A cast-rolled asymmetric copper-aluminum composite foil and a stacked bipolar battery using the foil

Abstract

This invention relates to a cast-rolled asymmetric copper-aluminum composite foil and a stacked bipolar battery using the foil. The asymmetric copper-aluminum composite foil is manufactured by pouring molten aluminum onto the roll gap of a casting roll. After the molten aluminum solidifies, it forms a metallurgical bond with the copper strip on that side, resulting in an aluminum-copper double-layer composite strip blank. The composite strip blank is then rolled thin to form the copper-aluminum composite foil. The beneficial effects of the above embodiments of this invention are: the copper-aluminum composite foil has high interfacial metallurgical bonding strength, ensuring long-term cycle stability; and the casting-rolling process forms an atomically pure interface through the liquid-solid metallurgical bonding of the molten aluminum and the copper strip, completely eliminating the oxidation inclusion problem of traditional rolling methods.

Description

Technical Field

[0001] This invention relates to an improvement of a composite foil, and also to a stacked bipolar battery using the foil. Background Technology

[0002] In the development of battery technology, copper-aluminum composite foil in stacked bipolar batteries has gradually become a research hotspot. Its development history is closely linked to the progress of battery technology. In the early days, battery technology was relatively simple, and the performance requirements for current collectors were not high. With the increasing demand for high power and high energy density batteries, copper-aluminum composite foil emerged.

[0003] Structurally, copper-aluminum composite foils typically have an asymmetric structure, with a copper layer on one side and an aluminum layer on the other. This structural design is intended to accommodate the different electrochemical environments of the positive and negative electrodes in bipolar batteries, with the copper layer serving as the negative electrode current collector and the aluminum layer as the positive electrode current collector.

[0004] In terms of preparation methods, the traditional solid-solid rolling composite method was mainly used in the early stages. This method combines solid copper strips and aluminum strips together by rolling. However, this method requires extremely high surface cleanliness of the raw materials and is prone to introducing oxide inclusions during the preparation process, resulting in insufficient interfacial bonding strength. Moreover, when rolling ultra-thin foil materials with a thickness of less than 100 micrometers, problems such as delamination and cracking are prone to occur, making it difficult to meet the requirements of high reliability and thinness of the current collector in batteries.

[0005] Traditional composite foils suffer from high interfacial resistance and poor thermal conductivity, resulting in insufficient reliability over long-term use, and their manufacturing processes are complex. Single metal sheets, such as nickel and stainless steel, struggle to simultaneously meet the electrochemical window compatibility requirements of both positive and negative electrodes, often necessitating complex surface modification coatings, which not only increase costs but also reduce process stability. Traditional rolled composite asymmetric foils are prone to interfacial defects and insufficient bonding strength during ultrathin foil production, failing to meet the high requirements of batteries for current collectors. Summary of the Invention

[0006] To overcome the shortcomings of current ultra-thin composite foil production, which is prone to interface defects, this invention provides a cast-rolled asymmetric copper-aluminum composite foil and a stacked bipolar battery using the foil.

[0007] The technical solution of this invention to solve its technical problem is: a cast-rolled asymmetric copper-aluminum composite foil, wherein the asymmetric copper-aluminum composite foil is manufactured by the following method: aluminum melt is poured onto the roll gap of a casting roll, and copper strip is simultaneously supplied and pressed into one side of the aluminum melt; after the aluminum melt solidifies, it forms a metallurgical bond with the copper strip on that side, and an aluminum-copper double-layer composite strip blank is output; the composite strip blank is then rolled into a copper-aluminum composite foil; the thickness ratio of the aluminum layer to the copper layer in the copper-aluminum composite foil is between 1 / 1 and 9 / 1, and the thickness of the copper-aluminum composite foil is between 10 micrometers and 150 micrometers; one side of the copper-aluminum composite foil is an aluminum surface, and the other side is a copper surface.

[0008] To enhance the adhesion of the copper surface, the copper surface of the copper-aluminum composite foil is chemically etched using a sulfuric acid-hydrogen peroxide system after rolling to form a uniformly rough surface; the aluminum surface is then routinely cleaned.

[0009] In order to reduce stress during the forming process and increase the adhesion stability between copper and aluminum materials, the composite strip blank is subjected to annealing heat treatment after being rolled into copper-aluminum composite foil.

[0010] Alternatively, the aluminum layer material in the copper-aluminum composite foil can be an alloy material rather than pure aluminum, such as aluminum alloys like AA8030.

[0011] Alternatively, the copper layer in the copper-aluminum composite foil may be an alloy material, such as a copper-zinc alloy.

[0012] The present invention also includes an intermediate bipolar current collector using the above-mentioned cast-rolled asymmetric copper-aluminum composite foil as the main body, wherein a positive electrode paste is coated on the aluminum surface of the asymmetric copper-aluminum composite foil to form a positive electrode active material layer, and a negative electrode paste is coated on the copper surface of the asymmetric copper-aluminum composite foil to form a negative electrode active material layer.

[0013] Further preferably, the positive electrode slurry is made of lithium iron phosphate, conductive carbon black and binder, and the negative electrode slurry is made of artificial graphite, conductive carbon black and binder.

[0014] Further preferably, the binder of the positive electrode slurry is PVDF, and the binder of the negative electrode slurry is SBR and CMC.

[0015] This invention also includes a stacked bipolar battery using the aforementioned cast-rolled asymmetric copper-aluminum composite foil as an intermediate bipolar current collector. The stacked bipolar battery comprises several battery cells connected in series. From positive to negative, each battery cell includes a positive electrode, a positive active material layer, an electrolyte, a negative active material layer, and a negative electrode. An intermediate bipolar current collector replaces the connected positive and negative electrodes between two battery cells. This intermediate bipolar current collector is a copper-aluminum composite foil, with the aluminum surface of the foil in contact with the positive active material layer and the copper surface in contact with the negative active material layer. The copper-aluminum composite foil physically separates adjacent battery cells, while achieving a series connection in the circuit, with current passing perpendicularly through the composite foil.

[0016] Furthermore, the positive electrode at the head end is an aluminum foil, and the negative electrode at the tail end is a copper foil.

[0017] In this invention, the stacked bipolar battery is constructed by vertically connecting multiple battery cells in a planar plane as positive, electrolyte, and negative electrodes. A copper-aluminum composite foil is used as the intermediate bipolar current collector, replacing the central positive and negative electrodes, making installation very convenient. In this structure, the bipolar current collector is key to achieving efficient series connection, resulting in a significant reduction in internal resistance and an effective increase in power density.

[0018] The beneficial effects of this invention are as follows: 1. The copper-aluminum composite foil exhibits high interfacial metallurgical bonding strength, ensuring long-term cycle stability. The casting and rolling process achieves atomically pure interfaces through liquid-solid metallurgical bonding between molten aluminum and copper strip, completely eliminating the oxidation inclusion problem inherent in traditional rolling methods. This interface maintains >95% bonding strength after 500 cycles, with no microcracks or intermetallic compound growth, significantly improving battery life and effectively suppressing polarization voltage rise under high-rate charge and discharge, providing reliable support for fast-charging batteries. 2. The thermal conductivity of the copper-aluminum composite foil far exceeds that of polymer-based current collectors (<5 W / m·K). Through the synergistic heat conduction of the copper layer (401 W / m·K) and the aluminum layer (237 W / m·K), uniform heat dissipation in the lateral direction and rapid heat conduction in the longitudinal direction are achieved; local overheating is avoided, significantly improving safety, especially suitable for high power density scenarios. 3. The asymmetric design optimizes battery performance and cost. The aluminum surface is resistant to high-voltage oxidation and adapts to the positive electrode, while the copper surface is stable at low potential and adapts to the negative electrode, avoiding compatibility issues associated with traditional single metals. The lightweight aluminum-based body reduces raw material costs while simplifying assembly processes and lowering system costs. This structure reduces battery internal resistance, increases power density, and supports ultra-thin designs ranging from 10 to 150 μm, meeting high energy density requirements. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of casting and rolling according to an embodiment of the present invention.

[0020] Figure 2This is a schematic diagram of a composite metal foil according to an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a stacked bipolar battery according to an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of an intermediate bipolar current collector according to an embodiment of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example 1

[0024] Combined with appendix Figures 1 to 2 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. The aluminum material used was industrial pure aluminum Al1100, which has high purity and provides good basic properties for the composite foil.

[0025] The copper strip 1 is pretreated by first performing alkaline washing to remove surface oil and impurities, and then performing acid washing and activation to make the surface of the copper strip 1 active, which is beneficial for subsequent metallurgical bonding with aluminum melt 2.

[0026] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0027] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum molten material 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum molten material 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0028] In subsequent processing, the composite strip obtained above is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at a temperature of 300°C for 2 hours to reduce stress during the forming process and increase the adhesion stability between the copper and aluminum materials. Finally, the composite strip is rolled into a composite foil with a total thickness of 80 μm, wherein the aluminum layer thickness is approximately 64 μm, the copper layer thickness is approximately 16 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 4:1, which meets the thickness ratio requirement of 1 / 1 to 9 / 1 of this invention.

[0029] For surface treatment, the copper surface of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum surface of the aluminum layer is then routinely cleaned to remove impurities and oxide layers.

[0030] The cast-rolled asymmetric copper-aluminum composite foil prepared by the above process has an aluminum surface on one side and a copper surface on the other side, with a total thickness of 80μm, which is within the thickness range of 10μm-150μm of this invention. It also has good physical properties and bonding strength, and can be widely used in electronics, power and other fields.

[0031] Example 2 Combined with appendix Figures 1 to 2 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. The aluminum material used was industrial pure aluminum Al1100, which has high purity and provides good basic properties for the composite foil.

[0032] The copper strip 1 is pretreated by first performing alkaline washing to remove surface oil and impurities, and then performing acid washing and activation to make the surface of the copper strip 1 active, which is beneficial for subsequent metallurgical bonding with aluminum melt 2.

[0033] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0034] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum melt 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum melt 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0035] In subsequent processing, the composite strip obtained above is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at a temperature of 300°C for 2 hours to reduce stress during the forming process and increase the adhesion stability between the copper and aluminum materials. Finally, the composite strip is rolled into a composite foil with a total thickness of 10 μm, wherein the aluminum layer thickness is approximately 6.67 μm, the copper layer thickness is approximately 3.33 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 2.0:1, which meets the thickness ratio requirement of 1 / 1–9 / 1 of this invention.

[0036] For surface treatment, the copper layer of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum layer surface is then routinely cleaned to remove impurities and oxide layers.

[0037] The cast-rolled asymmetric copper-aluminum composite foil prepared by the above process has an aluminum surface on one side and a copper surface on the other side, with a total thickness of 10 μm, which is within the thickness range of 10 μm–150 μm of the present invention. It also has good physical properties and bonding strength, and is suitable for micro electronic interconnect devices.

[0038] Example 3 Combined with appendix Figures 1 to 2 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. The aluminum material used was industrial pure aluminum Al1100, which has high purity and provides good basic properties for the composite foil.

[0039] The copper strip 1 is pretreated by first performing alkaline washing to remove surface oil and impurities, and then performing acid washing and activation to make the surface of the copper strip 1 active, which is beneficial for subsequent metallurgical bonding with aluminum melt 2.

[0040] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0041] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum melt 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum melt 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0042] In subsequent processing, the composite strip obtained above is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at a temperature of 300°C for 2 hours to reduce stress during the forming process and increase the adhesion stability between the copper and aluminum materials. Finally, the composite strip is rolled into a composite foil with a total thickness of 50 μm, wherein the aluminum layer thickness is approximately 37.5 μm, the copper layer thickness is approximately 12.5 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 3.0:1, which meets the thickness ratio requirement of 1 / 1–9 / 1 of this invention.

[0043] For surface treatment, the copper layer of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum layer surface is then routinely cleaned to remove impurities and oxide layers.

[0044] The cast-rolled asymmetric copper-aluminum composite foil prepared by the above process has an aluminum surface on one side and a copper surface on the other side, with a total thickness of 50 μm, which is within the thickness range of 10 μm–150 μm of the present invention. It also has good physical properties and bonding strength, and is suitable for power battery current collector substrates.

[0045] Example 4 Combined with appendix Figures 1 to 2 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. Industrial pure aluminum Al1100 was used, which has high purity and provides good basic properties for the composite foil. The copper strip (1) underwent pretreatment, firstly by alkaline washing to remove surface oil and impurities, followed by acid pickling and activation to keep the surface of the copper strip (1) in an active state, which is beneficial for subsequent metallurgical bonding with molten aluminum (2).

[0046] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0047] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum melt 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum melt 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0048] In subsequent processing, the obtained composite strip blank is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at 300°C for 2 hours to reduce stress during forming and increase the adhesion stability between the copper and aluminum materials. Finally, the composite strip blank is rolled into a composite foil with a total thickness of 100 μm, wherein the aluminum layer thickness is approximately 87.5 μm, the copper layer thickness is approximately 12.5 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 7.0:1, which meets the thickness ratio requirement of 1 / 1–9 / 1 of this invention.

[0049] For surface treatment, the copper layer of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum layer surface is then routinely cleaned to remove impurities and oxide layers.

[0050] The cast-rolled asymmetric copper-aluminum composite foil prepared by the above process has an aluminum surface on one side and a copper surface on the other side, with a total thickness of 100μm, which is within the thickness range of 10μm–150μm of the present invention. It also has good physical properties and bonding strength, and is suitable for high thermal conductivity energy storage electrode substrates.

[0051] Example 5 Combined with appendix Figures 1 to 2 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. The aluminum material used was industrial pure aluminum Al1100, which has high purity and provides good basic properties for the composite foil.

[0052] The copper strip 1 is pretreated by first performing alkaline washing to remove surface oil and impurities, and then performing acid washing and activation to make the surface of the copper strip 1 active, which is beneficial for subsequent metallurgical bonding with aluminum melt 2.

[0053] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0054] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum melt 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum melt 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0055] In subsequent processing, the composite strip obtained above is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at a temperature of 300°C for 2.5 hours to alleviate the residual stress accumulated under the large thickness and enhance the stability of the copper-aluminum interface bonding. Finally, the composite strip is rolled into a composite foil with a total thickness of 150 μm, wherein the aluminum layer thickness is approximately 125.0 μm, the copper layer thickness is approximately 25.0 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 5.0:1, which meets the thickness ratio requirement of 1 / 1–9 / 1 of this invention.

[0056] For surface treatment, the copper layer of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum layer surface is then routinely cleaned to remove impurities and oxide layers.

[0057] The cast-rolled asymmetric copper-aluminum composite foil prepared by the above process has an aluminum surface on one side and a copper surface on the other side, with a total thickness of 150μm, which is within the thickness range of 10μm–150μm of the present invention. It also has good physical properties and bonding strength, and is suitable for high-current power interconnection systems.

[0058] Example 6 Combined with appendix Figures 1 to 4 The asymmetric copper-aluminum composite foil was prepared by casting and rolling. A 1.2mm thick C1020 oxygen-free copper strip (1) was selected as the copper strip raw material, as it possesses good electrical conductivity and processing performance. The aluminum material used was industrial pure aluminum Al1100, which has high purity and provides good basic properties for the composite foil.

[0059] The copper strip 1 is pretreated by first performing alkaline washing to remove surface oil and impurities, and then performing acid washing and activation to make the surface of the copper strip 1 active, which is beneficial for subsequent metallurgical bonding with aluminum melt 2.

[0060] Aluminum molten material 2 is poured by heating industrial pure aluminum to 700°C to form aluminum molten material 2, and pouring aluminum molten material 2 above a pair of horizontally arranged casting rolls 3 with a roll gap set to 5mm through a controllable pouring nozzle.

[0061] In the composite forming process, preheated copper strip 1 is introduced from one side and pressed into the surface of the not-yet-fully-solidified aluminum melt 2 under the pressure of casting roll 3. Under the cooling and rolling action of casting roll 3, the aluminum melt 2 solidifies rapidly and forms a metallurgical bond with the copper strip 1 under high temperature and high pressure, ultimately outputting an aluminum-copper double-layer composite strip blank with a thickness of 6mm and a width of 500mm, wherein the copper layer is located on one side.

[0062] In subsequent processing, the composite strip obtained above is subjected to multiple cold rolling passes, with a total reduction rate exceeding 99%. During the cold rolling process, an intermediate annealing treatment is performed at a temperature of 300°C for 2 hours to reduce stress during the forming process and increase the adhesion stability between the copper and aluminum materials. Finally, the composite strip is rolled into a composite foil with a total thickness of 10 μm, wherein the aluminum layer thickness is approximately 6.67 μm, the copper layer thickness is approximately 3.33 μm, and the thickness ratio of aluminum layer 4 to copper layer 5 is 2.0:1, which meets the thickness ratio requirement of 1 / 1–9 / 1 of this invention.

[0063] For surface treatment, the copper layer of the composite foil is chemically etched using a sulfuric acid and hydrogen peroxide system to form a uniformly rough surface with a surface roughness Ra≈1.2μm, thereby increasing the adhesion of the copper surface. The aluminum layer surface is then routinely cleaned to remove impurities and oxide layers.

[0064] Using two composite foils as bipolar current collectors, and combining them with a pure aluminum foil 8 and a pure copper foil 9 as the head and tail electrodes, a stacked lithium-ion bipolar battery module with a nominal voltage of 6V is constructed by connecting two 3V-level LFP graphite units in series. A positive electrode slurry is coated on one side of the aluminum foil at the head electrode, the slurry consisting of lithium iron phosphate (LFP), conductive carbon black, and PVDF binder, forming a positive electrode active material layer 10. A positive electrode slurry is coated on the aluminum surface 6 of the first bipolar current collector to form the positive electrode active material layer 10, and a negative electrode slurry is coated on the copper surface 7 to form the negative electrode active material layer 11, the negative electrode slurry consisting of artificial graphite, conductive carbon black, and SBR / CMC binder. A negative electrode slurry is coated on one side of the copper foil 9 at the tail electrode to form the negative electrode active material layer 11.

[0065] Stacked sequentially, with the aluminum foil 8 at the head end facing inwards, the separator impregnated with electrolyte 12, the first bipolar current collector, the separator impregnated with electrolyte 12, the second bipolar current collector, the separator impregnated with electrolyte 12, and the copper foil 9 at the tail end, ensuring that all aluminum surfaces bear the positive electrode and all copper surfaces bear the negative electrode, this stacked bipolar battery, composed of multiple battery units connected in series, after overall packaging, electrolyte injection, and formation, has an internal resistance that is about 30% lower than the traditional "copper foil + aluminum foil" external series structure. Under 3C rate discharge, the voltage platform is increased by 0.12V and the temperature rise is reduced by 4.7°C, demonstrating excellent power density and thermal stability.

[0066] The beneficial effects of the above embodiments of the present invention are as follows: 1. The copper-aluminum composite foil has high interfacial metallurgical bonding strength, ensuring long-term cycle stability. The casting and rolling process forms an atomically pure interface through the liquid-solid metallurgical bonding of molten aluminum and copper strip, completely eliminating the oxidation inclusion problem of traditional rolling methods. This interface still maintains >95% bonding strength after 500 cycles, with no microcracks or intermetallic compound growth, significantly improving battery life and effectively suppressing the rise of polarization voltage under high-rate charging and discharging, providing reliable support for fast-charging batteries. 2. The thermal conductivity of the copper-aluminum composite foil is far higher than that of polymer-based current collectors (<5W / m·K). Through the synergistic heat conduction of the copper layer (401W / m·K) and the aluminum layer (237W / m·K), uniform heat dissipation in the lateral direction and rapid conduction in the longitudinal direction are achieved; local overheating is avoided, significantly improving safety, especially suitable for high power density scenarios. 3. The asymmetric design optimizes battery performance and cost. The aluminum surface is resistant to high-voltage oxidation and adapts to the positive electrode, while the copper surface is stable at low potential and adapts to the negative electrode, avoiding the compatibility problems of traditional single metals. The lightweight aluminum-based body reduces raw material costs while simplifying assembly processes and lowering system costs. This structure reduces battery internal resistance, increases power density, and supports ultra-thin designs ranging from 10 to 150 μm, meeting high energy density requirements.

Claims

1. A cast-rolled asymmetric copper-aluminum composite foil, characterized in that: Asymmetric copper-aluminum composite foil is manufactured by pouring molten aluminum onto the roll gap of a casting roll while simultaneously feeding and pressing copper strip into one side of the molten aluminum. After solidification, the molten aluminum forms a metallurgical bond with the copper strip on that side, resulting in an aluminum-copper double-layer composite strip blank. The composite strip blank is then rolled into a copper-aluminum composite foil. The thickness ratio of the aluminum layer to the copper layer in the copper-aluminum composite foil is between 1 / 1 and 9 / 1, and the thickness of the copper-aluminum composite foil is between 10 micrometers and 150 micrometers. One surface of the copper-aluminum composite foil is an aluminum surface, and the other surface is a copper surface.

2. The cast-rolled asymmetric copper-aluminum composite foil according to claim 1, characterized in that: After the copper-aluminum composite foil is rolled, the copper surface is chemically etched using a sulfuric acid-hydrogen peroxide system to form a uniformly rough surface; the aluminum surface is then routinely cleaned.

3. The cast-rolled asymmetric copper-aluminum composite foil according to claim 1, characterized in that: The composite strip blank is then subjected to annealing heat treatment after being rolled into copper-aluminum composite foil.

4. The cast-rolled asymmetric copper-aluminum composite foil according to claim 1, characterized in that: The aluminum layer material in the copper-aluminum composite foil is an alloy material.

5. The cast-rolled asymmetric copper-aluminum composite foil according to claim 1, characterized in that: The copper layer in the copper-aluminum composite foil is an alloy material.

6. An intermediate bipolar current collector using the cast-rolled asymmetric copper-aluminum composite foil of claim 1 as the main body, characterized in that: The asymmetric copper-aluminum composite foil has a positive electrode paste coated on the aluminum surface to form a positive electrode active material layer, and a negative electrode paste coated on the copper surface to form a negative electrode active material layer.

7. The intermediate bipolar current collector with cast-rolled asymmetric copper-aluminum composite foil as the main body according to claim 6, characterized in that: The positive electrode slurry is made of lithium iron phosphate, conductive carbon black and binder, and the negative electrode slurry is made of artificial graphite, conductive carbon black and binder.

8. The intermediate bipolar current collector with cast-rolled asymmetric copper-aluminum composite foil as the main body according to claim 7, characterized in that: The positive electrode slurry uses PVDF as a binder, and the negative electrode slurry uses SBR and CMC as binders.

9. A stacked bipolar battery using the cast-rolled asymmetric copper-aluminum composite foil of claim 1 as an intermediate bipolar current collector, the stacked bipolar battery comprising a plurality of battery cells connected in series, the battery cells comprising, from positive to negative, a positive electrode, a positive electrode active material layer, an electrolyte, a negative electrode active material layer, and a negative electrode; characterized in that: The stacked bipolar battery uses an intermediate bipolar current collector to replace the positive and negative electrodes connected between the two battery cells. The intermediate bipolar current collector is a copper-aluminum composite foil. The aluminum surface of the copper-aluminum composite foil is in contact with the positive electrode active material layer, and the copper surface of the composite foil is in contact with the negative electrode active material layer.

10. The stacked bipolar battery with the cast-rolled asymmetric copper-aluminum composite foil as the intermediate bipolar current collector according to claim 9, characterized in that: The positive electrode at the head end is an aluminum foil, and the negative electrode at the tail end is a copper foil.

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