Negative current collector and preparation method thereof, secondary battery and electric equipment

Abstract

The invention provides a negative electrode current collector and a preparation method thereof, a secondary battery and electric equipment, the negative electrode current collector comprises a base material layer, a composite layer and a current collecting layer, the composite layer is arranged on at least one side of two opposite sides of the base material layer, and the composite layer comprises a metal bonding layer, a conductive layer, a first protective layer and a second protective layer which are stacked in sequence, the metal bonding layer is adjacent to the base material layer, the current collecting layer is arranged on the second protective layer, and the thickness of the current collecting layer is larger than that of the composite layer; the conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is smaller than or equal to that of the first protective layer, and the second protective layer comprises a metal or non-metal material with lower reducibility than that of the first protective layer. The negative electrode current collector provided by the invention has fewer defect points and improved performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode current collector and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] The negative electrode current collector is the component that transmits the negative electrode current of the battery. The negative electrode current collector usually includes pure copper foil and composite copper foil. At present, the production process of composite copper foil for negative electrode current collector is usually to prepare a 5-15 nanometer thick nickel-chromium alloy bonding layer on the polymer base material layer, and to prepare a 20-30 nanometer thick conductive copper layer (usually called copper seed layer) on the nickel-chromium alloy bonding layer, and then cut it to a preset width by a slitting machine, and then perform water electroplating to thicken the metal layer to about 1000 nanometers to prepare a composite copper foil. Among them, the function of the copper seed layer is to allow the current to pass through during the water electroplating process so that the electroplated copper can be deposited on the foil, and the electroplated copper layer is the main body of the negative electrode current collector to transmit the current. However, the negative electrode current collector prepared in this way often has defects, resulting in poor performance. Summary of the invention

[0003] Based on this, the present application provides a negative electrode current collector and a preparation method thereof, a secondary battery and an electrical device, wherein the negative electrode current collector has fewer defects and improved performance.

[0004] The first aspect of the present application provides a negative electrode current collector, comprising a substrate layer, a composite layer, and a current collecting layer, wherein the composite layer is disposed on at least one of two opposite sides of the substrate layer, the composite layer comprises a metal bonding layer, a conductive layer, a first protective layer, and a second protective layer stacked in sequence, the metal bonding layer is adjacent to the substrate layer, the current collecting layer is disposed on the second protective layer, and the thickness of the current collecting layer is greater than that of the composite layer;

[0005] The conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is less than or equal to the thickness of the first protective layer, and the second protective layer comprises a metal or non-metal material having a lower reducing property than the first protective layer.

[0006] In some embodiments of the present application, one or more of the following conditions are met:

[0007] (1) The thickness of the metal bonding layer is 1.5 nm to 10.5 nm;

[0008] (2) The thickness of the conductive layer is 15 nm to 45 nm;

[0009] (3) The thickness of the first protective layer is 1.5 nm to 10.5 nm;

[0010] (4) The ratio of the thickness of the second protective layer to the first protective layer is (0.5-1):1;

[0011] Optionally, the thickness of the second protective layer is 1.5 nm to 3.75 nm;

[0012] (5) The ratio of the thickness of the metal bonding layer to the first protective layer is 1 to 1.5;

[0013] Optionally, the thickness of the metal bonding layer is equal to that of the first protective layer;

[0014] (6) The metal bonding layer contains nickel and / or chromium;

[0015] (7) The second protective layer comprises one or more of copper, silver and carbon;

[0016] (8) The current collecting layer comprises copper;

[0017] Optionally, the sum of the thickness of the composite layer and the current collecting layer is 500nm~2000nm;

[0018] (9) The first protective layer contains one or more of nickel, chromium, aluminum, magnesium, zinc, and silver;

[0019] Optionally, the first protective layer contains nickel and / or chromium.

[0020] In some embodiments of the present application, one or more of the following conditions are met:

[0021] (1) In the composite layer, the thickness of all copper-containing film layers in the composite layer accounts for 55% to 88%;

[0022] (2) the first protective layer contains nickel and chromium, and the mass percentage of nickel is greater than the mass percentage of chromium;

[0023] (3) The first protective layer further contains copper.

[0024] In some embodiments of the present application, the composite layer is disposed on two opposite sides of the substrate layer, and on a first side of the two opposite sides, the bonding force between the first protective layer and the second protective layer is w1; on the second side, the bonding force between the first protective layer and the second protective layer is w2, satisfying: w1>w2.

[0025] In some embodiments of the present application, on the first sides of the two opposite sides, the thickness of the conductive layer is d1′;

[0026] On the second side, the thickness of the conductive layer is d2', and the thickness of the second protective layer is d3', satisfying: d2'-d1'=d3'.

[0027] The third aspect of the present application provides a method for preparing a negative electrode current collector, comprising:

[0028] A composite layer is prepared on at least one side of two opposite sides of a substrate layer by magnetron sputtering, wherein the composite layer comprises a metal bonding layer, a conductive layer, a first protective layer and a second protective layer stacked in sequence, and the metal bonding layer is adjacent to the substrate layer;

[0029] forming a current collecting layer on the second protective layer by electroplating;

[0030] The conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is less than or equal to the thickness of the first protective layer, and the second protective layer comprises a metal or non-metal material having a lower reducing property than the first protective layer.

[0031] In some embodiments of the present application, before preparing the composite layer, the method further includes: performing plasma treatment on the substrate layer.

[0032] In some embodiments of the present application, before the electroplating, the process further includes: allowing the composite layer formed by magnetron sputtering to stand for 15 hours to 30 hours.

[0033] The third aspect of the present application provides a secondary battery, comprising the negative electrode current collector described in the first aspect of the present application or the negative electrode current collector prepared by the preparation method described in the second aspect of the present application.

[0034] The fourth aspect of the present application provides an electrical device, comprising the secondary battery described in the third aspect of the present application.

[0035] The multi-layer composite layer structure included in the negative electrode current collector provided in the present application can reduce the adhesion phenomenon during the slitting and water electroplating unwinding process, and reduce the impact on the overall current transmission (i.e., conductivity) of the composite layer, thereby reducing the light transmission phenomenon caused by leakage plating, which is beneficial to the improvement of the tensile strength, elongation at break, corrosion resistance and bonding strength of the negative electrode current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the negative electrode current collector according to one embodiment of the present application.

[0037] Reference numerals: 1 substrate layer; 2 composite layer; 3 current collecting layer; 21 metal bonding layer; 22 conductive layer; 23 first protective layer; 24 second protective layer. DETAILED DESCRIPTION

[0038] In order to facilitate understanding of the present application, the present application will be described more comprehensively below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0039] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that, unless otherwise specified, the term "and / or" used herein includes any and all combinations of one or more related listed items, and "above" and "below" are inclusive of the number, and the meaning of "multiple" in "one or more" is more than two.

[0041] Herein, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is considered to be continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to integers within the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0042] In this article, if there are multiple steps involved in the method flow, unless there is a clear different description in this article, there is no strict order restriction for the execution of these steps, and they can be executed in other orders than described. Moreover, any step can include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn, alternating or simultaneously with other steps or parts of sub-steps or stages of other steps.

[0043] The above application content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0044] At present, the production process of traditional negative electrode current collectors is usually to magnetron sputter a 5-15nm thick nickel-chromium alloy bonding layer on the opposite sides of the polymer substrate layer, and magnetron sputter a 20-30nm thick conductive copper layer (usually called copper seed layer) on the nickel-chromium alloy bonding layer. The magnetron layer prepared by magnetron sputtering is then cut to a preset width by a slitting machine, and then water electroplating is performed to thicken the copper layer.

[0045] However, the inventors found that during the slitting and water electroplating unwinding process, the wound composite film layer will cause the copper seed layer in the inner winding circle to contact and bond with the copper seed layer in the outer winding circle; because the bonding force between the conductive copper layer and the bonding layer is usually not strong, and the thickness of the copper seed layer that contacts and bonds is much higher than the thickness of the metal bonding layer, the mutual bonding between the thicker seed copper layers can easily cause the conductive copper layer, or even the entire magnetron layer, to be torn off from the polymer substrate layer and fall off, thereby forming a fall-off point. During the water electroplating process, these fall-off points cannot pass the current, and the copper layer cannot be deposited in the fall-off point area. Finally, the negative electrode current collector prepared by water electroplating has a serious defect point - light transmission phenomenon (i.e., leakage plating), which is manifested as the place where light transmission occurs as a defect point is very easy to deform first and directly affect the tensile strength and elongation at break of the negative electrode current collector; and such a negative electrode current collector is also very easy to corrode first from the defect point after being used in the battery cell, which affects the subsequent battery cell performance. In view of this, the present application proposes the following technical solution.

[0046] In a first aspect, the present application provides a negative electrode current collector, referring to Figure 1, which comprises a substrate layer 1, a composite layer 2, and a current collecting layer 3, wherein the composite layer 2 is disposed on at least one side of two opposite sides of the substrate layer 1, the composite layer 2 comprises a metal bonding layer 21, a conductive layer 22, a first protective layer 23, and a second protective layer 24 stacked in sequence, the metal bonding layer 21 is adjacent to the substrate layer 1, the current collecting layer 3 is disposed on the second protective layer 24, and the thickness of the current collecting layer 3 is greater than that of the composite layer 2;

[0047] The conductive layer 22 comprises copper, the first protective layer 23 comprises a metal material, the thickness of the second protective layer 24 is less than or equal to the thickness of the first protective layer 23 , and the second protective layer 24 comprises a metal or non-metal material having a lower reducibility than the first protective layer 23 .

[0048] The negative electrode current collector provided by the present application includes the above structure, which arranges the conductive layer that bears the main conductive function in electroplating between the metal bonding layer and the first protective layer, which can protect the conductive layer. At the same time, a second protective layer is provided on this basis. Then, before the subsequent water electroplating to prepare the current collector layer, during the slitting and water electroplating unwinding process, the wound composite film layer will be the second protective layer in the inner circle of the winding and the second protective layer in the outer circle of the winding in contact with each other; because the thickness of the second protective layer is equivalent to or less than the thickness of the first protective layer, even if there is a bonding effect between the second protective layer in the inner circle of the winding and the second protective layer in the outer circle of the winding, at most the second protective layer is torn off and separated from the first protective layer, and the first protective layer can still cover and protect the conductive layer used for current transmission, so that the bonding phenomenon in the unwinding process can be reduced, and the influence on the current transmission property (i.e., conductivity) of the composite layer as a whole can be reduced, and then the light transmission phenomenon caused by leakage plating can be reduced, which is beneficial to the improvement of the tensile strength, elongation at break, corrosion resistance and bonding force of the negative electrode current collector.

[0049] In addition, the film layers of the metal bonding layer and the first protective layer have higher hardness and better density, while the film layers of the conductive layer and the second protective layer are relatively loose. The multilayer structure thus formed is similar to a structure in which a layer of sand and a layer of cement are stacked. Compared with the aforementioned traditional two-layer structure (i.e., metal bonding layer + conductive copper layer), the multilayer structure of the present application can improve the hardness and tensile strength of the composite layer, which is beneficial to improving the processing performance of the negative electrode current collector.

[0050] The first protective layer can also serve as an anti-penetration layer for the conductive layer, which can reduce the corrosion of copper in the conductive layer during water electroplating, so that even if the second protective layer is corroded, good conductivity can be maintained.

[0051] The provision of a second protective layer containing a metal or non-metal material with a lower reducibility than the first protective layer is not only conducive to the subsequent thickening of the copper layer by electroplating, but also conducive to the copper foil having a suitable square resistance. If the second protective layer is not provided, the metal material contained in the first protective layer is easy to directly combine with oxygen in the air to form a dense oxide layer, and it is difficult to directly plate the thickened copper layer by electroplating, and it is also difficult to ensure the bonding strength between the metal material contained in the first protective layer and the copper contained in the thickened copper layer. In addition, if the second protective layer is not provided, the first protective layer needs to be thicker in thickness to better prevent the substrate layer from being corroded by the electrolyte, and an overly thick first protective layer is likely to lead to an increase in square resistance; accordingly, the second protective layer can play a certain anti-corrosion role, so that even if the thickness of the first protective layer is relatively small, it is not easy to be corroded by the electrolyte.

[0052] In some embodiments, the metallic bonding layer comprises nickel and / or chromium.

[0053] In some embodiments, the thickness of the metal bonding layer is 1.5 nm to 10.5 nm. For example, the thickness of the metal bonding layer can be 1.5 nm, 3 nm, 4.5 nm, 6 nm, 7.5 nm, 9 nm, 10.5 nm, or within a range of any of the above values.

[0054] The nickel and / or chromium contained in the metal bonding layer has a high hardness, which makes the metal bonding layer have good compactness and corrosion resistance, can reduce the corrosion of the electrolyte on the base layer, and can also serve as an anti-permeation layer to reduce the influence of copper on the aging of the base layer (copper damage). By controlling the thickness of the metal bonding layer within the above range, it can have better compactness and corrosion resistance, and further reduce the influence of copper on the aging of the base layer.

[0055] In some embodiments, the thickness of the conductive layer is 15 nm to 45 nm. For example, the thickness of the conductive layer can be 15 nm, 22.5 nm, 30 nm, 37.5 nm, 45 nm, or any range thereof. In this way, an excellent conductive effect can be achieved.

[0056] In some embodiments, the thickness of the first protective layer is 1.5 nm to 10.5 nm. For example, the thickness of the first protective layer can be 1.5 nm, 3 nm, 4.5 nm, 6 nm, 7.5 nm, 9 nm, 10.5 nm, or within the range of any of the above values. In this way, the first protective layer can not only protect the negative electrode current collector but also maintain a suitable square resistance.

[0057] In some embodiments, the thickness ratio of the metal bonding layer to the first protective layer is 1 to 1.5. For example, the thickness ratio can be 1, 1.1, 1.2, 1.3, 1.4, 1.5 or within the range of any of the above values. In this way, on the one hand, the internal stress of the copper foil can be evenly distributed to improve its stability; on the other hand, since the bonding force between the substrate layer and the composite layer is relatively weak, the thickness ratio of the metal bonding layer to the first protective layer is within the above range, which can minimize the separation of the composite layer from the substrate layer.

[0058] In some embodiments, the thickness of the metal bonding layer is equal to that of the first protective layer, so that the corrosion resistance of the entire composite layer can be uniform.

[0059] In some embodiments, the second protective layer comprises one or more of copper, silver, and carbon.

[0060] In some embodiments, the thickness ratio of the second protective layer to the first protective layer is (0.5-1):1. For example, the thickness ratio of the second protective layer to the first protective layer can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1 or within the range of any of the above values. In this way, during the slitting and water electroplating unwinding process, it can be avoided that when the second protective layer in the inner circle of the winding contacts and adheres to the second protective layer in the outer circle of the winding, the first protective layer or even the entire composite layer is pulled or even separated and falls off, resulting in a decrease in the performance of the copper foil; and the negative electrode current collector can have a suitable square resistance.

[0061] In some embodiments, the thickness of the second protective layer is 1.5nm~3.75nm. For example, the thickness of the second protective layer can be 1.5nm, 1.95nm, 2.4nm, 2.85nm, 3.15nm, 3.45nm, 3.75nm or within the range of any of the above values. In this way, it is beneficial to play the aforementioned protective role, and even if the second protective layer of the composite layer partially falls off due to mutual contact and bonding after the slitting and electroplating unwinding, the composite layer can still maintain a relatively uniform resistance and make the subsequent electroplating effect better; it can also avoid that the bonding force between the overly thick second protective layer and the first protective layer is too large, so that the first protective layer or even the entire composite layer is pulled or even separated and falls off when bonding occurs, resulting in a decrease in the performance of the copper foil.

[0062] In some embodiments, the first protective layer comprises one or more of nickel, chromium, aluminum, magnesium, and zinc. Optionally, the first protective layer comprises nickel and / or chromium.

[0063] On the basis of the second protective layer, the first protective layer containing nickel and / or chromium can additionally provide a wear-resistant layer and a corrosion-resistant layer with high hardness and good density, thereby protecting the metal bonding layer and the conductive layer, and avoiding pitting corrosion caused by stress concentration caused by friction during slitting and electroplating unwinding, resulting in partial shedding of the conductive layer.

[0064] In some embodiments, in the composite layer, the thickness of all copper-containing film layers in the composite layer accounts for 55% to 88%. In this way, the copper in the composite layer can constitute the main body to ensure the subsequent electroplating effect; and the copper foil can have a higher elongation at break and flexibility, and better processing performance.

[0065] In some embodiments, the first protective layer comprises nickel and chromium, and the mass percentage of nickel is greater than the mass percentage of chromium, so as to reduce oxidation of the first protective layer.

[0066] In some embodiments, the first protective layer further comprises copper, which is helpful to further reduce the oxidation rate of the first protective layer.

[0067] In some embodiments, the composite layer is disposed on two opposite sides of the substrate layer, and on a first side of the two opposite sides, the bonding force between the first protective layer and the second protective layer is w1; on a second side, the bonding force between the first protective layer and the second protective layer is w2, satisfying: w1>w2.

[0068] During the slitting and water electroplating unwinding process, the second protective layer of the inner winding circle will be partially adhered to the second protective layer of the outer winding circle, or partially rubbed to other areas on the same side during winding and unwinding, resulting in uneven surface thickness and uneven resistance of the composite layer. On this basis, the subsequent electroplating process will cause more serious unevenness (thin areas have high resistance and slow deposition speed, thick areas have low resistance and fast deposition speed), affecting the uniformity of the final negative electrode current collector, and causing problems for the coating link in subsequent battery production. In view of this, on the opposite sides of the substrate layer, the bonding force w1 between the second protective layer on the first side and the first protective layer is greater than the bonding force w2 between the second protective layer on the second side and the first protective layer, and because the thickness of the second protective layer is thin, the second protective layer on the second side (corresponding to the inner winding circle) is easily pulled off and attached to the second protective layer on the first side (corresponding to the outer winding circle) during electroplating unwinding, which is beneficial to the improvement of the surface thickness and resistance uniformity of the film material during electroplating.

[0069] It can be understood that the bonding force between the first protective layer and the second protective layer can be controlled by adjusting the roughness of the first protective layer or the density of the second protective layer; and the roughness of the first protective layer or the density of the second protective layer can be controlled by adjusting the preparation parameters in their respective preparation processes (such as the rate and power of magnetron sputtering, etc.).

[0070] In some embodiments, the composite layer is disposed on two opposite sides of the substrate layer, and on the first side of the two opposite sides, the thickness of the conductive layer is d1'; on the second side, the thickness of the conductive layer is d2', and the thickness of the second protective layer is d3', satisfying: d2'-d1'=d3'. In this way, it is beneficial to make the overall square resistance of the composite layer on the two opposite sides of the substrate layer the same, which is beneficial to improve the resistance uniformity on both sides of the negative electrode current collector, and avoid the phenomenon that the electroplating copper deposition speed on the second side is slow due to the high square resistance of the composite layer on the second side, thereby increasing the square resistance difference on both sides.

[0071] In some embodiments, the current collecting layer 3 comprises copper.

[0072] In some embodiments, the sum of the thickness of the composite layer and the current collecting layer is 500 nm to 2000 nm. For example, the sum of the thickness of the composite layer and the current collecting layer can be 500 nm, 800 nm, 1000 nm, 1300 nm, 1500 nm, 1800 nm, 2000 nm or any range thereof.

[0073] In some embodiments, the material of the substrate layer includes one or more of polyethylene terephthalate (PET), polypropylene (PP), and polyphenylene sulfide (PPS).

[0074] In a second aspect, the present application provides a method for preparing a negative electrode current collector, which can be used to prepare the negative electrode current collector of the first aspect of the present application, and may include the following steps:

[0075] A composite layer is prepared on at least one side of two opposite sides of a substrate layer by magnetron sputtering, wherein the composite layer comprises a metal bonding layer, a conductive layer, a first protective layer and a second protective layer stacked in sequence, and the metal bonding layer is adjacent to the substrate layer;

[0076] forming a current collecting layer on the second protective layer by electroplating;

[0077] The conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is less than or equal to the thickness of the first protective layer, and the second protective layer comprises a metal or non-metal material having a lower reducing property than the first protective layer.

[0078] In some embodiments, before preparing the composite layer, the following step may be further included: plasma treatment of the substrate layer. The main function of plasma treatment (O2) is to clean and modify the surface of the substrate layer and introduce some polar groups to improve the subsequent bonding force.

[0079] In some embodiments, before the electroplating, the method further includes: allowing the composite layer formed by magnetron sputtering to stand for 15 hours to 30 hours.

[0080] During the standing process, the composite layer, especially the conductive layer, will undergo grain fusion, which will reduce its square resistance and improve its conductivity. Moreover, since the inner conductive layer is protected by the first protective layer and the second protective layer, the square resistance will not increase due to oxidation.

[0081] In some embodiments, if the second protective layer contains carbon, since the bonding strength between carbon and nickel and / or chromium in the first protective layer is relatively poor, the carbon can be cleaned by water flow before preparing the second protective layer to avoid particle agglomeration in the second protective layer after preparation, thereby affecting the performance of the copper foil.

[0082] In a third aspect, the present application provides a secondary battery, comprising the negative electrode current collector described in the first aspect of the present application or the negative electrode current collector prepared by the preparation method described in the second aspect of the present application.

[0083] It can be understood that the negative electrode current collector can be used as a positive electrode current collector or a negative electrode current collector in a secondary battery.

[0084] In a fourth aspect, the present application provides an electrical device, comprising the secondary battery described in the third aspect of the present application.

[0085] In some embodiments, the type of the electric device is not particularly limited, and it can be any electronic device known in the prior art. For example, the electric device can include, but is not limited to, power tools, electric cars, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, etc.

[0086] Example

[0087] The following are specific examples, which more specifically describe the contents disclosed in this application, and these examples are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0088] Example 1

[0089] (1) Preparation of a metal bonding layer on the surface of a polymer film: A biaxially oriented PP film (polypropylene) with a thickness of 4.5 μm was placed in a magnetron sputtering machine, and a nickel-chromium alloy target was used as the target material to deposit a 7.5 nm metal bonding layer on the first side of the PP film. The specific process conditions were: two nickel-chromium targets (purity: 99.99%) were used as the target material, the target power was 9 kW, the argon gas flow rate was 150 sccm, the coating vacuum was 0.3 Pa, the line speed was 10 m / min, and the temperature of the main roller during the coating process was -20 °C. Thus, a PP composite film with a metal bonding layer on the surface was prepared.

[0090] (2) Preparing a conductive layer (30 nm thick) on the surface of the metal bonding layer: using 10 copper targets (purity: 99.99%) as target materials, the target power is 7.2 kW, the argon flow rate is 150 sccm, the coating vacuum is 0.3 Pa, the line speed is 10 m / min, and the temperature of the main roller during the coating process is -20 °C, that is, a conductive layer with a thickness of 30 nm is prepared;

[0091] (3) Preparing a first protective layer (nickel-chromium alloy, thickness of 7.5 nm) on the surface of the conductive layer: using two nickel-chromium targets (purity: 99.99%) as target materials, the target power is 9 kW, the argon gas flow rate is 150 sccm, the coating vacuum is 0.3 Pa, the line speed is 10 m / min, and the temperature of the main roller during the coating process is -20 °C, that is, a first protective layer with a thickness of 7.5 nm is prepared;

[0092] (4) Preparing a second protective layer (copper layer, thickness of 3.75 nm) on the surface of the first protective layer: using 10 copper targets (purity: 99.99%) as target materials, the target power is 0.9 kW, the argon gas flow rate is 150 sccm, the coating vacuum is 0.3 Pa, the line speed is 10 m / min, and the temperature of the main roller during the coating process is -20 °C, that is, a second protective layer with a thickness of 3.75 nm is prepared;

[0093] Repeat steps (1) to (4) to coat the second side of the PP film with a 7.5 nm thick metal bonding layer, a 30 nm thick conductive layer, a 7.5 nm thick first protective layer, and a 3.75 nm thick second protective layer.

[0094] (5) Electroplating a current collecting layer on the surface of the second protective layer on both sides simultaneously (equivalent to thickening the copper layer, and making the sum of the thickness of the composite layer and the current collecting layer on both sides 1000 nm respectively).

[0095] Example 2

[0096] The preparation method is similar to that of Example 1, with the main difference being that the target power in step (3) is adjusted to 4.5 kW, so that the thickness of both sides of the first protective layer is 3.75 nm.

[0097] Example 3

[0098] The preparation method is similar to that of Example 1, with the main difference being that the target power in step (3) is adjusted to 7.2 kW, so that the thickness of both sides of the first protective layer is 6 nm.

[0099] Example 4

[0100] The preparation method is similar to that of Example 3, with the main difference being that the target power in step (1) is adjusted to 10.8 kW, so that the thickness of both sides of the metal bonding layer is 9 nm.

[0101] Example 5

[0102] The preparation method is similar to that of Example 1, with the main difference being that the target power in step (1) is adjusted to 10.8 kW, so that the thickness of both sides of the metal bonding layer is 9 nm.

[0103] Example 6

[0104] The preparation method is similar to that of Example 2, with the main difference being that the target power in step (4) is adjusted to 0.54 kW, so that the thickness of both sides of the second protective layer is 2.25 nm.

[0105] Example 7

[0106] The preparation method is similar to that of Example 1, with the main difference being that the target power for preparing the first protective layer on the first side is adjusted to 18 kW and the line speed is adjusted to 20 m / min, and the target power for preparing the first protective layer on the second side is maintained at 9 kW and the line speed is maintained at 10 m / min, so that the roughness of the first protective layer on the first side is higher than that of the first protective layer on the second side, and the bonding force w1 between the first protective layer and the second protective layer on the first side is 4.5 N / mm, and the bonding force w2 between the first protective layer and the second protective layer on the second side is 4.2 N / mm, and w1>w2.

[0107] Example 8

[0108] The preparation method is similar to that of Example 7, with the main difference being that the target power during preparation of the first-side conductive layer is adjusted to 6.3 kW, so that the thickness of the conductive layer on the first side is 26.25 nm.

[0109] Comparative Example 1

[0110] The preparation method is similar to that of Example 1, with the main difference being that steps (3) and (4) are omitted, and a current collecting layer is electroplated on the surface of the conductive layer through step (5), and the thickness of both sides (metal bonding layer + conductive layer + current collecting layer) is made to be 1000 nm, thereby obtaining a traditional composite current collector.

[0111] Comparative Example 2

[0112] The preparation method is similar to that of Example 1, with the main difference being that the target power in step (4) is adjusted to 1.9 kW, so that the thickness of both sides of the second protective layer is 8 nm.

[0113] The negative electrode current collectors prepared in Examples 1-8 and Comparative Examples 1-2 were subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0114] Among them, the test conditions or test standards for each performance test item are as follows:

[0115] (1) Adhesion test between layers in negative electrode current collector

[0116] Take a sample with a size of 150mm×200mm, clamp one end of the sample in the fixture of the tensile testing machine, stick the tape on the surface of the sample, and perform a 180° peel test using the tensile testing machine to measure the adhesion.

[0117] (2) Corrosion resistance test

[0118] The samples were immersed in lithium-ion battery electrolyte at a test temperature of 85°C for 72 hours. The sample size was 3×3 cm, and the proportion of the area where the metal layer fell off to the total area was calculated.

[0119] (3) Square resistance test

[0120] The four-probe tester applies a known current to the sample surface and measures the resulting voltage drop to calculate the sample's square resistance. Since the substrate layer of the composite current collector is an insulating layer, the square resistance measured by the four-probe tester is the square resistance of a single side of the composite current collector.

[0121] (4) Tensile strength test

[0122] The tensile strength of the composite current collector at break was measured using a universal tensile testing machine with a strip width of 15 mm, a clamp distance of 50 mm, and a test speed of 200 m / min.

[0123] (5) Light transmission point test

[0124] Place the sample inside the light box and observe whether there is light passing through the sample.

[0125] Table 1

[0126]

[0127] Table 2

[0128]

[0129] Table 3

[0130]

[0131] In Tables 1 and 2, it can be seen from the comparison of Examples 1 to 6 with Comparative Example 1 that, compared with the traditional composite current collector, the negative electrode current collector of the present application has fewer defects and improved performance; it can be seen from the comparison of Examples 1 to 6 with Comparative Example 2 that the thickness of the second protective layer is less than that of the first protective layer, which can reduce the defects (light transmission) of the negative electrode current collector and improve its performance. In Table 3, it can be seen from the comparison of Examples 1, 7, and 8 that w1>w2 and d2'-d1'=d3', which is conducive to reducing the square resistance difference on both sides.

[0132] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A negative electrode current collector, characterized in that: It includes a substrate layer, a composite layer, and a current collecting layer, wherein the composite layer is disposed on at least one side of two opposite sides of the substrate layer, the composite layer includes a metal bonding layer, a conductive layer, a first protective layer, and a second protective layer stacked in sequence, the metal bonding layer is adjacent to the substrate layer, the current collecting layer is disposed on the second protective layer, and the thickness of the current collecting layer is greater than that of the composite layer; The conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is less than or equal to the thickness of the first protective layer, and the second protective layer comprises a metal or non-metal material having a lower reducing property than the first protective layer.

2. The negative electrode current collector according to claim 1, characterized in that: One or more of the following conditions are met: (1) The thickness of the metal bonding layer is 1.5 nm to 10.5 nm; (2) The thickness of the conductive layer is 15 nm to 45 nm; (3) The thickness of the first protective layer is 1.5 nm to 10.5 nm; (4) The ratio of the thickness of the second protective layer to the first protective layer is (0.5-1):1; Optionally, the thickness of the second protective layer is 1.5 nm to 3.75 nm; (5) The ratio of the thickness of the metal bonding layer to the first protective layer is 1 to 1.5; Optionally, the thickness of the metal bonding layer is equal to that of the first protective layer; (6) The metal bonding layer contains nickel and / or chromium; (7) The second protective layer comprises one or more of copper, silver and carbon; (8) The current collecting layer comprises copper; Optionally, the sum of the thickness of the composite layer and the current collecting layer is 500nm~2000nm; (9) The first protective layer contains one or more of nickel, chromium, aluminum, magnesium, zinc, and silver; Optionally, the first protective layer contains nickel and / or chromium.

3. The negative electrode current collector according to claim 1 or 2, characterized in that: One or more of the following conditions are met: (1) In the composite layer, the thickness of all copper-containing film layers in the composite layer accounts for 55% to 88%; (2) the first protective layer contains nickel and chromium, and the mass percentage of nickel is greater than the mass percentage of chromium; (3) The first protective layer further contains copper.

4. The negative electrode current collector according to claim 1 or 2, characterized in that: The composite layer is arranged on two opposite sides of the substrate layer, and on a first side of the two opposite sides, the bonding force between the first protective layer and the second protective layer is w1; on a second side, the bonding force between the first protective layer and the second protective layer is w2, satisfying: w1>w2.

5. The negative electrode current collector according to claim 4, characterized in that: On the first sides of the two opposite sides, the thickness of the conductive layer is d1′; On the second side, the thickness of the conductive layer is d2', and the thickness of the second protective layer is d3', satisfying: d2'-d1'=d3'.

6. A method for preparing a negative electrode current collector, characterized in that: include: A composite layer is prepared on at least one side of two opposite sides of a substrate layer by magnetron sputtering, wherein the composite layer comprises a metal bonding layer, a conductive layer, a first protective layer and a second protective layer stacked in sequence, and the metal bonding layer is adjacent to the substrate layer; forming a current collecting layer on the second protective layer by electroplating; The conductive layer comprises copper, the first protective layer comprises a metal material, the thickness of the second protective layer is less than or equal to the thickness of the first protective layer, and the second protective layer comprises a metal or non-metal material having a lower reducing property than the first protective layer.

7. The preparation method according to claim 6, characterized in that: Before preparing the composite layer, the method further includes: performing plasma treatment on the substrate layer.

8. The preparation method according to claim 6 or 7, characterized in that: Before the electroplating, the method further includes: allowing the composite layer formed by magnetron sputtering to stand for 15 hours to 30 hours.

9. A secondary battery, characterized in that: The negative electrode current collector comprises the negative electrode current collector according to any one of claims 1 to 5 or the negative electrode current collector prepared by the preparation method according to any one of claims 6 to 8.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 9.

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