A binder for lithium battery separator cold-pressing process and a preparation method thereof

Abstract

The application discloses a kind of binder for lithium battery separator cold pressing process and preparation method thereof, it is related to lithium battery separator binder technical field, binder includes the following component is made: acid monomer, amide monomer, nitrile monomer, acrylic ester monomer, ether bond containing multifunctional monomer, long side chain hydrocarbon chain monomer, neutralizing agent, initiator.Preparation method includes the following steps: after mixing binder component, it is formed into mixed solution in deionized water;Nitrogen protection is added to initiator, heating reaction;After reaction is completed, neutralizing agent is added to adjust pH value, dilution and vacuum removal residual monomer are obtained after.The application forms three-dimensional network structure by introducing ether bond containing multifunctional monomer, reduces cohesion, makes dry film soft, adapts 25 DEG C cold pressing process;While introducing long side chain hydrocarbon chain monomer improves compatibility and wettability with PE / PP separator, realizes low energy consumption cold pressing bonding.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery separator adhesive, and particularly relates to an adhesive for a lithium battery separator cold pressing process and a preparation method thereof. BACKGROUND

[0002] The lithium ion battery separator is an important component of a battery, which is used to separate the positive and negative electrodes to prevent short circuit and allow electrolyte ions to pass through. In a traditional lithium battery manufacturing process, the separator is usually coated with 1-2 mu m of polyvinylidene fluoride (PVDF) and polyacrylate (PAA) compound adhesive, and is hot-pressed to the positive and negative electrode sheets at 80-90 DEG C and 5-30 tons of pressure to enhance the hardness of the battery, the strength of the separator, the shrinkage performance, reduce the internal resistance and improve the cycle performance. However, the traditional hot pressing process increases the production cost due to high energy consumption, and it is difficult to meet the green manufacturing demand; and the traditional PAA is a linear polymer with high cohesion, and the dry film is hard, which needs high temperature activation for bonding, and cannot realize 25 DEG C cold pressing. SUMMARY

[0003] In order to solve the above technical problems, the present application provides an adhesive for a lithium battery separator cold pressing process and a preparation method thereof, and the specific technical scheme is as follows:

[0004] An adhesive for a lithium battery separator cold pressing process, which is prepared from the following components in percentage by weight: 5-30% of an acid monomer, 5-30% of an amide monomer, 10-70% of a nitrile monomer, 5-30% of an acrylate monomer, 1-5% of an ether bond-containing multifunctional monomer, 1-5% of a long side chain hydrocarbon chain monomer, 5-30% of a neutralizing agent, and 0.1-2% of an initiator.

[0005] Preferably,

[0006] The acid monomer is selected from at least one of acrylic acid, methacrylic acid, maleic acid, itaconic acid, or a derivative anhydride thereof;

[0007] The amide monomer is selected from at least one of acrylamide, methacrylamide, N-isopropyl acrylamide, N,N-dimethyl acrylamide, and N-hydroxymethyl acrylamide;

[0008] The nitrile monomer is selected from at least one of acrylonitrile, methacrylonitrile, styrylnitrile, fluorinated acrylonitrile, and cyanoethyl vinyl ether;

[0009] The acrylate monomer is selected from at least one of methyl methacrylate, (meth)acrylic acid ethyl ester, (meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid isooctyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid glycidyl ester, and (meth)acrylic acid lauryl ester;

[0010] The ether bond-containing multifunctional monomer is selected from at least one of trimethylolpropane diallyl ether, ethoxy ethoxy ethyl acrylate, ethoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, ethoxylated pentaerythritol tetraacrylate, and ethoxylated 1,6-hexanediol diacrylate;

[0011] The long side chain hydrocarbon chain monomer is selected from at least one of tricyclodecane dimethanol (dimethyl) acrylate, bicyclo pentane (methyl) acrylate, 1-adamantyl acrylate, t-butyl cyclohexyl acrylate, and trimethyl cyclohexyl acrylate;

[0012] The neutralizing agent is selected from at least one of sodium hydroxide, lithium hydroxide, ammonia, ethanolamine, triethanolamine, and isobutanolamine;

[0013] The initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0014] Preferably, further comprising:

[0015] The high-temperature-resistant monomer is 2% to 10%;

[0016] The dynamic crosslinking monomer is 1% to 5%.

[0017] Preferably:

[0018] The high-temperature-resistant monomer is selected from at least one of N-phenyl maleimide and vinyl trimethoxysilane;

[0019] The dynamic crosslinking monomer is selected from at least one of a disulfide bond-containing monomer or a Diels-Alder bond-containing monomer.

[0020] Preferably:

[0021] The disulfide bond-containing monomer is dithiodipropyl acrylate;

[0022] The Diels-Alder bond-containing monomer is furanyl acrylate.

[0023] The application also provides a preparation method for preparing the binder for the cold pressing process of the lithium battery separator membrane as described in any one of the above.

[0024] a. After mixing the binder component, deionized water is added, and stirring is performed to form a uniform mixture, wherein the binder component includes acid monomers, amide monomers, nitrile monomers, acrylate monomers, ether bond-containing multifunctional monomers, and long side chain hydrocarbon chain monomers;

[0025] b. Under nitrogen protection, an initiator is added, and heating is performed to carry out a free radical polymerization reaction;

[0026] c. After the reaction is complete, add a neutralizing agent to adjust the pH to 6.5~8.0, dilute and remove residual monomers by vacuum to obtain the final product.

[0027] Preferably:

[0028] In the mixing step, the stirring speed is 200~500 rpm, and the liquid-solid content of the mixture is 20%~30%.

[0029] The free radical polymerization reaction is carried out at 60~80℃ for 5~15 hours;

[0030] The vacuum level during the vacuuming step is -0.09 MPa.

[0031] Preferably, the nitrile monomers include fluoroacrylonitrile and / or cyanoethyl vinyl ether, and the binder components further include imidazole ionic liquid monomers and antioxidant monomers, wherein:

[0032] The imidazole-based ionic liquid monomer accounts for 0.5% to 3% of the total mass of the binder components;

[0033] The antioxidant monomer accounts for 0.5% to 2% of the total mass of the binder components. The preparation process of the antioxidant monomer specifically includes the following steps: 4-hydroxybenzoic acid and hydroxyethyl acrylate are mixed in a molar ratio of (1 to 1.2):1, toluene solvent and p-toluenesulfonic acid catalyst are added, and esterification reaction is carried out at 95 to 105°C for 3 to 5 hours under nitrogen protection. The product is obtained after purification by distillation.

[0034] Preferably, the long-side-chain hydrocarbon monomer comprises phosphonic acid-modified tricyclodecanedimethyl acrylate, and its preparation process specifically includes the following steps: mixing tricyclodecanedimethyl acrylate and dimethylphosphonic acid in a molar ratio of (1.5~2.5):1, adding dichloromethane solvent and catalyst N,N-dicyclohexylcarbodiimide, and carrying out an esterification reaction at 25~35°C for 5~7 hours under nitrogen protection, and obtaining the product by extraction and purification.

[0035] The binder provided by this invention for the cold pressing process of lithium battery separators has the following beneficial effects:

[0036] 1. By forming a three-dimensional network structure through monomers with ether bonds and multifunctional groups, the cohesive force of polyacrylate is reduced, making the dry film flexible. It can effectively bond PE / PP separators to positive and negative electrode sheets at 25℃ and 5~30 tons of pressure, breaking through the high energy consumption limitation of traditional 80~90℃ hot pressing process and meeting the requirements of green manufacturing.

[0037] 2. The polar functional groups provided by acid monomers and nitrile monomers enhance the adhesion to the electrode, resulting in higher initial discharge efficiency.

[0038] 3. The long side chain hydrocarbon chain monomer improves the compatibility and wettability of the PE / PP separator, improves the electrolyte conduction efficiency, and has excellent rate performance.

[0039] 4. The amide monomer and the acrylate monomer provide flexibility and chemical stability, and have high capacity retention rate after 300 cycles. DETAILED DESCRIPTION

[0040] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be described in detail below, and the description in this part is only exemplary and explanatory, and should not have any limiting effect on the protection scope of the present application.

[0041] The present embodiment provides a binder for a lithium battery separator cold pressing process, which is made of the following components in percentage by weight: 5-30% of an acid monomer, 5-30% of an amide monomer, 10-70% of a nitrile monomer, 5-30% of an acrylate monomer, 1-5% of an ether bond-containing multifunctional monomer, 1-5% of a long side chain hydrocarbon chain monomer, 5-30% of a neutralizing agent, and 0.1-2% of an initiator.

[0042] The ether bond-containing multifunctional monomer forms a three-dimensional network structure, reduces cohesion, and makes the dry film soft, suitable for a 25℃ cold pressing process; at the same time, the long side chain hydrocarbon chain monomer improves the compatibility and wettability of the PE / PP separator, and realizes low-energy cold pressing bonding.

[0043] Further,

[0044] The acid monomer is selected from at least one of acrylic acid, methacrylic acid, maleic acid, itaconic acid, or a derivative anhydride thereof.

[0045] The amide monomer is selected from at least one of acrylamide, methacrylamide, N-isopropyl acrylamide, N,N-dimethyl acrylamide, and N-hydroxymethyl acrylamide.

[0046] The nitrile monomer is selected from at least one of acrylonitrile, methacrylonitrile, styrylnitrile, fluorinated acrylonitrile, and cyanoethyl vinyl ether.

[0047] The acrylate monomer is selected from at least one of methyl methacrylate, (meth)acrylic acid ethyl ester, (meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid isooctyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid glycidyl ester, and (meth)acrylic acid lauryl ester.

[0048] The ether bond-containing multifunctional monomer is selected from at least one of trimethylolpropane diallyl ether, ethoxy ethoxy ethyl acrylate, ethoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, ethoxylated pentaerythritol tetraacrylate, and ethoxylated 1,6-hexanediol diacrylate.

[0049] The long side chain carbon and hydrogen chain monomer is selected from at least one of tricyclodecane dimethanol (dimethyl) acrylate, dicyclopentyl (meth) acrylate, 1-adamantyl acrylate, t-butylcyclohexyl acrylate, trimethylcyclohexyl acrylate.

[0050] The neutralizing agent is selected from at least one of sodium hydroxide, lithium hydroxide, ammonia, ethanolamine, triethanolamine, isobutanolamine.

[0051] The initiator is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate.

[0052] Among them, the amide monomer (such as N-isopropyl acrylamide) and the acrylate monomer (such as hydroxyethyl methacrylate) provide flexibility and polar groups to form hydrogen bonds with PE / PP separators and pole pieces; the long side chain monomer (such as tricyclodecane dimethanol acrylate) matches the hydrophobic surface of the PE / PP separator through the carbon and hydrogen chain, improves the wettability, improves the electrolyte conduction efficiency, and has excellent rate performance; the ether bond-containing monomer (such as ethoxylated trimethylolpropane triacrylate) forms a three-dimensional network, reduces the cohesive force, supports the 25°C cold pressing process, and reduces energy consumption; the neutralizing agent (such as ammonia) adjusts the pH to 6.5~8.0, and ensures the storage stability of the water-based adhesive.

[0053] Further, it also includes:

[0054] The high-temperature-resistant monomer is 2%~10%.

[0055] The dynamic crosslinking monomer is 1%~5%.

[0056] Among them, the high-temperature-resistant monomer (such as N-phenyl maleimide) enhances the thermal stability of the polymer chain, which can reduce the decline rate of the adhesion strength at high temperature; the dynamic crosslinking monomer (such as a monomer containing a disulfide bond or a Diels-Alder bond) forms a reversible crosslinking network, which can realize self-repairing of the coating through bond breaking and recombination at a battery operating temperature of 40~60°C, maintain the adhesion strength, and improve the cycle performance; the high-temperature-resistant monomer and the acid and nitrile monomers synergistically enhance the chemical stability, and the dynamic crosslinking monomer and the ether bond-containing monomer synergistically optimize the network structure.

[0057] Further:

[0058] The high-temperature-resistant monomer is selected from at least one of N-phenyl maleimide and vinyltrimethoxysilane.

[0059] The dynamic crosslinking monomer is selected from at least one of a monomer containing a disulfide bond or a monomer containing a Diels-Alder bond.

[0060] The rigid aromatic ring of N-phenyl maleimide and the silicon-oxygen bond (Si-O) of vinyl trimethoxysilane significantly improve the heat resistance of the coating, and can effectively reduce the decline rate of the high-temperature bonding strength; the disulfide bond-containing monomer (such as dithiodipropenylate) repairs the micro-cracks of the coating at high temperature through disulfide bond exchange and Diels-Alder bond monomer through reversible addition reaction, and enhances the cycle stability.

[0061] Further:

[0062] The disulfide bond-containing monomer is dithiodipropenylate.

[0063] The Diels-Alder bond-containing monomer is furan acrylate.

[0064] The disulfide bond (-S-S-) of dithiodipropenylate can be dynamically repaired at 40-60°C through breakage-recombination, maintaining the integrity of the coating and reducing the decline rate of the high-temperature bonding strength; furan acrylate forms reversible crosslinking through Diels-Alder reaction, depolymerizes to repair micro-cracks at high temperature, and re-crosslinks at low temperature, enhancing the stability of the coating in battery cycling; the disulfide bond and the Diels-Alder bond synergize with high-temperature-resistant monomers such as N-phenyl maleimide to strengthen the thermal stability of the polymer chain and reduce the risk of softening at high temperature; the self-repairing ability of the dynamic crosslinking monomer reduces the peeling of the coating and improves the cycle capacity retention rate.

[0065] The present embodiment also provides a preparation method for preparing the binder for the cold pressing process of the lithium battery separator membrane as described in any one of the above embodiments, which comprises the following steps:

[0066] a. After mixing the binder components, add deionized water and stir to form a uniform mixture, wherein the binder components include acid monomers, amide monomers, nitrile monomers, acrylate monomers, ether bond-containing multifunctional monomers, and long side chain hydrocarbon chain monomers.

[0067] b. Under nitrogen protection, add an initiator and heat to perform a free radical polymerization reaction.

[0068] c. After the reaction is completed, add a neutralizing agent to adjust the pH value to 6.5-8.0, dilute and vacuum to remove residual monomers.

[0069] Further:

[0070] In the mixing step, the stirring speed is 200-500 rpm, and the solid content of the mixture is 20%-30%.

[0071] The free radical polymerization reaction is performed at 60-80°C, and the reaction time is 5-15 hours.

[0072] The vacuum degree of the vacuumizing step is -0.09 MPa.

[0073] Further, the nitrile monomer includes fluorinated acrylonitrile and / or cyanoethyl vinyl ether, the binder component further includes an imidazole-based ionic liquid monomer and an antioxidant monomer, wherein:

[0074] The imidazole-based ionic liquid monomer accounts for 0.5% to 3% of the total mass of the binder component.

[0075] The antioxidant monomer accounts for 0.5% to 2% of the total mass of the binder component, and the preparation process of the antioxidant monomer specifically includes the following steps: mixing 4-hydroxybenzoic acid and hydroxyethyl acrylate at a molar ratio of (1-1.2):1, adding toluene solvent and catalyst p-toluenesulfonic acid, esterification reaction at 95-105°C for 3-5 hours under nitrogen protection, and then purified by distillation.

[0076] The imidazole-based ionic liquid monomer is specifically an imidazole-based acrylate (IL-Monomer), and the imidazole group in the imidazole-based acrylate has a wide electrochemical window, which can coordinate with LiPF6 in the LiPF6 electrolyte to form a protective interfacial layer, effectively inhibiting the defluorination reaction of fluorinated acrylonitrile (free radicals leading to polymer degradation) and the oxidative cleavage of the ether bond of cyanoethyl vinyl ether at high voltage. + and PF 6- The antioxidant monomer is specifically 4-hydroxybenzoic acid acrylate (AO-Monomer), and the phenolic hydroxyl group in the 4-hydroxybenzoic acid acrylate has strong antioxidant properties, which can capture free radicals in the high-voltage or electrolyte environment, preventing the defluorination chain reaction of fluorinated acrylonitrile and the oxidative degradation of cyanoethyl vinyl ether.

[0077] The ionic liquid property of the IL-Monomer enhances the ionic conductivity of the polymer coating, is compatible with the LiPF6 / EC / DMC electrolyte, promotes Li + conduction, and reduces the internal resistance of the battery cell. The AO-Monomer stabilizes the nitrile monomer, reduces the interfacial side reaction, further reduces the impedance of the electrode / separator interface, and improves the first discharge efficiency.

[0078] Further, the long side chain hydrocarbon chain monomer includes phosphonic acid modified tricyclodecane dimethylol acrylate, and the preparation process thereof specifically includes the following steps: mixing tricyclodecane dimethylol acrylate and dimethyl phosphonic acid at a molar ratio of (1.5-2.5):1, adding dichloromethane solvent and catalyst N,N-dicyclohexyl carbodiimide, esterification reaction at 25-35°C for 5-7 hours under nitrogen protection, and then purified by extraction.

[0079] Among them, phosphonic acid modified tricyclodecane dimethylol acrylate (P-TCDDA) retains the hydrophobicity of tricyclodecane groups, matches PE / PP separators (low surface energy materials), reduces surface tension, and improves wettability. The phosphonic acid group forms a dynamic reversible bond through hydrogen bonding and coordination with the metal oxide / graphite on the surface of the polar sheet, supporting the repair of micro-cracks in the coating at 40-60°C, and enhancing mechanical toughness.

[0080] P-TCDDA is prepared by esterification reaction, with mild reaction conditions, less by-products, and easy purification. It synergizes with ether-containing multifunctional monomers to reduce polymer cohesion, making the dry film soft and suitable for 25°C cold pressing process, saving energy and protecting the environment.

[0081] The following provides specific examples, which can enable those skilled in the art to have a more comprehensive understanding of the present application, but in no way limit the present application.

[0082] Example 1

[0083] In a 5L reaction kettle, 750g of deionized water was added, and then acrylic acid (150g), N-hydroxymethyl acrylamide (100g), acrylonitrile (500g), hydroxyethyl methacrylate (150g), ethoxylated trimethylolpropane triacrylate (40g), and tricyclodecane dimethylol acrylate (30g) were added in sequence. A magnetic stirrer (400 rpm) was used to stir for 30 minutes until uniform, and the solid content of the mixture was 25%.

[0084] Nitrogen was introduced (flow rate 0.5 L / min, 10 minutes) to remove oxygen, and nitrogen protection was maintained. The reaction kettle was heated to 60°C (temperature control accuracy ±0.1°C), and ammonium persulfate (10g dissolved in 20g deionized water) was added. The temperature was maintained at 60°C, and stirring (300 rpm) was carried out for 10 hours to obtain a polyacrylate emulsion.

[0085] Cooling to 25°C, adding ammonia water (120g, 25% concentration), stirring (200 rpm, 10 minutes), adjusting pH to 7.0. Diluted with deionized water (about 250g) to a solid content of 20%, and vacuumed for 30 minutes using a vacuum pump (-0.09 MPa) to remove residual monomers.

[0086] The emulsion was coated on a PE separator (thickness 16μm) using a coating machine, with a coating thickness of 1.5μm. Drying in a constant temperature oven at 80°C for 4 minutes to form a uniform dry film.

[0087] Using a hydraulic cold press, the coated separator was laminated with positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite) at 25°C and a pressure of 10 tons, and the pressure was maintained for 12 seconds.

[0088] The cold-pressed separator was assembled with positive and negative electrode sheets into a soft pack battery, and electrolyte (1M LiPF6, EC / DMC = 1:1) was injected. After sealing, formation was carried out (0.1C charging to 4.2V, standing for 24 hours).

[0089] The internal resistance was tested by AC impedance method, the frequency range was 0.1 Hz~100 kHz, the test temperature was 25℃, and the internal resistance (unit: mΩ) was measured after the battery was fully charged to 4.2V. Eight samples were tested respectively, and the average value was taken. The test data is shown in Table 1-1.

[0090] At 25℃, 0.1C constant current charging to 4.2V, constant voltage charging to current <0.01C, discharging to 3.0V. The initial capacity was 0.5C and 3C, and the capacity retention rate (300 times capacity / 3C initial capacity x 100%) was calculated. Two groups of samples were tested, and the test data is shown in Table 1-4.

[0091] At 25℃, 0.1C charging to 4.2V, discharging to 3.0V at 0.2C, 0.5C, 1C, 1.5C, and 2C respectively, and recording the discharge capacity (mAh). The rate retention rate (relative to 0.2C) was calculated. Two groups of samples were tested, and the test data is shown in Table 1-3.

[0092] At 25℃, 3C charging to 4.2V, constant voltage to current <0.01C, 3C discharging to 3.0V, and cycling 300 times. The initial capacity (0.5C and 3C) and the capacity after 300 times were recorded, and the capacity retention rate (300 times capacity / 3C initial capacity x 100%) was calculated. Two groups of samples were tested, and the test data is shown in Table 1-4.

[0093] At 25℃, 1C charging to 4.2V, constant voltage to current <0.01C, 1C discharging to 3.0V, and cycling 300 times. The initial capacity and the capacity after 300 times were recorded, and the residual capacity ratio (300 times capacity / initial capacity x 100%) was calculated. One group of samples was tested, and the test data is shown in Table 1-5.

[0094] The binder-coated PE separator (16 μm, coating thickness 1.5 μm) was cold-pressed (25℃, 10 tons, 12 seconds) with the positive electrode sheet (NCM811), and cut into 1 cm wide strips. Adjusted to 25℃, 45℃, and 60℃ (humidity 50%RH, ±0.5℃) respectively in a constant temperature and humidity box. 180° peeling test, speed 50 mm / min, record the peeling force (N / cm). Each temperature point was tested 3 times, and the average value was taken. The high temperature drop rate was calculated: [(25℃ peeling force-high temperature peeling force) / 25℃ peeling force] x 100%. The test data is shown in Table 1-6.

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] Example 2

[0102] In a 5L reaction kettle, 750g of deionized water was added, and then acrylic acid (120g), N-isopropyl acrylamide (120g), acrylonitrile (480g), hydroxyethyl methacrylate (180g), ethoxylated trimethylolpropane triacrylate (50g), tricyclodecane dimethanol acrylate (40g) were added in sequence. A magnetic stirrer (400 rpm) was used to stir for 30 minutes to uniformity, and the solid content of the mixture was 25%.

[0103] Nitrogen was introduced (flow rate 0.5 L / min, 10 minutes) to remove oxygen, and nitrogen protection was maintained. The reaction kettle was heated to 60°C (temperature control accuracy ±0.1°C), and ammonium persulfate (10g, dissolved in 20g deionized water) was added. The temperature was maintained at 60°C, and stirring (300 rpm) was carried out for 10 hours to obtain a polyacrylate emulsion.

[0104] Cooling to 25°C, adding ammonia (100g, 25% concentration), stirring (200 rpm, 10 minutes), adjusting the pH to 7.0. Diluted with deionized water (about 250g) to a solid content of 20%, and vacuumed for 30 minutes using a vacuum pump (-0.09 MPa) to remove residual monomers.

[0105] The emulsion was coated on a PE separator (thickness 16μm) using a coating machine, and the coating thickness was 1.5μm. Dried in a constant temperature oven at 80°C for 4 minutes to form a uniform dry film.

[0106] The coated separator was laminated with positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite) using a hydraulic cold press at 25°C and a pressure of 10 tons, and the pressure was maintained for 12 seconds.

[0107] The cold-pressed separator and positive and negative electrode sheets were assembled into a soft-pack battery, and electrolyte (1M LiPF6, EC / DMC=1:1) was injected. After sealing, formation was carried out (0.1C charging to 4.2V, standing for 24 hours).

[0108] The test items and test methods were the same as in Example 1, and the test data is shown in Tables 2-1 to 2-6.

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115] Example 3

[0116] In a 5L reactor, 750g of deionized water was added, and then acrylic acid (100g), N-isopropyl acrylamide (150g), acrylonitrile (450g), hydroxyethyl methacrylate (200g), ethoxylated 1,6-hexanediol diacrylate (50g), tricyclodecane dimethanol acrylate (40g) were added in sequence. A magnetic stirrer (400 rpm) was used to stir for 30 minutes to uniformity, and the solid content of the mixture was 25%.

[0117] Nitrogen was introduced (flow rate 0.5 L / min, 10 minutes) to remove oxygen, and nitrogen protection was maintained. The reactor was heated to 60°C (temperature control accuracy ±0.1°C), and ammonium persulfate (10g, dissolved in 20g of deionized water) was added. The temperature was maintained at 60°C, and stirring (300 rpm) was carried out for 10 hours to obtain a polyacrylate emulsion.

[0118] The temperature was cooled to 25°C, and ammonia water (100g, 25% concentration) was added. Stirring (200 rpm, 10 minutes) was carried out, and the pH was adjusted to 7.0. Deionized water (about 250g) was added to dilute to a solid content of 20%, and a vacuum pump (-0.09 MPa) was used to remove residual monomers for 30 minutes.

[0119] The emulsion was coated on a PE separator (thickness 16μm) using a coating machine, and the coating thickness was 1.5μm. The coated separator was dried in a constant temperature oven at 80°C for 4 minutes to form a uniform dry film.

[0120] The coated separator was laminated with positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite) using a hydraulic cold press at 25°C and a pressure of 10 tons, and the pressure was maintained for 12 seconds.

[0121] The cold-pressed separator was assembled with positive and negative electrode sheets to form a soft-pack battery, and electrolyte (1M LiPF6, EC / DMC=1:1) was injected. After sealing, formation was carried out (0.1C charging to 4.2V, standing for 24 hours).

[0122] Test items and test methods are the same as Example 1, and test data is shown in Tables 3-1 to 3-6.

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129] Example 4

[0130] In a 5L reaction kettle, 750g of deionized water was added, and then acrylic acid (150g), N-hydroxymethyl acrylamide (100g), acrylonitrile (500g), hydroxyethyl methacrylate (150g), ethoxylated trimethylolpropane triacrylate (40g), tricyclodecane dimethanol acrylate (30g), N-phenyl maleimide (50g), and dithiodipropyl acrylate (30g) were sequentially added. A magnetic stirrer (400 rpm) was used to stir for 30 minutes until uniform, and the solid content of the mixture was 25.2%.

[0131] Nitrogen was introduced (flow rate 0.5L / min, 10 minutes) to remove oxygen, and nitrogen protection was maintained. The reaction kettle was heated to 60°C (temperature control accuracy ±0.1°C), and ammonium persulfate (10g dissolved in 20g deionized water) was added. The temperature was maintained at 60°C, and stirring (300 rpm) was performed for 10.5 hours to obtain a polyacrylate emulsion.

[0132] The temperature was cooled to 25°C, and ammonia water (125g, 25% concentration) was added. Stirring (200 rpm, 10 minutes) was performed, and the pH was adjusted to 7.1. Deionized water (about 260g) was added to dilute to a solid content of 20.1%, and a vacuum pump (-0.09 MPa) was used to remove residual monomers for 30 minutes.

[0133] The emulsion was coated on a PE separator (thickness 16μm) using a coating machine, and the coating thickness was 1.5μm. The coated separator was dried in a constant temperature oven at 80°C for 4 minutes to form a uniform dry film.

[0134] The coated separator was laminated with positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite) using a hydraulic cold press at 25°C and a pressure of 10 tons, and the pressure was maintained for 12 seconds.

[0135] The cold-pressed separator was assembled with the positive and negative electrode sheets to form a soft-pack battery, electrolyte (1M LiPF6, EC / DMC = 1:1) was injected, and after sealing, formation (0.1C charging to 4.2V, standing for 24 hours) was performed.

[0136] The test items and test methods were the same as in Example 1, and the test data is shown in Tables 4-1 to 4-6.

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143] Example 5

[0144] In a 5L reaction kettle, 750g of deionized water was added, and then acrylic acid (150g), N-hydroxymethyl acrylamide (100g), fluorinated acrylonitrile (250g), cyanoethyl vinyl ether (250g), hydroxyethyl methacrylate (150g), ethoxylated trimethylolpropane triacrylate (40g), and tricyclodecane dimethanol acrylate (30g) were added in sequence. A magnetic stirrer (400 rpm) was used to stir for 30 minutes until uniform, and the solid content of the mixture was 25.3%.

[0145] Nitrogen was introduced (flow rate 0.5L / min, 10 minutes) to remove oxygen, and nitrogen protection was maintained. The reaction kettle was heated to 60°C (temperature control accuracy ±0.1°C), and ammonium persulfate (10g, dissolved in 20g deionized water) was added. The temperature was maintained at 60°C, and stirring (300 rpm) was performed for 10.2 hours to obtain a polyacrylate emulsion.

[0146] Cooling to 25°C, adding ammonia water (122g, 25% concentration), stirring (200 rpm, 10 minutes), adjusting the pH to 7.0. Diluted with deionized water (about 255g) to a solid content of 20.2%, and vacuumed for 30 minutes using a vacuum pump (-0.09 MPa) to remove residual monomers.

[0147] The emulsion was coated on a PE separator (thickness 16μm) using a coater, and the coating thickness was 1.5μm. Drying in a constant temperature oven at 80°C for 4 minutes to form a uniform dry film.

[0148] Using a hydraulic cold press, at 25°C and 10 tons of pressure, the coated diaphragm is bonded to the positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite), and the pressure is maintained for 12 seconds.

[0149] The cold-pressed separator is assembled with the positive and negative electrode sheets into a soft-pack battery, and the electrolyte (1M LiPF6, EC / DMC=1:1) is injected. After sealing, it is formed (charged to 4.2V at 0.1C and left to stand for 24 hours).

[0150] The test items and test methods are the same as in Example 1, and the test data are shown in Tables 5-1 to 5-6.

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157] Comparative Example

[0158] Add 1000g of N-methylpyrrolidone to a 5L reactor, followed by 500g of polyvinylidene fluoride and 500g of polyacrylate. Stir with a magnetic stirrer (400rpm) at 50°C for 2 hours until completely dissolved to obtain an adhesive solution with a solid content of 20.1%.

[0159] Using a coating machine, the solution is coated onto a PE membrane (16 μm thick), resulting in a coating thickness of 1.5 μm. The membrane is then dried in a constant temperature oven at 120°C for 5 minutes to form a uniform dry film.

[0160] Using a hydraulic hot press, at 85°C and 10 tons of pressure, the coated diaphragm is bonded to the positive and negative electrode sheets (positive electrode: NCM811, negative electrode: graphite), and the pressure is maintained for 12 seconds.

[0161] The hot-pressed separator is assembled with the positive and negative electrode sheets into a soft-pack battery, and the electrolyte (1M LiPF6, EC / DMC=1:1) is injected. After sealing, it is formed (charged to 4.2V at 0.1C and left to stand for 24 hours).

[0162] The test items and test methods are the same as in Example 1, and the test data are shown in Tables 9-1 to 9-6.

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169] From the above data, it can be seen that Examples 1-5 realize the 25℃ cold pressing process by using multifunctional monomers containing ether bonds, reduce energy consumption; long side chain monomers (P-TCDDA), high temperature resistant monomers and dynamic crosslinking monomers synergistically improve the electrochemical performance and high temperature stability, which are significantly better than the traditional PVDF / PAA binder.

[0170] Among them, Example 3 performs best in rate performance (96.22%), because the ethoxylation of 1,6-hexanediol diacrylate forms a more optimized three-dimensional network structure, but the internal resistance (107.75 mΩ) is higher, and the cycle performance (76.72%) is not as good as Examples 4-5.

[0171] Example 4 significantly improves the cycle performance (92.02%) and high temperature peel force stability (10.75%) by using high temperature resistant and dynamic crosslinking monomers.

[0172] The principles and implementation modes of the present application are described by applying specific examples in this paper, and the above examples are only used to help understand the method of the present application and its core idea. The above is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the technical field should be within the technical scope disclosed by the present application, according to the technical scheme and the inventive concept of the present application to make equivalent replacement or change, which should be within the protection scope of the present application.

Claims

1. An adhesive for use in the cold pressing process of lithium battery separators, characterized in that: The product is composed of the following components by weight percentage: 5%~30% acid monomers, 5%~30% amide monomers, 10%~70% nitrile monomers, 5%~30% acrylate monomers, 1%~5% ether-containing polyfunctional monomers, 1%~5% long-side-chain hydrocarbon monomers, 5%~30% neutralizing agent, 0.1%~2% initiator, 2%~10% high-temperature resistant monomers, and 1%~5% dynamic crosslinking monomers; The acid monomers are selected from at least one of acrylic acid, methacrylic acid, maleic acid, itaconic acid or their derivative anhydrides; The amide monomer is selected from at least one of acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, and N-hydroxymethylacrylamide; The nitrile monomer is selected from at least one of acrylonitrile, methacrylonitrile, styrene nitrile, fluoroacrylonitrile, and cyanoethyl vinyl ether; The acrylate monomers are selected from at least one of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, isooctyl methacrylate, n-butyl methacrylate, glycidyl methacrylate, and lauryl methacrylate. The ether-containing polyfunctional monomer is selected from at least one of trimethylolpropane diallyl ether, ethoxyethoxyethyl acrylate, ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tetraacrylate, and ethoxylated 1,6-hexanediol diacrylate. The long side-chain hydrocarbon monomer is selected from at least one of tricyclodecanediethanol (dimethyl) acrylate, 1-adamantane acrylate, tert-butylcyclohexyl acrylate, and trimethylcyclohexyl acrylate; The high-temperature resistant monomer is selected from at least one of N-phenylmaleimide and vinyltrimethoxysilane; The dynamic crosslinking monomer is selected from at least one of monomers containing disulfide bonds or monomers containing Diels-Alder bonds.

2. The adhesive for the cold pressing process of lithium battery separators according to claim 1, characterized in that: The neutralizing agent is selected from at least one of sodium hydroxide, lithium hydroxide, ammonia, ethanolamine, triethanolamine, and isobutanolamine; The initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate.

3. The adhesive for the cold pressing process of lithium battery separators according to claim 1, characterized in that: The monomer containing disulfide bonds is a dithiodiacrylate; The monomer containing Diels-Alder bonds is furanyl acrylate.

4. A preparation method, characterized in that: The method for preparing the binder for the cold pressing process of lithium battery separators as described in any one of claims 1 to 3 comprises the following steps: a) After mixing the binder components, add them to deionized water and stir to form a homogeneous mixture. The binder components include acid monomers, amide monomers, nitrile monomers, acrylate monomers, ether-containing polyfunctional monomers, long-side-chain hydrocarbon monomers, high-temperature resistant monomers, and dynamic crosslinking monomers. b) Under nitrogen protection, an initiator is added, and the mixture is heated to carry out a free radical polymerization reaction; c) After the reaction is complete, add a neutralizing agent to adjust the pH to 6.5~8.0, dilute and remove residual monomers by vacuum to obtain the final product.

5. The preparation method according to claim 4, characterized in that: In the mixing step, the stirring speed is 200~500 rpm, and the liquid-solid content of the mixture is 20%~30%. The free radical polymerization reaction is carried out at 60~80℃ for 5~15 hours; the vacuum degree of the vacuuming step is -0.09 MPa.

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