at 120°C for 18 h to obtain a carbon-coated polyanionic material (carbon-coated sodium vanadium fluorophosphate);

[0194] (2) The carbon-coated polyanion material is subjected to an in-situ polyaniline coating treatment according to steps (2), (3) and (4) in Example 1 to obtain the polyanion composite positive electrode material.

[0195] The electrochemical properties of the polyanion cathode materials provided in Examples 1-11 and Comparative Examples 1-6 were tested using the following methods:

[0196] The sodium ion button cell was assembled using the positive electrode material to be tested: the positive electrode material, conductive agent (carbon black, KB), and binder (polyvinylidene fluoride, PVDF) were mixed at a mass ratio of 8:1:1, and the solvent N-methylpyrrolidone (NMP) was added for homogenization to obtain a slurry with a solid content of 16%; the slurry was then coated on aluminum foil, rolled, punched, and vacuum dried to form a positive electrode sheet; the prepared positive electrode sheet was used as the working electrode, metallic sodium as the counter electrode, and glass fiber cloth as the separator. A 1M NaPF6 solution was used as the electrolyte (the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and also included 5% by mass of fluoroethylene carbonate (FEC); button cells were assembled in a glove box filled with an argon atmosphere; after the button cells were assembled, the electrochemical performance was tested on a blue battery test system according to the following steps, with a test voltage range of 2.5-4.2V, a cycle rate of 1.0C, and a conventional constant current charge and discharge procedure.

[0197] The test results are shown in Table 1:

[0198] Table 1

[0199]

[0200]

[0201] Combined with the performance test data in Table 1, it can be seen that compared with the polyanion positive electrode materials sodium vanadium fluorophosphate (Comparative Example 1) and sodium vanadium manganese fluorophosphate (Comparative Example 2) prepared by ball milling without coating modification, the preparation method provided by the present invention introduces aniline monomer and performs a specific two-step coating process. Through the design of raw materials and the coordination and synergy of specific process methods, the obtained polyanion composite positive electrode material has significantly improved conductivity and structural stability. Its first-week discharge capacity at 1.0C is greater than 105mAh / g, and can reach 105.81-114.37mAh / g. The capacity retention rate after 100 cycles is 90.8-95.7%. It has excellent electrochemical properties, especially excellent rate performance and cycle stability at 1C, and can be used as an ideal positive electrode active material in the field of energy storage. In addition, the present invention can further optimize the electrochemical performance of the polyanion composite positive electrode material by designing the dosage of aniline monomer, screening the organic acid DBSA, and compounding the process routes; if the dosage of aniline monomer is too high (Example 10) and the preferred DBSA is not used (Example 11), the capacity and cycle performance of the material will be reduced.

[0202] In the preparation method provided by the present invention, a polyanion material is first prepared by ball milling, and then an aniline monomer is introduced. A process route including two coating processes is designed to form a polyaniline (PANI) coating layer with uniform performance and thickness on the surface of the polyanion material, so that the obtained polyanion composite positive electrode material has excellent electrochemical performance. If the preparation method defined by the present invention is not adopted, a polyaniline coating layer with uniform thickness and complete structure cannot be obtained (Comparative Examples 3-4), and the conductive performance of the positive electrode material is not effectively improved; Comparative Example 5 is a sodium vanadium phosphate material, and the active main material does not contain F. The coated PANI cannot form PFANI with F, and the overall stability of the material is deteriorated; Comparative Example 6 first prepares a carbon-coated sodium vanadium fluorophosphate material. The in-situ coated PANI material is isolated from the active main material by the carbon material, and the structure cannot be effectively stabilized, resulting in poor material performance.

[0203] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the polyanion composite cathode material, its preparation method, and application. However, the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a polyanion composite positive electrode material, characterized in that: The preparation method comprises the following steps: (1) mixing a sodium source, a vanadium source, a phosphorus source, and a fluorine source and ball milling the mixture to obtain a polyanion material; (2) mixing the polyanionic material obtained in step (1), the organic acid, and the aniline with water and dispersing the mixture to obtain a mixed solution; and subjecting the mixed solution to a polymerization reaction in the presence of an oxidant to obtain a primary product; (3) mixing the initial product obtained in step (2) with an organic solvent, and performing solid-liquid separation to obtain a solid phase and a liquid phase; (4) mixing and drying the solid phase and the liquid phase obtained in step (3) in sequence to obtain the polyanion composite positive electrode material; The ball milling in step (1) is dry ball milling. In step (2), the mass of the polyanion material is 100%, the mass of the aniline is 0.05-8%, and the organic acid is dodecylbenzenesulfonic acid.

2. The preparation method according to claim 1, characterized in that The sodium source in step (1) includes any one or a combination of at least two of sodium metavanadate, sodium vanadate, sodium fluoride, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium bromide, sodium chloride, sodium carbonate, and sodium hydroxide.

3. The preparation method according to claim 1, characterized in that The vanadium source in step (1) includes any one of sodium metavanadate, sodium vanadate, vanadium oxysulfate, ammonium metavanadate, ammonium vanadate, vanadium dioxide, vanadium trioxide, and vanadium chloride, or a combination of at least two thereof.

4. The preparation method according to claim 1, characterized in that The phosphorus source in step (1) includes any one of sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and phosphoric acid, or a combination of at least two thereof.

5. The preparation method according to claim 1, characterized in that The fluorine source in step (1) includes sodium fluoride and / or ammonium fluoride.

6. The preparation method according to claim 1, characterized in that The molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphorus in the phosphorus source, and fluorine in the fluorine source is (1-10):1:(1-8):(0.5-8).

7. The preparation method according to claim 1, characterized in that The vanadium source in step (1) includes a pentavalent vanadium source, and the mixed material also includes a reducing agent.

8. The preparation method according to claim 7, characterized in that The molar ratio of the pentavalent vanadium source to the reducing agent is 1:(1-5).

9. The preparation method according to claim 1, characterized in that The mixed material in step (1) further includes a transition metal source; the transition metal source includes any one of a manganese source, an iron source, a nickel source, a cobalt source, a copper source, a titanium source, and a tin source, or a combination of at least two thereof.

10. The preparation method according to claim 9, characterized in that The molar ratio of the transition metal in the transition metal source to the vanadium in the vanadium source is (0.1-1):

1.

11. The preparation method according to claim 1, characterized in that The rotation speed of the ball mill in step (1) is 400-800 rpm.

12. The preparation method according to claim 1, characterized in that The ball milling time in step (1) is 0.5-8h.

13. The preparation method according to claim 1, characterized in that After the ball milling in step (1) is completed, the process also includes washing and drying steps.

14. The preparation method according to claim 1, characterized in that The molar ratio of the organic acid to aniline in step (2) is (0.5-1.0):

1.

15. The preparation method according to claim 1, characterized in that In step (2), based on the mass of the organic acid being 1 g, the volume of the water is 100-500 mL.

16. The preparation method according to claim 1, characterized in that In step (2), based on the mass of the organic acid being 1 g, the volume of the water is 200-400 mL.

17. The preparation method according to claim 1, characterized in that The oxidant in step (2) is persulfate.

18. The preparation method according to claim 1, characterized in that The oxidant in step (2) is ammonium persulfate.

19. The preparation method according to claim 1, characterized in that The molar ratio of the oxidant to aniline in step (2) is (0.5-2.0):

1.

20. The preparation method according to claim 1, characterized in that The temperature of the polymerization reaction in step (2) is 15-40°C.

21. The preparation method according to claim 1, characterized in that The polymerization reaction time in step (2) is 5-8h.

22. The preparation method according to claim 1, characterized in that The polymerization reaction in step (2) is carried out in a protective atmosphere.

23. The preparation method according to claim 1, characterized in that The organic solvent in step (3) includes any one of dichloromethane, chloroform, tetrachloromethane, chlorobenzene, and dichlorobenzene, or a combination of at least two thereof.

24. The preparation method according to claim 1, characterized in that The organic solvent in step (3) is chloroform.

25. The preparation method according to claim 1, characterized in that The volume ratio of the initial product to the organic solvent in step (3) is 1:(0.1-2.0).

26. The preparation method according to claim 1, characterized in that The solid phase obtained by the solid-liquid separation in step (3) is further subjected to a washing step.

27. The preparation method according to claim 1, characterized in that The liquid phase obtained by the solid-liquid separation in step (3) includes an organic phase and an aqueous phase. The organic phase is washed and then enters step (4).

28. The preparation method according to claim 1, characterized in that The mixing time in step (4) is 0.1-12h.

29. The preparation method according to claim 1, characterized in that The mixing time in step (4) is 0.1-1h.

30. The preparation method according to claim 1, characterized in that The drying method in step (4) is vacuum drying.

31. The preparation method according to claim 1, characterized in that The drying temperature in step (4) is 80-170°C.

32. The preparation method according to claim 1, characterized in that The drying time in step (4) is 6-48h.

33. The preparation method according to claim 1, characterized in that The preparation method specifically comprises the following steps: (1) mixing a sodium source, a vanadium source, a phosphorus source, a fluorine source, a reducing agent, and a transition metal source and ball milling the mixture to obtain a polyanion material; Wherein, the transition metal source is selected from any one of manganese source, iron source, nickel source, cobalt source, copper source, titanium source, and tin source, or a combination of at least two thereof; the ball milling is dry ball milling with a rotation speed of 400-800 rpm and a time of 0.5-8 h; (2) mixing the polyanion material obtained in step (1), dodecylbenzenesulfonic acid, and aniline with water and dispersing the mixture to obtain a mixed solution; adding an oxidant to the mixed solution, causing the mixed solution to undergo a polymerization reaction in the presence of the oxidant to obtain a primary product; The method comprises the following steps: based on the mass of the polyanion material being 100%, the mass of the aniline is 0.05-8%; the molar ratio of the dodecylbenzenesulfonic acid, the oxidant, and the aniline is (0.5-1.0):(0.5-2.0):1; and the polymerization reaction is carried out in a protective atmosphere at a temperature of 15-40° C. for 5-8 hours. (3) mixing the primary product obtained in step (2) with an organic solvent to demulsify, and after layering, performing solid-liquid separation and oil-water separation to obtain a solid phase and an organic phase; the volume ratio of the primary product to the organic solvent is 1:(0.5-2.0); (4) The solid phase and the organic phase obtained in step (3) are mixed evenly, and dried at 80-170° C. for 6-48 hours to obtain the polyanion composite positive electrode material.

34. A polyanion composite positive electrode material, characterized in that The polyanion composite positive electrode material is prepared by the preparation method according to any one of claims 1 to 33.

35. The polyanion composite cathode material according to claim 34, characterized in that The polyanion composite cathode material is a polyaniline-coated polyanion material, and the polyanion material is Na3(VO x ) 2-y M y (PO4)2F 3-2x ; Wherein, M is selected from any one or a combination of at least two of Ni, Co, Mn, Fe, Cu, Ti, and Sn; 0≤x≤1, 0≤y≤1.

36. A use of the polyanion composite cathode material according to claim 34, characterized in that: The polyanion composite positive electrode material is applied to electrochemical devices.

37. The use according to claim 36, characterized in that The electrochemical device includes a sodium ion battery or a capacitor.

38. A sodium ion battery, characterized in that The sodium ion battery comprises the polyanion composite positive electrode material as described in claim 34 or 35.

Images