Carboxylated styrene-butadiene latex and method for preparing the same, and negative electrode binder for secondary battery

Abstract

The application discloses a carboxyl styrene butadiene latex and a preparation method thereof, and a secondary battery negative electrode binder, and belongs to the technical field of latex preparation, and overcomes the defects of embedding acid and high free acid content in the water phase in the prior art, and low surface acid content.The preparation method of the carboxyl styrene butadiene latex comprises the following steps: step 1, preparing a macromolecular emulsifier; and step 2, preparing carboxyl styrene butadiene latex A; the macromolecular emulsifier and second raw materials are added into a solvent, and polymerization reaction is carried out to obtain the carboxyl styrene butadiene latex A; the second raw materials comprise a second polymerization monomer and a second initiator, and the second polymerization monomer comprises an aromatic vinyl monomer and an aliphatic conjugated diene monomer.The bonding strength of the carboxyl styrene butadiene latex is significantly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of latex preparation, and in particular relates to a carboxylated styrene-butadiene latex and a preparation method thereof, and a secondary battery negative electrode binder. Background Art

[0002] In the development of secondary battery technology, particularly lithium-ion secondary battery technology, anode materials have a crucial impact on the overall performance of the battery. Although used in small quantities, anode binders are key materials for ensuring stable anode material performance, and their performance directly impacts the battery's cycle life and safety. Therefore, developing anode binders with excellent overall performance has long been a hot topic in the battery field.

[0003] Carboxylated styrene butadiene latex (CSB) is the most commonly used battery negative electrode binder and has a large application market. Surface acid content is a key factor affecting the bonding performance of CSB latex. The higher the surface acid content, the stronger the bonding. However, during the preparation of CSB latex, there are problems with high levels of embedded acid and aqueous free acid. This makes it difficult to increase the surface acid content of CSB latex, making it difficult to meet the high bonding strength requirements of high-performance batteries. In addition, embedded acid and aqueous free acid not only fail to enhance the bonding strength of the binder, but also adversely affect the viscosity stability of the slurry and may also pose a potential threat to the overall safety performance of the battery. Therefore, reducing the content of embedded acid and aqueous free acid is key to improving the performance of battery negative electrode binders. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art in that the carboxylated styrene butadiene latex has a high content of embedded acid and free acid in the aqueous phase, resulting in a low surface acid content, thereby providing a carboxylated styrene butadiene latex and a preparation method thereof, and a secondary battery negative electrode binder.

[0005] To this end, the present invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing carboxylated styrene-butadiene latex, comprising the following steps:

[0007] Step 1: Preparation of macromolecular emulsifier:

[0008] Using water as a solvent, mixing and polymerizing first raw materials to obtain a macromolecular emulsifier; the first raw materials include a first polymerizable monomer, a molecular weight regulator, a first emulsifier, and a first initiator; the first polymerizable monomer includes an unsaturated carboxylic acid a1 and an acrylate monomer b1;

[0009] Step 2, preparing carboxylated styrene-butadiene latex A;

[0010] In water as solvent, a macromolecular emulsifier and a second raw material are added into the solvent, and a polymerization reaction is performed to obtain a carboxyl styrene-butadiene latex A; the second raw material comprises a second polymerization monomer and a second initiator, and the second polymerization monomer comprises an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

[0011] In a possible implementation, the unsaturated carboxylic acid a1 accounts for 5% to 80%, preferably 10% to 60%, and more preferably 12% to 40% of the mass of the first raw material;

[0012] In a possible implementation, the acrylic ester monomer b1 accounts for 15% to 85%, preferably 30% to 80%, and more preferably 60% to 78% of the mass of the first raw material;

[0013] In a possible implementation, the molecular weight regulator accounts for 1% to 15%, preferably 4% to 8% of the mass of the first raw material;

[0014] In a possible implementation, the first emulsifier accounts for 0.2% to 2.5% of the mass of the first raw material;

[0015] In a possible implementation, the first initiator accounts for 1.5% to 3% of the mass of the first polymerization monomer.

[0016] In a possible implementation, step 2 satisfies at least one of the following conditions:

[0017] (1) The mass of the first raw material accounts for 5% to 50%, preferably 10% to 30% of the sum of the mass of the first raw material and the second raw material;

[0018] (2) The aromatic vinyl monomer accounts for 10% to 60%, preferably 20% to 50% of the sum of the mass of the first raw material and the second raw material;

[0019] (3) The aliphatic conjugated diene monomer accounts for 10% to 60%, preferably 20% to 50% of the sum of the mass of the first raw material and the second raw material;

[0020] (4) The second initiator accounts for 1% to 2% of the mass of the second polymerization monomer.

[0021] In a possible implementation, the unsaturated carboxylic acid a1 is selected from one or more of monobasic acid and dibasic acid;

[0022] Optionally, the unsaturated carboxylic acid a1 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid;

[0023] In a possible implementation, the acrylate monomer b1 is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, t-butyl acrylate, and isooctyl acrylate;

[0024] In a possible implementation, the molecular weight regulator is selected from one or more of alkyl mercaptan and xanthate compound;

[0025] Optionally, the alkyl mercaptan includes one or more of n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan;

[0026] In a possible implementation, the aromatic vinyl monomer is selected from one or more of styrene, α-methyl styrene, vinyl toluene, and divinyl benzene;

[0027] In a possible implementation, the aliphatic conjugated diene monomer is selected from one or more of 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted straight-chain conjugated pentadiene, and substituted side-chain conjugated hexadiene;

[0028] The initiator is a conventional initiator used in emulsion polymerization, and in a possible implementation, the first initiator and the second initiator are independently selected from at least one of potassium persulfate, ammonium persulfate, and cumene peroxide.

[0029] In a possible implementation, the method further comprises step 3, preparing carboxyl styrene-butadiene latex B: adding an agglomeration agent to the carboxyl styrene-butadiene latex A to obtain the carboxyl styrene-butadiene latex B.

[0030] In a possible implementation, the preparation method of the agglomeration agent comprises: mixing third raw materials and performing polymerization reaction to obtain the agglomeration agent, with water as a solvent.

[0031] The third raw materials include third polymerization monomers, a third emulsifier, and a third initiator; the third polymerization monomers include unsaturated carboxylic acid a2 and acrylate monomer b2.

[0032] In a possible implementation, the preparation method of the agglomeration agent satisfies at least one of the following conditions:

[0033] (1) The unsaturated carboxylic acid a2 accounts for 5% to 80%, preferably 10% to 60%, and more preferably 15% to 40% of the mass of the third raw materials;

[0034] (2) The acrylate monomer b2 accounts for 15% to 85%, preferably 30% to 80%, and more preferably 60% to 75% of the mass of the third raw materials;

[0035] (3) the third emulsifier accounts for 0.2% to 2.5% of the mass of the third raw material;

[0036] (4) the third initiator accounts for 0.5% to 1% by mass of the third polymerization monomer;

[0037] (5) unsaturated carboxylic acid a2 is one or more selected from monobasic acids and dibasic acids;

[0038] Optionally, the unsaturated carboxylic acid a2 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid;

[0039] (6) the acrylic acid ester monomer b2 is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, tert-butyl acrylate, and isooctyl acrylate;

[0040] (7) The third initiator is selected from at least one of potassium persulfate, ammonium persulfate, and cumene peroxide.

[0041] When step 3 is included, the mass of the first raw material accounts for 5% to 50% of the sum of the mass of the first raw material, the second raw material and the third raw material, preferably 10% to 30%;

[0042] In one possible embodiment, the aromatic vinyl monomer accounts for 10% to 60% of the total mass of the first raw material, the second raw material and the third raw material, preferably 20% to 50%;

[0043] In one possible embodiment, the aliphatic conjugated diene monomer accounts for 10% to 60% of the total mass of the first raw material, the second raw material and the third raw material, preferably 20% to 50%;

[0044] In a possible implementation, the third raw material accounts for 0.5% to 5% of the total mass of the first raw material, the second raw material and the third raw material, preferably 1% to 3%.

[0045] In a second aspect, the present invention provides a carboxylated styrene-butadiene latex prepared by the above preparation method.

[0046] In a third aspect, the present invention provides a secondary battery negative electrode binder comprising the carboxylated styrene-butadiene latex.

[0047] In one possible embodiment, after the polymerization reaction in step 1, the pH is adjusted to 6.5-9.0 to obtain a macromolecular emulsifier.

[0048] Optionally, the polymerization reaction temperature in step 1 is 50-120°C.

[0049] Optionally, a neutralizing agent is used to adjust the pH of the first latex. The neutralizing agent is not particularly limited, and the neutralizing agent is optionally selected from at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and potassium carbonate, preferably at least one of aqueous ammonia and sodium hydroxide.

[0050] There is no particular limitation on the type and amount of the first emulsifier. Optionally, the first emulsifier can be selected from sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium dodecyldiphenylether disulfonate, and reactive emulsifiers having unsaturated bonds, preferably reactive emulsifiers.

[0051] The prepared agglomerating agent is a high molecular weight agglomerating agent. Optionally, the polymerization reaction temperature for preparing the agglomerating agent is 50-70°C.

[0052] There is no particular limitation on the type and amount of the third emulsifier. Optionally, the third emulsifier can be selected from sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium dodecyldiphenylether disulfonate, and reactive emulsifiers having unsaturated bonds, preferably reactive emulsifiers.

[0053] The solid content of the carboxylated styrene butadiene latex B is 15-60 wt%, preferably 35-55 wt%. Too low a solid content will affect the stability of the latex and increase transportation costs; too high a solid content will complicate the production process and increase production costs.

[0054] The pH value of the carboxylated styrene butadiene latex B is preferably 4 to 11, more preferably 5 to 9; the average particle size of the solid phase particles in the carboxylated styrene butadiene latex B system is preferably 100 to 350 nm, more preferably 150 to 250 nm.

[0055] The technical solution of the present invention has the following advantages:

[0056] 1. The preparation method of carboxylated styrene butadiene latex of the present invention comprises the following steps: Step 1, using water as a solvent, mixing and polymerizing first raw materials to obtain a macromolecular emulsifier; the first raw materials include a first polymerizable monomer, a molecular weight regulator, a first emulsifier and a first initiator; the first polymerizable monomer includes an unsaturated carboxylic acid a1 and an acrylate monomer b1; Step 2, preparing carboxylated styrene butadiene latex A; using water as a solvent, adding the macromolecular emulsifier and a second raw material to the solvent, polymerizing and obtaining carboxylated styrene butadiene latex A; the second raw materials include a second polymerizable monomer and a second initiator, and the second polymerizable monomer includes an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

[0057] The present invention uses unsaturated carboxylic acid a1 and acrylic ester monomer b1 to synthesize a high-acid-content macromolecular emulsifier. The carboxyl groups are on the macromolecular emulsifier, which can reduce surface tension and play a stabilizing role, uniformly dispersing and stabilizing water-insoluble latex particles in water. Therefore, most of the macromolecular emulsifier is present on the surface of the latex particles. Therefore, using the macromolecular emulsifier to replace the traditional small-molecule emulsifier can introduce a high content of carboxyl groups on the surface of the latex particles while significantly reducing the content of embedded acid and free acid in the aqueous phase, thereby significantly improving the bonding strength of the carboxyl styrene-butadiene latex.

[0058] 2. The method for preparing carboxylated styrene butadiene latex of the present invention further comprises step 3, preparing carboxylated styrene butadiene latex B: adding an agglomerating agent to carboxylated styrene butadiene latex A to obtain carboxylated styrene butadiene latex B. By increasing the particle size of the carboxylated styrene butadiene latex through an agglomeration process, the bonding strength of the carboxylated styrene butadiene latex is improved while maintaining the stability of the slurry viscosity, thereby enhancing the operational convenience of the product and improving the electrical performance and safety of the battery.

[0059] The present invention provides a novel method for preparing a carboxylated styrene-butadiene latex with high adhesion, which provides a new direction for the research and development of battery negative electrode binders and has broad application prospects and important social value.

[0060] Improve the adhesion between the negative electrode active material and the current collector of the secondary battery, and increase the cycle life of the battery. DETAILED DESCRIPTION

[0061] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0062] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0063] 1. Test method:

[0064] Particle size test: Use Malvern particle size analyzer according to WHPU / T011 682 2015 standard at 25°C; Slurry dispersion evaluation: Observe the appearance of the prepared negative electrode after baking, including cracking, curling, black spots and pits.

[0065] Peel strength test: The test method for peel strength refers to the American Society for Testing and Materials standard ASTM D3330, and the equipment used is a computerized tensile testing machine (KJ 1065).

[0066] Surface acid content and aqueous phase free acid content test: The surface acid content and aqueous phase acid content of the latex were tested according to the method in patent CN110061187B.

[0067] Embedded acid amount: the total amount of carboxylic acid in moles minus the surface acid amount and the amount of free acid in the aqueous phase.

[0068] Unless otherwise specified, the "parts" of raw materials in each embodiment refer to "parts by mass".

[0069] 2. Source of raw materials:

[0070] Styrene: purchased from Aladdin Reagents, purity 99%.

[0071] Butadiene: purchased from Wanhua Chemical and used after vaporization and condensation.

[0072] Methacrylic acid: purchased from Aladdin Reagents with a purity of 98%.

[0073] Methyl methacrylate: purchased from Aladdin Reagents, purity 99%.

[0074] Butyl acrylate: purchased from Aladdin Reagents, purity 99%.

[0075] n-Dodecyl mercaptan: purchased from Aladdin Reagent, purity 99%.

[0076] Reactive emulsifier SR-10: purchased from Solvay, purity 97%.

[0077] Sodium dodecylbenzenesulfonate: purchased from Solvay, purity 22.5%.

[0078] Potassium persulfate: purchased from Aladdin Reagent, purity 99%.

[0079] Sodium hydroxide: purchased from Aladdin Reagent, purity 99%.

[0080] Example 1

[0081] The present embodiment provides a method for preparing carboxylated styrene-butadiene latex, comprising the following steps:

[0082] Step 1: Preparation of macromolecular emulsifier:

[0083] (1) 100 g of methacrylic acid, 250 g of methyl methacrylate, 4 g of reactive emulsifier SR-10, 21 g of n-dodecyl mercaptan, and 120 g of water were prepared into a monomer pre-emulsion.

[0084] (2) Prepare an initiator solution by adding 2 g of potassium persulfate and 80 g of water.

[0085] (3) Add 490 g of water and 6 g of potassium persulfate into a four-necked flask, start stirring and heat to 89°C. When the temperature reaches 89°C, add the monomer pre-emulsion and initiator solution dropwise into the four-necked flask over 2 hours, and continue to keep warm for 1 hour.

[0086] (4) 744 g of a sodium hydroxide solution with a mass concentration of 5% was added, and the pH was adjusted to 7-8 to obtain a macromolecular emulsifier with a mass concentration (mass of the first raw material / mass of the macromolecular emulsifier) ​​of 21%.

[0087] Step 2: Preparation of agglomerating agent:

[0088] (1) 25 g of methacrylic acid, 40 g of methyl methacrylate, 35 g of butyl acrylate, 2.25 g of reactive emulsifier SR-10, and 30 g of water were prepared into a monomer pre-emulsion.

[0089] (2) Prepare an initiator solution by adding 0.5 g of potassium persulfate and 40 g of water.

[0090] (3) 84 g of water and 0.25 g of potassium persulfate were added to a four-necked flask, stirred and heated to 80°C. When the temperature reached 80°C, the monomer pre-emulsion and the initiator solution were added dropwise to the four-necked flask over 4 hours, and the temperature was kept warm for 1 hour to obtain a polymer agglomerate with a mass concentration (mass of the third raw material / mass of the agglomerate) of 40%.

[0091] Step 3: preparing carboxylated styrene-butadiene latex:

[0092] To an autoclave, add 1246g of a macromolecular emulsifier, 525g of water, 19g of potassium persulfate, 700g of styrene, and 466g of butadiene. Stirring was initiated and the mixture was heated to 70°C for 12 hours. After the reaction, the emulsion was vacuumed to remove residual monomers. 62.75g of a polymer agglomerating agent was added, stirred for 0.5 hours, and finally, water was added to adjust the solids content to 40%.

[0093] Example 2

[0094] This embodiment is substantially the same as embodiment 1, except that no agglomerating agent is prepared or added in this embodiment.

[0095] Specifically, the preparation of carboxylated styrene-butadiene latex includes sequentially adding 1246 g of a macromolecular emulsifier (A), 525 g of water, 19 g of potassium persulfate, 700 g of styrene, and 466 g of butadiene to an autoclave, stirring, heating to 70° C., and reacting for 12 hours. After the reaction, residual monomers are removed from the emulsion, and water is added to adjust the solid content to 40%.

[0096] Example 3

[0097] The present embodiment provides a method for preparing carboxylated styrene-butadiene latex, comprising the following steps:

[0098] Step 1: Preparation of macromolecular emulsifier:

[0099] (1) A monomer pre-emulsion was prepared by mixing 25 g of methacrylic acid, 325 g of methyl methacrylate, 4 g of reactive emulsifier SR-10, 21 g of n-dodecyl mercaptan, and 120 g of water.

[0100] (2) Prepare an initiator solution by adding 2 g of potassium persulfate and 80 g of water.

[0101] (3) Add 1000 g of water and 6 g of potassium persulfate into a four-necked flask, start stirring and heat to 89°C. When the temperature reaches 89°C, add the monomer pre-emulsion and initiator solution dropwise into the four-necked flask over 2 hours, and continue to keep warm for 1 hour.

[0102] (4) Add 186 g of a 5% sodium hydroxide solution and adjust the pH to 7-8 to obtain a macromolecular emulsifier with a mass concentration of 22%.

[0103] Step 2: Prepare an agglomerating agent according to step 2 of Example 1.

[0104] Step 3: preparing carboxylated styrene-butadiene latex:

[0105] To an autoclave, add 4927g of a macromolecular emulsifier (repeat step 1 to prepare a sufficient amount of macromolecular emulsifier), 19g of potassium persulfate, 700g of styrene, and 466g of butadiene. Stirring was initiated and the mixture was heated to 70°C for 12 hours. After the reaction, residual monomers were removed from the emulsion, and 62.75g of a polymer agglomerating agent was added. Stirring was continued for 0.5 minutes, and the solids content was adjusted to 40%.

[0106] Example 4

[0107] The present embodiment provides a method for preparing carboxylated styrene-butadiene latex, comprising the following steps:

[0108] Step 1: Preparation of macromolecular emulsifier:

[0109] (1) 290 g of methacrylic acid, 60 g of methyl methacrylate, 4 g of reactive emulsifier SR-10, 21 g of n-dodecyl mercaptan, and 120 g of water were prepared into a monomer pre-emulsion.

[0110] (2) Prepare an initiator solution by adding 2 g of potassium persulfate and 80 g of water.

[0111] (3) Add 490 g of water and 6 g of potassium persulfate into a four-necked flask, start stirring and heat to 89°C. When the temperature reaches 89°C, add the monomer pre-emulsion and initiator solution dropwise into the four-necked flask over 2 hours, and continue to keep warm for 1 hour.

[0112] (4) Add 899 g of a sodium hydroxide solution with a mass concentration of 12%, adjust the pH to 7-8, and obtain a macromolecular emulsifier with a mass concentration of 19%.

[0113] Step 2, prepare the agglomerating agent according to Step 2 of Example 1

[0114] Step 3, prepare the carboxyl styrene-butadiene latex:

[0115] In a high-pressure reaction kettle, sequentially add 450 g of the macromolecular emulsifier, 650 g of water, 19 g of potassium persulfate, 700 g of styrene, and 466 g of butadiene, start stirring and heat to 70°C, and react for 12 h. After the reaction is completed, remove the residual monomers from the emulsion, add 62.75 g of the high-molecular agglomerating agent, stir for 0.5, and finally add water to adjust the solid content to 40%.

[0116] Example 5

[0117] The present example provides a method for preparing a carboxyl styrene-butadiene latex, including the following steps:

[0118] Step 1, prepare the macromolecular emulsifier:

[0119] (1) Prepare a monomer pre-emulsion by mixing 50 g of methacrylic acid, 300 g of methyl methacrylate, 4 g of a reactive emulsifier SR-10, 21 g of n-dodecyl mercaptan, and 120 g of water.

[0120] (2) Prepare an initiator solution by mixing 2 g of potassium persulfate and 80 g of water.

[0121] (3) Add 900 g of water and 6 g of potassium persulfate to a four-necked flask, start stirring and heat to 89°C, and when the temperature reaches 89°C, drop the monomer pre-emulsion and the initiator solution into the four-necked flask over 2 h, and continue to keep warm for 1 h.

[0122] (4) Add 372 g of a sodium hydroxide solution with a mass concentration of 5%, adjust the pH to 7-8, and obtain a macromolecular emulsifier with a mass concentration of 21%.

[0123] Step 2, prepare the agglomerating agent according to Step 2 of Example 1.

[0124] Step 3, prepare the carboxyl styrene-butadiene latex:

[0125] In a high-pressure reaction kettle, sequentially add 2571 g of the macromolecular emulsifier (sufficient amount of the macromolecular emulsifier can be prepared according to Step 1), 19 g of potassium persulfate, 700 g of styrene, and 466 g of butadiene, start stirring and heat to 70°C, and react for 12 h. After the reaction is completed, remove the residual monomers from the emulsion, add 62.75 g of the high-molecular agglomerating agent, stir for 0.5, and finally adjust the solid content to 40%.

[0126] Example 6

[0127] The present embodiment provides a method for preparing carboxylated styrene-butadiene latex, comprising the following steps:

[0128] Step 1: Preparation of macromolecular emulsifier:

[0129] (1) 150 g of methacrylic acid, 200 g of methyl methacrylate, 4 g of reactive emulsifier SR-10, 21 g of n-dodecyl mercaptan, and 120 g of water were prepared into a monomer pre-emulsion.

[0130] (2) Prepare an initiator solution by adding 2 g of potassium persulfate and 80 g of water.

[0131] (3) Add 300 g of water and 6 g of potassium persulfate into a four-necked flask, start stirring and heat to 89°C. When the temperature reaches 89°C, add the monomer pre-emulsion and initiator solution dropwise into the four-necked flask over 2 hours, and continue to keep warm for 1 hour.

[0132] (4) Add 1116 g of a sodium hydroxide solution with a mass concentration of 5% and adjust the pH to 7-8 to obtain a macromolecular emulsifier with a mass concentration of 19%.

[0133] Step 2: Prepare an agglomerating agent according to step 2 of Example 1.

[0134] Step 3: preparing carboxylated styrene-butadiene latex:

[0135] To an autoclave, add 907g of a macromolecular emulsifier, 1000g of water, 19g of potassium persulfate, 700g of styrene, and 466g of butadiene. Stirring was initiated and the mixture was heated to 70°C for 12 hours. After the reaction, residual monomers were removed from the emulsion, and 62.75g of a high-molecular-weight agglomerant was added. Stirring was continued for 0.5 minutes, and the solid content was adjusted to 40%.

[0136] Comparative Example 1

[0137] This comparative example provides a method for preparing a carboxylated styrene-butadiene latex, comprising: sequentially adding 1740 g of water, 19 g of potassium persulfate, 28 g of an emulsifier (sodium dodecylbenzenesulfonate), 70 g of methacrylic acid, 700 g of styrene, and 466 g of butadiene to an autoclave; stirring the mixture, heating the mixture to 70°C, and reacting the mixture for 12 hours. After the reaction, the pH of the latex is adjusted to 7 using a 5% aqueous sodium hydroxide solution. Residual monomers are removed from the neutralized latex, and water is added to adjust the solids content to 40%.

[0138] Test example

[0139] The carboxylated styrene butadiene latex prepared in the embodiment and the comparative example were respectively used as a binder to prepare the negative electrode sheet of a lithium ion battery. The specific steps are as follows:

[0140] (1) Slurry preparation: 0.5 parts of sodium carboxymethyl cellulose (CMC) was added to 100 parts of deionized water at room temperature and stirred at high speed for about 20 minutes. Then, 1 part of carbon black conductive agent (Super P), 96.5 parts of negative electrode active material (graphite) and 2 parts of binder were added respectively. After each material was added, it was stirred at high speed for about 10 minutes to mix evenly. After filtering through a 100-mesh filter, the negative electrode slurry was obtained.

[0141] (2) Pole sheet coating: The prepared negative electrode slurry was evenly coated on the current collector (copper foil) with a coating thickness of 100 μm, placed in an 80°C oven to dry for 5 minutes, and rolled on a roller press at room temperature to obtain a negative electrode sheet with a thickness of 70 μm.

[0142] The surface acidity, acidity in the aqueous phase, and embedded acidity of each prepared latex binder were tested; the slurry dispersibility and peel strength of the prepared negative electrode plates were evaluated, and the test results are shown in Table 1.

[0143] Table 1

[0144]

[0145] By comparing Examples 1-6 with Comparative Example 1, it can be seen that by replacing the traditional small molecule emulsifier with a macromolecular emulsifier, a high content of carboxyl groups can be introduced on the surface of the latex particles while significantly reducing the content of embedded acid and free polymeric acid, which can significantly improve the peel strength of the adhesive, that is, significantly improve the bonding force.

[0146] Comparing Example 1 with Example 2, it can be seen that increasing the particle size of the carboxylated styrene butadiene latex by adopting an agglomeration process can further enhance the adhesion of the carboxylated styrene butadiene latex.

[0147] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing carboxylated styrene-butadiene latex, characterized in that: The following steps are involved: Step 1: Preparation of macromolecular emulsifier: Using water as a solvent, mixing and polymerizing first raw materials to obtain a macromolecular emulsifier; the first raw materials include a first polymerizable monomer, a molecular weight regulator, a first emulsifier, and a first initiator; the first polymerizable monomer includes an unsaturated carboxylic acid a1 and an acrylate monomer b1; The unsaturated carboxylic acid a1 accounts for 5% to 80% of the mass of the first raw material, and the acrylic acid ester monomer b1 accounts for 15% to 85% of the mass of the first raw material; Step 2, preparing carboxylated styrene-butadiene latex A; Using water as solvent, a macromolecular emulsifier and a second raw material are added to the solvent for polymerization reaction to obtain carboxylated styrene butadiene latex A; the second raw material includes a second polymerization monomer and a second initiator, and the second polymerization monomer includes an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

2. The method for preparing carboxylated styrene-butadiene latex according to claim 1, wherein Step 1: At least one of the following conditions must be met: (1) the unsaturated carboxylic acid a1 accounts for 10% to 60% by mass of the first raw material; (2) the acrylic acid ester monomer b1 accounts for 30% to 80% of the mass of the first raw material; (3) the molecular weight regulator accounts for 1% to 15% of the mass of the first raw material; (4) the first emulsifier accounts for 0.2% to 2.5% by mass of the first raw material; (5) The first initiator accounts for 1.5% to 3% of the mass of the first polymerization monomer.

3. The preparation method of carboxylated styrene-butadiene latex according to claim 2, wherein The unsaturated carboxylic acid a1 accounts for 12% to 40% of the mass of the first raw material.

4. The method for preparing carboxylated styrene-butadiene latex according to claim 2, wherein The acrylic acid ester monomer b1 accounts for 60% to 78% of the mass of the first raw material.

5. The method for preparing carboxylated styrene-butadiene latex according to claim 2, wherein The molecular weight regulator accounts for 4% to 8% of the mass of the first raw material.

6. The method for preparing carboxylated styrene-butadiene latex according to claim 2, wherein Step 2: At least one of the following conditions must be met: (1) The mass of the first raw material accounts for 5% to 50% of the sum of the mass of the first raw material and the second raw material; (2) the aromatic vinyl monomer accounts for 10% to 60% of the sum of the mass of the first raw material and the second raw material; (3) the aliphatic conjugated diene monomer accounts for 10% to 60% of the sum of the mass of the first raw material and the second raw material; (4) The second initiator accounts for 1% to 2% of the mass of the second polymerization monomer.

7. The method for preparing carboxylated styrene-butadiene latex according to claim 6, wherein The mass of the first raw material accounts for 10% to 30% of the sum of the mass of the first raw material and the second raw material.

8. The method for preparing carboxylated styrene-butadiene latex according to claim 6, wherein The aromatic vinyl monomer accounts for 20% to 50% of the total mass of the first raw material and the second raw material.

9. The method for preparing carboxylated styrene-butadiene latex according to claim 6, wherein The aliphatic conjugated diene monomer accounts for 20% to 50% of the total mass of the first raw material and the second raw material.

10. The method for preparing carboxylated styrene-butadiene latex according to claim 1, 2 or 6, wherein: At least one of the following conditions is met: (1) The unsaturated carboxylic acid a1 is selected from one or more of monobasic acids and dibasic acids; (2) the acrylic acid ester monomer b1 is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, tert-butyl acrylate, and isooctyl acrylate; (3) The molecular weight regulator is selected from one or more of alkyl mercaptans and xanthate compounds; (4) The aromatic vinyl monomer is selected from one or more of styrene, α-methylstyrene, vinyltoluene, and divinylbenzene; (5) The aliphatic conjugated diene monomer is selected from one or more of 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted straight-chain conjugated pentadienes, and substituted side-chain conjugated hexadienes; (6) The first initiator and the second initiator are independently selected from at least one of potassium persulfate, ammonium persulfate, and cumene peroxide.

11. The method for preparing carboxylated styrene-butadiene latex according to claim 10, wherein The unsaturated carboxylic acid a1 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

12. The method for preparing carboxylated styrene-butadiene latex according to claim 10, wherein: The alkyl mercaptan includes one or more of n-octyl mercaptan, n-dodecyl mercaptan, and tert-dodecyl mercaptan.

13. The method for preparing carboxylated styrene-butadiene latex according to claim 1, 2 or 6, wherein: The method further comprises step 3, preparing carboxylated styrene butadiene latex B: adding an agglomerating agent to carboxylated styrene butadiene latex A to obtain carboxylated styrene butadiene latex B.

14. The method for preparing carboxylated styrene-butadiene latex according to claim 13, wherein: The preparation method of the agglomerating agent comprises: using water as a solvent, mixing a third raw material, and subjecting the mixture to a polymerization reaction to obtain the agglomerating agent; The third raw material includes a third polymerizable monomer, a third emulsifier and a third initiator; the third polymerizable monomer includes an unsaturated carboxylic acid a2 and an acrylate monomer b2.

15. The method for preparing carboxylated styrene-butadiene latex according to claim 14, wherein: The preparation method of the agglomerating agent satisfies at least one of the following conditions: (1) the unsaturated carboxylic acid a2 accounts for 5% to 80% by mass of the third raw material; (2) the acrylic acid ester monomer b2 accounts for 15% to 85% of the mass of the third raw material; (3) the third emulsifier accounts for 0.2% to 2.5% of the mass of the third raw material; (4) the third initiator accounts for 0.5% to 1% by mass of the third polymerization monomer; (5) unsaturated carboxylic acid a2 is one or more selected from monobasic acids and dibasic acids; (6) the acrylic acid ester monomer b2 is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, tert-butyl acrylate, and isooctyl acrylate; (7) The third initiator is selected from at least one of potassium persulfate, ammonium persulfate, and cumene peroxide.

16. The method for preparing carboxylated styrene-butadiene latex according to claim 15, wherein: The unsaturated carboxylic acid a2 accounts for 10% to 60% of the mass of the third raw material.

17. The method for preparing carboxylated styrene-butadiene latex according to claim 15, wherein: The unsaturated carboxylic acid a2 accounts for 15% to 40% of the mass of the third raw material.

18. The method for preparing carboxylated styrene-butadiene latex according to claim 15, wherein: The acrylic acid ester monomer b2 accounts for 30% to 80% of the mass of the third raw material.

19. The method for preparing carboxylated styrene-butadiene latex according to claim 15, wherein: The acrylic acid ester monomer b2 accounts for 60% to 75% of the mass of the third raw material.

20. The method for preparing carboxylated styrene-butadiene latex according to claim 15, wherein: The unsaturated carboxylic acid a2 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

21. The method for preparing carboxylated styrene-butadiene latex according to claim 14, wherein: Meet at least one of the following conditions: (1) The mass of the first raw material accounts for 5% to 50% of the sum of the mass of the first raw material, the second raw material, and the third raw material; (2) the aromatic vinyl monomer accounts for 10% to 60% of the total mass of the first raw material, the second raw material and the third raw material; (3) the aliphatic conjugated diene monomer accounts for 10% to 60% of the total mass of the first raw material, the second raw material and the third raw material; (4) The third raw material accounts for 0.5% to 5% of the total mass of the first raw material, the second raw material and the third raw material.

22. The method for preparing carboxylated styrene-butadiene latex according to claim 21, wherein: The mass of the first raw material accounts for 10% to 30% of the total mass of the first raw material, the second raw material and the third raw material.

23. The method for preparing carboxylated styrene-butadiene latex according to claim 21, wherein: The aromatic vinyl monomer accounts for 20% to 50% of the total mass of the first raw material, the second raw material and the third raw material.

24. The method for preparing carboxylated styrene-butadiene latex according to claim 21, wherein: The aliphatic conjugated diene monomer accounts for 20% to 50% of the total mass of the first raw material, the second raw material and the third raw material.

25. The method for preparing carboxylated styrene-butadiene latex according to claim 21, wherein: The third raw material accounts for 1% to 3% of the total mass of the first raw material, the second raw material and the third raw material.

26. A carboxylated styrene-butadiene latex prepared according to the preparation method according to any one of claims 1 to 25.

27. A secondary battery negative electrode binder, characterized in that: Including the carboxylated styrene-butadiene latex according to claim 26.

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