Composite binder and preparation method thereof, pole piece and battery

Abstract

The invention provides a composite binder and a preparation method thereof, a pole piece and a battery. The composite binder comprises a PTFE core body, a polydopamine coating layer coating the surface of the PTFE core body, polyacrylic acid grafted to the polydopamine coating layer and sodium alginate grafted to the polydopamine coating layer. When the composite binder is applied to the battery, the expansion of silicon volume is favorably inhibited, and the first coulombic efficiency and the cycling stability are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to a composite binder and its preparation method, an electrode using the composite binder, and a battery using the electrode. Background Technology

[0002] Silicon (Si) is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries due to its extremely high theoretical specific capacity (~4200 mAh / g). However, silicon undergoes drastic volume changes (>300%) during charge and discharge, leading to electrode pulverization, separation of active material from current collector, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, ultimately resulting in rapid capacity decay and the end of cycle life.

[0003] Binders are key components for mitigating silicon volume expansion and maintaining electrode structural integrity. Traditional binders such as polyvinylidene fluoride (PVDF) rely on weak van der Waals forces and cannot effectively confine silicon particles. Water-based binders such as polyacrylic acid (PAA) and sodium alginate (SA) can form stronger hydrogen bonds or covalent bonds with the silicon surface through carboxyl groups, exhibiting better performance, but their mechanical strength and elasticity are still insufficient to withstand large stress and strain over long periods. Polytetrafluoroethylene (PTFE) has excellent fibrillation ability and elasticity, and can form a three-dimensional network structure, which can physically confine the expansion of silicon particles. However, the CF bonds on the PTFE surface can undergo irreversible reactions with lithium ions, consuming active lithium and resulting in low initial coulombic efficiency (ICE), and its inert surface has weak adhesion to active materials.

[0004] Therefore, developing a novel composite binder that combines strong adhesion, high elasticity, good mechanical strength, reduced side reactions, and suppression of silicon expansion is crucial for promoting the practical application of silicon-based anodes. Summary of the Invention

[0005] This application provides a method for preparing a composite binder, which is beneficial for suppressing silicon volume expansion, improving initial coulombic efficiency, and enhancing cycle stability.

[0006] In addition, this application also provides a composite binder prepared by the above preparation method, an electrode sheet using the above composite binder, and a battery using the electrode sheet.

[0007] The first aspect of this application provides a method for preparing a composite adhesive, comprising the following steps: dispersing PTFE powder in a buffer solution to obtain a first dispersion; adding dopamine hydrochloride while stirring the first dispersion and reacting to allow the dopamine to self-polymerize on the surface of the PTFE powder to form a polydopamine coating layer, and then separating, washing and drying to obtain a composite material in which the polydopamine coating layer coats the PTFE powder; dispersing the composite material in water to form a uniformly dispersed composite material dispersion, and sequentially adding the composite material dispersion and an aqueous solution of polyacrylic acid while stirring a sodium alginate solution to form a suspension; and adding a carbodiimide coupling agent and N-hydroxysuccinimide to the above-mentioned suspension under an inert atmosphere, and heating to react so that the polyacrylic acid and the sodium alginate are covalently grafted with the polydopamine, and then separating, washing and drying to obtain a composite adhesive powder.

[0008] Based on the first aspect, in some possible embodiments, the average particle size of the PTFE powder ranges from 20 micrometers to 800 micrometers, and the thickness of the polydopamine coating in the composite material ranges from 20 nm to 100 nm.

[0009] Based on the first aspect, in some possible implementations, the step "dispersing PTFE powder in a buffer solution to obtain a first dispersion" includes: adding PTFE powder to a buffer solution and then mechanically stirring it under ice-water bath conditions while simultaneously dispersing it using an ultrasonic cell disruptor to form a stable and uniform first dispersion.

[0010] Based on the first aspect, in some possible implementations, the mechanical stirring speed is 50 rpm to 400 rpm; the ultrasonic cell disruptor has a power of 200W and operates for 2 seconds with a 3-second interval; the dispersion treatment lasts for 1 minute to 50 minutes.

[0011] Based on the first aspect, in some possible embodiments, when forming the polydopamine coating layer, the mass ratio of the PTFE powder to the dopamine hydrochloride is 2:1 to 10:1.

[0012] Based on the first aspect, in some possible embodiments, the dopamine hydrochloride is added to the first dispersion at a speed of 200 rpm to 400 rpm at room temperature to form a reaction solution, and the reaction is continuously stirred for 12 hours to 24 hours, wherein, during the process of adding the dopamine hydrochloride to the first dispersion to form the reaction solution, the concentration of the dopamine hydrochloride in the reaction solution is controlled to be 0.5 mg / mL to 50.0 mg / mL.

[0013] Based on the first aspect, in some possible implementations, at least one of the following conditions is also satisfied: When the suspension is formed, the mass ratio of the composite material, the polyacrylic acid and the sodium alginate is (50-90):(5-40):(5-40); The molar ratio of the carbodiimide coupling agent to the N-hydroxysuccinimide is 1:0.5 to 1:1, and the total molar amount of the carbodiimide coupling agent is 1.5 to 2 times the total molar amount of the carboxyl groups in the polyacrylic acid and the sodium alginate in the suspension.

[0014] A second aspect of this application provides a composite adhesive comprising a PTFE core, a polydopamine coating layer covering the surface of the PTFE core, polyacrylic acid grafted to the polydopamine coating layer, and sodium alginate grafted to the polydopamine coating layer.

[0015] A third aspect of this application provides an electrode sheet comprising a current collector and an active layer disposed on the surface of the current collector, the active layer comprising the composite binder described above.

[0016] A fourth aspect of this application provides a battery including a separator, an electrolyte, and electrodes as described above.

[0017] When this composite binder is applied to a battery, the polydopamine coating layer covering the PTFE powder helps reduce the risk of direct contact between the PTFE powder and the electrolyte, reduces side reactions, thus lowers lithium consumption, and consequently improves the battery's initial coulombic efficiency. Furthermore, by surface grafting modification of the PTFE powder rather than bulk blending, the fibrillation capability of the PTFE powder core is preserved while introducing active functional groups. This allows the composite binder to form an effective fiber network under shear force to physically restrain the expansion of the silicon-based anode active material. The polyacrylic acid and sodium alginate grafted onto the polydopamine coating layer can interact with the silicon-based anode active material and the current collector via covalent and hydrogen bonds, respectively, achieving multi-level bonding in conjunction with the PTFE powder. Specifically, the polyacrylic acid can form high-energy Si-OC=O bonds with the silicon-based anode active material, thus facilitating the fixation of the silicon-based anode active material. The sodium alginate forms multiple hydrogen bonds with the silicon-based anode active material, encapsulating the silicon-based anode active material. This dynamically reversible hydrogen bond network effectively dissipates stress when the silicon-based anode active material expands in volume, thus helping to buffer mechanical shocks. Furthermore, the hydrophilic groups and microporous structure on the sodium alginate facilitate electrolyte wetting and lithium ion transport, thereby improving the ionic conductivity of the electrode. Detailed Implementation

[0018] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. 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 in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0019] The embodiments of this application will be described in detail below. However, this application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided to provide a thorough and detailed understanding of this application to those skilled in the art.

[0020] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0021] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising," when used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof. A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0022] In this application, the design relationships of greater than, less than, or not equal to parameter values ​​need to exclude reasonable errors of the measuring equipment.

[0023] One embodiment of this application provides a method for preparing a composite adhesive, which includes the following steps: Step S1: Disperse PTFE powder in a buffer solution to obtain a first dispersion.

[0024] Specifically, PTFE powder can be added to a buffer solution and mechanically stirred in an ice-water bath while being dispersed using an ultrasonic cell disruptor to form a stable and uniform first dispersion. These steps help break up soft agglomerates of PTFE powder, preventing phase changes or hardening due to temperature, thus ensuring thorough dispersion of the PTFE powder in the buffer solution. This lays the foundation for the subsequent formation of a uniform and continuous coating layer.

[0025] During the dispersion process, the mechanical stirring speed can be 300 rpm to 400 rpm; the ultrasonic cell disruptor has a power of 200W and operates for 2 seconds followed by a 3-second pause. The dispersion process can last from 1 minute to 50 minutes, for example, 30 minutes.

[0026] In some embodiments, the buffer solution may be a Tris-HCl solution or a HEPES buffer solution. Specifically, the pH of the buffer solution may be 8 to 8.5, and the buffer solution can precisely maintain the weakly alkaline environment required for the reaction, which is beneficial for the subsequent spontaneous oxidative polymerization of dopamine. In some embodiments, the concentration of the buffer solution may be from 1 mg / mL to 50 mg / mL.

[0027] In some embodiments, the concentration of the PTFE powder in the first dispersion may be from 5 mg / mL to 500 mg / mL. In some embodiments, the average particle size of the PTFE powder may be from 20 micrometers to 800 micrometers.

[0028] In step S2, dopamine hydrochloride (DA) is added to the first dispersion while mechanically stirring, and the reaction causes the dopamine to self-polymerize on the surface of the PTFE powder to form a polydopamine (PDA) coating layer. The mixture is then separated, washed, and dried to obtain a composite material in which the PTFE powder is coated with the polydopamine coating layer. Specifically, the dopamine hydrochloride undergoes oxidation, intramolecular rearrangement, and further polymerization under the influence of oxygen dissolved in the first dispersion to form polydopamine. Polydopamine exhibits strong adhesiveness and can firmly adhere to the surface of the PTFE powder particles through various non-covalent forces such as π-π stacking, van der Waals forces, and hydrogen bonds, thereby forming a polydopamine coating layer that encapsulates the PTFE powder.

[0029] In some embodiments, the mass ratio of the PTFE powder to the dopamine hydrochloride can be from 2:1 to 5:1.

[0030] The specific steps for forming the polydopamine coating layer are as follows: while mechanically stirring the first dispersion at a speed of 200 rpm to 400 rpm at room temperature (25°C), add the dopamine hydrochloride to form a reaction solution and continue stirring for 12 to 24 hours.

[0031] Furthermore, during the process of adding the dopamine hydrochloride to the first dispersion to form the reaction solution, the concentration of the dopamine hydrochloride in the reaction solution can be controlled to be between 0.5 mg / mL and 2.0 mg / mL. The thickness of the polydopamine coating is defined as δ, the concentration of the dopamine hydrochloride in the reaction solution is defined as C, and the time for the dopamine hydrochloride to react and form the polydopamine is defined as t. The thickness of the polydopamine coating, the concentration of the dopamine hydrochloride, and the time for the dopamine hydrochloride to react and form the polydopamine approximately satisfy the following relationship: δ ∝ (k × C × √t), where k is the reaction rate constant. Therefore, by using low concentration and short reaction time parameters in this application, it is beneficial to ensure that the dopamine hydrochloride is mainly adsorbed on the surface of the PTFE powder and undergoes in-situ polymerization in the initial stage of the reaction, thereby facilitating the obtaining of a dense and uniform polydopamine coating layer. Furthermore, it is also beneficial to precisely control the thickness of the polydopamine coating layer.

[0032] In some embodiments, the thickness of the polydopamine coating in the composite material can be from 20 nm to 100 nm. This thickness range is sufficient to effectively isolate PTFE from the electrolyte when the composite binder is applied in the battery, thus helping to solve the lithium consumption problem. It also provides sufficient active sites for subsequent grafting of sodium alginate and polyacrylic acid solution. Furthermore, considering the PTFE powder with the aforementioned particle size range, the thickness range of the polydopamine coating is much smaller than that of the PTFE powder with the aforementioned particle size range. Under the shear force of subsequent electrode processing, the polydopamine coating will not significantly hinder the deformation and fibrillation of the PTFE powder, thus helping to retain the fibrous network formation capability of the PTFE core. The thickness of the polydopamine coating can be calibrated using transmission electron microscopy (TEM).

[0033] The separation can be centrifugal separation or vacuum filtration separation. During centrifugation, the rotation speed can be from 3000 rpm to 8000 rpm, and the time can be 10 minutes.

[0034] The washing process can involve repeated washing with deionized water three to five times until the washing solution is colorless and transparent, which helps to thoroughly remove unreacted dopamine hydrochloride and physically adsorbed polydopamine.

[0035] The drying process can be freeze-drying, or the PTFE powder coated with the washed polydopamine coating can be placed in a vacuum drying oven and dried at 60°C for 12 hours.

[0036] Step S3: The above composite material is dispersed in water to form a uniformly dispersed composite material dispersion, and the composite material dispersion and the polyacrylic acid aqueous solution are sequentially added to a sodium alginate solution under continuous stirring to form a suspension.

[0037] The mass ratio of the composite material, the polyacrylic acid (PAA), and the sodium alginate (SA) can be (50-90):(5-40):(5-40). Preferably, the mass ratio of the polyacrylic acid and the sodium alginate can be 1:2 to 2:1.

[0038] In some embodiments, the concentration of the composite material in the composite dispersion can be from 10 mg / mL to 100 mg / mL. This concentration range helps ensure sufficient solid content in the subsequent reaction system, providing ample surface sites for grafting PDA coatings per unit volume, thereby improving grafting efficiency and product yield. It also helps reduce the risk of particle agglomeration caused by excessive dispersion viscosity, thus minimizing the impact on subsequent grafting uniformity and consequently reducing the impact on the performance uniformity of the composite binder.

[0039] In some embodiments, the concentration of the polyacrylic acid solution can be from 0.5 wt% to 5 wt%, and the molecular weight of the polyacrylic acid can be approximately 450,000 Da. The abundant carboxyl groups in the polyacrylic acid provide active sites for subsequent reactions with the amino groups on the surface of the composite material and for subsequent bonding with the silicon surface. The above concentration range helps ensure a sufficient number of carboxyl groups in the system to guarantee the grafting rate with the PDA coating layer. This helps reduce the impact on the subsequent covalent bonding ability with the silicon-based anode active material, while also reducing the impact of excessive solution viscosity on the overall dispersion uniformity of the suspension. It also reduces the risk of cross-linking between polyacrylic acid molecules or premature reaction with sodium alginate, thereby reducing the impact on the subsequent grafting rate and the risk of forming gel-like byproducts.

[0040] In some embodiments, the concentration of the sodium alginate solution can be from 0.5 wt% to 5 wt%, and the guluronic acid content in the sodium alginate is greater than 65%. Since sodium alginate is a natural anionic polysaccharide, its molecular chain is linked by 1,4-glycosidic bonds between β-D-mannuronic acid (M segment) and α-L-guluronic acid (G segment). Its unique "egg-box" structure originates from the abundant carboxyl and hydroxyl groups in the G segment, which can generate extremely strong interactions with SiO2 on the silicon surface through multiple hydrogen bonds. The above concentration range is beneficial for ensuring the grafting amount of sodium alginate, thus ensuring the ability to buffer silicon expansion through multiple hydrogen bonds and maintaining the ionic conductivity of the subsequent electrode. It also helps reduce the risk of sodium alginate molecular chain entanglement, thereby reducing the risk of self-gelling or non-target cross-linking with PAA, ensuring the grafting rate of sodium alginate in the PDA coating layer, and reducing the impact on reaction efficiency caused by hindering the contact between the subsequent coupling agent and carboxyl groups.

[0041] Furthermore, the concentration of the polyacrylic acid solution is preferably similar to or the same as the concentration of the sodium alginate solution, which helps to ensure that the two have comparable diffusion and reaction kinetics in the grafting competition, reducing the risk that one of the substances will dominate the grafting and disrupt the performance balance.

[0042] In this application, the concentrations of the polyacrylic acid solution and the sodium alginate solution are not limited to the values ​​mentioned above, as long as the mass ratio of the composite material, the polyacrylic acid, and the sodium alginate in the formed suspension is within the range mentioned above.

[0043] Step S4: Under an inert atmosphere, a carbodiimide coupling agent (EDC) and N-hydroxysuccinimide (NHS) are added to the stirred suspension. The mixture is heated to react and covalently graft the polyacrylic acid and sodium alginate onto the polydopamine, respectively. The mixture is then separated, washed, and dried to obtain a composite binder powder. The carbodiimide coupling agent activates the carboxyl groups in both the polyacrylic acid and sodium alginate to form active esters, which react with the groups in the polydopamine coating layer to form stable amide bonds. This covalently links the polyacrylic acid and sodium alginate to the surface of the composite material. The combination of N-hydroxysuccinimide and the carbodiimide coupling agent forms an active ester intermediate, which improves the efficiency and stability of the coupling reaction and prevents hydrolysis of the O-acylisourea intermediate.

[0044] The molar ratio of the carbodiimide coupling agent to the N-hydroxysuccinimide can be from 1:0.5 to 1:1, and the total molar amount of the carbodiimide coupling agent is 1.5 to 2 times the total molar amount of the carboxyl groups in the polyacrylic acid and sodium alginate in the suspension.

[0045] The step "heating reaction to covalently graft the polyacrylic acid and sodium alginate with the polydopamine" can be specifically described as follows: heating to 30°C to 40°C, maintaining the temperature and stirring continuously for 6 to 12 hours, so that the carboxyl groups in the polyacrylic acid and sodium alginate undergo sufficient amidation with the amino groups on the surface of the composite material to achieve covalent grafting. Temperature control not only improves efficiency but also helps reduce the risk of copolymerization between the polyacrylic acid and sodium alginate, thus ensuring that the grafting reaction mainly occurs at the thin-layer interface of the polydopamine coating layer in the composite material. This reduces the risks associated with copolymerization between the polyacrylic acid and sodium alginate adhering to the surface of the polydopamine coating layer (such as inhibiting the fibrillation ability of the PTFE core, weakening its effect of forming a three-dimensional network to confine silicon expansion; excessively thick polymer layers may reduce the overall elastic modulus and toughness of the binder, which is not conducive to buffering silicon volume changes; and dense polymer layers may hinder electrolyte wetting and lithium ion transport at the binder-active material interface). By optimizing the grafting reaction conditions, it is beneficial to ensure that PAA and SA are grafted onto the PDA surface mainly in the form of covalent monolayers or thin layers. This helps to avoid the formation of excessively thick, unintended polymer coating layers, thereby helping to maintain the fibrillation capability of the PTFE core and the overall mechanical and transport properties of the composite binder.

[0046] The separation can specifically involve obtaining a solid product by centrifugation or filtration after the reaction is completed and cooled to room temperature.

[0047] The washing process can specifically involve repeatedly washing the solid product with deionized water, and then placing the solid product in a Soxhlet extractor and continuously extracting it with deionized water for 24 hours to completely remove unreacted polyacrylic acid, sodium alginate, and byproducts.

[0048] The drying process can specifically involve placing the solid product in a vacuum freeze dryer and drying it for 48 hours to finally obtain a composite binder powder.

[0049] In the composite binder prepared by the above-described method of this application, the polydopamine coating layer covering the PTFE powder helps reduce the risk of direct contact between the PTFE powder and the electrolyte, reduces side reactions, thereby reducing lithium consumption and improving the initial coulombic efficiency of the battery. Furthermore, by surface grafting modification of the PTFE powder rather than bulk blending, the fibrillation capability of the PTFE powder core is preserved while introducing active functional groups. This allows the composite binder to form an effective fiber network under shear force to physically restrain the expansion of the silicon-based anode active material. The polyacrylic acid and sodium alginate grafted onto the polydopamine coating layer can interact with the covalent and hydrogen bonds formed between the silicon-based anode active material and the current collector, respectively, achieving multi-level bonding in conjunction with the PTFE powder. Specifically, the polyacrylic acid can form high-energy Si-OC=O bonds with the silicon-based anode active material, thus facilitating the fixation of the silicon-based anode active material. The sodium alginate forms multiple hydrogen bonds with the silicon-based anode active material, encapsulating the silicon-based anode active material. This dynamically reversible hydrogen bond network effectively dissipates stress when the silicon-based anode active material expands in volume, thus helping to buffer mechanical shocks. Furthermore, the hydrophilic groups and microporous structure on the sodium alginate facilitate electrolyte wetting and lithium ion transport, thereby improving the ionic conductivity of the electrode.

[0050] This application also provides an electrode sheet, the electrode sheet comprising a current collector and an active layer disposed on the surface of the current collector, the active layer comprising the aforementioned composite binder.

[0051] In some embodiments, the electrode is a negative electrode. Further, in some embodiments, the negative electrode is a silicon-based negative electrode.

[0052] The aforementioned electrode is also used in batteries, which also include a separator and an electrolyte.

[0053] The present application will be further illustrated below through embodiments and comparative examples. Some parameters not mentioned in the embodiments and comparative examples, such as the thickness of the active layer, are the same.

[0054] Example 1 Preparation of the composite binder: 2.0 g of PTFE powder was dispersed in 200 mL of Tris-HCl buffer solution (pH=8.5, 2 mg / mL). The dispersion was carried out for 30 minutes under ice-water bath conditions with mechanical stirring at 350 rpm and ultrasonic cell disruptor (200 W, 2 seconds operation followed by 3 seconds pause). Subsequently, 0.4 g of dopamine hydrochloride (PTFE:DA mass ratio 5:1) was added at room temperature, and the mixture was stirred at 300 rpm for 18 hours. After the reaction, the mixture was centrifuged, washed with water, and vacuum dried at 60 °C to obtain the composite material. 1.7 g of the composite material was dispersed in 100 mL of water. Under stirring, the composite material dispersion and 17 mL of 1 wt% PAA solution were sequentially added to 17 mL of 1 wt% SA solution to form a suspension. Under nitrogen protection, EDC and NHS (n(EDC):n(NHS) = 1:0.8, EDC being 1.8 times the total molar amount of carboxyl groups) were added to the suspension, and the mixture was stirred at 35 °C for 8 hours. After the reaction, the mixture was centrifuged, washed with water, extracted with Soxhlet for 24 hours, and freeze-dried for 48 hours to obtain a composite binder powder.

[0055] Preparation of the electrode sheet: Weigh 9.0g of nano-silicon-carbon composite, 0.5g of Super P, and 0.5g of the above composite binder powder, and place them in the mixing chamber of a V-type mixer for premixing at 20 rpm for 20 minutes. Then, add the premixed powder to a high-speed mixer for PTFE fibrillation modification. Specifically, mix at 500 rpm for 1 minute to initially disperse the material; then increase the speed to 3000 rpm and continue mixing for 30 minutes. During this process, the PTFE powder is subjected to strong mechanical shearing, initiating fibrillation and forming microfibers, which initially entangle with the active material and conductive agent. Transfer the material to the feeding hopper of a dry electrode film forming and composite machine, then perform hot rolling film formation on 6 rollers (roller temperature 80℃). Finally, perform hot pressing composite with a copper foil current collector under a linear pressure of 5.0 MPa, followed by cooling and winding to obtain a self-supporting dry electrode sheet.

[0056] Battery fabrication: The above-mentioned electrode sheets were punched into 14mm diameter discs as working electrodes. In a glove box filled with high-purity argon (H2O / O2<0.1ppm), lithium metal sheets were used as reference electrodes, Celgard 2400 polypropylene membranes were used as separators, and 1.0M LiPF6 in EC / DEC / EMC (v / v / v=1:1:1, containing 10wt% FEC) was used as electrolyte. The cells were assembled sequentially in a CR2032 battery case and sealed using a sealing machine at a pressure of about 1.2MPa, thus finally preparing a lithium-ion coin cell half-cell.

[0057] Example 2 The difference from Example 1 is that the amount of PAA solution and SA solution is increased to 34 mL each, so that the mass ratio of PTFE:PAA:SA in the final composite adhesive is about 50:25:25.

[0058] Example 3 The difference from Example 1 is that the amount of dopamine hydrochloride was reduced to 0.2g (PTFE:DA mass ratio of 10:1) and the reaction time was shortened to 12 hours in order to obtain a thinner (about 20-30nm) PDA coating.

[0059] Comparative Example 1 The difference from Example 1 is that the composite binder powder is directly replaced with PTFE powder to prepare the electrode sheet.

[0060] Comparative Example 2 The difference from Example 1 is that 9.0g of nano-silicon-carbon composite, 0.5g of Super P, 0.4g of PTFE powder, 0.05g of polyacrylic acid (PAA) powder, and 0.05g of sodium alginate (SA) powder were premixed.

[0061] The peel strength of the active layer of the negative electrode and the electrochemical performance of the battery were tested for each of the above embodiments and comparative examples. The electrochemical performance tests included initial coulombic efficiency, initial charge capacity, initial discharge capacity, capacity retention after 100 cycles, and volume expansion control effect after 100 cycles. The compaction density (corresponding to the electrode density in Table 1) of the negative electrode sheets of each embodiment and comparative example was measured, and film integrity was observed. The test results are recorded in the corresponding tables below.

[0062] The peel strength test method is as follows: A 90° peel test is used to quantify the bond strength. Specifically, the current collector surface of the electrode sample (20mm × 150mm) is fixed to a steel plate, and the free end of the active layer is peeled vertically at a rate of 100mm / min. The average peel force (F_avg) is recorded using a universal testing machine. The peel strength (σ, N / m) is calculated using σ = (F_avg / 0.02), and the result is the average of three parallel experiments. (Mechanical testing machine) Table 1 The initial coulombic efficiency test method is as follows: After discharging the lithium-ion coin cell to 0.005V at 0.1C, the initial discharge capacity of the lithium-ion coin cell is recorded; then, it is charged to 3V at a constant current of 0.1C, and the initial charge capacity of the lithium-ion coin cell is recorded. Initial coulombic efficiency = Initial charge capacity / Initial discharge capacity Table 2 The capacity retention rate test at 25℃ is as follows: The battery under test is placed at 25℃ and allowed to stand for 10 minutes. Then, it is discharged at a constant current of 1C to 0.005V, and the discharge capacity is recorded. After standing for 10 minutes, it is charged at a constant current of 1C to 3V, and the charging capacity is recorded. This charge-discharge cycle is repeated 100 times, and the capacity after 100 cycles is recorded. The capacity retention rate after 100 cycles at 25℃ is the initial capacity divided by the capacity after 100 cycles, expressed as %.

[0063] Table 3 The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A method for preparing a composite adhesive, characterized in that, Includes the following steps: The first dispersion was obtained by dispersing PTFE powder in a buffer solution; While stirring the first dispersion, dopamine hydrochloride is added and reacted to allow the dopamine to self-polymerize on the surface of the PTFE powder to form a polydopamine coating layer. Then, the powder is separated, washed, and dried to obtain a composite material in which the polydopamine coating layer coats the PTFE powder. The composite material is dispersed in water to form a uniformly dispersed composite material dispersion, and while stirring the sodium alginate solution, the composite material dispersion and the polyacrylic acid aqueous solution are added sequentially to form a suspension. as well as Under an inert atmosphere, a carbodiimide coupling agent and N-hydroxysuccinimide are added to the above-mentioned suspension while it is being stirred, and the mixture is heated to react so that the polyacrylic acid and the sodium alginate are covalently grafted with the polydopamine, respectively. The mixture is then separated, washed, and dried to obtain a composite binder powder.

2. The method for preparing the composite adhesive as described in claim 1, characterized in that, The average particle size of the PTFE powder ranges from 20 micrometers to 800 micrometers, and the thickness of the polydopamine coating layer in the composite material ranges from 20 nm to 100 nm.

3. The method for preparing the composite adhesive as described in claim 1, characterized in that, The step "dispersing PTFE powder in a buffer solution to obtain a first dispersion" includes: After adding PTFE powder to the buffer solution, the mixture is mechanically stirred in an ice-water bath while being dispersed using an ultrasonic cell disruptor to form a stable and uniform first dispersion.

4. The method for preparing the composite adhesive as described in claim 3, characterized in that, The mechanical stirring speed is 50 rpm to 400 rpm; the ultrasonic cell disruptor has a power of 200W and operates for 2 seconds with a 3-second interval; the dispersion treatment time is 1 minute to 50 minutes.

5. The method for preparing the composite adhesive as described in claim 1, characterized in that, When forming the polydopamine coating layer, the mass ratio of the PTFE powder to the dopamine hydrochloride is 2:1 to 10:

1.

6. The method for preparing the composite adhesive as described in claim 2, characterized in that, The dopamine hydrochloride was added to the first dispersion at a speed of 200 rpm to 400 rpm at room temperature to form a reaction solution, and the reaction was continued to be stirred for 12 hours to 24 hours. During the process of adding the dopamine hydrochloride to the first dispersion to form the reaction solution, the concentration of the dopamine hydrochloride in the reaction solution was controlled to be 0.5 mg / mL to 50.0 mg / mL.

7. The method for preparing the composite adhesive as described in claim 5 or 6, characterized in that, It also meets at least one of the following conditions: When the suspension is formed, the mass ratio of the composite material, the polyacrylic acid and the sodium alginate is (50-90):(5-40):(5-40); The molar ratio of the carbodiimide coupling agent to the N-hydroxysuccinimide is 1:0.5 to 1:1, and the total molar amount of the carbodiimide coupling agent is 1.5 to 2 times the total molar amount of the carboxyl groups in the polyacrylic acid and the sodium alginate in the suspension.

8. A composite adhesive, characterized in that, It includes a PTFE core, a polydopamine coating layer covering the surface of the PTFE core, polyacrylic acid grafted to the polydopamine coating layer, and sodium alginate grafted to the polydopamine coating layer.

9. An electrode, comprising a current collector and an active layer disposed on the surface of the current collector, characterized in that, The active layer contains the composite adhesive as described in claim 8.

10. A battery comprising a separator and an electrolyte, characterized in that, It also includes the electrode as described in claim 9.

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