A composite current collector, a preparation method thereof and a lithium battery positive plate containing the composite current collector

Abstract

The application discloses a composite current collector and a preparation method thereof, and a lithium battery positive plate containing the composite current collector and a preparation method thereof. The composite current collector comprises a substrate layer, a temperature control layer and a metal layer. The temperature control layer is arranged on the opposite surfaces of the substrate layer respectively, and the metal layer is arranged on the surface of the temperature control layer away from the substrate layer. The temperature control layer is made of glass fiber. When the positive plate made of the composite current collector is hot-rolled, the edge margin area for cutting the tab will not soften and deform due to heating, and when the positive plate is cold-rolled, the shrinkage and deformation of the substrate layer of the composite current collector will not be caused due to the poor ductility of the substrate layer itself, so that the wrinkle problem of the substrate layer of the composite current collector is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite current collector and its preparation method, and a lithium battery positive electrode containing the composite current collector and its preparation method. Background Technology

[0002] Lithium-ion batteries, as a new energy source, have advantages such as high operating voltage, high specific capacity, long charge / discharge life, and no memory effect. As lithium-ion batteries gradually become the mainstream energy choice, the demand for them is increasing. At the same time, the safety of lithium-ion batteries is becoming a growing concern, and the manufacturing direction of lithium-ion batteries is gradually shifting towards high energy and high capacity. This leads to the development of battery cells towards lightweighting and enhanced safety.

[0003] Currently, commercially available lithium batteries primarily use copper and aluminum foil as current collectors for electron transport. Both copper and aluminum foil have very high densities. To reduce the impact of copper or aluminum foil on battery energy density, composite current collectors with lower-density polymer materials as the substrate and metal-plated surfaces are used instead of pure metal foils. While this solves the weight reduction problem, it also brings other adverse effects. For example, in ternary lithium-ion cells, the positive electrode rolling process typically uses heating, reaching temperatures of 100–120°C. The polymer layer of the substrate covering the active material area on the composite current collector is less affected by temperature, but the coated blank areas, which serve as the tabs, are affected by high temperatures during hot pressing. After rolling, the polymer layer in these blank areas softens, resulting in wrinkles. Chinese patent application CN113707886A discloses a composite current collector that uses a polyurethane-based material with low thermal conductivity deposited between the base layer and the metal layer to completely isolate heat conduction. However, the substrate layer of the composite current collector itself has poor ductility, and the current collector, which completely isolates heat, will shrink and deform during rolling due to its poor ductility. Therefore, the current use of composite current collectors results in wrinkles at the edges of the rolled electrode, and is also detrimental to subsequent laser cutting and sheet fabrication of the electrode, and may even cause the electrode tabs to fold during the winding process, leading to serious short circuits. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a composite current collector that does not experience thermal softening or cold shrinkage during the rolling process of the positive electrode sheet.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] A composite current collector includes a substrate layer, a temperature control layer, and a metal layer; the temperature control layer is disposed on two opposite surfaces of the substrate layer, and the metal layer is disposed on the surface of the temperature control layer away from the substrate layer; wherein the temperature control layer is made of glass fiber.

[0007] Preferably, the substrate layer is a polymer film substrate.

[0008] Preferably, the material of the substrate layer includes one or more of polyethylene, polytetrafluoroethylene, polypropylene, polyacrylonitrile, polyethylene terephthalate, polyethylene naphthalate, and acrylonitrile-styrene copolymer.

[0009] Preferably, the glass fiber has a tensile strength ≥210MPa and an elongation range of 0.2% to 0.5%.

[0010] Preferably, the thickness of the temperature control layer is in the range of 0.01 to 0.1 μm.

[0011] Preferably, during the hot roller pressing of the electrode sheet, the temperature control layer conducts a temperature of 50-80°C to the substrate layer; the thermal conductivity of the temperature control layer material is in the range of 0.03-0.1 W / mK.

[0012] Preferably, the thickness of the metal layer is in the range of 0.4 to 0.7 μm; the metal layer is an aluminum layer.

[0013] The present invention also proposes a method for preparing the aforementioned composite current collector, comprising the following steps:

[0014] S1. Perform plasma cleaning on the substrate surface to remove surface impurities;

[0015] S2. Prepare temperature control layers on both surfaces of the substrate after plasma cleaning;

[0016] S3. Prepare a metal layer on the surface of the temperature control layer to obtain the composite current collector.

[0017] Preferably, in S2, a temperature control layer is prepared on both surfaces of the plasma-cleaned substrate by electrospinning.

[0018] Preferably, in S3, a metal layer is prepared on the surface of the temperature control layer by means of vapor deposition or magnetic controlled sputtering to obtain the composite current collector.

[0019] The present invention also proposes a lithium battery positive electrode sheet containing the aforementioned composite current collector.

[0020] This invention also proposes a method for preparing the aforementioned lithium battery positive electrode sheet, comprising the following steps:

[0021] S1. A positive electrode active material is uniformly coated on a composite current collector to form a positive electrode active material layer, thereby obtaining a coated electrode sheet, wherein the thickness of the positive electrode active material layer is 120-130 μm.

[0022] S2. Roll the coated electrode sheet as described above. The rolling process is carried out using a hot roller method at a temperature of 100-120℃ to obtain the lithium battery positive electrode sheet.

[0023] The advantages of this invention are as follows: This invention proposes a composite current collector. By adding a temperature control layer made of glass fiber between the substrate polymer layer and the metal layer, the current collector can conduct 50-80°C of temperature to the substrate layer during the hot rolling pressing of the electrode. Through the heat absorption capacity of the material, the heat energy absorbed by the outer surface metal is prevented from directly affecting the thermal softening of the substrate polymer layer. It also prevents complete heat isolation; by regulating the temperature through the temperature control layer, partial heat transfer is achieved, avoiding cold shrinkage and deformation of the substrate layer. This invention ensures that the current collector does not experience thermal softening or cold shrinkage during the rolling process of the positive electrode, especially in the uncoated blank areas.

[0024] This invention improves the structural layer of the composite current collector, making the polymer material of the current collector substrate layer less susceptible to the temperature effect of positive electrode rolling. This greatly improves the processing performance of the electrode sheet, increases the pass rate of rolling, sheet making, and winding, and reduces defects such as rolling strip breakage, electrode ear shrinkage and wrinkling, and electrode ear folding. At the same time, it also reduces the production cost problem caused by scrap. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in Embodiment 1 of the present invention;

[0026] Figure description: 1-Substrate layer, 2-Temperature control layer, 3-Metal layer, which are the basic components of the composite current collector; 4-Positive electrode active material layer;

[0027] Figure 2 This is a diagram showing the edge wrinkling of the electrode sheet prepared in Example 1 of the present invention;

[0028] Figure 3 This is a diagram showing the edge wrinkling of the electrode sheet prepared in Example 2 of the present invention;

[0029] Figure 4 This is a diagram showing the edge wrinkling of the electrode sheet prepared in Example 3 of the present invention;

[0030] Figure 5 This is a diagram showing the edge wrinkling of the electrode sheet prepared in Example 4 of the present invention;

[0031] Figure 6 This is a diagram showing the edge wrinkling of the electrode sheet prepared in Comparative Example 1 of this invention;

[0032] Figure 7 This is a diagram showing the edge wrinkles of the electrode prepared in Comparative Example 2 of this invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0035] Unless otherwise specified in the embodiments, any techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0036] In the following embodiments, the glass fiber has a tensile strength ≥210MPa and an elongation range of 0.3%.

[0037] Example 1

[0038] A method for preparing a composite current collector includes the following steps:

[0039] S1. An organic polymer polyethylene terephthalate resin film is used as the substrate layer, and the substrate layer is subjected to plasma treatment to remove impurities on the surface of the substrate layer.

[0040] S2. A temperature control layer with a thickness of 0.08 μm is prepared on the upper and lower surfaces of the plasma-treated film by electrospinning; the temperature control layer is made of glass fiber with a thermal conductivity of 0.05 W / mK.

[0041] S3. A 0.5 μm thick aluminum layer is prepared on the surface of the temperature control layer by vacuum evaporation to obtain a composite current collector.

[0042] A coated electrode sheet is obtained by coating a positive electrode active material with the aforementioned composite current collector as foil to form a positive electrode active material layer. The electrode sheet is then rolled to obtain a lithium battery positive electrode sheet. The rolling process uses a hot roller method at 120°C. During the rolling process, a temperature control layer conducts a temperature of 60°C to the substrate layer. The positive electrode sheet has uncoated blank areas at its edges, and the active material layer has a thickness of 125 μm. A schematic diagram of the lithium battery positive electrode sheet is shown below. Figure 1 As shown, 1 is the substrate layer, 2 is the temperature control layer, 3 is the aluminum metal layer, which are the basic components of the composite current collector; 4 is the positive electrode active material layer.

[0043] Example 2

[0044] A method for preparing a composite current collector includes the following steps:

[0045] S1. An organic polymer polyethylene terephthalate resin film is used as the substrate layer, and the substrate layer is subjected to plasma treatment to remove impurities on the surface of the substrate layer.

[0046] S2. A temperature control layer with a thickness of 0.08 μm is prepared on the upper and lower surfaces of the plasma-treated film by electrospinning; the temperature control layer is made of glass fiber with a thermal conductivity of 0.08 W / mK.

[0047] S3. A 0.5 μm thick aluminum layer is prepared on the surface of the temperature control layer by vacuum evaporation to obtain a composite current collector.

[0048] The positive electrode is coated with a positive active material by using the above-mentioned composite current collector as foil to form a positive active material layer, and then rolled to obtain a lithium battery positive electrode sheet. The rolling process is carried out by hot rolling at a temperature of 120°C. During the rolling process, the temperature control layer conducts a temperature of 65°C to the substrate layer. The positive electrode sheet has an uncoated blank area at the edge, and the active material layer has a thickness of 125μm.

[0049] Example 3

[0050] A method for preparing a composite current collector includes the following steps:

[0051] S1. An organic polymer polytetrafluoroethylene film is used as the substrate layer, and the substrate layer is subjected to plasma treatment to remove impurities on the surface of the substrate layer.

[0052] S2. A temperature control layer with a thickness of 0.1 μm is prepared on the upper and lower surfaces of the plasma-treated film by electrospinning; the temperature control layer is made of glass fiber with a thermal conductivity of 0.03 W / mK.

[0053] S3. A 0.7 μm thick aluminum layer is prepared on the surface of the temperature control layer by vacuum evaporation to obtain a composite current collector.

[0054] The positive electrode is formed by coating the positive electrode active material with the above-mentioned composite current collector as foil to obtain a coated electrode sheet, which is then rolled to obtain a lithium battery positive electrode sheet. The rolling process is carried out by hot rolling at a temperature of 100°C. During the rolling process, the temperature control layer conducts a temperature of 55°C to the substrate layer. The positive electrode sheet has an uncoated blank area at the edge, and the active material layer has a thickness of 120μm.

[0055] Example 4

[0056] A method for preparing a composite current collector includes the following steps:

[0057] S1. An organic polymer polyethylene film is used as the substrate layer, and the substrate layer is subjected to plasma treatment to remove impurities on the surface of the substrate layer.

[0058] S2. A temperature control layer with a thickness of 0.1 μm is prepared on the upper and lower surfaces of the plasma-treated film by electrospinning; the temperature control layer is made of glass fiber with a thermal conductivity of 0.08 W / mK.

[0059] S3. A 0.4 μm thick aluminum layer is prepared on the surface of the temperature control layer by vacuum evaporation to obtain a composite current collector.

[0060] The positive electrode is coated with a positive active material by using the above-mentioned composite current collector as foil to form a positive active material layer, and then rolled to obtain a lithium battery positive electrode sheet. The rolling process is carried out by hot rolling at a temperature of 120°C. During the rolling process, the temperature control layer conducts a temperature of 65°C to the substrate layer. The positive electrode sheet has an uncoated blank area at the edge, and the active material layer has a thickness of 130μm.

[0061] Comparative Example 1

[0062] The only difference between the preparation method of the composite current collector and Example 1 is that it does not include step S2, resulting in a composite current collector without a temperature control layer; the composite current collector without a temperature control layer is used as the coating foil to prepare the positive electrode sheet of the lithium battery according to the method of Example 1.

[0063] Comparative Example 2

[0064] S1. An organic polymer polyethylene terephthalate resin film is used as the substrate layer, and the substrate layer is subjected to plasma treatment to remove impurities on the surface of the substrate layer.

[0065] S2. Polyurethane with a thickness of 0.08 μm was prepared on the upper and lower surfaces of the plasma-treated film by electrospinning; the thermal conductivity of the polyurethane material was 0.018 W / mK.

[0066] S3. A 0.5 μm thick aluminum layer is prepared on the surface of the polyurethane by vacuum evaporation to obtain a composite current collector;

[0067] S4. The positive electrode sheet is obtained by coating and rolling using the above composite current collector as foil material. The rolling is carried out by hot rolling at a temperature of 120°C. The positive electrode sheet has an uncoated blank area at the edge, and the coating active material layer has a thickness of 125μm.

[0068] The following table compares the edge wrinkling of the electrodes prepared in Examples 1-4 and Comparative Examples 1-2:

[0069]

[0070] From the above table and Figure 2-7 The verification results show that the electrode sheet of the present invention exhibits significantly better shrinkage and wrinkling of the composite current collector under hot rolling pressure than the comparative example. This demonstrates that the present invention effectively improves the rolling pressure process of traditional composite current collectors.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite current collector, characterized in that: It includes a substrate layer, a temperature control layer, and a metal layer; the temperature control layer is disposed on two surfaces opposite to the substrate layer, and the metal layer is disposed on the surface of the temperature control layer away from the substrate layer; wherein, the temperature control layer is made of glass fiber; during hot roller pressing of the electrode sheet, the temperature control layer conducts a temperature of 50~80°C to the substrate layer; the thermal conductivity of the temperature control layer material is in the range of 0.03~0.1W / mK.

2. The composite current collector according to claim 1, characterized in that: The substrate layer is a polymer thin film substrate.

3. The composite current collector according to claim 1, characterized in that: The material of the substrate layer includes one or more of polyethylene, polytetrafluoroethylene, polypropylene, polyacrylonitrile, polyethylene terephthalate, polyethylene naphthalate, and acrylonitrile-styrene copolymer.

4. The composite current collector according to claim 1, characterized in that: The glass fiber has a tensile strength ≥210MPa and an elongation range of 0.2%~0.5%.

5. The composite current collector according to claim 1, characterized in that: The thickness of the temperature control layer ranges from 0.01 to 0.1 μm.

6. The composite current collector according to claim 1, characterized in that: During the hot roller pressing of the electrode sheet, the temperature control layer conducts a temperature of 50~80℃ to the substrate layer; the thermal conductivity of the temperature control layer material is in the range of 0.08W / mK.

7. The composite current collector according to any one of claims 1-6, characterized in that: The thickness of the metal layer ranges from 0.4 to 0.7 μm; the metal layer is an aluminum layer.

8. A method for preparing a composite current collector as described in any one of claims 1-7, characterized in that: Includes the following steps: S1. Perform plasma cleaning on the substrate surface to remove surface impurities; S2. Prepare temperature control layers on both surfaces of the substrate after plasma cleaning; S3. Prepare a metal layer on the surface of the temperature control layer to obtain the composite current collector.

9. A lithium battery positive electrode sheet, characterized in that: Contains a composite current collector as described in any one of claims 1-7.

10. A method for preparing a lithium battery positive electrode sheet as described in claim 9, characterized in that: Includes the following steps: S1. A positive electrode active material is uniformly coated on a composite current collector to form a positive electrode active material layer, thereby obtaining a coated electrode sheet, wherein the thickness of the positive electrode active material layer is 120~130μm; S2. Roll the coated electrode sheet as described above. The rolling process is carried out using a hot roller method at a temperature of 100-120℃ to obtain the lithium battery positive electrode sheet.

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