Binder for conductive paste, preparation method of binder, conductive paste and preparation process of conductive paste

Abstract

The invention discloses a binder for conductive paste, a preparation method of the binder, the conductive paste and a preparation process of the conductive paste. The binder for the conductive paste comprises the following components: polyacrylic acid, carboxylic butadiene-styrene latex and a dynamic cross-linking agent, wherein on the basis of dry weight, the mass ratio of the polyacrylic acid to the carboxylic butadiene-styrene latex is (2-9): 1, and the addition amount of the dynamic cross-linking agent is 0.1%-3% of the total dry weight of the polyacrylic acid and the carboxylic butadiene-styrene latex; the dynamic cross-linking agent is at least one of phenylboronic acid, 4-formyl phenylboronic acid or a water-based polymer containing phenylboronic acid groups. The carbon coating slurry which is water-resistant, high in conductivity, strong in adhesion and suitable for water-based solvents can be constructed.

Description

Technical Field

[0001] This invention relates to a binder for conductive paste and its preparation method, as well as conductive paste and its preparation process. Background Technology

[0002] Currently, in lithium-ion batteries, carbon-coated copper foil is commonly used as the negative electrode current collector to improve performance. The conductive carbon black coating on its surface can reduce the electrode interface resistance, improve current distribution, enhance the bonding strength between the active material and the current collector, and inhibit copper foil corrosion. However, traditional PAA binder systems face the serious challenge of being intolerant to water: the negative electrode slurry is an aqueous slurry system, and if the water resistance of the carbon coating layer is insufficient, it will damage the conductive carbon black coating when the negative electrode slurry is applied, leading to a decrease in coating performance or even failure of coating function; moisture weakens the intermolecular forces of the binder and its bonding force with the substrate, affecting the integrity and conductivity of the coating.

[0003] In existing technologies, PAA is often blended with rubber particles such as carboxylated nitrile butadiene rubber (XNBR) to improve flexibility. However, this relies on a physical hydrogen bond network, which is prone to reversible breakage under continuous water molecule erosion or stress, leading to permanent damage to the network structure. Therefore, there is still room for improvement in water resistance and structural durability. Thus, developing a binder capable of forming a more stable, self-healing network structure is crucial for preparing high-performance water-resistant carbon-coated copper foil. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a binder for conductive paste that can construct a water-resistant, highly conductive, strongly adhesive, and suitable for water-based solvents for carbon coating paste.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a binder for conductive paste, comprising the following components: polyacrylic acid, carboxylated styrene-butadiene latex, and a dynamic crosslinking agent; wherein,

[0006] On a dry weight basis, the mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (2~9):1, and the amount of dynamic crosslinking agent added is 0.1%~3% of the total dry weight of polyacrylic acid and carboxylated styrene-butadiene latex;

[0007] The dynamic crosslinking agent is at least one of phenylboronic acid, 4-formylphenylboronic acid, or an aqueous polymer containing phenylboronic acid groups.

[0008] Furthermore, the mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (4~8):1.

[0009] The present invention also provides a method for preparing an adhesive for conductive paste, the method comprising the following steps:

[0010] After preparation, polyacrylic acid is dissolved in pure water to form a homogeneous solution with a solid content of 15-30%.

[0011] Then, carboxylated styrene-butadiene latex is added to the solution for the first shear dispersion.

[0012] Then add a dynamic crosslinking agent for a second shear dispersion.

[0013] Add an appropriate amount of alkali solution to adjust the pH of the system to 8.5-9.5;

[0014] The system is heated to 50-70°C and stirred after heating to promote dynamic cross-linking reaction, thus obtaining a binder for conductive paste.

[0015] Furthermore, the rotational speed for shear dispersion is 10,000-12,000 rpm.

[0016] Furthermore, the time for the first shear dispersion is 30-50 minutes and / or the time for the second shear dispersion is 10-20 minutes.

[0017] Furthermore, the stirring time is 4-8 hours and / or the stirring speed is 20-50 rpm.

[0018] The present invention also provides a conductive paste containing the following components: a conductive agent, a binder, and a solvent; wherein the binder is the same as the one used in the conductive paste, and the solvent is pure water; the dry weight ratio of the binder to the conductive agent is (4~6):(4~6).

[0019] Furthermore, the conductive agent is conductive carbon black.

[0020] Furthermore, the process includes the following steps:

[0021] The conductive agent is pre-dispersed by mixing it with an appropriate amount of pure water;

[0022] Add binder and add pure water to adjust to the required solid content, then continue dispersing;

[0023] After dispersion, the mixture is ground to obtain a conductive slurry.

[0024] Furthermore, the pre-dispersion parameters are as follows: rotation speed 2000-4000 rpm and / or time 20-40 minutes;

[0025] And / or continue to disperse for 20-40 minutes;

[0026] The grinding and / or polishing process takes 1 to 4 hours.

[0027] After adopting the above technical solution, the basic adhesive of the present invention is formed by physical compounding and dynamic covalent cross-linking process of polyacrylic acid (PAA) and carboxylated styrene-butadiene latex (XSBR). It relies on the hydrogen bond and ionic bond formed between the carboxyl group (-COOH) on the PAA chain and the carboxyl group (-COOH) on the XSBR chain, and additionally introduces a borate ester dynamic cross-linking agent to form reversible borate ester bonds with the hydroxyl group (-OH, partly from the incompletely esterified chain segment) and carboxyl group of PAA and XSBR, thus constructing a three-dimensional dynamic network structure adhesive with high strength, high flexibility and self-healing potential.

[0028] The present invention has the following beneficial effects:

[0029] 1. Superior water resistance and structural durability: The introduction of dynamic covalent bonds (boron ester bonds) forms higher energy and more stable crosslinking points on the basis of traditional hydrogen bond networks. These bonds are stable under normal conditions, giving the coating excellent resistance to water erosion. When subjected to micro-stress, reversible fracture occurs to dissipate energy, and the coating can be reconstituted and repaired after the stress is eliminated, which greatly improves the coating's crack resistance and long-term structural integrity.

[0030] 2. Excellent overall performance: XSBR provides a good foundation of flexibility and adhesion. The synergistic network formed with PAA and dynamic crosslinking agent gives the coating better flexibility while maintaining high peel strength, and can better adapt to the deformation of copper foil during battery manufacturing and use.

[0031] 3. Environmental protection and economy: The entire system uses water as a solvent, requires a small amount of phenylboronic acid crosslinking agent, has controllable costs, and is compatible with existing equipment, making it easy to implement in industrial applications. Detailed Implementation

[0032] This invention provides a binder for conductive pastes and its preparation method, as well as a conductive paste and its preparation process. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of protection of this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0033] A conductive paste binder comprising the following components: polyacrylic acid, carboxylated styrene-butadiene latex, and a dynamic crosslinking agent; wherein,

[0034] On a dry weight basis, the mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (2~9):1, and the amount of dynamic crosslinking agent added is 0.1%~3% of the total dry weight of polyacrylic acid and carboxylated styrene-butadiene latex;

[0035] The dynamic crosslinking agent is at least one of phenylboronic acid, 4-formylphenylboronic acid, or an aqueous polymer containing phenylboronic acid groups.

[0036] In this invention, the amount of carboxylated styrene-butadiene latex is 1 part, and the mass of polyacrylic acid can be selected from the following values: 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts. Of course, it can also be selected within the range of the above values ​​as upper and lower limits. Preferably, the mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (4~8):1.

[0037] The percentage of the total dry weight of polyacrylic acid and carboxylated styrene-butadiene latex added by the dynamic crosslinking agent can be selected from the following values: 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%. Of course, the above values ​​can also be selected within the range of upper and lower limits.

[0038] The present invention also provides a method for preparing an adhesive for conductive paste, the method comprising the following steps:

[0039] After preparation, polyacrylic acid is dissolved in pure water to form a homogeneous solution with a solid content of 15-30%.

[0040] Then, slowly add carboxylated styrene-butadiene latex to the solution, turn on the high-speed shear emulsification equipment, and perform the first shear dispersion.

[0041] Then add a dynamic crosslinking agent for a second shear dispersion.

[0042] Add an appropriate amount of alkali solution to adjust the pH of the system to 8.5-9.5;

[0043] The system is heated to 50-70°C and stirred after heating to promote dynamic cross-linking reaction, thus obtaining a binder for conductive paste.

[0044] Specifically, the rotational speed for shear dispersion is 10,000-12,000 rpm.

[0045] Specifically, the first shear dispersion takes 30-50 minutes; the second shear dispersion takes 10-20 minutes.

[0046] Specifically, the stirring time is 4 to 8 hours and the stirring speed is 20 to 50 rpm.

[0047] The present invention also provides a conductive paste containing the following components: a conductive agent, a binder, and a solvent; wherein the binder is the same as the one used in the conductive paste, and the solvent is pure water; the dry weight ratio of the binder to the conductive agent is (4~6):(4~6).

[0048] In this invention, the dry weight ratio of the binder and the conductive agent can be (4 or 5 or 6): (4 or 5 or 6), or it can be a value selected within the range of upper and lower limits of 4, 5, and 6.

[0049] Specifically, the conductive agent can be conductive carbon black.

[0050] Specifically, the process includes the following steps:

[0051] The conductive agent is pre-dispersed by mixing it with an appropriate amount of pure water;

[0052] Add binder and add pure water to adjust to the required solid content, then continue dispersing;

[0053] After dispersion, the mixture is ground to obtain a conductive slurry.

[0054] Specifically, the pre-dispersion parameters are as follows: rotation speed 2000-4000 rpm, time 20-40 minutes;

[0055] The dispersal period will continue for 20-40 minutes;

[0056] The grinding process takes 1 to 4 hours.

[0057] The basic adhesive of this invention is formed by physical compounding and dynamic covalent crosslinking of polyacrylic acid (PAA) and carboxylated styrene-butadiene latex (XSBR). It relies on the hydrogen bonds and ionic bonds formed between the carboxyl groups (-COOH) on the PAA chain and the carboxyl groups (-COOH) on the XSBR chain, and additionally introduces a borate ester dynamic crosslinking agent to form reversible borate ester bonds with the hydroxyl groups (-OH, partly from incompletely esterified segments) and carboxyl groups of PAA and XSBR, thus constructing a three-dimensional dynamic network structure adhesive with high strength, high flexibility and self-healing potential.

[0058] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments.

[0059] Example 1:

[0060] PAA (Carbosperse™ K-702):XSBR (50% solids content) dry weight ratio = 8:2.

[0061] ① Weigh out 80g of PAA and 20g of XSBR dry matter (corresponding to 40g of emulsion).

[0062] ② Add PAA to 320g of pure water and stir to dissolve.

[0063] ③ Slowly add XSBR emulsion and shear disperse at 11,000 rpm for 40 minutes.

[0064] ④ Add 1.0 g of phenylboronic acid (1% of the dry weight of the base binder), and continue to disperse for 15 minutes.

[0065] ⑤ Add 10% NaOH solution to adjust the pH to 9.0.

[0066] ⑥ Heat up to 60 °C, stir at a speed of 30 rpm for 6 hours to obtain binder A1.

[0067] Preparation of conductive paste: Take 60 g of conductive carbon black (Li-400) and 40 g of binder A1 (dry weight), and prepare a paste with a solid content of 10% according to the preparation process of the conductive paste, and grind for 3 hours. Coat it on a 6-μm copper foil with a surface density of 0.4 g / m², and dry it at 130 °C.

[0068] Performance testing:

[0069] ① Water resistance test: Dip a cotton swab in pure water, with a weight of the weight of 15 g, wipe back and forth on the coating surface for 50 times. After wiping, the coating is intact, and there is no phenomenon of copper exposure due to damage, which is qualified. The equipment is the wire wool abrasion resistance tester of Shenzhen Zhijia Equipment Co., Ltd.

[0070] ② Adhesive strength: Test the bonding force between the coating and the copper foil through a 3M600 tape and 180° peel strength. The equipment is the microcomputer-controlled electronic universal testing machine of MTS Industry System (China) Co., Ltd.

[0071] ③ Conductivity: Measure the film resistance, and the equipment is the four-probe film resistance meter of Chuanyuan Technology.

[0072] ④ Flexibility test: Take a sample of the dried carbon-coated copper foil with a width of 30 mm and a length of 150 mm, and wind it flat with the coating facing outwards on a mandrel with an outer diameter of 1 mm and a length of 300 mm. Clamp both ends of the mandrel and bend it by 10°, hold for 5 seconds, and conduct the bending test 10 times. Unwind the copper foil and observe it under a microscope at a magnification of 20 times.

[0073] ⑤ Electrolyte resistance test: Dip a cotton swab in the electrolyte (Shenghua New Material SHNL-2401 electrolyte), with a weight of the weight of 15 g, wipe back and forth on the coating surface for 50 times. After wiping, the coating is intact, and there is no phenomenon of copper exposure due to damage, which is qualified. The equipment is the wire wool abrasion resistance tester of Shenzhen Zhijia Equipment Co., Ltd.

[0074] Examples 2-9: Comparison of different mass ratios of PAA and XSBR

[0075] Fix the dynamic crosslinking agent as phenylboronic acid, with an addition amount of 1% of the dry weight of the base binder, the dry weight ratio of the binder to the conductive carbon black is 4:6, and the coating surface density is 0.4 g / m².

[0076] Example 2: PAA:XSBR dry weight ratio = 9:1. Example 3: PAA:XSBR dry weight ratio = 8:1. The preparation method is the same as in Example 1, with corresponding adjustments to the raw material amounts.

[0077] Example 4: PAA:XSBR dry weight ratio = 7:1. The preparation method is the same as in Example 1, with the raw material amounts adjusted accordingly.

[0078] Example 5: PAA:XSBR dry weight ratio = 6:1. The preparation method is the same as in Example 1, with the raw material amounts adjusted accordingly.

[0079] Example 6: PAA:XSBR dry weight ratio = 5:1. The preparation method is the same as in Example 1, with the raw material amounts adjusted accordingly.

[0080] Example 7: PAA:XSBR dry weight ratio = 3:1. The preparation method is the same as in Example 1, with the raw material amounts adjusted accordingly.

[0081] Example 8: PAA:XSBR dry weight ratio = 2:1. The preparation method is the same as in Example 1, with the raw material amounts adjusted accordingly.

[0082] Example 9: Comparison of different types of dynamic crosslinking agents

[0083] The PAA:XSBR dry weight ratio was fixed at 8:1, and the amount of dynamic crosslinking agent added was 1.5% of the dry weight of the base binder. The preparation method was the same as in Example 1.

[0084] Example 9-1: Using phenylboronic acid as a dynamic crosslinking agent.

[0085] Example 9-2: Using 4-formylphenylboronic acid as a dynamic crosslinking agent.

[0086] Example 9-3: An aqueous solution of an acrylic copolymer containing phenylboronic acid groups (20% solids content, 5% phenylboronic acid group content) was used as a dynamic crosslinking agent.

[0087] Examples 10-11: Comparison of different amounts of dynamic crosslinking agent

[0088] The PAA:XSBR dry weight ratio was fixed at 6:1, and the preparation method was the same as in Example 1.

[0089] Example 10: The amount of phenylboronic acid added was 0.2% (low addition amount).

[0090] Example 11: The amount of phenylboronic acid added was 2.5% (high addition amount).

[0091] Example 12: Comparison of changes in the ratio of adhesive to conductive agent.

[0092] The PAA:XSBR dry weight ratio was fixed at 7:1, the amount of phenylboronic acid added was 1%, and the preparation method was the same as in Example 1.

[0093] Example 12-1: The dry weight ratio of binder to conductive carbon black is 4.5:5.5.

[0094] Example 12-2: Adhesive: Conductive carbon black dry weight ratio = 5.5:4.5.

[0095] Example 13: Optimization of process parameters.

[0096] PAA:XSBR dry weight ratio = 8:2, phenylboronic acid addition amount is 1%, preparation method is the same as in Example 1.

[0097] Adjustments in the preparation process: In step ⑤, the temperature is raised to 65℃ and stirred at 40 rpm for 5 hours.

[0098] Drying conditions after coating: Segmented drying is adopted, first drying at 100℃ for 1 minute, then increasing to 140℃ for 2 minutes.

[0099] Comparative Example 1 (Blank Comparison)

[0100] PAA:XSBR dry weight ratio = 8:2, no dynamic crosslinking agent added, otherwise the same as in Example 1.

[0101] Comparative Example 2 (Pure PAA Comparison)

[0102] Pure PAA was used as the binder, and the amount added was the same as the total dry weight of the binder in Example 1. No XSBR or dynamic crosslinking agent was added.

[0103] Comparative Example 3 (Comparison with Traditional Crosslinking Agents)

[0104] PAA:XSBR dry weight ratio = 8:2, using the traditional irreversible crosslinking agent aziridine (addition amount 1%) instead of phenylboronic acid, the rest is the same as in Example 1.

[0105] Comparative Example 4 (Comparison of different rubber matrices)

[0106] Carboxylated acrylonitrile butadiene rubber (XNBR) emulsion was used instead of XSBR, the PAA:XNBR dry weight ratio was 8:2, the amount of phenylboronic acid added was 1%, and the rest was the same as in Example 1.

[0107] Comparative Example 5 (proportion outside the range)

[0108] PAA:XSBR dry weight ratio = 1:1, phenylboronic acid addition amount is 1%, the rest is the same as in Example 1.

[0109] Performance test results:

[0110]

[0111] Conclusion Analysis:

[0112] 1. Effectiveness of the formulation: Examples 1-8 show that the coatings exhibit excellent water resistance (no damage after 50 wiping cycles) within a PAA:XSBR ratio range of 2:1 to 9:1. Overall, a ratio between 4:1 and 8:1 results in lower diaphragm resistance (≤2.25mΩ), higher peel strength (≥365 N / M), and good flexibility, representing the preferred range. A ratio that is too low (e.g., Comparative Example 5) leads to a significant increase in resistance; performance declines as the ratio moves towards either extreme.

[0113] 2. The key role of dynamic crosslinking agents: All examples (Examples 1-13) with added phenylboronic acid-based dynamic crosslinking agents showed significantly better water resistance than Comparative Example 1 without the agent, and the peel strength was also generally improved. This demonstrates the decisive role of dynamic covalent networks in enhancing water resistance and interfacial bonding.

[0114] 3. Unique Advantages of Dynamic Crosslinking: Comparative Example 3 uses the traditional irreversible crosslinking agent aziridine, which, although exhibiting high peel strength, results in severe coating embrittlement (bending cracking). In contrast, the dynamic crosslinking agent system of this invention (as in Example 4) maintains excellent flexibility while achieving high peel strength, demonstrating the "combination of rigidity and flexibility" advantage of dynamic covalent bonds. Because ordinary crosslinking agents undergo irreversible reactions during prolonged storage after use, the coating formed by the binder using this crosslinking agent becomes a dense, indestructible film, affecting subsequent processing. Since the anode slurry applied later is water-based, this film causes the carbon coating layer and the anode slurry to become isolated, increasing interfacial resistance and preventing effective fusion and communication. The dynamic bonds of this invention can better accommodate the coating of the anode slurry during subsequent processing, preventing the carbon coating layer from failing to form an effective bond with the anode slurry after film formation and creating more conductive pathways, thereby improving peel strength and conductivity.

[0115] 4. Preferred use of XSBR: Comparing Example 2 and Comparative Example 4, under the same PAA:rubber ratio and the same dynamic crosslinking agent, the system using XSBR is superior to the system using XNBR in terms of conductivity (2.20 vs 2.38 mΩ) and water resistance (no damage vs slight powdering), demonstrating that XSBR has a better synergistic effect in constructing dynamic networks with PAA and phenylboronic acid.

[0116] 5. Process and Component Optimization: Example 13 achieved better peel strength (405 N / M) and conductivity (2.10 mΩ) by optimizing the process (temperature, segmented drying). Example 12 shows that a better balance between performance can be achieved by appropriately adjusting the ratio of binder to conductive agent.

[0117] In summary, this invention successfully constructs a dynamic covalent network by introducing a phenylboronic acid-based dynamic crosslinking agent into the PAA / XSBR composite system. Numerous systematic examples and comparative examples fully demonstrate that this invention can stably prepare carbon-coated copper foils with excellent water resistance, high conductivity, strong adhesion, and good flexibility within a PAA:XSBR ratio range of 2:1 to 9:1, a dynamic crosslinking agent addition range of 0.1% to 3%, and a binder to conductive agent ratio range of 4:6 to 6:4. In particular, a PAA:XSBR ratio between 4:1 and 8:1 is the preferred solution, significantly surpassing traditional physical blending systems and comparative solutions using other types of rubber or crosslinking agents, demonstrating outstanding innovation and industrial application value.

[0118] The specific embodiments described above further illustrate the technical problems, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A binder for conductive pastes, characterized in that, Its components are as follows: polyacrylic acid, carboxylated styrene-butadiene latex, and dynamic crosslinking agent; among which, On a dry weight basis, the mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (2~9):1, and the amount of dynamic crosslinking agent added is 0.1%~3% of the total dry weight of polyacrylic acid and carboxylated styrene-butadiene latex; The dynamic crosslinking agent is at least one of phenylboronic acid, 4-formylphenylboronic acid, or an aqueous polymer containing phenylboronic acid groups.

2. The binder for conductive paste according to claim 1, characterized in that: The mass ratio of polyacrylic acid to carboxylated styrene-butadiene latex is (4~8):

1.

3. A method for preparing an adhesive for conductive paste as described in claim 1 or 2, characterized in that... The method includes the following steps: After preparation, polyacrylic acid is dissolved in pure water to form a homogeneous solution with a solid content of 15-30%. Then, carboxylated styrene-butadiene latex is added to the solution for the first shear dispersion. Then add a dynamic crosslinking agent for a second shear dispersion. Add an appropriate amount of alkali solution to adjust the pH of the system to 8.5-9.5; The system is heated to 50-70°C and stirred after heating to promote dynamic cross-linking reaction, thus obtaining a binder for conductive paste.

4. The preparation method according to claim 3, characterized in that, The rotational speed for shear dispersion is 10,000-12,000 rpm.

5. The preparation method according to claim 3, characterized in that, The first shear dispersion takes 30-50 minutes and / or the second shear dispersion takes 10-20 minutes.

6. The preparation method according to claim 3, characterized in that, The stirring time is 4 to 8 hours and / or the stirring speed is 20 to 50 rpm.

7. A conductive paste, characterized in that, The components are as follows: conductive agent, binder and solvent; wherein the binder is the conductive paste binder as described in claim 1 or 2, and the solvent is pure water; the dry weight ratio of the binder and the conductive agent is (4~6):(4~6).

8. The conductive paste according to claim 7, characterized in that, The conductive agent is conductive carbon black.

9. The preparation process according to claim 7, characterized in that... The process includes the following steps: The conductive agent is pre-dispersed by mixing it with an appropriate amount of pure water; Add binder and add pure water to adjust to the required solid content, then continue dispersing; After dispersion, the mixture is ground to obtain a conductive slurry.

10. The preparation process according to claim 9, characterized in that, The pre-dispersion parameters are as follows: rotation speed 2000-4000 rpm and / or time 20-40 minutes; And / or continue to disperse for 20-40 minutes; The grinding and / or polishing process takes 1 to 4 hours.

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