Binder, preparation method, pole piece and battery thereof

Abstract

The invention belongs to the technical field of batteries, and particularly discloses a binder, a preparation method, a pole piece and a battery thereof. The disclosed binder comprises: an ABA-type triblock polymer in which a block A comprises a polyacrylate-based block comprising an aromatic group, a block B comprises a main chain segment and at least one branch grafted on the main chain segment, and the main chain segment comprises a butadiene chain segment; the branched chain includes at least one of a polyacrylic acid segment, a polyacrylate segment, or a polyacrylonitrile segment. The binder disclosed by the invention can be used for well binding an active material and a metal foil, and has excellent flexibility and good wettability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a binder, a preparation method, an electrode sheet, and a battery thereof. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, and low self-discharge rate, making them widely used in portable electronic devices, electric vehicles, and energy storage systems. In recent years, researchers have conducted extensive studies on cathode materials, anode materials, and electrolytes to improve the fast-charging performance of lithium-ion batteries. For example, high-nickel ternary materials have been developed to replace lithium iron phosphate batteries.

[0003] However, in addition to active materials, the electrode sheets of lithium-ion batteries also include binders with high adhesion and flexibility. For example, commonly used linear acrylic binders have good adhesion properties, but they are less flexible and brittle, making it easy for the battery cell to detach during winding. While styrene-butadiene emulsion binders have good flexibility, they only form a dotted bond with the current collector metal foil, resulting in poor adhesion.

[0004] In view of the problems existing in the above-mentioned technologies, how to obtain an adhesive that has both excellent flexibility and excellent adhesion has become an important research topic. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides an adhesive, a preparation method, an electrode sheet, and a battery thereof, which can effectively bond active materials and metal foils and possesses excellent flexibility; moreover, it also exhibits good wettability.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0007] According to one aspect of the present invention, an adhesive is provided comprising an ABA-type triblock polymer, wherein block A comprises a polyacrylate block containing an aromatic group, and block B comprises a main chain segment and at least one side chain grafted onto the main chain segment, wherein the main chain segment comprises a butadiene segment.

[0008] The branched chain includes at least one of polyacrylic acid segments, polyacrylate segments, or polyacrylonitrile segments.

[0009] In some of these embodiments, the weight-average molecular weight of the ABA-type triblock polymer is 90,000 to 800,000.

[0010] In some of these embodiments, the structure of the B-block is as follows:

[0011]

[0012] Where b = 600 to 6000; R1, R2, R3 or R4 are each independently selected from any one of the same or different H, polyacrylic acid segment, polyacrylate segment or polyacrylonitrile segment.

[0013] In some embodiments, the polyacrylic acid segment has the following structural formula:

[0014] Where x = 1 to 10.

[0015] In some embodiments, the polyacrylate segment has the following structural formula:

[0016] Where z = 1 to 10; R7 is (CH2). n CH3, n = 1 to 5.

[0017] In some embodiments, the polyacrylonitrile segment has the following structural formula:

[0018] Where y = 1 to 10.

[0019] In some embodiments, the polyacrylate block of the aromatic group has the following structural formula:

[0020]

[0021] Where 'a' ranges from 100 to 600; R5 is selected from H, CH3, and (CH2). p CH3, (CH2) p -NH2 or (CH2) p Any one of the -OH groups; where p = 1–5; R6 is selected from (CH2). m It can be any one of C(CH3)H or C(CH3)2; where m = 1 to 5.

[0022] In some of these embodiments, the molar ratio of the A block to the B block satisfies 1:(3-4).

[0023] Secondly, the present invention provides a method for preparing an adhesive, comprising the following steps:

[0024] A first monomer, an initiator, and an emulsifier are added to a solvent to react and generate butadiene segments; wherein, the first monomer includes 1,3-butadiene;

[0025] A second monomer and an initiator are added to a mixture containing the butadiene segments to react and generate a B-block polymer; wherein the second monomer includes at least one of an acrylic acid compound, an acrylonitrile compound, or an acrylate compound;

[0026] A third monomer and an initiator are added to a mixture containing the B-block polymer to react and generate an adhesive; wherein the third monomer comprises an acrylate compound containing an aromatic group.

[0027] In some embodiments, the initiator includes at least one of sodium persulfate, potassium persulfate, hydrogen peroxide, or ammonium persulfate.

[0028] In some embodiments, the emulsifier includes at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or sodium laurylate.

[0029] In some of these embodiments, the solvent includes at least one of water or an alcohol.

[0030] In some embodiments, the mass ratio of the first monomer, initiator, emulsifier and solvent is (65-105):(0.1-1):(0.1-5):(120-170).

[0031] In some of these embodiments, the mass ratio of the second monomer to the initiator is (20-35):(0.1-1).

[0032] In some of these embodiments, the mass ratio of the third monomer to the initiator is (28–42):(0.1–1).

[0033] In some of these embodiments, the reaction temperature is 50°C to 60°C.

[0034] In some embodiments, the adhesive has a solid content of 6 wt% to 20 wt%.

[0035] Thirdly, the present invention provides an electrode sheet comprising: the binder described in any embodiment of the first aspect of the present invention, and / or the binder prepared by the preparation method described in any embodiment of the second aspect of the present invention.

[0036] Fourthly, the present invention provides a battery comprising: a binder as described in any embodiment of the first aspect of the present invention, and / or a binder prepared by the preparation method described in any embodiment of the second aspect of the present invention, and / or an electrode sheet as described in an embodiment of the third aspect of the present invention.

[0037] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0038] 1. In this invention, the adhesive includes an ABA-type triblock polymer. The B block has a linear structure, which can effectively improve the flexibility of the adhesive. The A block contains aromatic groups, which can generate strong adhesion with active materials and metal foils, so that the adhesive has both excellent adhesion performance and flexibility.

[0039] 2. In a preferred embodiment of some embodiments of the present invention, grafting at least one of polyacrylic acid segments, polyacrylate segments, or polyacrylonitrile segments onto the B block can further improve the adhesive properties of the binder, while also improving the wettability of the binder in the electrolyte, thereby improving the battery capacity and cycle performance.

[0040] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] In lithium-ion batteries, the positive and negative electrodes are typically made by uniformly mixing active materials, binders, and conductive agents to form a slurry, which is then coated onto metal foil. As the requirements for fast-charging performance in batteries increase, the demands on binders (such as those used in the negative electrode) to enhance fast-charging capabilities also increase. Furthermore, these binders need to possess high adhesion and flexibility. Existing binders, such as styrene-butadiene emulsion binders, have good flexibility, allowing the electrode to be bent freely without the active material falling off, thus not affecting the battery's charge / discharge performance. However, using styrene-butadiene emulsion binders results in point-like adhesion between the slurry and the metal foil, meaning the adhesion between the slurry and the metal foil is poor, and the active material easily falls off the metal foil. While linear acrylic binders have good adhesion performance, bonding to the metal foil in a planar manner with high adhesion strength, their poor flexibility and brittleness also cause electrode material to fall off.

[0048] Based on this, the present invention provides an adhesive that, by designing an ABA-type triblock polymer adhesive, can effectively bond active materials and metal foils, and has excellent flexibility; moreover, it has good wettability, which can effectively alleviate the above-mentioned problems of existing adhesives.

[0049] The specific technical solution of the present invention is as follows:

[0050] [Adhesive]

[0051] In some embodiments of the present invention, an adhesive is provided comprising an ABA-type triblock polymer, wherein block A comprises a polyacrylate block containing an aromatic group, block B comprises a main chain segment and at least one side chain grafted onto the main chain segment, the main chain segment comprising a butadiene segment; and the side chain comprising at least one of a polyacrylic acid segment, a polyacrylate segment, or a polyacrylonitrile segment.

[0052] The A block in the above-mentioned ABA-type triblock polymer includes a polyacrylate block containing an aromatic group, which includes, but is not limited to, phenyl, tolyl, phenoxy, or phenylamino groups. The polyacrylate block containing an aromatic group can be polyacrylic acid with at least one aromatic group grafted onto it. For example, polybenzyl methacrylate obtained by reacting polyacrylic acid with benzyl alcohol, or polyethyl methacrylate obtained by reacting polyacrylic acid with phenylethanol. The polyacrylate block containing an aromatic group can also be a polyacrylic acid compound with at least one aromatic group grafted onto it. For example, polyethyl methacrylate obtained by reacting polyacrylic acid with phenylethanol.

[0053] The B-block in the aforementioned ABA-type triblock polymer comprises a main chain segment containing polybutadiene polymerized from 1,3-butadiene. The B-block also comprises branches grafted onto the main chain segment, which can be one, two, three, or more. These branches include one or more of polyacrylic acid segments, polyacrylate segments, or polyacrylonitrile segments. On the repeating unit of the butadiene segment, any one branch can be grafted, or multiple identical branches can be grafted, or multiple different branches can be grafted. For example, three branches are grafted onto the butadiene segment: a polyacrylic acid segment, a polyacrylate segment, and a polyacrylonitrile segment. The polyacrylic acid segment can include polyacrylic acid with different weight-average molecular weights; the polyacrylate segment can include polyacrylic acid obtained by reacting polyacrylic acid with different alcohols such as methanol, ethanol, or propanol; and the polyacrylonitrile segment can include polyacrylonitrile with different weight-average molecular weights.

[0054] The aforementioned binder includes an ABA-type triblock polymer exhibiting an alternating distribution of ABA segments. The A-block compound contains a benzene ring, which can form a strong chemical adsorption with active substances containing planar structures. For example, the benzene ring structure in the A-block compound forms a π-π interaction with the graphite surface, thereby exhibiting a strong adsorption effect on graphite particles. The B-block compound's main chain is a linear segment, possessing good flexibility, which improves the flexibility of the electrode sheet using this binder during hot pressing. Thus, the resulting binder possesses both good flexibility and excellent adhesion properties. In addition, the main chain of the B-block compound is grafted with at least one side chain; for example, if the side chain is a polyacrylic acid segment, it can improve the adhesion between the adhesive and the metal foil, and at the same time improve the dispersion of the adhesive; if the side chain is a polyacrylate segment, since the electrolyte solvent is usually a carbonate substance, this can improve the wetting performance of the adhesive, as well as the entire electrode and the electrolyte; if the side chain is a polyacrylonitrile segment, it can further improve the adhesion performance between the adhesive and the metal foil.

[0055] Furthermore, compared to PAA (linear acrylic acid) binders, the B-block compounds in ABA-type triblock polymers have more concentrated adhesive segments, enabling them to form more effective adhesion to metal foils and active materials such as graphite particles. They also exhibit better flexibility, significantly improving electrode processing performance. Additionally, the adsorption regions of the B-block compounds in ABA-type triblock polymers for active materials like graphite particles are more concentrated, and the repulsion of acrylic acid anions is also more concentrated. This enhances the dispersion of active materials like graphite, reduces the amount of CMC (hydroxymethyl cellulose), and increases the proportion of active materials in the electrode, thereby improving battery capacity and cycle performance.

[0056] In some embodiments, the weight-average molecular weight of the ABA-type triblock polymer is 90,000 to 800,000.

[0057] Those skilled in the art will understand that the weight-average molecular weight of ABA-type triblock polymers can be any value between 90,000, 100,000, 200,000, 300,000, 500,000, 600,000, 700,000, or 800,000. By limiting the weight-average molecular weight of ABA-type triblock polymers, it can be ensured that the binder has both good bonding performance and excellent dispersion and flexibility. If the weight-average molecular weight of the ABA-type triblock polymer is too low, the bonding performance of the binder may deteriorate, thereby reducing the adhesion between active materials and between the active slurry and the metal foil, causing material loss during bending and winding of the electrode, thus affecting the battery's capacity and cycle performance. If the weight-average molecular weight of the ABA-type triblock polymer is too high, the dispersion performance of the binder may deteriorate, resulting in poor dispersion of the active materials after mixing with the binder, leading to uneven coating of the active slurry on the metal foil surface, which will also affect the overall performance of the electrode and the battery.

[0058] In some embodiments, the structure of the B block is as follows:

[0059] Where b = 600 to 6000; R1, R2, R3 or R4 are each independently selected from any one of the same or different H, polyacrylic acid segment, polyacrylate segment or polyacrylonitrile segment.

[0060] The structural formula of the B-block compound in the ABA-type triblock polymer is shown above, where the value of b can be any one of 600, 1000, 2000, 3000, 4000, 5000, or 6000, or any value between any two. By limiting the degree of polymerization of the B-block compound, the binder can be guaranteed to have good flexibility. Since the main chain of the B-block compound is linear, it mainly plays a role in flexibility in the ABA-type triblock polymer. If the polymerization degree of the B-block compound is too low, the flexibility of the binder will be reduced, and the active coating on the surface of the metal foil will be damaged under mechanical force when the electrode is bent or wound. If the polymerization degree of the B-block compound is too high, it will affect the dispersion and adhesion properties of the binder, and thus affect the overall performance of the battery.

[0061] Those skilled in the art will understand that, in the above-mentioned B-block compound structure, R1, R2, R3, or R4 can be independently selected from any one of H, polyacrylic acid segment, polyacrylate segment, or polyacrylonitrile segment. Of course, R1, R2, R3, or R4 can be the same or different. For example, R1, R2, R3, and R4 can all be H; or, any one of R1, R2, R3, and R4 is a polyacrylate segment, and the other three are H; or, any one of R1, R2, R3, and R4 is H, and the other three are polyacrylic acid segment, polyacrylate segment, and polyacrylonitrile segment, respectively. Regarding the specific selection of R1, R2, R3, or R4 mentioned above, those skilled in the art can make adjustments based on the present invention. For example, if the binder is used as a negative electrode binder, and the negative electrode active material is graphite, and the solvent in the electrolyte is a carbonate substance, then any one of R1, R2, R3, and R4 in the B-block compound of the binder can be H, and the other three can be polyacrylic acid segments, polyacrylate segments, and polyacrylonitrile segments, respectively. In this way, the binder can be guaranteed to have good flexibility while enabling π-π interaction between the binder and graphite, thereby enabling the binder to have good adhesion performance with the metal foil and graphite respectively, and enabling the electrode to have good wetting performance in the electrolyte.

[0062] As an example, in the above B-block structure, R3 is H, and R1, R4, and R2 are polyacrylic acid segments, polyacrylate segments, and polyacrylonitrile segments, respectively; or, R2 is H, and R3, R1, and R4 are polyacrylic acid segments, polyacrylate segments, and polyacrylonitrile segments, respectively. Therefore, the main chain segment of the B-block is a highly flexible segment, which improves the flexibility of the electrode during hot pressing. The polyacrylic acid segments in the branches mainly serve to bond with metal foils such as copper foil and disperse the negative electrode binder; the polyacrylate segments in the branches mainly improve wettability with the electrolyte (the electrolyte solvent is mainly carbonate-based substances, according to the principle of like dissolves like); the polyacrylonitrile segments in the branches further enhance the adhesion to the copper foil. Compared to traditional randomly distributed PAA-type negative electrode binders, its bonding segments are more concentrated, enabling more effective adhesion to copper foil and better adhesion to graphite particles. Furthermore, its main chain flexibility is better, significantly improving the electrode processing performance.

[0063] In some embodiments, the structural formula of the polyacrylic acid segment is:

[0064] Where x = 1 to 10.

[0065] The structural formula of the polyacrylic acid segment is shown above, where the degree of polymerization x of the polypropylene segment can be any one of 1, 2, 3, 4, 5, 8, or 10, or any value between any two. As a branch chain that can be grafted onto the B-block, the polyacrylic acid segment can effectively improve the adhesion between the adhesive and the metal foil, and at the same time, it can also improve the dispersion performance of the adhesive. By further limiting the degree of polymerization of the polyacrylic acid segment, the adhesive can be guaranteed to have good adhesion and dispersion performance. If the degree of polymerization of the polyacrylic acid segment is too high, the B-block will have a linear structure, and the polyacrylic acid segment will be too long, which may affect the flexibility of the adhesive.

[0066] In some embodiments, the structural formula of the polyacrylate segment is:

[0067] Where z = 1 to 10; R7 is (CH2). n CH3, n = 1 to 5.

[0068] The structural formula of the polyacrylate segment is shown above. The degree of polymerization z of the polyacrylate segment can be any one of 1, 2, 3, 4, 5, 8 or 10 or any value between any two. As a branch that can be grafted onto the B block, the polyacrylate segment can effectively improve the wettability of the adhesive in the electrolyte. R7 on the polyacrylate segment can be any one of CH2CH3, (CH2)2CH3, (CH2)3CH3, (CH2)4CH3 or (CH2)5CH3. By limiting the degree of polymerization and R7 of the polyacrylate segment, the adhesive can be guaranteed to have excellent flexibility and adhesion. If z and n exceed the above range, the branch segments of the B block in the adhesive may become too long, causing the linear B block compound and the branched polyacrylate segment to form a complex network, thereby affecting the flexibility of the adhesive.

[0069] In some embodiments, the structural formula of the polyacrylonitrile segment is:

[0070] Where y = 1 to 10.

[0071] The structural formula of the polyacrylonitrile segment is shown above, wherein the degree of polymerization y of the polyacrylonitrile segment can be any one of 1, 2, 3, 4, 5, 8 or 10 or any point value between any two; by limiting the degree of polymerization of the polyacrylonitrile segment, the adhesive can have good bonding performance and flexibility; if y exceeds the above range, the flexibility of the adhesive may be affected.

[0072] In some embodiments, the structural formula of the polyacrylate block containing aromatic groups is as follows:

[0073]

[0074] Where 'a' ranges from 100 to 600; R5 is selected from H, CH3, and (CH2). p CH3, (CH2) p -NH2 or (CH2) p Any one of the -OH groups; where p = 1–5; R6 is selected from (CH2). m It can be any one of C(CH3)H or C(CH3)2; where m = 1 to 5.

[0075] In this application, the benzene ring side groups contained in the A block can form π-π conjugation with the graphite surface to adsorb active materials such as graphite particles.

[0076] The structural formula of the polyacrylate block containing the aromatic group in block A is shown above, wherein the degree of polymerization 'a' can be any one of 100, 150, 200, 300, 400, 500, or 600, or any value between any two; in the above structural formula, R5 can be H, CH3, CH2CH3, (CH2)2CH3, (CH2)3CH3, (CH2)4CH3, (CH2)5CH3, CH2-NH2, (CH2)2-NH2, (CH2)3-NH2, (CH2)4-NH2, (CH2)5-NH2, CH2-OH, (CH2)2-OH, (CH2)3-OH, (C R6 can be any one of (CH2)4-OH or (CH2)5-OH; R6 can be any one of CH2, (CH2)2, (CH2)3, (CH2)4, (CH2)5, C(CH3)H or C(CH3)2; by limiting a, as well as R5 and R6, the adhesive can be guaranteed to have excellent bonding performance, and can firmly bond the metal foil and the active material respectively; if a exceeds the above range, it may affect the dispersion performance of the adhesive; while if a is less than the above range, it may make the bonding effect of the adhesive worse; at the same time, limiting the type of groups of R5 and R6 in the above block compound can further improve the wettability and flexibility of the adhesive in the electrolyte.

[0077] In some embodiments, the molar ratio of segment A to segment B satisfies 1:(3 to 4.5).

[0078] Those skilled in the art will understand that in ABA-type triblock polymers, the molar ratio of A-block to B-block can be any one of 1:3, 1:3.05, 1:3.1, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, or 1:4.5, or any ratio between any two. Since A-block and B-block need to work synergistically to give the binder good adhesion, flexibility, and electrolyte wetting properties, this can be achieved by limiting the molar ratio of A-block and B-block. If the molar ratio of A-block and B-block is not within the above range, it may affect the overall performance of the binder. For example, if the molar ratio of A-block is high, the flexibility of the binder will be worse. Similarly, if the molar ratio of B-block is high, the adhesion performance of the binder may be worse, which may lead to electrode shedding and affect the overall performance of the battery.

[0079] [Preparation method of adhesive]

[0080] In some embodiments of the present invention, a method for preparing an adhesive is provided, comprising the following steps:

[0081] S101. The first monomer, initiator and emulsifier are added to the solvent to react and generate butadiene segments; wherein the first monomer includes 1,3-butadiene.

[0082] A first monomer containing 1,3-butadiene (CAS: 106-99-0) is added to a solvent, which can be one or more of methanol, ethanol, cyclopropanol, and water, to polymerize 1,3-butadiene. During the polymerization process, initiators such as benzoyl oxide (BPO) and emulsifiers such as sodium dodecyl sulfate (SDS) are added to cause 1,3-butadiene to undergo a free radical polymerization reaction to generate polybutadiene, i.e., butadiene segments.

[0083] S102. The second monomer and the initiator are added to a mixture containing butadiene segments to react and generate a B-block polymer; wherein the second monomer includes at least one of an acrylic acid compound, an acrylonitrile compound, or an acrylate compound.

[0084] The second monomer includes at least one of acrylic acid compounds, acrylonitrile, and acrylate compounds, such as one or more of acrylic acid, acrylonitrile compounds, and ethyl acrylate. The second monomer is added to step S101 or to a mixture containing butadiene segments for reaction, such that at least one branch is grafted onto the butadiene block.

[0085] S103. A third monomer and an initiator are added to a mixture containing a B-block polymer to react and generate an adhesive; wherein the third monomer includes an acrylate compound containing an aromatic group.

[0086] The third monomer includes an acrylate compound containing aromatic groups, which is added to step S102 or to a mixture containing a B-block polymer to react and generate an adhesive.

[0087] In some embodiments, the initiator includes at least one of sodium persulfate, potassium persulfate, hydrogen peroxide, or ammonium persulfate. Those skilled in the art will understand that the initiator includes, but is not limited to, one or more of sodium persulfate, potassium persulfate, hydrogen peroxide, or ammonium persulfate.

[0088] In some embodiments, the emulsifier includes at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or sodium laurate. The emulsifier includes, but is not limited to, one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or sodium laurate. By adding an initiator and an emulsifier, the above-mentioned monomers, as well as the monomers and block compounds, undergo free radical polymerization.

[0089] In some embodiments, the solvent includes at least one of water or alcohol.

[0090] The solvent may include water and alcohol in any proportion, or either water or alcohol, wherein the alcohol includes, but is not limited to, methanol, ethanol or propanol.

[0091] In some embodiments, the mass ratio of the first monomer, initiator, emulsifier and solvent is (65-105):(0.1-1):(0.1-5):(120-170).

[0092] The mass ratio of the first monomer, initiator, emulsifier, and solvent can be any one of 65:0.1:0.1:120, 75:0.5:3:140, 90:0.6:4.5:160, or 100:1:5:170, or any ratio between any two of these ratios. By limiting the mass ratio of the above substances, the normal reaction of the polymerization reaction can be guaranteed, resulting in polybutadiene with high purity. If it is outside this range, side reactions may increase, cross-linking reactions may occur, and the performance of the product may be reduced; or the content of long-chain polymers formed may be less, which will lead to poorer flexibility of the binder.

[0093] In some embodiments, the mass ratio of the second monomer to the initiator is (20-35):(0.1-1).

[0094] Similarly, the mass ratio of the second monomer to the initiator can be any one of 21:0.1, 25:0.5, 30:0.8 or 35:1 or any ratio between any two; by limiting the above ratio, the side reactions generated in step S102 can be reduced, thereby improving the overall performance of the product.

[0095] In some embodiments, the mass ratio of the third monomer to the initiator is (28-42):(0.1-1).

[0096] Similarly, the mass ratio of the third monomer to the initiator can be any one of 30:0.1, 35:0.5, 38:0.8 or 40:1 or any ratio between any two; by limiting the above ratio, the side reactions generated in step S103 can be reduced, thereby improving the overall performance of the product.

[0097] In some embodiments, the reaction temperature is 50°C to 60°C.

[0098] Those skilled in the art will understand that the reaction temperature in steps S101 to S103 can be any one of 50°C, 55°C, or 60°C, or any value between any two; by limiting the above reaction temperature, the polymerization reaction can be completed quickly, and the product can have a high degree of polymerization, thus ensuring the comprehensive performance of the product.

[0099] In some embodiments, the solid content of the adhesive is 6 wt% to 20 wt%.

[0100] The solid content of the adhesive can be any one of 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 15wt%, 18wt%, or 20wt%, or any value between any two. By limiting the solid content of the adhesive, excellent bonding effect can be guaranteed. If the solid content is too high, the dispersion performance of the adhesive will be reduced; if the solid content is too low, the bonding effect will be poor.

[0101] For example, the method for preparing the adhesive specifically includes:

[0102] Add 120-170 parts by weight of solvent such as water or alcohol to a stirring container, add 65-105 parts of the first monomer such as butadiene, then add 0.1-1 parts of water-soluble initiator and 0.1-5 parts of emulsifier, heat to 50-60°C and keep warm for a period of time (e.g., 1-2 hours) to form the main chain segment, i.e., the butadiene chain segment.

[0103] Then, 280-390 parts of solvent such as water or alcohol are added, along with 20-35 parts of a second monomer and 0.1-1 parts of an initiator. The second monomer may include acrylic compounds (short-chain acrylic acid (composed of 1-10 monomers, with other branches having similar structures), or acrylonitrile, acrylacetic acid short-chain segments), acrylate compounds (such as methyl acrylate, butyl acrylate, isooctyl acrylate, ethyl acrylate, etc.), and acrylonitrile compounds (such as acrylonitrile). The reaction time is 1-2 hours, so that at least one branch is grafted onto the butadiene block to obtain the B block.

[0104] Add 28-42 parts of A-block monomer (i.e., the third monomer) and 0.1-1 parts of initiator to a mixture containing B-block polymer, and react for 0.5-1 h to obtain an ABA-type triblock polymer, which is a negative electrode binder with a solid content of 6 wt%-20 wt%.

[0105] [Extreme Film]

[0106] In some embodiments of the present invention, an electrode sheet is provided, comprising the binder of any of the above embodiments.

[0107] In some embodiments, the electrode comprises an adhesive prepared by the method for preparing the adhesive in any of the above embodiments.

[0108] Optionally, the electrode can be a positive electrode or a negative electrode. Preferably, the electrode is a negative electrode.

[0109] The binder of this application can be used as a binder in positive electrode sheets, negative electrode sheets, or even in separators. The binder of this application is particularly preferred as a binder for negative electrode sheets because the problems caused by adhesion are more pronounced in negative electrode sheets, especially silicon negative electrodes, in batteries.

[0110] As an example, the binder in this embodiment is used for the preparation of positive / negative electrode sheets. A mixture containing positive / negative active materials and a binder is prepared into a slurry, coated onto a current collector, and dried to obtain the positive / negative electrode sheet. The binder provided in this application is particularly preferred as a binder for the negative electrode sheet of a battery because the problems caused by adhesion of the negative electrode sheet in a secondary battery are more significant.

[0111] In some embodiments, the electrode is a negative electrode, which includes a negative current collector and a layer of negative active material disposed on at least one surface of the negative current collector along the thickness direction.

[0112] The negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its thickness direction. Here, "surface" can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0113] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on the two opposite surfaces of the negative electrode current collector. It can be understood that the negative electrode active material layer can also be stacked on either of the two surfaces of the negative electrode current collector.

[0114] In some embodiments, the negative electrode active material layer in the above-mentioned negative electrode sheet includes a negative electrode active material, a conductive agent and a binder, wherein the binder is the aforementioned binder provided in this embodiment.

[0115] Optionally, the negative electrode active material layer also includes a thickener. Optionally, the thickener may be sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxyethyl cellulose, lithium carboxyethyl cellulose, acrylate-modified sodium carboxymethyl cellulose, or lithium, etc.

[0116] In a preferred embodiment, the binder can be used as a negative electrode binder, the negative electrode active material is selected from graphite, and the current collector is copper foil; specifically, the graphite can be at least one of the graphite negative electrode materials obtained by shaping, graphitizing, granulating, and coating, such as needle coke, pitch tar, and petroleum coke. Thus, a π-π interaction can occur between the binder and the graphite, resulting in excellent adhesion between the obtained negative electrode active slurry and the copper foil, while also ensuring excellent adhesion between the negative electrode active materials.

[0117] This application does not impose any particular limitation on the negative electrode current collector; any known current collector can be used as the negative electrode current collector to retain the negative electrode active material. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is preferably copper foil.

[0118] This application does not impose any particular limitation on the conductive agent in the negative electrode active material layer. For example, the conductive agent includes, but is not limited to, at least one of conductive carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, carbon black (such as Ketjen black, acetylene black, etc.), conductive graphite, or graphene.

[0119] In some embodiments, the above-mentioned negative electrode active material layer comprises, by mass parts:

[0120] The composition comprises 95-99 parts of negative electrode active material, 0.5-2.0 parts of conductive agent, 0-1.5 parts of thickener, and 1-3.5 parts of binder as described in any of the above embodiments. In a preferred embodiment, the negative electrode active material layer comprises, by weight, 95-98.5 parts of negative electrode active material, 0.5-1.5 parts of conductive agent, 0-1.2 parts of thickener, and 1.0-3.0 parts of binder. The thickener is one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, acrylate flexible chain modified sodium carboxymethyl cellulose, or acrylate flexible chain modified lithium carboxymethyl cellulose.

[0121] The method of preparing negative electrode sheets using binders is well known to those skilled in the art. Optionally, one method of preparing negative electrode sheets using the binder of this application is as follows: the binder, conductive agent, negative electrode active material and optional thickener of this application are mixed in deionized water to obtain a slurry; the obtained slurry is coated on a negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode active material layer is formed on the negative electrode current collector, thereby obtaining a negative electrode sheet.

[0122] [Battery]

[0123] In some embodiments of the present invention, a battery is provided, comprising: the binder in any of the above embodiments.

[0124] In some embodiments, the battery includes a binder prepared by the binder preparation method described in any of the above embodiments of the present invention.

[0125] In some embodiments, the battery includes the electrodes described in the above embodiments.

[0126] In some embodiments, the electrode is a negative electrode. Furthermore, the battery also includes a positive electrode.

[0127] Optionally, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector along its thickness direction. The phrase "positive active material layer disposed on at least one surface of the positive current collector" means that the positive active material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. Here, "surface" can refer to the entire area of ​​the positive current collector or only a portion of it; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0128] As an example, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer is disposed on the two opposite surfaces of the positive electrode current collector. It can be understood that the positive electrode active material layer can also be stacked on either of the two surfaces of the positive electrode current collector.

[0129] As an improvement to the positive electrode sheet of this application, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0130] The embodiments of this application do not have any particular restrictions on the types of conductive agents and binders in the positive electrode active material layer, as long as they can achieve the purpose of this application.

[0131] Optionally, the binder in the positive electrode active material layer may include, but is not limited to, one or more of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or sodium carboxymethyl cellulose. The conductive agent in the positive electrode active material layer may include, but is not limited to, at least one of the following: conductive carbon black, carbon nanotubes, carbon fibers, Ketjen black, graphene, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0132] Optionally, the positive electrode active material in the positive electrode active material layer may include any positive electrode material known in the art. Examples of positive electrode active materials may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron manganese phosphate, and lithium iron phosphate.

[0133] Optionally, the content of positive electrode active material in the positive electrode active material layer is 85% to 99.5%.

[0134] Optionally, the positive electrode active material has a mass percentage content of 85% to 99.4%, the binder has a mass percentage content of 0.3% to 7%, and the conductive agent has a mass percentage content of 0.3% to 8%.

[0135] The positive electrode sheet can be prepared using methods known in the art. For example, the positive electrode sheet can be obtained by mixing a positive electrode active material, a conductive agent, and a binder in a mass ratio of 85–99.4:0.3–8:0.3–7 with a solvent such as N-methylpyrrolidone (NMP) and stirring until homogeneous to obtain a positive electrode slurry. This positive electrode slurry is then coated onto aluminum foil, dried, rolled, and subsequently die-cut and welded to obtain the positive electrode sheet.

[0136] In some embodiments, the battery further includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. Optionally, the separator includes, but is not limited to, a polymer separator made of at least one of polyethylene, polypropylene, polyacrylonitrile, polysulfonyl, polyarylethersulfone, polyvinyl alcohol, and polyvinylidene fluoride.

[0137] In some embodiments, the battery also includes an electrolyte, which can be any electrolyte well known to those skilled in the art and is not particularly limited. As an example, the electrolyte includes lithium salts and non-aqueous organic solvents.

[0138] In some embodiments, the battery described above is a lithium-ion secondary battery. The preparation of the lithium-ion secondary battery includes: cutting the negative electrode sheet, die-cutting to remove part of the blank foil, winding / stacking the negative electrode sheet, separator, and positive electrode sheet to obtain a single bare cell, packaging the single bare cell (such as aluminum-plastic film, aluminum-steel shell, etc.), drying, electrolyte injection, encapsulation, formation, and capacity testing to obtain the lithium-ion secondary battery.

[0139] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0140] The present invention will be specifically described below with reference to examples, but the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present invention and are not intended to limit the present invention.

[0141] Example 1

[0142] A method for preparing an adhesive, comprising:

[0143] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0144] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 21 parts, branch 1 is 12 parts of acrylic acid, branch 2 is 5 parts of butyl acrylate, and branch 3 is 4 parts.

[0145] S13. Add 30 parts of the third monomer benzyl methacrylate to the B-block mixed solution, then add 0.2 parts of the initiator and react for 0.5 h. The final product is an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 20.7%, which is the binder.

[0146] Example 2

[0147] A method for preparing an adhesive, comprising:

[0148] S11. Add 125 parts of high-purity water, 70 parts of butadiene (first monomer), 0.2 parts of potassium persulfate (initiator), and 0.25 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1 hour, to generate butadiene blocks.

[0149] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 21 parts, branch 1 is 12 parts of acrylic acid, branch 2 is 5 parts of butyl acrylate, and branch 3 is 4 parts.

[0150] S13. Add 30 parts of the third monomer benzyl methacrylate to the B-block mixed solution, then add 0.2 parts of initiator, react for 0.5 h, and finally form an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 12.9%, which is the binder.

[0151] Example 3

[0152] A method for preparing an adhesive, comprising:

[0153] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0154] S12. Then, add 370 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.25 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 33 parts, branch 1 is 19 parts of acrylic acid, branch 2 is 8 parts of butyl acrylate, and branch 3 is 6 parts.

[0155] S13. Add a third monomer (benzyl methacrylate, ethyl methacrylate, ethyl methacrylate) in a total of 30 parts to the B-block mixed solution, and then add 0.2 parts of initiator. React for 1 hour to finally form an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 16.8%, which is the binder.

[0156] Example 4

[0157] A method for preparing an adhesive, comprising:

[0158] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0159] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 21 parts, branch 1 is 12 parts of acrylic acid, branch 2 is 5 parts of butyl acrylate, and branch 3 is 4 parts.

[0160] S13. Add 40 parts of the third monomer benzyl methacrylate to the B-block mixed solution, then add 0.3 parts of the initiator and react for 1.4 hours. The final product is an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 20.2%, which is the binder.

[0161] Example 5

[0162] A method for preparing an adhesive, comprising:

[0163] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0164] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (octyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 30 parts, branch 1 is 12 parts of acrylic acid, branch 2 is 5 parts of butyl acrylate, and branch 3 is 4 parts.

[0165] S13. Add 30 parts of the third monomer benzyl methacrylate to the B-block mixed solution, then add 0.2 parts of the initiator and react for 1 hour. The final product is an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 21.2%, which is the binder.

[0166] Example 6

[0167] A method for preparing an adhesive, comprising:

[0168] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0169] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 21 parts, branch 1 is 16 parts of acrylic acid, and branch 2 is 5 parts of butyl acrylate.

[0170] S13. Add 30 parts of the third monomer benzyl methacrylate to the B-block mixed solution, then add 0.2 parts of the initiator and react for 1 hour. The final product is an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 20.0%, which is the binder.

[0171] Example 7

[0172] A method for preparing an adhesive, comprising:

[0173] S11. Add 166 parts of high-purity water, 100 parts of butadiene (first monomer), 0.25 parts of potassium persulfate (initiator), and 0.4 parts of sodium dodecylbenzenesulfonate (emulsifier) ​​to a stirring container. Heat to 60°C and keep warm for a period of time, such as 1.3 hours, to generate butadiene blocks.

[0174] S12. Then, add 300 parts of high-purity water, and add branch 1 (acrylic acid), branch 2 (butyl acrylate), branch 3 monomer (acrylonitrile) and 0.15 parts of initiator respectively; react for 0.5 hours to generate B block; wherein, the total number of branches 1 + branch 2 + branch 3 is 21 parts, branch 1 is 12 parts of acrylic acid, branch 2 is 5 parts of butyl acrylate, and branch 3 is 4 parts.

[0175] S13. Add 30 parts of the third monomer ethyl acrylate to the B-block mixed solution, then add 0.2 parts of the initiator and react for 1 hour. The final product is an ABA-type triblock polymer with a solid content of 15% and a swelling rate of 19.6%, which is the binder.

[0176] Comparative Example 1

[0177] It uses existing conventional PAA-type water-based adhesives with a solid content of 6% and a swelling rate of 9.0%.

[0178] Comparative Example 2

[0179] A typical styrene-butadiene rubber latex (SBR) has a solid content of 40% and a swelling rate of 52%.

[0180] Battery assembly and performance testing:

[0181] 1. Battery assembly:

[0182] Application Example 1:

[0183] Negative electrode sheet: The negative electrode active material is graphite; the binder is the binder obtained in the above examples and comparative examples. 97.1 parts of graphite (negative electrode active material), 1 part of conductive agent (conductive carbon black), 0.6 parts of thickener sodium carboxymethyl cellulose (CMC), and 1.5 parts of binder (from Example 1, solid content 15%, swelling rate 20.7%) were mixed with 100 parts of deionized water to achieve a solid content of 50% by mass and to control the viscosity to 2000 mPa·s and the fineness to 30 μm, thus obtaining a negative electrode slurry. The negative electrode slurry was gradually extruded and coated onto a negative electrode current collector, such as copper foil, dried, and rolled to obtain a negative electrode. Then, it was slited and sliced ​​to form negative electrode sheets of a set size.

[0184] Application Example 2:

[0185] The negative electrode binder used was prepared in Example 2 (solid content 15%, swelling rate 12.9%, the rest is the same as in Example 1).

[0186] Application Example 3:

[0187] The negative electrode binder used was prepared in Example 3 (solid content 15%, swelling rate 16.8%), and the rest was the same as in Example 1.

[0188] Application Example 4:

[0189] The negative electrode binder used was prepared in Example 4 (solid content 15%, swelling rate 20.2%), and the rest was the same as in Example 1.

[0190] Application Example 5:

[0191] The negative electrode binder used was prepared in Example 5 (solid content 15%, swelling rate 21.2%), and the rest was the same as in Example 1.

[0192] Application Example 6:

[0193] The negative electrode binder used was prepared in Example 6 (solid content 15%, swelling rate 20.0%), and the rest was the same as in Example 1.

[0194] Application Example 7:

[0195] The negative electrode binder used was prepared in Example 7 (solid content 15%, swelling rate 19.6%), and the rest was the same as in Example 1.

[0196] Application Comparative Example 1:

[0197] The negative electrode binder used was Comparative Example 1, with a solid content of 6% and a swelling rate of 9%. The amount of CMC added in the negative electrode formulation was 1.0%, and the content of the negative electrode active material was 96.5%. The rest was the same as in Example 1.

[0198] Application Comparative Example 2:

[0199] The negative electrode binder used was Comparative Example 2, with a solid content of 40% and a swelling rate of 52%. The amount of CMC added in the negative electrode formulation was 1.2%, and the amount of negative electrode active material was 96.3%. The rest was the same as in Example 1.

[0200] Positive electrode sheet: The positive electrode active material ternary material NCM (97.2%), conductive carbon black (1%), binder polymethyl methacrylate (PMMA, 1.7%), dispersant 0.1%, and N-methylpyrrolidone (NMP) are mixed and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil, dried, rolled, and then die-cut and welded to obtain the positive electrode sheet.

[0201] Lithium-ion secondary battery: The negative electrode is cut and die-cut to remove some blank foil. The negative electrode sheet, separator and positive electrode sheet are wound / stacked to obtain a single bare cell. The single bare cell is packaged (such as aluminum-plastic film, aluminum-steel shell, etc.), dried, electrolyte injected, encapsulated, formed and capacity tested to obtain a lithium-ion secondary battery.

[0202] 2. Performance Testing

[0203] (1) Test method for wettability (liquid absorption time) of negative electrode sheet:

[0204] Take a negative electrode and drop 10 μL of electrolyte onto it using a micropipette. Test the time it takes for the electrolyte to completely disappear from the electrode. The longer the time, the worse the wettability between the negative electrode and the electrolyte.

[0205] (2) Electrode peel strength test:

[0206] Take a sample of the negative electrode sheet cut into 50mm wide pieces, gently peel off one end of the separator, clamp it vertically on the tensile testing instrument, and test the adhesion of the negative electrode sheet material area at 180°.

[0207] (3) Electrode flexibility test: Take the negative electrode sheet and cut it into a strip 50mm wide. Take a winding needle of different diameter and let the electrode strip be wound around the steel needle. The smaller the diameter of the steel needle, the less likely the electrode sheet will crack when wound, and the better the corresponding electrode sheet flexibility.

[0208] (4) Adhesive swelling rate test:

[0209] Add an appropriate amount of adhesive to a round aluminum weighing pan, let it stand at room temperature for 3-4 days to eliminate air bubbles, then vacuum bake at 85℃ for 4 hours to form a film. Take it out and place it in a drying room (dew point -30℃) to cool. Weigh the sample m1 and add it to a glass container, then add electrolyte to soak the film. Seal and place it at 60℃ for 72 hours. Take it out and place it in a drying room (dew point -30℃) to cool to room temperature. Wipe off the surface electrolyte with lint-free paper and weigh the mass m2. Swelling rate % = (m2 / m1-1)*100%.

[0210] The test results for the above liquid absorption time test, electrode peeling force test, flexibility test, and swelling rate test are shown in Table 1 below.

[0211] (5) DC internal resistance test:

[0212] Under normal temperature conditions, each embodiment and comparative example was charged at 1C to 3.65V, and the current was cut off at 0.05C. Then, it was discharged at 1C to 50% SOC. The ambient temperature was adjusted to -20℃, and the discharge DC internal resistance was recorded after 0.36 seconds of discharge for 30 seconds.

[0213] (6) Loop testing:

[0214] After being left to stand at 45°C for 2 days, the aforementioned lithium-ion secondary battery was first discharged at 1C to 2.0V. Then, at 25°C, the battery was clamped using a double-sided clamp with a clamping force of 3000N. The charging process was as follows: constant current charging at 1C to 3.65V, constant voltage charging at 3.65V until the current <0.5C, resting for 5 minutes, then constant current charging at 1C to 3.65V, constant voltage charging at 3.65V until the current <0.1C, resting for 5 minutes, then constant current charging at 1C to 3.65V, constant voltage charging at 3.65V until the current <0.05C. The discharging process was as follows: resting for 5 minutes, then constant current discharging at 1C to 2.0V, and so on until the discharge capacity reached 80% of the initial capacity from the 1C constant current discharge to 2.0V.

[0215] The results of the DC internal resistance and cyclic test are shown in Table 2.

[0216] Table 1. Test results of wettability, peel strength, and flexibility of negative electrode sheet in electrolyte.

[0217]

[0218]

[0219] As shown in Table 1, the negative electrode binder in Application Example 1 exhibits an alternating ABA segment distribution. The A-block compound contains a benzene ring, which can form a strong chemical adsorption with active materials containing planar structures. For example, the benzene ring structure in the A-block compound forms a π-π interaction with the graphite surface. Its ester groups improve electrolyte wettability to a certain extent (most electrolyte solvents are carbonates, according to the principle of "like dissolves like") and flexibility (ester groups have good flexibility, providing some flexibility during rolling to prevent localized stress concentration and material loss). The B-segment has a flexible main chain and short branches consisting of carboxyl and nitrile groups that form a strong bond with the copper foil. The bonding sites are also relatively concentrated, resulting in good adhesion. Therefore, its liquid absorption time, peel force, and flexibility are significantly improved compared to Comparative Example 1.

[0220] Comparing Application Example 1 and Application Example 2, the proportion of segment B in Application Example 2 is relatively smaller. The segments that mainly improve flexibility and adhesion are worse, and the segments that mainly improve electrolyte wettability are fewer. Consequently, the liquid absorption time is longer, the peeling force is worse, and the flexibility is worse.

[0221] Comparing Application Example 1 and Application Example 3, the proportion of branches in the B segment of Application Example 3 is significantly higher. Although the bonding sites are increased, the entanglement between more branches is not conducive to flexibility and will also make the electrolyte wettability worse. Therefore, the corresponding flexibility is worse, the adhesion is reduced, and the liquid absorption time is longer.

[0222] Comparing Application Example 1 and Application Example 4, in Application Example 4, the increased proportion of A-segment can improve the adhesion between the A-segment and the active particles. However, the A-segment is relatively more rigid, which is not conducive to the flexibility of the binder. Therefore, the corresponding peel force and flexibility are reduced. Although the increased ester content of A-segment is beneficial to improving electrolyte wettability, the increased rigidity of the molecular chain is not conducive to increasing electrolyte wettability. Overall, the electrolyte wettability is slightly reduced (corresponding to an increase in liquid absorption time).

[0223] Comparing Application Example 1 and Application Example 5, the increased flexibility of the branch 2 on the B segment in Application Example 5 will improve flexibility and adhesion to a certain extent.

[0224] Comparing Application Example 1 and Application Example 6, Application Example 6 removed the acrylonitrile segment of the branch 3, increased the proportion of the acrylic segment of the branch 1, and improved the wettability of the nitrile group with the electrolyte. Therefore, the liquid absorption time was slightly increased. Relatively speaking, the branches 1 were more entangled with each other, which slightly reduced the flexibility. Its adhesion was also weaker, so the electrode peeling force was slightly worse.

[0225] Comparing Application Example 1 and Application Example 7, Application Example 7 increases the flexibility and electrolyte wettability of the A-segment, thus reducing the liquid absorption time, slightly increasing the electrode peeling force, and slightly increasing the flexibility.

[0226] In Comparative Example 2, SBR exhibits excellent flexibility but poor peel strength. This is because SBR uses dot-like bonding, resulting in a significantly smaller total bonding area.

[0227] Table 2. Comparison Results of DC Internal Resistance and Cyclic Performance

[0228]

[0229] As can be seen from Table 2, compared with Comparative Example 1, the electrolyte swelling rate of the binder in Application Example 1 is greater. In addition, the amount of CMC used is reduced, which is also conducive to reducing internal resistance. Reducing internal resistance is beneficial to improving cycle performance.

[0230] Comparing Application Example 1 and Application Example 2, the proportion of segment B in Application Example 2 is relatively smaller. The segments that mainly improve flexibility and adhesion are worse, and the segments that mainly improve electrolyte wettability are fewer. Consequently, the liquid absorption time is longer, the peeling force is worse, and the flexibility is worse, thus reducing its cycle performance.

[0231] Comparing Application Example 1 and Application Example 3, the proportion of branches in the B segment of Application Example 3 is significantly higher. Although the bonding sites are larger, the entanglement between more branches is not conducive to flexibility and will also make the electrolyte wettability worse. Therefore, its flexibility is worse, the adhesion is reduced, and the liquid absorption time is longer. However, the higher adhesion is beneficial to improving the cycle performance, and overall its cycle performance is better.

[0232] Comparing Application Example 1 and Application Example 4, in Application Example 4, the increased proportion of A-segment can improve the adhesion between the A-segment and the active particles. However, the A-segment is relatively more rigid, which is not conducive to the flexibility of the binder. Therefore, the corresponding peel force and flexibility are reduced. The increased content of ester segment in A-segment can improve the wettability of the electrolyte to a certain extent. However, the increased proportion of A-segment corresponds to the increased rigidity of the molecular chain. Overall, the wettability of the electrolyte is slightly reduced, while the internal resistance is increased, which is not conducive to improving cycle performance. The rigid molecular chain is beneficial to improving cycle performance to a certain extent. Overall, the cycle performance is comparable to that of Example 1.

[0233] Comparing Application Example 1 and Application Example 5, the increased flexibility of the branch 2 on segment B in Application Example 5 improves flexibility and adhesion to some extent. Furthermore, its internal resistance is significantly lower, resulting in better cycle performance.

[0234] Comparing Application Example 1 and Application Example 6, Application Example 6 removed the acrylonitrile segment of the branch 3, increasing the proportion of the acrylic segment of the branch 1. The nitrile group has higher wettability with the electrolyte, resulting in a slight increase in the liquid absorption time and a certain increase in internal resistance, which is not conducive to improving cycle performance. Relatively speaking, the branches 1 are more entangled with each other, which slightly reduces flexibility, while their adhesion is weaker, resulting in slightly worse electrode peeling force. However, their molecular chain rigidity is better, which is beneficial to improving cycle performance. Overall, the cycle performance is quite good.

[0235] Comparing Application Example 1 and Application Example 7, Application Example 7 increases the flexibility and electrolyte wettability of the A-segment, thus reducing the liquid absorption time, slightly increasing the electrode peeling force, and slightly increasing the flexibility. Consequently, the internal resistance is significantly reduced, which is beneficial for improving cycle performance.

[0236] In Comparative Example 2, the SBR exhibits excellent flexibility but poor peel strength. This is because the SBR uses point-like adhesion, resulting in a significantly smaller total adhesion area. Consequently, its cycle performance is considerably worse.

[0237] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0238] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0239] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0240] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0241] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An adhesive, characterized in that, The adhesive comprises an ABA-type triblock polymer, wherein block A comprises a polyacrylate block containing an aromatic group, and block B comprises a main chain segment and at least one side chain grafted onto the main chain segment, wherein the main chain segment comprises a butadiene segment. The branched chain includes at least one of polyacrylic acid segments, polyacrylate segments, or polyacrylonitrile segments.

2. The adhesive according to claim 1, characterized in that, The weight-average molecular weight of the ABA-type triblock polymer is 90,000 to 800,000.

3. The adhesive according to claim 1, characterized in that, The structural formula of the B-block is as follows: Where b = 600 to 6000; R1, R2, R3, or R4 are each independently selected from any one of the same or different H, polyacrylic acid segment, polyacrylate segment, or polyacrylonitrile segment.

4. The adhesive according to claim 3, characterized in that, The structural formula of the polyacrylic acid segment is: Where x = 1 to 10; And / or, the structural formula of the polyacrylate segment is: Where z = 1 to 10; R7 is (CH2). n CH3, n = 1 to 5; And / or, the structural formula of the polyacrylonitrile segment is: Where y = 1 to 10.

5. The adhesive according to claim 1, characterized in that, The structural formula of the polyacrylate block of the aromatic group is as follows: Where the value of a ranges from 100 to 600; R5 is selected from H, CH3, and (CH2). p CH3, (CH2) p -NH2 or (CH2) p Any one of the -OH groups; where p = 1 to 5; R6 is selected from (CH2) m It can be any one of C(CH3)H or C(CH3)2; where m = 1 to 5.

6. The adhesive according to claim 1, characterized in that, The molar ratio of the A block to the B block satisfies 1:(3 to 4.5).

7. A method for preparing an adhesive, characterized in that, Includes the following steps: A first monomer, an initiator, and an emulsifier are added to a solvent to react and generate butadiene segments; wherein, the first monomer includes 1,3-butadiene; A second monomer and an initiator are added to a mixture containing the butadiene segments to react and generate a B-block polymer; wherein the second monomer includes at least one of an acrylic acid compound, an acrylonitrile compound, or an acrylate compound; A third monomer and an initiator are added to a mixture containing the B-block polymer to react and generate an adhesive; wherein the third monomer comprises an acrylate compound containing an aromatic group.

8. The preparation method according to claim 7, characterized in that, The preparation method satisfies at least one of features (1) to (8): (1) The initiator includes at least one of sodium persulfate, potassium persulfate, hydrogen peroxide or ammonium persulfate; (2) The emulsifier includes at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or sodium laurylate; (3) The solvent includes at least one of water or alcohol; (4) The mass ratio of the first monomer, initiator, emulsifier and solvent is (65-105):(0.1-1):(0.1-5):(120-170); (5) The mass ratio of the second monomer to the initiator is (20-35):(0.1-1); (6) The mass ratio of the third monomer to the initiator is (28-42):(0.1-1); (7) The reaction temperature is 50℃~60℃; (8) The solid content of the adhesive is 6wt% to 20wt%.

9. An electrode sheet, characterized in that, include: The adhesive according to any one of claims 1 to 4, and / or the adhesive prepared by the preparation method according to any one of claims 5 to 8.

10. A battery, characterized in that, include: The adhesive according to any one of claims 1 to 4, and / or the adhesive prepared by the preparation method according to any one of claims 5 to 8, and / or the electrode according to claim 9.

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