Conductive base coating for lithium ion battery and preparation method thereof

Abstract

The present invention provides a conductive base coating for lithium ion batteries and a preparation method thereof. The conductive properties of the coating can be improved by using graphene-modified polyurethane. The inventors have found that when polyurethane is used as a binder and a methacrylate silane coupling agent is used as a compatibilizer, the carboxyl groups in the methacrylate silane form stable chemical bonds with the amino and hydroxyl functional groups of the polyurethane, and the methacrylate silane can form a cross-linked structure with graphite fibers and graphene inorganic fillers in the polyurethane, thereby further enhancing the bonding properties of the coating and improving the compatibility with the inorganic filler.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery conductive coatings, and in particular to a conductive base coating for lithium ion batteries and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are secondary batteries (rechargeable batteries) that typically use lithium alloy metal oxides as the positive electrode material, graphite as the negative electrode material, and a non-aqueous electrolyte. They rely primarily on the movement of lithium ions between the positive and negative electrodes to charge and discharge. Due to this excellent charge and discharge capability, they are widely used in consumer electronics, electric vehicles and transportation, energy storage, aerospace, medical equipment, military and security fields, and other fields.

[0003] Existing lithium-ion batteries have been significantly improved in terms of energy density, memory effect, self-discharge, cycle life, etc., but the conductive coating on the surface of the battery still has certain defects in terms of performance. For example, the invention patent with application number CN201410238020.2 provides a conductive coating and its preparation method, a lithium-ion battery positive electrode sheet and its preparation method, and a lithium-ion battery. By preparing a resin containing a carboxylic acid group as a binder, the resin containing a carboxylic acid group can produce a carboxylic acid ammonium salt structure with strong hydrophilicity during the neutralization process with ammonia water, thereby improving the adhesion and reducing the internal resistance of the electrode. However, there is a serious and unresolved problem of the dispersion of the conductive agent in this technology. For example, the patent with application number 202310988730.6 discloses a conductive coating for lithium-ion batteries and its preparation method. In this technical solution, four acrylic resins are compounded to improve the adhesion of the coating, but the compatibility problem between the inorganic filler and the binder in the conductive base coating of the lithium-ion battery is still not solved. Lithium-ion batteries are prone to thermal runaway under extreme conditions such as high temperature, overcharging, and over-discharging, which reduces the compatibility of the binder and inorganic filler in the coating, causes the surface coating of the conductive coating to expand and fall off due to heat, accelerates coating aging, and causes battery short circuits.

[0004] Based on this, there is an urgent need for a lithium-ion battery conductive base coating with good compatibility and adhesion to avoid damage to the lithium-ion battery caused by defects in the coating performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a conductive base coating for lithium ion batteries with good bonding performance and a preparation method thereof.

[0006] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a conductive base coating for lithium-ion batteries, comprising at least the following components in parts by mass: 45-60 parts of a binder, 15-30 parts of a conductive inorganic filler, 180-240 parts of an organic solvent, 1.5-3 parts of a dispersant, and 0.6-2.8 parts of a compatibilizer, wherein the binder comprises at least polyurethane, and the compatibilizer is a methacrylate silane coupling agent.

[0007] As a preferred technical solution, the polyurethane is graphene-modified polyurethane.

[0008] As a preferred technical solution, the method for graphene-modified polyurethane comprises at least the following steps:

[0009] (1) adding graphene to a solvent and mixing uniformly to obtain a dispersion A;

[0010] (3) adding polyurethane to dispersion A and mixing uniformly to obtain dispersion B;

[0011] (3) Sodium dodecylbenzenesulfonate and methacrylate silane coupling agent are added to the dispersion B and mixed evenly to obtain the product.

[0012] As a preferred technical solution, the raw materials for preparing the polyurethane include polyether carbonate polyol, isocyanate prepolymer and polyisocyanate, the polyether carbonate polyol has a functionality of 2 to 4, a hydroxyl value of 50-60 mgKOH / g, a CO2 mass percentage content of 5 to 35%, and the mass ratio between the isocyanate prepolymer and the polyisocyanate is 1 to 3:1.

[0013] As a preferred technical solution, the isocyanate prepolymer and polyisocyanate are obtained by modifying hollow glass microspheres and silicon dioxide, and the mass ratio of the hollow glass microspheres to silicon dioxide is 2 to 5:1.

[0014] As a preferred technical solution, the NCO content of the polyisocyanate is 10-20%.

[0015] As a preferred technical solution, the method for preparing the polyurethane comprises at least the following steps:

[0016] (1) preparing component A: adding 15 to 50 parts by weight of polyether carbonate polyol and 5 to 10 parts by weight of chain extender, and stirring uniformly to obtain component A;

[0017] (2) preparing component B: adding 30-70 parts of isocyanate prepolymer, 6-28 parts of polyisocyanate, 5-25 parts of hollow glass microspheres, 0.1-2 parts of fumed silica, and 0.1-0.5 parts of dehydrating agent in parts by weight, stirring evenly and then discharging to obtain component B; wherein the isocyanate prepolymer is prepared by reacting polyether carbonate polyol and polyisocyanate in a mass ratio of 1:0.5-2;

[0018] (3) Component A and component B are mixed evenly in a volume ratio of 1:0.8 to 1.5 to obtain polyurethane.

[0019] As a preferred technical solution, the conductive inorganic filler is a mixture of modified graphite fiber and modified graphene, the mass ratio between the modified graphite fiber and the modified graphene is 1-3:10-15, and the modified graphite fiber and modified graphene are obtained by modifying graphite fiber and graphene with an organosilicon coupling agent.

[0020] As a preferred technical solution, the solvent in the method of graphene-modified polyurethane is at least one of dimethyl sulfoxide, N-methylpyrrolidone, and N-methylpyridine.

[0021] As a preferred technical solution, the solvent in the method for graphene-modified polyurethane is a mixture of dimethyl sulfoxide and N-methylpyrrolidone, and the mass ratio between the dimethyl sulfoxide and N-methylpyrrolidone is 3:1.

[0022] As a preferred technical solution, the conductive inorganic filler is a mixture of graphite fiber and graphene, and the mass ratio of the graphite fiber to the graphene is 1-3:10-15.

[0023] As a preferred technical solution, the dispersant is selected from at least one of sodium lignin sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium polyacrylate and potassium polyacrylate.

[0024] As a preferred technical solution, the organic solvent is at least one of dimethylformamide, acetone and ethyl acetate.

[0025] As a preferred technical solution, the organic solvent is a mixture of dimethylformamide, acetone and ethyl acetate, and the mass ratio of dimethylformamide, acetone and ethyl acetate is 1-2:1-2:3-5.

[0026] A method for preparing the above-mentioned conductive base coating for lithium ion batteries comprises at least the following steps:

[0027] (1) Weigh the binder and the organic solvent, mix them, and stir them evenly;

[0028] (2) Adding the conductive inorganic filler, dispersant and compatibilizer to the mixture prepared in step (1), and performing ultrasonication and stirring until a uniform mixture is obtained.

[0029] Beneficial effects

[0030] The present invention provides a conductive base coating for lithium-ion batteries and a preparation method thereof. The present invention combines multiple components for synergistic synergy. The conductive properties of the coating can be improved by using graphene-modified polyurethane. The inventors have discovered that in the system of the present invention, polyurethane is used as a binder and a methacrylate silane coupling agent is used as a compatibilizer. The carboxyl groups in the methacrylate silane form stable chemical bonds with the amino and hydroxyl functional groups of the polyurethane. Furthermore, the methacrylate silane can form a cross-linked structure with the graphite fibers and graphene inorganic fillers in the polyurethane, further enhancing the coating's bonding properties while improving its compatibility with the inorganic filler. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0032] Example 1

[0033] A conductive base coating for a lithium-ion battery in this embodiment includes the following components in parts by mass: 45 parts of a binder, 15 parts of a conductive inorganic filler, 180 parts of an organic solvent, 1.5 parts of a dispersant, and 0.6 parts of a compatibilizer. The binder is graphene-modified polyurethane, the compatibilizer is a methacrylate silane coupling agent, the conductive inorganic filler is a mixture of graphite fiber modified with an organosilicon coupling agent and graphene modified with an organosilicon coupling agent, and the mass ratio between the graphite fiber and the graphene is 1:14. The dispersant is sodium lignin sulfonate, and the organic solvent is a mixture of dimethylformamide, acetone, and ethyl acetate, and the mass ratio between the dimethylformamide, acetone, and ethyl acetate is 1:1:5.

[0034] In parts by mass, the method for graphene-modified polyurethane comprises the following steps:

[0035] (1) adding 3 parts of graphene to a mixed solvent consisting of 30 parts of dimethyl sulfoxide and 10 parts of N-methylpyrrolidone and mixing them uniformly to obtain a dispersion A;

[0036] (3) adding polyurethane to dispersion A and mixing uniformly to obtain dispersion B;

[0037] (3) Add 0.1 parts of sodium dodecylbenzenesulfonate and 0.1 parts of methacrylate silane coupling agent to the dispersion B and mix well.

[0038] The preparation method of the polyurethane comprises the following steps:

[0039] (1) Preparation of component A: 15 parts of polyether carbonate polyol and 5 parts of chain extender were added by weight and stirred to obtain component A. The polyether carbonate polyol had a functionality of 3, a hydroxyl value of 57 mgKOH / g, and a CO2 mass percentage of 9.4%. The polyether carbonate polyol was purchased from Zhejiang Huangma New Materials Co., Ltd. and had a designation of PCE-3015E. The chain extender was glycerol.

[0040] (2) Preparation of component B: adding 30 parts by weight of isocyanate prepolymer, 6 parts of polyisocyanate, wherein the NCO content of the polyisocyanate is 13.4%, purchased from Jintao Chemical under the brand name MDILL, 5 parts of hollow glass microspheres, 0.1 parts of fumed silica, and 0.1 parts of a desiccant, wherein the desiccant is alumina, and stirring well to obtain component B; wherein the isocyanate prepolymer is prepared by reacting polyether carbonate polyol and polyisocyanate in a mass ratio of 1:2;

[0041] (3) Component A and component B are mixed evenly in a volume ratio of 1:1.5 to obtain polyurethane.

[0042] The conductive inorganic filler is a mixture of modified graphite fiber and modified graphene, and the mass ratio between the modified graphite fiber and the modified graphene is 1:10;

[0043] In parts by mass, the modified graphite fiber and modified graphene are obtained by modifying graphite fiber and graphene with an organosilicon coupling agent, specifically: 1 part of graphite fiber and graphene are mixed with 100 parts of 55wt% ethanol aqueous solution and 0.1 part of organosilicon coupling agent KH-550, stirred and reacted at 60°C for 2h, filtered to obtain a solid, washed and dried.

[0044] A method for preparing a conductive base coating for lithium ion batteries comprises the following steps:

[0045] (1) mixing graphene-modified polyurethane with a mixture of dimethylformamide, acetone, and ethyl acetate, and stirring uniformly;

[0046] (2) adding the modified graphite fiber, modified graphene, sodium lignin sulfonate and methacrylate silane coupling agent to the mixture prepared in step (1), and ultrasonicating and stirring until a uniform mixture is obtained.

[0047] Example 2

[0048] A conductive base coating for a lithium-ion battery in this embodiment includes the following components in parts by mass: 60 parts of a binder, 30 parts of a conductive inorganic filler, 240 parts of an organic solvent, 3 parts of a dispersant, and 2.8 parts of a compatibilizer. The binder is graphene-modified polyurethane, the compatibilizer is a methacrylate silane coupling agent, the conductive inorganic filler is a mixture of graphite fiber modified with an organosilicon coupling agent and graphene modified with an organosilicon coupling agent, and the mass ratio between the graphite fiber and the graphene is 1:14. The dispersant is sodium lignin sulfonate, and the organic solvent is a mixture of dimethylformamide, acetone, and ethyl acetate, and the mass ratio between the dimethylformamide, acetone, and ethyl acetate is 1:1:5.

[0049] In parts by mass, the method for graphene-modified polyurethane comprises the following steps:

[0050] (1) adding 3 parts of graphene to a mixed solvent consisting of 30 parts of dimethyl sulfoxide and 10 parts of N-methylpyrrolidone and mixing them uniformly to obtain a dispersion A;

[0051] (3) adding polyurethane to dispersion A and mixing uniformly to obtain dispersion B;

[0052] (3) Add 0.1 parts of sodium dodecylbenzenesulfonate and 0.1 parts of methacrylate silane coupling agent to the dispersion B and mix well.

[0053] The preparation method of the polyurethane comprises the following steps:

[0054] (1) Preparation of component A: 15 parts of polyether carbonate polyol and 5 parts of chain extender were added by weight and stirred to obtain component A. The polyether carbonate polyol had a functionality of 3, a hydroxyl value of 57 mgKOH / g, and a CO2 mass percentage of 9.4%. The polyether carbonate polyol was purchased from Zhejiang Huangma New Materials Co., Ltd. and had a designation of PCE-3015E. The chain extender was glycerol.

[0055] (2) Preparation of component B: adding 30 parts by weight of isocyanate prepolymer, 6 parts of polyisocyanate, wherein the NCO content of the polyisocyanate is 13.4%, purchased from Jintao Chemical under the brand name MDILL, 5 parts of hollow glass microspheres, 0.1 parts of fumed silica, and 0.1 parts of a desiccant, wherein the desiccant is alumina, and stirring well to obtain component B; wherein the isocyanate prepolymer is prepared by reacting polyether carbonate polyol and polyisocyanate in a mass ratio of 1:2;

[0056] (3) Component A and component B are mixed evenly in a volume ratio of 1:1.5 to obtain polyurethane.

[0057] The conductive inorganic filler is a mixture of modified graphite fiber and modified graphene, and the mass ratio between the modified graphite fiber and the modified graphene is 1:10;

[0058] In parts by mass, the modified graphite fiber and modified graphene are obtained by modifying graphite fiber and graphene with an organosilicon coupling agent, specifically: 1 part of graphite fiber and graphene are mixed with 100 parts of 55wt% ethanol aqueous solution and 0.1 part of organosilicon coupling agent KH-550, stirred and reacted at 60°C for 2h, filtered to obtain a solid, washed and dried.

[0059] A method for preparing a conductive base coating for lithium ion batteries comprises the following steps:

[0060] (1) mixing graphene-modified polyurethane with a mixture of dimethylformamide, acetone, and ethyl acetate, and stirring uniformly;

[0061] (2) adding the modified graphite fiber, modified graphene, sodium lignin sulfonate and methacrylate silane coupling agent to the mixture prepared in step (1), and ultrasonicating and stirring until a uniform mixture is obtained.

[0062] Comparative Example 1

[0063] The specific implementation of this comparative example is the same as that of Example 1, except that the binder is graphene-modified polyacrylate, which is purchased from Feiyue Chemical with the brand number 9003-01-4.

[0064] The method for modifying polyacrylate with graphene comprises the following steps:

[0065] (1) adding 3 parts of graphene to a mixed solvent consisting of 30 parts of dimethyl sulfoxide and 10 parts of N-methylpyrrolidone and mixing them uniformly to obtain a dispersion A;

[0066] (3) adding polyacrylate to dispersion A and mixing uniformly to obtain dispersion B;

[0067] (3) Add 0.1 parts of sodium dodecylbenzenesulfonate and 0.1 parts of methacrylate silane coupling agent to the dispersion B and mix well.

[0068] Comparative Example 2

[0069] The specific implementation of this comparative example is the same as that of Example 1, except that the binder is polyurethane.

[0070] Comparative Example 3

[0071] The specific implementation of this comparative example is the same as that of Example 1, except that no compatibilizer is included.

[0072] Comparative Example 4

[0073] The specific implementation of this comparative example is the same as that of Example 1, except that the polyurethane is commercially available and purchased from Jining Tangyi Chemical Co., Ltd.

[0074] The specific implementation of this comparative example is the same as that of Example 1, except that the mass ratio between the graphite fiber and the graphene is 14:1.

[0075] Comparative Example 6

[0076] The specific implementation of this comparative example is the same as that of Example 1, except that the mass ratio between the modified graphite fiber and the modified graphene is 10:1.

[0077] Performance Testing

[0078] The conductive coatings prepared in Examples 1-2 and Comparative Examples 1-6 were applied to aluminum and cured. The samples were subjected to peel strength tests at room temperature, peel strength tests after oven treatment at 60°C for 12 hours, and peel strength tests after immersion in electrolyte at 60°C for 200 hours, according to the standard GB / T2792-2014. The specific test results are shown in Table 1 below.

[0079] Table 1 - Conductive coating peel strength performance test

[0080]

[0081]

[0082] As can be seen from the above table, the coatings using the polyurethane adhesive and the methacrylate silane coupling agent compatibilizer in Examples 1 and 2 have better bonding properties.

[0083] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A conductive base coating for lithium ion batteries, characterized in that: The invention comprises at least the following components in parts by mass: 45-60 parts of a binder, 15-30 parts of a conductive inorganic filler, 180-240 parts of an organic solvent, 1.5-3 parts of a dispersant, and 0.6-2.8 parts of a compatibilizer, wherein the binder comprises at least polyurethane, and the compatibilizer is a methacrylate silane coupling agent; The polyurethane is graphene-modified polyurethane; The method for modifying polyurethane with graphene comprises at least the following steps: (1) Add graphene to the solvent and mix evenly to obtain dispersion A; (2) Adding polyurethane to dispersion A and mixing evenly to obtain dispersion B; (3) Sodium dodecylbenzenesulfonate and methacrylate silane coupling agent are added to dispersion B and mixed evenly to obtain the product; The preparation method of the polyurethane comprises at least the following steps: (1) preparing component A: adding 15 to 50 parts by weight of polyether carbonate polyol and 5 to 10 parts by weight of chain extender, and stirring uniformly to obtain component A; (2) preparing component B: adding 30-70 parts of isocyanate prepolymer, 6-28 parts of polyisocyanate, 5-25 parts of hollow glass microspheres, 0.1-2 parts of fumed silica, and 0.1-0.5 parts of dehydrating agent in parts by weight, stirring evenly and then discharging to obtain component B; wherein the isocyanate prepolymer is prepared by reacting polyether carbonate polyol and polyisocyanate in a mass ratio of 1:0.5-2; (3) Mix component A and component B in a volume ratio of 1:0.8-1.5 to obtain polyurethane. ester; The conductive inorganic filler is a mixture of modified graphite fiber and modified graphene. The mass ratio between the modified graphite fiber and the modified graphene is 1-3:10-15, Graphite fiber and modified graphene as organosilicon coupling agent Obtained by coupling agent modified graphene.

2. The conductive base coating for lithium ion batteries according to claim 1, characterized in that: The raw materials for preparing the polyurethane include polyether carbonate polyol, isocyanate prepolymer and polyisocyanate. The polyether carbonate polyol has a functionality of 2 to 4, a hydroxyl value of 50 to 60 mgKOH / g, a mass percentage of CO2 of 5 to 35%, and a mass ratio between the isocyanate prepolymer and the polyisocyanate of 1 to 3:

1.

3. The conductive base coating for lithium ion batteries according to claim 2, characterized in that: The isocyanate prepolymer and polyisocyanate are obtained by modifying hollow glass microspheres and silicon dioxide, and the mass ratio of the hollow glass microspheres to silicon dioxide is 2-5:

1.

4. The conductive base coating for lithium ion batteries according to claim 3, characterized in that: The NCO content of the polyisocyanate is 10-20%.

5. The conductive base coating for lithium ion batteries according to claim 1, characterized in that: The organic solvent is a mixture of dimethylformamide, acetone and ethyl acetate, and the mass ratio of the dimethylformamide, acetone and ethyl acetate is 1-2:1-2:3-5.

6. A method for preparing the conductive base coating for lithium ion batteries according to any one of claims 1 to 5, characterized in that: At least the following steps are included: (1) Weigh the binder and organic solvent, mix them, and stir them evenly; (2) Adding the conductive inorganic filler, dispersant and compatibilizer to the mixture prepared in step (1), and ultrasonicating and stirring until a uniform mixture is obtained.

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