Preparation method of emulsion type adhesive and application thereof in lithium ion battery negative electrode

Abstract

This invention discloses a method for preparing an emulsion-type binder and its application in the negative electrode of a lithium-ion battery. The binder consists of a core-shell structure, wherein the shell layer is mainly obtained by copolymerization of monomers resistant to electrolyte swelling and has a high glass transition temperature, which can ensure the structural stability of binder particles under high temperature and electrolyte immersion conditions, which is beneficial to improving the high temperature performance and cycle life of lithium-ion batteries; while the shell layer is composed of soft monomers and hydrophilic monomers and has a low glass transition temperature, which gives the chain segments strong mobility, which is beneficial to improving its adhesion, slurry dispersibility and film-forming properties.

Description

Technical Field

[0001] This invention relates to an adhesive, and more particularly to a method for preparing an emulsion-type adhesive and its application in the negative electrode of a lithium-ion battery, belonging to the field of polymer materials technology. Background Technology

[0002] Lithium-ion batteries are widely used in electronic products, electric vehicles, and energy storage devices due to their advantages such as high energy density, long cycle life, and ease of design. As the application scenarios and functional requirements of various products become increasingly diverse, the market is placing higher demands on the energy density, reliability, and cost of lithium-ion batteries.

[0003] Negative electrode binders are important polymer materials in lithium-ion batteries. Their main function is to adhere the negative electrode active material (graphite, silicon carbide, silicon, etc.) and conductive agents to the current collector. Although the amount of binder used is not large (about 1.5-5% of the negative electrode material), its performance has a significant impact on the performance of lithium batteries, such as specific capacity, coulombic efficiency, internal resistance, and cycle life.

[0004] Currently, the most widely used negative electrode binder is styrene-butadiene rubber latex (SBR), which requires the addition of carboxymethyl cellulose (CMC) as a thickener and dispersant during use. The material composition of SBR / CMC limits the content of polar functional groups such as carboxyl, ester, and cyano groups, resulting in weak interactions with the negative electrode material, especially silicon-carbon negative electrodes. Consequently, the overall battery performance, particularly low-temperature performance, is increasingly failing to meet application requirements. Polyacrylic acid binders, due to their high content of polar functional groups, exhibit complexation and decomplexation interactions with lithium ions during charge and discharge, promoting lithium-ion conduction and reducing battery internal resistance. Furthermore, polyacrylic acid binders can form hydrogen bonds with the silicon negative electrode surface, improving the dispersion and adhesion of the negative electrode material, thereby suppressing the volume expansion of the negative electrode active material during charge and discharge, improving the performance of the SEI film, and preventing electrolyte decomposition during electrochemical cycling.

[0005] CN111500228B discloses a polyacrylic acid adhesive for solution-type batteries. This adhesive is a polymer with both hydrophilic and hydrophobic units. It precipitates in water but dissolves as a salt upon the addition of an alkaline solution. The invented adhesive exhibits strong adhesion, but the polymerization method used is precipitation polymerization, which is complex and costly. CN109777328B discloses an aqueous adhesive for lithium-ion battery negative electrodes, prepared by emulsion polymerization of hard monomers, soft monomers, functional monomers, acidic monomers, and a crosslinking agent. This adhesive maintains good liquid absorption, adhesion, and charge / discharge performance. CN111057184A discloses a method for preparing an aqueous adhesive for negative electrode sheets, employing soap-free emulsion polymerization. By copolymerizing hydrophilic monomers, lipophilic monomers, and functional monomers, the surface tension of the aqueous adhesive is reduced, resulting in a shorter dispersion time and improved production efficiency of the negative electrode sheets.

[0006] From the perspective of application requirements, in addition to having strong adhesion to adhere negative electrode active materials, conductive agents and other materials to the current collector, the negative electrode binder also needs to provide good slurry dispersibility during the slurry preparation stage, good film-forming properties and flexibility during the electrode coating stage, and easy drying and rolling. After being assembled into a lithium-ion battery, it should have excellent resistance to electrolyte swelling, lithium-ion conductivity and electrochemical stability.

[0007] Although existing technologies have optimized some properties of negative electrode binders, the performance requirements of negative electrode binders vary in different application stages because they play an important role in slurry preparation, electrode coating, and the final lithium battery. How to achieve a balance of various performance requirements through specific structural design remains the focus of research on negative electrode binders. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method for preparing an emulsion-type binder and its application in the negative electrode of a lithium-ion battery. This binder consists of a core-shell structure. The core layer is primarily obtained by copolymerizing monomers resistant to electrolyte swelling and has a high glass transition temperature, ensuring the structural stability of the binder particles under high temperature and electrolyte immersion conditions, which is beneficial for improving the high-temperature performance and cycle life of lithium-ion batteries. The shell layer is composed of soft monomers and hydrophilic monomers and has a low glass transition temperature, giving the chain segments strong mobility, which is beneficial for improving its adhesion, slurry dispersibility, and film-forming properties.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing an emulsion-type adhesive includes the following steps:

[0011] 1) Add emulsifier and water to the reactor as a base, turn on the stirring and heat to the set temperature;

[0012] 2) Add emulsifier, water, vinyl aromatic monomer, alkyl acrylate monomer, functional monomer acid and crosslinking monomer to pre-emulsification tank 1 for pre-emulsification to obtain core layer pre-emulsified liquid;

[0013] 3) Add emulsifier, water, alkyl acrylate monomer, cyano monomer, functional monomer acid and crosslinking monomer to pre-emulsification tank 2 for pre-emulsification to obtain shell pre-emulsion;

[0014] 4) Add 1-10% of the mass of the core layer pre-emulsion to the reactor, and add initiator solution to initiate polymerization;

[0015] 5) After keeping warm for 5-20 minutes, simultaneously add the core layer pre-emulsion and initiator solution; the adding time is 1-2 hours.

[0016] 6) After the core pre-emulsion is finished, start the simultaneous addition of the shell pre-emulsion and initiator solution. The addition time is 1-2 hours. After the addition is finished, continue to keep warm for 1-2 hours.

[0017] 7) After the heat preservation is completed, the mixture is cooled to room temperature and a neutralizing agent is added to adjust the pH of the emulsion to 7-9. The mixture is then filtered to obtain the emulsion-type binder.

[0018] In a preferred embodiment, the core layer preemulsion comprises, by mass ratio of raw materials, 0.1-0.7% emulsifier, 20-30% water, 50-70% vinyl aromatic monomer, 5-25% alkyl acrylate monomer, 1-5% functional monomeric acid, and 0.2-1.5% crosslinking monomer;

[0019] The shell pre-emulsion contains, by mass ratio of raw materials, 0.1-0.7% emulsifier, 20-30% water, 40-60% alkyl acrylate monomers, 5-25% cyano monomers, 5-10% functional monomeric acid, and 0.1-1.0% crosslinking monomers.

[0020] In a preferred embodiment, the mass ratio of the core preemulsion to the shell preemulsion is (10-40):(60-90).

[0021] In a preferred embodiment, the vinyl aromatic monomer is at least one of styrene, 2-methylstyrene, 4-methylstyrene, 2-(n-butyl)styrene, 4-(n-butyl)styrene, and 4-(n-quinyl)styrene, preferably styrene.

[0022] In a preferred embodiment, the alkyl acrylate monomer is at least one of ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, sec-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, dodecyl acrylate, and their methyl-substituted derivatives.

[0023] In a preferred embodiment, the cyano monomer is selected from acrylonitrile and / or methacrylonitrile.

[0024] In a preferred embodiment, the functional monomeric acid is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid, preferably methacrylic acid;

[0025] Preferably, the crosslinking monomer is at least one selected from divinylbenzene, allyl methacrylate, diallyl phthalate, pentaerythritol triallyl ether, ethylene glycol dimethacrylate, and N,N-methylenebisacrylamide, with N,N-methylenebisacrylamide being the most preferred.

[0026] Preferably, the emulsifier is selected from surfactants containing at least one olefinic unsaturated functional group, and is more preferably selected from at least one of allyloxyisomeric alcohol ether sulfate ammonium salt, allyl polyether phosphate, allyl-containing special thiols sulfate, allyl polyoxyethylene ether sulfate salt, allyl alkyl succinate sulfonate salt, allyl ether hydroxypropane sulfonate salt, and polyoxyethylene styrene phenyl ether sulfate salt;

[0027] Preferably, the initiator is at least one selected from ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, ammonium persulfate, and sodium bisulfite; preferably, the total amount of the initiator is 0.1-10% of the total mass of the vinyl aromatic monomer, alkyl acrylate monomer, functional monomer acid, crosslinking monomer, and cyano monomer, more preferably 0.2-0.5%; the amount of the initiator added in step 4) is 30-50% of its total mass, the amount of the initiator added in step 5) is 6-24% of its total mass, and the amount of the initiator added in step 6) is 36-54% of its total mass.

[0028] Preferably, the neutralizing agent is an inorganic alkali metal hydroxide, and more preferably one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0029] In a preferred embodiment, the amount of emulsifier used in steps 2) and 3) accounts for 11-52% and 43-80% of the total amount, respectively;

[0030] Preferably, the amount of water added during the preparation process is such that the emulsion solid content reaches 20-60%, more preferably 40-50%.

[0031] In a preferred embodiment, in step 1), the temperature is set to 75-90°C.

[0032] The emulsion-type adhesive prepared by the above method has a glass transition temperature of 60-100℃ for the core polymer and a glass transition temperature of -30℃ to 10℃ for the shell polymer.

[0033] This invention also provides the application of an emulsion-type binder prepared by the method described above in the negative electrode sheet of a lithium-ion battery. The emulsion-type binder is suitable for negative electrode active materials such as artificial graphite, natural graphite, hard carbon, silicon, and silicon-carbon, and can be used to prepare the negative electrode sheet and assemble it into a lithium-ion battery using methods known in the art.

[0034] The present invention has the following beneficial effects:

[0035] (1) The emulsion-type binder of the present invention has a core-shell structure with a hard inner layer and a soft outer layer. The core layer is composed of polymers with high glass transition temperature, which is beneficial to improving the mechanical properties and resistance to electrolyte swelling of the binder. The shell layer is composed of polymers with low glass transition temperature, which can give the binder good bonding performance, slurry dispersion performance and film-forming performance, and avoid powdering and cracking of the electrode during the electrode baking process.

[0036] (2) The shell of the emulsion-type binder of the present invention is rich in carboxyl groups, which on the one hand gives the surface of the latex particles strong hydrophilicity. During the film formation process, water vapor is released rapidly along the hydrophilic surface of the latex particles, which is beneficial to eliminating defects such as bulging or even cracking that occur during the baking of the electrode. On the other hand, the presence of a large number of carboxyl groups also improves the interaction between the latex particles and the negative electrode active material, conductive agent and dispersant, thereby improving the slurry dispersion performance.

[0037] (3) The emulsion binder of the present invention uses an emulsifier that is a surfactant containing at least one olefinic unsaturated functional group, which can participate in polymerization and graft onto the polymer, providing good colloidal stability for latex particles, while reducing the residue of small molecules and effectively improving the electrochemical stability of lithium-ion batteries.

[0038] (4) The emulsion-type negative electrode binder of the present invention incorporates crosslinking monomers during the polymerization process, and has a high crosslinking density in the core layer and a low crosslinking density in the shell layer. The high crosslinking of the core layer can significantly improve the mechanical strength and electrolyte swelling resistance of the binder, while the moderate crosslinking of the shell layer, while ensuring mechanical strength and electrolyte swelling resistance, imparts good film-forming properties and flexibility to the latex particles.

[0039] (5) The emulsion binder of the present invention incorporates cyano monomers during the polymerization process. The presence of polar functional groups is beneficial to promoting the conduction of lithium ions, reducing the internal resistance of lithium batteries, and improving the low-temperature performance of lithium batteries. In addition, cyano monomers can also enhance the interaction between the binder and the negative electrode active material and the current collector. Detailed Implementation

[0040] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0041] The main raw materials and their sources in the examples and comparative examples are shown in Table 1:

[0042] Table 1. Main Raw Materials and Their Sources

[0043]

[0044]

[0045] Unless otherwise specified, all other chemical reagents used in the examples were purchased from the market and were of analytical grade.

[0046] The testing methods used in the following embodiments of the present invention are as follows:

[0047] Slurry dispersibility evaluation: Observe the appearance of the prepared negative electrode sheet after baking, including the condition of electrode sheet cracking, curling, black spots and pits.

[0048] Electrolyte swelling test: The binder emulsion was dried into a film in a 50℃ oven, and a film with a mass of M1 was taken. The film was immersed in the electrolyte and placed in a 60℃ oven for 48 hours. The electrolyte on the surface of the film was wiped dry with filter paper, and the weight was taken as M2. Electrolyte swelling degree = (M2-M1) / M1×100%.

[0049] Peel strength evaluation: The peel strength test method refers to the American Society for Testing and Materials standard ASTM D3330, and the equipment used is a computerized tensile testing machine (KJ-1065).

[0050] Electrochemical performance evaluation: The prepared negative electrode sheet and the positive electrode sheet with lithium iron phosphate as the positive electrode material are prepared and assembled into an aluminum-plastic soft package according to the lithium-ion battery production process familiar to technicians in this industry, and the internal resistance of the membrane is tested.

[0051] Unless otherwise specified, the number of "parts" of raw materials in each embodiment refers to "parts by mass".

[0052]

Example 1

[0053] (1) Add 0.07 parts of SR-10 and 180 parts of deionized water into the reactor, turn on the stirring and heat to 85°C;

[0054] (2) Add 0.25 parts SR-10, 16 parts deionized water, 3 parts MAA, 50 parts ST, 10 parts BA and 0.63 parts MBA to the pre-emulsification tank one in sequence and start stirring to obtain the core layer pre-emulsion.

[0055] (3) Add 0.70 parts SR-10, 40 parts deionized water, 13 parts MAA, 120 parts BA, 25 parts AN and 1.0 parts MBA to the pre-emulsification kettle and start stirring to obtain shell pre-emulsion;

[0056] (4) Take 4% of the mass of the pre-emulsion and add it to the reactor. Add the prepared APS aqueous solution (0.2 parts APS dissolved in 20 parts deionized water) to initiate polymerization. Keep warm for 10 minutes to obtain the seed emulsion.

[0057] (5) After the seed emulsion is prepared, start to add the remaining nuclear pre-emulsion and APS solution (0.09 parts APS dissolved in 6 parts deionized water) simultaneously, and control the addition time to 1.5 hours;

[0058] (6) After the core pre-emulsion is added, the shell pre-emulsion and APS solution (0.18 parts APS dissolved in 12 parts deionized water) are added simultaneously. The addition time is controlled to be 1.5 hours. After the addition is completed, the temperature is kept warm for another 1.5 hours.

[0059] (7) After cooling to room temperature, add a neutralizing agent lithium hydroxide solution (mass concentration 15%) to adjust the pH of the emulsion to about 8.0, filter and discharge to obtain an emulsion-type binder.

[0060] [Examples 2-8 and Comparative Examples 1-4]

[0061] The emulsion adhesive was prepared using a method essentially the same as that used in Example 1, except that the selection and amount of each raw material were changed according to Table 2.

[0062]

Example 9

[0063] The emulsion binder was prepared using the method of Example 1, with the following adjustments to the raw materials and operating steps: the initiator used in the raw materials was changed from APS to potassium persulfate; the temperature of the reactor in operating step (1) was changed to 75°C; the heat preservation time in step (4) was 20 minutes; the drop addition time of the core pre-emulsion and initiator solution in step (5) was controlled to be 2 hours; and the drop addition time of the shell pre-emulsion and initiator solution in step (6) was controlled to be 2 hours, and the heat preservation was continued for 2 hours after the drop addition was completed.

[0064]

Example 10

[0065] The emulsion binder was prepared using the method and raw materials of Example 1, with the following adjustments to the raw materials and operating steps: the initiator used in the raw materials was changed from APS to sodium persulfate; the temperature of the reactor in operating step (1) was changed to 90°C; the heat preservation time in step (4) was 5 minutes; the drop addition time of the core pre-emulsion and initiator solution in step (5) was controlled to be 1 hour; and the drop addition time of the shell pre-emulsion and initiator solution in step (6) was controlled to be 1 hour, and the heat preservation was continued for 1 hour after the drop addition was completed.

[0066]

Application Example

[0067] The emulsion-type binders prepared in the examples and comparative examples were applied to the preparation of lithium-ion battery negative electrode sheets. The specific steps are as follows:

[0068] (1) Slurry preparation: At room temperature, 1 part of sodium carboxymethyl cellulose (CMC) was added to 100 parts of deionized water and stirred at high speed for about 20 minutes. Then, 1 part of carbon black conductive agent (Super P), 96 parts of negative electrode active material (graphite) and 2 parts of emulsion binder were added. After each material was added, the mixture was stirred at high speed for about 10 minutes to ensure uniform mixing. The negative electrode slurry was obtained after filtration through a 100-mesh filter.

[0069] (2) Electrode coating: The prepared negative electrode slurry is uniformly coated on the current collector (copper foil) with a coating thickness of 100 μm. It is then dried in an oven at 100°C for 3 minutes and rolled at room temperature to obtain a negative electrode sheet with a thickness of 70 μm.

[0070] Electrolyte swelling tests were conducted on the prepared emulsion-type binders, and the prepared negative electrode sheets were evaluated for slurry dispersibility, peel strength, and electrochemical performance. The test results are shown in Table 3.

[0071] As can be seen from the performance results in Table 3, the negative electrode slurry prepared using the binders obtained in Examples 1-10 exhibits normal dispersibility, while Comparative Example 1 shows a bluish tinge. This indicates that the presence of acidic functional monomers in the shell layer improves the affinity between latex particles and the components in the slurry, resulting in better slurry dispersion performance. Compared to Comparative Example 1, the membrane prepared using the binders obtained in Examples 1-10 has lower electrolyte swelling, because increasing the content of crosslinking functional monomers is beneficial for improving the binder's resistance to electrolyte swelling. Compared to Comparative Example 2, the negative electrode sheet prepared using the binders obtained in Examples 1-10 does not exhibit black spots or film cracking, because excessive crosslinking is detrimental to the dispersion of conductive agents and film formation. Compared to Comparative Example 3, the negative electrode sheet prepared using the binders obtained in Examples 1-10 has lower internal resistance, because when the content of cyano functional monomers is too low, the binder's conductivity to lithium ions weakens, resulting in higher internal resistance of the electrode sheet. Compared with Comparative Example 4, the negative electrode sheets prepared using the binders obtained in Examples 1-10 do not exhibit electrode cracking and have higher peel strength. This is because the copolymers constituting the shell in the examples have lower glass transition temperatures, which is beneficial for electrode film formation. Furthermore, due to the stronger polymer chain mobility, it is easier to form a "mechanical interlock" with the current collector and the surface of the negative electrode material, resulting in higher binder strength.

[0072] Table 2. Mass parts of each raw material in Examples 1-8 and Comparative Examples 1-4

[0073]

[0074]

[0075]

[0076] Table 3. Performance Test Results

[0077] performance Slurry dispersibility Electrode film formation Electrolyte swelling degree / % Peel strength (N / m) Diaphragm internal resistance / Ω Example 1 normal No cracks 65 10.0 3.5 Example 2 normal No cracks 50 9.8 3.9 Example 3 normal No cracks 60 11.0 3.0 Example 4 normal No cracks 55 10.2 3.2 Example 5 normal No cracks 60 9.8 4.0 Example 6 normal No cracks 58 10.5 3.7 Example 7 normal No cracks 63 10.7 3.4 Example 8 normal No cracks 61 9.9 3.5 Example 9 normal No cracks 55 10.6 4.1 Example 10 normal No cracks 57 10.3 3.6 Comparative Example 1 Blue No cracks 200 11.0 4.5 Comparative Example 2 Dark spots cracking 40 5.5 6.0 Comparative Example 3 normal No cracks 55 7.0 6.5 Comparative Example 4 normal cracking 55 3.1 4.0

Claims

1. A method for preparing an emulsion-type adhesive, characterized in that, Includes the following steps: 1) Add emulsifier and water to the reactor as a base, turn on stirring and heat to the set temperature; 2) Add emulsifier, water, vinyl aromatic monomer, alkyl acrylate monomer, functional monomer acid and crosslinking monomer to pre-emulsification tank 1 for pre-emulsification to obtain core layer pre-emulsion; 3) Add emulsifier, water, alkyl acrylate monomer, cyano monomer, functional monomer acid and crosslinking monomer to pre-emulsification tank 2 for pre-emulsification to obtain shell pre-emulsion; 4) Add 1-10% of the mass of the core layer pre-emulsion to the reactor, and add initiator solution to initiate polymerization; 5) After keeping warm for 5-20 minutes, simultaneously add the core layer pre-emulsion and initiator solution over a period of 1-2 hours; 6) After the core pre-emulsion is finished, start the simultaneous addition of the shell pre-emulsion and initiator solution. The addition time is 1-2 hours. After the addition is finished, continue to keep warm for 1-2 hours. 7) After the heat preservation is completed, the mixture is cooled to room temperature and a neutralizing agent is added to adjust the pH of the emulsion to 7-9. The mixture is then filtered to obtain the emulsion-type binder. The core layer pre-emulsion, by mass ratio of raw materials, comprises 0.1-0.7% emulsifier, 20-30% water, 50-70% vinyl aromatic monomers, 5-25% alkyl acrylate monomers, 1-5% functional monomeric acid, and 0.2-1.5% crosslinking monomers; The shell pre-emulsion, by mass ratio of raw materials, comprises 0.1-0.7% emulsifier, 20-30% water, 40-60% alkyl acrylate monomers, 5-25% cyano monomers, 5-10% functional monomeric acid, and 0.1-1.0% crosslinking monomers; The mass ratio of the core preemulsion to the shell preemulsion is (10-40):(60-90).

2. The method for preparing the emulsion-type adhesive according to claim 1, characterized in that, The vinyl aromatic monomer is at least one of styrene, 2-methylstyrene, 4-methylstyrene, 2-(n-butyl)styrene, 4-(n-butyl)styrene, and 4-(n-decyl)styrene.

3. The method for preparing the emulsion-type adhesive according to claim 2, characterized in that, The alkyl acrylate monomer is at least one of ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, sec-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, dodecyl acrylate, and their methyl-substituted derivatives.

4. The method for preparing the emulsion-type adhesive according to claim 2, characterized in that, The cyano monomer is selected from acrylonitrile and / or methacrylonitrile.

5. The method for preparing the emulsion-type adhesive according to claim 2, characterized in that, The functional monomeric acid is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid.

6. The method for preparing the emulsion-type adhesive according to claim 5, characterized in that, The crosslinking monomer is at least one of divinylbenzene, allyl methacrylate, diallyl phthalate, pentaerythritol triallyl ether, ethylene glycol dimethacrylate, and N,N-methylenebisacrylamide.

7. The method for preparing the emulsion-type adhesive according to claim 5, characterized in that, The emulsifier is selected from surfactants containing at least one olefinic unsaturated functional group.

8. The method for preparing the emulsion-type adhesive according to claim 7, characterized in that, The emulsifier is selected from at least one of allyloxyisomeric alcohol ether sulfate ammonium salt, allyl polyether phosphate, allyl-containing special thiol sulfate, allyl polyoxyalkylene ether sulfate salt, allyl alkyl succinate sulfonate salt, allyl ether hydroxypropane sulfonate salt, and polyoxyethylene styrene phenyl ether sulfate salt.

9. The method for preparing the emulsion-type adhesive according to claim 5, characterized in that, The initiator is at least one selected from ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, ammonium persulfate, and sodium bisulfite.

10. The method for preparing the emulsion-type adhesive according to claim 5, characterized in that, The total amount of the initiator is 0.1-10% of the total mass of vinyl aromatic monomers, alkyl acrylate monomers, functional monomeric acids, crosslinking monomers, and cyano monomers.

11. The method for preparing the emulsion-type adhesive according to claim 10, characterized in that, The total amount of the initiator is 0.2-0.5% of the total mass of the vinyl aromatic monomers, alkyl acrylate monomers, functional monomeric acids, crosslinking monomers, and cyano monomers.

12. The method for preparing the emulsion-type adhesive according to claim 5, characterized in that, The neutralizing agent is an inorganic alkali metal hydroxide.

13. The method for preparing the emulsion-type adhesive according to claim 12, characterized in that, The neutralizing agent is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

14. The method for preparing the emulsion-type adhesive according to any one of claims 1-13, characterized in that, In steps 2) and 3), the amount of emulsifier used accounts for 11-52% and 43-80% of the total amount, respectively.

15. The method for preparing the emulsion-type adhesive according to claim 14, characterized in that, The amount of water added during the preparation process should be based on the emulsion solid content reaching 20-60%.

16. The method for preparing the emulsion-type adhesive according to claim 15, characterized in that, The amount of water added during the preparation process should be based on the emulsion solid content reaching 40-50%.

17. The method for preparing the emulsion-type adhesive according to any one of claims 1-13, characterized in that, In step 1), the temperature is set to 75-90℃.

18. The application of an emulsion-type binder prepared by any one of claims 1-17 in the negative electrode sheet of a lithium-ion battery.

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