Bipolar current collector and manufacturing method therefor, battery, and application

Abstract

The present application provides a bipolar current collector and a manufacturing method therefor, a battery, and an application. The bipolar current collector comprises a negative electrode conductive layer and a positive electrode conductive layer arranged in a stacked manner, and at least one transition layer is stacked between the negative electrode conductive layer and the positive electrode conductive layer. The material of the transition layer comprises a nickel-chromium alloy, the nickel-chromium alloy has a crystallinity of 5-80%, and the transition layer is of a non-porous structure. In the present application, starting from the material and structural design of the bipolar current collector, the non-porous transition layer made of a nickel-chromium alloy is added, and the crystallinity of the nickel-chromium alloy is defined to be 5-80%. In this way, the adhesion between the negative electrode conductive layer and the positive electrode conductive layer can be improved, thereby enhancing interface stability and ensuring that the bipolar current collector has good structural stability, and the application stability of the bipolar current collector in batteries can also be promoted, thereby improving the cycle performance of batteries.

Description

A bipolar current collector, its preparation method, battery and application Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a bipolar current collector and its preparation method, battery, and application. Background Technology

[0002] Currently, with the continuous development of electric vehicles, the market has placed higher demands on their range. To solve the range problem of electric vehicles, the development of high-energy-density batteries is imperative. Among numerous solutions, bipolar batteries, as a promising high-energy-density battery, have continued to attract attention. A bipolar battery is a battery in which bipolar electrodes (electrodes coated with positive and negative electrode materials on both sides of a current collector) are stacked in series. Because it relies on the series conduction of its own current collectors, it eliminates the need for wires between electrodes in traditional batteries, thereby reducing battery mass and volume, increasing battery energy density, and its series battery structure can improve the battery's output voltage and power, thus enhancing the battery's output power. It has been reported that using bipolar batteries, a battery pack of the same size can accommodate 1.4 times the number of cells as a traditional battery, and the battery's output power is approximately 1.5 times that of a traditional battery, demonstrating excellent potential.

[0003] As a crucial component of bipolar batteries, the bipolar current collector's structural stability significantly impacts the battery's performance. Currently, copper-aluminum composite current collectors are commonly used. However, the adhesion between the copper and aluminum layers in these composite current collectors is poor, leading to an unstable interface. This makes them prone to delamination during battery processing and use, resulting in increased interfacial resistance and consequently, a decline in the cycle performance of the prepared bipolar battery.

[0004] Therefore, how to effectively improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer in the bipolar current collector, improve the interface stability, and thus improve the cycle performance of the bipolar battery is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a bipolar current collector, its preparation method, battery, and application. Starting from the material and structural design of the bipolar current collector, this application adds a transition layer made of nickel-chromium alloy, while limiting the crystallinity of the nickel-chromium alloy to 5-80%. This design not only improves the adhesion between the negative and positive conductive layers, thereby enhancing interface stability and ensuring good structural stability of the bipolar current collector, but also promotes the stability of the bipolar current collector in battery applications and improves the battery's cycle performance.

[0006] In a first aspect, this application provides a bipolar current collector, which includes a negative electrode conductive layer and a positive electrode conductive layer stacked together, and at least one transition layer is stacked between the negative electrode conductive layer and the positive electrode conductive layer.

[0007] The transition layer is made of a nickel-chromium alloy with a crystallinity of 5-80%.

[0008] Starting from the material and structural design of the bipolar current collector, this application adds a transition layer made of nickel-chromium alloy, while limiting the crystallinity of the nickel-chromium alloy to 5-80%. This design can not only improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer, thereby improving the stability of the interface and ensuring that the bipolar current collector has good structural stability, but also promote the application stability of the bipolar current collector in bipolar batteries and improve the cycle performance of bipolar batteries.

[0009] In this application, the nickel-chromium alloy possesses a variety of excellent properties, including good mechanical properties (such as high strength, high toughness and wear resistance), corrosion resistance, heat resistance, electrical conductivity and plasticity.

[0010] In this application, the crystallinity of the nickel-chromium alloy is 5-80%, for example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, preferably 20-60%. If the crystallinity of the nickel-chromium alloy is too low, its resistance to electrolyte corrosion is poor; if the crystallinity of the nickel-chromium alloy is too high, the transition layer is brittle and is prone to breakage during the rolling process of the prepared electrode, resulting in defects, which leads to poor material stability and poor battery cycle performance.

[0011] Preferably, the transition layer has a non-porous structure.

[0012] In this application, the transition layer has a non-porous structure. If the nickel-chromium alloy has pores, the interface is easily corroded by the electrolyte, leading to poor interface stability and a decrease in capacity retention during battery cycling. Furthermore, when there are pore defects in the adjacent positive and negative conductive layers of the nickel-chromium alloy layer, the lack of an interface layer can easily cause electrolyte flow between the adjacent positive and negative conductive layers, resulting in a battery short circuit. In addition, the non-porous structure can ensure more beneficial mechanical properties (such as tensile strength and elongation at break) and battery capacity retention.

[0013] It should be noted that the bipolar current collector refers to the two-polar current collector.

[0014] Preferably, in the nickel-chromium alloy, the mass percentage of nickel is 10-90%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, etc.

[0015] In this application, an appropriate nickel mass percentage helps the transition layer achieve good bonding with the positive and negative electrode conductive layers. If the nickel mass percentage is too low, it is not conducive to improving the interface stability between the negative electrode conductive layer and the positive electrode conductive layer, thus leading to poor cycle performance of the battery; if the nickel mass percentage is too high, it is not conducive to improving the interface stability between the negative electrode conductive layer and the positive electrode conductive layer, thus leading to poor cycle performance of the assembled battery.

[0016] Preferably, the thickness of the single layer of the transition layer is 5-100nm, for example, it can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, and is more preferably 10-100nm.

[0017] In this application, an appropriate thickness of the single-layer transition layer can better improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer. If the thickness of the single-layer transition layer is too small, it cannot effectively improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer, and it is prone to breakage during the rolling process of the prepared electrode sheet, resulting in defects, deteriorating material stability, and causing poor battery cycle performance. If the thickness of the single-layer transition layer is too large, it cannot further improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer, increases material cost, and also leads to poor battery cycle performance.

[0018] In this application, when the transition layer simultaneously satisfies the relationship between crystallinity and thickness, the following problems that arise when there is a crystallinity mismatch between the conductive layer and the transition layer can be effectively avoided:

[0019] (1) Stress concentration is likely to occur at the interface, which in turn leads to cracks at the interface, thereby weakening the mechanical strength of the overall structure.

[0020] (2) Poor adhesion at the interface leads to delamination during use.

[0021] When the transition layer satisfies both the crystallinity and thickness requirements, improvements in adhesion, stability, and mechanical properties can be achieved without considering the crystallinity matching between the transition layer and the conductive layer, greatly reducing the difficulty of controlling the production process.

[0022] Preferably, at least two transition layers are stacked between the negative electrode conductive layer and the positive electrode conductive layer, and the mass content of nickel in the at least two transition layers increases gradually along the direction away from the negative electrode conductive layer or the positive electrode conductive layer.

[0023] In this application, the design of multiple transition layers, combined with the gradient change of nickel mass content, helps to reduce the interface resistance between the transition layer and the conductive layer and improve the structural stability of the transition layer.

[0024] Preferably, the total thickness of the at least two transition layers is 10-100nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc.

[0025] Preferably, the thickness of the negative electrode conductive layer is ≥0.1μm, for example, it can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, and preferably 1-10μm.

[0026] In this application, considering the cost and the impact on battery energy density, the thickness of the negative electrode conductive layer is preferably 1-10 μm. If it is too thin, the conductivity will be poor; if it is too thick, the areal density of the current collector will be too high, resulting in a low energy density of the prepared battery.

[0027] Preferably, the thickness of the positive electrode conductive layer is ≥0.5μm, for example, it can be 0.5μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, etc., and is preferably 1-10μm.

[0028] In this application, considering the cost and the impact on battery energy density, the thickness of the positive electrode conductive layer is preferably 1-10 μm. If it is too thin, the conductivity will be poor; if it is too thick, the areal density of the current collector will be too high, resulting in a low energy density of the prepared battery.

[0029] Preferably, the total thickness of the negative electrode conductive layer and the positive electrode conductive layer is ≥2μm, for example, it can be 2μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, etc.

[0030] In this application, if the total thickness of the negative electrode conductive layer and the positive electrode conductive layer is too low, the mechanical strength and conductivity of the prepared repolar current collector are relatively poor, which affects the processing performance of the repolar current collector and the cycle performance of the assembled battery.

[0031] Preferably, the material of the negative electrode conductive layer includes any one or a combination of at least two of copper, nickel, titanium, carbon, gold, or silver, and more preferably any one or a combination of at least two of copper, nickel, or carbon. Specifically, it can be, for example, stainless steel, copper-nickel alloy, nickel-titanium alloy, copper-titanium alloy, or gold-silver alloy.

[0032] Preferably, the negative electrode conductive layer further includes doping elements.

[0033] Preferably, the doping element includes any one or a combination of at least two of the following elements: tungsten, manganese, iron, chromium, cobalt, zirconium, tantalum, niobium, or tin.

[0034] Preferably, the mass fraction of the dopant element in the negative electrode conductive layer is 0.01-10%, for example, it can be 0.01%, 0.1%, 1%, 5% or 10%.

[0035] This application incorporates the aforementioned doping elements into the negative electrode conductive layer to improve its mechanical properties and corrosion resistance. However, the content should not be too high, as excessively high content will lead to poor conductivity of the prepared bipolar current collector, while excessively low content will have no effect.

[0036] Preferably, the material of the positive electrode conductive layer includes any one or a combination of at least two of aluminum, carbon, gold, or silver, with aluminum and / or carbon being more preferred. Specifically, it can be, for example, an aluminum-gold alloy, a gold-silver alloy, or a silver-aluminum alloy.

[0037] Preferably, a protective layer is provided on the surface of the negative electrode conductive layer and / or the positive electrode conductive layer away from the transition layer.

[0038] In this application, the protective layer is designed to prevent the negative electrode conductive layer from being oxidized.

[0039] Preferably, the thickness of the protective layer is 5-100nm, for example, it can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, and is more preferably 10-80nm.

[0040] Preferably, the material of the protective layer includes any one or a combination of at least two of the following: elemental metals, carbon materials, alloys, or oxides. Specifically, the elemental metals are nickel or chromium, the carbon materials are graphite, carbon black, carbon nanotubes, carbon nanofibers, or graphene, the alloys are nickel-based alloys and / or copper-based alloys, and the oxides are aluminum oxide, silicon oxide, nickel oxide, chromium oxide, cobalt oxide, or copper-chromium oxide.

[0041] It should be noted that when the negative electrode conductive layer is a copper layer, the protective layer is provided on the surface of the copper layer away from the transition layer.

[0042] Preferably, a protective layer is disposed on the surface of the positive electrode conductive layer away from the transition layer. The thickness of the protective layer is 5-100nm, for example, it can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc. The material of the protective layer includes any one or a combination of at least two of the following: elemental metal, carbon material, alloy or oxide.

[0043] Secondly, this application provides a method for preparing a bipolar current collector as described in the first aspect, the method comprising the following steps:

[0044] A positive electrode conductive layer is provided, and then at least one transition layer and a negative electrode conductive layer are sequentially laminated on one side surface of the positive electrode conductive layer to obtain the bipolar current collector;

[0045] Alternatively, a negative conductive layer is provided, and then at least one transition layer and a positive conductive layer are sequentially laminated on one side surface of the negative conductive layer to obtain the bipolar current collector.

[0046] It should be noted that the positive conductive layer can be made of commercially available foil, such as aluminum foil.

[0047] Preferably, the composite method of the at least one transition layer includes at least one of mechanical rolling, bonding, vapor deposition, electroless plating or electroplating.

[0048] Preferably, the vapor deposition method includes magnetron sputtering and / or vacuum evaporation.

[0049] Preferably, the composite method for the at least one transition layer is magnetron sputtering, and the specific parameters each independently include:

[0050] The target material is a nickel-chromium target with a nickel content of 10-90% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%). The power supply is a pulsed DC power supply with a frequency of 5-50kHz (e.g., 5kHz, 10kHz, 20kHz, 30kHz, 40kHz, or 50kHz). The target power is 2-20kW (e.g., 2kW, 5kW, 10kW, 15kW, or 20kW). The gas flow rate is 3... The flow rate can be 0-500 mL / min, for example, 30 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min, etc.; the chamber vacuum degree can be ≤0.1 Pa, for example, 0.1 Pa, 0.05 Pa or 0.01 Pa, etc.; and the cooling temperature of the coating main roller can be 5-30℃, for example, 5℃, 10℃, 15℃, 20℃, 25℃ or 30℃, etc.

[0051] Preferably, the preparation methods of the positive electrode conductive layer and the negative electrode conductive layer are each independently any one or a combination of at least two of the following: physical vapor deposition, chemical vapor deposition, rolling, or coating-drying. Specifically, physical vapor deposition can be magnetron sputtering, etc., and chemical vapor deposition can be plasma-enhanced chemical vapor deposition, etc.

[0052] It should be noted that when the negative electrode conductive layer or the positive electrode conductive layer is a carbon layer, the coating-drying method is used for deposition.

[0053] Preferably, when the material of the negative electrode conductive layer is copper, a protective layer is disposed on the surface of the negative electrode conductive layer away from the transition layer. The preparation method of the protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ forming, or coating. It should be noted that the physical vapor deposition method is preferably vacuum evaporation or magnetron sputtering, the chemical vapor deposition method is preferably atmospheric pressure chemical vapor deposition or plasma-enhanced chemical vapor deposition, the in-situ forming method is preferably a method of forming a protective layer in situ on the surface of the copper layer, and the coating method is preferably die coating, blade coating, or extrusion coating, etc.

[0054] Thirdly, this application provides an application of the bipolar current collector as described in the first aspect in the fields of electromagnetic shielding, flexible circuits, and printed circuit boards.

[0055] Fourthly, this application provides a battery in which the electrode comprises a bipolar current collector as described in the first aspect.

[0056] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0057] Compared with the prior art, this application has the following advantages:

[0058] (1) Starting from the material and structural design of the bipolar current collector, this application adds a transition layer made of nickel-chromium alloy, while limiting the crystallinity of the nickel-chromium alloy to 5-80%. This design can not only improve the adhesion between the negative electrode conductive layer and the positive electrode conductive layer, thereby improving the stability of the interface and ensuring that the bipolar current collector has good structural stability, but also promote the application stability of the bipolar current collector in bipolar batteries and improve the cycle performance of the battery.

[0059] (2) The preparation method provided in this application is simple, easy to operate, and suitable for large-scale promotion. Detailed Implementation

[0060] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0061] Example 1

[0062] This embodiment provides a bipolar current collector, which includes a negative electrode protective layer, a negative electrode conductive layer, a transition layer, a positive electrode conductive layer, and a positive electrode protective layer stacked together.

[0063] The transition layer is made of a nickel-chromium alloy, in which nickel accounts for 80% of the mass; the crystallinity of the nickel-chromium alloy is 51%, and the transition layer has a non-porous structure; the transition layer is a single layer with a thickness of 10 nm.

[0064] The negative electrode protective layer is made of copper-chromium oxide and has a thickness of 5 nm. The negative electrode conductive layer is made of copper and has a thickness of 1 μm. The positive electrode conductive layer is commercially available aluminum foil (commercially available aluminum foil has its own aluminum oxide protective layer) and has a thickness of 13 μm. The total thickness of the negative electrode conductive layer and the positive electrode conductive layer is 14 μm.

[0065] This embodiment also provides a method for preparing the above-mentioned bipolar current collector, the preparation method comprising the following steps:

[0066] (1) Commercially available aluminum foil is provided as the positive conductive layer. The aluminum foil is then placed in a magnetron sputtering machine, and a transition layer is deposited on one side of the aluminum foil. The specific process conditions for magnetron sputtering of the transition layer are as follows:

[0067] A nickel-chromium target (purity: 99.99%, nickel mass content: 80%) was used as the target material. A pulsed DC power supply with a power frequency of 20kHz, a target power of 5.0kW, an argon flow rate of 50mL / min, a chamber vacuum of 0.08Pa, a sputtering time of 2s, and a main roller temperature of 15℃ were used during the deposition process.

[0068] (2) Place the composite layer obtained in step (1) in a magnetron sputtering machine and deposit a copper layer on the surface of the transition layer. The specific process conditions are as follows:

[0069] A copper target (99.99% purity) was used as the target material, with a target power of 10kW, an argon flow rate of 80mL / min, a chamber pressure of 0.1Pa, a sputtering time of 130s, and a main roller cooling temperature of -10℃.

[0070] (3) The composite layer prepared in step (2) is placed in a 0.6 g / L chromic acid aqueous solution for 20 s, then the surface liquid is removed and dried at 70 °C to obtain the negative electrode protective layer, thus completing the preparation of the repolar current collector.

[0071] In this application, the surface porosity of the transition layer can be detected using the following methods:

[0072] Take the finished bipolar current collector, randomly select 5 locations on the bipolar current collector, and use focused ion beam (FIB) to prepare cross-sectional samples to meet the requirements of transmission electron microscopy (TEM) testing (the cross-section includes the negative electrode conductive layer, the positive electrode conductive layer and the transition layer). Then, use TEM to magnify and observe the transition layer of the cross-section. If the characterization result shows that there are no pores at any of the 5 locations, it is determined that the transition layer is pore-free.

[0073] Example 2

[0074] The difference between this embodiment and Embodiment 1 is that the nickel content in the nickel-chromium target is 50% by mass, the target power is 5.3kW, and the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 50:50.

[0075] The remaining preparation methods and parameters are consistent with those in Example 1.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 1 is that the nickel content in the nickel-chromium target is 10% by mass, the target power is 6.0kW, and the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 10:90.

[0078] The remaining preparation methods and parameters are consistent with those in Example 1.

[0079] Example 4

[0080] The difference between this embodiment and Embodiment 1 is that the nickel content in the nickel-chromium target is 90% and the target power is 4.7kW. Therefore, the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 90:10.

[0081] The remaining preparation methods and parameters are consistent with those in Example 1.

[0082] Example 5

[0083] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 1 second, so that the thickness of the transition layer is 5nm.

[0084] The remaining preparation methods and parameters are consistent with those in Example 1.

[0085] Example 6

[0086] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 10s, so that the thickness of the transition layer is 50nm.

[0087] The remaining preparation methods and parameters are consistent with those in Example 1.

[0088] Example 7

[0089] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 16s, so that the thickness of the transition layer is 80nm.

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Example 8

[0092] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 20s, so that the thickness of the transition layer is 100nm.

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Example 9

[0095] The difference between this embodiment and Embodiment 1 is that the sputtering time in the copper layer deposition process is adjusted to 65s, so that the thickness of the copper layer is 0.5μm.

[0096] The remaining preparation methods and parameters are consistent with those in Example 1.

[0097] Example 10

[0098] The difference between this embodiment and Embodiment 1 is that the sputtering time in the copper layer deposition process is adjusted to 650s, so that the thickness of the copper layer is 5μm.

[0099] The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Example 11

[0101] The difference between this embodiment and Embodiment 1 is that the sputtering time in the copper layer deposition process is adjusted to 1300s, so that the thickness of the copper layer is 10μm.

[0102] The remaining preparation methods and parameters are consistent with those in Example 1.

[0103] Example 12

[0104] The difference between this embodiment and Embodiment 1 is that the thickness of the commercially available aluminum foil is 1 μm.

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] Example 13

[0107] The difference between this embodiment and Embodiment 1 is that the negative electrode conductive layer is an electrolytic copper foil with a thickness of 1 μm. Then, a transition layer is deposited on one side of the electrolytic copper foil, and then an aluminum layer with a thickness of 0.5 μm is deposited on the surface of the transition layer by vapor deposition.

[0108] The remaining preparation methods and parameters are consistent with those in Example 1.

[0109] Example 14

[0110] The difference between this embodiment and Embodiment 1 is that the thickness of the commercially available aluminum foil is 20 μm.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 15

[0113] The difference between this embodiment and Embodiment 1 is that the negative electrode conductive layer is a nickel layer, the negative electrode protective layer is a nickel oxide layer, and the negative electrode conductive layer is prepared by electroplating, with the specific process conditions as follows:

[0114] An aqueous solution containing 300 g / L NiSO4·6H2O, 150 g / L NiCl2·6H2O, and 52 g / L H3BO3 was used as the electroplating solution, at a flow rate of 5 A / dm 2 Electroplating is performed at a current density for 95 seconds, followed by cleaning to remove residual liquid from the surface and drying at 70°C. The negative electrode protective layer is generated in situ during the nickel plating drying process.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 16

[0117] The difference between this embodiment and Embodiment 1 is that the negative electrode conductive layer is a copper-nickel alloy layer (copper to nickel mass ratio of 1:1), and the negative electrode protective layer is made of copper-chromium oxide. The preparation method is magnetron sputtering, and the specific process conditions are as follows:

[0118] The target material was copper-nickel material (purity 99.99%, copper to nickel mass ratio 1:1), the target power was 10kW, the argon flow rate was 80mL / min, the chamber vacuum degree was 0.1Pa, the sputtering time was 133s, and the main roller cooling temperature was -10℃.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Example 17

[0121] The difference between this embodiment and Embodiment 1 is that the negative electrode conductive layer is a copper foil with a thickness of 6 μm, and the positive electrode conductive layer is a carbon layer with a thickness of 1 μm. The preparation method includes:

[0122] A copper foil was placed in a magnetron sputtering machine with a graphite target (purity 99.99%) as the target material, a target power of 3kW, an argon flow rate of 50mL / min, a chamber vacuum of 0.08Pa, a sputtering time of 200s, and a main roller temperature of 0℃ during the deposition process, thereby preparing a carbon layer with a thickness of 1μm on the surface of the copper foil.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 18

[0125] The difference between this embodiment and Embodiment 1 is that the bipolar current collector includes two transition layers, namely a first transition layer and a second transition layer along the direction away from the negative electrode conductive layer, and the thickness of the first transition layer and the second transition layer is 10 nm.

[0126] The mass ratio of nickel to chromium in the nickel-chromium alloy of the first transition layer is 60:40; in the preparation method parameters, the target power is 5.2kW and the sputtering time is 1s.

[0127] The nickel-chromium alloy of the second transition layer has a nickel-to-chromium mass ratio of 80:20; in the preparation method parameters, the target power is 5.0kW and the sputtering time is 1s.

[0128] During the preparation process, magnetron sputtering is used to deposit two transition layers on one side of the aluminum foil.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 19

[0131] The difference between this embodiment and Embodiment 1 is that the material of the negative electrode conductive layer includes copper and chromium, and the mass fraction of chromium in the negative electrode conductive layer is 1%, that is, the target material is adjusted to be a copper-chromium alloy during the preparation of the negative electrode conductive layer, and the mass content of chromium is 1%, and the target power is 12kW; the material of the negative electrode protective layer is copper-chromium oxide.

[0132] The remaining preparation methods and parameters are consistent with those in Example 1.

[0133] Example 20

[0134] The difference between this embodiment and Embodiment 1 is that the nickel content in the nickel-chromium target is 5% and the target power is 6.2kW, so that the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 5:95.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Example 21

[0137] The difference between this embodiment and Embodiment 1 is that the nickel content in the nickel-chromium target is 95% and the target power is 4.5kW, so that the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 95:5.

[0138] The remaining preparation methods and parameters are consistent with those in Example 1.

[0139] Example 22

[0140] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 0.6s, so that the thickness of the transition layer is 3nm.

[0141] The remaining preparation methods and parameters are consistent with those in Example 1.

[0142] Example 23

[0143] The difference between this embodiment and Embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 22s, so that the thickness of the transition layer is 110nm.

[0144] The remaining preparation methods and parameters are consistent with those in Example 1.

[0145] Example 24

[0146] The difference between this embodiment and Embodiment 1 is that the sputtering time in the copper layer deposition process is adjusted to 39s, so that the thickness of the copper layer is 0.3μm.

[0147] The remaining preparation methods and parameters are consistent with those in Example 1.

[0148] Example 25

[0149] The difference between this embodiment and Embodiment 1 is that the negative electrode conductive layer is an electrolytic copper foil with a thickness of 1 μm. Then, a transition layer is deposited on one side of the electrolytic copper foil, and then an aluminum layer with a thickness of 0.3 μm is deposited on the surface of the transition layer by vapor deposition.

[0150] The remaining preparation methods and parameters are consistent with those in Example 1.

[0151] Example 26

[0152] The difference between this embodiment and Embodiment 1 is that the power supply frequency is adjusted to 50kHz, the sputtering time is adjusted to 1.5s, and the temperature of the coating main roller is adjusted to 30℃ in the deposition process of the transition layer.

[0153] The remaining preparation methods and parameters are consistent with those in Example 1.

[0154] Example 27

[0155] The difference between this embodiment and Embodiment 1 is that the power supply frequency is adjusted to 5kHz, the sputtering time to 3.0s, and the temperature of the coating main roller to 5℃ in the deposition process of the transition layer.

[0156] The remaining preparation methods and parameters are consistent with those in Example 1.

[0157] Comparative Example 1

[0158] The difference between this comparative example and Example 1 is that the transition layer is made of elemental nickel and the target power is 4.5 kW.

[0159] The remaining preparation methods and parameters are consistent with those in Example 1.

[0160] Comparative Example 2

[0161] The difference between this comparative example and Example 1 is that the transition layer is made of elemental chromium and the target power is 6.5 kW.

[0162] The remaining preparation methods and parameters are consistent with those in Example 1.

[0163] Comparative Example 3

[0164] The difference between this comparative example and Example 1 is that no transition layer is provided.

[0165] The remaining preparation methods and parameters are consistent with those in Example 1.

[0166] Comparative Example 4

[0167] The difference between this embodiment and Embodiment 1 is that the power supply frequency in the deposition process of the transition layer is adjusted to 4.5 kHz, the sputtering time is 3.2 s, and the temperature of the coating main roller is 5 ℃.

[0168] The remaining preparation methods and parameters are consistent with those in Example 1.

[0169] Comparative Example 5

[0170] The difference between this embodiment and Embodiment 1 is that the power supply frequency in the deposition process of the transition layer is adjusted to 55kHz, the sputtering time is 1.2s, and the temperature of the coating main roller is 30℃.

[0171] The remaining preparation methods and parameters are consistent with those in Example 1.

[0172] Performance testing

[0173] I. The adhesion strength, tensile strength, elongation at break, sheet resistance, and crystallinity of the bipolar current collectors provided in the above embodiments and comparative examples were tested. The specific test methods are as follows:

[0174] 1) Adhesion force

[0175] The bipolar current collector was placed in an adhesion testing device and tested as follows: a layer of Permacel P-94 double-sided adhesive was adhered to a 1 mm thick aluminum foil. The positive conductive layer of the bipolar current collector was then adhered on top of the double-sided adhesive. A layer of ethylene-acrylic acid copolymer film (DuPont Nurcel 0903, 50 μm thick) was then covered on the negative conductive layer. Finally, a 1.3 × 10⁻⁶ adhesion test was performed. 5 N / m 2The sample was hot-pressed at 120℃ for 10 seconds, cooled to room temperature (25℃), and cut into strips of 150mm × 15mm. The ethylene-acrylic acid copolymer film of the sample strips was then fixed to the upper clamp of a tensile testing machine, while the remaining portion was fixed to the lower clamp. After fixing, the two were peeled at an angle of 180° and a speed of 100mm / min. The peel force was tested, and the obtained peel force is the adhesive force between the negative and positive conductive layers in the bipolar current collector.

[0176] 2) Tensile strength and elongation at break

[0177] Refer to national standard GB / T 1040.3-2006.

[0178] 3) Shear resistance

[0179] The bipolar current collector sample was placed on the sample stage, and the sheet resistance of the two opposite surfaces of the sample was tested using a four-probe sheet resistance meter.

[0180] 4) Crystallinity

[0181] The crystallinity of the transition layer in a bipolar current collector was tested using X-ray diffraction. A finished bipolar current collector was taken, and the copper layer was first thinned to zero (using methods such as focused ion beam thinning). The treated sample was then placed in an X-ray diffractometer and scanned at a rate of 2° / min within the range of 5-90° to obtain the diffraction curve. The crystallinity was calculated using the following formula: Xc = Ic / (Ic + Ia) × 100%

[0182] Where Ic is the diffraction integral intensity of the crystalline part, Ia is the diffraction integral intensity of the amorphous part, and Xc is the crystallinity.

[0183] The test results are shown in Table 1.

[0184] Table 1

[0185] II. Based on the above embodiments and comparative examples, a solid-state lithium battery is obtained using the bipolar current collector system. The specific steps include:

[0186] ① Coating electrode material onto the positive conductive layer side, the electrode material including LiNi 0.8 Co 0.1 Mn 0.1 The composition of O2 (NCM811), conductive carbon black Super P, PVDF 5130, and carbon nanotubes (CNT) is in a mass ratio of 96:1.8:1.7:0.5.

[0187] ② Coat the negative electrode conductive layer side with electrode materials, including graphite, conductive carbon black SuperP, carbon nanotubes and CMC, in a mass ratio of 96:3.0:0.6:0.4.

[0188] ③ Using Li6PS5Cl as the solid electrolyte, a pouch cell with a capacity of 3Ah was assembled according to the assembly process of a bipolar solid-state battery.

[0189] The assembled pouch battery was subjected to cycle performance testing. The test conditions were as follows: charge and discharge at a rate of 1C constant current constant voltage (CCCV) and discharge at a rate of 1C constant current (CC). The battery was cycled 2000 times, and the battery capacity retention rate after 2000 cycles was recorded, which is the battery capacity after 2000 cycles / the initial capacity of the battery × 100%.

[0190] The test results are shown in Table 2.

[0191] Table 2

[0192] analyze:

[0193] As shown in Tables 1 and 2, this application, by adding a transition layer made of nickel-chromium alloy, not only enhances the adhesion between the negative electrode conductive layer and the positive electrode conductive layer, thereby improving the stability of the interface and ensuring that the repolar current collector has good structural stability, but also promotes the application stability of the repolar current collector in bipolar batteries and improves the cycle performance of bipolar batteries.

[0194] As shown in Examples 1-4, 20, and 21, as the mass percentage of nickel in the transition layer increases, the adhesion between the negative and positive conductive layers in the prepared bipolar current collector first increases and then decreases. This is because the interaction force between the transition layer and the conductive layer first increases and then decreases with increasing nickel content. Furthermore, the corresponding tensile strength and elongation at break also show a trend of first increasing and then decreasing, due to changes in adhesion force. The corresponding sheet resistance changes relatively little, because sheet resistance mainly depends on the materials and thicknesses of the positive and negative conductive layers. In addition, if the nickel content in the transition layer is too low, the cycle performance of the battery deteriorates; if the nickel content in the transition layer is too high, the cycle performance of the battery deteriorates.

[0195] As shown in Examples 1, 5-8, 22, and 23, the adhesion force between the negative and positive conductive layers in the bipolar current collector increases with the thickness of the transition layer. Due to the increased thickness of the transition layer, its uniformity initially increases and then remains constant, resulting in an initial increase and then a constant interaction force with the conductive layer. Consequently, the tensile strength and elongation at break also exhibit the same trend. The corresponding sheet resistance changes relatively little, as it mainly depends on the materials and thicknesses of the positive and negative conductive layers. When the thickness exceeds 100 nm, the mechanical properties of the prepared bipolar current collector no longer change. Furthermore, if the transition layer thickness is too small, the battery's cycle performance is poor; if the transition layer thickness is too large, the improvement in battery cycle performance is small. Therefore, the preferred thickness of the transition layer is 10-100 nm.

[0196] As shown in Examples 1, 9-11, and 24, as the thickness of the negative electrode conductive layer increases, the sheet resistance of the repolar current collector decreases, conductivity improves, the tensile strength increases accordingly, the elongation at break decreases, and the adhesion remains unchanged. This is because the adhesion mainly depends on the properties of the transition layer. Considering conductivity, the thickness of the negative electrode conductive layer should be ≥0.5μm. Further considering the decrease in battery energy density caused by increasing the thickness of the conductive layer, the preferred range for the thickness of the negative electrode conductive layer is 1-10μm.

[0197] As shown in Examples 1, 12-14, and 25, as the thickness of the positive electrode conductive layer increases, the sheet resistance of the repolar current collector decreases, the conductivity improves, the tensile strength increases, the elongation at break decreases, and the adhesion remains unchanged. This is because the adhesion mainly depends on the properties of the transition layer. Considering conductivity, the thickness of the positive electrode conductive layer should be ≥0.5μm. Further considering the decrease in battery energy density caused by increasing the thickness of the conductive layer, the preferred range for the thickness of the positive electrode conductive layer is 1-10μm.

[0198] As can be seen from Examples 1 and 15-17, replacing the material of the positive electrode conductive layer or the negative electrode conductive layer with other materials can also achieve good results.

[0199] As shown in Examples 1 and 18-19, using two transition layers, and adjusting the mass ratio of nickel to chromium in the nickel-chromium alloy of the first transition layer to 60:40 and the mass ratio of nickel to chromium in the nickel-chromium alloy of the second transition layer to 80:20, results in a gradient change in the nickel content between the two transition layers. This helps to reduce the interfacial resistance between the transition layer and the conductive layer, and improves the structural stability of the transition layer, thereby improving the cycle performance of the battery. If the material of the negative electrode conductive layer includes copper and chromium, their combination helps to improve the mechanical properties and corrosion resistance of the repolar current collector, thereby improving the cycle performance of the assembled battery.

[0200] As can be seen from Examples 1, 26-27 and Comparative Examples 4-5, as the frequency of the magnetron sputtering power supply increases, the crystallinity increases, and the battery cycle performance first increases and then decreases. This is because the crystallinity of the transition layer is too high, which makes the transition layer more brittle. It is prone to breakage and defects during the preparation of the electrode roll forming process, resulting in poor material stability and thus poor battery cycle performance.

[0201] As can be seen from Example 1 and Comparative Examples 1-2, if the material of the transition layer is elemental nickel or elemental chromium, it is not conducive to the tight bonding between the positive and negative conductive layers, resulting in a decrease in the structural stability of the bipolar current collector, which in turn leads to a decrease in the cycle performance of the assembled battery.

[0202] The applicant declares that this application illustrates the process method through the above embodiments, but this application is not limited to the above process steps, that is, it does not mean that this application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used in this application, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A bipolar current collector, comprising a negative electrode conductive layer and a positive electrode conductive layer stacked together, wherein at least one transition layer is stacked between the negative electrode conductive layer and the positive electrode conductive layer; The transition layer is made of a nickel-chromium alloy with a crystallinity of 5-80%.

2. The bipolar current collector according to claim 1, wherein, The transition layer has a non-porous structure.

3. The bipolar current collector according to claim 1 or 2, wherein, In the nickel-chromium alloy, the mass percentage of nickel is 10-90%; Preferably, the crystallinity of the nickel-chromium alloy is 20-60%; Preferably, the thickness of the transition layer is 5-100 nm, and more preferably 10-100 nm.

4. The bipolar current collector according to any one of claims 1-3, wherein, At least two transition layers are stacked between the negative electrode conductive layer and the positive electrode conductive layer, and the mass content of nickel in the at least two transition layers increases gradually along the direction away from the negative electrode conductive layer or the positive electrode conductive layer. Preferably, the total thickness of the at least two transition layers is 10-100 nm.

5. The bipolar current collector according to any one of claims 1-4, wherein, The thickness of the negative electrode conductive layer is ≥0.1μm, preferably 1-10μm; Preferably, the thickness of the positive electrode conductive layer is ≥0.5μm, and more preferably 1-10μm; Preferably, the total thickness of the negative electrode conductive layer and the positive electrode conductive layer is ≥2μm.

6. The bipolar current collector according to any one of claims 1-5, wherein, The material of the negative electrode conductive layer includes any one or a combination of at least two of copper, nickel, titanium, carbon, gold or silver, preferably any one or a combination of at least two of copper, nickel or carbon. Preferably, the negative electrode conductive layer further includes doping elements; Preferably, the doping element includes any one or a combination of at least two of the following elements: tungsten, manganese, iron, chromium, cobalt, zirconium, tantalum, niobium, or tin. Preferably, the mass fraction of the dopant element in the negative electrode conductive layer is 0.01-10%.

7. The bipolar current collector according to any one of claims 1-6, wherein, The material of the positive electrode conductive layer includes any one or a combination of at least two of aluminum, carbon, gold or silver, preferably aluminum and / or carbon.

8. The bipolar current collector according to any one of claims 1-7, wherein, A protective layer is provided on the surface of the negative electrode conductive layer and / or the positive electrode conductive layer away from the transition layer. Preferably, the thickness of the protective layer is 5-100 nm, and more preferably 10-80 nm; Preferably, the material of the protective layer includes any one or a combination of at least two of the following: elemental metal, carbon material, alloy, or oxide.

9. A method for preparing a bipolar current collector as described in any one of claims 1-8, comprising the following steps: A positive electrode conductive layer is provided, and then at least one transition layer and a negative electrode conductive layer are sequentially laminated on one side surface of the positive electrode conductive layer to obtain the bipolar current collector; Alternatively, a negative conductive layer is provided, and then at least one transition layer and a positive conductive layer are sequentially laminated on one side surface of the negative conductive layer to obtain the bipolar current collector.

10. The preparation method according to claim 9, wherein, The composite method for the at least one transition layer includes at least one of mechanical rolling, bonding, chemical vapor deposition, electroless plating, or electroplating. Preferably, the vapor deposition method includes magnetron sputtering and / or vacuum evaporation. Preferably, the composite method for the at least one transition layer is magnetron sputtering, and the specific parameters each independently include: The target material is a nickel-chromium target with a nickel content of 10-90% by mass. The power supply is a pulsed DC power supply with a power frequency of 5-50kHz. The target power is 2-20kW, the gas flow rate is 30-500mL / min, the chamber vacuum degree is ≤0.1Pa, and the cooling temperature of the coating main roller is 5-30℃.

11. The preparation method according to claim 9 or 10, wherein, The preparation methods of the positive electrode conductive layer and the negative electrode conductive layer are each independently any one or a combination of at least two of the following: physical vapor deposition, chemical vapor deposition, rolling, or coating-drying.

12. The application of a bipolar current collector as described in any one of claims 1-8 in the fields of electromagnetic shielding, flexible circuits, and printed circuit boards.

13. A battery, wherein the electrode comprises a bipolar current collector as described in any one of claims 1-8.

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