CN115172753A

CN115172753A - Novel lithium ion battery water-soluble binder and preparation method and application thereof

Info

Publication number: CN115172753A
Application number: CN202210966680.7A
Authority: CN
Inventors: 岳敏; 董仕晋
Original assignee: Wuxi Zero One Future New Material Technology Research Institute Co Ltd
Current assignee: Wuxi Zero One Future New Material Technology Research Institute Co Ltd
Priority date: 2022-08-12
Filing date: 2022-08-12
Publication date: 2022-10-11

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a novel lithium ion battery water-soluble binder and a preparation method and application thereof.

Description

Novel lithium ion battery water-soluble binder and preparation method and application thereof

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a novel lithium ion battery water-soluble binder and a preparation method and application thereof.

Background

With the gradual exhaustion of fossil energy and the rapid development of modern science and technology, the energy problem becomes a big theme of development in the world today, and lithium ion battery has the characteristics of high security performance, good cycle stability and convenient to use as a novel green energy that has a wide development prospect, has extensive use in fields such as portable electronic product, electric automobile, unmanned aerial vehicle, energy storage battery.

The problem of 'endurance and charging' in lithium ion battery application products has higher and higher requirements on the energy density of the lithium ion battery, wherein a negative electrode material of the lithium ion battery plays a key role in the lithium ion battery, the negative electrode material of the lithium ion battery continuously reacts with lithium ions in the charging and discharging processes, graphite is taken as the most mature carbon-based negative electrode active material at present, the specific capacity of the graphite is basically and fully exerted, and in the potential negative electrode material of the lithium ion battery, a silicon material can reach 4200mAh/g due to the theoretical specific capacity, so that the lithium ion battery has the advantages of being rich in storage capacity, controllable in cost and the like and is concerned. The silicon material is used as the negative electrode material, so that the energy density of the battery can be effectively improved, and the manufacturing cost of the battery can be reduced. However, the silicon material does not have a layered crystal structure, and stores lithium ions by forming a lithium silicon alloy, during which lithium ions are deintercalated, during which Li is deintercalated ₁₅ Si ₄ The conversion with amorphous silicon is carried out, and severe volume expansion and contraction exist, so that great volume change is generated.

At present, the components of the silicon anode material are bonded by a binder, and the mechanical strength of the silicon anode material is limited. Stress generated by the volume change of the silicon material in the circulation process can damage the structure of the silicon cathode, so that the contact between the active material and the conductive agent is separated, and the conductive network collapses, thereby influencing the circulation stability of the battery. Furthermore, the volume expansion of the silicon negative electrode also destroys the solid electrolyte layer between the electrolyte and the pole piece. In the process, a large amount of lithium ions and electrolyte are consumed, and irreversible capacity loss is caused, so that the service life of the lithium ion battery is influenced.

The effective adhesion of the binder to the electrode material is divided into two steps of "penetration" and "hardening". In the permeation process, the binder can infiltrate the surface of the electrode material and permeate into the electrode material through the microporous structure on the surface of the electrode material, so that the binder is fully contacted with the electrode material; in the hardening process, the adhesive is hardened through physical and chemical reactions, and the electrode particles and the adhesive are combined through mechanical linkage and interfacial interaction force to form joints, so that the adhesion is completed. The mechanical strength of the binder is affected by mechanical interlocking effects, interfacial interaction forces, the mechanical strength of the binder, and the mechanical strength of the electrode material. Therefore, the bonding strength can be improved by enhancing the mechanical interlocking effect and the interfacial interaction force. Methods for enhancing interfacial interactions are known: (1) enhancing hydrogen bonding interaction forces; (2) introducing electrostatic interaction force through ionic bonds; (3) the binder forms a covalent bond with the active material.

Chinese patent application CN112310399A discloses a lithium ion battery silicon negative electrode binder and an electrode preparation method and application thereof, the lithium ion battery silicon negative electrode binder is composed of polyvinylidene fluoride (PVDF) and polyvinyl alcohol, and on the basis of improving the whole adhesion of the electrode, irreversible lithium consumption of the electrode is effectively inhibited, but the effect of improving the adhesion of the electrode is general, and at present, the scientific community has determined that a large amount of volume changes of silicon in the repeated charge-discharge cycle process are the main source of insufficient cycle life of the silicon negative electrode. Weak van der waals interaction between the traditional polyvinylidene fluoride binder and silicon is difficult to bear huge volume expansion of silicon in the charging and discharging process, the electrode layer structure can be disintegrated, and meanwhile, the electrode layer can fall off from a conductive current collector, so that the circulation decline of the electrode capacity is caused. Therefore, PVDF binders, which currently dominate the industry, are not suitable for silicon anodes and the application requirements currently being developed.

Disclosure of Invention

In order to solve the technical problems, the invention provides a novel lithium ion battery water-soluble binder, a preparation method and application thereof, and the stripping force and electrochemical performance of the original material are improved.

In order to achieve the purpose, the invention discloses a preparation method of a novel lithium ion battery water-soluble binder, which comprises the following steps:

step one, stirring and mixing absolute ethyl alcohol, a carbon nano tube and gamma-methacryloxypropyltrimethoxysilane, heating to react, cooling and filtering after the reaction is finished, washing filter residues by using ethyl alcohol, and drying in vacuum for 6-10 hours at the temperature of 60-65 ℃ to obtain an alkenyl modified carbon nano tube;

step two, uniformly mixing deionized water and tannic acid, adding the alkenyl modified carbon nano tube, acrylonitrile, N-diethyl-2-acrylamide and acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH value to be 4-5, adding an initiator, heating to react, drying after the reaction is finished, wherein the drying temperature is 75-85 ℃, and the reaction time is 10-15 hours to obtain a multipolymer;

and step three, uniformly mixing N, N-dimethylformamide, a multipolymer and stannous octoate, adding isocyanate terminated polyurethane in a nitrogen atmosphere, reacting in a heating reflux process, cooling after the reaction is finished, precipitating by using petroleum ether, filtering, drying for 8-12h in vacuum at 50-60 ℃ to obtain a cross-linked copolymer, adding deionized water into the cross-linked copolymer, adjusting the pH value to 7-8 by using lithium hydroxide, stirring and mixing to obtain the novel water-soluble binder for the lithium ion battery.

Preferably, the mass ratio of the absolute ethyl alcohol to the carbon nano tube to the gamma-methacryloxypropyltrimethoxysilane in the first step is 3500-5500.

Preferably, the temperature of the reaction in the first step is 60-70 ℃, and the reaction time is 18-24h.

Preferably, in the second step, the mass ratio of the deionized water, the tannic acid, the alkenyl modified carbon nanotube, the acrylonitrile, the N, N-diethyl-2-acrylamide, the acrylic acid and the initiator is 1800-3500.

Preferably, the reaction temperature in the second step is 50-65 ℃, and the reaction time is 3-8h.

Preferably, the initiator in the second step comprises one of potassium peroxydisulfate, benzoyl peroxide and ammonium persulfate.

Preferably, the mass ratio of the N, N-dimethylformamide, the multipolymer, the stannous octoate and the isocyanate terminated polyurethane in the step three is 400-900.

Preferably, the reaction temperature in the third step is 75-90 ℃, and the reaction time is 5-12h.

Preferably, the mass ratio of the deionized water to the crosslinked copolymer in the third step is 100.

Preferably, the stirring temperature in the third step is 60-80 ℃, the stirring time is 2-5h, and the stirring speed is 1200-1800rpm.

Preferably, the novel lithium ion battery water-soluble binder is prepared by the method for preparing the novel lithium ion battery water-soluble binder.

The lithium ion battery is prepared by the novel lithium ion battery water-soluble binder prepared by the method.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the invention, gamma-methacryloxypropyltrimethoxysilane is used for modifying the carbon nanotube to obtain the alkenyl modified carbon nanotube, the acrylonitrile monomer, the N, N-diethyl-2-acrylamide monomer, the acrylic acid monomer and the tannin monomer are subjected to polymerization reaction under the action of an initiator to obtain a multi-component copolymer, hydroxyl in the multi-component copolymer reacts with an isocyanate group of isocyanate-terminated polyurethane in a nitrogen atmosphere to obtain a cross-linked copolymer, and the cross-linked copolymer is stirred and mixed with deionized water to obtain the novel lithium ion battery water-soluble binder under the action of lithium hydroxide.

2. The carbon nano tube has excellent electronic conductivity, can form a continuous conductive network in an electrode active material, can greatly improve the permeability of electrolyte in the electrode material, and is beneficial to the transmission of electrons; meanwhile, the carbon nano tube has excellent toughness and mechanical strength, can improve the peeling of materials caused by volume change in the charging and discharging processes, and can prolong the cycle life of the lithium ion battery to a great extent.

3. The acrylic monomer used in the invention contains a large amount of carboxyl functional groups, can generate hydrogen bonds with strong interaction with silicon electrodes, establishes strong interface interaction, enhances the adhesion of nano silicon particles to a current collector, promotes the generation of a thin and compact solid electrolyte interface film on the surface of the electrode, reduces the decomposition of electrolyte on the surface of the electrode, and thus obviously improves the electrochemical performance.

4. The tannin used in the invention has rich polar structures such as phenolic hydroxyl, carbonyl and the like, has strong hydrophilicity and reaction activity, the multipolymer prepared by polymerization reaction has strong electrostatic adsorption effect, and the prepared water-based binder has good water solubility and can improve the uniformity of electrode slurry when being applied to the preparation process of an electrode plate of a lithium ion battery, thereby enabling the electrode slurry to form a film on a current collector in a uniform and smooth way; the bonding strength among the electrode active substance, the conductive agent and the current collector can be enhanced, the conduction of electrons/ions in the charge-discharge process is facilitated, the electrochemical interface impedance of a pole piece is reduced, the electrochemical performance of the adhesive is obviously improved, the long-period cycle performance of a silicon electrode assembled by using the water-soluble adhesive under high current density and the charge-discharge performance under high-rate current are improved, the transmission of ions is facilitated, the bonding force when polyacrylic acid is used alone is improved, the overall stability of an electrode material and the wettability of the adhesive to the electrode material are improved, and the peeling strength of the electrode is greatly improved.

5. According to the invention, isocyanate terminated polyurethane is added to react with hydroxyl on tannic acid to obtain a crosslinked copolymer, the crosslinked copolymer has a three-dimensional network structure, molecules are entangled and chemically acted to obtain the crosslinked copolymer containing hydrophilicity and functionality, the crosslinked copolymer has good cohesiveness and supporting mechanical properties, and meanwhile, the heat resistance is better.

Drawings

FIG. 1 is a flow chart of the present invention for preparing a novel water-soluble binder for lithium ion batteries;

FIG. 2 is a diagram illustrating the capacity retention rate of a lithium ion battery according to the present invention.

In the figure: 1. a first sample; 2. sample two; 3. sample three; 4. comparing the sample I; 5. comparing a sample II; 6. comparative sample three.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without any creative work based on the embodiments of the present invention belong to the protection scope of the present invention.

Example one

A preparation method of a novel water-soluble binder for a lithium ion battery comprises the following steps:

(1) Adding 10g of carbon nano tube into 350g of absolute ethyl alcohol, stirring and mixing uniformly, adding 8.5g of gamma-methacryloxypropyltrimethoxysilane, heating to react at the temperature of 60 ℃ for 24h, cooling after the reaction is finished, filtering, washing filter residues with ethanol, and drying at the temperature of 60 ℃ for 10h in vacuum to obtain the alkenyl modified carbon nano tube;

(2) Adding 10g of tannic acid into 180g of deionized water, uniformly mixing, then adding 0.3g of alkenyl modified carbon nanotube, 0.8g of acrylonitrile, 1.5g of N, N-diethyl-2-acrylamide and 1.2g of acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH to 4, adding 0.3g of initiator potassium peroxodisulfate, heating for reaction at the reaction temperature of 50 ℃ for 8 hours, drying after the reaction is finished at the drying temperature of 75 ℃, and reacting for 15 hours to obtain a multipolymer;

(3) Uniformly mixing 40g of N, N-dimethylformamide, 10g of multipolymer and 0.05g of stannous octoate, adding 3.5g of isocyanate-terminated polyurethane in a nitrogen atmosphere, reacting in a heating reflux process at 75 ℃ for 12h, cooling after the reaction is finished, precipitating by using petroleum ether, filtering, and drying in vacuum at 50 ℃ for 12h to obtain a crosslinked copolymer; adding 2g of the cross-linked copolymer into 20g of deionized water, adjusting the pH value to 7 by using lithium hydroxide, stirring and mixing at the temperature of 60 ℃ for 5h at the stirring speed of 1200rpm to obtain the novel lithium ion battery water-soluble binder.

Example two

A preparation method of a novel lithium ion battery water-soluble binder comprises the following steps:

(1) Adding 10g of carbon nano tube into 450g of absolute ethyl alcohol, stirring and mixing uniformly, adding 12g of gamma-methacryloxypropyl trimethoxy silane, heating to react at 65 ℃ for 20 hours, cooling after the reaction is finished, filtering, washing filter residue with ethanol, and drying in vacuum at 60 ℃ for 8 hours to obtain the alkenyl modified carbon nano tube;

(2) Adding 10g of tannic acid into 280g of deionized water, uniformly mixing, adding 0.7g of alkenyl modified carbon nanotube, 2g of acrylonitrile, 3.5g of N, N-diethyl-2-acrylamide and 2.5g of acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH to 4.5, adding 0.6g of initiator potassium peroxodisulfate, heating to react at 65 ℃ for 5 hours, drying after the reaction is finished, wherein the drying temperature is 80 ℃, and the reaction time is 12 hours to obtain the multipolymer;

(3) Uniformly mixing 70g of N, N-dimethylformamide, 10g of multipolymer and 0.08g of stannous octoate, adding 6g of isocyanate-terminated polyurethane in a nitrogen atmosphere, reacting in a heating reflux process at 85 ℃ for 10 hours, cooling after the reaction is finished, precipitating by using petroleum ether, filtering, and drying in vacuum at 55 ℃ for 10 hours to obtain a crosslinked copolymer; adding 3.5g of cross-linked copolymer into 20g of deionized water, adjusting the pH value to 7.5 by using lithium hydroxide, stirring and mixing, wherein the stirring temperature is 75 ℃, the stirring time is 4h, and the stirring speed is 1500rpm, so as to obtain the novel lithium ion battery water-soluble binder.

EXAMPLE III

(1) Adding 10g of carbon nano tube into 550g of absolute ethyl alcohol, stirring and mixing uniformly, adding 15g of gamma-methacryloxypropyl trimethoxy silane, heating to react at the temperature of 70 ℃ for 18h, cooling after the reaction is finished, filtering, washing filter residue with ethanol, and drying in vacuum at the temperature of 65 ℃ for 6h to obtain the alkenyl modified carbon nano tube;

(2) Adding 10g of tannic acid into 350g of deionized water, uniformly mixing, adding 1g of alkenyl modified carbon nano tube, 3g of acrylonitrile, 5g of N, N-diethyl-2-acrylamide and 3.5g of acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH to 5, adding 0.8g of initiator potassium peroxodisulfate, heating to react at the temperature of 65 ℃ for 3 hours, drying after the reaction is finished at the temperature of 85 ℃, and reacting for 10 hours to obtain a multipolymer;

(3) Uniformly mixing 90g of N, N-dimethylformamide, 10g of multipolymer and 0.1g of stannous octoate, adding 7.5g of isocyanate-terminated polyurethane in a nitrogen atmosphere, reacting in a heating reflux process at 90 ℃ for 5 hours, cooling after the reaction is finished, precipitating by using petroleum ether, filtering, and drying in vacuum at 60 ℃ for 8 hours to obtain a crosslinked copolymer; and adding 5g of the crosslinked copolymer into 20g of deionized water, adjusting the pH value to 8 by using lithium hydroxide, stirring and mixing at the temperature of 80 ℃ for 2h at the stirring speed of 1800rpm to obtain the novel lithium ion battery water-soluble binder.

Example four

(2) Adding 10g of tannic acid into 280g of deionized water, uniformly mixing, adding 0.7g of alkenyl modified carbon nanotube, 2g of acrylonitrile, 3.5g of N, N-diethyl-2-acrylamide and 2.5g of acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH to 4.5, adding 0.6g of initiator benzoyl peroxide, heating to react at 65 ℃ for 5 hours, drying after the reaction is finished, wherein the drying temperature is 80 ℃, and the reaction time is 12 hours to obtain the multipolymer;

EXAMPLE five

(2) Adding 10g of tannic acid into 280g of deionized water, uniformly mixing, adding 0.7g of alkenyl modified carbon nanotube, 2g of acrylonitrile, 3.5g of N, N-diethyl-2-acrylamide and 2.5g of acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH to 4.5, adding 0.6g of initiator ammonium persulfate, heating to react at the reaction temperature of 65 ℃ for 5 hours, drying after the reaction is finished at the drying temperature of 80 ℃, and reacting for 12 hours to obtain a multipolymer;

Comparative example 1

(2) Adding 1g of alkenyl modified carbon nanotube, 3g of acrylonitrile, 5g of N, N-diethyl-2-acrylamide and 3.5g of acrylic acid into 350g of deionized water, stirring and mixing, adding potassium hydroxide to adjust the pH value to be 5, adding 0.8g of initiator potassium peroxodisulfate, heating to react at 65 ℃ for 3 hours, drying after the reaction is finished at 85 ℃, and reacting for 10 hours to obtain a multipolymer;

(3) Adding 5g of multipolymer into 20g of deionized water, adjusting the pH value to 8 by using lithium hydroxide, stirring and mixing, wherein the stirring temperature is 80 ℃, the stirring time is 2h, and the stirring speed is 1800rpm, so as to obtain the novel lithium ion battery water-soluble binder.

Comparative example No. two

(1) Adding 10g of carbon nano tube into 550g of absolute ethyl alcohol, stirring and mixing uniformly, adding 15g of gamma-methacryloxypropyltrimethoxysilane, heating to react at the temperature of 70 ℃ for 18h, cooling after the reaction is finished, filtering, washing filter residues with ethanol, and drying in vacuum at the temperature of 65 ℃ for 6h to obtain the alkenyl modified carbon nano tube;

(2) Adding 3g of acrylonitrile and 5g of N, N-diethyl-2-acrylamide into 350g of deionized water, stirring and mixing, adding potassium hydroxide to adjust the pH to 5, adding 0.8g of initiator potassium peroxodisulfate, heating to react at 65 ℃ for 3 hours, drying after the reaction is finished at 85 ℃ for 10 hours to obtain a multipolymer;

Comparative example No. three

(2) Adding 3g of acrylonitrile, 5g of N, N-diethyl-2-acrylamide and 3.5g of acrylic acid into 350g of deionized water, stirring and mixing, adding potassium hydroxide to adjust the pH to 5, adding 0.8g of initiator potassium peroxodisulfate, heating to react at 65 ℃ for 3 hours, drying after the reaction is finished at 85 ℃ for 10 hours to obtain a multipolymer;

(3) And (2) adding 5g of the multipolymer into 20g of deionized water, adjusting the pH value to 8 by using lithium hydroxide, stirring and mixing at the temperature of 80 ℃ for 2h at the stirring speed of 1800rpm to obtain the novel water-soluble binder for the lithium ion battery.

The carbon nanotubes used in the examples and comparative examples were obtained from Beijing Deke island gold technologies, inc. under the type of CNT204 carbon nanotubes; the adopted tannic acid is tannic acid consisting of resorcinol A ring; the isocyanate-terminated polyurethane is prepared from isophorone diisocyanate and 2, 2-dimethylolpropionic acid to obtain an isocyanate-terminated linear hydrophilic prepolymer.

The water-soluble adhesive for the lithium ion battery can be used for manufacturing an electrode plate of the lithium ion battery together with active materials of a positive electrode and a negative electrode, wherein the positive electrode can be lithium iron phosphate, lithium cobaltate, lithium manganate, nickel cobalt aluminum and nickel cobalt manganese, and the negative electrode can be artificial graphite, natural graphite, active carbon and silicon-based composite negative electrode materials.

Preparing a lithium ion battery cathode by using the lithium ion battery water-soluble adhesives prepared in the first embodiment, the second embodiment, the third embodiment, the first comparative embodiment, the second comparative embodiment and the third comparative embodiment; selecting SiO _x the/C composite material is used as a silicon-based negative electrode material, the mass fractions of the silicon-based negative electrode material and the lithium ion battery water-soluble binder are 95.5wt% and 4.5wt%, deionized water is added according to the proportion that the total solid content is 45%, and the deionized water is uniformly stirred and mixed to respectively prepare negative electrode plate slurry; and (3) passing the uniformly dispersed slurry through a 100-mesh screen, coating the slurry on a 10-micron thick copper foil serving as a current collector, drying the slurry at 120 ℃ for 5min, naturally cooling the dried slurry to room temperature, and rolling the dried slurry with a unit length load of 10 multiplied by 104N/m to obtain electrode pieces, so as to obtain the lithium ion battery negative electrodes corresponding to a sample I, a sample II, a sample III, a sample IV, a sample V and a sample VI.

(1) Measurement of peel strength: cutting the first, second, third, fourth, fifth and sixth samples into strips of 20cm × 2.5cm, respectively, bonding a steel plate having a thickness of 1mm to the collector side with a double-sided adhesive tape, bonding a transparent adhesive tape to the coated layer side, peeling the steel plate at 180 ° with a tensile tester at a speed of 100mm/min, and measuring the peel stress, the test results are shown in table 1;

TABLE 1 Peel Strength test Meter

Sample (I)	Sample one	Sample two	Sample three	Sample No. 4	Sample five	Sample six
							Peel force (N/m)	28.15	45.07	48.75	29.72	26.54	28.10

According to the test results in table 1, it can be seen that tannic acid is not added to the novel lithium ion battery water-soluble binders used in the lithium ion battery negative electrode materials in sample four, sample five and sample six, compared with sample two and sample three phases, the peel strength is obviously reduced, and the peel strength of the electrode plate of the composite material added with tannic acid is obviously increased;

(2) Determination of Tg: mettler Toledo-DSC/TGA thermogravimetric analyzer is adopted to carry out the analysis on the samples in the first embodiment, the second embodiment and the third embodiment,The novel lithium ion battery water-soluble binder in the first comparative example, the second comparative example and the third comparative example is subjected to thermogravimetric analysis, and the test conditions are as follows: at N ₂ Testing in the atmosphere, wherein the heating rate is 10 ℃/min, and the heating range is 20-800 ℃;

TABLE 2 Tg test Table

Sample (I)	Example one	Example two	EXAMPLE III	Example four	EXAMPLE five	Example six
							Tg（℃）	279.84	287.58	289.10	262.58	210.30	232.59

According to the test results in table 2, it can be seen that the thermal stability of the obtained novel lithium ion battery water-soluble binder is improved with the increase of the contents of the added carbon nanotubes, the added polymeric monomers and the added isocyanate-terminated polyurethane in the first, second and third examples, and the improvement of the cycling stability of the battery is facilitated;

(3) Testing the internal resistance of the battery: respectively using the samples I-VI as the negative electrode of the lithium ion battery, using the nickel cobalt lithium manganate NCM523 as the positive electrode of the lithium ion battery, and mixing 1M LiPF ₆ Dissolving the lithium ion battery in a mixed solution of ethylene carbonate EC, ethyl methyl carbonate EMC and diethyl carbonate DEC according to the mass ratio of 3;

TABLE 3 Battery internal resistance testing chart

Sample(s)	Sample No	Sample No. 2	Sample No. three	Comparative sample 1	Comparative sample No. 2	Comparative sample No. three
							Internal resistance of battery (m omega)	34.42	31.34	30.45	35.78	40.30	38.21

According to the test results in table 3, it can be seen that the sheet resistance of the first sample, the second sample and the third sample is significantly reduced compared with that of the first comparative sample, the second comparative sample and the third comparative sample, and the carbon nanotube has an excellent conductive effect, which indicates that the internal resistance of the electrode sheet can be effectively reduced by adding the carbon nanotube.

The lithium ion batteries of the first sample, the second sample, the third sample, the first comparative sample, the second comparative sample and the third comparative sample are subjected to charge and discharge cycles at 0.5C under the voltage range of 2.5-4.2V at 25 ℃, the charge and discharge cycles are tested by adopting a constant current method, and the obtained result of the capacity retention rate after 50 weeks of the charge and discharge cycles is shown in figure 2.

As can be seen from fig. 2, the cycle stability of the samples i, ii and iii was significantly improved by adding tannic acid and carbon nanotubes.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A preparation method of a novel water-soluble binder for a lithium ion battery is characterized by comprising the following steps:

stirring and mixing absolute ethyl alcohol, a carbon nano tube and gamma-methacryloxypropyl trimethoxy silane, heating to react, cooling, filtering, washing and drying after the reaction is finished to obtain an alkenyl modified carbon nano tube;

step two, uniformly mixing deionized water and tannic acid, adding the alkenyl modified carbon nano tube, acrylonitrile, N-diethyl-2-acrylamide and acrylic acid, stirring and mixing, adding potassium hydroxide to adjust the pH value to 4-5, adding an initiator, heating for reaction, and drying after the reaction is finished to obtain a multi-component copolymer;

and step three, uniformly mixing N, N-dimethylformamide, a multipolymer and stannous octoate, adding isocyanate terminated polyurethane in a nitrogen atmosphere, reacting in a heating reflux process, cooling, precipitating, filtering and drying after the reaction is finished to obtain a crosslinked copolymer, adding deionized water into the crosslinked copolymer, adjusting the pH value to 7-8 by using lithium hydroxide, and stirring and mixing to obtain the novel lithium ion battery water-soluble binder.

2. The method as claimed in claim 1, wherein in the second step, the mass ratio of the deionized water, the tannic acid, the alkenyl modified carbon nanotube, the acrylonitrile, the N, N-diethyl-2-acrylamide, the acrylic acid and the initiator is 1800-3500.

3. The method according to claim 1, wherein the reaction temperature in the second step is 50-65 ℃ and the reaction time is 3-8h.

4. The method of claim 1, wherein the initiator in the second step comprises one of potassium peroxodisulfate, benzoyl peroxide and ammonium persulfate.

5. The method according to claim 1, wherein the mass ratio of N, N-dimethylformamide, multipolymer, stannous octoate and isocyanate terminated polyurethane in the third step is 400-900.

6. The method according to claim 1, wherein the reaction temperature in the third step is 75-90 ℃ and the reaction time is 5-12h.

7. The method according to claim 1, wherein the mass ratio of the deionized water to the crosslinked copolymer in the third step is 100.

8. The method of claim 1, wherein the temperature of the stirring in the third step is 60-80 ℃, the stirring time is 2-5h, and the stirring speed is 1200-1800rpm.

9. The novel lithium ion battery water-soluble binder prepared by the method for preparing the novel lithium ion battery water-soluble binder according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that the preparation of said lithium ion battery comprises the novel lithium ion battery water-soluble binder of claim 9.