A water-based binder and its preparation method and application

Abstract

The present invention discloses a water-based binder, its preparation method, and application. The binder is obtained by copolymerizing a first monomer, a second monomer, and a third monomer; wherein the first monomer is a compound having the structural formula shown in Formula I; the second monomer is 1,3-butadiene; and the third monomer has the structural formula shown in Formula II, wherein R1 is H or a methyl group, R2 is a carboxyl group or an amino group, and X is a segment between the linking group R2 and the vinyl group. The water-based binder has high electrical conductivity and excellent bonding ability, can effectively suppress electrode expansion, and imparts excellent cycle efficiency and stability to secondary batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and in particular relates to a water-based adhesive and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have become the most commonly used energy storage devices for portable electronic products and electric vehicles. They have advantages such as high energy density, good cycle stability, and fast charge and discharge. Furthermore, with the development of technology, higher performance requirements have been placed on lithium-ion batteries.

[0003] One of the more common problems in the use of lithium-ion batteries is that the negative electrode material of lithium-ion batteries will undergo severe volume expansion during the charge and discharge process, resulting in damage to the active material electrode structure and capacity decay. In response to the above problems, in addition to developing high-performance new materials, high-performance design of existing materials is also an effective approach. Among them, binders are one of the key materials affecting lithium-ion batteries. They can form carbon-binder domains (CBDs) with conductive carbon nanoparticles, directly affecting the transmission efficiency of ions and electrons in the electrode, as well as the quality of the passivation layer (such as SEI and CEI films) formed on the surface of the active material in contact with the electrolyte. Therefore, the selection, optimization and development of binders are of great value.

[0004] The existing more conventional lithium-ion battery binders mainly include polyvinyl alcohol, polyvinylidene fluoride, functional styrene-butadiene rubber SBR, sodium carboxymethyl cellulose CMC or a combination of the above. Among them, the functional styrene-butadiene rubber and sodium carboxymethyl cellulose combination binder is widely used in lithium-ion batteries due to its stable performance and price advantage. However, styrene-butadiene rubber (SBR) has a weak affinity for electrolyte due to the strong rigidity of the benzene rings it contains and the lack of lyophilic groups. During the preparation process of lithium-ion batteries, there are problems such as poor electrode liquid absorption and low temperature resistance, which affect the battery cycle performance. In order to increase the affinity of SBR, other functional monomers such as acrylic substances are usually used, but the improvement effect is limited. In addition, SBR is arranged in a linear manner, has weak bonding force, and has a low inhibitory effect on the negative electrode.

[0005] Therefore, there is an urgent need to develop an adhesive with strong bonding force that can effectively inhibit the expansion of the electrode. Summary of the Invention

[0006] In view of this, the primary purpose of the present invention is to provide an aqueous binder having high electrical conductivity and excellent bonding ability, which can effectively inhibit electrode expansion and endow secondary batteries with excellent cycle efficiency and stability.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention first provides a water-based binder obtained by copolymerizing a first monomer, a second monomer and a third monomer;

[0009] Wherein, the first monomer is a compound having a structural formula as shown in Formula I:

[0010]

[0011] The second monomer is 1,3-butadiene;

[0012] The third monomer is a compound having a structural formula as shown in Formula II:

[0013]

[0014] Wherein, R1 is H or methyl, R2 is carboxyl or amino, and X is a segment between the connecting group R2 and the vinyl group.

[0015] In a further embodiment, the aqueous binder is obtained by copolymerizing a first monomer, a second monomer, a third monomer and a functional monomer.

[0016] In a further embodiment, the method for preparing the first monomer comprises the following steps:

[0017] Take dimethyl 2,5-dihydroxyterephthalate, dichloromethane, water, tert-butylammonium bromide and sodium hydroxide, mix and stir, then add allyl bromide dropwise at room temperature, continue stirring, then add sodium hydroxide, continue to react at room temperature, adjust the system pH to 1, filter and dry, to obtain the first monomer.

[0018] In a further embodiment, the third monomer is at least one of N-2,2-propenyl-2-acrylamide, N-trimethylol acrylamide, 2-vinylpropane-1,3-diol, allyl alcohol, 1,4-cyclohexanedimethanol monoacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, polyethylene glycol methacrylate, 3-hydroxy-1-adamantyl methacrylate, 2,3-dihydroxypropyl acrylate, glycerol 1,3-diglycerol alcohol diacrylate, N-hydroxymethyl acrylamide, polypropylene glycol-methacrylate, hydroxyethyl acrylamide, and polyethylene glycol monoallyl ether.

[0019] In a further embodiment, the functional monomer is at least one of an unsaturated organic acid or a derivative thereof, an alkenyl alcohol or a derivative thereof, an alkenyl nitrile or a derivative thereof, an alkenyl amine, and an alkenyl ether or a derivative thereof.

[0020] In a further embodiment, the functional monomer is diacetone acrylamide, N,N-dimethylacrylamide, acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, carbodiimide, maleamide, tert-butylacrylamide, tert-butylacrylamidesulfonic acid, acrylonitrile, bis[2-(methacryloyloxy)ethyl]phosphate, 3-trimethoxysilane propyl acrylate, 2-cyanoacrylate ethylene glycol monomethyl ether acrylate, methacrylic acid, 1,4-cyclohexanedimethanol monoacrylate, triallyl phosphate, 3-sulfopropyl methacrylate, bis[2-(methacryloyloxy)ethyl]phosphoric acid, 2-methacrylic acid, allyl sulfonic acid, styrenesulfonic acid, sodium 2-methyl-2-propylene-1-sulfonate, crotonic acid, maleic acid, fumaric acid, or the corresponding lithium salt, sodium salt, potassium salt or calcium salt of an unsaturated organic acid.

[0021] The present invention further provides a method for preparing the aforementioned aqueous binder, comprising the following steps:

[0022] After the first monomer and water are evenly mixed, the remaining monomers are added, and then the initiator is added. The temperature is raised to 70-90° C. and the reaction is carried out for 2.5-3.5 hours. An inorganic base is added to adjust the pH of the system to 6-8, and the temperature is lowered to obtain a water-based adhesive.

[0023] In a further embodiment, the molar ratio of the first monomer: the second monomer: the third monomer is (10-65): (10-95): (10-85); or the molar ratio of the first monomer: the second monomer: the third monomer: the functional monomer is (10-65): (10-95): (10-85): (5-75).

[0024] In a further embodiment, the inorganic base is lithium hydroxide, sodium hydroxide, potassium hydroxide or calcium hydroxide.

[0025] In a further embodiment, the initiator is at least one of azobisisobutyronitrile, potassium persulfate, and ammonium persulfate.

[0026] In a further embodiment, the mass percentage of the initiator to the total polymerization monomers is 0.1%-5%.

[0027] The present invention further provides a negative electrode slurry containing the aforementioned aqueous binder or the aqueous binder prepared by the aforementioned preparation method.

[0028] The present invention further provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains the aforementioned aqueous binder or the aqueous binder prepared by the aforementioned preparation method.

[0029] In a further embodiment, the mass proportion of the aqueous binder in the negative electrode active material layer is 0.01% to 10%.

[0030] The present invention further provides a lithium-ion battery comprising the aforementioned negative electrode plate.

[0031] Beneficial effects of the present invention:

[0032] The water-based binder of the present invention is obtained by copolymerizing a first monomer, a second monomer, and a third monomer, all of which are carboxyl-containing phenyl ether olefin monomers. Compared to the SBR monomer styrene, the first monomer of the present invention, due to its high polarity of the carboxyl group, can improve the water-based binder's water solubility and lyophilicity. Furthermore, the introduction of an ether bond through the parent ring of the first monomer helps improve the toughness of the water-based binder. The ether bond and the carboxyl group synergistically increase the adhesion between the water-based binder and the electrode. Furthermore, the first monomer is a diolefin, and the polymerized segments formed by the first monomer, the second monomer, and the third monomer interlace to form a network structure, which can enhance the direct interaction between the current collector and the active material.

[0033] In general, the first monomer used in this invention possesses high polarity and cross-linking activity, thus imparting superior lyophilicity to the water-based binder. Compared to conventional SBR, the water-based binder prepared in this invention exhibits higher conductivity and stronger adhesion, resulting in lithium-ion batteries with improved cycle efficiency and stability, while effectively suppressing electrode expansion.

[0034] In addition, the preparation method of the water-based binder of the present invention is green and environmentally friendly, the process is simple and controllable, high temperature and high pressure are not required, and the reaction conditions are mild. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 FIG1 is a nuclear magnetic resonance spectrum of the first monomer in a preferred embodiment of the present invention.

[0036] Figure 2 These are the charge and discharge performance test results of button batteries assembled with the adhesives in Example 5 and Comparative Example 2. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0038] The first aspect of the present invention discloses an aqueous binder obtained by copolymerizing a first monomer, a second monomer and a third monomer.

[0039] This water-based binder is obtained by copolymerizing multiple monomers. The polymer chains formed by cross-linking between the monomers are intertwined to form a network structure, so the water-based binder has excellent bonding strength; the introduction of special groups gives the water-based binder excellent lyophilicity; at the same time, the water-based binder can effectively inhibit the expansion of the electrode and improve the cycle efficiency and stability of the lithium-ion battery.

[0040] The first monomer described herein is a compound having a structural formula as shown in Formula I:

[0041]

[0042] As can be seen in the structure of the first monomer, the highly polar carboxyl group improves the water solubility and lyophilicity of the water-based binder. Furthermore, after cross-linking, the introduction of ether bonds through the parent ring of the first monomer helps enhance the toughness of the water-based binder. The ether bonds and carboxyl groups synergistically enhance the adhesion between the water-based binder and the electrode. Furthermore, the first monomer contains a double bond, which can be cross-linked with other monomers. The cross-linked polymer segments intertwine to form a network structure, which enhances the adhesion of the water-based binder.

[0043] Furthermore, the preparation of the first monomer described herein comprises the following steps:

[0044] Take dimethyl 2,5-dihydroxyterephthalate, dichloromethane, water, tert-butylammonium bromide and sodium hydroxide, mix and stir, then add allyl bromide dropwise at room temperature, continue stirring, then add sodium hydroxide, continue to react at room temperature, adjust the system pH to 1, filter and dry, to obtain the first monomer.

[0045] The present invention adopts a sodium hydroxide + dichloromethane system and can prepare the first monomer at room temperature through a two-phase liquid-liquid reaction. The post-processing process is simple, the raw materials are easy to obtain, the cost is lower, the process steps are simple, and the yield is high.

[0046] In some specific embodiments of the present invention, the first monomer is prepared by the following method:

[0047] To the reaction flask, dimethyl 2,5-dihydroxyterephthalate (226 g), dichloromethane (2000 ml), water (2000 ml), tert-butylammonium bromide (15 g), and sodium hydroxide (80 g) were added respectively. After stirring, allyl bromide (240 g) was added dropwise at room temperature. After stirring for 5 h, sodium hydroxide (120 g) was added. The reaction was continued at room temperature for 10 h. Hydrochloric acid was added to adjust the pH of the system to 1. The mixture was filtered and the filter cake was dried to obtain the first monomer with a molar yield of 92%.

[0048] It is understandable that the specific amount of raw materials used can be adjusted or optimized within an appropriate range based on the known methods in the present invention, and will not be elaborated here one by one.

[0049] Furthermore, the second monomer described herein is 1,3-butadiene.

[0050] Furthermore, the third monomer described herein is a compound having a structural formula as shown in Formula II:

[0051]

[0052] Wherein, R1 is H or methyl, R2 is carboxyl or amino, and X is a segment between the connecting group R2 and the vinyl group. The segment here is not particularly limited and can be any common organic segment in the art.

[0053] In some specific embodiments of the present invention, the third monomer is at least one of N-2,2-propenyl-2-acrylamide, N-trimethylol acrylamide, 2-vinylpropane-1,3-diol, allyl alcohol, 1,4-cyclohexanedimethanol monoacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, polyethylene glycol methacrylate, 3-hydroxy-1-adamantyl methacrylate, 2,3-dihydroxypropyl acrylate, glycerol 1,3-diglycerol alcohol diacrylate, N-hydroxymethyl acrylamide, polypropylene glycol-methacrylate, hydroxyethyl acrylamide, and polyethylene glycol monoallyl ether.

[0054] In other specific embodiments of the present invention, the water-based binder is obtained by copolymerization of a first monomer, a second monomer, a third monomer and a functional monomer.

[0055] On the basis of copolymerization of the first monomer, the second monomer and the third monomer, a functional monomer is introduced, and the cross-linking of the carboxyl group in the first monomer and the functional monomer is utilized to further improve the effect of suppressing the expansion of the electrode.

[0056] Furthermore, the functional monomer described herein is at least one of an unsaturated organic acid or a derivative thereof, an alkenyl alcohol or a derivative thereof, an alkenyl nitrile or a derivative thereof, an alkenyl amine, and an alkenyl ether or a derivative thereof.

[0057] The unsaturated organic acid mentioned here refers to a carboxylic acid containing a double bond in its structure, and the derivatives of the unsaturated organic acid include its corresponding amide, ester or metal salt; wherein the metal salt includes but is not limited to lithium salt, sodium salt, potassium salt or calcium salt.

[0058] In some preferred embodiments of the present invention, specific examples of the functional monomer include diacetone acrylamide, N,N-dimethylacrylamide, acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, carbodiimide, maleamide, tert-butylacrylamide, tert-butylacrylamidesulfonic acid, acrylonitrile, di[2-(methacryloyloxy)ethyl]phosphate, 3-trimethoxysilane propyl acrylate, 2-cyanoacrylate ethylene glycol monomethyl ether acrylate, methacrylic acid, 1,4-cyclohexanedimethanol monoacrylate, triallyl phosphate, 3-sulfopropyl methacrylate, di[2-(methacryloyloxy)ethyl]phosphoric acid, 2-methacrylic acid, allyl sulfonic acid, styrenesulfonic acid, sodium 2-methyl-2-propylene-1-sulfonate, crotonic acid, maleic acid or fumaric acid, and can also be the corresponding lithium salt, sodium salt, potassium salt or calcium salt of the aforementioned unsaturated organic acid.

[0059] The second aspect of the present invention discloses a method for preparing the aqueous binder according to the first aspect of the present invention, comprising the following steps:

[0060] After the first monomer and water are evenly mixed, the remaining monomers are added, and then the initiator is added. The temperature is raised to 70-90° C. and the reaction is carried out for 2.5-3.5 hours. An inorganic base is added to adjust the pH of the system to 6-8, and the temperature is lowered to obtain a water-based adhesive.

[0061] The amount of each monomer can be determined as needed or based on the known methods of the present invention. In some specific embodiments of the present invention, the molar ratio of the first monomer: the second monomer: the third monomer is (10-65): (10-95): (10-85); or the molar ratio of the first monomer: the second monomer: the third monomer: the functional monomer is (10-65): (10-95): (10-85): (5-75).

[0062] Furthermore, the inorganic base described herein is a hydroxide, and specific examples include lithium hydroxide, sodium hydroxide, potassium hydroxide or calcium hydroxide, but are not limited thereto.

[0063] Furthermore, the initiator described herein can be selected from the more conventional types in the art according to the specific monomer types and the type of polymerization reaction. Specific examples include at least one of azobisisobutyronitrile, potassium persulfate, and ammonium persulfate. The specific amount can be determined according to the conventional amount in the art and the amount of polymerized monomers. In some specific embodiments of the present invention, the mass percentage of the initiator to the total weight of all monomers is 0.1%-5%.

[0064] The third aspect of the present invention discloses a negative electrode slurry containing the aqueous binder as described in the first aspect of the present invention or the aqueous binder prepared by the preparation method described in the second aspect.

[0065] It is understood that the negative electrode slurry can be prepared by methods known in the art, and in addition to containing the above-mentioned aqueous binder, it also contains necessary components or other functional components required for preparing negative electrode slurry in the art, such as negative electrode active materials, conductive agents, etc. as needed.

[0066] The negative electrode active material and conductive agent are conventionally selected in the art. Preferably, in some specific embodiments of the present invention, the negative electrode active material is at least one of a carbon-based material, a silicon-based material, or a composite material thereof. The conductive agent can be at least one of single-walled carbon nanotubes, graphene, conductive graphite, conductive carbon black, Ketjen black, and carbon fiber.

[0067] The fourth aspect of the present invention discloses a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains the aqueous binder as described in the first aspect of the present invention or the aqueous binder prepared by the preparation method described in the second aspect.

[0068] Specifically, first, a negative electrode slurry containing the above-mentioned aqueous binder is prepared as needed, and then the negative electrode slurry is coated on at least one surface of the negative electrode current collector, and the negative electrode sheet is obtained after drying, roll pressing and other processes, which will not be elaborated here.

[0069] In some specific embodiments of the present invention, the mass proportion of the aqueous binder in the negative electrode active material layer is 0.01% to 10%.

[0070] The fifth aspect of the present invention discloses a lithium-ion battery comprising the negative electrode sheet described in the fourth aspect of the present invention. Other materials of the lithium-ion battery, such as the positive electrode sheet, separator, and electrolyte, can be conventionally used in the art and will not be further elaborated here.

[0071] It is understandable that the negative electrode slurry, negative electrode plate and lithium ion battery described in the present invention have the same advantages or beneficial effects as the aqueous binder, which will not be elaborated in detail here.

[0072] Below by concrete implementation, technical scheme of the present invention is specifically elaborated, unless otherwise defined, all technology and scientific terms used herein are identical with the meaning generally understood by those skilled in the art belonging to the technical field of the present invention.Term used herein in description of the present invention is just for the purpose of describing specific embodiment, is not intended to limit the present invention.In addition, if not otherwise specified, the method for not specifically recording condition or step is conventional method, and the reagent and material adopted all can be obtained from commercial sources.

[0073] In the following examples, the first monomer was prepared by the following method:

[0074] To the reaction flask, dimethyl 2,5-dihydroxyterephthalate (226 g), dichloromethane (2000 ml), water (2000 ml), tert-butylammonium bromide (15 g), and sodium hydroxide (80 g) were added respectively. After stirring, allyl bromide (240 g) was added dropwise at room temperature. After stirring for 5 h, sodium hydroxide (120 g) was added. The reaction was continued at room temperature for 10 h. Hydrochloric acid was added to adjust the pH of the system to 1. The mixture was filtered and the filter cake was dried to obtain the first monomer with a molar yield of 92%.

[0075] Figure 1 The NMR results of the first monomer are shown in: 1 H NMR (400MHz, CDCl3) δ7.55 (s, 2H), 7.26 (m, 2H), 6.04 (m, 2H), 5.50 (t, J = 14.7Hz, 1H), 5.37 (d, J = 10.6Hz, 2H), 4.67 (m, 4H).

[0076] Example 1

[0077] This embodiment discloses a method for preparing a water-based binder, and the specific steps are as follows:

[0078] 10 L of deionized water was added to the reaction flask, which was connected to a condensing reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), 2,3-dihydroxypropyl acrylate (1 mol, 146 g) and the functional monomer tert-butyl acrylamide sulfonic acid (1 mol, 105 g) were then added in sequence. Then, the initiator azobisisobutyronitrile (0.05 mol, 8 g) was added, the temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0079] Example 2

[0080] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0081] 10 L of deionized water was added to the reaction flask, which was connected to a condensing reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), propylene alcohol (1 mol, 58 g) and the functional monomer tert-butyl acrylamide sulfonic acid (1 mol, 207 g) were then added in sequence, and then the initiator azobisisobutyronitrile (0.05 mol, 8 g) was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and finally the temperature was lowered to room temperature to prepare the water-based adhesive.

[0082] Example 3

[0083] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0084] 10 L of deionized water was added to the reaction flask, which was connected to a condenser reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), and 3-hydroxy-1-adamantyl (meth) acrylate (1 mol, 236 g) were then added in sequence. Diacetone acrylamide (1 mol, 170 g) was added, and then an initiator, azobisisobutyronitrile (0.05 mol, 8 g), was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0085] Example 4

[0086] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0087] 10 L of deionized water was added to the reaction flask, which was connected to a condensing reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), hydroxyethyl methacrylate (1 mol, 130 g), diacetone acrylamide (1 mol, 170 g), and sodium allyl sulfonate (1 mol, 140 g) were then added. Then, an initiator, azobisisobutyronitrile (0.05 mol, 8 g), was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0088] Example 5

[0089] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0090] 10 L of deionized water was added to the reaction flask, which was connected to a condenser reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), acrylamide (1 mol, 72 g), and polyethylene glycol methacrylate (1 mol, 400 g) were then added in sequence. Then, an initiator, azobisisobutyronitrile (0.05 mol, 8 g), was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0091] Example 6

[0092] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0093] 10 L of deionized water was added to the reaction flask, which was connected to a condensing reflux device. The first monomer 1 (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), acrylamide (1 mol, 72 g), acrylic acid (0.5 mol, 36 g), and acrylonitrile (1 mol, 53 g) were then added in sequence. Then, an initiator, azobisisobutyronitrile (0.05 mol, 8 g), was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0094] Example 7

[0095] This embodiment discloses another method for preparing a water-based binder, and the specific steps are as follows:

[0096] 10 L of deionized water was added to the reaction flask, which was connected to a condenser reflux device. The first monomer (1 mol, 280 g), 1,3-butadiene (1 mol, 54 g), N-hydroxyethyl acrylamide (1 mol, 101 g), and sodium methallyl sulfonate (1 mol, 160 g) were then added in sequence. Then, an initiator, azobisisobutyronitrile (0.05 mol, 8 g), was added. The temperature was raised to 80 ° C. and the reaction was carried out for 3 hours. Lithium hydroxide was added to adjust the pH of the system to 7, and the temperature was finally lowered to room temperature to prepare the aqueous binder.

[0097] Comparative Example 1

[0098] This comparative example discloses a method for preparing a water-based binder, which is similar to that of Example 1, except that the first monomer is replaced with an equal molar amount of styrene. Other process conditions are the same as those of Example 1.

[0099] Comparative Example 2

[0100] This comparative example discloses a lithium-ion battery negative electrode binder, which is composed of a mixture of CMC and commercially available SBR in a mass ratio of 1:1.

[0101] Comparative Example 3

[0102] This comparative example discloses a lithium ion battery negative electrode binder, which is commercially available SBR.

[0103] Performance Testing

[0104] 1. The binders in Examples 1-7 and Comparative Examples 1-2 were assembled into corresponding lithium-ion batteries according to the following methods:

[0105] Negative electrode sheet: The binder, CMC, active material nano-silicon, graphite, and Ketjen black are weighed and mixed in a mass ratio of 1:1:5:90:3, deionized water is added, and the mixture is stirred at room temperature to prepare a negative electrode slurry; the above slurry is evenly coated on a current collector copper foil with a thickness of 8 μm with a scraper, and the mixture is dried and rolled in a vacuum drying oven at 60°C to prepare a negative electrode sheet.

[0106] The positive electrode is a lithium cobalt oxide positive electrode; the electrolyte is 1M LiPF6 (the electrolyte solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1); the diaphragm is a ceramic-coated polyolefin diaphragm (9+2+2 microns).

[0107] The above materials were assembled in a glove box to obtain button batteries, and the button batteries and negative electrode sheets were tested as follows:

[0108] (1) The charge and discharge cycle performance of the button cell was tested in accordance with GB / T18287-2000. The specific test method and conditions are as follows:

[0109] The constant current method was used to test the first coulombic efficiency and cycle capacity retention of the charge and discharge cycle, with a potential window of 0.01-1.5V.

[0110]

[0111] The test results are shown in Table 1.

[0112] (2) Electrode rebound rate test, the specific method is as follows:

[0113] The initial thickness of the negative electrode is recorded as h0. After 100 cycles of charge and discharge cycle test at high temperature of 45°C (the charge and discharge cycle process is the same as (1)), the thickness h of the negative electrode of the electrode is measured, and the expansion rate of the electrode is calculated by the following formula:

[0114]

[0115] The test results are shown in Table 1.

[0116] (3) The peel strength was tested using the national standard GB / T2790-1995 method, with the unit being kN / m. The test results are shown in Table 1.

[0117] Table 1. Test results of button cell and negative electrode performance

[0118]

[0119] From Table 1 and Figure 2It can be seen from the test results in that the binder prepared in the present invention has high bonding force and has a good inhibitory effect on the expansion of the negative electrode material. The button battery assembled with the negative electrode sheet made of the binder in the present invention has excellent charge and discharge cycle performance and stability.

[0120] 2. Films were prepared from the samples of Examples 1-7 and Comparative Example 1 before pH adjustment, and a film was prepared from Comparative Example 3. Toughness and lyophilicity were compared. The films were prepared by coating the samples on a copper foil surface and drying at 50°C. Lyophilicity was expressed as liquid absorption.

[0121] (1) Liquid absorption rate test method: The membranes prepared from the samples of Examples 1-7 and Comparative Example 1 before neutralization were immersed in an electrolyte (1M LiPF6, the electrolyte solvent is a mixture of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1) at room temperature for 1 hour. The liquid absorption rate was calculated according to the following formula:

[0122]

[0123] Where m1 is the mass before immersion, and m2 is the mass after being kept in the electrolyte at room temperature for 1 hour.

[0124] (2) Elongation at break: Films prepared from the samples of Examples 1-7 and Comparative Example 1 before pH adjustment, and a film prepared from Comparative Example 3 were tested using a tensile tester (referring to ASTM D882).

[0125] The test results are shown in Table 2.

[0126] Table 2 Test results of adhesive toughness and lyophilicity

[0127]

[0128]

[0129] It can be seen from the test results in Table 2 that the aqueous binder prepared in the present invention has a high liquid absorption rate, indicating good affinity with the electrolyte, high ion transmission efficiency, and lower conductivity; the aqueous binder of the present invention has higher toughness and strong elasticity, and can effectively adapt to the expansion of the negative electrode sheet.

[0130] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0131] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A water-based adhesive, characterized in that: It is obtained by copolymerizing a first monomer, a second monomer and a third monomer; Wherein, the first monomer is a compound having a structural formula as shown in Formula I: ； The second monomer is 1,3-butadiene; The third monomer is a compound having a structural formula as shown in Formula II: ， Wherein, R1 is H or methyl, R2 is carboxyl or amino, and X is a segment between the connecting group R2 and the vinyl group.

2. The aqueous adhesive according to claim 1, wherein The polyol is obtained by copolymerizing a first monomer, a second monomer, a third monomer and a functional monomer.

3. The aqueous adhesive according to claim 1 or 2, wherein The preparation method of the first monomer comprises the following steps: Take dimethyl 2,5-dihydroxyterephthalate, dichloromethane, water, tert-butylammonium bromide and sodium hydroxide, mix and stir, then add allyl bromide dropwise at room temperature, continue stirring, then add sodium hydroxide, continue to react at room temperature, adjust the system pH to 1, filter and dry, to obtain the first monomer.

4. The aqueous adhesive according to claim 1 or 2, wherein The third monomer is at least one of N-2,2-propenyl-2-acrylamide, N-trimethylol acrylamide, 2-vinylpropane-1,3-diol, allyl alcohol, 1,4-cyclohexanedimethanol monoacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, polyethylene glycol methacrylate, 3-hydroxy-1-adamantyl methacrylate, 2,3-dihydroxypropyl acrylate, glycerol 1,3-diglycerol alcohol diacrylate, N-hydroxymethyl acrylamide, polypropylene glycol-methacrylate, hydroxyethyl acrylamide, and polyethylene glycol monoallyl ether.

5. The aqueous adhesive according to claim 2, wherein The functional monomer is at least one of an unsaturated organic acid or a derivative thereof, an alkenyl alcohol or a derivative thereof, an alkenyl nitrile or a derivative thereof, an alkenyl amine, an alkenyl ether or a derivative thereof.

6. The aqueous adhesive according to claim 5, wherein The functional monomer is diacetone acrylamide, N,N-dimethylacrylamide, acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, carbodiimide, maleamide, tert-butylacrylamide, tert-butylacrylamidesulfonic acid, acrylonitrile, di[2-(methacryloyloxy)ethyl]phosphate, 3-trimethoxysilane propyl acrylate, 2-cyanoacrylate ethylene glycol monomethyl ether acrylate, 1,4-cyclohexanedimethanol monoacrylate, triallyl phosphate, 3-sulfonic acid propyl methacrylate, di[2-(methacryloyloxy)ethyl]phosphoric acid, 2-methacrylic acid, allyl sulfonic acid, styrenesulfonic acid, sodium 2-methyl-2-propylene-1-sulfonate, crotonic acid, maleic acid, fumaric acid, or the corresponding lithium salt, sodium salt, potassium salt or calcium salt of an unsaturated organic acid.

7. A method for preparing the aqueous binder according to any one of claims 1 to 6, characterized in that: The following steps are involved: After the first monomer and water are evenly mixed, the remaining monomers are added, and then the initiator is added. The temperature is raised to 70-90°C and the reaction is carried out for 2.5-3.5 hours. An inorganic base is added to adjust the pH of the system to 6-8, and the temperature is lowered to obtain a water-based adhesive.

8. The method according to claim 7, wherein The molar ratio of the first monomer: the second monomer: the third monomer is (10-65): (10-95): (10-85); or the molar ratio of the first monomer: the second monomer: the third monomer: the functional monomer is (10-65): (10-95): (10-85): (5-75).

9. The method according to claim 7, wherein The inorganic base is lithium hydroxide, sodium hydroxide, potassium hydroxide or calcium hydroxide.

10. The method according to claim 7, wherein: The initiator is at least one of azobisisobutyronitrile, potassium persulfate, and ammonium persulfate.

11. The method according to claim 7, wherein The mass percentage of the initiator to the total polymerization monomers is 0.1%-5%.

12. A negative electrode slurry, characterized in that: Contains the aqueous binder according to any one of claims 1 to 6 or an aqueous binder prepared by the method according to any one of claims 7 to 11.

13. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, characterized in that: The negative electrode active material layer contains the aqueous binder according to any one of claims 1 to 6 or the aqueous binder prepared by the method according to any one of claims 7 to 11.

14. The negative electrode sheet according to claim 13, wherein: The mass proportion of the aqueous binder in the negative electrode active material layer is 0.01% to 10%.

15. A lithium ion battery, characterized in that: Contains the negative electrode sheet as claimed in claim 13 or 14.

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