Carbon-coated current collector and preparation method thereof, electrode plate and battery

Abstract

The invention discloses a carbon-coated current collector and a preparation method thereof, an electrode plate and a battery, the carbon-coated current collector has a carbon-coated layer formed by carbon-coated slurry, and the carbon-coated slurry contains polymethyl methacrylate microspheres and a first high-molecular polymer material capable of providing a hydrogen bond donor. The polymethyl methacrylate microsphere is of a core-shell structure formed by wrapping an elastic second high-molecular polymer material with polymethyl methacrylate; hydrogen bonds are formed between the first high-molecular polymer material and the polymethyl methacrylate microspheres. An interaction network formed between the first high-molecular polymer material capable of providing a hydrogen bond donor and the polymethyl methacrylate microspheres can remarkably improve the bonding force, the peeling strength and the overall stability of a pole piece are improved, and when the pole piece is prepared through the carbon-coated current collector, the damage of pressure to a three-dimensional bonding network of a carbon-coated layer is small, so that the service life of the pole piece is prolonged, and the service life of the pole piece is prolonged. And the slurry on the electrode can be more fully compacted, so that the battery has higher energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a carbon-coated current collector and a preparation method thereof, an electrode sheet and a battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, energy storage and automotive power due to their advantages such as good cycle performance, high energy density, high output voltage and low self-discharge. With the rapid development of electric vehicles powered by lithium-ion batteries, higher requirements are placed on the safety, rate performance and energy performance of lithium-ion batteries. The preparation of high-performance lithium-ion batteries is inseparable from its core components. In recent years, the battery industry has been conducting endless research on current collectors. The biggest technological change is the change from single plain aluminum foil to carbon-coated aluminum foil.

[0003] The current collector is an important component of lithium-ion batteries. It is not only the main place for electrons to gather and transmit, but also plays a supporting and protective role for electrodes and electrolytes. However, the current carbon-coated current collector technology and its preparation process are relatively complicated. The carbon-coated layer needs to be rolled after being coated on the current collector. The three-dimensional bonding network of the carbon-coated layer is easily destroyed during the rolling process, which causes the performance of the carbon-coated layer to be lost. In addition, from the perspective of energy saving and environmental protection, simple process and easy mass production, it is necessary to develop a high-performance carbon-coated current collector, especially one with improved bonding performance. Summary of the invention

[0004] The object of the present invention is to provide a carbon-coated current collector and a preparation method thereof, an electrode sheet and a battery in view of the above problems.

[0005] The present invention is achieved through the following technical solutions:

[0006] The first aspect of the present application provides a carbon-coated current collector, which has a carbon-coated layer formed by a carbon-coated slurry, wherein the carbon-coated slurry contains polymethyl methacrylate microspheres and a first high molecular polymer material capable of providing a hydrogen bond donor, and the polymethyl methacrylate microspheres are a core-shell structure formed by polymethyl methacrylate wrapping a second high molecular polymer material with elasticity; hydrogen bonds are formed between the first high molecular polymer material and the polymethyl methacrylate microspheres.

[0007] To optimize the above technical solutions, the specific measures taken also include:

[0008] The first high molecular polymer material is a polymer material containing a functional group capable of providing a hydrogen bond donor; and the second high molecular polymer material is an elastomer.

[0009] Specifically, the first polymer material is selected from at least one of polyvinyl butyral, polymaleic anhydride or polyvinyl alcohol-vinyl acetate-acrylic acid copolymer; the second polymer material is selected from at least one of polybutadiene, ethylene-acrylic acid copolymer and ethylene-propylene diene copolymer.

[0010] Furthermore, the particle sizes of the polymethyl methacrylate microspheres are D10: 0-5 μm, D50: 0-7 μm, and D90: 0-10 μm.

[0011] The second aspect of the present application provides a method for preparing a carbon-coated current collector, wherein a binder and a conductive agent are mixed to prepare a carbon-coated slurry, and the carbon-coated slurry is used to prepare a carbon-coated layer on the surface of the current collector;

[0012] Wherein, the binder includes a first binder and a second binder; the first binder contains a first high molecular polymer material capable of providing a hydrogen bond donor; the second binder contains polymethyl methacrylate microspheres, and the polymethyl methacrylate microspheres are core-shell structures formed by polymethyl methacrylate wrapping a second high molecular polymer material with elasticity.

[0013] Furthermore, the mixing mass ratio of the first binder to the second binder is 2-5:1.

[0014] Furthermore, the mixing mass ratio of the binder to the conductive agent is 2:1-5.

[0015] The preparation method of the present application specifically comprises the following steps:

[0016] Mixing the first binder and the second binder with water to prepare a glue solution;

[0017] Adding the conductive agent to the glue solution in batches, and after each addition of the conductive agent, stirring the mixture to disperse at a high speed of 2000-3000 rpm / min;

[0018] Add curing agent and disperse the mixture at a high speed of 2000-3000 rpm / min by stirring;

[0019] Then add the wetting agent and disperse the mixture by stirring at a low speed of 10-20 rpm / min;

[0020] Discharging the material, grinding the slurry fully to obtain a carbon-coated slurry;

[0021] The carbon coating slurry is applied to the surface of the current collector and dried.

[0022] The third aspect of the present application provides an electrode sheet, comprising a carbon-coated current collector provided by the first aspect of the present application or prepared by the method of the second aspect of the present application.

[0023] The fourth aspect of the present application provides a battery, comprising the electrode sheet provided in the third aspect of the present application.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The first adhesive and the second adhesive are used in the carbon-coated slurry of the present invention in coordination, wherein polymethyl methacrylate wraps a second high molecular polymer material with elasticity to form a core-shell structure, and when the first high molecular polymer material capable of providing a hydrogen bond donor, such as a polymer containing a large number of functional groups capable of providing a hydrogen bond donor, is mixed with polymethyl methacrylate microspheres, the first high molecular polymer material forms a hydrogen bond with the carbonyl group in the outer shell of the polymethyl methacrylate microsphere (PMMA), and the intermolecular interaction force is enhanced at the interface through the action of hydrogen bonds, thereby improving the adhesion of the pole piece; the first high molecular polymer material also makes the polymer network formed by PMMA more flexible through its flexible chain segments, increases the interface contact area, and enhances the bonding effect. Through the above effects, the interaction network formed between the polymethyl methacrylate microspheres formed by the polymethyl methacrylate wrapping the second high molecular polymer material with elasticity and the first high molecular polymer material capable of providing a hydrogen bond donor can significantly improve the adhesion, and improve the peel strength and overall stability of the pole piece.

[0026] In addition, the core-shell structure formed by polymethyl methacrylate wrapping a second high-molecular polymer material with elasticity can make the carbon-coated current collector have compressive resistance. The acrylic material polymethyl methacrylate has high hardness, transparency and good weather resistance. It wraps the second high-molecular polymer material with elasticity to form a three-dimensional bonding network containing a core-shell structure. PMMA as the shell of the core-shell structure gives the composite surface the required hardness and optical properties, while protecting the elastic material of the core; the elastic second high-molecular polymer material as the core of the core-shell structure can significantly improve the toughness and impact resistance of the material. Therefore, when the pole piece is prepared by the carbon-coated current collector, the pressure has less damage to the three-dimensional bonding network of the carbon-coated layer, and there is no need to consider the impact of the rolling process on the carbon-coated current collector. The slurry on the electrode can be more fully compacted, so that the battery can have a higher energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : A schematic diagram of the preparation process of one embodiment of the present invention. DETAILED DESCRIPTION

[0028] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0029] The experimental methods used in the following examples are all conventional methods unless otherwise specified, and the reagents, methods and equipment used are all conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0030] For the sake of simplicity, this document only specifically discloses some numerical values ​​and optional ranges. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range. Similarly, any upper limit can be combined with any other upper limit to form an unambiguous range; the optional items in the optional range can also be combined arbitrarily.

[0031] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art.

[0032] For the sake of simplicity, this document only specifically discloses some numerical values ​​and optional ranges. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range. Similarly, any upper limit can be combined with any other upper limit to form an unambiguous range; the optional items in the optional range can also be combined arbitrarily.

[0033] The present invention provides a carbon-coated current collector, which has a carbon-coated layer formed by a carbon-coated slurry. The carbon-coated slurry contains polymethyl methacrylate microspheres and a first high molecular polymer material that can provide a hydrogen bond donor. The polymethyl methacrylate microspheres are a core-shell structure formed by polymethyl methacrylate (PMMA) wrapping a second high molecular polymer material with elasticity; hydrogen bonds are formed between the first high molecular polymer material and the polymethyl methacrylate microspheres.

[0034] The first high molecular polymer material is a polymer material containing a functional group capable of providing a hydrogen bond donor; and the second high molecular polymer material is an elastomer.

[0035] Specifically, the first high polymer material can be selected from at least one of polyvinyl butyral (PVB), polymaleic anhydride (PMA) or polyvinyl alcohol-vinyl acetate-acrylic acid copolymer (PVA-co-AA); the second high polymer material can be selected from at least one of polybutadiene (PB), ethylene-acrylic acid copolymer (EPM), and ethylene-propylene diene copolymer (EPDM).

[0036] The particle sizes of the polymethyl methacrylate microspheres are D10: 0-5 μm, D50: 0-7 μm, and D90: 0-10 μm.

[0037] Preferably, the Shore hardness D of the polymethyl methacrylate microspheres is 85-95.

[0038] In some embodiments, the carbon coating slurry further contains a curing agent and a wetting agent.

[0039] The curing agent that can be used in the present application includes but is not limited to: sodium hydroxide, lithium hydroxide, etc.

[0040] The wetting agents that can be used in the present application include, but are not limited to, isopropyl alcohol, isobutyl alcohol, ethylene glycol butyl ether, tert-butyl alcohol, and the like.

[0041] The mass proportion of the wetting agent in the carbon coating slurry is 10-18%.

[0042] The present invention also provides a method for preparing a carbon-coated current collector, wherein a binder and a conductive agent are mixed to prepare a carbon-coated slurry, and the carbon-coated slurry is used to prepare a carbon-coated layer on the surface of the current collector;

[0043] The binder comprises a first binder and a second binder; the first binder comprises a first high molecular polymer material capable of providing a hydrogen bond donor; the second binder comprises polymethyl methacrylate microspheres, which are core-shell structures formed by polymethyl methacrylate wrapping a second high molecular polymer material having elasticity.

[0044] In some embodiments, the mixing mass ratio of the first binder to the second binder is 2-5:1; preferably, the mixing mass ratio of the first binder to the second binder is 3:1.

[0045] In some embodiments, the mixing mass ratio of the binder to the conductive agent is 2:1-5; preferably, the mixing mass ratio of the binder to the conductive agent is 2:3.

[0046] In some embodiments, the solid content of the first binder and the second binder is 10-30%, and the viscosity of the first binder and the second binder is 400-1500 mPa.s.

[0047] The conductive agent that can be used in the present application includes but is not limited to: carbon black, graphite, graphene, CNT, VGCF, etc.; preferably, the particle size of the conductive agent is 1-50 μm, wherein the specific surface area of ​​carbon black or graphene with a particle size of 1-50 μm is independently 30-100 m 2 / g solution has better dispersion effect.

[0048] In some embodiments, the method for preparing the carbon-coated current collector of the present application specifically includes the following steps: Figure 1 As shown:

[0049] Mixing the first binder and the second binder with water to prepare a glue solution;

[0050] Add the conductive agent to the glue solution in batches. After each addition of the conductive agent, stir the mixture to disperse at a high speed of 2000-3000 rpm / min.

[0051] Add curing agent and disperse the mixture at a high speed of 2000-3000 rpm / min by stirring;

[0052] Then add the wetting agent and disperse the mixture by stirring at a low speed of 10-20 rpm / min;

[0053] Discharging the material, grinding the slurry fully to obtain a carbon-coated slurry; the obtained carbon-coated slurry has a particle size of D50 < 1.8 μm, D90 < 7 μm, and D97 < 9 μm;

[0054] The carbon coating slurry is applied to the surface of the current collector and dried.

[0055] The thickness of the current collector used in the present application can be 4 μm to 20 μm; the current collector of the present application is selected from traditional current collectors such as aluminum foil, copper foil, or multilayer current collectors (functional current collectors).

[0056] The present invention also provides an electrode sheet comprising the above-mentioned carbon-coated current collector.

[0057] The electrode sheet of the present application also contains an electrode sheet active material, and the electrode sheet slurry containing the electrode sheet active material is coated on a current collector having a carbon coating layer; the electrode sheet slurry is uniformly coated on the carbon-coated current collector to obtain an unrolled electrode sheet, and then rolled at a compaction density of 2.3-2.7g / cc to obtain a rolled electrode sheet, and then the peel strength is tested using an electronic peel tester.

[0058] The electrode active materials that can be used in this application include but are not limited to: lithium iron phosphate, lithium iron manganese phosphate, ternary materials, lithium cobalt oxide, lithium manganese oxide, etc.

[0059] The present invention also provides a battery comprising the above-mentioned electrode sheet.

[0060] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments:

[0061] Example 1

[0062] The preparation process of a carbon-coated current collector and electrode sheet is as follows:

[0063] S1: Mixing deionized water with the first binder and the second binder to prepare a low-solid glue solution;

[0064] S2: add half of the conductive agent and disperse at high speed of 2400rpm / min in a 200L Double Star stirring tank for 60min;

[0065] S3: add the remaining half of the conductive agent and disperse at high speed of 2400 rpm / min in a 200L Double Star stirring tank for 60 min;

[0066] S4: Add all the curing agent and disperse at high speed of 2400rpm / min in a 200L Double Star stirring tank for 90min;

[0067] S4: Add wetting agent, stir at low speed of 15 rpm / min in a 200L double star stirring tank for 45 minutes, and then discharge;

[0068] S5: Grind the slurry 7 times with a grinder to obtain a carbon-coated slurry with a particle size of D50 < 1.8 μm and D90 < 7 μm.

[0069] D97<9μm;

[0070] S6: Use a gravure coater to evenly coat the slurry onto the aluminum foil and dry it.

[0071] The mass ratio of the binder to the conductive agent is 2:1, and the mass ratio of the first binder to the second binder is 2:1; the wetting agent is

[0072] The carbon coating slurry accounts for 15% by weight, and the curing agent accounts for 7% by weight of the binder; the first binder is polymaleic anhydride PMA; the second binder is PMMA microspheres, whose shell is polymethyl methacrylate and the core is ethylene-acrylic acid copolymer (EPM), and the particle size is D10: 1.8μm, D50: 2.9μm, D90: 4.5μm; the conductive agent is a mixture of carbon black and graphite

[0073] The mass ratio of carbon black to graphite is 4:1; sodium hydroxide is selected as the curing agent, and isopropyl alcohol is selected as the wetting agent;

[0074] A carbon-coated aluminum foil was prepared according to steps S1-S6, and a pole piece slurry containing a pole piece active material was coated on a current collector having a carbon coating layer; lithium iron phosphate was used as the pole piece active material, PVDF was used as a dispersant, and NMP was used as a solvent, and a positive electrode slurry was prepared according to a mass ratio of lithium iron phosphate (LFP): conductive carbon black: PVDF = 93:3:3, PVDF: NMP = 8:92; the positive electrode slurry was uniformly coated on the carbon-coated aluminum foil to obtain an unrolled positive electrode sheet, and then rolled at a compaction density of 2.5 g / cc to obtain a rolled positive electrode sheet, and then the peeling strength was tested using an electronic peeling tester.

[0075] Example 2

[0076] The mass ratio of the binder to the conductive agent is 2:2, and the rest is the same as in Example 1.

[0077] Example 3

[0078] The mass ratio of the binder to the conductive agent is 2:3, and the rest is the same as in Example 1.

[0079] Example 4

[0080] The mass ratio of the binder to the conductive agent is 2:4, and the rest is the same as in Example 1.

[0081] Example 5

[0082] The mass ratio of the binder to the conductive agent is 2:5, and the rest is the same as in Example 1.

[0083] Example 6

[0084] The mass ratio of the binder to the conductive agent is 2:3, the mass ratio of the first binder to the second binder is 3:1, and other conditions are the same as those in Example 1.

[0085] Example 7

[0086] The mass ratio of the binder to the conductive agent is 2:3, the mass ratio of the first binder to the second binder is 4:1, and other conditions are the same as those in Example 1.

[0087] Example 8

[0088] The mass ratio of the binder to the conductive agent is 2:3, the mass ratio of the first binder to the second binder is 5:1, and other conditions are the same as those in Example 1.

[0089] Example 9

[0090] Second binder: PMMA microspheres, D10: 3.8 μm, D50: 6.7 μm, D90: 9.5 μm, and the rest are the same as in Example 6.

[0091] Example 10

[0092] Second binder: PMMA microspheres, D10: 1.5 μm, D50: 1.8 μm, D90: 2.9 μm, and the rest are the same as in Example 6.

[0093] Embodiment 11

[0094] The first high molecular polymer material of the first adhesive is polyvinyl butyral, and the rest is the same as in Example 9.

[0095] Example 12

[0096] The second high molecular polymer material of the second adhesive is polybutadiene, and the rest is the same as in Example 9.

[0097] Comparative Example 1

[0098] The scheme and test process of this comparative example are basically the same as those of Example 9, except that only one binder, polymaleic anhydride (PMA), is used.

[0099] Comparative Example 2

[0100] The scheme and test process of this comparative example are basically the same as those of Example 9, except that only one binder PMMA microspheres are used, wherein the shell is polymethyl methacrylate, the core is ethylene-acrylic acid copolymer (EPM), and the particle sizes are D10: 1.8μm, D50: 2.9μm, and D90: 4.5μm.

[0101] The examples and comparative examples were tested and the results are shown in Table 1:

[0102] Table 1 Comparison of test results of various embodiments and comparative examples

[0103]

[0104] Judgment criteria: The greater the peel strength of the electrode, the better; the penetration resistance of the carbon-coated aluminum foil is ≤5mΩ.

[0105] The test results are shown in Table 1 and analyzed as follows:

[0106] From the comparison of Examples 1-5, it can be seen that Examples 1-3 have better electrode peeling strength, Examples 4 and 5 have better carbon coating layer penetration resistance, among which Example 3 has better electrode peeling strength and better carbon coating layer penetration resistance, and has better comprehensive performance. Therefore, the mass ratio of binder to conductive agent is 2:3, which is a better solution.

[0107] From the comparison between Example 3 and Examples 6-8, it can be seen that Examples 3 and 6 have better electrode peeling strength, and Examples 6-8 have better carbon coating layer penetration resistance, among which Example 6 has better electrode peeling strength and better carbon coating layer penetration resistance, and has better comprehensive performance. Therefore, the mass ratio of the first binder to the second binder is 3:1, which is the best choice.

[0108] From the comparison between Example 6, Example 9 and Example 10, it can be seen that when the particle size of the polymethyl methacrylate microspheres is changed, the electrode peeling strength and the carbon coating layer penetration resistance are affected to a certain extent, but within the particle size range of the present application, better measured values ​​can be obtained.

[0109] From the comparison between Example 9, Example 11 and Example 12, it can be seen that when the first high molecular polymer material of the first adhesive and the second high molecular polymer material of the second adhesive are changed, the electrode peeling strength and the carbon coating layer penetration resistance in the test results also have good values ​​due to the same principle. The scheme of the present application is not limited to the listed chemical substances and can be replaced by other substances that can meet the implementation of the scheme.

[0110] From the comparison between Example 9 and Comparative Example 1, it can be seen that when only the first adhesive containing the first high molecular polymer material is used, although the same compaction density and other conditions are used, the electrode peeling strength and the carbon coating layer penetration resistance of Comparative Example 1 are significantly reduced; similarly, from the comparison between Example 9 and Comparative Example 2, it can be seen that when only the second adhesive containing PMMA microspheres is used, the test results are slightly better than those of Comparative Example 1, but far less than the embodiment scheme of the present application; the coordinated use of the first adhesive and the second adhesive is very critical to achieving the technical effect of the present application.

[0111] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A carbon-coated current collector, characterized in that: The carbon-coated current collector has a carbon-coated layer formed by a carbon-coated slurry, wherein the carbon-coated slurry contains polymethyl methacrylate microspheres and a first high molecular polymer material capable of providing a hydrogen bond donor, wherein the polymethyl methacrylate microspheres are a core-shell structure formed by polymethyl methacrylate wrapping a second high molecular polymer material having elasticity; hydrogen bonds are formed between the first high molecular polymer material and the polymethyl methacrylate microspheres.

2. The carbon-coated current collector according to claim 1, characterized in that: The first high molecular polymer material is a polymer material containing a functional group capable of providing a hydrogen bond donor; and the second high molecular polymer material is an elastomer.

3. The carbon-coated current collector according to claim 2, characterized in that: The first polymer material is selected from at least one of polyvinyl butyral, polymaleic anhydride or polyvinyl alcohol-vinyl acetate-acrylic acid copolymer; the second polymer material is selected from at least one of polybutadiene, ethylene-acrylic acid copolymer and ethylene-propylene diene copolymer.

4. The carbon-coated current collector according to claim 1, characterized in that: The particle sizes of the polymethyl methacrylate microspheres are D10: 0-5 μm, D50: 0-7 μm, and D90: 0-10 μm.

5. A method for preparing a carbon-coated current collector, characterized in that: Mixing a binder and a conductive agent to prepare a carbon coating slurry, and using the carbon coating slurry to prepare a carbon coating layer on the surface of a current collector; Wherein, the binder includes a first binder and a second binder; the first binder contains a first high molecular polymer material capable of providing a hydrogen bond donor; the second binder contains polymethyl methacrylate microspheres, and the polymethyl methacrylate microspheres are core-shell structures formed by polymethyl methacrylate wrapping a second high molecular polymer material with elasticity.

6. The method for preparing a carbon-coated current collector according to claim 5, characterized in that: The mixing mass ratio of the first binder to the second binder is 2-5:

1.

7. The method for preparing a carbon-coated current collector according to claim 5, characterized in that: The mixing mass ratio of the binder to the conductive agent is 2:1-5.

8. The method for preparing a carbon-coated current collector according to claim 5, characterized in that: The following steps are involved: Mixing the first binder and the second binder with water to prepare a glue solution; Adding the conductive agent to the glue solution in batches, and after each addition of the conductive agent, stirring the mixture to disperse at a high speed of 2000-3000 rpm / min; Add curing agent and disperse the mixture at a high speed of 2000-3000 rpm / min by stirring; Then add the wetting agent and disperse the mixture by stirring at a low speed of 10-20 rpm / min; Discharging the material, grinding the slurry fully to obtain a carbon-coated slurry; The carbon coating slurry is applied to the surface of the current collector and dried.

9. An electrode sheet, characterized in that: A carbon-coated current collector comprising the method described in any one of claims 1 to 4 or prepared by the method described in any one of claims 5 to 8.

10. A battery, characterized in that: The electrode sheet comprising claim 9.

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