Lithium battery negative electrode material binder and preparation method thereof

Abstract

The application discloses a lithium battery negative electrode material binder, and preparation raw materials include, by weight: 0.5-10 parts of base emulsion, 1-5 parts of film forming additive, 2-3 parts of thickening agent, 10-20 parts of water, and 8-9 parts of filler. The base emulsion is prepared from butadiene compounds, styrene compounds and polyacrylonitrile, the prepared binder has excellent wetting effect on the negative electrode material, can realize good bonding effect with the negative electrode material, and propylene sulfite is used as the film forming additive, has good compatibility with the base emulsion, forms a uniform and stable system, and can significantly improve the elasticity of the binder, greatly improves the stability of the battery negative electrode, and prolongs the cycle life of the electrode; meanwhile, the base emulsion and the film forming additive propylene sulfite adopt a weight ratio of 1:(0.5-2), can balance the mechanical properties, adhesion properties and battery cycle performance of the binder, and realize improvement of comprehensive performance.

Description

Technical Field

[0001] This invention relates to a binder for lithium battery anode materials and its preparation method, and specifically to the field of binders. Background Technology

[0002] Battery binders are substances that firmly bond electrode materials, conductive additives, and other components together. They require wetting the electrode surface to ensure effective adhesion. Effective fixation significantly impacts electrode flexibility, battery energy density, and cycle life. Existing battery binders cannot simultaneously possess multiple properties, only meeting some requirements. Commonly used binders like polyvinylidene fluoride (PVDF) lack flexibility and easily absorb water and lose adhesion in humid environments. Carboxymethyl cellulose (CMC) binders have high hardness and brittleness, making them unsuitable for adapting to volume changes in electrode materials during charge and discharge. Therefore, developing a battery negative electrode material binder with good toughness and stable electrical cycle performance is crucial.

[0003] Chinese invention patent CN201910288198.0 discloses a lithium battery negative electrode binder, its preparation method, and its application. The binder prepared by polymerizing acrylic acid has the advantages of low impedance and resistance to breakage during processing. However, the binder has poor toughness when applied to the battery, and the volume change of the battery during charging and discharging affects the performance of the binder. Chinese invention patent CN202210826356.5 discloses the application of modified polyacrylonitrile, a binder, a negative electrode sheet, and a lithium-ion battery. The proposed modified polyacrylonitrile binder, under the synergistic effect of multiple beneficial functional groups, can form a strong interaction with the active material and current collector, and has high bonding strength and excellent mechanical properties. It can effectively alleviate the volume expansion of the negative electrode sheet during charging and discharging, and improve the battery's capacity retention and cycle stability. However, this binder is prone to cracking during coating, and its processing performance is unstable. Summary of the Invention

[0004] To improve the tensile properties of the binder for the negative electrode material of a battery, the first aspect of the present invention provides a binder for the negative electrode material of a lithium battery, wherein the raw materials for preparation include, by weight, 0.5-10 parts of matrix emulsion, 1-5 parts of film-forming additive, 2-3 parts of thickener, 10-20 parts of water, and 8-9 parts of filler.

[0005] In a preferred embodiment, the raw materials for preparing the matrix emulsion include 10-20 parts by weight of butadiene compounds, 10-20 parts by weight of styrene compounds, and 40-50 parts by weight of polyacrylonitrile.

[0006] In a preferred embodiment, the film-forming additive is selected from one or a combination of several of vinylene carbonate, ethylene carbonate, vinyl sulfite, propylene sulfite, diethyl carbonate, dimethyl sulfite, diethyl sulfite, and 1,2-trifluoroacetyl ethane.

[0007] In a preferred embodiment, the film-forming additive is propylene sulfite.

[0008] During the experiment, the applicant discovered that the matrix emulsion prepared by reacting butadiene, styrene, and polyacrylonitrile, used for bonding battery negative electrode materials, exhibited significant brittleness and poor tensile strength within the battery, failing to accommodate the substantial volume changes of the negative electrode material during charge / discharge cycles. Introducing propylene sulfite significantly improved the elasticity of the binder, greatly enhancing the stability of the battery negative electrode and extending its cycle life. The applicant speculates that this is because the introduced propylene sulfite forms a robust three-dimensional cross-linked network with the matrix emulsion, enhancing the mechanical strength of the battery negative electrode material and effectively buffering its volume changes.

[0009] In a preferred embodiment, the butadiene compound is selected from one or a combination of several of 1,3-butadiene, cyclobutadiene, ethyl 2,3-butadiene acid, butadiene diepoxide, methyl 1,3-butadiene-carboxylate, and phenyl-butadiene.

[0010] In a preferred embodiment, the butadiene compound is 1,3-butadiene.

[0011] In a preferred embodiment, the styrene compound is selected from one or a combination of several of styrene, methylstyrene, isoprene-styrene, and acrylonitrile-styrene.

[0012] In a preferred embodiment, the styrene compound is methylstyrene.

[0013] In a preferred embodiment, the weight ratio of the matrix emulsion to the film-forming additive is 1:(0.5-2).

[0014] In a preferred embodiment, the weight ratio of the matrix emulsion to the film-forming additive is 1:1.25.

[0015] The applicant further discovered that the combination of the matrix emulsion and propylene sulfite leads to a certain decrease in the adhesive's adhesion ability and a partial deterioration in battery cycle performance. By optimizing the addition ratio of the matrix emulsion and propylene sulfite, the mechanical properties, adhesion properties, and cycle performance of the binder can be balanced. This may be because the presence of propylene sulfite within the preferred weight range improves the lithium-ion transport performance of the electrode, which is beneficial to the continuity of the electrode conductive network. However, when it is not within the preferred weight ratio range, the bonding strength between the electrode and the negative electrode material particles is small. When the volume of the negative electrode material changes during charging and discharging, the electrode material may detach, resulting in a decrease in electrical cycle performance.

[0016] In a preferred embodiment, the thickener is selected from one or a combination of several of sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxyethyl cellulose, sodium alginate, xanthan gum, and guar gum.

[0017] In a preferred embodiment, the thickener is a combination of sodium hydroxyethyl cellulose and xanthan gum.

[0018] In a preferred embodiment, the weight ratio of sodium hydroxyethyl cellulose to xanthan gum is 1:(0.5-1).

[0019] In a preferred embodiment, the weight ratio of sodium hydroxyethyl cellulose to xanthan gum is 1:0.75.

[0020] The applicant discovered that using sodium hydroxyethyl cellulose and xanthan gum as a combined thickener can control the viscosity of the adhesive, increase the bond between the adhesive and the electrode material, and make the adhesive easy to apply and process at a suitable viscosity.

[0021] In a preferred embodiment, the filler is selected from one or a combination of several of carbon black, calcium carbonate, barium sulfate, glass fiber, and graphene.

[0022] In a preferred embodiment, the filler is carbon black with a particle size of 10-50 nm.

[0023] The applicant discovered that using carbon black with a particle size of 10-50 nm as a filler can increase the uniformity of the bonding system, reduce the resistance of the adhesive, increase the heat dissipation effect of the adhesive, and prevent the adhesive from deforming in high-temperature environments.

[0024] A second aspect of the present invention provides a method for preparing a binder for a lithium battery negative electrode material, comprising the following steps:

[0025] (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 20-40 min to obtain a matrix emulsion;

[0026] (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain premixed slurry;

[0027] (3) Mix the matrix emulsion obtained in step 1 with the premixed slurry evenly and sieve to obtain the negative electrode material binder.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The lithium battery negative electrode material binder of the present invention uses butadiene compounds, styrene compounds and polyacrylonitrile to prepare a matrix emulsion. The prepared binder has excellent wetting effect on the negative electrode material and can achieve good bonding effect with the negative electrode material.

[0030] (2) The lithium battery negative electrode material binder of the present invention uses propylene sulfite as a film-forming additive, which has good compatibility with the matrix emulsion, forms a uniform and stable system, and can significantly improve the elasticity of the binder, which can greatly improve the stability of the battery negative electrode and extend the cycle life of the electrode.

[0031] (3) The lithium battery negative electrode material binder of the present invention uses a weight ratio of 1:(0.5-2) between the matrix emulsion and the film-forming additive propylene sulfite, which can balance the mechanical properties, adhesion properties and battery cycle performance of the binder, thereby improving the overall performance.

[0032] (4) The lithium battery negative electrode material binder of the present invention uses sodium hydroxyethyl cellulose and xanthan gum as thickeners in synergy, which can control the binder to have a suitable viscosity, and has a good bonding effect on the electrode material while being easy to process.

[0033] (5) The lithium battery negative electrode material binder of the present invention uses water as the basic solvent and the binder prepared is a water-soluble glue, which is green and environmentally friendly. At the same time, the binder has good high temperature resistance and good heat dissipation performance when the battery is used and heats up, and will not cause the binder to soften or degenerate. Detailed Implementation

[0034] Example 1

[0035] A binder for lithium battery anode materials, the raw materials for which are prepared include, by weight: 5.5 parts of matrix emulsion, 2.5 parts of film-forming additive, 2.5 parts of thickener, 15 parts of water, and 8.5 parts of filler.

[0036] The raw materials for preparing the matrix emulsion include, by weight, 15 parts of butadiene compounds, 15 parts of styrene compounds, and 45 parts of polyacrylonitrile.

[0037] The film-forming additive is propylene sulfite. The butadiene compound is 1,3-butadiene. The styrene compound is methylstyrene. The polyacrylonitrile was purchased from Jinan Jinbang Environmental Protection Technology Co., Ltd.

[0038] The thickener is a combination of sodium hydroxyethyl cellulose and xanthan gum in a weight ratio of 1:0.75.

[0039] The filler is carbon black with a particle size of 10-50 nm, purchased from Jiaxing Nake New Materials Co., Ltd.

[0040] A method for preparing a binder for lithium battery anode materials includes the following steps:

[0041] (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 30 min to obtain a matrix emulsion;

[0042] (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain premixed slurry;

[0043] (3) Mix 5.5 parts by weight of the matrix emulsion obtained in step 1 with the premixed slurry evenly, and sieve to obtain the negative electrode material binder.

[0044] Example 2

[0045] A binder for lithium battery anode materials, the raw materials for which are prepared include, by weight: 1 part matrix emulsion, 1 part film-forming additive, 2 parts thickener, 10 parts water, and 8 parts filler.

[0046] The raw materials for preparing the matrix emulsion include, by weight, 10 parts of butadiene compounds, 10 parts of styrene compounds, and 40 parts of polyacrylonitrile.

[0047] The film-forming additive is vinyl sulfite. The butadiene compound is methyl 1,3-butadiene-carboxylate. The styrene compound is styrene. The polyacrylonitrile was purchased from Jinan Jinbang Environmental Protection Technology Co., Ltd.

[0048] The thickener is a combination of sodium hydroxyethyl cellulose and xanthan gum in a weight ratio of 1:0.5.

[0049] The filler is carbon black with a particle size of 10-50 nm, purchased from Jiaxing Nake New Materials Co., Ltd.

[0050] A method for preparing a binder for lithium battery anode materials includes the following steps:

[0051] (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 30 min to obtain a matrix emulsion;

[0052] (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain premixed slurry;

[0053] (3) Mix 1 part by weight of the matrix emulsion obtained in step 1 with the premixed slurry evenly, and sieve to obtain the negative electrode material binder.

[0054] Example 3

[0055] A binder for lithium battery anode materials, the raw materials for which are prepared include, by weight: 10 parts of matrix emulsion, 5 parts of film-forming additive, 3 parts of thickener, 20 parts of water, and 9 parts of filler.

[0056] The raw materials for preparing the matrix emulsion include, by weight, 20 parts of butadiene compounds, 20 parts of styrene compounds, and 50 parts of polyacrylonitrile.

[0057] The film-forming additive is vinylene carbonate. The butadiene compound is ethyl 2,3-butadiene acid. The styrene compound is styrene. The polyacrylonitrile was purchased from Jinan Jinbang Environmental Protection Technology Co., Ltd.

[0058] The thickener is a combination of sodium hydroxyethyl cellulose and xanthan gum in a weight ratio of 1:1.

[0059] The filler is carbon black with a particle size of 10-50 nm, purchased from Jiaxing Nake New Materials Co., Ltd.

[0060] A method for preparing a binder for lithium battery anode materials includes the following steps:

[0061] (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 40 min to obtain a matrix emulsion;

[0062] (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain premixed slurry;

[0063] (3) Mix 10 parts by weight of the matrix emulsion obtained in step 1 with the premixed slurry evenly, and sieve to obtain the negative electrode material binder.

[0064] Example 4

[0065] A binder for lithium battery anode material, the specific steps are the same as in Example 1, the difference being that the film-forming additive is ethylene oxide.

[0066] Example 5

[0067] A binder for lithium battery anode materials, the specific steps are the same as in Example 1, except that the weight ratio of the matrix emulsion to the film-forming additive is 1:0.1.

[0068] Example 6

[0069] A binder for lithium battery anode material, the specific steps are the same as in Example 1, the difference being that the thickener is a combination of sodium carboxymethyl cellulose and xanthan gum in a weight ratio of 1:2.

[0070] Performance testing

[0071] The binder obtained in Examples 1-6 of this application is used to prepare an electrode negative sheet, which includes graphite, conductive current collector (copper foil), and binder. The binder binds the graphite and conductive current collector into a whole.

[0072] 1. Peel strength: The prepared negative electrode sheet is cut into 15mm×20mm size. The negative electrode sheet is attached to the electrode surface on one side and to the steel plate on the other side with 3M pressure-sensitive adhesive (model VHB). Then, the steel plate and the electrode are fixed on the tensile fixture and the negative electrode sheet to be tested is stretched at a certain speed to perform a 180-degree peel test. When the conductive current collector is completely peeled off, the data detected is the peel force.

[0073] 2. Tensile modulus: The adhesives obtained in Examples 1-6 were poured into the mold, dried, and then subjected to a tensile test on an Instron 5965 universal testing machine. The uniaxial tensile test was performed at a constant rate of 2 mm / min. The test was stopped after the yield point was reached, and the data was recorded.

[0074] The test results are shown in Table 1.

[0075] Table 1

[0076] Example 1 30 0.29 Example 2 28 0.27 Example 3 29 0.28 Example 4 25 0.42 Example 5 23 0.45 Example 6 24 0.51

Claims

1. A binder for lithium battery anode materials, characterized in that, The raw materials for preparation include, by weight: 0.5-10 parts of base emulsion, 1-5 parts of film-forming additive, 2-3 parts of thickener, 10-20 parts of water, and 8-9 parts of filler; The raw materials for preparing the matrix emulsion include 10-20 parts by weight of butadiene compounds, 10-20 parts by weight of styrene compounds, and 40-50 parts by weight of polyacrylonitrile. The weight ratio of the matrix emulsion to the film-forming additive is 1:(0.5-2). The film-forming additive is propylene sulfite; the filler is carbon black. The thickener is a combination of sodium hydroxyethyl cellulose and xanthan gum, wherein the weight ratio of sodium hydroxyethyl cellulose to xanthan gum is 1:(0.5-1). The preparation method of the binder for the lithium battery negative electrode material includes the following steps: (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 20-40 min to obtain a matrix emulsion; (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain a premixed slurry; (3) Mix the matrix emulsion obtained in step (1) with the premixed slurry evenly and sieve to obtain the negative electrode material binder.

2. The lithium battery negative electrode material binder according to claim 1, characterized in that, The butadiene compounds are selected from one or a combination of several of 1,3-butadiene, 1,3-butadiene-methyl carboxylate, and phenyl-butadiene.

3. The lithium battery negative electrode material binder according to claim 1, characterized in that, The styrene compounds are selected from one or a combination of styrene and methylstyrene.

4. The lithium battery negative electrode material binder according to claim 1, characterized in that, The carbon black has a particle size of 10-50 nm.

5. A method for preparing a binder for a lithium battery negative electrode material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Mix butadiene compounds and styrene compounds, add them to polyacrylonitrile and react for 20-40 min to obtain a matrix emulsion; (2) Add the film-forming additive and thickener to water and mix evenly, then add filler to obtain a premixed slurry; (3) Mix the matrix emulsion obtained in step (1) with the premixed slurry evenly and sieve to obtain the negative electrode material binder.