Carboxylic butadiene-styrene latex for negative electrode of lithium battery and preparation method of carboxylic butadiene-styrene latex

Abstract

The invention relates to the technical field of carboxylic butadiene-styrene latex, in particular to carboxylic butadiene-styrene latex for a negative electrode of a lithium battery and a preparation method of the carboxylic butadiene-styrene latex, and the carboxylic butadiene-styrene latex with excellent performance is prepared by introducing a multifunctional cross-linking monomer, doping conductive nanoparticles and the like and adopting a microemulsion polymerization and in-situ cross-linking synergistic process, a microwave-assisted synthesis technology and the like. The latex is used for the negative electrode of the lithium battery, can remarkably improve the adhesive property, the conductivity, the electrolyte corrosion resistance and the low-temperature performance, and has the advantages of environmental protection and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of carboxylated styrene-butadiene latex, and particularly relates to a carboxylated styrene-butadiene latex for the negative electrode of a lithium battery and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, lithium batteries, as an efficient and environmentally friendly energy storage device, are widely used in electric vehicles, portable electronic devices and other fields. However, the existing lithium battery negative electrode materials still face many challenges in practical applications, which seriously restricts the further improvement of lithium battery performance and the expansion of the scope of application. The bonding force between traditional carboxylated styrene butadiene latex and active materials (such as graphite, silicon-based materials, etc.) in the negative electrode of lithium batteries is not strong enough. During the battery charging and discharging process, due to the volume change of the electrode material, the active material is easily detached from the current collector, causing the electrode structure to be destroyed, thereby affecting the battery's cycle life and charge and discharge stability. For example, in high-capacity silicon-based negative electrode materials, because the volume of silicon expands by up to 300% during the charging and discharging process, ordinary binders are difficult to maintain a stable connection between the active material and the current collector, resulting in rapid attenuation of the battery capacity, and the capacity retention rate after 100 cycles is only 50%-60%. The current carboxylated styrene butadiene latex itself has poor conductivity and cannot effectively promote electron transfer in the negative electrode system. This increases the internal resistance of the electrode, resulting in serious polarization of the battery during the charging and discharging process, especially when charging and discharging at high rates, the voltage platform of the battery drops significantly, and the energy conversion efficiency decreases. For example, when charging and discharging at a 2C rate, the actual discharge capacity of the battery is only 60%-70% of the theoretical capacity, which cannot meet the needs of high-power application scenarios. The electrolyte of lithium batteries contains a variety of highly corrosive lithium salts and organic solvents. When traditional carboxylated styrene butadiene latex is immersed in the electrolyte for a long time, it is prone to swelling, degradation and other phenomena. This not only destroys the integrity of the electrode structure, but also causes changes in the composition of the electrolyte, affecting the electrochemical performance of the battery. For example, in a high temperature environment (above 50°C), after 1000 hours of electrolyte immersion, the performance of the latex binder drops significantly, and the battery capacity decays by more than 30%. In a low temperature environment (such as below -20°C), the flexibility and ion transmission capacity of traditional carboxylated styrene butadiene latex are significantly reduced. This increases the interface impedance between the electrode and the electrolyte, and the charge and discharge performance of the battery deteriorates sharply, which cannot meet the use requirements in cold areas or special environments. For example, at -30°C, the discharge capacity of the battery is only 30%-40% of that at room temperature, which severely limits the application scope of lithium batteries. The existing preparation process of carboxylated styrene butadiene latex may involve some toxic and harmful raw materials or additives, causing potential pollution to the environment. At the same time, some preparation processes are complex and energy-intensive, resulting in high production costs. For example, the organic solvents used in some traditional preparation processes are difficult to recycle, which increases the cost of environmental protection treatment; and the production process requires special conditions such as high temperature and high pressure, which consumes a lot of energy, making it difficult to reduce the cost of latex, which is not conducive to large-scale industrial application.

[0003] However, there is currently no carboxylated styrene-butadiene latex for lithium battery anodes and its preparation method that can comprehensively and effectively solve these key problems. Existing improvement solutions often trigger other new problems when solving one problem, or have unsatisfactory effects in practical applications and cannot meet the urgent market demand for high-performance lithium battery anode materials. Therefore, it is of great practical significance to develop an innovative carboxylated styrene-butadiene latex for lithium battery anodes and its preparation method that can break through the bottleneck of existing technologies. Summary of the Invention

[0004] The present invention provides a carboxylated styrene-butadiene latex for lithium battery anodes, and the latex comprises:

[0005] A styrene-butadiene rubber main chain formed by a polymerization reaction, wherein the main chain contains carboxyl groups for enhancing the interaction with other materials; a crosslinked structure formed by introducing a multifunctional crosslinking monomer, and the multifunctional crosslinking monomer is a copolymer of hydroxyethyl acrylate-vinyltrimethoxysilane, which forms a double crosslinked network with the styrene-butadiene rubber main chain and the surface of the active substance in the latex.

[0006] Furthermore, the latex further comprises uniformly doped conductive nanoparticles, and the conductive nanoparticles are carbon nanotubes with carboxyl groups on the surface, and the carbon nanotubes are doped in-situ during the latex synthesis process, and the addition amount thereof is 1%-3% of the total mass fraction of the monomers, for constructing a conductive network and improving the conductivity of the latex.

[0007] Furthermore, the latex contains 1%-10% of poly(hexafluoropropylene-vinyl ether)-styrene-butadiene rubber block copolymer by mass fraction, and the poly(hexafluoropropylene-vinyl ether) chain segment forms a protective film on the surface of the latex particles, for enhancing the stability of the latex in the electrolyte and improving the resistance to electrolyte erosion.

[0008] Furthermore, polyethylene glycol diacrylate is added as a low-temperature plasticizer and an 18-crown-6 ether derivative is added as an ion carrier to the latex, and the addition amount of polyethylene glycol diacrylate is 5%-10% of the mass of the latex, and the addition amount of the 18-crown-6 ether derivative is 1%-3% of the mass of the latex, for improving the performance of the latex in a low-temperature environment.

[0009] Furthermore, part of the butadiene monomer is replaced by methyl soyate in the preparation of the latex, and the replacement ratio of the methyl soyate is 30%-50%, and lipase is used as a catalyst for the polymerization reaction to achieve the purpose of green and environmentally friendly preparation and cost reduction.

[0010] This solution also discloses a preparation method of a carboxylated styrene-butadiene latex for lithium battery anodes, comprising the following steps:

[0011] Synthesis steps of the multifunctional crosslinking monomer: Add 0.1 mol of hydroxyethyl acrylate and 0.1 mol of vinyltrimethoxysilane into a three-necked flask equipped with a stirrer, a thermometer and a reflux condenser. Using 100 mL of toluene as a solvent, add 0.005 mol of p-toluenesulfonic acid as a catalyst. Under nitrogen protection, react at 80 - 90 °C for 6 - 8 hours to obtain a hydroxyethyl acrylate-vinyltrimethoxysilane copolymer; after the reaction is completed, remove the solvent and unreacted monomers by vacuum distillation, and characterize its structure by NMR and FTIR methods to confirm the successful synthesis of the copolymer;

[0012] Basic polymerization steps of carboxylated styrene-butadiene latex: Add 500 mL of deionized water, 5 g of emulsifier, and 3 g of buffer into a four-necked flask equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser. After stirring evenly, introduce nitrogen for 30 - 60 minutes to remove oxygen in the system; sequentially add 50 g of butadiene, 30 g of styrene, 5 g of acrylic acid, and the above-synthesized HEA-VTMS monomer, heat up to 50 - 60 °C, add 0.5 g of initiator, and start the polymerization reaction. The reaction time is 8 - 12 hours;

[0013] Post-treatment steps: After the reaction is completed, add 0.2 g of terminator and adjust the pH value of the latex to 7 - 8 to obtain carboxylated styrene-butadiene latex for the negative electrode of lithium batteries.

[0014] This solution also provides a negative electrode for a lithium battery, which uses the above-mentioned carboxylated styrene-butadiene latex for the negative electrode of a lithium battery.

[0015] The above-mentioned negative electrode of the lithium battery is made by mixing an active material, a conductive additive and a latex in a mass ratio of 85:10:5 and stirring evenly to form an electrode slurry. The slurry is coated on a copper foil current collector and vacuum dried at 80 - 100 °C for 12 - 16 hours, and then roll-pressed into shape to make a negative electrode sheet. The active material and the carboxylated styrene-butadiene latex are tightly combined through the crosslinking structure in the latex, and the conductive additive and the conductive nanoparticles in the carboxylated styrene-butadiene latex act synergistically to construct an efficient electron transport channel.

[0016] Beneficial technical effects:

[0017] Excellent adhesion performance: By introducing multifunctional crosslinking monomers and adopting innovative processes such as microemulsion polymerization and in-situ crosslinking synergy, the adhesion between carboxylated styrene-butadiene latex and the active material is significantly enhanced, effectively solving the problem of shedding of the active material during charge and discharge, and greatly improving the cycle life of the battery. In the silicon-based negative electrode system, the capacity retention rate of the battery can reach more than 80% after 500 cycles, which is 20% - 30% higher than that of traditional latex.

[0018] Excellent electrical conductivity: By means of measures such as doping conductive nanoparticles and optimizing the latex molecular structure, an efficient electron transport channel is constructed, the internal resistance of the electrode is reduced, and the charge-discharge performance of the battery is significantly improved. Especially during high-rate charge and discharge, the voltage platform decline is reduced by 30%-50%, and the energy conversion efficiency is greatly enhanced. When charging and discharging at a rate of 2C, the actual discharge capacity of the battery can reach 80%-90% of the theoretical capacity, meeting the requirements of high-power application scenarios.

[0019] Powerful resistance to electrolyte erosion: Design polymer segments resistant to electrolyte erosion to enable the latex to have good stability in the electrolyte. After long-term immersion in high-temperature electrolyte, the battery capacity decay is controlled within 10%, effectively extending the service life of the battery and improving the safety and reliability of the battery.

[0020] Outstanding low-temperature performance: By adding low-temperature plasticizers and ion carriers, and using methods such as gradient temperature polymerization process, the charge-discharge performance of the battery in low-temperature environments is significantly improved. Under low-temperature conditions of -30°C, the discharge capacity of the battery can be increased to 60%-70% of that at room temperature, broadening the application range of lithium batteries and enabling them to be used normally in cold regions or special environments.

[0021] Environmental protection and low-cost advantages: Using green and environmentally friendly raw materials and catalysts, combined with highly energy-efficient preparation processes such as microwave-assisted synthesis technology and supercritical fluid drying technology, not only reduces environmental pollution but also lowers production costs. Compared with traditional processes, the raw material cost is reduced by 20%-30%, and the production energy consumption is reduced by 30%-50%, which is conducive to large-scale industrial application and promotes the sustainable development of the lithium battery industry.

[0022] Multi-dimensional performance improvement: Through a series of innovative methods such as bionic interface design, nanostructure regulation, self-healing function construction, and multi-scale structure optimization, the lithium battery negative electrode is optimized from multiple dimensions, comprehensively improving performance indicators such as the energy density, power density, and cycle life of the battery, opening up a new path for the development of lithium battery technology. Specific implementation methods

[0023] Example 1

[0024] Preparation of carboxylated styrene-butadiene latex containing multifunctional crosslinking monomers

[0025] Material innovation:

[0026] Design and synthesize 2-hydroxyethyl acrylate-vinyltrimethoxysilane copolymer (HEA-VTMS) as a multifunctional crosslinking monomer. The monomer molecule contains both a hydroxyl group that can react with a carboxyl group and a siloxy group that can react with the hydroxyl group on the surface of the active substance, and can form a double crosslinking network between carboxylated styrene-butadiene latex and the active substance, enhancing the bonding performance. In the silicon-based anode system, this double crosslinking structure can increase the binding force between the active substance and the current collector by 50%-80%, effectively inhibiting the problem of active substance shedding caused by the volume expansion of silicon during charge and discharge.

[0027] The styrene-butadiene rubber main chain formed by the polymerization reaction, which contains carboxyl groups on the main chain and is used to enhance the interaction with other materials; the crosslinking structure formed by the introduced multifunctional crosslinking monomer, the multifunctional crosslinking monomer is 2-hydroxyethyl acrylate-vinyltrimethoxysilane copolymer (HEA-VTMS), which forms a double crosslinking network with the styrene-butadiene rubber main chain and the surface of the active substance in the latex to improve the bonding performance. Among them, the addition amount of the multifunctional crosslinking monomer HEA-VTMS is 5%-10% (mass fraction) of the total monomer amount.

[0028] Preparation method:

[0029] Synthesis steps of the multifunctional crosslinking monomer: Add 0.1 mol of 2-hydroxyethyl acrylate (HEA) and 0.1 mol of vinyltrimethoxysilane (VTMS) into a three-necked flask equipped with a stirrer, a thermometer and a reflux condenser. Using 100 mL of toluene as the solvent, add 0.005 mol of p-toluenesulfonic acid as the catalyst. Under nitrogen protection, react at 80-90 °C for 6-8 hours to obtain 2-hydroxyethyl acrylate-vinyltrimethoxysilane copolymer (HEA-VTMS). After the reaction is completed, remove the solvent and unreacted monomers by vacuum distillation, and characterize its structure by means of NMR, FTIR, etc. to confirm the successful synthesis of the copolymer.

[0030] Basic polymerization steps of carboxylated styrene-butadiene latex: Add 500 mL of deionized water, 5 g of emulsifier (such as sodium dodecyl sulfate), and 3 g of buffer (such as sodium bicarbonate) into a four-necked flask equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser. After stirring evenly, introduce nitrogen for 30-60 minutes to remove the oxygen in the system. Add 50 g of butadiene, 30 g of styrene, 5 g of acrylic acid, and the above-synthesized HEA-VTMS monomer in sequence, heat up to 50-60 °C, add 0.5 g of initiator (such as potassium persulfate), and start the polymerization reaction. The reaction time is 8-12 hours.

[0031] Post-treatment steps: After the reaction is completed, 0.2 g of a terminator (such as hydroquinone) is added, and the pH value of the latex is adjusted to 7 - 8 to obtain carboxylated styrene-butadiene latex for the negative electrode of lithium batteries. The particle size distribution and stability of the latex are tested using a particle size analyzer, Zeta potential meter, etc., to ensure that the latex particle size is uniform, the absolute value of the Zeta potential is greater than 30 mV, and it has good stability.

[0032] Performance advantages: In the silicon-based negative electrode system, this dual cross-linked structure can increase the binding force between the active material and the current collector by 50% - 80%, effectively inhibiting the problem of active material shedding caused by the volume expansion of silicon during charge and discharge. After 500 cycles of charge and discharge at a 0.5C rate, the battery capacity retention rate reaches 82%, which is significantly higher than that of the battery using traditional carboxylated styrene-butadiene latex.

[0033] Example 2

[0034] Preparation of carboxylated styrene-butadiene latex doped with conductive nanoparticles

[0035] Material innovation:

[0036] Synthesize the HEA-VTMS monomer using the same method as in Example 1.

[0037] Select carbon nanotubes with carboxyl groups on the surface (CNTs-COOH) as conductive nanoparticles. By introducing CNTs-COOH during the synthesis of carboxylated styrene-butadiene latex, and using the carboxyl groups on its surface to react with the active groups on the molecular chain of styrene-butadiene rubber, in-situ doping of carbon nanotubes in the latex is achieved. The unique one-dimensional structure and excellent conductivity of CNTs-COOH can build an efficient conductive network inside the latex, which is expected to increase the conductivity of the latex by 5 - 10 times, effectively improving the electron transport performance of the negative electrode of lithium batteries and reducing polarization.

[0038] The main chain of styrene-butadiene rubber formed by polymerization reaction, the main chain contains carboxyl groups, which are used to enhance the interaction with other materials; uniformly doped conductive nanoparticles, the conductive nanoparticles are carbon nanotubes with carboxyl groups on the surface (CNTs-COOH), and the carbon nanotubes are in-situ doped during the latex synthesis process, and their addition amount is 1% - 3% of the total mass of the monomers, which are used to build a conductive network and improve the conductivity of the latex.

[0039] Preparation method:

[0040] CNTs-COOH Pretreatment: 1 g of purchased carbon nanotubes was added to a mixed acid of 50 mL concentrated nitric acid and concentrated sulfuric acid (volume ratio 3:1), and refluxed and stirred at 80 - 100 °C for 6 - 8 hours to oxidize the carbon nanotubes and attach carboxyl groups to their surfaces. After the reaction, surface-carboxylated carbon nanotubes were obtained through steps such as centrifugation, washing, and drying. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to characterize their surface functional groups and purity.

[0041] Preparation of Carboxylated Styrene-Butadiene Rubber Latex: 500 mL of deionized water, 5 g of emulsifier (such as sodium dodecylbenzenesulfonate), and 3 g of buffer (such as disodium hydrogen phosphate) were added to a four-necked flask. After stirring evenly, nitrogen was introduced for 30 - 60 minutes. 50 g of butadiene, 30 g of styrene, 5 g of acrylic acid, and the above-synthesized HEA-VTMS monomer were added in sequence. At the same time, the pretreated CNTs-COOH was added, and the temperature was raised to 55 - 65 °C. 0.5 g of initiator (such as ammonium persulfate) was added, and a polymerization reaction was carried out for 8 - 10 hours. After the reaction, 0.2 g of terminator (such as hydroquinone) was added to adjust the pH value of the latex to 7 - 8, and carboxylated styrene-butadiene rubber latex doped with conductive nanoparticles was obtained. Scanning electron microscopy (SEM) was used to observe the dispersion of carbon nanotubes in the latex to ensure their uniform dispersion in the latex particles.

[0042] Performance Advantages: The unique one-dimensional structure and excellent conductivity of CNTs-COOH can build an efficient conductive network inside the latex, which can increase the conductivity of the latex by 5 - 10 times, effectively improve the electron transport performance of the negative electrode of lithium batteries, and reduce polarization. In the 2C high-rate charge-discharge test, the actual discharge capacity of the battery reached 85% of the theoretical capacity, and the voltage platform drop was reduced by 40% compared with the undoped battery, effectively improving the high-rate charge-discharge performance of the battery.

[0043] Example 3

[0044] Preparation of Carboxylated Styrene-Butadiene Rubber Latex Containing Polymer Segments Resistant to Electrolyte Erosion

[0045] Material Innovation:

[0046] The HEA-VTMS monomer was synthesized by the same method as in Example 1.

[0047] Poly(hexafluoropropylene-vinyl ether) (PHFPE)-styrene-butadiene rubber block copolymer was designed and synthesized. First, the PHFPE segment was synthesized, and then it was connected to the styrene-butadiene rubber segment through a living polymerization method. The PHFPE segment has high chemical stability and low surface energy, and can form a dense protective film on the surface of the latex particles, which is expected to reduce the swelling rate of the latex in the electrolyte by 50% - 70%, effectively improving the stability of the latex in the lithium battery electrolyte and extending the battery life.

[0048] The main chain of styrene-butadiene rubber formed by polymerization reaction, which contains carboxyl groups on the main chain and is used to enhance the interaction with other materials; poly(hexafluoropropylene-vinyl ether) (PHFPE)-styrene-butadiene rubber block copolymer, and the poly(hexafluoropropylene-vinyl ether) chain segment forms a protective film on the surface of latex particles, which is used to enhance the stability of latex in the electrolyte and improve the resistance to electrolyte erosion.

[0049] Preparation method:

[0050] Synthesis of PHFPE: In a high-pressure reactor, using hexafluoropropylene and vinyl ether as monomers, under the action of 0.5 g of initiator (such as dibenzoyl peroxide), react at 60 - 80 °C and 2 - 3 MPa for 4 - 6 hours to synthesize PHFPE. Use nuclear magnetic resonance hydrogen spectrum ( 1 HNMR) and gel permeation chromatography (GPC) to characterize its structure and molecular weight.

[0051] Preparation of block copolymer: Adopt atom transfer radical polymerization (ATRP) method to copolymerize the synthesized PHFPE chain segment with butadiene, styrene, acrylic acid, and the above-mentioned synthesized HEA-VTMS monomer. Add 0.05 mol of catalyst (such as copper chloride / bipyridine), 0.1 mol of ligand, and PHFPE chain segment into a four-necked flask. After introducing nitrogen for 30 - 60 minutes, add 50 g of butadiene, 30 g of styrene, and 5 g of acrylic acid monomer, heat up to 70 - 80 °C, and react for 8 - 10 hours. After the reaction, purify the product by methods such as column chromatography to obtain PHFPE-styrene-butadiene rubber block copolymer.

[0052] Preparation of carboxylated styrene-butadiene latex: Dissolve the above block copolymer in 100 mL of toluene, add 500 mL of deionized water and 5 g of emulsifier (such as Tween-80), and prepare carboxylated styrene-butadiene latex by ultrasonic emulsification. Use dynamic light scattering (DLS) to test the particle size distribution of the latex to ensure that the latex particle size is uniform.

[0053] Performance advantages: The PHFPE chain segment containing 1% - 10% by mass fraction has high chemical stability and low surface energy, can form a dense protective film on the surface of latex particles, can reduce the swelling rate of latex in the electrolyte by 50% - 70%, effectively improve the stability of latex in the lithium battery electrolyte, and extend the battery life. After soaking the battery in the electrolyte at 60 °C for 1000 hours and then performing charge-discharge tests, the battery capacity attenuation is only 8%, while the battery capacity attenuation using traditional latex exceeds 30%.

[0054] Example 4

[0055] Preparation of carboxylated styrene-butadiene latex added with low-temperature plasticizer and ion carrier

[0056] Material Innovation:

[0057] Synthesize the HEA-VTMS monomer using the same method as in Example 1.

[0058] Select polyethylene glycol diacrylate (PEGDA) as the low-temperature plasticizer and 18-crown-6 ether derivative as the ion carrier. PEGDA has good low-temperature flexibility and can reduce the glass transition temperature of the latex, which is expected to increase the flexibility of the latex by 30%-50% at -30°C; the 18-crown-6 ether derivative can form a stable complex with lithium ions and promote the migration of lithium ions at low temperatures, which is expected to increase the migration rate of lithium ions at low temperatures by 20%-40%, effectively improving the low-temperature performance of the battery.

[0059] The main chain of styrene-butadiene rubber formed by polymerization reaction contains carboxyl groups, which are used to enhance the interaction with other materials; polyethylene glycol diacrylate (PEGDA) is added as the low-temperature plasticizer, and 18-crown-6 ether derivative is added as the ion carrier. The addition amount of PEGDA is 5%-10% of the mass of the latex, and the addition amount of 18-crown-6 ether derivative is 1%-3% of the mass of the latex, which are used to improve the performance of the latex in a low-temperature environment.

[0060] Preparation Method:

[0061] Preparation of carboxylated styrene-butadiene latex: Add 500 mL of deionized water, 5 g of emulsifier (such as sodium dodecyl sulfate), and 3 g of buffer (such as sodium bicarbonate) into a four-necked flask, stir evenly, and then introduce nitrogen for 30-60 minutes. Add 50 g of butadiene, 30 g of styrene, 5 g of acrylic acid, and the above-synthesized HEA-VTMS monomer in sequence, heat up to 50-60°C, add 0.5 g of initiator (such as potassium persulfate), and carry out the polymerization reaction for 8-12 hours. After the reaction is completed, add 0.2 g of terminator (such as hydroquinone) to adjust the pH value of the latex to 7-8.

[0062] Addition of additives: Add PEGDA (5%-10% of the mass of the latex) and 18-crown-6 ether derivative (1%-3% of the mass of the latex) to the prepared carboxylated styrene-butadiene latex, stir at 30-40°C for 2-4 hours to make them evenly dispersed in the latex. Use differential scanning calorimetry (DSC) to measure the glass transition temperature of the latex and confirm the plasticizing effect of PEGDA.

[0063] Performance advantages: PEGDA has good low-temperature flexibility, can reduce the glass transition temperature of the latex, and can improve the flexibility of the latex at -30°C by 30% - 50%; the 18-crown-6 ether derivative can form a stable complex with lithium ions, promote the migration of lithium ions at low temperatures, and can increase the migration rate of lithium ions at low temperatures by 20% - 40%, effectively improving the low-temperature performance of the battery. When the charge-discharge test is carried out in a low-temperature environment of -30°C, the discharge capacity of the battery reaches 65% of that at room temperature, while the discharge capacity of the battery using traditional latex is only 35% of that at room temperature.

[0064] Example 5

[0065] Preparation of carboxylated styrene-butadiene latex using green and environmentally friendly raw materials and catalysts

[0066] Material innovation:

[0067] Synthesize the HEA-VTMS monomer using the same method as in Example 1.

[0068] Use soybean oil fatty acid methyl ester (SME) to replace part of the butadiene monomer and carry out the polymerization reaction using lipase as a catalyst. SME is a renewable vegetable oil-based monomer with a wide source and environmental friendliness. Using SME can not only reduce the dependence on petroleum-based raw materials but also reduce production costs, and it is expected to reduce the raw material cost by 20% - 30%. At the same time, lipase, as an environmentally friendly catalyst, has mild reaction conditions, reducing energy consumption and environmental pollution.

[0069] In the preparation of the latex, soybean oil fatty acid methyl ester (SME) is used to replace part of the butadiene monomer, and the replacement ratio of the soybean oil fatty acid methyl ester is 30% - 50%, and the polymerization reaction is carried out using lipase as a catalyst to achieve the purpose of green and environmentally friendly preparation and cost reduction. Among them, the dosage of lipase is 0.5% - 1% of the total mass of the monomers.

[0070] Preparation method:

[0071] Pretreatment of soybean oil fatty acid methyl ester: Carry out the transesterification reaction of soybean oil and methanol under the action of an alkaline catalyst (such as sodium hydroxide) to obtain soybean oil fatty acid methyl ester. Purify SME by methods such as distillation and analyze its purity using gas chromatography (GC).

[0072] Preparation of carboxylated styrene-butadiene latex: Add 500 mL of deionized water, 5 g of emulsifier (such as Tween-80), and 3 g of buffer (such as potassium dihydrogen phosphate) into a four-necked flask. After stirring evenly, introduce nitrogen for 30 - 60 minutes. Then add SME (substituting part of butadiene, with a substitution ratio of 30% - 50%), 30 g of styrene, 5 g of acrylic acid, and the above-synthesized HEA-VTMS monomer successively. At the same time, add an appropriate amount of lipase (calculated as 0.5% - 1% of the total mass of the monomers). React at 40 - 50 °C for 10 - 15 hours to carry out the polymerization reaction. After the reaction is completed, add 0.2 g of terminator (such as hydroquinone) and adjust the pH value of the latex to 7 - 8 to obtain carboxylated styrene-butadiene latex using green and environmentally friendly raw materials and catalysts. Determine the content of vegetable oil-based monomers in the latex by methods such as elemental analysis.

[0073] Performance advantages: SME is a renewable vegetable oil-based monomer with a wide source and environmental friendliness. Using SME can not only reduce the dependence on petroleum-based raw materials but also lower the production cost, and can reduce the raw material cost by 20% - 30%. At the same time, as an environmentally friendly catalyst, lipase has mild reaction conditions, reducing energy consumption and environmental pollution. After cost accounting, the cost of battery raw materials using this green preparation process is reduced by 25% compared with the traditional process, and the electrochemical performance indicators of the battery are equivalent to those of the battery prepared using traditional raw materials.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any other modifications or equivalent substitutions made by those of ordinary skill in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A carboxylated styrene-butadiene latex for a lithium battery negative electrode, characterized in that: The latex comprises: The main chain of styrene-butadiene rubber is formed by polymerization reaction, and the main chain contains carboxyl groups for enhancing the interaction with other materials; the cross-linking structure is formed by the introduced multifunctional cross-linking monomer, and the multifunctional cross-linking monomer is hydroxyethyl acrylate-vinyl trimethoxysilane copolymer, which forms a double cross-linking network with the main chain of styrene-butadiene rubber and the surface of the active substance in the latex.

2. The carboxylated styrene-butadiene latex for lithium battery negative electrode according to claim 1, characterized in that: The latex also contains uniformly doped conductive nanoparticles, which are carbon nanotubes with carboxyl groups on the surface. The carbon nanotubes are in-situ doped during the latex synthesis process, and the added amount is 1%-3% of the total monomer mass fraction, which is used to construct a conductive network and improve the conductivity of the latex.

3. The carboxylated styrene-butadiene latex for lithium battery negative electrode according to claim 1, characterized in that: The latex contains 1%-10% by mass of poly(hexafluoropropylene-vinyl ether)-styrene-butadiene rubber block copolymer. The poly(hexafluoropropylene-vinyl ether) chain segments form a protective film on the surface of the latex particles to enhance the stability of the latex in the electrolyte and improve the electrolyte corrosion resistance.

4. The carboxylated styrene-butadiene latex for lithium battery negative electrode according to claim 1, characterized in that: The latex is added with polyethylene glycol diacrylate as a low-temperature plasticizer and 18-crown-6 ether derivative as an ion carrier. The addition amount of the polyethylene glycol diacrylate is 5%-10% of the mass of the latex, and the addition amount of the 18-crown-6 ether derivative is 1%-3% of the mass of the latex, so as to improve the performance of the latex in a low-temperature environment.

5. The carboxylated styrene-butadiene latex for lithium battery negative electrode according to claim 1, characterized in that: The preparation of the latex adopts soybean oil fatty acid methyl ester to replace part of butadiene monomer, the replacement ratio of the soybean oil fatty acid methyl ester is 30%-50%, and lipase is used as a catalyst for polymerization reaction to achieve the purpose of green and environmentally friendly preparation and cost reduction.

6. A method for preparing carboxylated styrene-butadiene latex for lithium battery negative electrode according to any one of claims 1 to 5, characterized in that: The following steps are involved: The synthesis steps of the multifunctional cross-linking monomer are as follows: 0.1 mol of hydroxyethyl acrylate and 0.1 mol of vinyltrimethoxysilane are added to a three-necked flask equipped with a stirrer, a thermometer and a reflux condenser, 100 mL of toluene is used as a solvent, 0.005 mol of p-toluenesulfonic acid is added as a catalyst, and the mixture is reacted at 80-90° C. for 6-8 hours under nitrogen protection to obtain a hydroxyethyl acrylate-vinyltrimethoxysilane copolymer; after the reaction is completed, the solvent and unreacted monomers are removed by reduced pressure distillation, and the structure is characterized by NMR and FTIR methods to confirm that the copolymer is successfully synthesized; Carboxylated styrene butadiene latex basic polymerization steps: add 500 mL of deionized water, 5 g of emulsifier, and 3 g of buffer into a four-necked flask equipped with a stirrer, a thermometer, a dropping funnel, and a reflux condenser, stir evenly, and introduce nitrogen for 30-60 minutes to remove oxygen in the system; add 50 g of butadiene, 30 g of styrene, 5 g of acrylic acid, and the multifunctional cross-linking monomer synthesized above in sequence, heat to 50-60° C., add 0.5 g of initiator, and start polymerization reaction for 8-12 hours; Post-treatment step: After the reaction is completed, 0.2 g of terminator is added, and the pH value of the latex is adjusted to 7-8 to obtain carboxylated styrene butadiene latex for lithium battery negative electrode.

7. A lithium battery negative electrode, characterized in that: The invention comprises the carboxylated styrene-butadiene latex for lithium battery negative electrode as claimed in any one of claims 1 to 6.