Iron-based mixed phosphate positive electrode material, preparation method thereof and application of iron-based mixed phosphate positive electrode material and sodium battery

Abstract

The invention relates to the technical field of battery materials, in particular to an iron-based mixed phosphate positive electrode material, a preparation method thereof and application of the iron-based mixed phosphate positive electrode material and a sodium battery. The iron-based mixed phosphate positive electrode material comprises polyacrylic acid as well as a sodium source, an iron source, a phosphorus source and a carbon source according to a stoichiometric ratio, the mass ratio of the polyacrylic acid to the carbon source is 1%-30%, and the carbon content in the iron-based mixed phosphate positive electrode material is 0.5%-10%; according to the invention, polyacrylic acid is taken as a functional additive, a carbon coating layer of the iron-based mixed phosphate positive electrode material is formed by combining a carbon source, and the iron-based mixed phosphate positive electrode material with high tap density, uniform carbon coating layer and good conductivity can be obtained by utilizing the gathering effect of polyacrylic acid and the effect of forming a cross-linked template; the energy density, the rate capability and the cycle life of the corresponding sodium ion battery are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to an iron-based mixed phosphate positive electrode material and a preparation method thereof, and application in sodium batteries. Background Art

[0002] Among the many battery materials, sodium-ion batteries have attracted widespread attention due to their advantages such as low development cost, high safety, and wide temperature adaptability.

[0003] Sodium-ion battery cathode materials are primarily classified into three categories: layered oxides, Prussian blue compounds, and polyanion materials. Layered oxide cathode materials typically have high specific capacity but poor cycling stability, and they often contain elements such as cobalt and nickel, resulting in high material costs. Prussian blue compound cathode materials offer high energy density, but are difficult to remove water from and contain cyanide, posing a significant environmental risk. Polyanion cathode materials, on the other hand, offer advantages such as high structural stability, long cycle life, and excellent thermal stability, making them a promising candidate for sodium-ion battery applications. Among polyanion cathode materials, the iron-based mixed phosphate cathode material Na₄Fe₃(PO₄)₂P₂Oₐ (NFPP) has attracted considerable attention due to its pollution-free and low-cost properties. However, NFPP also suffers from poor conductivity and low tap density, which limit its practical application.

[0004] In view of this, providing a new iron-based mixed phosphate positive electrode material and its preparation method, and its application in sodium batteries has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of the defects in the prior art, the purpose of the present invention is to provide an iron-based mixed phosphate positive electrode material and its preparation method, and sodium battery application, which can effectively solve the problems of poor conductivity and low tap density of iron-based mixed phosphate positive electrode materials.

[0006] The purpose of the present invention can be achieved through the following technical solutions: On one hand, the present invention provides an iron-based mixed phosphate positive electrode material, comprising: polyacrylic acid and a sodium source, an iron source, a phosphorus source and a carbon source in a stoichiometric ratio, wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%, and the carbon content in the iron-based mixed phosphate positive electrode material is 0.5% to 10%.

[0007] According to one embodiment of the present invention, the sodium source includes: one or more of sodium carbonate, sodium chloride, sodium nitrate, sodium acetate, sodium hydroxide, disodium hydrogen phosphate and sodium dihydrogen phosphate; the iron source includes: one or more of ferric oxalate, ferric phosphate and ferric nitrate; the phosphorus source includes: one or more of phosphoric acid, disodium hydrogen phosphate and sodium dihydrogen phosphate; the carbon source includes: one or more of tartaric acid, citric acid, malic acid, glucose, acetic acid and tannic acid.

[0008] Another aspect of the present invention provides a method for preparing an iron-based mixed phosphate cathode material, comprising the following steps: S1: adding polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into deionized water, and stirring until the mixture is uniform to obtain a spray slurry; wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%; S2: spray drying the spray slurry to obtain a precursor material; S3: sintering the precursor material in an argon-hydrogen atmosphere to obtain the iron-based mixed phosphate positive electrode material.

[0009] According to one embodiment of the present invention, in step S1, the amount of deionized water added is such as to control the solid content of the spray slurry to be between 5% and 50%.

[0010] According to one embodiment of the present invention, in the step S1, after the stirring until the mixture is uniformly mixed, the process further includes: adding oxalic acid for stirring, with a stirring rate of 200~500r / min and a stirring time of 1~15h, so as to control the pH of the spray slurry between 1~5; in the step S2, the nozzle temperature of the spray drying is 100~300°C, and the peristaltic pump rate is controlled between 10%~50%; in the step S3, the sintering temperature is 400~600°C, and the sintering time is 1~15h.

[0011] Another aspect of the present invention provides a method for preparing an iron-based mixed phosphate cathode material, comprising the following steps: S1: adding polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into a ball mill, adding ethanol, and wet ball milling in an inert atmosphere to obtain a precursor material; wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%; S2: preheating the precursor material in an argon-hydrogen atmosphere, taking it out and grinding it until it is evenly mixed to obtain a powder; S3: sintering the powder in an argon-hydrogen atmosphere to obtain the iron-based mixed phosphate positive electrode material.

[0012] According to one embodiment of the present invention, in the step S1, the amount of ethanol added is to control the solid content of the precursor material to be between 60% and 70%; the ball mill speed of the wet ball milling is 200-500 r / min, and the ball milling time is 1-15 hours, wherein the ball mill is paused for 1-5 minutes every 1-10 minutes of ball milling; in the step S2, the preheating temperature is 200-400°C, and the preheating time is 1-15 hours; in the step S3, the sintering temperature is 400-600°C, and the sintering time is 1-15 hours.

[0013] On the other hand, the present invention provides a positive electrode, including the iron-based mixed phosphate positive electrode material or the positive electrode material prepared by the method for preparing the iron-based mixed phosphate positive electrode material or the positive electrode material prepared by the method for preparing the iron-based mixed phosphate positive electrode material.

[0014] On the other hand, the present invention provides a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material or the positive electrode material prepared by the method for preparing the iron-based mixed phosphate positive electrode material or the positive electrode material prepared by the method for preparing the iron-based mixed phosphate positive electrode material or the positive electrode.

[0015] Another aspect of the present invention provides an electrical device comprising the sodium ion battery.

[0016] Beneficial effects: The iron-based mixed phosphate positive electrode material of the present invention comprises: polyacrylic acid and a sodium source, an iron source, a phosphorus source and a carbon source in a stoichiometric ratio, the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%, and the carbon content in the iron-based mixed phosphate positive electrode material is 0.5% to 10%; polyacrylic acid is used as a functional additive and is combined with the carbon source to form a carbon coating layer of the iron-based mixed phosphate positive electrode material. By utilizing the aggregation effect of polyacrylic acid and the role of forming a cross-linking template, an iron-based mixed phosphate positive electrode material with high tap density, uniform carbon coating layer and good conductive performance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of a method for preparing an iron-based mixed phosphate positive electrode material according to an embodiment of the present invention.

[0018] Figure 2 It is a schematic flow chart of a method for preparing an iron-based mixed phosphate positive electrode material according to another embodiment of the present invention.

[0019] Figure 3 These are scanning electron microscope morphology images of the iron-based mixed phosphate positive electrode materials prepared in Example 1 and Comparative Example 1 of the present invention; wherein (a) is the scanning electron microscope morphology image of Comparative Example 1, and (b) is the scanning electron microscope morphology image of Example 1.

[0020] Figure 4This is the X-ray diffraction pattern of the iron-based mixed phosphate positive electrode material prepared in Example 1 of the present invention.

[0021] Figure 5 The iron-based mixed phosphate cathode material prepared in Example 1 of the present invention was tested in a sodium ion button half cell at 0.1C (10 mA ) The charge and discharge curves of the first three cycles of the next cycle.

[0022] Figure 6 The rate performance of the iron-based mixed phosphate cathode material prepared in Example 1 of the present invention in a sodium ion button half-cell.

[0023] Figure 7 Cycling stability of the iron-based mixed phosphate cathode material prepared in Example 1 of the present invention at 20C in a sodium ion button half cell. DETAILED DESCRIPTION

[0024] The technical solutions of the present invention are described below by means of specific examples. The raw materials and reagents used in the present invention are all commercially available.

[0025] Embodiments of the present invention disclose an iron-based mixed phosphate cathode material comprising polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in stoichiometric proportions. The mass ratio of the polyacrylic acid to the carbon source is 1% to 30%, and the carbon content of the iron-based mixed phosphate cathode material is 0.5% to 10%. Preferably, the mass ratio of the polyacrylic acid to the carbon source is 5% to 20%.

[0026] In some feasible embodiments, the sodium source includes one or more of sodium carbonate, sodium chloride, sodium nitrate, sodium acetate, sodium hydroxide, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Preferably, the sodium source is sodium hydroxide or sodium carbonate.

[0027] In some feasible embodiments, the iron source includes one or more of ferric oxalate, ferric phosphate, and ferric nitrate. Preferably, the iron source is ferric phosphate or ferric nitrate.

[0028] In some feasible embodiments, the phosphorus source includes one or more of phosphoric acid, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Preferably, the phosphorus source is disodium hydrogen phosphate.

[0029] In some feasible embodiments, the carbon source comprises: one or more of tartaric acid, citric acid, malic acid, glucose, acetic acid and tannic acid. Preferably, the carbon source is tartaric acid, citric acid or glucose.

[0030] The iron-based mixed phosphate positive electrode material of the embodiment of the present invention uses polyacrylic acid as a functional additive, combined with a low-cost carbon source to form a carbon coating layer of the iron-based mixed phosphate positive electrode material. By utilizing the aggregation effect of polyacrylic acid and the role of forming a cross-linked template, an iron-based mixed phosphate positive electrode material with high tap density, uniform carbon coating layer and good conductive performance can be obtained.

[0031] Related carbon coating technologies are prone to structural collapse during the sintering process of precursor materials, resulting in problems such as irregular particle morphology and uneven coating (such as Figure 3 (a), which reduces the material's tap density and electrical conductivity, ultimately reducing the material's energy density and affecting its practical application. The following two preparation methods can significantly improve the tap density and electrical conductivity of iron-based mixed phosphate cathode materials.

[0032] The first is the spray drying synthesis route, see Figure 1 , an embodiment of the present invention discloses a method for preparing an iron-based mixed phosphate positive electrode material, comprising the following steps: S1: Add polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into deionized water, and stir until the mixture is uniform to obtain a spray slurry; wherein the mass ratio of polyacrylic acid to the carbon source is 1% to 30%.

[0033] In step S1, deionized water is added in an amount sufficient to control the solids content of the spray slurry to be between 5% and 50%. The stirring time is 1 to 15 hours. Preferably, the mass ratio of polyacrylic acid to carbon source is between 5% and 20%, and the stirring time is 10 hours.

[0034] Furthermore, after the stirring step until the mixture is uniformly mixed, the step further includes: adding oxalic acid as a chelating agent and pH control agent to the mixed solution and stirring at a stirring rate of 200 to 500 r / min for 1 to 15 hours to control the pH of the spray slurry to be between 1 and 5. Preferably, the stirring rate is 400 r / min and the stirring time is 12 hours to control the pH of the spray slurry to be between 1 and 3.

[0035] S2: spray drying the spray slurry to obtain a precursor material.

[0036] In step S2, the nozzle temperature for spray drying is 100-300°C, and the peristaltic pump rate is controlled between 10% and 50%. Preferably, the nozzle temperature for spray drying is 250°C, and the peristaltic pump rate is controlled between 10% and 20%. During the spray drying process, polyacrylic acid, as a functional additive, utilizes the properties of its carboxyl functional groups and polymer chains to exert bonding and ball-forming effects, promoting the aggregation of precursor particles and forming highly spherical particles.

[0037] S3: Sintering the precursor material in an argon-hydrogen atmosphere to obtain an iron-based mixed phosphate positive electrode material.

[0038] In step S3, the argon-hydrogen atmosphere includes 95% argon and 5% hydrogen, the sintering temperature is 400-600° C., and the sintering time is 1-15 hours. Preferably, the sintering temperature is 520° C. and the sintering time is 8 hours.

[0039] During the sintering process, in the low-temperature heating stage (200-400°C), the polyacrylic acid molecular chains dehydrate to form cross-linked polymer anhydrides, which interact with the carboxyl groups of the carbon source to form a three-dimensional network structure, acting as a rigid template to maintain the integrity of the spherical structure. During the high-temperature carbonization / sintering stage (400-600°C), the polyacrylic acid template is thermally decomposed and released, while the carbon source is converted into a conductive carbon layer that uniformly coats the particle surface. Thanks to the support of the rigid template, the spherical particles undergo isotropic shrinkage, maximizing the retention of their high sphericity, significantly improving the material's tap density and the uniformity of the carbon coating.

[0040] The preparation method of the iron-based mixed phosphate cathode material of the embodiment of the present invention introduces polyacrylic acid as a multifunctional additive, combines a low-cost carbon source as a carbon precursor, and cooperates with spray drying and granulation to form a material coating layer and a spherical morphology precursor with uniform material, strong structure and excellent conductivity, thereby improving the conductivity of the iron-based mixed phosphate cathode material and ensuring that the material can still maintain a micron-scale spherical morphology after sintering (such as Figure 3 b), effectively improving the tap density, carbon coating uniformity, rate performance and cycle stability of the iron-based mixed phosphate positive electrode material.

[0041] Furthermore, the preparation method for this iron-based mixed phosphate cathode material utilizes abundant raw materials, is low-cost, and is environmentally friendly. Furthermore, this preparation method not only produces an iron-based mixed phosphate cathode material with uniform composition and coating thickness, but also facilitates industrial mass production.

[0042] The second is the solid phase reaction synthesis route, see Figure 2 , an embodiment of the present invention discloses a method for preparing an iron-based mixed phosphate positive electrode material, comprising the following steps: S1: Add polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into a ball mill, add ethanol, and perform wet ball milling in an inert atmosphere to obtain a precursor material; wherein the mass ratio of polyacrylic acid to the carbon source is 1% to 30%.

[0043] In step S1, ethanol is added in an amount sufficient to control the solid content of the precursor material to between 60% and 70%. The wet milling process is performed at a ball mill speed of 200 to 500 rpm for 1 to 15 hours, with a rest period of 1 to 5 minutes for every 1 to 10 minutes of milling. Preferably, the mass ratio of polyacrylic acid to carbon source is 5% to 20%. The wet milling process is performed at a ball mill speed of 400 rpm for 10 hours, with a rest period of 1 minute for every 5 minutes of milling.

[0044] S2: Preheat the precursor material in an argon-hydrogen atmosphere, take it out and grind it until it is evenly mixed to obtain a powder.

[0045] In step S2, the argon-hydrogen atmosphere includes 95% argon and 5% hydrogen. The preheating equipment is a tubular furnace, the preheating temperature is 100-400°C, and the preheating time is 1-15 hours. Preferably, the preheating temperature is 300°C, and the preheating time is 6 hours. Specifically, the precursor material is placed in the tubular furnace, and the tubular furnace is vacuumed and ventilated three times to exhaust the air in the tubular furnace, and an argon-hydrogen mixed gas is passed through, preheated at 300°C for 6 hours, taken out and ground until the mixture is uniform, to obtain a powder.

[0046] S3: Sintering the powder in an argon-hydrogen atmosphere to obtain an iron-based mixed phosphate positive electrode material.

[0047] In step S3, the argon-hydrogen atmosphere comprises 95% argon and 5% hydrogen. The sintering equipment is a tubular furnace, the sintering temperature is 400-600°C, and the sintering time is 1-15 hours. Preferably, the sintering temperature is 520°C and the sintering time is 8 hours. Specifically, the powder is placed in the tubular furnace, and the tubular furnace is evacuated and ventilated three times to expel the air in the tubular furnace. The argon-hydrogen mixed gas is then passed through and sintered at 520°C for 8 hours to obtain the iron-based mixed phosphate positive electrode material.

[0048] The preparation method of the iron-based mixed phosphate positive electrode material in the embodiment of the present invention introduces polyacrylic acid as a multifunctional additive and combines it with a low-cost carbon source as a carbon precursor to form a material coating layer with uniform material, strong structure and excellent conductivity, thereby effectively improving the tap density, carbon coating uniformity, rate performance and cycle stability of the iron-based mixed phosphate positive electrode material.

[0049] Furthermore, the preparation method for this iron-based mixed phosphate cathode material utilizes abundant raw materials, is low-cost, and is environmentally friendly. Furthermore, this preparation method not only produces an iron-based mixed phosphate cathode material with uniform composition and coating thickness, but also features a simple process, making it easily scalable for mass industrial production.

[0050] Example 1 This embodiment discloses a method for preparing an iron-based mixed phosphate cathode material, comprising the following steps: adding polyacrylic acid and FePO4, NaOH, Na2HPO4 in a stoichiometric ratio, and a carbon source to deionized water, mixing and stirring for 10 hours to obtain a spray slurry; wherein the mass ratio of polyacrylic acid to the carbon source is 15%; spray drying the spray slurry at a nozzle temperature of 250°C and a peristaltic pump controlled between 10% and 20% to obtain a precursor material after spraying; evacuating a tubular furnace and circulating the evacuated air (argon and hydrogen) three times to completely exhaust the air; placing the precursor material in the tubular furnace and sintering it at 520°C for 8 hours to obtain the iron-based mixed phosphate cathode material.

[0051] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0052] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0053] Example 2 This embodiment discloses a method for preparing an iron-based mixed phosphate positive electrode material. The only difference between this embodiment and Example 1 is that the mass ratio of polyacrylic acid to carbon source is 20%.

[0054] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0055] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0056] Example 3 This embodiment discloses a method for preparing an iron-based mixed phosphate positive electrode material. The only difference between this embodiment and Example 1 is that the mass ratio of polyacrylic acid to carbon source is 10%.

[0057] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0058] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0059] Example 4 This embodiment discloses a method for preparing an iron-based mixed phosphate positive electrode material. The only difference between this embodiment and Example 1 is that the mass ratio of polyacrylic acid to carbon source is 5%.

[0060] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0061] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0062] Example 5 This embodiment discloses a method for preparing an iron-based mixed phosphate positive electrode material, comprising the following steps: adding polyacrylic acid and Na2CO3, Fe(NO3)3, NaH2PO4, NH4H2PO4 and a carbon source in a stoichiometric ratio into a ball mill in a glove box, adding ethanol and wet ball milling in an inert atmosphere to obtain a precursor material; wherein the mass ratio of polyacrylic acid to the carbon source is 15%, the ball mill speed is 400 r / min, the running time is 10 hours, and the grinding is paused for 1 minute every 5 minutes; the precursor material is placed in a tubular furnace filled with argon and hydrogen mixed gas and preheated at 300°C for 6 hours, taken out and ground evenly, then placed in a tubular furnace filled with argon and hydrogen mixed gas, and sintered at 520°C for 8 hours to obtain an iron-based mixed phosphate positive electrode material.

[0063] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0064] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0065] Comparative Example 1 This embodiment discloses a method for preparing an iron-based mixed phosphate positive electrode material. The only difference between this embodiment and Example 1 is that polyacrylic acid is not added in this embodiment.

[0066] This embodiment also discloses a positive electrode, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment.

[0067] This embodiment also discloses a sodium ion battery, comprising the iron-based mixed phosphate positive electrode material prepared in this embodiment or the positive electrode of this embodiment.

[0068] test (1) The iron-based mixed phosphate cathode materials prepared in Example 1 and Comparative Example 1 were tested by scanning electron microscopy. The morphologies are shown in the following figure: Figure 3 shown; among them, Figure 3 a is the morphology of the comparative example, Figure 3 b is the morphology image of Example 1.

[0069] (2) The iron-based mixed phosphate cathode material prepared in Example 1 was subjected to XRD testing. The test results are as follows: Figure 4 shown.

[0070] (3) The tap density of the iron-based mixed phosphate cathode materials prepared in Examples 1 to 5 and Comparative Example 1 was tested. The test results are shown in Table 1.

[0071] (4) Electrochemical performance tests were performed on the sodium ion batteries prepared in Examples 1 to 5 and Comparative Example 1, including: In an Ar-filled glove box, the prepared cathode sheet was combined with sodium metal (approximately 1 mm thick) to form a CR2032 coin cell. The separator was Whatman GF / D glass fiber, the electrolyte was a 1 mol / L NaPF6 solution, and the solvent was EC (ethylene carbonate) / diethyl carbonate (DEC) (v:v = 1:1), with a 5 vol% fluoroethylene carbonate (FEC) additive.

[0072] The obtained CR2032 button cell was subjected to constant current charge and discharge experiments at 1.7 to 4 V on a Xinwei battery test system. The test results are shown in Table 1. Among them, the iron-based mixed phosphate cathode material prepared in Example 1 was 0.1C (10 mA) in a sodium ion button half cell. ) The charge and discharge curves of the first three cycles of the next cycle are as follows Figure 5 As shown; the rate performance of the iron-based mixed phosphate cathode material prepared in Example 1 in the sodium ion button half cell is as shown Figure 6 As shown in Example 1, the cycle stability of the iron-based mixed phosphate cathode material in the sodium ion button half cell at 20C is shown in Figure 7 shown.

[0073] Table 1: Tap density and electrochemical performance test results of Examples 1 to 5 and Comparative Example 1.

[0074] As shown in Table 1, the iron-based mixed phosphate cathode material prepared by the spray-drying synthesis route, when the polyacrylic acid is added at a ratio of 15%, exhibits excellent rate and cycle performance, as well as a high tap density. This achieves synergistic optimization of rate performance (20C capacity retention >85%) and cycle life (1000-cycle capacity retention close to 99%). The iron-based mixed phosphate cathode material prepared by the solid-phase reaction synthesis route, when the polyacrylic acid is added at a ratio of 15%, exhibits similar electrochemical properties to the iron-based mixed phosphate cathode material prepared by the spray-drying synthesis route, but differs in morphology and, therefore, in tap density.

[0075] Combine Figure 3 As shown in Table 1 (see Example 1 and Comparative Example 1), the iron-based mixed phosphate cathode material prepared by adding polyacrylic acid in Example 1 maintains a good spherical morphology, such as Figure 3 b; Comparative Example 1 did not add polyacrylic acid, the morphology of the obtained iron-based mixed phosphate cathode material was irregular, as shown in FIG. Figure 3As shown in a, the added polyacrylic acid can prevent the destruction of the material morphology during the sintering process, avoid structural collapse, and effectively improve the tap density, carbon coating uniformity, rate performance and cycle stability of the iron-based mixed phosphate positive electrode material.

[0076] The above are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An iron-based mixed phosphate cathode material, characterized in that: include: Polyacrylic acid and a sodium source, an iron source, a phosphorus source and a carbon source in a stoichiometric ratio, wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%, and the carbon content in the iron-based mixed phosphate positive electrode material is 0.5% to 10%.

2. The iron-based mixed phosphate cathode material according to claim 1, characterized in that The sodium source includes one or more of sodium carbonate, sodium chloride, sodium nitrate, sodium acetate, sodium hydroxide, disodium hydrogen phosphate and sodium dihydrogen phosphate; the iron source includes one or more of ferric oxalate, ferric phosphate and ferric nitrate; the phosphorus source includes one or more of phosphoric acid, disodium hydrogen phosphate and sodium dihydrogen phosphate; and the carbon source includes one or more of tartaric acid, citric acid, malic acid, glucose, acetic acid and tannic acid.

3. A method for preparing an iron-based mixed phosphate positive electrode material, characterized in that: The following steps are involved: S1: adding polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into deionized water, and stirring until the mixture is uniform to obtain a spray slurry; wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%; S2: spray drying the spray slurry to obtain a precursor material; S3: sintering the precursor material in an argon-hydrogen atmosphere to obtain the iron-based mixed phosphate positive electrode material.

4. The method for preparing the iron-based mixed phosphate cathode material according to claim 3, characterized in that: In step S1, the amount of deionized water added is such as to control the solid content of the spray slurry to be between 5% and 50%.

5. The method for preparing the iron-based mixed phosphate cathode material according to claim 3, characterized in that: In the step S1, after stirring until the mixture is uniformly mixed, the method further includes: adding oxalic acid for stirring at a stirring rate of 200-500 r / min and a stirring time of 1-15 hours to control the pH of the spray slurry between 1 and 5; in the step S2, the nozzle temperature of the spray drying is 100-300° C., and the peristaltic pump rate is controlled between 10% and 50%; in the step S3, the sintering temperature is 400-600° C., and the sintering time is 1-15 hours.

6. A method for preparing an iron-based mixed phosphate positive electrode material, characterized in that: The following steps are involved: S1: adding polyacrylic acid and a sodium source, an iron source, a phosphorus source, and a carbon source in a stoichiometric ratio into a ball mill, adding ethanol, and wet ball milling in an inert atmosphere to obtain a precursor material; wherein the mass ratio of the polyacrylic acid to the carbon source is 1% to 30%; S2: preheating the precursor material in an argon-hydrogen atmosphere, taking it out and grinding it until it is evenly mixed to obtain a powder; S3: sintering the powder in an argon-hydrogen atmosphere to obtain the iron-based mixed phosphate positive electrode material.

7. The method for preparing the iron-based mixed phosphate cathode material according to claim 6, characterized in that: In the step S1, the amount of ethanol added is to control the solid content of the precursor material between 60% and 70%; the ball mill speed of the wet ball milling is 200-500 r / min, and the ball milling time is 1-15 hours, wherein the ball mill is paused for 1-5 minutes every 1-10 minutes of ball milling; in the step S2, the preheating temperature is 200-400°C, and the preheating time is 1-15 hours; in the step S3, the sintering temperature is 400-600°C, and the sintering time is 1-15 hours.

8. A positive electrode, characterized in that The invention comprises the iron-based mixed phosphate positive electrode material as described in any one of claims 1 to 2, or the positive electrode material prepared by the preparation method of the iron-based mixed phosphate positive electrode material as described in any one of claims 3 to 5, or the positive electrode material prepared by the preparation method of the iron-based mixed phosphate positive electrode material as described in any one of claims 6 to 7.

9. A sodium ion battery, characterized in that: Including the iron-based mixed phosphate positive electrode material as described in any one of claims 1 to 2, or the positive electrode material prepared by the preparation method of the iron-based mixed phosphate positive electrode material as described in any one of claims 3 to 5, or the positive electrode material prepared by the preparation method of the iron-based mixed phosphate positive electrode material as described in any one of claims 6 to 7, or the positive electrode as described in claim 8.

10. An electrical device, characterized in that: Including the sodium ion battery as claimed in claim 9.

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