Composite current collectors and battery electrodes

Abstract

This utility model belongs to the field of lithium-ion battery technology and discloses a composite current collector and battery electrode. The composite current collector includes a base film and a first conductive layer disposed on a first surface and a second conductive layer disposed on a second surface of the base film. The first and second surfaces are disposed opposite to each other. Along the width direction of the base film, the thickness of the base film decreases from the middle position in the width direction to both sides of the width direction. The base film is axially symmetrically disposed in the width direction. The total thickness of the composite current collector remains consistent throughout the entire composite current collector. When the polymer film is electroplated in an electroplating bath, it can avoid the surface undulation of the base film along the width direction caused by the difference in current density in the electroplating solution. This avoids the situation where the surface of the base film wrinkles or slips and cannot be rolled up, thus reducing the difficulty of subsequent application of the current collector inside the lithium-ion battery.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery technology, and in particular to a composite current collector and battery electrode. Background Technology

[0002] Currently, composite current collectors based on polymer thin films are receiving widespread attention and application in the new energy industry. Composite current collectors consist of a base film layer and conductive layers on both sides of the base film.

[0003] Electroplating is commonly used to deposit a conductive layer on a base film. However, when depositing a conductive layer on a base film using electroplating, the metal ions in the electroplating bath solution are affected by the current density and will be deposited unevenly along the width direction of the base film. This results in a coating that is thick at both ends and thin in the middle on the surface of the base film, which in turn causes wrinkles on the polymer base film and may even cause slippage and prevent the film from being rolled up, significantly reducing the production yield of the current collector.

[0004] Therefore, there is an urgent need to design a polymer membrane to solve the aforementioned problems in the existing technology. Utility Model Content

[0005] The purpose of this invention is to provide a composite current collector and battery electrode, which can improve the production yield of the composite current collector.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] Composite current collectors include:

[0008] A base film, a first conductive layer disposed on a first surface and a second conductive layer disposed on a second surface, the first surface and the second surface being disposed opposite to each other, the thickness of the base film decreasing from the middle position in the width direction to both sides of the width direction, and the base film being axially symmetrical in the width direction;

[0009] The total thickness of the composite current collector remains consistent throughout the entire composite current collector.

[0010] Preferably, along the width direction of the base film, the thickness of both the first conductive layer and the second conductive layer increases from the middle of the width direction to the two sides of the width direction, and the first conductive layer and the second conductive layer are symmetrically distributed on both sides of the base film.

[0011] Preferably, the base film is arranged axially symmetrically in the thickness direction.

[0012] Preferably, along the width direction of the base film, the thickness of the base film continuously decreases from the middle position in the width direction to both sides of the width direction.

[0013] Preferably, along the width direction of the base film, the thickness of the base film decreases in a stepwise manner from the middle position in the width direction to the two sides of the width direction.

[0014] Preferably, the thickness of the base film at the midpoint of its width direction is 60%-98% of the total thickness of the composite current collector.

[0015] Preferably, along the width direction of the base film, the ratio of the thickness of the middle position of the base film to the thickness of the two side edges of the base film is 2:1 to 5:1.

[0016] Preferably, the base film includes at least one of a polyimide base film, a polypropylene base film, or a polyethylene terephthalate base film.

[0017] Preferably, the base film has a first deposition pore with a pore size of 0.1 μm-10 μm and the porosity of the base film is 50%-80%.

[0018] Preferably, both the first conductive layer and the second conductive layer are copper-plated layers.

[0019] Preferably, the composite current collector satisfies at least one of the following conditions:

[0020] The thickness of the composite current collector is ≤12μm;

[0021] The areal density of the composite current collector is 20 g / m³. 2 -30g / m 2 ;

[0022] The tensile strength of the composite current collector is ≥250MPa;

[0023] The elongation at break of the composite current collector is 25%-50%;

[0024] The surface sheet resistance of the composite current collector is 15 mΩ / sq-20 mΩ / sq.

[0025] The battery electrode includes the aforementioned composite current collector and an active material layer disposed on at least one side of the composite current collector.

[0026] The beneficial effects of this utility model are as follows:

[0027] The composite current collector provided by this invention includes a base film, which has a special structure in the transverse direction, being thicker in the middle and narrower at both ends. In the actual electroplating process, the electric field lines on both sides of the polymer film are more densely packed, resulting in a higher current density, while the electric field lines in the middle are fewer, and the current density is lower. This leads to a thicker, even charred, plating layer (copper layer) on both sides of the base film in the transverse direction. When electroplating the conductive layer of the composite current collector, considering the thickness distribution of the base film, it is beneficial to prepare a composite current collector with a uniform overall thickness, thereby reducing the processing difficulty and improving the production yield of the composite current collector. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the composite current collector provided in Embodiment 1 of this utility model;

[0029] Figure 2 This is a schematic diagram of the composite current collector provided in Embodiment 2 of this utility model;

[0030] Figure 3 This is a schematic diagram of the composite current collector provided in Embodiment 3 of this utility model;

[0031] Figure 4 This is a schematic diagram of the composite current collector provided in Embodiment 4 of this utility model.

[0032] In the picture:

[0033] 1-Base film;

[0034] 2-First conductive layer;

[0035] 3-Second conductive layer. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, not the entire structure.

[0037] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0038] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0039] In the description of this embodiment, the terms "upper," "lower," "right," and "left," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0040] like Figures 1 to 4 As shown, this utility model provides a composite current collector, which includes a base film 1, a first conductive layer 2 disposed on a first surface of the base film 1 and a second conductive layer 3 disposed on a second surface of the base film 1. The first surface and the second surface are disposed opposite to each other. Along the width direction of the base film 1, the thickness of the base film 1 decreases from the middle position in the width direction to the two sides of the width direction. The base film 1 is axially symmetrically disposed in the width direction. The total thickness of the composite current collector remains consistent throughout the entire composite current collector. In this embodiment, since the thickness of the base film 1 decreases from the middle position to both sides along the width direction, when the composite current collector is electroplated in the electroplating bath, it can avoid the appearance of surface undulations on the base film 1 along the width direction due to the different current densities in the electroplating solution. This avoids the situation where the surface of the base film 1 is wrinkled or slipped and cannot be rolled up, thus facilitating the preparation of a composite metal foil with a uniform overall thickness. Since the base film 1 is axially symmetrically arranged in the width direction, it can ensure the overall uniformity of the first conductive layer 2 and the second conductive layer 3 on the base film 1, which greatly improves the production yield of the subsequent composite metal foil and ensures the uniformity of the sheet resistance on the surface of the composite metal foil. Since the total thickness of the entire composite current collector is kept consistent, the processing and application difficulty of the composite current collector is greatly simplified.

[0041] In the embodiments of this application, the width direction of the base film 1 is... Figures 1 to 4 The first direction is the direction perpendicular to the direction of movement of the base film 1 during its fabrication. The thickness direction of the base film 1 is... Figures 1 to 4The second direction in the embodiment of this application; the total thickness of the composite current collector is kept consistent on the whole composite current collector, which means that the thickness difference measured at two random locations within a certain area of ​​the composite current collector using the same measurement method is not greater than 5%, which can be understood as the total thickness being kept consistent.

[0042] like Figures 1 to 4 As shown, along the width direction of the base film 1, the thickness of both the first conductive layer 2 and the second conductive layer 3 increases from the middle of the width direction towards both sides. In some embodiments of this application, the first conductive layer 2 and the second conductive layer 3 have the same structure, with the same thickness at each corresponding position, and are symmetrically disposed on opposite sides of the base film 1. In other embodiments of this application, the thickness of the first conductive layer 2 and the second conductive layer 3 at each corresponding position is different, and they are respectively disposed on the first surface and the second surface of the base film 1. It can be understood that the thickness of the first conductive layer 2 and the second conductive layer 3 is adapted to the thickness of the base film 1 along the width direction to ensure that the total thickness of the entire composite current collector remains consistent.

[0043] The base film 1 includes at least one of polyimide base film, polypropylene base film or polyethylene terephthalate base film, and the specific material of the base film 1 can be selected according to the actual situation.

[0044] like Figures 1 to 4 As shown, the base film 1 is axially symmetrical in the thickness direction, so the base film 1 has a symmetrical structure in both the width and thickness directions. Correspondingly, the first conductive layer 2 and the second conductive layer 3 have the same structure and are symmetrically arranged in the thickness direction of the base film 1, which further reduces the processing difficulty of the base film 1, the first conductive layer 2 and the second conductive layer 3.

[0045] Along the width direction of the base film 1, the thickness of the base film 1 decreases from the middle position in the width direction towards both sides of the width direction; in some embodiments of this application, such as Figure 1 and Figure 2 As shown, the thickness of the base film 1 continuously decreases from the middle position in the width direction to both sides of the width direction. For example, the cross-section of the base film 1 along the width direction can be spindle-shaped or rhomboid. In this case, the first and second surfaces of the base film 1 are both continuous arc surfaces or planes. In other embodiments of this application, such as... Figure 3 and Figure 4 As shown, the thickness of the base film 1 decreases in a stepped manner from the middle position in the width direction to both sides of the width direction. The first and second surfaces of the base film 1 are both stepped or stepped structures formed by splicing multiple parallel planes. Specifically, the preparation process of the base film 1 can be selected from one or more of the commonly used processes in the art, such as molding, calendering, injection molding, casting, thermoforming, multilayer composite, and local stretching.

[0046] Along the width direction of the base film 1, the thickness at the middle position of the base film 1 is 60%-98% of the total thickness of the composite current collector; since the middle position of the base film 1 along the width direction is the position with the greatest thickness of the base film 1, the thickness at the thickest position of the base film 1 along the width direction accounts for 60%-98% of the total thickness of the composite current collector. Further, along the width direction of the base film 1, the ratio of the thickness at the middle position of the base film 1 to the thickness at both sides of the base film 1 is 2:1 to 5:1. It can be understood that, as... Figure 1 or Figure 2 As shown, if the thickness of the base film 1 decreases continuously from the middle position in the width direction to both sides of the width direction, then the two ends of the base film 1 in the width direction still have a certain thickness. That is, the cross-section of the base film 1 in the width direction is an incomplete spindle shape or rhombus shape with both ends cut off. Then the ratio of the thickness of the base film 1 in the middle position to the thickness of the two ends is 2:1 to 5:1. If the thickness of the base film 1 decreases stepwise from the middle position in the width direction to both sides of the width direction, then the ratio of the thickness of the thickest layer in the middle of the base film 1 to the thickness of the thinnest layer at both ends is 2:1 to 5:1.

[0047] It should be noted that during the electroplating of the first conductive layer 2 or the second conductive layer 3, the electric field lines on both sides of the base film 1 are more dense and the current density is higher, while the electric field lines in the middle of the base film 1 are sparsely distributed and the current density is lower. According to the test, the thickness ratio between the thickest part in the middle region and the thinnest part in the edge region of the base film 1 is between 2:1 and 5:1, which is more conducive to the preparation of a composite current collector with a uniform overall thickness.

[0048] To reduce the internal resistance of the base film 1 and accelerate the electroplating process, a first deposition hole is formed on the base film 1. The pore size of the first deposition hole is 0.1 μm-10 μm, and the porosity of the base film 1 is 50%-80%. Specifically, the first deposition hole is formed on both the first and second surfaces of the base film 1. The first deposition hole facilitates the deposition and adhesion of metal particles in the electroplating solution and also facilitates the passage of electrons, thereby reducing the internal resistance of the composite current collector and improving the fast-charging performance of the lithium battery. Further, in the embodiments of this application, a second deposition hole is formed on both the first conductive layer 2 and the second conductive layer 3. The pore size of the second deposition hole is 50 nm-200 nm, and the porosity of the first conductive layer 2 and the second conductive layer 3 is 50%-80%. The second deposition hole can reduce the weight of the conductive layer, further increasing the energy density of the lithium battery. It also facilitates the penetration of the electrolyte into the interior to improve the wettability of the conductive layer, thereby improving the cycle stability of the composite current collector. Specifically, the second deposition hole can be formed on the surface of the conductive layer by chemical etching or laser etching.

[0049] Both the first conductive layer 2 and the second conductive layer 3 are copper-plated layers. The deposition process of the first conductive layer 2 and the second conductive layer 3 on the base film 1 can be selected from, but is not limited to, one or more of the commonly used vapor deposition, electroplating, and chemical plating methods in the art. The vapor deposition method can specifically include atomic layer deposition, physical vapor deposition, and chemical vapor deposition. Specifically, the physical vapor deposition method can include at least one of laser pulse deposition, vacuum sputtering deposition, and vacuum evaporation. The vacuum sputtering deposition method can specifically include vacuum DC sputtering, vacuum magnetron sputtering, vacuum radio frequency sputtering, and vacuum reactive sputtering. The vacuum evaporation method can specifically include at least one of resistance heating evaporation, electron beam evaporation, high frequency heating evaporation, and laser heating evaporation. In the embodiments of this application, the deposition process can be selected from, but is not limited to, a two-step method of magnetron sputtering and electroplating, a three-step method of magnetron sputtering, vacuum evaporation and electroplating, a one-step dry method of magnetron sputtering and vacuum evaporation, and a one-step wet method of electroless plating and electroplating. It should be understood that, in addition to the deposition processes shown above, other processes can also be used to deposit metallic copper on the surface of the base film 1.

[0050] In the embodiments of this application, the thickness of the composite current collector does not exceed 12 μm, and can be, for example, a range of 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm or any combination thereof, preferably 4 μm-8 μm. A thinner thickness is more conducive to improving the energy density of the battery, and can also carry out effective and stable electron conduction under high mechanical deformation.

[0051] In the embodiments of this application, the areal density of the composite current collector is 20 g / m³. 2 -30g / m 2 For example, it could be 20g / m 2 21g / m 2 22g / m 2 23g / m 2 24g / m 2 25g / m 2 26g / m 2 27g / m 2 28g / m 2 29g / m 2 30g / m 2 or a range consisting of any two of them 2 At this point, the areal density of the composite current collector is relatively low, which improves the energy density of the battery while ensuring the excellent mechanical properties of the composite current collector.

[0052] In the embodiments of this application, the composite current collector has a tensile strength greater than 250 MPa and an elongation at break of 15%-35%, which can withstand a certain degree of tensile deformation without breaking, thus facilitating subsequent processing and application.

[0053] In the embodiments of this application, the surface sheet resistance of the composite current collector is 15mΩ / sq-20mΩ / sq, and the peel strength of the first conductive layer 2 and the second conductive layer 3 is not less than 400N / m.

[0054] Embodiments of this application also provide a battery electrode, which includes the aforementioned composite current collector and an active material layer disposed on at least one side of the composite current collector.

[0055] When this composite current collector is applied to lithium-ion batteries, the battery tab can be placed on the thicker side of the first conductive layer 2 and the second conductive layer 3. This results in a thinner copper plating layer and a thicker base film 1 at the location away from the tab, and a thicker copper plating layer and a thinner base film 1 at the location near the tab. This effectively avoids the base film 1 melting and breaking due to excessively high temperatures during the welding process, and also significantly improves the utilization rate of the base film 1. This is because the current density and heat generation are greater at the location near the tab in the battery, requiring a thicker base film 1 for transmission, while the current density and temperature are lower at the location away from the tab, and a thinner base film 1 can meet the requirements. Therefore, the composite current collector of this application can achieve both cost reduction and energy density improvement, and also solve the problem of tab welding, making it highly practical.

[0056] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below, and appropriate modifications can be made without changing the main claims of this application.

[0057] Example 1

[0058] A composite current collector, such as Figure 1 As shown, copper layers are deposited on the first and second surfaces of the base film 1 using a two-step method of magnetron sputtering and electroplating. The first conductive layer 2 and the second conductive layer 3 are symmetrical structures with the same thickness at corresponding positions. The specific preparation method is as follows:

[0059] S1: Preparation of base film 1

[0060] In a twin-screw extruder, polypropylene powder (purchased from Daehan Oil & Chemical) and white oil are mixed and then extruded and cooled to form polypropylene cast sheets through a casting machine with a special die (purchased from Shenzhen Xingyuan Material Technology Co., Ltd., self-made). After biaxial stretching, extraction and drying, a base film 1 is obtained. The thickness L1 at the center of the width direction of the base film 1 is 4.5 μm, and the thickness decreases linearly from the center to the two edges. The thickness L2 at the thinnest edge is 1.5 μm. The pore size of the first deposition pore on the base film 1 is 200 nm, and the porosity of the base film 1 is 65%.

[0061] S2: Preparation of composite current collector

[0062] The base film 1 was transferred into a vacuum magnetron sputtering coating machine (the prototype was purchased from Guangdong Tengsheng Technology Innovation Co., Ltd., model TS-1300JRC IIPro; subsequent accessory modifications and process parameter optimizations were completed independently). A 50nm thick copper underlay layer was deposited on the first and second surfaces of the base film 1 using vacuum magnetron sputtering. The vacuum level of the vacuum magnetron sputtering equipment chamber was 10... -3 Pa, the film winding tension is set to 90 N / m, the coating rate is set to 10 m / min, and a metallized polypropylene film with a surface sheet resistance of 1 Ω / sq is obtained.

[0063] The copper layer on the metallized polypropylene film is then thickened by electroplating using a roller-type horizontal plating process. The metallized polypropylene film is used as the cathode and the copper plate as the anode. The current density of the electroplating tank is increased from 0.5 ASD to 5 ASD. The copper ion concentration in the electroplating solution is maintained at 2 mol / L, and the plating rate is maintained at 10 m / min. The process involves alkaline ion replacement, water washing, acidic ion replacement, anti-oxidation treatment, and drying. The first conductive layer 2 and the second conductive layer 3 are deposited on both sides of the metallized polypropylene film to obtain a copper composite current collector.

[0064] The thickness d1 of the first conductive layer 2 at its thinnest point (center) is 0.5 μm, and the thickness d1' of the two sides (thickest points) is 2 μm. L0 is the total thickness of the composite current collector. The thickness d2 of the second conductive layer 3 at its thinnest point (center) is 0.5 μm, and the thickness d2' of the two sides (thickest points) is 2 μm. The pore size of the second deposition pores on the first conductive layer 2 and the second conductive layer 3 is 100 nm, and the porosity of the first conductive layer 2 and the second conductive layer 3 is 80%.

[0065] Example 2

[0066] A composite current collector, such as Figure 2As shown, the difference between it and Example 1 is that: the thickness L1 at the center of the width direction of the base film 1 is 6.5 μm, the thickness decreases in an arc shape from the center to the two edges, the thickness L2 at the thinnest edge is 1.5 μm, the pore size of the first deposition pore on the base film 1 is 300 nm, and the porosity of the base film 1 is 70%.

[0067] Correspondingly, the thicknesses d1 and d2 at the middle (thinnest) of the conductive layers on both sides are 0.5 μm, and the thicknesses d1' and d2' at the two sides (thickest) are 3 μm.

[0068] The pore size of the second deposited pores on the first conductive layer 2 and the second conductive layer 3 is 150 nm, and the porosity of the first conductive layer 2 and the second conductive layer 3 is 80%.

[0069] Example 3

[0070] A composite current collector, such as Figure 3 As shown, the difference between this and Example 1 is that: when preparing the base film 1, a first polypropylene film with a width of 700 mm and a thickness of 1 μm, a second polypropylene film with a width of 1000 mm and a thickness of 2 μm, a third polypropylene film with a width of 1300 mm and a thickness of 2 μm, a fourth polypropylene film with a width of 1000 mm and a thickness of 2 μm, and a fifth polypropylene film with a width of 700 mm and a thickness of 1 μm are stacked sequentially in the center, and unwound and multilayered on a laminating machine (Guangdong Keshuo, KS-LAL1212S) to obtain the base film 1. The thickness L1 at the center position of the width direction of the base film 1 is 8 μm, and the thickness at the two side edges decreases in two levels, namely 6 μm and 2 μm respectively. The pore size of the first deposition pore on the base film 1 is 200 nm, and the porosity of the base film 1 is 70%.

[0071] The thicknesses d1 and d2 at the middle (thinnest) of the conductive layers on both sides are 0.1 μm, while the thicknesses of the conductive layers on both sides increase in two gradients, with thicknesses of 1.1 μm and 3.1 μm respectively.

[0072] The pore size of the second deposited pores on the first conductive layer 2 and the second conductive layer 3 is 200 nm, and the porosity of the first conductive layer 2 and the second conductive layer 3 is 80%.

[0073] Example 4

[0074] A composite current collector, such as Figure 4As shown, the difference between this and Example 1 is that: in preparing the base film 1, a first polypropylene film with a width of 700 mm and a thickness of 1 μm, a second polypropylene film with a width of 1000 mm and a thickness of 2 μm, a third polypropylene film with a width of 1300 mm and a thickness of 2 μm, a fourth polypropylene film with a width of 1000 mm and a thickness of 2 μm, and a fifth polypropylene film with a width of 700 mm and a thickness of 1 μm are sequentially stacked in the center, and unwound and multilayered on a laminating machine (Guangdong Keshuo, KS-LAL1212S) to obtain the base film 1. The thickness of the base film 1 at the center position in the width direction is 8 μm, and the thickness at the two side edges decreases in a gradient manner. The first deposited pores on the base film 1 have diameters of 6 μm and 2 μm, respectively. The pore size of the first deposited pore on the base film 1 is 200 nm, and the porosity of the base film 1 is 70%. The first conductive layer 2 and the second conductive layer 3 have an asymmetric structure and are respectively disposed on the first surface and the second surface of the base film 1. The thickness d1 of the first conductive layer 2 at the middle position (thinnest part) is 0.1 μm, and the thickness of the conductive layer at both sides increases in two levels, with the thickness d1' of the thickest conductive layer being 3 μm. The thickness d2 of the second conductive layer 3 at the middle position (thinnest part) is 0.5 μm, and the thickness of the conductive layer at both sides increases in a gradient, with the thickness d2' of the thickest conductive layer being 3.6 μm.

[0075] The pore size of the second deposited pores on the first conductive layer 2 and the second conductive layer 3 is 200 nm, and the porosity of the first conductive layer 2 and the second conductive layer 3 is 80%.

[0076] Comparative Example 1

[0077] A composite current collector, which differs from Example 1 in that:

[0078] A copper composite current collector was prepared using a conventional biaxially stretched polypropylene film as the substrate. The biaxially stretched polypropylene film had a thickness of 6.5 μm (purchased from Shenzhen Xingyuan Material Technology Co., Ltd., SQ865F), a pore size of 50 nm, and a porosity of 60%. The preparation process of the copper composite current collector was the same as in the above embodiment. The copper layers on both sides of the biaxially stretched polypropylene film had a thickness of 1 μm, a pore size of 100 nm, and a porosity of 80%.

[0079] Performance testing:

[0080] The polypropylene microporous membranes and composite current collectors provided in Examples 1-4 and Comparative Example 1 were tested using the following methods:

[0081] Thickness: The thickness of at least 10 points along the TD direction of the composite current collector was measured using a German Mahr thickness gauge (model: C1216), and the average value was taken as the thickness.

[0082] Surface sheet resistance: The resistance was measured at five locations around and in the center of the composite current collector using a four-probe resistance tester, and the average value was taken.

[0083] Porosity: Tested by gravimetric method, referring to standard GB / T 36363-2018.

[0084] Tensile strength and elongation at break: The tensile strength and elongation at break were tested according to the national standard GB / T 16492-2008 on a tensile testing machine (model: EM6.202) of Meters Industrial Systems (China) Co., Ltd. The higher the elongation at break, the less likely the composite current collector is to break and the better its extensibility.

[0085] Areal density: Tested according to national standard GB / T36363-2018. Cut the product into 3 samples of 100mm*100mm, weigh them, and take the average value.

[0086] Surface tension: The surface tension of the composite current collector was tested according to GB / T 14216-2008.

[0087] The test results of the composite current collectors prepared in the embodiments and comparative examples of this utility model are shown in Table 1.

[0088] Table 1

[0089]

[0090] As can be seen from Table 1, the composite current collectors prepared in Examples 1-4 have a uniform overall thickness, and their mechanical properties such as tensile strength and elongation at break are significantly improved, which reduces the processing difficulty of composite current collectors and improves the production yield of composite current collectors.

[0091] Obviously, the above embodiments of this utility model are merely examples for clearly illustrating the present utility model, and are not intended to limit the implementation of the present utility model. Those skilled in the art can make various obvious changes, readjustments, and substitutions without departing from the protection scope of this utility model. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the protection scope of the claims of this utility model.

Claims

1. A composite current collector, characterized by, include: A base film (1), a first conductive layer (2) disposed on a first surface and a second conductive layer (3) disposed on a second surface, the first surface and the second surface being disposed opposite to each other, the thickness of the base film (1) decreasing from the middle position in the width direction to the two sides of the width direction along the width direction, and the base film (1) being axially symmetrical in the width direction; The total thickness of the composite current collector remains consistent throughout the entire composite current collector.

2. The composite current collector of claim 1, wherein Along the width direction of the base film (1), the thickness of the first conductive layer (2) and the second conductive layer (3) both increase from the middle of the width direction to the two sides of the width direction, and the first conductive layer (2) and the second conductive layer (3) are symmetrically distributed on both sides of the base film (1).

3. The composite current collector of claim 2, wherein, The base film (1) is arranged axially symmetrically in the thickness direction.

4. The composite current collector of claim 3, wherein, Along the width direction of the base film (1), the thickness of the base film (1) decreases continuously from the middle position in the width direction to both sides of the width direction.

5. The composite current collector according to claim 3, characterized in that, Along the width direction of the base film (1), the thickness of the base film (1) decreases in a stepwise manner from the middle position of the width direction to the two sides of the width direction.

6. The composite current collector of claim 4 or 5, wherein, Along the width direction of the base film (1), the thickness of the base film (1) at the middle position in the width direction is 60%-98% of the total thickness of the composite current collector.

7. The composite current collector of claim 6, wherein, Along the width direction of the base film (1), the ratio of the thickness of the middle position of the base film (1) to the thickness of the two side edges of the base film (1) is 2:1 to 5:

1.

8. The composite current collector of claim 1, wherein The base film (1) includes at least one of a polyimide base film, a polypropylene base film, or a polyethylene terephthalate base film.

9. The composite current collector of claim 1, wherein, The base film (1) has a first deposition pore with a pore size of 0.1 μm-10 μm and a porosity of 50%-80%.

10. The composite current collector of claim 1, wherein Both the first conductive layer (2) and the second conductive layer (3) are copper-plated layers.

11. The composite current collector according to any one of claims 1-10, characterized in that, The composite current collector satisfies at least one of the following conditions: The thickness of the composite current collector is ≤12μm; The areal density of the composite current collector is 20 g / m 2 - 30 g / m 2 ; The tensile strength of the composite current collector is >250MPa; The elongation at break of the composite current collector is 25%-50%; The surface sheet resistance of the composite current collector is 15 mΩ / sq-20 mΩ / sq.

12. A battery electrode sheet, characterized by, The battery electrode includes a composite current collector as described in any one of claims 1-11 and an active material layer disposed on at least one side of the composite current collector.

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