A lithium battery negative electrode binder and a preparation method thereof

Abstract

The application discloses a lithium battery negative electrode adhesive and a preparation method thereof. The adhesive is prepared from acrylic acid and derivatives thereof, a polyacrylate macromolecular emulsifier, cross-linking monomers, an initiator and water. The preparation method comprises the following steps: putting water into a reaction device, starting stirring, adding the macromolecular emulsifier, adjusting the pH of the system to 7-9, adding polymerization monomers and cross-linking monomers, adjusting the pH of the system to 7-9 again, stirring and emulsifying, and passing in nitrogen; the temperature is increased to 55-80 DEG C, constant temperature stirring is kept, and part of an aqueous initiator solution is added at a constant speed under the nitrogen atmosphere to start polymerization reaction, the duration of the constant speed adding of the initiator is 8-16 hours; after the constant speed adding is finished, the remaining aqueous initiator solution is supplemented, and the reaction is continuously carried out for 1-3 hours to obtain the adhesive product. The adhesive has the advantages of strong adhesive force and good water resistance, is beneficial to bearing the volume expansion of a lithium battery negative electrode containing a silicon-based active substance in a charge-discharge cycle, and improves the service life of the battery.

Description

Technical Field

[0001] This invention relates to the field of adhesives for lithium battery anodes containing silicon-based active materials, and specifically to a polyacrylate emulsion adhesive containing a polyacrylate macromolecular emulsifier and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, small electronic products, and energy storage devices, and market demands for their capacity, lifespan, and other performance characteristics are constantly increasing. As one of the four main components of a battery, the negative electrode is currently made of graphite, with a theoretical specific capacity of approximately 327 mAh / g. This performance is increasingly insufficient to meet market and policy demands for high-energy-density lithium-ion batteries. Research has found that silicon, as a negative electrode active material, has a theoretical capacity more than 10 times that of graphite (4200 mAh / g), and is also abundant and inexpensive, showing significant application potential. However, silicon-based materials experience substantial volume expansion and contraction (up to 400%) during charging and discharging due to lithium-ion insertion and extraction, far exceeding that of graphite. This makes the battery negative electrode structure easily damaged during charge-discharge cycles, thus impairing battery life. Currently, to balance the contradiction between battery capacity and the expansion of silicon-based anodes, most technologies choose to use graphite as the main material while blending in a certain proportion of silicon-based anode materials. This increases capacity while avoiding excessive expansion. However, even the addition of a small amount of silicon-based material still causes a significant expansion problem that urgently needs to be addressed. Besides the active material, the main components of a lithium-ion battery anode include conductive agents and binders. The binder bonds the active material and conductive agent together and attaches them as a whole to the current collector, making it one of the key materials for ensuring the stability of the lithium-ion battery anode structure during charge-discharge cycles.

[0003] Polyvinylidene fluoride (PVDF) was a mainstream anode binder in the early stages of lithium battery development. Dispersed in the organic solvent N-methylpyrrolidone, it was considered an oil-based binder. Later, more environmentally friendly water-based binders gradually became the mainstream products in the market. Currently, the main water-based anode binder on the market is styrene-butadiene latex (SBR), which is copolymerized from styrene, butadiene, and a small amount of functional monomers. Although SBR can meet the requirements for anodes made from graphite materials, its main body has fewer polar functional groups, and the interaction force between it and silicon-based materials is insufficient to cope with the latter's volume expansion. Furthermore, its mechanical properties are relatively soft, making it less suitable for anodes containing silicon-based active materials. Polyacrylate (PAA) adhesives are a relatively new type of waterborne adhesive for negative electrodes. Depending on the type of monomer, they possess different types of polar functional groups (carboxyl, amino, nitrile, etc.), which can form strong interactions such as chemical bonds and hydrogen bonds with the functional groups (mainly hydroxyl groups) on the surface of silicon-based negative electrodes. They also have strong mechanical properties and are more advantageous in withstanding the expansion of silicon-based active materials. Therefore, PAA adhesives are gradually becoming a type of waterborne adhesive suitable for negative electrodes containing silicon-based active materials.

[0004] PAA adhesives are mainly divided into two categories: emulsion type and solution type. Solution-type adhesives can only use water-soluble monomer raw materials, which limits the use of functional non-water-soluble monomers, restricts their various properties, and also results in strong water absorption, which is detrimental to the performance of the prepared lithium batteries. Emulsion-type adhesives have a wider range of applications, but they generally require the addition of emulsifiers during their preparation. Traditional small-molecule emulsifiers can migrate to the surface of the negative electrode during the film formation process after electrode coating, causing problems such as decreased adhesion and easy water absorption. How to solve the above problems caused by small-molecule emulsifiers is a major problem for PAA emulsion adhesives, and various technologies have been developed to solve this problem.

[0005] Patent documents ZL01108511.8 and ZL01108524.X use soap-free emulsion technology (i.e., emulsion polymerization technology without emulsifiers or with trace amounts of emulsifiers) to prepare PAA emulsion-type emulsifiers. However, the stability of soap-free emulsion polymerization is relatively poor, and it is difficult to prepare soap-free emulsions with high solid content. Patent document CN110364735 uses reactive emulsifiers to prepare PAA emulsion products without free small molecule emulsifiers, which improves the product's adhesion, water resistance, and processing performance. However, the addition of reactive emulsifiers introduces new structures into the PAA molecular chain, affecting the designability of its performance.

[0006] Macromolecular emulsifiers that are neither free-floating nor affect the main structure of the adhesive are a highly promising option. Patent document CN105131875 uses a water-soluble macromolecular cellulose-grafted amphiphilic copolymer as a dispersant in polymerization to replace the emulsifier in preparing an aqueous electrode adhesive. However, the dispersant mainly plays a dispersing role and cannot completely replace the emulsifier in providing the environment for emulsion polymerization. Furthermore, the macromolecular cellulose-grafted amphiphilic copolymer has a significantly different bulk structure from the PAA adhesive, inevitably affecting the adhesive's bonding strength and other properties, impacting the structural stability of the electrode during subsequent battery cycles, and resulting in a shorter battery life. Summary of the Invention

[0007] This invention aims to provide a lithium battery negative electrode emulsion-type PAA adhesive suitable for silicon-based active materials and its preparation method. The system introduces a self-made PAA-type macromolecular emulsifier, which avoids the emulsifier seepage that occurs after the adhesive dries when using traditional small-molecule emulsifiers, thus preventing the adverse effects of the above situation on adhesion and water resistance. At the same time, this type of macromolecular emulsifier and the PAA adhesive body are of the same type of substance, and the two have good compatibility. Moreover, it has a relatively low glass transition temperature, which ensures that the adhesive maintains high adhesion while having relatively more flexible mechanical properties.

[0008] The emulsion-type lithium battery negative electrode binder of the present invention is made from the following raw materials in the indicated weight proportions:

[0009] 100 parts of monomer A;

[0010] Crosslinking monomer 0.5–3.0 parts;

[0011] 3-5 parts of PAA-type macromolecular emulsifier;

[0012] Initiator A1 – 3 parts;

[0013] 190-250 parts pure water;

[0014] The polymer monomer A is acrylic acid and its derivatives, and the macromolecular emulsifier is a polyacrylate macromolecular emulsifier.

[0015] Polymer monomer A includes at least two of the following: acrylic acid, methacrylic acid, methyl methacrylate, styrene, methylstyrene, acrylonitrile, isobornyl methacrylate, cyclohexyl methacrylate, isopropyl methacrylate, n-butyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, n-octyl acrylate, isooctyl acrylate, sodium acrylate, sodium methacrylate, lithium acrylate, lithium methacrylate, acrylamide, methacrylamide, vinyl acetate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0016] The crosslinking monomers include at least one of glycidyl acrylate, glycidyl methacrylate, allyl methacrylate, diallyl phthalate, and N,N-bis(hydroxymethyl)acrylamide;

[0017] Initiator A includes at least one of ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide;

[0018] The method for preparing emulsion-type lithium battery negative electrode binder according to the present invention includes the following steps:

[0019] Step 1: Add distilled water or deionized water to the reaction apparatus, turn on the stirrer (speed 100-200 rpm), add macromolecular emulsifier, and add pH buffer lithium hydroxide to adjust the pH of the system to 7-9.

[0020] Step 2: Add monomer A and crosslinking monomer, adjust the pH of the system to 7-9 again, and stir to emulsify for 30-60 minutes;

[0021] Step 3: Purge with nitrogen gas for 0.5–1.5 hours;

[0022] Step 4: Raise the reaction temperature to 55-80℃ and keep it constant while stirring. Under a nitrogen atmosphere, add 80-90% of the aqueous solution (20% concentration) of initiator A at a uniform rate to start the polymerization reaction. The duration of uniform initiator addition is 8-16 hours.

[0023] Step 5: After the uniform addition is completed, add the remaining 10-20% of the aqueous solution (20% concentration) of initiator A, and continue the reaction for 1-3 hours to obtain the adhesive product; under normal circumstances, the initiators in steps 4 and 5 are distributed according to the mass ratio.

[0024] Step 6: After the reaction is complete, cool and collect the material.

[0025] The PAA-type macromolecular emulsifier of this invention is made from the following raw materials in the indicated weight proportions:

[0026] 100 parts of monomer B;

[0027] Initiator B1 – 5 parts;

[0028] Solvent: 100-200 parts;

[0029] The polymer monomer B includes at least two of acrylic acid, methacrylic acid, methyl methacrylate, styrene, methylstyrene, n-butyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylonitrile, isobutyl acrylate, isooctyl acrylate, and dimethylaminoethyl methacrylate, thereby making the PAA-type macromolecular emulsifier have better overall performance.

[0030] Initiator B includes at least one of azobisisoheptanenitrile, azobisisobutyronitrile, benzoyl peroxide, cumene hydroperoxide, tert-butyl peroxyisooctanoate, and di-tert-butyl peroxide.

[0031] Solvents include one of ethyl acetate, n-butanol, diethylene glycol dimethyl ether, and dimethyl maleate.

[0032] This macromolecular emulsifier has amphiphilic properties, with its lipophilic end binding more firmly to the polymer inside the latex particles and its hydrophilic end extending into the water to promote the dispersion of the latex particles. At the same time, its macromolecular structure makes it less free, and the adhesive does not tend to accumulate on the surface like small molecule emulsifiers after drying. This avoids the problems of poor water resistance and poor adhesion caused by the surface accumulation of small molecule emulsions in conventional emulsion-type PAA adhesives.

[0033] This macromolecular emulsifier and the applicable adhesives are both PAA-based, exhibiting good compatibility. Furthermore, this macromolecular emulsifier is a copolymer with a glass transition temperature of 0–50°C. Its relatively low glass transition temperature is beneficial for improving the final adhesive strength and flexibility of the adhesive.

[0034] The preparation steps of the PAA-type macromolecular emulsifier described in this invention are as follows:

[0035] Step 1: Add the reaction solvent to the reactor equipped with a reflux condenser and turn on the stirrer (speed 100-200 rpm);

[0036] Step 2: Add monomer B to the reactor, purge with nitrogen for at least 30 minutes, and heat to 65–120°C;

[0037] Step 3: Add initiator B to the reactor and maintain a constant temperature with stirring. The reaction time is 4-8 hours.

[0038] Step 4: After the reaction is complete, the reaction system is subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Then, distilled water is added, and the mixture is stirred for 30-60 minutes before drying to obtain PAA-type macromolecular emulsifier.

[0039] Nitrogen gas is introduced during the preparation of macromolecular emulsifiers to remove oxygen and avoid the adverse effects of oxygen on the activity of the initiator.

[0040] The beneficial effects of this invention are as follows: By introducing a self-made PAA-type macromolecular emulsifier to replace the conventional small-molecule emulsifier, the problem of adverse effects on adhesion and water resistance caused by the seepage of small-molecule emulsifiers after drying of conventional emulsion adhesives is improved, resulting in a PAA adhesive with strong adhesion and good water resistance. Simultaneously, this type of macromolecular emulsifier and the PAA adhesive body are of the same type of substance, exhibiting good compatibility compared to other types of macromolecular emulsifiers, with minimal impact on the adhesive's bonding effect. Furthermore, the external PAA emulsifier layer has a low glass transition temperature (0–50°C), which can enhance the final adhesive's adhesion and flexibility to a certain extent. These characteristics make this PAA adhesive beneficial for withstanding the volume expansion of silicon-based active material lithium battery anodes during charge-discharge cycles, improving battery life, and is particularly suitable for silicon-based active material lithium battery anodes. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] Example 1

[0043] A method for preparing a PAA binder suitable for lithium-ion battery anodes containing silicon-based active materials includes the following steps:

[0044] 1. Preparation of macromolecular emulsifier: 20g of ethyl acetate was added to a reactor equipped with a reflux condenser, and stirring was started (120 rpm). 6g of methacrylic acid, 2g of hydroxyethyl methacrylate, 5g of isobutyl acrylate, and 7g of styrene were added to the reactor, nitrogen gas was introduced for 30 min, and the temperature was raised to 70℃. Then, 1g of azobisisobutyronitrile was added to the reactor, and the mixture was stirred at a constant temperature for 4.5 h. After the reaction was completed, the reaction system was subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Distilled water was then added, and the mixture was stirred for 30 min before drying to obtain a PAA-type macromolecular emulsifier.

[0045] 2. Preparation of negative electrode binder: 196g of pure water was added to the reaction apparatus, and stirring was started (120 rpm). 3g of the macromolecular emulsifier prepared above was added, and lithium hydroxide was added to adjust the pH of the system to 7.5. 15g of methacrylic acid, 75g of methyl methacrylate, 10g of cyclohexyl methacrylate, and 1g of glycidyl acrylate were added. The pH of the system was adjusted to 7.5 again, and the mixture was stirred and emulsified for 40 minutes. After purging with nitrogen for 1 hour, the temperature was raised to 70℃. Under a nitrogen atmosphere, 4g of an aqueous solution containing 0.8g of ammonium persulfate (i.e., 20% concentration) was added at a uniform rate using a push pump, and the addition was continued for 10 hours. Afterward, 1g of an aqueous solution containing 0.2g of ammonium persulfate was added, and the reaction was continued at a constant temperature for 1.5 hours. After the reaction was completed, the material was cooled and collected.

[0046] Example 2

[0047] A method for preparing a PAA binder suitable for lithium-ion battery anodes containing silicon-based active materials includes the following steps:

[0048] 1. Preparation of macromolecular emulsifier: 25g of n-butanol was added to a reactor equipped with a reflux condenser, and stirring was started (150 rpm); 4g of methacrylic acid, 11g of isooctyl acrylate, and 5g of methylstyrene were added to the reactor, nitrogen gas was introduced for 30 min, and the temperature was raised to 95℃; then 0.8g of azobisisobutyronitrile was added to the reactor, and the reaction was carried out for 6 h. After the reaction was completed, the reaction system was subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Then distilled water was added, stirred for 40 min, and dried to obtain PAA-type macromolecular emulsifier.

[0049] 2. Preparation of negative electrode binder: 197g of pure water was added to the reaction apparatus, and stirring was started (110 rpm). 3.5g of the macromolecular emulsifier prepared above was added, and lithium hydroxide was added to adjust the pH of the system to 8. 11g of methacrylic acid, 22g of acrylamide, 50g of isobornyl methacrylate, 17g of n-butyl acrylate, and 2g of allyl methacrylate were added. The pH of the system was adjusted to 8 again, and the mixture was stirred and emulsified for 35 minutes. After purging with nitrogen for 1 hour, the temperature was raised to 80℃. Under a nitrogen atmosphere, 6g of an aqueous solution containing 1.2g of ammonium persulfate was added at a uniform rate using a pusher pump, and the addition was continued for 10 hours. Afterward, 1.5g of an aqueous solution containing 0.3g of ammonium persulfate was added, and the reaction was continued at a constant temperature for 1 hour. After the reaction was completed, the material was cooled and collected.

[0050] Example 3

[0051] A method for preparing a PAA binder suitable for lithium-ion battery anodes containing silicon-based active materials includes the following steps:

[0052] 1. Preparation of macromolecular emulsifier: 30g of diethylene glycol dimethyl ether was added to a reactor equipped with a reflux condenser, and stirring was started (170 rpm); 4g of acrylic acid, 7g of n-butyl acrylate, 4g of acrylonitrile, and 5g of styrene were added to the reactor, nitrogen gas was introduced for 30 min, and the temperature was raised to 105℃; then 0.5g of tert-butyl peroxyisooctanoate was added to the reactor, and the reaction was carried out for 5 h. After the reaction was completed, the reaction system was subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Then distilled water was added, stirred for 50 min, and dried to obtain PAA-type macromolecular emulsifier.

[0053] 2. Preparation of negative electrode binder: 212g of pure water was added to the reaction apparatus, and stirring was started (150 rpm). 3.2g of the macromolecular emulsifier prepared above was added, and lithium hydroxide was added to adjust the pH of the system to 8.5. 10g of acrylic acid, 58g of methylstyrene, 16g of isopropyl methacrylate, 16g of acrylonitrile, and 1.5g of N,N-di(hydroxymethyl)acrylamide were added. The pH of the system was adjusted to 8.5 again, and the mixture was stirred and emulsified for 45 minutes. After purging with nitrogen for 1.2 hours, the temperature was raised to 60℃. Under a nitrogen atmosphere, 8g of an aqueous solution containing 1.6g of ammonium persulfate was added at a uniform rate using a pusher pump over a period of 15 hours. Then, 2g of an aqueous solution containing 0.4g of ammonium persulfate was added, and the reaction was continued at a constant temperature for 3 hours. After the reaction was completed, the mixture was cooled and the material was collected.

[0054] Example 4

[0055] A method for preparing a PAA binder suitable for lithium-ion battery anodes containing silicon-based active materials includes the following steps:

[0056] 1. Preparation of macromolecular emulsifier: 33g of dimethyl maleate was added to a reactor equipped with a reflux condenser, and stirring was started (180 rpm); 4g of acrylic acid, 9g of n-butyl acrylate, 4g of methyl methacrylate, and 3g of acrylonitrile were added to the reactor, nitrogen gas was introduced for 30 min, and the temperature was raised to 110℃; then 0.3g of di-tert-butyl peroxide was added to the reactor, and the reaction was carried out for 7 h. After the reaction was completed, the reaction system was subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Then distilled water was added, stirred for 50 min, and dried to obtain PAA-type macromolecular emulsifier.

[0057] 2. Preparation of negative electrode binder: 224.15g of pure water was added to the reaction apparatus, and stirring was started (180 rpm). 3.7g of the macromolecular emulsifier prepared above was added, and lithium hydroxide was added to adjust the pH of the system to 8.9. 11g of acrylic acid, 56g of styrene, 15g of vinyl acetate, 18g of acrylonitrile, and 2.5g of glycidyl acrylate were added, and the pH of the system was adjusted to 8.9 again. The mixture was stirred for 55 min. After purging with nitrogen for 1.5 h, the temperature was raised to 75℃. Under a nitrogen atmosphere, 9g of an aqueous solution containing 1.8g of ammonium persulfate was added at a uniform rate using a pusher pump over a period of 12 h. Then, 2.1g of an aqueous solution containing 0.42g of ammonium persulfate was added, and the reaction was continued at a constant temperature for 2 h. After the reaction was completed, the mixture was cooled and the material was collected.

[0058] Comparative Example 1

[0059] Except for using the conventional small molecule emulsifier sodium dodecyl sulfate instead of the self-made PAA macromolecular emulsifier, the aqueous lithium battery negative electrode PAA binder was prepared in the same manner as in Example 1.

[0060] Comparative Example 2

[0061] Except for using the macromolecular emulsifier polyisobutylene succinimide instead of the self-made PAA macromolecular emulsifier, an aqueous lithium battery negative electrode PAA binder was prepared in the same manner as in Example 1.

[0062] Comparative Example 3

[0063] Except for using the macromolecular emulsifier allyloxy fatty alcohol polyoxyethylene ether instead of the self-made PAA macromolecular emulsifier, the aqueous lithium battery negative electrode PAA binder was prepared in the same manner as in Example 1.

[0064] Comparative Example 4

[0065] A commercially available PAA emulsion adhesive was purchased and compared with the adhesive of this invention.

[0066] Comparative Example 5

[0067] A commercially available SBR emulsion adhesive was purchased and compared with the adhesive of this invention.

[0068] Application Example 1

[0069] A negative electrode sheet composed of silicon-carbon materials and graphite materials was prepared using conventional methods in the art:

[0070] Graphite material (350mAh / g) and silicon-carbon material (1650mAh / g) were mixed in a mass ratio of 12:1 to obtain a negative electrode active material with a specific capacity of approximately 450mAh / g.

[0071] The emulsion-type binders obtained in Examples 1-4 and Comparative Examples 1-5 were respectively mixed with the negative electrode active material, carbon powder, sodium carboxymethyl cellulose, emulsion-type binder (solid mass), and deionized water in a disperser at a mass ratio of 95:2:1:2:100 to obtain a lithium battery negative electrode slurry. The above slurry was uniformly coated on the surface of copper foil with a thickness of about 150 μm, dried at 80°C, and rolled to obtain a lithium battery negative electrode sheet.

[0072] Application Example 2

[0073] According to conventional methods in the art, the emulsion-type adhesives obtained in Examples 1-4 and Comparative Examples 1-5 were used to assemble the lithium battery negative electrode sheet prepared in Application Example 1 into an aluminum-plastic film soft-pack battery, which was then used for battery charge-discharge cycle testing.

[0074] Experiment Example 1 Performance Test

[0075] The peel strength and moisture content of the lithium battery negative electrode sheets prepared according to Application Example 1 were tested using the emulsion-type adhesives obtained in Examples 1-4 and Comparative Examples 1-5 as described above. The testing methods are as follows:

[0076] 1. The 90° coating peel strength was tested according to the method described in GB / T2792-2014.

[0077] 2. After drying, the negative electrode sheet was left to stand for 24 hours at room temperature with a relative humidity of 60%, and the moisture content was tested using a Karl Fischer moisture meter.

[0078] Table 1. Results of peel strength and moisture content tests

[0079] Sample group Peel strength (N / m) Moisture content (ppm) Example 1 190 1320 Example 2 184 1298 Example 3 187 1340 Example 4 188 1312 Comparative Example 1 162 1814 Comparative Example 2 172 1344 Comparative Example 3 174 1351 Comparative Example 4 166 1750 Comparative Example 5 153 1782

[0080] As shown in Table 1, the emulsion-type PAA adhesives for lithium-ion battery anodes prepared using the method described in Examples 1-4, suitable for silicon-based active materials, have a more favorable surface structure for bonding silicon-based active materials compared to the SBR emulsion-type adhesive represented by Comparative Example 5, resulting in higher peel strength. Furthermore, the lithium-ion battery anode emulsion-type PAA adhesives prepared in Examples 1-4, compared to the PAA emulsion-type adhesives containing conventional small-molecule emulsifiers represented by Comparative Examples 1 and 4, and the SBR emulsion-type adhesive represented by Comparative Example 5, exhibit superior peel strength. The system does not contain small molecule emulsifiers that easily migrate to the surface of the cured adhesive, resulting in a lower water content in the prepared negative electrode sheet and thus a significantly higher coating peel strength. Compared with the adhesives containing non-PAA type macromolecular emulsifiers represented by Comparative Examples 2 and 3, the lithium battery negative electrode emulsion-type PAA adhesives prepared in Examples 1-4 still have higher peel strength. This may be due to the good compatibility between its emulsifier and the adhesive body, and the fact that PAA type emulsifiers themselves also have stronger adhesion to lithium battery negative electrode materials containing silicon-based active materials.

[0081] The soft-pack batteries prepared according to Application Example 2 in the above embodiments and comparative examples were subjected to charge-discharge cycle tests using a battery testing system. The performance test results of the prepared lithium-ion batteries are as follows:

[0082] Table 2 Battery performance test results

[0083] Sample group Initial discharge specific capacity (mAh·g) Capacity retention rate after 100 cycles (%) Capacity retention rate after 300 cycles (%) Example 1 450.3 97.9％ 95.8％ Example 2 448.7 98.2％ 95.7％ Example 3 449.2 98.1％ 95.3％ Example 4 447.4 97.7％ 95.2％ Comparative Example 1 449.0 95.0％ 91.7％ Comparative Example 2 446.2 96.3％ 93.3％ Comparative Example 3 448.1 96.5％ 93.1％ Comparative Example 4 451.5 95.6％ 92.2％ Comparative Example 5 445.2 93.1％ 90.4％

[0084] As shown in Table 2, the emulsion-type PAA adhesives for lithium-ion battery anodes prepared using the method described in Examples 1-4, which are suitable for silicon-based active materials, are superior to the SBR emulsion-type adhesives represented by Comparative Example 5, likely due to the presence of additional functional groups that interact with silicon-based active materials. This results in stronger adhesion, and the assembled aluminum-plastic film soft-pack lithium-ion batteries exhibit significantly better long-term cycle performance. Compared to the PAA emulsion-type adhesives containing conventional small-molecule emulsifiers represented by Comparative Examples 1 and 4, the lithium-ion battery anode emulsion-type PAA adhesives prepared in Examples 1-4 do not contain free emulsifiers, resulting in stronger adhesion. Furthermore, the external PAA emulsifier layer enhances its adhesion and flexibility to a certain extent, making it more resistant to the volume expansion of silicon-based active materials during long-term cycling, thus leading to better capacity retention. Compared to the PAA emulsion adhesives containing non-PAA type macromolecular emulsifiers represented by Comparative Examples 2 and 3, the lithium battery negative electrode emulsion PAA adhesives prepared in Examples 1-4 have better compatibility because the emulsifier and adhesive are of the same type of material. In addition, the emulsifier layer improves its adhesion and flexibility to a certain extent, so it can better withstand the volume expansion of silicon-based active materials during long-term cycling, and therefore its capacity retention is also better.

[0085] In summary, the present invention provides an emulsion-type PAA adhesive suitable for lithium-ion battery anodes containing silicon-based active materials. By introducing a self-made PAA-type macromolecular emulsifier to replace the traditional small-molecule emulsifier, it improves the problem of adverse effects on adhesion and water resistance caused by the seepage of small-molecule emulsifiers after drying in conventional emulsion adhesives. This results in a PAA adhesive with strong adhesion and good water resistance. Furthermore, this macromolecular emulsifier is of the same type as the PAA adhesive itself, exhibiting good compatibility compared to other types of macromolecular emulsifiers, and has minimal impact on the adhesive's bonding effect. Additionally, the external PAA emulsifier layer has a low glass transition temperature (0–50°C), which can enhance the final adhesive's adhesion and flexibility to a certain extent. These characteristics make this PAA adhesive suitable for withstanding the volume expansion of silicon-based active material lithium-ion battery anodes during charge-discharge cycles, improving battery life, and making it suitable for lithium-ion battery anodes containing silicon-based active materials.

[0086] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A lithium battery negative electrode adhesive, characterized in that, Made from the following ingredients by weight: 100 parts of monomer A; Crosslinking monomer 0.5–3.0 parts; 3-5 parts of macromolecular emulsifier; Initiator A: 1-3 parts; 190-250 parts water; The polymeric monomer A is one of the following combinations: A combination of methacrylic acid, methyl methacrylate, and cyclohexyl methacrylate. A combination of methacrylic acid, acrylamide, isobornyl methacrylate, and n-butyl acrylate. A combination of acrylic acid, styrene, vinyl acetate, and acrylonitrile; The crosslinking monomer is selected from at least one of glycidyl acrylate, glycidyl methacrylate, allyl methacrylate, and diallyl phthalate; The macromolecular emulsifier is a polyacrylate macromolecular emulsifier with a glass transition temperature of 0–50°C, and the macromolecular emulsifier is made from the following raw materials in the indicated weight proportions: 100 parts of monomer B; Initiator B: 1-5 parts; Solvent: 100-200 parts; The polymeric monomer B is selected from any one of the following combinations: A combination of methacrylic acid, hydroxyethyl methacrylate, isobutyl acrylate, and styrene; A combination of methacrylic acid, isooctyl acrylate, and methylstyrene; A combination of acrylic acid, n-butyl acrylate, acrylonitrile, and methyl methacrylate.

2. The lithium battery negative electrode adhesive according to claim 1, characterized in that, The initiator A is selected from at least one of ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide.

3. The lithium battery negative electrode adhesive according to claim 1, characterized in that, The initiator B is selected from at least one of azobisisoheptanenitrile, azobisisobutyronitrile, benzoyl peroxide, cumene hydroperoxide, tert-butyl peroxyisooctanoate, and di-tert-butyl peroxide.

4. The lithium battery negative electrode adhesive according to claim 1, characterized in that, The solvent is selected from one of ethyl acetate, n-butanol, diethylene glycol dimethyl ether, and dimethyl maleate.

5. The lithium battery negative electrode adhesive according to claim 1, characterized in that, The preparation steps of the macromolecular emulsifier are as follows: Step 1: Add the reaction solvent to the reactor equipped with a reflux condenser and start stirring; Step 2: Add monomer B to the reactor, purge with nitrogen for at least 30 minutes, and heat to 65~120℃; Step 3: Add initiator B to the reactor and maintain a constant temperature with stirring. The reaction time is 4-8 hours. Step 4: After the reaction is complete, the reaction system is subjected to vacuum distillation at the reaction temperature to remove most of the reaction solvent. Then, distilled water is added, stirred, and dried to obtain the macromolecular emulsifier.

6. The method for preparing the lithium battery negative electrode adhesive according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Add distilled water or deionized water to the reaction apparatus, turn on the stirrer, add macromolecular emulsifier, and adjust the pH of the system to 7-9. Step 2: Add monomer A and crosslinking monomer, adjust the pH of the system to 7-9 again, and stir to emulsify; Step 3: Introduce nitrogen gas; Step 4: Raise the reaction temperature to 55-80℃ and keep it constant while stirring. Under a nitrogen atmosphere, add 80-90% of the aqueous solution prepared by initiator A at a uniform rate to start the polymerization reaction. The duration of uniform initiator addition is 8-16 hours. Step 5: After the uniform addition is completed, add the remaining 10-20% of the aqueous solution prepared with initiator A, and continue the reaction for 1-3 hours to obtain the adhesive product.