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

Abstract

The invention 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, carrying out fluidized roasting on the precursor particles in a circulating fluidized bed reactor in a fluidizing medium to obtain iron-based phosphate material particles; and S4, the iron-based phosphate material particles are subjected to powder making treatment, and iron-based phosphate material powder is obtained. Precursor granulation and fluidized roasting are carried out, and the influence of the reaction heat effect on the purity and performance of the iron-based phosphate polyanion type sodium ion battery positive electrode material is solved; and by using the carbon source gas, the defects of a carbon coating layer of the material are reduced, the performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material is improved, and the positive electrode material has remarkable beneficial effects.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to an iron-based phosphate material, a preparation method thereof, and a sodium-ion cathode material. Background Art

[0002] In the context of achieving the goal, with the energy upgrade and the rapid development of renewable energy, large-scale electrochemical energy storage technology has become the key to achieving green sustainability, and electrochemical energy storage has also become the key technology to solve the problems of unstable and discontinuous power generation of renewable energy such as wind energy and solar energy. Sodium-ion batteries have the advantages of rich raw material resources, low cost, high cost performance, excellent performance, etc., and have broad application prospects in the fields of electric bicycles, low-speed electric vehicles, distributed energy storage, and large-scale energy storage. Sodium-ion batteries achieve the conversion of chemical energy and electrical energy by the shuttling of sodium ions between 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 increasingly mature. As an important part of sodium-ion batteries, the positive and negative electrode materials play a decisive role in the working voltage, energy density, cycle performance, rate performance, etc. of the battery. Excellent sodium-ion battery cathode materials should meet the characteristics of high redox potential, high reversible specific capacity, high electronic conductivity and ion mobility, high stability, simple preparation process, rich raw materials, low price, and environmental friendliness.

[0003] Polyanion-type materials such as sodium iron phosphate, sodium pyrophosphate iron, sodium fluorophosphate iron, and sodium pyrophosphate iron phosphate have become preferred cathode materials for alkali metal ion batteries due to their advantages such as stable structure and high safety. In the production process of preparing phosphate-based and fluorophosphate-based polyanion-type materials, the precursors are mixed by ball milling or sand milling, and then the precursors are calcined at high temperature to form a phase. However, in the phase-forming reaction, the chemical reaction mechanisms between different types of precursors are different, and the reaction heat effects are also different. When the cathode material is prepared on a large scale, the amount of the precursor increases, and the above reaction heat effect has a great influence on the uniformity of the product, and even promotes the formation of impurity phases, thereby affecting the product purity. The rate performance and cycle stability of the final product in sodium-ion batteries are greatly affected. Summary of the Invention

[0004] In view of this, the present invention provides an iron-based phosphate material, a preparation method thereof, and a sodium-ion cathode material, and the main purpose is to solve the technical problem that the purity and performance of the battery cathode material are affected by the reaction heat effect during the preparation process of the sodium-ion cathode material.

[0005] On the one hand, the present invention provides a preparation method of an iron-based phosphate material, and the method includes the following steps:

[0006] S1: Mix the raw materials including sodium source, iron source, phosphorus source, carbon source, solvent, and binder to obtain a precursor mixture;

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

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

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

[0010] In order to solve the influence of reaction heat effect on the purity and performance of the cathode material of the polyanionic sodium-ion battery based on iron phosphate, the present invention prepares the polyanionic sodium-ion cathode material based on iron phosphate by granulating the precursor of the polyanionic compound based on iron phosphate and then using circulating fluidized bed roasting. The polyanionic sodium-ion cathode material based on iron phosphate prepared by the method of the present invention has high purity, high coulomb efficiency, high reversible specific capacity and other characteristics. Using this material as the cathode in a sodium-ion battery can improve the energy density of the sodium-ion battery, and the full battery shows excellent performance.

[0011] Optionally, in step S1, the precursor mixture further includes 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 the range value between any two of 0.1, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 μm.

[0014] Optionally, 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 shapes.

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

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

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

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

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

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

[0021] Optionally, the temperature of the lower section is selected from any value among 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C or the range value between any two of them.

[0022] Optionally, the time of the lower section is selected from any value among 30, 50, 80, 100, 120, 150, 180, 200, 250, 280, 300, 330, 360 min or the range value between any two of them.

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

[0024] Optionally, the time of the middle section is selected from any value among 5, 10, 15, 20, 25, 30 min or the range value between any two of them.

[0025] Optionally, the temperature of the upper section is selected from any value among 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C or the range value between any two of them.

[0026] Optionally, the time of the upper section is selected from any value among 30, 50, 80, 100, 150, 180 min or the range value between any two of them.

[0027] Optionally, in step S3, the flow velocity of the precursor particles during the fluidized bed reactor for fluidized circulation roasting is 200 - 1000 mm / min.

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

[0029] Optionally, in step S3, the fluidization 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 process; the carbon source gas is selected from at least one of methane, ethane, propane, n-butane, isobutane, ethylene, propylene, n-butene, isobutene, butadiene, cis-2-butene, trans-2-butene, cyclopropane, acetylene, and propyne.

[0031] Optionally, in step S3, the volume ratio of the carbon source gas to the total recycle gas volume is 1-15%; the introduction duration of the carbon source gas is 20-100 min, and the introduction of the carbon source gas stops simultaneously with the fluidized roasting.

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

[0033] Optionally, the introduction duration of the carbon source gas is selected from any value of 20, 30, 40, 50, 60, 70, 80, 90, 100 min or the range value between any two of them.

[0034] Optionally, in step S4, the powder making treatment sequentially includes ball milling, jet milling, and screening processes; the particle size of the iron-based phosphate material powder is 0.1-20 μm. Preferably 0.1-10 μm.

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

[0036] Optionally, the iron-based phosphate material powder is an iron-based phosphate polyanion-type compound; it 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 structural formula of the iron-based polyanionic phosphate compound is Formula a, the molar ratio of the sodium source, iron source, and phosphorus source in its precursor mixture is (3.9 - 4.2):(2.9 - 3.1):(3.9 - 4.1); preferably 4:3:4.

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

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

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

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

[0046] Na2FePO4F (Formula e),

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

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

[0049] Optionally, when the structural formula of the fluorine-containing iron-based polyanionic phosphate compound is Formula f, the molar ratio of the sodium source, iron source, phosphorus source, and fluorine source in its 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 polyanionic phosphate compound of the present invention, the molar ratios of the sodium source, iron source, and phosphorus source are calculated based on the molar amounts of sodium element, iron element, and phosphorus element, respectively.

[0051] Optionally, 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 hydrated compounds.

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

[0053] Optionally, 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 hydrated compounds.

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

[0055] Optionally, 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, glucose, sucrose, maltose and maltodextrin.

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

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

[0058] Optionally, in step S1, the precursor mixture further includes a dispersant;

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

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

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

[0062] Optionally, the addition amount of the solvent is any value among 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 addition amount of the dispersant is any value among 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 addition amount of the binder is any value among 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, isopropanol, and acetone.

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

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

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

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

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

[0071] Optionally, the sodium-ion cathode further includes a conductive agent and a binder; 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 nanofibers, carbon nanotubes, and graphene;

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

[0074] Fourthly, the present invention provides a sodium ion battery, including a positive electrode; the positive electrode includes the above-mentioned sodium ion positive electrode.

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

[0076] (1) In the present invention, the precursor of the iron-based polyanionic sodium ion battery positive electrode material is uniformly mixed and granulated, and then circulated fluidized bed roasting is used. The heat transfer of the reaction is faster and more uniform, the influence of the heat effect between raw materials can be suppressed, and the prepared material has high purity and its performance is greatly improved.

[0077] (2) The three temperature intervals in the circulating fluidized bed of the present invention enable the reaction of the material to proceed fully at different stages. By introducing a carbon source gas in the middle section with a higher temperature, carbon can be deposited on the surface of the material, reducing the defects of the carbon coating layer of the material and improving the material performance.

[0078] (3) The prominent advantage of the present invention is that the precursor of the iron-based phosphate polyanionic compound is granulated and then circulated fluidized bed roasting is used to solve 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, by using a carbon source gas, the defects of the carbon coating layer of the material are reduced, and the performance of the iron-based phosphate polyanionic sodium ion battery positive electrode material is improved. Description of the Drawings

[0079] Figure 1 It is a schematic structural diagram of the circulating roasting fluidized bed used in Examples 1 to 11 of the present invention;

[0080] Figure 2 It is an XRD pattern of the iron-based phosphate polyanionic sodium ion battery positive electrode material prepared in Example 1 and Comparative Example 1 of the present invention. Specific Embodiments

[0081] The following combines specific embodiments to further elaborate the present application. The following descriptions are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments, it is not used to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are equivalent to equivalent implementation cases and all belong to the scope of the technical solution.

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

[0083] Example 1 Preparation of Sodium Iron Pyrophosphate Phosphate Na4Fe3(PO4)2P2O7 Material

[0084] (1) Grind the solid raw materials separately and screen them to control the particle size of the raw material powder to be 0.1 - 30 μm. Then weigh 150.8 g of iron phosphate, 90 g of ferrous oxalate dihydrate, 142 g of disodium hydrogen phosphate, and 116 g of starch as raw materials, add 5.0 g of polyacrylamide, add 7.5 g of carboxymethyl cellulose, and then gradually add 99.7 g of deionized water. Mix well to obtain the precursor material.

[0085] (2) Add the uniformly mixed precursor raw materials into a granulator to granulate and obtain spherical precursor material particles. The particle size of the precursor material particles after granulation and drying is 120 - 200 μm.

[0086] (3) Load the precursor material particles dried in step (2) into a circulating fluidized bed reactor for fluidized roasting. The fluidizing medium is nitrogen. The flow rate of the precursor material particles is 400 mm / min. The temperature at the lower section of the fluidized bed reactor is 580 °C, the length of the lower section interval is 2.7 meters, and the total residence time in the lower section is 80 min. The temperature in the middle section is 750 °C, the length of the middle section interval is 0.33 meters, and the total residence time in the middle section is 10 min. The temperature at the upper section is 600 °C, the length of the upper section interval is 3 meters, and the total residence time in the upper section is 90 min. Conduct 12 cycles of circulating fluidized roasting in the reactor. During the roasting process, introduce ethylene gas accounting for 5% of the total circulating gas volume into the middle section of the circulating fluidized bed reactor, and the total introduction time is 30 min. Stop introducing the carbon source gas at the end of the circulating fluidized roasting. After the fluidized roasting is completed, wait for the material particles to cool to obtain the sodium iron pyrophosphate material particles.

[0087] (4) Grind, air pulverize, and screen the sodium iron pyrophosphate material particles obtained in step (3) to obtain a powder material with a particle size of 0.1 - 20 μm, which is the sodium iron pyrophosphate material product. This material product is the cathode material for sodium-ion batteries.

[0088] (5) Mix the sodium iron pyrophosphate cathode material obtained in step (4) with conductive carbon black, carbon nanotubes, and PVDF5130 in a ratio of 92:3:1:4, add N-methylpyrrolidone solvent and stir evenly to obtain the sodium-ion cathode material slurry, and coat it on aluminum foil to prepare the sodium-ion battery cathode of the sodium iron pyrophosphate material.

[0089] Sample purity test: Conduct XRD test on the sodium iron pyrophosphate material product prepared in Example 1 to detect the sample purity.

[0090] Sample battery performance test: Use the sodium-ion battery cathode of the prepared sodium iron pyrophosphate material to conduct material performance tests on a sodium metal-based coin-type half-cell, and test the initial Coulomb efficiency and mass specific capacity of the material at a 0.2C rate, as well as the capacity retention rate after 500 cycles at a 2C rate.

[0091] Example 2

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

[0093] (2) Add the uniformly mixed precursor raw materials into a granulator for granulation to obtain spherical precursor material particles. The particle size of the precursor material particles after granulation and drying is 300 - 400 μm;

[0094] The remaining steps are the same as those of Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 2. The test methods, test conditions, and test contents are the same as 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 in step 2 of Example 3, the particle size of the precursor material particles after granulation is different, specifically as follows:

[0097] (2) Add the uniformly mixed precursor raw materials into a granulator for granulation to obtain spherical precursor material particles. The particle size of the precursor material particles after granulation and drying is 800 - 1000 μm;

[0098] The remaining steps are the same as those of Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 3. The test methods, test conditions, and test contents are the same as 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 in step 2 of Example 4, the granulation method is different, specifically as follows:

[0101] (2) Add the uniformly mixed precursor raw materials into an extrusion granulator for granulation to obtain short columnar precursor material particles. The longest side size of the precursor material particles after granulation and drying is 600 - 800 μm;

[0102] The remaining steps are the same as those of Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 4. The test methods, test conditions, and test contents are the same as those of Example 1.

[0103] Example 5

[0104] The process and conditions of Example 5 are the same as those of Example 1. The differences are in step 1 and step 2 of this Example 5, where the mixing and granulation methods of the precursor materials are different, specifically as follows:

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

[0106] (2) Granulate the uniformly mixed precursor raw materials in a centrifugal spray granulator to obtain spherical precursor material particles. The size of the precursor material particles after granulation and drying is 100 - 800 μm.

[0107] The remaining steps are the same as those in Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 5. The test methods, test conditions, and test contents are the same as those in Example 1.

[0108] Example 6

[0109] The process and conditions of Example 6 are the same as those of Example 1, except that in step 3 of this Example 6, the flow rate of the precursor material particles in the circulating fluidized bed reactor is different, specifically as follows:

[0110] (3) Load the precursor material particles dried in step (2) into a circulating fluidized bed reactor for fluidized roasting. The fluidizing medium is nitrogen, the flow rate of the precursor material particles is 260 mm / min, and perform 7 cycles of circulating fluidized roasting in the reactor.

[0111] The remaining steps are the same as those in Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 6. The test methods, test conditions, and test contents are the same as those in Example 1.

[0112] Example 7

[0113] The process and conditions of Example 7 are the same as those of Example 1, except that in step 3 of this Example 7, the flow rate of the precursor material particles in the circulating fluidized bed reactor is different, specifically as follows:

[0114] (3) Load the precursor material particles dried in step (2) into a circulating fluidized bed reactor for fluidized roasting. The fluidizing medium is nitrogen, the flow rate of the precursor material particles is 700 mm / min, and perform 16 cycles of circulating fluidized roasting in the reactor.

[0115] The remaining steps are the same as those in Example 1. Perform battery performance tests on the sodium iron pyrophosphate phosphate material products prepared in Example 7. The test methods, test conditions, and test contents are the same as those in Example 1.

[0116] Example 8

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

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

[0119] The remaining steps are the same as those of Example 1. The battery performance of the sodium iron pyrophosphate phosphate material product prepared in Example 8 is tested, and the test method, test conditions, and test content are the same as 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 in step 3 of this example, the temperatures in the three reaction zones of the fluidized bed reactor are different, specifically as follows:

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

[0123] The remaining steps are the same as those of Example 1. The battery performance of the sodium iron pyrophosphate phosphate material product prepared in Example 9 is tested, and the test method, test conditions, and test content are the same as 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 in step 3 of this example, the carbon source gas introduced in the middle section of the fluidized bed reactor is different, specifically as follows:

[0126] (3) During the roasting process, propane gas accounting for 5% of the total circulating gas volume is introduced into the middle section of the circulating fluidized bed reactor, and the total introduction time is 30 min. The introduction of the carbon source gas stops at the end of the circulating fluidized roasting.

[0127] The remaining steps are the same as those of Example 1. The battery performance of the sodium iron pyrophosphate phosphate material product prepared in Example 10 is tested, and the test method, test conditions, and test content are the same as 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 in step 3 of this example, the total time of the carbon source gas introduced in the middle section of the fluidized bed reactor is different, specifically as follows:

[0130] (3) During the roasting process, ethylene gas accounting for 5% of the total circulating gas volume is introduced into the middle section of the circulating fluidized bed reactor, and the total introduction time is 90 min. The introduction of the carbon source gas stops at the end of the circulating fluidized roasting.

[0131] The remaining steps are the same as those in Example 1. The sodium iron pyrophosphate material product prepared in Example 11 is subjected to battery performance testing. The testing method, testing conditions, and testing content are the same as those in 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 in Comparative Example 1, the precursor material is not granulated and subjected to circulating fluidized bed roasting, and the precursor material is stacked in a sagger and roasted in a roller hearth kiln. The specific steps are as follows:

[0134] (1) The solid raw materials are respectively finely ground and screened 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, and then 99.7 g of deionized water is gradually added and mixed thoroughly to obtain the precursor material.

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

[0136] (3) The square sagger containing the material powder in step (2) is loaded into a roller hearth kiln reactor for roasting. The atmosphere in the kiln is nitrogen circulation, and the sagger containing the precursor material powder travels uniformly in the roller hearth kiln. The temperature in the front section of the roller hearth kiln is 580 °C, the length of the front section is 2.7 m, and the total residence time in the front section is 80 min; the temperature in the middle section is 750 °C, the length of the middle section is 0.33 m, and the total residence time in the middle section is 10 min; the temperature in the upper section is 600 °C, the length of the rear section is 3 m, and the total residence time in the rear section is 90 min. During the roasting process, ethylene gas accounting for 5% of the total circulating gas volume is introduced into the middle section of the roller hearth kiln reactor for a total of 30 min, and the carbon source gas is stopped when the roasting ends. After the roasting ends, 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 ball milled, air pulverized, and screened 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 cathode material obtained in step (4) is mixed with conductive carbon black, carbon nanotubes, and PVDF5130 in a ratio of 92:3:1:4, and N-methylpyrrolidone solvent is added and stirred evenly to obtain a sodium ion cathode material slurry, which is coated on aluminum foil to prepare the sodium ion battery cathode of the sodium iron pyrophosphate material.

[0139] Consistent with Example 1, the sodium iron pyrophosphate phosphate material sample of Comparative Example 1 was subjected to sample purity testing and battery performance testing, and the testing conditions and contents were the same as those of Example 1.

[0140] Comparative Example 2

[0141] The process and conditions of Comparative Example 2 were the same as those of Comparative Example 1, except for Step 3. In Comparative Example 2, no carbon source gas was introduced in the middle section of the roller hearth kiln. The specific different steps were as follows:

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

[0143] The remaining steps were the same as those of Comparative Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 2, the sample battery performance test was carried out with reference to Example 1, and the testing conditions and contents were the same as those of Example 1.

[0144] Comparative Example 3

[0145] The process and conditions of Comparative Example 3 were the same as those of Example 1, except for Step 3. In Comparative Example 3, the granulated and dried precursor material particles were roasted in a square crucible using a roller hearth kiln reactor. The specific different steps were as follows:

[0146] (3) The granulated and dried precursor material particles in step (2) were piled up and loaded into a square crucible, and then placed in the roller hearth kiln reactor for roasting. The atmosphere in the kiln was nitrogen circulation. The crucible containing the precursor material powder traveled uniformly in the roller hearth kiln. The temperature in the front section of the roller hearth kiln was 580 °C, the length of the front section was 2.7 meters, and the total residence time in the front section was 80 min; the temperature in the middle section was 750 °C, the length of the middle section was 0.33 meters, and the total residence time in the middle section was 10 min; the temperature in the upper section was 600 °C, the length of the rear section was 3 meters, and the total residence time in the rear section was 90 min. During the roasting process, ethylene gas accounting for 5% of the total circulation gas volume was introduced in the middle section of the roller hearth kiln reactor for a total of 30 min, and the carbon source gas was stopped when the roasting was completed. After the roasting was completed, the material particles were cooled to obtain the sodium iron pyrophosphate phosphate material particles.

[0147] The remaining steps are the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 3, refer to Example 1 for the performance test of the sample battery, and the test conditions and test contents are the same as those in Example 1.

[0148] Comparative Example 4

[0149] The process and conditions of Comparative Example 4 are the same as those in Example 1, except for Step 3. The temperature in the lower section of the fluidized roasting reactor in Comparative Example 3 is different from that in Example 1. The specific different steps are as follows:

[0150] (3) Load the precursor material particles dried in Step (2) into a circulating fluidized bed reactor for fluidized roasting, and the temperature in the lower section of the fluidized bed reactor is 250 °C.

[0151] The remaining steps are the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 4, refer to Example 1 for the performance test of the sample battery, and the test conditions and test contents are the same as those in Example 1.

[0152] Comparative Example 5

[0153] The process and conditions of Comparative Example 5 are the same as those in Example 1, except for Step 3. The temperature in the middle section of the fluidized roasting reactor in Comparative Example 3 is different from that in Example 1. The specific different steps are as follows:

[0154] (3) Load the precursor material particles dried in Step (2) into a circulating fluidized bed reactor for fluidized roasting, and the temperature in the middle section of the fluidized bed reactor is 450 °C.

[0155] The remaining steps are the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 5, refer to Example 1 for the performance test of the sample battery, and the test conditions and test contents are the same as those in Example 1.

[0156] Comparative Example 6

[0157] The process and conditions of Comparative Example 6 are the same as those in Example 1, except for Step 3. The temperature in the upper section of the fluidized roasting reactor in Comparative Example 3 is different from that in Example 1. The specific different steps are as follows:

[0158] (3) Load the precursor material particles dried in Step (2) into a circulating fluidized bed reactor for fluidized roasting, and the temperature in the upper section of the fluidized bed reactor is 350 °C.

[0159] The remaining steps are the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 6, refer to Example 1 for the performance test of the sample battery, and the test conditions and test contents are the same as those in Example 1.

[0160] Comparative Example 7

[0161] The process and conditions of Comparative Example 7 were the same as those of Example 1, except for Step 3. The flow rate of the precursor material particles in the fluidized roasting reaction in Comparative Example 3 was different from that in Example 1. The specific different steps were as follows:

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

[0163] The remaining steps were the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 7, the performance test of the sample battery was carried out with reference to Example 1, and the test conditions and test contents were the same as those in Example 1.

[0164] Comparative Example 8

[0165] The process and conditions of Example 8 were the same as those of Example 1, except for Step 3. The flow rate of the precursor material particles in the fluidized roasting reaction in Comparative Example 3 was different from that in Example 1. The specific different steps were as follows:

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

[0167] The remaining steps were the same as those in Example 1. For the sodium iron pyrophosphate phosphate material prepared in Comparative Example 8, the performance test of the sample battery was carried out with reference to Example 1, and the test conditions and test contents were the same as those in Example 1.

[0168] XRD was used to test and analyze the purity of the samples prepared in Example 1 and Comparative Example 1. The XRD patterns of the iron-based polyanionic sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 were as Figure 2 shown. There were obvious impurity peaks in the material pattern of Comparative Example 1.

[0169] The positive electrode sheets prepared from the iron-based polyanionic sodium-ion battery cathode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 8 were used to prepare button-type half cells with sodium metal for the material battery performance test. The test contents were the initial Coulomb efficiency and mass specific capacity of the material at a rate of 0.2C, and the capacity retention rate after 500 cycles at a rate of 2C. The specific test results are compared in Table 1.

[0170] The conditions for the positive electrode sheet prepared from the iron-based polyanionic sodium-ion battery cathode material were that the slurry ratio was positive electrode material: conductive carbon black: carbon nanotube: PVDF5130 = 92:3:1:4, and the electrode surface loading was 3 mg / cm 2 .

[0171] The test conditions for preparing the sodium metal button half-cell are as follows: voltage range: 0 - 2.5 V, test ambient temperature: 25 °C, the test rate for the initial Coulombic efficiency and mass specific capacity is 0.2 C, and the test conditions for the cycling performance are 2 C for 500 charge-discharge cycles.

[0172] Table 1. Comparison of battery performance test results of polyanionic sodium-ion battery cathode materials based on iron phosphate for Examples 1 - 10 and Comparative Examples 1 - 8

[0173]

[0174]

[0175] From the analysis of the XRD patterns of the materials, it can be seen that the polyanionic sodium-ion battery cathode materials based on iron phosphate prepared by the method of the present invention have higher purity. There are no impurity peaks in the XRD diffraction peaks of the sample corresponding to Example 1, while there are obvious impurity peaks in the sample of Comparative Example 1. At the same time, the intensity of the XRD diffraction peaks of the sample of Example 1 is higher than that of the sample of Comparative Example 1, indicating that the crystallinity of the material of Example 1 prepared by the method of the present invention is better than that of Comparative Example 1.

[0176] From the comparison of the battery performance test results, it can be seen that the polyanionic sodium-ion battery cathode materials based on iron phosphate prepared by the method of the present invention have higher mass specific capacity, initial Coulombic efficiency, and cycling capacity retention rate. The mass specific capacity of the half-cells of the polyanionic sodium-ion battery cathode materials based on iron phosphate in Examples 1 - 11 is higher than 115 mAh / g, the initial Coulombic efficiency is higher than 95.0%, and the capacity retention rate after 500 cycles at 2 C is higher than 95.0%. Compared with the comparative examples, it has obvious performance advantages.

[0177] The present invention granulates the polyanionic compound precursor based on iron phosphate and then uses a circulating fluidized bed for roasting to solve the influence of the reaction heat effect on the purity and performance of the polyanionic sodium-ion battery cathode materials based on iron phosphate. At the same time, using a carbon source gas reduces the defects of the carbon coating layer of the material and improves the performance of the polyanionic sodium-ion battery cathode materials. The method of the present invention has significant beneficial effects.

[0178] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the disclosed technical content is equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A method for preparing an iron-based phosphate material, characterized in that, The method comprises the following steps: S1: Mix raw materials including a sodium source, an iron source, a phosphorus source, a carbon source, a solvent, and a binder to obtain a precursor mixture; S2: Granulate the precursor mixture in step S1 to obtain precursor particles; S3: Fluidized calcine the precursor particles in step S2 in a circulating fluidized bed reactor in a fluidization medium to obtain iron-based phosphate material particles; S4: Pulverize the iron-based phosphate material particles obtained in step S3 to obtain iron-based phosphate material powder.

2. 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 fluorine source; Preferably, in step S1, the particle size of the solid raw materials in the precursor mixture is 0.1 - 74 μm; Preferably, in step S2, the particle size of the precursor particles is 80 - 1000 μm, and the morphology presents at least one of spherical, ellipsoidal, columnar, and polyhedral shapes; Preferably, in step S2, the granulation is performed using an extrusion granulator or a centrifugal spray granulator.

3. The method for preparing an iron-based phosphate material according to claim 1, characterized in that, In step S3, the fluidized bed reactor is divided into lower, middle, and upper sections; wherein, The temperature of the lower section is controlled at 300 - 600 °C, and the time for the precursor particles to pass through the lower section after fluidization is 30 - 360 min; The temperature of the middle section is controlled at 500 - 900 °C, and the time for the precursor particles to pass through the middle section after fluidization is 5 - 30 min; The temperature of the upper section is controlled at 400 - 650 °C, and the time for the precursor particles to pass through the upper section after fluidization is 30 - 180 min; Preferably, in step S3, the flow rate of the precursor particles during the fluidized circulation calcination in the fluidized bed reactor is 200 - 1000 mm / min; Preferably, in step S3, the fluidization medium is an inert gas; the inert gas includes nitrogen or argon; Preferably, in step S3, a carbon source gas is introduced into the reactor during the fluidized calcination; the carbon source gas is selected from at least one of methane, ethane, propane, n-butane, isobutane, ethylene, propylene, n-butene, isobutene, butadiene, cis-2-butene, trans-2-butene, cyclopropane, acetylene, and propyne; Preferably, in step S3, the volume ratio of the carbon source gas to the total circulating gas volume is 1 - 15%; the introduction duration of the carbon source gas is 20 - 100 min, and the introduction of the carbon source gas stops simultaneously with the fluidized calcination; Preferably, in step S4, the pulverization process sequentially includes ball milling, air flow pulverization, and screening processes; In step S4, the particle size of the iron-based phosphate material powder is 0.1 - 20 μm.

4. 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 polyanion compound; it has at least one of the structures shown in formula a, formula b, formula c, and formula d; Na4Fe3(PO4)2P2O7 formula a, Na3Fe2(PO4)1P2O7 formula b, NaFePO4 formula c, Na2FeP2O7 formula d; Preferably, when the structural formula of the iron-based phosphate polyanionic compound is Formula a, the molar ratio of the sodium source, iron source, and phosphorus source in its precursor mixture is (3.9 - 4.2):(2.9 - 3.1):(3.9 - 4.1); Preferably, when the structural formula of the iron-based phosphate polyanionic compound is Formula b, the molar ratio of the sodium source, iron source, and phosphorus source in its precursor mixture is (2.9 - 3.2):(1.9 - 2.1):(2.9 - 3.1); Preferably, when the structural formula of the iron-based phosphate polyanionic compound is Formula c, the molar ratio of the sodium source, iron source, and phosphorus source in its precursor mixture is (0.9 - 1.2):(0.9 - 1.1):(0.9 - 1.1); Preferably, when the structural formula of the iron-based phosphate polyanionic compound is Formula d, the molar ratio of the sodium source, iron source, and phosphorus source in its precursor mixture is (1.9 - 2.2):(0.9 - 1.1):(1.9 - 2.1).

5. 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 polyanionic compound; it has the structure shown in Formula e and / or f; Na2FePO4F (Formula e), Na5Fe2(PO4)2F3 (Formula f); Preferably, when the structural 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 its precursor mixture is (1.9 - 2.2):1:1:1; Preferably, when the structural 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 its precursor mixture is (4.9 - 5.2):(1.9 - 2.1):(1.9 - 2.1):

3.

6. The preparation method of an iron-based phosphate material according to claim 1, wherein, 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 hydrated compounds; Preferably, in step S1, the iron source is selected from at least one of iron powder, magnetite, ferric oxide, ferrous oxide, iron oxalate, ferrous oxalate, iron phosphate, iron pyrophosphate, ferrous citrate, iron nitrate, ferrous nitrate, iron sulfate, ferrous sulfate, ferric chloride, ferrous chloride, iron acetate, ammonium ferrous sulfate, ferric citrate, ammonium ferric citrate, sodium succinate citrate, and their hydrated compounds; Preferably, 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 hydrated compounds; Preferably, 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 maltodextrin; The addition amount of the carbon source is 4 - 8% of the mass of carbon in the iron-based phosphate material powder.

7. The preparation method of an iron-based phosphate material according to claim 2, wherein, In step S1, the fluorine source is selected from at least one of sodium fluoride, ammonium fluoride, polyvinylidene fluoride, polytetrafluoroethylene, and hydrofluoric acid; Preferably, in step S1, a dispersant is further included in the precursor mixture; The addition amount of the solvent is 10-120 wt% of the precursor mixture; The addition amount of the dispersant is 0.5-5 wt% of the precursor mixture; The addition amount of the binder is 0.3-8 wt% of the precursor mixture; Preferably, the solvent is selected from at least one of deionized water, ethanol, methanol, ethylene glycol, isopropanol, and acetone; Preferably, the dispersant is selected from at least one of sodium dodecyl sulfate, methyl amyl alcohol, polyacrylamide, guar gum, fatty acid polyethylene glycol ester, and polyether; Preferably, the binder is selected from at least one of carboxymethyl cellulose, polyvinyl alcohol, and polyacrylamide.

8. A cathode material for a sodium-ion battery of the polyanionic type based on iron phosphate, wherein, It is an iron-based phosphate material prepared by the method according to any one of claims 1 to 7.

9. A sodium-ion cathode, wherein, The active material of the sodium ion positive electrode includes the iron-based phosphate material prepared by the method according to any one of claims 1 to 7.

10. The sodium-ion cathode according to claim 9, wherein, The content of the iron-based phosphate material in the sodium ion positive electrode is 60-98 wt%; Preferably, a conductive agent and a binder are further included in the sodium ion positive electrode; the mass ratio of the sodium ion positive electrode material, the conductive agent, and the binder is (60-98) wt%:(1-39) wt%:(1-39) wt%; Preferably, the conductive agent is selected from at least one of conductive carbon black, conductive graphite, carbon nanofibers, carbon nanotubes, and graphene; The binder is selected from at least one of polyvinylidene fluoride PVDF5130, HSV900, and kynar761A.

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