A composite current collector and a method for fabricating a battery cell containing the composite current collector.

Abstract

This invention belongs to the field of battery technology and mainly relates to a composite current collector, including an aluminum foil layer and protective layers disposed on both sides of the aluminum foil layer in the thickness direction; the protective layers include polymer materials, metal oxides, and conductive agents, wherein the conductive agent is one or more of SP, CNT, and graphene; the protective layers include a first layer and a second layer, the first layer being coated on the first side of the aluminum foil layer and the second layer being coated on the second side of the aluminum foil layer; the materials of the first layer and the second layer may be the same or different; the composite current collector of this application forms a novel composite current collector by combining the aluminum foil layer with a conductive polymer layer (e.g., PET, PP, PE), thereby significantly reducing the risk of short circuit caused by direct contact between the negative electrode graphite and the aluminum foil in the event of cell damage; at the same time, this application also relates to a cell preparation method including the above-mentioned composite current collector, further improving cell performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a composite current collector and a method for preparing a battery cell containing the composite current collector. Background Technology

[0002] Current collectors play a crucial role in lithium-ion batteries, primarily functioning to conduct electricity and connect the positive and negative electrode materials, ensuring efficient current flow. With the rapid development of electronic products and the continuous improvement in battery energy density and charge / discharge rates, the performance requirements for current collectors are becoming increasingly stringent. However, while traditional aluminum foil as a battery current collector offers low cost and good conductivity, its application still presents numerous safety hazards, especially when the battery cell is damaged by external forces, potentially leading to catastrophic consequences. Therefore, improving current collectors to enhance their safety and reliability is of great significance.

[0003] In existing technologies, when a battery cell is damaged by external forces, the positive and negative electrode plates may come into direct contact, causing a short circuit and potentially leading to safety issues such as thermal runaway. Battery damage typically results in four different types of short circuits: graphite contact with the positive electrode material, graphite contact with the positive electrode aluminum foil, copper foil contact with the aluminum foil, and the positive electrode material contact with the negative electrode copper foil. Among these, direct contact between the negative electrode graphite and the aluminum foil is the primary cause of thermal runaway. Current collector structures in existing technologies lack effective protection for the aluminum foil, failing to prevent direct contact between the negative electrode graphite and the aluminum foil when the battery cell is damaged by external forces, thus significantly increasing safety risks.

[0004] Therefore, it is urgent to improve the existing current collector and cell manufacturing methods to solve the above-mentioned technical defects. Summary of the Invention

[0005] One of the objectives of this invention is to provide a composite current collector that can alleviate the short circuit of the battery cell under external force, in order to address the shortcomings of the existing technology.

[0006] To achieve the above technical objectives, this application implements the following technical solution:

[0007] A composite current collector includes an aluminum foil layer and protective layers disposed on both sides of the aluminum foil layer in the thickness direction;

[0008] The protective layer comprises polymer materials, metal oxides, and conductive agents, wherein the conductive agents are one or more of SP, CNT, graphene, and Ketjen black.

[0009] The protective layer includes a first layer and a second layer, wherein the first layer is coated on the first side of the aluminum foil layer and the second layer is coated on the second side of the aluminum foil layer;

[0010] The materials of the first layer and the second layer may be the same or different.

[0011] The above technical solution produces the following technical effects:

[0012] This patent proposes an innovative composite current collector solution to address the short-circuit risk problem in existing technologies. By combining an aluminum foil layer with a conductive polymer layer (such as PET, PP, PE) to form a composite current collector, the possibility of a short circuit caused by direct contact between the negative electrode graphite and the aluminum foil is significantly reduced when the battery cell is damaged. The formation of this composite current collector not only ensures the safety of the battery when subjected to external hazards but also avoids the risk of aluminum foil exposure due to cell deformation and coating shrinkage. Simultaneously, by introducing conductive agents (such as SP, CNT, graphene, etc.) and metal oxides (such as aluminum oxide, titanium oxide, etc.), conductivity is improved while the rigidity of the material is enhanced, further improving the overall performance and safety of the battery.

[0013] As a further improvement to the composite current collector of the present invention, the polymer of the protective layer is any one of polyethylene terephthalate, polypropylene and polyethylene.

[0014] As a further improvement to the composite current collector of the present invention, the metal oxide includes one or more of borosilicate, aluminum oxide, titanium oxide and magnesium oxide.

[0015] As a further improvement to the composite current collector of the present invention, the mass ratio of polymer material, metal oxide and conductive agent is 80:10:10.

[0016] As a further improvement to the composite current collector of the present invention, at least one groove is provided through the first surface and the first layer disposed on the first surface by laser cleaning. The groove includes a first through hole disposed through the first layer and a first countersunk hole disposed on the first surface.

[0017] As a further improvement to the composite current collector of the present invention, at least one groove is provided through the second surface and the second layer disposed on the second surface by laser cleaning. The groove includes a second through hole disposed through the second layer and a second countersunk hole disposed on the second surface.

[0018] As a further improvement to the composite current collector of the present invention, the thickness of the protective layer is A, and the value of A ranges from 1um to 5um.

[0019] As a further improvement to the composite current collector of the present invention, the thickness of the aluminum foil layer is B, and the value of B ranges from 5um to 8um.

[0020] One of the objectives of this invention is to provide a battery cell manufacturing method that can mitigate short circuits caused by external forces, addressing the shortcomings of existing technologies.

[0021] To achieve the above technical objectives, this application implements the following technical solution:

[0022] A method for manufacturing a battery cell comprising any of the above-mentioned composite current collectors includes the following steps:

[0023] S101. A protective layer is prepared by mixing polymer materials, metal oxides and conductive agents, kneading and melting the mixed material through a screw extruder, and casting.

[0024] S201. The aluminum foil is treated with a corona process to prepare an aluminum foil layer. The protective layer prepared in step S101 is laminated onto the aluminum foil layer to form a composite current collector.

[0025] S301. The active material is coated onto the surface of the composite current collector and dried at a temperature of 80-120℃ to form the final product.

[0026] S401. The electrode sheet prepared in step S301 is rolled, slit, and then wound with a separator to prepare a battery cell.

[0027] The above technical solution produces the following technical effects:

[0028] The battery cell manufacturing method of this invention ensures the stability of the composite current collector and the reliability of the battery cell through a specific process flow. In step S101, by precisely controlling the mixing ratio and the melting conditions, a uniform protective layer with excellent conductivity can be obtained. In step S201, the power of the corona treatment and the temperature control of the lamination process further guarantee the bonding strength of the composite current collector and the performance of the battery cell. In step S301, the coating and drying of the active material, and in step S401, the winding preparation of the battery cell, are all carried out under strictly controlled conditions to ensure the uniformity and consistency of the battery cell. Ultimately, the battery cell manufacturing method provided by this invention not only improves battery safety but also optimizes battery charge and discharge performance and extends battery life.

[0029] As a further improvement to the cell manufacturing method of this application, the power of the corona process is controlled between 2KW and 10KW;

[0030] The ambient temperature during the lamination process is controlled between 100-200℃. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1This is one of the structural schematic diagrams of the composite current collector in this invention;

[0033] Figure 2 This is the second schematic diagram of the composite current collector in this invention;

[0034] Figure 3 This is the third schematic diagram of the composite current collector in this invention;

[0035] in:

[0036] 1-Aluminum foil layer;

[0037] 11-First page;

[0038] 12 - Second page;

[0039] 2-Protective layer;

[0040] 21 - First Floor;

[0041] 22 - Second layer;

[0042] 3-groove;

[0043] 31 - First through hole;

[0044] 32 - First countersunk hole;

[0045] 33 - Second through hole;

[0046] 34 - Second countersunk hole. Detailed Implementation

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0048] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

[0050] It is known that when a battery cell is damaged by external forces, the positive and negative electrodes come into direct contact, leading to a short circuit and greatly increasing the risk of thermal runaway. There are four main short circuit modes caused by contact between the positive and negative electrodes: contact between graphite and the positive electrode material, contact between graphite and the positive electrode aluminum foil, contact between copper foil and aluminum foil, and contact between the positive electrode material and the negative electrode copper foil. Among these, the short circuit caused by direct contact between the negative electrode graphite material and the aluminum foil is the primary factor leading to thermal runaway. The core objective of this application is to provide a composite current collector that prevents the most severe short circuit caused by direct contact between the negative electrode graphite and the aluminum foil when the battery cell is damaged by external forces, thereby increasing the safety of the battery cell.

[0051] Specifically, in order to solve the above-mentioned technical defects, the composite current collector designed in this application includes an aluminum foil layer 1 and protective layers 2 disposed on both sides of the aluminum foil layer 1 in the thickness direction (Y-axis direction); the protective layer 2 includes a polymer material, a metal oxide and a conductive agent, wherein the conductive agent is one or more of SP, CNT, graphene and Ketjen black; the protective layer 2 includes a first layer 21 and a second layer 22, the first layer 21 is coated on the first side 11 of the aluminum foil layer 1, and the second layer 22 is coated on the second side 12 of the aluminum foil layer 1; in addition, the materials of the first layer 21 and the second layer 22 may be the same or different.

[0052] The principle behind the aforementioned technical solution, which avoids short circuits caused by direct contact between the negative electrode graphite material and the aluminum foil when the battery cell is damaged, leading to excessive heat generation and thermal runaway, is that when the battery cell is damaged by external force, the protective layer 2 in the composite current collector provides additional physical isolation, reducing direct contact between the negative electrode graphite and the aluminum foil layer 1. Due to the presence of the protective layer 2, even in the event of cell damage, the risk of short circuits between the positive and negative electrode materials is significantly reduced. Furthermore, the material selection of the protective layer 2 further enhances the mechanical strength and electrochemical stability of the composite current collector, thereby improving the overall safety and reliability of the battery cell. In this way, the composite current collector not only effectively alleviates the problem of short circuits caused by external forces but also improves the battery's charge / discharge efficiency and cycle life.

[0053] The aluminum foil layer 1, serving as the base of the current collector, provides excellent conductivity and mechanical strength. It plays a crucial role in collecting and conducting current within the battery. Its lightweight and high conductivity also contribute to increasing the overall energy density of the battery and ensures efficient current conduction during charging and discharging, providing a stable electrical connection. The protective layer 2 consists of polymer materials, metal oxides, and conductive agents. The polymer materials provide flexibility and adhesion to the protective layer 2, helping to resist mechanical stress and protect the aluminum foil layer 1. The metal oxides, being insulating materials, do not improve conductivity upon addition; their primary function is to enhance the stability and rigidity of the protective layer. The conductive agents significantly improve conductivity, enhancing current distribution and transmission efficiency.

[0054] It is worth noting that in the design of the first layer 21 and the second layer 22 in this application, the first layer 21 is coated on the first side 11 of the aluminum foil layer 1, providing good contact with the positive electrode active material. The second layer 22 is coated on the second side 12 of the aluminum foil layer 1, providing good contact with the negative electrode material. This design ensures that the two polar materials can make full contact, improving the overall electrochemical performance of the battery. The design of the first layer 21 and the second layer 22 increases the effective contact area between the electrode and the current collector, improving the battery efficiency. Furthermore, the use of the same or different materials for the first layer 21 and the second layer 22 is to ensure that the technical solution of this application can select the most suitable material for different electrochemical environments of the positive and negative electrodes, thereby improving the battery performance.

[0055] Furthermore, the polymer of protective layer 2 is any one of polyethylene terephthalate (PET), polypropylene, and polyethylene. PET, in particular, possesses high strength and rigidity, providing excellent structural support during battery operation. Moreover, PET can withstand the operating temperatures of the battery at high energy density, reducing the risk of thermal runaway, and exhibits good corrosion resistance to electrolytes and other chemicals, extending battery life. Thus, by using PET, protective layer 2 improves the mechanical stability and durability of the battery, reducing the risk of damage.

[0056] Polypropylene (PP) is lightweight, which helps reduce the overall weight of the battery and increase energy density. While serving as part of the protective layer 2, PP itself has good insulation properties, preventing unwanted short circuits. This also provides stability against common battery chemicals, effectively protecting the aluminum foil from corrosion. Polyethylene (PE) has excellent flexibility and impact resistance, accommodating the expansion and contraction during battery operation. Its strong adaptability to electrolytes prevents performance degradation caused by chemical corrosion. During manufacturing, PE is easy to process and form into complex shapes, facilitating the production of large battery modules.

[0057] As a further improvement to the composite current collector of the present invention, the metal oxide includes one or more of burlite, aluminum oxide, titanium oxide, and magnesium oxide. It is worth noting that oxides generally have poor conductivity. After addition, the internal resistance will increase, and the conductivity of the battery cell will decrease. Therefore, a certain amount of conductive agents such as SP and CNT mentioned above needs to be added to this layer.

[0058] Furthermore, Boron Nitrite possesses certain thermal conductivity, which helps improve the effective heat dissipation of the composite current collector under high-temperature operating conditions. Simultaneously, this material exhibits good durability in battery environments (such as electrolytes), reducing the risk of performance degradation during long-term battery use. Magnesium Oxide exhibits good high-temperature stability, making it suitable for high-power operation conditions, and is not easily degraded. In addition, magnesium oxide can improve the toughness of the current collector, preventing brittle fracture under extreme conditions.

[0059] Furthermore, the mass ratio of polymer material, metal oxide, and conductive agent is 80:10:10. Thus, as the basic component of the composite current collector, the polymer material provides the necessary mechanical strength, flexibility, and chemical resistance. The high proportion of polymer material helps ensure that the current collector maintains stable physical properties under battery operating conditions. The high proportion of polymer enables the current collector to effectively resist cracking or breakage under physical stress. An appropriate amount of metal oxide enhances the conductivity and thermal management performance of the composite current collector. Although the proportion is relatively low, they play a significant role in improving performance.

[0060] It is worth noting that, considering the current mainstream composite current collectors have a PET layer in the middle and metal layers on both sides, the tab welding is relatively difficult and the internal resistance is relatively high. However, the present application has a metal layer in the middle and protective layer 2 on both sides, allowing for easy cleaning of the welding tabs in the tank area using laser cleaning. The cleaning tank area can be cleaned before or after coating, and the internal resistance is low after welding. It is worth noting that, as... Figure 2As shown, in this invention, at least one groove 3 is formed through the first surface 11 of the composite current collector and the first layer 21 disposed on the first surface 11 by laser cleaning. The groove 3 includes a first through hole 31 penetrating the first layer 21 and a first countersunk hole 21 disposed on the first surface 11. The through hole is positioned at the alignment point of the negative electrode tab, thereby reducing the thickness of the finished cell and increasing its energy density. The groove 3, including the first through hole 31 penetrating the first layer 21 and the first countersunk hole 21 disposed on the first surface 11, increases the surface area of ​​the material to enhance the contact between the electrode and the current collector, and effectively improves the energy density and power density of the battery. This solves the technical defect in the prior art where the groove 3, even when designed within the protective layer 2, does not involve the aluminum foil layer 1, resulting in poor contact between the electrode and the current collector due to gas expansion caused by electrochemical reactions during battery charging and discharging, thus affecting battery performance.

[0061] In addition, such as Figure 3 As shown, at least one groove 3 is formed through the second surface 12 and the second layer 22 disposed on the second surface 12 by laser cleaning. The groove 3 includes a second through hole 33 disposed through the second layer 22 and a second countersunk hole 34 disposed on the second surface 12. The first surface 11 and the second surface 12 are used to connect electrodes or tabs of different polarities. In specific implementation, the first groove 3 and the second groove 3 respectively generate two different composite current collectors, thereby providing a more stable and uniform current distribution during battery charging and discharging. The groove 3 design of the second surface 12 is also achieved through laser cleaning technology, ensuring the bonding strength between the second layer 22 and the second surface 12, while increasing the contact area between the electrode and the current collector, further improving the battery's charging and discharging efficiency and cycle life. Through this design, the battery can maintain good electrochemical performance during high-rate charging and discharging, reducing local overheating and battery performance degradation caused by uneven current density.

[0062] Specifically, the thickness of protective layer 2 is valued as A, with a range of 1µm to 5µm. In practice, A can be 1µm, 1.5µm, 2µm, 2.5µm, 3µm, 3.5µm, 4µm, 4.5µm, or 5µm. The thickness of protective layer 2 directly affects battery performance; too thin a layer may lead to uneven current distribution, while too thick a layer may increase the battery's internal resistance, affecting charge and discharge efficiency. Therefore, selecting an appropriate thickness for protective layer 2 is crucial. In practical applications, the thickness of protective layer 2 can be flexibly adjusted according to the battery's usage requirements and performance indicators to achieve optimal electrochemical performance. Furthermore, the material selection for protective layer 2 must also consider its conductivity, chemical stability, and compatibility with electrode materials to ensure the overall stability and reliability of the battery.

[0063] As a further improvement to the composite current collector of this invention, the thickness of the aluminum foil layer 1 is B, and the value of B ranges from 5um to 8um. In specific implementations, the value of B can be 5um, 5.5um, 6um, 6.5um, 7um, 7.5um, or 8um. As the supporting structure for the current collector, the thickness of the aluminum foil layer 1 also has a significant impact on the mechanical strength and safety of the battery. While a thinner aluminum foil layer 1 can reduce the battery weight, it may reduce the battery's mechanical strength, while a thicker aluminum foil layer 1 can improve mechanical strength, but it will increase the battery's weight and cost. Therefore, choosing a suitable thickness for the aluminum foil layer 1 can ensure battery performance while balancing the battery's weight and cost. In practical applications, the thickness of the aluminum foil layer 1 needs to be optimized according to the battery's operating environment and performance requirements to achieve the best overall performance.

[0064] Furthermore, to further improve the safety of the battery cell, this application also designs a battery cell manufacturing method that includes any of the above-mentioned composite current collectors, specifically including the following steps:

[0065] S101. By mixing polymer materials, metal oxides and conductive agents, the mixed materials are kneaded and melted through a screw extruder, and the protective layer 2 is prepared by casting.

[0066] S201. Aluminum foil layer 1 is prepared by treating aluminum foil with corona process. The protective layer 2 prepared in step S101 is laminated onto aluminum foil layer 1 to form a composite current collector.

[0067] S301. The active material is coated onto the surface of the composite current collector and dried at a temperature of 80-120℃ to form the final product.

[0068] S401. The anode sheet prepared in step S301 is rolled, slit, and then wound with a diaphragm to prepare a battery cell.

[0069] Through the above technical solution, in step S201, the aluminum foil is treated with a corona process to make its surface more active, and then the prepared protective layer 2 is laminated onto the treated aluminum foil layer 1. The corona treatment increases the surface energy of the aluminum foil, enhances the adhesion between the protective layer 2 and the aluminum foil, and reduces the risk of delamination or peeling. Furthermore, the corona process can remove organic matter from the surface of the aluminum foil layer 1, making the surface cleaner; on the other hand, through this physical etching method, the surface of the aluminum foil layer 1 becomes rougher, further effectively improving the bonding force between the protective layer 2 and the aluminum foil layer 1, making them less prone to detachment.

[0070] Furthermore, the active material is coated onto the surface of the composite current collector and dried at a temperature of 80-120°C to form the electrode. In specific implementation, the active material in this application is a positive electrode active slurry (containing 97.6 wt% LiCoO2, 0.8 wt% SP, 0.7 wt% CNT) to prepare the positive electrode sheet. Moreover, under controlled temperature conditions, uniform coating of the positive electrode slurry can be ensured, while avoiding material degradation due to excessive temperature. A good coating effect can improve the contact between the electrode and the electrolyte, thereby increasing the energy density of the battery.

[0071] Furthermore, the power of the corona treatment process is controlled between 2KW and 10KW; the ambient temperature during the lamination process is controlled between 100-200℃. Therefore,

[0072] The power of the corona treatment is controlled between 2KW and 10KW to ensure proper surface treatment of the aluminum foil. Too low a power would negatively impact surface activity, while too high a power would damage the material. Precise control of the corona power ensures uniform surface treatment of the aluminum foil, guaranteeing good adhesion between the protective layer 2 and the aluminum foil layer 1 of the composite current collector. The ambient temperature during lamination is controlled between 100℃ and 200℃ to ensure full fusion between the protective layer 2 and the aluminum foil layer 1, while preventing material degradation due to excessive temperature. Appropriate lamination temperature contributes to the formation of a stable structure.

[0073] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto. Simultaneously, this application performs nail penetration tests and battery rate performance tests on Examples 1-20 and Comparative Examples 1-3. Specifically, the nail penetration test process is as follows: 10 cells from each of the comparative examples and examples are taken, charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 0.02C. The fully charged cells are then pierced at 25±2℃ using a tungsten steel needle with a diameter of 4mm, a taper of 15°, and a total length of 100mm, directly into the center of the cell. The needle must penetrate the cell completely; if the cell does not ignite or explode, it is considered to have passed. The battery rate performance test method involves taking 3 cells from each of Comparative Examples 1-3 and Examples 1-20, charging at a constant current of 0.5C to 4.5V, and then discharging at 1.5C to 3V for testing.

[0074] Example 1

[0075] In this embodiment, the protective layer 2 of the composite current collector has a thickness of 1 μm. It is made by fully mixing PET, Al2O3 and SP in a mass ratio of 80:10:10, then mixing and melting them through a screw extruder, and then casting the mixture.

[0076] The aluminum foil layer 1 has a thickness of 6 μm and is prepared by corona treatment. The protective layer 2 is laminated on both sides of the aluminum foil layer 1 at an environment of 150°C to form a composite current collector.

[0077] The active slurry of the positive electrode is composed of 97.6 wt% LiCoO2, 0.7 wt% SP and 0.7 wt% CNT, which are coated on the surface of the composite current collector. After drying at 100°C, the slurry is rolled, slit, and sheeted, and then wound with the separator and negative electrode to form a bare cell. The cell is then packaged, baked, injected with electrolyte, formed, and sealed again to prepare the cell.

[0078] Example 2

[0079] Unlike Example 1, the conductive agent in protective layer 2 is 10% by mass of CNTs. Other aspects are as described in Example 1 and will not be repeated here.

[0080] Example 3

[0081] Unlike Example 1, the conductive agent in protective layer 2 is 10% by mass graphene. Other details are as described in Example 1 and will not be repeated here.

[0082] Example 4

[0083] Unlike Example 1, the conductive agent in protective layer 2 is 10% by mass of Ketjen Black. Other details are as described in Example 1 and will not be repeated here.

[0084] Example 5

[0085] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass SP and 5% by mass CNT. Other details are as described in Example 1 and will not be repeated here.

[0086] Example 6

[0087] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass SP and 5% by mass Ketjen Black. Other details are as described in Example 1 and will not be repeated here.

[0088] Example 7

[0089] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass SP and 5% by mass graphene. Other details are as described in Example 1 and will not be repeated here.

[0090] Example 8

[0091] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass CNT and 5% by mass Ketjen Black. Other aspects are as described in Example 1 and will not be repeated here.

[0092] Example 9

[0093] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass CNT and 5% by mass graphene. Other details are as described in Example 1 and will not be repeated here.

[0094] Example 10

[0095] Unlike Example 1, the conductive agent in protective layer 2 is a blend of 5% by mass Ketjen black and 5% by mass graphene. Other details are as described in Example 1 and will not be repeated here.

[0096] Example 11

[0097] Unlike Example 1, the conductive agent in the protective layer 2 is a blend of 3.3% by mass of CNT, 3.3% by mass of Ketjen Black, and 3.3% by mass of graphene (the mass fraction of the conductive agent after blending is approximately 10%). Other aspects are as described in Example 1 and will not be repeated here.

[0098] Example 12

[0099] Unlike Example 1, the conductive agent in the protective layer 2 is a blend of 3.3% by mass of SP, 3.3% by mass of Ketjen Black and 3.3% by mass of graphene (the mass fraction of the conductive agent after blending is approximately 10%). Other aspects are as described in Example 1 and will not be repeated here.

[0100] Example 13

[0101] Unlike Example 1, the conductive agent of the protective layer 2 is a blend of 3.3% by mass of SP, 3.3% by mass of CNT and 3.3% by mass of graphene (the mass fraction of the conductive agent after blending is approximately 10%). Other aspects are as described in Example 1 and will not be repeated here.

[0102] Example 14

[0103] Unlike Example 1, the metal oxide of the protective layer 2 is boehmite, and the other properties are as described in Example 1, which will not be repeated here.

[0104] Example 15

[0105] Unlike Example 1, the metal oxide of the protective layer 2 is TiO2. Other aspects are as described in Example 1 and will not be repeated here.

[0106] Example 16

[0107] Unlike Example 1, the metal oxide of the protective layer 2 is MgO. Other details are as described in Example 1 and will not be repeated here.

[0108] Example 17

[0109] Unlike Example 1, the thickness of the protective layer 2 is changed to 2 μm. Other aspects are as described in Example 1 and will not be repeated here.

[0110] Example 18

[0111] Unlike Example 1, the thickness of the protective layer 2 is changed to 3 μm. Other details are as described in Example 1 and will not be repeated here.

[0112] Example 19

[0113] Unlike Example 1, the thickness of the protective layer 2 is changed to 4 μm. Other details are as described in Example 1 and will not be repeated here.

[0114] Example 20

[0115] Unlike Example 1, the thickness of the protective layer 2 is changed to 5 μm. Other details are as described in Example 1 and will not be repeated here.

[0116] Comparative Example 1

[0117] Unlike Example 1, the aluminum foil layer 1 has no protective layer 2 on its surface, and the thickness of the aluminum foil layer 1 is 6 μm. Other details are as described in Example 1 and will not be repeated here.

[0118] Comparative Example 2

[0119] Unlike Example 1, the protective layer 2 does not contain metal oxides, the mass percentage of PET is increased to 90%, and other aspects are as described in Example 1, which will not be repeated here.

[0120] Comparative Example 3

[0121] The difference from Example 1 is that the mass percentage of conductive agent SP in the conductive PET layer is reduced to 0.5%, and the mass percentage of PET is increased to 89.5%. Other details are as described in Example 1 and will not be repeated here.

[0122] The results of the acupuncture tests in Examples 1-20 and Comparative Examples 1-3 are shown in Table 1 below:

[0123]

[0124]

[0125] Table 1

[0126] As shown in Table 1, compared with Comparative Example 1, the safety of the battery cell made using the composite current collector of this application is significantly improved. This is because during needle penetration, the protective layer 2 provides better protection for the aluminum foil layer 1, preventing direct contact between the aluminum foil and graphite, which could lead to thermal runaway and battery cell failure. Table 1 also shows that the needle penetration pass rates of the composite current collectors with protective layers 2 mixed with different metal oxides are comparable, while the group without metal oxides has relatively poor safety. This is because with the addition of metal oxides, the protective layer 2 shrinks less under heat during needle penetration, thus preventing short circuits between the aluminum foil and the negative electrode to a greater extent, thereby improving battery safety. Table 1 further shows that the safety is relatively better when a single-component conductive agent is mixed into the protective layer 2. The relative deviation of multiple components may be related to the relatively poor conductive network formed by the single-component conductive agent. When the conductive network is relatively poor, the short-circuit current is relatively small, the heat generation of the battery cell is small, the shrinkage of the protective layer 2 is smaller, and the direct contact area between the aluminum foil and graphite is reduced, thereby improving the overall safety of the battery cell. From the perspective of the thickness of the second protective layer, the overall safety is improved when the thickness of the second protective layer increases, indicating that the PET layer thickness is increased, and its resistance to damage is stronger, thus increasing the protection of the aluminum foil.

[0127] The results of the rate performance tests for the batteries in Examples 1-20 and Comparative Examples 1-3 are shown in Table 2 below:

[0128]

[0129] Table 2

[0130] According to the data in Table 2, it is evident that the rate performance of the battery cell with the composite current collector introduced in this application decreases significantly compared to Comparative Examples 1-3. This is because the internal resistance of the composite current collector is greater than that of ordinary current collectors. Among the composite current collector battery cell groups, it can be observed that the rate performance of the cell is worse when a single-component conductive agent is added compared to when two or three conductive agents are added together. This is because single-component conductive agents are less likely to form a long-range conductive network, while when multiple conductive agents are added together, a better conductive network can be formed due to point-to-line, point-to-surface, or line-to-surface combinations, thus improving the conductivity of the current collector and consequently enhancing the overall rate performance of the battery cell. The table also shows that when different metal oxides are mixed in the composite current collector, the difference in battery cell rate performance is not significant. The battery cell rate is more related to the conductive network formed by the conductive agent and less related to the type of inorganic metal oxide.

[0131] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite current collector, characterized in that, It includes an aluminum foil layer (1) and protective layers (2) disposed on both sides of the aluminum foil layer (1) in the thickness direction; The protective layer (2) comprises a polymer material, a metal oxide and a conductive agent, wherein the conductive agent is one or more of SP, CNT, graphene and Ketjen black; The protective layer (2) includes a first layer (21) and a second layer (22), wherein the first layer (21) is coated on the first side (11) of the aluminum foil layer (1) and the second layer (22) is coated on the second side (12) of the aluminum foil layer (1); The first layer (21) and the second layer (22) may be made of the same or different materials; The polymer of the protective layer (2) is any one of polyethylene terephthalate, polypropylene and polyethylene; The metal oxide includes one or more of burgundy, aluminum oxide, titanium oxide, and magnesium oxide; The mass ratio of polymer material, metal oxide and conductive agent is 80:10:10; The thickness of the protective layer (2) is A, and the value of A ranges from 1um to 5um.

2. The composite current collector according to claim 1, characterized in that, The first surface (11) and the first layer (21) disposed on the first surface (11) are provided with at least one groove (3) through laser cleaning. The groove (3) includes a first through hole (31) disposed through the first layer (21) and a first countersunk hole (32) disposed on the first surface (11).

3. A composite current collector according to claim 1, characterized in that, The second surface (12) and the second layer (22) disposed on the second surface (12) are provided with at least one groove (3) through laser cleaning. The groove (3) includes a second through hole (33) disposed through the second layer (22) and a second countersunk hole (34) disposed on the second surface (12).

4. A composite current collector according to claim 1, characterized in that, The thickness of the aluminum foil layer (1) is B, and the value of B ranges from 5um to 8um.

5. A method for manufacturing a battery cell comprising the composite current collector as described in any one of claims 1-4, characterized in that, Includes the following steps: S101. By mixing polymer materials, metal oxides and conductive agents, the mixed materials are kneaded and melted by a screw extruder, and a protective layer is prepared by casting (2). S201. Aluminum foil layer (1) is prepared by treating aluminum foil with corona process. The protective layer prepared in step S101 is laminated onto the aluminum foil layer (1) to form a composite current collector. S301. The active material is coated onto the surface of the composite current collector and dried at a temperature of 80-120°C to form the final product. S401. The electrode sheet prepared in step S301 is rolled, slit, and then wound with a separator to prepare a battery cell.

6. The cell manufacturing method according to claim 5, characterized in that, The power of the corona treatment process is controlled between 2KW and 10KW; the ambient temperature during the lamination process is controlled between 100-200℃.

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