CN113991118A - Silicon-carbon negative electrode material adhesive and preparation method and application thereof - Google Patents
Silicon-carbon negative electrode material adhesive and preparation method and application thereof Download PDFInfo
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- CN113991118A CN113991118A CN202111277418.3A CN202111277418A CN113991118A CN 113991118 A CN113991118 A CN 113991118A CN 202111277418 A CN202111277418 A CN 202111277418A CN 113991118 A CN113991118 A CN 113991118A
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/386—Silicon or alloys based on silicon
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- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Abstract
The invention discloses a silicon-carbon cathode material adhesive and a preparation method and application thereof, the adhesive is an amphiphilic copolymer, organic unification of a hydrophobic polymer and a hydrophilic polymer is realized by copolymerizing polyvinyl acetate and polyacrylic acid and regulating and controlling the proportion of the polyvinyl acetate and the polyacrylic acid in the adhesive, and the prepared amphiphilic copolymer adhesive can be uniformly dispersed and dissolved in water, so that the adhesion effect of the polyvinyl acetate on carbon and the adhesion effect of the polyacrylic acid on silicon are respectively exerted; the adhesive has the characteristic of multiple functions, polyvinyl acetate is bonded with carbon through hydrophobic interaction, polyacrylic acid is bonded with silicon through hydrogen bond interaction, and simultaneously, the pH value of the polymer is adjusted by introducing lithium hydroxide monohydrate, so that the gas generation problem of carboxyl groups is reduced.
Description
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a silicon-carbon negative electrode material adhesive and a preparation method and application thereof.
Background
Lithium ion batteries have been widely used in electric vehicles, 3C products, and renewable energy and energy storage devices for smart grids. Currently commercialized cathode materials for lithium ion batteries are oxide cathode materials such as LiCoO2、LiMn2O4And LiFePO4Mainly, etc.; the negative electrode material is graphite and various carbon materials using graphite as a precursor. Although the carbon material has good reversible charge and discharge performance, the theoretical capacity is low (372mAh/g), and the high-rate charge and discharge performance is poor. And when the battery is overcharged, lithium dendrite is easily formed on the surface of the carbon material, short circuit is caused, and potential safety hazard is generated. Since the carbon material is difficult to meet the requirement of rapid development of current electronic information and energy technology, the development of a novel and reliable high-capacity lithium ion battery cathode material becomes a technical bottleneck of the development of a high-performance lithium ion battery.
Silicon can be used as a negative electrode material of a lithium ion battery, and is increasingly emphasized by the advantages of high specific capacity (4200mAh/g), abundant materials, low price and the like. However, the silicon negative electrode material generates huge volume change in the charging and discharging processes, so that the electrode capacity is quickly attenuated, the cycle performance is poor, and the commercialization is difficult. The silicon-carbon material combines the advantages of silicon and carbon, presents high specific capacity, ensures excellent mechanical property in the charging and discharging process, and has wide commercial prospect.
A strong binder is a prerequisite for the application of the silicon carbon anode material. In the lithium ion battery, the binder is a high molecular material which bonds an active material and a conductive additive to a current collector to form an electronic guide path and ensure the normal operation of the battery. In the process of charging and discharging, the binder effectively maintains the structural integrity of the electrode, and ensures that the electrode material can repeatedly insert and remove lithium, but in the aspect of the binder, the research on the binder of the silicon-carbon material is relatively few at present, and most of the widely reported pure silicon binders are mainly used for realizing the binding by establishing interaction with polar functional groups on the surface of pure silicon, and due to the introduction of carbon in the silicon-carbon material, the surface property of the silicon-carbon material is different from that of pure silicon, the silicon surface is hydrophilic, the carbon surface is hydrophobic, and the binder suitable for the pure silicon material is probably not suitable for the silicon-carbon material, so the binder suitable for the silicon-carbon composite material needs to be further developed on the basis of the pure silicon binder.
Meanwhile, aiming at the situation that in the commercialized electrode, the energy density is required to be improved, the using amount of the adhesive is less, and is about 5% or less, and the electrode piece is subjected to processing processes such as rolling and the like, the powder falling and cracking of the electrode piece are often caused in the process, and the integrity of the electrode piece is seriously influenced, so that the improvement of the flexibility and the adhesion of the electrode piece is significant, and the adhesive plays an increasingly important role in maintaining the stability of the electrode.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a silicon-carbon negative electrode material adhesive, a preparation method and application thereof so as to solve the problem of the adhesive suitable for the silicon-carbon negative electrode material in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the silicon-carbon negative electrode material binder is polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid, and the molecular structural formula of the binder is as follows:
wherein: x: y: z is 30, (10-20) and (50-60).
A preparation method of a silicon-carbon negative electrode material binder comprises the following steps:
step 2, dissolving acrylic acid, lithium hydroxide monohydrate and vinyl acetate in the solution A in sequence, adding an initiator after bubbling into the mixed solution to form a reaction system B, heating the reaction system B, and generating a copolymer C after reaction, wherein the copolymer C is polyvinyl acetate-co-polyacrylic acid;
and 3, adding a lithium hydroxide monohydrate aqueous solution into the copolymer C, and heating for reaction to obtain the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid.
The invention is further improved in that:
preferably, in the step 1, the heating temperature is 80-90 ℃, and the heating time is 20-40 min.
Preferably, in the step 2, the reaction temperature is 65-75 ℃, and the reaction time is 30-60 min.
Preferably, in step 1 and step 2, the mixing ratio of the polyvinyl alcohol, the emulsifier, the acrylic acid, the lithium hydroxide monohydrate, the vinyl acetate and the initiator is 5: (30-70): (0-70): (30-70): 1.
Preferably, in step 2, the concentration of copolymer C in the product system is 20 wt.%.
Preferably, in the step 3, the reaction temperature is 50-65 ℃ and the reaction time is 60-90 min.
Preferably, in step 1, the emulsifier is OP-10, and in step 2, the initiator is ammonium persulfate.
The application of the silicon-carbon negative electrode material adhesive in a lithium battery.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a silicon-carbon cathode material adhesive, which is an amphiphilic copolymer, wherein organic unification of a hydrophobic polymer and a hydrophilic polymer is realized by copolymerizing polyvinyl acetate and polyacrylic acid and regulating and controlling the proportion of the polyvinyl acetate and the polyacrylic acid in the adhesive, and the prepared amphiphilic copolymer adhesive can be uniformly dispersed and dissolved in water, so that the adhesion effect of the polyvinyl acetate on carbon and the adhesion effect of the polyacrylic acid on silicon are respectively exerted; the adhesive has the characteristic of multiple functions, polyvinyl acetate is bonded with carbon through hydrophobic interaction, polyacrylic acid is bonded with silicon through hydrogen bond interaction, and simultaneously, the pH value of the polymer is adjusted by introducing lithium hydroxide monohydrate, so that the gas generation problem of carboxyl groups is reduced. Meanwhile, the vinyl acetate monomer with low glass transition temperature is introduced, so that the glass transition temperature of the final integral polymer is reduced, the mechanical property of the polymer can be regulated and controlled, the flexibility of the polymer is enhanced, and the processability of the pole piece is improved. The adhesive realizes effective adhesion to the silicon-carbon cathode, and effectively improves the cycling stability of the silicon-carbon cathode. And meanwhile, deionized water is adopted as a solvent in the whole process of the adhesive synthesis, so that the adhesive is green and environment-friendly.
The invention also discloses a preparation method of the silicon-carbon cathode material adhesive, wherein in the preparation process, the adhesive is prepared by a three-step method, firstly, polyvinyl alcohol and an emulsifier are dissolved under the heating condition, then, polyvinyl acetate-co-polyacrylic acid copolymer is prepared, and finally, the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer is prepared by lithiation. Pure polyvinyl acetate polymer has good flexibility, can interact with carbon with hydrophobic surface, but is insoluble in water and cannot be used as an aqueous adhesive. In the invention, the organic unification of the hydrophobic polymer and the hydrophilic polymer is realized by copolymerizing the polyvinyl acetate and the polyacrylic acid and regulating and controlling the proportion of the two, and the prepared amphiphilic copolymer adhesive can be uniformly dispersed and dissolved in water, thereby respectively playing the adhesive action of the polyvinyl acetate on carbon and the adhesive action of the polyacrylic acid on silicon.
The invention also discloses application of the silicon-carbon cathode material adhesive, the adhesive shows good adhesive effect when being applied to the silicon-carbon cathode material, and the silicon-carbon cathode shows good electrochemical stability.
Drawings
FIG. 1 is an infrared spectrum of polyvinyl acetate-polyacrylic acid polymers prepared in examples 1 and 2 of the present invention and comparative example 1.
FIG. 2 shows the results of DSC tests of examples 1, 2 and 3.
FIG. 3 is a graph showing a comparison of peel strengths of adhesives in application examples 1, 2 and 3 and comparative example 1.
FIG. 4 is a graph showing the comparison of the cycle performance of the adhesives of application examples 1, 2 and 3 and comparative example 1.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention discloses a binder for a silicon-carbon negative electrode material of a lithium ion battery and a preparation method thereof, wherein the binder polymer is polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA) which is an amphiphilic copolymer. The adhesive is prepared by conventional free radical polymerization. This adhesive demonstrates the water-solubility, green, polyvinyl acetate can pass through hydrophobic interaction carbon adhesion, lithium polyacrylate can reduce the gas production problem of carboxyl in the battery, promote peel strength simultaneously, polyacrylic acid can glue the silicon through hydrogen bond effect, introduce vinyl acetate simultaneously and reduced the glass transition temperature of polymer, the pliability of polymer has been promoted, the common synergistic effect of three part, guarantee the structural integrity of silicon carbon negative pole in the circulation process, the pliability of polymer has been promoted, the processability of pole piece in the battery has been improved. The molecular structural formula of the compound is as follows:
wherein: x: y: z is 30, (10-20) and (50-60).
The preparation method of the device is a traditional free radical polymerization method and comprises the following steps:
Step 2, sequentially dissolving acrylic acid, lithium hydroxide monohydrate and vinyl acetate in the solution A to form a reaction system B, wherein the acrylic acid and the lithium hydroxide monohydrate can provide a salt environment for dissolving the vinyl acetate, the solubility of the lithium hydroxide monohydrate in the whole system is improved, oxygen in the reaction system B is removed by bubbling for 30min, and finally an initiator is added, wherein the time for the bubbling to remove oxygen is ensured to be 30min, and the initiator is reacted due to insufficient oxygen removal time; the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: (30-70): (0-70): (30-70) 1, wherein the reaction temperature is 65-75 ℃, and the reaction time is 30-60 min; after the reaction, a copolymer C of polyvinyl acetate-co-polyacrylic acid was produced, the concentration of copolymer C being 20% by weight.
Step 3, synthesizing polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), adding a lithium hydroxide monohydrate aqueous solution into the copolymer C, wherein the concentration is changed from 20% wt to 10% wt, so that the viscosity can meet the reaction requirement; the reaction temperature is 50-65 ℃, the reaction time is 60-90 min, and a reaction system D is formed; on a molar basis, copolymer C: the mixing ratio of the lithium hydroxide monohydrate is (70-90): (30-50), and reacting to obtain polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), thereby completing the preparation of the adhesive.
According to the invention, the (PVAc-co-PAALi-co-PAA) copolymer is prepared by traditional free radical polymerization, the reaction process is easy to control, the characteristic of multifunctional polymerization is realized, the polyvinyl acetate can be used for carbon adhesion through hydrophobic interaction, the lithium polyacrylate can reduce the gas generation problem of carboxyl in the battery, the peeling strength is improved, the polyacrylic acid can be used for silicon adhesion through hydrogen bond interaction, the vinyl acetate is introduced to reduce the glass transition temperature of the polymer, the flexibility of the polymer is improved, the three parts have synergistic interaction, the structural integrity of a silicon-carbon cathode in the circulation process is ensured, the flexibility of the polymer is improved, and the processability of a pole piece in the battery is improved.
Based on the functions, when the adhesive is applied to a silicon-carbon negative electrode, the adhesive can show better adhesive force to an electrode material, and can improve the cycle stability, the flexibility and the processability of a battery.
The lithium ion battery silicon-carbon negative electrode comprises a current collector and silicon-carbon negative electrode slurry attached to the current collector; the silicon-carbon negative electrode slurry comprises a silicon-carbon active material, a conductive additive and a binder, and the mass ratio of the silicon-carbon negative electrode active material to the conductive additive is as follows: conductive additive: (ii) a binder (70-95): (3.5-15): (1.5-15); the silicon-carbon negative electrode active material comprises the following components in percentage by mass: carbon is 2:3,1:4 and 1:32, and the conductive additive comprises Super P, acetylene black and Ketjen black; the adhesive is the polyvinyl acetate adhesive vinyl ester-lithium polyacrylate-polyacrylic acid.
The adhesive can be used for preparing a silicon-carbon cathode of a lithium ion battery and the lithium ion battery containing the silicon-carbon cathode, and comprises the following steps:
(1) the preparation method comprises the following steps of (70-95): (3.5-15): (1.5-15), and uniformly dispersing the silicon carbide anode slurry in deionized water by ball milling to obtain uniformly mixed silicon carbide anode slurry.
(2) And (3) uniformly coating the slurry in the step (1) on a copper foil with the thickness of 12 microns by using an automatic coating machine, wherein the coating thickness is 180 microns, and then placing the copper foil in a vacuum drying oven to dry and remove the solvent. And cutting the silicon-carbon negative electrode plate into a silicon-carbon negative electrode plate with the diameter of 12 mm after drying.
(3) And (3) transferring the electrode plates prepared in the step (2) into a glove box filled with argon gas, and assembling into a 2032 button half cell. A pure lithium sheet was used as the counter electrode and a Celgard2325 polypropylene-polyethylene-polypropylene (PP-PE-PP) membrane was used as the separator. The electrolyte solution used was a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) containing 1M lithium hexafluorophosphate (LiPF6), and 10% volume fraction fluoroethylene carbonate (FEC) was added.
(4) And (3) standing the button cell assembled in the step (3) for 8 hours, and then cycling at a rate of 0.1C for one week in a voltage range of 0.01-1.50V and then performing charge-discharge cycling at a rate of 0.3C. Wherein 1C is 500 mAh/g.
Example 1
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 85 deg.C for 30min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting for 30min at 75 ℃ to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), adding 0.8g of lithium hydroxide monohydrate to the copolymer C, adding water to change the concentration from 20% to 10% by weight, reacting at 60 ℃ for 60min to obtain the polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA), and completing preparation of the adhesive A1 to serve as the adhesive A1, wherein the mass ratio of three blocks is vinyl acetate: lithium acrylate: acrylic acid 30:52.5: 17.5.
The mixing ratio of the polyvinyl alcohol, the emulsifier, the acrylic acid, the total lithium hydroxide monohydrate, the vinyl acetate and the initiator is 5: 70: 52.5: 30: 1, preparing a silicon-carbon cathode of the lithium ion battery by using an adhesive A1 according to the method and assembling the silicon-carbon cathode into a lithium ion battery to test performance, wherein the silicon-carbon cathode material, the conductive additive and the adhesive are mixed according to a mass ratio of 80: 10: 10, and the conductive additive is Super P.
Example 2
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 50:37.5: 50:1, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 50:37.5:12.5, completing the preparation of adhesive a 2.
The adhesive A2 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Example 3
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 30: 22.5: 70: 1, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 70:22.5:7.5, completing the preparation of adhesive a 3.
The adhesive A3 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Comparative example 1
Dissolving 4g of acrylic monomer in water, deoxidizing the reaction system by using a bubbling deoxidization method, then filling nitrogen and adding an ammonium persulfate initiator, wherein the ammonium persulfate accounts for 0.6 wt% of the mass of the acrylic monomer, the concentration of the monomer is 20 wt%, reacting at 70 ℃ for 40min, and cooling to finish the preparation of the adhesive B1.
The adhesive B1 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
FIG. 1 is an infrared spectrum of the poly (vinyl acetate-co-lithium polyacrylate-co-polyacrylic acid) copolymer prepared in this example, from which it can be seen that in the spectrum of PAA, PAA is at 3300-2500cm-1，1720cm-1And 1132cm-1Shows characteristic peaks corresponding to O-H, C ═ O and C-O stretches, respectively, whereas PVAc-PAA compares with PAA at 1250cm-1And 1032cm-1New peaks appear corresponding to C- (C ═ O) -O and C-O-C stretching vibrations in PVAc, where PVAc-PAA ═ 5-5 compared to PVAc-PAA ═ 3-7, 1250cm with increasing vinyl acetate monomer-1And 1032cm-1The absorption peak is more intense, demonstrating the successful synthesis of two ratios of PVAc-PAA.
Fig. 2 shows the DSC test results for the adhesives a1, a2, A3 prepared in examples 1, 2, 3, the glass transition temperature of the adhesives of the invention decreasing gradually with increasing incorporation of vinyl acetate, demonstrating that the incorporation of vinyl acetate helps to lower the glass transition temperature of the polymer.
Fig. 3 shows the results of the peel performance tests of the binders a1, a2, A3 prepared in examples 1, 2, 3 and comparative example 1, showing a tendency of increasing and decreasing the peel strength of the binder of the present invention as the amount of vinyl acetate introduced increases, wherein the peel strength of the binder a2 is the highest (77N/m), higher than that of comparative example 1(50N/m), demonstrating that the binder has good adhesion to a silicon carbon anode.
Table 1 and fig. 4 show the charge-discharge cycle test results of lithium ion batteries manufactured by using silicon carbon negative electrodes according to examples of the present invention and comparative examples:
| numbering | First week efficiency (%) | Capacity maintenance Rate (%) after 200 weeks |
| Example 1 | 84.3 | 81.2 |
| Example 2 | 85.7 | 84.2 |
| Example 3 | 83.3 | 80.5 |
| Comparative example 1 | 81.8 | 68.2 |
From the results in table 1, the first-cycle coulombic efficiencies of the silicon-carbon negative electrode binders provided by the invention are all above 83%, and the capacity retention rates after 200-cycle cycles are all above 80%, but the first-cycle efficiencies of the comparative binders are about 82%, and the capacity retention rates after 200-cycle cycles are 68.2%. Therefore, the adhesive provided by the invention obviously improves the cycle stability of the silicon-carbon negative electrode material.
Example 4
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 50:0: 50:1, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 50:0:50, completing the preparation of adhesive a 4.
The adhesive A4 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Example 5
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 50:12.5: 50:1, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 50:12.5:37.5, completing the preparation of adhesive a 5.
The adhesive A5 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Example 6
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 50:25: 50:1, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 50:25:25, completing the preparation of adhesive a 6.
The adhesive A6 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Example 7
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 50:50: 50:1, but with different charge ratios, wherein the mass ratio of the three blocks is vinyl acetate: lithium acrylate: acrylic acid 50:50:0, completing the preparation of adhesive a 7.
The adhesive A7 is used for preparing the silicon-carbon cathode of the lithium ion battery according to the method and assembling the silicon-carbon cathode into the lithium ion battery for testing performance.
Table 2 shows the results of peel performance tests of adhesives prepared in inventive examples 2, 4, 5, 6, 7 and comparative example 1.
As seen from the results of table 1, the adhesive provided by the present invention was higher than the peel strength of the comparative example, both before and after rolling, and the optimum ratio was when the proportion of PAALi to total AA was 75%, i.e., PAALi: when PAA is 3:1, the peel strength is optimum. From this, it is understood that the adhesive of the present invention contributes not only to the improvement of the peel strength before rolling but also to the reduction of the peel strength against rolling. The adhesive provided by the invention is proved to remarkably improve the processability of the silicon-carbon negative electrode material.
Example 8
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 70: 70: 30: 1.
example 9
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 40: 30: 35: 1.
example 10
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 60: 40: 50: 1.
example 11
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 35: 35: 45: 1.
example 12
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 45: 45: 45: 1.
example 13
The preparation method and reaction conditions of the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid copolymer are the same as those of example 1, and the feeding ratio is that the mixing ratio of polyvinyl alcohol, emulsifier, acrylic acid, total lithium hydroxide monohydrate, vinyl acetate and initiator is 5: 55: 20: 30: 1.
example 14
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 85 deg.C for 25min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting at 65 ℃ for 60min to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, and water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 65 ℃ and the reaction time was 65min, and after the reaction, polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained.
Example 15
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 82 deg.C for 38min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting at 68 ℃ for 55min to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, and water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 62 ℃ and the reaction time was 70min, and after the reaction, polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained.
Example 16
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 85 deg.C for 35min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting at 70 ℃ for 50min to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 60 ℃ and the reaction time was 75min, and polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained after the reaction.
Example 17
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 87 deg.C for 30min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting at 72 ℃ for 40min to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, and water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 58 ℃ and the reaction time was 80min, and after the reaction, polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained.
Example 18
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 89 deg.C for 25min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting at 73 ℃ for 35min to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, and water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 55 ℃ and the reaction time was 85min, and after the reaction, polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained.
Example 19
(1) Dissolving 0.2g of polyvinyl alcohol and 0.2gOP-10 in water, heating at 90 deg.C for 20min to dissolve the above substances, and cooling to obtain solution A.
(2) Dissolving 2.8g of acrylic acid, 0.4g of lithium hydroxide monohydrate and 1.2g of vinyl acetate in the solution A in sequence to form a reaction system B, removing oxygen by bubbling for 30min, removing oxygen in the reaction system B, finally adding 0.04g of ammonium persulfate as an initiator, wherein the concentration of a monomer is 20 wt%, and reacting for 30min at 75 ℃ to obtain a copolymer solution C for later use.
(3) Synthesis of polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid (PVAc-co-PAALi-co-PAA), 0.8g of lithium hydroxide monohydrate was added to the copolymer C, and water was added to change the concentration from 20% by weight to 10% by weight, the reaction temperature was 50 ℃ and the reaction time was 90min, and after the reaction, polyvinyl acetate-lithium polyacrylate-polyacrylic acid (PVAc-co-PAALi-co-PAA) was obtained.
The invention provides a preparation method and application of a lithium ion battery silicon-carbon negative electrode material adhesive for improving the flexibility of a pole piece. The organic unification of the hydrophobic polymer and the hydrophilic polymer is realized by copolymerizing the polyvinyl acetate and the polyacrylic acid and regulating the proportion of the polyvinyl acetate and the polyacrylic acid, and the prepared amphiphilic copolymer adhesive can be uniformly dispersed and dissolved in water, so that the adhesion effect of the polyvinyl acetate on carbon and the adhesion effect of the polyacrylic acid on silicon are respectively exerted; the adhesive has the characteristic of multiple functions, polyvinyl acetate is bonded with carbon through hydrophobic interaction, polyacrylic acid is bonded with silicon through hydrogen bond interaction, and simultaneously, the pH value of the polymer is adjusted by introducing lithium hydroxide monohydrate, so that the gas generation problem of carboxyl groups is reduced. Meanwhile, the vinyl acetate monomer with low glass transition temperature is introduced, so that the glass transition temperature of the final integral polymer is reduced, the mechanical property of the polymer can be regulated and controlled, the flexibility of the polymer is enhanced, and the processability of the pole piece is improved. When applied in a silicon carbon negative electrode, the silicon carbon negative electrode shows good adhesive force and electrochemical stability. And meanwhile, deionized water is adopted as a solvent in the whole process of the adhesive synthesis, so that the adhesive is green and environment-friendly.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. The silicon-carbon negative electrode material adhesive is characterized by being polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid, and the molecular structural formula of the adhesive is as follows:
wherein: x: y: z is 30, (10-20) and (50-60).
2. The preparation method of the silicon-carbon negative electrode material adhesive is characterized by comprising the following steps of:
step 1, sequentially adding polyvinyl alcohol and an emulsifier into water, heating for dissolving, and cooling for later use to obtain a solution A;
step 2, dissolving acrylic acid, lithium hydroxide monohydrate and vinyl acetate in the solution A in sequence, adding an initiator after bubbling into the mixed solution to form a reaction system B, heating the reaction system B, and generating a copolymer C after reaction, wherein the copolymer C is polyvinyl acetate-co-polyacrylic acid;
and 3, adding a lithium hydroxide monohydrate aqueous solution into the copolymer C, and heating for reaction to obtain the polyvinyl acetate-co-lithium polyacrylate-co-polyacrylic acid.
3. The preparation method of the silicon-carbon negative electrode material binder as claimed in claim 2, wherein in the step 1, the heating temperature is 80-90 ℃ and the heating time is 20-40 min.
4. The method for preparing the silicon-carbon anode material binder as claimed in claim 2, wherein in the step 2, the reaction temperature is 65-75 ℃ and the reaction time is 30-60 min.
5. The method for preparing the silicon-carbon negative electrode material binder according to claim 2, wherein in the step 1 and the step 2, the mixing ratio of the polyvinyl alcohol, the emulsifier, the acrylic acid, the lithium hydroxide monohydrate, the vinyl acetate and the initiator is 5: (30-70): (0-70): (30-70): 1.
6. The method for preparing the silicon-carbon anode material binder as claimed in claim 2, wherein in the step 2, the concentration of the copolymer C in the product system is 20 wt.%.
7. The method for preparing the silicon-carbon anode material binder as claimed in claim 2, wherein in the step 3, the reaction temperature is 50-65 ℃ and the reaction time is 60-90 min.
8. The method for preparing the silicon-carbon anode material binder according to any one of claims 2 to 8, wherein in the step 1, the emulsifier is OP-10, and in the step 2, the initiator is ammonium persulfate.
9. Use of the silicon carbon negative electrode material binder of claim 1 in a lithium battery.
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