A water-based binder for lithium-ion battery cathode and its preparation method

Abstract

This invention discloses an aqueous binder for lithium-ion battery cathodes and its preparation method. The binder comprises an emulsion dispersion formed from a multi-component copolymer polymerized from acrylic acid and its derivatives. The multi-component copolymer forms an ABC three-segment structure according to the polarity of its side groups and the polymerization process, representing strongly polar, weakly polar, and non-polar segments, respectively. The strongly polar segments are polymerized from monomers of acrylic acid or acrylic acid derivatives with strongly polar groups, or from acrylates. The weakly polar segments are polymerized from acrylates and their derivatives with weakly polar groups. The non-polar segments are polymerized from acrylates and their derivatives with non-polar groups. This invention synthesizes strongly polar, weakly polar, and non-polar segments separately. The resulting binder emulsion exhibits good mechanical stability and does not exhibit demulsification or agglomeration during dispersion. It also has low surface tension, which is more conducive to the dispersion of conductive agents and cathode materials, significantly improving dispersion efficiency and film-forming properties.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and mainly to an aqueous binder for the positive electrode of a lithium-ion battery and its preparation method. Background Technology

[0002] With the development of science and technology and the improvement of people's material and cultural living standards, people's requirements for portable rechargeable batteries are also increasing. Lithium-ion rechargeable batteries can meet people's requirements for portable power sources in many aspects. Currently, lithium-ion batteries are widely used in mobile phones, digital products, model airplanes, electric vehicles, and automobiles. At the same time, with the continuous growth of my country's economy, people's attention to the living environment has greatly increased. Therefore, while developing any project, we must protect our living environment. It is evident that even new energy projects that are strongly promoted must not be developed at the expense of environmental protection.

[0003] In current traditional lithium-ion battery manufacturing processes, particularly in the preparation of the positive electrode, traditional solvent-based binders are still used. This requires a large amount of solvent to dissolve the binder, which is then evaporated during the manufacturing process. This not only results in significant energy waste but also releases the solvent into the atmosphere (even with the best current recycling systems, 100% recovery is difficult to achieve), causing environmental pollution. Therefore, converting the binder from oil to water has become an unavoidable issue in lithium-ion battery manufacturing.

[0004] Currently, researchers both domestically and internationally have conducted extensive research on this topic. CN01108511.8 and CN01108524.X disclose an adhesive, but this adhesive still has the following drawbacks in practical use: it requires low-temperature baking, resulting in low generation efficiency; the prepared electrode sheets are brittle and have poor flexibility, making them prone to breakage during battery manufacturing; and they are also prone to warping during manufacturing, leading to the formation of scrap batteries and increasing battery production costs. CN201410731027.8 and CN200910300150.3 use a low-polarity polymer as the core and a high-polarity polymer as the shell to synthesize a lithium-ion aqueous adhesive with improved flexibility. However, because it uses an existing polymer as the reaction core, the selectivity and designability are poor, and this product has not been able to effectively improve the problems existing in the lithium-ion battery manufacturing process. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides an emulsifier-free aqueous binder for lithium-ion battery cathodes with a stable structure and low surface tension. A second objective is to provide a method for preparing this aqueous binder for lithium-ion battery cathodes.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A water-based binder for the positive electrode of a lithium-ion battery, characterized in that it comprises an emulsion dispersion formed by a multi-component copolymer polymerized from acrylic acid and its derivatives. The multi-component copolymer forms an ABC three-segment structure according to the polarity of the monomers and the polymerization process, where segment A is a strongly polar segment, segment B is a weakly polar segment, and segment C is a non-polar segment. The strongly polar segment is polymerized from acrylic acid or acrylic acid derivative monomers with strongly polar groups, or their corresponding salts; the weakly polar segment is polymerized from acrylates and their derivatives with weakly polar groups; and the non-polar segment is polymerized from acrylates and their derivatives with non-polar groups. The mass ratio of the strongly polar segment, the weakly polar segment, and the non-polar segment is (10–80):(10–60):(10–60).

[0008] Thus, the water-based adhesive of this invention, using water as the dispersion medium, solves the environmental protection problem of adhesives used in lithium batteries, making it an environmentally friendly adhesive. The adhesive of this invention exhibits excellent emulsion bonding performance, good flexibility, and produces a smooth and flat positive electrode sheet with good cycle performance.

[0009] Furthermore, the monomer or acrylate of the acrylic acid or acrylic acid derivative with a strongly polar group includes methacrylic acid and its salts, itaconic acid, maleate, acrylamide methylpropanesulfonic acid and its salts, acrylamide isopropyl sulfonic acid and its salts, 2-allyl ether 3-hydroxypropane-1-sulfonic acid and its salts, vinyl sulfonic acid and its salts, allyl sulfonic acid and its salts, methacrylic acid sulfonic acid and its salts, styrene sulfonic acid and its salts, and any one or any two of these components are mixed in a proportion greater than zero percent, or any three are mixed in a proportion greater than zero percent, or any four are mixed in a proportion greater than zero percent, or any five are mixed in a proportion greater than zero percent, until all the aforementioned components are mixed in a proportion greater than zero percent; wherein the cation of the salt is lithium ion, sodium ion, potassium ion, or ammonium ion. The total amount of the polar group is 10-80% of the total mass.

[0010] Furthermore, the acrylates and their derivatives with weakly polar groups include acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, acryloylmorpholine, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, methacryloylmorpholine, hydroxypropyl methacrylate, acrylonitrile, and butadiene nitrile. 5-Hexenonitrile cyclohexene-1-nitrile, 2-NonenonitrileVinyl acetate, N-hydroxymethylacrylamide, hydroxyethylacrylurea, diacetone acrylamide, diallyl phthalate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, bisphenol A glycerol dimethyl acrylate Glycerol 1,3-diglycerol diglyceride acrylate 1,6-Hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, glycidyl methacrylate, polyethylene glycol monomethyl ether acrylate, polyethylene glycol monomethyl ether methacrylate, allyl polyethylene glycol, allyl polypropylene glycol; obtained by mixing any one or any two of these components in a proportion greater than zero percent, or any three of these components in a proportion greater than zero percent, or any four of these components in a proportion greater than zero percent, or any five of these components in a proportion greater than zero percent, until all of the aforementioned components are mixed in a proportion greater than zero percent.

[0011] Furthermore, the acrylates and their derivatives with nonpolar groups include ethyl acrylate, propyl acrylate, n- / isobutyl acrylate, n-octyl acrylate, 2-isooctyl acrylate, n- / isodecyl acrylate, dodecyl acrylate, tetradecyl acrylate, hexadecyl acrylate, lauryl acrylate, octadecyl acrylate, dodecyl acrylate, isobornyl acrylate, n- / isobutyl methacrylate, 2-isooctyl methacrylate, vinyl neodecanoate, dibutyl maleate, and octadecyl methacrylate; any one, or any two, mixed in a proportion greater than 0%, or any three, or any four, or any five, mixed in a proportion greater than 0%, until all the aforementioned components are mixed and polymerized in a proportion greater than 0%.

[0012] Furthermore, the initiator used in the adhesive is potassium persulfate, ammonium persulfate, sodium persulfate, sodium sulfite, sodium bisulfite, azobisisobutyronitrile, or azobisisobutyronitrile. Ding Mi The mixture may contain any one or two of the following: azobisisobutyrazoline hydrochloride (AIBA), azobisisobutyronitrile (AIBI), and azobisisobutyronitrile (AIBI), in a proportion greater than zero percent; or any three of the following: in a proportion greater than zero percent; or any four of the following: in a proportion greater than zero percent; until all of the aforementioned components are mixed in a proportion greater than zero percent.

[0013] Furthermore, the adhesive has a solids content of 8-30% and a viscosity of 5000-100000 mPa.

[0014] Furthermore, the mass percentage of the strongly polar chain segment in the whole molecule is 20-50%, the mass percentage of the weakly polar chain segment is 20-40%, and the mass percentage of the nonpolar chain segment is 20-40%.

[0015] Furthermore, the combination of the strongly polar segments, weakly polar segments, and non-polar segments, as well as the combination of segments with different polarities, are all formed by the self-polymerization or copolymerization of carbon-carbon double bonds to form the ABC three-segment structure.

[0016] Thus, the combination of strong polar segments, weak polar segments, and non-polar segments, as well as the combination of segments with different polarities, in this invention are all formed by the free radical self-polymerization or copolymerization of carbon-carbon double bonds to form the ABC three-segment structure.

[0017] A method for preparing an aqueous binder for the positive electrode of a lithium-ion battery, characterized by comprising the following steps:

[0018] 1) Prepare the aforementioned components according to the components and proportions required by the process; including monomers of acrylic acid or acrylic acid derivatives with strong polar groups, or monomers or mixtures of acrylates, monomers or mixtures of acrylates and their derivatives with weak polar groups, monomers or mixtures of acrylates and their derivatives with non-polar groups, as well as initiators and deionized water.

[0019] 2) Add the monomer or mixture with strong polar groups and deionized water to the reaction apparatus and stir to mix evenly; heat to 50℃-90℃, add the initiator to initiate the polymerization reaction, and keep the reaction at a constant temperature for a period of time;

[0020] 3) Add a monomer or mixture with a weakly polar group and an initiator dropwise to the reaction apparatus of step 2), control the temperature at 60℃-90℃, and stir; then react at a constant temperature of 60℃-90℃ for a period of time.

[0021] 4) Add the monomer or mixture with nonpolar groups and the initiator dropwise to the reaction apparatus of step 3). The temperature is controlled at 60℃-90℃ during addition, and the mixture is stirred. After the addition is completed, maintain the temperature at 60℃-90℃ for a period of time as required by the constant temperature process.

[0022] Thus, the method of the present invention employs a synthesis method that separately synthesizes strongly polar, weakly polar, and non-polar segments. The combination of strongly polar, weakly polar, and non-polar segments, as well as the combination of segments with different polarities, are all achieved through free radical self-polymerization or copolymerization of carbon-carbon double bonds to form the aforementioned ABC three-segment structure. The prepared adhesive emulsion has good mechanical stability and will not exhibit demulsification phenomena such as agglomeration during dispersion. It also has low surface tension, which is more conducive to the dispersion of conductive agents and positive electrode materials, greatly improving dispersion efficiency and film-forming properties.

[0023] The isothermal reaction time is 0.2–5 hours.

[0024] Compared with existing technologies, the aqueous binder for lithium-ion battery cathodes and its preparation method obtained in this invention have the following advantages:

[0025] 1. The adhesive of this invention uses water as a dispersion medium, which solves the environmental protection problem of adhesives used in lithium batteries and is an environmentally friendly adhesive.

[0026] 2. The present invention employs a synthesis method that separately synthesizes strong polar, weak polar, and non-polar adhesives. The prepared adhesive emulsions have good mechanical stability and do not exhibit demulsification phenomena such as agglomeration during dispersion. They also have low surface tension, which is more conducive to the dispersion of conductive agents and positive electrode materials, greatly improving dispersion efficiency and film-forming properties.

[0027] 3. The adhesive emulsion of the present invention has excellent bonding performance and good flexibility, and the prepared positive electrode sheet is smooth and flat with good cycle performance.

[0028] 4. This invention is superior to existing adhesives in both capacity utilization and capacity retention, and is conducive to large-scale promotion. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the adhesion of the adhesive in Embodiment 2 of the present invention;

[0030] Figure 2 This is a schematic diagram showing the capacity utilization of the LMO cathode coating of the adhesive in Embodiment 2 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] This invention relates to an aqueous binder for lithium-ion battery cathodes, comprising an emulsion dispersion formed from a multi-component copolymer polymerized from acrylic acid and its derivatives. It is an aqueous emulsion free of traditional emulsifiers. The emulsion is composed of a polymer consisting of strongly polar segments, weakly polar segments, and non-polar segments. The multi-component copolymer forms an ABC three-segment structure according to the polarity of its side groups and the polymerization process, consisting of a strongly polar segment (A segment) with strongly polar groups, a weakly polar segment (B segment) with weakly polar groups, and a non-polar segment (C segment) with non-polar groups. The solid content of the emulsion is 5-30%, and the mass ratio of the strongly polar segments to the weakly polar segments and the non-polar segments is (10-80):(10-60):(10-60).

[0033] The specific ratio of strongly polar chain segments, weakly polar chain segments, and non-polar chain segments can be: 10:30:60, or 10:40:50, or 10:50:40, or 20:30:50, or 30:40:30, or 40:20:40, or 50:10:40, or 60:30:10, or 70:15:15, or 80:10:10, etc., all of which can meet the needs of the present invention.

[0034] The combination of strong polar segments, weak polar segments, and non-polar segments, as well as the combination of segments with different polarities, in this invention are all formed by free radical self-polymerization or copolymerization of carbon-carbon double bonds to form the ABC three-segment structure.

[0035] The highly polar segment (Segment A) of the emulsion is polymerized from monomers or acrylates containing highly polar groups, including methacrylic acid and its salts, itaconic acid, maleate, acrylamide methylpropanesulfonic acid and its salts, acrylamide isopropyl sulfonic acid and its salts, 2-allyl ether 3-hydroxypropane-1-sulfonic acid and its salts, vinyl sulfonic acid and its salts, allyl sulfonic acid and its salts, methacrylic acid sulfonic acid and its salts, and styrene sulfonic acid and its salts. Any one or two of these components are mixed in a proportion greater than zero percent, or any three are mixed in a proportion greater than zero percent, or any four are mixed in a proportion greater than zero percent, or any five are mixed in a proportion greater than zero percent, until all the aforementioned components are mixed in a proportion greater than zero percent. The cation of the salt is lithium ion, sodium ion, potassium ion, or ammonium ion, and the entire highly polar segment containing the highly polar groups constitutes 10-80% of the total mass.

[0036] The weakly polar segments (B segments) of the emulsion containing weakly polar groups are polymerized from acrylates and their derivatives containing weakly polar groups, including acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, acryloylmorpholine, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, methacryloylmorpholine, hydroxypropyl methacrylate, acrylonitrile, and butadiene nitrile. 5-Hexenonitrile cyclohexene-1-nitrile, 2-Nonenonitrile Vinyl acetate, N-hydroxymethylacrylamide, hydroxyethylacrylurea, diacetone acrylamide, diallyl phthalate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, bisphenol A glycerol dimethyl acrylate Glycerol 1,3-diglycerol diglyceride acrylic acid esterThe mixture comprises 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, glycidyl methacrylate, polyethylene glycol monomethyl ether acrylate, polyethylene glycol monomethyl ether methacrylate, allyl polyethylene glycol, allyl polypropylene glycol, etc.; and is obtained by mixing any one, or any two, in a proportion greater than zero percent, or any three, or any four, or any five, until all the aforementioned components are mixed in a proportion greater than zero percent; the entire weakly polar chain segment accounts for 10-60% of the total mass.

[0037] The nonpolar segment (C segment) of the emulsion is polymerized from acrylates and their derivatives containing nonpolar groups, including ethyl acrylate, propyl acrylate, n- / isobutyl acrylate, n-octyl acrylate, 2-isooctyl acrylate, n- / isodecyl acrylate, dodecyl acrylate, tetradecyl acrylate, hexadecyl acrylate, lauryl acrylate, octadecyl acrylate, dodecyl acrylate, isobornyl acrylate, n- / isobutyl methacrylate, 2-isooctyl methacrylate, vinyl neodecanoate, dibutyl maleate, and octadecyl methacrylate; any one, two, three, four, or five of these components are mixed in a proportion greater than 0%, or any three, four, or five of these components are mixed in a proportion greater than 0%, or any five of these components are mixed in a proportion greater than 0%, until all of the aforementioned components are polymerized in a proportion greater than 0%. The total amount of the nonpolar segment is 10-60% of the total mass.

[0038] The initiators used in the polymerization reaction of the adhesive in this invention are potassium persulfate, ammonium persulfate, sodium persulfate, sodium sulfite, sodium bisulfite, azobisisobutyronitrile, and azobisisobutyronitrile. Ding Mi The mixture may contain any one or two of the following: azobisisobutyrazoline hydrochloride (AIBA), azobisisobutyronitrile (AIBI), and azobisisobutyronitrile (AIBI), in a proportion greater than zero percent; or any three of the following: in a proportion greater than zero percent; or any four of the following: in a proportion greater than zero percent; until all of the aforementioned components are mixed in a proportion greater than zero percent.

[0039] In the adhesive, the mass percentage of the strongly polar chain segment (A segment) in the whole molecule is 10-80, preferably 20-50%; the mass percentage of the weakly polar chain segment (B segment) is 10-60, preferably 20-40%; and the mass percentage of the non-polar chain segment (C segment) is 10-60, preferably 20-40%.

[0040] The adhesive has a solid content of 8-30% and a viscosity of 5000-100000 MPa.

[0041] The present invention discloses a method for preparing an aqueous binder for the positive electrode of a lithium-ion battery, comprising the following steps:

[0042] 1) Prepare the aforementioned components according to the components and proportions required by the process, including monomers of acrylic acid or acrylic acid derivatives with strong polar groups, or monomers or mixtures of acrylates, monomers or mixtures of acrylates and their derivatives with weak polar groups, monomers or mixtures of acrylates and their derivatives with non-polar groups, as well as initiators and deionized water.

[0043] 2) Add the monomer or mixture with strong polar groups and deionized water to the reaction apparatus and stir to mix evenly; heat to 50℃-90℃, add an initiator to initiate the polymerization reaction, and keep the reaction at a constant temperature for a period of time, such as 0.2-5 hours; this polymerization reaction mainly yields the strong polar chain segment (A segment) of the present invention.

[0044] 3) Add the monomer or mixture with a weakly polar group and the initiator dropwise into the reaction apparatus of step 2), controlling the rate of addition of the monomer or mixture with a weakly polar group, usually completing the addition within 1-8 hours, while maintaining the temperature at 60℃-90℃ and stirring; then, maintain the temperature at 60℃-90℃ for a period of time, such as 0.2-5 hours; in this step, through the polymerization reaction, the weakly polar chain segment (B segment) can be linked together with the chain segment A during the polymer formation process;

[0045] 4) Add a monomer or mixture with nonpolar groups and an initiator dropwise into the reaction apparatus of step 3).

[0046] The rate of addition of monomers or mixtures containing nonpolar groups is controlled, and the temperature is maintained at 60℃-90℃ during addition, with stirring. Addition is typically completed within 1-5 hours. After addition, the temperature is maintained at 60℃-90℃ for the required period of time as per the isothermal process. In this invention, the combination of strongly polar, weakly polar, and nonpolar segments, as well as the combination of segments with different polarities, is achieved through free radical self-polymerization or copolymerization of carbon-carbon double bonds to form the aforementioned ABC three-segment structure.

[0047] Example 1:

[0048] In this embodiment, sodium vinyl sulfonate and lithium acrylate are used as monomers with strongly polar groups, acrylamide and acrylonitrile are used as monomers with weakly polar groups, and methyl acrylate and ethyl acrylate are used as monomers with non-polar groups to form segments A, B, and C of the emulsion, respectively. The specific composition by mass is as follows:

[0049] Section A: Sodium vinyl sulfonate 5g, lithium acrylate 20g, deionized water 144.8g;

[0050] Section B: Acrylamide 10g, Acrylonitrile 15g, Sodium persulfate initiator 0.3g, Deionized water 154.7g;

[0051] Section C: 15g ethyl acrylate, 10g methyl acrylate, 0.3g sodium persulfate initiator, and 127.7g deionized water.

[0052] The preparation method of the above-mentioned binder emulsion for lithium-ion battery cathode is as follows: Monomers or mixtures forming segment A are added sequentially, stirred at 200 rpm under nitrogen protection, heated to 75°C, and 0.2 g of sodium persulfate is added to initiate polymerization for 1 hour. Then, monomers or mixtures with weakly polar groups forming segment B and an initiator are slowly added dropwise (stirring is required during addition), with the temperature controlled at 78°C. The addition is completed in 3 hours, followed by a constant temperature of 78°C for 30 minutes. Finally, monomers or mixtures with non-polar groups forming segment C and an initiator are added dropwise (stirring is required during addition), with the temperature controlled at 78°C. The addition is completed in 3 hours, followed by a temperature increase to 82°C and a constant temperature for 3 hours. This yields an aqueous binder with the above-mentioned composition and a viscosity of 5000-6500 centipoise.

[0053] Example 2:

[0054] This implementation case adopts the process method of the above case. The difference from case 1 is that the initiator is ammonium persulfate. The rest is the same. The emulsion prepared by this method has a slightly higher viscosity, ranging from 8000 to 12000 centipoise.

[0055] Take 200g of the adhesive emulsion synthesized in this embodiment, 500g of deionized water, and stir slowly for 10 minutes. Then add 30g of conductive agent and disperse at high speed for 60 minutes. Next, add 1440g of lithium manganese oxide in two portions and disperse at high speed for 120 minutes each time. Then add an appropriate amount of water to adjust the viscosity. The prepared lithium manganese oxide slurry has a solid content of 68% and a viscosity of 5500. After standing for 24 hours, there is no obvious precipitation. When coated on aluminum foil, it has a uniform appearance, good adhesion, and good electrical properties. See [link to relevant documentation]. Figure 1 , Figure 2 .

[0056] Example 3:

[0057] The preparation method of the adhesive in this embodiment is basically the same as that in 1, except that the initiator is ammonium persulfate, and the components of segments A, B, and C of the emulsion are different: sodium 2-allyl ether-3-hydroxypropane-1-sulfonate and sodium acrylate are monomers with strong polar groups; acryloylmorpholine, hydroxybutyl acrylate, hydroxyethyl acrylate, and acrylamide are mixtures with weak polar groups; and methyl acrylate and butyl acrylate are mixtures with non-polar groups. The specific composition is as follows:

[0058] Section A: 4g of sodium 2-allyl ether 3-hydroxypropane-1-sulfonate, 12g of sodium acrylate, and 96g of deionized water;

[0059] Section B: Acryloylmorpholine 7g, hydroxybutyl acrylate 10g, hydroxyethyl acrylate 5g, acrylamide 3g, ammonium persulfate 0.3g, deionized water 150g;

[0060] Section C: 12g methyl acrylate, 10g butyl acrylate, 0.3g ammonium persulfate, 110g deionized water.

[0061] The preparation method of the above-mentioned lithium-ion battery adhesive emulsion is as follows: Monomers or mixtures with strongly polar groups forming emulsion segment A are added sequentially, stirred at 200 rpm under nitrogen protection, and heated to 72°C. 0.2 g of sodium persulfate initiator is added to initiate polymerization for 1 hour. Then, monomers with weakly polar groups forming emulsion segment B and the initiator are slowly added dropwise (stirring is required during addition). The temperature is controlled at 76°C during addition, and the addition is completed in 3 hours. The temperature is then maintained at 76°C for 1 hour. Finally, monomers or mixtures with non-polar groups forming emulsion segment C and the initiator are added dropwise (stirring is required during addition). The addition temperature is controlled at 76°C, and the addition is completed in 3 hours. The temperature is then raised to 80°C and maintained for 6 hours. This yields a core-shell aqueous adhesive with the above-mentioned composition and a solid content of 15%.

[0062] This embodiment introduces flexible hydroxybutyl acrylate and hydroxyethyl acrylate into the weakly polar segments and butyl acrylate into the non-polar segments, thus the resulting adhesive film is more flexible and has excellent elasticity.

[0063] Example 4:

[0064] The method and process in this embodiment are basically the same as those in Example 3, the main difference being that the initiator used is azobisisobutyric acid (AI). Ding Mi The hydrochloride salt, with the reaction temperature controlled at 50-60℃ and the overall reaction time extended by 6 hours, produces an adhesive emulsion with high viscosity, good fluidity, and water resistance. This adhesive also exhibits excellent thermal stability and a high decomposition temperature.

[0065] Example 5:

[0066] The preparation method of the adhesive in this embodiment is basically the same as that in 1, except that the initiator is ammonium persulfate, and the components of segments A, B, and C of the emulsion are different: sodium acrylamide (methyl)propanesulfonate, lithium itaconic acid, and lithium acrylate are used as monomers with strong polar groups, acrylamide, acrylonitrile, and hydroxypropyl methacrylate are used as monomers with weak polar groups, and 2-isooctyl acrylate and lauryl acrylate are used as monomers with non-polar groups. The specific composition is as follows:

[0067] Section A: Sodium acrylamide (methyl)propanesulfonate 5g, lithium itaconic acid 2g, lithium acrylate 10g, deionized water 90g;

[0068] Section B: Acrylamide 8g, Acrylonitrile 10g, Hydroxypropyl Methacrylate 2g, Deionized Water 127g;

[0069] Section C: 10g of 2-isooctyl acrylate, 9g of lauryl acrylate, 0.3g of ammonium persulfate, and 100g of deionized water.

[0070] The preparation method of the above-mentioned binder emulsion for lithium-ion battery cathode is as follows: Monomers or mixtures with strongly polar groups forming emulsion segment A are added sequentially, stirred at 200 rpm under nitrogen protection, and heated to 72°C. 0.2 g of sodium persulfate is added to initiate polymerization, and the reaction time is 1 hour. Then, monomers or mixtures with weakly polar groups forming emulsion segment B and an initiator are slowly added dropwise (stirring is required during addition). The temperature is controlled at 76°C during addition, and the addition is completed in 3 hours. The temperature is then maintained at 76°C for 1 hour. Finally, monomers or mixtures with non-polar groups forming emulsion segment C and an initiator are added dropwise (stirring is required during addition). The addition temperature is controlled at 76°C, and the addition is completed in 3 hours. The temperature is then raised to 80°C and maintained for 6 hours, thus obtaining the aqueous binder with the above-mentioned composition and a solid content of 15%.

[0071] This embodiment introduces isooctyl acrylate and laurate acrylate, which have better flexibility, into the core and transition layer, resulting in an adhesive film that is soft and has excellent elasticity.

[0072] Example 6

[0073] The method and process in this embodiment are basically the same as those in Example 3. The main change is that the initiator used is sodium persulfate. The prepared adhesive emulsion has a high viscosity, good fluidity, and water resistance. The adhesive has excellent thermal stability and a high decomposition temperature.

[0074] Example 7:

[0075] The method and process in this embodiment are basically the same as those in Example 3. The main changes are that the initiator used is azobisisobutyrazoline hydrochloride (AIBA), the reaction temperature is controlled at 50-60℃, the overall reaction time is extended by 6 hours, the prepared adhesive emulsion has a large viscosity, good fluidity, and water resistance, and the adhesive has excellent thermal stability and high decomposition temperature.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A process for the preparation of an aqueous binder for lithium-ion battery cathodes, characterized in that: The adhesive is composed of emulsion dispersion of multi-copolymer formed by polymerization of acrylic acid and its derivatives, the adhesive takes water as dispersion medium, the multi-copolymer forms ABC three-segment structure according to the polarity of polymerized monomer and polymerization process, A segment is strong polarity segment, B segment is weak polarity segment, and C segment is non-polar segment; the strong polarity segment is polymerized by monomer of acrylic acid or acrylic acid derivative with strong polarity group, or acrylic acid salt, the weak polarity segment is polymerized by acrylic ester and its derivatives with weak polarity group, and the non-polar segment is polymerized by acrylic ester and its derivatives with non-polar group; The combination of the strong polarity segment, the weak polarity segment and the non-polar segment, and the combination between different polarity segments, are formed by free radical self-polymerization or copolymerization of carbon-carbon double bond to form the ABC three-segment structure; The mass percentage of the strong polarity segment in the whole molecule is 20-50%, the mass percentage of the weak polarity segment is 20-40%, and the mass percentage of the non-polar segment is 20-40%. The preparation method of the lithium ion battery positive electrode water-based adhesive comprises the following steps, 1) preparing components according to process requirements and proportioning; 2) adding monomer or mixture with strong polarity group and deionized water into a reaction device, stirring and mixing uniformly, heating to 50-90 DEG C, adding initiator to initiate polymerization reaction, and constant temperature reaction for 0.2-5 hours; 3) adding monomer or mixture with weak polarity group and initiator into the reaction device of step 2) dropwise, controlling the temperature at 60-90 DEG C, and stirring, then constant temperature reaction for 0.2-5 hours at 60-90 DEG C; 4) adding monomer or mixture with non-polar group and initiator into the reaction device of step 3) dropwise, controlling the temperature at 60-90 DEG C when adding, and stirring, after dropwise adding, keeping the temperature at 60-90 DEG C, and constant temperature process for 0.2-5 hours.

2. The method of preparing an aqueous binder for lithium-ion battery cathodes according to claim 1, characterized in that, The monomer or mixture of acrylic acid or acrylic acid derivative with strong polarity group, or acrylic acid salt, includes methacrylic acid and its salt, itaconate, maleate, acrylamide methanesulfonic acid and its salt, acrylamidoisopropyl sulfonic acid and its salt, 2-allyl ether 3-hydroxypropane-1-sulfonic acid and its salt, vinyl sulfonic acid and its salt, allyl sulfonic acid and its salt, methacrylic acid sulfonic acid and its salt, styrene sulfonic acid and its salt, any one of them, or any two of them mixed in each more than zero percentage, or any three of them mixed in each more than zero percentage, or any four of them mixed in each more than zero percentage, or any five of them mixed in each more than zero percentage, until all the foregoing components are mixed in each more than zero percentage; wherein the cation of the salt is lithium ion, sodium ion, potassium ion, or ammonium ion.

3. The method for preparing a lithium-ion battery cathode aqueous binder according to claim 1 or 2, characterized in that, The acrylates with weak polar groups and their derivatives, including acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, acryloylmorpholine, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, methacryloylmorpholine, hydroxypropyl methacrylate, acrylonitrile, butenitrile, 5-hexenenitrile, cyclohexene-1-nitrile, 2-nonenitrile, vinyl acetate, N-hydroxymethyl acrylamide, hydroxyethyl acryloyl urea, diacetone acrylamide, diallyl phthalate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, bisphenol A glyceryl dimethacrylate, glycerol 1,3-diglyceryl diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, glycidyl methacrylate, polyethylene glycol mono methyl ether acrylate, polyethylene glycol mono methyl ether methacrylate, allyl polyethylene glycol, allyl polypropylene glycol; any one of them, or any two mixed in a proportion greater than zero percent of each, or any three mixed in a proportion greater than zero percent of each, or any four mixed in a proportion greater than zero percent of each, or any five mixed in a proportion greater than zero percent of each, up to all the foregoing components mixed in a proportion greater than zero percent of each.

4. The method of preparing a lithium-ion battery cathode aqueous binder according to claim 1 or 2, characterized in that, The acrylates with non-polar groups and their derivatives, including ethyl acrylate, propyl acrylate, n / isobutyl acrylate, n-octyl acrylate, 2-isooctyl acrylate, n / isodecyl acrylate, dodecyl acrylate, tetradecyl acrylate, hexadecyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, isobornyl acrylate, n / isobutyl methacrylate, 2-isooctyl methacrylate, vinyl neodecanoate, dibutyl maleate, stearyl methacrylate; any one of them, or any two mixed in a proportion greater than zero percent of each, or any three mixed in a proportion greater than zero percent of each, or any four mixed in a proportion greater than zero percent of each, or any five mixed in a proportion greater than zero percent of each, up to all the foregoing components polymerized in a proportion greater than zero percent of each.

5. The method of preparing an aqueous binder for lithium-ion battery cathodes according to claim 1, characterized in that, The initiator for the adhesive polymerization reaction is any one of potassium persulfate, ammonium persulfate, sodium persulfate, sodium sulfite, sodium bisulfite, azobisisoheptyl nitrile, azobisdimethylamidopropylidine hydrochloride, azobisdimethylimidazoline hydrochloride, and azobisdimethyl nitrile, or any two mixed in a proportion greater than zero percent of each, or any three mixed in a proportion greater than zero percent of each, or any four mixed in a proportion greater than zero percent of each, up to all the foregoing components mixed in a proportion greater than zero percent of each.

6. The method of preparing an aqueous binder for lithium-ion battery cathodes according to any one of claims 1, 2, 5, characterized in that, The solid content of the adhesive is 8-30%, and the viscosity is 5000-100000 mpas.

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