Composite current collector, preparation method thereof and lithium battery

Abstract

The invention relates to a composite current collector and a preparation method thereof and a lithium battery, the composite current collector comprises a base material layer and at least two metal layers, and the metal layers are respectively arranged on two opposite side surfaces of the base material layer. Wherein the overall elastic modulus of the composite current collector at 25 DEG C is less than or equal to 600 MPa, and the thickness ratio of the base material layer to the metal layer is 3-10. The overall elasticity modulus of the composite current collector at 25 DEG C is limited to be less than or equal to 600MPa, so that the composite current collector has proper flexibility; meanwhile, the thickness ratio of the base material layer to the metal layer is limited to be 3-10, the flexibility of the base material layer and the structural supporting performance of the metal layer are balanced, and performance unbalance caused by the fact that a single layer body is too thick or too thin is avoided. The design is favorable for inhibiting the growth of lithium dendrites and preventing the lithium dendrites from puncturing the diaphragm, the safety performance of the battery can be improved, the flexibility and the structural stability of the composite current collector can be balanced, and the structural integrity of the battery in the assembling and circulating processes can be ensured.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a composite current collector, its preparation method, and a lithium battery. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in new energy vehicles, portable electronic devices, energy storage systems, and other fields. As one of the core components of a lithium battery, the current collector's main function is to carry the active material and conduct current; its performance directly affects the battery's energy density, cycle stability, and safety performance.

[0003] Traditional lithium-ion battery current collectors typically use pure copper foil as the negative electrode material and pure aluminum foil as the positive electrode material. However, pure metal current collectors suffer from drawbacks such as high density, high cost, and poor flexibility, limiting the development of lithium-ion batteries towards lightweight and high energy density. To address these issues, composite current collectors have emerged. Among them, PET (polyethylene terephthalate) composite copper foil has become a research hotspot and industrialization direction in recent years due to its advantages such as lightweight, high flexibility, and low cost.

[0004] However, when existing PET composite copper foil is actually applied to lithium batteries, it is prone to the technical problem of lithium dendrite growth and piercing the separator: during the charge and discharge cycle of lithium batteries, the deposition of lithium ions on the negative electrode surface is prone to unevenness, forming needle-like lithium dendrites; as the number of cycles increases, lithium dendrites continue to grow, and existing PET composite copper foil cannot effectively inhibit the growth of lithium dendrites, eventually causing lithium dendrites to pierce the separator, causing internal short circuits in the battery, leading to serious safety problems such as thermal runaway, fire, or even explosion, which greatly limits the large-scale application of PET composite copper foil in the field of lithium batteries. Summary of the Invention

[0005] Therefore, it is necessary to provide a composite current collector, its preparation method, and a lithium battery, which can adapt to and alleviate the stress generated by lithium dendrite growth through specific mechanical property regulation, thereby improving the intrinsic safety of lithium batteries.

[0006] The technical solution is as follows: A composite current collector, comprising: a substrate layer and a metal layer, wherein the metal layer comprises at least two layers and is respectively provided with opposite sides of the substrate layer, wherein the overall elastic modulus of the composite current collector at 25°C is ≤600 MPa, and the thickness ratio of the substrate layer to the metal layer is 3~10.

[0007] In one embodiment, the overall elastic modulus of the composite current collector is 300~500MPa.

[0008] In one embodiment, the flexural stiffness of the composite current collector is 1~50 N·mm.2 .

[0009] In one embodiment, the elastic modulus of the substrate layer is between 100 MPa and 400 MPa.

[0010] In one embodiment, the thickness of the substrate layer is 1 μm to 10 μm.

[0011] In one embodiment, the thickness of the metal layer is 0.5 μm to 2 μm.

[0012] In one embodiment, the metal layer comprises copper, and the copper purity of the metal layer is ≥99.5% and the conductivity is ≥58 MS / m.

[0013] In one embodiment, the metal layer further includes trace elements, which are at least one of Ag, Sn, and Zn, and the mass fraction of the trace elements is 0.01 to 0.5 wt%.

[0014] In one embodiment, the substrate layer is modified PET, the modified PET comprising a PET matrix and a modifier, the modifier being at least one of polyethylene glycol, adipic acid or isophthalic acid, and the mass fraction of the modifier being 1-5 wt%.

[0015] In one embodiment, an antioxidant and a UV absorber are also added to the substrate layer. The antioxidant is a hindered phenolic antioxidant, and the amount added is 0.1 to 0.3% of the PET matrix mass. The UV absorber is a benzotriazole UV absorber, and the amount added is 0.05 to 0.2% of the PET matrix mass.

[0016] A method for preparing a composite current collector includes the following steps:

[0017] Substrate layer pretreatment: The PET film is subjected to plasma cleaning or corona treatment to remove surface oil and impurities;

[0018] Transition layer preparation: Transition layers were sequentially deposited on both sides of the pretreated PET substrate using magnetron sputtering with a sputtering power of 50~200W and a vacuum degree of 1×10⁻⁶. -3 ~5×10 -3 Pa, deposition rate is 0.01~0.05 μm / min;

[0019] A metal layer is deposited on the surface of the transition layer using magnetron sputtering or electroplating. The magnetron sputtering process parameters are: sputtering power of 100~300W and vacuum degree of 1×10⁻⁶. -3 ~5×10 -3Pa, deposition rate is 0.05~0.2μm / min; electroplating process parameters are: electroplating solution is copper sulfate plating solution or copper alloy plating solution, current density is 1~5A / dm², electroplating temperature is 20~40℃;

[0020] Post-treatment: The deposited composite film is annealed at a temperature of 80-150℃ for 1-3 hours. If a copper alloy layer is to be prepared, passivation is required after annealing. The passivation solution is a chromate solution or a phosphate solution, and the passivation temperature is 25-40℃ for 1-5 minutes.

[0021] A lithium battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and a composite current collector as described above, wherein the composite current collector serves as a negative electrode current collector carrying a negative electrode active material.

[0022] The beneficial effects of the above technical solution are as follows:

[0023] The aforementioned composite current collector, by limiting its overall elastic modulus at 25°C to ≤600MPa, possesses suitable flexibility. When lithium dendrite growth generates localized stress on the current collector, it can disperse the stress through minute elastic deformation, preventing rapid growth of lithium dendrites due to stress concentration. Simultaneously, by limiting the thickness ratio of the substrate layer to the metal layer to 3~10, it balances the flexibility of the substrate layer with the structural support of the metal layer, avoiding performance imbalances caused by excessively thick or thin single layers. This design helps suppress lithium dendrite growth and prevents it from piercing the separator, improving battery safety performance. It also helps balance the flexibility and structural stability of the composite current collector, ensuring structural integrity during battery assembly and cycling.

[0024] The aforementioned method for preparing composite current collectors involves pre-treating the substrate layer to remove impurities and enhance surface activity, laying the foundation for subsequent layer bonding. The preparation of the transition layer strengthens the bond between the substrate and metal layers, preventing interlayer delamination. Precisely controlled magnetron sputtering or electroplating processes ensure the uniformity and performance stability of the metal layer. Annealing eliminates internal stress in the composite film and regulates its mechanical properties to a set range. Passivation of the copper alloy layer improves the corrosion resistance of the metal layer. This coordinated process facilitates the preparation of composite current collectors with stable performance, strong interlayer bonding, and compliant mechanical parameters, improving the yield and performance consistency of composite current collectors and providing reliable assurance for battery safety.

[0025] The aforementioned lithium battery uses the optimized composite current collector as the negative electrode current collector. The composite current collector, through its suitable mechanical properties, can effectively disperse the stress generated by lithium dendrite growth, suppressing lithium dendrite growth and membrane puncture. Simultaneously, its excellent interlayer bonding stability and structural stability maintain the integrity of the battery's internal structure. This design improves the safety performance of lithium batteries, reduces short-circuit risks, enhances cycle stability, extends battery life, and improves the overall performance of lithium batteries, making them suitable for various application scenarios such as new energy vehicles and energy storage. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the composite current collector described in one embodiment;

[0029] Figure 2 This is a flowchart illustrating the preparation method of the composite current collector described in one embodiment.

[0030] Explanation of reference numerals in the attached figures:

[0031] 100, Composite current collector; 110, Substrate layer; 120, Metal layer. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., 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, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0037] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0038] See Figure 1 Figure 1 shows a schematic diagram of the structure of a composite current collector 100 according to an embodiment of the present invention. The composite current collector 100 includes a substrate layer 110 and a metal layer 120. The metal layer 120 consists of at least two layers and is respectively disposed on opposite sides of the substrate layer 110. The overall elastic modulus of the composite current collector 100 at 25°C is ≤600 MPa, and the thickness ratio of the substrate layer 110 to the metal layer 120 is 3~10.

[0039] The aforementioned composite current collector 100, by limiting its overall elastic modulus at 25°C to ≤600MPa, possesses suitable flexibility. When lithium dendrite growth generates localized stress on the current collector, it can disperse the stress through minute elastic deformation, preventing rapid growth of lithium dendrites due to stress concentration. Simultaneously, by limiting the thickness ratio of the substrate layer 110 to the metal layer 120 to 3~10, it balances the flexibility of the substrate layer 110 with the structural support of the metal layer 120, avoiding performance imbalances caused by excessively thick or thin single layers. This design helps suppress lithium dendrite growth and prevents it from piercing the separator, improving battery safety performance. It also helps balance the flexibility and structural stability of the composite current collector 100, ensuring structural integrity during battery assembly and cycling.

[0040] Furthermore, the metal layer 120 on each side of the substrate layer 110 has two or more layers.

[0041] In one embodiment, the overall elastic modulus of the composite current collector 100 is 300~500 MPa. This range of elastic modulus more precisely matches the stress buffering requirements during lithium dendrite growth. It avoids excessive deformation of the current collector due to an excessively low elastic modulus, which could affect the internal structure of the battery, while also preventing rapid lithium dendrite growth due to an excessively high elastic modulus that cannot effectively disperse stress. This design can more precisely suppress the growth and puncture behavior of lithium dendrites, which is beneficial to improving the stability of battery safety performance, while better balancing the structural support and flexibility of the current collector.

[0042] Specifically, the overall elastic modulus of the composite current collector 100 can be any value within the range of 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 430, 450, 460, 480, 490, 500 MPa.

[0043] In one embodiment, the flexural stiffness of the composite current collector 100 is 1~50 N·mm. 2 This stiffness range allows the current collector to possess sufficient flexibility to buffer the stress of lithium dendrite growth while maintaining good structural stability, preventing excessive deformation during battery assembly, transportation, and charge / discharge cycles. This design helps maintain the integrity of the battery's internal structure, reduces the shedding of electrode active material due to current collector deformation, improves battery cycle stability, and prevents voids created by excessive deformation from becoming sites for lithium dendrite deposition and growth, thus enhancing battery safety.

[0044] Optionally, the bending stiffness of the composite current collector 100 can be 1, 3, 5, 7, 8, 10, 20, 30, 32, 35, 36, 38, 40, 41, 42, 44, 46, 48, or 50 N·mm. 2 Or any value within the range.

[0045] In one embodiment, the elastic modulus of the substrate layer 110 is between 100 MPa and 400 MPa. This range of elastic modulus enables the substrate layer 110 to possess good flexibility, providing core support for the overall flexibility of the composite current collector 100, while also achieving a reasonable match with the elastic modulus of the metal layer 120, avoiding stress concentration between layers due to excessive differences in their elastic moduli. This design improves the interlayer bonding stability between the substrate layer 110 and the metal layer 120, prevents interlayer delamination, and helps suppress the deposition and growth of lithium dendrites in the voids formed by interlayer delamination, thereby improving the battery's safety performance and the structural stability of the composite current collector 100.

[0046] Optionally, the elastic modulus of the substrate layer 110 may be any value within the range of 100, 110, 120, 130, 140, 150, 160, 200, 210, 230, 250, 280, 290, 310, 330, 340, 360, 400 MPa.

[0047] In one embodiment, the thickness of the substrate layer 110 is 1 μm to 10 μm. This thickness range ensures that the substrate layer 110 has sufficient flexibility to buffer lithium dendrite stress while also providing a certain level of support strength. This avoids the substrate layer 110 being too thick, which would increase the overall thickness of the composite current collector 100 and affect the battery energy density, or too thin, which would result in insufficient support and easy breakage. This design helps to balance the flexibility and support performance of the substrate layer 110, taking into account both the battery's energy density and structural stability, and can improve the overall performance of the battery.

[0048] Optionally, the substrate layer 110 may be PET, PI, PP, PVC or other materials.

[0049] Furthermore, the substrate layer 110 is a microporous membrane or a nanofiber porous membrane, and the porosity of the substrate layer 110 is 20%~70%, with an average pore size of 10 nm~500 nm.

[0050] In one embodiment, the thickness of the metal layer 120 is 0.5 μm to 2 μm. This thickness range ensures good conductivity of the metal layer 120 while preventing excessive thickness from increasing the overall rigidity and decreasing the flexibility of the composite current collector 100, and also prevents insufficient conductivity and easy breakage caused by an excessively thin metal layer 120. This design maintains the overall flexibility of the composite current collector 100 while ensuring smooth current transmission, which helps suppress lithium dendrite growth and improves the conductivity stability and safety performance of the battery.

[0051] Optionally, the metal layer 120 may be pure copper foil or copper alloy material.

[0052] Specifically, the metal layer 120 comprises copper, and the copper purity of the metal layer 120 is ≥99.5%, with a conductivity ≥58 MS / m. High-purity copper reduces impurities and defects within the metal layer 120, lowers resistance during current transmission, and avoids localized heating and uneven lithium-ion deposition caused by excessive local resistance. High conductivity ensures uniform current transmission within the metal layer 120, further optimizing the lithium-ion deposition environment. This design improves the uniformity of current transmission, reduces localized heating, suppresses uneven lithium dendrite growth, and enhances the cycle stability and safety performance of the battery.

[0053] Furthermore, the metal layer 120 also includes trace elements, which are at least one of Ag, Sn, and Zn, with a mass fraction of 0.01~0.5wt%. These trace elements refine the grain structure of the metal layer 120, improving its mechanical strength and corrosion resistance without significantly affecting its electrical conductivity. This design enhances the mechanical stability and corrosion resistance of the metal layer 120, reduces damage and corrosion during charge-discharge cycles, extends the lifespan of the composite current collector 100, and improves the battery's cycle stability and safety performance.

[0054] In one embodiment, the metal layer 120 is an amorphous metal layer 120 or a nanocrystalline metal layer 120, with a grain size ≤100 nm.

[0055] Optionally, the organic polymer layer is a copolymer or polymer blend.

[0056] Preferably, the copolymer is at least one of polybutylene terephthalate (PBAT), polyether ester elastomer, or polyamide elastomer. The polymer blend is a blend of polypropylene (PP) and polyethylene (PE), or a blend of polyethylene terephthalate (PET) and polyolefin elastomer (POE).

[0057] Furthermore, the organic polymer layer contains a plasticizer, the plasticizer having a mass content of 0.5% to 15% of the polymer substrate mass.

[0058] Optionally, the plasticizer is selected from at least one of phthalates, citrates, polyethylene glycol (PEG) or dioctyl adipate (DOA).

[0059] In one embodiment, the substrate layer 110 is modified PET. The modified PET comprises a PET matrix and a modifier. The modifier is at least one selected from polyethylene glycol, adipic acid, or isophthalic acid, and the mass fraction of the modifier is 1-5 wt%. The modifier can improve the flexibility and interfacial compatibility of the PET matrix, enhance the bonding force between the substrate layer 110 and the metal layer 120, and optimize the mechanical properties of the substrate layer 110 to better meet the performance requirements of the overall composite current collector 100. This design is beneficial for improving the flexibility and interlayer bonding stability of the substrate layer 110, enhancing the overall mechanical properties of the composite current collector 100, and improving the safety performance and cycle stability of the battery.

[0060] In one embodiment, the substrate layer 110 further includes an antioxidant and a UV absorber. The antioxidant is a hindered phenolic antioxidant, added at 0.1-0.3% of the PET matrix mass; the UV absorber is a benzotriazole UV absorber, added at 0.05-0.2% of the PET matrix mass. The antioxidant can delay the oxidative aging of the PET substrate during long-term use, preventing a decline in the mechanical properties of the substrate layer 110. The UV absorber can absorb ultraviolet light, reducing the degradation effect of ultraviolet light on the PET substrate and maintaining the long-term stability of the substrate layer 110. This design can improve the long-term stability of the substrate layer 110, slow down its aging and degradation rate, and help extend the service life of the composite current collector 100 and the battery, thereby improving the long-term safety performance of the battery.

[0061] Please see Figure 2 , Figure 2 A flowchart illustrating the preparation method of a composite current collector 100 is shown. An embodiment of the present invention also provides a preparation method of the composite current collector 100, comprising the following steps:

[0062] S10: Substrate layer 110 pretreatment: The PET film is subjected to plasma cleaning or corona treatment to remove surface oil and impurities;

[0063] S20: Transition Layer Preparation: A transition layer is sequentially deposited on both sides of the pretreated PET substrate using magnetron sputtering with a sputtering power of 50~200W and a vacuum degree of 1×10⁻⁶. -3 ~5×10 -3 Pa, deposition rate is 0.01~0.05 μm / min;

[0064] S30: A metal layer 120 is deposited on the surface of the transition layer using magnetron sputtering or electroplating. The magnetron sputtering process parameters are: sputtering power of 100~300W and vacuum degree of 1×10⁻⁶. -3 ~5×10 -3 Pa, deposition rate is 0.05~0.2μm / min; electroplating process parameters are: electroplating solution is copper sulfate plating solution or copper alloy plating solution, current density is 1~5A / dm², electroplating temperature is 20~40℃;

[0065] S40: Post-treatment: Anneal the deposited composite film at a temperature of 80~150℃ for 1~3h. If a copper alloy layer is to be prepared, passivation is required after annealing. The passivation solution is a chromate solution or a phosphate solution, and the passivation temperature is 25~40℃ for 1~5min.

[0066] The aforementioned method for preparing the composite current collector 100 involves pre-treating the substrate layer 110 to remove impurities and enhance surface activity, laying the foundation for subsequent layer bonding. The preparation of the transition layer strengthens the bond between the substrate layer 110 and the metal layer 120, preventing interlayer delamination. Precisely controlled magnetron sputtering or electroplating processes ensure the uniformity and performance stability of the metal layer 120. Annealing eliminates internal stress in the composite film and regulates its mechanical properties to a set range. Passivation of the copper alloy layer improves the corrosion resistance of the metal layer 120. This coordinated process facilitates the preparation of a composite current collector 100 with stable performance, strong interlayer bonding, and compliant mechanical parameters. This improves the yield rate and performance consistency of the composite current collector 100, providing a reliable guarantee for battery safety.

[0067] It should be noted that corona treatment of PET substrates, also known as electrocautery treatment, is a physical modification process for the surface of PET films. High-voltage discharge generates plasma, which acts on the surface of the PET substrate. The high energy of the plasma breaks down the molecular chains on the substrate surface and forms active groups, while simultaneously removing surface contaminants such as oil and impurities. Furthermore, the corona treatment process involves a processing power of 200-500W, a processing speed of 10-50m / min, an electrode-film spacing of 0.5-2mm, and is conducted in ambient air at normal pressure. Corona treatment enhances the polarity and activity of the PET substrate surface, strengthening its interfacial bonding with subsequent functional layers such as the transition layer and metal layer 120. This prevents interlayer delamination problems during the subsequent fabrication of the composite current collector 100, laying the foundation for the fabrication of a structurally stable and reliable composite current collector 100.

[0068] An embodiment of the present invention also provides a lithium battery, including a positive electrode, a negative electrode, a separator, an electrolyte, and a composite current collector of any one of the above, wherein the composite current collector serves as a negative electrode current collector carrying the negative electrode active material.

[0069] This lithium battery uses the aforementioned optimized composite current collector as the negative electrode current collector. The composite current collector, through its suitable mechanical properties, can effectively disperse the stress generated by lithium dendrite growth, suppressing lithium dendrite growth and membrane puncture. Simultaneously, its excellent interlayer bonding stability and structural stability maintain the integrity of the battery's internal structure. This design improves the safety performance of the lithium battery, reduces the risk of short circuits, enhances cycle stability, extends battery life, and improves the overall performance of the lithium battery, making it suitable for various application scenarios such as new energy vehicles and energy storage.

[0070] To verify the beneficial effects of the technical solution of the present invention, the following embodiments and comparative examples were designed, and their key performance was tested and compared.

[0071] Example 1

[0072] A 4μm thick modified PET substrate with an elastic modulus of 280MPa was used as the substrate layer. 2wt% polyethylene glycol was used as the modifier. Copper layers (99.8% purity) with a thickness of 0.8μm were deposited on both sides via magnetron sputtering to prepare a composite current collector. The overall elastic modulus was measured to be 380MPa, the flexural stiffness to be 12 N·mm², and the substrate layer to metal layer thickness ratio was 5. This current collector was used to prepare the negative electrode, which was then assembled into an Ah-level soft-pack lithium battery for testing. Under harsh cycling conditions of 1C charging and -10℃, the battery exhibited a voltage drop only after 450 cycles. Simulated dendrite piercing experiments showed significant plastic indentation on the current collector surface, effectively dispersing stress. The battery energy density retention rate was 96%.

[0073] Example 2

[0074] A 6 μm thick porous polypropylene (PP) membrane with a porosity of approximately 40% and an elastic modulus of 150 MPa was used as the substrate layer. A 5 nm chromium transition layer was sputtered onto both sides of the membrane, followed by electroplating of a 1 μm thick Cu-0.1 wt% Sn alloy layer to prepare the composite current collector. The overall elastic modulus was measured to be 220 MPa, the flexural stiffness to be 8 N·mm², and the thickness ratio to be 6. Under the same stringent testing conditions, the corresponding battery did not experience an internal short circuit after 580 cycles. The separator showed no damage in the dendrite penetration simulation test. The porous structure of the current collector facilitates electrolyte adsorption and buffers volume changes.

[0075] Example 3

[0076] A substrate layer (total thickness 5 μm) composed of 2 μm TPU and 3 μm PET was used, with an overall elastic modulus of 190 MPa. A 0.5 μm copper layer (containing 0.05 wt% Ag) was deposited on both sides, and the surface underwent micro-roughening treatment (Ra≈80 nm). The resulting composite current collector had an overall modulus of 260 MPa, a bending stiffness of 10 N·mm², and a thickness ratio of 10. The corresponding battery exhibited excellent fast-charging performance; after 300 cycles of 2C fast charging, the negative electrode current collector showed no wrinkles or peeling, the battery capacity retention reached 92%, and no thermal runaway occurred.

[0077] Comparative Example 1

[0078] The battery used a conventional 8μm pure copper foil as the negative electrode current collector with an elastic modulus of 110GPa. In the same 1C, -10℃ low-temperature cycling test, the battery experienced a voltage drop and short circuit after only about 120 cycles. Disassembly revealed that the separator was clearly punctured and the dendrites were large and concentrated.

[0079] Comparative Example 2

[0080] Using a 4μm thick high-modulus PET (elastic modulus 3.5GPa) as the substrate, with 0.5μm copper deposited on each side, a composite current collector was fabricated with an overall modulus of approximately 1.1GPa, far exceeding 600MPa, and a bending stiffness of 65 N·mm². The battery exhibited a short circuit after approximately 200 cycles under harsh conditions. Simulation tests showed no significant deformation after dendrites contacted the current collector; stress concentration caused the dendrites to grow rapidly laterally and puncture the separator.

[0081] Comparative Example 3

[0082] The substrate layer uses an ultrathin PI film with a thickness of 1 μm and an elastic modulus of 2.5 GPa. A 1.5 μm copper layer is deposited on each side, with a thickness ratio of 0.67. Although the resulting current collector has an overall modulus of approximately 1.8 GPa, due to the excessively thin substrate and excessively thick metal layer, it has poor flexibility and is prone to breakage during the rolling process, resulting in a low battery yield. It fails after only 79 cycles due to a sharp increase in internal resistance caused by localized fracture of the current collector.

[0083] Comparative Example 4

[0084] The substrate layer is ordinary PET with a thickness of 12μm and an elastic modulus of 2.2GPa. Only an extremely thin copper layer of 0.1μm is deposited on both sides, resulting in a thickness ratio as high as 120. The overall modulus of this current collector is about 1.5GPa. Due to the excessively thin metal layer, the sheet resistance increases significantly, resulting in poor battery rate performance. Furthermore, the metal layer cracks and falls off during cycling, leading to the stripping of active material and rapid capacity decay, making it unsuitable for normal use.

[0085] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite current collector, characterized in that, The composite current collector includes: The composite current collector has a substrate layer and a metal layer, wherein the metal layer consists of at least two layers and is provided on opposite sides of the substrate layer, wherein the overall elastic modulus of the composite current collector at 25°C is ≤600 MPa, and the thickness ratio of the substrate layer to the metal layer is 3~10.

2. The composite current collector according to claim 1, characterized in that, The overall elastic modulus of the composite current collector is 300~500MPa.

3. The composite current collector according to claim 1, characterized in that, The flexural stiffness of the composite current collector is 1~50 N·mm. 2 ; and / or, The elastic modulus of the substrate layer is between 100 MPa and 400 MPa.

4. The composite current collector according to claim 1, characterized in that, The thickness of the substrate layer is 1μm~10μm; and / or, The thickness of the metal layer is 0.5μm to 2μm.

5. The composite current collector according to claim 1, characterized in that, The metal layer comprises copper, and the copper purity of the metal layer is ≥99.5%, and the conductivity is ≥58 MS / m.

6. The composite current collector according to claim 5, characterized in that, The metal layer also includes trace elements, which are at least one of Ag, Sn, and Zn, and the mass fraction of the trace elements is 0.01~0.5wt%.

7. The composite current collector according to claim 1, characterized in that, The substrate layer is modified PET, and the modified PET comprises a PET matrix and a modifier. The modifier is at least one of polyethylene glycol, adipic acid, or isophthalic acid, and the mass fraction of the modifier is 1-5 wt%.

8. The composite current collector according to claim 7, characterized in that, The substrate layer also contains an antioxidant and a UV absorber. The antioxidant is a hindered phenolic antioxidant, and the amount added is 0.1-0.3% of the PET matrix mass. The UV absorber is a benzotriazole UV absorber, and the amount added is 0.05-0.2% of the PET matrix mass.

9. A method for preparing a composite current collector as described in any one of claims 1-8, characterized in that, Includes the following steps: Substrate layer pretreatment: The PET film is subjected to plasma cleaning or corona treatment to remove surface oil and impurities; Transition layer preparation: Transition layers were sequentially deposited on both sides of the pretreated PET substrate using magnetron sputtering with a sputtering power of 50~200W and a vacuum degree of 1×10⁻⁶. -3 ~5×10 -3 Pa, deposition rate is 0.01~0.05 μm / min; A metal layer is deposited on the surface of the transition layer using magnetron sputtering or electroplating. The magnetron sputtering process parameters are: sputtering power of 100~300W and vacuum degree of 1×10⁻⁶. -3 ~5×10 -3 Pa, deposition rate is 0.05~0.2μm / min; electroplating process parameters are: electroplating solution is copper sulfate plating solution or copper alloy plating solution, current density is 1~5A / dm², electroplating temperature is 20~40℃; Post-treatment: The deposited composite film is annealed at a temperature of 80-150℃ for 1-3 hours. If a copper alloy layer is to be prepared, passivation is required after annealing. The passivation solution is a chromate solution or a phosphate solution, and the passivation temperature is 25-40℃ for 1-5 minutes.

10. A lithium battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, an electrolyte, and a composite current collector according to any one of claims 1-8, wherein the composite current collector serves as a negative electrode current collector carrying the negative electrode active material.

Images