Carboxylic butadiene-styrene latex, preparation method thereof and secondary battery negative electrode binder

Abstract

The invention relates to carboxylic butadiene-styrene latex, a preparation method thereof and a secondary battery negative electrode binder, belongs to the technical field of latex preparation, and overcomes the defect of low surface acid content caused by high content of embedded acid and water-phase free acid in the carboxylic butadiene-styrene latex in the prior art. The preparation method of the carboxylic butadiene-styrene latex comprises the following steps: step 1, preparing a macromolecular emulsifier; step 2, preparing carboxylic butadiene-styrene latex A; taking water as a solvent, adding the macromolecular emulsifier and the second raw material into the solvent, and carrying out polymerization reaction to obtain carboxylic butadiene-styrene latex A; the second raw material comprises a second polymeric monomer and a second initiator, and the second polymeric monomer comprises an aromatic vinyl monomer and an aliphatic conjugated diene monomer. The bonding strength of the carboxylic butadiene-styrene latex is remarkably 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, especially lithium-ion secondary battery technology, negative electrode materials have a crucial impact on the overall performance of the battery. Although the amount of negative electrode binder is small, as a key material to ensure the stable performance of negative electrode materials, its performance directly affects the cycle life and safety performance of the battery. Therefore, the development of negative electrode binders with excellent comprehensive performance has always been a hot topic in the battery field.

[0003] As the most commonly used battery negative electrode binder, carboxylated styrene butadiene latex has a large application market. The surface acid content is a key factor affecting the bonding performance of carboxylated styrene butadiene latex. The higher the surface acid content, the stronger the bonding. However, in the preparation process of carboxylated styrene butadiene latex, there are problems with high embedded acid and aqueous free acid content, which makes it difficult to increase the surface acid content of carboxylated styrene butadiene latex and it is difficult to meet the high bonding 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 have an adverse effect on 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 the 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 that the carboxylated butadiene styrene latex has high embedded acid and aqueous phase free acid content, resulting in low surface acid content, thereby providing a carboxylated butadiene styrene 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 solvent, mixing first raw materials and polymerizing them 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] With 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 polymerizable monomer and a second initiator, and the second polymerizable monomer includes an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

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

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

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

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

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

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

[0017] (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, preferably 10% to 30%;

[0018] (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, preferably 20% to 50%;

[0019] (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, preferably 20% to 50%;

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

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

[0024] In a possible embodiment, the molecular weight regulator is selected from one or more of alkyl mercaptans, xanthate-based compounds and phenolic compounds;

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

[0026] In a possible embodiment, the aromatic vinyl monomer is selected from one or more of styrene, α-methylstyrene, vinyltoluene, and divinylbenzene;

[0027] In one possible embodiment, 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;

[0028] The initiator is a conventional initiator for emulsion polymerization. In one 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 manner, the method further includes 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.

[0030] In a possible implementation, the method for preparing the agglomerating agent includes: using water as a solvent, mixing the third raw material, and subjecting the mixture to a polymerization reaction to obtain the agglomerating agent;

[0031] 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.

[0032] In one possible embodiment, the preparation method of the agglomerating agent satisfies at least one of the following conditions:

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

[0034] (2) the acrylic acid ester monomer b2 accounts for 15% to 85% by mass of the third raw material, preferably 30% to 80%, more preferably 60% to 75%;

[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% of the mass of the third polymerization monomer;

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

[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 sum of the mass of the first raw material, the second raw material and the third raw material, preferably 20% to 50%;

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

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

[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 a possible implementation, after the polymerization reaction in step 1, the pH is adjusted to 6.5 to 9.0 to obtain a macromolecular emulsifier.

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

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

[0050] There is no special restriction on the type and amount of the first emulsifier. Optionally, the first emulsifier can be selected from sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, and reactive emulsifiers with unsaturated bonds, preferably reactive emulsifiers.

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

[0052] There is no special restriction on the type and amount of the third emulsifier. Optionally, the third emulsifier can be selected from sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, reactive emulsifiers with unsaturated bonds, preferably reactive emulsifiers.

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

[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 solvent, mixing first raw materials, polymerizing and reacting to obtain macromolecular emulsifier; the first raw materials include first polymerizable monomers, molecular weight regulator, first emulsifier and first initiator; the first polymerizable monomers include unsaturated carboxylic acid a1 and acrylate monomer b1; step 2, preparing carboxylated styrene butadiene latex A; using water as solvent, adding macromolecular emulsifier and second raw materials into the solvent, polymerizing and reacting to obtain carboxylated styrene butadiene latex A; the second raw materials include second polymerizable monomers and second initiator, and the second polymerizable monomers include aromatic vinyl monomers and aliphatic conjugated diene monomers.

[0057] The present invention adopts unsaturated carboxylic acid a1 and acrylate monomer b1 to synthesize a high-acid-content macromolecular emulsifier. The carboxyl group is on the macromolecular emulsifier. The macromolecular emulsifier can reduce surface tension and play a stabilizing role. The water-insoluble latex particles are evenly dispersed and stabilized in water. Therefore, most of the macromolecular emulsifier exists on the surface of the latex particles. Therefore, the macromolecular emulsifier is used to replace the traditional small-molecule emulsifier. At the same time, a high-content carboxyl group can be introduced on the surface of the latex particles, and the content of embedded acid and free acid in the water phase can be greatly reduced, 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 invention provides a new method for preparing a carboxylated styrene-butadiene latex with high adhesion, 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, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope 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 the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[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 evaluation: The test method of 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 water phase free acid content test: The surface acid content and water phase acid content of latex were tested according to the method in patent CN110061187B.

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

[0068] Unless otherwise specified, the "parts" of raw materials in each example 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 gasification and condensation.

[0072] Methacrylic acid: purchased from Aladdin Reagents, purity 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 mixing 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 h, and continue to keep warm for 1 h.

[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: preparing 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 potassium persulfate and 40 g 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 agglomerating agent with a mass concentration (mass of the third raw material / mass of the agglomerating agent) of 40%.

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

[0092] 1246g of macromolecular emulsifier, 525g of water, 19g of potassium persulfate, 700g of styrene and 466g of butadiene were added to the autoclave in sequence, stirring was started and the mixture was heated to 70°C for 12h. After the reaction was completed, the emulsion was vacuumed to remove residual monomers, 62.75g of polymer agglomerating agent was added, stirring was performed for 0.5h, and finally water was added to adjust the solid 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: adding 1246g of macromolecular emulsifier (A), 525g of water, 19g of potassium persulfate, 700g of styrene and 466g of butadiene in a high-pressure reactor in sequence, stirring and heating to 70°C, and reacting for 12 hours. After the reaction is completed, the 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) 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 were prepared into a monomer pre-emulsion.

[0100] (2) Prepare an initiator solution by mixing 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 h, and continue to keep warm for 1 h.

[0102] (4) Add 186 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 22%.

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

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

[0105] In the autoclave, 4927 g of macromolecular emulsifier (step 1 can be repeated to prepare a sufficient amount of macromolecular emulsifier), 19 g of potassium persulfate, 700 g of styrene and 466 g of butadiene were added in sequence, stirring was started and heated to 70°C, and the reaction was carried out for 12 hours. After the reaction was completed, the residual monomers were removed from the emulsion, 62.75 g of high molecular weight agglomerating agent was added, stirred for 0.5, and finally the solid 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 mixing 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 h, and continue to keep warm for 1 h.

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

[0113] Step 2: Prepare agglomerating agent according to step 2 of Example 1

[0114] Step 3, preparing carboxylated styrene butadiene latex:

[0115] 450g macromolecular emulsifier, 650g water, 19g potassium persulfate, 700g styrene and 466g butadiene were added to the autoclave in sequence, stirring was started and heated to 70°C, and the reaction was continued for 12h. After the reaction was completed, the residual monomers were removed from the emulsion, 62.75g macromolecular agglomerating agent was added, stirred for 0.5, and finally water was added to adjust the solid content to 40%.

[0116] Example 5

[0117] The present embodiment provides a method for preparing carboxylated styrene butadiene latex, comprising the following steps:

[0118] Step 1: Preparation of macromolecular emulsifier:

[0119] (1) 50 g of methacrylic acid, 300 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.

[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 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 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% and adjust the pH to 7-8 to 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, preparing carboxylated styrene butadiene latex:

[0125] 2571g of macromolecular emulsifier (step 1 can be repeated to prepare a sufficient amount of macromolecular emulsifier), 19g of potassium persulfate, 700g of styrene and 466g of butadiene were added to the autoclave in sequence, stirring was started and heated to 70°C, and the reaction was carried out for 12 hours. After the reaction was completed, the residual monomers were removed from the emulsion, 62.75g of high molecular weight agglomerating agent was added, stirred for 0.5, and finally the solid content was adjusted 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 mixing 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 h, and continue to keep warm for 1 h.

[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 the agglomerating agent according to step 2 of Example 1.

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

[0135] 907g of macromolecular emulsifier, 1000g of water, 19g of potassium persulfate, 700g of styrene and 466g of butadiene were added to the autoclave in sequence, stirring was started and heated to 70°C, and the reaction was carried out for 12 hours. After the reaction was completed, the residual monomers were removed from the emulsion, 62.75g of high molecular weight agglomerating agent was added, stirred for 0.5, and finally the solid content was adjusted to 40%.

[0136] Comparative Example 1

[0137] This comparative example provides a method for preparing carboxylated styrene butadiene latex, comprising: sequentially adding 1740 g of water, 19 g of potassium persulfate, 28 g of emulsifier sodium dodecylbenzene sulfonate, 70 g of methacrylic acid, 700 g of styrene and 466 g of butadiene into a high-pressure reactor, stirring and heating to 70° C., and reacting for 12 hours. After the reaction is completed, the pH of the latex is adjusted to 7 using a 5% sodium hydroxide aqueous solution. The residual monomers are removed from the neutralized emulsion and water is added to adjust the solid content to 40%.

[0138] Test example

[0139] The carboxylated styrene butadiene latex prepared in the embodiment and the comparative example was respectively used as a binder to prepare the negative electrode sheet of a lithium ion battery, and 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 oven at 80°C 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 acid amount, acid amount in the aqueous phase, and embedded acid amount 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 greatly 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 strength.

[0146] From the comparison between Example 1 and Example 2, it can be seen that the particle size of carboxylated styrene butadiene latex is increased by using an agglomeration process, and the adhesion of the carboxylated styrene butadiene latex can be further improved.

[0147] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the 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 solvent, mixing first raw materials and polymerizing them 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; With 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 polymerizable monomer and a second initiator, and the second polymerizable 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 is met: (1) the unsaturated carboxylic acid a1 accounts for 5% to 80% by mass of the first raw material, preferably 10% to 60%, more preferably 12% to 40%; (2) the acrylic acid ester monomer b1 accounts for 15% to 85% by mass of the first raw material, preferably 30% to 80%, more preferably 60% to 78%; (3) the molecular weight regulator accounts for 1% to 15% by mass of the first raw material, preferably 4% to 8%; (4) the first emulsifier accounts for 0.2% to 2.5% of the mass of the first raw material; (5) The first initiator accounts for 1.5% to 3% of the mass of the first polymerizable monomer.

3. The method for preparing carboxylated styrene-butadiene latex according to claim 2, wherein Step 2 satisfies 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 and the second raw material, preferably 10% to 30%; (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, preferably 20% to 50%; (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, preferably 20% to 50%; (4) The second initiator accounts for 1% to 2% of the mass of the second polymerization monomer.

4. The method for preparing the carboxylated styrene-butadiene latex according to any one of claims 1 to 3, characterized in that: 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; Optionally, the unsaturated carboxylic acid a1 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; (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, xanthogen ester compounds and phenolic compounds; Optionally, the alkyl mercaptan includes one or more of n-octyl mercaptan, n-dodecyl mercaptan, and tert-dodecyl mercaptan; (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.

5. The method for preparing the carboxylated styrene-butadiene latex according to any one of claims 1 to 3, characterized in that: The method further comprises step 3, preparing carboxylated styrene butadiene latex B: adding an agglomerating agent into carboxylated styrene butadiene latex A to obtain carboxylated styrene butadiene latex B.

6. The method for preparing carboxylated styrene butadiene latex according to claim 5, wherein: The preparation method of the agglomerating agent comprises: using water as a solvent, mixing a third raw material, and polymerizing the mixture 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.

7. The method for preparing carboxylated styrene-butadiene latex according to claim 6, 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, preferably 10% to 60%, more preferably 15% to 40%; (2) the acrylic acid ester monomer b2 accounts for 15% to 85% by mass of the third raw material, preferably 30% to 80%, more preferably 60% to 75%; (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% of the mass of the third polymerization monomer; (5) unsaturated carboxylic acid a2 is selected from one or more of monobasic acid and dibasic acid; Optionally, the unsaturated carboxylic acid a2 is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; (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.

8. The method for preparing carboxylated styrene-butadiene latex according to claim 6, wherein: Satisfy 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, preferably 10% to 30%; (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, preferably 20% to 50%; (3) the aliphatic conjugated diene monomer accounts for 10% to 60% of the sum of the mass of the first raw material, the second raw material and the third raw material, preferably 20% to 50%; (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, preferably 1% to 3%.

9. A carboxylated styrene-butadiene latex prepared according to the preparation method according to any one of claims 1 to 8.

10. A secondary battery negative electrode binder, characterized in that: Including the carboxylated styrene-butadiene latex as claimed in claim 9.

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