Silicon negative electrode material adhesive as well as preparation method and application thereof

Abstract

The invention relates to the field of lithium ion battery silicon negative electrode materials, and discloses a silicon negative electrode material adhesive as well as a preparation method and application thereof. Firstly, acrylic acid, methyl acrylate and acrylonitrile monomer free radicals are polymerized to synthesize a copolymer P (AA-MA-AN); then, through reversible coulomb crosslinking between the P (AA-MA-AN) and branched chain type polyethyleneimine, a self-healing adhesive P (AA-MA-AN) coPEI with a rich three-dimensional space structure is formed; the silicon negative electrode material adhesive is used for a silicon negative electrode material of a lithium battery, so that the comprehensive performance and the cycling stability of the silicon negative electrode material can be remarkably improved, and meanwhile, environment-friendly recycling and regeneration can be realized.

Description

Technical Field

[0001] The invention belongs to the field of silicon negative electrode materials for lithium ion batteries, and in particular relates to a silicon negative electrode material adhesive and a preparation method and application thereof. Background Art

[0002] As the core energy storage device in electric vehicles, portable electronic devices and other fields, the market demand for high-performance lithium batteries continues to grow. Electrode materials, as key factors that determine the energy density, cycle life and safety of lithium batteries, have become a research hotspot in academia and industry. Among them, the type of active material determines the upper limit of battery capacity. Traditional active materials are mainly various forms of graphite based on carbon elements, but their theoretical capacity limit is 375mAh / g, while the theoretical capacity of silicon-based materials reaches 4200mAh / g (about 11 times the theoretical capacity of traditional graphite negative electrode 375 mAh / g), so it is currently the best choice to replace graphite as the next generation of lithium battery negative electrode material.

[0003] During the transition from carbon to silicon, researchers found that lithium will undergo volume changes during battery operation due to the detachment and intercalation of silicon, with fluctuations ranging up to 300% to 400%, leading to damage to the electrode structure and battery capacity attenuation, seriously affecting the battery life and safety. At the same time, electrodes with silicon as the active material also have problems with poor electron migration ability and unstable growth of the solid electrolyte interface.

[0004] In order to solve the above problems, the existing technology mainly develops new adhesives to improve the mechanical stability and electrochemical performance of negative electrode materials. Currently, commercial adhesives mainly include polyvinyl pyrrolidone (PVP), polyurethane (PU) and polyimide (PI). However, these adhesives can improve the stability and conductivity of the electrode to a certain extent, but there are still the following shortcomings: First, the compatibility with silicon materials is poor, resulting in unsatisfactory bonding effect; second, most traditional adhesives have insufficient thermal stability under high temperature conditions, which may affect the safety and life of the battery; third, the environmental friendliness is low, and the preparation process may cause a certain impact on the environment.

[0005] In recent years, adhesives represented by polyacrylic acid (PAA) and its modified derivatives have attracted attention due to their high carboxyl density (-COOH) and strong chemical affinity with silicon. However, the PAA main chain is relatively rigid, and main chain breakage or interface desorption is prone to occur during repeated expansion / contraction of silicon volume, which cannot meet the requirements of long cycle life.

[0006] Therefore, developing a silicon-based negative electrode material adhesive that has strong interface adhesion, dynamic flexibility and self-healing function has become the key to breaking through the existing technical bottleneck and realizing the industrialization of high-energy-density silicon-based lithium batteries. Summary of the invention

[0007] In view of the above technical problems, the purpose of the present invention is to provide a silicon negative electrode material binder and a preparation method and application thereof, which can not only better adapt to the volume change of silicon materials, but also facilitate the recovery of negative electrode active material substances to a certain extent.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention is to provide a method for preparing a silicon negative electrode material binder, comprising the following steps:

[0010] S1. The molar ratio of acrylic acid: methyl acrylate: acrylonitrile = (4-5): (1-2): (4-5) The acrylic acid solution, methyl acrylate and acrylonitrile are injected into the same closed container, and nitrogen is pumped in the closed container for 3-5 times while stirring to fully exhaust the air, and the closed container is heated and stirred continuously, and then the initiator solution is injected into the closed container to initiate a free radical polymerization reaction to obtain a first mixed solution containing P (AA-MA-AN);

[0011] S2. Adding a pH adjusting agent to the first mixed solution, stirring while adding, adjusting the pH value of the first mixed solution to acidic, to obtain a second mixed solution containing P (AA-MA-AN);

[0012] S3. Mix the second mixed solution and the PEI solution in a mass ratio of P(AA-MA-AN):PEI=1:(0.8~1.4), add deionized water to dilute to a solid content of 4%~10%, mix and stir at 20~30°C for 30~40min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0013] Furthermore, the acrylic acid solution in step S1 is specifically prepared by measuring acrylic acid, preparing an equal volume of sodium hydroxide or lithium hydroxide solution with a concentration of 8-12 wt %, adding the solution to the acrylic acid for neutralization, and obtaining the acrylic acid solution.

[0014] Furthermore, in step S1, the initiator solution is an ammonium persulfate solution, the concentration of which is 0.4wt% to 0.6wt%, and the amount added is 0.1% to 0.5% of the total mass of acrylic acid, methyl acrylate and acrylonitrile.

[0015] Furthermore, in step S1, the heating temperature of the free radical polymerization reaction is 70-80° C., and the reaction time is 5 h-10 h.

[0016] Furthermore, in step S2, the pH adjuster is a sodium hydroxide or lithium hydroxide solution with a concentration of 8wt% to 12wt%.

[0017] Further, the structural formula of P(AA-MA-AN) is

[0018]

[0019] Among them, a:b:c=(4~5):(1~2):(4~5).

[0020] Furthermore, in step S1, the molar ratio of acrylic acid:methyl acrylate:acrylonitrile=4.5:1:4.5.

[0021] Furthermore, in step S2, the pH value of the second mixed solution is 3.5-4.5.

[0022] Furthermore, in step S3, PEI is branched polyethyleneimine, and its molecular weight is 55000-65000.

[0023] Furthermore, in step S3, the concentration of the PEI solution is 40wt~60wt%.

[0024] Furthermore, in step S3, the mass ratio P(AA-MA-AN):PEI=1:1.

[0025] Furthermore, in step S3, the structural formula of the P(AA-MA-AN)coPEI adhesive is

[0026]

[0027] Among them, a:b:c=(4~5):(1~2):(4~5).

[0028] The second aspect of the present invention is to provide a silicon negative electrode material binder prepared according to the above preparation method.

[0029] The third aspect of the present invention is to provide a use of the above silicon negative electrode material binder in a lithium battery.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The silicon negative electrode material binder prepared by the preparation method of the present invention forms a self-healing binder with a rich three-dimensional spatial structure through reversible Coulomb crosslinking between P(AA-MA-AN) and branched polyethyleneimine, which can not only significantly improve the comprehensive performance and cycle stability of the silicon negative electrode material, but also realize environmentally friendly recycling and regeneration, which is mainly reflected in the following aspects:

[0032] 1. In the copolymer P(AA-MA-AN), the abundant carboxyl groups on the polyacrylic acid will provide enough hydrogen bonds to form a stable bonding effect with the silicon particles. The nitrile group of acrylonitrile can improve the electron transmission capacity, thereby improving the conductivity of the electrode material, and the chain segments formed by acrylamide can significantly improve the chemical resistance and thermal stability of the main chain; the branched polyethyleneimine is a cyclically extended network structure, and the amino ions on it can combine with the carboxyl ions on the polyacrylic acid chain segments in the copolymer P(AA-MA-AN) through Coulomb crosslinking to form a three-dimensional network structure, tightly and firmly encapsulating the silicon particles therein. The flexibility and reversible crosslinking of the P(AA-MA-AN)coPEI adhesive molecule itself enable the adhesive to restore the bonding effect after the silicon volume expands and shrinks, thereby significantly improving the cycle life and stability of the battery, so that the battery has a capacity retention rate of ≥81% after 200 cycles at a current density of 0.5C, and the electrodes are intact before and after the cycle without cracking;

[0033] 2. The reversible Coulomb crosslinking between the copolymer P(AA-MA-AN) and the branched polyethyleneimine has pH-responsive characteristics. Based on the response characteristics of the P(AA-MA-AN)coPEI adhesive, the active substances in waste battery materials can be recovered by alkaline washing: the electrode sheet is treated with 1M NaOH solution at room temperature (25°C), the adhesive network is disintegrated within 2 hours, and the recovery rate of electrode active substances is ≥70%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is an SEM image of the electrode surfaces of some embodiments of the present invention and comparative examples, wherein (a) is an SEM image of the electrode surface of embodiment 1 of the present invention after 200 cycles, (b) is an SEM image of the electrode surface of embodiment 2 of the present invention after 200 cycles, (c) is an SEM image of the electrode surface of embodiment 3 of the present invention after 200 cycles, (d) is an SEM image of the electrode surface of embodiment 4 of the present invention after 200 cycles, (e) is an SEM image of the electrode surface of embodiment 5 of the present invention after 200 cycles, (f) is an SEM image of the electrode surface of embodiment 6 of the present invention after 200 cycles, and (g) is an SEM image of the electrode surface of comparative example 1 after 200 cycles.

[0035] Figure 2 The infrared spectra of PEI, P(AA-MA-AN) and P(AA-MA-AN)coPEI in the present invention are compared.

[0036] Figure 3 The capacity retention curves of the batteries of Example 1, Example 4, Example 5 and Example 6 after 200 cycles of the present invention are shown. DETAILED DESCRIPTION

[0037] The present invention will be further described below by specific embodiments in conjunction with the accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0038] A first aspect of the present invention provides a method for preparing a silicon negative electrode material binder, comprising the following steps:

[0039] (1) Preparation of acrylic acid solution: a certain amount of acrylic acid is measured, and an equal volume of sodium hydroxide or lithium hydroxide solution with a concentration of 8-12 wt% is prepared and added to the acrylic acid for neutralization to obtain an acrylic acid solution; since the free radical polymerization reaction of pure acrylic acid is relatively active and is prone to implosion; and the preferred molecular weight of P(AA-MA-AN) in the present invention is 500,000, a certain amount of sodium hydroxide is added to reduce the molecular weight of the polymer;

[0040] (2) Preparation of methyl acrylate solution: a certain amount of methyl acrylate is measured and placed in a flask, and deionized water is added to obtain a methyl acrylate solution;

[0041] (3) measuring a certain amount of acrylonitrile; wherein the molar ratio of acrylic acid:methyl acrylate:acrylonitrile measured in steps (1), (2) and (3) is (4-5):(1-2):(4-5);

[0042] (4) Preparation of initiator solution: dissolve ammonium persulfate in deionized water to prepare an ammonium persulfate solution with a concentration of 0.4 wt% to 0.6 wt%;

[0043] (5) The acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) are injected into the same closed container, and nitrogen is pumped in and out for 3 to 5 times at a stirring speed of 220 to 280 rpm to fully exhaust the air (the stirring speed is subsequently maintained until the reaction is completed), and then the closed container is heated. When the internal temperature reaches 70 to 80° C., the initiator solution obtained in step (4) is injected into the closed container (the amount added is 0.1% to 0.5% of the total mass of acrylic acid, methyl acrylate and acrylonitrile monomers) to initiate a free radical polymerization reaction, and the reaction temperature is maintained at 70 to 80° C. for 5 to 10 hours to obtain a first mixed solution containing P(AA-MA-AN); wherein the structural formula of P(AA-MA-AN) is

[0044]

[0045] Among them, a:b:c=(4~5):(1~2):(4~5).

[0046] (6) adding 8-12 wt % sodium hydroxide or lithium hydroxide solution to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH of the first mixed solution to 3.5-4.5 to obtain a second mixed solution containing P(AA-MA-AN);

[0047] (7) The second mixed solution and the PEI solution are mixed at a mass ratio of P(AA-MA-AN):PEI=1:(0.8-1.4) (PEI is a branched polyethyleneimine with a molecular weight of 55,000-65,000 and a concentration of 40-60 wt%), and deionized water is added to dilute the mixture to a solid content of 4%-10%. The mixture is stirred at 20-30°C for 30-40 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive. The structural formula of the P(AA-MA-AN)coPEI adhesive is:

[0048]

[0049] Among them, a:b:c=(4~5):(1~2):(4~5).

[0050] The silicon negative electrode material binder provided by the present invention and its preparation method and application form a self-healing binder P(AA-MA-AN)coPEI with a rich three-dimensional spatial structure through reversible Coulomb crosslinking between P(AA-MA-AN) and branched polyethyleneimine; P(AA-MA-AN) is synthesized by free radical polymerization of acrylic acid, methyl acrylate and acrylonitrile monomers; the silicon negative electrode material binder provided by the present invention has excellent water solubility, self-healing property, thermal stability and high bonding strength; a large number of carboxyl groups on the main chain PAA of the binder molecule are tightly bonded to silicon through the action of hydrogen bonds, and PMA can improve the flexibility of the polymer and provide sufficient stress space for the binder molecule when the volume of silicon particles expands and contracts; the nitrile group (C≡N) on the main chain of acrylonitrile has a strong polarity and can interact with the electrolyte in the lithium ion battery to improve the ionic conductivity and accelerate the Li +The transmission rate during the charge and discharge process, however, the introduction of the nitrile group will reduce the solubility of the adhesive molecule in water, and the branched polyethyleneimine PEI is a cationic polyelectrolyte that can be mixed with water in any proportion. It has better processability and mechanical properties than the linear type. It has a highly branched structure, a larger surface area, and can provide more amino functional sites, so that the adhesive molecules formed in the subsequent cross-linking reaction have a broad spatial structure to accommodate silicon particles and other electrode materials; PEI greatly increases the solubility of the binder system in water after participating in the cross-linking, and is easily soluble in water. At the same time, under acidic conditions, the primary amine of the branched polyethyleneimine PEI will dissociate to form amino ions, which are easy to form coulomb crosslinks with carboxyl ions in the solution under electrostatic action. In addition, when the pH value is greater than 7, the metal cations combine with the carboxyl ions to disconnect the crosslinking of the amino ions and the carboxyl ions. Based on this characteristic, the electrode material containing the silicon negative electrode material binder of the present invention can be soaked in alkali solution to better separate the negative electrode active material and the conductive carbon, and the recovered material can also be made into batteries for use, realizing environmentally friendly recycling and regeneration.

[0051] It should be noted that the first mixed solution containing P(AA-MA-AN), the second mixed solution containing P(AA-MA-AN), and the solution containing P(AA-MA-AN)coPEI adhesive prepared in the present invention are all viscous liquids, which can be used directly as adhesives or can be used as adhesives after dilution or concentration.

[0052] Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples.

[0053] The battery cycle stability test of the present invention is to directly use the solution containing P(AA-MA-AN)coPEI binder obtained in step (7) as the silicon negative electrode material binder, assemble it into a button-type half-cell for charge and discharge test, comprising the following steps:

[0054] 1) Preparation of button half-cell;

[0055] 2) Standing: Let the assembled battery stand for 12 hours to allow the electrolyte to fully infiltrate the electrode materials;

[0056] 3) Charge and discharge cycle test;

[0057] a. Test system: Use the battery test system of Blue Power Electronics Co., Ltd. to perform constant current charge and discharge cycle tests.

[0058] b. Test conditions

[0059] Temperature: Room temperature (25°C).

[0060] Voltage range: 0.01–1.2 V (vs Li / Li⁺).

[0061] c.Testing process:

[0062] First, cycle 4 times at 0.05 C (210 mAh·g⁻¹) to activate the electrode material.

[0063] Then, a long cycle test was carried out at 0.5 C to evaluate the battery cycling stability.

[0064] The preparation of button-type half-cell includes the following steps:

[0065] Step 1: Electrode material mixing and slurry preparation

[0066] Place nano silicon (Si) and conductive carbon black (Super P) in a vacuum oven and dry at 50°C for 8 hours to remove moisture from the surface of the material; take nano silicon powder, Super P and silicon negative electrode material binder at a solid mass ratio of 8:1:1, add nano silicon powder and Super P into a quartz mortar and grind for 30 minutes to ensure that the two are fully mixed, and then add the mixture to the silicon negative electrode material binder and stir for 12 hours; (Note: Because the viscosity of the binder is very high, it is necessary to add an appropriate amount of deionized water to adjust the viscosity and ensure uniform mixing)

[0067] Step 2: Electrode preparation

[0068] Use a four-sided preparation device (scraper) to evenly coat the electrode slurry onto the copper foil (current collector) to control the coating thickness to be uniform; place the coated electrode in a vacuum oven and dry it at 80°C for 12 hours to remove the solvent.

[0069] Use a slicer to cut the electrode into discs with a diameter of 9 mm and put them in the glove box for later use;

[0070] Step 3: Battery Assembly

[0071] Complete assembly in a vacuum glove box, ensuring that the water and oxygen value in the glove box is less than 0.01 ppm;

[0072] Electrolyte: 1 M LiPF 6 Dissolved in a mixed solution of dimethyl carbonate (DMC), ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1:1);

[0073] Diaphragm: Celgaed 2400 polypropylene membrane;

[0074] Counter electrode: Lithium metal sheet.

[0075] Example 1

[0076] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0077] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0078] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0079] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0080] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0081] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0082] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 499523, and the solid content of the second mixed solution is 17.5%;

[0083] (7) Take 10 g of the second mixed solution, 3.5 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 56.5 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0084] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 93%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; the surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (a), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 1.27Mpa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0085] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 78.3%.

[0086] The PEI, P(AA-MA-AN) and P(AA-MA-AN)coPEI adhesives in this embodiment were characterized by infrared spectroscopy. Figure 2 ; Figure 2 In the spectrum of P(AA-MA-AN), a wavelength of 3130 cm −1 The broad absorption band at 1724 cm −1 The strong peak at 3130 cm is attributed to the C=O stretching vibration of -COOH; in the spectrum of P(AA-MA-AN)coPEI, −1 The broad absorption band of OH stretching vibration at 1724 cm −1 The C=O stretching vibration of −1 , which is the result of ionic interaction between carboxyl ions and ammonium ions to form ammonium carboxylate salts, indicating that the P(AA-MA-AN)coPEI adhesive was successfully synthesized.

[0087] Comparative Example 1

[0088] The preparation method of the silicon negative electrode material binder of this comparative example comprises the following steps:

[0089] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0090] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0091] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0092] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0093] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0094] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 499523, and the solid content of the second mixed solution is 17.5%;

[0095] The first mixed solution containing P(AA-MA-AN) obtained in step (6) of this comparative example was used as a silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was circulated 200 times in the test system, its capacity retention rate was 75%, which was significantly lower than that of Example 1 (93%); its surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1As described in (g), it can be seen that the electrode has obvious cracks after cycling. By comparing the battery cycling performance test and SEM characterization results of the button half-cell made of P(AA-MA-AN)coPEI adhesive in Example 1, it can be clearly concluded that: in the presence of PEI cross-linking, due to the reversible cross-linking reaction formed, the adhesive can better maintain the integrity of the electrode during the charge and discharge process, thereby improving the cycle life of the electrode.

[0096] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 42.5%, which was significantly lower than Example 1 (78.3%).

[0097] Example 2

[0098] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0099] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 8 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0100] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0101] (3) 12 ml of acrylonitrile is measured; at this point, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) is 4:1:5;

[0102] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0103] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0104] (6) adding a sodium hydroxide solution of the same concentration as in step (1) to the first mixed solution obtained in step (5) while stirring, adjusting the pH of the first mixed solution to 4, and obtaining a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) was measured by gel permeation chromatography (GPC) to be 442448, and the solid content of the second mixed solution was 14.6%;

[0105] (7) Take 10 g of the second mixed solution, 2.92 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 45.48 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0106] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 86%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; the surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (b), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 0.65Mpa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0107] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 71.7%.

[0108] Example 3

[0109] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0110] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; weigh 12.5 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0111] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0112] (3) 7.68 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 5:1:4;

[0113] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0114] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0115] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 578075, and the solid content of the second mixed solution is 19.2%;

[0116] (7) Take 10 g of the second mixed solution, 3.84 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 62.69 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0117] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 81%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; the surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (c), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 1.41 MPa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0118] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 69.1%.

[0119] The test results of battery cycle performance, peel strength and recovery rate in Examples 1 to 3 are summarized in Table 1.

[0120] Table 1. Cyclic performance, peel strength and recovery rate of Examples 1 to 3

[0121]

[0122] As can be seen from Table 1, in the preparation of P(AA-MA-AN)coPEI adhesive, since acrylic acid has a higher polymerization activity, when the molar ratio of acrylic acid increases, the bonding strength will increase, but the lack of ionic conductivity provided by acrylonitrile will not always enhance the electrical properties of the electrode. At the same time, the increase in the molar ratio of acrylic acid will also lead to a decrease in the recovery rate of active substances. Therefore, in the present invention, the best effect is achieved when the molar ratio of acrylic acid to acrylonitrile is 1:1.

[0123] Example 4

[0124] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0125] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0126] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0127] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0128] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0129] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0130] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 499523, and the solid content of the second mixed solution is 17.5%;

[0131] (7) Take 10 g of the second mixed solution, 2.8 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 50.2 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:0.8; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0132] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 84%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; the surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (d), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 0.94Mpa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0133] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 75.6%.

[0134] Example 5

[0135] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0136] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0137] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0138] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0139] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0140] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0141] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 499523, and the solid content of the second mixed solution is 17.5%;

[0142] (7) Take 10 g of the second mixed solution, 4.2 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 62.8 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1.2; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0143] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 90%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; its surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (e), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 1.15 MPa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0144] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 79.8%.

[0145] Example 6

[0146] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0147] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0148] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0149] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0150] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0151] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0152] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 499523, and the solid content of the second mixed solution is 17.5%;

[0153] (7) Take 10 g of the second mixed solution, 4.9 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 69.1 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1.4; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0154] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder, and nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps, and a charge and discharge test was performed; after the button half-cell was cycled 200 times in the test system, its capacity retention rate was 87%, indicating that the electrode material had a stable structure in long-term cycles and no obvious capacity decay; the surface was characterized by scanning electron microscopy, and the results were as follows: Figure 1 As shown in (f), it can be seen that the electrode structure is intact before and after the cycle without any cracks. The 180° peeling test was performed by a universal testing machine. The test parameters are: length: 16mm, width: 24mm; overlap area: 384mm 2 , the highest breaking load was obtained and the bonding strength was calculated to be 1.09Mpa, indicating that the binder was firmly bonded to the current collector (copper foil).

[0155] After the cycle experiment, the cycled battery was disassembled in a vacuum glove box and the electrode materials were collected. The collected electrodes were immersed in a sodium hydroxide solution (pH=13), heated and stirred for 5 hours to dissolve the copper foil, and the current collector copper foil fell off immediately. The solid mixture obtained after filtration was a mixture of silicon and Super P. After calculation, the total material recovery rate of silicon and Super P was 75.4%.

[0156] The test results of battery cycle performance, peel strength and recovery rate in Examples 1, 4 to 6 are summarized in Table 2.

[0157] Table 2. Cyclic performance, peel strength and recovery rate of Examples 1, 4 to 6

[0158]

[0159] The capacity retention rate variation diagram of Example 1, 4 to 6 after 200 cycles is shown in Figure 3 , observe Table 2 and Figure 3It can be found that when the mass ratio of P(AA-MA-AN) and PEI is 1:(0.8~1.4), the synthesized P(AA-MA-AN)coPEI adhesive has a significant improvement on the battery cycle performance, and when the PEI content increases, the active material recovery rate increases to a certain extent, but after exceeding 1:1, the bonding strength begins to decrease, and the capacity retention rate will also decrease accordingly.

[0160] Example 7

[0161] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0162] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0163] (2) Preparation of methyl acrylate solution: 6.92 ml of methyl acrylate was added to a flask, and 68.08 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0164] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:2:4.5;

[0165] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0166] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully exhaust the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0167] (6) adding a sodium hydroxide solution of the same concentration as in step (1) to the first mixed solution obtained in step (5) while stirring, adjusting the pH of the first mixed solution to 4, and obtaining a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) was measured by gel permeation chromatography (GPC) to be 511634, and the solid content of the second mixed solution was 17.9%;

[0168] (7) Take 10 g of the second mixed solution, 3.58 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 56.5 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0169] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was used as a silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, a charge and discharge test, a peel test and electrode material recovery were carried out according to the same test methods as in Example 1. The cycle performance, peel strength and recovery rate are shown in Table 3.

[0170] Example 8

[0171] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0172] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0173] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0174] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0175] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0176] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully expel the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 6 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0177] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) was 512213, and the solid content in the second mixed solution was 18.1%;

[0178] (7) Take 10 g of the second mixed solution, 3.62 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 58.78 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0179] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, the charge and discharge test, peeling test and electrode material recovery were carried out according to the same test method as in Example 1. The cycle performance, peeling strength and recovery rate are shown in Table 3.

[0180] Example 9

[0181] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0182] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0183] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0184] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0185] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0186] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully expel the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 7 h to obtain a first mixed solution containing P(AA-MA-AN);

[0187] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) was measured by gel permeation chromatography (GPC) to be 526948, and the solid content of the second mixed solution was 18.6%;

[0188] (7) Take 10 g of the second mixed solution, 3.72 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 60.68 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0189] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, the charge and discharge test, peeling test and electrode material recovery were carried out according to the same test method as in Example 1. The cycle performance, peeling strength and recovery rate are shown in Table 3.

[0190] Example 10

[0191] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0192] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0193] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0194] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0195] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0196] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully expel the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 70° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 70° C. for 8 h to obtain a first mixed solution containing P(AA-MA-AN);

[0197] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH of the first mixed solution to 4 to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) was 545579, and the solid content of the second mixed solution was 20.2%;

[0198] (7) Take 10 g of the second mixed solution, 4.04 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 66.76 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0199] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, the charge and discharge test, peeling test and electrode material recovery were carried out according to the same test method as in Example 1. The cycle performance, peeling strength and recovery rate are shown in Table 3.

[0200] Embodiment 11

[0201] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0202] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0203] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0204] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0205] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0206] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully expel the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 75° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 75° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0207] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 497217, and the solid content of the second mixed solution is 17.2%;

[0208] (7) Take 10 g of the second mixed solution, 3.44 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 55.36 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0209] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, the charge and discharge test, peeling test and electrode material recovery were carried out according to the same test method as in Example 1. The cycle performance, peeling strength and recovery rate are shown in Table 3.

[0210] Example 12

[0211] The method for preparing the silicon negative electrode material binder of this embodiment comprises the following steps:

[0212] (1) Preparation of acrylic acid solution: weigh 1.12 g of sodium hydroxide and dissolve it in 10 ml of deionized water to obtain a sodium hydroxide solution; measure 10 ml of acrylic acid and add the sodium hydroxide solution to the acrylic acid to obtain an acrylic acid solution;

[0213] (2) Preparation of methyl acrylate solution: 3.46 ml of methyl acrylate was added to a flask, and 71.54 ml of deionized water was added to dissolve the methyl acrylate solution to obtain a methyl acrylate solution;

[0214] (3) 9.6 ml of acrylonitrile was measured; at this time, the molar ratio of acrylic acid: methyl acrylate: acrylonitrile measured in steps (1), (2), and (3) was 4.5:1:4.5;

[0215] (4) Preparation of initiator solution: Weigh 25 mg of ammonium persulfate and dissolve it in 5 ml of deionized water to prepare an ammonium persulfate solution with a concentration of 0.5 wt%;

[0216] (5) using a syringe to inject the acrylic acid solution obtained in step (1), the methyl acrylate solution obtained in step (2), and the acrylonitrile obtained in step (3) into the flask through a rubber stopper, respectively, and pumping nitrogen gas three times at a stirring speed of 250 rpm to fully expel the air (the stirring speed is subsequently maintained at 250 rpm until the reaction is completed), heating the flask, and when the internal temperature reaches 80° C., using a syringe to draw 3.75 ml of the ammonium persulfate solution obtained in step (4) to initiate a free radical polymerization reaction, and maintaining the reaction temperature at 80° C. for 5 hours to obtain a first mixed solution containing P(AA-MA-AN);

[0217] (6) adding a sodium hydroxide solution of the same concentration as in step (1) dropwise to the first mixed solution obtained in step (5), stirring while adding, and adjusting the pH value of the first mixed solution to 4, to obtain a second mixed solution containing P(AA-MA-AN); the weight average molecular weight of P(AA-MA-AN) measured by gel permeation chromatography (GPC) is 469422, and the solid content of the second mixed solution is 16.7%;

[0218] (7) Take 10 g of the second mixed solution, 3.34 g of 50 wt% PEI (branched polyethyleneimine with a molecular weight of 60,000) solution, and 55.36 g of deionized water and place them in the same container; at this time, the mass ratio of P(AA-MA-AN) to PEI is 1:1; mix and stir at room temperature (25°C) for 30 min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

[0219] The solution containing P(AA-MA-AN)coPEI binder obtained in step (7) of this embodiment was directly used as the silicon negative electrode material binder. Nano silicon powder, Super P and silicon negative electrode material binder were taken at a solid mass ratio of 8:1:1 to prepare a button half-cell according to the above button half-cell preparation steps. Then, the charge and discharge test, peeling test and electrode material recovery were carried out according to the same test method as in Example 1. The cycle performance, peeling strength and recovery rate are shown in Table 3.

[0220] Table 3 Cyclic performance, peel strength and recovery rate of Examples 7 to 12

[0221]

[0222] In summary, the silicon negative electrode material binder obtained by the preparation method of the silicon negative electrode material binder of the present invention can significantly improve the cycle life and stability of the battery, so that the capacity retention rate of the battery is ≥81% after 200 cycles at a current density of 0.5C, and the electrode is intact before and after the cycle without cracking; based on the response characteristics of the P(AA-MA-AN)coPEI binder, the active substances in the waste battery materials are recovered by alkali solution washing: the electrode sheet is treated with alkali solution, and the recovery rate of the electrode active substance is ≥70%.

[0223] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon negative electrode material binder, characterized in that: The following steps are involved: Step S1. The molar ratio of acrylic acid: methyl acrylate: acrylonitrile is (4-5): (1-2): (4-5). The acrylic acid solution, methyl acrylate and acrylonitrile are injected into the same closed container, and nitrogen is pumped into the closed container for 3-5 times while stirring to fully exhaust the air, and the closed container is heated and stirred continuously, and then an initiator solution is injected into the closed container to initiate a free radical polymerization reaction, thereby obtaining a first mixed solution containing P(AA-MA-AN); Step S2. Adding a pH adjuster to the first mixed solution, stirring while adding, adjusting the pH value of the first mixed solution to acidic, to obtain a second mixed solution containing P(AA-MA-AN); Step S3. Mix the second mixed solution and the PEI solution in a mass ratio of P(AA-MA-AN):PEI=1:(0.8~1.4), add deionized water to dilute to a solid content of 4%~10%, mix and stir at 20~30°C for 30~40min to obtain a solution containing P(AA-MA-AN)coPEI adhesive.

2. The preparation method according to claim 1, characterized in that: The preparation of the acrylic acid solution in step S1 is specifically as follows: acrylic acid is measured, and an equal volume of sodium hydroxide or lithium hydroxide solution with a concentration of 8-12 wt % is prepared and added to the acrylic acid for neutralization to obtain an acrylic acid solution.

3. The preparation method according to claim 1, characterized in that: In the step S1, the initiator solution is an ammonium persulfate solution, the concentration of which is 0.4wt% to 0.6wt%, and the amount added is 0.1% to 0.5% of the total mass of acrylic acid, methyl acrylate and acrylonitrile.

4. The preparation method according to claim 1, characterized in that: In the step S1, the heating temperature of the free radical polymerization reaction is 70-80° C., and the reaction time is 5 h-10 h.

5. The preparation method according to claim 1, characterized in that: In step S2, the pH adjuster is a sodium hydroxide or lithium hydroxide solution with a concentration of 8wt% to 12wt%.

6. The preparation method according to claim 1, characterized in that: The structural formula of P(AA-MA-AN) is Among them, a:b:c=(4~5):(1~2):(4~5).

7. The preparation method according to claim 1, characterized in that: In the step S1, the molar ratio of acrylic acid:methyl acrylate:acrylonitrile is 4.5:1:4.

5.

8. The preparation method according to claim 1, characterized in that: In step S2, the pH value of the second mixed solution is 3.5-4.

5.

9. The preparation method according to claim 1, characterized in that: In the step S3, PEI is branched polyethyleneimine, and its molecular weight is 55000-65000.

10. The preparation method according to claim 1, characterized in that: In step S3, the concentration of the PEI solution is 40wt% to 60wt%.

11. The preparation method according to claim 1, characterized in that: In step S3, the mass ratio P(AA-MA-AN):PEI=1:

1.

12. The preparation method according to claim 1, characterized in that: In step S3, the structural formula of the P(AA-MA-AN)coPEI adhesive is Among them, a:b:c=(4~5):(1~2):(4~5).

13. A silicon negative electrode material binder prepared according to the preparation method according to any one of claims 1 to 12.

14. Use of the silicon negative electrode material binder according to claim 13 in a lithium battery.

Images