Aqueous binder, preparation method thereof, negative plate and lithium ion battery

Abstract

The invention relates to a water-based binder and a preparation method thereof, a negative plate and a lithium ion battery, organic acid with multiple hydroxyl groups, acrylic monomers, a cross-linking agent containing ether bonds and rigid acrylate are mixed with water according to the mass ratio of 1: (2-3): (1.5-2.5): (2-3) and then preheated, and the glass transition temperature of the rigid acrylate is larger than or equal to 84 DEG C; and adding a cationic functional monomer and an initiator at the same time, carrying out polymerization reaction to obtain the aqueous binder, and the mass of the cationic functional monomer is 8-15% of the sum of the mass of the organic acid with multiple hydroxyls, the mass of the acrylic monomer, the mass of the cross-linking agent containing ether bonds and the mass of the rigid acrylate. According to the preparation method disclosed by the invention, the aqueous binder with high bonding strength, expansion resistance and excellent conductivity can be prepared, and when the aqueous binder disclosed by the invention is applied to a negative plate, the cycling stability and rate capability of a lithium ion battery can be synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to aqueous binders and their preparation methods, negative electrode sheets, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles, consumer electronics and industrial tools. As the main body of lithium-ion insertion and extraction reactions, the performance of the negative electrode material directly determines the energy density, cycle life and safety characteristics of the battery. In the negative electrode preparation process, the choice of binder is particularly critical. Traditional binders mainly have the following technical bottlenecks: (1) Structural characteristics: Traditional binders are mostly rigid structures, which are difficult to adapt to the volume changes of the negative electrode active material during charging and discharging. Especially in silicon-based negative electrode systems, silicon materials will generate up to 300% volume expansion during lithium insertion and extraction, which can easily lead to the peeling of the active material layer from the current collector, thereby causing problems such as rapid capacity decay and sharp increase in interface impedance; (2) Solvent system: Traditional processes usually require the use of toxic N-methylpyrrolidone (NMP) as a solvent, which not only poses environmental risks but also has high recycling costs. Traditional aqueous binders lack effective electron conduction paths, which can lead to a significant decrease in electrode conductivity. Summary of the Invention

[0003] Therefore, it is necessary to provide an aqueous binder and its preparation method, a negative electrode sheet, and a lithium-ion battery to address the above problems. The preparation method can produce an aqueous binder with high bonding strength, expansion resistance, and excellent conductivity. When the aqueous binder of the present invention is used in a negative electrode sheet, it can synergistically improve the cycle stability and rate performance of the lithium-ion battery.

[0004] A method for preparing a water-based adhesive includes the following steps:

[0005] An organic acid with multiple hydroxyl groups, an acrylic monomer, a crosslinking agent containing ether bonds, and a rigid acrylate are mixed with water in a mass ratio of 1:2~3:1.5~2.5:2~3, and then preheated, wherein the glass transition temperature of the rigid acrylate is greater than or equal to 84°C.

[0006] Simultaneously, cationic functional monomers and initiators are added to carry out a polymerization reaction to obtain an aqueous binder. The mass of the cationic functional monomer is 8% to 15% of the sum of the mass of the organic acid with multiple hydroxyl groups, the acrylic monomer, the crosslinking agent containing ether bonds, and the rigid acrylate.

[0007] In one embodiment, the organic acid having multiple hydroxyl groups is selected from at least one of shikimic acid, gallic acid, quinic acid, or mucilage.

[0008] And / or, the acrylic monomer is selected from at least one of acrylic acid, methacrylic acid or ethylacrylic acid;

[0009] And / or, the ether-containing crosslinking agent is selected from at least one of the adducts of hydroxyethyl methacrylate and ε-caprolactone, polyethylene glycol methacrylate, or polyethylene glycol dimethacrylate;

[0010] And / or, the rigid acrylate is selected from at least one of cyclohexyl methacrylate, isobornyl methacrylate, or adamantane acrylate;

[0011] And / or, the cationic functional monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethylaminoethyl methacrylate, or allyltrimethylammonium chloride;

[0012] And / or, the initiator is selected from at least one of potassium sulfate, ammonium persulfate, sodium persulfate or azobisisobutyramidine hydrochloride.

[0013] In one embodiment, the mass of the initiator is 0.8% to 1.5% of the sum of the masses of the organic acid having multiple hydroxyl groups, the acrylic monomer, the crosslinking agent containing ether bonds, and the rigid acrylate.

[0014] In one embodiment, the preheating temperature is 65°C to 80°C, and the time is 15 min to 45 min;

[0015] And / or, the polymerization reaction is carried out at a temperature of 70°C to 85°C for a time of 4 to 6 hours.

[0016] In one embodiment, after the polymerization reaction is completed, the pH is adjusted to 6.5-7.5.

[0017] In one embodiment, the solid content of the water-based adhesive is 48% to 54%.

[0018] A water-based adhesive prepared using the aforementioned method.

[0019] A negative electrode includes a current collector and an active material layer attached to the current collector, the active material layer using the aforementioned aqueous binder.

[0020] In one embodiment, the negative electrode active material in the active material layer is selected from silicon-based materials.

[0021] A lithium-ion battery that uses a negative electrode as described above.

[0022] The water-based adhesive prepared by the method of this invention has advantages such as high bonding strength, resistance to expansion and excellent conductivity, and it replaces traditional organic solvent systems such as N-methylpyrrolidone, greatly reducing environmental pollution.

[0023] When the aqueous binder of this invention is applied to the negative electrode of a lithium-ion battery, the acrylic monomers can improve the chain flexibility of the aqueous binder, preventing the negative electrode from becoming brittle. The cationic functional monomers can enable the aqueous binder to electrostatically adsorb onto the negative electrode active material. The rigid acrylates can improve the adhesion of the aqueous binder to substrates such as metals and ceramics, while also improving the creep resistance and heat resistance of the aqueous binder. The hydroxyl groups in the organic acid can form reversible hydrogen bonds between the aqueous binder and the hydroxyl groups on the surface of the negative electrode active material. During charge and discharge, the "breakage-reconstruction" of the reversible hydrogen bonds buffers volume expansion, especially when silicon-based materials are used as negative electrode active materials, effectively alleviating the collapse of the negative electrode structure. Thus, through the synergistic effect of multiple aspects, the peel strength between the active material layer and the current collector in the negative electrode can be effectively improved. In addition, the ether bonds in the crosslinking agent can complex the aqueous binder with lithium ions, reducing the lithium ion migration barrier, promoting lithium ion transport, and improving the conductivity of the aqueous binder. Therefore, the cycle stability and rate performance of the lithium-ion battery can be synergistically improved. Detailed Implementation

[0024] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0026] The method for preparing the water-based adhesive provided by this invention includes the following steps:

[0027] S1, an organic acid with multiple hydroxyl groups, an acrylic monomer, a crosslinking agent containing ether bonds, and a rigid acrylate are mixed with water in a mass ratio of 1:2~3:1.5~2.5:2~3, and then preheated, wherein the glass transition temperature of the rigid acrylate is greater than or equal to 84°C.

[0028] S2, simultaneously adding cationic functional monomers and initiators, and carrying out polymerization reaction to obtain an aqueous binder, wherein the mass of the cationic functional monomer is 8% to 15% of the sum of the mass of the organic acid with multiple hydroxyl groups, the acrylic monomer, the crosslinking agent containing ether bonds, and the rigid acrylate.

[0029] The water-based adhesive prepared by the method of this invention has advantages such as high bonding strength, resistance to expansion and excellent conductivity, and it replaces traditional organic solvent systems such as N-methylpyrrolidone, greatly reducing environmental pollution.

[0030] When the aqueous binder of the present invention is applied to the negative electrode of a lithium-ion battery, the acrylic monomers can improve the chain segment flexibility of the aqueous binder and prevent the negative electrode from becoming brittle. It is understood that the acrylic monomers are different from rigid acrylates. Optionally, the acrylic monomers are selected from at least one of acrylic acid, methacrylic acid, or ethyl acrylic acid, which can better improve the chain segment flexibility of the aqueous binder.

[0031] When the aqueous binder of the present invention is applied to the negative electrode sheet of a lithium-ion battery, the cationic functional monomer can enable the aqueous binder to electrostatically adsorb onto the negative electrode active material. Optionally, the cationic functional monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethylaminoethyl methacrylate, or allyltrimethylammonium chloride, which can enable the aqueous binder to better adsorb the negative electrode active material.

[0032] When the aqueous binder of the present invention is applied to the negative electrode sheet of a lithium-ion battery, the rigid acrylate can improve the adhesion of the aqueous binder to substrates such as metals and ceramics, and at the same time improve the creep resistance and heat resistance of the aqueous binder. Optionally, the rigid acrylate is selected from at least one of cyclohexyl methacrylate, isobornyl methacrylate, or adamantane acrylate, which can further improve the adhesion, creep resistance, and heat resistance of the aqueous binder to the substrate.

[0033] When the aqueous binder of this invention is applied to the negative electrode of a lithium-ion battery, the hydroxyl groups in the organic acid can form reversible hydrogen bonds between the aqueous binder and the hydroxyl groups on the surface of the negative electrode active material. During charging and discharging, the volume expansion is buffered through the "breaking and reconstruction" of the reversible hydrogen bonds, especially when silicon-based materials are used as negative electrode active materials, effectively mitigating the collapse of the negative electrode structure. Optionally, the organic acid having multiple hydroxyl groups is selected from at least one of shikimic acid, gallic acid, quinic acid, or viscous acid, which can better buffer volume expansion.

[0034] Therefore, through the synergistic effect of organic acids with multiple hydroxyl groups, acrylic monomers, rigid acrylates, and cationic functional monomers, the peel strength between the active material layer and the current collector in the negative electrode sheet can be effectively improved.

[0035] Furthermore, when the aqueous binder of the present invention is applied to the negative electrode of a lithium-ion battery, the ether bonds in the crosslinking agent can complex the aqueous binder with lithium ions, reduce the lithium-ion migration barrier, promote lithium-ion transport, and improve the conductivity of the aqueous binder. Optionally, the crosslinking agent containing ether bonds is selected from at least one of the adduct of hydroxyethyl methacrylate and ε-caprolactone, polyethylene glycol methacrylate, or polyethylene glycol dimethacrylate, which is more conducive to improving the conductivity of the aqueous binder.

[0036] Therefore, the use of the aqueous binder of the present invention in the negative electrode of lithium-ion batteries can synergistically improve the cycle stability and rate performance of lithium-ion batteries.

[0037] In step S1, the preheating temperature of the aqueous solution of the organic acid with multiple hydroxyl groups, acrylic monomer, crosslinking agent containing ether bonds, and rigid acrylate is preferably 65℃~80℃. Any value among 65℃, 70℃, 75℃, or 80℃, or any range between two, can be selected. Within this temperature range, when adding cationic functional monomers and initiators to carry out the polymerization reaction in step S2, the polymerization reaction can proceed smoothly, avoid excessively wide molecular weight distribution, and reduce branching side reactions caused by chain transfer.

[0038] During the polymerization reaction, adding the cationic functional monomer and the initiator simultaneously can prevent premature local polymerization caused by adding the initiator first, which could lead to a broadening of the molecular weight distribution. It can also prevent monomer self-polymerization or side reactions with the main chain that might occur if the cationic functional monomer is added first. To better control the polymerization rate and avoid overly vigorous local reactions, the cationic functional monomer and the initiator can be pre-prepared as an aqueous solution, appropriately diluted, and then slowly added dropwise to the reaction system.

[0039] Preferably, the initiator is selected from at least one of potassium sulfate, ammonium persulfate, sodium persulfate, or azobisisobutyramidine hydrochloride, and the mass of the initiator is 0.8% to 1.5% of the sum of the masses of the organic acid having multiple hydroxyl groups, the acrylic monomer, the polyester polyol, and the rigid acrylate, and can be any value of 0.8%, 1.0%, or 1.5% or any range between the two.

[0040] In step S2, the polymerization temperature is preferably 70℃~85℃, and can be any value or a range between any two of 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃ or 85℃; the polymerization time is preferably 4h~6h, and can be any value or a range between any two of 4h, 5h or 6h. Under these conditions, by strictly controlling the reaction temperature, it is possible to avoid excessively high temperatures that could trigger explosive polymerization, increase oligomer formation and reduce bond strength, and also to prevent excessively low temperatures that could lead to incomplete reaction.

[0041] When the polymerization reaction is carried out in the manner described above, the conversion rate of the polymerization reaction is greater than or equal to 98%.

[0042] After the polymerization reaction is complete, pH adjustment can be performed to control the pH of the water-based adhesive within the range of 6.5-7.5. Any value or a range between 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, or 7.5 can be selected. Within this pH range, the stability and adhesion to the substrate of the water-based adhesive can be improved, and the corrosiveness of the water-based adhesive can be reduced.

[0043] Optionally, the solid content of the aqueous binder is preferably controlled within the range of 48% to 54%. Any value of 48%, 49%, 50%, 51%, 52%, 53%, or 54% or any range between two can be selected. This can effectively balance the cohesive strength and flexibility of the aqueous binder, avoid the problem of decreased storage stability of the aqueous binder and difficulty in coating after the negative electrode slurry is made due to excessive solid content, and at the same time prevent the problem of cracking of the active material layer of the negative electrode sheet caused by increased film shrinkage due to excessively low solid content.

[0044] The present invention also provides an aqueous adhesive prepared by the above-described preparation method, wherein the aqueous adhesive has a viscosity of 5000 mPa·s to 20000 mPa·s at 25°C, a swelling rate of less than or equal to 15% when the aqueous adhesive is placed in water for 24 hours, a glass transition temperature of -25°C to 10°C, a weight-average molecular weight of 200,000 g / mol to 500,000 g / mol, and a gel content of less than 1%.

[0045] The present invention also provides a negative electrode sheet, the negative electrode sheet comprising a current collector and an active material layer attached to the current collector, the active material layer using the aforementioned aqueous binder.

[0046] Optionally, the negative electrode active material in the active material layer is selected from silicon-based materials, such as silicon materials or silicon-carbon materials.

[0047] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery uses the aforementioned negative electrode sheet.

[0048] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0049] Example 1

[0050] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:1.5:1.5:2:2:0.8:0.096.

[0051] Shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 75°C to 80°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 6890 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 8%. The glass transition temperature of the aqueous binder was -15°C, the weight average molecular weight was 300,000 g / mol, and the gel content was 0.2%.

[0052] Example 2

[0053] The raw materials were weighed according to the following mass ratio: gallic acid, methacrylic acid, hydroxyethyl methacrylate and ε-caprolactone adduct, isobornyl methacrylate, dimethylaminoethyl methacrylate and ammonium persulfate, in a ratio of 1:2:1.5:2:0.52:0.052.

[0054] Gallic acid, methacrylic acid, an adduct of hydroxyethyl methacrylate and ε-caprolactone, isobornyl methacrylate, and deionized water were mixed and preheated to 80°C for 15 min. Then, under a nitrogen atmosphere, an aqueous solution of dimethylaminoethyl methacrylate and ammonium persulfate was slowly added dropwise. The polymerization reaction was carried out at a temperature controlled within the range of 70°C to 75°C for 6 h. After the reaction was completed, the pH of the system was adjusted to 7.5, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 7010 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 10%. The glass transition temperature of the aqueous binder was -10°C, the weight-average molecular weight was 400,000 g / mol, and the gel content was 0.4%.

[0055] Example 3

[0056] The raw materials were weighed according to the mass ratio of viscous acid, ethyl acrylic acid, polyethylene glycol dimethacrylate, adamantane acrylate, allyltrimethylammonium chloride and potassium persulfate of 1:3:2.5:3:1.425:0.1425.

[0057] Viscous acid, ethyl acrylic acid, polyethylene glycol dimethacrylate, adamantane acrylate, and deionized water were mixed and preheated to 65°C for 45 min. Then, under nitrogen atmosphere protection, an aqueous solution of allyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 75°C to 85°C for 4 h. After the reaction was completed, the pH of the system was adjusted to 7.5, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 7142 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 9%. The glass transition temperature of the aqueous binder was -8°C, the weight average molecular weight was 350,000 g / mol, and the gel content was 0.4%.

[0058] Comparative Example 1

[0059] The raw materials were weighed according to the mass ratio of acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1.5:1.5:2:2:0.8:0.096.

[0060] Acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain a water-based binder with a solid content of 52%. The viscosity of the water-based binder at 25°C was 6480 mPa·s. After the water-based binder was placed in water for 24 h, the swelling rate was tested to be 16%. The glass transition temperature of the water-based binder was -26°C, the weight average molecular weight was 250,000 g / mol, and the gel content was 1.2%.

[0061] Comparative Example 2

[0062] The raw materials were weighed according to the mass ratio of shikimic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:2:2:0.8:0.096.

[0063] Shikimic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction was carried out at 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 5431 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 21%. The glass transition temperature of the aqueous binder was 10°C, the weight average molecular weight was 200,000 g / mol, and the gel content was 1.2%.

[0064] Comparative Example 3

[0065] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:1.5:1.5:2:0.8:0.096.

[0066] Shikimic acid, acrylic acid, methacrylic acid, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 6574 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 17%. The glass transition temperature of the aqueous binder was -26°C, the weight average molecular weight was 250,000 g / mol, and the gel content was 2.0%.

[0067] Comparative Example 4

[0068] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:1.5:1.5:2:0.8:0.096.

[0069] Shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction was carried out at 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 7410 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 18%. The glass transition temperature of the aqueous binder was -23°C, the weight average molecular weight was 300,000 g / mol, and the gel content was 1.3%.

[0070] Comparative Example 5

[0071] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, sodium p-styrene sulfonate, and potassium persulfate of 1:1.5:1.5:2:2:0.8:0.096.

[0072] Shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of sodium p-styrene sulfonate and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 8541 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 10%. The glass transition temperature of the aqueous binder was -10°C, the weight average molecular weight was 500,000 g / mol, and the gel content was 1.0%.

[0073] Comparative Example 6

[0074] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:1:3:3:1:0.8:0.096.

[0075] Shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 min. Then, under nitrogen atmosphere protection, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction temperature was controlled within the range of 70°C to 75°C for 5 h. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 8895 mPa·s. After the aqueous binder was placed in water for 24 h, the swelling rate was tested to be 15%. The glass transition temperature of the aqueous binder was 15°C, the weight average molecular weight was 800,000 g / mol, and the gel content was 2%.

[0076] Comparative Example 7

[0077] The raw materials were weighed according to the mass ratio of shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, methacryloyloxyethyltrimethylammonium chloride and potassium persulfate of 1:1.5:1.5:2:2:0.4:0.096.

[0078] Shikimic acid, acrylic acid, methacrylic acid, polyethylene glycol dimethacrylate, cyclohexyl methacrylate, and deionized water were mixed and preheated to 75°C for 30 minutes. Then, under a nitrogen atmosphere, an aqueous solution of methacryloyloxyethyltrimethylammonium chloride and potassium persulfate was slowly added dropwise. The polymerization reaction was carried out at a temperature controlled within the range of 70°C to 75°C for 5 hours. After the reaction was completed, the pH of the system was adjusted to 7, and the mixture was cooled to room temperature to obtain an aqueous binder with a solid content of 52%. The viscosity of the aqueous binder at 25°C was 4075 mPa·s. After the aqueous binder was placed in water for 24 hours, the swelling rate was tested to be 22%. The glass transition temperature of the aqueous binder was -30°C, the weight-average molecular weight was 50,000 g / mol, and the gel content was 5%.

[0079] The aqueous binders prepared in Examples 1-3 and Comparative Examples 1-7 were mixed with silicon carbon materials and graphene in a mass ratio of 2:5:93. Water was used as a solvent to prepare a negative electrode slurry, which was uniformly coated on a copper foil current collector. After drying and rolling, a negative electrode sheet was obtained. A lithium-ion battery was assembled using PP-composite alumina as a separator, lithium hexafluorophosphate with a mass fraction of 18% as an electrolyte, and lithium nickel cobalt aluminum oxide as a positive electrode. Charge and discharge tests were performed using a battery tester, and the results are shown in Table 1.

[0080] Table 1

[0081]

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a water-based adhesive, characterized in that, Includes the following steps: An organic acid with multiple hydroxyl groups, an acrylic monomer, a crosslinking agent containing ether bonds, and a rigid acrylate are mixed with water in a mass ratio of 1:2~3:1.5~2.5:2~3, and then preheated, wherein the glass transition temperature of the rigid acrylate is greater than or equal to 84°C. Simultaneously, cationic functional monomers and initiators are added to carry out a polymerization reaction to obtain an aqueous binder. The mass of the cationic functional monomer is 8% to 15% of the sum of the mass of the organic acid with multiple hydroxyl groups, the acrylic monomer, the crosslinking agent containing ether bonds, and the rigid acrylate.

2. The method for preparing the water-based adhesive according to claim 1, characterized in that, The organic acid having multiple hydroxyl groups is selected from at least one of shikimic acid, gallic acid, quinic acid, or mucilage. And / or, the acrylic monomer is selected from at least one of acrylic acid, methacrylic acid or ethylacrylic acid; And / or, the ether-containing crosslinking agent is selected from at least one of the adducts of hydroxyethyl methacrylate and ε-caprolactone, polyethylene glycol methacrylate, or polyethylene glycol dimethacrylate; And / or, the rigid acrylate is selected from at least one of cyclohexyl methacrylate, isobornyl methacrylate, or adamantane acrylate; And / or, the cationic functional monomer is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethylaminoethyl methacrylate, or allyltrimethylammonium chloride; And / or, the initiator is selected from at least one of potassium sulfate, ammonium persulfate, sodium persulfate or azobisisobutyramidine hydrochloride.

3. The method for preparing the water-based adhesive according to claim 1 or 2, characterized in that, The mass of the initiator is 0.8% to 1.5% of the sum of the masses of the organic acid having multiple hydroxyl groups, the acrylic monomer, the crosslinking agent containing ether bonds, and the rigid acrylate.

4. The method for preparing the water-based adhesive according to claim 1 or 2, characterized in that, The preheating temperature is 65℃~80℃, and the time is 15min~45min; And / or, the polymerization reaction is carried out at a temperature of 70°C to 85°C for a time of 4 to 6 hours.

5. The method for preparing the water-based adhesive according to claim 1 or 2, characterized in that, After the polymerization reaction is completed, adjust the pH to 6.5-7.

5.

6. The method for preparing the water-based adhesive according to claim 1 or 2, characterized in that, The solid content of the water-based adhesive is 48% to 54%.

7. A water-based adhesive prepared by the method of any one of claims 1 to 6.

8. A negative electrode sheet, characterized in that, The negative electrode includes a current collector and an active material layer attached to the current collector, wherein the active material layer uses the aqueous binder as described in claim 7.

9. The negative electrode sheet according to claim 8, characterized in that, The negative electrode active material in the active material layer is selected from silicon-based materials.

10. A lithium-ion battery, characterized in that, The lithium-ion battery uses the negative electrode sheet as described in claim 8 or 9.

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