Iron-based phosphate material, preparation method thereof and sodium-ion positive electrode material

Abstract

The application discloses an iron-based phosphate material, a preparation method thereof and a sodium-ion positive electrode material. The preparation method of the iron-based phosphate material comprises the following steps: S1, mixing raw materials containing a sodium source, an iron source, a phosphorus source and a carbon source to obtain a precursor mixture; S2, granulating the precursor mixture to obtain precursor particles; S3, fluidizing and roasting the precursor particles in a fluidized medium in a circulating fluidized bed reactor to obtain iron-based phosphate material particles; and S4, performing powder processing on the iron-based phosphate material particles to obtain iron-based phosphate material powder. The precursor is granulated and fluidized and roasted, the influence of reaction heat effect on the purity and performance of the iron-based phosphate polyanion-type sodium-ion battery positive electrode material is solved, a carbon source gas is used to reduce defects of a carbon coating layer of the material, the performance of the iron-based phosphate polyanion-type sodium-ion battery positive electrode material is improved, and the method has remarkable beneficial effects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and particularly relates to an iron-based phosphate material, a preparation method thereof and a sodium-ion positive electrode material. BACKGROUND

[0002] In the context of achieving the goal, energy upgrading and rapid development of renewable energy, large-scale electrochemical energy storage technology has become the key to realizing green and sustainable development, and electrochemical energy storage has become a key technology for solving the instability and discontinuity of renewable energy generation such as wind and solar energy. Sodium-ion batteries have the advantages of abundant raw material resources, low cost, high performance-price ratio, excellent performance, and have wide application prospects in the fields of electric bicycles, low-speed electric vehicles, distributed energy storage and large-scale energy storage. Sodium-ion batteries realize the conversion of chemical energy and electrical energy through the shuttling of sodium ions in the positive and negative electrode materials, and the basic principle is similar to that of lithium-ion batteries. In recent years, driven by market demand, sodium-ion battery technology has become mature. As an important part of sodium-ion batteries, the positive and negative electrode materials play a decisive role in battery operating voltage, energy density, cycle performance, rate performance, etc. Excellent sodium-ion battery positive electrode materials should meet the requirements of high redox potential, high reversible specific capacity, high electronic conductivity and ion mobility, high stability, simple preparation process, abundant raw materials, low price, environmental friendliness and other characteristics.

[0003] Polyanionic materials such as sodium iron phosphate, sodium iron pyrophosphate, sodium iron fluorophosphate, and sodium iron phosphate pyrophosphate have become the preferred positive electrode materials for alkali metal ion batteries due to their structural stability, safety and other advantages. In the production process of phosphate and fluorophosphate polyanionic materials, the precursors are mixed by ball milling or sand milling, and then calcined at high temperature to form a phase. However, in the phase formation reaction, the chemical reaction mechanisms of different types of precursors are different, and the reaction heat effects are also different. When the positive electrode material is prepared on a large scale, the amount of precursor increases, and the above-mentioned reaction heat effects have a great influence on the uniformity of the product, and even promote the generation of impurity phases, thereby affecting the purity of the product. The rate performance and cycle stability of the final product in the sodium-ion battery are greatly affected. SUMMARY

[0004] Therefore, the application provides an iron-based phosphate material, a preparation method thereof and a sodium-ion positive electrode material, and the main purpose is to solve the technical problem of affecting the purity and performance of the battery positive electrode material due to the reaction heat effect in the preparation process of the sodium-ion positive electrode material.

[0005] In one aspect, the application provides a preparation method of an iron-based phosphate material, which comprises the following steps:

[0006] S1: mixing raw materials containing a sodium source, an iron source, a phosphorus source, a carbon source, a solvent, and a binder to obtain a precursor mixture;

[0007] S2: granulating the precursor mixture in step S1 to obtain precursor particles;

[0008] S3: fluidizing and calcining the precursor particles in step S2 in a fluidizing medium in a circulating fluidized bed reactor to obtain iron-based phosphate material particles;

[0009] S4: powdering the iron-based phosphate material particles obtained in step S3 to obtain iron-based phosphate material powder.

[0010] The present application aims to solve the influence of reaction heat effect on the purity and performance of iron-based phosphate polyanion sodium ion battery positive electrode material. The iron-based phosphate polyanion sodium ion positive electrode material is prepared by granulating the iron-based phosphate polyanion compound precursor and then using a circulating fluidized bed calcination. The iron-based phosphate polyanion sodium ion positive electrode material prepared by the method has high purity, high-order coulomb efficiency, and high reversible specific capacity. The use of the material as a positive electrode in a sodium ion battery can improve the energy density of the sodium ion battery, and the full battery exhibits excellent performance.

[0011] Optionally, in step S1, the precursor mixture further comprises a fluorine source.

[0012] Optionally, in step S1, the particle size of the solid raw materials in the precursor mixture is 0.1-74 μm, preferably 0.1-50 μm.

[0013] Optionally, the particle size of the solid raw materials in the precursor mixture is selected from any value or a range between any two values of 0.1, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 μm.

[0014] Optionally, in step S2, the particle size of the precursor particles is 80-1000 μm, and the morphology is at least one of spherical, ellipsoidal, cylindrical, and polyhedral.

[0015] Optionally, the particle size of the precursor particles is selected from any value or a range between any two values of 80, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, and 1000 μm.

[0016] Optionally, in step S2, the granulation is performed using an extrusion granulator or a centrifugal spray granulator.

[0017] Optionally, in step S3, the fluidized bed reactor is divided into three sections, lower, middle and upper sections; wherein,

[0018] The temperature of the lower section is controlled at 300-600℃, and the time for the precursor particles to pass through the lower section after fluidization is 30-360min;

[0019] The temperature of the middle section is controlled at 500-900℃, and the time for the precursor particles to pass through the middle section after fluidization is 5-30min;

[0020] The temperature of the upper section is controlled at 400-650℃, and the time for the precursor particles to pass through the upper section after fluidization is 30-180min.

[0021] Optionally, the temperature of the lower section is selected from any value or a range between any two values selected from 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃.

[0022] Optionally, the time for the precursor particles to pass through the lower section after fluidization is selected from any value or a range between any two values selected from 30, 50, 80, 100, 120, 150, 180, 200, 250, 280, 300, 330, 3600min.

[0023] Optionally, the temperature of the middle section is selected from any value or a range between any two values selected from 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃.

[0024] Optionally, the time for the precursor particles to pass through the middle section after fluidization is selected from any value or a range between any two values selected from 5, 10, 15, 20, 25, 30min.

[0025] Optionally, the temperature of the upper section is selected from any value or a range between any two values selected from 400℃, 450℃, 500℃, 550℃, 600℃, 650℃.

[0026] Optionally, the time for the precursor particles to pass through the upper section after fluidization is selected from any value or a range between any two values selected from 30, 50, 80, 100, 150, 180min.

[0027] Optionally, in step S3, the flow rate of the precursor particles during the fluidized bed circulating calcination in the fluidized bed reactor is 200-1000mm / min.

[0028] Optionally, the flow rate is selected from any value or a range between any two values selected from 200, 300, 400, 500, 600, 700, 800, 900, 1000mm / min.

[0029] Optionally, in step S3, the fluidizing medium is an inert gas; the inert gas includes nitrogen or argon.

[0030] Optionally, in step S3, a carbon source gas is introduced into the reactor during the fluidized roasting; the carbon source gas is selected from at least one of methane, ethane, propane, n-butane, isobutane, ethylene, propylene, n-butylene, isobutylene, butadiene, cis-dibutene, trans-dibutene, cyclopropane, acetylene, and propyne.

[0031] Optionally, in step S3, the volume ratio of the carbon source gas to the total circulating gas is 1-15%; the carbon source gas is introduced for 20-100 minutes, and the introduction of the carbon source gas is stopped simultaneously with the fluidized roasting.

[0032] Optionally, the volume ratio of the carbon source gas to the total circulating gas is selected from any value or a range between any two values of 1%, 3%, 8%, 10%, 12%, and 15%.

[0033] Optionally, the introduction time of the carbon source gas is selected from any value or a range between any two values of 20, 30, 40, 50, 60, 70, 80, 90, and 100 minutes.

[0034] Optionally, in step S4, the powdering process includes ball milling, jet milling, and sieving in sequence; the particle size of the iron-based phosphate material powder is 0.1-20 μm. Preferably, the particle size is 0.1-10 μm.

[0035] Optionally, the particle size of the iron-based phosphate material powder is selected from any value or a range between any two values of 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 μm.

[0036] Optionally, the iron-based phosphate material powder is an iron-based phosphate polyanionic compound; the iron-based phosphate polyanionic compound has at least one of the structures shown in formula a, formula b, formula c, and formula d.

[0037] Na4Fe3(PO4)2P2O7 formula a,

[0038] Na3Fe2(PO4)1P2O7 formula b,

[0039] NaFePO4 formula c,

[0040] Na2FeP2O7 formula d.

[0041] Optionally, when the structure formula of the iron-based phosphate polyanionic compound is formula a, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (3.9-4.2):(2.9-3.1):(3.9-4.1); preferably 4:3:4.

[0042] Optionally, when the structure formula of the iron-based phosphate polyanionic compound is formula b, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (2.9-3.2):(1.9-2.1):(2.9-3.1); preferably 3:2:3.

[0043] Optionally, when the structure formula of the iron-based phosphate polyanionic compound is formula c, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (0.9-1.2):(0.9-1.1):(0.9-1.1); preferably 1:1:1.

[0044] Optionally, when the structure formula of the iron-based phosphate polyanionic compound is formula d, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (1.9-2.2):(0.9-1.1):(1.9-2.1); preferably 2:1:2.

[0045] Optionally, the iron-based phosphate material powder is a fluorine-containing iron-based phosphate polyanionic compound; which has the structure shown in formula e and / or f;

[0046] Na2FePO4 F (formula e),

[0047] Na5Fe2(PO4)2F3 (formula f).

[0048] Optionally, when the structure formula of the fluorine-containing iron-based phosphate polyanionic compound is formula e, the molar ratio of the sodium source, iron source, phosphorus source and fluorine source in the precursor mixture is (1.9-2.2):1:1:1; preferably 2:1:1:1.

[0049] Optionally, when the structure formula of the fluorine-containing iron-based phosphate polyanionic compound is formula f, the molar ratio of the sodium source, iron source, phosphorus source and fluorine source in the precursor mixture is (4.9-5.2):(1.9:~2.1):(1.9-2.1):3; preferably 5:2:2:3.

[0050] In the precursor of the (fluorine-containing) iron-based phosphate polyanionic compound of the present application, the molar ratio of the sodium source, iron source and phosphorus source is calculated based on the molar amount of sodium element, iron element and phosphorus element, respectively.

[0051] Optionally, in step S1, the sodium source is at least one selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium pyrophosphate, sodium hydrogen pyrophosphate, and aqueous compounds thereof.

[0052] Optionally, in step S1, the iron source is at least one selected from the group consisting of iron powder, ferroferric oxide, ferrous oxide, ferrous oxide, iron oxalate, ferrous oxalate, iron phosphate, iron pyrophosphate, ferrous citrate, ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric acetate, ammonium ferrous sulfate, ferric citrate, ferric ammonium citrate, sodium succinate, and aqueous compounds thereof.

[0053] Optionally, in step S1, the phosphorus source is at least one selected from the group consisting of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate, and aqueous compounds thereof.

[0054] Optionally, in step S1, the fluorine source is at least one selected from the group consisting of sodium fluoride, ammonium fluoride, polyvinylidene fluoride, polytetrafluoroethylene, and hydrofluoric acid.

[0055] Optionally, in step S1, the carbon source is at least one selected from the group consisting of starch, carboxymethyl starch, sodium carboxymethyl starch, sodium alginate, citric acid, oxalic acid, ammonium citrate, ascorbic acid, formaldehyde, acetaldehyde, lactic acid, glucose, sucrose, maltose, and malt dextrin.

[0056] Optionally, the amount of the carbon source added is 4-8% of the mass of carbon in the iron-based phosphate material powder.

[0057] Optionally, the amount of the carbon source added is any value selected from the group consisting of 4%, 5%, 6%, 7%, 8% of the mass of carbon in the iron-based phosphate material powder, or a range value between any two of them.

[0058] Optionally, in step S1, the precursor mixture further comprises a dispersant.

[0059] Optionally, the amount of the solvent added is 10-120wt% of the precursor mixture.

[0060] Optionally, the amount of the dispersant added is 0.5-5wt% of the precursor mixture.

[0061] Optionally, the amount of the binder added is 0.3-8wt% of the precursor mixture.

[0062] Optionally, the solvent is added in an amount of any of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 wt% of the precursor mixture or a range value between any two of them.

[0063] Optionally, the dispersant is added in an amount of any of 0.5%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% of the precursor mixture or a range value between any two of them.

[0064] Optionally, the binder is added in an amount of any of 0.3, 1, 2, 3, 4, 5, 6, 7, 8 wt% of the precursor mixture or a range value between any two of them.

[0065] Optionally, the solvent is selected from at least one of deionized water, ethanol, methanol, ethylene glycol, isopropyl alcohol and acetone.

[0066] Optionally, the dispersant is selected from at least one of sodium dodecyl sulfate, methyl amyl alcohol, polyacrylamide, gum, fatty acid polyethylene glycol ester and polyether.

[0067] Optionally, the binder is selected from at least one of carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide.

[0068] In a second aspect, the present application provides an iron-based phosphate-based polyanionic sodium ion battery cathode material, which is prepared by the above method.

[0069] In a third aspect, the present application provides a sodium ion cathode, wherein the active material of the sodium ion cathode comprises the iron-based phosphate-based material prepared by the above method.

[0070] Optionally, the content of the iron-based phosphate-based material in the sodium ion cathode is 60-98 wt%.

[0071] Optionally, the sodium ion cathode further comprises a conductive agent and a binder; and the mass ratio of the sodium ion cathode material, the conductive agent and the binder is (60-98) wt%:(1-39) wt%:(1-39) wt%.

[0072] Optionally, the conductive agent is selected from at least one of conductive carbon black, conductive graphite, carbon nanofiber, carbon nanotube and graphene.

[0073] The binder is selected from at least one of polyvinylidene fluoride PVDF5130, HSV900, kynar761A.

[0074] In a fourth aspect, the present application provides a sodium ion battery, comprising a positive electrode; the positive electrode comprises the above sodium ion positive electrode.

[0075] Compared with the prior art, the present application has the following beneficial effects:

[0076] (1) The present application mixes and granulates the precursor of the iron-based polyanionic sodium ion battery positive electrode material, and then uses the circulating fluidized roasting, so that the reaction heat transfer is faster and more uniform, the influence of the reaction heat effect between raw materials can be inhibited, the prepared material has high purity, and the performance is also greatly improved.

[0077] (2) The three temperature intervals in the circulating fluidized bed of the present application enable the reactions of the material at different stages to be fully carried out, and the carbon source gas is introduced in the middle section at a higher temperature, which can deposit carbon on the surface of the material, reduce the defects of the carbon coating layer of the material, and improve the performance of the material.

[0078] (3) The outstanding advantage of the present application is that the iron-based phosphate polyanionic compound precursor is granulated and then roasted using the circulating fluidized bed, which solves the influence of the reaction heat effect on the purity and performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material. At the same time, the use of carbon source gas reduces the defects of the carbon coating layer of the material, and improves the performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 The structure diagram of the circulating roasting fluidized bed used for the present application examples 1-11 is shown in the figure.

[0080] Figure 2 The XRD pattern of the iron-based phosphate polyanionic sodium ion battery positive electrode material prepared in the present application examples 1 and comparative example 1 is shown in the figure. DETAILED DESCRIPTION

[0081] The present application will be further described below in combination with specific examples. The following description is only a few examples of the present application, and does not limit the present application in any form. Although the present application is disclosed as a preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the present application, which are equivalent to equivalent embodiments and belong to the scope of the technical solution.

[0082] Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels and used directly without any special treatment.

[0083] Example 1: Preparation of sodium iron pyrophosphate Na4Fe3(PO4)2P2O7 material

[0084] (1) The solid raw materials are finely ground and sieved respectively to control the particle size of the raw material powder to be 0.1-30 μm. Then 150.8 g of iron phosphate, 90 g of ferrous oxalate dihydrate, 142 g of disodium hydrogen phosphate, and 116 g of starch are weighed as raw materials, 5.0 g of polyacrylamide is added, 7.5 g of carboxymethyl cellulose is added, then 99.7 g of deionized water is gradually added, and the mixture is thoroughly mixed to obtain a precursor material;

[0085] (2) The mixed precursor raw material is added to a granulator to obtain spherical precursor material particles. The particle size of the dried precursor material particles is 120-200 μm.

[0086] (3) The dried precursor material particles obtained in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination. The fluidizing medium is nitrogen, the flow rate of the precursor material particles is 400 mm / min, the temperature of the lower section of the fluidized bed reactor is 580°C, the length of the lower section is 2.7 meters, and the total residence time in the lower section is 80 min. The temperature of the middle section is 750°C, the length of the middle section is 0.33 meters, and the total residence time in the middle section is 10 min. The temperature of the upper section is 600°C, the length of the upper section is 3 meters, and the total residence time in the upper section is 90 min. The reactor is subjected to 12 cycles of circulating fluidized calcination. During the calcination process, 5% of the total circulating gas is introduced into the middle section of the circulating fluidized bed reactor as an ethylene gas source, and the total introduction time is 30 min. The carbon source gas is stopped when the circulating fluidized calcination is completed. After the fluidized calcination is completed, the material particles are cooled to obtain sodium iron phosphate pyrophosphate material particles.

[0087] (4) The sodium iron phosphate pyrophosphate material particles obtained in step (3) are subjected to ball milling, jet milling, and sieving to obtain a powder material with a particle size of 0.1-20 μm, which is the sodium iron phosphate pyrophosphate material product. This material product is a sodium ion battery positive electrode material.

[0088] (5) The sodium iron phosphate pyrophosphate positive electrode material obtained in step (4) is mixed with conductive carbon black, carbon nanotubes, and PVDF5130 in a ratio of 92:3:1:4, N-methyl pyrrolidone solvent is added, and the mixture is stirred uniformly to obtain a sodium ion positive electrode material slurry. The slurry is coated onto an aluminum foil to prepare a sodium ion battery positive electrode of the sodium iron phosphate pyrophosphate material.

[0089] Sample purity test: The sodium iron phosphate pyrophosphate material product prepared in Example 1 is subjected to XRD testing to detect the purity of the sample.

[0090] Sample battery performance test: The sodium ion battery positive electrode of the sodium iron phosphate pyrophosphate material prepared is used to prepare a sodium metal button half-cell for material performance testing. The first coulombic efficiency and mass specific capacity of the material at 0.2C rate, and the capacity retention rate after 500 cycles at 2C rate are tested.

[0091] Example 2

[0092] The process and conditions of Example 2 are the same as those of Example 1, except that the particle size of the granulated precursor material in Step 2 of Example 2 is different, as follows:

[0093] (2) The uniformly mixed precursor raw materials are added to a granulator to obtain spherical precursor material particles, and the size of the dried granulated precursor material particles is 300-400 μm;

[0094] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 2 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0095] Example 3

[0096] The process and conditions of Example 3 are the same as those of Example 1, except that the particle size of the granulated precursor material in Step 2 of Example 3 is different, as follows:

[0097] (2) The uniformly mixed precursor raw materials are added to a granulator to obtain spherical precursor material particles, and the size of the dried granulated precursor material particles is 300-400 μm;

[0098] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 3 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0099] Example 4

[0100] The process and conditions of Example 4 are the same as those of Example 1, except that the granulation method in Step 2 of Example 4 is different, as follows:

[0101] (2) The uniformly mixed precursor raw materials are added to an extrusion granulator to obtain short columnar precursor material particles, and the size of the dried granulated precursor material particles is 600-800 μm in the longest dimension;

[0102] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 4 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0103] Example 5

[0104] The process and conditions of Example 5 are the same as those of Example 1, except that the mixing and granulation methods of the precursor material in Steps 1 and 2 of Example 5 are different, as follows:

[0105] (1) Add 5.0 g of polyacrylamide and 7.5 g of carboxymethyl cellulose to the raw material, and then add 498.8 g of deionized water, and mix well to obtain a precursor material;

[0106] (2) The well-mixed precursor raw material is granulated in a centrifugal spray granulator to obtain spherical precursor material particles, and the particle size of the precursor material particles after granulation and drying is 100-800 μm;

[0107] The remaining steps are consistent with Example 1, and the battery performance of the sodium iron phosphate pyrophosphate material product prepared in Example 5 is tested, and the test method, test conditions, and test content are consistent with Example 1.

[0108] Example 6

[0109] The process and conditions of Example 6 are the same as those of Example 1, except that in this Example 6, the flow rate of the precursor material particles in the circulating fluidized bed reactor is different, as follows:

[0110] (3) The precursor material particles after drying in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination, the fluidizing medium is nitrogen, the flow rate of the precursor material particles is 260 mm / min, and 7 cycles of fluidized calcination are carried out in the reactor.

[0111] The remaining steps are consistent with Example 1, and the battery performance of the sodium iron phosphate pyrophosphate material product prepared in Example 6 is tested, and the test method, test conditions, and test content are consistent with Example 1.

[0112] Example 7

[0113] The process and conditions of Example 7 are the same as those of Example 1, except that in this Example 7, the flow rate of the precursor material particles in the circulating fluidized bed reactor is different, as follows:

[0114] (3) The precursor material particles after drying in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination, the fluidizing medium is nitrogen, the flow rate of the precursor material particles is 700 mm / min, and 16 cycles of fluidized calcination are carried out in the reactor.

[0115] The remaining steps are consistent with Example 1, and the battery performance of the sodium iron phosphate pyrophosphate material product prepared in Example 7 is tested, and the test method, test conditions, and test content are consistent with Example 1.

[0116] Example 8

[0117] The process and conditions of Example 8 are the same as those of Example 1, except that the temperature of the three-stage reaction zone of the fluidized bed reactor in step 3 of this example is different, specifically as follows:

[0118] (3) The temperature of the lower section of the fluidized bed reactor is 500°C; the temperature of the middle section is 800°C; and the temperature of the upper section is 580°C.

[0119] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 8 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0120] Example 9

[0121] The process and conditions of Example 9 are the same as those of Example 1, except that the temperature of the three-stage reaction zone of the fluidized bed reactor in step 3 of this example is different, specifically as follows:

[0122] (3) The temperature of the lower section of the fluidized bed reactor is 450°C; the temperature of the middle section is 850°C; and the temperature of the upper section is 650°C.

[0123] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 9 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0124] Example 10

[0125] The process and conditions of Example 10 are the same as those of Example 1, except that the carbon source gas introduced into the middle section of the fluidized bed reactor in step 3 of this example is different, specifically as follows:

[0126] (3) During the calcination process, 5% of the total circulating gas is propane gas, which is introduced into the middle section of the circulating fluidized bed reactor for a total of 30 minutes. The introduction of the carbon source gas is stopped when the circulating fluidized calcination is completed.

[0127] The remaining steps are consistent with those of Example 1. The battery performance of the sodium iron phosphate material product prepared in Example 10 is tested, and the test method, test conditions, and test content are consistent with those of Example 1.

[0128] Example 11

[0129] The process and conditions of Example 11 are the same as those of Example 1, except that the total time of the carbon source gas introduced into the middle section of the fluidized bed reactor in step 3 of this example is different, specifically as follows:

[0130] (3) During the calcination process, 5% of the total circulating gas is ethylene gas, which is introduced into the middle section of the circulating fluidized bed reactor for a total of 90 minutes. The introduction of the carbon source gas is stopped when the circulating fluidized calcination is completed.

[0131] The remaining steps are consistent with Example 1, and the battery performance of the sodium iron pyrophosphate material product prepared in Example 11 is tested. The test method, test conditions, and test content are consistent with Example 1.

[0132] Comparative Example 1

[0133] The process and conditions of Comparative Example 1 are the same as those of Example 1, except that the precursor material in Comparative Example 1 is not granulated and cyclically fluidized and calcined, but is stacked in a sagger and calcined in a roller hearth kiln. The specific steps are as follows:

[0134] (1) The solid raw materials are finely ground and sieved respectively, and the particle size of the raw material powder is controlled to be 0.1-30 μm. Then 150.8 g of iron phosphate, 90 g of ferrous oxalate dihydrate, 142 g of sodium hydrogen phosphate, and 116 g of starch are weighed as raw materials, 5.0 g of polyacrylamide is added, 7.5 g of carboxymethyl cellulose is added, and then 99.7 g of deionized water is gradually added. The precursor material is mixed uniformly.

[0135] (2) The uniformly mixed precursor material is dried, and the material powder is directly loaded into a square sagger.

[0136] (3) The square sagger loaded with the material powder in step (2) is loaded into a roller hearth kiln reactor for calcination. The atmosphere in the kiln is nitrogen circulation. The sagger loaded with the precursor material powder travels at a uniform speed in the roller hearth kiln. The front section temperature of the roller hearth kiln is 580°C, the front section length is 2.7 meters, and the front section residence time is 80 minutes in total. The middle section temperature is 750°C, the middle section length is 0.33 meters, and the middle section residence time is 10 minutes in total. The rear section temperature is 600°C, the rear section length is 3 meters, and the rear section residence time is 90 minutes in total. During the calcination process, 5% of the total circulating gas volume of ethylene gas is introduced into the middle section of the roller hearth kiln reactor, and the total introduction time is 30 minutes. The carbon source gas is stopped when the calcination is completed. After the calcination is completed, the material particles are cooled to obtain the sodium iron pyrophosphate material powder.

[0137] (4) The sodium iron pyrophosphate material powder obtained in step (3) is subjected to ball milling, jet milling, and sieving to obtain a powder material with a particle size of 0.1-20 μm, which is the sodium iron pyrophosphate material product prepared in Comparative Example 1.

[0138] (5) The sodium iron pyrophosphate positive electrode material obtained in step (4) is mixed with conductive carbon black, carbon nanotubes, and PVDF5130 in a ratio of 92:3:1:4, N-methyl pyrrolidone solvent is added, and stirring is performed to obtain a sodium ion positive electrode material slurry. The sodium ion battery positive electrode of the sodium iron pyrophosphate material is prepared by coating on an aluminum foil.

[0139] Consistent with Example 1, the sample of the sodium iron pyrophosphate phosphate material of Comparative Example 1 is subjected to sample purity testing and battery performance testing, and the testing conditions and testing contents are consistent with Example 1.

[0140] Comparative Example 2

[0141] The process and conditions of Comparative Example 2 are the same as those of Comparative Example 1, except that in step 3, no carbon source gas is introduced into the middle section of the roller kiln. The specific different steps are as follows:

[0142] (3) The square sagger containing the material powder of step (2) is loaded into the roller kiln reactor for calcination. The atmosphere in the kiln is nitrogen circulation. The sagger containing the precursor material powder is uniformly moved in the roller kiln. The front section temperature of the roller kiln is 580°C, the front section length is 2.7 meters, and the total front section residence time is 80 minutes. The middle section temperature is 750°C, the middle section length is 0.33 meters, and the total middle section residence time is 10 minutes. The upper section temperature is 600°C, the rear section length is 3 meters, and the total rear section residence time is 90 minutes. After the calcination is completed, the sodium iron pyrophosphate phosphate material powder is obtained after the material particles are cooled.

[0143] The remaining steps are consistent with Comparative Example 1. The sodium iron pyrophosphate phosphate material prepared in Comparative Example 2 is subjected to sample battery performance testing according to Example 1, and the testing conditions and testing contents are consistent with Example 1.

[0144] Comparative Example 3

[0145] The process and conditions of Comparative Example 3 are the same as those of Example 1, except that in step 3, the precursor material particles after granulation and drying are calcined in the roller kiln reactor using a sagger. The specific different steps are as follows:

[0146] (3) The precursor material particles after granulation and drying of step (2) are loaded into a square sagger and then placed in the roller kiln reactor for calcination. The atmosphere in the kiln is nitrogen circulation. The sagger containing the precursor material powder is uniformly moved in the roller kiln. The front section temperature of the roller kiln is 580°C, the front section length is 2.7 meters, and the total front section residence time is 80 minutes. The middle section temperature is 750°C, the middle section length is 0.33 meters, and the total middle section residence time is 10 minutes. The upper section temperature is 600°C, the rear section length is 3 meters, and the total rear section residence time is 90 minutes. During the calcination process, 5% of the total circulating gas volume of ethylene gas is introduced into the middle section of the roller kiln reactor for a total of 30 minutes, and the introduction of the carbon source gas is stopped at the end of the calcination. After the calcination is completed, the sodium iron pyrophosphate phosphate material particles are obtained after the material particles are cooled.

[0147] The remaining steps are consistent with Example 1, and the sodium iron phosphate pyrophosphate material prepared in Comparative Example 3 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with Example 1.

[0148] Comparative Example 4

[0149] Comparative Example 4 has the same process and conditions as Example 1, except that in step 3, the temperature of the lower section of the fluidized calcination reactor in Comparative Example 3 is different from that in Example 1, and the specific different steps are as follows:

[0150] (3) The precursor material particles after drying in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination, and the temperature of the lower section of the fluidized bed reactor is 250°C.

[0151] The remaining steps are consistent with Example 1, and the sodium iron phosphate pyrophosphate material prepared in Comparative Example 4 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with Example 1.

[0152] Comparative Example 5

[0153] Comparative Example 5 has the same process and conditions as Example 1, except that in step 3, the temperature of the middle section of the fluidized calcination reactor in Comparative Example 3 is different from that in Example 1, and the specific different steps are as follows:

[0154] (3) The precursor material particles after drying in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination, and the temperature of the middle section of the fluidized bed reactor is 450°C.

[0155] The remaining steps are consistent with Example 1, and the sodium iron phosphate pyrophosphate material prepared in Comparative Example 5 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with Example 1.

[0156] Comparative Example 6

[0157] Comparative Example 6 has the same process and conditions as Example 1, except that in step 3, the temperature of the upper section of the fluidized calcination reactor in Comparative Example 3 is different from that in Example 1, and the specific different steps are as follows:

[0158] (3) The precursor material particles after drying in step (2) are loaded into a circulating fluidized bed reactor for fluidized calcination, and the temperature of the upper section of the fluidized bed reactor is 350°C.

[0159] The remaining steps are consistent with Example 1, and the sodium iron phosphate pyrophosphate material prepared in Comparative Example 6 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with Example 1.

[0160] Comparative Example 7

[0161] The process and conditions of Comparative Example 7 are the same as those of Example 1, except that in step 3, the flow rate of the fluidized roasting of the precursor material particles in Comparative Example 3 is different from that in Example 1, and the specific different steps are as follows:

[0162] (3) The precursor material particles dried in step (2) are loaded into a circulating fluidized bed reactor for fluidized roasting, the fluidizing medium is nitrogen, and the flow rate of the precursor material particles is 100 mm / min.

[0163] The remaining steps are consistent with those of Example 1. The sodium iron phosphate pyrophosphate material prepared in Comparative Example 7 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with those of Example 1.

[0164] Comparative Example 8

[0165] The process and conditions of Example 8 are the same as those of Example 1, except that in step 3, the flow rate of the fluidized roasting of the precursor material particles in Comparative Example 3 is different from that in Example 1, and the specific different steps are as follows:

[0166] (3) The precursor material particles dried in step (2) are loaded into a circulating fluidized bed reactor for fluidized roasting, the fluidizing medium is nitrogen, and the flow rate of the precursor material particles is 1200 mm / min.

[0167] The remaining steps are consistent with those of Example 1. The sodium iron phosphate pyrophosphate material prepared in Comparative Example 8 is subjected to sample battery performance testing according to Example 1, and the test conditions and test contents are consistent with those of Example 1.

[0168] The purity of the samples prepared in Example 1 and Comparative Example 1 is analyzed using XRD testing. The XRD pattern of the iron-based phosphate polyanion-type sodium ion battery cathode material prepared in Example 1 and Comparative Example 1 is as shown in Figure 2 The material pattern of Comparative Example 1 has obvious impurity peaks.

[0169] The positive electrode sheets prepared from the iron-based phosphate polyanion-type sodium ion battery cathode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 8 are subjected to material battery performance testing by preparing a half-cell button with sodium metal, and the test contents are the first coulombic efficiency and mass specific capacity of the material at 0.2C rate, and the capacity retention rate after 500 cycles at 2C rate. The specific test results are shown in Table 1.

[0170] The conditions for preparing the positive electrode sheets from the iron-based phosphate polyanion-type sodium ion battery cathode materials are as follows: the slurry ratio is positive electrode material: conductive carbon black: carbon nanotube: PVDF 5130 = 92:3:1:4, and the electrode surface loading is 3 mg / cm 2 .

[0171] The test conditions of the sodium metal preparation button-type half battery are: voltage interval: 0-2.5V, test environment temperature: 25 DEG C, the test rate of the first coulombic efficiency and the mass specific capacity is 0.2C, and the test conditions of the cycle performance are 2C, 500 cycles of charge-discharge cycles.

[0172] Table 1. Comparison of battery performance test results of iron-based phosphate polyanionic sodium ion battery positive electrode materials of examples 1-10 and comparative examples 1-8

[0173]

[0174]

[0175] It can be seen from the XRD pattern analysis of the material that the iron-based phosphate polyanionic sodium ion battery positive electrode material prepared by the method has higher purity, there is no impurity peak in the XRD diffraction peak of the sample of example 1, and the sample of comparative example 1 has obvious impurity peaks, and the XRD diffraction peak intensity of the sample of example 1 is higher than that of the sample of comparative example 1, which indicates that the crystallinity of the material of example 1 prepared by the method is better than that of comparative example 1.

[0176] It can be seen from the comparison of the battery performance test results that the iron-based phosphate polyanionic sodium ion battery positive electrode material prepared by the method has higher mass specific capacity, first coulombic efficiency and cycle capacity retention rate. The mass specific capacity of the iron-based phosphate polyanionic sodium ion battery positive electrode material half battery in examples 1-11 is higher than 115 mAh / g, the first coulombic efficiency is higher than 95.0%, and the 2C cycle capacity retention rate is higher than 95.0%. Compared with the comparative examples, the performance has obvious advantages.

[0177] In the application, the iron-based phosphate polyanionic compound precursor is granulated, and then is calcined by using a circulating fluidized bed, so that the influence of the reaction heat effect on the purity and performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material is solved. Meanwhile, the carbon source gas is used to reduce the defects of the carbon coating layer of the material, and the performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material is improved, and the method has obvious beneficial effects.

[0178] The above is only a few embodiments of the application, and does not limit the application in any form. Although the application discloses the above preferred embodiments, it is not intended to limit the application. Any skilled person in the art can make some changes or modifications to the above disclosed technical contents without departing from the scope of the technical scheme of the application, and the equivalent embodiments are equivalent to the equivalent embodiments, which are within the scope of the technical scheme.

Claims

1. A method for producing an iron-based phosphate-based material, characterized in that, The method comprises the following steps: S1: mixing raw materials containing a sodium source, an iron source, a phosphorus source, a carbon source, a solvent and a binder to obtain a precursor mixture; S2: granulating the precursor mixture in step S1 to obtain precursor particles; S3: fluidized roasting the precursor particles in step S2 in a fluidized bed reactor in a fluidizing medium to obtain iron-based phosphate material particles; S4: powdering the iron-based phosphate material particles obtained in step S3 to obtain iron-based phosphate material powder; In step S3, the fluidized bed reactor is divided into three sections: lower, middle and upper; wherein, The temperature of the lower section is controlled at 300-600°C, and the precursor particles flow through the lower section for 30-360 min after fluidization; The temperature of the middle section is controlled at 500-900°C, and the precursor particles flow through the middle section for 5-30 min after fluidization; The temperature of the upper section is controlled at 400-650°C, and the precursor particles flow through the upper section for 30-180 min after fluidization; In step S3, the flow speed of the precursor particles during the fluidized roasting in the fluidized bed reactor is 200-1000 mm / min; In step S3, the fluidizing medium is a non-active gas; the non-active gas includes nitrogen or argon; In step S3, a carbon source gas is introduced into the reactor during the fluidized roasting.

2. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the precursor mixture further comprises a fluorine source.

3. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the particle size of the solid raw materials in the precursor mixture is 0.1-74 μm.

4. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S2, the particle size of the precursor particles is 80-1000 μm, and the morphology presents at least one of spherical, ellipsoidal, cylindrical and polyhedral.

5. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S2, the granulation is performed by using an extrusion granulator or a centrifugal spray granulator.

6. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S3, the carbon source gas is selected from at least one of methane, ethane, propane, n-butane, isobutane, ethylene, propylene, n-butene, isobutene, butadiene, cis-dibutene, trans-dibutene, cyclopropane, acetylene and propyne.

7. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S3, the volume ratio of the carbon source gas to the total circulating gas is 1-15%; the introduction time of the carbon source gas is 20-100 min, and the introduction of the carbon source gas is stopped simultaneously with the fluidized roasting.

8. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S4, the powdering process comprises ball milling, jet milling and sieving in sequence; In step S4, the particle size of the iron-based phosphate material powder is 0.1-20 μm.

9. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, The iron-based phosphate material powder is an iron-based phosphate polyanionic compound; it has at least one of the structures shown in formula a, formula b, formula c and formula d; When the structure formula of the iron-based phosphate polyanionic compound is formula a, the molar ratio of the precursor mixture of the sodium source, the iron source and the phosphorus source is (3.9-4.2):(2.9-3.1):(3.9-4.1). When the structure formula of the iron-based phosphate poly-anionic compound is formula b, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (2.9~3.2):(1.9~2.1):(2.9~3.1); When the structure formula of the iron-based phosphate poly-anionic compound is formula c, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (0.9~1.2):(0.9~1.1):(0.9~1.1); When the structure formula of the iron-based phosphate poly-anionic compound is formula d, the molar ratio of the precursor mixture of sodium source, iron source and phosphorus source is (1.9~2.2):(0.9~1.1):(1.9~2.1).

10. The method for preparing an iron-based phosphate material according to claim 2, characterized in that, The iron-based phosphate material powder is a fluorine-containing iron-based phosphate poly-anionic compound; it has the structure shown in formula e and / or f; When the structure formula of the fluorine-containing iron-based phosphate poly-anionic compound is formula e, the molar ratio of the sodium source, iron source, phosphorus source and fluorine source in the precursor mixture is (1.9~2.2):1:1:1; When the structure formula of the fluorine-containing iron-based phosphate poly-anionic compound is formula f, the molar ratio of the sodium source, iron source, phosphorus source and fluorine source in the precursor mixture is (4.9~5.2):(1.9~2.1):(1.9~2.1):

3.

11. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the sodium source is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium pyrophosphate, sodium hydrogen pyrophosphate and their aqueous compounds.

12. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the iron source is selected from at least one of iron powder, ferric oxide, ferrous oxide, ferrous oxide, iron oxalate, ferrous oxalate, iron phosphate, iron pyrophosphate, ferrous citrate, ferric nitrate, ferrous nitrate, iron sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric acetate, ammonium ferrous sulfate, ferric citrate, ferric ammonium citrate, succinate sodium citrate and their aqueous compounds.

13. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate and their aqueous compounds.

14. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the carbon source is selected from at least one of starch, carboxymethyl starch, sodium carboxymethyl starch, sodium alginate, citric acid, oxalic acid, ammonium citrate, ascorbic acid, formaldehyde, acetaldehyde, lactic acid, malic acid, glucose, sucrose, maltose and malt dextrin; The addition amount of the carbon source is 4~8% of the mass of carbon in the iron-based phosphate material powder.

15. The method for preparing an iron-based phosphate material according to claim 2, characterized in that, In step S1, the fluorine source is selected from at least one of sodium fluoride, ammonium fluoride, polyvinyl fluoride, polyperfluoroethylene and hydrofluoric acid.

16. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the precursor mixture further includes a dispersant; The addition amount of the solvent is 10~120wt% of the precursor mixture; The addition amount of the dispersant is 0.5~5wt% of the precursor mixture; The addition amount of the binder is 0.3~8wt% of the precursor mixture.

17. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the solvent is selected from at least one of deionized water, ethanol, methanol, ethylene glycol, isopropyl alcohol and acetone.

18. The method for preparing an iron-based phosphate material according to claim 16, characterized in that, In step S1, the dispersant is selected from at least one of sodium dodecyl sulfate, methyl amyl alcohol, polyacrylamide, gum, fatty acid polyethylene glycol ester and polyether.

19. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S1, the binder is selected from at least one of carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide.

20. An iron-based phosphate-based polyanionic sodium-ion battery cathode material, characterized in that, It is an iron-based phosphate material prepared by the method of any one of claims 1-19.

21. A sodium-ion positive electrode, characterized by, The active material of the sodium ion positive electrode comprises the iron-based phosphate material prepared by the method of any one of claims 1-19.

22. The sodium-ion positive electrode of claim 21, wherein, The content of the iron-based phosphate material in the sodium ion positive electrode is 60-98 wt%.

23. The sodium-ion positive electrode of claim 21, wherein, The sodium ion positive electrode further comprises a conductive agent and a binder; the mass ratio of the iron-based phosphate material, the conductive agent and the binder is (60-98) wt%:(1-39) wt%:(1-39) wt%.

24. The sodium-ion positive electrode of claim 23, wherein, The conductive agent is selected from at least one of conductive carbon black, conductive graphite, carbon nanofiber, carbon nanotube and graphene. The binder is selected from at least one of PVDF5130, HSV900 and kynar761A.

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