Composite current collector and preparation method thereof

Abstract

The invention discloses a composite current collector and a preparation method thereof, the composite current collector comprises a thin film layer and metal conductive layers arranged on the upper side and the lower side of the thin film layer, and the upper end face and the lower end face of the thin film layer are constructed to be of a stepped structure so as to be in direct or indirect contact with the metal conductive layers. Compared with a composite current collector of a traditional structure, the composite current collector has the advantages that when the metal conductive layer and the thin film layer are directly or indirectly combined, the contact area of the metal conductive layer and the thin film layer can be increased due to the arrangement of the stepped structure, the binding force between the metal conductive layer and the thin film layer can be enhanced, and the tensile property of the composite current collector is better; meanwhile, due to the existence of the step-shaped structure, the metal conducting layer is thicker, and the improvement of the flow conductivity of the composite current collector is facilitated.

Description

Technical Field

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

[0002] The composite current collector has a "sandwich" structure, with the middle layer being a polymer film layer, common materials include PP (polypropylene), PET (polyethylene terephthalate), etc., and metal conductive layers on both sides, such as copper metal or aluminum metal. In order to increase the bonding strength between the metal conductive layer and the film layer, the prior art often sets a conductive glue between the film layer and the metal conductive layer or adds other substances that improve the bonding strength between the metal conductive layer and the film layer; on the one hand, this will increase the cost of the composite current collector, making the composite current collector lose its cost advantage compared to traditional current collectors, limiting the commercial application of the composite current collector, and on the other hand, it has limited effect on improving the bonding strength between the metal conductive layer and the film layer, but instead increases the weight of the composite current collector.

[0003] In addition, when the middle film layer of the current composite current collector is welded to the pole ear on the edge of the composite current collector, due to the presence of the middle film layer, during welding, the middle film layer will form a mixture of metal and film melt at high temperature, which will greatly affect the electrons at the welding point of the pole ear and increase the heat generation of the battery using the composite current collector.

[0004] Therefore the prior art still needs to be improved and enhanced. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a composite current collector and a preparation method thereof, so as to solve at least one problem existing in the composite current collector described in the background art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A composite current collector comprises a thin film layer and a metal conductive layer arranged on the upper and lower sides of the thin film layer. The upper and lower end surfaces of the thin film layer are constructed to have a stepped structure so as to directly or indirectly contact the metal conductive layer.

[0008] The stepped structure has multiple step surfaces, including a top step surface, a bottom step surface and multiple intermediate step surfaces. Based on the reference plane of the thin film layer and along the length direction of the thin film layer, the intermediate step surfaces and the bottom step surfaces are sequentially arranged on both sides of the top step surface, and the height from the top step surface, the intermediate step surface to the bottom step surface gradually decreases.

[0009] The step-like structures are symmetrically distributed in the length direction of the film layer.

[0010] Based on the reference plane, a ratio of a height of the top step surface to a height of the bottom step surface is 3:1 to 6:1.

[0011] Along the length direction of the film layer, the width of the top step surface is 10 um-1 cm.

[0012] A filling space is formed at at least one of the top step surface, the middle step surface, and the bottom step surface to expose the inside of the film layer, and a bottom surface of the filling space is higher than the reference surface.

[0013] A cross section of the filling space taken along a plane parallel to the reference plane is circular, and a diameter of the filling space is 10 nm-100 nm.

[0014] A cross section of the filling space taken along a plane parallel to the reference plane has the same shape as the intermediate step surface.

[0015] An intermediate connection layer is also provided between the thin film layer and the metal conductive layer; the material of the intermediate connection layer is one of aluminum oxide, silicon nitride, nickel alloy, copper alloy, and aluminum alloy; the top step surface is flush with the end surface of the metal conductive layer.

[0016] A method for preparing the composite current collector comprises the following steps:

[0017] The end surface of the thin film layer is configured to have a stepped structure by etching;

[0018] The metal conductive layer is plated on the stepped structure of the thin film layer.

[0019] Compared with the prior art, the present invention provides a composite current collector and a preparation method thereof, wherein the composite current collector includes a thin film layer and a metal conductive layer disposed on the upper and lower sides of the thin film layer, and the upper and lower end surfaces of the thin film layer are configured to have a stepped structure to directly or indirectly contact the metal conductive layer. Compared with the composite current collector of the traditional structure, when the metal conductive layer and the thin film layer are directly or indirectly combined, the stepped structure of the composite current collector of the present application will increase the contact area between the two, which is beneficial to enhance the bonding force between the metal conductive layer and the thin film layer, so that the tensile properties of the composite current collector are better; at the same time, due to the presence of the stepped structure, the metal conductive layer is thicker, which is beneficial to improve the conductivity of the composite current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of a thin film layer with a stepped structure in the composite current collector provided by the present invention.

[0021] Figure 2This is a schematic structural diagram of the composite current collector according to the first embodiment of the present invention.

[0022] Figure 3 This is a schematic structural diagram of a composite current collector according to a second embodiment of the present invention.

[0023] Figure 4 This is a schematic structural diagram of a composite current collector according to a third embodiment of the present invention.

[0024] Figure 5 This is a schematic structural diagram of a composite current collector according to a fourth embodiment of the present invention.

[0025] Figure 6 A schematic diagram of the structure of a composite current collector provided by the present invention that is improved on the basis of the third embodiment.

[0026] Figure 7 A schematic structural diagram of a composite current collector provided with an intermediate connecting layer provided by the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] It should be noted that when a component is referred to as being "mounted on", "fixed on" or "disposed on" another component, it may be directly on the other component or there may be a central component at the same time. When a component is referred to as being "connected to" another component, it may be directly connected to the other component or there may be a central component at the same time.

[0029] It should also be noted that the directional terms such as left, right, up, and down in the embodiments of the present invention are merely relative concepts or are based on the normal use status of the product and should not be considered as restrictive.

[0030] The composite current collector has a "sandwich" structure, with the middle layer being a polymer film layer, common materials include PP (polypropylene), PET (polyethylene terephthalate), etc., and metal conductive layers on both sides, such as copper metal or aluminum metal. In order to increase the bonding strength between the metal conductive layer and the film layer, the prior art often sets a conductive glue between the film layer and the metal conductive layer or adds other substances that improve the bonding strength between the metal conductive layer and the film layer; on the one hand, this will increase the cost of the composite current collector, making the composite current collector lose its cost advantage compared to traditional current collectors, limiting the commercial application of the composite current collector, and on the other hand, it has limited effect on improving the bonding strength between the metal conductive layer and the film layer, but instead increases the weight of the composite current collector.

[0031] In addition, when the middle film layer of the current composite current collector is welded to the pole ear on the edge of the composite current collector, due to the presence of the middle film layer, during welding, the middle film layer will form a mixture of metal and film melt at high temperature, which will greatly affect the electrons at the welding point of the pole ear and increase the heat generation of the battery using the composite current collector.

[0032] The present invention provides a composite current collector, see Figure 1 - Figure 7 , including a thin film layer 1 and a metal conductive layer 2 respectively arranged on the upper and lower sides of the thin film layer 1, and the upper and lower end surfaces of the thin film layer 1 are constructed to have a stepped structure so as to directly or indirectly contact the metal conductive layer 2. Compared with the composite current collector of the traditional structure, when the metal conductive layer 2 is directly or indirectly combined with the thin film layer 1, the stepped structure of the composite current collector of the present application will increase the contact area between the two, which is beneficial to enhance the bonding force between the metal conductive layer 2 and the thin film layer 1, so that the tensile performance of the composite current collector is better; at the same time, due to the presence of the stepped structure, the metal conductive layer 2 is thicker, which is beneficial to improve the conductivity of the composite current collector.

[0033] Further, the stepped structure has a plurality of step surfaces, the step surfaces include a top step surface 31, a bottom step surface 32 and a plurality of intermediate step surfaces 33. Based on the reference plane 10 of the thin film layer 1 and along the length direction of the thin film layer 1, the intermediate step surface 33 and the bottom step surface 32 are sequentially arranged on both sides of the top step surface 31, and the height from the top step surface 31, the intermediate step surface 33 to the bottom step surface 32 gradually decreases. In the present application, since the height of the bottom step surfaces 32 on both sides is relatively low, after the thin film layer 1 is combined with the metal layer, the metal conductive layer 2 corresponding to the position of the bottom step surface 32 is relatively thick, which can reduce the internal resistance during the welding of the pole tab. In the embodiment of the present application, the number of the step surfaces is 6-11, that is, the number of the top step surface 31 is 1, the number of the bottom step surfaces 32 is 2 and they are respectively located at the outermost side of the step surface, and the rest are intermediate step surfaces 33. Preferably, the number of intermediate step surfaces 33 on both sides of the top step surface 31 is the same, and the tensile strength of the composite current collector is better at this time. It should be noted that the reference plane 10 in this application is virtual, which is used as a reference to define the height of the step surface later; Figure 1 A schematic diagram of the structure of the thin film layer 1 and Figure 2 - Figure 7 The structural schematic diagrams of the composite current collectors are all symmetrical from top to bottom. Figure 1 A schematic diagram of the structure of the thin film layer 1 and Figure 3 - Figure 7 The structural schematic diagram of the composite current collector is bilaterally symmetrical, so some corresponding positions in the accompanying drawings are omitted. Figure 1 - Figure 7 The structure of the structural schematic diagram shown is formed along the length direction and height direction of the film layer 1, wherein the horizontal direction is the length direction of the film layer 1, and the vertical direction is the height direction of the film layer 1. Figure 1 The top step surface 31 is located in the middle of the film layer 1 , the bottom step surface 32 is located on both sides of the film layer 1 , and a plurality of middle step surfaces 33 are arranged between the top step surface 31 and the bottom step surfaces 32 on both sides.

[0034] In the present application, the top step surface 31, the bottom step surface 32 and the plurality of intermediate step surfaces 33 are all arranged in the horizontal direction, and the top step surface 31 and the adjacent intermediate step surface 33, the two adjacent intermediate step surfaces 33, and the intermediate step surface 33 and the bottom step surface 32 are provided with a step height surface 35 in the thickness direction of the film layer 1 to connect the two adjacent step surfaces. The step height surfaces 35 in the embodiment of the present application are all parallel to the thickness direction of the film layer 1, that is, the setting direction of the step height surface 35 is perpendicular to the length direction of the film layer 1. Further, in order to avoid the stress concentration of the right-angle step formed by the step height surface 35 and the step surface, the step height surface 35 can be inclined, and the inclination angle of the step height surface 35 and the reference surface 10 is 30°-60°, so as to disperse the stress and improve the anti-bending fatigue life; in addition, the inclined step height surface 35 can better adapt to the processing technology, for example, a small angle is used for high laser etching precision, and a large angle is used for low chemical etching precision.

[0035] In the present application, the projected heights of the step height surface 35 between two adjacent step surfaces among the top step surface 31, the bottom step surface 32 and the multiple intermediate step surfaces 33 in the height direction of the thin film layer 1 are the same or different. The projected height of the step height surface 35 in the height direction of the thin film layer 1 can be set according to the difference in thermal expansion coefficients between the metal conductive layer 2 and the thin film layer 1 to reduce the shear stress under temperature cycling; the top step surface 31 occupies 10%-35% of the length direction of the thin film layer 1, and the width of the top step surface 31 can be beneficial to improving the overall tensile strength. Of course, alternatively, the step height surface 35 can also adopt a smooth arc transition or set an arc chamfer at the connection between the step surface and the step height surface 35, which is easier to achieve during the preparation process and can reduce stress concentration; further, by limiting the roughness Ra of the top step surface 31, the intermediate step surface 33, the bottom step surface 32 and the step height surface 35 to 0.01um-0.2um, good contact between the metal conductive layer 2 and the thin film layer 1 can be ensured. As Figure 6 As shown, the step height surface 35 between adjacent step surfaces adopts an arc line.

[0036] In the first embodiment of this application, please refer to Figure 1 and 2, the top step surface 31 is not in the middle position in the length direction of the film layer 1, that is, in this embodiment, the number of intermediate step surfaces 33 between the top step surface 31 and the bottom step surfaces 32 on both sides is different, the number of intermediate step surfaces 33 on one side is more, and the number of intermediate step surfaces 33 on the other side is less. In the second embodiment of this application, please refer to Figure 1 and Figure 3 , the step-like structure is symmetrically distributed up and down and left and right in the length direction of the thin film layer 1, that is, in this embodiment, the number of intermediate step surfaces 33 between the top step surface 31 and the bottom step surfaces 32 on both sides is the same. Compared with the second embodiment, the first embodiment has the disadvantage that when the thin film layer 1 is subjected to a tensile test along its length direction, the number of intermediate step surfaces 33 on both sides of the top step surface 31 is inconsistent, which will affect the tensile strength of the thin film layer 1, and further affect the tensile strength of the composite current collector; the structure of the second embodiment of the present application is conducive to balancing the electrical properties on both sides of the current collector.

[0037] Further, based on the reference plane 10, the ratio of the height of the top step surface 31 to the height of the bottom step surface 32 is 3:1 to 6:1. Specifically, the height of the bottom step surface 32 is 1um-1.5um, and the height of the top step surface 31 is 3um-6um. The height of the stepped structure is limited by the above values ​​to ensure that the film layer 1 has sufficient mechanical support to resist external force deformation during charging and discharging, and at the same time avoid the excessive thickness of the film layer 1, which leads to an increase in the weight of the composite current collector and reduces the effective space occupied inside the battery.

[0038] Furthermore, along the length direction of the film layer 1, the width of the top step surface 31 is 10um-1cm, which balances the electrical and mechanical properties of the current collector, adjusts the flexibility and rigidity of the current collector, ensures that the composite current collector is not easily damaged during battery assembly and use, and improves the overall reliability of the battery.

[0039] Further, a filling space 34 is formed at at least one of the top step surface 31, the middle step surface 33 and the bottom step surface 32 to expose the inside of the film layer 1, and the bottom surface of the filling space 34 is higher than the reference surface 10. In the embodiment of the present application, a filling space 34 is formed on the stepped structure by etching, laser processing and the like on at least one of the top step surface 31, the middle step surface 33 and the bottom step surface 32, and a deposition method such as vacuum evaporation and magnetron sputtering is used to make the metal conductive layer 2 enter the filling space 34 to enhance the bonding force between the film layer 1 and the metal conductive layer 2. The setting of the filling space 34 provides a new way to optimize the performance of the composite current collector; the filling space 34 exposes the inside of the film layer 1, can be filled with metal conductive materials, increase the ion transmission channel, and improve the battery charge and discharge speed and rate performance; at the same time, the filling space 34 changes the local structure of the current collector, helps to disperse stress, and improves the mechanical properties and stability of the current collector. Of course, alternatively, microscopic protrusions may be provided on the top step surface 31, the bottom step surface 32 and the plurality of intermediate step surfaces 33 to enhance the bonding force between the film layer 1 and the metal conductive layer 2. Specifically, the cross section of the filling space 34 taken along a plane parallel to the reference plane 10 may be provided in a circular, polygonal or grid shape, etc.

[0040] In the third embodiment of this application, please refer to Figure 1 and Figure 4 , the cross section of the filling space 34 taken along a plane parallel to the reference plane 10 is circular, and the diameter of the filling space 34 is 10nm-100nm; in this embodiment, on at least one of the top step surface 31, the middle step surface 33 and the bottom step surface 32, a cylindrical filling space 34 is formed on the stepped structure by removing part of the material by etching, laser processing, etc. for the metal conductive layer 2 to be deposited and combined with the thin film layer 1. The use of the filling space 34 with the aforementioned diameter size can reduce the interface resistance between the filling material and the stepped structure and improve the ion transmission efficiency.

[0041] In the fourth embodiment of this application, please refer to Figure 1 and Figure 5 , the cross section of the filling space 34 cut along a plane parallel to the reference plane 10 is the same shape as the middle step surface 33; in this embodiment, there is at least one middle step surface 33 corresponding to the top step surface 31 and the bottom step surfaces 32 on both sides to form a filling space 34, and the depth of the filling space 34 is less than the height difference between the middle step surface 33 and the reference plane 10, and the corresponding positions of two adjacent middle step surfaces 33 cannot form a space at the same time, so as to avoid affecting the flexibility of the composite current collector. The filling space 34 can be filled with an extension of the metal conductive layer 2 or other materials that enhance the bonding strength between the metal conductive layer 2 and the thin film layer 1. It should be noted that Figure 4 and Figure 5 The extended portion of the metal conductive layer 2 is filled in the filling space 34 in the composite current collector, and other materials that help to improve the bonding strength between the film layer 1 and the metal conductive layer 2 or materials that improve the conductivity can also be filled according to actual needs.

[0042] For further information, see Figure 1 and Figure 7 An intermediate connection layer 4 is also provided between the thin film layer 1 and the metal conductive layer 2; the material of the intermediate connection layer 4 is one of aluminum oxide, silicon nitride, nickel alloy, copper alloy, and aluminum alloy; the thin film layer 1 is connected to the metal conductive layer 2 through the intermediate connection layer 4, which is conducive to improving the bonding force between the metal conductive layer 2 and the stepped structure. The top step surface is flush with the end surface of the metal conductive layer 2, that is, the metal conductive layer 2 is not deposited on the top step surface, so that when the composite current collector is rolled and recut, the cutter can directly cut the stepped structure of the thin film layer 1 along the top step surface. The advantage is that since the metal conductive layer 2 is not deposited on the top step surface, the stress structure inside the metal conductive layer 2 will not be destroyed when the thin film layer 1 is cut, so that the edge of the cut composite current collector will not curl, thereby ensuring the flatness of the composite current collector. It should be noted that the composite current collector in the present application will construct both the upper and lower end surfaces of the thin film layer 1 into a stepped structure, that is, the composite current collector is symmetrical along the reference plane 10, so the composite current collector will not affect the metal conductive layer 2 when it is rolled and recut. Of course, on the basis of the first embodiment, the second embodiment, the third embodiment and the fourth embodiment, the intermediate connecting layer 4 is set between the thin film layer 1 and the metal conductive layer 2, which is also a foreseeable modification, and this application will not elaborate on it; the adaptive combination based on the structure in this application also falls within the scope of protection of this application.

[0043] The present application also provides a method for preparing the composite current collector, comprising the following steps:

[0044] The end surface of the thin film layer 1 is configured to have a stepped structure by etching;

[0045] The metal conductive layer 2 is plated on the stepped structure of the thin film layer 1 .

[0046] The preparation method of the composite current collector specifically comprises the following steps:

[0047] Step 1, cleaning the surface of the film layer 1 to remove impurities on the surface of the film layer 1;

[0048] Step 2, immersing the thin film layer 1 to be etched into a chemical solution, or applying chemical reagents on the thin film layer 1 by spraying or brushing;

[0049] Step 3, constructing a step-like structure on the end surface of the thin film layer 1 by etching, and controlling the etching time and temperature;

[0050] Step 4: Clean the film layer 1 with deionized water to remove residual chemical impurities;

[0051] Step 5, drying the film layer 1 at 60°C-100°C;

[0052] Step 6, coating the metal conductive layer 2 on the stepped structure of the thin film layer 1;

[0053] Step 7, plating a metal copper layer on the outer side of the metal conductive layer 2; the aforementioned method steps can be used to construct a stepped structure on the thin film layer 1, and the metal conductive layer 2 and the metal copper layer are plated on the stepped structure of the thin film layer 1.

[0054] In the preparation method of the composite current collector, the material of the thin film layer 1 can be PP film or PET film, the PP film is made of polypropylene, and the PET film is made of polyethylene terephthalate; the metal conductive layer 2 can be selected from aluminum oxide or a material with similar properties to aluminum oxide; the metal conductive layer 2 can be plated on the stepped structure of the thin film layer 1 by vacuum evaporation or magnetron sputtering, and the metal copper layer can also be plated on the metal conductive layer 2 by vacuum evaporation or magnetron sputtering; preferably, the present application adopts vacuum evaporation to plate the metal conductive layer 2 on the stepped structure of the thin film layer 1, and adopts magnetron sputtering to deposit the metal copper layer on the metal conductive layer 2, which has the advantage that the energy of magnetron sputtering is relatively high, and the aluminum oxide layer can be firmly fixed on the thin film layer 1, thereby improving the bonding force between the two.

[0055] In summary, the present invention provides a composite current collector and a method for preparing the same, wherein the composite current collector includes a thin film layer and a metal conductive layer respectively disposed on the upper and lower sides of the thin film layer, and the upper and lower end surfaces of the thin film layer are constructed to have a stepped structure so as to directly or indirectly contact the metal conductive layer. Compared with the composite current collector of the traditional structure, the composite current collector of the present application has a stepped structure that increases the contact area between the metal conductive layer and the thin film layer when the metal conductive layer is directly or indirectly combined, which is beneficial to enhance the bonding force between the metal conductive layer and the thin film layer, so that the tensile properties of the composite current collector are better; at the same time, due to the presence of the stepped structure, the metal conductive layer 2 is thicker, which is beneficial to improve the conductivity of the composite current collector.

[0056] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A composite current collector, characterized in that: It comprises a thin film layer and a metal conductive layer arranged on the upper and lower sides of the thin film layer. The upper and lower end surfaces of the thin film layer are constructed to have a stepped structure so as to directly or indirectly contact the metal conductive layer.

2. The composite current collector according to claim 1, characterized in that: The stepped structure has multiple step surfaces, including a top step surface, a bottom step surface and multiple intermediate step surfaces. Based on the reference plane of the thin film layer and along the length direction of the thin film layer, the intermediate step surfaces and the bottom step surfaces are sequentially arranged on both sides of the top step surface, and the height from the top step surface, the intermediate step surface to the bottom step surface gradually decreases.

3. The composite current collector according to claim 2, characterized in that: The step-like structures are symmetrically distributed in the length direction of the film layer.

4. The composite current collector according to claim 3, characterized in that: Based on the reference plane, a ratio of a height of the top step surface to a height of the bottom step surface is 3:1 to 6:

1.

5. The composite current collector according to claim 4, characterized in that: Along the length direction of the film layer, the width of the top step surface is 10 um-1 cm.

6. The composite current collector according to any one of claims 2 to 5, characterized in that: A filling space is formed at at least one of the top step surface, the middle step surface, and the bottom step surface to expose the inside of the film layer, and a bottom surface of the filling space is higher than the reference surface.

7. The composite current collector according to claim 6, characterized in that: A cross section of the filling space taken along a plane parallel to the reference plane is circular, and a diameter of the filling space is 10 nm-100 nm.

8. The composite current collector according to claim 6, characterized in that: A cross section of the filling space taken along a plane parallel to the reference plane has the same shape as the intermediate step surface.

9. The composite current collector according to claim 8, characterized in that: An intermediate connection layer is also provided between the thin film layer and the metal conductive layer; the material of the intermediate connection layer is one of aluminum oxide, silicon nitride, nickel alloy, copper alloy, and aluminum alloy; the top step surface is flush with the end surface of the metal conductive layer.

10. A method for preparing a composite current collector according to any one of claims 1 to 9, characterized in that: The following steps are involved: The end surface of the thin film layer is configured to have a stepped structure by etching; The metal conductive layer is plated on the stepped structure of the thin film layer.

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