Preparation method of composite current collector

Abstract

The invention discloses a preparation method of a composite current collector, which belongs to the technical field of current collectors, and comprises the following steps: providing a porous support layer; forming a first filling layer in the supporting layer, wherein the thickness of the first filling layer is smaller than the total thickness of the supporting layer; the supporting layer is filled with n filling layers corresponding to the first filling layer, n is an integer larger than or equal to 1, the total thickness of the formed filling layers is not larger than the total thickness of the supporting layer, and at least one filling layer is a rigid layer and has a relatively large elastic modulus so as to meet the overall mechanical performance of the thin film; a conductive layer is formed on at least one surface layer of the support layer. According to the composite current collector prepared by the invention, the overall mechanical performance of the current collector can be improved to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of current collectors, and in particular to a method for preparing a composite current collector. Background Art

[0002] In secondary batteries, a current collector is needed, which is the part that converges current and is generally made of aluminum foil or copper foil. In the prior art, for safety reasons, a method for preparing a composite current collector is proposed, which includes a polymer support layer and a metal layer arranged on both sides of the support layer, which can improve the safety of subsequent batteries. Compared with metal foil current collectors, this composite structure can also reduce the weight of the current collector and improve the energy density of lithium-ion batteries.

[0003] However, the metal layers on both sides of the composite current collector preparation method are not conductive to each other. In the process of preparing lithium-ion batteries, it is necessary to connect an aluminum sheet to each pole ear before or after the pole sheet is wound, which increases the difficulty of the process.

[0004] In the prior art, a composite matrix based on a conductive mesh and a polymer is used as a supporting layer to improve the electrical conductivity. The polymer layer is enriched as a whole inside the conductive mesh by hot pressing or cast coating. The preparation method is suitable for embedding polymer materials of the same component, but the setting of the polymer layer does not significantly improve the overall thermal conductivity, pressure resistance and deformation resistance.

[0005] Further improvement and optimization are needed.

[0006] Patent Literature:

[0007] 1.CN113451583B Summary of the invention

[0008] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, one object of the present invention is to provide a method for preparing a composite current collector, wherein the prepared current collector can improve the overall mechanical properties of the current collector to a certain extent.

[0009] The technical solution of the present invention is as follows:

[0010] In a first aspect, the present application discloses a method for preparing a composite current collector, comprising the following steps:

[0011] providing a porous support layer;

[0012] forming a first filling layer in the supporting layer, wherein the thickness of the first filling layer is less than the total thickness of the supporting layer;

[0013] Corresponding to the first filling layer, n filling layers are filled inside the supporting layer, where n is an integer greater than or equal to 1, and the total thickness of the formed filling layers is not greater than the total thickness of the supporting layer; wherein at least one filling layer is a rigid layer having a relatively large elastic modulus to meet the overall mechanical properties of the film;

[0014] A conductive layer is formed on at least one surface layer of the support layer.

[0015] Based on the above technical solution, a supporting layer with a high elastic modulus is formed in the supporting layer, so that the size of the supporting layer can be relatively more stable.

[0016] Further, the filling layer is filled in the support layer based on a hot pressing method; and / or, the filling layer is filled in the support layer based on a casting method.

[0017] Based on the above technical solution, a filling layer can be easily formed in the porous supporting layer.

[0018] Furthermore, the filling layer is first filled into the support layer by hot pressing, and the inner filling layer is filled into the support layer by casting.

[0019] Based on the above technical solution, a multi-layer filling layer structure can be formed efficiently and with high quality, which facilitates the formation of a filling layer with better film formation in the inner layer.

[0020] Furthermore, the filling layer is formed in a vacuum environment; preferably, the vacuum degree is set to a low vacuum environment.

[0021] Based on the above technical solution, in a vacuum environment, the gas in the porous support layer can be discharged, thereby forming a relative vacuum environment in the pores, promoting the penetration of the liquid filling layer material, and improving the coating effect and efficiency.

[0022] Furthermore, the porous support layer is a metal mesh layer or a foam metal; preferably, the thickness of the support layer is 4-300 μm.

[0023] Furthermore, the support layer is at least one of an aluminum mesh, a copper mesh, and a nickel mesh, and the filling layer is arranged in the pores of the metal mesh; preferably, the mesh size of the pores is 80-1000 meshes.

[0024] Furthermore, the support layer is at least one of foam copper, foam nickel, foam aluminum, etc., and the filling layer is arranged in the connecting holes of the foam metal; preferably, the porosity is 85%-98%.

[0025] Based on the above technical solution, the support layer material can be easily obtained, and the pore size of the material is suitable, which is conducive to subsequent processing.

[0026] Furthermore, the filling layer material includes a polymer material, which is convenient for filling into the porous support layer; preferably, the polymer material can be selected from PP and PET.

[0027] Based on the above technical solution, the material can be filled into the porous support layer under relatively mild conditions.

[0028] Furthermore, the filling layer material is filled with fillers, and preferably, the fillers are thermally conductive and / or electrically conductive fillers.

[0029] Based on the above technical solution, the filling layer increases the overall mechanical properties of the film and can coordinately control the elastic modulus through the content of the filler; and when the filler is thermally / electrically conductive, the electrical and thermal conductivity of the support layer can be further improved.

[0030] Furthermore, the total thickness of the filling layer with a larger elastic modulus is 0.6-0.8 times the thickness of the conductive mesh layer.

[0031] Based on the above technical solution, while controlling the compressive deformation of the composite support layer, it has a certain elastic deformation capacity, which is beneficial to the subsequent thermal expansion resistance of the battery and improves safety.

[0032] Furthermore, the filling layer having a high elastic modulus is arranged on the inner side of the supporting layer.

[0033] Based on the above technical solution, the clamping effect of other filling layers can be brought into play to avoid subsequent breakage and delamination problems due to large modulus, while ensuring the overall stability of the filling layer.

[0034] Furthermore, the material of the conductive layer is selected from copper, aluminum, nickel, and chromium; and the thickness thereof is set at 0.1-3 μm.

[0035] Furthermore, a local negative pressure area is arranged on one side of the laminating support layer close to the first filling layer.

[0036] Based on the above technical solution, setting a fitted local negative pressure area can promote the infiltration of the casting liquid into the interior, which is beneficial to improving the coating quality and efficiency during subsequent coating, and also makes it easier to control the coating thickness.

[0037] In a second aspect, the present application also discloses a composite current collector prepared based on the above method.

[0038] In a third aspect, the present application also discloses an energy storage device prepared based on the above-mentioned composite current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0040] Figure 1 It is a schematic diagram of the cross-sectional structure of a single-layer conductive mesh layer;

[0041] Figure 2 This is a case where the conductive layer and the pores are arranged on both sides, and the pores on both sides are arranged basically symmetrically.

[0042] The horizontal direction represents the lateral direction, and the vertical direction represents the thickness direction.

[0043] In the figure:

[0044] 1-conductive mesh layer; 21-first filling layer; 22-second filling layer; 23-third filling layer; 3-conductive layer; 4-negative pressure roller. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0046] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0047] In the first aspect, the present application discloses a method for preparing a composite current collector, referring to Figure 1 , including the following steps:

[0048] Providing a porous support layer 1;

[0049] A first filling layer 11 is formed in the support layer 1 near its outer surface, and the thickness of the first filling layer is less than the total thickness of the support layer 1;

[0050] Corresponding to the inner side of the first filling layer 21 ( Figure 1 n filling layers are filled inside the support layer, n is an integer greater than or equal to 1, and the total thickness of the formed filling layers is not greater than the total thickness of the support layer 1; wherein at least one filling layer is a rigid layer having a relatively large elastic modulus to meet the mechanical properties of the entire film;

[0051] A conductive layer 3 is formed on at least one surface layer of the support layer.

[0052] By adopting a segmented filling method, a support layer with a high elastic modulus is formed in the support layer, which can make the size of the support layer relatively more stable. This can solve the problem of composite support layers in the prior art, such as directly filling a polymer layer in a foam metal. In the subsequent battery manufacturing process, the pressure resistance is insufficient, resulting in a large change in the size of the support layer, causing the internal polymer to be squeezed out due to rolling, which is prone to delamination.

[0053] In some embodiments of the present application, the supporting layer of the porous material is a metal mesh layer or a foam metal with a thickness of 4-300 μm; for the metal mesh, such as at least one of an aluminum mesh, a copper mesh, and a nickel mesh, the filling layer is arranged in the pores of the metal mesh, and the mesh number of the pores is 80-1000 mesh; for the foam metal, such as selecting at least one of foam copper, foam nickel, foam aluminum, etc., the filling layer is arranged in the connecting pores of the foam metal, and the porosity is 85%-98%.

[0054] The main body of the filling layer is a polymer as the main carrier, which is convenient for filling into the porous support layer; the relevant polymer material is an existing conventional polymer material, and as a preference, the polymer material can be selected from PP and PET. For the formation of the first filling layer 21, after being bonded to the support layer, the polymer film is hot-pressed and composited at a temperature above the melting point (Tm) and cooled by hot pressing, and the hot pressing pressure is exemplarily set to 0.5-1.5MPa; since the film thickness of the first filling layer 21 is less than the thickness of the support layer, it is only partially embedded in the surface of the filling layer; the first filling layer 21 adopts a hot pressing film filling composite method, which can easily form local filling and also provides a fixed basis for the formation of subsequent filling layers. At the same time, the total thickness of the filling layer with a larger elastic modulus is 0.6-0.8 times the thickness of the conductive mesh layer 1. While controlling the pressure-resistant deformation of the composite support layer, it has a certain elastic deformation capacity, which is beneficial to the subsequent thermal expansion resistance of the battery and improves safety. Furthermore, the filling layer with a high elastic modulus is preferably arranged on the inner side of the supporting layer to give full play to the clamping effect of other filling layers and avoid the subsequent problem of easy breakage and delamination due to the large modulus.

[0055] For the filling layer as a rigid layer, its elastic modulus is exemplarily 1500-6000MPa; and for the filling layer with a smaller modulus, its elastic modulus is exemplarily 500-2000MPa. In addition, fillers such as inorganic fillers can be added to the filling layer to increase the overall mechanical properties of the film, and when conventional thermal conductive fillers such as graphite are further added (such as an addition amount of 3%-10%), the thermal conductivity can be increased to a certain extent, and the elastic modulus can be further controlled by the content of the filler.

[0056] Furthermore, the subsequent filling layer may be formed by casting and / or hot pressing.

[0057] Specifically, for a two-layer filling layer structure, a second filling layer can be further formed by directly adopting a hot pressing method;

[0058] For structures with more than two filling layers, the internal filling layers can be laminated sequentially by hot pressing. However, in this method, the material of the next filling layer can only penetrate inward more easily under pressure after the previous filling layer is melted, which will affect the processing efficiency and filling rate.

[0059] Therefore, if Figure 1 The filling layer of the middle three-layer structure, preferably the inner filling layer, is coated by scraping and casting to form a second filling layer 22. At this time, the second filling layer 22 corresponds to a filling layer with a high elastic modulus. The above-mentioned casting coating process is an existing conventional coating method and will not be repeated. At this time, the key lies in the selection of the coating amount. Based on the thickness of the support layer and the pore specifications (size or porosity), a suitable coating amount can be determined through a limited number of experiments to achieve local coating on the inner layer of the support layer. During coating, the temperature of the relevant polymer coating liquid during the casting coating process should be kept above its melting temperature to promote the gravity self-penetration effect of the coating; of course, a release agent can also be further coated on the composite side surface to prevent part of the filling layer material that is not completely filled into the interior of the support layer from being peeled off together with the release agent layer later. The release agent can be a release agent known in the art, such as: silicone release agent, fluorine release agent, etc.

[0060] To further increase the penetration effect, coating can be carried out in a vacuum environment, and related components can be set in a vacuum chamber. Cast coating is carried out in a vacuum environment. In a vacuum environment, the gas in the porous support layer can be discharged, and then a vacuum environment is relatively formed in the pores, which promotes the penetration of the coating liquid, improves the coating effect and efficiency, and forms a second filling layer 22 after curing; the vacuum degree is set to a low vacuum environment, such as 0.01-0.09MPa.

[0061] Similarly, a third filling layer 23 is formed on the surface of the second filling layer 22 by further hot pressing and laminating.

[0062] Finally, a conductive layer 3 is formed on the surface of the obtained composite support layer. Figure 1 In the figure, only the case of forming a conductive layer on one side is shown. At this time, based on the deposition process, vapor deposition, such as evaporation and sputtering, can be selected. Since the porous support layer is a conductive material, water electroplating can also be used. The material can be copper, aluminum, nickel, chromium, etc., and the thickness is set at 0.1-3μm. Of course, it can also be applied to the case of setting a conductive layer on both sides of the support layer.

[0063] Further references Figure 2The main difference is that, in order to further increase the quality of the filling layer after cast filling, a local negative pressure zone is set on the side of the bonding support layer close to the first filling layer 21, and the negative pressure zone forms a negative pressure relative to the ambient pressure.

[0064] Setting a close local negative pressure area can promote the infiltration of the casting liquid into the interior, which is beneficial to improving the coating quality and efficiency during cast coating, and also makes it easier to control the coating thickness.

[0065] Taking into account that the first filling layer 21 is hot-pressed composite, due to the heating and melting of the filling layer material, recrystallization will occur during the hot-pressing composite process to further increase the crystallinity, and after cooling and solidification, the volume of the filling layer filled in the pores of the support layer decreases and further shrinks, so that there will be a small number of pores in the porous support layer (that is, having a certain porosity). Therefore, under negative pressure, the gas in the support layer can be extracted more quickly, which is conducive to the penetration of the casting liquid and concentrated on the inner surface of the first filling layer 21, thereby forming the second filling layer 22 after solidification, and then continuing to form the third filling layer 23 on the surface of the second filling layer by hot pressing.

[0066] Specifically, the negative pressure zone is set as a negative pressure roller 4, a plurality of through holes are formed on the surface of the negative pressure roller 4, and an external vacuum device is connected through a rotary joint and a pipeline at one end of the rotating shaft of the negative pressure roller 4. The negative pressure device, such as a vacuum pump system, is used together with a filter. The relevant device is a conventional device available on the market and will not be described in detail. At this time, the supporting layer film material can be matched with other guide rollers to fit on the surface of the roller body for continuous processing.

[0067] In addition, the present invention is also applicable to the case of more filling layers; similarly, for the case of multiple supporting layers, the filling layers can be composited at the composite locations of the supporting layers by hot pressing, and connected at the interfaces by the filling layers.

[0068] The present application also discloses a composite current collector prepared based on the above preparation method, and an energy storage device based on the current collector, such as a lithium battery, the preparation method and process of which can be prepared according to the conventional lithium battery

[0069] Example

[0070] Embodiment 1

[0071] Choose aluminum foam of about 12μm with a porosity of 95%;

[0072] First, a PET filling layer of about 3 μm is filled by hot pressing, and then a PET filling layer containing 5% graphite is filled to form a filling layer with a total thickness of about 11 μm, and then an aluminum layer of about 1 μm is evaporated on the surface of the support layer.

[0073] Embodiment 2

[0074] The difference from the first embodiment is that a 15 μm aluminum mesh with a mesh size of 600 is selected.

[0075] Embodiment 3

[0076] According to Figure 1 The process of preparing the composite current collector is as follows:

[0077] Choose aluminum foam of about 30μm with a porosity of 95%;

[0078] First, a PP filling layer of about 6 μm is hot-pressed and filled. Subsequently, a PP filling layer containing about 5% graphite is cast under a vacuum degree of 0.05 MPa, with a filling thickness of about 15 μm. Finally, the PP filling layer is hot-pressed again to form a filling layer with a total thickness of about 28 μm, and then an aluminum layer of about 1 μm is evaporated on the surface of the support layer.

[0079] Embodiment 4

[0080] According to Figure 2 The process for preparing the composite current collector is different from that of Example 3 in that, during the casting process, a negative pressure roller is arranged on the side of the PP filling layer formed by hot pressing.

[0081] Embodiment 5

[0082] The difference between the embodiment 1 and the fourth embodiment is that five filling layers are formed with intervals.

[0083] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the drawings or conventionally expressed in the prior art, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0084] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0085] The term "multiple" as used in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple sheets" refers to more than two sheets (including two sheets).

[0086] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a composite current collector, comprising the following steps: providing a porous support layer; It is characterized in that forming a first filling layer in the supporting layer, wherein the thickness of the first filling layer is less than the total thickness of the supporting layer; Corresponding to the first filling layer, n filling layers are filled inside the supporting layer, where n is an integer greater than or equal to 1, and the total thickness of the formed filling layers is not greater than the total thickness of the supporting layer, wherein at least one filling layer is a rigid layer having a relatively large elastic modulus to meet the overall mechanical properties of the film; A conductive layer is formed on at least one surface layer of the support layer.

2. The method for preparing the composite current collector according to claim 1, characterized in that: The filling layer is filled in the support layer based on a hot pressing method; and / or, the filling layer is filled in the support layer based on a casting method.

3. The method for preparing the composite current collector according to claim 2, characterized in that: The filling layer is first filled in the support layer by hot pressing, and the inner filling layer is filled in the support layer by casting.

4. The method for preparing a composite current collector according to claim 2 or 3, characterized in that: The filling layer is formed under a vacuum environment.

5. The method for preparing the composite current collector according to claim 4, characterized in that: A local negative pressure area is arranged on one side of the laminating support layer close to the first filling layer.

6. The method for preparing the composite current collector according to claim 5, characterized in that: The porous support layer is a metal mesh layer or foam metal; the thickness of the support layer is 4-300 μm.

7. The method for preparing a composite current collector according to claim 6, characterized in that: The supporting layer is at least one of an aluminum mesh, a copper mesh, and a nickel mesh, and the filling layer is arranged in the pores of the metal mesh, and the mesh number of the pores is 80-1000 meshes; or, The supporting layer is at least one of foam copper, foam nickel, foam aluminum and the like, and the filling layer is arranged in the connecting holes of the foam metal, with a porosity of 85%-98%.

8. The method for preparing a composite current collector according to claim 5, characterized in that: The filling layer material includes a polymer material.

9. The method for preparing a composite current collector according to claim 8, characterized in that: The filling layer material is filled with fillers, and the fillers are thermally conductive and / or electrically conductive fillers.

10. The method for preparing a composite current collector according to claim 8 or 9, characterized in that: The total thickness of the filling layer with a larger elastic modulus is 0.6-0.8 times the thickness of the conductive mesh layer; and / or the filling layer with a high elastic modulus is arranged on the inner side of the support layer.

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