SBR adhesive, its preparation method and application

Abstract

This invention belongs to the field of lithium-ion battery materials technology, specifically relating to an SBR adhesive, its preparation method, and its application. The SBR adhesive of this invention comprises a core layer and a shell layer. The core layer includes butadiene, styrene, and hydroxyacrylate as main raw materials, while the shell layer includes isooctyl acrylate, β-hydroxyethyl methacrylate, itaconic acid, and N-vinylpyrrolidone as main raw materials. It is prepared through core layer prepolymerization, shell layer gradient polymerization, and dynamic crosslinking modification. The SBR adhesive provided by this invention balances cohesion and interfacial adhesion, and the preparation method is controllable and reproducible. This invention utilizes the SBR adhesive in batteries to improve electrode structural integrity and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to an SBR adhesive, its preparation method, and its application. Background Technology

[0002] In the process of upgrading lithium-ion batteries to higher energy density, silicon-based anodes and high-nickel ternary cathodes have become key material systems. However, the electrodes experience significant volume effects and interfacial stresses during charge-discharge cycles, placing high demands on water-based adhesives for high cohesion, strong adhesion, dynamic self-adaptation, and high-temperature stability. Styrene-butadiene rubber (SBR), with its advantages of low cost, good dispersibility, and moderate bonding strength, has become the mainstream choice for water-based anode adhesives and has been widely used in the preparation of graphite, silicon-based, and ternary electrode systems.

[0003] However, conventional SBR adhesives inherently present a dilemma: it's difficult to balance cohesion and adhesion. Simply increasing the crosslinking density leads to increased electrode brittleness and decreased flexibility, while decreasing the crosslinking density easily results in electrode powdering and insufficient peel strength. Furthermore, traditional SBR molecular chains lack dynamically responsive functional groups, and the crosslinking network is a static, irreversible structure. This makes it unable to repair microcracks generated during cycling and unable to buffer the stress concentration caused by the significant volume expansion of the silicon-based anode, easily leading to electrode breakage, powdering, and detachment. In addition, SBR is prone to swelling and degradation under high temperature and high voltage conditions, resulting in electrode structural failure, battery cycle and safety performance degradation, severely limiting its large-scale application in high-energy-density lithium-ion batteries.

[0004] To improve the performance of SBR adhesives, existing technologies have undergone extensive modification studies. For example, CN113555558A discloses a core-shell structured SBR latex adhesive, which improves bonding and mechanical properties through the design of high cohesive segments in the core layer and polar functional groups in the shell layer. However, its shell layer is a conventional copolymer structure and does not adopt a gradient grafting strategy, which makes it impossible to achieve a continuous transition from flexible bonding to polar anchoring, and the interface compatibility is still insufficient. Moreover, it relies only on hydrogen bonds and physical entanglement, without constructing a dynamic cross-linked network, resulting in limited self-healing and stress relaxation capabilities.

[0005] CN121555116A proposes a self-healing polyacrylic acid adhesive based on dynamic borate ester bonds, which utilizes the reversible reaction of boric acid-hydroxyl groups to achieve network repair. However, its matrix is ​​a polyacrylic acid system, not a core-shell structure SBR, which has problems such as poor compatibility with electrode slurry, insufficient flexibility, and poor processability. Furthermore, it does not combine gradient grafting structures to achieve synergistic optimization of interface and bulk properties.

[0006] Therefore, existing SBR modification technologies generally suffer from the following defects: core-shell structures are mostly simple two-stage copolymers, lacking gradient grafting design, and unable to simultaneously balance cohesion, adhesion, and interfacial gradient adaptability; crosslinking systems are mainly based on static covalent bonds or physical interactions, lacking reversible dynamic crosslinking networks, and do not possess self-healing and stress-adaptive capabilities; functional monomers and crosslinking agents have poor matching, resulting in insufficient stability under high temperature and high voltage, making it difficult to meet the long-term service requirements of silicon-based anodes and high-nickel cathodes. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the above-mentioned defects in the prior art and to provide an SBR adhesive and its preparation method. The prepared SBR adhesive balances cohesion and interfacial adhesion, and the preparation method is controllable and has good repeatability. This invention also provides applications of this SBR adhesive to improve electrode structural integrity and cycle stability.

[0008] The SBR adhesive of the present invention comprises a core layer and a shell layer. The core layer comprises butadiene, styrene, and hydroxy acrylate as the main raw materials, and the shell layer comprises isooctyl acrylate, β-hydroxyethyl methacrylate, itaconic acid, and N-vinylpyrrolidone as the main raw materials.

[0009] The core and shell layers also include emulsifiers and initiators, respectively. The core layer raw materials, by weight, include: 30-45 parts butadiene, 25-35 parts styrene, and 5-10 parts hydroxyacrylate; the shell layer raw materials, by weight, include: 10-20 parts isooctyl acrylate, 3-8 parts β-hydroxyethyl methacrylate, 2-5 parts itaconic acid, and 1-4 parts N-vinylpyrrolidone. The emulsifier for the core layer is a mixture of sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether at a mass ratio of 1-3:1, preferably 2:1; the emulsifier for the shell layer is sodium dodecyl sulfate. Both the core and shell layers use ammonium persulfate or potassium persulfate as initiators.

[0010] The preferred hydroxy acrylate is hydroxyethyl acrylate or hydroxypropyl acrylate.

[0011] The preferred core layer raw materials, by weight, are: 30-45 parts butadiene, 25-35 parts styrene, 5-10 parts hydroxy acrylate, 0.5-1.5 parts initiator, 1-3 parts emulsifier, and 80-120 parts deionized water.

[0012] Preferred shell gradient monomers: 10-20 parts isooctyl acrylate, 3-8 parts β-hydroxyethyl methacrylate, 2-5 parts itaconic acid, 1-4 parts N-vinylpyrrolidone, 0.3-1.0 parts initiator, 0.5-2 parts emulsifier, and 40-60 parts deionized water.

[0013] The preparation method of the SBR adhesive includes the following steps:

[0014] (1) Core layer prepolymerization: Dissolve the emulsifier in water, add butadiene, styrene and hydroxy acrylate to obtain a preemulsion, and heat it up; take a part of the preemulsion and a part of the initiator aqueous solution, keep it warm for seed polymerization, add the remaining part of the preemulsion and the remaining part of the initiator dropwise, keep it warm after the dropwise addition is completed to obtain the core layer latex solution;

[0015] (2) Shell gradient polymerization: Isooctyl acrylate and β-hydroxyethyl methacrylate are dissolved in emulsifier to obtain pre-emulsion A; itaconic acid and N-vinylpyrrolidone are dissolved in emulsifier, and then an initiator aqueous solution is added to obtain solution B; pre-emulsion A is added dropwise to the core latex solution obtained in step (1), and after the reaction is kept warm, solution B is added dropwise to keep warm to obtain functionalized SBR latex particles;

[0016] (3) Dynamic crosslinking modification: The pH of the functionalized SBR latex particles is adjusted to 6.5~7.5, and a dynamic crosslinking agent ethanol solution is added dropwise. The reaction is kept at a certain temperature and after post-treatment, the SBR adhesive is obtained.

[0017] The dynamic crosslinking agent is a condensation product of 3,5-dihydroxyphenylboronic acid and ethylene glycol diglycidyl ether.

[0018] The amount of the dynamic crosslinking agent added is 2-8 wt% of the dry weight of the functionalized SBR latex particles.

[0019] The reaction temperature for the core layer prepolymerization is 75~85℃.

[0020] The reaction temperature for the shell gradient polymerization is 65~75℃.

[0021] The reaction temperature for the dynamic crosslinking modification is 40~50℃.

[0022] Preferably, in step (1), the emulsifier is dissolved in water, and butadiene, styrene, and hydroxyacrylate are added to obtain a pre-emulsion, which is then heated. Separately, a 10% aqueous solution of the pre-emulsion (10% of the total mass) and a 20% aqueous solution of the initiator (20% of the total initiator mass) are taken and kept at this temperature for 30-60 minutes for seed polymerization. The remaining pre-emulsion and initiator are then added dropwise at a uniform rate for 3-4 hours. After the addition is completed, the mixture is kept at this temperature for 1-2 hours to obtain the core layer latex. The pre-emulsion is then stirred at 2000-3000 r / min for 30-40 minutes to obtain the final product.

[0023] Preferably, in step (2), pre-emulsion A is added dropwise to the core layer latex obtained in step (1) for 1-2 hours, and the reaction is maintained at a warm temperature for 30-60 minutes. Then, solution B is added dropwise for 1.5-2.5 hours, and the reaction is maintained at a warm temperature for 1-2 hours. Pre-emulsion A is obtained by stirring at 2000-3000 r / min for 30-40 minutes. Solution B is also prepared under the same conditions.

[0024] Preferably, in step (3), the pH is adjusted using ammonia or triethanolamine. The most preferred pH adjustment is 6.5 to 7.5. The dynamic crosslinking agent ethanol solution is prepared by dissolving the dynamic crosslinking agent in ethanol to achieve a mass concentration of 10 to 20 wt%.

[0025] Preferably, in step (3), the pH of the functionalized SBR latex particles is adjusted to neutral, and a dynamic crosslinking agent ethanol solution is added dropwise at 0.5~1mL / min. The reaction is kept at a temperature of 1~1.5h. After post-treatment, the SBR adhesive is obtained.

[0026] Preferably, in step (3), the post-processing step involves adding a chain transfer agent to terminate the reaction, cooling to below 30°C, filtering, and degassing to obtain the target adhesive. The chain transfer agent is dodecyl mercaptan.

[0027] Application of the SBR adhesive: The SBR adhesive is used in the preparation of positive and / or negative electrodes of lithium-ion batteries, with an addition amount of 2-8 wt% of the active material mass; the negative electrode active material is Si, SiO, Si / C or graphite-silicon composite material, and the positive electrode active material is NCM811, NCM90100 or lithium iron phosphate.

[0028] Negative electrode slurry: After dispersing the active material, conductive agent, and CMC in deionized water, add the adhesive and stir at 500~800 r / min for 1~2 h;

[0029] Positive electrode slurry: After dispersing the active material and conductive agent in deionized water, add the adhesive and stir at 800~1000r / min for 1.5~2.5h.

[0030] The adhesive of the present invention is a core-shell structured functionalized SBR latex particles, which together with a dynamic crosslinking agent form a reversible crosslinking network; the adhesive includes a core layer and a shell layer, the core layer being a high cohesive SBR chain segment, and the shell layer being a high-adhesion gradient grafted chain segment.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) The present invention adopts a gradient grafted core-shell structure design. The core layer provides high cohesive strength and structural stability, while the shell layer gradually transitions from flexible chain segments to highly polar and highly anchored chain segments. This balances cohesion and interfacial adhesion at the molecular structure level, effectively solving the inherent contradiction between cohesion and adhesion in traditional SBR.

[0033] (2) In the preparation of SBR adhesive, the present invention introduces a dynamic reversible cross-linking network of borate ester, which can realize the breaking and recombination of cross-linking bonds during the charge-discharge cycle of the electrode, and has dynamic self-repair and stress relaxation capabilities. It can significantly buffer the volume expansion of silicon-based negative electrode, inhibit the propagation of microcracks in electrode sheet, and improve the integrity of electrode structure and cycle stability.

[0034] (3) This invention significantly improves the interfacial bonding force between the adhesive and the active material, current collector and conductive agent through the synergistic effect of multiple functional groups such as hydroxyl, carboxyl and amide groups. At the same time, it improves the anti-swelling and anti-degradation ability under high temperature and high voltage, so that the adhesive can be adapted to both silicon-based anode and high-nickel ternary cathode, thus broadening the application range of SBR waterborne adhesive in high energy density lithium-ion batteries.

[0035] (4) The preparation process of the present invention adopts stepwise gradient emulsion polymerization, which is mild and controllable, does not require high-pressure equipment, and is easy to scale up industrially. It is compatible with a variety of positive and negative electrode systems, has a wide range of applications, and the resulting adhesive has uniform particle size, high stability, and excellent slurry dispersibility. It can directly replace the traditional SBR without changing the existing electrode sheeting process. Attached Figure Description

[0036] Figure 1 The image shows the DSC diagram of the SBR adhesive prepared in Example 1.

[0037] Figure 2 The image shows the FTIR spectrum of the SBR adhesive prepared in Example 1.

[0038] Figure 3 The image shows the DSC diagram of the SBR adhesive prepared in Example 2.

[0039] Figure 4 The image shows the FTIR spectrum of the SBR adhesive prepared in Example 2.

[0040] Figure 5 The image shows the DSC diagram of the SBR adhesive prepared in Example 3.

[0041] Figure 6 The image shows the FTIR spectrum of the SBR adhesive prepared in Example 3. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments.

[0043] Description of the core raw materials used in this invention:

[0044] Dynamic crosslinking agent: The condensation product of 3,5-dihydroxyphenylboronic acid and ethylene glycol diglycidyl ether; 3,5-dihydroxyphenylboronic acid was purchased from Sigma-Aldrich with a purity ≥98%. Ethylene glycol diglycidyl ether was purchased from TCI Chemicals with a purity ≥97%. The preparation steps were as follows: 3,5-dihydroxyphenylboronic acid (1.54 g, 10 mmol) and anhydrous potassium carbonate (2.07 g, 15 mmol) were added to a dry 100 mL round-bottom flask. Anhydrous acetone (30 mL) was then added, and a homogeneous suspension was formed under magnetic stirring. The reaction system was stirred at room temperature for 30 min to partially deprotonate the phenolic hydroxyl groups of potassium carbonate, generating phenoxy anions with strong nucleophilicity. Subsequently, ethylene glycol diglycidyl ether (2.09 g, 12 mmol) was slowly added dropwise to the reaction system. After the addition was complete, the reaction system was heated to the reflux temperature of acetone (56 °C) under nitrogen protection and stirred continuously for 12 h. Under these conditions, the phenoxy anion undergoes nucleophilic attack on the epoxy group, initiating an epoxy ring-opening reaction to form the target condensation product containing a β-hydroxy ether structure. The reaction process was monitored by HPLC. After the reaction, the system was cooled to room temperature, and inorganic salts were removed by vacuum filtration. The filter cake was washed with a small amount of acetone (10 mL). The filtrates were combined and the solvent was removed by rotary evaporation under reduced pressure. The resulting residue was dissolved in dichloromethane (30 mL) and transferred to a separatory funnel. It was washed once with deionized water (20 mL) to remove residual inorganic salts and once with saturated sodium chloride solution (20 mL) to reduce the water content of the organic phase. The organic layer was dried over anhydrous sodium sulfate for 30 min and then filtered. The filtrate was concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography with dichloromethane / methanol = 20:1 (v / v) as the eluent. The target product fraction was collected and the solvent was removed by rotary evaporation to obtain a pale yellow solid product. The product yield was approximately 80%, and the purity was 98%.

[0045] Chain transfer agent: dodecanethiol;

[0046] pH adjuster: ammonia or triethanolamine;

[0047] Hydroxyacrylates: hydroxyethyl acrylates or hydroxypropyl acrylates;

[0048] Initiator: Ammonium persulfate or potassium persulfate.

[0049] Conductive agents: The preferred positive electrode is conductive carbon black (model: Ketjen Black EC-300J), and the preferred negative electrode is conductive graphite (model: TIMCALKS6), both of which are commonly used in the lithium-ion battery industry.

[0050] Battery performance testing instructions: Peel strength is tested using an electronic tensile testing machine (GB / T2790-1995); Cycle capacity retention is tested using a battery charge-discharge tester, with 1C charge-discharge and a certain number of cycles, and the capacity retention is calculated; Swelling rate is tested by immersing the battery in electrolyte at 60℃ and 4.5V for 72 hours, and the mass change rate is calculated.

[0051] The specific method for preparing the SBR adhesive of this invention includes the following steps:

[0052] (1) Core layer prepolymerization: Dissolve the emulsifier in water, add butadiene, styrene and hydroxy acrylate to obtain a preemulsion, and heat to 75~85℃; take 10wt% of the preemulsion and 20wt% of the initiator aqueous solution, keep at 75~85℃ for 30~60min for seed polymerization, add the remaining part of the preemulsion and the remaining part of the initiator dropwise at a uniform rate, and keep at 1~2h after 3~4h of dropwise addition to obtain the core layer latex solution;

[0053] (2) Shell gradient polymerization: Keep the core layer latex solution temperature at 65~75℃, dissolve isooctyl acrylate and β-hydroxyethyl methacrylate in emulsifier to obtain pre-emulsion A; dissolve itaconic acid and N-vinylpyrrolidone in emulsifier, and then add an initiator aqueous solution to obtain solution B; add pre-emulsion A dropwise to the obtained core layer latex solution, the dropwise addition time is 1~2h, keep the temperature for 30min to react, then add solution B dropwise, the dropwise addition time is 1.5~2.5h, keep the temperature for 1~2h to react, and obtain functionalized SBR latex particles;

[0054] (3) Dynamic crosslinking modification: Keep the functionalized SBR latex particles at 40~50℃, add ammonia or triethylamine to adjust the pH to 6.5~7.5, add 10~20wt% dynamic crosslinking agent ethanol solution at 0.5-1mL / min, keep warm for 1~1.5h to react and form a reversible crosslinking network;

[0055] (4) Post-treatment: Add dodecyl mercaptan to terminate the reaction, cool down to below 30°C, filter and degas to obtain the target adhesive.

[0056] Example 1

[0057] The preparation process of the gradient grafted core-shell SBR adhesive of the present invention is as follows:

[0058] (1) Core layer prepolymerization: 80 parts of deionized water and 1 part of emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 2:1) are stirred and dissolved evenly. 30 parts of butadiene, 25 parts of styrene and 5 parts of hydroxyethyl acrylate are added and mixed to obtain a preemulsion. The temperature is raised to 75°C. 10% of the total amount of the preemulsion and 20% of the total amount of ammonium persulfate aqueous solution (0.5 parts of total ammonium persulfate, 20% refers to 20% of the mass of the ammonium persulfate aqueous solution, and the concentration of the ammonium persulfate aqueous solution is 50wt%) are taken and kept at the temperature for 30 min for seed polymerization. The remaining preemulsion and the remaining ammonium persulfate aqueous solution are added dropwise at a uniform rate. After adding for 3 h, the temperature is kept for 1 h to obtain the core layer latex solution.

[0059] (2) Shell gradient polymerization: Keep the core layer latex solution temperature at 65℃; dissolve 10 parts of isooctyl acrylate and 3 parts of β-hydroxyethyl methacrylate in 0.3 parts of sodium dodecyl sulfate to obtain pre-emulsion A; dissolve 2 parts of itaconic acid and 1 part of N-vinylpyrrolidone in 0.2 parts of sodium dodecyl sulfate, and then add 0.3 parts of ammonium persulfate to prepare an aqueous solution of ammonium persulfate (the concentration of ammonium persulfate in the aqueous solution is 50wt%) to obtain solution B; add pre-emulsion A dropwise to the obtained core layer latex solution for 1 hour, keep warm for 30 minutes, and then add solution B dropwise for 1.5 hours, keep warm for 1 hour to obtain functionalized SBR latex particles;

[0060] (3) Dynamic crosslinking modification: Keep the functionalized SBR latex particles at 40°C, add ammonia to adjust the pH to 6.5, and add 10wt% dynamic crosslinking agent ethanol solution at a rate of 0.5mL / min (the amount added is 2wt% of the dry weight of the functionalized SBR latex particles). Keep warm for 1h to react and form a reversible borate ester crosslinking network.

[0061] (4) Post-treatment: 0.1 parts of dodecanethiol were added to terminate the reaction. The reaction system was cooled to below 30°C, filtered, and degassed to obtain the target gradient grafted core-shell SBR adhesive with a solid content of 49.5%, a latex particle size / PDI of 175 nm, and a viscosity of 85 mPa·s at 25°C. Its differential scanning calorimetry (DSC) graph is shown below. Figure 1 As shown, the glass transition temperature Tg is 16.07℃. Its Fourier transform infrared (FTIR) spectrum is shown below. Figure 2 As shown, the successful construction of the gradient-grafted core-shell SBR structure and the dynamic cross-linked network of borate ester in the prepared target product is confirmed, and it is completely consistent with the designed structure.

[0062] Example 2

[0063] The preparation process of the gradient grafted core-shell SBR adhesive of the present invention is as follows:

[0064] (1) Core layer prepolymerization: 100 parts of deionized water and 2 parts of emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 2:1) are stirred and dissolved evenly. 38 parts of butadiene, 30 parts of styrene and 8 parts of hydroxypropyl acrylate are added and mixed and stirred to obtain a preemulsion. The temperature is raised to 80℃. 10% of the total amount of preemulsion and 20% of the total amount of potassium persulfate aqueous solution (total potassium persulfate 1.0 part, 20% refers to 20% of the mass of potassium persulfate aqueous solution, the concentration of potassium persulfate aqueous solution is 50wt%) are taken and kept at the temperature for 45 min for seed polymerization. The remaining preemulsion and the remaining potassium persulfate aqueous solution are added dropwise at a uniform rate. After adding for 3.5 h, the temperature is kept for 1.5 h to obtain the core layer latex solution.

[0065] (2) Shell gradient polymerization: Keep the core layer latex solution temperature at 70℃; dissolve 15 parts of isooctyl acrylate and 5 parts of β-hydroxyethyl methacrylate in 1.0 parts of sodium dodecyl sulfate to obtain pre-emulsion A; dissolve 3.5 parts of itaconic acid and 2.5 parts of N-vinylpyrrolidone in 0.2 parts of sodium dodecyl sulfate, and then add 0.6 parts of potassium persulfate to prepare potassium persulfate aqueous solution (the concentration of potassium persulfate in the aqueous solution is 50wt%) to obtain solution B; add pre-emulsion A dropwise to the obtained core layer latex solution for 1.5h, keep warm for 30min, and then add solution B dropwise for 2h, keep warm for 1.5h to obtain functionalized SBR latex particles;

[0066] (3) Dynamic crosslinking modification: keep the functionalized SBR latex particles at 45°C, add triethanolamine to adjust the pH to 7.0, add 15wt% dynamic crosslinking agent ethanol solution at a rate of 0.8mL / min (the amount added is 5wt% of the dry weight of the functionalized SBR latex particles), keep warm for 1.2h to react and form a reversible borate ester crosslinking network;

[0067] (4) Post-treatment: 0.3 parts of dodecanethiol were added to terminate the reaction. The reaction system was cooled to below 30°C, filtered, and degassed to obtain the target gradient grafted core-shell SBR adhesive with a solid content of 48.5%, a latex particle size / PDI of 155 nm, and a viscosity of 70 mPa•s at 25°C. Its differential scanning calorimetry (DSC) curve is shown below. Figure 3 As shown, the glass transition temperature Tg is 14.86℃. Its Fourier transform infrared (FTIR) spectrum is shown below. Figure 4 As shown, the successful construction of the gradient-grafted core-shell SBR structure and the dynamic cross-linked network of borate ester in the prepared target product is confirmed, and it is completely consistent with the designed structure.

[0068] Example 3

[0069] The preparation process of the gradient grafted core-shell SBR adhesive of the present invention is as follows:

[0070] (1) Core layer prepolymerization: 120 parts of deionized water and 3 parts of emulsifier A (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 2:1) are stirred and dissolved evenly. 45 parts of butadiene, 35 parts of styrene and 10 parts of hydroxyethyl acrylate are added and mixed and stirred to obtain a preemulsion. The temperature is raised to 85℃. 10% of the total amount of preemulsion and 20% of the total amount of ammonium persulfate aqueous solution (total ammonium persulfate 1.5 parts, 20% refers to 20% of the mass of the ammonium persulfate aqueous solution, the concentration of the ammonium persulfate aqueous solution is 50wt%) are taken and kept at the temperature for 60 min for seed polymerization. The remaining preemulsion and the remaining ammonium persulfate aqueous solution are added dropwise at a uniform rate. After 4 h of dropwise addition, the temperature is kept for 2 h to obtain the core layer latex solution.

[0071] (2) Shell gradient polymerization: Keep the core layer latex solution temperature at 75℃; dissolve 20 parts of isooctyl acrylate and 8 parts of β-hydroxyethyl methacrylate in 1 part of sodium dodecyl sulfate to obtain pre-emulsion A; dissolve 5 parts of itaconic acid and 4 parts of N-vinylpyrrolidone in 1 part of sodium dodecyl sulfate, and then add 1.0 part of ammonium persulfate to prepare an aqueous solution of ammonium persulfate (the concentration of ammonium persulfate in the aqueous solution is 50wt%) to obtain solution B; add pre-emulsion A dropwise to the obtained core layer latex solution for 2 hours, keep warm for 30 minutes, then add solution B dropwise for 2.5 hours, keep warm for 2 hours to obtain functionalized SBR latex particles;

[0072] (3) Dynamic crosslinking modification: Keep the functionalized SBR latex particles at 50°C, add ammonia to adjust the pH to 7.5, add 20wt% dynamic crosslinking agent ethanol solution at a rate of 1mL / min (the amount added is 8wt% of the dry weight of the functionalized SBR latex particles), keep warm for 1.5h to react and form a reversible borate ester crosslinking network.

[0073] (4) Post-treatment: Add 0.5 parts of dodecanethiol to terminate the reaction, cool the reaction system to below 30℃, filter and degas to obtain the target gradient grafted core-shell SBR adhesive with a solid content of 51.3%, a latex particle size / PDI of 195nm, and a viscosity of 58mPa•s at 25℃. The differential scanning calorimetry (DSC) graph is shown below. Figure 5 As shown, the glass transition temperature Tg is 8.10℃. Its Fourier transform infrared (FTIR) spectrum is shown below. Figure 6 As shown, the successful construction of the gradient-grafted core-shell SBR structure and the dynamic cross-linked network of borate ester in the prepared target product is confirmed, and it is completely consistent with the designed structure.

[0074] Example 4

[0075] This embodiment utilizes the SBR adhesive prepared in Example 1 for the preparation of Si / C composite materials. For the negative electrode preparation: the mass ratio of Si / C composite material: conductive graphite (TIMCALKS6): CMC: SBR adhesive = 93:3:2:2. First, the Si / C composite material, conductive graphite, and CMC are added to deionized water and stirred until evenly dispersed. Then, the prepared SBR adhesive is added, and the mixture is stirred at 500 r / min for 1.5 h to obtain a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto a copper current collector, and after drying and rolling, a Si / C negative electrode sheet is obtained.

[0076] Battery assembly: Using the prepared Si / C composite material as the negative electrode, NCM811 as the positive electrode, Celgard2400 as the separator, and 1 mol / L LiPF6 / EC, DMC, and EMC (volume ratio 1:1:1) as the electrolyte, a CR2032 coin cell lithium-ion battery was assembled.

[0077] The Si / C silicon-based negative electrode sheet prepared in this embodiment has a peel strength of 1.8 N / cm;

[0078] The CR2032 button lithium-ion battery retains 82.6% of its capacity after 500 cycles at 1C, with no obvious electrode powder shedding or damage during the cycle. According to GB / T2423, the low-temperature discharge retention rate at -20℃ is 71.2%, and the high-temperature discharge retention rate at 60℃ is 85.6%.

[0079] The mass swelling rate of the Si / C negative electrode sheet was 23.8% (the Si / C negative electrode sheet was placed in an electrolyte of 1 mol / L LiPF6 / EC, DMC, and EMC (volume ratio 1:1:1) at room temperature for 24 hours).

[0080] Example 5

[0081] This embodiment utilizes the SBR adhesive prepared in Example 2 for the fabrication of the NCM90100 positive electrode, as detailed below:

[0082] Positive electrode preparation: The positive electrode slurry was prepared according to the following mass ratio: NCM90100: conductive carbon black (Ketjen Black EC-300J): SBR adhesive = 93:3:4. The NCM90100 active material and conductive carbon black were added to deionized water and stirred until evenly dispersed. Then, the SBR adhesive prepared in this embodiment was added, and the mixture was stirred at 900 r / min for 2 h to obtain a uniform positive electrode slurry. Positive electrode preparation: The positive electrode slurry was uniformly coated onto an aluminum current collector, dried, and rolled to obtain the NCM90100 positive electrode sheet.

[0083] Battery assembly: Using the prepared NCM90100 positive electrode as the positive electrode, the graphite-silicon composite negative electrode as the negative electrode, Celgard2400 as the separator, and 1 mol / L LiPF6 / EC, DMC, EMC (volume ratio 1:1:1) as the electrolyte, a soft-pack lithium-ion battery (specification: 100mm×50mm×5mm) was assembled.

[0084] The peel strength of the NCM90100 positive electrode sheet prepared in this embodiment is 1.6 N / cm;

[0085] The capacity retention rate of the soft-pack battery after 500 cycles at 1C charge-discharge rate under high temperature and high voltage conditions of 60℃ and 4.5V is 86.4%, and there is no obvious powder shedding or damage of the electrode sheets during the cycle. According to GB / T2423, the discharge retention rate at -20℃ is 75.4%, and the discharge retention rate at 60℃ is 88.3%.

[0086] The mass swelling rate of the NCM90100 positive electrode is 19.5% (the NCM90100 positive electrode was placed in an electrolyte of 1 mol / L LiPF6 / EC, DMC, and EMC (volume ratio 1:1:1) at room temperature for 24 hours).

[0087] Example 6

[0088] This embodiment utilizes the SBR adhesive prepared in Example 3 for the preparation of a graphite-silicon composite anode, as detailed below:

[0089] Negative electrode slurry preparation: The graphite-silicon composite material, conductive graphite (TIMCALKS6), CMC, and SBR adhesive were mixed in a mass ratio of 88:4:3:5. First, the graphite-silicon composite material, conductive graphite, and CMC were added to deionized water and stirred to disperse evenly. Then, the prepared SBR adhesive was added and stirred at 800 r / min for 2 h to obtain a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on a copper current collector, and after drying and rolling, the graphite-silicon composite negative electrode sheet was obtained.

[0090] Battery assembly: Using the prepared graphite-silicon composite negative electrode as the negative electrode, NCM811 as the positive electrode, Celgard2400 as the separator, and 1 mol / L LiPF6 / EC, DMC, EMC (volume ratio 1:1:1) as the electrolyte, a square lithium-ion battery (size: 50mm×30mm×10mm) was assembled.

[0091] The peel strength of the graphite-silicon composite negative electrode sheet prepared in this embodiment is 2.5 N / cm;

[0092] The square battery retains 90.1% of its capacity after 1000 cycles at a 1C charge / discharge rate, with no obvious electrode powder shedding or damage during the cycle. According to GB / T2423, the low-temperature discharge retention rate at -20℃ is 79.8%, and the high-temperature discharge retention rate at 60℃ is 91.5%.

[0093] The mass swelling rate of the graphite-silicon composite negative electrode sheet was 15.2% (the graphite-silicon composite negative electrode sheet was placed in an electrolyte of 1 mol / L LiPF6 / EC, DMC, and EMC (volume ratio 1:1:1) at room temperature for 24 h).

[0094] Comparative Example 1

[0095] Using commercially available unmodified SBR adhesive (SBR emulsion SN-307R, Shanghai Wai Electric International Trade Co., Ltd.), Si / C silicon-based negative electrode sheets were prepared and CR2032 coin cells were assembled using the same process as in Example 4, and their performance was tested.

[0096] Performance test results: The peel strength of the Si / C silicon-based negative electrode sheet is 1.2 N / cm; the discharge capacity retention rate of the CR2032 coin cell after 500 cycles at a 1C charge-discharge rate is 54.8%, and obvious electrode powder shedding and damage occur during the cycle, and the battery capacity decays rapidly.

[0097] Comparative Example 2

[0098] The raw materials for the SBR adhesive are exactly the same as in Example 2. The only difference in the preparation process is the shell polymerization method (no gradient; all shell monomers are mixed to prepare a single pre-emulsion, which is added dropwise in one step without stepwise gradient addition). The remaining preparation processes, cathode preparation, and battery assembly processes are consistent with Example 2, specifically:

[0099] (1) Core layer prepolymerization: 100 parts of deionized water and 2 parts of emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 2:1) are stirred and dissolved evenly. 38 parts of butadiene, 30 parts of styrene and 8 parts of hydroxypropyl acrylate are added and mixed to obtain a preemulsion. The temperature is raised to 80°C. 10% of the total amount of preemulsion and 20% of the total amount of potassium persulfate aqueous solution (total potassium persulfate 1.0 part, potassium persulfate aqueous solution concentration is 50wt%) are taken and kept at the temperature for 45 min for seed polymerization. The remaining preemulsion and the remaining potassium persulfate aqueous solution are added dropwise at a uniform rate. After adding for 3.5 h, the temperature is kept for 1.5 h to obtain the core layer latex solution.

[0100] (2) Homogeneous polymerization of the shell layer (without gradient): The temperature of the core layer latex solution was kept at 70°C; 15 parts of isooctyl acrylate, 5 parts of β-hydroxyethyl methacrylate, 3.5 parts of itaconic acid, and 2.5 parts of N-vinylpyrrolidone were mixed, and 1.2 parts of sodium dodecyl sulfate and an appropriate amount of deionized water were added. The mixture was stirred and emulsified evenly to obtain a single pre-emulsion of the shell layer; 0.6 parts of potassium persulfate were dissolved in an appropriate amount of deionized water to prepare a 50wt% potassium persulfate aqueous solution as the shell initiator solution; the single pre-emulsion of the shell layer and the shell initiator solution were added dropwise to the core layer latex solution at a uniform rate for 2.0 h. After the addition was completed, the mixture was kept warm for 2 h to obtain functionalized SBR latex particles.

[0101] (3) Post-treatment: After the reaction is completed, cool to room temperature, adjust the pH to 7-8 with ammonia, filter to remove the coagulants, and obtain SBR adhesive emulsion.

[0102] Using the SBR adhesive prepared above, NCM90100 positive electrode sheets were prepared and assembled into soft-pack batteries according to the same process as in Example 5, and their performance was tested.

[0103] Performance test results: The peel strength of the NCM90100 positive electrode sheet is 1.1 N / cm;

[0104] Under high temperature and high voltage conditions of 60℃ and 4.5V, the capacity retention rate of the soft-pack battery after 500 cycles at 1C charge-discharge rate is 65.3%, the electrode structure is prone to failure, and the high temperature stability is poor.

[0105] Comparative Example 3

[0106] The SBR adhesive was prepared in exactly the same way as in Example 3. The only difference in the preparation process was the crosslinking method (benzoyl peroxide static crosslinking agent was used instead of dynamic crosslinking agent, and the amount added was the same as that of dynamic crosslinking agent in Example 3). The rest of the preparation process, anode preparation and battery assembly process were the same as in Example 6. Specifically, step (3) was replaced with the following steps:

[0107] (3) Static crosslinking modification: Keep the functionalized SBR latex particles at 50°C, add ammonia to adjust the pH to 7.5, and add an aqueous static crosslinking agent (ethylene glycol diglycidyl ether, the amount added is 2wt% of the dry weight of the functionalized SBR latex particles) at a rate of 1mL / min, and keep warm for 1.5h to react; an irreversible ring-opening esterification reaction occurs between the epoxy group and the shell carboxyl / hydroxyl group to form a static crosslinking network; other steps are the same as in Example 3.

[0108] Using the SBR adhesive prepared above, graphite-silicon composite negative electrode sheets were prepared and assembled into square batteries according to the same process as in Example 6, and their performance was tested.

[0109] Performance test results: The peel strength of the graphite-silicon composite negative electrode sheet is 1.0 N / cm;

[0110] Square batteries retain 68.5% of their capacity after 1000 cycles at a 1C charge / discharge rate. Microcracks appear on the electrodes during the cycle, which cannot be self-repaired, resulting in poor long-term cycle stability.

[0111] Comparative Example 4

[0112] The preparation process of a gradient-grafted core-shell SBR adhesive is as follows:

[0113] (1) Core layer prepolymerization: 80 parts of deionized water and 1 part of emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 2:1) are stirred and dissolved evenly. 30 parts of butadiene, 25 parts of styrene and 5 parts of hydroxyethyl acrylate are added and mixed to obtain a preemulsion. The temperature is raised to 75°C. 10% of the total amount of the preemulsion and 20% of the total amount of ammonium persulfate aqueous solution (0.5 parts of total ammonium persulfate, 20% refers to 20% of the mass of the ammonium persulfate aqueous solution, and the concentration of the ammonium persulfate aqueous solution is 50wt%) are taken and kept at the temperature for 30 min for seed polymerization. The remaining preemulsion and the remaining ammonium persulfate aqueous solution are added dropwise at a uniform rate. After adding for 3 h, the temperature is kept for 1 h to obtain the core layer latex solution.

[0114] (2) Shell gradient polymerization: The core layer latex solution temperature was maintained at 65℃; 10 parts of isooctyl acrylate and 3 parts of β-hydroxyethyl methacrylate were dissolved in 0.3 parts of sodium dodecyl sulfate to obtain pre-emulsion A; 2 parts of itaconic acid and 1 part of N-vinylpyrrolidone were dissolved in 0.2 parts of sodium dodecyl sulfate to obtain solution B; 0.3 parts of ammonium persulfate were prepared into an aqueous solution and placed separately. Solution B and the first 40% volume of ammonium persulfate aqueous solution were simultaneously and uniformly added to the obtained core layer latex solution at a constant rate for 1 hour. After reacting at a constant temperature for 30 minutes, pre-emulsion A and the remaining 60% of ammonium persulfate aqueous solution were simultaneously and uniformly added at a constant rate for 1.5 hours. After reacting at a constant temperature for 1 hour, functionalized SBR latex particles were obtained.

[0115] (3) Dynamic crosslinking modification: Keep the functionalized SBR latex particles at 40°C, add ammonia to adjust the pH to 6.5, and add 10wt% dynamic crosslinking agent ethanol solution at a rate of 0.5mL / min (the amount added is 2wt% of the dry weight of the functionalized SBR latex particles). Keep warm for 1h to react and form a reversible borate ester crosslinking network.

[0116] (4) Post-treatment: Add 0.1 parts of dodecanethiol to terminate the reaction, cool the reaction system to below 30°C, and obtain SBR adhesive by filtration and degassing.

[0117] Using the SBR adhesive prepared above, Si / C silicon-based anodes were prepared according to the same process as in Example 4, and assembled into CR2032 coin-type lithium-ion batteries. Performance was then tested. Performance test results: The peel strength of the Si / C silicon-based anode sheet prepared in this comparative example was 1.5 N / cm; the capacity retention rate of the CR2032 coin-type lithium-ion battery after 500 cycles at 1C was 75%.

Claims

1. An SBR adhesive, characterized in that: It includes a core layer and a shell layer. The core layer mainly consists of butadiene, styrene, and hydroxy acrylate, while the shell layer mainly consists of isooctyl acrylate, β-hydroxyethyl methacrylate, itaconic acid, and N-vinylpyrrolidone. The core layer and shell layer also include emulsifiers and initiators, respectively. The preparation method of the SBR adhesive includes the following steps: (1) Core layer prepolymerization: Dissolve the emulsifier in water, add butadiene, styrene and hydroxy acrylate to obtain a preemulsion, and heat it up; take a part of the preemulsion and a part of the initiator aqueous solution, keep it warm for seed polymerization, add the remaining part of the preemulsion and the remaining part of the initiator dropwise, keep it warm after the dropwise addition is completed to obtain the core layer latex solution; (2) Shell gradient polymerization: Isooctyl acrylate and β-hydroxyethyl methacrylate are dissolved in emulsifier to obtain pre-emulsion A; itaconic acid and N-vinylpyrrolidone are dissolved in emulsifier, and then an initiator aqueous solution is added to obtain solution B; pre-emulsion A is added dropwise to the core latex solution obtained in step (1), and after the reaction is kept warm, solution B is added dropwise to keep warm to obtain functionalized SBR latex particles; (3) Dynamic crosslinking modification: The pH of the functionalized SBR latex particles is adjusted to 6.5~7.5, and a dynamic crosslinking agent ethanol solution is added dropwise. The reaction is kept at a certain temperature and after post-treatment, the SBR adhesive is obtained. The dynamic crosslinking agent is a condensation product of 3,5-dihydroxyphenylboronic acid and ethylene glycol diglycidyl ether.

2. The SBR adhesive according to claim 1, characterized in that: The raw materials of the core layer, in parts by weight, include: 30-45 parts butadiene, 25-35 parts styrene, and 5-10 parts hydroxy acrylate.

3. The SBR adhesive according to claim 1, characterized in that: The raw materials for the shell layer, by weight, include: 10-20 parts isooctyl acrylate, 3-8 parts β-hydroxyethyl methacrylate, 2-5 parts itaconic acid, and 1-4 parts N-vinylpyrrolidone.

4. The SBR adhesive according to claim 1, characterized in that: The emulsifier for the core layer is a mixture of sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether in a mass ratio of 1 to 3:1, and the emulsifier for the shell layer is sodium dodecyl sulfate.

5. The SBR adhesive according to claim 1, characterized in that: Both the core and shell layers are initiated with ammonium persulfate or potassium persulfate.

6. The SBR adhesive according to claim 1, characterized in that: The amount of the dynamic crosslinking agent added is 2-8 wt% of the dry weight of the functionalized SBR latex particles.

7. The SBR adhesive according to claim 1, characterized in that: The reaction temperature for the core layer prepolymerization is 75~85℃, the reaction temperature for the shell layer gradient polymerization is 65~75℃, and the reaction temperature for the dynamic crosslinking modification is 40~50℃.

8. The application of the SBR adhesive according to any one of claims 1-7, characterized in that: SBR adhesive is used in the preparation of positive and / or negative electrodes of lithium-ion batteries, with an addition amount of 2-8 wt% of the active material mass; the negative electrode active material is Si, SiO, Si / C or graphite-silicon composite material, and the positive electrode active material is NCM811, NCM90 / 10 or lithium iron phosphate.

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