High-stripping-degree water-based acrylic resin binder as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of binders, and particularly relates to a high-stripping-degree water-based acrylic resin binder as well as a preparation method and application thereof. The high-stripping-degree water-based acrylic resin adhesive is prepared from the following components in parts by mass: 100 parts of polymeric monomers, 0.5 to 5 parts of an emulsifier, 0.2 to 3 parts of an initiator, 0.1 to 2 parts of a buffering agent and 120 to 170 parts of deionized water, the high-stripping-degree water-based acrylic resin adhesive provided by the invention has relatively high viscosity and stripping degree, and can improve the electrochemical performance of a silicon negative electrode lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and particularly relates to a high-peelability water-based acrylic resin adhesive, a preparation method and an application thereof. Background Art

[0002] Silicon anodes for lithium-ion batteries have the advantages of high specific capacity and low lithium insertion potential, making them a preferred alternative to traditional graphite anodes. However, silicon materials undergo severe volume expansion during the delithiation process. During the operation of lithium-ion batteries, repeated volume changes can easily lead to silicon particle rupture, electrical connection failure, continuous formation of solid electrolyte interfaces, and electrode structure collapse, thereby reducing the initial coulombic efficiency of lithium-ion batteries.

[0003] Binders are essential materials in lithium-ion batteries, and silicon anodes place even higher demands on binder performance. They not only require excellent adhesion to adhere the active material and conductive additives to the current collector, but also need to buffer the volume expansion of silicon during cycling and maintain the stability of the electrode structure. However, the rigid structures of linear polymer binders such as CMC and PVDF, as well as linear water-based acrylic resins, are unable to withstand the huge volume changes of silicon electrodes. During the charge and discharge process, polymer chains are prone to breakage and irreversible slip, leading to binder failure.

[0004] In the prior art, Chinese patent publication number CN 104356979 B discloses an aqueous binder for lithium-ion battery electrode materials, a preparation method, and a lithium-ion battery electrode sheet. This binder is a cross-linked, high-solids polyacrylate-based aqueous binder. The polymer molecular segments consist of hydrophilic and oleophilic segments, cross-linked by a crosslinker to form a spatial network structure. Electrode sheets made with this binder avoid shedding during charging and discharging, exhibit excellent adhesion to both positive and negative lithium-ion battery electrode materials, and inhibit expansion of graphite-based negative electrode materials, particularly silicon-based materials. Chinese patent publication number CN 119463007 A discloses a water-based acrylic polymer, its preparation method, and its application. This water-based acrylic polymer is copolymerized from the following monomers in the following mass percentages: acrylic acid: 35% to 80%; monohydroxyl-containing acrylic compound: 10% to 58%; and polyhydroxyl-containing acrylic compound: 2% to 10%. The acrylic binder made from the water-based acrylic polymer in this technical solution is highly flexible and has excellent adhesion. Using it as a binder can well accommodate the high volume expansion of silicon-based anodes, resulting in excellent cycle performance for the assembled lithium-ion battery. However, the peel strength of the anode produced using this binder needs to be improved. Summary of the Invention

[0005] The present invention aims to address one or more technical problems existing in the above-mentioned prior art and to provide at least a beneficial alternative. Specifically, the present invention provides a high-peelability water-based acrylic resin binder, its preparation method, and its application. The binder exhibits high viscosity and peelability, and is capable of improving the electrochemical performance of silicon-anode lithium-ion batteries.

[0006] In one aspect, the present invention provides a high-peelability water-based acrylic resin adhesive, comprising the following components, calculated by mass: 100 parts of a polymerizable monomer, 0.5-5 parts of an emulsifier, 0.2-3 parts of an initiator, 0.1-2 parts of a buffer, and 120-170 parts of deionized water; The polymerizable monomers include monomer A, monomer B and monomer C; The monomer A is selected from one or more combinations of acrylic acid, methacrylic acid, butyl acrylate, ethyl acrylate, methyl methacrylate and butyl methacrylate; The monomer B is selected from one or more combinations of divinylbenzene, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, diacrylamide and N,N-methylenebisacrylamide; The monomer C is selected from one or more combinations of hydroxyethyl acrylate, hydroxypropyl acrylate, acrylamide, methacrylamide, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

[0007] Preferably, the mass ratio of monomer A, monomer B and monomer C is 90-95:2-5:3-5.

[0008] Preferably, the mass ratio of monomer A, monomer B and monomer C is 95:2:3.

[0009] Preferably, the monomer A is a mixture of acrylic acid and butyl acrylate.

[0010] Preferably, the mass ratio of acrylic acid to butyl acrylate is 1.5-2.5:1.

[0011] Preferably, the monomer B is pentaerythritol tetraacrylate.

[0012] Preferably, the monomer C is acrylamide.

[0013] The present invention adopts monomer A as an acrylic monomer, monomer B as a branching monomer, and monomer C as a functional monomer. By optimizing the types and ratios of monomer A, monomer B, and monomer C, a water-based acrylic resin with a branched structure is obtained. The resin has good adhesion and high peel strength when used for a silicon negative electrode of a lithium-ion battery.

[0014] Preferably, the high-stripping water-based acrylic resin adhesive further comprises 1-2 parts of modified lignin.

[0015] Preferably, the modified lignin preparation method comprises the following steps: under nitrogen protection, mixing alkali lignin and N,N-dimethylformamide, adding glycidyl methacrylate and stirring evenly, heating to react, and after the reaction, performing reduced pressure distillation, washing, and drying to obtain the modified lignin. Preferably, the mass ratio of the alkali lignin, glycidyl methacrylate, and N,N-dimethylformamide is 1:0.6-0.8:1.1-1.4.

[0016] Preferably, the heating reaction temperature is 80-85° C., and the reaction time is 4-6 hours.

[0017] Lignin is a natural polymer compound with a three-dimensional network structure. The present invention modifies lignin by introducing unsaturated bonds so that it can copolymerize with polymerizable monomers, and then introduces lignin into the structure of a water-based acrylic resin. This not only improves the stripping degree of the water-based acrylic resin, but also effectively resists the volume expansion of the silicon negative electrode, thereby improving the electrochemical performance of the battery.

[0018] Preferably, the high-stripping water-based acrylic resin adhesive comprises the following components, in parts by mass: 100 parts of polymerizable monomer, 1-2 parts of modified lignin, 0.5-2 parts of emulsifier, 0.5-1 part of initiator, 0.1-1 part of buffer, and 120-170 parts of deionized water.

[0019] Preferably, the emulsifier is selected from one or more combinations of sodium lauryl sulfate, octylphenol polyoxyethylene ether, Tween-80 and polyvinyl alcohol.

[0020] Preferably, the emulsifier further comprises acryloxypropionic acid / carboxyethyl acrylate.

[0021] Preferably, the emulsifier is sodium lauryl sulfate and acryloxypropionic acid / carboxyethyl acrylate in a mass ratio of 2-4:0.5-1.5.

[0022] The present invention adds a reactive emulsifier acryloxypropionic acid / carboxyethyl acrylate, which works together with the modified lignin to make the water-based acrylic resin have excellent peeling properties, effectively resist the volume expansion of the silicon negative electrode, and improve the electrochemical performance of the battery.

[0023] Preferably, the initiator is selected from one or more combinations of ammonium persulfate, sodium persulfate, azobisisobutyronitrile and benzoyl peroxide.

[0024] Preferably, the buffer is selected from one or more combinations of sodium bicarbonate, disodium hydrogen phosphate, sodium citrate and sodium acetate.

[0025] On the other hand, the present invention provides a method for preparing the above-mentioned high-peelability water-based acrylic resin adhesive, comprising the following steps: (1) Mixing the polymerization monomer, modified lignin, emulsifier and deionized water to obtain a monomer emulsion; (2) Mix the initiator and deionized water evenly to obtain an initiator solution; (3) The initiator solution is added dropwise to the monomer emulsion, and a polymerization reaction is carried out after the addition is completed. After the polymerization reaction is completed, a buffer is added to obtain a high-peelability water-based acrylic resin adhesive.

[0026] Preferably, step (1), step (2) and step (3) are all carried out under nitrogen protection.

[0027] Preferably, the amount of deionized water added in step (1) is 1.2-1.6 times the mass of the polymerized monomers.

[0028] Preferably, the amount of deionized water added in step (2) is 8-12 times the mass of the initiator.

[0029] Preferably, the polymerization reaction temperature in step (3) is 65-85° C., and the polymerization reaction time is 3-6 h.

[0030] Preferably, in step (3), the initiator solution is added dropwise to the monomer emulsion slowly, and the addition temperature is 50-85°C.

[0031] In another aspect, the present invention provides use of the above-mentioned high-stripping water-based acrylic resin binder in preparing a silicon negative electrode.

[0032] In another aspect, the present invention provides a silicon negative electrode sheet comprising the above-mentioned high-peelability water-based acrylic resin binder.

[0033] Compared with the prior art, the present invention has the following beneficial effects: First, the present invention uses monomer A as an acrylic monomer, monomer B as a branching monomer, and monomer C as a functional monomer. By optimizing the types and ratios of monomers A, B, and C, a water-based acrylic resin with a branched structure is obtained. The resin has good adhesion and a peel strength of 8 N / m or above when used for a lithium-ion battery silicon negative electrode. Secondly, the present invention modifies lignin and introduces unsaturated bonds, enabling it to copolymerize with polymerizable monomers, thereby introducing lignin into the structure of a water-based acrylic resin. This not only improves the exfoliation of the water-based acrylic resin, but also effectively resists the volume expansion of the silicon negative electrode, thereby improving the electrochemical performance of the battery, and can maintain a high capacity and good cycle performance at different charge and discharge rates. Third, the present invention adds a reactive emulsifier acryloxypropionic acid / carboxyethyl acrylate, which works together with the modified lignin to make the water-based acrylic resin have excellent peeling properties, effectively resist the volume expansion of the silicon negative electrode, and improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a cycle performance diagram at 0.2C of a battery prepared using the high-peelability water-based acrylic resin binder of Example 6 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0036] Unless otherwise specified, the raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0037] Example 1 This embodiment provides a high-peelability water-based acrylic resin adhesive, which is composed of the following components in parts by mass: 100 parts of polymerization monomer, 2 parts of emulsifier, 0.5 parts of initiator, 0.3 parts of buffer, and 155 parts of deionized water.

[0038] The polymerizable monomers, by mass percentage, are composed of 65% acrylic acid (monomer A), 30% butyl acrylate (monomer A), 3% trimethylolpropane triacrylate (monomer B), and 3% acrylamide (monomer C).

[0039] The emulsifier is sodium lauryl sulfate; the initiator is ammonium persulfate; and the buffer is ammonia water.

[0040] The preparation method of the high-peelability water-based acrylic resin adhesive is as follows: under nitrogen protection, (1) Mix the polymerization monomer, emulsifier and 150 parts of deionized water to obtain a monomer emulsion; (2) Mix the initiator and 5 parts of deionized water to obtain an initiator solution; (3) The initiator solution is added dropwise to the monomer emulsion at 60°C. After the addition is completed, the polymerization reaction is carried out at 75°C for 5 hours. After the polymerization reaction is completed, a buffer is added to obtain a high-peelability water-based acrylic resin adhesive.

[0041] Example 2 This embodiment provides a high-peelability water-based acrylic resin adhesive, which differs from Example 1 only in that the polymerizable monomers, by mass percentage, are composed of 64% acrylic acid (monomer A), 30% butyl acrylate (monomer A), 3% trimethylolpropane triacrylate (monomer B), and 3% acrylamide (monomer C); all other components are the same.

[0042] Example 3 This embodiment provides a high-peelability water-based acrylic resin adhesive, which differs from Example 1 only in that the high-peelability water-based acrylic resin adhesive is composed of the following components, calculated by mass: 100 parts of polymerizable monomer, 3 parts of emulsifier, 0.5 parts of initiator, 0.3 parts of buffer, and 155 parts of deionized water; the rest are the same.

[0043] Example 4 This embodiment provides a high-peelability water-based acrylic resin adhesive, which differs from Example 1 only in that the polymerizable monomers, by mass percentage, are composed of 55% acrylic acid (monomer A), 40% butyl acrylate (monomer A), 2% trimethylolpropane triacrylate (monomer B), and 3% acrylamide (monomer C); all other components are the same.

[0044] Example 5 This embodiment provides a high-peelability water-based acrylic resin adhesive, which differs from Example 1 only in that the high-peelability water-based acrylic resin adhesive is composed of the following components, calculated by mass: 100 parts of polymerizable monomer, 2 parts of emulsifier, 1 part of initiator, 0.3 parts of buffer, and 155 parts of deionized water; the rest are the same.

[0045] Example 6 This embodiment provides a high-peelability water-based acrylic resin adhesive, which is composed of the following components in parts by mass: 100 parts of polymerization monomer, 1 part of modified lignin, 2 parts of emulsifier, 1 part of initiator, 0.3 parts of buffer, and 155 parts of deionized water.

[0046] The polymerizable monomers, by mass percentage, are composed of 65% acrylic acid (monomer A), 30% butyl acrylate (monomer A), 3% trimethylolpropane triacrylate (monomer B), and 3% acrylamide (monomer C).

[0047] The modified lignin is prepared by mixing 10 g of alkali lignin (CAS: 8068-05-1) and 12 g of N,N-dimethylformamide under nitrogen protection, adding 7 g of glycidyl methacrylate and stirring evenly, heating at 80° C. for reaction for 5 h, and performing reduced pressure distillation, washing, and drying after the reaction to obtain the modified lignin.

[0048] The emulsifier is sodium lauryl sulfate and acryloyloxypropionic acid / carboxyethyl acrylate (Yinhuang (Shanghai) Industrial Co., Ltd., product name: SIPOMERβ-CEA) in a mass ratio of 3:1; the initiator is ammonium persulfate; and the buffer is ammonia water.

[0049] The preparation method of the high-peelability water-based acrylic resin adhesive is as follows: under nitrogen protection, (1) The polymerization monomer, modified lignin, emulsifier and 150 parts of deionized water were mixed uniformly to obtain a monomer emulsion; (2) Mix the initiator and 5 parts of deionized water to obtain an initiator solution; (3) The initiator solution is added dropwise to the monomer emulsion at 60°C. After the addition is completed, the polymerization reaction is carried out at 75°C for 5 hours. After the polymerization reaction is completed, a buffer is added to obtain a high-peelability water-based acrylic resin adhesive.

[0050] Comparative Example 1 This comparative example provides a high-peelability water-based acrylic resin adhesive, which is different from Example 6 only in that trimethylolpropane triacrylate is replaced with ethoxylated trimethylolpropane triacrylate; all other aspects are the same.

[0051] Comparative Example 2 This comparative example provides a high-peelability water-based acrylic resin adhesive, which is different from Example 6 only in that the modified lignin is 0 parts; all other aspects are the same.

[0052] Comparative Example 3 This comparative example provides a high-peelability water-based acrylic resin adhesive, which is different from Example 6 only in that the emulsifier is sodium lauryl sulfate; all other aspects are the same.

[0053] Comparative Example 4 This comparative example provides a high-peelability water-based acrylic resin adhesive, which differs from Example 6 only in that the emulsifier is sodium lauryl sulfate and 2-acrylamido-2-methylpropanesulfonic acid sodium salt (CAS: 5165-97-9) in a mass ratio of 3:1; all other aspects are the same.

[0054] Test Example 1: The viscosity of the high-peelability water-based acrylic resin adhesives of Examples 1-6 and Comparative Examples 1-4 at 25° C. was tested using a viscometer. The results are shown in Table 1.

[0055] Test Example 2: The high-peelability water-based acrylic resin binder of Examples 1-6 and Comparative Examples 1-4, silicon carbon particles (particle size of 150 nm), and conductive carbon black Super P were mixed in a mass ratio of 1:8:1, deionized water was added and stirred to form a slurry with a solid content of 35%. The resulting slurry was coated on a copper foil and dried at 100°C for 12 hours to obtain a negative electrode sheet with a thickness of 150 μm. The peel strength of the negative electrode sheet was tested using a 180° peeling method (a: a 25 mm wide transparent tape was horizontally attached to the bottom of a scaleless steel ruler flush with the end surface; b: a double-sided tape was then attached to the transparent tape with a length equal to the width of the transparent tape and centered). Finally, stick the electrode test sample with a width of 25mm on the double-sided tape with the end faces flush, and use a pressure wheel to roll back and forth freely on the surface of the electrode for 3 times; c: Fold the unpasted end of the electrode of the test sample 180°, clamp it on the upper clamp of the tensile testing machine, and peel the electrode at a tensile speed of 5mm / min. When the electrode current collector and the coating are completely separated, read the peel strength test results, and take the average value of the stable stage as the peel strength value). The results are shown in Table 1.

[0056] Table 1 As can be seen from Table 1, when comparing Examples 1 to 5, as the content of monomer B increases (Example 2), the viscosity of the obtained high-peelability water-based acrylic resin adhesive increases, and the peeling force also improves; as the content of emulsifier increases (Example 3), the viscosity of the obtained high-peelability water-based acrylic resin adhesive decreases, and the peeling force also decreases; as the ratio of acrylic acid to butyl acrylate changes (Example 4), the viscosity of the obtained high-peelability water-based acrylic resin adhesive decreases, and the peeling force also decreases; as the content of initiator increases (Example 5), the viscosity of the obtained high-peelability water-based acrylic resin adhesive increases, and the peeling force also increases; Comparison of Example 5, Example 6, and Comparative Example 2-Comparative Example 4: When modified lignin and acryloxypropionic acid / carboxyethyl acrylate are added simultaneously, the viscosity of the obtained high-peelability water-based acrylic resin adhesive increases, and the peeling force also increases; Comparison between Example 6 and Comparative Example 1: When trimethylolpropane triacrylate is replaced with ethoxylated trimethylolpropane triacrylate, the viscosity of the obtained high-peelability water-based acrylic resin adhesive decreases, and the peeling force also decreases.

[0057] Test Example 3 The negative electrode sheets of Example 5, Example 6, Comparative Example 1, Comparative Example 2, and Comparative Example 4 in Test Example 2 were used to assemble the battery: The positive electrode is a lithium sheet; The electrolyte contains 1 mol / L LiPF6 as solute and ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 as solvent; The diaphragm is PP diaphragm; The negative electrode sheet, positive electrode, electrolyte, and separator were assembled into a C2032 button half-cell in a glove box. The charge and discharge performance was tested under the conditions of a charge and discharge voltage window of 0.01-3 V and current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. The results are shown in Table 2.

[0058] Table 2 As can be seen from Table 2, the negative electrode sheets prepared using the high-peelability aqueous acrylic resin binders of Examples 5 and 6 have good structural stability and can maintain a high capacity at different charge and discharge rates; while the electrochemical performance of the negative electrode sheets prepared using the binders of Comparative Examples 1, 2, and 4 is significantly deteriorated at different charge and discharge rates.

[0059] Test Example 4 The battery prepared by using the high-peelability water-based acrylic resin binder of Example 6 in Test Example 3 was subjected to 100 cycle performance tests at 0.2C. The test results are as follows: Figure 1 shown.

[0060] Depend on Figure 1 It can be seen that the battery prepared with the high-peelability water-based acrylic resin binder of Example 6 has good cycle performance; after 100 cycles at 0.2C, the capacity can still reach 641 mAh g -1 .

[0061] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A high-peelability water-based acrylic resin adhesive, characterized in that: The composition comprises the following components by weight: 100 parts of polymerization monomer, 0.5-5 parts of emulsifier, 0.2-3 parts of initiator, 0.1-2 parts of buffer, and 120-170 parts of deionized water; The polymerizable monomers include monomer A, monomer B and monomer C; The monomer A is selected from one or more combinations of acrylic acid, methacrylic acid, butyl acrylate, ethyl acrylate, methyl methacrylate and butyl methacrylate; The monomer B is selected from one or more combinations of divinylbenzene, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, diacrylamide and N,N-methylenebisacrylamide; The monomer C is selected from one or more combinations of hydroxyethyl acrylate, hydroxypropyl acrylate, acrylamide, methacrylamide, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

2. The high-peelability water-based acrylic resin adhesive according to claim 1, wherein The mass ratio of the monomer A, monomer B and monomer C is 90-95:2-5:3-5.

3. The high-peelability water-based acrylic resin adhesive according to claim 2, wherein The monomer A is a mixture of acrylic acid and butyl acrylate; the mass ratio of the acrylic acid to butyl acrylate is 1.5-2.5:

1.

4. The high-peelability water-based acrylic resin adhesive according to claim 3, wherein The monomer B is pentaerythritol tetraacrylate; and the monomer C is acrylamide.

5. The high-peelability water-based acrylic resin adhesive according to any one of claims 1 to 4, characterized in that: The high-peelability water-based acrylic resin adhesive further comprises 1-2 parts of modified lignin.

6. The high-peelability water-based acrylic resin adhesive according to claim 5, characterized in that: The preparation method of the modified lignin comprises the following steps: under nitrogen protection, alkali lignin and N,N-dimethylformamide are mixed, glycidyl methacrylate is added and stirred evenly, heating for reaction, and after the reaction is completed, vacuum distillation, washing, and drying are performed to obtain the modified lignin.

7. The high-peelability water-based acrylic resin adhesive according to claim 6, characterized in that: The high-peelability water-based acrylic resin adhesive comprises the following components, calculated by mass: 100 parts of polymerizable monomers, 1-2 parts of modified lignin, 0.5-2 parts of emulsifiers, 0.5-1 parts of initiators, 0.1-1 parts of buffers, and 120-170 parts of deionized water.

8. The method for preparing the high-peelability water-based acrylic resin adhesive according to any one of claims 5 to 7, characterized in that: The following steps are involved: (1) Mixing the polymerization monomer, modified lignin, emulsifier and deionized water to obtain a monomer emulsion; (2) Mix the initiator and deionized water evenly to obtain an initiator solution; (3) The initiator solution is added dropwise to the monomer emulsion, and a polymerization reaction is carried out after the addition is completed. After the polymerization reaction is completed, a buffer is added to obtain a high-peelability water-based acrylic resin adhesive.

9. Use of the high-peelability aqueous acrylic resin binder according to any one of claims 1 to 7 in the preparation of a silicon negative electrode.

10. A silicon negative electrode sheet, characterized in that: The invention comprises the high-peelability water-based acrylic resin adhesive according to any one of claims 1 to 7.

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