A method for preparing a silicon-carbon negative electrode water-based binder

Abstract

The application relates to the technical field of water-based adhesives, and particularly provides a preparation method of a silicon-carbon negative electrode water-based adhesive, which comprises the following steps: mixing a first hydrophilic monomer and a first hydrophobic monomer, adding the mixture into water, heating to a preset reaction temperature, dropping a first water-soluble initiator solution, continuously reacting for 0-8 hours after the dropping is completed, dropping a second hydrophilic monomer and a second hydrophobic monomer, continuously reacting for 0-6 hours after the dropping is completed, and cooling, so that the silicon-carbon negative electrode water-based adhesive is obtained; the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is 10-60%; the proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer is not more than 20%; and the proportion of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is 4:6-9:1. The water-based adhesive prepared by the preparation method can simultaneously better disperse hydrophobic graphite active particles and hydrophilic silicon material active particles, and the electrical performance of a lithium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water-based adhesives, in particular to a preparation method of a silicon-carbon negative electrode water-based adhesive. BACKGROUND

[0002] The theoretical gravimetric capacity of silicon elemental material is 4200mAh / g, far exceeding the theoretical gravimetric capacity of 340mAh / g of graphite materials. Therefore, the prior art mixes silicon materials such as silicon monoxide and silicon carbide with graphite to form a silicon-carbon negative electrode, so as to improve the gravimetric capacity of the negative electrode material and thus the energy density of the lithium ion battery. However, the silicon material has a large volume change during lithium extraction, with a theoretical change of more than 300%, so the expansion rate of the electrode sheet during charging and discharging is high. How to control the expansion of the electrode sheet is a key to the use of silicon-carbon negative electrode materials.

[0003] In the preparation of lithium ion battery electrode sheets, the negative electrode material adhesive is used to disperse and mix the electrode active material and the like uniformly, and then coated on the current collector such as copper foil, and then treated by drying and the like. The adhesive is a non-active substance in the electrode material, but it plays a crucial role in the electrochemical performance of the electrode sheet and the final lithium ion battery.

[0004] For the silicon-carbon negative electrode adhesive, its role is not only to connect the electrode active material, the conductive agent and the electrode current collector, so as to reduce the impedance of the electrode, but also to more effectively inhibit the large volume expansion and shrinkage of the silicon material during the cycle process, so as to achieve higher cycle stability. Of course, in addition to the inhibition of the volume change of the adhesive, how to more effectively disperse the silicon-carbon negative electrode active material is also an important factor affecting the cycle stability of the final electrode sheet. SUMMARY

[0005] At present, the cycle stability of silicon-carbon negative electrode material sheet prepared by using polyacrylate adhesive is obviously better than that of CMC (cellulose) + SBR (styrene-butadiene rubber) binder. However, the silicon-carbon negative electrode material sheet prepared by using polyacrylate derivative as the binder on the market still has the defects of low cycle number, hard and brittle sheet, etc., which limits the application of high-capacity silicon-carbon negative electrode material. The main reasons for the hard and brittle sheet and the low cycle number are as follows: 1) the dispersion of silicon monoxide and graphite particles in the sheet is not enough, and the particle agglomeration still exists, so that the stress distribution of the sheet is uneven and easy to crack; at the same time, the volume expansion, shrinkage and other changes of the agglomerated active particles during the lithium extraction process do not match the volume changes of other well-dispersed particles, thereby causing the destruction of the sheet structure and affecting the cycle stability, 2) the interaction between the polyacrylate derivative binder and the particles such as silicon monoxide is not strong enough. Specifically, the hydrophobicity of the graphite negative electrode surface is relatively high, and the hydrophilicity of the silicon material such as silicon monoxide and silicon carbide is better. When the binder interacts well with the hydrophobic graphite active particles, it is difficult to interact well with the hydrophilic silicon monoxide active particles. Therefore, for the silicon-carbon negative electrode, it is difficult for the water-based binder to achieve good wettability and dispersibility of the two different interface materials, which is a technical point that needs to be urgently broken through.

[0006] To solve the above technical problems, the application provides a preparation method of a silicon-carbon negative electrode water-based binder.

[0007] The application adopts the following technical scheme:

[0008] A preparation method of a silicon-carbon negative electrode water-based binder, comprising: mixing a first hydrophilic monomer with a chemical formula of CH2=CR 1 R 2 and a first hydrophobic monomer with a chemical formula of CH2=CR 3 R 4 , adding to water, heating to a preset reaction temperature, dropping a first water-soluble initiator solution, continuing to react for 0-8 hours after dropping, then dropping a second hydrophilic monomer with a chemical formula of CH2=CR 5 R 6 and a second hydrophobic monomer with a chemical formula of CH2=CR 7 R 8 , stopping dropping, continuing to react for 0-6 hours, cooling, and obtaining the product.

[0009] The proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is 10-60%;

[0010] The proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer is not more than 20%;

[0011] The ratio of the weight of the second hydrophilic monomer and the second hydrophobic monomer to the weight of the first hydrophilic monomer and the first hydrophobic monomer is 4:6-9:1;

[0012] R 1 R 3 R 5 and R 7 Individually selected from H or C1-C4 alkyl groups;

[0013] R 2 and R 6 Individually selected from C1-C18 carboxylates, C1-C18 sulfonates, C1-C18 sulfates, C1-C18 phosphates, hydroxyl-containing C1-C4 substituted alkyl groups, amino-containing C1-C4 substituted alkyl groups, carboxyl-containing C1-C8 substituted alkyl groups, with the molecular formula CONR 9 R 10 The amide group or molecular formula is COO(CH2CH2O). m R 11 Polyether-modified ester, wherein R 9 and R 10 The individual is selected from H, methyl or ethyl, R 11 Selected from H, C1-C4 alkyl or C1-C4 substituted alkyl, m = 1-30;

[0014] R 4 and R 8 The single one is selected from the molecular formula COOR 12 The ester group, phenyl, substituted phenyl or nitrile group, wherein R 12 It is a C1-C22 alkyl group.

[0015] Preferably, the proportion of the first hydrophobic monomer in the total weight of the first hydrophilic monomer and the first hydrophobic monomer is not higher than 50%.

[0016] Preferably, the proportion of the second hydrophobic monomer in the total weight of the second hydrophilic monomer and the second hydrophobic monomer does not exceed 15%.

[0017] Preferably, the ratio of the weight of the second hydrophilic monomer and the second hydrophobic monomer to the weight of the first hydrophilic monomer and the first hydrophobic monomer is not less than 4:6 and less than 5:5.

[0018] Preferably, the ratio of the weight of the second hydrophilic monomer and the second hydrophobic monomer to the weight of the first hydrophilic monomer and the first hydrophobic monomer is higher than 5:5 and lower than 7:3.

[0019] More preferably, the ratio of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is not less than 6:4.

[0020] Preferably, the first water-soluble initiator is selected from one or a combination of persulfate initiators, peroxide initiators, azo initiators and redox initiators, and the amount of the first water-soluble initiator is 0.05-1.0% of the weight sum of the first hydrophilic monomer and the first hydrophobic monomer.

[0021] Preferably, the second hydrophilic monomer of the formula CH2=CR 5 R 6 and the second hydrophobic monomer of the formula CH2=CR 7 R 8 are added simultaneously with the second water-soluble initiator aqueous solution.

[0022] More preferably, the second water-soluble initiator is selected from one or a combination of persulfate initiators, peroxide initiators, azo initiators and redox initiators, and the amount of the second water-soluble initiator is 0.05-1.0% of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer.

[0023] Preferably, the second hydrophilic monomer of the formula CH2=CR 5 R 6 and the second hydrophobic monomer of the formula CH2=CR 7 R 8 are added simultaneously with the second water-soluble initiator aqueous solution.

[0024] In summary, the present application has the following beneficial effects:

[0025] 1. The structure design of the acrylic ester polymer in the water-based adhesive of the present application is based on the hydrophobic surface of graphite and the hydrophilic surface of silicon material in two dimensions, forming a 2-block or 3-block copolymer with alternating hydrophilic and hydrophobic properties, which has good wetting and dispersion for active particulate matter such as hydrophobic graphite and hydrophilic silicon monoxide particles, can effectively improve the wetting and dispersion of active particles, and reduce the agglomeration of active particles. The dispersion of active particles is improved, and the problem of unstable charge-discharge performance and short service life caused by volume change of silicon material during lithium extraction is also improved. At the same time, the active particles are more uniformly dispersed, and the softness of the electrode sheet is also improved.

[0026] 2、The application adopts a 2-stage polymerization method, which is simple and easy to operate. According to the reaction time after the first monomer is added and before the second monomer is added, the obtained acrylic ester polymer can be divided into 2-stage polymer and 3-stage polymer. When the first monomer is added and the reaction continues for a period of time until the first hydrophilic monomer and the first hydrophobic monomer are substantially reacted, the 2-stage polymer is obtained after the second hydrophilic monomer and the second hydrophobic monomer are added. The hydrophobicity of the first-stage polymer obtained by the reaction of the first hydrophilic monomer and the first hydrophobic monomer is higher than that of the second-stage polymer obtained by the reaction of the second hydrophilic monomer and the second hydrophobic monomer. The first-stage polymer has good interaction with the hydrophobic carbon black conductive agent and the graphite active particle, and the second-stage polymer has good interaction with the hydrophilic silicon material, achieving good wetting and dispersion of the graphite active particle and the silicon material active particle at the same time. When the reaction time after the first monomer is added and before the second monomer is added is not enough for the first hydrophilic monomer and the first hydrophobic monomer to be substantially reacted, the 3-stage polymer is obtained after the second hydrophilic monomer and the second hydrophobic monomer are added. That is, after the second hydrophilic monomer and the second hydrophobic monomer are added, the weight ratio of the unreacted hydrophilic monomer and hydrophobic monomer (intermediate-stage polymer) in the reaction system is between the weight ratio of the first hydrophilic monomer and the first hydrophobic monomer and the weight ratio of the second hydrophilic monomer and the second hydrophobic monomer. The hydrophobicity of the first-stage polymer, the intermediate-stage polymer, and the second-stage polymer decreases in turn, and the hydrophilicity increases in turn. The first-stage polymer has good interaction with the hydrophobic carbon black conductive agent and the graphite active particle, and the intermediate-stage polymer plays a transitional role. Alternatively, the intermediate-stage polymer can also interact with the carbon black conductive agent, the graphite particle, and the silicon material particle according to the hydrophilic and hydrophobic states, respectively. The second-stage polymer has good interaction with the hydrophilic silicon material, achieving good dispersion of the graphite active particle and the silicon material active particle at the same time.

[0027] 3、By adjusting the weight ratio of the hydrophilic monomer / hydrophobic monomer, the ratio of the weight of the first-stage monomer (i.e., the first hydrophilic monomer and the first hydrophobic monomer) to the weight of the second-stage monomer (i.e., the second hydrophilic monomer and the second hydrophobic monomer), and the polymerization process in the 2-stage polymerization method, the application achieves adjustment of the wetting and dispersion ability of the water-based adhesive, and obtains a water-based adhesive that has good wetting and dispersion ability for both hydrophobic graphite and hydrophilic silicon material, and has strong adhesion. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The stability test results of the negative electrode slurry obtained from the water-based adhesive of Example 1.

[0029] Figure 2 The stability test results of the negative electrode slurry obtained from the water-based adhesive of Comparative Example 1.

[0030] Figure 3Impedance comparison chart of Example 1, Comparative Example 2, Comparative Example 5;

[0031] Wherein, curve a-Example 1, curve b-Comparative Example 2, curve c-Comparative Example 5.

[0032] Figure 4 Cycle stability comparison chart of Example 1 and Comparative Example 4;

[0033] Wherein, curve d-Example 1, curve e-Comparative Example 4. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described in detail below.

[0035] Throughout the specification, unless otherwise specifically indicated, the terms used herein are to be understood in the sense that they are commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. If there is a conflict, the present specification takes precedence.

[0036] The present application proposes a preparation method of a silicon-carbon negative electrode water-based binder, comprising: mixing a first hydrophilic monomer with a chemical formula of CH2=CR 1 R 2 and a first hydrophobic monomer with a chemical formula of CH2=CR 3 R 4 , adding to water, heating to a preset reaction temperature, dropping a first water-soluble initiator solution, continuing to react for 0-8 hours after dropping is completed, then dropping a second hydrophilic monomer with a chemical formula of CH2=CR 5 R 6 and a second hydrophobic monomer with a chemical formula of CH2=CR 7 R 8 , continuing to react for 0-6 hours after dropping is completed, cooling, and obtaining the product.

[0037] The proportion of the above-mentioned first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is 10-60%; the weight sum of the first hydrophilic monomer and the first hydrophobic monomer refers to the weight of the composition composed of the first hydrophilic monomer and the first hydrophobic monomer.

[0038] The proportion of the above-mentioned second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer is not more than 20%; the weight sum of the second hydrophilic monomer and the second hydrophobic monomer refers to the weight of the composition composed of the second hydrophilic monomer and the second hydrophobic monomer.

[0039] The proportion of the weight sum of the above-mentioned second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the above-mentioned first hydrophilic monomer and the first hydrophobic monomer is 4:6-9:1.

[0040] R 1 , R 3 , R 5 and R 7 are independently selected from H or C1-C4 alkyl;

[0041] R 2 and R 6 represent hydrophilic functional groups. R 2 and R 6 are independently selected from C1-C18 carboxylate, C1-C18 sulfonate, C1-C18 sulfate, C1-C18 phosphate, hydroxyl-containing C1-C4 substituted alkyl, amine-containing C1-C4 substituted alkyl, carboxyl-containing C1-C8 substituted alkyl, amide groups of the formula CONR 9 R 10 amide groups of the formula COO(CH2CH2O) m R 11 polyether-modified esters, wherein R 9 and R 10 are independently selected from H, methyl or ethyl, R 11 is selected from H, C1-C4 alkyl or C1-C4 substituted alkyl, and m = 1-30;

[0042] R 4 and R 8 represent hydrophobic functional groups. R 4 and R 8 are independently selected from ester groups of the formula COOR 12 , phenyl, substituted phenyl or nitrile groups, wherein R 12 is C1-C22 alkyl.

[0043] In the present application, by way of example, the first hydrophilic monomer and the second hydrophilic monomer can be selected from acrylic acid (AA), methacrylic acid (MAA), sodium acrylate (AANa), lithium acrylate (AALi), sodium methacrylate (MAANa), lithium methacrylate (MAALi), hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate (HEA), hydroxypropyl methacrylate (HPMA), hydroxypropyl acrylate (HPA), acrylamide (AM), N,N-dimethyl acrylamide (DMAA), monomethoxypolyether (meth) acrylate, and the like. The first hydrophobic monomer and the second hydrophobic monomer can be selected from acrylonitrile (AN), methyl methacrylate (MMA), methyl acrylate (MA), ethyl methacrylate (EMA), ethyl acrylate (EA), lauryl methacrylate (LMA), lauryl acrylate (LA), stearyl methacrylate (SMA), stearyl acrylate (SA), isooctyl methacrylate (2-EHA), isooctyl acrylate (2-EHMA), n-butyl methacrylate (BMA), n-butyl acrylate (BA), styrene (St), p-methylstyrene, and the like.

[0044] In a preferred embodiment of the present application, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is not more than 50%; in a more preferred embodiment, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is less than 30%; in a still more preferred embodiment, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is more than 35% and less than 50%. In a still further preferred embodiment, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is more than 40% and less than 50%.

[0045] In a preferred embodiment of the present application, the proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer is not more than 15%.

[0046] More preferably, in this application, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is not less than the proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer. More preferably, the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is 5% or more higher than the proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer. That is, for example, if the proportion of the second hydrophobic monomer in the weight sum of the second hydrophilic monomer and the second hydrophobic monomer is 10%, then the proportion of the first hydrophobic monomer in the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is not less than 15%, and can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%. For example, if the second hydrophobic monomer accounts for 15% of the total weight of the second hydrophilic monomer and the second hydrophobic monomer, then the first hydrophobic monomer accounts for no less than 20% of the total weight of the first hydrophilic monomer and the first hydrophobic monomer, which can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%. More preferably, the proportion of the first hydrophobic monomer in the total weight of the first hydrophilic monomer and the first hydrophobic monomer is 10% or more higher than the proportion of the second hydrophobic monomer in the total weight of the second hydrophilic monomer and the second hydrophobic monomer.

[0047] In a preferred embodiment of this application, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is not less than 4:6 and less than 5:5. That is, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is between 4:6 and 5:5, but not including 5:5.

[0048] In a preferred embodiment of this application, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is higher than 5:5 and lower than 7:3. That is, the ratio of the sum of the weights of the second hydrophilic monomer and the second hydrophobic monomer to the sum of the weights of the first hydrophilic monomer and the first hydrophobic monomer is between 5:5 and 7:3, but does not include 5:5 and 7:3.

[0049] By adjusting the weight ratio of the second hydrophilic monomer and the second hydrophobic monomer to the weight ratio of the first hydrophilic monomer and the first hydrophobic monomer within the above range, good wetting and dispersing ability of the waterborne adhesive on hydrophobic graphite active particles and hydrophilic silica active particles can be achieved.

[0050] In a more preferred embodiment of the present application, the ratio of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is not less than 6:4. That is, the ratio of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the first hydrophilic monomer and the first hydrophobic monomer is between 6:4 and 7:7, but does not include 7:3.

[0051] Further adjusting the ratio of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer to the weight sum of the first hydrophilic monomer and the first hydrophobic monomer in the above range can achieve better wetting and dispersing ability of the aqueous binder to the hydrophobic graphite active particles and the hydrophilic silicon monoxide active particles.

[0052] In a preferred embodiment of the present application, the first water-soluble initiator is selected from one or a combination of several of peroxysulfate initiators, peroxide initiators, azo initiators and redox initiators, and the amount of the first water-soluble initiator is 0.05-1.0% of the weight sum of the first hydrophilic monomer and the first hydrophobic monomer. In a more preferred embodiment, the amount of the first water-soluble initiator is 0.2-1.0% of the weight sum of the first hydrophilic monomer and the first hydrophobic monomer. In a further preferred embodiment, the amount of the first water-soluble initiator is 0.3-0.8% of the weight sum of the first hydrophilic monomer and the first hydrophobic monomer, and specifically, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%.

[0053] In a preferred embodiment of the present application, the above second hydrophilic monomer of the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer of the chemical formula CH2=CR 7 R 8 are simultaneously added with the second water-soluble initiator aqueous solution.

[0054] In a more preferred embodiment of the present application, the second water-soluble initiator is selected from one or a combination of several of peroxysulfate initiators, peroxide initiators, azo initiators and redox initiators, and the amount of the second water-soluble initiator is 0.05-1.0% of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer. In a further preferred embodiment, the amount of the second water-soluble initiator is 0.1-1.0% of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer. In a still further preferred embodiment, the amount of the second water-soluble initiator is 0.2-0.5% of the weight sum of the second hydrophilic monomer and the second hydrophobic monomer, and specifically, it can be 0.2%, 0.3%, 0.4% or 0.5%.

[0055] In the present application, the first water-soluble initiator and the second water-soluble initiator can be selected from persulfate initiators, for example, ammonium persulfate, potassium persulfate, sodium persulfate, etc. The first water-soluble initiator and the second water-soluble initiator can also be selected from peroxide initiators, for example, hydrogen peroxide. The first water-soluble initiator and the second water-soluble initiator can also be selected from azo initiators, for example, azobisdimethylamidinum hydrochloride (AIBA), azobisdimethylimidazolinium hydrochloride (AIBI), etc. The first water-soluble initiator and the second water-soluble initiator can also be selected from redox initiators, for example, ammonium persulfate / sodium bisulfite, potassium persulfate / sodium bisulfite, hydrogen peroxide / tartaric acid, hydrogen peroxide / oxone, ammonium persulfate / ferrous sulfate, hydrogen peroxide / ferrous sulfate, etc.

[0056] In the preferred embodiments of the present application, the dropwise addition time of the second hydrophilic monomer of the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer of the chemical formula CH2=CR 7 R 8 is 30 minutes to 8 hours. In more preferred embodiments, the dropwise addition time of the second hydrophilic monomer of the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer of the chemical formula CH2=CR 7 R 8 is 1 hour to 4 hours.

[0057] In the present application, the dropwise addition time of the second water-soluble initiator is not more than or more than the dropwise addition time of the second hydrophilic monomer of the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer of the chemical formula CH2=CR 7 R 8 . For example, the dropwise addition time of the second hydrophilic monomer of the chemical formula CH2=CR 5 R 6 and the second hydrophobic monomer of the chemical formula CH2=CR 7 R 8 is 4 hours, and the dropwise addition time of the second water-soluble initiator can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, etc.

[0058] In the present application, the concentration of the first water-soluble initiator solution and the second water-soluble initiator solution is not particularly limited and can be 1-10 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%.

[0059] In the present application, the continued reaction time after the first water-soluble initiator solution is added dropwise has an effect on the structure of the acrylate polymer of the water-based adhesive. When the continued reaction time is relatively long, for example, 6 hours, 7 hours or 8 hours, the first hydrophilic monomer and the first hydrophobic monomer are completely reacted, and when the second hydrophilic monomer and the second hydrophobic monomer are added dropwise, the composition of the monomers being reacted in the reaction system is basically the same as that of the second hydrophilic monomer and the second hydrophobic monomer, and the acrylate polymer is a 2-stage polymer, the first stage of which is composed of the first hydrophilic monomer and the first hydrophobic monomer, and the second stage of which is composed of the second hydrophilic monomer and the second hydrophobic monomer. When the continued reaction time is not enough, there are still a large amount of unreacted first hydrophilic monomer and first hydrophobic monomer in the reaction system, and the second hydrophilic monomer and the second hydrophobic monomer are added dropwise. The composition of the hydrophilic monomer and the hydrophobic monomer being reacted in the reaction system is between the composition of the first hydrophilic monomer and the first hydrophobic monomer and the composition of the second hydrophilic monomer and the second hydrophobic monomer. With the continuous polymerization reaction and the continuous addition of the second hydrophilic monomer and the second hydrophobic monomer, the composition of the hydrophilic monomer and the hydrophobic monomer in the reaction system tends to be closer and closer to the composition of the second hydrophilic monomer and the second hydrophobic monomer, until the composition of the hydrophilic monomer and the hydrophobic monomer in the reaction system is equivalent to the composition of the second hydrophilic monomer and the second hydrophobic monomer, and the acrylate polymer is a 3-stage polymer, and there is an intermediate transition segment between the first stage segment and the second stage segment.

[0060] In the preparation method of the silicon-carbon negative electrode water-based adhesive of the present application, the stirring speed of the reaction system is not particularly limited and can be 100-1000 rpm, or further, 200-600 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm.

[0061] The preparation method of the silicon-carbon negative electrode water-based adhesive of the present application will be described in detail below in combination with examples, comparative examples and experimental data. Unless otherwise specified, the parts in the following examples and comparative examples are parts by weight.

[0062] Example 1

[0063] A reaction bottle was added with 200 parts of water, 24 parts of MAA monomer, sodium bicarbonate was added to adjust the pH to neutral, 8 parts of EA monomer and 8 parts of HEA monomer were added, the monomers were fully mixed under stirring at a speed of 200 rpm, the temperature was raised to 70°C, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 240 min, after the dropping was completed, the temperature was kept for 1 h; 6 parts of EA monomer and 54 parts of AA monomer were added dropwise, the dropping time was 240 min, and 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was added dropwise at the same time, the dropping time was 270 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 2 h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 15.2% and a viscosity (25°C) of 3700 mPa·s was prepared.

[0064] Example 2

[0065] A reaction bottle was added with 250 parts of water, 20 parts of MAA monomer, sodium bicarbonate was added to adjust the pH to neutral, 9 parts of EA monomer and 7 parts of HEA monomer were added, the monomers were fully mixed under stirring at a speed of 200 rpm, the temperature was raised to 70°C, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 240 min, after the dropping was completed, the temperature was kept for 4 h; 6 parts of EA monomer and 58 parts of MAA monomer were added dropwise, the dropping time was 300 min, and 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was added dropwise at the same time, the dropping time was 330 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 2 h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 15.0% and a viscosity (25°C) of 3800 mPa·s was prepared.

[0066] Example 3

[0067] A reaction bottle was added with 200 parts of water, 25 parts of MAA monomer, sodium bicarbonate was added to adjust the pH to neutral, 25 parts of 2-EHA monomer and 5 parts of HEA monomer were added, the monomers were fully mixed under stirring at a speed of 200 rpm, the temperature was raised to 70°C, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 300 min, then 6.5 parts of EA and 38.5 parts of MAA monomer were continuously added dropwise, the dropping time was 240 min, and 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was added dropwise at the same time, the dropping time was 210 min, after the dropping of the monomers was completed, the reaction temperature was kept at 70°C for 4 h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 18.2% and a viscosity (25°C) of 4600 mPa·s was prepared.

[0068] Example 4

[0069] Into a reaction bottle, 200 parts of water was added, 24 parts of AA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 16 parts of 2-EHA was added, 200 rpm stirring speed was used to stir and mix the monomers, the temperature was increased to 70°C, 30 parts of 3wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 300 min, after the dropping was completed, the reaction was kept for 120 min, then 54 parts of MAA monomer and 6 parts of EA monomer was added dropwise, the dropping time was 180 min, at the same time, 10 parts of 2wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 240 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 3 hours, after the keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 17.9% and a viscosity (25°C) of 4500 mPa·s was prepared.

[0070] Example 5

[0071] Into a reaction bottle, 200 parts of water was added, 24 parts of AA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 16 parts of 2-EHA was added, 200 rpm stirring speed was used to stir and mix the monomers, the temperature was increased to 70°C, 30 parts of 3wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 300 min, after the dropping was completed, the reaction was kept for 120 min, then 54 parts of MAA monomer and 6 parts of EA monomer was added dropwise, the dropping time was 180 min, at the same time, 10 parts of 2wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 240 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 3 hours, after the keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 17.9% and a viscosity (25°C) of 4500 mPa·s was prepared.

[0072] Example 6

[0073] Into a reaction bottle, 200 parts of water was added, 24 parts of AA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 16 parts of 2-EHA was added, 200 rpm stirring speed was used to stir and mix the monomers, the temperature was increased to 70°C, 30 parts of 3wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 300 min, after the dropping was completed, the reaction was kept for 120 min, then 54 parts of MAA monomer and 6 parts of EA monomer was added dropwise, the dropping time was 180 min, at the same time, 10 parts of 2wt% ammonium persulfate aqueous solution was added dropwise, the dropping time was 240 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 3 hours, after the keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 17.9% and a viscosity (25°C) of 4500 mPa·s was prepared.

[0074] Comparative Example 1

[0075] Into a reaction bottle, 200 parts of water was added, 54 parts of AA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 6 parts of EA monomer was added, 200 rpm stirring speed was used to stir to make the monomers fully mixed, the temperature was raised to 70℃, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropwise addition was carried out for 240 min, after the dropwise addition was completed, the temperature was kept for 1h; 24 parts of MAA monomer, 8 parts of EA monomer and 8 parts of HEA monomer were started to be added dropwise, the dropwise addition time was 240 min, at the same time, 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was started to be added dropwise, the dropwise addition time was 270 min, after the dropwise addition of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70℃ for 2h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and the pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 15.2% and a viscosity (25℃) of 3600mPa·s was prepared.

[0076] Comparative Example 2

[0077] Into a reaction bottle, 200 parts of water was added, 8 parts of MAA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 28 parts of EA monomer and 4 parts of HEA monomer were added, 200 rpm stirring speed was used to stir to make the monomers fully mixed, the temperature was raised to 70℃, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropwise addition was carried out for 240 min, after the dropwise addition was completed, the temperature was kept for 1h; 6 parts of EA monomer and 54 parts of AA monomer were started to be added dropwise, the dropwise addition time was 240 min, at the same time, 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was started to be added dropwise, the dropwise addition time was 270 min, after the dropwise addition of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70℃ for 2h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and the pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 15.5% and a viscosity (25℃) of 3800mPa·s was prepared.

[0078] Comparative Example 3

[0079] Into a reaction bottle, 200 parts of water was added, 14 parts of MAA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 49 parts of EA monomer and 7 parts of HEA monomer were added, 200 rpm stirring speed was used to stir to make the monomers fully mixed, the temperature was raised to 70℃, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropwise addition was carried out for 240 min, after the dropwise addition was completed, the temperature was kept for 1h; 3 parts of EA monomer and 27 parts of AA monomer were started to be added dropwise, the dropwise addition time was 240 min, at the same time, 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was started to be added dropwise, the dropwise addition time was 270 min, after the dropwise addition of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70℃ for 2h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content and the pH of the adhesive to neutral, thus an aqueous adhesive with a solid content of 14.9% and a viscosity (25℃) of 3600mPa·s was prepared.

[0080] Comparative Example 4

[0081] Into the reaction bottle, 200 parts of water was added, 26 parts of MAA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 4 parts of EA monomer and 10 parts of HEA monomer were added, 200 rpm stirring speed was used to stir to mix the monomers, the temperature was raised to 70°C, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 240 min, after the dropping was completed, the temperature was kept for 1 h; 6 parts of EA monomer and 54 parts of AA monomer were added dropwise, the dropping time was 240 min, at the same time, 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was added dropwise, the dropping time was 270 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 2 h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content of the adhesive and the pH to neutral, thus an aqueous adhesive with a solid content of 15.0% and a viscosity (25°C) of 3600 mPa·s was prepared.

[0082] Comparative Example 5

[0083] Into the reaction bottle, 200 parts of water was added, 16 parts of MAA monomer was added, sodium bicarbonate was added to adjust the pH to neutral, 20 parts of EA monomer and 4 parts of HEA monomer were added, 200 rpm stirring speed was used to stir to mix the monomers, the temperature was raised to 70°C, 30 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 240 min, after the dropping was completed, the temperature was kept for 1 h; 18 parts of EA monomer and 32 parts of AA monomer were added dropwise, the dropping time was 240 min, at the same time, 10 parts of ammonium persulfate aqueous solution with a concentration of 2wt% was added dropwise, the dropping time was 270 min, after the dropping of the ammonium persulfate aqueous solution was completed, the reaction temperature was kept at 70°C for 2 h, after the temperature keeping was completed, deionized water and sodium carbonate solution were added to adjust the solid content of the adhesive and the pH to neutral, thus an aqueous adhesive with a solid content of 15.0% and a viscosity (25°C) of 3600 mPa·s was prepared.

[0084] Comparative Example 6

[0085] Into the reaction bottle, 200 parts of water was added, 24 parts of MAA monomer and 54 parts of AA monomer were added, sodium bicarbonate was added to adjust the pH to neutral, 14 parts of EA monomer and 8 parts of HEA monomer were added, 200 rpm stirring speed was used to stir to mix the monomers, the temperature was raised to 70°C, 40 parts of ammonium persulfate aqueous solution with a concentration of 3wt% was added dropwise, the dropping time was 240 min, after the dropping was completed, the temperature was kept for 3 h, deionized water and sodium carbonate solution were added to adjust the solid content of the adhesive and the pH to neutral, thus an aqueous adhesive with a solid content of 15.1% and a viscosity (25°C) of 3800 mPa·s was prepared.

[0086] Test Method

[0087] Preparation of Silicon-carbon Negative Electrode Sheet

[0088] The water content was calculated based on the solid content of the negative electrode slurry before adjusting the viscosity. The water-based binder of Examples 1-6 and Comparative Examples 1-6 was mixed with 3.5 parts and 50% water, respectively, and dispersed at a speed of 300 rpm for 12 minutes. Then, 1 part of SP conductive carbon black was added, and stirred at a speed of 150 rpm for 10 minutes, followed by high-speed stirring at 800 rpm for 120 minutes. The speed was then reduced to 300 rpm, and 47.725 parts of negative electrode material (80% graphite + 20% silicon monoxide) was added and dispersed for 20 minutes. Then, 47.725 parts of negative electrode material and the remaining 50% water were added and dispersed for 30 minutes, followed by high-speed stirring at 800 rpm for 120 minutes. Then, 0.05 parts of SWCNTs were added, and dispersed at 1000 rpm for 30 minutes. After the dispersion was completed, the viscosity (25°C) was adjusted to be between 4000-6000 mPa·s, and the slurry was filtered with a 150 mesh filter screen to obtain the negative electrode slurry. The copper foil was placed on the coating machine, the doctor blade scale of the wet film maker was adjusted, the above-mentioned negative electrode slurry was uniformly poured, and the copper foil was sent into an environment of 100°C for air baking until dry. The negative electrode sheet with a size of 12.5 cm x 5 cm and a single side area density of 70-80 g / m 2 was obtained.

[0089] Slurry stability test: The Turbiscan LAB stability tester of Formulaction Company was used for the test.

[0090] Bulk density test: The middle and four corners of the negative electrode sheet were selected, and the thickness of the sheet was measured with a screw micrometer and recorded. After removing one maximum value and one minimum value, the average thickness of the sheet was calculated, and the bulk density = the average thickness of the sheet - the average thickness of the copper foil.

[0091] Sheet resistance test: A clean glass sheet with a size of 20 cm x 15 cm was selected, weighed m1, and the above-mentioned negative electrode slurry was uniformly poured on one end of the glass sheet. A 20 cm x 8 cm coating layer was uniformly coated with a wet film maker of 250 μm, and the glass sheet was sent into an environment of 100°C for air drying for 30 min. The multimeter was adjusted to an appropriate range, the dried glass sheet was taken out, two current collectors were placed on both ends of the glass sheet, and the resistance value of the coating layer was measured. Then, the glass sheet with coating layer was weighed m2, and the sheet resistance = coating resistance x (m2-m1).

[0092] The steps for making the coin cell were as follows:

[0093] The assembly sequence from bottom to top was negative electrode shell - spring - gasket - lithium sheet - electrolyte - separator - electrolyte - electrode sheet - positive electrode shell.

[0094] The composition of the electrolyte: 1M LiPF6 in EC:DMC:EMC = 1:1:1;

[0095] Separator: Celgard 2325;

[0096] Lithium sheet: Kurrary 15.0*1.0mm;

[0097] The first discharge capacity, the first coulombic efficiency, the AC impedance and the cycle test are as follows:

[0098] The capacity test current is 0.1C, and the charge-discharge is 0.005-1.5V; the impedance scan is from 100kHz to 0.1Hz.

[0099] The results are shown in Table 1.

[0100] Table 1

[0101]

[0102] From the data results of Table 1, it can be seen that the water-based binder of the application is used for the dispersion of silicon-carbon negative electrode active particles, the bulk density is high, and the coating resistance is low, which shows that the water-based binder of the application has good dispersion performance for the negative electrode active material, and can ensure the stability of the pole piece structure in the charge-discharge process, thereby bringing better cycle performance. Comparing Comparative Example 1 and Example 1, the hydrophilic segment is prepared first and then the hydrophobic segment is prepared in Comparative Example 1, and the performance of the water-based binder is worse than that of Example 1; comparing Comparative Example 2 and Example 1, the weight ratio of the first hydrophobic monomer in the first hydrophilic monomer and the first hydrophobic monomer composition is increased in Comparative Example 2, and the difference between the hydrophilic and hydrophobic of the front and rear polymers is too large, and it is difficult to achieve good dispersion for both the hydrophobic graphite particles and the hydrophilic silicon monoxide particles; comparing Comparative Example 3 and Example 1, the weight and ratio of the second hydrophilic monomer and the second hydrophobic monomer is lower than that of the first hydrophilic monomer and the first hydrophobic monomer, and the difference between the hydrophilic and hydrophobic of the front and rear polymers is too large, and it is difficult to achieve good dispersion for both the hydrophobic graphite particles and the hydrophilic silicon monoxide particles; comparing Comparative Example 4 and Example 1, the weight ratio of the second hydrophobic monomer in the second hydrophilic monomer and the second hydrophobic monomer composition is equal to the weight ratio of the first hydrophobic monomer in the first hydrophilic monomer and the first hydrophobic monomer composition, and the hydrophilic and hydrophobic of the front and rear polymers are too close, and it is difficult to achieve good dispersion for both the hydrophobic graphite particles and the hydrophilic silicon monoxide particles; comparing Comparative Example 5 and Example 1, the proportion of the first hydrophobic monomer in the first hydrophilic monomer and the first hydrophobic monomer composition and the proportion of the second hydrophobic monomer in the second hydrophilic monomer and the second hydrophobic monomer composition are increased respectively, and due to the overall increase of the hydrophobicity, it is difficult to achieve good dispersion for both the hydrophobic graphite particles and the hydrophilic silicon monoxide particles; comparing Comparative Example 6 and Example 1, all the hydrophilic monomers and the hydrophobic monomers are fed at one time, and the random copolymer obtained is difficult to achieve good dispersion for both the hydrophobic graphite particles and the hydrophilic silicon monoxide particles.

[0103] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing a silicon-carbon negative electrode aqueous binder, characterized by, The following steps are included: 200 parts of water are added to a reaction bottle, 25 parts of MAA monomer are added, sodium bicarbonate is added to adjust the pH to neutral, 25 parts of 2-EHA monomer and 5 parts of HEA monomer are added, the monomers are mixed well under stirring at a speed of 200 rpm, the temperature is raised to 70°C, 30 parts of an ammonium persulfate aqueous solution with a concentration of 3 wt% are added dropwise, the dropping is continued for 300 min, 6.5 parts of EA and 38.5 parts of MAA monomer are added dropwise, the dropping time is 240 min, at the same time, 10 parts of an ammonium persulfate aqueous solution with a concentration of 2 wt% are started to be added dropwise, the dropping time is 210 min, after the monomer dropping is completed, the reaction temperature is kept at 70°C for 4 hours, after the holding is completed, deionized water is added to adjust the solid content of the adhesive and a sodium carbonate solution is added to adjust the pH to neutral.

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