A bipolar current collector, its preparation method and application

Abstract

This invention belongs to the field of battery manufacturing technology, and relates to a bipolar current collector, its preparation method, and its application. The bipolar current collector includes at least a negative electrode conductive layer and a positive electrode conductive layer stacked together, and a surface layer is provided on the side of the negative electrode conductive layer away from the positive electrode conductive layer. By adding a surface layer to the bipolar current collector, this invention effectively covers the material defects of the positive electrode conductive layer that leak from the negative electrode conductive layer in traditional rolled bipolar current collectors, avoiding local micro-short circuits in the battery and improving the battery's cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, and relates to a bipolar current collector, and more particularly to a bipolar current collector and its preparation method and application. Background Technology

[0002] Traditional lithium-ion batteries rely on independent electrodes connected in series with external wires, resulting in a high proportion of inactive components and limited energy density improvement, making it difficult to meet the performance requirements of next-generation electric vehicles.

[0003] Based on the above situation, bipolar batteries, with their innovative structural design, have become an important development direction for high-energy-density batteries. They form bipolar electrodes by coating positive and negative active materials on both sides of the current collector, eliminating the need for additional wires when stacked in series, thus significantly reducing the proportion of inactive components. It is roughly estimated that a bipolar battery pack of the same size can hold 1.4-1.5 times more cells than a traditional battery, significantly improving energy density and output power, providing an effective solution to range anxiety.

[0004] As a core component of bipolar batteries, the bipolar current collector plays a crucial role in conducting electricity, supporting the active materials, and isolating the positive and negative electrodes. Its performance directly determines the battery's reliability. Currently, the mainstream industry method for preparing bipolar current collectors is rolling, using a composite copper (negative electrode conductive layer) and aluminum (positive electrode conductive layer) to form the substrate. However, copper and aluminum have significant differences in physical properties, and uneven interfacial stress during rolling can easily lead to weak interlayer bonding, resulting in the typical defect of leakage of positive electrode conductive layer material from the negative electrode conductive layer.

[0005] If the above defects occur, during battery cycle charging and discharging, the leaked aluminum-based material reacts with the electrolyte to form an unstable interface film, and at the same time forms a local conductive channel, eventually causing an internal micro short circuit. This not only accelerates the battery capacity decay, but also easily leads to concentrated heat release, and may even cause thermal runaway, seriously reducing the battery's cycle performance and safety.

[0006] Therefore, developing a bipolar current collector that can effectively solve side leakage defects and balance structural stability and energy density has become the key to promoting the implementation of bipolar battery technology and breaking through the limitations of electric vehicle range and safety performance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a bipolar current collector, its preparation method, and its application, which covers the defects of the positive electrode conductive layer material leaking from the negative electrode conductive layer side of traditional rolled bipolar current collectors, and solves the problems of local micro-short circuits and poor cycle performance in batteries caused by this.

[0008] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a bipolar current collector, comprising at least a negative electrode conductive layer and a positive electrode conductive layer stacked together, wherein a surface layer is provided on the side of the negative electrode conductive layer away from the positive electrode conductive layer.

[0009] This invention adds a surface layer to the negative conductive layer of the bipolar current collector. By utilizing its dense structural features, it effectively covers the material defects of the positive conductive layer that leak from the negative conductive layer of the traditional rolled bipolar current collector. This fundamentally solves the problem of local micro-short circuits during battery cycling and significantly improves the cycle performance of bipolar batteries.

[0010] Preferably, the material of the surface 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.

[0011] Preferably, the thickness of the surface layer is 0.1~10μm, and more preferably 2~6μm.

[0012] Preferably, the bipolar current collector satisfies at least one of the following conditions: (a) The surface roughness of the side of the surface layer away from the negative electrode conductive layer is less than the surface roughness of the side of the negative electrode conductive layer away from the positive electrode conductive layer, and the surface roughness Ra of the negative electrode conductive layer is 0.15~0.30μm.

[0013] (b) The grain morphology of the negative electrode conductive layer is fibrous, and the grain morphology of the surface layer is equiaxed or columnar.

[0014] (c) The average orientation difference between adjacent grains in the negative electrode conductive layer is less than the average orientation difference between adjacent grains in the surface layer, and the average orientation difference between adjacent grains in the negative electrode conductive layer is ≤15°, while the average orientation difference between adjacent grains in the surface layer is >15°.

[0015] (d) The water contact angle of the surface layer is less than the water contact angle of the negative electrode conductive layer, and the water contact angle of the surface layer is ≤70°, preferably 0°~60°; the water contact angle of the negative electrode conductive layer is >70°.

[0016] Preferably, the relationship between the thickness h1 of the surface layer and the thickness h2 of the negative electrode conductive layer is: h1 / h2 = 0.1~1, preferably 0.1~0.5.

[0017] Preferably, the bipolar current collector satisfies at least one of the following conditions: (A) The bipolar current collector further includes a negative electrode protective layer, which is disposed on the surface of the surface layer away from the negative electrode conductive layer.

[0018] The material of the negative electrode protective layer includes any one or a combination of at least two of the following: chromium, nickel, nickel-based alloys, copper-based alloys, copper-chromium oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, carbon nanotubes, carbon nanofibers, or graphene.

[0019] And / or, the thickness of the negative electrode protective layer is 5~100nm, preferably 10~80nm.

[0020] And / or, the material of the negative electrode conductive layer includes copper or a copper alloy.

[0021] And / or, the thickness of the negative electrode conductive layer is 0.5~10μm.

[0022] (B) The bipolar current collector further includes a positive electrode protective layer, which is disposed on the side surface of the positive electrode conductive layer away from the negative electrode conductive layer.

[0023] The positive electrode protective layer is made of any one or a combination of at least two of the following: aluminum oxide, silicon oxide, graphene, carbon nanotubes, carbon nanofibers, or carbon nanotubes.

[0024] And / or, the thickness of the positive electrode protective layer accounts for 0.05% to 0.1% of the total thickness of the substrate, and the substrate refers to a composite structure of the negative electrode conductive layer, the interface layer, the positive electrode conductive layer and the positive electrode protective layer.

[0025] And / or, the material of the positive conductive layer includes aluminum or an aluminum alloy.

[0026] And / or, the thickness of the positive electrode conductive layer is 5~100μm.

[0027] (C) The bipolar current collector further includes an interface layer, which is disposed between the negative electrode conductive layer and the positive electrode conductive layer.

[0028] The material of the interface layer includes a copper-aluminum alloy, specifically any one or a combination of at least two of Al2Cu, AlCu, Al2Cu3, Al3Cu4 or Al4Cu9.

[0029] And / or, the thickness of the interface layer is 0.05~5μm.

[0030] In a second aspect, the present invention provides a method for preparing a bipolar current collector as described in the first aspect, comprising the following steps: (1) A negative electrode conductive layer and a positive electrode conductive layer are prepared by solid-liquid composite rolling method; (2) Prepare a surface layer on the surface of the negative electrode conductive layer.

[0031] Preferably, the solid-liquid composite rolling method in step (1) includes copper plate pretreatment, copper-aluminum melt rolling, cold rolling, heat treatment and foil rolling performed sequentially.

[0032] Preferably, the copper plate pretreatment includes: first immersing the copper plate in acetone or alkaline solution to remove surface oil, then cleaning the copper plate with acid solution to remove surface oxides, and finally cleaning the copper plate with anhydrous ethanol and drying it.

[0033] Preferably, the copper-aluminum melt rolling process includes: first melting a clean high-purity aluminum plate, then casting the resulting molten aluminum onto the surface of a copper plate under oxygen-free conditions, and rolling it into a copper-aluminum composite plate.

[0034] Preferably, the cold rolling process reduces the thickness of the copper-aluminum composite plate to 80-120 μm.

[0035] Preferably, the temperature of the heat treatment is 300~550℃.

[0036] Preferably, the foil rolling process rolls the copper-aluminum composite plate to a thickness of 20~30μm.

[0037] Preferably, the method for preparing the surface layer in step (2) includes any one or a combination of at least two of physical vapor deposition, electroplating, or electroless plating.

[0038] Preferably, the preparation method further includes: preparing a negative electrode protective layer on the surface of the surface layer.

[0039] Preferably, the method for preparing the negative electrode protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ molding, or coating.

[0040] Thirdly, the present invention provides a bipolar electrode sheet, comprising at least the bipolar current collector as described in the first aspect.

[0041] Fourthly, the present invention provides a bipolar battery, comprising at least a bipolar current collector as described in the first aspect or a bipolar electrode as described in the third aspect.

[0042] Compared with the prior art, the present invention has the following beneficial effects: This invention adds a surface layer to the negative conductive layer of the bipolar current collector. By utilizing its dense structural features, it effectively covers the material defects of the positive conductive layer that leak from the negative conductive layer of the traditional rolled bipolar current collector. This fundamentally solves the problem of local micro-short circuits during battery cycling and significantly improves the cycle performance of bipolar batteries. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the bipolar current collector structure provided by the present invention.

[0044] Wherein: 1-negative electrode protective layer; 2-negative electrode conductive layer; 3-interface layer; 4-positive electrode conductive layer; 5-positive electrode protective layer; 6-surface layer. Detailed Implementation

[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0046] One embodiment of the present invention provides a bipolar current collector, which includes at least a negative electrode conductive layer and a positive electrode conductive layer stacked together, and a surface layer is provided on the side of the negative electrode conductive layer away from the positive electrode conductive layer.

[0047] This invention adds a surface layer to the negative conductive layer of the bipolar current collector. By utilizing its dense structural features, it effectively covers the material defects of the positive conductive layer that leak from the negative conductive layer of the traditional rolled bipolar current collector. This fundamentally solves the problem of local micro-short circuits during battery cycling and significantly improves the cycle performance of bipolar batteries.

[0048] In some embodiments, the surface layer is made of 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.

[0049] In some embodiments, the thickness of the surface layer is 0.1 to 10 μm, for example, it can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, more preferably 2 to 6 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0050] This invention limits the thickness of the surface layer to a reasonable range. If the thickness of the surface layer is less than 0.1 μm, it cannot effectively cover the defects in the positive electrode conductive layer material leaking from the negative electrode conductive layer; if the thickness of the surface layer is greater than 10 μm, the areal density of the resulting repolar current collector is too high, crowding out the coating space of the active material, thus resulting in a low areal density of the battery.

[0051] In some embodiments, the bipolar current collector satisfies at least one of the following conditions: (a) The surface roughness of the side of the surface layer away from the negative electrode conductive layer is less than the surface roughness of the side of the negative electrode conductive layer away from the positive electrode conductive layer, and the surface roughness Ra of the negative electrode conductive layer is 0.15~0.30μm, for example, it can be 0.15μm, 0.16μm, 0.17μm, 0.18μm, 0.19μm, 0.20μm, 0.21μm, 0.22μm, 0.23μm, 0.24μm, 0.25μm, 0.26μm, 0.27μm, 0.28μm, 0.29μm or 0.30μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0052] The implementation of condition (a) above includes, but is not limited to: roughening the negative electrode conductive layer to increase its roughness, or polishing the surface layer, adjusting the deposition process, etc. to reduce its roughness, or setting an uneven structure on the rolling roll of the negative electrode conductive layer.

[0053] This invention specifies that the repolar current collector, when meeting condition (a), can increase the adhesion between the negative electrode conductive layer and the surface layer, while simultaneously improving the adhesion between the surface layer and the active material. Furthermore, the inventors' experimental research has revealed that by adjusting the roughness, the surface layer can better conceal / fill the defect areas of the negative electrode during growth.

[0054] (b) The grain morphology of the negative electrode conductive layer is fibrous, and the grain morphology of the surface layer is equiaxed or columnar.

[0055] The implementation of condition (b) above includes, but is not limited to: preparing the negative electrode conductive layer by rolling; and preparing the surface layer by atomic deposition.

[0056] The present invention specifies that the bipolar current collector can break the epitaxial continuity, introduce multi-directional growth mode and high-density grain boundary, so that the upper material “bypasses” rather than “replicates” the defects of the bottom layer, thereby achieving defect masking on a macroscopic level. At the same time, it can hinder dislocation slip, improve the resistance to cyclic bending / stretching, and effectively improve the adhesion.

[0057] (c) The average orientation difference between adjacent grains in the negative electrode conductive layer is less than the average orientation difference between adjacent grains in the surface layer, and the average orientation difference between adjacent grains in the negative electrode conductive layer is ≤15°, while the average orientation difference between adjacent grains in the surface layer is >15°.

[0058] The average orientation difference between adjacent grains in the negative electrode conductive layer is ≤15°, for example, it can be 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14° or 15°. The average orientation difference between adjacent grains in the surface layer is >15°, for example, it can be 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29° or 30°, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0059] In this invention, the average misorientation of grains (Grain Average Misorientation) GAM (Orientation Gradient Aspect) is an important indicator characterizing the orientation gradient within a grain. It is defined as the average nucleus average orientation difference (KAM) of all measurement points within the grain. Its testing is mainly carried out using electron backscatter diffraction (EBSD) technology. During the test, the sample needs to be electropolished or ion polished to eliminate the surface stress layer. The scanning step size is set to 1 / 10 to 1 / 5 of the grain size (usually 0.5-2 μm), 15° is used as the grain boundary recognition threshold, and 5° is used as the KAM calculation cutoff angle. The GAM distribution map can be obtained by calculating the average orientation difference of adjacent pixels within each grain using professional software. For the GAM control of the negative electrode layer, cross rolling can be used instead of unidirectional rolling to weaken the texture and improve the uniformity of the orientation difference distribution. Asynchronous rolling can be combined to improve deformation energy storage, and the recrystallization annealing temperature and time can be adjusted. For magnetron sputtered metal layers, GAM control needs to be approached from two aspects: deposition process and post-annealing. During the deposition stage, the average orientation difference of the surface layer grains is controlled by controlling the substrate temperature, optimizing sputtering power and gas pressure parameters, and annealing temperature and time.

[0060] The present invention specifies that the condition (c) for the bipolar current collector can effectively increase the difficulty of electrolyte penetration.

[0061] (d) The water contact angle of the surface layer is less than the water contact angle of the negative electrode conductive layer, and the water contact angle of the surface layer is ≤70°, for example, it can be 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65° or 70°, preferably 0°~60°; the water contact angle of the negative electrode conductive layer is >70°, for example, it can be 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115° or 120°, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0062] The ways to achieve the above condition (d) include, but are not limited to: adjusting the material and roughness of the surface layer, introducing -OH, -COOH, -NH2 through plasma treatment (O2, air, NH3, etc.), or using ultraviolet / ozone (UV / O3) oxidation to generate hydrophilic functional groups or modifying the product surface.

[0063] The present invention specifies that the condition (d) of the bipolar current collector can improve the wettability of the bipolar current collector, which helps the electrolyte to fully wet the electrolyte. In addition, through the synergy between the surface layer and the inner layer, the inner layer has high density and no through channels, and the inner layer has lower wettability than the surface layer, thereby forming an interface barrier. Even if the surface layer is damaged, the electrolyte is less likely to penetrate into the deep part of the inner layer.

[0064] In some embodiments, the relationship between the thickness h1 of the surface layer and the thickness h2 of the negative electrode conductive layer is: h1 / h2 = 0.1~1, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, preferably 0.1~0.5, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0065] The present invention limits the ratio between the thickness h1 of the surface layer and the thickness h2 of the negative electrode conductive layer to the above range, which can effectively balance the mechanical properties, defect rate and energy density of the bipolar current collector.

[0066] In some embodiments, the bipolar current collector satisfies at least one of the following conditions: (A) The bipolar current collector further includes a negative electrode protective layer, which is disposed on the surface of the surface layer away from the negative electrode conductive layer.

[0067] In some embodiments, the material of the negative electrode protective layer includes any one or a combination of at least two of chromium, nickel, nickel-based alloys, copper-based alloys, copper-chromium oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, carbon nanotubes, carbon nanofibers, or graphene, used to protect the surface layer from oxidation or scratches.

[0068] In some embodiments, the thickness of the negative electrode protective layer is 5 to 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, and more preferably 10 to 80 nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0069] In some embodiments, the negative electrode conductive layer is made of copper or a copper alloy to provide conductivity to the negative electrode side of the battery.

[0070] In some embodiments, the thickness of the negative electrode conductive layer is 0.5~10μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0071] This invention limits the thickness of the negative electrode conductive layer to a reasonable range. If the thickness of the negative electrode conductive layer is less than 0.5 μm, rolling is difficult and the risk of aluminum leakage in the prepared negative electrode conductive layer is high; if the thickness of the negative electrode conductive layer is greater than 10 μm, the areal density of the resulting repolar current collector is too high, which occupies the coating space of the active material, resulting in a low areal density of the battery.

[0072] (B) The bipolar current collector further includes a positive electrode protective layer, which is disposed on the side surface of the positive electrode conductive layer away from the negative electrode conductive layer.

[0073] In some embodiments, the positive electrode protective layer is made of any one or a combination of at least two of the following: aluminum oxide, silicon oxide, graphene, carbon nanotubes, carbon nanofibers, or carbon nanotubes, to protect the positive electrode conductive layer from oxidation.

[0074] In some embodiments, the thickness of the positive electrode protective layer accounts for 0.05% to 0.1% of the total thickness of the substrate, for example, it can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0075] The substrate refers to a composite structure consisting of a negative electrode conductive layer, an interface layer, a positive electrode conductive layer, and a positive electrode protective layer.

[0076] In some embodiments, the positive conductive layer is made of aluminum or an aluminum alloy, providing conductivity to the positive electrode side of the battery.

[0077] In some embodiments, the thickness of the positive electrode conductive layer is 5 to 100 μm, for example, it can be 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0078] This invention limits the thickness of the positive electrode conductive layer to a reasonable range. If the thickness of the positive electrode conductive layer is less than 5 μm, rolling is difficult, and there is a high risk of leakage of the positive electrode conductive layer material from the negative electrode conductive layer. If the thickness of the positive electrode conductive layer is greater than 100 μm, the areal density of the repolar current collector is too high, which encroaches on the coating space of the active material, resulting in a low areal density of the battery.

[0079] (C) The bipolar current collector further includes an interface layer, which is disposed between the negative electrode conductive layer and the positive electrode conductive layer.

[0080] In some embodiments, the material of the interface layer includes a copper-aluminum alloy, specifically any one or a combination of at least two of Al2Cu, AlCu, Al2Cu3, Al3Cu4, or Al4Cu9.

[0081] In this invention, the interface layer is located between the negative electrode conductive layer and the positive electrode conductive layer, and is formed by the mutual diffusion of the metals on both sides during the rolling process.

[0082] In some embodiments, the thickness of the interface layer is 0.05~5μm, for example, it can be 0.05μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0083] In this invention, if the thickness of the interface layer is less than 0.05 μm, rolling becomes difficult; if the thickness of the interface layer is greater than 5 μm, the interface strength is low, which in turn leads to a deterioration in the mechanical properties of the bipolar current collector.

[0084] In a second aspect, the present invention provides a method for preparing a bipolar current collector as described in the first aspect, comprising the following steps: (1) A negative electrode conductive layer and a positive electrode conductive layer are prepared by solid-liquid composite rolling method; (2) Prepare a surface layer on the surface of the negative electrode conductive layer.

[0085] In some embodiments, the solid-liquid composite rolling method in step (1) includes copper plate pretreatment, copper-aluminum melt rolling, cold rolling, heat treatment and foil rolling performed sequentially.

[0086] In some embodiments, the copper plate pretreatment includes: first immersing the copper plate in acetone or alkaline solution to remove surface oil, then cleaning the copper plate with acid to remove surface oxides, and finally cleaning the copper plate with anhydrous ethanol and drying it.

[0087] In some embodiments, the copper-aluminum melt rolling process includes: first melting a clean high-purity aluminum plate, then casting the resulting molten aluminum onto the surface of a copper plate under oxygen-free conditions, and rolling it into a copper-aluminum composite plate.

[0088] In some embodiments, the cold rolling process rolls the copper-aluminum composite plate to a thickness of 80-120 μm, for example, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm or 120 μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0089] In some embodiments, the heat treatment temperature is 300~550°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C or 550°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0090] The present invention involves heat treatment at 300~550℃, the purpose of which is to strengthen the interface layer and eliminate internal stress in the material.

[0091] In some embodiments, the foil rolling process rolls the copper-aluminum composite plate to a thickness of 20-30 μm, for example, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0092] In some embodiments, the method for preparing the surface layer in step (2) includes any one or a combination of at least two of physical vapor deposition, electroplating, or electroless plating.

[0093] In some embodiments, the preparation method further includes: preparing a negative electrode protective layer on the surface of the surface layer.

[0094] In some embodiments, the method for preparing the negative electrode protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ molding, or coating.

[0095] In this invention, the physical vapor deposition is preferably vacuum evaporation or magnetron sputtering; the chemical vapor deposition is preferably atmospheric pressure chemical vapor deposition or plasma-enhanced chemical vapor deposition; the in-situ forming is preferably forming a metal oxide passivation layer in situ on the surface of the metal layer; and the coating is preferably die coating, doctor blade coating or extrusion coating.

[0096] One embodiment of the present invention also provides a bipolar electrode, which includes at least the bipolar current collector described in any of the above embodiments.

[0097] One embodiment of the present invention also provides a bipolar battery, comprising at least the bipolar current collector or the bipolar electrode sheet described in any of the above embodiments.

[0098] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0099] Example 1 This embodiment provides a bipolar current collector and its preparation method, such as... Figure 1 As shown, the bipolar current collector includes a negative electrode protective layer 1, a surface layer 6, a negative electrode conductive layer 2, an interface layer 3, a positive electrode conductive layer 4, and a positive electrode protective layer 5, which are stacked together. The surface layer 6 is used to cover defects in the material of the positive electrode conductive layer 4 that leak from the negative electrode conductive layer 2.

[0100] Specifically, the negative electrode protective layer 1 is a 10 nm thick chromium layer; the surface layer 6 is a 1 μm thick copper layer; the negative electrode conductive layer 2 is a 3 μm thick copper layer; the positive electrode conductive layer 4 is a 20 μm thick aluminum layer; the interface layer 3 between the two is a 0.5 μm thick Al2Cu layer; and the positive electrode protective layer 5 is a 5 nm thick aluminum oxide layer. The ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.33.

[0101] Upon testing, the surface roughness of the side of the surface layer 6 away from the negative electrode conductive layer 2 is 0.35 μm, and the surface roughness of the side of the negative electrode conductive layer 2 away from the positive electrode conductive layer 4 is 0.32 μm; the average orientation difference between adjacent grains in the negative electrode conductive layer 2 is 19°, and the average orientation difference between adjacent grains in the surface layer 6 is 13°; the water contact angle of the surface layer 6 is 74°, and the water contact angle of the negative electrode conductive layer 2 is 65°.

[0102] Upon observation, the grain morphology of the negative electrode conductive layer 2 is fibrous, and the grain morphology of the surface layer 6 is columnar.

[0103] The preparation method of the above-mentioned bipolar current collector includes the following steps: (1) The negative electrode conductive layer 2, the interface layer 3, the positive electrode conductive layer 4, and the positive electrode protective layer 5 are prepared by solid-liquid composite rolling method: (1.1) Copper plate pretreatment: First, immerse the 30μm thick copper plate in 0.05mol / L sodium hydroxide solution to remove surface oil stains. Then, clean the copper plate with 0.05mol / L hydrochloric acid solution to remove surface oxides. Finally, clean the copper plate with anhydrous ethanol and dry it at low temperature. (1.2) Copper-aluminum melt rolling: First, aluminum ingots with clean surface and 99.99% purity are melted, and then the resulting aluminum liquid is cast onto the cleaned copper plate surface under oxygen-free conditions and rolled into a copper-aluminum composite plate with a thickness of 230μm. (1.3) Cold rolling: The copper-aluminum composite plate is further rolled to a thickness of 100 μm; (1.4) Heat treatment: The copper-aluminum composite plate is annealed at 450℃ for 1 hour to strengthen the interface layer 3 and eliminate the internal stress of the material; (1.5) Foil rolling: The heat-treated copper-aluminum composite plate is further rolled to obtain a substrate with a total thickness of 23.505 μm. The substrate includes a negative electrode conductive layer 2, an interface layer 3, a positive electrode conductive layer 4 and a positive electrode protective layer 5 stacked together.

[0104] (2) The obtained substrate is placed in a magnetron sputtering machine. First, the negative electrode conductive layer 2 is surface treated with plasma to remove surface contaminants. Then, a copper layer is deposited on one side of the treated negative electrode conductive layer 2. The specific process is as follows: a copper target (purity: 99.99%) is used as the target material, the target power is 10.0kW, the argon flow rate is 100mL / min, the coating vacuum degree is 0.1Pa, the temperature of the main roller during the coating process is -15℃, and a copper layer with a thickness of 1μm is deposited on the surface of the negative electrode conductive layer 2 to obtain the surface layer 6.

[0105] (3) The obtained composite material is placed in a magnetron sputtering machine with a chromium target (purity: 99.99%) as the target material, a target power of 8.0kW, an argon flow rate of 80mL / min, a coating vacuum of 0.08Pa, and a main roller temperature of -15℃ during the coating process. A chromium layer with a thickness of 10nm is deposited on the surface of the surface layer 6 to obtain the negative electrode protective layer 1.

[0106] Example 2 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 0.1 μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.03. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0107] Example 3 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 2μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.67. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0108] Example 4 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 0.3 μm, and correspondingly, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.1, the rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0109] Example 5 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 10 μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 3.33. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0110] Example 6 This embodiment provides a bipolar current collector and its preparation method, except that the surface layer 6 is replaced with a nickel layer. The nickel layer is prepared as follows: a nickel target (purity: 99.99%) is used as the target material, the target power is 8.0 kW, the argon flow rate is 100 mL / min, the coating vacuum degree is 0.1 Pa, and the temperature of the main roller during the coating process is -10℃. A nickel layer with a thickness of 2 μm is deposited on the surface of the negative electrode conductive layer 2. Correspondingly, the surface roughness of the side of the surface layer 6 away from the negative electrode conductive layer 2 is 0.35 μm, the average orientation difference between adjacent grains is 13°, and the water contact angle is 74°. The remaining structure and conditions are the same as in Example 3, and will not be described in detail here.

[0111] Example 7 This embodiment provides a bipolar current collector and its preparation method, except that the surface layer 6 is replaced with a carbon layer. The carbon layer is prepared as follows: a carbon target (purity: 99.99%) is used as the target material, the target power is 6.0 kW, the argon flow rate is 80 mL / min, the coating vacuum degree is 0.08 Pa, and the temperature of the main roller during the coating process is -20℃. A carbon layer with a thickness of 2 μm is deposited on the surface of the negative electrode conductive layer 2. Correspondingly, the surface roughness of the side of the surface layer 6 away from the negative electrode conductive layer 2 is 0.35 μm, the average orientation difference between adjacent grains is 13°, and the water contact angle is 74°. The remaining structure and conditions are the same as in Example 3, and will not be described in detail here.

[0112] Example 8 This embodiment provides a bipolar current collector and its preparation method. Except for the surface roughness of the side of the surface layer 6 away from the negative electrode conductive layer 2 being changed to 0.21 μm by polishing, and the surface roughness of the side of the negative electrode conductive layer 2 away from the positive electrode conductive layer 4 being 0.28 μm, the rest of the structure and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0113] Example 9 This embodiment provides a bipolar current collector and its preparation method. Except for adjusting the deposition conditions to change the average orientation difference between adjacent grains in the surface layer 6 to 18° and the average orientation difference between adjacent grains in the negative electrode conductive layer 2 to 12°, the other structures and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0114] Example 10 This embodiment provides a bipolar current collector and its preparation method. Except for changing the water contact angle of the surface layer 6 to 66° by ozone treatment and changing the water contact angle of the negative electrode conductive layer 2 to 75°, the rest of the structure and conditions are the same as in embodiment 1, and will not be described in detail here.

[0115] Example 11 This embodiment provides a bipolar current collector and its preparation method. Except for changing the thickness of the positive electrode conductive layer 4 to 5μm, the other structures and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0116] Example 12 This embodiment provides a bipolar current collector and its preparation method. Except for changing the thickness of the positive electrode conductive layer 4 to 100 μm, the other structures and conditions are the same as in Example 1, and will not be described in detail here.

[0117] Example 13 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the negative electrode conductive layer 2 is changed to 0.5 μm, and correspondingly, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 2, the rest of the structure and conditions are the same as in embodiment 1, and will not be described in detail here.

[0118] Example 14 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the negative electrode conductive layer 2 is changed to 10 μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.1. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0119] Example 15 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 0.05 μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 0.02. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0120] Example 16 This embodiment provides a bipolar current collector and its preparation method. Except that the thickness of the surface layer 6 is changed to 11 μm, the ratio h1 / h2 between the thickness h1 of the surface layer 6 and the thickness h2 of the negative electrode conductive layer 2 is 3.67. The rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0121] Example 17 This embodiment provides a bipolar current collector and its preparation method, except that the preparation method of the negative electrode conductive layer 2 is changed to magnetron sputtering to obtain a negative electrode conductive layer 2 with columnar grain morphology. Correspondingly, the surface roughness of the side of the negative electrode conductive layer 2 away from the positive electrode conductive layer 4 is 0.31 μm, the average orientation difference between adjacent grains is 20°, and the water contact angle is 63°. The remaining structure and conditions are the same as in Example 1, and will not be described in detail here.

[0122] Example 18 This embodiment provides a bipolar current collector and its preparation method. Except that the roughness of the surface of the surface layer 6 away from the negative electrode conductive layer 2 is changed to 0.2 μm by polishing and the roughness of the surface of the negative electrode conductive layer 2 away from the positive electrode conductive layer 4 is 0.29 μm; the average orientation difference between adjacent grains in the surface layer 6 is changed to 18° by adjusting the deposition conditions and the average orientation difference between adjacent grains in the negative electrode conductive layer 2 is changed to 10°; and the water contact angle of the surface layer 6 is changed to 64° and the water contact angle of the negative electrode conductive layer 2 is changed to 77° by ozone treatment, the rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0123] Comparative Example 1 Comparative Example 1 provides a bipolar current collector and its preparation method. Except that the surface layer 6 is not provided, but the negative electrode protective layer 1 is directly provided on the surface of the negative electrode conductive layer 2, the rest of the structure and conditions are the same as those in Example 1, and will not be described in detail here.

[0124] Performance testing The methods for detecting various physical property parameters in Examples 1-18 and Comparative Example 1 are as follows: (1) Roughness: Clean the surface of the sample to be tested, remove oil, dust and other impurities, and ensure that the measurement area is flat and burr-free; use a standard sample block to calibrate the instrument and check the wear of the stylus (to avoid measurement errors caused by stylus wear). After calibration, confirm that the stylus is in perpendicular contact with the surface; manually or automatically adjust the stylus to the surface of the sample to be tested, start the measurement program, and slide the stylus at a constant speed (usually 0.5-2 mm / s) along the direction perpendicular to the rolling direction to measure the roughness value.

[0125] (2) Average orientation difference between adjacent grains: The sample is electropolished or ion polished to eliminate the surface stress layer, and the scanning step size is set to 1 / 10 to 1 / 5 of the grain size (usually 0.5-2μm). 15° is used as the grain boundary recognition threshold and 5° is used as the KAM calculation cutoff angle. The average value of the orientation difference between adjacent pixels in each grain is calculated by professional software.

[0126] (3) Water contact angle: all are contact angles 10s after the liquid (water) is dropped. Ten points were measured for each sample, and the average value was taken.

[0127] The number of defects in the negative electrode conductive layer side leakage positive electrode conductive layer material in the bipolar current collectors obtained in Examples 1-18 and Comparative Example 1 were counted respectively. The specific operation was as follows: the functional current collector was placed in the pinhole defect detection system (micro-visual charge-coupled device CCD), scanned, and then the optical signal was converted into an electrical signal and transmitted to the computer to count the number of pinhole defects in the sample.

[0128] The battery is then assembled using the bipolar current collector obtained in the above embodiments and comparative examples, specifically including the following steps: (a) Coating a positive electrode active material, including LiNi, onto one side of the positive electrode conductive layer. 0.8 Co 0.1 Mn 0.1 The composition of the materials is: O2 (NCM811), conductive carbon black Super P, PVDF 5130, and carbon nanotubes (CNT), with a mass ratio of 96:1.8:1.7:0.5. (b) A negative electrode active material, including graphite, conductive carbon black Super P, carbon nanotubes, and CMC, is coated on one side of the negative electrode conductive layer, and the mass ratio of the above four materials is 96:3:0.6:0.4. (c) 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.

[0129] The assembled pouch battery was subjected to cycle performance testing under the following conditions: charging at 1C constant current constant voltage (CCCV) and discharging at 1C constant current (CC), with 2000 charge-discharge cycles. The battery capacity retention rate after 2000 charge-discharge cycles was recorded, which is calculated as battery capacity after 2000 charge-discharge cycles / initial battery capacity × 100%.

[0130] The relevant statistical results are shown in Table 1 below.

[0131] Table 1 As shown in Table 1: (1) As can be seen from Examples 1 to 18 and Comparative Example 1, compared with the traditional bipolar current collector, the present invention can effectively reduce the number of defects in the positive electrode conductive layer material leaking from the negative electrode conductive layer side of the bipolar current collector by constructing a surface layer on the negative electrode conductive layer side of the traditional bipolar current collector, and significantly improve the cycle performance of the battery.

[0132] (2) As can be seen from Examples 1-5 and 15-16, the preferred range of the ratio h1 / h2 between the thickness h1 of the surface layer and the thickness h2 of the negative electrode conductive layer is 0.1-1.

[0133] (3) As can be seen from Examples 1, 6-7, good technical effects can still be achieved by replacing the surface layer with other materials.

[0134] (4) As can be seen from Examples 1 and 8: limiting the roughness of the surface of the surface layer away from the negative electrode conductive layer to be less than the roughness of the surface of the negative electrode conductive layer away from the positive electrode conductive layer can further reduce the number of defects in the negative electrode conductive layer material leaking into the positive electrode conductive layer in the bipolar current collector, while improving the cycle performance of the battery.

[0135] (5) As can be seen from Examples 1 and 9: limiting the average orientation difference between adjacent grains in the negative electrode conductive layer to less than the average orientation difference between adjacent grains in the surface layer can further reduce the number of defects in the negative electrode conductive layer material leaking into the positive electrode conductive layer in the repolar current collector, while improving the cycle performance of the battery.

[0136] (6) As can be seen from Examples 1 and 10: limiting the water contact angle of the surface layer to less than the water contact angle of the negative electrode conductive layer can further reduce the number of defects in the negative electrode conductive layer material leaking into the positive electrode conductive layer in the repolar current collector, while improving the cycle performance of the battery.

[0137] (7) As can be seen from Examples 1 and 11-12: by appropriately increasing the thickness of the positive electrode conductive layer, the number of defects in the positive electrode conductive layer material leaking from the negative electrode conductive layer in the resulting compound current collector is further reduced.

[0138] (8) As can be seen from Examples 1, 13-14: by appropriately increasing the thickness of the negative electrode conductive layer, the number of defects in the negative electrode conductive layer material leaking from the positive electrode conductive layer in the resulting composite current collector is further reduced.

[0139] Therefore, this invention effectively covers the defects of the positive electrode conductive layer material leaking from the negative electrode conductive layer side of the traditional rolled bipolar current collector by adding a surface layer on the negative electrode conductive layer of the bipolar current collector and utilizing its dense structural characteristics. This fundamentally solves the problem of local micro-short circuits during battery cycling and significantly improves the cycle performance of bipolar batteries.

[0140] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A bipolar current collector, comprising at least a negative electrode conductive layer and a positive electrode conductive layer stacked thereon, characterized in that, A surface layer is provided on the side of the negative electrode conductive layer away from the positive electrode conductive layer.

2. The bipolar current collector according to claim 1, characterized in that, The surface layer is made of 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. And / or, the thickness of the surface layer is 0.1~10μm, preferably 2~6μm.

3. The bipolar current collector according to claim 1 or 2, characterized in that, The bipolar current collector must satisfy at least one of the following conditions: (a) The surface roughness of the side of the surface layer away from the negative electrode conductive layer is less than the surface roughness of the side of the negative electrode conductive layer away from the positive electrode conductive layer, and the surface roughness Ra of the negative electrode conductive layer is 0.15~0.30μm; (b) The grain morphology of the negative electrode conductive layer is fibrous, and the grain morphology of the surface layer is equiaxed or columnar; (c) The average orientation difference between adjacent grains in the negative electrode conductive layer is less than the average orientation difference between adjacent grains in the surface layer, and the average orientation difference between adjacent grains in the negative electrode conductive layer is ≤15°, while the average orientation difference between adjacent grains in the surface layer is >15°. (d) The water contact angle of the surface layer is less than the water contact angle of the negative electrode conductive layer, and the water contact angle of the surface layer is ≤70°, preferably 0°~60°; the water contact angle of the negative electrode conductive layer is >70°.

4. The bipolar current collector according to claim 1 or 2, characterized in that, The relationship between the thickness h1 of the surface layer and the thickness h2 of the negative electrode conductive layer is: h1 / h2 = 0.1~1, preferably 0.1~0.

5.

5. The bipolar current collector according to claim 1 or 2, characterized in that, The bipolar current collector must satisfy at least one of the following conditions: (A) The bipolar current collector further includes a negative electrode protective layer, which is disposed on the surface of the surface layer away from the negative electrode conductive layer; The material of the negative electrode protective layer includes any one or a combination of at least two of the following: chromium, nickel, nickel-based alloys, copper-based alloys, copper-chromium oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, carbon nanotubes, carbon nanofibers, or graphene. And / or, the thickness of the negative electrode protective layer is 5~100nm, preferably 10~80nm; And / or, the material of the negative electrode conductive layer includes copper or a copper alloy; And / or, the thickness of the negative electrode conductive layer is 0.5~10μm; (B) The bipolar current collector further includes a positive electrode protective layer, which is disposed on the surface of the positive electrode conductive layer away from the negative electrode conductive layer; The positive electrode protective layer is made of any one or a combination of at least two of the following: aluminum oxide, silicon oxide, graphene, carbon nanotubes, carbon nanofibers, or carbon nanofibers. And / or, the thickness of the positive electrode protective layer accounts for 0.05% to 0.1% of the total thickness of the substrate, and the substrate refers to a composite structure of negative electrode conductive layer, interface layer, positive electrode conductive layer and positive electrode protective layer; And / or, the material of the positive electrode conductive layer includes aluminum or an aluminum alloy; And / or, the thickness of the positive electrode conductive layer is 5~100μm; (C) The bipolar current collector further includes an interface layer, which is disposed between the negative electrode conductive layer and the positive electrode conductive layer; The material of the interface layer includes copper-aluminum alloy, specifically any one or a combination of at least two of Al2Cu, AlCu, Al2Cu3, Al3Cu4 or Al4Cu9; And / or, the thickness of the interface layer is 0.05~5μm.

6. A method for preparing a bipolar current collector as described in any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: (1) A negative electrode conductive layer and a positive electrode conductive layer are prepared by solid-liquid composite rolling method; (2) Prepare a surface layer on the surface of the negative electrode conductive layer.

7. The method for preparing the bipolar current collector according to claim 6, characterized in that, The solid-liquid composite rolling method in step (1) includes copper plate pretreatment, copper-aluminum melt rolling, cold rolling, heat treatment and foil rolling performed sequentially; The copper plate pretreatment includes: first immersing the copper plate in acetone or alkaline solution to remove surface oil, then cleaning the copper plate with acid solution to remove surface oxides, and finally cleaning the copper plate with anhydrous ethanol and drying it. And / or, the copper-aluminum melt rolling process includes: first melting a clean high-purity aluminum plate, then casting the resulting molten aluminum onto the surface of a copper plate under oxygen-free conditions, and rolling it into a copper-aluminum composite plate; And / or, the cold rolling process reduces the thickness of the copper-aluminum composite plate to 80-120 μm; And / or, the temperature of the heat treatment is 300~550℃; And / or, the foil rolling process rolls the copper-aluminum composite plate to a thickness of 20~30μm.

8. The method for preparing the bipolar current collector according to claim 6 or 7, characterized in that, The surface layer preparation method in step (2) includes any one or a combination of at least two of physical vapor deposition, electroplating, or electroless plating; And / or, the preparation method further includes: preparing a negative electrode protective layer on the surface of the surface layer; The method for preparing the negative electrode protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ molding, or coating.

9. A composite electrode sheet, characterized in that, The bipolar electrode comprises at least the bipolar current collector as described in any one of claims 1 to 5.

10. A bipolar battery, characterized in that, The bipolar battery comprises at least the bipolar current collector as described in any one of claims 1 to 5 or the bipolar electrode as described in claim 9.

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