A core-shell type acrylate adhesive and a preparation method thereof

Abstract

This invention discloses a core-shell acrylate adhesive and its preparation method, belonging to the technical field of electrode material adhesives. The invention employs a hard-core, soft-shell structure, with the core layer primarily composed of acryloyloxysilane supplemented with styrene and acrylic acid, and the shell layer primarily composed of hydroxyethyl methacrylate supplemented with isooctyl acrylate and styrene. Through emulsion polymerization, a core-shell acrylate adhesive with excellent bonding properties, high particle size stability, and high solids content is obtained. This adhesive, applied to lithium-ion battery electrode materials, improves energy efficiency and extends battery life. Simultaneously, the adhesive of this invention ensures safety and environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of electrode material adhesive technology, specifically relating to a core-shell type acrylate adhesive and its preparation method. Background Technology

[0002] The long-term stability and performance optimization of lithium-ion batteries directly depend on the effective bonding of electrode materials. Currently, widely used binders include oil-based binders and water-based binders.

[0003] Polyvinylidene fluoride (PVDF) is a representative oil-based binder, offering the best overall performance among cathode binders. However, PVDF uses organic solvents as the dispersion medium, which are flammable and toxic, posing a safety concern. Furthermore, the high polarity of fluorine atoms on the side groups of PVDF results in poor flexibility, potentially causing the active material to detach from the current collector, leading to poor stability and consequently affecting the migration of lithium ions and electrons, thus increasing the battery's internal resistance.

[0004] Commonly used water-based binders include carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), sodium alginate (SA), and polyacrylic acid (PAA), which are more widely used in the bonding of graphite anodes. Similarly, existing technologies have proposed a water-based binder, lithium carboxymethyl cellulose (CMC-Li), synthesized from cotton. CMC-Li, as a binder, can improve the bonding performance of Li... + The increased content of CMC improves diffusion efficiency and specific capacity. However, CMC is very hard and has a very low elongation at break, making it unsuitable for use as an elastic binder.

[0005] Existing technology also discloses an aqueous binder obtained by emulsion polymerization of a hard monomer (methyl acrylate), a soft monomer (butyl acrylate), a functional monomer (hydroxypropyl methacrylate), an acidic monomer (acrylic acid), and a crosslinking agent (dallyl phthalate). This binder, suitable for graphite anode materials, is limited to bonding anode materials; it does not form a core-shell composite structure, cannot achieve a balance between flexibility and rigidity in bonding, and has poor adhesion; its application requires slurry preparation, which is complex and results in low production efficiency.

[0006] Therefore, developing a core-shell acrylate adhesive with excellent adhesion properties, high particle size stability, and high solid content, and its preparation method, which can be used as a binder for the positive and negative electrodes of lithium-ion batteries, is of great research significance and application value. Summary of the Invention

[0007] To address the aforementioned deficiencies in the existing technology, the primary objective of this invention is to provide a core-shell type acrylic adhesive with a hard core and soft shell structure. The core layer is mainly composed of acryloyloxysilane, supplemented with acrylic acid and propylene, while the shell layer is mainly composed of hydroxyethyl methacrylate, supplemented with isooctyl acrylate and styrene. This achieves excellent bonding performance, high particle size stability, and high solids content.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned core-shell type acrylate adhesive.

[0009] Another object of the present invention is to provide the application of the above-mentioned core-shell type acrylate adhesive in bonding lithium-ion battery electrode materials.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention provides a core-shell type acrylic adhesive, comprising the following components in parts by weight:

[0012] Core layer: 20-130 parts acryloyloxysilane, 2-10 parts styrene, 4-20 parts acrylic acid, 1-5 parts divinylbenzene;

[0013] Shell: 30-75 parts hydroxyethyl methacrylate, 4-15 parts isooctyl acrylate, 4-10 parts styrene, 3-10 parts acrylic acid;

[0014] The functional monomer hydroxyethyl methacrylate in the shell layer has a mass percentage of 65% to 85% of the shell layer mass.

[0015] The core-shell ratio is 1:3 to 3:1, where the core-shell ratio is the ratio of the total mass fraction of the core components to the total mass fraction of the shell components.

[0016] The introduction of small amounts of acrylic acid and acryloyloxysilane improves the adhesion, hydrophilicity and stability; the soft shell is made of hydroxyethyl methacrylate, isooctyl acrylate, styrene and acrylic acid copolymer, and the carboxyl groups of acrylic acid and the hydroxyl groups introduced by hydroxyethyl methacrylate can bring better adhesion.

[0017] The mass percentage of the shell functional monomer hydroxyethyl methacrylate is 100% × m(hydroxyethyl methacrylate) / (m(hydroxyethyl methacrylate) + m(isooctyl acrylate) + m(styrene)).

[0018] The core-shell ratio is the ratio of the total mass fractions of the core and shell components. By fixing the total mass fractions of the shell components, the total mass fractions of the core components are changed accordingly.

[0019] Preferably, the core-shell ratio of the core-shell type acrylic adhesive is 1:2 to 2:1.

[0020] More preferably, the core-shell ratio of the core-shell type acrylate adhesive is 1:1.

[0021] Preferably, the divinylbenzene is a crosslinking agent selected from one or more of meta-divinylbenzene, ortho-divinylbenzene, or para-divinylbenzene.

[0022] More preferably, the divinylbenzene is meta-divinylbenzene.

[0023] Divinylbenzene, acting as a crosslinking agent, undergoes addition reactions with the active functional groups of the polymer chains in the emulsion via its olefin double bonds, forming stable chemical bonds and establishing a three-dimensional network structure within the emulsion. This structure improves the emulsion's thermal stability and solvent resistance, making it less prone to decomposition into oligomers at high temperatures, thereby enhancing its overall performance and stability.

[0024] Preferably, the acryloyloxysilane is one or more of 3-acryloyloxypropylmethyldimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-(methacryloyloxy)propyltrimethoxysilane.

[0025] The present invention also provides a method for preparing the above-mentioned core-shell type acrylic adhesive, comprising the following steps:

[0026] The components of the core layer and the components of the shell layer are mixed separately, and emulsifiers and water are added to prepare core pre-emulsions and shell pre-emulsions respectively.

[0027] The core pre-emulsion and initiator are added sequentially to the emulsion polymerization substrate containing emulsifier, water, and pH buffer and reacted for 8-10 minutes. The shell pre-emulsion is added in small amounts multiple times and reacted at 75-85°C. After adjusting the pH to 7-8, the core-shell type acrylate adhesive is obtained.

[0028] Preferably, the emulsifier is at least one of SR-10 anionic emulsifier or OP-10 nonionic emulsifier.

[0029] Preferably, the total mass fraction of the components of the core layer is 27-165 parts.

[0030] Preferably, the total mass fraction of the components of the shell layer is 41-110 parts.

[0031] Preferably, the mass fraction of emulsifier added when preparing the nuclear preemulsion is 2-6 parts.

[0032] Preferably, the mass fraction of emulsifier added when preparing the shell preemulsion is 1-4 parts.

[0033] Preferably, the pH-adjusting reagent is at least one of ammonia, sodium carbonate, or sodium bicarbonate.

[0034] Preferably, the pH buffer is sodium bicarbonate. More preferably, the sodium bicarbonate is 0.01-0.05 parts by mass.

[0035] Preferably, the initiator is a persulfate commonly used in the prior art. More preferably, the initiator is ammonium persulfate, in parts by weight of 0.8-2 parts.

[0036] Preferably, the mass fraction of water added when preparing the nuclear preemulsion is 42-52 parts.

[0037] Preferably, the mass fraction of water added when preparing the shell preemulsion is 42-52 parts.

[0038] Preferably, the water is deionized water.

[0039] The application of the aforementioned core-shell type acrylic adhesive in bonding lithium-ion battery electrode materials is also within the scope of protection of this invention.

[0040] Preferably, the bonding is a point bonding.

[0041] Core-shell acrylic adhesives have a rigid core and an adhesive shell, making them suitable for point bonding. This allows the adhesive to bond between electrode materials in an elastomer-like manner, reducing the contact area between the adhesive and electrode materials while increasing the contact area between the electrode materials. This results in lower battery impedance, improved energy efficiency, and extended battery life.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The core-shell type acrylic adhesive of the present invention has excellent bonding performance, high particle size stability and high solid content, and the bonding strength can reach more than 167 kPa.

[0044] 2. The core-shell type acrylic adhesive of the present invention has a soft shell and hard core structure, which can be used to bond lithium-ion battery electrode materials in a point-to-point manner, thereby increasing the contact area between the electrode materials, reducing battery impedance, improving energy efficiency, and extending battery life. Detailed Implementation

[0045] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0046] The core-shell acrylic adhesives of the various embodiments and comparative examples of the present invention were prepared by the following process:

[0047] S1. The core layer components 3-acryloyloxypropylmethyldimethoxysilane, styrene acrylic acid, and crosslinking agent divinylbenzene are mixed evenly according to the mass parts and then added dropwise to a four-necked flask containing 4 parts by mass of emulsifier and 47 parts by mass of deionized water to prepare a core pre-emulsion. The emulsifier is 2 parts by mass of SR-10 anionic emulsifier and 2 parts by mass of OP-10 nonionic emulsifier.

[0048] S2. The shell components hydroxyethyl methacrylate, isooctyl acrylate, styrene and acrylic acid are mixed evenly according to the mass parts and then added dropwise to a four-necked flask containing 3 parts by mass of emulsifier and 47 parts by mass of deionized water to prepare a shell pre-emulsion. The emulsifier is 1.5 parts of SR-10 anionic emulsifier and 1.5 parts of OP-10 nonionic emulsifier.

[0049] S3. Weigh 0.4 parts of SR-10 emulsifier, 0.4 parts of OP-10 emulsifier, 0.04 parts of sodium bicarbonate, and 45 parts of deionized water as the base material for emulsion polymerization. Separately weigh 1.2 parts of ammonium persulfate initiator to prepare an initiator aqueous solution. Add the core pre-emulsion to the flask containing the emulsion polymerization base material, and simultaneously add the ammonium persulfate aqueous solution dropwise into the flask. After the addition is complete, wait 10 minutes, and then add the shell pre-emulsion to the flask in small amounts several times. Complete the addition of all the shell pre-emulsion within 30 minutes. The reaction temperature is 85℃, and the temperature is maintained for 1 hour after the addition is complete.

[0050] S4. Cool the constant temperature water bath and add ammonia to adjust the pH to 7. After the emulsion cools to 40°C, put it into a storage tank for subsequent characterization and performance testing.

[0051] The performance test methods and indicators of the core-shell type acrylic adhesives of the various embodiments and comparative examples of the present invention are as follows:

[0052] (1) Solid content (%):

[0053]

[0054] Where C is the solid content (%); m1 is the mass of the petri dish (g); m2 is the total mass of the emulsion and petri dish before drying (g); and m3 is the total mass of the emulsion and petri dish after drying (g).

[0055] Acrylic esters with high solids content have high production efficiency: because the emulsion has a high solids content, more active ingredients are retained in the final product, thus improving the conversion rate. This is beneficial to the quality of finished products and production efficiency in industrial production;

[0056] Emulsions with high solids content have low water content, therefore requiring less energy to evaporate water during production. This helps reduce production costs and improve energy efficiency.

[0057] A higher solids content emulsion has a higher concentration of solid substances, which helps the emulsion form a film more quickly. This facilitates subsequent adhesion performance testing.

[0058] (2) Average particle size (nm);

[0059] (3) Polydispersion index:

[0060] The emulsion product was diluted 1000 times with an appropriate amount of deionized water to obtain a sample. 0.5 mL of the sample was weighed into the sample cell, and then deionized water was added to 2 / 3 of the sample cell capacity. The sample was placed in the test chamber of a Zeta potentiometer to measure the particle size of the emulsion. After the measurement was completed, the average particle size and polydispersity index were recorded.

[0061] Particle size and particle size distribution of latex are important indicators for characterizing emulsion properties. They can also be used to classify the application areas of emulsions based on different particle sizes and, to some extent, reflect the degree of polymerization completion. Emulsions containing nanoscale particles exhibit good mechanical stability, and the coated films formed have good density, low roughness, high light transmittance, and good solvent resistance. The polydispersity index (PDI) characterizes the particle size distribution of an emulsion; a lower PDI indicates a narrower distribution and better particle size stability. Conversely, larger particle sizes correspond to a higher PDI, resulting in a wider particle size distribution and poorer particle size stability.

[0062] (4) Shear strength (KPa):

[0063] Dilute all emulsions to a solid content of 15 wt%. Prepare 25 mm × 80 mm copper foil strips and 25 mm × 80 mm PE diaphragm strips. Mark a 10 mm wide area at the end of each PE diaphragm strip. Place one diaphragm strip on a glass slide and use a dropper to apply 3 drops of emulsion to the marked area, ensuring the emulsion is evenly distributed across the test area. Place the diaphragm strip in an oven at 80°C for 5 minutes. After removing it, place one end of the copper foil strip on the test area, ensuring complete coverage. Cover with another glass slide and clamp the test area between the slides with clips. Place in an oven at 120°C for 20 minutes. After cooling, obtain the diaphragm-copper foil test strip. Using this as a standard, bond the remaining strips with emulsions synthesized under different conditions, making one test strip for each condition. Then, cut each strip into three equal parts.

[0064] Replace the kit of the electronic universal testing machine with a fixture, and stretch each sample to test the shear strength of the adhesive.

[0065] Examples 1-20

[0066] This embodiment provides a series of core-shell type acrylic adhesives, the mass fractions of each component in the formulation are shown in Table 1 and Table 2.

[0067] The mass percentage of the shell functional monomer hydroxyethyl methacrylate is 100% × m(hydroxyethyl methacrylate) / (m(hydroxyethyl methacrylate) + m(isooctyl acrylate) + m(styrene)).

[0068] Table 1. Formulations (portions) for Examples 1-10

[0069]

[0070] Table 2 Formulations (parts) for Examples 11-20

[0071]

[0072]

[0073] Comparative Examples 1-19

[0074] This comparative example provides a series of core-shell acrylic adhesives, the mass fractions of each component in the formulation are shown in Table 3.

[0075] Table 3. Formulations (per serving) for Comparative Examples 1–19

[0076]

[0077]

[0078] The performance test results of the core-shell acrylate adhesives in each embodiment according to the methods mentioned above are shown in Table 4.

[0079] Table 4 Performance test results for each embodiment

[0080]

[0081]

[0082] The performance test results of the core-shell acrylate adhesives in each comparative example according to the method mentioned above are shown in Table 5.

[0083] Table 5 Performance test results of each comparative example

[0084]

[0085] As can be seen from Table 4, the core-shell acrylate adhesives prepared in Examples 1 to 20 of the present invention all have excellent bonding performance, high particle size stability and high production efficiency, among which Example 1 has the best overall performance.

[0086] The bonding performance was characterized by the average shear strength (KPa) (diaphragm-copper foil). With the increase of the core-shell ratio of the emulsion, the shear strength of the diaphragm-copper foil system showed a decreasing trend. With the increase of the functional monomer content of the emulsion, the shear strength of the diaphragm-copper foil system generally showed an increasing trend.

[0087] Particle size stability is characterized by a combination of average particle size and polydispersity index. A smaller average particle size and a lower polydispersity index indicate a narrower distribution and better emulsion particle size stability. Experiments show that as the core-shell ratio increases (i.e., as the core content increases), both the average particle size and polydispersity index of the emulsion tend to decrease.

[0088] Acrylic esters with high solid content have advantages such as high production efficiency, low energy consumption, and fast emulsion film formation. Therefore, acrylic esters with high solid content are suitable for commercial use.

[0089] From Comparative Examples 1-19 in Table 5, it can be seen that Comparative Examples 1-16 show that the effect of the monomers being outside the range is worse than that of the examples, illustrating the importance of controlling the proportions. Comparative Examples 9 and 10 show that the effect of the functional monomer content being outside the range is worse. Comparative Examples 17-18 are core-shell ratios that are outside the range. When the core-shell ratio is 1:1, the average particle size of the particles in the emulsion is 142.6 nm. When the amount of hydrophilic monomers in the core is increased (core-shell ratio of 3:1), the average particle size of the particles in the emulsion is 137.5 nm. However, too much will cause the emulsion to break down, that is, the emulsion is completely destroyed and becomes two immiscible phases, and the emulsion is unstable (Comparative Example 18, core-shell ratio of 5:1). Comparative Example 19 uses dimethyldimethoxysilane to replace acryloyloxysilane, and the effect is worse than that of the examples, indicating that acryloyloxysilane can help realize the core-shell type acrylate adhesive of the present invention.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A core-shell type acrylic adhesive, characterized in that, The components include the following parts by weight: Core layer: 20-130 parts acryloyloxysilane, 2-10 parts styrene, 4-20 parts acrylic acid, 1-5 parts divinylbenzene; Shell: 30-75 parts hydroxyethyl methacrylate, 4-15 parts isooctyl acrylate, 4-10 parts styrene, 3-10 parts acrylic acid; The functional monomer hydroxyethyl methacrylate in the shell layer has a mass percentage of 65% to 85% of the shell layer mass. The core-shell ratio is 1:3 to 3:1, where the core-shell ratio is the ratio of the total mass fraction of the core components to the total mass fraction of the shell components.

2. The core-shell acrylic adhesive according to claim 1, characterized in that, The divinylbenzene is selected from one or more of meta-divinylbenzene, ortho-divinylbenzene, or para-divinylbenzene.

3. The core-shell acrylic adhesive according to claim 1, characterized in that, The acryloyloxysilane is one or more of 3-acryloyloxypropylmethyldimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-(methacryloyloxy)propyltrimethoxysilane.

4. A method for preparing the core-shell type acrylic adhesive according to any one of claims 1 to 3, characterized in that, Includes the following steps: The components of the core layer and the components of the shell layer are mixed separately, and emulsifiers and water are added to prepare core pre-emulsions and shell pre-emulsions respectively. The core pre-emulsion and initiator are added sequentially to the emulsion polymerization substrate containing emulsifier, water, and pH buffer and reacted for 8-10 minutes. The shell pre-emulsion is added in small amounts multiple times and reacted at 75-85°C. After adjusting the pH to 7-8, the core-shell type acrylate adhesive is obtained.

5. The method according to claim 4, characterized in that, The emulsifier is at least one of SR-10 anionic emulsifier or OP-10 nonionic emulsifier.

6. The method according to claim 4, characterized in that, The mass fraction of emulsifier added during the preparation of the nuclear preemulsion is 2-6 parts.

7. The method according to claim 4, characterized in that, The mass fraction of emulsifier added during the preparation of the shell preemulsion is 1-4 parts.

8. The method according to claim 4, characterized in that, The pH-adjusting reagent is at least one of ammonia, sodium carbonate, or sodium bicarbonate.

9. The method according to claim 4, characterized in that, The initiator is ammonium persulfate, in parts by weight of 0.8-2 parts.

10. The use of the core-shell type acrylate adhesive according to any one of claims 1 to 3 in bonding lithium-ion battery electrode materials.

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