A bipolar current collector, a preparation method thereof, a battery and application thereof

Abstract

The application provides a bipolar current collector, a preparation method thereof, a battery and an application, the bipolar current collector comprises a negative electrode conductive layer and a positive electrode conductive layer which are arranged in a laminated mode, and at least one transition layer is arranged in a laminated mode between the negative electrode conductive layer and the positive electrode conductive layer; the material of the transition layer comprises a nickel-chromium alloy, the crystallinity of the nickel-chromium alloy is 5-80%, and the transition layer is a non-porous structure. The application is designed from the material and structure of the bipolar current collector, a non-porous transition layer with a material of a nickel-chromium alloy is added, and the crystallinity of the nickel-chromium alloy is limited to 5-80%. The 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 can promote the application stability of the bipolar current collector in the battery, and improve the cycle performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a bipolar current collector and a preparation method thereof, a battery and applications. Background Art

[0002] At present, with the continuous penetration of electric vehicles, the market has put forward higher requirements for the battery life of electric vehicles. In order to solve the battery life problem of electric vehicles, it is imperative to develop batteries with high specific energy. Among the many solutions, bipolar batteries have continued to attract people's attention as high-specific energy batteries with good prospects. Bipolar batteries are batteries with bipolar pole pieces (pole pieces prepared by coating positive and negative electrode materials on both sides of the current collector) stacked in series. Because they rely on the series conduction of their own current collectors, the wires between the electrodes in traditional batteries are eliminated, thereby reducing the mass and volume of the battery and improving the battery energy density. In addition, the battery structure connected in series can increase the output voltage and power of the battery, thereby increasing the output power of the battery. It is reported that using bipolar batteries, the number of cells that can be accommodated in a battery pack of the same size is equivalent to 1.4 times that of a traditional battery, and the output power of the battery is about 1.5 times that of a traditional battery, showing good potential.

[0003] As a key component of bipolar batteries, the bipolar current collector has a significant impact on the battery's structural stability. Currently, copper-aluminum composite current collectors are commonly used. However, the adhesion between the copper and aluminum layers in copper-aluminum composite current collectors is poor, resulting in an unstable interface. This easily leads to delamination during battery processing and use, causing increased interfacial resistance and, consequently, decreased cycling performance of the resulting bipolar battery.

[0004] Therefore, how to effectively improve the bonding force 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 needs to be solved urgently. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a bipolar current collector, a preparation method thereof, a battery, and applications thereof. Based on the material and structural design of the bipolar current collector, the present invention adds a transition layer made of a 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 the stability of the interface and ensuring good structural stability of the bipolar current collector, but also promotes the stability of the bipolar current collector in the battery and improves the battery's cycling performance.

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

[0007] In a first aspect, the present invention provides a bipolar current collector, comprising a negative electrode conductive layer and a positive electrode conductive layer stacked together, with at least one transition layer stacked between the negative electrode conductive layer and the positive electrode conductive layer.

[0008] The material of the transition layer includes nickel-chromium alloy, and the crystallinity of the nickel-chromium alloy is 5-80%.

[0009] The present invention, based on the material and structural design of the bipolar current collector, adds a transition layer made of a 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 the stability of the interface and ensuring good structural stability of the bipolar current collector, but also promotes the application stability of the bipolar current collector in bipolar batteries and improves the cycle performance of bipolar batteries.

[0010] In the present invention, the nickel-chromium alloy has 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.

[0011] In the present invention, 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, the electrolyte corrosion resistance 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, resulting in poor material stability and poor battery cycle performance.

[0012] Preferably, the transition layer is a non-porous structure.

[0013] In the present invention, the transition layer has a non-porous structure. If the nickel-chromium alloy has holes, the interface is susceptible to electrolyte corrosion, resulting in poor interfacial stability and a decrease in capacity retention during battery cycling. Furthermore, when holes exist between the positive and negative conductive layers adjacent to the nickel-chromium alloy layer, the lack of the barrier effect of the interface layer allows electrolyte to flow between the adjacent positive and negative conductive layers, causing a battery short circuit. Furthermore, the non-porous structure ensures more beneficial mechanical properties (such as tensile strength and elongation at break) and battery capacity retention.

[0014] It should be noted that the bipolar current collector refers to the bipolar current collector.

[0015] Preferably, in the nickel-chromium alloy, the mass proportion of nickel is 10-90%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%.

[0016] In the present invention, an appropriate nickel content by weight helps the transition layer achieve good composite bonding with the positive and negative electrode conductive layers. If the nickel content by weight is too low, it is not conducive to improving the interfacial stability between the negative and positive electrode conductive layers, which in turn leads to poor battery cycle performance. If the nickel content by weight is too high, it is not conducive to improving the interfacial stability between the negative and positive electrode conductive layers, which leads to poor cycle performance of the assembled battery.

[0017] Preferably, the single layer thickness of the transition layer is 5-100 nm, for example, it can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., preferably 10-100 nm.

[0018] In the present invention, an appropriate single-layer transition layer thickness can better improve the bonding strength between the negative and positive electrode conductive layers. If the single-layer thickness of the transition layer is too small, the bonding strength between the negative and positive electrode conductive layers cannot be effectively improved, and the prepared electrode sheet is prone to breakage and defects during rolling, resulting in poor material stability and poor battery cycle performance. If the single-layer thickness of the transition layer is too large, the bonding strength between the negative and positive electrode conductive layers cannot be further improved, the material cost is increased, and the battery cycle performance is poor.

[0019] In the present invention, when the transition layer satisfies the relationship between crystallinity and thickness at the same time, the following problems that exist when the crystallinity between the conductive layer and the transition layer does not match can be effectively avoided:

[0020] (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.

[0021] (2) Poor adhesion at the interface, resulting in delamination during use.

[0022] When the transition layer satisfies the relationship between crystallinity and thickness at the same time, it is possible to achieve improvements in technical effects such as adhesion, stability, and mechanical properties without considering the crystallinity matching between the transition layer and the conductive layer, greatly reducing the difficulty of controlling the production process.

[0023] 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 in a direction away from the negative electrode conductive layer or the positive electrode conductive layer.

[0024] In the present invention, the design of the multi-layer transition layer is combined with the gradient change of the nickel mass content, which helps to reduce the interface resistance between the transition layer and the conductive layer and improve the structural stability of the transition layer.

[0025] Preferably, the total thickness of the at least two transition layers is 10-100 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0026] Preferably, the thickness of the negative electrode conductive layer is ≥0.1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm, etc., preferably 1-10 μm.

[0027] In the present invention, 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 is poor; if it is too thick, the surface density of the current collector is too high, resulting in a battery with too low energy density.

[0028] Preferably, the thickness of the positive electrode conductive layer is ≥0.5 μm, for example, it can be 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm, etc., preferably 1-10 μm.

[0029] In the present invention, 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 is poor; if it is too thick, the surface density of the current collector is too high, resulting in a battery with too low energy density.

[0030] Preferably, the total thickness of the negative electrode conductive layer and the positive electrode conductive layer is ≥2 μm, for example, it can be 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0031] In the present invention, 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 complex electrode current collector are relatively poor, affecting the processing performance of the complex electrode current collector and the cycle performance of the assembled battery.

[0032] 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, preferably any one or a combination of at least two of copper, nickel, or carbon. Exemplary materials include stainless steel, copper-nickel alloy, nickel-titanium alloy, copper-titanium alloy, gold-silver alloy, and the like.

[0033] Preferably, the negative electrode conductive layer further includes a doping element.

[0034] Preferably, the doping element includes any one or a combination of at least two of tungsten, manganese, iron, chromium, cobalt, zirconium, tantalum, niobium or tin.

[0035] Preferably, the mass fraction of the doping element in the negative electrode conductive layer is 0.01-10%, for example, it can be 0.01%, 0.1%, 1%, 5% or 10%.

[0036] The present invention dopes the negative electrode conductive layer with the above-mentioned doping elements to improve its mechanical properties and corrosion resistance, but the content should not be too high, as too high will lead to poor conductivity of the prepared bipolar current collector, while too low will have no effect.

[0037] Preferably, the material of the positive electrode conductive layer includes any one of aluminum, carbon, gold or silver, or a combination of at least two thereof, preferably aluminum and / or carbon. For example, it may be aluminum-gold alloy, gold-silver alloy or silver-aluminum alloy.

[0038] 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.

[0039] In the present invention, the protective layer is designed to prevent the negative electrode conductive layer from being oxidized.

[0040] Preferably, the thickness of the protective layer is 5-100 nm, for example, it can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., preferably 10-80 nm.

[0041] Preferably, the material of the protective layer includes any one of a metal element, a carbon material, an alloy, or an oxide, or a combination of at least two thereof. For example, the metal element is nickel or chromium, the carbon material is graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, or graphene, the alloy is a nickel-based alloy and / or a copper-based alloy, and the oxide is aluminum oxide, silicon oxide, nickel oxide, chromium oxide, cobalt oxide, or copper-chromium oxide.

[0042] 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.

[0043] Preferably, a protective layer is provided on the surface of the positive electrode conductive layer away from the transition layer, and the thickness of the protective layer is 5-100 nm, for example, it can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc. The material of the protective layer includes any one of a metal element, a carbon material, an alloy or an oxide, or a combination of at least two of them.

[0044] In a second aspect, the present invention provides a method for preparing the bipolar current collector as described in the first aspect, the preparation method comprising the following steps:

[0045] A positive electrode conductive layer is provided, and then at least one transition layer and a negative electrode conductive layer are compounded in sequence on one side surface of the positive electrode conductive layer to obtain the bipolar current collector.

[0046] Alternatively, a negative electrode conductive layer is provided, and then at least one transition layer and a positive electrode conductive layer are compounded in sequence on one side surface of the negative electrode conductive layer to obtain the bipolar current collector.

[0047] It should be noted that the positive electrode conductive layer can be made of commercial foil materials, such as aluminum foil.

[0048] Preferably, the composite method of the at least one transition layer comprises at least one method selected from the group consisting of a mechanical rolling method, a bonding method, a vapor deposition method, a chemical plating method, and an electroplating method.

[0049] Preferably, the vapor deposition method includes magnetron sputtering and / or vacuum evaporation.

[0050] Preferably, the composite method of the at least one transition layer is magnetron sputtering, and the specific parameters independently include:

[0051] The target material is a nickel-chromium target with a nickel mass content of 10-90% (for example, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc.), the power supply is a pulsed DC power supply, the power frequency is 5-50kHz, for example, 5kHz, 10kHz, 20kHz, 30kHz, 40kHz or 50kHz, etc., the target power is 2-20kW, for example, 2kW, 5kW, 10kW, 15kW or 20kW, etc., and the gas flow rate is 3 0-500mL / min, for example, it can be 30mL / min, 50mL / min, 100mL / min, 200mL / min, 300mL / min, 400mL / min or 500mL / min, etc. The chamber vacuum degree is ≤0.1Pa, for example, it can be 0.1Pa, 0.05Pa or 0.01Pa, etc. The cooling temperature of the coating main roller is 5-30℃, for example, it can be 5℃, 10℃, 15℃, 20℃, 25℃ or 30℃, etc.

[0052] Preferably, the positive electrode conductive layer and the negative electrode conductive layer are each independently prepared by any one of physical vapor deposition, chemical vapor deposition, rolling, or coating-drying methods, or a combination of at least two thereof. For example, the physical vapor deposition method may be magnetron sputtering, and the chemical vapor deposition method may be plasma-enhanced chemical vapor deposition.

[0053] It should be noted that when the negative electrode conductive layer or the positive electrode conductive layer is a carbon layer, it is deposited using a coating-drying method.

[0054] Preferably, when the negative electrode conductive layer is made of copper, a protective layer is provided on the surface of the negative electrode conductive layer away from the transition layer. The protective layer may be prepared by any one of physical vapor deposition, chemical vapor deposition, in-situ forming, or coating, or a combination of at least two of these methods. 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 the protective layer in situ on the surface of the copper layer, and the coating method is preferably die coating, blade coating, or extrusion coating.

[0055] In a third aspect, the present invention 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.

[0056] In a fourth aspect, the present invention provides a battery, wherein the electrode in the battery includes the bipolar current collector as described in the first aspect.

[0057] The numerical range described in the present invention 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 simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) The present invention starts from the material and structural design of the bipolar current collector, adds a transition layer made of nickel-chromium alloy, and limits 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 the bipolar battery and improve the cycle performance of the battery.

[0060] (2) The preparation method provided by the present invention is simple and easy to operate, and is suitable for large-scale promotion. DETAILED DESCRIPTION

[0061] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] Example 1

[0063] This embodiment provides a bipolar current collector, which includes a negative electrode protection layer, a negative electrode conductive layer, a transition layer, a positive electrode conductive layer, and a positive electrode protection layer that are stacked.

[0064] The material of the transition layer is nickel-chromium alloy, in which nickel accounts for 80% by 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.

[0065] 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 made of commercial aluminum foil (commercial aluminum foil has its own aluminum oxide protective layer) and has a thickness of 13 μm. The total thickness of the negative and positive electrode conductive layers is 14 μm.

[0066] This embodiment also provides a method for preparing the above-mentioned bipolar current collector, which comprises the following steps:

[0067] (1) A commercial aluminum foil is provided as the positive electrode conductive layer, and then the aluminum foil is placed in a magnetron sputtering machine to deposit a transition layer on one side of the aluminum foil. The specific process conditions of the transition layer magnetron sputtering are as follows:

[0068] A nickel-chromium target (purity: 99.99%, nickel mass content of 80%) was used as the target material, a pulsed DC power supply was used, the power frequency was 20 kHz, the target power was 5.0 kW, the argon flow rate was 50 mL / min, the chamber vacuum was 0.08 Pa, the sputtering time was 2 s, and the temperature of the main roller during the deposition process was 15°C.

[0069] (2) The composite layer obtained in step (1) is placed in a magnetron sputtering machine to deposit a copper layer on the surface of the transition layer. The specific process conditions are as follows:

[0070] A copper target (purity 99.99%) was used as the target material, the target power was 10 kW, the argon flow rate was 80 mL / min, the chamber pressure was 0.1 Pa, the sputtering time was 130 s, and the main roller cooling temperature was -10°C.

[0071] (3) The composite layer prepared in step (2) was placed in a 0.6 g / L chromic acid aqueous solution for 20 seconds, and then the surface liquid was removed and dried at 70° C. to obtain the negative electrode protective layer, thereby completing the preparation of the bipolar current collector.

[0072] In the present invention, the surface pores of the transition layer can be detected by the following methods:

[0073] Take the finished bipolar current collector, randomly select 5 positions on the bipolar current collector, and use focused ion beam (FIB) to prepare cross-sectional samples to prepare cross-sectional analysis samples that meet the requirements of transmission electron microscopy (TEM) testing (the cross-section includes the negative conductive layer, the positive conductive layer and the transition layer). Then, use TEM to magnify and observe the transition layer of the cross-section. The characterization results show that there are no holes at all 5 positions, and it is judged that the transition layer has no holes.

[0074] Example 2

[0075] The difference between this embodiment and embodiment 1 is that the mass content of nickel in the nickel-chromium target is 50%, the target power is 5.3 kW, and the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 50:50.

[0076] The rest of the preparation methods and parameters remained the same as in Example 1.

[0077] Example 3

[0078] The difference between this embodiment and embodiment 1 is that the mass content of nickel in the nickel-chromium target is 10%, the target power is 6.0 kW, and the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 10:90.

[0079] The rest of the preparation methods and parameters remained the same as in Example 1.

[0080] Example 4

[0081] The difference between this embodiment and embodiment 1 is that the mass content of nickel in the nickel-chromium target is 90%, the target power is 4.7 kW, and the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 90:10.

[0082] The rest of the preparation methods and parameters remained the same as in Example 1.

[0083] Example 5

[0084] 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 s, so that the thickness of the transition layer is 5 nm.

[0085] The rest of the preparation methods and parameters remained the same as in Example 1.

[0086] Example 6

[0087] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 10 s, so that the thickness of the transition layer is 50 nm.

[0088] The rest of the preparation methods and parameters remained the same as in Example 1.

[0089] Example 7

[0090] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 16 seconds, so that the thickness of the transition layer is 80 nm.

[0091] The rest of the preparation methods and parameters remained the same as in Example 1.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 20 s, so that the thickness of the transition layer is 100 nm.

[0094] The rest of the preparation method and parameters remain the same as embodiment 1.

[0095] Embodiment 9

[0096] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the copper layer is adjusted to 65 s, so that the thickness of the copper layer is 0.5 μm.

[0097] The rest of the preparation method and parameters remain the same as embodiment 1.

[0098] Embodiment 10

[0099] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the copper layer is adjusted to 650 s, so that the thickness of the copper layer is 5 μm.

[0100] The rest of the preparation method and parameters remain the same as embodiment 1.

[0101] Embodiment 11

[0102] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the copper layer is adjusted to 1300 s, so that the thickness of the copper layer is 10 μm.

[0103] The rest of the preparation method and parameters remain the same as embodiment 1.

[0104] Embodiment 12

[0105] The difference between this embodiment and embodiment 1 is that the thickness of the commercialized aluminum foil is 1 μm.

[0106] The rest of the preparation method and parameters remain the same as embodiment 1.

[0107] Embodiment 13

[0108] The difference between this embodiment and embodiment 1 is that the thickness of the commercialized aluminum foil is 20 μm.

[0109] The rest of the preparation method and parameters remain the same as embodiment 1.

[0110] Embodiment 14

[0111] The difference between this embodiment and embodiment 1 is that the thickness of the commercialized aluminum foil is 20 μm.

[0112] The rest of the preparation methods and parameters remained the same as in Example 1.

[0113] Example 15

[0114] 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. The specific process conditions are:

[0115] An aqueous solution containing 300 g / L NiSO4·6H2O, 150 g / L NiCl2·6H2O and 52 g / L H3BO3 was used as the plating solution at 5 A / dm 2 The nickel plate is electroplated at a current density of 1000 nm for 95 seconds, then cleaned to remove residual liquid on the surface, and dried at 70° C. The negative electrode protective layer is generated by in-situ oxidation during the nickel electroplating and drying process.

[0116] The rest of the preparation methods and parameters remained the same as in Example 1.

[0117] Example 16

[0118] The difference between this embodiment and embodiment 1 is that the negative electrode conductive layer is a copper-nickel alloy layer (the mass ratio of copper to nickel is 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:

[0119] Copper-nickel material (purity 99.99%, mass ratio of copper to nickel is 1:1) is used as the target material, the target power is 10 kW, the argon flow rate is 80 mL / min, the chamber vacuum is 0.1 Pa, the sputtering time is 133 s, and the main roller cooling temperature is -10 °C.

[0120] The rest of the preparation methods and parameters remained the same as in Example 1.

[0121] Example 17

[0122] 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:

[0123] The copper foil was placed in a magnetron sputtering machine with a graphite target (purity of 99.99%) as the target material, a target power of 3 kW, an argon flow rate of 50 mL / min, a chamber vacuum of 0.08 Pa, a sputtering time of 200 s, and a main roller temperature of 0°C during the deposition process, thereby preparing a 1 μm thick carbon layer on the surface of the copper foil.

[0124] The rest of the preparation methods and parameters remained the same as in Example 1.

[0125] Example 18

[0126] 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 in a direction away from the negative electrode conductive layer, and the thickness of the first transition layer and the second transition layer are both 10 nm.

[0127] 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 5.2 kW and the sputtering time is 1 s.

[0128] The mass ratio of nickel to chromium in the nickel-chromium alloy of the second transition layer is 80:20; in the preparation method parameters, the target power is 5.0 kW and the sputtering time is 1 s.

[0129] During the preparation process, magnetron sputtering is used to deposit two transition layers on one surface of the aluminum foil.

[0130] The rest of the preparation methods and parameters remained the same as in Example 1.

[0131] Example 19

[0132] The difference between this embodiment and Example 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, during the preparation process of the negative electrode conductive layer, the target material is adjusted to a copper-chromium alloy, and the mass content of chromium is 1%, and the target power is 12 kW; the material of the negative electrode protective layer is copper-chromium oxide.

[0133] The rest of the preparation methods and parameters remained the same as in Example 1.

[0134] Example 20

[0135] The difference between this embodiment and embodiment 1 is that the mass content of nickel in the nickel-chromium target is 5%, and the target power is 6.2 kW, so that the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 5:95.

[0136] The rest of the preparation methods and parameters remained the same as in Example 1.

[0137] Example 21

[0138] The difference between this embodiment and embodiment 1 is that the mass content of nickel in the nickel-chromium target is 95%, and the target power is 4.5 kW, so that the mass ratio of nickel to chromium in the nickel-chromium alloy of the transition layer is 95:5.

[0139] The rest of the preparation methods and parameters remained the same as in Example 1.

[0140] Example 22

[0141] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 0.6 s, so that the thickness of the transition layer is 3 nm.

[0142] The rest of the preparation methods and parameters remained the same as in Example 1.

[0143] Example 23

[0144] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the transition layer is adjusted to 22 seconds, so that the thickness of the transition layer is 110 nm.

[0145] The rest of the preparation methods and parameters remained the same as in Example 1.

[0146] Example 24

[0147] The difference between this embodiment and embodiment 1 is that the sputtering time in the deposition process of the copper layer is adjusted to 39 seconds, so that the thickness of the copper layer is 0.3 μm.

[0148] The rest of the preparation methods and parameters remained the same as in Example 1.

[0149] Example 25

[0150] The difference between this embodiment and embodiment 1 is that the negative electrode conductive layer uses an electrolytic copper foil with a thickness of 1 μm, and then a transition layer is deposited on one side of the electrolytic copper foil, and then a layer of aluminum with a thickness of 0.3 μm is deposited on the surface of the transition layer by vapor deposition.

[0151] The rest of the preparation methods and parameters remained the same as in Example 1.

[0152] Example 26

[0153] The difference between this embodiment and embodiment 1 is that the power frequency in the deposition process of the transition layer is adjusted to 50 kHz, the sputtering time is 1.5 s, and the temperature of the coating main roller is adjusted to 30°C.

[0154] The rest of the preparation methods and parameters remained the same as in Example 1.

[0155] Example 27

[0156] The difference between this embodiment and embodiment 1 is that the power frequency in the deposition process of the transition layer is adjusted to 5 kHz, the sputtering time is 3.0 s, and the temperature of the coating main roller is adjusted to 5°C.

[0157] The rest of the preparation methods and parameters remained the same as in Example 1.

[0158] Comparative Example 1

[0159] The difference between this comparative example and Example 1 is that the material of the transition layer is elemental nickel and the target power is 4.5 kW.

[0160] The rest of the preparation methods and parameters remained the same as in Example 1.

[0161] Comparative Example 2

[0162] The difference between this comparative example and Example 1 is that the material of the transition layer is elemental chromium and the target power is 6.5 kW.

[0163] The rest of the preparation methods and parameters remained the same as in Example 1.

[0164] Comparative Example 3

[0165] The difference between this comparative example and Example 1 is that no transition layer is provided.

[0166] The rest of the preparation methods and parameters remained the same as in Example 1.

[0167] Comparative Example 4

[0168] The difference between this embodiment and embodiment 1 is that the power frequency in the deposition process of the transition layer is adjusted to 4.5 kHz, the sputtering time is adjusted to 3.2 s, and the temperature of the coating main roller is adjusted to 5°C.

[0169] The rest of the preparation methods and parameters remained the same as in Example 1.

[0170] Comparative Example 5

[0171] The difference between this embodiment and embodiment 1 is that the power frequency in the deposition process of the transition layer is adjusted to 55 kHz, the sputtering time is 1.2 s, and the temperature of the coating main roller is 30°C.

[0172] The rest of the preparation methods and parameters remained the same as in Example 1.

[0173] Performance Testing

[0174] 1. The adhesion, tensile strength, elongation at break, square resistance and crystallinity of the bipolar current collectors provided in the above embodiments and comparative examples were tested. The specific testing methods are as follows:

[0175] 1) Adhesion

[0176] The bipolar current collector was placed in an adhesion test device and tested as follows: a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the positive conductive layer of the bipolar current collector was adhered on top of the double-sided tape, and then a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the negative conductive layer. 5 N / m 2The film was hot-pressed at 120°C for 10 seconds, cooled to room temperature (25°C), and cut into 150mm x 15mm strips. The ethylene acrylic acid copolymer film strip was fixed to the upper fixture of the tensile testing machine, and the remaining film strip was fixed to the lower fixture. After the two strips were fixed, they were peeled off at an angle of 180° and a speed of 100mm / min. The peel force was measured. The obtained peel force is the bonding strength between the negative and positive conductive layers in the bipolar current collector.

[0177] 2) Tensile strength and elongation at break

[0178] Refer to national standard GB / T 1040.3-2006.

[0179] 3) Square resistance

[0180] The bipolar current collector sample is placed on the sample stage, and the square resistance of the two opposite surfaces of the sample is tested respectively using a four-probe square resistance meter.

[0181] 4) Crystallinity

[0182] The crystallinity of the transition layer in the bipolar current collector is tested by X-ray diffraction. The finished bipolar current collector is taken, and the copper layer is first thinned to a thickness of 0 (thinning methods such as focused ion beam can be used). The treated sample is then placed in an X-ray diffractometer and scanned at a rate of 2° / min within the range of 5-90 degrees to obtain a diffraction curve. The crystallinity can be calculated by combining the diffraction curve and using the following formula:

[0183] Xc=Ic / (Ic+Ia)×100%

[0184] Wherein, Ic is the diffraction integrated intensity of the crystalline part, Ia is the diffraction integrated intensity of the amorphous part, and Xc is the crystallinity.

[0185] The test results are shown in Table 1.

[0186] Table 1

[0187]

[0188]

[0189]

[0190] 2. A solid-state lithium battery is prepared based on the bipolar current collector provided in the above embodiment and comparative example. The specific steps include:

[0191] ① Coating electrode materials on the positive conductive layer side, the electrode materials include LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black Super P, PVDF 5130 and carbon nanotubes CNT, with a mass ratio of 96:1.8:1.7:0.5.

[0192] ② Coating the electrode material on the negative conductive layer side. The electrode material includes graphite, conductive carbon black SuperP, carbon nanotubes and CMC with a mass ratio of 96:3.0:0.6:0.4.

[0193] ③ Use Li6PS5Cl as the solid electrolyte and assemble it into a soft-pack battery with a capacity of 3Ah according to the assembly process of bipolar solid-state batteries.

[0194] The soft-pack battery assembled above was subjected to a cycle performance test. The test conditions were as follows: charge and discharge at a constant current constant voltage (CCCV) rate of 1C, and discharge at a constant current (CC) rate of 1C, for 2000 cycles. The battery capacity retention rate after 2000 cycles of charge and discharge was recorded, that is, the battery capacity after 2000 cycles of charge and discharge / the initial capacity of the battery × 100%.

[0195] The test results are shown in Table 2.

[0196] Table 2

[0197]

[0198]

[0199]

[0200] analyze:

[0201] As can be seen from Tables 1 and 2, the present invention adopts a design in which a transition layer including a nickel-chromium alloy is added. This design not only improves the bonding force 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 promotes the application stability of the bipolar current collector in the bipolar battery and improves the cycle performance of the bipolar battery.

[0202] It can be seen from Examples 1-4, Example 20 and Example 21 that as the mass proportion of nickel in the transition layer continues to increase, the bonding force between the negative electrode conductive layer and the positive electrode conductive layer in the prepared bipolar current collector first increases and then decreases. This is because as the nickel content increases, the interaction force between the transition layer and the conductive layer first increases and then decreases. In addition, the corresponding tensile strength and elongation at break also show a trend of first increasing and then decreasing, which is due to the change in bonding force. The corresponding square resistance changes little, because the square resistance mainly depends on the material and thickness of the positive and negative electrode 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.

[0203] As can be seen from Example 1, Examples 5-8, Example 22 and Example 23, as the thickness of the transition layer increases, the adhesion between the negative conductive layer and the positive conductive layer in the bipolar current collector shows a trend of improvement. Due to the increase in the thickness of the transition layer, the uniformity of the transition layer first improves and then remains unchanged, so the force between the conductive layer first improves and then remains unchanged, and therefore the corresponding tensile strength and elongation at break also show the same trend. The corresponding square resistance changes little, because the square resistance mainly depends on the material and thickness 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. In addition, if the thickness of the transition layer is too small, the cycle performance of the battery is poor; if the thickness of the transition layer is too large, the cycle performance of the battery improves little. Therefore, the thickness of the transition layer is preferably 10-100 nm.

[0204] As can be seen from Example 1, Examples 9-11 and Example 24, as the thickness of the negative conductive layer increases, the square resistance of the bipolar current collector decreases, the conductivity improves, the tensile strength increases, the elongation at break decreases, and the adhesion remains unchanged, because the adhesion mainly depends on the properties of the transition layer. Considering the conductivity, the thickness of the negative conductive layer should be ≥0.5 μm, and further considering the problem of the decrease in the energy density of the battery caused by the increase in the thickness of the conductive layer, the thickness of the negative conductive layer is preferably in the range of 1-10 μm.

[0205] As can be seen from Example 1, Examples 12-14 and Example 25, as the thickness of the positive conductive layer increases, the square resistance of the bipolar current collector decreases, the conductivity improves, the tensile strength increases, the elongation at break decreases, and the adhesion remains unchanged, because the adhesion mainly depends on the properties of the transition layer. Considering the conductivity, the thickness of the positive conductive layer should be ≥0.5 μm, and further considering the problem of the decrease in the energy density of the battery caused by the increase in the thickness of the conductive layer, the thickness of the positive conductive layer is preferably in the range of 1-10 μm.

[0206] As can be seen from Example 1, Examples 15-17, replacing the material of the positive conductive layer or the negative conductive layer with other materials also achieves good results.

[0207] As can be seen from Example 1 and Examples 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, makes the nickel content in the two transition layers show a gradient change, which helps to reduce the interface resistance between the transition layer and the conductive layer, and improve the structural stability of the transition layer, and further improve the cycle performance of the battery. If the material of the negative conductive layer includes copper and chromium, the combination of the two helps to improve the mechanical properties and corrosion resistance of the bipolar current collector, and further improve the cycle performance of the assembled battery.

[0208] It can be seen from Example 1, Examples 26-27 and Comparative Examples 4-5 that 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 transition layer has excessive crystallinity, which makes the transition layer brittle and prone to breakage during the rolling process of the prepared pole piece, resulting in defects, resulting in poor material stability and thus poor battery cycle performance.

[0209] It can be seen from Example 1 and Comparative Examples 1-2 that if the material of the transition layer is elemental nickel or elemental chromium, it is not conducive to the close bonding between the positive and negative conductive layers, resulting in poor structural stability of the bipolar current collector, and further causing poor cycle performance of the assembled battery.

[0210] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A bipolar current collector for a battery, characterized in that: The bipolar current collector comprises a negative electrode conductive layer, at least one transition layer and a positive electrode conductive layer stacked in sequence; The material of the transition layer is a nickel-chromium alloy, and the crystallinity of the nickel-chromium alloy is 5-80%; The transition layer has a non-porous structure; the mass proportion of nickel in the nickel-chromium alloy is 10-90%; the thickness of a single layer of the transition layer is 5-100 nm; The material of the negative electrode conductive layer includes any one of copper, nickel, titanium, carbon, gold or silver, or a combination of at least two of them; the material of the positive electrode conductive layer includes any one of aluminum, carbon, gold or silver, or a combination of at least two of them.

2. The bipolar current collector according to claim 1, characterized in that The nickel-chromium alloy has a crystallinity of 20-60%.

3. The bipolar current collector according to claim 1, characterized in that: The single layer thickness of the transition layer is 10-100 nm.

4. The bipolar current collector according to claim 1, characterized in that: 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 in a direction away from the negative electrode conductive layer or the positive electrode conductive layer.

5. The bipolar current collector according to claim 4, characterized in that: The total thickness of the at least two transition layers is 10-100 nm.

6. The bipolar current collector according to claim 1, characterized in that: The thickness of the negative electrode conductive layer is ≥0.1 μm.

7. The bipolar current collector according to claim 6, characterized in that: The thickness of the negative electrode conductive layer is 1-10 μm.

8. The bipolar current collector according to claim 1, characterized in that: The thickness of the positive electrode conductive layer is ≥0.5 μm.

9. The bipolar current collector according to claim 8, characterized in that: The thickness of the positive electrode conductive layer is 1-10 μm.

10. The bipolar current collector according to claim 1, characterized in that: The total thickness of the negative electrode conductive layer and the positive electrode conductive layer is ≥2 μm.

11. The bipolar current collector according to claim 1, characterized in that: The material of the negative electrode conductive layer is any one of copper, nickel or carbon, or a combination of at least two of them.

12. The bipolar current collector according to claim 1, characterized in that: The negative electrode conductive layer also includes a doping element; The doping element includes any one of tungsten, manganese, iron, chromium, cobalt, zirconium, tantalum, niobium or tin, or a combination of at least two of them.

13. The bipolar current collector according to claim 12, characterized in that: The mass fraction of the doping element in the negative electrode conductive layer is 0.01-10%.

14. The bipolar current collector according to claim 1, characterized in that: The material of the positive electrode conductive layer is aluminum and / or carbon.

15. The bipolar current collector according to claim 1, characterized in that: 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.

16. The bipolar current collector according to claim 15, characterized in that: The thickness of the protective layer is 5-100 nm.

17. The bipolar current collector according to claim 16, characterized in that: The thickness of the protective layer is 10-80 nm.

18. The bipolar current collector according to claim 15, characterized in that: The material of the protective layer includes any one of a metal element, a carbon material, an alloy or an oxide, or a combination of at least two of them.

19. A method for preparing a bipolar current collector according to any one of claims 1 to 18, characterized in that: The preparation method comprises the following steps: Providing a positive electrode conductive layer, and then sequentially compounding at least one transition layer and a negative electrode conductive layer on one side surface of the positive electrode conductive layer to obtain the bipolar current collector; Alternatively, a negative electrode conductive layer is provided, and then at least one transition layer and a positive electrode conductive layer are compounded in sequence on one side surface of the negative electrode conductive layer to obtain the bipolar current collector.

20. The preparation method according to claim 19, characterized in that The composite method of the at least one transition layer includes at least one method selected from the group consisting of mechanical rolling, bonding, vapor deposition, chemical plating, and electroplating.

21. The preparation method according to claim 20, characterized in that The vapor deposition method includes magnetron sputtering and / or vacuum evaporation.

22. The preparation method according to claim 21, characterized in that The composite method of the at least one transition layer is magnetron sputtering, and the specific parameters independently include: The target material is a nickel-chromium target with a nickel mass content of 10-90%, the power supply is a pulsed DC power supply, the power frequency is 5-50kHz, the target power is 2-20kW, the gas flow is 30-500mL / min, the chamber vacuum is ≤0.1Pa, and the cooling temperature of the coating main roller is 5-30℃.

23. The preparation method according to claim 19, characterized in that The preparation methods of the positive electrode conductive layer and the negative electrode conductive layer are independently any one of physical vapor deposition, chemical vapor deposition, rolling or coating-drying methods, or a combination of at least two thereof.

24. A battery, characterized in that: The electrode piece in the battery includes the bipolar current collector according to any one of claims 1 to 18.

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