Preparation method and application of water-based conductive binder for silicon-based negative electrode of lithium ion battery

Abstract

The application discloses a preparation method and application of a water-based conductive binder for a silicon-based negative electrode of a lithium ion battery. The water-based conductive binder is a kind of polymer aqueous solution prepared by copolymerization of monomer A, monomer B and monomer C in water, and then grafting reaction with amino sulfonate monomer D containing a long-chain ether bond. The obtained solution has a solid content of 2.5-5% after dialysis purification, and has the characteristics of water solubility, heat crosslinking and enhanced ionic conductivity, thereby solving the problem of large viscosity of the crosslinked network binder slurry and difficulty in dispersion. The electrode material coated on the copper foil has the characteristics of strong dry and wet adhesion and difficulty in falling off, the binder is used for the silicon-based negative electrode, the influence of the volume expansion of silicon can be relieved, the battery has high specific capacity and good cycle performance. The application has the advantages of low cost, simplicity, universality, environmental friendliness, good coating effect and the like, and is suitable for the silicon-based negative electrode of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a method for preparing and applying a silicon-based aqueous conductive binder for lithium-ion battery anodes. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy efficiency, high power density, lightweight, and environmental friendliness, and have been widely used in electronic devices such as mobile phones, laptops, and digital cameras. However, with the development of electric vehicles and emerging technologies such as artificial intelligence, lithium-ion batteries require even higher energy density while ensuring safety. The anode material plays a crucial role in the energy density and performance of lithium-ion batteries. Currently, graphite is the most widely used anode material, although its theoretical specific capacity is only 372 mAh·g. -1 Furthermore, with the increasing maturity of the graphite industry, the actual specific capacity of high-end graphite products is very close to this theoretical value. Silicon has a specific capacity of 3579 mAh·g at room temperature. -1 Silicon boasts an ultra-high specific capacity. Furthermore, silicon anode materials offer advantages such as low electrochemical potential during lithiation and delithiation processes, high safety, and environmental friendliness. Therefore, silicon is considered a very promising candidate to replace traditional graphite anode materials as the next generation of high-energy-density lithium-ion battery anode materials in the future.

[0003] Silicon anode materials undergo volume expansion of up to 300% during lithium intercalation, severely damaging the integrity of the electrode and leading to rapid capacity decay. Possible causes of silicon anode material failure include: (1) the formation of an unstable and thick solid electrolyte intercalation (SEI). The drastic volume change of silicon during intercalation damages the original SEI layer, exposing silicon on the surface and forming a new SEI layer with the electrolyte. This process continuously consumes lithium ions and electrolyte, eventually depleting the electrolyte. (2) Large volume changes lead to high internal stress on silicon particles, causing the material (active materials, etc.) to break and pulverize. (3) Peeling effect. Continuous volume changes and pulverization of the silicon anode material cause many active materials to lose their connection with the conductive network and current collector, resulting in the electrode layer peeling off from the current collector. Currently, to address the issue of decreased battery cycle performance caused by changes in the volume of silicon anodes, improvement methods include silicon nanomaterials, composite materials, pre-lithiation technology, and high-performance binders. The first three methods are costly and complex, while high-performance binders have lower development costs and simpler methods. Furthermore, binders play a crucial role in the electrochemical performance of electrodes, reducing the impact of silicon volume expansion and improving battery cycle performance.

[0004] To date, the scientific community has proposed various working mechanisms for binders, which can be mainly categorized into wetting theory, mechanical interlocking theory, chemical bonding theory, acid-base theory, diffusion theory, electrostatic theory, and weak boundary layer theory. Among these, wetting theory, mechanical interlocking theory, and chemical bonding theory are the three most widely used theories to explain the adhesion between binders and active materials in lithium-ion battery binders. From a wetting perspective, the goal is for the binder to completely wet the surfaces of the active material and conductive additives, thereby achieving close contact between the binder and the adherends and reducing defects at the bonding interface. From a mechanical interlocking perspective, to achieve significant mechanical interlocking, it is necessary to increase the surface roughness and porosity of the electrode material, select a suitable bonding system, and prepare a binder solution with appropriate viscosity to ensure effective mixing and dispersion. From a chemical bonding theory perspective, the goal is to generate strong interactions such as hydrogen bonds, covalent bonds, and coordination bonds between the binder and the active material. Existing silicon-based anode binders suffer from drawbacks such as weak interactions with silicon, the use of environmentally harmful organic solvents, large dosage requirements, poor stability, and poor cycle performance, making it difficult to meet industrial demands. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing and applying a water-based conductive binder for silicon-based negative electrodes in lithium-ion batteries. This method solves the problem of environmental harm caused by the need to dissolve the binder with organic solvents. By forming a network structure in situ with silicon particles through thermal self-crosslinking, the impact of silicon volume expansion on battery cycle performance is reduced. The ionic conductivity of the binder is enhanced by introducing functional monomers, and the strong adhesion of the binder can reduce the amount of binder used.

[0006] The objective of this invention is achieved through the following technical solutions.

[0007] A method for preparing a silicon-based aqueous conductive binder for lithium-ion battery anodes includes the following steps:

[0008] (1) Dissolve lithium hydroxide in water and add monomer A for neutralization, with a (carboxyl) neutralization degree of 60-80%; wherein monomer A is at least one of acrylic acid, methacrylic acid, maleic acid, and itaconic acid;

[0009] (2) The neutralized solution from step (1) is mixed with monomer B, monomer C and water, and an initiator solution is added to obtain a mixed solution. At the same time, a protective gas is passed through to remove oxygen, and then the temperature is raised to 60-80℃ and reacted for 24-36 hours. The monomer B is at least one of hydroxyethyl acrylate, butyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. The monomer C is at least one of N-hydroxymethyl acrylamide, polyethylene glycol diacrylate acrylamide and N-hydroxypropyl acrylamide.

[0010] (3) Dissolve the polymer aqueous solution obtained in step (2) in a buffer solution, add carbodiimide hydrochloride, N-hydroxysuccinimide and monomer D, and stir the reaction for 9-12 h; wherein the monomer D is an aminosulfonate containing a long chain ether bond;

[0011] (4) Dialyze the solution obtained in step (3) to obtain a water-based conductive binder for silicon-based negative electrodes of lithium-ion batteries.

[0012] Preferably, in step (1), monomer A is added in a water bath at room temperature;

[0013] Preferably, in step (2), the protective gas is nitrogen.

[0014] Preferably, in step (2), the initiator is one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, ammonium persulfate, and potassium persulfate;

[0015] Preferably, in step (2), the mass of the initiator is 0.5% to 1% of the total mass of monomers A, B, and C;

[0016] Preferably, in step (2), the initiator solution is added in 3 to 4 portions during the reaction.

[0017] Preferably, the mass percentage content of monomer A, monomer B, and monomer C is 40-60% for monomer A, 20-40% for monomer B, and 10-20% for monomer C, and the sum of the mass percentages of monomer A, monomer B, and monomer C is 100%.

[0018] Preferably, in step (2), the ratio of the total mass of monomers A, B, and C in the mixed solution to the mass of water is (10-15):(90-85).

[0019] Preferably, in step (3), the buffer solution is a phosphate buffer solution; the pH of the buffer solution is 6.5-7; the ratio of the polymer aqueous solution to the buffer solution is 50g:(100-150)mL;

[0020] Preferably, in step (3), the total mass of the carbodiimide hydrochloride and N-hydroxysuccinimide (the catalyst for the grafting reaction) is 8-15% of the solid content in the polymer aqueous solution; the mass ratio of the carbodiimide hydrochloride to N-hydroxysuccinimide is (3-2):2.

[0021] Preferably, in step (3), the molar ratio of monomer D to the molar ratio of carboxyl group in monomer A is 40-60%.

[0022] Preferably, in step (3), the stirring reaction is carried out at room temperature.

[0023] Preferably, in step (3), the structural formula of the monomer D is as follows: Figure 1 As shown, the average value of n is 6.

[0024] Preferably, in step (4), the dialysis bag is a 10-15 kDa dialysis bag; and the number of dialysis sessions is 2-3.

[0025] A water-based conductive binder for silicon-based negative electrodes in lithium-ion batteries is prepared by the above-described method.

[0026] Preferably, the solid content of the water-based conductive adhesive is 2.5% to 5%.

[0027] A lithium-ion battery negative electrode sheet comprises, by mass percentage: 80-90% negative electrode active material, 5-10% conductive agent, and 5-10% aqueous binder, with the sum of the mass percentages of each component being 100%; wherein the aqueous binder is the aforementioned lithium-ion battery silicon-based negative electrode aqueous conductive binder.

[0028] Preferably, the negative electrode active material is a silicon-oxygen composite material or a silicon-carbon composite material;

[0029] Preferably, the conductive agent is at least one of conductive carbon black, acetylene black, graphene, conductive graphite, Ketjen black, Super P, carbon nanotubes, and conductive carbon fibers; it has the advantages of small particle size and good conductivity.

[0030] Preferably, the negative electrode active material content of the lithium-ion battery negative electrode sheet is 1.2–2.0 mg·cm³. -2 .

[0031] A method for preparing a negative electrode sheet for a lithium-ion battery includes the following steps:

[0032] After mixing the negative electrode active material, conductive agent, the above-mentioned lithium-ion battery silicon-based negative electrode aqueous binder and water, grind thoroughly and control the viscosity. Coat the slurry onto copper foil with a scraper, place it in an oven at 110-150℃ for 3-5 hours, and then place it in a vacuum drying oven at 60-80℃ for 9-12 hours.

[0033] Preferably, the viscosity of the slurry is controlled at 1000-2000 mPa·s to achieve better coating results.

[0034] The above-mentioned aqueous conductive binder for lithium-ion battery silicon-based negative electrode or the above-mentioned negative electrode sheet for lithium-ion battery are used in the preparation of lithium-ion batteries.

[0035] A method for preparing a lithium-ion half-cell includes the following steps:

[0036] In the glove box, the lithium sheet is placed on the negative electrode shell, a separator is added, electrolyte is added, and the negative electrode sheet, gasket, and spring are placed in sequence. Then the positive electrode shell is added, and finally the battery is sealed under pressure using a battery packaging machine.

[0037] Preferably, the electrolyte needs to contain fluoroethylene carbonate (FEC) to enhance the cycle stability of the battery.

[0038] More preferably, the content of fluoroethylene carbonate (FEC) is 10%.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The water-based conductive binder provided by the present invention can increase the molecular weight of the polymer by using lithium hydroxide lithiation, and at the same time replenish the small amount of lithium consumed by the negative electrode, thereby further improving the initial coulombic efficiency.

[0041] (2) The water-based conductive binder provided by the present invention contains a large number of functional groups with multiple hydrogen bonds that have strong interaction with silicon-based electrodes, which can reduce the impact of silicon volume expansion and improve the battery capacity and cycle performance.

[0042] (3) The water-based conductive binder provided by the present invention can achieve thermal self-crosslinking, so that the slurry preparation will not be too viscous and difficult to coat, thereby increasing the loading of active material. At the same time, the thermal crosslinking network can limit the expansion of silicon volume, thereby reducing the impact of shedding and improving the stability and cycle performance of the battery.

[0043] (4) The water-based conductive binder provided by the present invention introduces water-based aminosulfonate containing long-chain ether bonds through the side chain, which can enhance the ionic conductivity of the binder, thereby reducing the amount of conductive agent, increasing the proportion of active material, and increasing battery capacity.

[0044] (5) The water-based conductive adhesive provided by the present invention has readily available raw materials, does not use other organic solvents, and has a simple and environmentally friendly synthesis process, and has certain industrial application prospects. Attached Figure Description

[0045] Figure 1 The structural formula is for monomer D.

[0046] Figure 2 The reaction formula for the water-based adhesive in Example 1 is shown.

[0047] Figure 3 This is a flowchart illustrating the preparation process of the water-based adhesive in Example 1.

[0048] Figure 4 The infrared spectrum of the water-based adhesive in Example 1 is shown.

[0049] Figure 5aA 0.325 A·g half-cell was prepared using the aqueous binder of Example 1. -1 The cyclic performance diagram.

[0050] Figure 5b Half-cells with a capacity of 0.65 A·g prepared using the aqueous binders of Example 1, Comparative Example 1, and Comparative Example 2 -1 The cyclic performance diagram.

[0051] Figure 6a and 6b The images show scanning electron microscope (SEM) images of the electrode prepared with the aqueous binder in Example 1 before and after 100 cycles. Detailed Implementation

[0052] To illustrate the technical solutions of the present invention in detail, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without any inventive effort are all within the protection scope of the present invention.

[0053] Example 1

[0054] A method for preparing an aqueous conductive adhesive (reaction formula see below) Figure 2 The preparation process flowchart is shown below. Figure 3 Specifically, it includes the following steps:

[0055] 1) Weigh 3.15g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 9g of acrylic acid to neutralize it (neutralization degree is 60%). Weigh 0.075g of azobisisobutyramidine hydrochloride and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 3g of hydroxyethyl acrylate, 3g of N-hydroxymethylacrylamide, and 40g of deionized water. Add about 5mL of initiator solution with a syringe, purge with nitrogen and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution and continue reacting for 8 hours. Add the remaining initiator solution and react for another 8 hours to end the reaction. Pour out the binder solution while it is still hot.

[0056] 2) Weigh 50g of adhesive solution (solid content 14.29%), add it to 60mL of phosphate buffer (Ph=6.5), and stir on a magnetic stirrer for 1h to disperse the adhesive solution. Weigh 0.4g of carbodiimide hydrochloride and 0.3g of N-hydroxysuccinimide and dissolve them in 20mL of phosphate buffer. Add 6g of monomer D (structural formula as shown) Figure 1The solution (with an average value of 6) was dissolved in 20 mL of phosphate buffer. The three solutions were poured into a 250 mL three-necked flask and mixed. After purging with nitrogen to remove air, the mixture was stirred at room temperature for 9 h to obtain an aqueous conductive adhesive solution.

[0057] 3) The aqueous conductive adhesive solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. The solution was dialyzed twice for purification to remove a small amount of unreacted monomers, and the aqueous conductive adhesive PAHN-PPS (solid content of 3.23%) was obtained.

[0058] A method for preparing a half-cell using the aqueous conductive binder specifically includes the following steps:

[0059] 1) Weigh out silicon carbide active material, Ketjen black, and the purified water-based conductive binder (by solid mass) in a mass ratio of 8:1:1. Add deionized water according to viscosity, grind thoroughly in a mortar, and then coat the slurry onto copper foil using a scraper. The silicon carbide active material content on the copper foil should be 1.46 mg·cm³. -2 The electrodes were placed in a 130℃ oven for 5 hours, and then in a 60℃ vacuum drying oven for 9 hours. The dried electrodes were then pressed into small electrodes with a diameter of 10 mm.

[0060] 2) Place the lithium sheet on the negative electrode shell in the glove box, add a separator, add electrolyte, and then place the negative electrode sheet, gasket, and spring in sequence. Finally, add the positive electrode shell and seal it with pressure using a battery packaging machine. Let it stand for 24 hours to allow the electrodes to fully dissolve the electrolyte.

[0061] Figure 4 The infrared spectrum of this water-based conductive adhesive is shown, with wavenumbers ranging from 3500 to 3100 cm⁻¹. -1 The broad absorption peak is formed by hydroxyl and amino groups, with a wavenumber of 2929 cm⁻¹. -1 The absorption peak of the methylene group is located at 1712 cm⁻¹. -1 and 1264cm -1 The absorption peaks are for the carbon group and carbon-oxygen bond, respectively, indicating the presence of the carboxyl group, with a wavenumber of 1160 cm⁻¹. -1 The peak represents the carbon-nitrogen bond stretching vibration, indicating the presence of amide, with a wavenumber of 1163 cm⁻¹. -1 This is the absorption peak of the ether bond in long-chain aliphatic ethers, with a wavenumber of 1070 cm⁻¹. -1 and 623cm -1 The position is where the characteristic peak of the sulfonic acid group is located, and it is in the wavenumber range of 1680–1640 cm⁻¹. -1 The absence of absorption peaks within the range indicates that the binder does not contain carbon-carbon double bonds, and the monomer reaction is relatively complete.

[0062] Figure 5a The adhesive is used at a current density of 0.325 A·g -1The cycling performance curve shows a specific capacity of up to 873 mAh·g in the first cycle. -1 After 131 cycles, the capacity decreased to 766.52 mAh·g. -1 The capacity retention rate was 87.71%, and the coulomb efficiency was stable.

[0063] Figure 5b The adhesive is used at a current density of 0.65 A·g -1 The cycling performance curve shows a specific capacity of 835.88 mAh·g in the first cycle. -1 After 354 cycles, the capacity drops to 669.77 mAh·g. -1 The capacity retention rate was 80.13%, and the capacity decreased to 589.00 mAh·g after 468 cycles. -1 The capacity retention rate was 70.46%, and the coulombic efficiency remained stable under these conditions. Constant current charge-discharge tests of the half-cell showed that the binder exhibited high capacity under both low and high current conditions, and the battery demonstrated excellent cycle performance.

[0064] Figure 6a The image shows a scanning electron microscope (SEM) image of the electrode prepared with the aqueous conductive binder in Example 1 before cycling. It can be seen that the electrode prepared with the silicon-carbon anode has a large number of smooth graphite flakes.

[0065] Figure 6b The scanning electron microscope image of the electrode prepared by the aqueous conductive binder in Example 1 after 100 cycles shows that a rough SEI layer has been formed on the surface, while no obvious cracks have appeared on the graphite sheet, indicating that the SEI layer is stable, which is one of the reasons for the excellent cycle performance of the battery.

[0066] Example 2

[0067] A water-based conductive adhesive, specifically comprising the following steps:

[0068] 1) Weigh 3.5g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 7.5g of acrylic acid to neutralize it (neutralization degree is 80%). Weigh 0.075g of azobisisobutyronitrile and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 4.5g of hydroxyethyl methacrylate, 3g of N-hydroxymethylacrylamide, and 40g of deionized water. Add about 5mL of initiator solution with a syringe, purge with nitrogen and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution and continue reacting for 8 hours. Add the remaining initiator solution and react for another 8 hours to end the reaction. Pour out the binder solution while it is still hot.

[0069] 2) Weigh 50g of adhesive solution (solid content 14.41%), add it to 60mL of phosphate buffer (Ph=6.5), and stir on a magnetic stirrer for 1h to disperse the adhesive solution. Weigh 0.4g of carbodiimide hydrochloride and 0.3g of N-hydroxysuccinimide and dissolve them in 20mL of phosphate buffer. Add 6g of monomer D (structural formula as shown) Figure 1 The solution (with an average value of 6) was dissolved in 20 mL of phosphate buffer. The three solutions were poured into a 250 mL three-necked flask and mixed. After purging with nitrogen to remove air, the mixture was stirred at room temperature for 9 h to obtain an aqueous conductive adhesive solution.

[0070] 3) The aqueous conductive adhesive solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. The solution was dialyzed twice for purification to remove a small amount of unreacted monomers and obtain the aqueous conductive adhesive (solid content of 3.52%).

[0071] The method for preparing the half-cell of this water-based binder is the same as in Example 1.

[0072] Example 3

[0073] A water-based conductive adhesive, specifically comprising the following steps:

[0074] 1) Weigh 3.87g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 9g of itaconic acid to neutralize it (neutralization degree is 60%). Weigh 0.15g of azobisisobutyramidine hydrochloride and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 4.5g of hydroxyethyl acrylate, 1.5g of N-hydroxymethylacrylamide, and 50g of deionized water. Add about 5mL of initiator solution using a syringe, purge with nitrogen gas and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution and continue reacting for 8 hours. Add the remaining initiator solution and react for another 8 hours to end the reaction. Pour out the binder solution while it is still hot.

[0075] 2) Weigh 50g of adhesive solution (solid content 14.35%), add it to 60mL of phosphate buffer (Ph=6.5), and stir on a magnetic stirrer for 1h to disperse the adhesive solution. Weigh 0.37g of carbodiimide hydrochloride and 0.28g of N-hydroxysuccinimide and dissolve them in 20mL of phosphate buffer. Add 9g of monomer D (structural formula as shown) Figure 1 The solution (with an average value of 6) was dissolved in 20 mL of phosphate buffer. The three solutions were poured into a 250 mL three-necked flask and mixed. After purging with nitrogen to remove air, the mixture was stirred at room temperature for 9 h to obtain an aqueous adhesive conductive agent solution.

[0076] 3) The aqueous conductive adhesive solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. The solution was dialyzed twice for purification to remove a small amount of unreacted monomers and obtain the aqueous conductive adhesive (solid content of 4.45%).

[0077] A method for preparing a half-cell using the aqueous conductive binder specifically includes the following steps:

[0078] 1) Weigh out silicon carbide active material, Ketjen black, and purified water-based conductive binder (by solid mass) in a mass ratio of 90:5:5. Add deionized water according to viscosity. Grind thoroughly in a mortar. Apply the slurry to copper foil using a scraper. The silicon carbide active material content on the copper foil should be 1.73 mg·cm³. -2 Place the dried electrode in an oven at 110–150℃ for 3–5 hours, then in a vacuum drying oven at 60℃ for 9–12 hours. Press the dried electrode into small electrode sheets with a diameter of 10 mm.

[0079] 2) Place the lithium sheet on the negative electrode shell in the glove box, add a separator, add electrolyte, and then place the negative electrode sheet, gasket, and spring in sequence. Finally, add the positive electrode shell and seal it with pressure using a battery packaging machine. Let it stand for 24 hours to allow the electrodes to fully dissolve the electrolyte.

[0080] Example 4

[0081] A water-based adhesive, specifically comprising the following steps:

[0082] 1) Weigh 3.5g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 7.5g of acrylic acid to neutralize it (neutralization degree is 60%). Weigh 0.075g of azobisisobutyramidine hydrochloride and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 6g of polyethylene glycol diacrylate, 1.5g of N-hydroxymethylacrylamide, and 50g of deionized water. Add about 5mL of initiator solution with a syringe, purge with nitrogen and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution. Continue reacting for another 8 hours, then add the remaining initiator solution. After reacting for another 8 hours, stop the reaction and pour out the binder solution while it is still hot.

[0083] 2) Weigh 50g of adhesive solution (solid content 14.31%), add it to 60mL of phosphate buffer (Ph=6.5), and stir on a magnetic stirrer for 1h to disperse the adhesive solution. Weigh 0.37g of carbodiimide hydrochloride and 0.28g of N-hydroxysuccinimide and dissolve them in 20mL of phosphate buffer. Add 6g of monomer D (structural formula as shown) Figure 1The solution (with an average value of 6) was dissolved in 20 mL of phosphate buffer. The three solutions were poured into a 250 mL three-necked flask and mixed. After purging with nitrogen to remove air, the mixture was stirred at room temperature for 9 h to obtain an aqueous conductive adhesive solution.

[0084] 3) The aqueous conductive adhesive solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. The solution was dialyzed twice for purification to remove a small amount of unreacted monomers and obtain the aqueous conductive adhesive (solid content of 3.13%).

[0085] The method for preparing the half-cell of this water-based binder is the same as in Example 3.

[0086] Comparative Example 1

[0087] A water-based adhesive, specifically comprising the following steps:

[0088] 1) Weigh 3.15g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 9g of acrylic acid to neutralize it (neutralization degree is 60%). Weigh 0.075g of azobisisobutyramidine hydrochloride and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 3g of hydroxyethyl acrylate, 3g of N-hydroxymethylacrylamide, and 40g of deionized water. Add about 5mL of initiator solution with a syringe, purge with nitrogen and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution and continue reacting for 8 hours. Add the remaining initiator solution and react for another 8 hours to end the reaction. Pour out the binder solution while it is still hot.

[0089] 2) The binder solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. Dialysis was performed twice in total to purify the solution and remove a small amount of unreacted monomers, resulting in an aqueous binder (solid content of 2.89%).

[0090] The method for preparing the half-cell of this water-based binder is the same as in Example 1.

[0091] Comparative Example 2

[0092] A water-based adhesive, specifically comprising the following steps:

[0093] 1) Weigh 3.15g of lithium hydroxide monohydrate and dissolve it in 40g of deionized water. Under room temperature water bath conditions, slowly add 9g of acrylic acid to neutralize it (neutralization degree is 60%). Weigh 0.075g of azobisisobutyramidine hydrochloride and dissolve it in 10g of deionized water. Transfer the neutralized solution to a 250mL three-necked flask equipped with a condenser. Add 40g of deionized water. Add about 5mL of initiator solution with a syringe. Purge with nitrogen and turn on mechanical stirring. After 15 minutes, start heating to 60℃. After reacting for 8 hours, add another 3mL of initiator solution. Continue reacting for another 8 hours. Add the remaining initiator solution. After reacting for another 8 hours, stop the reaction. Pour out the binder solution while it is still hot.

[0094] 2) The binder solution was placed in a 10kDa dialysis bag for dialysis. After dialysis for 8 hours, the deionized water was replaced. The process was repeated twice to purify the solution and remove a small amount of unreacted monomers, resulting in an aqueous binder (solid content of 2.78%).

[0095] The method for preparing the half-cell of this water-based binder is the same as in Example 1.

[0096] Comparative Example 3

[0097] Using LA133 binder, half-cells were prepared according to the preparation methods of Examples 1 and 3, respectively.

[0098] Figure 5b The long-term cycling performance of three binders—PAHN-PPS from Example 1, PAHN from Comparative Example 1, and PAA from Comparative Example 2—was compared at a current density of 0.65 A / g. As shown in the figure, the capacity and cycling performance of Comparative Example 1 are superior to those of Comparative Example 2, indicating that the network structure formed by thermal self-crosslinking is beneficial for stabilizing silicon particles, reducing the impact of silicon volume expansion, and resulting in a more stable SEI layer with a longer lifespan. Furthermore, the capacity and cycling performance of Example 1 are better than those of Comparative Example 1, indicating that the aminosulfonate containing long-chain ether bonds, introduced as a side chain, enhances the ion-conducting ability of the binder, reducing the resistance to lithium-ion conduction at the negative electrode, thereby increasing the battery capacity. It also contributes to the long-term stability of the SEI layer, thus improving cycling performance.

[0099] Table 1 shows the viscosity, slurry ratio (ratio of active material, conductive agent, and binder), slurry characteristics, and 0.65 A·g of the 1% solids binder solution of Examples 1-4, Comparative Example 1, Comparative Example 2, and the market sample. -1 The first-cycle specific capacity at current density and the number of cycles required to reduce the specific capacity to 80% of the first-cycle specific capacity.

[0100] Table 1

[0101]

[0102] As shown in Table 1, the viscosity of the binder prepared in this invention is higher than that of commercially available binders. Furthermore, at the same slurry ratio, the slurry's flowability and adhesion are improved to some extent, and it is less prone to bubble formation. At the same current density, the battery capacity and cycle performance are also significantly improved. Therefore, the binder provided by this invention can be well used in silicon-based anodes to enhance conductivity, reduce the impact of silicon volume expansion, form a stable SEI layer, and improve battery capacity and cycle performance.

[0103] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any simple changes, substitutions, combinations, or simplifications made by those skilled in the art based on the technical content disclosed in the present invention should be regarded as equivalent substitutions and are included or fall within the protection scope of the present invention.

Claims

1. A method for preparing a water-based conductive binder for silicon-based anodes of lithium-ion batteries, characterized in that, The preparation method comprises the following steps: (1) dissolving lithium hydroxide in water, adding monomer A for neutralization, and the neutralization degree is 60-80%; the monomer A is at least one of acrylic acid, methacrylic acid, maleic acid and itaconic acid; (2) mixing the solution after neutralization in step (1) with monomer B, monomer C and water, adding an initiator solution, obtaining a mixed solution, removing oxygen by passing a protective gas, and then heating to 60-80 DEG C for 24-36 h; the monomer B is at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate; the monomer C is at least one of N-hydroxymethyl acrylamide, polyethylene glycol diacrylate and N-hydroxypropyl acrylamide; (3) dissolving the polymer aqueous solution obtained in step (2) in a buffer solution, adding carbodiimide hydrochloride, N-hydroxysuccinimide and monomer D, and stirring for 9-12 h; the monomer D is an amino sulfonate salt containing a long-chain ether bond having the structure of formula (I): (I); (4) dialyzing the solution obtained in step (3) to obtain a lithium ion battery silicon-based negative electrode water-based conductive binder.

2. The production method according to claim 1, characterized by, In step (1), the monomer A is added in a room temperature water bath; In step (2), the protective gas is nitrogen.

3. The preparation method according to claim 1, characterized in that, In step (2), the initiator is one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, ammonium persulfate and potassium persulfate; In step (2), the mass of the initiator is 0.5-1% of the total mass of monomer A, monomer B and monomer C; In step (2), the initiator solution is added in 3-4 times during the reaction.

4. The method of claim 1, wherein, The mass percentage content of monomer A, monomer B and monomer C is 40-60% of monomer A, 20-40% of monomer B and 10-20% of monomer C, and the sum of the mass percentages of monomer A, monomer B and monomer C is 100%; The ratio of the total mass of monomer A, monomer B and monomer C to the mass of water in the mixed solution is (10-15):(90-85).

5. The preparation method according to claim 1, characterized in that, In step (3), the buffer solution is a phosphate buffer solution; the pH of the buffer solution is 6.5-7; and the dosage ratio of the polymer aqueous solution to the buffer solution is 50 g:(100-150) mL; In step (3), the total mass of the carbodiimide hydrochloride and N-hydroxysuccinimide is 8-15% of the solid content in the polymer aqueous solution; and the mass ratio of the carbodiimide hydrochloride to N-hydroxysuccinimide is (3-2):2; In step (3), the molar ratio of monomer D to the residual carboxyl groups after neutralization of monomer A is 40-60%; In step (3), the stirring reaction is carried out at room temperature; In step (4), the dialysis bag for dialysis is a 10-15 kDa dialysis bag; and the dialysis is performed for 2-3 times.

6. A waterborne conductive binder for silicon-based anodes of lithium-ion batteries, characterized in that it comprises: The lithium ion battery silicon-based negative electrode water-based conductive binder is prepared by the preparation method in any one of claims 1-5.

7. A lithium-ion battery negative electrode sheet, characterized by, The negative electrode active material is 80-90% by mass, the conductive agent is 5-10% by mass, the water-based binder is 5-10% by mass, and the sum of the mass percentages of the components is 100%; and the water-based binder is the lithium ion battery silicon-based negative electrode water-based conductive binder in claim 6.

8. The lithium-ion battery anode web of claim 7, wherein, The negative electrode active material is a silicon-oxygen composite material or a silicon-carbon composite material; and the conductive agent is at least one of conductive carbon black, graphene, conductive graphite, carbon nanotubes and conductive carbon fibers.

9. The lithium-ion battery anode web of claim 8, wherein, The conductive carbon black is acetylene black, Ketjen black or super P.

10. The lithium-ion battery anode web of claim 7, wherein, The negative active material content of the lithium ion battery negative electrode sheet is 1.2-2.0 mg•cm -2 .

11. Use of the aqueous conductive binder for silicon-based anodes of lithium-ion batteries according to claim 6 or of the negative electrode web for lithium-ion batteries according to any one of claims 7 to 10 for the manufacture of lithium-ion batteries.

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