Solution type negative electrode adhesive as well as preparation method and application thereof

Abstract

The invention discloses a solution type negative electrode adhesive as well as a preparation method and application thereof. The preparation method of the adhesive comprises the following steps: a, mixing and stirring polyacrylonitrile fibers and a modifier in water, and treating to obtain a pretreatment solution; b, uniformly dispersing the pretreatment liquid obtained in the step a by using a high-pressure homogenizer to obtain polyacrylonitrile fiber dispersion liquid; c, mixing and reacting the polyacrylonitrile fiber dispersion liquid, unsaturated monomers and an initiator to generate a polymer, and taking out a precipitate; and d, adding the polymer precipitate into water, and adding a neutralizer to adjust the pH value so as to prepare the solution type negative electrode adhesive. According to the invention, the PAA adhesive is modified by a special means, so that the embedding and de-embedding efficiency of lithium ions in the silicon-carbon / silicon negative electrode is improved, the surface cracking and powder falling of a pole piece caused by volume expansion of the silicon-carbon / silicon negative electrode in the charging and discharging process are avoided, and the cycling stability and the cycling efficiency of the silicon-carbon / silicon negative electrode are improved.

Description

Technical Field

[0001] This invention relates to a negative electrode adhesive, and more particularly to a solution-type negative electrode adhesive, its preparation method and application, belonging to the field of battery material technology. Background Technology

[0002] Lithium-ion batteries boast advantages such as high energy density, high conversion efficiency, long cycle life, no memory effect, and low self-discharge rate, making them widely used in various fields including electronic products, electric vehicles, and energy storage devices. Against the backdrop of the global trend towards carbon neutrality and the rapid growth in the penetration rate of new energy vehicles, the global lithium battery industry maintains a high level of prosperity. As the industry matures, technological innovation in lithium batteries remains a key focus for battery manufacturers.

[0003] Traditional lithium-ion battery anode active materials are graphite, but their theoretical capacity is relatively low, only 372 mA·h / g. Silicon-based anodes, on the other hand, have a theoretical capacity as high as 4200 mA·h / g, far exceeding graphite, and are expected to replace graphite as the next generation of high-energy-density lithium-ion battery anode active materials. However, silicon-carbon or silicon-based anodes have a higher volume expansion rate than graphite. Maintaining the structural and volume stability of lithium batteries during charge and discharge processes, preventing active material shedding, and improving electrode cycle stability are current research priorities.

[0004] In lithium-ion battery anode materials, the anode binder is an important polymer material that adheres the anode active material and conductive agent to the anode current collector. To meet the application requirements of silicon-carbon or silicon-based anodes, the anode binder needs to have sufficiently high adhesion strength and sufficient toughness to suppress the volume expansion rate of the anode active material and ensure that the anode active material does not fall off during the lithium-ion intercalation-deintercalation process.

[0005] Polyacrylic acid (PAA) binders contain a high content of polar groups, enabling them to form strong hydrogen bonds and thus suppress the volume expansion of high-silicon anodes. They are widely used in silicon-carbon or silicon-based anodes. While existing PAA binders are constantly being innovated, most still rely on polymerization using conventional acrylic monomers. Consequently, the final performance is often brittle and lacks toughness due to the characteristics of acrylic monomers, making them prone to breakage in high-silicon systems. Therefore, finding more effective methods to impart superior performance to anode binders remains a major research focus. Summary of the Invention

[0006] To address the above technical problems, this invention proposes a solution-type negative electrode adhesive, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a solution-type negative electrode adhesive includes the following steps:

[0009] a. Preparation of pretreatment solution for polyacrylonitrile fibers: Polyacrylonitrile fibers and a modifier are mixed and stirred in water to obtain a pretreatment solution; the modifier is an alkali and / or an oxidizing agent;

[0010] b. Preparation of polyacrylonitrile fiber dispersion: Using a high-pressure homogenizer, the pretreated liquid obtained in step a is dispersed evenly in the presence of an optional dispersing agent to obtain a polyacrylonitrile fiber dispersion.

[0011] c. Polymerization reaction: The polyacrylonitrile fiber dispersion, unsaturated monomer, and initiator are mixed and reacted to generate a polymer, and the precipitate is removed.

[0012] d. Add the polymer precipitate to water and add a neutralizing agent to adjust the pH to obtain a solution-type negative electrode binder.

[0013] Polyacrylonitrile (PAA) fibers possess high strength and good toughness. Using PAA fibers to toughen and modify PAA adhesives is the main method proposed by the inventors to solve the aforementioned technical problems. However, introducing PAA fibers into PAA adhesives and enabling them to exert a toughening and modifying effect presents significant challenges.

[0014] Through continuous research, the inventors first pre-treated and modified polyacrylonitrile fibers with alkali and / or oxidants to increase their surface polar groups. Then, they used a high-pressure homogenizer to strongly disperse the pre-treated polyacrylonitrile fiber solution, opening up the interaction forces between the fibers to obtain a uniform and stable dispersion. This dispersion was then mixed with PAA monomers and initiators to participate in the polymerization process of PAA and to fully disperse and cross-link with the formed PAA macromolecules. This improved the overall strength and toughness of the PAA adhesive, effectively solving the problems of adhesive breakage and flaking during electric cycling caused by insufficient toughness of traditional negative electrode adhesives. This ensures the excellent electrochemical performance of lithium-ion batteries.

[0015] As a preferred embodiment of the preparation method of the present invention, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and ammonia water;

[0016] Preferably, the oxidant is selected from one or more of hydrogen peroxide, sodium persulfate, ammonium persulfate, potassium persulfate, potassium permanganate, nitric acid, sodium hypochlorite, and potassium dichromate.

[0017] As a preferred embodiment of the preparation method of the present invention, the mass ratio of the polyacrylonitrile fiber to the modifier is 1:(0.5-1);

[0018] Preferably, the pretreatment conditions in step a are: stirring at 50-100°C for 12-24 hours.

[0019] As a preferred embodiment of the preparation method of the present invention, the weight-average molecular weight of the polyacrylonitrile fiber is 50,000 to 1,000,000; the mass concentration of the polyacrylonitrile fiber in the pretreatment solution is 0.1% to 1%.

[0020] As a preferred embodiment of the preparation method of the present invention, the dispersing agent is selected from one or more of polyacrylic acid, modified cellulose (such as carboxymethyl cellulose), and their salts; their salts may be one or more of sodium salts, potassium salts, and lithium salts;

[0021] Preferably, the amount of the dispersing agent added is 20-120% of the mass of the polyacrylonitrile fiber used to prepare the pretreatment solution.

[0022] As a preferred embodiment of the preparation method of the present invention, the operating pressure of the high-pressure homogenizer is 20-400 MPa absolute pressure, and the operating temperature is 20-60℃.

[0023] This invention pretreats polyacrylonitrile fibers with alkali and / or oxidizing agents, introducing highly polar groups into the fiber molecules. This first enhances the hydrophilicity of the fibers and improves their dispersibility in water. Then, the pretreated solution is further dispersed using a high-pressure homogenizer to open up the interaction forces between the fibers, resulting in a stable and uniform fiber dispersion. This avoids the fibers from being unable to participate in the polymerization reaction due to excessive agglomeration or precipitation, and also improves the performance of the adhesive.

[0024] As a preferred embodiment of the preparation method of the present invention, in step c, the relative mass ratio of polyacrylonitrile fiber dispersion, unsaturated monomer and initiator is (0.4-4):100:(0.1-0.4), wherein the relative amount of polyacrylonitrile fiber dispersion is based on the mass of polyacrylonitrile fiber.

[0025] Preferably, the unsaturated monomer is selected from one or more of acrylic acid, acrylamide, acrylonitrile, and methacrylic acid, preferably comprising a composition of acrylic acid, acrylamide, and acrylonitrile compounded in any mass ratio, more preferably comprising a composition of 15-50% acrylic acid, 20-40% acrylamide, and 20-60% acrylonitrile by mass percentage.

[0026] Preferably, the initiator is selected from one or more of sodium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, isoascorbic acid, sodium bisulfite, and sodium metabisulfite;

[0027] Preferably, the unsaturated monomer and initiator are mixed and reacted with the polyacrylonitrile fiber dispersion by dropwise addition for 4-8 hours, and the mixture is kept warm for 1-3 hours after the dropwise addition is completed.

[0028] Preferably, the polymerization reaction temperature in step c is 25-85℃.

[0029] As a preferred embodiment of the preparation method of the present invention, the neutralizing agent is selected from one or more of sodium hydroxide, lithium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, and lithium carbonate;

[0030] Preferably, the amount of neutralizing agent used is such that the solution pH is 7-10;

[0031] Preferably, step d involves adjusting the pH at a temperature of 30-80°C;

[0032] Preferably, step d adjusts the product solid content to 4-10 wt%.

[0033] The present invention also proposes a solution-type negative electrode adhesive prepared according to the method described above.

[0034] The present invention also proposes the application of a solution-type negative electrode binder prepared according to the method described above in the negative electrode of a lithium-ion battery.

[0035] This invention modifies the PAA binder through special means, which is beneficial to improving the insertion and extraction efficiency of lithium ions in silicon-carbon / silicon anodes, avoiding surface cracking and powder shedding of silicon-carbon / silicon anodes caused by volume expansion during charging and discharging, and improving the cycle stability and cycle efficiency of silicon-carbon / silicon anodes. Detailed Implementation

[0036] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0037] The main raw material information in the following examples is as follows:

[0038] Acrylic acid (AA), Wanhua Chemical Group Co., Ltd.

[0039] Acrylonitrile (AN), Wanhua Chemical Group Co., Ltd.

[0040] Acrylamide (AM), Wanhua Chemical Group Co., Ltd.

[0041] Sodium persulfate (SPS), Unid Initiator Hefei Co., Ltd.

[0042] Ammonium persulfate (APS), Unite Initiator Hefei Co., Ltd.

[0043] tert-butyl hydroperoxide, Merck Chemicals

[0044] Sodium bisulfite, Wanhua Chemical Group Co., Ltd.

[0045] Sodium isoascorbate (IAA), Wanhua Chemical Group Co., Ltd.

[0046] Polyacrylonitrile, weight average molecular weight 50,000, 500,000, 1,000,000, Sigma-Aldrich

[0047] Sodium polyacrylate (40wt%), Wanhua Chemical Group Co., Ltd.

[0048] Polyacrylic acid (40wt%), Wanhua Chemical Group Co., Ltd.

[0049] Sodium carboxymethyl cellulose, Weiyi New Materials

[0050] Nano-silicon powder, Beijing Innocare Technology Co., Ltd.

[0051] Conductive carbon black, Erystal Group

[0052] Unless otherwise specified, all other raw materials can be purchased through commercial channels.

[0053]

Example 1

[0054] A method for preparing a solution-type negative electrode adhesive includes the following steps:

[0055] a. Preparation of pretreatment solution for polyacrylonitrile fiber: Mix 0.2 kg of polyacrylonitrile fiber (weight average molecular weight 500,000) and 0.2 kg of NaOH in 59.6 kg of water and stir at 80°C for 12 h to obtain the pretreatment solution;

[0056] b. Preparation of polyacrylonitrile fiber dispersion: Adjust the pressure of the high-pressure homogenizer to 100MPa and the temperature to 20℃, and disperse the pretreated liquid obtained in step a evenly in the presence of sodium polyacrylate, wherein the amount of sodium polyacrylate added is 20% of the mass of polyacrylonitrile fiber in step a, and a polyacrylonitrile fiber dispersion is obtained.

[0057] c. Polymerization reaction: The polyacrylonitrile fiber dispersion obtained above (based on the mass of polyacrylonitrile fiber), unsaturated monomer, and initiator were added dropwise at a mass ratio of 0.4:100:0.1 for 6 hours. The reaction temperature was controlled at 38°C. After the monomer and initiator were added, the mixture was kept at the temperature for 2 hours. After filtration and washing, polymer precipitate was obtained.

[0058] The unsaturated monomers include 30% AA, 30% AM and 40% AN by mass percentage;

[0059] The initiator is a mixture of APS and NaHSO3 in a mass ratio of 1.5:1;

[0060] d. Add the polymer precipitate to water, control the solution temperature at 35℃, add sodium hydroxide as a neutralizing agent to adjust the pH to 7, and adjust the solid content to 6.0±0.3wt% to obtain a solution-type negative electrode binder.

[0061]

Example 2

[0062] A method for preparing a solution-type negative electrode adhesive includes the following steps:

[0063] a. Preparation of pretreatment solution for polyacrylonitrile fiber: Mix 0.2 kg of polyacrylonitrile fiber (weight average molecular weight 50,000) and 0.1 kg of sodium persulfate in 39.7 kg of water and stir at 50°C for 18 h to obtain the pretreatment solution.

[0064] b. Preparation of polyacrylonitrile fiber dispersion: Adjust the pressure of the high-pressure homogenizer to 100MPa and the temperature to 60℃, and disperse the pretreated liquid obtained in step a evenly in the presence of sodium carboxymethyl cellulose, wherein the amount of sodium carboxymethyl cellulose added is 75% of the mass of polyacrylonitrile fiber in step a, and a polyacrylonitrile fiber dispersion is obtained.

[0065] c. Polymerization reaction: The polyacrylonitrile fiber dispersion obtained above (based on the mass of polyacrylonitrile fiber), unsaturated monomer, and initiator were added dropwise at a mass ratio of 0.4:100:0.4 for 4 hours. The reaction temperature was controlled at 70°C. After the monomer and initiator were added, the mixture was kept at the temperature for 3 hours. The mixture was then filtered and washed to obtain a polymer precipitate.

[0066] The unsaturated monomers include 20% AA, 20% AM and 60% AN by mass percentage;

[0067] The initiator is a mixture of SPS and NaHSO3 in equal mass ratio;

[0068] d. Add the polymer precipitate to water, control the solution temperature at 35℃, add sodium carbonate as a neutralizing agent to adjust the pH to 7, and adjust the solid content to 6.0±0.3wt% to obtain a solution-type negative electrode binder.

[0069]

Example 3

[0070] A method for preparing a solution-type negative electrode adhesive includes the following steps:

[0071] a. Preparation of pretreatment solution for polyacrylonitrile fiber: Mix 0.2 kg of polyacrylonitrile fiber (weight average molecular weight 800,000) and 0.2 kg of potassium persulfate in 19.6 kg of water and stir at 60°C for 24 h to obtain the pretreatment solution;

[0072] b. Preparation of polyacrylonitrile fiber dispersion: Adjust the pressure of the high-pressure homogenizer to 150MPa and the temperature to 40℃, and disperse the pretreated liquid obtained in step a evenly in the presence of sodium polyacrylate, wherein the amount of sodium polyacrylate added is 120% of the mass of polyacrylonitrile fiber in step a, and a polyacrylonitrile fiber dispersion is obtained.

[0073] c. Polymerization reaction: The polyacrylonitrile fiber dispersion obtained above (based on the mass of polyacrylonitrile fiber), unsaturated monomer, and initiator were added dropwise at a mass ratio of 4:100:0.4 for 8 hours. The reaction temperature was controlled at 25°C. After the monomer and initiator were added, the mixture was kept at this temperature for 2.5 hours. The mixture was then filtered and washed to obtain a polymer precipitate.

[0074] The unsaturated monomers include 15% AA, 40% AM and 45% AN by mass percentage;

[0075] The initiator is a mixture of APS and IAA in equal mass ratio;

[0076] d. Add the polymer precipitate to water, control the solution temperature at 35℃, add sodium hydroxide as a neutralizing agent to adjust the pH to 8, and adjust the solid content to 6.0±0.3wt% to obtain a solution-type negative electrode binder.

[0077]

Example 4

[0078] A method for preparing a solution-type negative electrode adhesive includes the following steps:

[0079] a. Preparation of pretreatment solution for polyacrylonitrile fiber: Mix 0.2 kg of polyacrylonitrile fiber (weight average molecular weight 1 million) and 0.15 kg of potassium permanganate in 50 kg of water and stir at 100°C for 12 h to obtain the pretreatment solution.

[0080] b. Preparation of polyacrylonitrile fiber dispersion: Adjust the pressure of the high-pressure homogenizer to 300 MPa and the temperature to 30℃, and disperse the pretreated liquid obtained in step a evenly in the presence of polyacrylic acid, wherein the amount of polyacrylic acid added is 120% of the mass of polyacrylonitrile fiber in step a, and a polyacrylonitrile fiber dispersion is obtained.

[0081] c. Polymerization reaction: The polyacrylonitrile fiber dispersion obtained above (based on the mass of polyacrylonitrile fiber), unsaturated monomer, and initiator were added dropwise at a mass ratio of 2:100:0.2 for 5 hours. The reaction temperature was controlled at 50°C. After the monomer and initiator were added, the mixture was kept at the temperature for 2 hours. The mixture was then filtered and washed to obtain a polymer precipitate.

[0082] The unsaturated monomers include 50% AA, 30% AM and 20% AN by mass percentage;

[0083] The initiator is a mixture of tert-butyl hydroperoxide and NaHSO3 in a mass ratio of 2:1;

[0084] d. Add the polymer precipitate to water, control the solution temperature at 35℃, add sodium hydroxide as a neutralizing agent to adjust the pH to 9, and adjust the solid content to 6.0±0.3wt% to obtain a solution-type negative electrode binder.

[0085] Comparative Example 1

[0086] The adhesive was prepared using essentially the same method as in Example 1, except that NaOH was not added in step a.

[0087] Comparative Example 2

[0088] The adhesive was prepared using a method essentially the same as in Example 1, except that the pretreatment solution obtained in step a was directly added to step c for polymerization without step b.

[0089] Comparative Example 3

[0090] The adhesive was prepared using essentially the same method as in Example 1, except that the polyacrylonitrile fibers in step a were replaced with the same mass of sodium carboxymethyl cellulose.

[0091]

Application Example

[0092] Peel strength tests were conducted on the adhesives prepared in the examples and comparative examples respectively: according to the American Society for Testing and Materials (ASTM) standard D3330, peel strength tests were conducted using a dedicated adhesive strength tester - Kejian tensile testing machine.

[0093] Then, each adhesive was applied to the silicon anode sheet according to the following method, and its electrochemical performance was tested separately:

[0094] (1) Disperse nano-silicon powder, conductive carbon black (Super-P), binder and water in water at a mass ratio of 6:2:2:10, then add ethanol accounting for 20% of the water mass, and stir at high speed for 10 minutes to obtain active material slurry.

[0095] (2) Electrode Coating: The above slurry is uniformly coated onto the copper foil current collector, dried at 130°C under vacuum, and then cut into electrode sheets with a diameter of 16 mm. The solid active material loading after drying is 1 mg / cm³. 2 .

[0096] (3) Electrochemical test: The above negative electrode and lithium iron phosphate positive electrode are assembled into a button cell and charged and discharged in a voltage range of 3.5V. The capacity retention rate after 100 cycles is tested by constant current method. Capacity retention rate = 100-cycle discharge capacity / 1-cycle discharge capacity.

[0097] Table 1. Performance Test Results of Adhesives or Negative Electrode Sheets

[0098]

[0099]

[0100] As can be seen from the performance test results in Table 1, the electrode films prepared using the binders obtained in Examples 1-4 exhibit good film formation. Due to the specific introduction of polyacrylonitrile fibers, the adhesive strength of the prepared binder increases, resulting in increased peel strength of the electrode film. Simultaneously, in terms of electrochemical performance, the strength and toughness of the binder increase, manifesting as better resistance to expansion and contraction of the anode material during the charge and discharge process of the silicon anode battery, leading to an increase in the initial charge capacity and capacity retention rate after 100 cycles.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a solution-type negative electrode adhesive, characterized in that, Includes the following steps: a. Preparation of pretreatment solution for polyacrylonitrile fiber: Polyacrylonitrile fiber and modifier are mixed and stirred in water to obtain pretreatment solution; The modifier is an alkali and / or an oxidizing agent; b. Preparation of polyacrylonitrile fiber dispersion: Using a high-pressure homogenizer, the pretreated liquid obtained in step a is dispersed evenly in the presence of an optional dispersing agent to obtain a polyacrylonitrile fiber dispersion. c. Polymerization reaction: The polyacrylonitrile fiber dispersion, unsaturated monomer, and initiator are mixed and reacted to generate a polymer, and the precipitate is removed. d. Add the polymer precipitate to water and add a neutralizing agent to adjust the pH to obtain a solution-type negative electrode binder.

2. The method for preparing the solution-type negative electrode adhesive according to claim 1, characterized in that, The alkali is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and ammonia water; Preferably, the oxidant is selected from one or more of hydrogen peroxide, sodium persulfate, ammonium persulfate, potassium persulfate, potassium permanganate, nitric acid, sodium hypochlorite, and potassium dichromate.

3. The method for preparing the solution-type negative electrode adhesive according to claim 1 or 2, characterized in that, The mass ratio of the polyacrylonitrile fiber to the modifier is 1:(0.5-1); Preferably, the pretreatment conditions in step a are: stirring at 50-100°C for 12-24 hours.

4. The method for preparing the solution-type negative electrode adhesive according to any one of claims 1-3, characterized in that, The polyacrylonitrile fiber has a weight-average molecular weight of 50,000 to 1,000,000; the mass concentration of the polyacrylonitrile fiber in the pretreatment solution is 0.1% to 1%.

5. The method for preparing the solution-type negative electrode adhesive according to any one of claims 1-4, characterized in that, The dispersing agent is selected from one or more of polyacrylic acid, modified cellulose, and their salts; Preferably, the amount of the dispersing agent added is 20-120% of the mass of the polyacrylonitrile fiber used to prepare the pretreatment solution.

6. The method for preparing the solution-type negative electrode adhesive according to any one of claims 1-5, characterized in that, The high-pressure homogenizer operates at an absolute pressure of 20-400 MPa and an operating temperature of 20-60℃.

7. The method for preparing the solution-type negative electrode adhesive according to any one of claims 1-6, characterized in that, In step c, the relative mass ratio of polyacrylonitrile fiber dispersion, unsaturated monomer, and initiator is (0.4-4):100:(0.1-0.4), wherein the relative amount of polyacrylonitrile fiber dispersion is based on the mass of polyacrylonitrile fiber. Preferably, the unsaturated monomer is selected from one or more of acrylic acid, acrylamide, acrylonitrile, and methacrylic acid, preferably comprising a composition of acrylic acid, acrylamide, and acrylonitrile compounded in any mass ratio, more preferably comprising a composition of 15-50% acrylic acid, 20-40% acrylamide, and 20-60% acrylonitrile by mass percentage. Preferably, the initiator is selected from one or more of sodium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, isoascorbic acid, sodium bisulfite, and sodium metabisulfite; Preferably, the unsaturated monomer and initiator are mixed and reacted with the polyacrylonitrile fiber dispersion by dropwise addition for 4-8 hours, and the mixture is kept warm for 1-3 hours after the dropwise addition is completed. Preferably, the polymerization reaction temperature in step c is 25-85℃.

8. The method for preparing the solution-type negative electrode adhesive according to any one of claims 1-7, characterized in that, The neutralizing agent is selected from one or more of sodium hydroxide, lithium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, and lithium carbonate; Preferably, the amount of neutralizing agent used is such that the solution pH is 7-10; Preferably, step d involves adjusting the pH at a temperature of 30-80°C; Preferably, step d adjusts the product solid content to 4-10 wt%.

9. A solution-type negative electrode adhesive prepared by the method according to any one of claims 1-8.

10. The application of a solution-type negative electrode binder prepared according to any one of claims 1-8 in the negative electrode of a lithium-ion battery.

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