Composite metal foil and battery

Abstract

This invention discloses a composite metal foil and a battery. The composite metal foil includes a base film layer and a metal layer. The metal layer is disposed on at least one side of the base film layer. A plurality of holes are disposed on the side of the metal layer away from the base film layer. Each hole includes a first opening on the side away from the base film layer and a second opening on the side closer to the base film layer. The light transmittance of the composite metal foil is 15%-60%. This invention improves the safety and reliability of the battery by creating holes in the metal layer of the composite metal foil, allowing lithium dendrites to grow into the holes, preventing them from piercing the separator and causing internal short circuits.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a composite metal foil and a battery. Background Technology

[0002] As an emerging and comprehensive economic form, the low-altitude economy has seen rapid development across its entire industrial chain globally in recent years, with electric vertical takeoff and landing (eVTOL) aircraft demonstrating particularly strong growth momentum. The rapid development of new energy vehicles, in turn, places higher demands on the safety, stability, lightweight design, and energy density of battery systems.

[0003] Existing technologies employ a "sandwich" composite metal foil technique, placing extremely thin metal foils on both sides of an organic polymer film. Its high energy density and long cycle life make it a key technology for modern energy storage. However, during battery operation, lithium dendrite formation is a critical factor posing safety hazards. When a battery is charged and discharged, lithium ions migrate back and forth between the positive and negative electrodes. During charging, lithium ions escape from the positive electrode and embed into the negative electrode through the electrolyte. These lithium ions unevenly deposit on the negative electrode surface, gradually forming needle-like or dendritic lithium dendrites. Once formed and growing, these dendrites may penetrate the battery's internal separator, causing direct contact between the positive and negative electrodes, resulting in an internal short circuit and thermal runaway. This poses a serious threat to battery safety, and battery safety during use remains a bottleneck restricting its further development and widespread application.

[0004] To address these issues, it is urgent to develop composite metal foils and batteries that can improve battery safety. Summary of the Invention

[0005] The purpose of this invention is to provide a composite metal foil that can prevent the formation of lithium dendrites during battery operation, which could puncture the separator and cause an internal short circuit, thereby improving the safety and reliability of the battery.

[0006] To achieve the above objectives, embodiments of the present invention provide a composite metal foil, comprising a base film layer and a metal layer. The base film layer has the metal layer disposed on at least one side. The metal layer has a plurality of holes on the side away from the base film layer, wherein the holes include a first opening on the side away from the base film layer and a second opening on the side closer to the base film layer. The light transmittance of the composite metal foil is 15%-60%.

[0007] At least a portion of the holes satisfy the following condition: D1 / D2 > 1, where D1 is the maximum width of the first opening and D2 is the maximum width of the second opening.

[0008] As an improvement to the above scheme, at least a portion of the holes satisfy the following condition: 2≤D1 / D2≤8.

[0009] As an improvement to the above scheme, at least 40%-80% of the holes satisfy the following condition: D1 / D2 > 1.

[0010] As an improvement to the above scheme, the line connecting the center of the first opening and the center of the second opening of at least a portion of the hole makes an angle of 15°-60° with the thickness direction of the composite metal foil.

[0011] As an improvement to the above scheme, the line connecting the center of the first opening and the center of the second opening of more than 40% of the holes makes an angle of 15°-60° with the thickness direction of the composite metal foil.

[0012] As an improvement to the above scheme, the maximum width of the first opening is 0.05-5μm.

[0013] As an improvement to the above scheme, the density of the holes is 600-10000 holes / mm2.

[0014] As an improvement to the above solution, the metal layer includes a first metal layer and a second metal layer, which are respectively disposed on both sides of the base film layer.

[0015] As an improvement to the above solution, the second metal layer is provided with a number of holes.

[0016] As an improvement to the above solution, at least some of the holes on the first metal layer are staggered with the holes on the second metal layer.

[0017] As an improvement to the above solution, the holes on the second metal layer are located between two adjacent holes on the first metal layer.

[0018] As an improvement to the above solution, the holes on the first metal layer are located between two adjacent holes on the second metal layer.

[0019] As an improvement to the above scheme, the thickness of the metal layer is 0.05-8 μm.

[0020] As an improvement to the above scheme, the base film layer includes at least one of polyester, polyimide, epoxy resin, polyethylene terephthalate, polypropylene, polyvinyl chloride, polystyrene, polyphenylene sulfide, or rubber.

[0021] To achieve the above objectives, embodiments of the present invention also provide a battery, the battery comprising the composite metal foil described in any of the above embodiments.

[0022] Compared to existing technologies, the beneficial effects of this invention are that by creating holes in the metal layer of the composite metal foil, lithium dendrites formed on the negative electrode grow into the holes during charging, preventing penetration and thus avoiding battery short circuits and thermal runaway, thereby improving battery safety and reliability. Simultaneously, the active material formed on the surface of the metal layer forms a rivet structure through the holes, enhancing the bonding force between the active material and the metal layer, significantly improving battery performance and safety. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the first composite metal foil provided in the embodiments of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of the second composite metal foil provided in the embodiments of the present invention;

[0025] Figure 3 This is a partially enlarged schematic diagram of the second type of composite metal foil provided in an embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of the structure of the third type of composite metal foil provided in the embodiments of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure of the fourth type of composite metal foil provided in the embodiments of the present invention;

[0028] Figure 6 This is a schematic diagram of the structure of the fifth composite metal foil provided in the embodiments of the present invention;

[0029] Figure 7 This is a schematic diagram of the sixth type of composite metal foil provided in the embodiments of the present invention.

[0030] Wherein, 1, base film layer; 2, metal layer; 21, first metal layer; 22, second metal layer; 3, hole on the first metal layer; 31, first opening of hole on the first metal layer; 32, second opening of hole on the first metal layer; 4, included angle; 5, hole on the second metal layer. Detailed Implementation

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] See Figure 1 , Figure 1This is a schematic diagram of the structure of a composite metal foil according to an embodiment of the present invention. The present invention provides a composite metal foil comprising: a base film layer 1 and a metal layer 2. At least one side of the base film layer 1 is provided with the metal layer 2. The metal layer 2 has a plurality of holes 3 on the side of the metal layer 2 away from the base film layer 1, wherein each hole 3 includes a first opening 31 on the side away from the base film layer 1 and a second opening 32 on the side closer to the base film layer 1. The light transmittance of the composite metal foil is 15%-60%.

[0033] Among them, at least a portion of the holes 3 satisfy the following condition: D1 / D2>1, where D1 is the maximum width of the first opening 31 and D2 is the maximum width of the second opening 32.

[0034] The composite metal foil of this invention comprises a base film layer 1 and a metal layer 2, which can reduce the weight of the composite metal foil and thus the weight of the battery. Simultaneously, it can improve the energy density of the battery and extend its driving range. By providing holes 3 on the metal layer 2 of the composite metal foil, lithium dendrites formed on the negative electrode during charging grow into the holes, preventing penetration and short circuits that could lead to thermal runaway, thereby improving the battery's safety and reliability. Furthermore, the active material formed on the surface of the metal layer forms a rivet structure through the holes, increasing the bonding force between the active material and the metal layer, significantly enhancing battery performance and safety.

[0035] Furthermore, the hole 3 includes at least one of a blind hole or a through hole.

[0036] Furthermore, the base film layer 1 serves to support the ultra-thin metal layer 2 and reduce the weight of the composite metal foil, and includes at least one of polyester, polyimide, epoxy resin, polyethylene terephthalate, polypropylene, polyvinyl chloride, polystyrene, polyphenylene sulfide, or rubber.

[0037] In this embodiment of the invention, the transmittance of the composite metal foil is 15%-60%. By limiting the transmittance of the composite metal foil to 15%-60%, the total area of ​​the holes 3 is kept within a suitable range. Excessive transmittance would result in an overly large total area of ​​the holes 3, leading to decreased conductivity of the metal layer 2, increased internal resistance of the battery, more severe temperature rise within the battery, and a reduced overcurrent limit of the metal layer 2, making it difficult to match high-current applications. Conversely, excessively low transmittance would prevent the total area of ​​the holes 3 from being too small, which would leave insufficient space for lithium dendrites to grow during battery operation, potentially piercing the separator, causing an internal short circuit, and leading to thermal runaway. Therefore, limiting the transmittance of the composite metal foil to 15%-60% ensures that thermal runaway does not occur during battery operation, improving battery performance and safety. Optionally, the transmittance of the composite metal foil can be any value or a range of any two values ​​from 15%, 20%, 30%, 35%, 50%, or 60%.

[0038] Furthermore, at least a portion of the holes 3 satisfy the following condition: D1 / D2 > 1, where D1 is the maximum width of the first opening 31 and D2 is the maximum width of the second opening 32. For example, D1 / D2 can be 1.5, 2, 2.5, 3, 3.5, 4, 5, 7, 8, 10, or 15, etc.

[0039] It is worth noting that by limiting the ratio of D1 / D2 of the hole 3 to >1, meaning that the first opening 31 of the metal layer 2 furthest from the base film layer 1 is larger than the second opening 32 of the metal layer 2 closest to the base film layer 1, lithium dendrites can smoothly grow into the hole 3 through the first opening 31 during battery operation. Simultaneously, because the maximum width of the second opening 32 is smaller than that of the first opening 31, it prevents lithium dendrites from rapidly growing into the hole 3 and piercing the base film layer 1, thus avoiding battery short-circuit failure. Furthermore, it increases the contact area between the metal layer 2 and the battery active material, enhancing their bonding strength. Therefore, limiting the ratio of D1 / D2 of the hole 3 to >1 can further improve battery performance and safety reliability.

[0040] Preferably, at least 40%-80% of the holes on the metal layer 2 of the composite metal foil satisfy the following condition: D1 / D2 > 1.

[0041] Furthermore, at least a portion of the holes 3 on the metal layer 2 of the composite metal foil satisfy the following condition: 2≤D1 / D2≤8.

[0042] Specifically, in this embodiment of the invention, the formation of holes 3 includes one or more of the following production methods: laser etching, direct chemical etching, or circuit fabrication. Laser etching, by controlling the laser energy, creates holes 3; this physical processing method is highly efficient and pollution-free. Direct chemical etching forms holes 3 by etching the grain boundaries of the metal layer 2 with a chemical solution; the distribution of these holes can be irregular. Circuit fabrication involves forming holes 3 of uniform size and regular distribution on the surface of the metal layer 2 through film application, exposure, and development.

[0043] See Figure 2 , Figure 2 This is a schematic diagram of another composite metal foil according to an embodiment of the present invention. In the composite metal foil provided by the embodiment of the present invention, the line connecting the center of the first opening 31 and the center of the second opening 32 of at least a portion of the holes 3 forms an angle 4 of 15°-60° with the thickness direction of the composite metal foil. Figure 3 This is a magnified view of the included angle 4.

[0044] It is worth noting that by limiting the angle 4 between the line connecting the center of the first opening 31 and the center of the second opening 32 of the hole 3 and the thickness direction of the composite metal foil to 15°-60°, the growth direction of lithium dendrites into the hole 3 is limited to a suitable range. On the one hand, this avoids the risk of lithium dendrites growing towards the base film layer 1 and piercing it if the angle 4 is too small; on the other hand, it avoids the risk of lithium dendrites growing in a tortuous direction and piercing the separator if the angle 4 is too large. Therefore, limiting the angle 4 between the line connecting the center of the first opening 31 and the center of the second opening 32 of the hole 3 and the thickness direction of the composite metal foil to 15°-60° is beneficial for lithium dendrites to grow rapidly into the hole 3, while avoiding the risk of lithium dendrites growing towards the base film layer 1 and piercing it, further improving the safety and reliability of the battery. Optionally, the angle 4 can be any value or a range of any two values ​​from 15°, 22°, 34°, 40°, 45°, or 60°.

[0045] Preferably, the line connecting the center of the first opening 31 and the center of the second opening 32 of the hole 3, which accounts for more than 40% of the total holes, forms an angle of 15°-60° with the thickness direction of the composite metal foil.

[0046] In this embodiment of the invention, the maximum width of the first opening 31 of the composite metal foil is 0.05-5 μm. By limiting the maximum width of the first opening 31 to 0.05-5 μm, the maximum width of the first opening 31 is kept within a suitable range. This prevents lithium dendrites from growing too small, which could puncture the separator, causing an internal short circuit and thermal runaway. Conversely, it also prevents the maximum width of the first opening 31 from being too large, which could lead to decreased conductivity of the metal layer 2, increased internal resistance, more severe temperature rise, and reduced overcurrent limit of the metal layer 2, making it unsuitable for high-current applications; or severely degrade the mechanical properties of the composite copper foil. Therefore, limiting the maximum width of the first opening 31 to 0.05-5 μm ensures that thermal runaway will not occur during battery operation, improving battery performance and safety. Optionally, the maximum width of the first opening 31 can be any value or an interval of any two values ​​among 0.05μm, 0.1μm, 0.3μm, 1μm, 1.5μm, 3μm, 4.3μm or 5μm.

[0047] Preferably, the density of pores 3 is 600-10000 pores / mm2.

[0048] Furthermore, the thickness of metal layer 2 is 0.05-8 μm. By limiting the thickness of metal layer 2 to 0.05-8 μm, the thickness of metal layer 2 is kept within a suitable range. This prevents the metal layer 2 from becoming too thin, which would lead to decreased conductivity, increased internal resistance, more severe temperature rise within the battery, and a lower overcurrent limit, making it unsuitable for high-current applications. Conversely, an excessively thick metal layer 2 would not result in decreased energy density or an excessively heavy battery, thus failing to meet the requirements for long battery life. Therefore, by limiting the thickness of metal layer 2 to 0.05-8 μm, energy density can be improved while ensuring battery safety and reliability. Optionally, the thickness of metal layer 2 can be any value or a range of any two values ​​from 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 5.5 μm, 7 μm, or 8 μm, preferably 0.1-2 μm.

[0049] See Figure 4 , Figure 4 This is a schematic diagram of another composite metal foil according to an embodiment of the present invention. The composite metal foil provided in this embodiment of the present invention has a metal layer 2 comprising a first metal layer 21 and a second metal layer 22, wherein the first metal layer 21 and the second metal layer 22 are respectively disposed on both sides of the base film layer 1.

[0050] It is worth noting that a first metal layer 21 and a second metal layer 22 are respectively disposed on both sides of the base film layer 1. On the one hand, during battery charging and discharging, the two metal layers can provide efficient conductive channels for the active material from both sides, making current transmission more uniform and efficient, reducing internal resistance, reducing energy loss, and improving battery charging and discharging efficiency and overall performance. For example, in lithium-ion batteries, this allows lithium ions to migrate more smoothly between the positive and negative electrodes, ensuring high-rate charging and discharging performance of the battery. On the other hand, the two metal layers can better provide support and protection for the base film from both sides, reducing the possibility of damage such as cracking and perforation of the base film due to external forces during production, assembly, and use. At the same time, the two metal layers can disperse the heat inside the battery to a certain extent, reducing the risk of local overheating, improving the thermal stability of the battery, and reducing the possibility of thermal runaway.

[0051] Specifically, the second metal layer 22 may have holes 5 on its surface; or the second metal layer 22 may not have holes 5 on its surface.

[0052] For example, hole 5 includes at least one of blind hole and through hole.

[0053] Furthermore, at least a portion of the holes 5 satisfy the following condition: D3 / D4 > 1, where D3 is the maximum width of the third opening and D4 is the maximum width of the fourth opening.

[0054] The method for manufacturing the composite metal foil according to an embodiment of the present invention is as follows:

[0055] S1: A first metal layer 21 and a second metal layer 22 are disposed on the surface of the base film layer 1;

[0056] S2: Holes 3 and 5 are formed on the surfaces of the first metal layer 21 and the second metal layer 22, respectively.

[0057] It is worth noting that in step S1, a first metal layer 21 and a second metal layer 22 are formed on the surface of the base film layer 1 using at least one of vacuum sputtering, evaporation, and electroless plating. Vacuum sputtering and evaporation are physical methods and are environmentally friendly. Vacuum sputtering relies on accelerating metal ions to achieve deposition, thus resulting in excellent adhesion to the base film layer 1. Evaporation relies on metal vaporization to deposit on the base film layer 1, resulting in a slightly weaker adhesion between the metal layer 2 and the base film layer 1. Electroless plating is a wet chemical process and has some environmental impact.

[0058] Another method for manufacturing the composite metal foil according to an embodiment of the present invention is as follows:

[0059] S1: A seed layer is set on the surface of the base film layer 1;

[0060] S2: Thicken the seed layer to form a first metal layer 21 and a second metal layer 22;

[0061] S3: Holes 3 and 5 are formed on the surfaces of the first metal layer 21 and the second metal layer 22, respectively.

[0062] It is worth noting that the seed layer in step S1 is formed using at least one of vacuum sputtering, evaporation, and electroless plating. Vacuum sputtering and evaporation are physical methods and are environmentally friendly. Vacuum sputtering relies on accelerating metal ions to achieve deposition, thus resulting in excellent adhesion to the base film layer 1. Evaporation relies on metal vaporization to deposit on the base film layer 1, but its adhesion to the base film layer 1 is relatively weaker. Electroless plating is a chemical wet process and has some environmental impact. The method for thickening the metal layer 2 in step S2 includes electroplating.

[0063] Specifically, after step S3, an anti-oxidation layer can be applied to prevent oxidation of the metal layer 2 during manufacturing, transportation, storage, and use. Oxidation of the metal layer 2 during these processes would reduce its conductivity, increase the battery's internal resistance, exacerbate temperature rise, and lower its overcurrent limit, making it unsuitable for high-current applications. This, in turn, improves the battery's safety and reliability.

[0064] The method for manufacturing composite metal foil in the above embodiments of the invention is a partial implementation method and does not represent all implementation methods. Therefore, it does not constitute a limitation on the scope of protection of the present invention.

[0065] See Figure 5 , Figure 5This is a schematic diagram of another composite metal foil according to an embodiment of the present invention. In this other composite metal foil according to an embodiment of the present invention, at least a portion of the holes 3 on the first metal layer 21 and the holes 5 on the second metal layer 22 are alternately arranged.

[0066] It is worth noting that at least some of the holes 3 on the first metal layer 21 and the holes 5 on the second metal layer 22 are staggered, including the center of the opening of the hole 3 on the first metal layer 21 away from the base film layer 1 and the center of the opening of the hole 5 on the second metal layer 22 away from the base film layer 1; or the center of the opening of the hole 3 on the first metal layer 21 near the base film layer 1 and the center of the opening of the hole 5 on the second metal layer 22 near the base film layer 1; or the center of the opening of the hole 3 on the first metal layer 21 away from the base film layer 1 and the center of the opening of the hole 5 on the second metal layer 22 near the base film layer 1; or a combination of the above. By staggering the holes 3 on at least a portion of the first metal layer 21 with the holes 5 on the second metal layer 22 to form an interlaced mesh, the mechanical force acting on the composite metal foil can be dispersed, the elongation of the composite metal foil can be improved, and foil breakage can be avoided during the winding process.

[0067] Preferably, in this embodiment of the invention, the holes 3 on the first metal layer 21 and the holes 5 on the second metal layer 22 of the composite metal foil are respectively located on both sides of the line connecting the center of the opening of the hole 3 on the first metal layer 21 near the base film layer 1 and the center of the opening of the hole 5 on the second metal layer 22 near the base film layer 1, and are staggered. By limiting the distribution of the holes 3 on the first metal layer 21 and the holes 5 on the second metal layer 22 to the center of the line connecting the center of the opening of the hole 3 on the first metal layer 21 near the base film layer 1 and the center of the opening of the hole 5 on the second metal layer 22 near the base film layer 1, and staggered arrangement, when the composite metal foil is subjected to external force for stretching, the tensile stress directions of the holes 3 and 5 are consistent, which greatly improves the elongation of the composite metal foil and makes it less prone to breakage.

[0068] Further, see Figure 6 , Figure 6This is another composite metal foil according to an embodiment of the present invention. In this embodiment, the holes 5 on the second metal layer 22 of the composite metal foil are located between two adjacent holes 3 on the first metal layer 21. Specifically, the opening of the hole 5 on the second metal layer 22 near the base film layer 1, when projected vertically onto the first metal layer 21, is located between the openings of two adjacent holes 3 on the first metal layer 21 near the base film layer; simultaneously, the opening of the hole 5 on the second metal layer 22 away from the base film layer 1, when projected vertically onto the first metal layer 21, is located between the openings of two adjacent holes 3 on the first metal layer 21 away from the base film layer. By placing the holes 5 on the second metal layer 22 of the composite metal foil between two adjacent holes 3 on the first metal layer 21, forming a triangular shape, it can effectively resist mechanical tension, improve the tensile properties of the composite metal foil, and prevent foil breakage during use.

[0069] Further, see Figure 7 , Figure 7 This is another composite metal foil according to an embodiment of the present invention. In this embodiment, the holes 3 on the first metal layer 21 of the composite metal foil are located between two adjacent holes 5 on the second metal layer 22. Specifically, the opening of the hole 3 on the first metal layer 21 near the base film layer 1, when projected vertically onto the second metal layer 22, is located between the openings of two adjacent holes 5 on the second metal layer 22 near the base film layer; simultaneously, the opening of the hole 3 on the first metal layer 21 away from the base film layer 1, when projected vertically onto the second metal layer 22, is located between the openings of two adjacent holes 5 on the second metal layer 22 away from the base film layer. By placing the holes 3 on the first metal layer 21 of the composite metal foil between two adjacent holes 5 on the second metal layer 22, forming a triangular shape, it can effectively resist mechanical tension, improve the tensile properties of the composite metal foil, and prevent foil breakage during use.

[0070] This invention provides a battery comprising a composite metal foil as described in any of the preceding embodiments.

[0071] The composite metal foil and battery provided in this invention have the following advantages: The composite metal foil includes a base film layer 1 and a metal layer 2, which can reduce the weight of the composite metal foil, thereby reducing the weight of the battery. Simultaneously, it can improve the energy density of the battery and extend its driving range. By providing holes 3 on the metal layer 2 of the composite metal foil, lithium dendrites formed on the negative electrode during charging grow into the holes, preventing penetration and short circuits that could lead to thermal runaway, thus improving the battery's safety and reliability. Furthermore, the active material formed on the surface of the metal layer forms a rivet structure through the holes, increasing the bonding force between the active material and the metal layer, significantly improving the battery's performance and safety. Furthermore, the maximum width D1 of the first opening 31 on the side of the hole 3 furthest from the base film layer 1 and the maximum width D2 of the second opening 32 on the side closer to the base film layer 1 are both designed to satisfy at least a portion of D1 / D2 > 1. This means the first opening 31 of the metal layer 2 furthest from the base film layer 1 is larger than the second opening 32 of the metal layer 2 closer to the base film layer 1. This allows lithium dendrites to grow smoothly into the hole 3 through the first opening 31 during battery operation. Simultaneously, because the maximum width of the second opening 32 is smaller than the first opening 31, it prevents lithium dendrites from rapidly growing into the hole 3 and piercing the base film layer 1, thus avoiding short-circuit failure and further improving battery performance and reliability. The transmittance of the composite metal foil is further limited to 15%-60%, ensuring the total area of ​​the hole 3 is within a suitable range. Excessive transmittance would result in an excessively large total area of ​​the hole 3, preventing a decrease in the conductivity of the metal layer 2, increased internal resistance, more severe temperature rise within the battery, and a reduction in the overcurrent limit of the metal layer 2, making it difficult to match high-current applications. At the same time, due to excessively low light transmittance and a small total area of ​​pore 3, lithium dendrites generated during battery operation will not have enough space to grow and puncture the separator, causing an internal short circuit and thermal runaway. This ensures that thermal runaway will not occur during battery operation, improving battery performance and safety.

[0072] To demonstrate the beneficial effects of the composite metal foil and battery provided in the embodiments of the present invention, the following description is provided in conjunction with several embodiments and comparative examples.

[0073] Example 1:

[0074] A composite metal foil includes: a base film layer 1 and a metal layer 2, wherein the metal layer 2 is disposed on at least one side of the base film layer 1, the base film layer 1 has a thickness of 6 μm, and the metal layer 2 has a thickness of 1-2 μm; a plurality of holes 3 are disposed on the side of the metal layer 2 away from the base film layer 1, wherein the holes 3 include a first opening 31 on the side away from the base film layer 1 and a second opening 32 on the side closer to the base film layer 1, and the light transmittance of the composite metal foil is 40%-60%;

[0075] At least a portion of the holes 3 satisfy the following condition: D1 / D2 > 2, where D1 is the maximum width of the first opening 31 and D2 is the maximum width of the second opening 32. D1 is 1-3 μm and D2 is 0.2-0.8 μm.

[0076] The composite metal foil, hot melt adhesive, and composite metal foil were pressed together (100℃, 2 min, 80 kg / cm2), and the peel strength was tested. The composite metal foil was then assembled into a battery, and a charge-discharge cycle test was conducted. When the capacity dropped to 80% of the initial capacity, the number of cycles was recorded as the battery life.

[0077] Test results: The peel strength between the composite metal foil and the hot melt adhesive in this embodiment is 1.5 N / cm, and the battery life of the composite metal foil assembly in this embodiment is 2051 cycles.

[0078] Example 2:

[0079] The composite metal foil structure in this embodiment is the same as that in Embodiment 1, except that the angle between the line connecting the center of the first opening 31 and the center of the second opening 32 of at least a portion of the holes 3 and the thickness direction of the composite metal foil is 20°-30°.

[0080] The composite metal foil, hot melt adhesive, and composite metal foil were pressed together (100℃, 2 min, 80 kg / cm2), and the peel strength was tested. The composite metal foil was then assembled into a battery, and a charge-discharge cycle test was conducted. When the capacity dropped to 80% of the initial capacity, the number of cycles was recorded as the battery life.

[0081] Test results: The peel strength between the composite metal foil and the hot melt adhesive in this embodiment is 1.8 N / cm, and the battery life of the composite metal foil assembly in this embodiment is 2490 cycles.

[0082] Example 3:

[0083] The composite metal foil structure in this embodiment is the same as that in Embodiment 1, except that: the metal layer 2 includes a first metal layer 21 and a second metal layer 22, which are respectively disposed on both sides of the base film layer 1. Furthermore, more than 70% of the holes 3 on the first metal layer 21 and the holes 5 on the second metal layer 22 are staggered, with the holes 5 on the second metal layer 22 located between two adjacent holes 3 on the first metal layer 21.

[0084] The composite metal foil, hot melt adhesive, and composite metal foil were pressed together (100℃, 2 min, 80 kg / cm2), and the peel strength was tested. The composite metal foil was then assembled into a battery, and a charge-discharge cycle test was conducted. When the capacity dropped to 80% of the initial capacity, the number of cycles was recorded as the battery life.

[0085] Test results: The peel strength between the composite metal foil and the hot melt adhesive in this embodiment is 1.3 N / cm, and the battery life of the composite metal foil assembly in this embodiment is 2736 cycles.

[0086] Comparative Example 1:

[0087] A composite metal foil, wherein the metal layer 2 includes a first metal layer 21 and a second metal layer 22, which are respectively disposed on both sides of a base film layer 1. The first metal layer 21 and the second metal layer 22 have the same thickness, which is 1-2 μm. The base film layer 1 has a thickness of 6 μm.

[0088] The composite metal foil, hot melt adhesive, and composite metal foil were pressed together (100℃, 2 min, 80 kg / cm2), and the peel strength was tested. The composite metal foil was then assembled into a battery, and a charge-discharge cycle test was conducted. When the capacity dropped to 80% of the initial capacity, the number of cycles was recorded as the battery life.

[0089] Test results: The peel strength between the composite metal foil and the hot melt adhesive in this embodiment is 0.7 N / cm, and the battery life of the composite metal foil assembly in this embodiment is 1100 cycles.

[0090] Table 1 below shows the performance test results of the composite metal foils of Examples 1-3 and Comparative Example 1.

[0091] Table 1. Performance test results of composite metal foils of Examples 1-3 and Comparative Example 1

[0092]

[0093] Therefore, by applying the composite metal foil described in this embodiment, the safety and reliability of the battery can be improved, the bonding force with the active material can be enhanced, and the high battery life can be achieved.

[0094] In summary, the composite metal foil, comprising a base film layer 1 and a metal layer 2, can reduce the weight of the composite metal foil, thereby reducing the weight of the battery. By creating holes 3 in the metal layer 2 of the composite metal foil, lithium dendrites formed on the negative electrode during charging grow into the holes, preventing them from penetrating and causing short circuits and thermal runaway, thus improving the safety and reliability of the battery. Simultaneously, the active material formed on the surface of the metal layer forms a rivet structure through the holes, increasing the bonding force between the active material and the metal layer, significantly improving battery performance and safety. Furthermore, the maximum width D1 of the first opening 31 on the side of the hole 3 furthest from the base film layer 1 and the maximum width D2 of the second opening 32 on the side closer to the base film layer 1 are both designed to satisfy at least a portion of D1 / D2 > 1. This means the first opening 31 of the metal layer 2 furthest from the base film layer 1 is larger than the second opening 32 of the metal layer 2 closer to the base film layer 1. This allows lithium dendrites to grow smoothly into the hole 3 through the first opening 31 during battery operation. Simultaneously, because the maximum width of the second opening 32 is smaller than the first opening 31, it prevents lithium dendrites from rapidly growing into the hole 3 and piercing the base film layer 1, thus avoiding short-circuit failure and further improving battery performance and reliability. The transmittance of the composite metal foil is further limited to 15%-60%, ensuring the total area of ​​the hole 3 is within a suitable range. Excessive transmittance would result in an excessively large total area of ​​the hole 3, preventing a decrease in the conductivity of the metal layer 2, increased internal resistance, more severe temperature rise within the battery, and a reduction in the overcurrent limit of the metal layer 2, making it difficult to match high-current applications. At the same time, due to excessively low light transmittance and a small total area of ​​pore 3, lithium dendrites generated during battery operation will not have enough space to grow and puncture the separator, causing an internal short circuit and thermal runaway. This ensures that thermal runaway will not occur during battery operation, improving battery performance and safety.

Claims

1. A battery composite metal foil, characterized in that, The film includes a base film layer and a metal layer. The metal layer is disposed on at least one side of the base film layer. The thickness of the metal layer is 0.05-8 μm. A plurality of pores are disposed on the side of the metal layer away from the base film layer, and the density of the pores is 600-10000 pores / mm. 2 The aperture includes a first opening on the side away from the base film layer and a second opening on the side closer to the base film layer, and the light transmittance of the composite metal foil is 15%-60%. Wherein, the line connecting the center of the first opening and the center of the second opening of at least a portion of the holes makes an angle of 15°-60° with the thickness direction of the composite metal foil; and at least a portion of the holes satisfy the following conditions: D1 is 1-3μm, D2 is 0.2-0.8μm, D1 / D2>1, where D1 is the maximum width of the first opening and D2 is the maximum width of the second opening.

2. The battery composite metal foil as described in claim 1, characterized in that, At least a portion of the holes satisfy the following condition: 2≤D1 / D2≤8.

3. The battery composite metal foil as described in claim 1, characterized in that, At least 40%-80% of the holes satisfy the following condition: D1 / D2 > 1.

4. The battery composite metal foil as described in claim 1, characterized in that, For more than 40% of the holes, the line connecting the center of the first opening and the center of the second opening makes an angle of 15°-60° with the thickness direction of the composite metal foil.

5. The battery composite metal foil according to any one of claims 1-4, characterized in that, The metal layer includes a first metal layer and a second metal layer, which are respectively disposed on both sides of the base film layer.

6. The battery composite metal foil as described in claim 5, characterized in that, The second metal layer has a number of holes.

7. The battery composite metal foil as described in claim 6, characterized in that, At least a portion of the holes on the first metal layer are staggered with the holes on the second metal layer.

8. The battery composite metal foil as described in claim 7, characterized in that, The holes on the second metal layer are located between two adjacent holes on the first metal layer; Alternatively, the hole on the first metal layer may be located between two adjacent holes on the second metal layer.

9. The battery composite metal foil according to any one of claims 1-4, characterized in that, The base film layer includes at least one of polyester, polyimide, epoxy resin, polyethylene terephthalate, polypropylene, polyvinyl chloride, polystyrene, polyphenylene sulfide, or rubber.

10. A battery, characterized in that, Includes the battery composite metal foil as described in any one of claims 1-9.

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