Preparation method of highly flexible positive electrode aqueous binder and its product

Abstract

The present invention relates to the technical field of aqueous binders, and in particular to a preparation method and product of a highly flexible positive electrode aqueous binder, comprising at least the following steps: dissolving acrylamide in deionized water, and sequentially adding a carboxylic acid monomer, acrylonitrile and an acrylate monomer to obtain a mixture A; heating the mixture A to 50 60 ° C under inert gas protection, adding an initiator dropwise, filtering and washing to obtain a solid precipitate; adding an aqueous sodium hydroxide solution to the solid precipitate to obtain a highly flexible positive electrode aqueous binder. The present invention adopts a polymerization precipitation process, controls the solid content of the mixture A to be 45 60wt% and the reaction temperature to be 50 60 ° C, and the synthesized aqueous binder has good flexibility and peel strength while maintaining a viscosity of 5000 20000 mPa s.

Description

Technical Field

[0001] The present invention relates to the technical field of water-based binders, and in particular to a preparation method of a highly flexible positive electrode water-based binder and a product thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, excellent cycle performance, low self-discharge rate, and environmentally friendly nature, have become one of the most widely used and researched secondary batteries in the world today. Currently, lithium-ion batteries are not only widely used in portable electronic devices such as mobile phones and laptops, but are also gradually expanding into areas such as automotive power and energy storage systems. These new applications place higher demands on lithium-ion batteries' specific capacity, rate characteristics, cycle life, and other performance characteristics, necessitating further improvements in electrode energy density. This means that the proportion of active materials will gradually increase, while the proportion of inactive substances such as binders will further decrease. Therefore, maintaining the structural stability of the electrode during battery cycling while maintaining a low binder content will be a significant challenge.

[0003] Among the current binder preparation methods, water-based binders produced by the one-pot process, such as the one-pot preparation method for the conductive composite water-based binder provided in Chinese patent CN107663428B, have a wide molecular weight distribution. The synthesized water-based binder has a low peel strength of 3-4 N / m at a 2% positive electrode addition, and a viscosity of 1000-2000 mPa·s at a solid content of 15%. These physical and chemical indicators are far from those of conventional binders on the market and cannot meet market demand. Summary of the Invention

[0004] In view of the problems in the prior art, the present invention provides a method for preparing a highly flexible positive electrode aqueous binder, which comprises at least the following steps:

[0005] Dissolving acrylamide in deionized water, and sequentially adding a carboxylic acid monomer, acrylonitrile and acrylate monomer to obtain a mixture A;

[0006] The mixture A is heated to 50-60° C. under inert gas protection, an initiator is added dropwise, and then filtered and washed to obtain a solid precipitate;

[0007] A sodium hydroxide aqueous solution is added to the solid precipitate to obtain a highly flexible positive electrode aqueous binder.

[0008] In one embodiment, the solid content of the mixture A is 45-60 wt %, and can be 45 wt %, 50 wt %, 55 wt %, or 60 wt %.

[0009] In one embodiment, the acrylic acid ester monomer includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, and ethylene glycol dimethacrylate.

[0010] In one embodiment, the acrylic acid ester monomers include methyl acrylate and butyl acrylate; the mass ratio of methyl acrylate to butyl acrylate is 1:10.

[0011] In one embodiment, the acrylic acid ester monomer includes butyl methacrylate and butyl acrylate; the mass ratio of butyl methacrylate to butyl acrylate is 95:108.

[0012] In one embodiment, the acrylic acid ester monomers include ethyl methacrylate, methyl acrylate and butyl acrylate; the mass ratio of ethyl methacrylate, methyl acrylate and butyl acrylate is 18:1:1.

[0013] In one embodiment, when the acrylic acid ester monomer includes ethylene glycol dimethacrylate, the amount of ethylene glycol dimethacrylate does not exceed 10 wt % of the total amount of the acrylic acid ester monomer.

[0014] In one embodiment, the acrylic acid ester monomers include butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate; the mass ratio of butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate is 2:16:1.

[0015] In one embodiment, the carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, and maleic acid.

[0016] In one embodiment, the mass ratio of the acrylamide, carboxylic acid monomer, acrylonitrile and acrylic ester monomer is (15-20): (25-35): (35-45): (170-210).

[0017] In one embodiment, the mass ratio of acrylamide, carboxylic acid monomer, acrylonitrile and acrylic ester monomer is 16:30:40:(176-203), which can be exemplified by 16:30:40:176, 16:30:40:190, 16:30:40:200 and 16:30:40:203.

[0018] The present invention does not further limit the initiator, and an example thereof is an aqueous solution of ammonium persulfate with a mass fraction of 4%.

[0019] The second aspect of the present invention provides a product prepared by the above preparation method.

[0020] In one embodiment, the viscosity of the product at 40° C. is 5,000-20,000 mPa·s.

[0021] In one embodiment, the solid content of the product is 13-17 wt%.

[0022] In one embodiment, the pH of the product is 6.5-7.5.

[0023] Beneficial effects

[0024] 1. The highly flexible water-based binder prepared in this application is used in the preparation of lithium-ion positive electrode sheets. It can achieve high compaction with a low addition amount, and can also avoid broken bars, cracks, etc. It has good flexibility, thereby improving the continuity of the process, improving the product yield and product performance.

[0025] 2. The present invention adopts a polymerization precipitation method, which can effectively improve the purity of the product and reduce the amount of oligomers, thereby having greater viscosity and peel strength.

[0026] 3. In the polymerization precipitation process of the present invention, the solid content of the mixture A is controlled to be 45-60wt% and the reaction temperature is controlled to be 50-60°C. The synthesized aqueous adhesive has good flexibility and peel strength while maintaining a viscosity of 5000-20000 mPa.s.

[0027] 4. The amount of the highly flexible aqueous binder prepared by the present invention in the lithium-ion positive electrode sheet is only 2 wt %, but the peel strength reaches 8.9-11.14 N / m. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The experimental methods for which specific conditions are not specified in the examples are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used for which the manufacturer is not specified are all conventional products that can be purchased commercially.

[0029] Example 1

[0030] A first aspect of this embodiment provides a method for preparing a highly flexible positive electrode aqueous binder, comprising the following steps:

[0031] 16 g of acrylamide was dissolved in 240 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 176 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0032] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 10 h. A solid precipitate was obtained by filtration and washing.

[0033] A sodium hydroxide aqueous solution is added to the solid precipitate to adjust the pH value to 7.03, thereby obtaining a highly flexible positive electrode aqueous binder.

[0034] The sodium hydroxide aqueous solution is obtained by dissolving 15 g of sodium hydroxide in 500 g of deionized water.

[0035] The carboxylic acid monomer is acrylic acid.

[0036] The acrylic acid ester monomers are butyl acrylate and methyl acrylate, and the mass ratio of methyl acrylate to butyl acrylate is 1:10.

[0037] A second aspect of this embodiment provides a product prepared by the above preparation method, wherein the product is a highly flexible positive electrode aqueous binder. The highly flexible positive electrode aqueous binder has a viscosity of 9340 mPa·s at 40° C. and a solid content of 13.8 wt %.

[0038] Example 2

[0039] A first aspect of this embodiment provides a method for preparing a highly flexible positive electrode aqueous binder, comprising the following steps:

[0040] 16 g of acrylamide was dissolved in 250 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 203 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0041] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 10 h. A solid precipitate was obtained by filtration and washing.

[0042] A sodium hydroxide aqueous solution is added to the solid precipitate to adjust the pH value to 7.01, thereby obtaining a highly flexible positive electrode aqueous binder.

[0043] The sodium hydroxide aqueous solution is obtained by dissolving 13 g of sodium hydroxide in 500 g of deionized water.

[0044] The carboxylic acid monomer is methacrylic acid.

[0045] The acrylic acid ester monomers are butyl methacrylate and butyl acrylate; the mass ratio of butyl methacrylate to butyl acrylate is 95:108.

[0046] A second aspect of this embodiment provides a product prepared by the above preparation method, wherein the product is a highly flexible positive electrode aqueous binder. The highly flexible positive electrode aqueous binder has a viscosity of 17205 mPa·s at 40° C. and a solid content of 16.1 wt %.

[0047] Example 3

[0048] A first aspect of this embodiment provides a method for preparing a highly flexible positive electrode aqueous binder, comprising the following steps:

[0049] 16 g of acrylamide was dissolved in 250 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 190 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0050] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 10 h. A solid precipitate was obtained by filtration and washing.

[0051] A sodium hydroxide aqueous solution is added to the solid precipitate to adjust the pH value to 6.97, thereby obtaining a highly flexible positive electrode aqueous binder.

[0052] The sodium hydroxide aqueous solution is obtained by dissolving 16.5 g of sodium hydroxide in 500 g of deionized water.

[0053] The carboxylic acid monomer is maleic acid.

[0054] The acrylic acid ester monomers are butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate; the mass ratio of butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate is 2:16:1.

[0055] A second aspect of this embodiment provides a product prepared by the above preparation method, wherein the product is a highly flexible positive electrode aqueous binder. The highly flexible positive electrode aqueous binder has a viscosity of 11253 mPa·s at 40° C. and a solid content of 15.5 wt %.

[0056] Example 4

[0057] A first aspect of this embodiment provides a method for preparing a highly flexible positive electrode aqueous binder, comprising the following steps:

[0058] 16 g of acrylamide was dissolved in 250 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 200 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0059] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 12 h. A solid precipitate was obtained by filtration and washing.

[0060] A sodium hydroxide aqueous solution is added to the solid precipitate to adjust the pH value to 7.0, thereby obtaining a highly flexible positive electrode aqueous binder.

[0061] The sodium hydroxide aqueous solution is obtained by dissolving 15 g of sodium hydroxide in 500 g of deionized water.

[0062] The carboxylic acid monomer is acrylic acid.

[0063] The acrylic acid ester monomers are ethyl methacrylate, methyl acrylate and butyl acrylate; the mass ratio of ethyl methacrylate, methyl acrylate and butyl acrylate is 18:1:1.

[0064] A second aspect of this embodiment provides a product prepared by the above-mentioned preparation method, wherein the product is a highly flexible positive electrode aqueous binder. The highly flexible positive electrode aqueous binder has a viscosity of 11312 mPa·s at 40° C. and a solid content of 15.1 wt %.

[0065] Comparative Example 1

[0066] The first aspect of this comparative example provides a method for preparing a positive electrode aqueous binder, comprising the following steps:

[0067] 16 g of acrylamide was dissolved in 156 g of deionized water, and the mixture was added to a sodium hydroxide aqueous solution, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 176 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0068] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 12 h. A solid precipitate was obtained by filtration and washing.

[0069] A sodium hydroxide aqueous solution was added to the solid precipitate to adjust the pH value to 7.03, thereby obtaining a positive electrode aqueous binder.

[0070] The sodium hydroxide aqueous solution is obtained by dissolving 18 g of sodium hydroxide in 120 g of deionized water.

[0071] The carboxylic acid monomer is acrylic acid.

[0072] The acrylic acid ester monomers are butyl acrylate and methyl acrylate, and the mass ratio of methyl acrylate to butyl acrylate is 1:10.

[0073] The second aspect of this comparative example provides a product prepared by the above preparation method, wherein the product is a positive electrode aqueous binder. The positive electrode aqueous binder has a viscosity of 1340 mPa·s at 40° C. and a solid content of 15.4 wt %.

[0074] Comparative Example 2

[0075] The first aspect of this comparative example provides a method for preparing a positive electrode aqueous binder, comprising the following steps:

[0076] 16 g of acrylamide was dissolved in 650 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 190 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0077] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 10 h. A solid precipitate was obtained by filtration and washing.

[0078] A sodium hydroxide aqueous solution was added to the solid precipitate to adjust the pH value to 6.92, thereby obtaining a positive electrode aqueous binder.

[0079] The sodium hydroxide aqueous solution is obtained by dissolving 16 g of sodium hydroxide in 300 g of deionized water.

[0080] The carboxylic acid monomer is maleic acid.

[0081] The acrylic acid ester monomers are butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate; the mass ratio of butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate is 2:16:1.

[0082] The second aspect of this comparative example provides a product prepared by the above preparation method, wherein the product is a positive electrode aqueous binder. The positive electrode aqueous binder has a viscosity of 2104.5 mPa·s at 40° C. and a solid content of 15.7 wt %.

[0083] Comparative Example 3

[0084] The first aspect of this comparative example provides a method for preparing a positive electrode aqueous binder, comprising the following steps:

[0085] 16 g of acrylamide was dissolved in 250 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 200 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0086] The mixture A was heated to 40° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 12 h. A solid precipitate was obtained by filtration and washing.

[0087] A sodium hydroxide aqueous solution was added to the solid precipitate to adjust the pH value to 6.88, and deionized water was added to adjust the solid content to obtain a positive electrode aqueous binder with a solid content of 8.67 wt %.

[0088] The sodium hydroxide aqueous solution is obtained by dissolving 15.5 g of sodium hydroxide in 500 g of deionized water.

[0089] The carboxylic acid monomer is acrylic acid.

[0090] The acrylic acid ester monomers are ethyl methacrylate, methyl acrylate and butyl acrylate; the mass ratio of ethyl methacrylate, methyl acrylate and butyl acrylate is 18:1:1.

[0091] In a second aspect, this comparative example provides a product prepared by the above preparation method, wherein the product is a positive electrode aqueous binder, and the viscosity of the positive electrode aqueous binder at 40° C. is 43782 mPa·s.

[0092] Comparative Example 4

[0093] The first aspect of this comparative example provides a method for preparing a positive electrode aqueous binder, comprising the following steps:

[0094] 16 g of acrylamide was dissolved in 250 g of deionized water, and 30 g of a carboxylic acid monomer, 40 g of acrylonitrile and 190 g of an acrylate monomer were added in sequence to obtain a mixture A;

[0095] The mixture A was heated to 60° C. under nitrogen protection, 50 g of a 4% ammonium persulfate aqueous solution was added dropwise, and the mixture was kept warm for 10 h. A solid precipitate was obtained by filtration and washing.

[0096] A sodium hydroxide aqueous solution was added to the solid precipitate to adjust the pH value to 7.45, thereby obtaining a positive electrode aqueous binder.

[0097] The sodium hydroxide aqueous solution is obtained by dissolving 16.5 g of sodium hydroxide in 500 g of deionized water.

[0098] The carboxylic acid monomer is maleic acid.

[0099] The acrylic acid ester monomers are butyl acrylate and ethylene glycol dimethacrylate; the mass ratio of butyl acrylate to ethylene glycol dimethacrylate is 2:17.

[0100] The second aspect of this comparative example provides a product prepared by the above preparation method, wherein the product is a positive electrode aqueous binder. The positive electrode aqueous binder has a viscosity of 4253 mPa·s at 40° C. and a solid content of 15.1 wt %.

[0101] Performance Testing

[0102] 1. Peel strength test: The aqueous binder prepared in each embodiment and comparative example was mixed with the conductive agent and lithium manganate material in a mass ratio of 2:2:96 to obtain a positive electrode slurry; the positive electrode slurry was coated on the surface of the conductive aluminum foil current collector (coating surface density 4.2 g / dm 2 ), heating and drying, roller pressing density 2.8g / dm 3 The finished electrode pieces were sliced ​​and subjected to a peel strength test (referring to standard GB / T 2790-1995). The test results are shown in Table 1.

[0103] 2. Flexibility test: The aqueous binder prepared in each embodiment and comparative example was mixed with the conductive agent and lithium manganese oxide material in a mass ratio of 2:2:96 to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of the conductive aluminum foil current collector, heated and dried, and rolled to obtain a compaction density of 2.8 g / dm 3 , 2mm winding needle winding; after unfolding, observe whether the coating can still remain opaque and unbroken, so as to evaluate its flexibility; if it can still remain opaque and unbroken, the flexibility is good, otherwise, the flexibility is poor. The test results are shown in Table 1.

[0104] The lithium manganese oxide material is conventional lithium manganese oxide (QN-C-101) from Hebei Qiangneng Lithium Battery Technology Co., Ltd., and the conductive agent is conductive carbon black from Shanghai Huiping New Energy Co., Ltd.

[0105] Table 1

[0106]

[0107] As can be seen from the table above, the finished electrode prepared by the aqueous binder of the present application has a compaction density of 3.0 g / dm 3 , and after being wound under a 2mm winding needle, it can still remain opaque and unbroken, and has higher flexibility than the aqueous binders prepared in Comparative Examples 1-4; and the amount of high-flexibility aqueous binder used in the lithium-ion positive electrode sheet is only 2wt% to make the peel strength reach 8.9-11.14N / m, which can achieve a balance between high peel strength and high flexibility.

Claims

1. A method for preparing a highly flexible positive electrode aqueous binder, characterized in that: At least the following steps are included: Dissolving acrylamide in deionized water, and sequentially adding a carboxylic acid monomer, acrylonitrile and acrylate monomer to obtain a mixture A; The mixture A is heated to 50-60° C. under inert gas protection, an initiator is added dropwise, and then filtered and washed to obtain a solid precipitate; adding a sodium hydroxide aqueous solution to the solid precipitate to obtain a highly flexible positive electrode aqueous binder; The solid content of the highly flexible positive electrode aqueous binder is 13-17 wt %; The solid content of the mixture A is 45-60wt%; The acrylic acid ester monomer includes one or more of methyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, and ethylene glycol dimethacrylate; when the acrylic acid ester monomer includes ethylene glycol dimethacrylate, the amount of ethylene glycol dimethacrylate does not exceed 10 wt % of the total amount of the acrylic acid ester monomer.

2. The method for preparing a highly flexible positive electrode aqueous binder according to claim 1, wherein: The carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, and maleic acid.

3. The method for preparing a highly flexible positive electrode aqueous binder according to claim 1, wherein: The mass ratio of the acrylamide, carboxylic acid monomer, acrylonitrile and acrylic ester monomer is (15-20): (25-35): (35-45): (170-210).

4. The method for preparing a highly flexible positive electrode aqueous binder according to claim 3, wherein: The mass ratio of the acrylamide, carboxylic acid monomer, acrylonitrile and acrylic ester monomer is 16:30:40:(176-203).

5. A product prepared according to the method for preparing a highly flexible positive electrode aqueous binder according to any one of claims 1 to 4.

6. The product obtained by the method for preparing a highly flexible positive electrode aqueous binder according to claim 5, characterized in that: The viscosity of the product at 40° C. is 5000-20000 mPa·s.

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