Binder and preparation method thereof, negative plate and lithium ion battery

Abstract

The invention relates to the field of battery materials, in particular to a binder and a preparation method thereof, a negative plate and a lithium ion battery. According to the preparation method of the adhesive provided by the invention, a monomer 1 (an itaconic acid-based monomer and / or a fumaric acid-based monomer) is adopted as a main flexible monomer and is copolymerized with conjugated diene, a monomer 2 (a carboxylic acid-based monomer shown in a formula (2)) and a cross-linking monomer, and meanwhile, an amino polyoxyethylene ether nonionic emulsifier is introduced, so that the adhesive is prepared. And by means of a pre-emulsification process, monomer ratio regulation and control, pre-lithiation realized by using lithium alkali in the later stage and the like, a low swelling rate is realized, so that the bonding strength of the material and high conductivity of electrode electrons and ions are ensured, and excellent low-temperature performance is also realized.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and in particular to a binder and its preparation method, a negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are currently the most important energy storage devices, and their performance is highly dependent on the structure and integrity of the electrodes. Electrode binders are key auxiliary materials in electrode manufacturing; although used in small quantities, their role is crucial. In the electrode, the binder is the material that adheres the negative electrode active material to the current collector. Its main function is to bond the active material, conductive agent, and current collector, forming a stable conductive network, and maintaining the stability of the electrode's mechanical structure and the battery's electrochemical performance during battery production and use.

[0003] The technical requirements for binders are generally as follows: ① Electrolyte compatibility: Insoluble in electrolyte solution and does not react chemically with electrolyte; ② Electrochemical stability: Within the operating voltage range, the binder will not be oxidized or reduced; during battery charging and discharging, it will not undergo side reactions with active materials, Li, or other substances; ③ Processing performance: Provides good processing performance for slurry, electrodes, and batteries; ④ Bonding performance: Provides sufficient bonding strength to ensure that active materials do not detach from the electrodes and fail during battery production and use (storage, cycling); ⑤ Power performance: The binder should have high lithium-ion conductivity; ⑥ Safety performance: The binder should at least not degrade the safety performance of the battery.

[0004] Currently, the most widely used commercially available water-based cathode binders are styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) based binders. However, the following problems still exist:

[0005] (1) High electrolyte swelling rate and insufficient bonding strength: The existing SBR latex molecular chain has a low degree of cross-linking. Its non-polar hydrocarbon backbone has poor compatibility with polar electrolytes (such as carbonates) and is prone to swelling. The linear structure of PAA is also prone to swelling with electrolyte, resulting in a loose electrode structure and broken electron and ion conduction pathways during cycling. Moreover, both types of materials lack specific cross-linking structures and have limited bonding strength, which cannot meet the stability requirements of electrodes under high-rate charge and discharge.

[0006] (2) Poor mechanical stability and lithium-ion conduction: The latex particles in the existing technology have poor dispersibility and low mechanical stability (e.g., they are prone to demulsification when stirred at high speed); and they cannot assist lithium-ion diffusion through complexation / de-complexation reactions, resulting in low battery ion conduction efficiency;

[0007] (3) Poor particle size and low temperature performance: The existing SBR latex particle size is usually 100-200nm, with few contact points with active materials and weak interfacial bonding; and the molecular structure is easy to harden and crack at low temperature, resulting in the battery capacity decay of more than 30% in environments below -10℃, which cannot meet the requirements of low temperature application scenarios (such as northern winters and outdoor equipment).

[0008] (4) Low lithium-ion conductivity: Existing binders do not specifically introduce lithium salt components and do not have lithium-ion conduction capabilities themselves. They rely entirely on electrolyte penetration, which limits the lithium-ion transport rate inside the electrode. Summary of the Invention

[0009] In view of this, the present invention provides an adhesive and its preparation method, a negative electrode sheet, and a lithium-ion battery. The adhesive provided by the present invention can overcome the problems of high swelling rate in electrolyte, which leads to obstructed electron and ion conduction and insufficient bonding strength in existing battery cathode adhesives, as well as the problems of low lithium-ion diffusion efficiency and significant performance degradation in existing adhesive latex.

[0010] This invention provides a method for preparing an adhesive, comprising the following steps:

[0011] S1. Preparation of pre-emulsion:

[0012] Water, emulsifier, electrolyte, reducing agent, monomer 1, monomer 2 and conjugated diene monomer are mixed and pre-emulsified to obtain a pre-emulsion;

[0013] S2, Aggregation:

[0014] Initiator 1 is added to the system to initiate a first-stage polymerization. When the reaction conversion rate reaches 50% to 90%, a molecular weight regulator, crosslinking monomer, and initiator 2 are added. The temperature is raised to carry out a second-stage polymerization. When the reaction conversion rate reaches more than 95%, a terminator and an antioxidant are added to terminate the polymerization.

[0015] S3, Post-processing:

[0016] Cool down and adjust the pH value to obtain a latex adhesive;

[0017] in,

[0018] The monomer 1 is a compound of formula (1-1) and / or a compound of formula (1-2);

[0019] The monomer 2 is the compound shown in formula (2);

[0020] Equation (1-1),

[0021] Equation (1-2);

[0022] Equation (2);

[0023] In equation (1-1):

[0024] R1 and R2 are independently selected from: H, C1-C8 hydrocarbon groups;

[0025] In equation (1-2):

[0026] R1 and R2 are independently selected from: H, C1-C8 hydrocarbon groups;

[0027] In formula (2):

[0028] R 11 R 22 Independently selected from: H, C1-C15 hydrocarbon groups.

[0029] Preferably, in formula (1-1), the hydrocarbon group is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group; wherein, the aliphatic hydrocarbon group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, or octyl; the alicyclic hydrocarbon group is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl, or cyclooctene; and the aromatic hydrocarbon group is phenyl, benzyl, phenethyl, or tolyl.

[0030] In formula (1-2), the hydrocarbon group is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group; wherein, the aliphatic hydrocarbon group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, or octyl; the alicyclic hydrocarbon group is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl, or cyclooctene; and the aromatic hydrocarbon group is phenyl, benzyl, phenethyl, or tolyl.

[0031] Preferably, the compound of formula (1-1) is at least one selected from itaconic acid, 1-methyl itaconic acid, 4-methyl itaconic acid, dimethyl itaconic acid, 1-ethyl itaconic acid, 4-ethyl itaconic acid, diethyl itaconic acid, 1-propyl itaconic acid, 4-propyl itaconic acid, dipropyl itaconic acid, 1-butyl itaconic acid, 4-butyl itaconic acid, dibutyl itaconic acid, and 1-ethyl-4-methyl itaconic acid.

[0032] The compounds of formula (1-2) are at least one selected from fumaric acid, 1-methyl fumarate, 4-methyl fumaric acid, dimethyl fumarate, 1-ethyl fumarate, 4-ethyl fumarate, diethyl fumarate, 1-propyl fumarate, 4-propyl fumarate, dipropyl fumarate, 1-butyl fumarate, 4-butyl fumarate, dibutyl fumarate, and 1-ethyl-4-methyl fumarate.

[0033] The compound represented by formula (2) is at least one of acrylic acid and methacrylic acid;

[0034] The conjugated diene monomer is at least one of 1,3-butadiene, isoprene and 2,3-dimethyl-1,3-butadiene;

[0035] The crosslinking monomer is at least one of divinylbenzene, divinyl adipate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, N-hydroxymethylacrylamide, diacetone acrylamide, adipate dihydrazide, triallyl isocyanurate, diallyl phthalate, glycidyl methacrylate, dimethylaminoethyl methacrylate, diallyl phthalate, glycidyl tert-carbonate, vinyltrimethoxysilane, and vinyltriisopropoxysilane.

[0036] Preferably, the emulsifier includes emulsifier 1 and emulsifier 2; wherein, emulsifier 1 is a fatty amine polyoxyethylene ether; and emulsifier 2 is an organic acid salt emulsifier;

[0037] The pH adjuster used to adjust the pH value is at least one of lithium hydroxide and lithium carbonate;

[0038] The electrolyte is at least one of lithium nitrate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, sodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0039] The reducing agent is sodium ferric EDTA, or a mixture of ferrous sulfate, sodium formaldehyde sulfoxylate, and EDTA-2Na.

[0040] The initiator 1 is at least one of diisopropylbenzene hydroperoxide, p-menthol hydroperoxide, and p-pyranoyl hydroperoxide.

[0041] The initiator 2 is at least one of potassium persulfate, ammonium persulfate, lithium persulfate, 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile hydrochloride, azobisisopropionitrile imidazoline hydrochloride, and azobiscyanopentanoic acid.

[0042] The molecular weight regulator is at least one of alkyl thiols or polythiols.

[0043] Preferably, the emulsifier 1 is at least one of dodecylamine polyoxyethylene ether and octadecylamine polyoxyethylene ether;

[0044] The emulsifier 2 is at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, alkyl naphthalene sulfonate formaldehyde condensate, sodium dibutylnaphthalene sulfonate, sodium α-olefin sulfonate, succinate sulfonate, sodium decyl succinate sulfonate, ethoxylated alcohol half ester sulfosuccinate, and sodium lauryl ether sulfate.

[0045] The molecular weight regulator is at least one of tert-dodecyl mercaptan and n-dodecyl mercaptan.

[0046] Preferably, in step S1, the pre-emulsification temperature is 3~45℃ and the time is 30~60min;

[0047] In step S2, the temperature of the first-stage polymerization is 3~45℃; the temperature of the second-stage polymerization is 45~85℃.

[0048] In step S3, the cooling is to reduce the temperature to below 40°C; the pH adjustment is to adjust the pH value to 6-8.

[0049] Preferably, the amounts of each monomer are as follows:

[0050] Monomer 1: 20-80 parts by weight;

[0051] Monomer 2: ≤20 parts by weight;

[0052] Conjugated diene monomer: 20~80 parts by mass;

[0053] Crosslinking monomer: ≤20 parts by weight;

[0054] The total amount of the above monomers is 100 parts by mass.

[0055] The present invention also provides an adhesive, which is prepared by the preparation method described in the above technical solution.

[0056] The present invention also provides a negative electrode sheet, wherein the binder used includes the adhesive described in the above technical solution.

[0057] The present invention also provides a lithium-ion battery, wherein the negative electrode is the negative electrode described in the above technical solution.

[0058] The adhesive preparation method provided by this invention uses monomer 1 (itaconic acid-based monomers and / or fumaric acid-based monomers) as the main flexible monomer, copolymerizing it with conjugated diene, monomer 2 (carboxylic acid monomers shown in formula (2)) and crosslinking monomer. Through the synergistic effect of molecular weight regulator and crosslinking monomer, the crosslinking network structure of the polymer is precisely controlled (gel content > 90%), achieving low swelling rate and high bonding strength. At the same time, an amino-based polyoxyethylene ether nonionic emulsifier is introduced, which not only provides excellent steric stabilization and ensures the stability of high solids content and small particle size latex, but also has lone pair electrons in its ether oxygen (-O-) and tertiary amine group (-N<), which can serve as "temporary sites" for lithium ions. Through a continuous complexation-decomplexation process, it promotes the transport of lithium ions in the adhesive phase, thereby actively improving the ionic conductivity. Furthermore, this invention prepares 70-100nm small-particle-size latex through pre-emulsification and monomer ratio control, increasing contact points with active materials. Using monomer 1 as the main monomer, its ester structure enhances affinity with the electrolyte, exhibiting excellent anti-swelling properties. In addition, the use of lithium alkali instead of sodium alkali or ammonia to adjust the pH value in the later stages achieves pre-lithiation of carboxyl groups (-COOLi), avoiding the harmful effects of impurity ions such as Na⁺ on battery performance and further reducing the migration resistance of lithium ions in the binder phase. In summary, this invention, by introducing a special emulsifier with lithium-ion complexing capabilities and a pre-lithiation process, transforms the binder from a traditional "insulating inert phase" to an "ion-conducting active phase," significantly improving the battery's rate performance. Simultaneously, the design of the crosslinking structure and monomer selection ensures good processability and adhesion even at extremely high gel content, achieving synergistic improvements in multiple performance aspects. The overall technical effect is significantly superior to existing technologies.

[0059] The test results show that the adhesive obtained by the present invention has a peel force of more than 5.5N to the substrate and an interfacial peel strength of more than 30N / cm, exhibiting excellent adhesion; its swelling rate is less than 139%, exhibiting excellent anti-swelling properties; at the same time, the battery assembled with the adhesive of the present invention has a 3C / 0.2C capacity retention rate of more than 85%, and a capacity retention rate of more than 88% after 500 cycles, exhibiting excellent rate performance and cycle performance. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0061] Figure 1 This is a particle size distribution diagram of the adhesive obtained in Example 1 of the present invention. Detailed Implementation

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0063] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0064] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0065] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0066] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~45℃ means that the units for the left endpoint "3" and the right endpoint "45" are both in degrees Celsius (℃).

[0067] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0068] In a first aspect, the present invention provides a method for preparing an adhesive, comprising the following steps:

[0069] S1. Preparation of pre-emulsion:

[0070] Water, emulsifier, electrolyte, reducing agent, monomer 1, monomer 2 and conjugated diene monomer are mixed and pre-emulsified to obtain a pre-emulsion;

[0071] S2, Aggregation:

[0072] Initiator 1 is added to the system to initiate a first-stage polymerization. When the reaction conversion rate reaches 50% to 90%, a molecular weight regulator, crosslinking monomer, and initiator 2 are added. The temperature is raised to carry out a second-stage polymerization. When the reaction conversion rate reaches more than 95%, a terminator and an antioxidant are added to terminate the polymerization.

[0073] S3, Post-processing:

[0074] Cool down and adjust the pH value to obtain a latex adhesive;

[0075] in,

[0076] The monomer 1 is a compound of formula (1-1) and / or a compound of formula (1-2);

[0077] The monomer 2 is the compound shown in formula (2);

[0078] Equation (1-1),

[0079] Equation (1-2);

[0080] Equation (2);

[0081] In equation (1-1):

[0082] R1 and R2 are independently selected from: H, C1-C8 hydrocarbon groups;

[0083] In equation (1-2):

[0084] R1 and R2 are independently selected from: H, C1-C8 hydrocarbon groups;

[0085] In formula (2):

[0086] R 11 R 22 Independently selected from: H, C1-C15 hydrocarbon groups.

[0087] Regarding step S1 :

[0088] S1. Preparation of pre-emulsion: Water, emulsifier, electrolyte, reducing agent, monomer 1, monomer 2 and conjugated diene monomer are mixed and pre-emulsified to obtain pre-emulsion.

[0089] [Regarding Monomer 1]:

[0090] In this invention, monomer 1 is a compound of formula (1-1) and / or a compound of formula (1-2):

[0091] Equation (1-1), Equation (1-2).

[0092] In this invention, formula (1-1) is an itaconic acid group compound with the following functional groups:

[0093] R1 and R2 are independently selected from H and C1-C8 hydrocarbon groups; the independent selection means that R1 and R2 can be the same or different. The hydrocarbon group can be a straight-chain group, a branched group, or a cyclic group, including aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups; preferably, it is an aliphatic hydrocarbon group.

[0094] The aliphatic hydrocarbon group is preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, or octyl; more preferably methyl, ethyl, or n-butyl; and most preferably ethyl.

[0095] The alicyclic hydrocarbon group is preferably a C3-C8 alicyclic hydrocarbon group, more preferably a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl or cyclooctene group.

[0096] The aromatic hydrocarbon group is preferably a C6-C8 aromatic hydrocarbon group, and more preferably a phenyl, benzyl, phenethyl or toluene group.

[0097] The compound of formula (1-1) is preferably at least one of itaconic acid, 1-methyl itaconic acid, 4-methyl itaconic acid, dimethyl itaconic acid, 1-ethyl itaconic acid, 4-ethyl itaconic acid, diethyl itaconic acid, 1-propyl itaconic acid, 4-propyl itaconic acid, dipropyl itaconic acid, 1-butyl itaconic acid, 4-butyl itaconic acid, dibutyl itaconic acid, and 1-ethyl-4-methyl itaconic acid, more preferably at least one of dimethyl itaconic acid, diethyl itaconic acid, and dibutyl itaconic acid.

[0098] In this invention, formula (1-2) refers to fumaric acid-based substances with the following functional groups:

[0099] R1 and R2 are independently selected from H and C1-C8 hydrocarbon groups; the independent selection means that R1 and R2 can be the same or different. The hydrocarbon group can be a straight-chain group, a branched group, or a cyclic group, including aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups; preferably, it is an aliphatic hydrocarbon group. More preferably,

[0100] The aliphatic hydrocarbon group is preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, or octyl; more preferably methyl, ethyl, or n-butyl; and most preferably ethyl.

[0101] The alicyclic hydrocarbon group is preferably a C3-C8 alicyclic hydrocarbon group, more preferably a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl or cyclooctene group.

[0102] The aromatic hydrocarbon group is preferably a C6-C8 aromatic hydrocarbon group, and more preferably a phenyl, benzyl, phenethyl or toluene group.

[0103] The compound of formula (1-2) is preferably at least one of fumaric acid, 1-methyl fumarate, 4-methyl fumaric acid, dimethyl fumarate, 1-ethyl fumarate, 4-ethyl fumarate, diethyl fumarate, 1-propyl fumarate, 4-propyl fumarate, dipropyl fumarate, 1-butyl fumarate, 4-butyl fumarate, dibutyl fumarate, and 1-ethyl-4-methyl fumarate, more preferably at least one of dimethyl fumarate, diethyl fumarate, and dibutyl fumarate.

[0104] In this invention, the amount of monomer 1 used is 20 to 80 parts, specifically 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 43 parts, 45 parts, 50 parts, 53 parts, 55 parts, 60 parts, 62 parts, 65 parts, 70 parts, 75 parts, and 80 parts.

[0105] [Regarding Monomer 2]:

[0106] In this invention, monomer 2 is the compound shown in formula (2):

[0107] Equation (2).

[0108] Formula (2) is a carboxylic acid monomer, and the groups are as follows:

[0109] R 11 R 22 Independently selected from: H, C1-C15 hydrocarbon groups.

[0110] The compound represented by formula (2) is preferably at least one of acrylic acid (AA) and methacrylic acid (MAA).

[0111] In this invention, the amount of monomer 2 is ≤20 parts, specifically 1 part, 3 parts, 5 parts, 7 parts, 8 parts, 10 parts, 13 parts, 15 parts, or 20 parts.

[0112] [Regarding conjugated diene monomers]:

[0113] In this invention, the conjugated diene monomer is preferably at least one selected from 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene. The amount of the conjugated diene monomer used in this invention is 20-80 parts, specifically 20 parts, 25 parts, 27 parts, 28 parts, 30 parts, 35 parts, 38 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, and 80 parts.

[0114] [Regarding emulsifiers]:

[0115] In this invention, preferably, the emulsifier includes emulsifier 1 and emulsifier 2.

[0116] The emulsifier 1 is a fatty amine polyoxyethylene ether. Preferably, the alkyl chain in the fatty amine polyoxyethylene ether is a C12-C18 alkyl chain, and the EO number is 1-10. More preferably, the emulsifier 1 is at least one of dodecylamine polyoxyethylene ether and octadecylamine polyoxyethylene ether. The dodecylamine polyoxyethylene ether is preferably dodecylamine polyoxyethylene ether 1205; the octadecylamine polyoxyethylene ether is preferably octadecylamine polyoxyethylene ether 1805. In this invention, based on 100 parts by weight of total monomers, the amount of emulsifier 1 is 0.2-6 parts, specifically 0.2 parts, 0.5 parts, 0.6 parts, 0.8 parts, 1 part, 1.4 parts, 1.5 parts, 1.8 parts, 2 parts, 2.5 parts, 3 parts, 3.1 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, and 6 parts. The total amount of monomers refers to the total amount of all monomers introduced into the system, that is, the total mass of monomer 1, monomer 2, conjugated diene monomer and crosslinking monomer, and the same applies to the following text.

[0117] The emulsifier 2 is an organic acid salt emulsifier. Preferably, the emulsifier 2 is at least one selected from sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium dodecyl sulfate, alkyl naphthalene sulfonate formaldehyde condensate, sodium dibutylnaphthalene sulfonate, sodium α-olefin sulfonate, succinate sulfonate, sodium decyl succinate sulfonate, ethoxylated alcohol half-ester sulfosuccinate, and sodium lauryl ether sulfate. More preferably, the emulsifier 2 is at least one selected from sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and alkyl naphthalene sulfonate formaldehyde condensate. The alkyl naphthalene sulfonate formaldehyde condensate is preferably sodium methylene dinaphthalene sulfonate. In this invention, based on 100 parts by mass of total monomers, the amount of emulsifier 2 is 0.1 to 5 parts, specifically 0.1 parts, 0.5 parts, 1.0 parts, 1.7 parts, 2.1 parts, 2.4 parts, 2.9 parts, 3.1 parts, 3.3 parts, 3.5 parts, 4.0 parts, 4.5 parts, and 5.0 parts.

[0118] [Regarding electrolytes]:

[0119] In this invention, the electrolyte is preferably at least one selected from lithium nitrate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, sodium hydrogen phosphate, and sodium dihydrogen phosphate. In this invention, based on 100 parts by mass of the total monomer content, the amount of the electrolyte is 0.05 to 10 parts, specifically 0.05 parts, 0.1 parts, 0.23 parts, 0.28 parts, 0.29 parts, 0.3 parts, 0.35 parts, 0.42 parts, 0.5 parts, 0.55 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, and 10 parts.

[0120] [Regarding reducing agents]:

[0121] In this invention, the reducing agent is preferably sodium ferric EDTA, or a mixture of ferrous sulfate, sodium formaldehyde sulfoxylate, and EDTA-2Na, more preferably sodium ferric EDTA. In this invention, based on 100 parts by mass of the total monomers, the amount of the reducing agent is 0.01 to 10 parts, specifically 0.01 parts, 0.1 parts, 0.12 parts, 0.16 parts, 0.2 parts, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, and 10 parts.

[0122] [Regarding water]:

[0123] In this invention, the water is preferably deionized water. In this invention, based on 100 parts by mass of the total monomer, the amount of water used is 130 to 160 parts, specifically 130 parts, 135 parts, 140 parts, 145 parts, 150 parts, 155 parts, or 160 parts.

[0124] In this invention, step S1 can be carried out in a reaction vessel. The pre-emulsification temperature is preferably 3~45℃, specifically 3℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, or 45℃. The pre-emulsification time is preferably 30~60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0125] In this invention, the pre-emulsification is preferably carried out in a protective atmosphere. This invention does not have any particular limitations on the type of gas providing the protective atmosphere; any conventional inert gas in the art, such as nitrogen, helium, or argon, is acceptable.

[0126] In this invention, step S1 specifically includes: adding water, emulsifier, electrolyte, reducing agent, monomer 1, and monomer 2 to the reaction vessel, performing gas replacement in the reaction vessel, and then adding a conjugated diene monomer for pre-emulsification to obtain a pre-emulsion. The gas replacement in the reaction vessel refers to replacing the air in the reaction vessel with a protective gas to create a protective atmosphere. The types of gases are as described above and will not be repeated here.

[0127] Regarding step S2 :

[0128] S2. Polymerization: Initiator 1 is added to the system to initiate a first-stage polymerization. When the reaction conversion rate reaches 50% to 90%, a molecular weight regulator, crosslinking monomer, and initiator 2 are added. The temperature is raised to carry out a second-stage polymerization. When the reaction conversion rate reaches more than 95%, a terminator and antioxidant are added to terminate the polymerization.

[0129] In this invention, the numbers 1 and 2 in initiator 1 and initiator 2 have no special meaning and do not imply the type or importance of the initiator. They are simply used to indicate that the initiator appeared in two different places.

[0130] In this invention, the initiator 1 is preferably at least one selected from dicumyl peroxide, p-menthol peroxide, cumyl peroxide, and p-pyran. In this invention, based on 100 parts by mass of the total monomer, the amount of initiator 1 is 0.05 to 2 parts, specifically 0.05 parts, 0.1 parts, 0.5 parts, 0.54 parts, 0.59 parts, 0.85 parts, 0.9 parts, 1 part, 1.15 parts, 1.5 parts, and 2 parts.

[0131] In this invention, the initiator 2 is preferably at least one selected from potassium persulfate, ammonium persulfate, lithium persulfate, 2,2'-azobis(2,4-dimethylvalerate), azobisisobutyronitrile hydrochloride, azobisisopropionitrile imidazoline hydrochloride, and azobiscyanopentanoic acid. In this invention, based on 100 parts by mass of the total monomer, the amount of initiator 2 is 0.05 to 2.5 parts, specifically 0.05 parts, 0.1 parts, 0.5 parts, 1 part, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 2 parts, 2.1 parts, and 2.5 parts.

[0132] In this invention, the molecular weight regulator is preferably at least one of alkyl thiols or polythiols, more preferably at least one of tert-dodecyl mercaptan and n-dodecyl mercaptan. In this invention, based on 100 parts by mass of the total monomer, the amount of the molecular weight regulator is 0.01 to 1.2 parts, specifically 0.01 parts, 0.012 parts, 0.015 parts, 0.02 parts, 0.03 parts, 0.05 parts, 0.1 parts, 0.5 parts, 1.0 parts, or 1.2 parts.

[0133] In this invention, the crosslinking monomer is preferably at least one of divinylbenzene, divinyl adipate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, N-hydroxymethylacrylamide, diacetone acrylamide, adipate dihydrazide, triallyl isocyanurate, diallyl phthalate, glycidyl methacrylate, dimethylaminoethyl methacrylate, diallyl phthalate, glycidyl tert-carbonate, vinyltrimethoxysilane, and vinyltriisopropoxysilane. In this invention, the amount of the crosslinking monomer is ≤20 parts, specifically 1 part, 1.2 parts, 1.8 parts, 2 parts, 3 parts, 5 parts, 10 parts, 15 parts, and 20 parts. In this invention, in steps S1-S2, the total amount of all monomers (i.e., monomer 1, monomer 2, conjugated diene monomer, and crosslinking monomer) is preferably 100 parts.

[0134] In this invention, the antioxidant is preferably at least one selected from N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-phenyl-β-naphthylamine, 2,6-di-tert-butyl-p-cresol, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, tris(2,4-di-tert-butylphenyl) phosphite, dilauryl thiodipropionate, and distearate thiodipropionate. In this invention, based on 100 parts by weight of the total monomer content, the amount of the antioxidant is 0.2 to 10 parts, specifically 0.2 parts, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, and 10 parts.

[0135] In this invention, the terminator is preferably at least one selected from sodium fumarate, isopropyl hydroxylamine, diethyl hydroxylamine, hydroquinone, tert-butylcatechol, sodium nitrite, and sodium bisulfite. In this invention, based on 100 parts by weight of the total monomers, the amount of the terminator is 0.2 to 10 parts, specifically 0.2 parts, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, and 10 parts.

[0136] In this invention, the preferred temperature for the primary polymerization step is 3~45℃, specifically 3℃, 5℃, 8℃, 10℃, 12℃, 15℃, 18℃, 20℃, 25℃, 30℃, 35℃, 40℃, and 45℃. The degree of primary polymerization is such that the reaction conversion rate reaches 50%~90%, specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90%.

[0137] In this invention, after the first-stage polymerization reaches the aforementioned degree of polymerization, a molecular weight regulator, crosslinking monomer, and initiator 2 are added, and the temperature is raised to carry out a second-stage polymerization. In this invention, the temperature of the second-stage polymerization is higher than that of the first-stage polymerization, preferably 45~85℃, specifically 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 78℃, 80℃, and 85℃. The maturation reaction is completed through the second-stage polymerization, and the degree of reaction in the second-stage polymerization is until the reaction conversion rate reaches 95% or more, at which point a terminator and an antioxidant are added to terminate the polymerization.

[0138] Regarding step S3 :

[0139] S3. Post-treatment: Cool down and adjust the pH value to obtain the latex adhesive.

[0140] In this invention, the cooling is preferably reduced to below 40°C, more preferably to 15~40°C, specifically 15°C, 20°C, 25°C, 30°C, 35°C, or 40°C.

[0141] In this invention, after cooling, the material is discharged, and a pH adjuster is added to adjust the pH value. Preferably, the pH adjuster used to adjust the pH value is at least one of lithium hydroxide and lithium carbonate. In this invention, based on 100 parts by mass of the total monomer, the amount of the pH adjuster is 0.05 to 30 parts, specifically 0.05 parts, 1 part, 2 parts, 2.8 parts, 2.9 parts, 3.2 parts, 3.5 parts, 4.1 parts, 4.3 parts, 4.6 parts, 4.8 parts, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, or 30 parts, preferably to achieve a pH value of 6 to 8, specifically 6, 6.5, 7, 7.5, or 8. In this invention, after adding the pH adjuster, the mixture is stirred until completely dissolved. In this invention, after the above treatment, filtration is preferably performed to remove a small amount of gel particles. The filtration preferably uses an 80-300 mesh filter, specifically 80, 100, 150, 200, 250, or 300 mesh, and more preferably a 200 mesh filter. After filtration, the target latex product, i.e., the binder, is obtained. In this invention, the particle size of the obtained latex binder is 70-100 nm.

[0142] Secondly, the present invention also provides a binder prepared by the method described in the above technical solution. In the present invention, the particle size of the binder is 70-100 nm. In the present invention, the gel content of the binder is >90%. In the present invention, the binder is a lithium-ion battery negative electrode binder.

[0143] Thirdly, the present invention also provides a negative electrode sheet, wherein the binder used includes the adhesive described in the above-mentioned technical solutions.

[0144] Fourthly, the present invention also provides a lithium-ion battery, wherein the negative electrode is the negative electrode described in the above technical solution.

[0145] Compared with the prior art, the present invention has the following advantages:

[0146] (1) Achieving extremely low electrolyte swelling rate: By precisely controlling the amount of molecular weight regulator and crosslinking monomer, a crosslinking system with high gel content (>90%) and uniform and dense network structure is constructed, which fundamentally inhibits swelling and ensures the long-term stability of the electrode structure.

[0147] (2) Significantly improves the mechanical and chemical stability of latex: By introducing a special amine-based polyoxyethylene ether nonionic emulsifier, the stability of the latex is greatly improved. Electronegative elements are introduced to assist lithium-ion diffusion, while the molecular structure is optimized to enhance low-temperature flexibility, enabling the battery to maintain a high capacity retention rate even at -20℃.

[0148] (3) Imparting high lithium-ion conductivity to the binder: On the one hand, the amine group and ether oxygen atom in the emulsifier molecule provide lithium-ion transport sites; on the other hand, by introducing lithium salt in the later stage, the carboxyl group is pre-lithiated, reducing the lithium-ion migration barrier.

[0149] (4) Balancing high bonding strength and good flexibility: Monomer 1 is selected as the main monomer. Its long side chain ester group provides flexibility and electrolyte affinity, while the carboxyl group on the main chain provides strong bonding force. At the same time, the cohesive strength is enhanced by cross-linking monomers to achieve the best balance of performance.

[0150] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0151] Example 1

[0152] S1. Preparation of pre-emulsion:

[0153] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 25°C for 40 min to obtain a pre-emulsion.

[0154] S2, Aggregation:

[0155] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 12°C until the reaction conversion rate reached 80%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 70°C to carry out a second-stage polymerization until the reaction conversion rate reached 98.50%. Terminator and antioxidant were added to terminate the polymerization.

[0156] S3, Post-processing:

[0157] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 7.1, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0158] The materials and their quantities used in the above preparation process are as follows:

[0159] Monomer 1: Dimethyl itaconic acid, 53 parts;

[0160] Monomer 2: Acrylic acid, 2 parts;

[0161] Conjugated diene monomer: 1,3-butadiene, 38 parts;

[0162] Crosslinking monomer: glycidyl methacrylate, 2 parts;

[0163] Emulsifier 1: Dodecylamine polyoxyethylene ether 1205, 0.8 parts;

[0164] Emulsifier 2: Sodium dodecyl sulfate, 2.1 parts; Sodium dodecylbenzene sulfonate, 1.2 parts;

[0165] Molecular weight regulator: tert-dodecyl mercaptan, 0.015 parts;

[0166] Initiator 1: Dicumyl peroxide, 0.54 parts;

[0167] Initiator 2: Ammonium persulfate, 1.6 parts;

[0168] Reducing agent: Sodium iron EDTA, 0.12 parts;

[0169] Electrolyte: Potassium chloride, 0.28 parts;

[0170] Deionized water: 130 parts;

[0171] pH adjuster: lithium hydroxide, 2.8 parts;

[0172] Terminating agent: Diethylhydroxylamine, 0.5 parts;

[0173] Anti-aging agent: N-isopropyl-N'-phenyl-p-phenylenediamine, 0.5 parts.

[0174] Example 2

[0175] S1. Preparation of pre-emulsion:

[0176] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 20°C for 45 min to obtain a pre-emulsion.

[0177] S2, Aggregation:

[0178] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 8°C until the reaction conversion rate reached 85%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 65°C to carry out a second-stage polymerization until the reaction conversion rate reached 98.80%. Terminator and antioxidant were added to terminate the polymerization.

[0179] S3, Post-processing:

[0180] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 6.8, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0181] The materials and their quantities used in the above preparation process are as follows:

[0182] Monomer 1: Diethyl itaconic acid, 62 parts;

[0183] Monomer 2: Methacrylic acid, 8 parts;

[0184] Conjugated diene monomer: 1,3-butadiene, 28 parts;

[0185] Crosslinking monomer: divinylbenzene, 2 parts;

[0186] Emulsifier 1: Dodecylamine polyoxyethylene ether 1205, 1.5 parts;

[0187] Emulsifier 2: Sodium dodecyl sulfate, 2.1 parts; Sodium methylene dinaphthalene sulfonate, 0.3 parts;

[0188] Molecular weight regulator: tert-dodecyl mercaptan, 0.02 parts;

[0189] Initiator 1: Dicumyl peroxide, 0.85 parts;

[0190] Initiator 2: Potassium persulfate, 1.5 parts;

[0191] Reducing agent: Sodium iron EDTA, 0.1 parts;

[0192] Electrolyte: Lithium chloride, 0.23 parts;

[0193] Deionized water: 130 parts;

[0194] pH adjuster: lithium hydroxide, 3.2 parts.

[0195] Terminator: Diethylhydroxylamine, 1 part;

[0196] Anti-aging agent: dilauryl thiodipropionate, 1 part.

[0197] Example 3

[0198] S1. Preparation of pre-emulsion:

[0199] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 25°C for 45 min to obtain a pre-emulsion.

[0200] S2, Aggregation:

[0201] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 15°C until the reaction conversion rate reached 70%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 50°C to carry out a second-stage polymerization until the reaction conversion rate reached 99.20%. Terminator and antioxidant were added to terminate the polymerization.

[0202] S3, Post-processing:

[0203] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 7.1, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0204] The materials and their quantities used in the above preparation process are as follows:

[0205] Monomer 1: Dibutyl itaconic acid, 55 parts;

[0206] Monomer 2: Methacrylic acid, 15 parts;

[0207] Conjugated diene monomer: 1,3-butadiene, 27 parts;

[0208] Crosslinking monomer: diacetone acrylamide, 3 parts;

[0209] Emulsifier 1: Octadecylamine polyoxyethylene ether 1805, 1.8 parts;

[0210] Emulsifier 2: Sodium dodecylbenzenesulfonate, 0.5 parts; Sodium dodecyl sulfate, 2.4 parts;

[0211] Molecular weight regulator: n-dodecyl mercaptan, 0.01 parts;

[0212] Initiator 1: Hydrogen peroxide p-mentholane, 0.59 parts;

[0213] Initiator 2: Azodicarbonyl diisopropionitrile imidazoline hydrochloride, 2.1 parts;

[0214] Reducing agent: Sodium iron EDTA, 0.16 parts;

[0215] Electrolyte: Lithium chloride, 0.42 parts;

[0216] Deionized water: 135 parts;

[0217] pH adjuster: lithium hydroxide, 4.6 parts.

[0218] Terminating agent: Isopropyl hydroxylamine, 0.5 parts;

[0219] Antioxidant: Tris(2,4-di-tert-butylphenyl) phosphite, 1 part.

[0220] Example 4

[0221] S1. Preparation of pre-emulsion:

[0222] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 30°C for 60 min to obtain a pre-emulsion.

[0223] S2, Aggregation:

[0224] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 25°C until the reaction conversion rate reached 75%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 70°C to carry out a second-stage polymerization until the reaction conversion rate reached 99.60%. Terminator and antioxidant were added to terminate the polymerization.

[0225] S3, Post-processing:

[0226] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 7.2, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0227] The materials and their quantities used in the above preparation process are as follows:

[0228] Monomer 1: Diethyl fumarate, 45 parts;

[0229] Monomer 2: Methacrylic acid, 13 parts;

[0230] Conjugated diene monomer: isoprene, 40 parts;

[0231] Crosslinking monomer: divinylbenzene, 2 parts;

[0232] Emulsifier 1: Dodecylamine polyoxyethylene ether 1205, 2.5 parts;

[0233] Emulsifier 2: Sodium dodecylbenzenesulfonate, 1.1 parts; Sodium methylene dinaphthalenesulfonate, 1 part;

[0234] Molecular weight regulator: n-dodecyl mercaptan, 0.012 parts;

[0235] Initiator 1: Hydrogen peroxide p-mentholane, 0.9 parts;

[0236] Initiator 2: Potassium persulfate, 1.6 parts;

[0237] Reducing agent: Sodium iron EDTA, 0.2 parts;

[0238] Electrolyte: Lithium nitrate, 0.55 parts;

[0239] Deionized water: 130 parts;

[0240] pH adjuster: lithium hydroxide, 4.3 parts.

[0241] Terminator: Isopropyl hydroxylamine, 1 part;

[0242] Antioxidant: Tris(2,4-di-tert-butylphenyl) phosphite, 1 part.

[0243] Example 5

[0244] S1. Preparation of pre-emulsion:

[0245] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 15°C for 60 min to obtain a pre-emulsion.

[0246] S2, Aggregation:

[0247] Initiator 1 was added to the above-mentioned reactor to initiate the first stage of polymerization. The temperature was controlled at 8°C until the reaction conversion rate reached 85%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 75°C to carry out the second stage of polymerization until the reaction conversion rate reached 99.40%. Terminator and antioxidant were added to terminate the polymerization.

[0248] S3, Post-processing:

[0249] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 6.9, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0250] The materials and their quantities used in the above preparation process are as follows:

[0251] Monomer 1: Dimethyl itaconic acid, 30 parts; Diethyl fumarate, 25 parts;

[0252] Monomer 2: Methacrylic acid, 13 parts;

[0253] Conjugated diene monomer: 1,3-butadiene, 38 parts;

[0254] Crosslinking monomer: divinylbenzene, 1.2 parts;

[0255] Emulsifier 1: Dodecylamine polyoxyethylene ether 1205, 0.5 parts;

[0256] Emulsifier 2: Sodium dodecyl sulfate, 1.8 parts; Sodium methylene dinaphthalene sulfonate, 0.5 parts; Sodium dodecylbenzene sulfonate, 1.2 parts;

[0257] Molecular weight regulator: tert-dodecyl mercaptan, 0.01 parts;

[0258] Initiator 1: Dicumyl peroxide, 0.9 parts;

[0259] Initiator 2: Ammonium persulfate, 1.4 parts;

[0260] Reducing agent: Sodium iron EDTA, 0.12 parts;

[0261] Electrolyte: Potassium chloride, 0.35 parts;

[0262] Deionized water: 130 parts;

[0263] pH adjuster: Lithium hydroxide, 2.9 parts.

[0264] Terminating agent: Sodium thiram, 1 part;

[0265] Anti-aging agent: 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 2 parts.

[0266] Example 6

[0267] S1. Preparation of pre-emulsion:

[0268] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 25°C for 60 min to obtain a pre-emulsion.

[0269] S2, Aggregation:

[0270] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 18°C ​​until the reaction conversion rate reached 75%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 70°C to carry out a second-stage polymerization until the reaction conversion rate reached 99.60%. Terminator and antioxidant were added to terminate the polymerization.

[0271] S3, Post-processing:

[0272] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 7.3, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0273] The materials and their quantities used in the above preparation process are as follows:

[0274] Monomer 1: Diethyl fumarate, 45 parts; Dibutyl fumarate, 20 parts;

[0275] Monomer 2: Methacrylic acid, 8 parts;

[0276] Conjugated diene monomer: 1,3-butadiene, 27 parts;

[0277] Crosslinking monomer: Dimethylaminoethyl methacrylate, 2 parts;

[0278] Emulsifier 1: Dodecylamine polyoxyethylene ether 1205, 0.6 parts; Octadecylamine polyoxyethylene ether 1805, 0.8 parts;

[0279] Emulsifier 2: Sodium dodecyl sulfate, 2.8 parts; Sodium methylene dinaphthalene sulfonate, 0.3 parts;

[0280] Molecular weight regulator: tert-dodecyl mercaptan, 0.03 parts;

[0281] Initiator 1: Dicumyl peroxide, 1.15 parts;

[0282] Initiator 2: Potassium persulfate, 1.2 parts;

[0283] Reducing agent: Sodium iron EDTA, 0.16 parts;

[0284] Electrolyte: Lithium chloride, 0.29 parts;

[0285] Deionized water: 130 parts;

[0286] pH adjuster: lithium hydroxide, 3.5 parts.

[0287] Terminating agent: Sodium thiram, 2 parts;

[0288] Anti-aging agent: Distearate thiodipropionate, 2 parts.

[0289] Example 7

[0290] S1. Preparation of pre-emulsion:

[0291] Deionized water, emulsifier 1, emulsifier 2, electrolyte, reducing agent, monomer 1 and monomer 2 were added to the reactor. The reactor was then purged with nitrogen. Conjugated diene monomers were added and pre-emulsified at 20°C for 60 min to obtain a pre-emulsion.

[0292] S2, Aggregation:

[0293] Initiator 1 was added to the above-mentioned reactor to initiate a first-stage polymerization, and the temperature was controlled at 20°C until the reaction conversion rate reached 70%. Molecular weight regulator, crosslinking monomer and initiator 2 were added, and the temperature was raised to 60°C to carry out a second-stage polymerization until the reaction conversion rate reached 99.10%. Terminator and antioxidant were added to terminate the polymerization.

[0294] S3, Post-processing:

[0295] Cool the material down to below 40°C, add a pH adjuster to adjust the pH of the latex to 7.2, stir for 30 minutes until completely dissolved, and filter through a 200-mesh nylon screen to obtain the latex binder.

[0296] The materials and their quantities used in the above preparation process are as follows:

[0297] Monomer 1: Dimethyl itaconic acid, 25 parts; Dimethyl fumarate, 28 parts;

[0298] Monomer 2: Methacrylic acid, 7 parts;

[0299] Conjugated diene monomer: 1,3-butadiene, 40 parts;

[0300] Crosslinking monomer: Vinyltrimethoxysilane, 3 parts;

[0301] Emulsifier 1: Octadecylamine polyoxyethylene ether 1805, 0.8 parts;

[0302] Emulsifier 2: Sodium dodecylbenzenesulfonate, 2.1 parts; Sodium methylene dinaphthalenesulfonate, 1 part;

[0303] Molecular weight regulator: n-dodecyl mercaptan, 0.01 parts;

[0304] Initiator 1: Hydrogen peroxide, p-pyran, 1.5 parts;

[0305] Initiator 2: 2,2'-azobis(2,4-dimethylpentanonitrile), 1.3 parts;

[0306] Reducing agent: Sodium iron EDTA, 0.12 parts;

[0307] Electrolyte: Lithium chloride, 0.3 parts;

[0308] Deionized water: 135 parts;

[0309] pH adjuster: lithium hydroxide, 4.1 parts.

[0310] Terminating agent: Sodium nitrite, 4 parts;

[0311] Anti-aging agent: 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 3 parts.

[0312] Comparative Example 1

[0313] SBR latex originates from Zeon, Japan.

[0314] Comparative Example 2

[0315] The method was implemented according to Example 7, except that the pH adjuster lithium hydroxide was replaced with potassium hydroxide.

[0316] Product Testing :

[0317] 1. Adhesive property testing:

[0318] The solid content, viscosity, pH value, and particle size of the adhesive products were tested separately. The test results are shown in Table 1.

[0319] ①Method for determining solid content:

[0320] Take two dried weighing bottles (labeled Weighing Bottle A and Weighing Bottle B) and copper foil. Place small pieces of copper foil at the bottom of Weighing Bottle A and Weighing Bottle B respectively. Weigh and record the weight of Weighing Bottle A (m1, including Weighing Bottle A itself + copper foil) and the weight of Weighing Bottle B (n1, including Weighing Bottle B itself + copper foil). Weigh two samples of approximately 1g each (labeled Sample 1 and Sample 2), and then place them into Weighing Bottle A and Weighing Bottle B respectively. Record the total weight of Weighing Bottle A (m2, including Weighing Bottle A itself + copper foil + Sample 1) and the total weight of Weighing Bottle B (n2, including Weighing Bottle B itself + copper foil + Sample 2). Cover the weighing bottles and place them in a forced-air drying oven. Open the caps, leaving sufficient space around the bottle to ensure airflow within the drying chamber. Close the oven door.

[0321] After drying for two hours, weighing bottles A and B were removed and placed in a desiccator to cool. The samples were weighed again, and the weighing values ​​were recorded. The samples were then placed back into the oven and baked at the same temperature for 0.5 hours. After cooling, the samples were weighed again. The difference between the two weighing results of the same sample was less than or equal to 0.001g. The weights of weighing bottles A and B after drying to constant weight were recorded as m3 and n3, respectively. (If the weight is greater than 0.001g, the samples were placed back into the oven and baked for 0.5 hours until the difference between two consecutive weighing values ​​was less than or equal to 0.001g.)

[0322] Solid content = [(m3-m1) / (m2-m1) ×100%+(n3-n1)(n2-n1)×100%] / 2.

[0323] ②pH test:

[0324] Take a sample of about 50 grams and place it in a constant temperature water bath (25℃) for ≥60 minutes. Use a pH meter to test the pH value of the latex.

[0325] ③ Viscosity test:

[0326] Turn on the power to the constant temperature water bath and raise the water temperature to 25℃ and maintain it at that temperature (the temperature fluctuation of the constant temperature water should not exceed ±0.2℃). Add approximately 250 ml of the test sample to a clean, sealed 500 ml plastic bottle and place it in the constant temperature water bath. Maintain the temperature for ≥60 minutes (during which time, remove the plastic bottle and shake it upside down for 1 minute every 15 minutes). Then, use a rotational viscometer to test the latex viscosity.

[0327] ④ Particle size test:

[0328] Take 2 drops of raw latex and dilute with 10 mL of deionized water. Draw the diluted solution into a syringe and filter it through a 0.45 μm aqueous filter membrane to remove dust and air bubbles. Preheat the instrument. Create a new "Size" measurement in the software and set the dispersant to water. Use a disposable square plastic cuvette, fill it to 3 / 4 full with the filtered sample, wipe the outer wall clean, and place it in the sample cell. Begin the measurement at a backscattering angle (173°). The instrument automatically displays the Z-Average average particle size and PDI polydispersity index. The test results for Example 1 are shown below. Figure 1 .

[0329] Table 1: Physical properties of the latex adhesives obtained in each embodiment

[0330]

[0331] 2. Adhesion test:

[0332] Preparation of battery slurry:

[0333] K1, CMC Pulping: Use deionized water to prepare CMC into a transparent slurry with a solid content of 1%. The slurry is transparent and uniform, and after standing, there are no particles or bubbles. The slurry viscosity is 4000 mPa.s.

[0334] K2. Weigh 50g of CMC slurry and slowly add 0.5g of conductive carbon powder (vacuum dried at 105℃ for 18h before use) at a low stirring speed (50rPM). Stir for 10 minutes in both directions, and then stir at high speed (600rPM) for 20 minutes.

[0335] K3, then slowly add graphite powder in two batches (the graphite powder is vacuum dried at 105℃ for 18 hours before use), and stir at high speed (600rPM) for 60 minutes each time.

[0336] K4. Finally, add 0.5g of binder latex to the system, stir evenly, and then add an appropriate amount of deionized water to adjust the product solid content to the range of 29-30% and viscosity to 5500±1000mPa.s.

[0337] Coated using a K5 250µm automatic coating machine, dried in a vacuum oven at 80℃ for 24 hours, and the film thickness was tested and recorded.

[0338] K6. Make the plate: Cut a 10cm wide piece of coated copper paper, stick a 10cm wide piece of special tape to the iron plate, then stick the coated side to the other side of the tape and press firmly.

[0339] Peel force and interfacial peel strength tests: The sample was fixed to a tensile testing machine, and the data settings were set to a tensile speed of 5 cm / min and a sample width of 10 cm. The peel force and interfacial peel strength were recorded. The test results are shown in Table 2.

[0340] 3. Swelling rate test:

[0341] Film forming:

[0342] Apply the adhesive to a flat substrate (such as a PTFE plate or glass plate) and dry it in a vacuum oven at 80°C for 24 hours until constant weight is achieved, with a film thickness of 1.0 ± 0.2 mm. Peel the dried film off the substrate and cut it into small pieces (e.g., 1 cm x 1 cm). Record the initial drying weight (Wd). Place the weighed film sample into a sealed glass bottle. Pour in 50 mL of electrolyte, ensuring the sample is completely submerged.

[0343] The membrane was completely immersed in the electrolyte at 25°C and stored at 25°C for 72 hours. After the time was up, the sample was removed with tweezers, and the surface residual electrolyte was quickly and gently blotted dry with filter paper. The weight after swelling (Ws) was recorded.

[0344] calculate:

[0345] Swelling rate (mass%) = [Ws / Wd] × 100%

[0346] 4. Electrochemical performance testing:

[0347] (4.1) Assemble the battery:

[0348] Preparation of the negative electrode sheet: 95.7 parts graphite, 2 parts negative electrode binder, 1.5 parts sodium carboxymethyl cellulose, 1.2 parts conductive carbon black, and 100 parts deionized water were mixed evenly using a mixer to prepare a slurry of suitable viscosity. The slurry was coated onto the surface of copper foil using a coating machine, and the negative electrode sheet was obtained after baking and rolling.

[0349] Preparation of the positive electrode sheet: 96.5 parts of positive electrode active material, 1.5 parts of polyvinylidene fluoride binder, 2.0 parts of conductive carbon black, and 100 parts of N-methylpyrrolidone were mixed evenly using a planetary mixer to form a slurry. The slurry was coated onto the surface of aluminum foil, and the positive electrode sheet was obtained after baking and rolling.

[0350] Assembly: The negative electrode, positive electrode, and separator are assembled into a battery. LiPF6 is dissolved at a concentration of 1 mol / L in an electrolyte with a volume ratio of EC / DEC / EMC = 2.5:2.8:1, and the lithium-ion battery is prepared after electrolyte injection.

[0351] (4.2) Test:

[0352] ① Cyclic performance:

[0353] a. Charging: Charge at a constant current of 0.5C (CC) to the upper limit voltage of 4.2V; then switch to constant voltage of 4.2V (CV) until the charging current decays to 0.05C;

[0354] b. Let stand for 10 minutes;

[0355] c. Discharge: Discharge at a constant current of 0.5C (CC) until the cutoff voltage of 3.0V;

[0356] d. Let stand for 10 minutes. Data recording: For each cycle: charging capacity, discharging capacity, coulombic efficiency;

[0357] Cycle: Repeat step ad for a total of 500 times or until the battery discharge capacity is less than 80% of its initial rated capacity.

[0358] ②Rate performance:

[0359] a. Charge using a constant current of 0.5C until the voltage reaches 4.2V, then charge at a constant voltage of 4.2V until the current is ≤0.05C and then stop charging;

[0360] b. Discharge to 3.0V using a constant current of 0.2C, let stand for 10 minutes after the discharge is finished, and record the discharge capacity;

[0361] c. Charge again with a constant current of 0.5C until the voltage reaches 4.2V, then charge at a constant voltage of 4.2V until the current drops to 0.05C and the charging ends.

[0362] d. Discharge the battery at currents of 0.5C, 1C, 2C, and 3C to evaluate its performance at different rates.

[0363] The test results are shown in Table 2.

[0364] Table 2: Test Results

[0365]

[0366] As can be seen from the test results in the table above, the adhesives obtained in Examples 1-7 of this invention have a peel force of more than 5.5N to the substrate and an interfacial peel strength of more than 30N / cm, exhibiting excellent adhesion; their swelling rate is less than 139%, exhibiting excellent anti-swelling properties; at the same time, the 3C / 0.2C capacity retention rate of the assembled battery is more than 85%, and the capacity retention rate after 500 cycles is more than 88%, exhibiting excellent rate performance and cycle performance.

[0367] Compared to the embodiments, Comparative Example 1 showed reduced adhesion and electrochemical performance, demonstrating that the adhesive of the present invention improves adhesion and electrochemical performance compared to conventional commercially available adhesives. Compared to Example 7, Comparative Example 2 showed reduced adhesion and electrochemical performance, demonstrating that the use of a specific pH adjuster for pre-lithiation in the present invention is beneficial for improving the adhesion and electrochemical performance of the material.

[0368] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for producing a binder, characterized by, The method comprises the following steps: S1, preparing a pre-emulsion: mixing water, an emulsifier, an electrolyte, a reducing agent, monomer 1, monomer 2 and a conjugated diene monomer to obtain a pre-emulsion; S2, polymerization: adding initiator 1 to the system to initiate the first-stage polymerization, when the reaction conversion rate reaches 50% to 90%, adding a molecular weight regulator, a crosslinking monomer and initiator 2, and performing the second-stage polymerization by heating, when the reaction conversion rate reaches more than 95%, adding a terminating agent and an antioxidant to terminate the polymerization; S3, post-treatment: cooling, adjusting the pH value, and obtaining the latex adhesive; wherein, the monomer 1 is at least one of a compound of formula (1-1) and / or a compound of formula (1-2); the monomer 2 is a compound represented by formula (2); Formula (1-1), Formula (1-2); Equation (2); in formula (1-1): R1 and R2 are independently selected from H, C1-C8 hydrocarbon groups; in formula (1-2): R1 and R2 are independently selected from H, C1-C8 hydrocarbon groups; in formula (2): R 11 , R 22 independently selected from the group consisting of H, C1-C15 hydrocarbyl.

2. The production method according to claim 1, characterized by, in formula (1-1), the hydrocarbon groups are aliphatic hydrocarbon groups, alicyclic hydrocarbon groups and aromatic hydrocarbon groups; wherein the aliphatic hydrocarbon groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl or octyl; the alicyclic hydrocarbon groups are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl or cyclooctenyl groups; and the aromatic hydrocarbon groups are phenyl, benzyl, phenethyl or tolyl; in formula (1-2), the hydrocarbon groups are aliphatic hydrocarbon groups, alicyclic hydrocarbon groups and aromatic hydrocarbon groups; wherein the aliphatic hydrocarbon groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl or octyl; the alicyclic hydrocarbon groups are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptyl or cyclooctenyl groups; and the aromatic hydrocarbon groups are phenyl, benzyl, phenethyl or tolyl.

3. The production method according to claim 1 or 2, characterized by, the compound of formula (1-1) is at least one of itaconic acid, 1-methyl itaconate, 4-methyl itaconic acid, dimethyl itaconate, 1-ethyl itaconate, 4-ethyl itaconate, diethyl itaconate, 1-propyl itaconate, 4-propyl itaconate, dipropyl itaconate, 1-butyl itaconate, 4-butyl itaconate, dibutyl itaconate and 1-ethyl-4-methyl itaconate; the compound of formula (1-2) is at least one of fumaric acid, 1-methyl fumarate, 4-methyl fumaric acid, dimethyl fumarate, 1-ethyl fumarate, 4-ethyl fumarate, diethyl fumarate, 1-propyl fumarate, 4-propyl fumarate, dipropyl fumarate, 1-butyl fumarate, 4-butyl fumarate, dibutyl fumarate and 1-ethyl-4-methyl fumarate; the compound represented by formula (2) is at least one of acrylic acid and methacrylic acid; the conjugated diene monomer is at least one of 1,3-butadiene, isoprene and 2,3-dimethyl-1,3-butadiene; The crosslinking monomer is at least one of divinylbenzene, adipic acid diethenyl ester, ethylene glycol dimethyl acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, N-methylol acrylamide, diacetone acrylamide, adipic acid dihydrazide, triallyl isocyanurate, diallyl phthalate, glycidyl methacrylate, dimethylaminoethyl methacrylate, diallyl phthalate, glycidyl versatate, vinyl trimethoxysilane, vinyl triisopropoxysilane.

4. The method of claim 1, wherein, The emulsifier comprises an emulsifier 1 and an emulsifier 2; wherein the emulsifier 1 is a fatty amine polyoxyethylene ether; and the emulsifier 2 is an organic acid salt emulsifier. The pH regulator used for adjusting the pH value is at least one of lithium hydroxide and lithium carbonate. The electrolyte is at least one of lithium nitrate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, sodium hydrogen phosphate and sodium dihydrogen phosphate. The reducing agent is EDTA iron sodium salt, or a mixture of ferrous sulfate, sodium sulfite and EDTA-2Na. The initiator 1 is at least one of dicumyl peroxide, p-menthane hydroperoxide, cumyl hydroperoxide and p-phenyl hydroperoxide. The initiator 2 is at least one of potassium persulfate, ammonium persulfate, lithium persulfate, 2,2'-azobis(2,4-dimethylvaleronitrile), azobis(isobutyronitrile) hydrochloride, azobis(isopropyl cyano imidazole) hydrochloride and azobis(cyanovaleric acid). The molecular weight regulator is at least one of an alkyl mercaptan or a polythiol compound.

5. The preparation method according to claim 4, characterized in that, The emulsifier 1 is at least one of dodecyl amine polyoxyethylene ether and octadecyl amine polyoxyethylene ether. The emulsifier 2 is at least one of sodium dodecyl benzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, alkyl naphthalene sulfonate formaldehyde condensate, sodium dibutyl naphthalene sulfonate, sodium alpha-olefin sulfonate, succinate sulfonate, sodium decyl succinate sulfonate, sodium ethoxylated alcohol half ester sulfosuccinate and sodium laureth sulfate. The molecular weight regulator is at least one of tert-dodecanethiol and n-dodecanethiol.

6. The method of claim 1, wherein, In step S1, the pre-emulsification temperature is 3-45℃, and the time is 30-60 minutes. In step S2, the temperature of the first-stage polymerization is 3-45℃, and the temperature of the second-stage polymerization is 45-85℃. In step S3, the temperature is lowered to below 40℃, and the pH value is adjusted to 6-8.

7. The preparation method according to claim 1, characterized in that, The amounts of the monomers are as follows: Monomer 1: 20-80 parts by mass; Monomer 2: ≤20 parts by mass; Conjugated diene monomer: 20-80 parts by mass; Crosslinking monomer: ≤20 parts by mass; The total amount of the monomers is 100 parts by mass.

8. A binder characterized by, The preparation method is prepared by any one of claims 1-7.

9. A negative electrode sheet characterized by comprising: The binder used comprises the binder of claim 8.

10. A lithium-ion battery, characterized by, The negative electrode sheet is the negative electrode sheet of claim 9.

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