Coated aluminum foil and preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of energy storage batteries, in particular to a coated aluminum foil, a preparation method thereof, a positive plate and a battery. The coated aluminum foil comprises an aluminum foil body and coatings arranged on the two sides of the aluminum foil body. The coating comprises a carbon layer arranged in the middle of the aluminum foil in the width direction of the aluminum foil and ceramic layers arranged on the two sides of the aluminum foil. The coated aluminum foil is composed of an aluminum foil base material, a middle conductive carbon layer and two side edge ceramic layers, the coating is designed in a partitioned mode, the conductive coating corresponds to an active substance area, the ceramic layers correspond to edge empty foil areas, the ceramic layers have a certain inhibition effect on short circuit, and therefore the risk of thermal runaway of the battery is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a coated aluminum foil, a preparation method thereof, a positive electrode sheet and a battery. BACKGROUND

[0002] As a high-efficiency energy storage device, lithium ion batteries have been widely used in portable electronic devices, electric vehicles, energy storage systems and other fields. With the continuous expansion of application scenarios, higher requirements are put forward for the safety, energy density and cycle performance of lithium ion batteries.

[0003] As one of the key components of lithium ion batteries, the main function of the current collector is to carry active materials and conduct electrons. Currently, aluminum foil is commonly used as the positive electrode current collector of lithium ion batteries. However, there are many safety hazards in the use of traditional aluminum foil current collectors: when the battery overheats or short circuits, the aluminum foil may melt or corrode, leading to battery failure or even fire; especially in the edge area of the electrode sheet, the exposed aluminum foil is prone to burr or corrosion, which may cause internal short circuit of the battery and lead to thermal runaway risk. SUMMARY

[0004] The purpose of the present application is to overcome the deficiencies and shortcomings of the prior art, and to provide a coated aluminum foil, a preparation method thereof, a positive electrode sheet and a battery.

[0005] In order to achieve the above-mentioned purpose, the following solutions are adopted in the present application:

[0006] A coated aluminum foil, comprising an aluminum foil and a coating layer arranged on both sides of the aluminum foil; the coating layer comprises a carbon layer arranged at the middle position of the aluminum foil along the width direction of the aluminum foil and a ceramic layer arranged on both sides of the aluminum foil.

[0007] The width of the carbon layer is 50-500mm, preferably 100-200mm; the width of the ceramic layer on one side is 2-10mm, preferably 6-8mm.

[0008] The thickness of the carbon layer is 1-5μm, preferably 1μm; the thickness of the ceramic layer is 1-5μm, preferably 2μm.

[0009] The carbon layer comprises a conductive agent and a conductive binder; preferably, the mass ratio of the conductive agent to the conductive binder is (70-90):(10:30), preferably (80-85):(15-20);

[0010] Preferably, the conductive agent comprises graphene and at least one of conductive carbon black, carbon nanotubes and layered conductive graphite;

[0011] Preferably, the conductive binder comprises at least one of polyvinylidene fluoride, polyacrylate, styrene butadiene rubber, sodium carboxymethyl cellulose.

[0012] The ceramic layer comprises ceramic and a binder; preferably, the mass ratio of the ceramic to the ceramic binder is (80-90):(10:20).

[0013] Preferably, the ceramic comprises at least one of alumina, zirconia, boehmite.

[0014] Preferably, the ceramic binder comprises at least one of polyvinylidene fluoride, polyacrylate, styrene butadiene rubber, sodium carboxymethyl cellulose, PVDF-PVP composite binder.

[0015] The PVDF-PVP composite binder comprises PVDF and PVP; the mass ratio of PVDF to PVP is (70-90):(10:30); preferably, the molecular weight of PVDF is 500,000-800,000, and the molecular weight of PVP is 40,000-50,000.

[0016] The application further comprises a preparation method of the coated aluminum foil, comprising the following steps: S1: preparing conductive slurry and ceramic slurry respectively; S2: coating the conductive slurry and the ceramic slurry at the middle position along the width direction of the aluminum foil and at the two side positions along the width direction of the aluminum foil respectively; S3: drying to complete the preparation of the coated aluminum foil.

[0017] The conductive slurry is prepared by mixing the conductive agent and the conductive binder in a proportion, then adding solvent N-methyl pyrrolidone, and mixing uniformly in a double planetary mixer.

[0018] The ceramic slurry is prepared by mixing the ceramic and the ceramic binder in a proportion, then adding solvent N-methyl pyrrolidone, and mixing uniformly in a double planetary mixer.

[0019] The application further comprises a positive electrode sheet comprising the coated aluminum foil and an active material layer arranged on the coated aluminum foil.

[0020] The active material layer is arranged on the carbon layer.

[0021] The application further comprises a battery comprising the positive electrode sheet.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] The coated aluminum foil of the present application is composed of "aluminum foil substrate + intermediate conductive carbon layer + two-side edge ceramic layer", and the coating is designed in zones: the conductive coating corresponds to the active material area, the ceramic layer corresponds to the edge empty foil area, and the ceramic layer has a certain inhibitory effect on short circuit, thereby reducing the risk of thermal runaway of the battery; as a preferred form, the ceramic layer uses a PVDF-PVP composite binder to achieve strong adhesion and electrolyte stability of the thin coating. The coated aluminum foil as a current collector can balance the safety, conductivity and processing performance of lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the overall schematic diagram of the coated aluminum foil of the present application. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with the drawings and specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0026] Figure 1 A coated aluminum foil is shown, which comprises an aluminum foil 1 and a coating layer arranged on both sides of the aluminum foil; the coating layer comprises a carbon layer 3 arranged at the middle position of the aluminum foil in the width direction of the aluminum foil and a ceramic layer 2 arranged on both sides of the aluminum foil.

[0027] The width of the carbon layer is 50-500mm, and can be 50mm, 100mm, 200mm, 300mm, 400mm, 500mm; preferably 100-200mm; the width of the ceramic layer on one side is 2-10mm; and can be 2mm, 4mm, 6mm, 8mm, 10mm; preferably 6-8mm.

[0028] The thickness of the carbon layer is 1-5μm; and can be 1μm, 2μm, 3μm, 4μm, 5μm; the thickness of the ceramic layer is 1-5μm, and can be 1μm, 2μm, 3μm, 4μm, 5μm.

[0029] The carbon layer comprises a conductive agent and a conductive binder; preferably, the mass ratio of the conductive agent to the conductive binder is (70-90):(10:30); and can be 70:30; 80:20; 90:10.

[0030] Preferably, the conductive agent comprises graphene and at least one of conductive carbon black, carbon nanotubes and layered conductive graphite.

[0031] Preferably, the conductive binder comprises at least one of polyvinylidene fluoride, polyacrylate, butadiene styrene rubber and sodium carboxymethyl cellulose.

[0032] The ceramic layer comprises ceramic and ceramic binder; preferably, the mass ratio of the conductive agent and the ceramic binder is (80-90):(10-20); which can be 80:20; 85:15; 90:10.

[0033] Preferably, the ceramic comprises at least one of alumina, zirconia and boehmite; and the ceramic binder comprises at least one of polyvinylidene fluoride, polyacrylate, styrene butadiene rubber, sodium carboxymethyl cellulose and PVDF-PVP composite binder.

[0034] Embodiment 1: a method for preparing an aluminum foil coated with a ceramic layer, comprising the following steps:

[0035] 1. Preparation of conductive slurry: mix the conductive agent and the conductive binder according to the mass percentage of 80% carbon nanotubes and 20% polyvinylidene fluoride, then add solvent N-methyl pyrrolidone and mix uniformly in a double planetary mixer to prepare the conductive slurry.

[0036] 2. Preparation of ceramic slurry: mix the ceramic powder and the ceramic binder according to the mass percentage of 85% boehmite and 15% PVDF-PVP composite binder (including PVDF and PVP, the mass ratio of which is 80:20, the molecular weight of PVDF is 500,000-800,000 and the molecular weight of PVP is 40,000-50,000), then add solvent N-methyl pyrrolidone and mix uniformly in a double planetary mixer to prepare the ceramic slurry.

[0037] 3. Coating of conductive coating: coat the conductive slurry on the surface of a 12 μm aluminum foil by gravure coating to a thickness of 1 μm and a width of 140 mm.

[0038] 4. Coating of ceramic coating: coat the ceramic slurry on the edges of the surface of the aluminum foil adjacent to the conductive coating by gravure coating to a width of 6 mm and a thickness of 2 μm.

[0039] 5. Drying to complete the preparation of the aluminum foil coated with a ceramic layer.

[0040] 6. Using the aluminum foil coated with a ceramic layer as the positive current collector, perform processes such as homogenization, coating, pressure cutting, laser cutting, winding, assembly, liquid injection, formation and aging to produce finished batteries.

[0041] Embodiment 2: the difference between Embodiment 2 and Embodiment 1 is that the width of the ceramic coating in step 4 is different: coat the ceramic slurry on the edges of the surface of the aluminum foil adjacent to the conductive coating by gravure coating to a width of 8 mm and a thickness of 2 μm.

[0042] Example 3: The difference between Example 3 and Example 1 is that the preparation of the ceramic slurry in Step 1 is different. The ceramic powder and the ceramic binder are mixed according to the mass percentage of 80% bormite and 20% PVDF-PVP composite binder (including PVDF and PVP, the mass ratio of which is 80:20, the molecular weight of PVDF is 500-800 thousand, and the molecular weight of PVP is 40-50 thousand), and then the solvent N-methyl pyrrolidone is added and mixed uniformly in a double planetary mixer to prepare the ceramic slurry.

[0043] Example 4: The difference between Example 4 and Example 1 is that the ceramic coating in Step 2 is different. The ceramic slurry is prepared by mixing the ceramic powder and the ceramic binder according to the mass percentage of 85% bormite and 15% PVDF, and then adding the solvent N-methyl pyrrolidone and mixing uniformly in a double planetary mixer.

[0044] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that Steps 2 and 4 are deleted, and the ceramic slurry is not prepared and coated.

[0045] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that Steps 1 and 3 are deleted, and the preparation and coating of the conductive coating are not performed. At the same time, the positive electrode slurry and the ceramic slurry are coated simultaneously during the coating process in Step 6 to directly obtain the positive electrode sheet. The coating density of the active material layer is 40 mg / cm 2 ; the thickness of the ceramic layer is 20 μm, and the width is 6 μm; it does not contain a conductive carbon layer, and the rest is the same;

[0046] In Step 6 of Examples 1-4 and Comparative Examples 1-2, the positive electrode current collector is coated with the positive electrode slurry, and the positive electrode slurry is coated on the carbon layer of the carbon-coated aluminum foil. The coating density of the active material layer is 40 mg / cm 2 ; the positive electrode slurry composition includes positive electrode active material, conductive agent, binder and solvent, the solid content of the slurry is 60%, and the viscosity is 3000-10000 cp. The positive electrode active material is lithium iron phosphate, the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride; the ratio is 95:2:3.

[0047] The batteries prepared in the above examples and comparative examples were subjected to 5 mΩ short circuit test and energy density comparison test, and the results are shown in Table 1 below.

[0048] Table 1

[0049]

[0050] The results show that the short circuit tests of Examples 1-4 mΩ are passed, and the energy density of the battery can be considered. The results of Examples 1-4 and Comparative Example 1 show that the ceramic safety coating can improve the safety of the battery, and then help the battery to pass the short circuit test, mainly because the ceramic coating has good electronic insulation, when the positive and negative electrodes are short-circuited, the ceramic coating will have a certain inhibitory effect on the short circuit, thereby reducing the risk of thermal runaway of the battery. The results of Examples 1-5 and Comparative Example 2 show that when the thickness of the ceramic coating is thick or mixed with the positive electrode slurry, it will cause the weight of the pole piece to increase, thereby affecting the energy density of the battery. By comparing Example 3 and Example 4, the preferred binder PVDF-PVP composite binder is used, and the thickness of the ceramic layer can be controlled to be thinner, and has almost no effect on the energy density of the battery.

[0051] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, and it is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application;

[0052] Therefore, from any point of view, the examples should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0053] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for clarity, those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be properly combined to form other embodiments that those skilled in the art can understand.

Claims

1. A coated aluminum foil, characterized by, The coated aluminum foil comprises an aluminum foil and coating layers arranged on both sides of the aluminum foil; the coating layers comprise a carbon layer arranged at a middle position of the aluminum foil along a width direction of the aluminum foil and ceramic layers arranged on both sides of the aluminum foil.

2. The coated aluminum foil according to claim 1, characterized in that, The carbon layer has a width of 50-500 mm, preferably 100-200 mm, and more preferably 140 mm; and the ceramic layer has a width of 2-10 mm on a single side, preferably 6-8 mm.

3. The coated aluminum foil according to claim 1, wherein The carbon layer has a thickness of 1-5 μm, preferably 1 μm; and the ceramic layer has a thickness of 1-5 μm, preferably 2 μm.

4. The coated aluminum foil according to claim 1, wherein The carbon layer comprises a conductive agent and a conductive binder; preferably, the mass ratio of the conductive agent to the conductive binder is (70-90):(10:30), and more preferably (80-85):(15-20). Preferably, the conductive agent comprises graphene and at least one of conductive carbon black, carbon nanotubes and layered conductive graphite. Preferably, the conductive binder comprises at least one of polyvinylidene fluoride (PVDF), polyacrylate, butadiene styrene rubber and sodium carboxymethyl cellulose.

5. The coated aluminum foil according to claim 1, wherein The ceramic layer comprises ceramic and a ceramic binder. Preferably, the mass ratio of the ceramic to the ceramic binder is (80-90):(10:20), and more preferably 85:

15. Preferably, the ceramic comprises at least one of alumina, zirconia and boehmite. Preferably, the ceramic binder comprises at least one of polyvinylidene fluoride (PVDF), polyacrylate, butadiene styrene rubber, sodium carboxymethyl cellulose and PVDF-PVP composite binder. Preferably, the ceramic binder is a PVDF-PVP composite binder; the PVDF-PVP composite binder comprises PVDF and PVP; and the mass ratio of the PVDF to the PVP is (70-90):(10:30); preferably, the molecular weight of the PVDF is 500,000-800,000, and the molecular weight of the PVP is 40,000-50,000.

6. A process for the production of the coated aluminium foil according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1: preparing a conductive slurry and a ceramic slurry respectively; S2: coating the conductive slurry and the ceramic slurry at a middle position along a width direction of an aluminum foil and on both sides of the aluminum foil along the width direction respectively; S3: drying to complete preparation of the coated aluminum foil. The conductive slurry is prepared by mixing a conductive agent and a conductive binder in a proportion, adding a solvent N-methyl pyrrolidone and mixing uniformly in a double planetary mixer. The ceramic slurry is prepared by mixing ceramic and a ceramic binder in a proportion, adding a solvent N-methyl pyrrolidone and mixing uniformly in a double planetary mixer.

7. The preparation method according to claim 6, characterized in that, The method comprises the following steps: S1: preparing a conductive slurry and a ceramic slurry respectively; S2: coating the conductive slurry and the ceramic slurry at a middle position along a width direction of an aluminum foil and on both sides of the aluminum foil along the width direction respectively; S3: drying to complete preparation of the coated aluminum foil. The active material layer is arranged on the carbon layer.

8. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the positive electrode tab.

9. The positive electrode sheet according to claim 8, characterized by ​ 10. A battery, characterized by ​

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