Sodium ferric pyrophosphate phosphate positive electrode material, preparation method thereof and sodium ion battery

Abstract

This application discloses a sodium iron pyrophosphate cathode material, its preparation method, and a sodium-ion battery, belonging to the field of batteries. The sodium iron pyrophosphate cathode material includes sodium iron pyrophosphate and a lanthanide oxide coating layer on the outer surface of the sodium iron pyrophosphate. This application uses a lanthanide oxide coating layer to nanoscale coat the surface of the sodium iron pyrophosphate, forming a protective layer on the surface of the sodium iron pyrophosphate material. This effectively improves the dissolution of transition metal iron ions during battery cycling and enhances the cycle stability of the battery. Simultaneously, it suppresses side reactions between the cathode active material and the electrolyte, thereby improving the battery's electrical performance.

Description

Technical Field

[0001] This application belongs to the field of batteries, and specifically relates to a sodium iron pyrophosphate cathode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries share similar working principles and manufacturing processes with lithium-ion batteries, and have become another important new type of energy storage battery after lithium-ion batteries. Due to the abundance and uniform distribution of raw materials, high cost-effectiveness, and environmental friendliness, as well as the long lifespan and wide temperature range characteristics of the battery products, sodium-ion batteries have attracted widespread attention.

[0003] Currently, mainstream sodium-ion battery cathode materials mainly include layered transition metal oxides, Prussian blue analogs, and polyanionic compounds. However, each of these materials has its own limitations. Layered transition metal oxides suffer from poor cycle performance and high cost; Prussian blue analogs face challenges such as low specific capacity and toxicity; in contrast, polyanionic compounds are more ideal, among which composite phosphate cathode materials have attracted much attention. In existing technologies, conventional additives are typically used to dope and modify cathode materials. However, during charge-discharge cycles, as the number of cycles increases, the structure of the sodium iron pyrophosphate active material changes, posing a risk of transition metal dissolution. Simultaneously, side reactions can occur between the cathode active material and the electrolyte, which will significantly reduce the battery's cycle stability.

[0004] Therefore, it is necessary to provide a sodium iron pyrophosphate cathode material, its preparation method, and a sodium-ion battery to improve the cycle stability of sodium-ion batteries. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a sodium iron pyrophosphate cathode material, comprising sodium iron pyrophosphate and a lanthanide oxide coating layer located on the outer surface of the sodium iron pyrophosphate.

[0006] Furthermore, the D of sodium iron pyrophosphate 50 The particle size is 6μm-8μm, and the specific surface area is 4m². 2 / g-6m 2 / g.

[0007] Furthermore, the thickness of the lanthanide oxide coating is 1 nm-10 nm.

[0008] This application also discloses a method for preparing a sodium iron pyrophosphate cathode material, including: Solid materials are added to deionized water according to a preset ratio and dispersed evenly to obtain a dispersion. The solid materials include sodium source, iron source, phosphorus source, carbon source and surfactant. The dispersion was spray-dried to obtain the precursor material; The precursor material and the lanthanide material are mixed and ground, and then sintered under gas protection to obtain the sintered material. The sintered material was ground and sieved to obtain sodium iron pyrophosphate cathode material.

[0009] Furthermore, the sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium acetate, sodium phosphate, sodium citrate, and sodium malate; The iron source includes at least one of ferrous oxalate, ferrous acetate, ferric phosphate, and ferric nitrate; Phosphorus sources include at least one of sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, ferric phosphate, and pyrophosphate; The carbon source includes at least one of glucose, sucrose, citric acid, starch, conductive carbon black, carbon nanotubes, mesophase carbon microspheres, and graphene. Surfactants include at least one of polyethylene glycol, ammonium polyacrylate, and polyvinylpyrrolidone.

[0010] Furthermore, the molar ratio of sodium source, iron source and phosphorus source is (3-4):(2-3):(3-4); The mass of the carbon source is 2%-9% of the total mass of the solid material; The mass of the surfactant is 0.1%-5% of the total mass of the dispersion; The ratio of the mass of deionized water to the total mass of solid materials is (10-15):1.

[0011] Furthermore, the lanthanide material includes at least one of lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, lanthanum acetate, cerium acetate, neodymium acetate, and praseodymium acetate, and the mass of the lanthanide material is 0.05%-0.5% of the mass of the precursor material.

[0012] Furthermore, the gas protection uses a mixture of Ar and H2, with H2 accounting for 5-10% of the volume of the mixture.

[0013] Furthermore, sintering employs a two-stage heating process, including: Heat at 300℃ for 5-8 hours; Heat at 400℃-700℃ for 6-10 hours.

[0014] This application also discloses a sodium-ion battery, wherein the positive electrode material is the aforementioned sodium iron pyrophosphate positive electrode material.

[0015] Compared with the prior art, this application has the following advantages: 1. This application uses a lanthanide oxide coating layer to nanoscale coat the surface of sodium iron pyrophosphate, which can form a protective layer on the surface of the sodium iron pyrophosphate material, effectively improving the dissolution of transition metal iron ions during battery cycling and the cycle stability of the battery. At the same time, it can suppress the side reactions between the positive electrode active material and the electrolyte, thereby improving the battery's electrical performance.

[0016] 2. This application uses a lanthanide oxide coating layer combined with carbon, which can improve the battery stability while enhancing the conductivity of sodium iron pyrophosphate material.

[0017] 3. By adding surfactants, this application can make the raw materials uniformly dispersed and regulate the structure and composition of the precursor materials, thereby effectively improving the yield and obtaining high-performance sodium iron pyrophosphate material.

[0018] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart illustrating a method for preparing a sodium iron pyrophosphate cathode material according to an embodiment of this application is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] To improve the cycle stability of sodium-ion batteries, a sodium iron pyrophosphate cathode material is provided, comprising sodium iron pyrophosphate and a lanthanide oxide coating layer on the outer surface of the sodium iron pyrophosphate. The Di of the sodium iron pyrophosphate... 50 The particle size is 6μm-8μm, and the specific surface area is 4m². 2 / g-6m 2 / g. The thickness of the lanthanide oxide coating layer is 1nm-10nm. Nanoscale coating of sodium iron pyrophosphate with lanthanide oxide layers forms a protective layer on the surface of the sodium iron pyrophosphate material, effectively improving the dissolution of transition metal iron ions during battery cycling and the battery's cycle stability. Simultaneously, it suppresses side reactions between the positive electrode active material and the electrolyte, thereby improving the battery's electrical performance.

[0023] like Figure 1 As shown, this application also discloses a method for preparing a sodium iron pyrophosphate cathode material, comprising: S1: Solid materials are added to deionized water according to a preset ratio and uniformly dispersed to obtain a dispersion. The solid materials include a sodium source, an iron source, a phosphorus source, a carbon source, and a surfactant. The sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium acetate, sodium phosphate, sodium citrate, and sodium malate; the iron source includes at least one of ferrous oxalate, ferrous acetate, ferric phosphate, and ferric nitrate; the phosphorus source includes at least one of sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, ferric phosphate, and pyrophosphate; the carbon source includes at least one of glucose, sucrose, citric acid, starch, conductive carbon black, carbon nanotubes, mesophase carbon microspheres, and graphene. By adding carbon to the precursor materials, the conductivity of sodium iron pyrophosphate material can be improved while improving battery stability; the surfactant includes at least one of polyethylene glycol, ammonium polyacrylate, and polyvinylpyrrolidone. By adding surfactants, the raw materials can be uniformly dispersed, and the structure and composition of the precursor materials can be controlled to achieve uniformity, thereby effectively improving the yield and obtaining a high-performance sodium iron pyrophosphate material. Preferably, the molar ratio of sodium source, iron source and phosphorus source is (3-4):(2-3):(3-4); the mass of carbon source is 2%-9% of the total mass of solid material; the mass of surfactant is 0.1%-5% of the total mass of dispersant; and the mass ratio of deionized water to the total mass of solid material is (10-15):1.

[0024] S2: Spray drying the dispersion to obtain the precursor material. The precursor material is obtained by spraying the solution or suspension into small droplets, which then evaporate rapidly in a hot gas stream.

[0025] S3: The precursor material and lanthanide material are mixed and ground, then sintered under gas protection to obtain the sintered material. The lanthanide material includes at least one of lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, lanthanum acetate, cerium acetate, neodymium acetate, and praseodymium acetate. The mass of the lanthanide material is 0.05%-0.5% of the precursor material mass. The gas protection uses a mixture of Ar and H2, with H2 accounting for 5-10% of the volume. An appropriate amount of H2 can effectively suppress Fe²⁺ in the precursor material. + Oxidized to Fe³+ To ensure the electrochemical performance of the material, Ar is predominant in the mixed gas to avoid excessive reduction or material structural damage, while also reducing the risk of explosion. Sintering employs a two-stage heating process: the first stage involves heating at 300℃ for 5-8 hours to remove surfactants and volatiles, while H2 promotes the decomposition of organic matter; the second stage, crystallization, involves heating at 400℃-700℃ for 6-10 hours, during which an appropriate amount of H2 prevents excessive reduction of NaFePO4.

[0026] After grinding and sieving, sodium iron pyrophosphate D50 was obtained with a particle size of 6μm-8μm and a specific surface area of ​​4m². 2 / g-6m 2 / g, sodium iron pyrophosphate cathode material with a lanthanide oxide coating thickness of 1nm-10nm.

[0027] This application also discloses a sodium-ion battery, wherein the positive electrode material is the aforementioned sodium iron pyrophosphate positive electrode material.

[0028] To better illustrate this solution, the following embodiments and comparative examples are provided.

[0029] Example 1 S1. Prepare sodium hydroxide, ferric nitrate, and phosphoric acid in a molar ratio of 4:3:4. Weigh glucose at 2% of the total mass of the solid materials and polyethylene glycol at 0.1% of the total mass of the dispersion. Weigh deionized water at a ratio of 10:1 to the total mass of the solid materials. Add the solid materials to the deionized water and disperse them evenly to obtain the dispersion. S2. Spray dry the dispersion to obtain the precursor material; S3. Add cerium nitrate to the precursor material, the mass of cerium nitrate being 0.1% of the mass of the precursor material. After grinding, heat at 300℃ for 5 hours in the first stage under Ar / H2 gas protection (Ar to H2 volume ratio 95:5), and then heat at 600℃ for 8 hours in the second stage to obtain the sintered material. S4. The sintered material is ground and sieved to obtain sodium iron pyrophosphate cathode material.

[0030] The steps for preparing a sodium-ion battery using the sodium iron pyrophosphate cathode material of this embodiment include: A1. A positive electrode slurry is prepared by homogenizing PVDF, conductive carbon black, sodium iron pyrophosphate positive electrode material and NMP solvent, and then coated, rolled and punched to obtain a positive electrode sheet. A2. After homogenizing CMC, conductive carbon black, hard carbon, SBR and deionized water, a negative electrode slurry is prepared. After coating, rolling and punching, a negative electrode sheet is prepared. A3. A sodium-ion battery is produced by stacking positive electrode, negative electrode and separator, and then encapsulating, injecting electrolyte, forming and capacity testing.

[0031] Example 2 S1. Prepare sodium hydroxide, ferric nitrate, and phosphoric acid in a molar ratio of 2:3:1. Weigh citric acid at 2% of the total mass of solid materials, carbon nanotubes at 0.5% of the total mass of solid materials, polyethylene glycol at 0.2% of the total mass of the dispersion, and deionized water at a mass ratio of 12:1 to the total mass of solid materials. Add the solid materials to the deionized water and disperse them evenly to obtain the dispersion. S2. Spray dry the dispersion to obtain the precursor material; S3. Lanthanum nitrate is added to the precursor material, with the mass of lanthanum nitrate being 0.2% of the mass of the precursor material. After grinding, the material is heated at 300°C for 7 hours in the first stage and at 600°C for 6 hours in the second stage under Ar / H2 gas (Ar to H2 volume ratio 90:10) protection to obtain the sintered material. S4. The sintered material is ground and sieved to obtain sodium iron pyrophosphate cathode material.

[0032] The steps for preparing a sodium-ion battery using the sodium iron pyrophosphate cathode material of this embodiment include: A1. A positive electrode slurry is prepared by homogenizing PVDF, conductive carbon black, sodium iron pyrophosphate positive electrode material and NMP solvent, and then coated, rolled and punched to obtain a positive electrode sheet. A2. After homogenizing CMC, conductive carbon black, hard carbon, SBR and deionized water, a negative electrode slurry is prepared. After coating, rolling and punching, a negative electrode sheet is prepared. A3. A sodium-ion battery is produced by stacking positive electrode, negative electrode and separator, and then encapsulating, injecting electrolyte, forming and capacity testing.

[0033] Example 3 S1. Prepare a mixture of sodium hydroxide, ferric nitrate, and phosphoric acid in a molar ratio of 4:3:4. Weigh sucrose at 3% of the total mass of the solid materials and polyvinylpyrrolidone at 0.1% of the total mass of the dispersion. Weigh deionized water at a ratio of 15:1 (mass of deionized water to total mass of solid materials). Add the solid materials to the deionized water and disperse them evenly to obtain the dispersion. S2. Spray dry the dispersion to obtain the precursor material; S3. Add neodymium nitrate to the precursor material, the mass of neodymium nitrate being 0.2% of the mass of the precursor material. After grinding, heat at 300℃ for 6 hours in the first stage under Ar / H2 gas protection (Ar to H2 volume ratio 93:7), and then heat at 700℃ for 5 hours in the second stage to obtain the sintered material. S4. The sintered material is ground and sieved to obtain sodium iron pyrophosphate cathode material.

[0034] The steps for preparing a sodium-ion battery using the sodium iron pyrophosphate cathode material of this embodiment include: A1. A positive electrode slurry is prepared by homogenizing PVDF, conductive carbon black, sodium iron pyrophosphate positive electrode material and NMP solvent, and then coated, rolled and punched to obtain a positive electrode sheet. A2. After homogenizing CMC, conductive carbon black, hard carbon, SBR and deionized water, a negative electrode slurry is prepared. After coating, rolling and punching, a negative electrode sheet is prepared. A3. A sodium-ion battery is produced by stacking positive electrode, negative electrode and separator, and then encapsulating, injecting electrolyte, forming and capacity testing.

[0035] Comparative Example 1 This comparative example did not include any surfactants or lanthanide materials; all other aspects were the same as in Example 1.

[0036] Cyclic tests were conducted on the batteries of Examples 1-3 and Comparative Example 1, and the results are shown in Table 1. Compared with the sodium-ion battery prepared in Comparative Example 1, the sodium-ion batteries prepared with the materials of Examples 1, 2 and 3 showed good high-temperature cycling performance and room-temperature cycling performance, indicating that the materials of Examples 1-3 have good structural stability.

[0037] Table 1

[0038] In summary, this application utilizes a lanthanide oxide coating layer on the surface of sodium iron pyrophosphate to effectively increase the stability of the positive electrode active material and suppress side reactions, thereby effectively improving the electrical performance of sodium-ion batteries. Furthermore, the addition of surfactants to the raw materials ensures uniform dispersion, allowing for the regulation of the precursor material's structure and composition, thus effectively increasing the yield and obtaining sodium iron pyrophosphate material with excellent kinetic properties.

[0039] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A sodium iron pyrophosphate cathode material, characterized in that, It includes sodium iron pyrophosphate and a lanthanide oxide coating layer located on the outer surface of the sodium iron pyrophosphate.

2. The sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The D of the sodium iron pyrophosphate 50 particle size of 6-8 μm, specific surface area of 4-6 m 2 / g-6 m 2 / g.

3. The sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The thickness of the lanthanide oxide coating is 1 nm to 10 nm.

4. A method for preparing a sodium iron pyrophosphate cathode material, characterized in that, include: Solid materials are added to deionized water according to a preset ratio and dispersed evenly to obtain a dispersion. The solid materials include sodium source, iron source, phosphorus source, carbon source and surfactant. The dispersion is spray-dried to obtain a precursor material; The precursor material is mixed and ground with lanthanide material and then sintered under gas protection to obtain sintered material; The sintered material was ground and sieved to obtain sodium iron pyrophosphate cathode material.

5. The method for preparing a sodium iron pyrophosphate cathode material according to claim 4, characterized in that, The sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium acetate, sodium phosphate, sodium citrate, and sodium malate. The iron source includes at least one of ferrous oxalate, ferrous acetate, ferric phosphate, and ferric nitrate. The phosphorus source includes at least one of sodium dihydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, iron phosphate, and pyrophosphate. The carbon source includes at least one of glucose, sucrose, citric acid, starch, conductive carbon black, carbon nanotubes, mesophase carbon microspheres, and graphene. The surfactant includes at least one of polyethylene glycol, ammonium polyacrylate, and polyvinylpyrrolidone.

6. The method for preparing a sodium iron pyrophosphate cathode material according to claim 4, characterized in that, The molar ratio of sodium source, iron source and phosphorus source is (3-4):(2-3):(3-4); The mass of the carbon source is 2%-9% of the total mass of the solid material; The mass of the surfactant is 0.1%-5% of the total mass of the dispersion; The ratio of the mass of deionized water to the total mass of the solid material is (10-15):

1.

7. The method for preparing a sodium iron pyrophosphate cathode material according to claim 4, characterized in that, The lanthanide material includes at least one of lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, lanthanum acetate, cerium acetate, neodymium acetate, and praseodymium acetate, and the mass of the lanthanide material is 0.05%-0.5% of the mass of the precursor material.

8. The method for preparing a sodium iron pyrophosphate cathode material according to claim 4, characterized in that, The gas protection uses a mixture of Ar and H2, with H2 accounting for 5-10% of the volume of the mixture.

9. The method for preparing a sodium iron pyrophosphate cathode material according to claim 4, characterized in that, The sintering process employs a two-stage heating method, including: Heat at 300℃ for 5-8 hours; Heat at 400℃-700℃ for 6-10 hours.

10. A sodium-ion battery, characterized in that, Its positive electrode material is a sodium iron pyrophosphate positive electrode material as described in any one of claims 1-3.

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