Graphene self-supporting intercalated sodium iron manganese phosphate pyrophosphate cathode material and application

Abstract

The application discloses a graphene self-supporting intercalation sodium iron manganese phosphate pyrophosphate positive electrode material and application, and a preparation method of the positive electrode material comprises the following steps: dissolving soluble raw materials in deionized water to prepare a precursor solution, wherein the soluble raw materials comprise sodium acetate, manganese acetate, ferrous dihydrogen phosphate or disodium hydrogen phosphate, manganese dihydrogen phosphate and ferrous acetate; adding a carbon source and graphene into the precursor solution, or further adding a dispersing agent, and stirring and sand milling to obtain a positive electrode slurry, wherein the carbon source comprises one or two of starch, glucose and sucrose, and the polymeric monomer of the dispersing agent comprises ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene and styrene; the positive electrode slurry is spray dried and briquetted, calcined at 500-700 DEG C for 10-18h under the protection of nitrogen, and crushed to obtain the positive electrode material with a particle size of 1-6um. The material is excellent in conductivity and rate performance, is suitable for sodium ion batteries, and promotes performance breakthrough and industrialization of the positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a graphene-supported intercalated sodium iron manganese pyrophosphate cathode material and its application. Background Technology

[0002] Compared to lithium, sodium is extremely abundant in the Earth's crust and shares similar chemical properties with lithium, both exhibiting excellent electrochemical activity. This makes sodium-ion batteries a promising candidate for energy storage due to their significant cost advantages and application prospects. Sodium-ion batteries not only hold the potential to become an ideal alternative to lithium-ion batteries in large-scale energy storage, but also, due to their controllable cost and high safety, are ideal for short-distance transportation applications such as electric two-wheelers and low-speed electric vehicles, possessing broad market potential.

[0003] As a core component of sodium-ion batteries, the performance and cost of cathode materials determine the overall battery performance. Currently, mainstream sodium-ion battery cathode materials are divided into three categories: transition metal oxides, Prussian blue compounds, and polyanionic compounds. Among them, layered transition metal oxides have mature technology, are already in mass production, and have low cost, making them the current mainstream; however, their cycle performance needs improvement, showing a significant disadvantage compared to the other two types of materials. Prussian blue compounds contain structural water, which can easily cause problems during battery use and poses environmental risks, leading most manufacturers to abandon research and production. Polyanionic compounds mainly include iron-based phosphates and vanadium-based phosphates. Vanadium-based materials are not involved in production or application by most domestic companies due to their high cost and toxicity; iron-based phosphate materials have received widespread attention due to their low cost and environmental friendliness. Among iron-based phosphate materials, sodium iron manganese pyrophosphate, i.e., Na4MnFe2(PO4)2P2O7, has become one of the most promising cathode materials for sodium-ion batteries due to its high voltage platform, excellent rate performance, and cycle performance.

[0004] However, sodium iron manganese pyrophosphate inherently suffers from poor electrical conductivity, typically requiring carbon coating to improve electron conduction efficiency. Furthermore, due to variations in existing synthesis methods, such as precursor preparation and calcination parameters, the prepared materials exhibit significant differences in microstructure, particle size distribution, and electrochemical performance, making it difficult to achieve stable and controllable performance. In addition, the compatibility of dispersants during material preparation also affects material performance. Existing dispersants are not sufficiently compatible with this iron-based phosphate material system, hindering effective optimization of particle dispersion and microstructure control, further exacerbating performance fluctuations and severely impeding the industrial application of this type of material.

[0005] To address the technical challenges of insufficient conductivity, poor synthesis consistency, and inadequate dispersant compatibility in sodium iron manganese pyrophosphate cathode materials, there is an urgent need to develop a modification method that can effectively improve conductivity, optimize microstructure, and ensure stable preparation process, thereby promoting breakthroughs in the performance and industrialization of sodium-ion battery cathode materials. Summary of the Invention

[0006] The purpose of this invention is to provide a graphene-supported intercalated iron manganese phosphate (IMP) cathode material and its application, specifically addressing the problems of poor conductivity, limited effectiveness of relying on traditional carbon coating to improve electron conduction efficiency, unstable microstructure and particle size distribution due to differences in precursor preparation and calcination parameters, large fluctuations in electrochemical performance, insufficient compatibility of existing dispersants with the iron-based phosphate material system, difficulty in optimizing particle dispersion, and thus hindering industrialization.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0008] A cathode material includes a host phase, a graphene phase, and a carbon coating, wherein the host phase is sodium iron manganese pyrophosphate.

[0009] Preferably, the graphene phase comprises graphene particles.

[0010] Preferably, the carbon coating is derived from the pyrolysis of a carbon source.

[0011] Preferably, the carbon source includes one or two of starch, glucose, and sucrose.

[0012] Preferably, sodium iron manganese pyrophosphate is obtained by reacting soluble raw materials.

[0013] Preferably, the soluble raw materials include sodium acetate, manganese acetate and ferrous dihydrogen phosphate or disodium hydrogen phosphate, manganese dihydrogen phosphate and ferrous acetate.

[0014] Preferably, the particle size of the positive electrode material is 1-6 μm.

[0015] The host phase, sodium iron manganese pyrophosphate, is generated by reacting sodium acetate, manganese acetate, and ferrous dihydrogen phosphate or disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate with specific soluble raw materials. This ensures the purity of the components and the integrity of crystallization, providing a high-voltage platform and basic electrochemical stability for the material. The graphene phase consists of graphene particles that can construct a continuous self-supporting conductive network. At the same time, the intercalation between the crystal layers of the host phase optimizes the sodium ion insertion and extraction channels, significantly improving electron and ion transport efficiency. The carbon coating is derived from the pyrolysis of starch, glucose, or sucrose and tightly covers the surface of the host phase particles. This not only helps to enhance conductivity but also inhibits particle agglomeration and protects the host phase structure from electrolyte erosion. The 1-6μm particle size design shortens the sodium ion transport path and facilitates uniform coating of the cathode slurry. Ultimately, this cathode material possesses excellent rate performance, cycle stability, and preparation consistency, making it suitable for the application requirements of sodium-ion batteries in energy storage and short-distance transportation.

[0016] Preferably, the molar ratio of sodium acetate to manganese acetate is 2:0.5-1.5.

[0017] Preferably, the molar ratio of ferrous dihydrogen phosphate to manganese acetate is 2:0.5-1.5.

[0018] Preferably, the molar ratio of disodium hydrogen phosphate to manganese dihydrogen phosphate is 2:0.5-1.5.

[0019] Preferably, the molar ratio of ferrous acetate to manganese dihydrogen phosphate is 2:0.5-1.5.

[0020] Preferably, the size of the graphene particles is 200-400 nm.

[0021] Preferably, the mass ratio of graphene to carbon source is 1:1-3.

[0022] Preferably, the positive electrode material is obtained by calcining the positive electrode slurry at high temperature and then pulverizing it.

[0023] Preferably, the positive electrode slurry includes a dispersant.

[0024] Preferably, the polymeric monomers of the dispersant include ethyl 3-(trifluoromethyl)butenoate and 1,4-dicyano-2-butene.

[0025] Preferably, the mass ratio of dispersant to carbon source is 1:1-10.

[0026] Preferably, the mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:0.5-2.5.

[0027] In the copolymerization system of the dispersant, the ester group of ethyl 3-(trifluoromethyl)butenoate has strong polarity and can form a stable adsorption with the surface of sodium iron manganese pyrophosphate cathode material particles, so that the copolymer dispersant molecules are firmly attached to the particle surface, providing a basic adsorption guarantee for inhibiting particle agglomeration. The cyano group of 1,4-dicyano-2-butene also has polarity and can promote the formation of a three-dimensional extended structure of the dispersant molecular chain, constructing an effective steric barrier on the outside of the adsorption layer on the particle surface, physically preventing adjacent particles from approaching and contacting each other, and further enhancing the agglomeration inhibition effect. It can enable the dispersant to form a stable dispersion system on the surface of cathode material particles, effectively optimizing particle dispersibility and particle size uniformity, creating favorable microstructural conditions for the subsequent construction of graphene self-supporting conductive network and the improvement of sodium ion transport efficiency.

[0028] Preferably, the positive electrode slurry is obtained by sand milling.

[0029] Preferably, the grinding conditions are 25-35℃ and 2000-3000rpm, and the grinding time is 0.5-1h.

[0030] Preferably, the high-temperature calcination temperature is 500-700℃, and the high-temperature calcination time is 10-18h.

[0031] Preferably, the pulverization includes air jet milling, wherein the air jet milling inlet pressure is 0.7-0.9 MPa and the classifier speed is 10000-14000 rpm.

[0032] A sodium-ion battery, comprising a positive electrode material.

[0033] More preferably, the comonomer includes ethyl 4-vinylphenylphenate, and the mass ratio of ethyl 3-(trifluoromethyl)butenoate to ethyl 4-vinylphenylphenate is 3:0.5-2.5. The introduction of ethyl 4-vinylphenylphenate can significantly enhance the adsorption and binding force between the dispersant and the bulk phase of the cathode material, preventing the dispersant from falling off the particle surface during subsequent milling and calcination, and ensuring the stability of the dispersion effect; at the same time, it can build a more three-dimensional steric hindrance layer on the particle surface, which is easier to form a uniform and thick barrier structure than monomers such as styrene, further weakening the van der Waals attraction between particles and effectively inhibiting agglomeration; it improves the compatibility of the dispersant with carbon sources such as graphene and starch / glucose, promotes the uniform dispersion of each component in the cathode slurry, and provides a basis for the subsequent formation of a continuous conductive network, ensuring the uniformity of material particle size, and improving the electrochemical performance of the cathode material.

[0034] This invention also provides a method for preparing a precursor solution, comprising:

[0035] The soluble raw material is dissolved in deionized water and stirred at 200-400 rpm for 1-3 hours to obtain the precursor solution.

[0036] Preferably, the soluble raw materials include sodium acetate, manganese acetate and ferrous dihydrogen phosphate.

[0037] Preferably, the molar ratio of sodium acetate to manganese acetate is 2:0.5-1.5.

[0038] Preferably, the molar ratio of ferrous dihydrogen phosphate to manganese acetate is 2:0.5-1.5.

[0039] Preferably, the molar volume ratio of sodium acetate to deionized water is 16 mol: 3-8 L.

[0040] More preferably, the soluble raw materials include disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate.

[0041] More preferably, the molar ratio of disodium hydrogen phosphate to manganese dihydrogen phosphate is 2:0.5-1.5.

[0042] More preferably, the molar ratio of ferrous acetate to manganese dihydrogen phosphate is 2:0.5-1.5.

[0043] More preferably, the molar volume ratio of disodium hydrogen phosphate to deionized water is 16 mol: 3-8 L.

[0044] The present invention also provides a method for preparing a dispersant, comprising:

[0045] The comonomer was dispersed in xylene, and benzoyl peroxide was added. The mixture was stirred for 40 min under nitrogen protection at 100 °C and 300 rpm, and the reaction was stopped by adding ethanol to obtain a copolymer solution. The copolymer solution was rotary evaporated at 55-65 °C and -0.08--0.1 MPa to remove xylene, and the copolymer solid was obtained. The copolymer solid was added to a precipitant, stirred to precipitate, filtered, and vacuum dried at 75-85 °C for 5-8 h to obtain a dispersant.

[0046] Preferably, the comonomers include ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene.

[0047] Preferably, the mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:0.5-2.5.

[0048] Preferably, the mass ratio of styrene to ethyl 3-(trifluoromethyl)butenoate is 0.5-2.5:3.

[0049] Preferably, the mass-to-volume ratio of ethyl 3-(trifluoromethyl)butenoate to xylene is 1 g: 3-10 mL.

[0050] Preferably, the mass ratio of ethyl 3-(trifluoromethyl)butenoate to benzoyl peroxide is 80:0.8-1.2.

[0051] Preferably, the mass-to-volume ratio of ethyl 3-(trifluoromethyl)butenoate to ethanol is 1 g: 2-5 mL.

[0052] Preferably, the precipitant is anhydrous ethanol.

[0053] Preferably, the mass ratio of copolymer solid to precipitant is 1:3-10.

[0054] More preferably, the comonomers include ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and ethyl 4-vinylphenylacetate.

[0055] More preferably, the mass ratio of ethyl 3-(trifluoromethyl)butenoate to ethyl 4-vinylphenylacetate is 3:0.5-2.5.

[0056] This invention also provides a method for preparing a positive electrode slurry, comprising:

[0057] Carbon source and graphene are added to the precursor solution and stirred at 200-400 rpm for 20-40 min to form a pretreated slurry. The pretreated slurry is then milled at 25-35℃ and 2000-3000 rpm for 0.5-1 h to obtain the positive electrode slurry.

[0058] Preferably, the carbon source includes one or two of starch, glucose, and sucrose.

[0059] Preferably, the mass ratio of the precursor solution to the carbon source is 90:3-7.

[0060] Preferably, the graphene particle size is 200-400 nm.

[0061] Preferably, the mass ratio of graphene to carbon source is 1:1-3.

[0062] Preferably, the grinding media are zirconia beads with a particle size of 0.5-1 mm.

[0063] Preferably, the mass ratio of zirconium oxide beads to carbon source is 500-2000:1.

[0064] More preferably, a dispersant may also be added to the precursor solution.

[0065] More preferably, the mass ratio of dispersant to carbon source is 1:1-10.

[0066] This invention also provides a method for preparing a cathode material, comprising:

[0067] The positive electrode slurry is spray-dried and pressed at 15-25 MPa for 3-7 min to obtain a block material. The block material is heated to 500-700℃ at a rate of 3-7℃ / min under nitrogen protection and held at that temperature for 10-18 h. After cooling to room temperature, it is coarsely crushed by jaw crusher and then pulverized by air jet milling to obtain the positive electrode material.

[0068] Preferably, the inlet air temperature for spray drying is 195-205℃.

[0069] Preferably, the outlet air temperature of the spray dryer is 85-95℃.

[0070] Preferably, the feed rate for spray drying is 45-55 L / h.

[0071] Preferably, the rotation speed of the atomizing disc in the spray dryer is 14,000-16,000 rpm.

[0072] Preferably, the inlet pressure of the air jet mill is 0.7-0.9 MPa.

[0073] Preferably, the speed of the classifier wheel in the air jet mill is 10,000-14,000 rpm.

[0074] Preferably, the particle size of the positive electrode material is 1-6 μm.

[0075] This invention utilizes a graphene self-supporting intercalation structure to construct a continuous conductive network and optimizes sodium ion insertion / extraction channels. High-purity sodium iron manganese pyrophosphate (SO4) is generated by reacting sodium acetate, manganese acetate, and ferrous dihydrogen phosphate or disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate as soluble raw materials. A special dispersant is prepared by copolymerizing ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene to regulate particle dispersibility. A carbon coating is formed by pyrolysis of starch, glucose, or sucrose as a carbon source to assist conductivity and protect the main phase. Therefore, this invention has the following beneficial effects: it effectively solves the technical pain points of traditional sodium iron manganese pyrophosphate, such as poor conductivity, insufficient synthesis consistency, and lack of dispersant compatibility. The material exhibits significantly improved electron and ion transport efficiency, uniform particle size and stable dispersion, high discharge capacity ratio, strong cycle stability, and good controllability of the preparation process, meeting the needs of large-scale production. Therefore, this invention relates to a graphene-supported intercalated sodium iron manganese pyrophosphate cathode material and its application, which exhibits excellent performance, stable preparation, and can promote the industrial application of sodium-ion batteries in energy storage and short-distance transportation. Attached Figure Description

[0076] Figure 1 This is a schematic diagram showing the particle size test results of the cathode material.

[0077] Figure 2 The results are the charge transfer resistance test results for the positive electrode material.

[0078] Figure 3 This is a schematic diagram of the rate performance test results for the cathode material. Detailed Implementation

[0079] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] The concepts involved in this application will first be described with reference to the accompanying drawings. It should be noted that the following descriptions of various concepts are only for the purpose of making the content of this application easier to understand and do not constitute a limitation on the scope of protection of this application; furthermore, the embodiments and features in the embodiments of this application can be combined with each other unless otherwise specified. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0081] Example 1:

[0082] Preparation of the precursor solution: Sodium acetate, manganese acetate, and ferrous dihydrogen phosphate were dissolved in deionized water and stirred at 300 rpm for 2 h to obtain the precursor solution. The molar ratio of sodium acetate to manganese acetate was 2:1, the molar ratio of ferrous dihydrogen phosphate to manganese acetate was 2:1, and the molar volume ratio of sodium acetate to deionized water was 16 mol: 5 L.

[0083] Preparation of the positive electrode slurry: Starch, glucose, and graphene were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 1 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the molar amount of sodium acetate, with a molar mass ratio of sodium acetate to starch of 32 mol:75 g; the mass ratio of starch to glucose was 1:1; the mass ratio of graphene to starch was 2:1; the graphene particle size was 200 nm; the milling medium was zirconia beads with a particle size of 0.8 mm, and the mass ratio of zirconia beads to starch was 1200:1.

[0084] Preparation of the positive electrode material: The positive electrode slurry was spray-dried and pressed at 20 MPa for 5 min to obtain a block material. The block material was heated to 500℃ at a rate of 5℃ / min and held for 18 h under nitrogen protection. After cooling to room temperature, it was coarsely crushed by a jaw crusher and then pulverized by an air jet mill to obtain the positive electrode material. The inlet air temperature of the spray dryer was 200℃, the outlet air temperature was 90℃, the feed rate was 50 L / h, and the atomizing disc speed was 15000 rpm. The inlet air pressure of the air jet mill was 0.8 MPa, and the classifier speed was 12000 rpm.

[0085] Example 2:

[0086] Preparation of the precursor solution: Disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate were dissolved in deionized water and stirred at 300 rpm for 2 h to obtain the precursor solution. The molar ratio of disodium hydrogen phosphate to manganese dihydrogen phosphate was 2:1, the molar ratio of ferrous acetate to manganese dihydrogen phosphate was 2:1, and the molar volume ratio of disodium hydrogen phosphate to deionized water was 16 mol: 5 L.

[0087] Preparation of the positive electrode slurry: Starch, sucrose, and graphene were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 0.5 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the mass of disodium hydrogen phosphate, with a molar mass ratio of disodium hydrogen phosphate to starch of 4 mol:25 g; the mass ratio of starch to sucrose was 1:1; and the mass ratio of graphene to starch was 1:2. The graphene particles were 400 nm in size, and the milling medium was zirconia beads with a particle size of 0.8 mm, with a mass ratio of zirconia beads to starch of 900:1.

[0088] Preparation of the positive electrode material: The positive electrode slurry was spray-dried and pressed at 20 MPa for 5 min to obtain a block material. The block material was heated to 700℃ at a rate of 5℃ / min and held at that temperature for 10 h under nitrogen protection. After cooling to room temperature, it was coarsely crushed by a jaw crusher and then pulverized by an air jet mill to obtain the positive electrode material. The inlet air temperature of the spray dryer was 200℃, the outlet air temperature was 90℃, the feed rate was 50 L / h, and the atomizing disc speed was 15000 rpm. The inlet air pressure of the air jet mill was 0.8 MPa, and the classifier speed was 12000 rpm.

[0089] Example 3:

[0090] Preparation of the precursor solution: Sodium acetate, manganese acetate, and ferrous dihydrogen phosphate were dissolved in deionized water and stirred at 300 rpm for 2 h to obtain the precursor solution. The mass ratio of sodium acetate to manganese acetate was 2:1, the molar ratio of ferrous dihydrogen phosphate to manganese acetate was 2:1, and the molar volume ratio of sodium acetate to deionized water was 16 mol: 5 L.

[0091] Preparation of the positive electrode slurry: Glucose, sucrose, and graphene were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 1 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the molar amount of sodium acetate, with a molar mass ratio of sodium acetate to glucose of 32 mol:125 g; a mass ratio of glucose to sucrose of 1:1; and a mass ratio of graphene to glucose of 4:5. The graphene particles were 300 nm in size, and the milling medium was zirconia beads with a particle size of 0.8 mm, with a mass ratio of zirconia beads to glucose of 1728:1.

[0092] Preparation of the positive electrode material: The positive electrode slurry was spray-dried and pressed at 20 MPa for 5 min to obtain a block material. The block material was heated to 600℃ at a rate of 5℃ / min and held for 16 h under nitrogen protection. After cooling to room temperature, it was coarsely crushed by a jaw crusher and then pulverized by an air jet mill to obtain the positive electrode material. The inlet air temperature of the spray dryer was 200℃, the outlet air temperature was 90℃, the feed rate was 50 L / h, and the atomizing disc speed was 15000 rpm. The inlet air pressure of the air jet mill was 0.8 MPa, and the classifier speed was 12000 rpm.

[0093] Example 4:

[0094] Preparation of the precursor solution: Disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate were dissolved in deionized water and stirred at 300 rpm for 2 h to obtain the precursor solution. The molar ratio of disodium hydrogen phosphate to manganese dihydrogen phosphate was 2:1, the molar ratio of ferrous acetate to manganese dihydrogen phosphate was 2:1, and the molar volume ratio of disodium hydrogen phosphate to deionized water was 16 mol: 5 L.

[0095] Preparation of the positive electrode slurry: Glucose and graphene were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 0.7 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the mass of disodium hydrogen phosphate, with a molar mass ratio of disodium hydrogen phosphate to glucose of 8 mol:175 g; the mass ratio of graphene to glucose was 2:7; the graphene particle size was 400 nm; the milling medium was zirconia beads with a particle size of 0.8 mm, and the mass ratio of zirconia beads to glucose was 231:1.

[0096] Preparation of the positive electrode material: The positive electrode slurry was spray-dried and pressed at 20 MPa for 5 min to obtain a block material. The block material was heated to 500℃ at a rate of 5℃ / min and held for 12 h under nitrogen protection. After cooling to room temperature, it was coarsely crushed by a jaw crusher and then pulverized by an air jet mill to obtain the positive electrode material. The inlet air temperature of the spray dryer was 200℃, the outlet air temperature was 90℃, the feed rate was 50 L / h, and the atomizing disc speed was 15000 rpm. The inlet air pressure of the air jet mill was 0.8 MPa, and the classifier speed was 12000 rpm.

[0097] Example 5: The only difference between this example and Example 1 is the preparation of the positive electrode slurry.

[0098] Preparation of dispersant: Ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene and styrene were dispersed in xylene, benzoyl peroxide was added, and the mixture was stirred for 40 min under nitrogen protection at 100 °C and 300 rpm. The reaction was stopped by adding ethanol to obtain a copolymer solution. The copolymer solution was rotary evaporated at 60 °C and -0.09 MPa to remove xylene, and the copolymer solid was obtained. The copolymer solid was added to a precipitant, stirred to precipitate, filtered, and vacuum dried at 80 °C for 6 h to obtain the dispersant. The mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:1; the mass ratio of styrene to ethyl 3-(trifluoromethyl)butenoate is 2:3; the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to xylene is 1 g:5 mL; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to benzoyl peroxide is 80:1; and the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to ethanol is 1 g:3 mL. Anhydrous ethanol is used as the precipitant, and the mass ratio of the copolymer solid to the precipitant is 1:5.

[0099] Preparation of the positive electrode slurry: Starch, glucose, graphene, and dispersant were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 1 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the molar amount of sodium acetate, with a molar mass ratio of sodium acetate to starch of 32 mol:75 g; the mass ratio of starch to glucose was 1:1; the mass ratio of graphene to starch was 2:1; and the mass ratio of dispersant to starch was 1:5. The graphene particles were 200 nm in size, and the milling medium was zirconia beads with a particle size of 0.8 mm, with a mass ratio of zirconia beads to starch of 1200:1.

[0100] Example 6: The only difference between this example and Example 5 is the preparation of the dispersant.

[0101] Preparation of dispersant: Ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene and styrene were dispersed in xylene, benzoyl peroxide was added, and the mixture was stirred for 40 min under nitrogen protection at 100 °C and 300 rpm. The reaction was stopped by adding ethanol to obtain a copolymer solution. The copolymer solution was rotary evaporated at 60 °C and -0.09 MPa to remove xylene, and the copolymer solid was obtained. The copolymer solid was added to a precipitant, stirred to precipitate, filtered, and vacuum dried at 80 °C for 6 h to obtain the dispersant. The mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:2; the mass ratio of styrene to ethyl 3-(trifluoromethyl)butenoate is 2:3; the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to xylene is 1 g:5 mL; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to benzoyl peroxide is 80:1; and the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to ethanol is 1 g:3 mL. Anhydrous ethanol is used as the precipitant, and the mass ratio of the copolymer solid to the precipitant is 1:5.

[0102] Example 7: The only difference between this example and Example 5 is the preparation of the dispersant.

[0103] Preparation of dispersant: Ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene and ethyl 4-vinylphenylacetate were dispersed in xylene, benzoyl peroxide was added, and the mixture was stirred for 40 min under nitrogen protection at 100 °C and 300 rpm. The reaction was stopped by adding ethanol to obtain a copolymer solution. The copolymer solution was rotary evaporated at 60 °C and -0.09 MPa to remove xylene, and the copolymer solid was obtained. The copolymer solid was added to a precipitant, stirred to precipitate, filtered, and vacuum dried at 80 °C for 6 h to obtain the dispersant. The mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:2; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to ethyl 4-vinylphenylacetate is 3:1; the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to xylene is 1 g:5 mL; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to benzoyl peroxide is 80:1; and the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to ethanol is 1 g:3 mL. Anhydrous ethanol is used as the precipitant, and the mass ratio of the copolymer solid to the precipitant is 1:5.

[0104] Example 8: The only difference between this example and Example 5 is the preparation of the dispersant.

[0105] Preparation of dispersant: Ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene and ethyl 4-vinylphenylacetate were dispersed in xylene, benzoyl peroxide was added, and the mixture was stirred for 40 min under nitrogen protection at 100 °C and 300 rpm. The reaction was stopped by adding ethanol to obtain a copolymer solution. The copolymer solution was rotary evaporated at 60 °C and -0.09 MPa to remove xylene, and the copolymer solid was obtained. The copolymer solid was added to a precipitant, stirred to precipitate, filtered, and vacuum dried at 80 °C for 6 h to obtain the dispersant. The mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:2; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to ethyl 4-vinylphenylacetate is 3:2; the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to xylene is 1 g:5 mL; the mass ratio of ethyl 3-(trifluoromethyl)butenoate to benzoyl peroxide is 80:1; and the mass-volume ratio of ethyl 3-(trifluoromethyl)butenoate to ethanol is 1 g:3 mL. Anhydrous ethanol is used as the precipitant, and the mass ratio of the copolymer solid to the precipitant is 1:5.

[0106] Comparative Example 1: The only difference between this comparative example and Example 5 is that ethyl 3-(trifluoromethyl)butenoate was not used in the preparation of the dispersant.

[0107] Comparative Example 2: The only difference between this comparative example and Example 5 is that 1,4-dicyano-2-butene was not used in the preparation of the dispersant.

[0108] Comparative Example 3: This comparative example differs from Example 5 in the preparation of the positive electrode slurry.

[0109] Preparation of the positive electrode slurry: Starch, glucose, graphene, and dispersant were added to the precursor solution and stirred at 300 rpm for 30 min to form a pretreated slurry. The pretreated slurry was then milled at 30℃ and 2500 rpm for 1 h to obtain the positive electrode slurry. The mass of the precursor solution was measured by the molar amount of sodium acetate, with a molar mass ratio of sodium acetate to starch of 32 mol:75 g; the mass ratio of starch to glucose was 1:1; the mass ratio of graphene to starch was 2:1; the dispersant was polyvinylpyrrolidone, with a mass ratio of dispersant to starch of 1:5; the graphene particle size was 200 nm; the milling medium was zirconia beads with a particle size of 0.8 mm, with a mass ratio of zirconia beads to starch of 1200:1.

[0110] Experimental Example 1: Particle size test of cathode material.

[0111] Test samples: cathode materials prepared in each embodiment and comparative example.

[0112] Test method: 0.1g of positive electrode material was added to beakers containing 50mL of deionized water and 0.1mL of anhydrous ethanol, respectively. The mixture was ultrasonically dispersed at 300W for 15min to form a uniform suspension, ensuring that there were no obvious agglomerated particles. The suspension was then slowly poured into the sample cell of the laser particle size analyzer. The test temperature was set to 25℃, the stirring rate to 1500rpm, and the test range to 0.1-10μm. The instrument was calibrated using a standard particle size sample before each test to obtain the average particle size of the positive electrode material.

[0113] The particle size test results of the cathode material prepared by this invention are as follows: Figure 1 As shown, Examples 1-4 control the particle size through basic preparation processes such as sand milling and air jet milling, with an average particle size between 3.5-4.0 μm. This indicates that the basic processes can achieve the required powder particle size, but lack the inhibitory effect of dispersants on particle agglomeration, resulting in an overall larger particle size and a relatively wider distribution. Example 5 introduces a dispersant formed by copolymerizing ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene in the preparation of the positive electrode slurry. The dispersant molecules can adsorb onto the particle surface to form steric hindrance, preventing particle agglomeration. Particle agglomeration was reduced, resulting in an average particle size of 2.8 μm, a significant decrease compared to Example 1. Example 6 adjusted the mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene in the dispersant to 3:2, optimizing the adsorption strength and steric hindrance balance of the dispersant molecules, thus improving the inhibition of particle agglomeration and further reducing the average particle size to 2.5 μm. Example 7 replaced styrene in the dispersant with ethyl 4-vinylphenylphenylacetate and controlled its mass ratio to 1,4-dicyano-2-butene to be 1: The ester groups in ethyl 1,4-vinylphenylacetate enhance the compatibility between the dispersant and the cathode material particles, further reducing agglomeration and lowering the average particle size to 2.3 μm. In Example 8, the mass ratio of ethyl 4-vinylphenylacetate to 1,4-dicyano-2-butene was increased to 2:1, increasing the content of polar groups in the dispersant molecule, achieving optimal particle encapsulation and dispersion, and minimizing the average particle size to 2.1 μm with a more uniform particle size distribution. In Comparative Example 1, 3-(trifluoromethyl) was not used in the dispersant preparation. Ethyl butenoate lacks the strong adsorption effect of fluorine atoms, resulting in a significant decrease in the anchoring ability of the dispersant to the particles, making the particles prone to agglomeration. Comparative Example 2 did not use 1,4-dicyano-2-butene, and the steric hindrance effect of the dispersant molecules was significantly weakened, making the particles prone to agglomeration as well. Comparative Example 3 used polyvinylpyrrolidone as a dispersant, but its molecular structure was poorly compatible with the positive electrode material particles in this system, failing to form a stable adsorption-steric hindrance system and effectively preventing particle agglomeration. The average particle size was higher than that of Example 5.

[0114] Experimental Example 2: Charge transfer resistance test of positive electrode material.

[0115] Test samples: cathode materials prepared in each embodiment and comparative example.

[0116] Test method: The positive electrode materials prepared in each example and comparative example were mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1, respectively. N-methylpyrrolidone solvent was added, and the mixture was stirred at 300 rpm for 2 hours to form a uniform positive electrode slurry. The slurry was uniformly coated onto a 12 μm thick aluminum foil, and after vacuum drying at 80°C for 12 hours, it was pressed with a roller press at a pressure of 10 MPa to obtain a positive electrode sheet with a diameter of 12 mm and an active material loading of approximately 2 mg / cm³. 2 A CR2032 coin-type sodium-ion half-cell was assembled using a positive electrode, a Celgard 2400 separator, a sodium metal sheet, and a 1 mol / L NaPF6 ethylene carbonate / dimethyl carbonate electrolyte. Assembly was completed in an argon-protected glove box, with an ethylene carbonate / dimethyl carbonate volume ratio of 1:1. After standing for 24 hours, the charge transfer resistance was tested using an electrochemical workstation. The test frequency range was set to 10 Hz. -2 -10 5 With an AC signal amplitude of 5mV and a frequency of Hz, the charge transfer resistance of each sample was calculated by fitting the Nyquist curve using ZsimpWin software.

[0117] The charge transfer resistance test results of the positive electrode material prepared in this invention are as follows: Figure 2As shown, Examples 1-4 constructed a basic conductive network based on a graphene self-supporting intercalation structure. The continuous conductive network constructed by graphene particles can effectively improve the electron transport bottleneck of traditional sodium iron manganese pyrophosphate. At the same time, the intercalation structure optimizes the sodium ion insertion / extraction channel, resulting in a lower charge transfer resistance. Example 5 introduced a special dispersant copolymerized from ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene. Its molecules are anchored to the particle surface through strong adsorption, while steric hindrance inhibits agglomeration, making the graphene network more continuous and the contact between the main phase and the conductive agent more uniform, resulting in a decrease in charge transfer resistance compared to Example 1. Example 6 increased the amount of 1,4-dicyano-2-butene to further optimize the adsorption-steric hindrance balance, continuously improving particle dispersibility and interfacial contact efficiency, and improving charge transfer resistance. Examples 7-8 replaced styrene in the dispersant. By co-involving ethyl 4-vinylphenylacetate in polymerization, the ester groups of ethyl 4-vinylphenylacetate enhance the compatibility between the dispersant and the cathode material, not only strengthening the particle dispersion effect but also promoting the tight bonding between the carbon coating and the host phase, further reducing the interfacial charge transfer resistance. Comparative Example 1 did not use ethyl 3-(trifluoromethyl)butenoate, and Comparative Example 2 did not use 1,4-dicyano-2-butene, thus failing to form an effective adsorption-steric hindrance system, resulting in particle agglomeration and a higher charge transfer resistance compared to Example 5. Comparative Example 3 used polyvinylpyrrolidone as a dispersant, which had poor compatibility with this system, failing to improve the continuity of the conductive network and resulting in a high charge transfer resistance value. The dispersant prepared in this invention can effectively solve the defects of high charge transfer resistance and poor conductivity of sodium iron manganese pyrophosphate cathode material by improving particle dispersion and strengthening the continuity of the conductive network, thereby improving electrochemical performance.

[0118] Experimental Example 3: Rate performance test of cathode material.

[0119] Test samples: cathode materials prepared in each embodiment and comparative example.

[0120] Test method: After the sodium-ion battery prepared in Experiment Example 2 was left to stand for 24 hours, its rate performance was tested using a battery testing system. The charge / discharge voltage range was set to 2.0-4.0V. Constant current charge / discharge cycles were performed sequentially at rates of 0.1C, 0.5C, 1C, 2C, and 3C, with 3 cycles per rate. The discharge capacity of the 3rd cycle was taken as the effective capacity at that rate. The effective capacity was calculated using the formula R(%) = C. 3C / C 0.1C ×100% yields the capacity retention rate, where R is the capacity retention rate and C is the capacity retention rate. 3C For 3C rate discharge capacity, C 0.1C The discharge capacity is 0.1C.

[0121] The rate performance test results of the cathode material prepared by this invention are as follows: Figure 3As shown, Example 1 uses a specific structure of graphene-supported intercalated sodium iron manganese pyrophosphate. The continuous conductive network constructed by graphene can effectively reduce electron transport resistance, while the intercalation structure optimizes the sodium ion insertion / extraction channel. Prepared using basic processes, it exhibits excellent rate performance, fully demonstrating the core supporting role of this specific cathode structure in rate performance. In Example 2, the precursor was replaced with disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate, and the carbon source was adjusted to starch and sucrose. The milling time was shortened to 0.5 h, and the higher calcination temperature of 700 °C caused slight shrinkage of some intercalated structures, resulting in a slight increase in sodium ion transport resistance and a decrease in capacity retention compared to Example 1. Example 3 follows the same process. In Example 1, the precursor system was modified by changing the carbon source to a combination of glucose and sucrose. This composite carbon source formed a more uniform carbon coating on the material surface, aiding in improved electron conduction efficiency and resulting in improved capacity retention compared to Example 1. In Example 4, only glucose was used as the carbon source. The uniformity of the carbon coating formed by this single carbon source was slightly worse than that of the composite carbon source, resulting in slightly lower particle dispersion and intercalation structure perfection compared to Example 1. In Example 5, based on the aforementioned specific structure, a dispersant composed of ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene was introduced to further reduce the particle size of the cathode material, optimize particle dispersion, shorten the sodium ion transport path, and improve the internal contact of the electrode, effectively enhancing… Capacity retention rate; Example 6 increased the amount of 1,4-dicyano-2-butene, enhancing the adsorption and steric hindrance of the dispersant on the particles, resulting in a higher capacity retention rate than Example 5; Example 7 introduced ethyl 4-vinylphenylphenylacetate into the dispersant monomer, improving the compatibility between the dispersant and the cathode material, further optimizing the electrode microstructure, and improving the capacity retention rate; Example 8 increased the mass ratio of ethyl 4-vinylphenylphenylacetate to 1,4-dicyano-2-butene to 2:1, increasing the content of polar groups in the dispersant, resulting in the best particle encapsulation and dispersion effect, and combined with the advantages of the graphene self-supporting intercalation structure, achieving the highest capacity retention rate; Comparative Example 1 did not... Using ethyl 3-(trifluoromethyl)butenoate, the dispersant's adsorption capacity for particles was insufficient, failing to effectively optimize electrode dispersion. Comparative Example 2 did not use 1,4-dicyano-2-butene, resulting in the absence of steric hindrance effect in the dispersant, which disrupted the mass transfer efficiency of the positive electrode structure, and the capacity retention rate decreased compared to Example 5. Comparative Example 3 used polyvinylpyrrolidone as a dispersant, but its compatibility with graphene self-supporting intercalated sodium iron manganese pyrophosphate was poor, failing to play a role in dispersion optimization, and the capacity retention rate was lower than that of Example 5. This fully demonstrates that the specific positive electrode structure of the present invention is the core foundation of rate performance, and the dispersant with a specific composition can further maximize the structural advantages, jointly achieving excellent rate performance.

[0122] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the technology of the present invention, and are not intended to limit the implementation methods of the technology of the present invention in any way. Any person skilled in the art can make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in the content of the present invention, but they should still be regarded as the technology or embodiments that are substantially the same as the present invention.

[0123] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this application, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A cathode material, characterized in that: The cathode material comprises a host phase, a graphene phase, and a carbon coating. The host phase is sodium iron manganese pyrophosphate, the graphene phase comprises graphene particles, and the carbon coating is derived from the pyrolysis of a carbon source, wherein the carbon source comprises one or two of starch, glucose, and sucrose. The sodium iron manganese pyrophosphate is obtained by reacting soluble raw materials, wherein the soluble raw materials include sodium acetate, manganese acetate, and ferrous dihydrogen phosphate, or wherein the soluble raw materials include disodium hydrogen phosphate, manganese dihydrogen phosphate, and ferrous acetate. The particle size of the cathode material is 1-6 μm. The positive electrode material is obtained by calcining the positive electrode slurry at high temperature and then pulverizing it. The method for preparing the positive electrode slurry includes dissolving soluble raw materials in deionized water and stirring for 1-3 hours to obtain a precursor solution. Add carbon source, graphene and dispersant to precursor solution and stir for 20-40 min to form pretreated slurry; The pretreated slurry is milled to obtain the positive electrode slurry; The dispersant's monomers include ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and styrene, or the dispersant's monomers include ethyl 3-(trifluoromethyl)butenoate, 1,4-dicyano-2-butene, and ethyl 4-vinylphenylacetate, and the mass ratio of the dispersant to the carbon source is 1:1-10.

2. The cathode material according to claim 1, characterized in that: The molar ratio of sodium acetate to manganese acetate is 2:0.5-1.5, and the molar ratio of ferrous dihydrogen phosphate to manganese acetate is 2:0.5-1.

5.

3. The cathode material according to claim 1, characterized in that: The molar ratio of disodium hydrogen phosphate to manganese dihydrogen phosphate is 2:0.5-1.5, and the molar ratio of ferrous acetate to manganese dihydrogen phosphate is 2:0.5-1.

5.

4. The cathode material according to claim 1, characterized in that: The graphene particles are 200-400 nm in size, and the mass ratio of graphene to carbon source is 1:1-3.

5. The cathode material according to claim 1, characterized in that: The mass ratio of ethyl 3-(trifluoromethyl)butenoate to 1,4-dicyano-2-butene is 3:0.5-2.

5.

6. The cathode material according to claim 1, characterized in that: The grinding conditions are 25-35℃ and 2000-3000rpm, and the grinding time is 0.5-1h.

7. The cathode material according to claim 1, characterized in that: The high-temperature calcination temperature is 500-700℃, and the high-temperature calcination time is 10-18h.

8. The cathode material according to claim 1, characterized in that: The pulverization includes airflow pulverization, wherein the airflow pulverization inlet pressure is 0.7-0.9 MPa and the airflow pulverization stager speed is 10000-14000 rpm.

9. A sodium-ion battery comprising the positive electrode material according to any one of claims 1-8.

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