Aqueous polyacrylic adhesive, its preparation method and use

Abstract

The application provides a water-based polyacrylic acid adhesive as well as a preparation method and application thereof. The water-based polyacrylic acid adhesive is a polyacrylic acid adhesive modified by an organic silicon material; the organic silicon material comprises at least one of a silane coupling agent, methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, methylphenyldichlorosilane or octamethylcyclotetrasiloxane. The water-based polyacrylic acid adhesive provided by the application not only has excellent high-temperature resistance and flexibility, but also has good adhesion, and has great application potential in the field of lithium ion battery negative electrode adhesives.

Description

Technical Field

[0001] This invention belongs to the field of adhesive materials technology, specifically relating to a water-based polyacrylic acid adhesive, its preparation method, and its application. Background Technology

[0002] In electrode materials, adhesives primarily function to bond the positive and negative electrode active materials to the current collector. As an active material, they play a crucial role in maintaining the mechanical structure and electrochemical performance stability of the electrodes during battery production and use. Currently, the adhesives used in lithium-ion batteries are mainly divided into oil-based and water-based adhesives. Oil-based adhesives pose problems such as organic solvent volatilization, flammability, explosiveness, and toxicity during battery manufacturing. Compared to oil-based adhesives, water-based adhesives offer advantages such as environmental friendliness, safety, and ease of processing, and are gradually becoming a research hotspot in the field of lithium-ion battery adhesives.

[0003] In recent years, the negative electrode adhesives used in commercial lithium-ion batteries mainly include styrene-butadiene rubber (SBR) latex, aqueous polyacrylic acid (PAA), and sodium carboxymethyl cellulose (CMC). On the one hand, SBR latex adhesives suffer from poor mechanical stability and are prone to demulsification and failure below freezing. Furthermore, SBR latex is prone to sedimentation and particle agglomeration during electrode processing, necessitating its use in conjunction with CMC. However, CMC has strong water absorption, leading to high swelling, low initial charge-discharge efficiency, poor cycle life, and safety issues when used in batteries. On the other hand, polyacrylic acid adhesives used in negative electrode sheets have drawbacks such as high Young's modulus, poor high-temperature resistance, and poor adhesion.

[0004] Therefore, there is an urgent need in this field to develop a water-based adhesive suitable for negative electrodes, which not only has good mechanical stability and adhesive properties, but also maintains good performance at high temperatures. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a water-based polyacrylic acid adhesive, its preparation method, and its applications. The water-based polyacrylic acid adhesive provided by this invention not only exhibits excellent high-temperature resistance and flexibility but also possesses good adhesion, making it a promising candidate for use in lithium-ion battery anode adhesives.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a water-based polyacrylic adhesive, wherein the water-based polyacrylic adhesive is a polyacrylic adhesive modified with organosilicon materials;

[0008] The organosilicon material includes at least one of silane coupling agent, methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, methylphenyldichlorosilane, or octamethylcyclotetrasiloxane.

[0009] This invention utilizes organosilicon materials to modify polyacrylic acid, resulting in a silicone-modified polyacrylic acid adhesive with a molecular structure containing Si-O bonds. The bond energy of the Si-O bond is 443.5 kJ / mol, which is greater than that of the C-C bond (347 kJ / mol). The higher the bond energy of the covalent bond, the better the thermal stability. Furthermore, the Si-O bond has high polarity and a 51% ionization tendency, which has a dipole induction effect on the hydroxyl groups attached to the silicon atoms, improving the stability of the attached hydroxyl groups against oxidation. The Si-O bond forms d-pπ bonds, further increasing thermal stability. During thermal oxidation, a cross-linked Si-O-Si bond protective layer is formed on the surface of the organosilicon in the silicone-modified polyacrylic acid adhesive, reducing the impact of heat on the polymer interior. In contrast, the C-C bonds in ordinary polymers (without organosilicon modification) are easily broken into low-molecular-weight compounds and volatilized when heated, failing to protect the polymer interior. The Si-O-Si bonds in silicone-modified polyacrylic acid can fuse with the copper foil used in the negative electrode sheet at high temperatures to form a Si-O-Cu silicate inorganic compound coating, enhancing adhesion to the copper substrate and providing high-temperature resistance. This significantly improves the safety performance of lithium-ion batteries during production and use. Furthermore, the silicone-modified polyacrylic acid adhesive prepared in this invention improves the flexibility of the negative electrode sheet during its fabrication, and the resulting negative electrode sheet exhibits extremely strong adhesion to the foil.

[0010] Preferably, the molecular weight of the water-based polyacrylic acid adhesive is 800,000 to 1,000,000, for example, it can be 800,000, 820,000, 850,000, 880,000, 900,000, 920,000, 950,000, 980,000, 1,000,000, etc

[0011] In this invention, the molecular weight of the water-based polyacrylic acid adhesive is adjusted to achieve excellent adhesion to copper foil. A lower molecular weight results in poorer peel strength and initial tack, while a higher molecular weight leads to better adhesion. However, an excessively high molecular weight negatively impacts dispersion and coating performance. To ensure sufficient solids content and good dispersibility, the molecular weight is designed to be between 800,000 and 1,000,000.

[0012] In a second aspect, the present invention provides a method for preparing the waterborne polyacrylic adhesive according to the first aspect, the method comprising the following steps:

[0013] (1) Mix acrylic acid, acrylamide, surfactant, initiator and chain extender and solvent to carry out a first reaction, then add initiator and chain extender to carry out a second reaction, cool down after the second reaction, carry out a third reaction to obtain polyacrylic acid prepolymer;

[0014] (2) The polyacrylic acid prepolymer, silicone material and solvent obtained in step (1) are mixed and reacted to obtain the water-based polyacrylic acid adhesive.

[0015] Preferably, the components in step (1) include, by weight, 25-45 parts acrylic acid, 3-5 parts acrylamide, 1-2 parts surfactant, 0.1-0.5 parts initiator and 0.01-0.5 parts chain extender, and more preferably 38-40 parts acrylic acid, 3-5 parts acrylamide, 1-2 parts surfactant, 0.1-0.3 parts initiator and 0.01-0.02 parts chain extender.

[0016] In this invention, the acrylic acid is in the amount of 25-45 parts by weight, preferably 38-40 parts, for example, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 39 parts, 40 parts, 42 parts, 45 parts, etc.

[0017] In this invention, the acrylamide is in the form of 3-5 parts by weight, for example, 3 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, etc.

[0018] In this invention, the surfactant is present in 1-2 parts by weight, for example, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, etc.

[0019] In this invention, the initiator is 0.1-0.5 parts by weight, preferably 0.1-0.3 parts, for example, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc.

[0020] In this invention, the chain extender is 0.01-0.5 parts by weight, preferably 0.01-0.02 parts, for example, 0.01 parts, 0.02 parts, 0.05 parts, 0.08 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc.

[0021] Preferably, the surfactant in step (1) includes polyoxyethylene ether.

[0022] Preferably, the polyoxyethylene ether comprises any one or a combination of at least two of the following: fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty amine polyoxyethylene ether (brand name 1807), bisphenol A polyoxyethylene ether, octylphenol polyoxyethylene ether, butanol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, isopentenol polyoxyethylene ether, methyl allyl polyoxyethylene ether, isomeric decacarbonol polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, CO-60, isomeric decacarbonol polyoxyethylene ether, or isomeric fatty alcohol polyoxyethylene ether.

[0023] Preferably, the initiator in step (1) includes any one or a combination of at least two of ammonium persulfate, potassium persulfate, sodium persulfate, or hydrogen peroxide.

[0024] Preferably, the chain extender in step (1) includes any one or a combination of at least two of the following: triallyl isocyanurate, diallyl phthalate, diallyl maleate, ethylene glycol dimethacrylate, polytetramethyl ether ethylene glycol acrylate, 1,4-butanediol, sorbitol, diethylaminoethanol, neopentyl glycol, 3,3'-dichloro-4,4'-diaminodiphenylmethane, ethylenediamine, N,N-dihydroxyaniline, ADR-4468 polymeric chain extender (purchased from BASF, Germany), anhydride-modified ethylene copolymer (purchased from DuPont Chemicals, USA, model N493), or dimethylthiotoluene diamine.

[0025] Preferably, the solvent in step (1) is deionized water.

[0026] Preferably, the mixing in step (1) is carried out in an inert atmosphere.

[0027] Preferably, the mixing in step (1) is carried out under stirring.

[0028] Preferably, the end speed of the stirring blade does not exceed 240 m / min.

[0029] Preferably, the temperature of the first reaction in step (1) is 50-65℃, for example, 50℃, 52℃, 55℃, 58℃, 60℃, 62℃, or 65℃; and the time is 2.5h-3.5h, for example, 2.5h, 2.8h, 3h, 3.2h, or 3.5h.

[0030] Preferably, the temperature of the secondary reaction in step (1) is 65-80℃, for example, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, or 80℃; and the time is 2.5h-3.5h, for example, 2.5h, 2.8h, 3h, 3.2h, or 3.5h.

[0031] Preferably, the temperature of the three reactions in step (1) is 35-40℃, for example, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃; and the time is 1.0h-2.0h, for example, 1.0h, 1.2h, 1.5h, 1.8h, 2.0h.

[0032] Preferably, in step (2), the polyacrylic acid prepolymer is 20-40 parts by weight, the silicone material is 1-5 parts by weight, and the solvent is 40-80 parts by weight. More preferably, the polyacrylic acid prepolymer is 28-38 parts by weight, the silicone material is 2.5-3.5 parts by weight, and the solvent is 53-56 parts by weight.

[0033] In this invention, the polyacrylic acid prepolymer is 20-40 parts by weight, preferably 28-38 parts, for example, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, etc.

[0034] In this invention, the weight of the organosilicon material is 1-5 parts, preferably 2.5-3.5 parts, for example, it can be 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.5 parts, 5 parts, etc.

[0035] In this invention, the solvent is present in 40-80 parts by weight, preferably 53-56 parts, for example, 40 parts, 42 parts, 45 parts, 48 ​​parts, 50 parts, 53 parts, 54 parts, 55 parts, 56 parts, 60 parts, 70 parts, 80 parts, etc.

[0036] Preferably, the organosilicon material in step (2) includes at least one of silane coupling agent, methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, methylphenyldichlorosilane or octamethylcyclotetrasiloxane.

[0037] Preferably, the silane coupling agent includes silane coupling agent KH-550, silane coupling agent KH-560, vinyltriethoxysilane (model A151), vinyltrimethoxysilane (model A171), vinyltri(β-methoxyethoxy)silane (A172), γ-ureidopropyltriethoxysilane (A-1160), silane coupling agent Y-5475, silane coupling agent Y-5669, 3-(2,3-epoxypropoxy)propyltrimethoxysilane (model A-187), γ-aminopropyltriethoxysilane (models include Union Carbide A-1100, Downing Z-6011, or Shin-Etsu Chemical KMB903), and 3-glycidyl etheroxypropyltrimethoxysilane (model is GE / OSI). A-187, Shin-Etsu KMB403 (Japan) or Dow Corning Z-403 (USA), 3-methacryloyloxypropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane or 3-(2-aminoethyl)aminopropyltrimethoxysilane, any one or at least two combinations thereof.

[0038] Preferably, the solvent in step (2) is deionized water.

[0039] Preferably, the mixing in step (2) is carried out under stirring.

[0040] Preferably, the end speed of the stirring blade does not exceed 140 m / min.

[0041] Preferably, the reaction temperature in step (2) is 60-90℃, for example, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, 82℃, 85℃, 88℃, or 90℃; and the time is 1.5h-2.5h, for example, 1.5h, 1.8h, 2h, 2.2h, or 2.5h.

[0042] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, the negative electrode active material layer comprising the water-based polyacrylic acid adhesive according to the first aspect.

[0043] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode is the negative electrode described in the third aspect.

[0044] In this invention, the negative electrode sheet prepared using the water-based polyacrylic acid adhesive provided by this invention exhibits increased flexibility and enhanced adhesion to the foil.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention provides a water-based polyacrylic acid adhesive, which utilizes an organosilicon material to modify polyacrylic acid. This results in an organosilicon-modified polyacrylic acid adhesive with excellent high-temperature resistance, thereby significantly improving the safety performance of lithium-ion batteries during production and use. Simultaneously, the organosilicon-modified polyacrylic acid adhesive prepared by this invention enhances the flexibility of the negative electrode sheet during its fabrication, and the resulting negative electrode sheet exhibits extremely strong adhesion to the foil material. Attached Figure Description

[0047] Figure 1 Internal resistance diagram of the lithium-ion battery provided in Application Example 1;

[0048] Figure 2 A capacity retention diagram of the lithium-ion battery provided in Application Example 1;

[0049] Figure 3 The high-temperature discharge capacity diagram of the lithium-ion battery provided for Application Example 1. Detailed Implementation

[0050] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0051] Example 1

[0052] This embodiment provides a water-based polyacrylic acid adhesive, which is a polyacrylic acid adhesive modified with silane coupling agent KH-550. The molecular weight of the water-based polyacrylic acid adhesive is 900,000.

[0053] This embodiment provides a method for preparing the above-mentioned water-based polyacrylic acid adhesive, which includes the following steps:

[0054] (1) 39 parts by weight of acrylic acid, 4 parts by weight of acrylamide, 1.5 parts by weight of fatty alcohol polyoxyethylene ether, 0.2 parts by weight of ammonium persulfate initiator and 0.015 parts by weight of triallyl isocyanurate chain extender and deionized water were stirred under a nitrogen atmosphere. The impeller tip speed of the stirrer did not exceed 240 m / min. The reaction was carried out at 60°C for 3 h. Then, ammonium persulfate initiator and triallyl isocyanurate chain extender were added and the reaction was carried out at 70°C for 3 h. After the second reaction was completed, the temperature was lowered and the reaction was carried out at 38°C for 1.5 h to obtain polyacrylic acid prepolymer.

[0055] (2) The 33 parts of polyacrylic acid prepolymer, 3 parts of silane coupling agent KH-550 and 54 parts of deionized water obtained in step (1) are stirred according to the weight. The blade speed of the stirrer does not exceed 140 m / min. After reacting at 75°C for 2 hours, water-based polyacrylic acid adhesive is obtained.

[0056] Example 2

[0057] This embodiment provides a water-based polyacrylic acid adhesive, which is a polyacrylic acid adhesive modified with silane coupling agent KH-550. The molecular weight of the water-based polyacrylic acid adhesive is 850,000.

[0058] This embodiment provides a method for preparing the above-mentioned water-based polyacrylic acid adhesive, which includes the following steps:

[0059] (1) 38 parts by weight of acrylic acid, 3 parts by weight of acrylamide, 1 part by weight of fatty alcohol polyoxyethylene ether, 0.1 part by weight of ammonium persulfate initiator and 0.01 part by weight of triallyl isocyanurate chain extender and deionized water were stirred under a nitrogen atmosphere. The blade tip speed of the stirrer did not exceed 240 m / min. The reaction was carried out at 60°C for 3 h. Then, ammonium persulfate initiator and triallyl isocyanurate chain extender were added and the reaction was carried out at 70°C for 3 h. After the second reaction was completed, the temperature was lowered and the reaction was carried out at 38°C for 1.5 h to obtain polyacrylic acid prepolymer.

[0060] (2) The 28 parts of polyacrylic acid prepolymer, 2.5 parts of silane coupling agent KH-550 and 53 parts of deionized water obtained in step (1) are stirred according to the weight. The blade speed of the stirrer does not exceed 140 m / min. After reacting at 75°C for 2 hours, water-based polyacrylic acid adhesive is obtained.

[0061] Example 3

[0062] This embodiment provides a water-based polyacrylic acid adhesive, which is a polyacrylic acid adhesive modified with silane coupling agent KH-550. The molecular weight of the water-based polyacrylic acid adhesive is 950,000.

[0063] This embodiment provides a method for preparing the above-mentioned water-based polyacrylic acid adhesive, which includes the following steps:

[0064] (1) 40 parts by weight of acrylic acid, 5 parts by weight of acrylamide, 2 parts by weight of fatty alcohol polyoxyethylene ether, 0.3 parts by weight of ammonium persulfate initiator and 0.02 parts by weight of triallyl isocyanurate chain extender and deionized water were stirred under a nitrogen atmosphere. The impeller tip speed of the stirrer did not exceed 240 m / min. The reaction was carried out at 60°C for 3 h. Then, ammonium persulfate initiator and triallyl isocyanurate chain extender were added and the reaction was carried out at 70°C for 3 h. After the second reaction was completed, the temperature was lowered and the reaction was carried out at 38°C for 1.5 h to obtain polyacrylic acid prepolymer.

[0065] (2) According to the weight, 38 parts of polyacrylic acid prepolymer, 3.5 parts of silane coupling agent KH-550 and 56 parts of deionized water obtained in step (1) are stirred. The blade speed of the stirrer does not exceed 140m / min. After reacting at 75°C for 2 hours, water-based polyacrylic acid adhesive is obtained.

[0066] Example 4

[0067] This embodiment provides a water-based polyacrylic acid adhesive, which is a polyacrylic acid adhesive modified with silane coupling agent Y-5475. The molecular weight of the water-based polyacrylic acid adhesive is 800,000.

[0068] This embodiment provides a method for preparing the above-mentioned water-based polyacrylic acid adhesive, which includes the following steps:

[0069] (1) 25 parts by weight of acrylic acid, 3 parts by weight of acrylamide, 1 part by weight of fatty alcohol polyoxyethylene ether, 0.1 part by weight of ammonium persulfate initiator and 0.01 part by weight of triallyl isocyanurate chain extender and deionized water were stirred under a nitrogen atmosphere. The impeller tip speed of the stirrer did not exceed 240 m / min. The reaction was carried out at 50°C for 3.5 h. Then, ammonium persulfate initiator and triallyl isocyanurate chain extender were added and the reaction was carried out at 65°C for 3.5 h. After the second reaction was completed, the temperature was lowered and the reaction was carried out at 35°C for 2.0 h to obtain polyacrylic acid prepolymer.

[0070] (2) According to the weight, 20 parts of polyacrylic acid prepolymer, 1 part of silane coupling agent Y-5475 and 40 parts of deionized water obtained in step (1) are stirred. The blade speed of the stirrer does not exceed 140m / min. After reacting at 60℃ for 2.5h, water-based polyacrylic acid adhesive is obtained.

[0071] Example 5

[0072] This embodiment provides a water-based polyacrylic acid adhesive, which is a polyacrylic acid adhesive modified with silane coupling agent Y-5475. The molecular weight of the water-based polyacrylic acid adhesive is 1 million.

[0073] This embodiment provides a method for preparing the above-mentioned water-based polyacrylic acid adhesive, which includes the following steps:

[0074] (1) 45 parts by weight of acrylic acid, 5 parts by weight of acrylamide, 2 parts by weight of fatty alcohol polyoxyethylene ether, 0.5 parts by weight of ammonium persulfate initiator and 0.5 parts by weight of triallyl isocyanurate chain extender and deionized water were stirred under a nitrogen atmosphere. The impeller tip speed of the stirrer did not exceed 240 m / min. The reaction was carried out at 65°C for 2.5 h. Then, ammonium persulfate initiator and triallyl isocyanurate chain extender were added and the reaction was carried out at 80°C for 2.5 h. After the second reaction was completed, the temperature was lowered and the reaction was carried out at 40°C for 1.0 h to obtain polyacrylic acid prepolymer.

[0075] (2) According to the weight, 33 parts of polyacrylic acid prepolymer, 3 parts of silane coupling agent Y-5475 and 54 parts of deionized water obtained in step (1) are stirred. The blade speed of the stirrer does not exceed 140m / min. After reacting at 90℃ for 1.5h, water-based polyacrylic acid adhesive is obtained.

[0076] Example 6

[0077] The difference between this embodiment and Example 1 is that the silane coupling agent KH-550 in step (2) is replaced with an equal number of methyltrichlorosilanes, while everything else is the same as in Example 1.

[0078] Example 7

[0079] The difference between this embodiment and Embodiment 1 is that the weight of acrylic acid in step (1) is adjusted to 20 parts and the weight of acrylamide is adjusted to 1 part, while all other aspects are the same as in Embodiment 1.

[0080] Example 8

[0081] The difference between this embodiment and Embodiment 1 is that the weight of acrylic acid in step (1) is adjusted to 50 parts and the weight of acrylamide is adjusted to 8 parts, while all other aspects are the same as in Embodiment 1.

[0082] Comparative Example 1

[0083] This comparative example provides a polyacrylic adhesive, LA136D, purchased from Chengdu Indile Power Technology Co., Ltd.

[0084] Comparative Example 2

[0085] This comparative example provides a styrene-butadiene rubber latex adhesive, purchased from Zeon Corporation of Japan, specifically BM-430B.

[0086] Application Examples 1 to 8 and Comparative Application Examples 1 to 2

[0087] Lithium-ion batteries were prepared using the aqueous polyacrylic acid adhesives provided in Examples 1 to 8 and Comparative Examples 1 to 2, and the preparation methods are as follows:

[0088] Preparation of negative electrode sheet: 2 wt.% of the above-mentioned water-based polyacrylic acid adhesive, 0.3 wt.% of the thickener sodium carboxymethyl cellulose, 1 wt.% of the conductive agent Super.P Li, 96.7 wt.% of graphite and deionized water are mixed to prepare a negative electrode slurry. The negative electrode slurry is then coated on the surface of copper foil, dried and rolled to obtain a negative electrode sheet.

[0089] Preparation of the positive electrode sheet: 96.80 wt.% of lithium nickel cobalt manganese oxide ternary material, 1.5 wt.% of conductive agent Super.P Li, 0.5 wt.% of conductive graphite KS-6, 1.20 wt.% of binder polyvinylidene fluoride and N-methylpyrrolidone were mixed to prepare a positive electrode slurry. The positive electrode slurry was then coated on the surface of aluminum foil, and the positive electrode sheet was obtained after drying and rolling.

[0090] Preparation of lithium-ion batteries: The positive electrode, negative electrode and electrolyte are assembled to obtain a soft pack battery with a capacity of 503040-550mAh.

[0091] Test conditions

[0092] The negative electrode sheets provided in Application Examples 1 to 8 and Comparative Application Examples 1 to 2 were tested using the following methods:

[0093] (1) Cohesion: (a) Cut the rolled positive / negative electrode sheets to a length of 400mm × width of 10-50mm. (b) Take a flat, thin steel plate with a length of 250mm and a width of 50mm; first, attach a strip of double-sided tape (longer than the sample test length, and the same width as the electrode sheet) to the center of the steel plate, and smooth it out to ensure that the double-sided tape is tightly attached to the center of the steel plate. Peel off the double-sided tape and attach the electrode sheet to the tape strip. It is essential to ensure that the electrode sheet and the tape are properly matched and attached; otherwise, the width of the peel force test will change, the test value will be inaccurate, and the peel curve will show jumps or waves. (c) Insert the steel plate with the attached electrode sheet into the lower clamp and fix it vertically; insert the electrode sheet without tape into the upper clamp and fix it so that the electrode sheet attached to the tape is at 180° (or 90°) to the electrode sheet fixed in the upper clamp. After fixing the test sample, first calibrate and zero the sample, set the test width, electrode peeling length of 50-150mm, and peeling speed of 75mm / min, then start the test to obtain the peel strength curve and average value. When processing the data, delete the beginning and end segments of the test to obtain the standard curve.

[0094] (2) Peel strength: Tested using an electronic tensile testing machine.

[0095] The lithium-ion batteries provided in Application Examples 1 to 8 and Comparative Application Examples 1 to 2 were tested using the following methods:

[0096] (1) Internal Resistance: The lithium-ion battery was standardly charged with a constant current of 0.22CA and a voltage limit of 4.2V; then discharged with a constant current of 0.2CA to 10% DOD, and a constant current charge-discharge experiment was conducted using a large current. The above steps were repeated, increasing the depth of discharge by 10% each time, until the depth of discharge reached 90%. The battery was then fully discharged with a constant current of 0.2CA until the termination voltage was 2.5V. The internal resistance during charging and discharging was calculated by measuring the voltage during the charge-discharge experiment. The calculation formula is R. d =(U2-U1) / I d and R c =(U2-U1) / I c

[0097] Where R d R represents the discharge internal resistance. c I represents the charging internal resistance. d Represents the discharge pulse current, I c Charging pulse current;

[0098] (2) Initial Coulomb efficiency: Charging process: Charged to 4.2V at a constant current of 0.5C, maintained at a constant voltage of 4.2V, and cut off current at a rate of 0.05C. Discharging process: Discharged to 3V at a constant current of 0.5C. The test temperature was 25℃.

[0099] (3) Rate performance: First, charge the battery to 4.2V with a constant current of 0.5C, then charge it to 4.2V with a constant voltage. The charging ends when the current drops to 0.05C. Next, discharge the battery to 3.0V with a constant current of 0.2C, then stop the discharge and let it rest for 10 minutes. Record the discharge capacity. Then charge the battery to 4.2V with a constant current of 0.5C, then charge it to 4.2V with a constant voltage of 4.2V. The charging ends when the current drops to 0.05C. Finally, discharge the battery at rates of 0.5C, 1C, 2C, 3C, and 5C respectively using the above steps. The rate performance of the prepared battery cell is tested at room temperature.

[0100] (4) High temperature discharge performance: Charge the battery to 4.2V at a constant current and constant voltage of 0.5C, and cut off the current of 0.05C. Then place the battery in an environment of 75℃±2℃ for 2 hours and discharge it to 3.0V at a constant current of 1C. Record the discharge capacity.

[0101] The test results are shown in Tables 1 and 2:

[0102] Table 1

[0103]

[0104] Table 2

[0105]

[0106] As can be seen from the data in Tables 1 and 2, the polyacrylic acid adhesive modified with organosilicon materials prepared in this invention can improve the flexibility of the negative electrode sheet during the preparation process, and the prepared negative electrode sheet has extremely strong adhesion to the foil.

[0107] like Figures 1-3 The results show that the prepared silicone-modified polyacrylic adhesive has excellent high-temperature resistance, which can significantly improve the safety performance of lithium-ion batteries during production and use. Comparative application examples 1 and 2 show that the polyacrylic adhesive and styrene-butadiene rubber emulsion adhesive disclosed in the prior art are not as effective as the water-based polyacrylic adhesive provided by the present invention.

[0108] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A water-based polyacrylic acid adhesive for negative electrode sheets, characterized in that, The water-based polyacrylic adhesive is a polyacrylic adhesive modified with organosilicon materials; The organosilicon material is a silane coupling agent or methyltrichlorosilane; the molecular weight of the water-based polyacrylic acid adhesive is 800,000 to 1,000,000. The water-based polyacrylic acid adhesive is prepared by the following method, which includes the following steps: (1) Acrylic acid, acrylamide, surfactant, initiator, chain extender and solvent are mixed and reacted once, then initiator and chain extender are added for a second reaction, after the second reaction is completed, the temperature is lowered and a third reaction is carried out to obtain polyacrylic acid prepolymer; the components include, by weight, 25-45 parts of acrylic acid, 3-5 parts of acrylamide, 1-2 parts of surfactant, 0.1-0.5 parts of initiator and 0.01-0.5 parts of chain extender; (2) The polyacrylic acid prepolymer, silicone material and solvent obtained in step (1) are mixed and reacted to obtain the water-based polyacrylic acid adhesive; the polyacrylic acid prepolymer is 20-40 parts by weight, the silicone material is 1-5 parts by weight and the solvent is 40-80 parts by weight.

2. A method for preparing the waterborne polyacrylic acid adhesive according to claim 1, characterized in that, The method includes the following steps: (1) Acrylic acid, acrylamide, surfactant, initiator, chain extender and solvent are mixed and reacted once, then initiator and chain extender are added for a second reaction, after the second reaction is completed, the temperature is lowered and a third reaction is carried out to obtain polyacrylic acid prepolymer; the components include, by weight, 25-45 parts of acrylic acid, 3-5 parts of acrylamide, 1-2 parts of surfactant, 0.1-0.5 parts of initiator and 0.01-0.5 parts of chain extender; (2) The polyacrylic acid prepolymer, silicone material and solvent obtained in step (1) are mixed and reacted to obtain the water-based polyacrylic acid adhesive; the polyacrylic acid prepolymer is 20-40 parts by weight, the silicone material is 1-5 parts by weight and the solvent is 40-80 parts by weight.

3. The method according to claim 2, characterized in that, The components mentioned in step (1) are, by weight, 38-40 parts of acrylic acid, 3-5 parts of acrylamide, 1-2 parts of surfactant, 0.1-0.3 parts of initiator and 0.01-0.02 parts of chain extender.

4. The method according to claim 2, characterized in that, The surfactant mentioned in step (1) includes polyoxyethylene ether; The polyoxyethylene ether comprises any one or a combination of at least two of the following: fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty amine polyoxyethylene ether, bisphenol A polyoxyethylene ether, octylphenol phenol polyoxyethylene ether, butanol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, isopentenol polyoxyethylene ether, methyl allyl polyoxyethylene ether, isomeric decaol polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, isomeric decacarbonol polyoxyethylene ether, or isomeric fatty alcohol polyoxyethylene ether.

5. The method according to claim 2, characterized in that, The initiator mentioned in step (1) includes any one or a combination of at least two of ammonium persulfate, potassium persulfate, sodium persulfate, or hydrogen peroxide; The chain extender mentioned in step (1) includes any one or a combination of at least two of the following: triallyl isocyanurate, diallyl phthalate, diallyl maleate, 1,4-butanediol, sorbitol, diethylaminoethanol, neopentyl glycol, 3,3'-dichloro-4,4'-diaminodiphenylmethane, ethylenediamine, N,N-dihydroxyaniline, ADR-4468 polymeric chain extender, anhydride-modified ethylene copolymer, or dimethylthiotoluene diamine. The solvent mentioned in step (1) is deionized water.

6. The method according to claim 2, characterized in that, The mixing described in step (1) is carried out in an inert atmosphere; The mixing described in step (1) is carried out under stirring.

7. The method according to claim 2, characterized in that, The temperature of the first reaction in step (1) is 50-65℃, and the time is 2.5h-3.5h; The temperature of the secondary reaction in step (1) is 65-80℃, and the time is 2.5h-3.5h; The temperature of the three reactions in step (1) is 35-40℃ and the time is 1.0h-2.0h.

8. The method according to claim 2, characterized in that, The polyacrylic acid prepolymer mentioned in step (2) consists of 28-38 parts by weight of the polyacrylic acid prepolymer, 2.5-3.5 parts by weight of the silicone material, and 53-56 parts by weight of the solvent.

9. The method according to claim 2, characterized in that, The silane coupling agent includes any one or at least a combination of two of the following: silane coupling agent KH-550, silane coupling agent KH-560, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-ureidopropyltriethoxysilane, silane coupling agent Y-5475, silane coupling agent Y-5669, 3-methacryloyloxy-propyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, or 3-(2-aminoethyl)aminopropyltrimethoxysilane. The solvent mentioned in step (2) is deionized water; The mixing described in step (2) is carried out under stirring; The reaction in step (2) is carried out at a temperature of 60-90℃ for 1.5-2.5 hours.

10. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes the water-based polyacrylic adhesive according to claim 1.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode as described in claim 10.

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