High molecular weight negative electrode binder, method of making and negative electrode slurry

Abstract

The present application relates to the technical field of high polymer material, and especially relates to a high molecular weight negative electrode binder, a preparation method thereof and a negative electrode slurry. The high molecular weight negative electrode binder is mainly prepared by a reverse microemulsion method with monomers and a crosslinking agent in a mass ratio of 1:(0.01-0.06), wherein the monomers include hard monomers, soft monomers, functional monomers and acid monomers; the functional monomers include at least one of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and trimethylsilyl acrylate; and the crosslinking agent includes at least one of N,N'-methylene bisacrylamide, vinyl triethoxysilane and divinyl benzene. The present application provides a negative electrode binder prepared by a reverse microemulsion, which has a higher molecular weight and a narrower molecular weight distribution width, and has good dispersion performance, excellent adhesive performance and suitable liquid absorption rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular material, and in particular to a high molecular weight negative electrode binder, a preparation method thereof and a negative electrode slurry. BACKGROUND

[0002] With the rapid development of lithium ion battery technology, from consumer electronics to electric vehicle power batteries, the market has put forward higher and higher requirements for the energy density and cycle life of lithium ion batteries. Increasing the electrode thickness and improving the loading are effective ways to increase the energy density, and the binder plays an important role in the electrode sheet, which not only can enhance the adhesion of active material and current collector, but also can give the electrode sheet the necessary mechanical strength and flexibility. Although the binder is used in small amount in the battery, it has a significant influence on the performance of the battery, such as capacity and cycle life.

[0003] The binder of lithium ion battery is generally divided into two categories: water-based and oil-based. The typical representative of oil-based binder is polyvinylidene fluoride (PVDF), and the typical representative of water-based binder includes styrene butadiene (SBR) emulsion and sodium carboxymethyl cellulose (CMC). PVDF is a common positive electrode binder, and SBR and CMC are common negative electrode binders. Although these binders are widely used in lithium ion batteries, PVDF has the problem of insufficient adhesion, and CMC and SBR can affect the penetration of electrolyte at high loading. Especially in the application of new type of silicon-based negative electrode material, the requirement for the binder is more stringent. Therefore, the development of water-based binder with high adhesion and good electrochemical performance has become the key.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a high molecular weight negative electrode binder, a preparation method thereof and a negative electrode slurry. The binder of the present application has excellent adhesion, moderate liquid absorption rate and good electrochemical performance, and is suitable for the adhesion of various negative electrode materials.

[0006] In order to achieve the above purpose of the present application, the first aspect of the present application provides a high molecular weight negative electrode binder, which is mainly prepared by inverse microemulsion method from monomer and crosslinking agent in a mass ratio of 1: (0.01-0.06):

[0007] The monomer includes the following components by weight fraction: 25-40 parts of hard monomer, 15-30 parts of soft monomer, 5-15 parts of functional monomer and 15-20 parts of acid monomer;

[0008] The functional monomer includes at least one of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and trimethylsilyl acrylate;

[0009] The crosslinking agent includes at least one of N,N'-methylene bisacrylamide, vinyl triethoxysilane and divinyl benzene.

[0010] In the specific embodiment of the present application, the hard monomer includes at least one of methyl methacrylate, styrene, acrylonitrile and acrylamide. Further, the hard monomer includes methyl methacrylate and acrylamide. Further, the mass ratio of the methyl methacrylate and the acrylamide is 1: (0.05-0.2).

[0011] In the specific embodiment of the present application, the soft monomer includes at least one of butyl acrylate, ethyl acrylate, butyl methacrylate, ethyl methacrylate and 2-ethylhexyl acrylate.

[0012] In the specific embodiment of the present application, the acid monomer includes at least one of acrylic acid, methacrylic acid and itaconic acid.

[0013] In the specific embodiment of the present application, the functional monomer includes 2-hydroxyethyl acrylate and trimethylsilyl acrylate. Further, the mass ratio of the 2-hydroxyethyl acrylate and the trimethylsilyl acrylate is 1: (0.5-1.5).

[0014] In the specific embodiment of the present application, the proportion of the hydrophobic monomer in the soft monomer and the hard monomer is ≥90wt%.

[0015] In the specific embodiment of the present application, the weight average molecular weight of the negative electrode binder is 1 million-2 million.

[0016] In the specific embodiment of the present application, the number average molecular weight of the negative electrode binder is 0.8 million-1.5 million.

[0017] In the specific embodiment of the present application, the Z average molecular weight of the negative electrode binder is 1.3 million-2.2 million.

[0018] In the specific embodiment of the present application, the dispersity index PDI of the negative electrode binder is ≤1.50.

[0019] In the specific embodiment of the present application, the reverse microemulsion method further includes an emulsifier, an initiator, water and a dispersion medium. Further, the amount of the emulsifier is 2%-6% of the total mass of the monomers; the amount of the initiator is 0.1%-3% of the total mass of the monomers; the amount of the water is 2-4 times of the total mass of the monomers; and the amount of the dispersion medium is 1-2 times of the mass of the water.

[0020] In the specific embodiment of the present application, the dispersion medium includes cyclohexane.

[0021] The second aspect of the present application provides a preparation method of the high molecular weight negative electrode binder according to the first aspect of the present application, comprising the following steps:

[0022] (a) dissolving monomers and cross-linking agents in water to obtain an aqueous phase; mixing and stirring emulsifiers and dispersion media to obtain an oil phase;

[0023] (b) adding the aqueous phase into the oil phase, then adding an initiator, and increasing the temperature to a polymerization temperature to react, to obtain polymer microspheres.

[0024] In the specific embodiment of the present application, the preparation method further comprises: dissolving the polymer microspheres with an alkali solution, adjusting the pH to 6-8, and filtering to obtain the high molecular weight negative electrode binder.

[0025] The third aspect of the present application provides a negative electrode slurry comprising the high molecular weight negative electrode binder according to the first aspect of the present application.

[0026] In the specific embodiment of the present application, the negative electrode active material in the negative electrode slurry comprises at least one of a graphite negative electrode material and a silicon-carbon negative electrode material.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The present application provides a negative electrode binder prepared by reverse microemulsion, which has a higher molecular weight and a narrower molecular weight distribution width, and has good dispersion performance, excellent bonding performance, and suitable liquid absorption rate.

[0029] (2) The negative electrode sheet prepared by using the negative electrode binder of the present application shows excellent peel strength, low liquid absorption rate, and the battery prepared by using the negative electrode sheet has good long-cycle capacity retention rate, and significantly improves the cycle stability of the battery. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described clearly and completely in combination with the specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0031] The acrylic water-based adhesive has gradually become a hotspot in the research field in recent years due to its rich carboxyl functional groups and good chemical properties. The carboxyl functional groups endow the adhesive with excellent adhesion and adaptability, so that the adhesive can perform well in various applications. In the prior art, the micro-morphology of the adhesive obtained by polymerization is adjusted by regulating the ratio of hydrophobic monomers and hydrophilic monomers, but in the preparation of the existing acrylic water-based adhesive, the particle size of the prepared adhesive is difficult to be uniformly distributed, the molecular weight of the adhesive is difficult to be further improved, the molecular weight distribution width is wide, and the performance of the adhesive is limited to be further improved and large-scale production. The inventors of the present application find that the main reason for the above problems is that the hydrophobic monomer has an important influence on the adhesion of the adhesive and is an indispensable monomer in the acrylic water-based adhesive; however, in the aqueous system, the reaction difficulty of the hydrophobic monomer and the hydrophilic monomer is significantly different, and the hydrophobic monomer is difficult to polymerize, thereby causing the problems of poor uniformity of the adhesive, wide molecular weight distribution width, and low molecular weight.

[0032] Based on this, the present application adopts certain mixed monomers and crosslinking agents to prepare the adhesive by the reverse microemulsion polymerization method, which can significantly improve the molecular weight of the adhesive and reduce the molecular weight distribution width, while ensuring the dispersibility and adhesion performance of the adhesive.

[0033] The present application provides a high molecular weight negative electrode adhesive in the first aspect, which is mainly prepared by the reverse microemulsion method from monomers and crosslinking agents in a mass ratio of 1: (0.01-0.06):

[0034] The monomers include the following components in parts by weight: 25-40 parts of hard monomers, 15-30 parts of soft monomers, 5-15 parts of functional monomers, and 15-20 parts of acid monomers;

[0035] The functional monomers include at least one of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and trimethylsilyl acrylate;

[0036] The crosslinking agent includes at least one of N,N'-methylenebisacrylamide, vinyltriethoxysilane, and divinylbenzene.

[0037] The present application adopts certain monomers and cross-linking agents to prepare a negative electrode binder by reverse microemulsion, which has higher molecular weight and narrower molecular weight distribution width, so that the binder has excellent bonding performance. Among them, the hard monomer can provide certain mechanical strength and rigidity to the binder, so as to enhance the stability of the electrode sheet structure; the soft monomer can provide certain flexibility and ductility to the binder, so as to avoid problems such as cracking of the binder caused by expansion of the electrode sheet; the functional monomer has special chemical groups, which are used to improve the compatibility of the binder with the negative electrode active material and improve the dispersion performance of the binder; the acidic monomer can improve the ion exchange characteristics of the binder; the introduction of the cross-linking agent can further improve the mechanical strength of the binder. Through the appropriate compounding of each monomer and cross-linking agent, the mechanical strength, bonding performance and dispersion performance of the binder are improved.

[0038] As in different embodiments, the amount of each type of monomer can be as follows:

[0039] The amount of the hard monomer can be 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, or a range formed by any two of them;

[0040] The amount of the soft monomer can be 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, or a range formed by any two of them;

[0041] The amount of the functional monomer can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, or a range formed by any two of them;

[0042] The amount of the acidic monomer can be 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, or a range formed by any two of them.

[0043] In the raw material of the binder of the present application, a certain type of cross-linking agent is used and the amount of the cross-linking agent is controlled within a certain range, so that the linear chain formed by the polymerization of the monomers can form a system with a certain three-dimensional network structure under the construction of the appropriate amount of cross-linking agent, thereby improving the mechanical properties and bonding performance. At the same time, it avoids the problem of too high cross-linking degree caused by too high amount of cross-linking agent, which is not conducive to the uniform dispersibility of the binder. The present application controls the amount of cross-linking agent to meet the mass ratio of mixed monomers and cross-linking agent: 1:(0.01-0.06), for example, it can be 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, or a range formed by any two of them, in order to balance the mechanical properties, bonding performance and uniform dispersibility.

[0044] In the specific embodiments of the present application, the functional monomer includes 2-hydroxyethyl acrylate and trimethylsilyl acrylate. Further, the mass ratio of 2-hydroxyethyl acrylate and trimethylsilyl acrylate is 1:(0.5-1.5), for example, it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5 or a range consisting of any two of them, thereby helping to improve the uniform dispersibility of the binder and the compatibility and wettability with the negative active material and the current collector, and further improve the binding performance.

[0045] In the specific embodiments of the present application, the hard monomer includes at least one of methyl methacrylate, styrene, acrylonitrile and acrylamide.

[0046] In the specific embodiments of the present application, the hard monomer includes methyl methacrylate and acrylamide. Further, the mass ratio of methyl methacrylate and acrylamide is 1:(0.05-0.2), for example, it can be 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.18, 1:0.2 or a range consisting of any two of them.

[0047] In the specific embodiments of the present application, the soft monomer includes at least one of butyl acrylate, ethyl acrylate, butyl methacrylate, ethyl methacrylate and 2-ethylhexyl acrylate.

[0048] In the specific embodiments of the present application, the acid monomer includes at least one of acrylic acid, methacrylic acid and itaconic acid.

[0049] In the specific embodiments of the present application, the proportion of hydrophobic monomers in the soft monomer and the hard monomer is ≥90wt%, for example, it can be 90wt%, 92wt%, 95wt%, 98wt%, 100wt% or a range consisting of any two of them. Controlling the proportion of hydrophobic monomers in the above range helps to improve the liquid absorption rate in the binder electrolyte and improve the electrochemical performance of the battery. Among them, methyl methacrylate, styrene, butyl acrylate, ethyl acrylate, butyl methacrylate and methyl methacrylate belong to hydrophobic monomers.

[0050] In the specific embodiments of the present application, the weight average molecular weight of the negative electrode binder is 1 million-2 million, for example, it can be 1 million, 1.2 million, 1.5 million, 1.8 million, 2 million or a range consisting of any two of them.

[0051] In the specific embodiments of the present application, the number average molecular weight of the negative electrode binder is 800-1.5 million, for example, it can be 800, 1 million, 1.2 million, 1.4 million, 1.5 million or a range consisting of any two of them.

[0052] In the detailed description of the present application, the Z-average molecular weight of the negative electrode binder is 1.3-2.2 million, for example, it can be 1.3 million, 1.5 million, 1.8 million, 2 million, 2.2 million or a range consisting of any two of them.

[0053] In the detailed description of the present application, the dispersion index PDI of the negative electrode binder is ≤1.50, for example, it can be 1.50, 1.45, 1.40, 1.35, 1.30, 1.25, 1.20 or a range consisting of any two of them.

[0054] In the detailed description of the present application, in the reverse microemulsion method, it also includes emulsifier, initiator, water and dispersion medium. Further, the amount of emulsifier is 2%-6% of the total mass of monomers; the amount of initiator is 0.1%-3% of the total mass of monomers; the amount of water is 2-4 times the total mass of monomers; the amount of dispersion medium is 1-2 times the mass of water.

[0055] As in different embodiments, the amount of emulsifier can be 2%, 3%, 4%, 5%, 6% or a range consisting of any two of them of the total mass of monomers; the amount of initiator can be 0.1%, 0.5%, 1%, 2%, 3% or a range consisting of any two of them of the total mass of monomers; the amount of water can be 2 times, 2.5 times, 3 times, 3.5 times, 4 times or a range consisting of any two of them of the total mass of monomers; the amount of dispersion medium can be 1 times, 1.2 times, 1.5 times, 1.8 times, 2 times or a range consisting of any two of them of the mass of water.

[0056] In the detailed description of the present application, the emulsifier includes Span-80 and Tween-80. Further, in the emulsifier, the mass ratio of Span-80 and Tween-80 is (3-5):1, for example, 4:1.

[0057] In the detailed description of the present application, the initiator includes at least one of azo initiator, peroxide initiator and persulfide initiator. Further, the azo initiator includes but is not limited to at least one of azobisisobutyronitrile, the peroxide initiator includes but is not limited to at least one of benzoyl peroxide, tert-butyl hydroperoxide, and the persulfide initiator includes but is not limited to at least one of potassium persulfate, ammonium persulfate and sodium persulfate.

[0058] In the detailed description of the present application, the dispersion medium includes cyclohexane.

[0059] The second aspect of the present application provides a preparation method of the high molecular weight negative electrode binder of the first aspect of the present application, comprising the following steps:

[0060] (a) dissolving monomers and cross-linking agent in water to obtain an aqueous phase; mixing and stirring emulsifiers and dispersion medium to obtain an oil phase;

[0061] (b) adding the aqueous phase into the oil phase, then adding an initiator, and heating to a polymerization temperature to react, to obtain polymer microspheres.

[0062] In actual operation, the preparation of the aqueous phase can include: adding monomers into water at one time or in several times, stirring and dissolving, then adding cross-linking agent, stirring and dissolving, to obtain the aqueous phase. The preparation of the oil phase can include: stirring the emulsifiers and dispersion medium uniformly, heating to 60-75℃, and continuing to stir for 20-40min, to obtain a stable oil phase. In the preparation of the aqueous phase and the oil phase, nitrogen or the like can be introduced to remove dissolved oxygen in the system.

[0063] In the specific embodiment of the present application, the aqueous phase is added into the oil phase while continuously stirring, and after the addition is completed, the initiator is added after the emulsion is stable. Further, the dropping time of the initiator can be 20-40min. In actual operation, the initiator can be previously dissolved in part of the water or part of the dispersion medium before being added.

[0064] In the specific embodiment of the present application, the polymerization temperature is 60-75℃, and the reaction time is 4-5h. The reverse microemulsion method of the present application has a short polymerization reaction time, and significantly improves the production efficiency.

[0065] In the specific embodiment of the present application, the preparation method further includes: dissolving the polymer microspheres with an alkali solution, adjusting the pH to 6-8, and filtering to obtain a high-molecular-weight negative electrode binder.

[0066] In actual operation, before the polymer microspheres are dissolved with the alkali solution, the material after the polymerization reaction is subjected to centrifugal treatment to remove the upper oil phase, and the lower polymer microspheres are collected, which are sequentially washed with ethanol and ethyl acetate by centrifugation, dried, and then subjected to water washing treatment.

[0067] In the specific embodiment of the present application, the alkali solution includes at least one of a triethylamine aqueous solution, a NaHCO3 aqueous solution, a NaOH aqueous solution, a LiOH aqueous solution, and a KOH aqueous solution. The concentration of the alkali solution can be 0.1-20wt%, such as 0.1wt%, 5wt%, 10wt%, 15wt%, 20wt%, or a range formed by any two of them.

[0068] In the specific embodiment of the present application, the solid content of the high-molecular-weight negative electrode binder is 13%-20%.

[0069] The third aspect of the present application provides a negative electrode slurry, which includes the high-molecular-weight negative electrode binder of the first aspect of the present application.

[0070] In the detailed description of the present application, the negative active material in the negative electrode slurry includes at least one of a graphite negative material and a silicon-carbon negative material.

[0071] Example 1

[0072] The present example provides a preparation method of a high molecular weight negative electrode binder, comprising the following steps:

[0073] (1) Preparation of water phase: 94.5 g of water was added into a container, then 14.17 g of methyl methacrylate, 11 g of butyl acrylate, 6 g of 2-hydroxyethyl acrylate, 8 g of acrylic acid and 1 g of N,N'-methylenebisacrylamide were added, stirred uniformly and heated to 70°C, and nitrogen was introduced for 1 h to remove dissolved oxygen.

[0074] (2) Preparation of oil phase: 165 g of cyclohexane, 1.08 g of Span-80 and 0.27 g of Tween-80 were added into another container, stirred uniformly, heated to 70°C, and continued to stir for 30 min, and nitrogen was introduced at the same time to remove dissolved oxygen.

[0075] (3) Polymerization reaction: the water phase was slowly added into the oil phase through a dropping funnel, which was equipped with a condenser, a thermometer and a stirring paddle, and the temperature was controlled at 70°C, a uniform and stable emulsion was formed, then an initiator solution was added dropwise into the emulsion, and the dropping was completed in 30 min, and then the reaction was carried out at 70°C for 4 h, and then cooled to room temperature. The preparation of the initiator solution includes: 1 g of azobisisobutyronitrile was dissolved in 10 g of water.

[0076] (4) Preparation of binder: the material after the reaction in step (3) was centrifuged to remove the upper oil phase, and the lower polymer microspheres were collected, and then washed with appropriate amount of ethyl acetate and ethanol by centrifugation, and dried. The polymer microspheres were washed with a small amount of distilled water, filtered, heated to 50°C, and 29 g of 15wt% NaOH aqueous solution was added dropwise and stirred until completely dissolved, then cooled to room temperature, and then an appropriate amount of 1wt% NaOH was added to adjust the pH to 7.4, and then deionized water was added to dilute to a solid content of 15%, and then the residue was removed by filtration to obtain the binder.

[0077] Example 2

[0078] The present example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, and the difference is only that in step (1), the composition of the water phase is different; and in step (3), the preparation of the initiator solution is different.

[0079] In the water phase of step (1) of the present example, 15 g of styrene was used to replace 14.17 g of methyl methacrylate in the water phase of Example 1, and the rest was the same as Example 1.

[0080] The preparation of the initiator solution in step (3) of this example comprises: dissolving 1 g of benzoyl peroxide in 10 g of cyclohexane.

[0081] Example 3

[0082] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different; in step (3), the preparation of the initiator solution is different.

[0083] The preparation of the aqueous phase of this example comprises: adding 94.5 g of water into a container, then adding 12 g of methyl methacrylate, 10 g of 2-ethylhexyl acrylate, 5 g of 2-hydroxyethyl acrylate, 6 g of acrylic acid and 1 g of N,N'-methylenebisacrylamide, stirring uniformly and heating to 70°C, and passing nitrogen for 1 h to remove dissolved oxygen.

[0084] The preparation of the initiator solution in step (3) of this example comprises: dissolving 0.8 g of azobisisobutyronitrile in 10 g of cyclohexane.

[0085] Example 4

[0086] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different; in step (3), the preparation of the initiator solution is different.

[0087] The preparation of the aqueous phase of this example comprises: adding 94.5 g of water into a container, then adding 13 g of methyl methacrylate, 10 g of butyl acrylate, 5 g of 2-hydroxyethyl acrylate, 7 g of acrylic acid and 1 g of divinylbenzene, stirring uniformly and heating to 70°C, and passing nitrogen for 1 h to remove dissolved oxygen.

[0088] The preparation of the initiator solution in step (3) of this example comprises: dissolving 1.0 g of ammonium persulfate in 10 g of water.

[0089] Example 5

[0090] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different; in step (3), the preparation of the initiator solution is different.

[0091] The preparation of the aqueous phase of this example comprises: adding 94.5 g of water into a container, then adding 13 g of methyl methacrylate, 10 g of butyl acrylate, 5 g of 2-hydroxyethyl acrylate, 6 g of acrylic acid, 1.5 g of acrylamide and 1 g of divinylbenzene, stirring uniformly and heating to 70°C, and passing nitrogen for 1 h to remove dissolved oxygen.

[0092] The preparation of the initiator solution in step (3) of this example includes dissolving 1.0 g of azobisisobutyronitrile and 0.5 g of NaHSO3 in 15 g of water.

[0093] Example 6

[0094] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different.

[0095] The preparation of the aqueous phase of this example includes adding 94.5 g of water into a container, then adding 12 g of methyl methacrylate, 10 g of butyl acrylate, 5 g of 2-hydroxyethyl acrylate, 10 g of acrylic acid and 1 g of divinylbenzene, stirring uniformly and heating to 70°C, and passing nitrogen for 1 h to remove dissolved oxygen.

[0096] The preparation of the initiator solution in step (3) of this example includes dissolving 1.0 g of tert-butyl hydroperoxide in 10 g of water.

[0097] Example 7

[0098] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different.

[0099] In the aqueous phase of step (1) of this example, 13.5 g of methyl methacrylate and 0.67 g of acryloyl are used to replace 14.17 g of methyl methacrylate in the aqueous phase of Example 1, and the rest are the same as in Example 1.

[0100] Example 8

[0101] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different.

[0102] In the aqueous phase of step (1) of this example, 11.8 g of methyl methacrylate and 2.37 g of acryloyl are used to replace 14.17 g of methyl methacrylate in the aqueous phase of Example 1, and the rest are the same as in Example 1.

[0103] Example 9

[0104] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the only difference being that in step (1), the composition of the aqueous phase is different.

[0105] In the aqueous phase of step (1) of this example, 11 g of methyl methacrylate and 3.17 g of acryloyl are used to replace 14.17 g of methyl methacrylate in the aqueous phase of Example 1, and the rest are the same as in Example 1.

[0106] Example 10

[0107] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the difference being that in step (1), the composition of the aqueous phase is different.

[0108] In the aqueous phase of step (1) of this example, 4 g of 2-hydroxyethyl acrylate and 2 g of trimethylsilyl acrylate are used instead of 6 g of 2-hydroxyethyl acrylate in the aqueous phase of Example 1, and the rest is the same as in Example 1.

[0109] Example 11

[0110] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the difference being that in step (1), the composition of the aqueous phase is different.

[0111] In the aqueous phase of step (1) of this example, 2.4 g of 2-hydroxyethyl acrylate and 3.6 g of trimethylsilyl acrylate are used instead of 6 g of 2-hydroxyethyl acrylate in the aqueous phase of Example 1, and the rest is the same as in Example 1.

[0112] Example 12

[0113] This example refers to the preparation method of the high molecular weight negative electrode binder of Example 1, the difference being that in step (1), the composition of the aqueous phase is different.

[0114] In the aqueous phase of step (1) of this example, 6 g of trimethylsilyl acrylate is used instead of 6 g of 2-hydroxyethyl acrylate in the aqueous phase of Example 1, and the rest is the same as in Example 1.

[0115] Comparative Example 1

[0116] Comparative Example 1 refers to the preparation method of Example 1, the difference being that in step (1), the composition of the aqueous phase is different.

[0117] In the aqueous phase of step (1) of Comparative Example 1, N,N'-methylenebisacrylamide is not included, and the rest is the same as in Example 1.

[0118] Comparative Example 2

[0119] Comparative Example 2 refers to the preparation method of Example 1, the difference being that in step (1), the amount of N,N'-methylenebisacrylamide in the aqueous phase is different.

[0120] In the aqueous phase of step (1) of Comparative Example 2, the amount of N,N'-methylenebisacrylamide is 2.5 g, and the rest is the same as in Example 1.

[0121] Comparative Example 3

[0122] Comparative Example 3 refers to the preparation method of Example 1, except that in step (1), the composition of the aqueous phase is different.

[0123] The preparation of the aqueous phase of Comparative Example 3 includes: adding 94.5 g of water into a container, then adding 15.99 g of methyl methacrylate, 12.41 g of butyl acrylate, 6.77 g of 2-hydroxyethyl acrylate, 4 g of acrylic acid and 1 g of divinyl benzene, stirring uniformly and heating to 70°C, and purging with nitrogen for 1 h to remove dissolved oxygen.

[0124] Comparative Example 4

[0125] Comparative Example 4 provides a preparation method of a negative electrode binder, including the following steps:

[0126] (1) Add 94.5 g of water into a container, then add 14.17 g of methyl methacrylate, 11 g of butyl acrylate, 6 g of 2-hydroxyethyl acrylate, 8 g of acrylic acid and 1 g of N,N'-methylenebisacrylamide, and stir until a uniform solution is formed. Add 0.5 g of sodium dodecyl sulfate to enhance solubility. Stir to raise the temperature to 70°C, and purging with nitrogen for 1 g to remove dissolved oxygen.

[0127] (2) Dissolve 1.0 g of azobisisobutyronitrile in 10 g of water and heat to 40°C to obtain an initiator solution. Slowly add the initiator solution to the solution of step (1) through a dropping funnel, keep the system temperature at 70°C, and continue stirring, the dropping time is 30 min, after the dropping is completed, continue to react at 70°C for 8 h, and then cool to room temperature.

[0128] (3) Add 29 g of 15 wt% NaOH aqueous solution to the material obtained in step (2), stir uniformly, then add 1 wt% NaOH solution to adjust the pH to 7.4, dilute with deionized water to a solid content of 15%, filter to remove residues, and obtain the binder.

[0129] Comparative Example 5

[0130] Comparative Example 5 provides a preparation method of a negative electrode binder, including the following steps:

[0131] (1) Add 200 mL of deionized water as a continuous phase into a container, then add 10 g of polyvinyl alcohol as a suspension stabilizer, and stir until the polyvinyl alcohol is completely dissolved.

[0132] (2) Mix 14.17 g of methyl methacrylate, 12.15 g of butyl acrylate, 6.08 g of 2-hydroxyethyl acrylate and 8.1 g of acrylic acid to prepare a monomer mixture. Dissolve 1.0 g of azobisisobutyronitrile in about 10 mL of ethanol to obtain an initiator solution.

[0133] (3) Add the monomer mixture from step (2) dropwise to the material from step (1), maintaining a suspended state at a stirring speed of 400 rpm, so that the monomer liquid is dispersed into fine particles suspended in the aqueous phase, ensuring that the suspension forms a uniform particle dispersion system. Slowly add the initiator solution to the aforementioned reaction system, continue stirring, and maintain the uniformity of the suspended particles. Gradually increase the reaction temperature to 70°C, and carry out the polymerization reaction for 6 hours while maintaining the suspension and stirring state.

[0134] (4) The microparticles obtained in step (3) are washed with deionized water and ethanol to remove residual monomers and impurities, and then dried. The dried microparticles are added to a small amount of distilled water, heated to 50°C, and 29g of 15wt% NaOH aqueous solution is added dropwise until completely dissolved under stirring. Then the temperature is lowered to room temperature, and 1wt% NaOH is added dropwise to adjust the pH to 7.4. After diluting with deionized water to a solid content of 15%, the residue is removed by filtration to obtain the binder.

[0135] Comparative Example 6

[0136] Comparative Example 6 provides a method for preparing a negative electrode binder, comprising the following steps:

[0137] (1) Add 200 mL of deionized water to the container as a continuous phase, and then add 2.0 g of sodium dodecyl sulfate and stir until evenly distributed.

[0138] (2) A monomer mixture was prepared by mixing 14.17 g of methyl methacrylate, 12.15 g of butyl acrylate, 6.08 g of 2-hydroxyethyl acrylate and 8.1 g of acrylic acid. 0.5 g of ammonium persulfate was dissolved in 20 mL of deionized water to obtain an initiator solution.

[0139] (3) Pour the monomer mixture from step (2) into the material from step (1) and stir vigorously to disperse the monomers into fine emulsion particles under the action of the emulsifier, forming a stable emulsion system. Then raise the temperature to 70°C and slowly add the initiator solution dropwise into the emulsion system through a dropping funnel, maintaining a stirring speed of about 300 rpm to ensure the homogeneity of the reaction system. The initiator solution is added dropwise within 30 minutes, and then the reaction continues at 70°C for 6 hours.

[0140] (4) Gradually cool the material from step (3) to room temperature, add 29g of NaOH aqueous solution with a mass concentration of 15wt%, then add NaOH solution with a concentration of 1wt% to adjust the pH to 7.4, then add deionized water to dilute to a solid content of 13%, filter to remove residue, and obtain the binder.

[0141] Experimental Example 1

[0142] The molecular weight and PDI of the binders prepared in different examples and comparative examples were tested, and the test results are shown in Table 1.

[0143] Table 1 Test results of molecular weight and PDI of different binders

[0144]

[0145] From the above test results, the binder of the present application has higher molecular weight and narrower molecular weight distribution width, and overcomes the problems of low solid content of the binder prepared by solution polymerization and poor solubility of the binder prepared by suspension polymerization, and can meet the higher performance requirements of the binder for the lithium ion battery negative material.

[0146] Experimental Example 2

[0147] The peel strength test, liquid absorption rate test and battery performance test were performed on the binders of different examples and comparative examples, and the test methods are as follows, and the test results are shown in Table 2.

[0148] Peel strength test:

[0149] The sample after pressing was cut into a strip with a width of 10 mm, and a 90° peel tester was used for peel test, the test speed was 50 mm / min, and the maximum peel strength during the peel process was recorded. Each group of experiments was repeated three times, and the average value was taken as the final peel strength result.

[0150] The preparation of the sample includes:

[0151] (1) The silicon-carbon-based negative material, the binder, the conductive carbon black SP, and the carbon nanotube were mixed uniformly at a mass ratio of 95:3.5:1.0:0.5, and a proper amount of deionized water was added to adjust the solid content to 50%, and then vacuum defoaming treatment was performed.

[0152] (2) The slurry was coated on the surface of the copper foil by a coating machine, the thickness of the copper foil was 10 μm, and the coating thickness was 100 μm; it was placed in a blowing drying oven and dried at 80°C for 6h to remove the surface moisture, and then transferred to a 105°C vacuum oven for drying for 12h to ensure complete evaporation of the moisture; then the dried electrode piece was compacted by a roller press, and the thickness of the electrode piece after rolling was 60 μm.

[0153] In the CMC+SBR group, the preparation method was as described above, and the only difference was that the slurry composition was different; in the CMC+SBR group, the silicon-carbon-based negative material, CMC, SBR, conductive carbon black SP, and carbon nanotube were mixed uniformly at a mass ratio of 95:1.5:2.0:1.0:0.5, and a proper amount of deionized water was added to adjust the solid content to 50%, and then vacuum defoaming treatment was performed.

[0154] Liquid absorption rate test: Pour the prepared binder into a pre-prepared polytetrafluoroethylene mold, and dry it in a vacuum drying oven at 60°C for 12h to form a cured binder film. Take the dried binder film out of the mold, cut it into 1cm x 1cm pieces, and weigh the dry weight W of the sample 干 . Soak these samples in electrolyte (EC: DMC volume ratio 1:1, FEC addition ratio 5wt%, LiFP6 concentration 1M), and place them in a 25°C environment for 24h. After taking out the sample, use filter paper to gently absorb the residual electrolyte on the surface, and weigh the wet weight W of the sample 湿 . Calculate the liquid absorption rate according to the following formula:

[0155] Liquid absorption rate (%) = (W 湿 -W 干 ) / W 干 x 100

[0156] Each group of experiments is repeated three times, and the average value is taken as the final liquid absorption rate result.

[0157] In the CMC+SBR group, the mass ratio of CMC to SBR is 1.5:2.0.

[0158] Battery performance test:

[0159] Using high-nickel ternary material (such as NCM811) as the positive electrode material and silicon-carbon composite material as the negative electrode material, the preparation of the positive electrode sheet includes: mixing PVDF (3%) with NMP (the amount is adjusted according to the viscosity of the slurry) and stirring until a uniform glue solution is obtained; adding NCM811 (94%) and carbon black (3%) to the glue solution and stirring until it is uniformly dispersed. Then, the slurry is uniformly coated on an aluminum foil current collector, the areal density is controlled to be 15.6mg / cm 2 , and the electrode sheet is dried at 80-120°C, and finally calendared and cut to the required size.

[0160] The preparation of the negative electrode sheet refers to the preparation of the sample in the peel strength sample test. Then it is assembled into a soft pack battery for charge-discharge test (EC: DMC volume ratio 1:1 in electrolyte, FEC addition ratio 5wt%, LiFP6 concentration 1M).

[0161] Table 2 Performance test results

[0162]

[0163] From the above test results, it can be seen that the binder of the present application shows excellent peel strength, low liquid absorption rate, and the battery prepared by using the negative electrode sheet has good long cycle capacity retention rate, significantly improving the cycle stability of the battery.

[0164] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high molecular weight negative electrode binder, characterized in that, It is mainly prepared by reverse microemulsion method using monomers and crosslinking agents in a mass ratio of 1:(0.01~0.06): The monomer comprises the following components by weight: 25-40 parts of hard monomer, 15-30 parts of soft monomer, 5-15 parts of functional monomer and 15-20 parts of acidic monomer. The functional monomer includes at least one of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and trimethylsilane acrylate; The crosslinking agent includes at least one of N,N'-methylenebisacrylamide and divinylbenzene; The preparation method of the high molecular weight negative electrode binder includes the following steps: (a) The monomer and crosslinking agent are dissolved in water to obtain an aqueous phase; the emulsifier and dispersion medium are mixed and stirred to obtain an oil phase; (b) The aqueous phase is added dropwise to the oil phase, then an initiator is added, and the mixture is heated to the polymerization temperature to react and obtain polymer microspheres.

2. The high molecular weight negative electrode binder according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The hard monomer includes at least one of methyl methacrylate, styrene and acrylonitrile; (2) The soft monomer includes at least one of butyl acrylate, ethyl acrylate, butyl methacrylate, ethyl methacrylate and 2-ethylhexyl acrylate; (3) The acidic monomer includes at least one of acrylic acid, methacrylic acid and itaconic acid.

3. The high molecular weight negative electrode binder according to claim 1, characterized in that, The hard monomer includes methyl methacrylate and acrylamide; the mass ratio of methyl methacrylate to acrylamide is 1:(0.05-0.2).

4. The high molecular weight negative electrode binder according to claim 1, characterized in that, The functional monomers include 2-hydroxyethyl acrylate and trimethylsilane acrylate; the mass ratio of 2-hydroxyethyl acrylate to trimethylsilane acrylate is 1:(0.5~1.5).

5. The high molecular weight negative electrode binder according to claim 1, characterized in that, The proportion of hydrophobic monomers in the soft monomers and the hard monomers is ≥90wt%.

6. The high molecular weight negative electrode binder according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The weight-average molecular weight of the negative electrode binder is 1 million to 2 million; (2) The number average molecular weight of the negative electrode binder is 800,000 to 1,500,000; (3) The Z-average molecular weight of the negative electrode binder is 1.3 million to 2.2 million; (4) The dispersibility index (PDI) of the negative electrode binder is ≤1.

50.

7. The high molecular weight negative electrode binder according to claim 1, characterized in that, The reverse microemulsion method further includes an emulsifier, an initiator, water, and a dispersion medium; and has at least one of the following characteristics: (1) The amount of the emulsifier used is 2% to 6% of the total mass of the monomers; (2) The amount of the initiator is 0.1% to 3% of the total mass of the monomer; (3) The amount of water used is 2 to 4 times the total mass of the monomer; (4) The amount of the dispersion medium is 1 to 2 times the mass of the water; (5) The dispersion medium includes cyclohexane.

8. The method for preparing the high molecular weight negative electrode binder according to any one of claims 1 to 7, characterized in that, Includes the following steps: (a) The monomer and crosslinking agent are dissolved in water to obtain an aqueous phase; the emulsifier and dispersion medium are mixed and stirred to obtain an oil phase; (b) The aqueous phase is added dropwise to the oil phase, then an initiator is added, and the mixture is heated to the polymerization temperature to react and obtain polymer microspheres.

9. The method for preparing the high molecular weight negative electrode binder according to claim 8, characterized in that, Also includes: The polymer microspheres were dissolved in an alkaline solution, the pH was adjusted to 6-8, and the mixture was filtered to obtain the high molecular weight negative electrode binder.

10. Anode slurry, characterized in that, Includes the high molecular weight negative electrode binder according to any one of claims 1 to 7 or the negative electrode binder prepared by the preparation method according to any one of claims 8 to 9.

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