A sodium-ion battery positive electrode slurry, a positive electrode sheet, a preparation method thereof and a sodium-ion battery

Abstract

The application provides a sodium ion battery positive electrode slurry, a positive electrode pole piece and a preparation method thereof and a sodium ion battery, and relates to the technical field of sodium ion batteries, and comprises a positive electrode active material, a conductive agent, a binder, a composite dispersing agent and a solvent; the composite dispersing agent is a product formed by mechanically mixing an ionic dispersing agent and a polyoxyethylene ether non-ionic dispersing agent or a composite formed by a chemical reaction between the ionic dispersing agent and the polyoxyethylene ether non-ionic dispersing agent, wherein the ionic dispersing agent is polyacrylic acid and its derivatives; and the positive electrode active material is a polyanion material. The ionic dispersing agent of polyacrylic acid and its derivatives and the polyoxyethylene ether non-ionic dispersing agent are used in combination in the positive electrode slurry, so that the positive electrode slurry has good dispersibility and stability; the provided positive electrode slurry has good dispersibility, the positive electrode pole piece has low resistance, and the sodium ion battery has excellent cycle performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion battery positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a sodium-ion battery. Background Technology

[0002] Against the backdrop of rapid global development of new energy technologies, sodium-ion batteries (SIBs) are widely considered an ideal choice for future large-scale energy storage systems due to their abundant resources, low cost, and environmental friendliness. However, the performance of sodium-ion batteries is limited by the selection and optimization of cathode materials. Currently, layered oxides, Prussian blue, and polyanionic materials are considered the most promising cathode materials.

[0003] Polyanionic materials, with their high operating voltage and open, stable structure, exhibit excellent structural and thermal stability, making them a research hotspot for sodium-ion battery cathode materials. However, these materials generally suffer from high resistivity, high specific surface area, small particle size, and high moisture content. This leads to interactions between active material particles in the cathode slurry system, forming large agglomerates and failing to achieve ideal dispersion, thus hindering the formation of uniform conductive pathways. Simultaneously, the viscosity stability of the cathode slurry deteriorates, resulting in poor coating density and electrode resistance consistency, which reduces battery life and safety. Therefore, it is urgent to rationally design cathode slurries to improve the dispersibility and stability of polyanionic materials, reduce electrode resistance, and optimize the cycle performance of sodium-ion batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a sodium-ion battery positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a sodium-ion battery. This positive electrode slurry combines an ionic dispersant of polyacrylic acid and its derivatives with a nonionic dispersant of polyoxyethylene ether. Specifically, it uses the product of polymerization of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid ionic dispersant with bisphenol A polyoxyethylene ether nonionic dispersant as a composite dispersant, and combines it with other raw materials to achieve good dispersibility and stability in the positive electrode slurry. The positive electrode slurry provided by this invention exhibits good dispersibility, low resistance in the positive electrode sheet, and excellent cycle performance of the sodium-ion battery.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a sodium-ion battery positive electrode slurry, comprising: a positive electrode active material, a conductive agent, a binder, a composite dispersant, and a solvent;

[0007] The composite dispersant is a product formed by mechanically mixing an ionic dispersant and a polyoxyethylene ether nonionic dispersant, or a complex formed by chemically reacting an ionic dispersant and a polyoxyethylene ether nonionic dispersant, wherein the ionic dispersant is polyacrylic acid and its derivatives.

[0008] The positive electrode active material is a polyanionic material.

[0009] Furthermore, the mass of the composite dispersant accounts for 0.2%-1.0% of the total mass of the positive electrode active material, conductive agent, binder, and composite dispersant;

[0010] And / or, the ionic dispersant is a copolymer of polyacrylic acid and other polycarboxylic acids or anhydrides;

[0011] And / or, the polyoxyethylene ether nonionic dispersant is an alcohol polyoxyethylene ether or a phenol polyoxyethylene ether;

[0012] And / or, in the complex formed by the chemical reaction between the ionic dispersant and the polyoxyethylene ether nonionic dispersant, the chemical reaction refers to the esterification reaction between the carboxyl group in the ionic dispersant and the hydroxyl group in the nonionic dispersant to form an ester bond;

[0013] And / or, in the preparation of the composite dispersant, the mass ratio of the ionic dispersant to the polyoxyethylene ether nonionic dispersant is (1-2):(2-5);

[0014] And / or, in the positive electrode slurry, the mass ratio of the positive electrode active material, conductive agent, binder and composite dispersant is (93-97):(1-2):(1-4):(0.2-1.0), and the sum of the mass ratios is 100;

[0015] And / or, the solid content of the positive electrode slurry is 55%-65%;

[0016] And / or, the viscosity of the positive electrode slurry is 3000-12000 mPa·S.

[0017] Furthermore, the ionic dispersant is maleic anhydride polyacrylic acid or maleic acid polyacrylic acid;

[0018] And / or, the polyoxyethylene ether nonionic dispersant is one or more of bisphenol A polyoxyethylene ether, glycerol polyoxyethylene ether, furanol methanol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and 1,2-propanediol polyoxypropylene polyoxyethylene ether.

[0019] And / or, the positive electrode active material is selected from at least one of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium vanadium phosphate, and sodium ferric phosphate;

[0020] And / or, the conductive agent is selected from at least one of carbon black, graphene, carbon nanotubes or carbon nanofibers;

[0021] And / or, the adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, or PFA emulsion;

[0022] And / or, the solvent is selected from at least one of N-methylpyrrolidone, ethanol, isopropanol or acetone;

[0023] And / or, the composite dispersant is prepared by adding deionized water to a mixture of an ionic dispersant and a polyoxyethylene ether nonionic dispersant to form a colloid, and then stirring and reacting it under vacuum at 140-160°C for 4-8 hours in the presence of a catalyst; subsequently, the reaction product is post-treated to obtain the composite dispersant.

[0024] Furthermore, the composite dispersant is a complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether.

[0025] Furthermore, the preparation method of the complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether includes the following steps:

[0026] S1: Add polyacrylic acid maleic anhydride or polyacrylic acid maleic acid and bisphenol A polyoxyethylene ether to the reaction vessel at a mass ratio of (1-2):(2-5), then add deionized water to form a gel solution, and stir and react at 140-160℃ under vacuum conditions for 4-8 hours under the action of a catalyst.

[0027] S2: After the reaction is complete, sodium carbonate solution is added to the reaction vessel of step S1 and stirred. Then, the solid product is washed with saturated brine, and the washed solid product is dissolved in ethyl acetate. Finally, the obtained liquid is vacuum dried to remove the ethyl acetate solvent, thus obtaining the complex.

[0028] Furthermore, the solid content of the adhesive solution is 8-12%;

[0029] And / or, the vacuum condition is to evacuate to 0.05-1.0 kPa;

[0030] And / or, the catalyst is p-toluenesulfonic acid, which is added in an amount of 0.6-1% of the total mass of the two reactants;

[0031] And / or, the sodium carbonate solution has a mass concentration of 8-12%, and the amount added is such that the added sodium carbonate is 1 / 5 to 1 / 3 of the mass of the added catalyst;

[0032] And / or, the stirring time in step S2 is 25-35 min.

[0033] A second aspect of the present invention provides a method for preparing the sodium-ion battery cathode slurry described in the first aspect, comprising the following steps:

[0034] The binder, composite dispersant and solvent are mixed and stirred, then a conductive agent is added for sizing, then the positive electrode active material is added for homogenization, and then an appropriate amount of solvent is added to adjust the solid content and viscosity of the slurry to obtain the positive electrode slurry.

[0035] Furthermore, when mixing and stirring the binder, composite dispersant and solvent, the amount of solvent added is controlled so that the solid content of the slurry reaches 5%-8%, and the stirring time is 120-180 minutes;

[0036] The mixing time for applying the adhesive is 90-150 minutes;

[0037] The homogenization time is 120-180 min.

[0038] A third aspect of the present invention provides a positive electrode sheet, comprising a current collector and a positive electrode active layer coated on the surface of the current collector, wherein the positive electrode active layer is made of the positive electrode slurry described in the first aspect of the present invention or a positive electrode slurry prepared by the preparation method described in the second aspect of the present invention.

[0039] A fourth aspect of the present invention provides a sodium-ion battery comprising the positive electrode sheet described in the third aspect.

[0040] The technical solution provided by this invention has the following beneficial effects:

[0041] Ionic dispersants of polyacrylic acid and its derivatives contain abundant carboxyl groups, which can adsorb onto the surface of positive electrode particles, reducing the surface energy of the particles. They also repel surrounding particles through the charge on the particle surface, exhibiting steric hindrance after adsorption to prevent particles from approaching each other, thus creating a composite stabilizing effect. To increase the number of carboxyl groups and improve the effect, the ionic dispersant is a copolymer of polyacrylic acid and other polycarboxylic acids or anhydrides.

[0042] When polyacrylic acid maleic anhydride is selected as the ionic dispersant, maleic anhydride will form maleic acid when it comes into contact with water. Therefore, this dispersant can reduce the impact of the water content of the material on sodium-ion batteries.

[0043] Polyoxyethylene ethers contain -OH groups, which can be effectively adsorbed onto the surfaces of cathode materials and conductive agents, forming hydrogen bonds. For conductive agents with large specific surface areas, to improve the adsorption effect of dispersants, polyoxyethylene ether dispersants are preferred, such as phenolic nonionic dispersants like bisphenol A polyoxyethylene ether. These dispersants can also effectively adsorb onto the conductive agent surface through π-π bonds of the benzene ring and short-chain alkane structures, free long chains... The structure generates a steric hindrance effect to prevent the conductive agent from entanglement and aggregation.

[0044] The present invention preferably provides a composite dispersant formed by further polymerization of polypropylene maleic anhydride ionic dispersant and bisphenol A polyoxyethylene ether nonionic dispersant. This composite dispersant combines the advantages of both polypropylene maleic anhydride ionic dispersant and bisphenol A polyoxyethylene ether nonionic dispersant. It utilizes the ortho-carboxyl group structure to enhance the electronegativity of the cathode particle surface and prevent particle agglomeration through electrostatic repulsion. At the same time, it utilizes a large number of -OH hydroxyl groups and benzene rings to anchor the particles and conductive agent. Combined with solvated long chains, it achieves a dispersion effect through steric hindrance. This not only ensures good dispersion of the cathode material and conductive agent but also promotes uniform dispersion of the conductive agent on the cathode material surface. Attached Figure Description

[0045] Figure 1 This is a schematic diagram showing the dispersant adsorbed on the surface of the positive electrode active material. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0047] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0048] According to a first aspect of the present invention, the present invention provides a sodium-ion battery positive electrode slurry comprising: a positive electrode active material, a conductive agent, a binder, a composite dispersant, and a solvent;

[0049] The composite dispersant is a product formed by mechanically mixing an ionic dispersant and a polyoxyethylene ether nonionic dispersant, or a complex formed by chemically reacting an ionic dispersant and a polyoxyethylene ether nonionic dispersant, wherein the ionic dispersant is polyacrylic acid and its derivatives.

[0050] The positive electrode active material is a polyanionic material.

[0051] Ionic dispersants of polyacrylic acid and its derivatives contain abundant carboxyl groups, which can adsorb onto the surface of positive electrode particles, reducing the surface energy of the particles. They also repel surrounding particles through the charge on the particle surface, exhibiting steric hindrance after adsorption to prevent particles from approaching each other, thus creating a composite stabilizing effect. To increase the number of carboxyl groups and improve the effect, the ionic dispersant is a copolymer of polyacrylic acid and other polycarboxylic acids or anhydrides. Examples include: polyacrylic acid with maleic anhydride, polyacrylic acid with maleic acid, polyacrylic acid with itaconic acid, and terpolymers of carboxylic acid-sulfonic acid-acrylate.

[0052] Polyoxyethylene ether nonionic dispersants adsorb onto the surface of cathode materials and conductive agents through hydroxyl groups. The free long-chain structure generates a steric hindrance effect, achieving a good dispersion effect.

[0053] To improve the dispersion effect, the polyoxyethylene ether nonionic dispersant is an alcohol polyoxyethylene ether or a phenol polyoxyethylene ether; preferably, it is one or more of bisphenol A polyoxyethylene ether, glycerol polyoxyethylene ether, furanol methanol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and 1,2-propanediol polyoxypropylene polyoxyethylene ether.

[0054] Alcohol-based or phenolic polyoxyethylene ethers contain -OH groups, which can be effectively adsorbed onto the surfaces of cathode materials and conductive agents, forming hydrogen bonds. However, compared to cathode materials (micrometer-scale), conductive agents have nanometer-scale particle sizes (below 40 nanometers) and large specific surface areas. Adsorption via -OH groups alone usually has limited effectiveness. For example, glycerol polyoxyethylene ethers, furanol methanol polyoxyethylene ethers, and 1,2-propanediol polyoxypropylene polyoxyethylene ethers can adsorb onto the conductive agent surface, but because the conductive agents are nanoscale materials (cathode materials are micrometer-scale), their effect is limited. In contrast, phenolic nonionic dispersants such as bisphenol A polyoxyethylene ethers can also effectively adsorb onto the conductive agent surface through π-π bonds of the benzene ring and short-chain alkane structures, free long chains... The structure generates a steric hindrance effect to prevent the conductive agent from entanglement and agglomeration; therefore, the polyoxyethylene ether nonionic dispersant is preferably bisphenol A polyoxyethylene ether or nonylphenol polyoxyethylene ether.

[0055] The composite dispersant can be a product formed by mechanical and physical mixing of an ionic dispersant and a polyoxyethylene ether nonionic dispersant, or it can be a complex formed by a chemical reaction between an ionic dispersant and a polyoxyethylene ether nonionic dispersant. The chemical reaction refers to the esterification reaction between the carboxyl group in the ionic dispersant and the hydroxyl group in the nonionic dispersant to form an ester bond.

[0056] It should be noted that the product formed by mechanically mixing the ionic dispersant and the polyoxyethylene ether nonionic dispersant is the product obtained by mechanically stirring and mixing the two. The product also contains cross-linking caused by esterification reaction. However, the final form and molecular weight of the product are difficult to control. The product formed by mechanical mixing is not as effective as the complex formed by a regular chemical reaction under catalyst and heating conditions. Furthermore, the stability of the slurry processing technology will be affected. Therefore, the complex has a better performance than the product formed by simple mechanical mixing.

[0057] In the composite dispersant, to improve the synergistic effect of the two dispersants used together, the mass ratio of the ionic dispersant to the polyoxyethylene ether nonionic dispersant is (1-2):(2-5) (e.g., 1:3, 1:4, 1.5:2, 1.5:3, 1.5:4, 2:3, 2:4);

[0058] If the mass ratio of ionic dispersant to polyoxyethylene ether nonionic dispersant is higher than (1-2):(2-5), there will be too much ionic dispersant and too little nonionic dispersant. This can play a certain role in dispersing the positive electrode material, but the dispersion of the conductive agent will be affected, and the resistance of the positive electrode sheet will be high. If the ratio is lower than this, there will be too little ionic dispersant and too much nonionic dispersant, which will result in long chain entanglement and unstable slurry viscosity.

[0059] The composite formed by the chemical reaction of an ionic dispersant and a polyoxyethylene ether nonionic dispersant is prepared as follows: Deionized water is added to a mixture of the ionic dispersant and the polyoxyethylene ether nonionic dispersant to form a gel. Then, under vacuum conditions with the aid of a catalyst, the mixture is stirred and reacted for 4-8 hours (e.g., 4.5 hours, 5.5 hours, 6.5 hours, 7.5 hours) for 140-160°C (e.g., 145°C, 150°C, 155°C, etc.) for 4-8 hours. Subsequently, the reaction product undergoes post-treatment to obtain the composite dispersant. The post-treatment includes purification and refining processes.

[0060] In a preferred embodiment, the composite dispersant is a complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether.

[0061] Polypropylene maleic anhydride ionic dispersant reacts with trace amounts of water in the slurry to generate polypropylene maleic acid, which contains abundant carboxyl groups. This carboxyl group can adsorb onto the surface of the positive electrode particles, reducing their surface energy. Furthermore, the surface charge of the particles repels surrounding particles, and the adsorption process creates a steric hindrance effect, preventing particles from approaching each other and resulting in a composite stabilizing effect. See details... Figure 1 Polypropylene maleic anhydride can reduce the impact of water content in materials on sodium-ion batteries.

[0062] Bisphenol A polyoxyethylene ether nonionic dispersant effectively adsorbs onto the surface of conductive agents through the π-π bonds of the benzene ring and the short-chain alkane structure, free long chains. The structure generates a steric hindrance effect to prevent the conductive agent from entanglement and aggregation.

[0063] Polypropylene maleic anhydride ionic dispersant and bisphenol A polyoxyethylene ether nonionic dispersant can be further polymerized to form a composite dispersant. The ortho-carboxyl structure enhances the electronegativity of the cathode particle surface and prevents particle agglomeration through electrostatic repulsion. At the same time, a large number of -OH hydroxyl groups and benzene rings are anchored on the particles and conductive agent. Combined with solvated long chains, the dispersion effect is achieved through steric hindrance. This not only ensures good dispersion of the cathode material and conductive agent, but also promotes uniform dispersion of the conductive agent on the cathode material surface.

[0064] The positive electrode active material is selected from at least one of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium vanadium phosphate, and sodium ferric phosphate.

[0065] The conductive agent can be a conventional sodium-ion battery conductive agent, typically and non-limitingly selected from at least one of carbon black, graphene, carbon nanotubes or carbon nanofibers.

[0066] The binder can be a conventional sodium-ion battery binder, typically and non-limitingly, the binder is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene or PFA emulsion;

[0067] The solvent can be a solvent used in conventional sodium-ion battery cathodes, typically and non-limitingly, the solvent is selected from at least one of N-methylpyrrolidone, ethanol, isopropanol or acetone.

[0068] The amount of the composite dispersant can be the amount of a conventional dispersant, but in order to further ensure the dispersion effect, the mass of the composite dispersant accounts for 0.1-1.8% (e.g., 0.2%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%) of the total mass of the positive electrode active material, conductive agent, binder and composite dispersant, preferably 0.2%-1.0%.

[0069] If the amount of the above-mentioned composite dispersant is too small, the dispersion effect will not be achieved; if the amount of the dispersant is too large, long chain entanglement will occur, reducing the dispersion effect.

[0070] The amounts of positive electrode active material, conductive agent, and binder used are all conventional amounts in the art. In the positive electrode slurry, the preferred mass ratio of the positive electrode active material, conductive agent, binder, and composite dispersant is (93-97):(1-2):(1-4):(0.2-1.0), and the sum of the mass ratios is 100.

[0071] The solid content of the positive electrode slurry can be a conventional solid content, typically 55%-65% (not limited to this).

[0072] The viscosity of the positive electrode slurry can be a conventional viscosity, typically and non-limitingly 3000-12000 mPa·s.

[0073] The preparation method of the complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether includes the following steps:

[0074] S1: Add polyacrylic acid maleic anhydride or polyacrylic acid maleic acid and bisphenol A polyoxyethylene ether to the reaction vessel at a mass ratio of (1-2):(2-5), then add deionized water to form a gel solution, and stir and react at 140-160℃ under vacuum conditions for 4-8 hours under the action of a catalyst.

[0075] S2: After the reaction is complete, sodium carbonate solution is added to the reaction vessel of step S1 and stirred. Then, the solid product is washed with saturated brine, and the washed solid product is dissolved in ethyl acetate. Finally, the obtained liquid is vacuum dried to remove the ethyl acetate solvent, thus obtaining the complex.

[0076] Furthermore, the solid content of the adhesive solution is 8-12%, preferably 10%;

[0077] Furthermore, the vacuum condition is to evacuate to 0.05-1.0 kPa;

[0078] Furthermore, the catalyst is p-toluenesulfonic acid, and its addition amount accounts for 0.6-1% of the total mass of the two reaction raw materials, preferably 0.8%;

[0079] Further, the mass concentration of the sodium carbonate solution is 8-12%, preferably 10%, and the amount added is such that the added sodium carbonate is 1 / 5 to 1 / 3, preferably 1 / 4, of the mass of the added catalyst.

[0080] Furthermore, the stirring time in step S2 is 30 minutes.

[0081] Specifically, the preparation method of the composite dispersant includes the following steps:

[0082] (1) Add polyacrylic acid maleic anhydride or polypropylene maleic acid and bisphenol A polyoxyethylene ether to a reaction vessel at a mass ratio of (1-2):(2-5), add deionized water to form a gel solution with a solid content of 10%, add catalyst, evacuate to 0.05-1.0 kPa (e.g. 0.1 kPa, 0.2 kPa, 0.3 kPa, 0.4 kPa, 0.5 kPa, 0.6 kPa, 0.7 kPa, 0.8 kPa, 0.9 kPa), heat to 140-160℃ (e.g. 145℃, 150℃, 155℃), and stir for 4-8 h (e.g. 5 h, 6 h, 7 h); the catalyst is p-toluenesulfonic acid, and its addition amount accounts for 0.8% of the total reactant mass.

[0083] (2) Add a 10% sodium carbonate solution to the reaction vessel. The amount of sodium carbonate added is 1 / 4 of the amount of toluenesulfonic acid added. Stir the reaction for 30 min. After washing the product with saturated brine, the solid and liquid are separated to obtain a solid mixture. Dissolve the solid mixture in ethyl acetate and vacuum dry the resulting liquid to obtain a composite dispersant.

[0084] The specific reactions are as follows:

[0085]

[0086] The above reaction formula only schematically shows one of the reaction sites of the two dispersants. In the actual reaction, maleic anhydride may also undergo esterification reaction with the terminal hydroxyl group of bisphenol A polyoxyethylene ether after decomposing into maleic acid upon contact with water.

[0087] The purpose of rinsing the product with saturated brine in the above steps is to remove sodium carbonate and sodium p-toluenesulfonate; dissolving the solid mixture in ethyl acetate can achieve solid-liquid separation and remove sodium chloride.

[0088] According to a second aspect of the present invention, the present invention provides a method for preparing a sodium-ion battery cathode slurry, comprising the following steps:

[0089] The binder, composite dispersant and solvent are mixed and stirred, then a conductive agent is added for sizing, then the positive electrode active material is added for homogenization, and then an appropriate amount of solvent is added to adjust the solid content and viscosity of the slurry to obtain the positive electrode slurry.

[0090] Specifically, binder, composite dispersant, and solvent are added to a container and mixed. The amount of solvent added is controlled to make the slurry solid content reach 5%-8% (e.g., 6% or 7%). The mixture is stirred for 120-180 minutes (e.g., 130 minutes, 140 minutes, 150 minutes, 160 minutes, or 170 minutes). Then, conductive agent is added for sizing and stirred for 90-150 minutes (e.g., 100 minutes, 110 minutes, 120 minutes, 130 minutes, or 140 minutes). Next, positive electrode active material is added and homogenized for 120-180 minutes (e.g., 130 minutes, 140 minutes, 150 minutes, 160 minutes, or 170 minutes). An appropriate amount of solvent is added to adjust the slurry solid content and viscosity to obtain the positive electrode slurry.

[0091] The positive electrode active material includes at least one of the following polyanionic materials: sodium ferric pyrophosphate, sodium ferrous sulfate, sodium vanadium phosphate, and sodium ferric phosphate.

[0092] The conductive agent includes at least one of carbon black, graphene, carbon nanotubes, or carbon nanofibers.

[0093] The binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or soluble polytetrafluoroethylene (PFA) emulsion;

[0094] The solvent includes at least one of N-methylpyrrolidone, ethanol, isopropanol, or acetone.

[0095] As an optional embodiment of the preparation method of the sodium-ion battery positive electrode slurry of the present invention, the solid content of the positive electrode slurry is 55%-65% (e.g., 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%).

[0096] And / or, the viscosity of the positive electrode slurry is 3000-12000 mPa·S (e.g., 4000 mPa·S, 5000 mPa·S, 6000 mPa·S, 7000 mPa·S, 8000 mPa·S, 9000 mPa·S, 10000 mPa·S, 11000 mPa·S).

[0097] According to a third aspect of the present invention, a positive electrode sheet is provided, comprising a current collector and a positive electrode active layer coated on the surface of the current collector, wherein the positive electrode active layer is made of the above-described positive electrode slurry or a positive electrode slurry prepared by the above-described preparation method.

[0098] According to a fourth aspect of the present invention, a sodium-ion battery is provided, comprising the above-described positive electrode sheet.

[0099] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0100] The sources of the dispersants used in the following examples and comparative examples are as follows:

[0101] The polyacrylic acid maleic anhydride was purchased from Hubei Shishun Biotechnology Co., Ltd., CAS number 26677-99-6;

[0102] Bisphenol A polyoxyethylene ether was purchased from Hubei Qifei Pharmaceutical Chemical Co., Ltd., CAS number 32492-61-8;

[0103] Glyceryl polyoxyethylene ether was purchased from Shandong Haizhou Bioengineering Co., Ltd., CAS number 31694-55-0;

[0104] The polyacrylic acid was purchased from Hubei Shixing Chemical Co., Ltd., CAS number 9007-20-9;

[0105] Nonylphenol polyoxyethylene ether was purchased from Shanghai Jieshikai Biotechnology Co., Ltd., CAS number 127087-87-0;

[0106] 1,2-Propane glycol polyoxypropylene ether was purchased from Haian Petrochemical Plant in Jiangsu Province, CAS number 53637-25-5.

[0107] Example 1

[0108] This embodiment provides a positive electrode slurry, comprising the following raw materials: positive electrode active material, conductive agent, binder, composite dispersant, and solvent. The positive electrode active material is sodium iron phosphate pyrophosphate, the conductive agent is conductive carbon black (SP), the binder is polyvinylidene fluoride (PVDF), the composite dispersant is a polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant, and the solvent is N-methylpyrrolidone (NMP). The mass ratio of the positive electrode active material, conductive agent, binder, and composite dispersant is 94.4:2.0:3.0:0.6. The amount of solvent added must ensure a solid content of 61%.

[0109] The method for preparing the positive electrode slurry provided in this embodiment includes the following steps:

[0110] (a) Add polyacrylic acid maleic anhydride and bisphenol A polyoxyethylene ether to a reaction vessel at a mass ratio of 1:3, add deionized water to form a gel with a solid content of 10%, add p-toluenesulfonic acid catalyst (0.8% of the total mass of the two raw materials), evacuate to 0.05-1.0 kPa, heat to 150°C, and stir for 6 h.

[0111] (b) A 10% sodium carbonate solution was added to a reaction vessel, with the amount of sodium carbonate being 1 / 4 of the amount of toluenesulfonic acid added. The mixture was stirred for 30 minutes. The product was washed with saturated brine to remove sodium carbonate and sodium p-toluenesulfonate, and a solid mixture was obtained by solid-liquid separation. The solid mixture was dissolved in ethyl acetate, and sodium chloride was removed by solid-liquid separation. The liquid was then vacuum dried to obtain a composite dispersant.

[0112] (c) According to the proportion of each substance in the positive electrode slurry, add the binder PVDF, part of the solvent NMP and the composite dispersant obtained in step (b) into the container, control the amount of NMP added so that the solid content of the slurry reaches 5%-8%, stir for 120 min, then add the conductive agent SP and stir for 150 min, add the positive electrode active material sodium iron phosphate pyrophosphate and homogenize for 180 min, add an appropriate amount of solvent NMP to adjust the slurry viscosity to 5100 mPa·S, and obtain a positive electrode slurry with a solid content of 61%.

[0113] Example 2

[0114] This embodiment provides a positive electrode slurry, comprising the following raw materials: positive electrode active material, conductive agent, binder, composite dispersant, and solvent. The positive electrode active material is sodium iron phosphate pyrophosphate, the conductive agent is conductive carbon black (SP), the binder is polyvinylidene fluoride (PVDF), the composite dispersant is a mixture of polyacrylic acid maleic anhydride ionic dispersant and bisphenol A polyoxyethylene ether nonionic dispersant, and the solvent is N-methylpyrrolidone (NMP). The mass ratio of the positive electrode active material, conductive agent, binder, and composite dispersant is 94.4:2.0:3.0:0.6. The amount of solvent added must ensure a solid content of 60%.

[0115] The method for preparing the positive electrode slurry provided in this embodiment includes the following steps:

[0116] (a) A composite dispersant is obtained by mechanically mixing polyacrylic acid maleic anhydride and bisphenol A polyoxyethylene ether at a mass ratio of 1:3.

[0117] (b) According to the proportions of each substance in the positive electrode slurry, the binder PVDF, part of the solvent NMP and the composite dispersant obtained in step (a) are added to the container. The amount of NMP added is controlled so that the solid content of the slurry reaches 6%. The mixture is stirred for 120 min, the conductive agent SP is added and stirred for 150 min, the positive electrode active material sodium iron phosphate pyrophosphate is added and homogenized for 180 min, and an appropriate amount of solvent NMP is added to adjust the viscosity of the slurry to 5200 mPa·S, so as to obtain a positive electrode slurry with a solid content of 60%.

[0118] Example 3

[0119] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with polyacrylic acid maleic anhydride-glycerol polyoxyethylene ether composite dispersant, the other raw material types, dosages and preparation methods are the same as in Example 1.

[0120] Example 4

[0121] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the mass ratio of positive electrode active material, conductive agent, binder and composite dispersant is replaced by 94:2.0:3.0:0.6 to 94:2.0:3.0:1.0, the other raw material types, amounts and preparation methods are the same as in Example 1.

[0122] Example 5

[0123] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the mass ratio of positive electrode active material, conductive agent, binder and composite dispersant is replaced from 94.4:2.0:3.0:0.6 to 94.8:2.0:3.0:0.2, the other raw material types, amounts and preparation methods are the same as in Example 1.

[0124] Example 6

[0125] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with polyacrylic acid-bisphenol A polyoxyethylene ether composite dispersant, the other raw material types, dosages and preparation methods are the same as in Example 1.

[0126] Example 7

[0127] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with polyacrylic acid maleic anhydride-nonylphenol polyoxyethylene ether composite dispersant, the other raw material types, dosages and preparation methods are the same as in Example 1.

[0128] Example 8

[0129] This embodiment provides a positive electrode slurry. Compared with Example 1, except that the polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with polyacrylic acid maleic anhydride-1,2-propanediol polyoxypropylene polyoxyethylene ether composite dispersant, the other raw material types, dosages and preparation methods are the same as in Example 1.

[0130] Comparative Example 1

[0131] This comparative example provides a positive electrode slurry. Compared with Example 1, the only difference is that the mass ratio of positive electrode active material, conductive agent, binder and composite dispersant is replaced with 95:2.0:3.0:0.6 instead of 94.4:2.0:3.0:0.6, i.e. the amount of composite dispersant added is adjusted to 0%. The other raw material types, amounts and preparation methods are the same as in Example 1.

[0132] Comparative Example 2

[0133] This comparative example provides a positive electrode slurry. Compared with Example 1, the only difference is that the mass ratio of positive electrode active material, conductive agent, binder and composite dispersant is replaced from 94.4:2.0:3.0:0.6 to 93.0:2.0:3.0:2.0, that is, the amount of composite dispersant added is adjusted to 2.0%. The other raw material types, amounts and preparation methods are the same as in Example 1.

[0134] Comparative Example 3

[0135] This comparative example provides a positive electrode slurry, except that the polypropylene maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with a polyacrylic acid maleic anhydride ionic dispersant, while the other raw material types, dosages, and preparation methods are the same as in Example 1.

[0136] Comparative Example 4

[0137] This comparative example provides a positive electrode slurry, except that the polypropylene maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant is replaced with a bisphenol A polyoxyethylene ether nonionic dispersant, while the other raw material types, dosages, and preparation methods are the same as in Example 1.

[0138] Performance testing

[0139] Assembly and performance testing of sodium-ion batteries:

[0140] Preparation of positive electrode sheet: Positive electrode sheets were prepared using the positive electrode slurries from Examples 1-8 and Comparative Examples 1-4, respectively. The positive electrode slurry was uniformly coated onto aluminum foil, with a single-sided coating areal density of 150 g / m². 2 The positive electrode sheet is obtained by baking and rolling, with an aluminum foil thickness of 14 μm and a compaction density of 2.0 g / cm³. 3 .

[0141] Preparation of negative electrode sheet: When using hard carbon material as active material and assembling sodium-ion batteries with different positive electrode sheets, the negative electrode sheets used are prepared by the same method and in the same batch.

[0142] Sodium-ion battery preparation: The above-mentioned positive electrode sheets are assembled with negative electrode sheets to form a cell, and a soft-pack sodium-ion battery is manufactured using a soft-pack stacking process. The sodium iron phosphate pyrophosphate positive electrode sheet, hard carbon negative electrode sheet, and polyethylene separator (e.g., PE+OBS separator) are stacked and assembled, then baked until the moisture content is within acceptable limits. Electrolyte is injected, followed by hot-pressing formation, high-temperature settling, and encapsulation. After capacity testing, the battery is settling at room temperature to obtain a finished soft-pack battery with a theoretical capacity of 5Ah.

[0143] The electrolyte solvents are ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), the sodium salts are NaPF6 and NaFSI, and the additives are vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and 1,3-propanesulfonyl lactone (1-3PS).

[0144] The electrolyte used is a conventional electrolyte in the art, comprising solvents of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), wherein the mass ratio of EC:PC:EMC:DMC is approximately 20:10:50:20, and comprising sodium salts of sodium hexafluorophosphate (NaPF6, concentration approximately 14 wt%) and sodium difluorosulfonyl imide (NaFSI, concentration approximately 3 wt%), and comprising additives of vinylene carbonate (VC, concentration approximately 0.8 wt%), fluoroethylene carbonate (FEC, concentration approximately 3 wt%), vinyl sulfate (DTD, concentration approximately 0.3 wt%), and 1,3-propanesulfonyl lactone (1-3PS, concentration approximately 0.3 wt%).

[0145] Cathode slurry stability test: The viscosity (25℃) of the cathode slurry provided in each embodiment and comparative example was tested at different times using a viscometer. The test results are shown in Table 1.

[0146] Positive electrode resistance test: The positive electrode provided in each embodiment and comparative example was tested using an electrode resistance meter, model BER2500 (IEST Yuaneng Technology), with an electrode diameter of 14mm, an applied pressure of 20MPa, and a duration of 15s. The test results are shown in Table 1.

[0147] Battery DC internal resistance (DCR) test: The battery was tested at 25°C on the battery testing system of the electrochemical workstation. The battery capacity was adjusted to 50% SOC and left to stand for 2 hours. The voltage at the end of the stand was recorded as U1. The battery was discharged with current I (2C) for 10 seconds and the voltage at the end of the discharge was recorded as U2. DCR = (U1-U2) / I. The test results are shown in Table 1.

[0148] Battery high-temperature cycle test:

[0149] The finished batteries prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to 1C charge-1C discharge cycle tests at 45°C, with a charge-discharge voltage range of 1.5V-3.4V. The discharge capacity retention rate after 2000 cycles is shown in Table 1.

[0150] Table 1

[0151]

[0152] Based on the static viscosity data of the slurry in Table 1, and through Examples 1-8 and Comparative Examples 1-4, it can be seen that the composite dispersant has excellent dispersion effect and can significantly improve the stability of the positive electrode slurry. The amount of composite dispersant should not be too much or too little. Preferably, the mass of the composite dispersant accounts for 0.2%-1.0% of the total mass of the positive electrode active material, conductive agent, binder and composite dispersant.

[0153] Based on the electrode resistance data and DCR DC resistance data in Table 1, and through Examples 1-8 and Comparative Examples 1-4, it can be seen that the composite dispersant can improve the dispersion effect of the positive electrode slurry, promote the uniform dispersion of positive electrode particles, prevent particle agglomeration, and the conductive agent can be better dispersed on the surface of the positive electrode particles to form a uniform conductive network, improve the electron transport rate, thereby reducing the electrode resistance and the DC internal resistance of the cell.

[0154] As can be seen from the high-temperature cycling test data in Table 1, after 2000 cycles, Example 1 showed the highest cycle retention rate and the best cycle stability for sodium-ion batteries. This further proves that the polyacrylic acid maleic anhydride-bisphenol A polyoxyethylene ether composite dispersant has the best effect. Although the viscosity stability, resistance and cycle performance of the composite dispersant used in Example 2, which is a simple mechanical mixture of polyacrylic acid maleic anhydride and bisphenol A polyoxyethylene ether, decreased compared to Example 1, it still has significant advantages over Comparative Examples 3 and 4, which use a single dispersant. It can achieve the best dispersion effect through the synergistic effect of electrostatic repulsion mechanism and steric hindrance mechanism, forming a homogenized electrode structure, reducing structural failure and polarization growth during cycling, and effectively improving the cycle performance of sodium-ion batteries.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium-ion battery positive electrode slurry, characterized in that, include: Positive electrode active material, conductive agent, binder, composite dispersant and solvent; The composite dispersant is a product formed by mechanically mixing an ionic dispersant and a polyoxyethylene ether nonionic dispersant, or a complex formed by chemically reacting an ionic dispersant and a polyoxyethylene ether nonionic dispersant. The positive electrode active material is a polyanionic material; In the preparation of the composite dispersant, the mass ratio of the ionic dispersant to the polyoxyethylene ether nonionic dispersant is (1-2):(2-5). In the complex formed by the chemical reaction between the ionic dispersant and the polyoxyethylene ether nonionic dispersant, the chemical reaction refers to the esterification reaction between the carboxyl group in the ionic dispersant and the hydroxyl group in the nonionic dispersant to form an ester bond. The ionic dispersant is polyacrylic acid maleic anhydride or polyacrylic acid maleic acid. The polyoxyethylene ether nonionic dispersant is one or more of bisphenol A polyoxyethylene ether and glycerol polyoxyethylene ether; The mass of the composite dispersant accounts for 0.2%-1.0% of the total mass of the positive electrode active material, conductive agent, binder and composite dispersant.

2. The sodium-ion battery positive electrode slurry according to claim 1, characterized in that, In the positive electrode slurry, the mass ratio of the positive electrode active material, conductive agent, binder and composite dispersant is (93-97):(1-2):(1-4):(0.2-1.0), and the sum of the mass ratios is 100; And / or, the solid content of the positive electrode slurry is 55%-65%; And / or, the viscosity of the positive electrode slurry is 3000-12000 mPa·S.

3. The sodium-ion battery positive electrode slurry according to claim 2, characterized in that, The positive electrode active material is selected from at least one of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium vanadium phosphate, and sodium ferric phosphate. And / or, the conductive agent is selected from at least one of carbon black, graphene, carbon nanotubes or carbon nanofibers; And / or, the adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, or PFA emulsion; And / or, the solvent is selected from at least one of N-methylpyrrolidone, ethanol, isopropanol or acetone; And / or, the composite dispersant is prepared by the following method: adding deionized water to a mixture of an ionic dispersant and a polyoxyethylene ether nonionic dispersant to form a gel, and then stirring and reacting at 140-160°C under vacuum for 4-8 hours under the action of a catalyst; subsequently, the reaction product is post-treated to obtain the composite dispersant.

4. The sodium-ion battery positive electrode slurry according to claim 1, characterized in that, The composite dispersant is a complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether.

5. The sodium-ion battery positive electrode slurry according to claim 4, characterized in that, The preparation method of the complex formed by the chemical reaction of polyacrylic acid maleic anhydride or polyacrylic acid maleic acid with bisphenol A polyoxyethylene ether includes the following steps: S1: Add polyacrylic acid maleic anhydride or polyacrylic acid maleic acid and bisphenol A polyoxyethylene ether to the reaction vessel at a mass ratio of (1-2):(2-5), then add deionized water to form a gel solution, and stir and react at 140-160℃ under vacuum for 4-8 hours under the action of a catalyst. S2: After the reaction is complete, sodium carbonate solution is added to the reaction vessel of step S1 and stirred. Then, the solid product is washed with saturated brine, and the washed solid product is dissolved in ethyl acetate. Finally, the obtained liquid is vacuum dried to remove the ethyl acetate solvent, thus obtaining the complex.

6. The sodium-ion battery positive electrode slurry according to claim 5, characterized in that, The solid content of the adhesive solution is 8-12%; And / or, the vacuum condition is to evacuate to 0.05-1.0 kPa; And / or, the catalyst is p-toluenesulfonic acid, and its addition amount accounts for 0.6-1% of the total mass of the two reactants; And / or, the sodium carbonate solution has a mass concentration of 8-12%, and the amount added is such that the added sodium carbonate is 1 / 5 to 1 / 3 of the mass of the added catalyst; And / or, the stirring time in step S2 is 25-35 min.

7. A method for preparing the sodium-ion battery positive electrode slurry according to any one of claims 1-6, characterized in that, Includes the following steps: The binder, composite dispersant and solvent are mixed and stirred, then a conductive agent is added for sizing, then the positive electrode active material is added for homogenization, and then an appropriate amount of solvent is added to adjust the solid content and viscosity of the slurry to obtain the positive electrode slurry.

8. The preparation method according to claim 7, characterized in that, When mixing the binder, composite dispersant and solvent, control the amount of solvent added so that the solid content of the slurry reaches 5%-8%, and the stirring time is 120-180 minutes. The mixing time for applying the adhesive is 90-150 minutes; The homogenization time is 120-180 min.

9. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode active layer coated on the surface of the current collector, wherein the positive electrode active layer is made of the positive electrode slurry according to claims 1-6 or the positive electrode slurry prepared by the method of claims 7-8.

10. A sodium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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