CN113066982B

CN113066982B - Modified water-based binder and preparation method and application thereof

Info

Publication number: CN113066982B
Application number: CN202110303241.3A
Authority: CN
Inventors: 雷雨; 魏迪锋; 李�昊; 徐永刚; 黄渭; 王进; 袁野
Original assignee: Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Current assignee: Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Priority date: 2021-03-22
Filing date: 2021-03-22
Publication date: 2022-06-14
Anticipated expiration: 2041-03-22
Also published as: CN113066982A

Abstract

The invention provides a modified water-based binder and a preparation method and application thereof, wherein the modified water-based binder comprises a main body, soft monomers and homopolymers; the main body comprises polyacrylate, the soft monomer comprises copolymerized 2-benzoyl-3-hydroxy-1-propylene and/or isooctyl acrylate, the homopolymer comprises polymethyl methacrylate, and the adhesive is high in overall adhesive strength, good in dispersity and stable in performance in electrolyte.

Description

Modified water-based binder and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium ion battery materials, and relates to a modified water-based binder, and a preparation method and application thereof.

Background

The demand of the current new energy market rises rapidly, especially in the lithium ion power battery field, more and more electric vehicles carrying lithium ion batteries come into the market, and the number limit policy of some cities also gives very large development space for lithium battery new energy vehicles. In recent two years, the electric automobile carrying the ternary anode material lithium ion battery has frequent fire accidents, the lithium iron phosphate (LFP) anode material lithium ion battery has great advantages in safety due to the stable structure and the high temperature decomposition resistance of the lithium iron phosphate material, in addition, the lithium iron phosphate material does not contain heavy metal, the cost is also low, and the high safety and cost reduction are key directions for the continuous development of the power/energy storage battery market technology.

The positive and negative electrode materials and the conductive agent are bonded on the metal current collector (aluminum foil and copper foil) by the binder, so that the battery pole piece is prepared, the contact between the active material and the conductive agent and between the active material and the current collector can be enhanced, the pole piece structure is stabilized, the pole piece structure is a connection medium of the electrode active material, and the characteristics of the pole piece structure directly influence the cycle performance, the rapid charge-discharge capacity, the high temperature, the DCR and other performances of the lithium battery.

At present, oil-soluble polyvinylidene fluoride (PVDF) is mostly adopted as a binder for preparing an LFP battery positive pole piece, N-methyl pyrrolidone (NMP) is added as a solvent for matching use, and other conductive agents and active substances are added to dissolve the PVDF; after sol dissolving, dispersing active substance powder in glue solution, coating the glue solution on the surface of an aluminum foil, drying and rolling to prepare the positive pole piece. However, the PVDF + NMP oil-soluble system has higher cost for manufacturing the electrode, and in addition, NMP has toxicity, NMP gas is easy to volatilize into the air when manufacturing the battery pole piece, the harm to the human body is great after the NMP gas is inhaled, and certain cost needs to be invested for recycling when the electrode is used.

In addition, the water-based binder mainly comprises Styrene Butadiene Rubber (SBR) emulsion, hydroxymethyl cellulose (CMC), polytetrafluoroethylene emulsion (PTFE), Polyacrylate (PAA) and the like, and the water-soluble binder for LFP developed on the market generally has the problems of uneven dispersion of solid matters, poor consistency of water-based anode slurry, low stability, easy occurrence of sedimentation and the like, and the performance of the lithium battery is seriously influenced.

CN110311139A discloses a lithium ion battery aqueous binder anode slurry, which comprises an anode active substance, a conductive agent, an aqueous binder, a dispersing agent and deionized water, wherein raw materials are selected according to the components in the anode slurry, the anode active substance, the conductive agent and a solid dispersing agent are respectively ground into powder, the anode active substance is lithium iron phosphate, the dispersing agent is used for replacing N-methylpyrrolidone (NMP) as a dispersing solvent, and the dispersing agent is one or more of mixture, so that the dispersing efficiency is improved, and the problems of environmental pollution, human body injury, high energy consumption and high cost caused by the N-methylpyrrolidone (NMP) as the dispersing solvent are solved; in the large-scale production of the lithium iron phosphate lithium ion battery, the environmental protection, no pollution and small harm to human bodies are kept, and the indexes of low energy consumption, low cost and low internal resistance of the battery are improved. However, the aqueous binder has low binding strength, so that the use amount of the binder in the lithium battery is high, the content of active substances in the pole piece is reduced, and the performance of the pole piece is influenced.

CN105261759A discloses a water-based binder for lithium batteries, a preparation method thereof and a lithium battery pole piece. The preparation method of the aqueous binder for the lithium battery comprises the following steps: dissolving polyvinyl alcohol in water, stirring the mixture in a first stirring state until the polyvinyl alcohol is completely dissolved to form a polyvinyl alcohol solution, adding an initiator into the polyvinyl alcohol solution, uniformly mixing the initiator and the polyvinyl alcohol solution to obtain a mixed solution, dropwise adding a monomer mixture at least comprising styrene and a first monomer into the mixed solution, and continuously stirring the mixture in a second stirring state until the monomer mixture is completely dropwise added to fully react to obtain the aqueous binder for the lithium battery. However, the aqueous binder has poor stability in electrolyte and high liquid absorption rate.

The aqueous binder according to the above-mentioned scheme has problems of low adhesive strength, poor stability, high liquid absorption rate, and the like, and therefore, it is necessary to develop an aqueous binder having high adhesive strength, good stability, or low liquid absorption rate.

Disclosure of Invention

The invention aims to provide a modified aqueous binder, which comprises a main body, a soft monomer and a homopolymer; the main body comprises polyacrylate, the soft monomer comprises copolymerized 2-benzoyl-3-hydroxy-1-propylene and/or isooctyl acrylate, the homopolymer comprises polymethyl methacrylate, and the adhesive is high in overall adhesive strength, good in dispersity and stable in performance in electrolyte.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a modified aqueous binder comprising a body, a soft monomer and a homopolymer; wherein the body comprises Polyacrylate (PAA), the soft monomer comprises copolymerized 2-benzoyl-3-hydroxy-1-propene (BAA) and/or isooctyl acrylate (EHA), and the homopolymer comprises Polymethylmethacrylate (PMMA).

The modified aqueous binder disclosed by the invention comprises a main body, a soft monomer and a homopolymer, has high overall bonding strength, can reduce the using amount of the binder in a lithium battery, improves the active substance ratio, and has the characteristics of good dispersibility, strong bonding force, good flexibility, strong alkali resistance, good stability, strong hydrophilicity and small ohmic resistance.

Preferably, the mass ratio of the main body, the soft monomer and the homopolymer is (50-60): 15-25): 15-30), for example: 50:20:30, 55:15:25, 60:18:25 or 55:20:25, etc.

Preferably, the modified aqueous binder further comprises a dispersion medium.

Preferably, the dispersion medium comprises deionized water.

In a second aspect, the present invention provides a method for preparing a modified aqueous binder as defined in the first aspect, said method comprising the steps of:

(1) adding 2-benzoyl-3-hydroxyl-1-propylene monomer and/or isooctyl acrylate monomer into polyacrylate, and heating to obtain a multi-component polymer;

(2) and (2) dissolving the multipolymer obtained in the step (1), adding a homopolymer and a dispersion medium, and mixing to obtain the modified water-based binder.

The preparation method combines chemical copolymerization and physical blending, and the prepared modified water-based binder has good consistency and high stability.

Preferably, the mass parts of the 2-benzoyl-3-hydroxy-1-propylene monomer and/or the isooctyl acrylate monomer in the step (1) are 15-25 parts, for example: 15 parts, 17 parts, 19 parts, 20 parts, 22 parts or 25 parts and the like.

Preferably, the mass part of the polyacrylate in the step (1) is 50-60 parts, for example: 50 parts, 52 parts, 54 parts, 56 parts, 58 parts or 60 parts and the like.

Preferably, the temperature of the heat treatment in the step (1) is 60-80 ℃, for example: 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃ and the like.

Preferably, the time of the heat treatment in the step (1) is 5-10 h, for example: 5h, 6h, 7h, 8h, 9h or 10h and the like.

Preferably, the dispersion medium of step (2) comprises deionized water.

Preferably, the mass part of the homopolymer in the step (2) is 15-30 parts, for example: 15 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts or 30 parts and the like.

Preferably, the mixing device in the step (2) comprises a V-shaped high-speed mixer.

Preferably, the mixing speed of the step (2) is 3000-6000 r/min, such as: 3000 r/min, 3500 r/min, 4000r/min, 4500r/min, 5000 r/min, 5500 r/min or 6000r/min and the like.

Preferably, the mixing time in the step (2) is 2-6 h, for example: 2h, 3h, 4h, 5h or 6h and the like.

As a preferable scheme of the invention, the preparation method comprises the following steps:

(1) adding 15-25 parts of 2-benzoyl-3-hydroxy-1-propylene monomer and/or isooctyl acrylate monomer into 50-60 parts of polyacrylate, and reacting at 60-80 ℃ for 5-10 h to obtain a precursor;

(2) and (2) dissolving the precursor obtained in the step (1), adding 15-30 parts of homopolymer and dispersion medium, and mixing at 3000-6000 r/min for 2-6 h to obtain the modified water-based binder.

In a third aspect, the present invention provides a positive electrode plate, which comprises the modified aqueous binder according to the first aspect.

In a fourth aspect, the invention further provides a lithium ion battery, where the lithium ion battery includes the positive electrode sheet described in the third aspect.

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

(1) the modified water-based binder disclosed by the invention has higher strength, can reduce the using amount of the binder in a lithium battery and improve the active substance ratio, and has the characteristics of good dispersibility, strong binding power, good flexibility, strong alkali resistance, good stability, strong hydrophilicity and small ohmic resistance.

(2) The modified aqueous binder disclosed by the invention has the advantages of stable performance in electrolyte, no expansion, no looseness, no powder falling, low liquid absorption rate, easiness in electrode coating, capability of participating in preparation of a positive pole piece and a battery with long cycle life and low cost, and environmental friendliness and safety.

(3) The positive pole piece using the modified aqueous binder has the elastic modulus of more than 35.7Mpa, the fracture elongation of more than 65.8 percent and the liquid absorption rate of electrolyte of less than 77.6 percent.

Drawings

FIG. 1 is a schematic representation of a modified aqueous binder according to example 1 of the present invention.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The embodiment provides a modified water-based binder, which is prepared by the following method:

(1) mixing 0.8 part of RAFT reagent, 0.3 part of initiator and 50 parts of acrylic monomer, and reacting at 65 ℃ for 12h to obtain 50 parts of polyacrylate;

(2) adding 25 parts of isooctyl p-acrylate monomer into the polyacrylate obtained in the step (1), and reacting for 8 hours at 70 ℃ to obtain acrylic acid and acrylate binary copolymer;

(3) and (3) dissolving the acrylic acid and acrylate binary copolymer obtained in the step (2), adding 25 parts of methyl methacrylate monomer and 431 parts of deionized water, and mixing at 4500r/min for 4 hours to obtain the modified water-based binder.

The schematic diagram of the modified aqueous binder is shown in fig. 1.

Example 2

(1) mixing 0.6 part of RAFT reagent, 0.5 part of initiator and 50 parts of acrylic monomer, and reacting at 70 ℃ for 15h to obtain 50 parts of polyacrylate;

(2) adding 20 parts of isooctyl acrylate monomer into the polyacrylate obtained in the step (1), and reacting for 9 hours at 75 ℃ to obtain acrylic acid and acrylate binary copolymer;

(3) and (3) dissolving the acrylic acid and acrylate binary copolymer obtained in the step (2), adding 30 parts of methyl methacrylate monomer and 573 parts of deionized water, and mixing for 5 hours at 4000r/min to obtain the modified waterborne adhesive.

Example 3

This example differs from example 1 only in that 55 parts of the acrylic acid monomer in step (1) and 20 parts of the isooctyl p-acrylate monomer in step (2) are used, and the other conditions and parameters are exactly the same as those in example 1.

Example 4

This example is different from example 1 only in that 60 parts of acrylic acid monomer in step (1) and 15 parts of isooctyl p-acrylate monomer in step (2) are used, and the other conditions and parameters are exactly the same as those in example 1.

Example 5

This example differs from example 1 only in that 60 parts of the acrylic acid monomer in step (1), 20 parts of the isooctyl acrylate monomer in step (2), and 20 parts of the methyl methacrylate monomer in step (3), and the other conditions and parameters are exactly the same as those in example 1.

Example 6

This example is different from example 1 only in that the isooctyl p-acrylate monomer described in step (2) is replaced with 2-benzoyl-3-hydroxy-1-propene monomer, and other conditions and parameters are exactly the same as those of example 1.

Comparative example 1

The comparative example differs from example 1 only in that no isooctyl p-acrylate monomer was added and the other conditions and parameters were exactly the same as in example 1.

Comparative example 2

This comparative example differs from example 1 only in that no methyl methacrylate monomer was added and the other conditions and parameters were exactly the same as in example 1.

And (3) performance testing:

and (3) tensile test:

(1) the adhesives obtained in examples 1-6 and comparative examples 1-2 were made into adhesive films, and the preparation process was as follows: directly pouring 1.2 g of polymer into a polytetrafluoroethylene surface dish with the diameter of 10 cm, covering a layer of filter paper, pressing the filter paper, putting the filter paper into a fume hood for convection air drying at normal temperature, and then putting the filter paper into a vacuum oven for vacuum drying for 12 hours at 60 ℃ to finish sample preparation;

(2) referring to GB 16421-: the measuring range of the force sensor is 50N, the stretching speed is 1 mm/min, and each sample test is repeated for 5 times;

(3) and (4) obtaining displacement load curve data and a sample after fracture through a tensile test, and calculating to obtain the elastic modulus and the elongation at break of the sample.

Adhesive film swelling test:

(1) and (3) testing conditions are as follows: 4g of the binder obtained in examples 1 to 6 and comparative examples 1 to 2 (actual sample size latex mass = binder mass/latex solid content, latex solid content generally 40%) was taken and poured into a teflon watch glass;

(2) covering a surface dish with filter paper, transferring the surface dish to a 40 ℃ blast oven, drying for 24h, cutting a dried adhesive film into a square with the size of 20mm x 20mm, placing the square in an aluminum plastic film bag filled with an electrolyte solvent (the composition and the proportion of the electrolyte solvent are EC: EMC: DEC =3:5:2 (v/v)), treating the square at 60 ℃ for 24h/7 days (after 24h measurement, placing the square in an aluminum plastic film for soaking for 6 days, taking out the square for testing), taking out the adhesive film, slightly wiping the electrolyte on the surface by filtration (taking care not to squeeze the electrolyte forcibly) and weighing the adhesive film;

(3) and collecting weighing data, and calculating to obtain a liquid absorption rate result of the electrolyte.

The test results are shown in table 1:

TABLE 1

As can be seen from Table 1, the positive electrode plate using the modified aqueous binder of the present invention has an elastic modulus of 35.7MPa or more, a breaking elongation of 65.8% or more, and a liquid absorption rate of 77.6% or less, as obtained in examples 1 to 6.

From the comparison of example 1 with examples 3-5, the ratio of the host, soft monomer and homopolymer affects the elastic modulus, elongation at break and liquid absorption of the resulting adhesive, and by adjusting the ratio of the host, soft monomer and homopolymer, adhesives with desired properties can be made as desired.

By comparing example 1 with example 6, a more effective binder can be obtained using 2-benzoyl-3-hydroxy-1-propene monomer as soft monomer.

As can be seen from comparison between example 1 and comparative example 1, the modified aqueous binder of comparative example 1 has an increased elastic modulus, a decreased elongation at break, and a decreased liquid absorption rate of the electrolyte.

As can be seen from comparison between example 1 and comparative example 2, the modified aqueous binder of comparative example 2 has a reduced elastic modulus, an increased elongation at break, and an increased liquid absorption rate of the electrolyte solution.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. A modified aqueous binder, characterized in that it comprises a body, a soft monomer, a homopolymer and a dispersion medium;

wherein the body comprises polyacrylate, the soft monomer comprises 2-benzoyl-3-hydroxy-1-propylene and/or isooctyl acrylate, the homopolymer comprises polymethyl methacrylate, and the modified aqueous binder is prepared by the following method:

2. The modified aqueous binder of claim 1 wherein the mass ratio of the main body, soft monomer and homopolymer is (50-60): (15-25): (15-30).

3. The modified aqueous binder of claim 1 wherein the dispersing medium comprises deionized water.

4. A method for preparing the modified aqueous binder as claimed in any one of claims 1 to 3, characterized in that it comprises the following steps:

5. The method according to claim 4, wherein the 2-benzoyl-3-hydroxy-1-propene monomer and/or the isooctyl acrylate monomer in the step (1) are present in an amount of 15 to 25 parts by mass.

6. The method according to claim 4, wherein the polyacrylate in the step (1) is 50 to 60 parts by mass.

7. The method according to claim 4, wherein the temperature of the heat treatment in the step (1) is 60 to 80 ℃.

8. The method according to claim 4, wherein the heating treatment in step (1) is carried out for 5 to 10 hours.

9. The method of claim 4, wherein the dispersion medium of step (2) comprises deionized water.

10. The method according to claim 4, wherein the homopolymer in the step (2) is 15 to 30 parts by mass.

11. The method of claim 4, wherein the mixing device of step (2) comprises a V-type high-speed mixer.

12. The method according to claim 4, wherein the mixing speed in the step (2) is 3000 to 6000 r/min.

13. The method according to claim 4, wherein the mixing in step (2) is carried out for 2 to 6 hours.

14. The method of claim 4, comprising the steps of:

(2) dissolving the precursor obtained in the step (1), adding 15-30 parts of homopolymer and dispersion medium, mixing, and mixing at 3000-6000 r/min for 2-6 h to obtain the modified water-based binder.

15. A positive electrode sheet, characterized in that it comprises the modified aqueous binder according to any one of claims 1 to 3.

16. A lithium ion battery comprising the positive electrode sheet of claim 15.