Styrene-butadiene emulsion for silicon-based negative electrode as well as preparation method and application of styrene-butadiene emulsion

Abstract

The invention relates to a styrene-butadiene emulsion for a silicon-based negative electrode and a preparation method and application thereof, and the styrene-butadiene emulsion for the silicon-based negative electrode is prepared from the following raw materials in parts by mass: 100 parts of butadiene, 90-120 parts of styrene, 5-20 parts of a seed emulsion, 20-60 parts of a functional monomer, 1-4 parts of an emulsifier, 0.6-2 parts of an initiator, 0.3-1.5 parts of a reducing agent, 0.01-0.1 part of a polymerization inhibitor and 350-500 parts of deionized water. According to the preparation method, the reactive emulsifier is innovatively selected to be matched with the nonionic emulsifier for use, so that the dosage of the emulsifier can be greatly reduced, and meanwhile, the nonionic emulsifier with relatively weak nucleation capability is used, so that the number of micelles is reduced, and the emulsion with large particle size up to 380nm is obtained; the reactive emulsifier is polymerized in a molecular chain in the later stage, so that no small molecules are left in the system, and the improvement of the electrical property of the product makes a part of contribution.

Description

A silicon-based styrene-butadiene emulsion for anodes, its preparation method and application Technical Field

[0001] This invention relates to the field of food technology, specifically to a silicon-based styrene-butadiene emulsion for anodes, its preparation method, and its application. Background Technology

[0002] As lithium battery technology develops towards higher energy density, higher safety, longer lifespan, and faster charging speed, silicon-based active materials are being used more and more in negative electrodes due to their ultra-high theoretical specific capacity and low electrochemical potential. However, a high silicon content of more than 15% can have negative effects. During battery cycling, the battery will undergo huge volume deformation, leading to the breakage or pulverization of active particles, damage to the electrode structure, and ultimately, battery performance degradation.

[0003] In the application of negative electrode adhesives, polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) are generally used in combination. PAA is relatively brittle, and the self-repair of the battery can only be achieved by improving the flexibility of SBR. However, traditional SBR has a low elastic modulus and insufficient strength, making it difficult to construct a stable three-dimensional network structure. Summary of the Invention

[0004] Based on the above description, the present invention provides a shiitake mushroom iron preparation for improving iron deficiency anemia, its preparation method and application, aiming to improve iron deficiency anemia while reducing digestive system side effects.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: The present invention provides a silicon-based anode styrene-butadiene emulsion, which is prepared from the following raw materials by mass parts: 100 parts butadiene, 90-120 parts styrene, 5-20 parts seed emulsion, 20-60 parts functional monomer, 1-4 parts emulsifier, 0.6-2 parts initiator, 0.3-1.5 parts reducing agent, 0.01-0.1 parts polymerization inhibitor, and 350-500 parts deionized water.

[0006] Furthermore, the seed emulsion has a particle size of 170 nm-185 nm and a solid content of 25%.

[0007] Furthermore, the initiator includes at least one of tert-butyl hydroperoxide, cumene hydroperoxide, ammonium persulfate, and potassium persulfate; and / or, the reducing agent includes at least one of ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium metabisulfite.

[0008] Furthermore, the emulsifier includes at least one of allyl polyoxyethylene ether ammonium sulfate, methacryloxy polyoxyethylene ether ammonium sulfate, lauryl polyoxyethylene ether, nonanol polyoxyethylene ether, and heptadecanol polyoxyethylene ether monophosphate.

[0009] Furthermore, the polymerization inhibitor is any one of sodium dimethyl dithiocarbamate, hydroxylamine, and sodium nitrite.

[0010] Furthermore, the functional monomer includes any one of N, N-methylenebisacrylamide, N-acryloylhydroxyethylmaleimide, diallyl phthalate, dimethacrylamide, vinyltrimethoxysilane, vinyltriisopropoxysilane, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, isooctyl methacrylate, and n-pentyl acrylate.

[0011] This invention also proposes a method for preparing a silicon-based anode styrene-butadiene emulsion as described above, characterized by the following steps: S1. Styrene, emulsifier, functional monomer, reducing agent, butadiene, and water are dispersed and emulsified to obtain a premix. The seed emulsion and water are mixed and heated to 50℃-60℃. An initiator is added within 6 h-7 h, and the premix is ​​added within 12 h-13 h, while monitoring the conversion rate. When the conversion rate reaches 30%, the temperature is raised to 60℃-70℃. When the conversion rate reaches 70%, the functional monomer is added and the temperature is raised to 70℃-80℃ until the conversion rate no longer increases. The temperature is then lowered to below 40℃, and a polymerization inhibitor is added to obtain a styrene-butadiene emulsion; S2. Lithium hydroxide is added to the styrene-butadiene emulsion until the pH is 7.9-8.1, and then the temperature is raised to 65℃-75℃ until the solid content is 45%-47%, thus obtaining the silicon-based anode styrene-butadiene emulsion.

[0012] Furthermore, before step S1, the process includes: S11. Mixing deionized water, styrene, emulsifier, acrylic acid, and n-dodecyl mercaptan, placing the mixture under a nitrogen atmosphere, adding butadiene, heating and mixing to react, adding sodium persulfate solution to continue the reaction, and obtaining a seed emulsion.

[0013] Furthermore, in step S11, the temperature for heating the mixing reaction is 58℃-62℃, and the heating reaction time is 0.4 h-0.6 h.

[0014] The present invention also proposes the application of a silicon-based anode styrene-butadiene emulsion in battery adhesives, wherein the silicon-based anode styrene-butadiene emulsion includes the silicon-based anode styrene-butadiene emulsion as described above, or is prepared by the silicon-based anode styrene-butadiene emulsion preparation method described above.

[0015] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: (1) The silicon-based negative electrode styrene-butadiene emulsion in this invention is a new generation of modified product. Through special process design, the step temperature is designed by reaching different degrees through polymerization reaction. When the conversion rate is less than 30%, low temperature polymerization is used to generate a large amount of homopolymer. When the conversion rate is above 30%, the temperature is increased, the molecular chain is rapidly crosslinked and the molecular weight of the polymer is significantly increased, and finally the high elongation performance of the film is obtained.

[0016] (2) In this invention, a reactive emulsifier is innovatively selected to be used in combination with a nonionic emulsifier, which can significantly reduce the amount of emulsifier used. At the same time, a nonionic emulsifier with weak nucleation ability is used to reduce the number of micelles and obtain an emulsion with a large particle size of up to 380 nm. The reactive emulsifier polymerizes in the molecular chain in the later stage, so that there are no residual small molecules in the system, which contributes to the improvement of the product's electrical properties.

[0017] (3) The timing of the addition of functional monomers and the combined dropping process in this invention play a role in controlling the particle structure and improving electrical performance. Adding a portion of functional monomers when the conversion rate reaches 70% in the later stage of the reaction introduces ester and amide monomers into the outer layer of the polymer, which is beneficial for better affinity with the electrolyte in the battery system and improves electrical performance. Controlling the dropping time of the initiator and monomers achieves a gradual increase in reaction particle size, a narrow particle size distribution, and uniform emulsion particle size, which is beneficial for electron transport when used as the negative electrode of the battery. At the same time, the large particle size also helps to obtain a high elongation of the film, thereby achieving a low expansion rate of the battery. Detailed Implementation

[0018] To facilitate understanding of this application, a more complete description will be provided below with reference to relevant embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be more thorough and complete.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0020] As lithium battery technology develops towards higher energy density, higher safety, longer lifespan, and faster charging speed, silicon-based active materials are being used more and more in negative electrodes due to their ultra-high theoretical specific capacity and low electrochemical potential. However, a high silicon content of more than 15% can have negative effects. During battery cycling, the battery will undergo huge volume deformation, leading to the breakage or pulverization of active particles, damage to the electrode structure, and ultimately, battery performance degradation.

[0021] In the application of negative electrode adhesives, polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) are generally used in combination. PAA is relatively brittle, and the self-repair of the battery can only be achieved by improving the flexibility of SBR. However, traditional SBR has a low elastic modulus and insufficient strength, making it difficult to construct a stable three-dimensional network structure.

[0022] In view of this, the present invention provides a styrene-butadiene emulsion for silicon-based anodes, which is prepared from the following raw materials by mass: 100 parts butadiene, 90-120 parts styrene, 5-20 parts seed emulsion, 20-60 parts functional monomer, 1-4 parts emulsifier, 0.6-2 parts initiator, 0.3-1.5 parts reducing agent, 0.01-0.1 parts polymerization inhibitor, and 350-500 parts deionized water.

[0023] In the technical solution of this invention, by employing functional monomers, abundant active functional groups are constructed on the SBR molecular chain, which, together with the butadiene-styrene main chain, form a three-dimensional network structure with both high elastic modulus and excellent ductility. This structure can buffer the volume change of silicon material during charging and discharging, thereby reducing the expansion rate of the electrode material. By controlling particle nucleation and growth through seed emulsion, and combined with an optimized emulsifier / initiator / reducing agent system, a latex with uniform particle size, stable solid content, and strong shear resistance is obtained.

[0024] It should be noted that the functional monomers referred to are a class of monomers that, in addition to providing the main chain structure, also possess specific functional groups (such as carboxyl, hydroxyl, amino, epoxy, sulfonic acid, phosphate ester, and amide groups) in the polymerization reaction. These functional groups endow the polymer with additional physical, chemical, or biological functions, enabling it to exhibit superior performance in specific applications. The specific types of functional groups in the functional monomers are not limited here.

[0025] Preferably, in some embodiments of the present invention, the silicon-based anode using styrene-butadiene emulsion is prepared from the following raw materials in parts by mass: 100 parts butadiene, 105 parts styrene, 10 parts seed emulsion with 25% solid content, 35 parts special monomer, 2 parts emulsifier, 1 part initiator, 0.5 parts reducing agent, 0.03 parts polymerization inhibitor, and 420 parts deionized water.

[0026] Furthermore, the seed emulsion has a particle size of 170 nm-185 nm and a solid content of 25%.

[0027] In the technical solution of this invention, the particle size of the seed emulsion is strictly controlled within the range of 170 nm-185 nm, which can serve as efficient and uniform nucleation sites. During the subsequent polymerization process, the newly generated particles are guided to grow in an orderly manner in the form of "seed growth", avoiding secondary nucleation, thereby significantly improving the particle size uniformity and batch repeatability of the final styrene-butadiene emulsion. With the addition of a seed emulsion with a solid content of 25%, sufficient and stable nucleation centers can be provided without increasing the total solid content of the system. This results in the final emulsion having a moderate viscosity and excellent shear thinning characteristics, which is beneficial for the uniform dispersion and stable coating of high solid content negative electrode slurry.

[0028] Furthermore, the initiator includes at least one of tert-butyl hydroperoxide, cumene hydroperoxide, ammonium persulfate, and potassium persulfate; and / or, the reducing agent includes at least one of ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium metabisulfite.

[0029] In the technical solution of this invention, the initiator and the reducing agent constitute a redox initiation system to improve the grafting rate of functional monomers on the butadiene / styrene copolymer chain, thereby ensuring that the binder molecular chain is rich in polar groups such as carboxyl groups, enhancing the chemical anchoring ability of silicon particles. By limiting the use of a specific type of redox initiation system, this invention not only achieves low-temperature, high-efficiency, and controllable emulsion polymerization, but also ensures high grafting rate, narrow molecular weight distribution, and high purity of the highly functionalized styrene-butadiene emulsion at the molecular structure level. This synergistically improves its bonding strength, anti-expansion ability, and electrochemical compatibility in silicon-based anodes, providing a key binder solution with both performance advantages and process feasibility for high-energy-density, long-life lithium-ion batteries.

[0030] Furthermore, the emulsifier includes at least one of allyl polyoxyethylene ether ammonium sulfate, methacryloxy polyoxyethylene ether ammonium sulfate, lauryl polyoxyethylene ether, nonanol polyoxyethylene ether, and heptadecanol polyoxyethylene ether monophosphate.

[0031] In the technical solution of this invention, by employing reactive anionic emulsifiers (allyl polyoxyethylene ether ammonium sulfate, methacryloxy polyoxyethylene ether ammonium sulfate), nonionic emulsifiers (lauryl alcohol polyoxyethylene ether, nonanol polyoxyethylene ether), and composite emulsifiers (heptadecanol polyoxyethylene ether monophosphate), some of these agents can participate in the reaction during polymerization, anchoring themselves on the surface of latex particles to form a "reactive emulsion layer," effectively preventing particle aggregation and ensuring uniform particle size in the final emulsion.

[0032] Specifically, in some embodiments of the present invention, the use of reactive emulsifiers in combination with nonionic emulsifiers can significantly reduce the amount of emulsifier used. At the same time, the use of nonionic emulsifiers with weak nucleation ability reduces the number of micelles, resulting in emulsions with large particle sizes up to 380 nm. The reactive emulsifier polymerizes in the molecular chain in the later stage, so that there are no residual small molecules in the system, which contributes to the improvement of the product's electrical properties.

[0033] Furthermore, the polymerization inhibitor is any one of sodium dimethyl dithiocarbamate, hydroxylamine, and sodium nitrite.

[0034] In the technical solution of this invention, by using the above-mentioned highly efficient free radical capturing or redox regulating stabilizers as polymerization inhibitors, residual free radicals or active centers initiated by dissolved oxygen in the system can be effectively removed after emulsion polymerization, preventing butadiene, styrene and functional monomers from undergoing slow self-polymerization or cross-linking during room temperature storage or transportation, thereby ensuring that the emulsion maintains stable solid content, viscosity and particle size distribution, and meeting the stringent requirements of the power battery industry chain for the long-term stability of raw materials.

[0035] Furthermore, the functional monomer includes any one of N, N-methylenebisacrylamide, N-acryloylhydroxyethylmaleimide, diallyl phthalate, dimethacrylamide, vinyltrimethoxysilane, vinyltriisopropoxysilane, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, isooctyl methacrylate, and n-pentyl acrylate.

[0036] In the technical solution of this invention, by employing functional monomers containing polar groups, the hydrophilicity of the adhesive film can be significantly improved, thereby promoting the penetration of carbonate electrolytes, reducing solid-liquid interface resistance (RCT), and improving rate performance when applied to lithium batteries. Specifically, carboxyl-containing monomers (such as acrylic acid and methacrylic acid) introduce a large number of carboxyl groups into the polymer backbone, which can form hydrogen bonds or partial esterification with the silicon surface, significantly improving peel strength. Monomers containing silane coupling groups (such as vinyltrimethoxysilane and vinyltriisopropoxysilane) generate... Silicon alcohols can form Si-O-Si covalent bonds with silicon active materials and current collector surfaces, achieving chemical anchoring and effectively preventing interfacial debonding during cycling; cross-linking monomers (such as N,N-methylenebisacrylamide and diallyl phthalate) introduce slight cross-linking points during polymerization, forming a three-dimensional network structure, which improves modulus while maintaining flexibility, giving the adhesive film resilience; long-chain flexible ester monomers (such as isooctyl methacrylate and n-pentyl acrylate) lower the glass transition temperature (Tg), enhance low-temperature ductility, and prevent electrode brittleness.

[0037] This invention also proposes a method for preparing a silicon-based anode styrene-butadiene emulsion as described above, characterized by the following steps: S1. Styrene, emulsifier, functional monomer, reducing agent, butadiene, and water are dispersed and emulsified to obtain a premix. The seed emulsion and water are mixed and heated to 50℃-60℃. An initiator is added within 6 h-7 h, and the premix is ​​added within 12 h-13 h, while monitoring the conversion rate. When the conversion rate reaches 30%, the temperature is raised to 60℃-70℃. When the conversion rate reaches 70%, the functional monomer is added and the temperature is raised to 70℃-80℃ until the conversion rate no longer increases. The temperature is then lowered to below 40℃, and a polymerization inhibitor is added to obtain a styrene-butadiene emulsion; S2. Lithium hydroxide is added to the styrene-butadiene emulsion until the pH is 7.9-8.1, and then the temperature is raised to 65℃-75℃ until the solid content is 45%-47%, thus obtaining the silicon-based anode styrene-butadiene emulsion.

[0038] In the technical solution of this invention, a "dual slow-release" strategy is adopted, initiator is slowly added dropwise over 6-7 hours and premix is ​​slowly added dropwise over 12-13 hours. This effectively suppresses explosive polymerization and local hot spots in the early stage of the reaction, making the polymerization rate stable. Combined with real-time monitoring of conversion rate and dynamic temperature adjustment, the monomers are ensured to react fully, while obtaining linear-slightly branched copolymers with a narrow molecular weight distribution, which is beneficial to the formation of dense and continuous adhesive films. Through a special process design with multi-stage temperature control, and by designing step temperature based on different degrees of polymerization reaction, low-temperature polymerization is used to produce a large amount of homopolymer when the conversion rate is below 30%. When the conversion rate is above 30%, the temperature is increased to rapidly crosslink and improve the molecular chain, significantly increasing the polymer molecular weight, and finally obtaining the high elongation performance of the film.

[0039] In this invention, the timing of the addition of functional monomers and the combined dropping process play a role in controlling particle structure and improving electrical performance. When the conversion rate reaches 70% in the later stage of the reaction, a portion of functional monomers is added. Introducing ester and amide monomers into the outer layer of the polymer is beneficial for better affinity with the electrolyte in the battery system, thereby improving electrical performance. Controlling the dropping time of the initiator and monomers achieves a gradual increase in reaction particle size, a narrow particle size distribution, and uniform emulsion particle size. When used as the negative electrode of the battery, this is beneficial for electron transport. At the same time, the large particle size also helps to obtain a high elongation of the film, thereby achieving a low expansion rate of the battery.

[0040] Furthermore, before step S1, the process includes: S11. Mixing deionized water, styrene, emulsifier, acrylic acid, and n-dodecyl mercaptan, placing the mixture under a nitrogen atmosphere, adding butadiene, heating and mixing to react, adding sodium persulfate solution to continue the reaction, and obtaining a seed emulsion.

[0041] In the technical solution of this invention, a styrene-butadiene copolymer seed emulsion containing acrylic acid and n-dodecyl mercaptan is pre-synthesized in S11. The resulting seed emulsion has a particle surface rich in hydrophilic functional groups and a controllable molecular weight inside. This functionalized seed not only serves as an efficient nucleation center for subsequent main polymerization, but also stabilizes the newly formed colloidal particles through electrostatic / steric hindrance effects, effectively inhibiting secondary nucleation and ensuring that the final emulsion has a highly uniform particle size.

[0042] Furthermore, in step S11, the temperature for heating the mixing reaction is 58℃-62℃, and the heating reaction time is 0.4 h-0.6 h.

[0043] In the technical solution of this invention, the heating and mixing reaction in the S11 stage is strictly controlled within a narrow window of 58℃-62℃ and 0.4 h-0.6 h, which is within the effective activation temperature range of the sodium persulfate initiation system. This allows for the efficient generation of primary free radicals and the initial nucleation of seed particles in a short time, but is insufficient to trigger violent chain growth. This condition effectively balances the reaction initiation rate and controllability, preventing gelation or cross-linking caused by local overheating or a rapid increase in molecular weight.

[0044] The present invention also proposes the application of a silicon-based anode styrene-butadiene emulsion in battery adhesives, wherein the silicon-based anode styrene-butadiene emulsion includes the silicon-based anode styrene-butadiene emulsion as described above, or is prepared by the silicon-based anode styrene-butadiene emulsion preparation method described above.

[0045] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0046] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0047] Example 1 This example provides a silicon-based anode styrene-butadiene emulsion, which is prepared from the following raw materials in parts by weight: 100 parts butadiene, 105 parts styrene, 10 parts seed emulsion with 25% solid content, 35 parts functional monomer, 2 parts emulsifier, 1 part initiator, 0.5 parts reducing agent, 0.03 parts polymerization inhibitor and 420 parts deionized water.

[0048] The preparation method of silicon-based anode styrene-butadiene emulsion in this embodiment includes the following steps: (1) Preparation of seed emulsion with 25% solid content: 8 parts of styrene, 0.2 parts of emulsifier allyl polyoxyethylene ether ammonium sulfate, 0.7 parts of acrylic acid, 0.05 parts of n-dodecyl mercaptan and 74 parts of deionized water are added to a 100L high-pressure reactor. The temperature is controlled at 25±1℃ and stirred for 10 minutes. Then, the system is evacuated and replaced with nitrogen three times to remove oxygen from the system. 16 parts of butadiene are introduced, the valve is closed, the speed is adjusted to 160 rpm and stirred quickly for 30 minutes. Then, when the temperature is raised to 60℃, sodium persulfate solution is added and the reaction is stopped when the conversion rate no longer increases. The reaction is cooled to room temperature and filtered to obtain seed emulsion.

[0049] (2) First, weigh the raw materials in the emulsification tank: add 280 parts of deionized water, 105 parts of styrene, 2 parts of emulsifier (1.5 parts of allyl polyoxyethylene ether ammonium sulfate and 0.5 parts of nonanol polyoxyethylene ether), 30 parts of functional monomer (15 parts of methacrylic acid and 15 parts of dimethacrylamide), 0.5 parts of reducing agent sodium formaldehyde sulfoxylate, and 100 parts of butadiene (the reaction vessel was purged with nitrogen three times before addition). Control the temperature at about 25°C and adjust the speed to 100 rpm for stirring, dispersion, and emulsification. Set aside. Place the initiator solution in another vessel and purge with nitrogen three times. Set aside.

[0050] (3) Weigh each raw material in the polymerization reactor according to the ratio: Add 280 parts of deionized water and 10 parts of seed emulsion with 25% solid content to the polymerization reactor, perform vacuum purging with nitrogen three times to remove oxygen from the system, and then raise the temperature to 55°C. At the same time, start adding the initiator solution and the raw materials in the emulsion reactor to the polymerization reactor for polymerization reaction. The initiator solution is added in 6 hours and the emulsion reactor flow rate is controlled to be added in 12-13 hours. Test the conversion rate every hour. When it reaches 30%, raise the temperature to 65°C to react. When the conversion rate reaches 70%, add 5 parts of functional monomer (5 parts of dimethylacrylamide) and raise the temperature to 75°C to react until the conversion rate no longer increases. Stop the reaction and cool down to below 40°C to add a polymerization inhibitor for dispersion. Add lithium hydroxide to the obtained emulsion to neutralize the pH to 8.0, and then remove low-boiling substances and some water at 70°C. The final solid content is 46%, which is the silicon-based styrene-butadiene emulsion for anodes.

[0051] Example 2 This example provides a silicon-based anode styrene-butadiene emulsion, which is prepared from the following raw materials in parts by weight: 100 parts butadiene, 120 parts styrene, 15 parts seed emulsion with 25% solid content, 35 parts functional monomer, 4 parts emulsifier, 1 part initiator, 0.5 parts reducing agent, 0.03 parts polymerization inhibitor and 420 parts deionized water.

[0052] The preparation method of silicon-based anode styrene-butadiene emulsion in this embodiment includes the following steps: (1) The preparation of seed emulsion with 25% solid content is the same as in Example 1.

[0053] (2) First, weigh the raw materials in the emulsification tank: add 280 parts of deionized water, 120 parts of styrene, 4 parts of emulsifier (3 parts of allyl polyoxyethylene ether ammonium sulfate and 1 part of nonanol polyoxyethylene ether), 30 parts of functional monomer (15 parts of methacrylic acid and 15 parts of dimethacrylamide), 0.5 parts of reducing agent sodium formaldehyde sulfoxylate, and 100 parts of butadiene (the reaction vessel was purged with nitrogen three times before addition). Control the temperature at about 25°C and adjust the speed to 100 rpm for stirring, dispersion, and emulsification. Set aside. Place the initiator solution in another vessel and purge with nitrogen three times. Set aside.

[0054] (3) Weigh each raw material in the polymerization reactor according to the ratio: Add 280 parts of deionized water and 15 parts of seed emulsion with 25% solid content to the polymerization reactor, perform vacuum purging with nitrogen three times to remove oxygen from the system, and then raise the temperature to 55°C. At the same time, start adding the initiator solution and the raw materials in the emulsion reactor to the polymerization reactor for polymerization reaction. The initiator solution is added in 6 hours and the emulsion reactor flow rate is controlled to be added in 12-13 hours. Test the conversion rate every hour. When it reaches 30%, raise the temperature to 65°C to react. When the conversion rate reaches 70%, add 5 parts of functional monomer (5 parts of dimethylacrylamide) and raise the temperature to 75°C to react until the conversion rate no longer increases. Stop the reaction and cool down to below 40°C to add a polymerization inhibitor for dispersion. Add lithium hydroxide to the obtained emulsion to neutralize the pH to 8.0, and then remove low-boiling substances and some water at 70°C. The final solid content is 46%, which is the silicon-based styrene-butadiene emulsion for anodes.

[0055] Example 3 The silicon-based anode styrene-butadiene emulsion provided in this example is prepared from the following raw materials in parts by weight: 100 parts butadiene, 105 parts styrene, 15 parts seed emulsion with 25% solid content, 48 parts functional monomer, 2 parts emulsifier, 1 part initiator, 0.5 parts reducing agent, 0.03 parts polymerization inhibitor and 420 parts deionized water.

[0056] The preparation method of silicon-based anode styrene-butadiene emulsion in this embodiment includes the following steps: (1) The preparation of seed emulsion with 25% solid content is the same as in Example 1.

[0057] (2) First, weigh the raw materials in the emulsification tank: add 280 parts of deionized water, 105 parts of styrene, 2 parts of emulsifier (1.5 parts of ammonium methacryloyloxy polyoxyethylene ether sulfate and 0.5 parts of nonanol polyoxyethylene ether), 40 parts of functional monomer (25 parts of methyl acrylate and 15 parts of dimethacrylamide), 0.5 parts of reducing agent sodium formaldehyde sulfoxylate, and 100 parts of butadiene (the reaction vessel was purged with nitrogen three times before addition). Control the temperature at about 25°C and adjust the speed to 100 rpm for stirring, dispersion, and emulsification. Set aside. Place the initiator solution in another vessel and purge with nitrogen three times. Set aside.

[0058] (3) Weigh each raw material in the polymerization reactor according to the ratio: Add 280 parts of deionized water and 15 parts of seed emulsion with 25% solid content to the polymerization reactor, perform vacuum purging with nitrogen three times to remove oxygen from the system, and then raise the temperature to 55°C. At the same time, start adding the initiator solution and the raw materials in the emulsion reactor to the polymerization reactor for polymerization reaction. The initiator solution is added in 6 hours and the emulsion reactor flow rate is controlled to be added in 12-13 hours. Test the conversion rate every hour. When it reaches 30%, raise the temperature to 65°C to react. When the conversion rate reaches 70%, add 8 parts of functional monomer (8 parts of dimethylacrylamide) and raise the temperature to 75°C to react until the conversion rate no longer increases. Stop the reaction and cool down to below 40°C to add a polymerization inhibitor for dispersion. Add lithium hydroxide to the obtained emulsion to neutralize the pH to 8.0, and then remove low-boiling substances and some water at 70°C. The final solid content is 46%, which is the silicon-based styrene-butadiene emulsion for anodes.

[0059] Example 4 This example provides a silicon-based styrene-butadiene emulsion for anodes, which has the same composition as the styrene-butadiene emulsion in Example 1. The difference is that all functional monomers are added in the early stage, and no more are added when the conversion rate reaches 70%.

[0060] Example 5 The silicon-based anode styrene-butadiene emulsion provided in this example has the same composition as the styrene-butadiene emulsion in Example 1, except that only one emulsifier (allyl polyoxyethylene ether ammonium sulfate) is used.

[0061] Comparative Example 1: The silicon-based anode styrene-butadiene emulsion provided in this comparative example has the same composition as the styrene-butadiene emulsion in Example 1. The difference is that: no staged heating is used, and the reaction is carried out at 65°C until the conversion rate reaches 70%, and the temperature is still raised to 75°C after the conversion rate reaches 70%.

[0062] Comparative Example 2: The silicon-based styrene-butadiene emulsion for the anode provided in this comparative example has the same composition as the styrene-butadiene emulsion in Example 1, except that it does not use a reactive emulsifier combined with a nonionic emulsifier, but instead uses a common single emulsifier, such as sodium dodecylbenzenesulfonate, which is completely replaced. The preparation method and process are the same as in Example 1.

[0063] Comparative Example 3: The silicon-based anode styrene-butadiene emulsion provided in this comparative example has the same composition as the styrene-butadiene emulsion in Example 1. The difference is that the dropwise addition process is not used; both are added in one step for direct reaction.

[0064] To further verify the technical effect, the following tests and corresponding test results are provided: The performance of the silicon-based anode styrene-butadiene emulsions of Examples 1 to 5 and Comparative Examples 1 to 3 were tested respectively. The test items and test methods are as follows: (1) Conversion rate test: 2g±0.5g of emulsion was weighed by electronic scale and recorded as W1. It was placed in a weighing pan with a mass of W0 and then placed in a constant temperature oven at 105±5℃ for 2 hours. After cooling, its mass was recorded as W2. The solid content was calculated as (W2-W0) / W1*100%. Then the conversion rate was calculated by solid content.

[0065] (2) Elongation test: 20g of styrene-butadiene emulsion was poured onto a clean aluminum foil and spread evenly using a 300µm scraper. It was dried at room temperature for 10 hours and then dried in a vacuum oven at 60℃ for 4 hours. It was cut according to GB / T 228.1-2010, and then the film was removed from the aluminum foil. The elongation was tested at a tensile rate of 50 mm / min, referring to the operating procedure of the electronic universal testing machine.

[0066] (3) Particle size test: The test was conducted according to GB / T 29022-2021 Dynamic Light Scattering (DLS) method for particle size analysis. The instrument parameters were set as follows: wavelength 633nm, laser power 4mW, scattering angle 173°, and refractive index method 1.48.

[0067] (4) Peel strength test: The negative electrode sheet is cut into strips using a lithium battery slitting machine. Each strip is 20mm wide. Double-sided tape is applied to a special steel plate for peel test, and the cut electrode sheet is attached to the double-sided tape. Then, the strip is flattened with a roller to ensure that the electrode sheet and the double-sided tape are fully bonded. Ten samples are taken from a set of electrode sheets. A 180° peel test is performed using a tesla force tester with a displacement speed set to 50mm / min. The average value is taken after all ten samples are tested.

[0068] (5) Internal resistance test at room temperature and low temperature: First, lithium-ion batteries are prepared. The positive electrode is composed of 96% lithium iron phosphate, 1.2% conductive agent, and 2% PVDF; the negative electrode is composed of 96% silicon-carbon composite, 1% CMC, 0.8% conductive carbon black, 2% of the above SBR emulsion, 0.6% PAA solution, and 90% deionized water. The positive and negative electrodes and other battery materials are respectively stirred and dispersed, coated, rolled, dried, wound, assembled, injected, formed, capacity tested, and packaged.

[0069] (6) Battery internal resistance test: After capacity grading, all cells are tested for internal resistance at 30% SOC. Cells with an initial efficiency below 85% are removed. Cells with capacity, internal resistance, and voltage all within mean ± 1σ are selected. According to the cell code, the corresponding test points are placed in a constant temperature chamber at 25℃ in ascending order. The test is performed using a blue battery cabinet. The battery is discharged at a rate of 0.33C until the voltage reaches 2.8V. After resting for 10 seconds, it is charged at a rate of 4.35V. Then, it is charged at a constant voltage of 4.35V until the current drops to 0.05C and the charging ends. The battery is then discharged at a constant current of 0.33C until it reaches 2.8V and the discharge ends. After resting, the 1C and 4C charge-discharge process is repeated. Finally, the internal resistance is recorded. After about 22 hours, when the test enters the 29th step of resting, the temperature chamber temperature is adjusted to -20℃ and the low-temperature internal resistance is tested.

[0070] The test results are shown in Table 1 below: Table 1 Test Results of Styrene-Butadiene Emulsion Performance

[0071] As shown in Table 1 above: 1. Compared with Comparative Examples 1 to 3, the styrene-butadiene emulsions of Examples 1 to 5 all have a particle size of 380 nm or larger, a film elongation of over 500%, and a battery rebound rate of 49% or less. This indicates that the process and formulation of this patent can produce large-particle-size emulsions with high elongation performance, which is beneficial to solving the expansion rate problem of silicon-carbon batteries, and the batteries have low rebound rate; 2. Compared with Comparative Example 2, the styrene-butadiene emulsions of Examples 1 to 5 have higher peel strength and lower internal resistance, indicating that the selection and combination of reactive emulsifiers in this invention are completely effective in improving peel strength and reducing battery internal resistance.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0073] In summary, the technical solution of this application has the following beneficial technical effects: (1) The silicon-based anode styrene-butadiene emulsion in this invention is a new generation of modified product. Through special process design, the step temperature is designed by reaching different degrees through polymerization reaction. When the conversion rate is less than 30%, low temperature polymerization is used to generate a large amount of homopolymer. When the conversion rate is above 30%, the temperature is increased, the molecular chain is rapidly crosslinked and the molecular weight of the polymer is significantly increased, and finally the high elongation performance of the film is obtained.

[0074] (2) In this invention, a reactive emulsifier is innovatively selected to be used in combination with a nonionic emulsifier, which can significantly reduce the amount of emulsifier used. At the same time, a nonionic emulsifier with weak nucleation ability is used to reduce the number of micelles and obtain an emulsion with a large particle size of up to 380 nm. The reactive emulsifier polymerizes in the molecular chain in the later stage, so that there are no residual small molecules in the system, which contributes to the improvement of the product's electrical properties.

[0075] (3) The timing of the addition of functional monomers and the combined dropping process in this invention play a role in controlling the particle structure and improving electrical performance. Adding a portion of functional monomers when the conversion rate reaches 70% in the later stage of the reaction introduces ester and amide monomers into the outer layer of the polymer, which is beneficial for better affinity with the electrolyte in the battery system and improves electrical performance. Controlling the dropping time of the initiator and monomers achieves a gradual increase in reaction particle size, a narrow particle size distribution, and uniform emulsion particle size, which is beneficial for electron transport when used as the negative electrode of the battery. At the same time, the large particle size also helps to obtain a high elongation of the film, thereby achieving a low expansion rate of the battery.

Claims

1. A styrene-butadiene emulsion for silicon-based anodes, characterized in that, The product is prepared from the following raw materials in parts by weight: 100 parts butadiene, 90-120 parts styrene, 5-20 parts seed emulsion, 20-60 parts functional monomer, 1-4 parts emulsifier, 0.6-2 parts initiator, 0.3-1.5 parts reducing agent, 0.01-0.1 parts polymerization inhibitor, and 350-500 parts deionized water.

2. The styrene-butadiene emulsion for silicon-based anodes according to claim 1, characterized in that, The seed emulsion has a particle size of 170 nm-185 nm and a solid content of 25%.

3. The styrene-butadiene emulsion for silicon-based anodes according to claim 1, characterized in that, The initiator includes at least one of tert-butyl hydroperoxide, cumene hydroperoxide, ammonium persulfate, and potassium persulfate; and / or, the reducing agent includes at least one of ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium metabisulfite.

4. The styrene-butadiene emulsion for silicon-based anodes according to claim 1, characterized in that, The emulsifier includes at least one of allyl polyoxyethylene ether ammonium sulfate, methacryloxy polyoxyethylene ether ammonium sulfate, lauryl polyoxyethylene ether, nonyl alcohol polyoxyethylene ether, and heptadecanol polyoxyethylene ether monophosphate.

5. The styrene-butadiene emulsion for silicon-based anodes according to claim 1, characterized in that, The polymerization inhibitor is any one of sodium dimethyl dithiocarbamate, hydroxylamine, and sodium nitrite.

6. The styrene-butadiene emulsion for silicon-based anodes according to claim 1, characterized in that, The functional monomers include any one of N, N-methylenebisacrylamide, N-acryloylhydroxyethylmaleimide, diallyl phthalate, dimethacrylamide, vinyltrimethoxysilane, vinyltriisopropoxysilane, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, isooctyl methacrylate, and n-pentyl acrylate.

7. A method for preparing a styrene-butadiene emulsion for a silicon-based anode as described in any one of claims 1 to 6, characterized in that, The process includes the following steps: S1. Styrene, emulsifier, functional monomer, reducing agent, butadiene, and water are dispersed and emulsified to obtain a premix. The seed emulsion and water are mixed and heated to 50℃-60℃. An initiator is added within 6 h-7 h, and the premix is ​​added within 12 h-13 h. The conversion rate is monitored while adding the premix. When the conversion rate reaches 30%, the temperature is raised to 60℃-70℃. When the conversion rate reaches 70%, the functional monomer is added and the temperature is raised to 70℃-80℃ until the conversion rate no longer increases. The temperature is then lowered to below 40℃ and a polymerization inhibitor is added to obtain a styrene-butadiene emulsion. S2. Lithium hydroxide is added to the styrene-butadiene emulsion until the pH is 7.9-8.

1. The mixture is then heated at 65℃-75℃ until the solid content is 45%-47% to obtain a styrene-butadiene emulsion for silicon-based anodes.

8. The method for preparing the styrene-butadiene emulsion for silicon-based anodes according to claim 7, characterized in that, Before step S1, the process also includes: S11. Mixing deionized water, styrene, emulsifier, acrylic acid, and n-dodecyl mercaptan, placing the mixture under a nitrogen atmosphere, adding butadiene, heating and mixing to react, adding sodium persulfate solution to continue the reaction, and obtaining a seed emulsion.

9. The method for preparing the styrene-butadiene emulsion for silicon-based anodes according to claim 8, characterized in that, In step S11, the temperature for heating the mixture is 58℃-62℃, and the heating time for the mixture is 0.4 h-0.6 h.

10. The application of a silicon-based styrene-butadiene emulsion for anodes in battery adhesives, characterized in that, The silicon-based anode styrene-butadiene emulsion includes the silicon-based anode styrene-butadiene emulsion as described in any one of claims 1 to 7, or is prepared by the method for preparing silicon-based anode styrene-butadiene emulsion as described in claim 8 or 9.

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