Base film, method for producing the same, composite current collector, electrode sheet, and electrochemical device

Abstract

This invention provides a base film and its preparation method, a composite current collector, an electrode sheet, and an electrochemical device, specifically relating to the field of current collector technology. The base film includes a polymer matrix and a mixed transition layer disposed on at least one surface of the polymer matrix; the mixed transition layer is made of polymer and metal; in the mixed transition layer, the content of the polymer decreases and the content of the metal increases along the direction away from the polymer matrix. The gradient structure in the base film provided by this invention achieves molecular-scale interlocking and chemical bonding, significantly improving interfacial bonding strength and enhancing structural stability; the continuously changing composition blocks the path of electrolyte capillary penetration along the interface, intrinsically inhibiting the erosion of the interface by solvents and corrosive components such as HF, thereby synergistically improving the interfacial bonding force and electrolyte immersion resistance of the base film.

Description

Technical Field

[0001] This invention relates to the field of current collector technology, and in particular to a base film and its preparation method, a composite current collector, an electrode sheet, and an electrochemical device. Background Technology

[0002] The current collector is a core component in a battery that collects electrons and carries active materials. It is typically composed of a cathode copper (Cu) foil and an anode aluminum (Al) foil. While it has a limited impact on improving the battery's energy storage performance, it accounts for more than 10% of the battery's total weight. Therefore, compared to optimizing active materials, reducing the weight of the current collector is a more effective way to improve the capacity of lithium-ion batteries.

[0003] Composite current collectors combine the lightweight and flexible properties of polymers with the excellent conductivity of metals by depositing a metal layer onto the polymer surface to form a thin film. Compared to the thinnest copper foil on the market, they can increase battery energy density by 16-26%. At the same time, their flexibility can accommodate battery volume expansion, making it possible to develop semi-solid and all-solid batteries. Furthermore, the polymer layer can prevent short circuits and avoid thermal runaway by melting and shrinking, thus improving battery safety.

[0004] Composite current collectors typically use polymer films such as PET and PP as the substrate, with metal conductive layers (copper or aluminum) prepared on both sides through processes such as magnetron sputtering, evaporation, or electroplating. This "sandwich" structure combines the advantages of lightweight, high safety, and low cost, but its application in lithium-ion batteries still faces two major challenges: 1. Poor coating adhesion: The polymer matrix and the metal conductive layer have significant differences in hardness, modulus and coefficient of thermal expansion, resulting in insufficient interfacial adhesion. They are easily peeled off during charge and discharge cycles, leading to increased battery internal resistance and capacity decay.

[0005] 2. Poor resistance to electrolyte immersion: During long-term use of lithium batteries, when the composite current collector is immersed in LiPF6 carbonate electrolyte, solvent molecules (such as ethylene carbonate and dimethyl carbonate) and hydrofluoric acid (HF) in the electrolyte will penetrate along the interface gaps, causing interface corrosion and weakening of the bonding force. In severe cases, it can lead to the peeling and detachment of the metal layer and battery failure.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a base film and its preparation method, a composite current collector, an electrode sheet, and an electrochemical device, aiming to solve at least one of the above-mentioned technical problems.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A first aspect of the present invention provides a base film comprising a polymer matrix and a mixed transition layer disposed on at least one surface of the polymer matrix; the mixed transition layer is made of a polymer and a metal; in the mixed transition layer, the content of the polymer decreases and the content of the metal increases along the thickness direction away from the polymer matrix.

[0009] Furthermore, in the hybrid transition layer, the metal content gradually increases from 0% to 100% from the inner surface in contact with the polymer matrix to the outer surface of the hybrid transition layer.

[0010] Furthermore, the thickness of the polymer matrix is ​​3μm to 10μm.

[0011] Preferably, the thickness of the hybrid transition layer is 100nm~500nm.

[0012] Furthermore, the polymer includes at least one of polyimide, polyethylene terephthalate, polypropylene, polyethylene, and polyetheretherketone.

[0013] Preferably, the metal includes copper or aluminum.

[0014] The second aspect of the present invention provides a method for preparing the base film, wherein a pretreated polymer matrix is ​​fixed in an ion implantation device, and after vacuuming, plasma excitation is performed followed by ion implantation to obtain the base film.

[0015] Furthermore, multi-energy state metal ion implantation or multi-charge state metal ion implantation.

[0016] In the ion implantation, the pulse frequency is 100Hz~1000Hz and the pulse width is 10μs~100μs.

[0017] Preferably, in the multi-energy-state metal ion implantation, the bias voltage amplitude is -10 kV to -40 kV, and the implantation energy is 10 keV to 40 keV.

[0018] Preferably, in the multi-charged metal ion implantation, at least two types of metal ions, including monovalent, divalent, and trivalent metal ions, are implanted simultaneously.

[0019] Preferably, the multi-energy state metal ion implantation includes high-energy implantation, medium-energy implantation and low-energy implantation performed sequentially.

[0020] Preferably, during the high-energy injection process, the bias voltage amplitude is -30 kV to -40 kV, the injection energy is 30 keV to 40 keV, and the dose is 5 × 10⁻⁶ kV. 15 ions / cm 2 ~1×10 16 ions / cm2 .

[0021] Preferably, during the medium-energy injection process, the bias voltage amplitude is -20 kV to -30 kV, the injected energy is 20 keV to 30 keV, and the dose is 1×10⁻⁶. 16 ions / cm 2 ~2×10 16 ions / cm 2 .

[0022] Preferably, during the low-energy injection process, the bias voltage amplitude is -10 kV to -20 kV, the injection energy is 10 keV to 20 keV, and the dose is 2 × 10⁻⁶ kV. 16 ions / cm 2 ~5×10 16 ions / cm 2 .

[0023] Furthermore, the plasma excitation is performed in an inert atmosphere.

[0024] Preferably, the gas used in the inert atmosphere includes argon.

[0025] Preferably, during the plasma excitation process, the working gas pressure is 0.1 Pa to 0.5 Pa, and the power of the radio frequency power supply is 100 W to 500 W, thereby generating argon plasma.

[0026] Preferably, after the vacuuming process, the background vacuum level is ≤5×10⁻⁶. -4 Pa.

[0027] Preferably, the pretreatment includes cleaning and drying the polymer matrix.

[0028] A third aspect of the present invention provides a composite current collector, comprising a base film and a metal layer disposed on at least one side of the base film; wherein the metal layer is disposed on the side of the mixing transition layer away from the polymer matrix; the base film is the base film described in the first aspect or the base film prepared by the preparation method described in the second aspect.

[0029] Furthermore, the material of the metal layer includes copper or aluminum.

[0030] Preferably, the thickness of the metal layer is 0.5μm to 2μm.

[0031] A fourth aspect of the present invention provides an electrode sheet comprising the composite current collector described in the third aspect.

[0032] A fifth aspect of the present invention provides an electrochemical device including the aforementioned electrode sheet.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects: The base film provided by this invention comprises a mixed transition layer on at least one side of a polymer matrix, in which polymer and metal components coexist. The polymer content in this layer decreases away from the matrix, while the metal content increases accordingly, forming a continuous gradient distribution structure. This gradient structure eliminates a clear physical interface between the mixed transition layer and the polymer matrix, achieving molecular-scale interlocking and chemical bonding, significantly improving interfacial bonding strength. Simultaneously, it eliminates the modulus mismatch and internal stress concentration caused by the abrupt interface between the matrix and the metal layer, enhancing structural stability. More importantly, the continuously varying composition blocks the capillary penetration path of the electrolyte along the interface, intrinsically inhibiting the erosion of the interface by solvents and corrosive components such as HF, thereby synergistically improving the interfacial bonding strength and electrolyte immersion resistance of the base film.

[0034] The preparation method provided by this invention eliminates the need for binders, intermediate layers, or secondary film formation steps, thus avoiding interface contamination and thermal / mechanical damage. The vacuum environment provides a contamination-free ion transport channel, reducing ion collisions and energy loss. The radio frequency excited argon plasma provides a large number of free electrons, which can promptly neutralize the accumulation of positive charges on the surface, improving implantation uniformity and efficiency. High-bias ion implantation provides the metal ions to be implanted and enables them to embed into the polymer surface layer with high kinetic energy, achieving atomic-level doping and bonding. This allows for the construction of an interface-free, gradient-continuous, physically interlocked, and chemically stable hybrid transition layer in a single process step, providing a highly bonded and corrosion-resistant intrinsically functionalized base film for subsequent conductive layers. Detailed Implementation

[0035] The embodiments and examples of the present invention will be described in detail below with reference to the implementation methods and examples. However, those skilled in the art will understand that the following implementation methods and examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] A first aspect of the present invention provides a base film comprising a polymer matrix and a mixed transition layer disposed on at least one surface of the polymer matrix; the mixed transition layer is made of a polymer and a metal; in the mixed transition layer, the content of the polymer decreases and the content of the metal increases along the thickness direction away from the polymer matrix.

[0037] The base film provided by this invention comprises a mixed transition layer on at least one side of a polymer matrix, in which polymer and metal components coexist. The polymer content in this layer decreases away from the matrix, while the metal content increases accordingly, forming a continuous gradient distribution structure. This gradient structure eliminates a clear physical interface between the mixed transition layer and the polymer matrix, achieving molecular-scale interlocking and chemical bonding, significantly improving interfacial bonding strength. Simultaneously, it eliminates the modulus mismatch and internal stress concentration caused by the abrupt interface between the matrix and the metal layer, enhancing structural stability. More importantly, the continuously varying composition blocks the capillary penetration path of the electrolyte along the interface, intrinsically inhibiting the erosion of the interface by solvents and corrosive components such as HF, thereby synergistically improving the interfacial bonding strength and electrolyte immersion resistance of the base film.

[0038] The present invention provides a first base film comprising a polymer matrix and a first hybrid transition layer disposed on one side surface of the polymer matrix.

[0039] The present invention provides a second base film comprising a polymer matrix and a second hybrid transition layer disposed on one side surface of the polymer matrix.

[0040] The present invention provides a third type of base film, comprising a polymer matrix and a first mixing transition layer and a second mixing transition layer disposed on both sides of the polymer matrix.

[0041] The location of the hybrid transition layer needs to match the actual application structure of the composite current collector in the electrochemical device. Its core function is to provide a highly bonded and corrosion-resistant interface support for the subsequently deposited metal layer.

[0042] Specifically: When the composite current collector is used in the middle layer of a tandem battery (i.e., both sides participate in electrode assembly), a mixing transition layer needs to be set on both sides of the polymer matrix to ensure that the metal layers on both sides can achieve a metallurgical bond with continuous composition and no clear interface; while when the composite current collector is located at the end of the tandem battery (such as the outermost current collector of the positive / negative electrode), only one side of the surface needs to carry the active material and connect to the external circuit. In this case, a mixing transition layer only needs to be set on the polymer matrix surface facing the inside of the battery, and the other side does not need to be functionalized, thus taking into account both performance requirements and process economy.

[0043] Furthermore, in the hybrid transition layer, the metal content gradually increases from 0% to 100% from the inner surface in contact with the polymer matrix to the outer surface of the hybrid transition layer. There is no clear interface between the hybrid transition layer and the polymer matrix, forming an interlocking bonding interface. This lack of a clear interface between the hybrid transition layer and the matrix allows metal ions to embed between the polymer molecular chains, forming a physically interlocked and chemically bonded structure. This eliminates the internal stress concentration caused by abrupt changes in modulus in traditional structures and structurally blocks the capillary channels through which the electrolyte permeates along the interface gaps.

[0044] Furthermore, the thickness of the polymer matrix is ​​3μm to 10μm.

[0045] Typically, but not limitingly, the thickness of the polymer matrix can be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, or any value in the range of 3 μm to 10 μm.

[0046] Preferably, the thickness of the hybrid transition layer is 100nm to 500nm.

[0047] Typically, but not limitingly, the thickness of the hybrid transition layer can be, for example, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm, or any value in the range of 100 nm to 500 nm.

[0048] Furthermore, the polymer includes at least one of polyimide, polyethylene terephthalate, polypropylene, polyethylene, and polyetheretherketone.

[0049] Preferably, the metal includes copper or aluminum.

[0050] The second aspect of the present invention provides a method for preparing the base film, wherein a pretreated polymer matrix is ​​fixed in an ion implantation device, and after vacuuming, plasma excitation is performed followed by ion implantation to obtain the base film.

[0051] The preparation method provided by this invention eliminates the need for binders, intermediate layers, or secondary film formation steps, thus avoiding interface contamination and thermal / mechanical damage. The vacuum environment provides a contamination-free ion transport channel, reducing ion collisions and energy loss. The radio frequency excited argon plasma provides a large number of free electrons, which can promptly neutralize the accumulation of positive charges on the surface, improving implantation uniformity and efficiency. High-bias ion implantation provides the metal ions to be implanted and enables them to embed into the polymer surface layer with high kinetic energy, achieving atomic-level doping and bonding. This allows for the construction of an interface-free, gradient-continuous, physically interlocked, and chemically stable hybrid transition layer in a single process step, providing a highly bonded and corrosion-resistant intrinsically functionalized base film for subsequent conductive layers.

[0052] The hybrid transition layer is formed by injecting metallic components from the surface of the polymer matrix into the interior through an ion implantation coating method.

[0053] Furthermore, the ion implantation includes multi-energy-state metal ion implantation or multi-charge-state metal ion implantation.

[0054] Preferably, the multi-energy-state metal ion implantation is equipped with a single-charge metal ion source and a bias pulse power supply.

[0055] The multi-charge metal ion implantation is equipped with a multi-charge metal ion source and a bias pulse power supply.

[0056] In the ion implantation, the pulse frequency is 100Hz~1000Hz and the pulse width is 10μs~100μs.

[0057] Preferably, in the multi-energy-state metal ion implantation, the bias voltage amplitude is -10 kV to -40 kV, and the implantation energy is 10 keV to 40 keV.

[0058] Preferably, in the multi-charged metal ion implantation, at least two types of metal ions, including monovalent, divalent, and trivalent metal ions, are implanted simultaneously.

[0059] Preferably, the multi-energy state metal ion implantation includes sequential high-energy implantation, medium-energy implantation, and low-energy implantation. High-energy implantation reaches a greater depth, forming a substrate concentration within the matrix; low-energy ion implantation reaches a shallower depth, forming an enriched concentration in the near-surface region; by adjusting the implantation dose corresponding to each energy, a smooth gradient curve with monotonically increasing concentration from the matrix interior to the surface can be superimposed.

[0060] The accelerating effect of implantation energy: The level of implantation energy directly determines the ion implantation depth. High-energy implantation gives ions high kinetic energy, allowing them to penetrate the polymer surface and embed deeper; low-energy implantation keeps ions in a shallower surface region. Selective implantation at different depths can be achieved by stepwise adjustment of the implantation energy (controlled by bias voltage amplitude and charge valence state).

[0061] Preferably, during the high-energy injection process, the bias voltage amplitude is -30 kV to -40 kV, the injection energy is 30 keV to 40 keV, and the dose is 5 × 10⁻⁶ kV. 15 ~1×10 16 ions / cm 2 .

[0062] Typically, but not limitingly, during the high-energy injection process, the injection energy can be, for example, 30keV, 32keV, 34keV, 36keV, 38keV, or 40keV, or any value within the range of 30keV to 40keV; the dose can be, for example, 5 × 10⁻⁶. 15 ions / cm 2 6×10 15 ions / cm 2 7×10 15 ions / cm 2 8×10 15 ions / cm 2 9×10 15 ions / cm2 Or 1×10 16 ions / cm 2 It can also be 5×10 15 ~1×10 16 ions / cm 2 Any value within the range.

[0063] Preferably, during the medium-energy injection process, the bias voltage amplitude is -20 kV to -30 kV, the injected energy is 20 keV to 30 keV, and the dose is 1×10⁻⁶. 16 ~2×10 16 ions / cm 2 .

[0064] Typically, but not limitingly, during the energy injection process, the injected energy can be, for example, 20keV, 22keV, 24keV, 25keV, or 30keV, or any value within the range of 20keV to 30keV; the dose can be, for example, 1×10⁻⁶. 16 ions / cm 2 1.2×10 16 ions / cm 2 1.5×10 16 ions / cm 2 1.8×10 16 ions / cm 2 Or 2×10 16 ions / cm 2 It can also be 1×10 16 ~2×10 16 ions / cm 2 Any value within the range.

[0065] Preferably, during the low-energy injection process, the bias voltage amplitude is -10 kV to -20 kV, the injection energy is 10 keV to 20 keV, and the dose is 2 × 10⁻⁶ kV. 16 ions / cm 2 ~5×10 16 ions / cm 2 .

[0066] Typically, but not limitingly, during the low-energy injection process, the injection energy can be, for example, 10 keV, 15 keV, 16 keV, 17 keV, 18 keV, 19 keV, or 20 keV, or any value within the range of 10 keV to 20 keV; the dose can be, for example, 2 × 10⁻⁶. 16 ions / cm 2 2.5×10 16 ions / cm 2 3×1016 ions / cm 2 4×10 16 ions / cm 2 Or 5×10 16 ions / cm 2 It can also be 2×10 16 ions / cm 2 ~5×10 16 ions / cm 2 Any value within the range.

[0067] Furthermore, the simultaneous implantation of multi-charged metal ions is performed by using a metal vapor vacuum arc ion source to extract multiple charge states of metal ions for ion implantation.

[0068] Preferably, in the simultaneous implantation of multi-charged metal ions, the implantation energy is 10 keV to 40 keV, and the implantation dose is 5 × 10⁻⁶. 15 ions / cm 2 ~5×10 16 ions / cm 2 The pulse frequency is 100Hz~1000Hz and the pulse width is 10μs~100μs.

[0069] Typically, but not limitingly, in the simultaneous implantation of multi-charged metal ions, the implantation energy can be, for example, 10keV, 15keV, 20keV, 25keV, 30keV, 35keV, or 40keV, or any value within the range of 10keV to 40keV; the pulse frequency can be, for example, 100Hz, 200Hz, 400Hz, 600Hz, 800Hz, or 1000Hz, or any value within the range of 100Hz to 1000Hz; the pulse width can be, for example, 10μs, 20μs, 40μs, 60μs, 80μs, or 100μs, or any value within the range of 10μs to 100μs; and the implantation dose can be 5 × 10⁻⁶. 15 ions / cm 2 8×10 15 ions / cm 2 10 16 ions / cm 2 3×10 16 ions / cm 2 Or 5×10 16 ions / cm 2 It can also be 5×10 15 ions / cm 2 ~5×10 16 ions / cm 2 Any value within the range.

[0070] It should be noted that ECR ion sources produce ions with a single valence state (such as Al). + Cu + The MEVVA ion source achieves multi-energy distribution injection by changing the bias voltage. Under a fixed bias voltage, ions of different valence states acquire different energies, naturally injecting to different depths to form a gradient. For multi-charge ions, the injection energy (keV) = charge number × bias voltage amplitude (kV). Under the same bias voltage, ions with higher valence states are injected with higher energy and to greater depths (ions of different valence states automatically acquire different energies and are injected to different depths under the same bias voltage).

[0071] Furthermore, the plasma excitation is performed in an inert atmosphere.

[0072] Preferably, the gas used in the inert atmosphere includes argon.

[0073] Preferably, during the plasma excitation process, the working gas pressure is 0.1Pa~0.5Pa, the frequency of the radio frequency power supply is 13.56MHz, and the power of the radio frequency power supply is 100W~500W, thereby generating argon plasma.

[0074] Typically, but not limitingly, during the plasma excitation process, the working gas pressure can be, for example, 0.1 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, or 0.5 Pa, or any value within the range of 0.1 Pa to 0.5 Pa; the frequency of the radio frequency power supply is 13.56 MHz; the power of the radio frequency power supply can be, for example, 100 W, 200 W, 300 W, 400 W, or 500 W, or any value within the range of 100 W to 500 W; argon plasma is generated during the excitation.

[0075] Preferably, after the vacuuming process, the background vacuum level is ≤5×10⁻⁶. -4 Pa.

[0076] Preferably, the pretreatment includes cleaning and drying the polymer matrix.

[0077] In some embodiments of the present invention, the pretreatment of the polymer matrix includes ultrasonic cleaning sequentially with anhydrous ethanol, acetone, and deionized water, with each solvent cleaning time being 10 minutes, to thoroughly remove surface organic contaminants and particles; subsequently, the cleaned matrix is ​​placed in a vacuum drying oven for drying: for polyethylene terephthalate (PET) matrix with good heat resistance, drying is performed at 80°C for 30 minutes; while for polypropylene (PP) matrix with lower heat resistance, drying is performed at 60°C for 30 minutes to avoid thermal deformation or degradation, ensuring that the matrix surface is clean, dry, and structurally stable, providing a reliable basis for subsequent ion implantation processes.

[0078] A third aspect of the present invention provides a composite current collector, comprising a base film and a metal layer disposed on at least one side of the base film; wherein the metal layer is disposed on the side of the mixing transition layer away from the polymer matrix; the base film is the base film described in the first aspect or the base film prepared by the preparation method described in the second aspect.

[0079] The composite current collector provided by the present invention, by directly setting the metal layer on the base film side containing the gradient mixing transition layer, forms a metallurgical bond between the metal layer and the transition layer with continuous composition and no interface structure, which significantly improves the interlayer bonding force and inhibits peeling during cycling; the mixing transition layer intrinsically blocks the electrolyte penetration path, and synergistically enhances the long-term stability of the metal layer under battery conditions.

[0080] Furthermore, the material of the metal layer includes copper or aluminum.

[0081] Preferably, the thickness of the metal layer is 0.5μm to 2μm.

[0082] Typically, but not limitingly, the thickness of the metal layer can be, for example, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm, or any value in the range of 0.5 μm to 2 μm.

[0083] In a preferred embodiment of the present invention, the metal material used in the metal layer is consistent with the type of metal introduced in the mixed transition layer (e.g., both are aluminum and copper), thereby constructing an interface structure between the mixed transition layer and the metal layer with continuous composition, high lattice matching degree, and excellent thermodynamic compatibility. This facilitates the realization of atomic-scale metallurgical bonding and chemical bonding, significantly suppressing interfacial diffusion hindrance, elemental segregation, and interlayer delamination induced by thermal stress. At the same time, it can avoid electrochemical corrosion and interfacial reaction byproducts caused by heterogeneous metal contact, fundamentally improving the structural integrity and electrochemical stability of the composite current collector under long-term charge-discharge cycles and electrolyte immersion conditions.

[0084] A fourth aspect of the present invention provides an electrode sheet comprising the composite current collector described in the third aspect.

[0085] A fifth aspect of the present invention provides an electrochemical device including the aforementioned electrode sheet.

[0086] The electrode sheet constructed based on this current collector exhibits strong interfacial bonding, high adhesion of the active material coating, and uniform stress transfer between the current collector and the active layer during charging and discharging. Lithium batteries or all-solid / semi-solid electrochemical devices assembled using this electrode sheet demonstrate lower interfacial impedance, higher capacity retention, and better safety.

[0087] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0088] Example 1 This embodiment provides a base film, which includes a polymer matrix and a hybrid transition layer located on both sides of the polymer matrix.

[0089] The polymer matrix is ​​a 6μm thick biaxially oriented polyethylene terephthalate (PET) film; the thickness of the mixing transition layer is 300nm; and an aluminum layer with a thickness of 1.0μm is disposed on the outer surface of the mixing transition layer on both sides.

[0090] The method for preparing the base film includes the following steps: 1. Polymer matrix pretreatment: Commercial 6μm PET films were sequentially placed in anhydrous ethanol, acetone, and deionized water, and ultrasonically cleaned at 40kHz for 10 minutes each to remove surface organic contaminants and particles; then transferred to an 80℃ vacuum drying oven (vacuum degree ≤10). -2 Dry at a constant temperature for 30 minutes in a solution containing Pa to completely remove adsorbed water.

[0091] 2. Construction of the hybrid transition layer: 2.1. Fix the dried PET film onto the sample stage of the ion implantation equipment and evacuate to a background vacuum of 5×10⁻⁶. -4 Pa; Introduce high-purity argon gas, adjust the working pressure to 0.3 Pa, turn on the 13.56 MHz RF power supply (300 W power) to generate stable argon plasma, and perform plasma pre-sputtering on the PET surface for 5 min to remove residual hydrocarbon contaminants and activate the surface CH / CO bonds.

[0092] 2.2. Start the ECR ion source and extract Al. + Aluminum ion beam; pulse frequency of 500 Hz, pulse width of 50 μs; for high-energy injection, bias amplitude of -35 kV, injection energy of 35 keV, and dose of 7.5 × 10⁻⁶. 15 ions / cm 2 During medium-energy injection, the bias amplitude is -25kV, the injected energy is 25keV, and the dose is 1.5×10⁻⁶. 16 ions / cm 2 At low energy injection, the bias amplitude is -15kV, the injection energy is 15keV, and the dose is 3.5×10⁻⁶. 16ions / cm 2 The entire process was completed in an argon inert atmosphere. After injection, the mixture was naturally cooled to room temperature to obtain a 300 nm thick hybrid transition layer, thus obtaining a double-sided hybrid transition layer PET base film.

[0093] A composite current collector is also provided, comprising a base film and aluminum layers disposed on both sides of the base film, and is prepared as follows: Metal layer evaporation: The above-mentioned base film is transferred to a high-vacuum electron beam evaporation equipment (background vacuum less than 5×10). - 3 Using 99.999% pure aluminum as the target material, the electron beam power was controlled at 10kW, and the deposition rate was stabilized at 30nm / s. The single-sided evaporation time was precisely controlled at 32s to ensure that the aluminum layer thickness was 1.0μm. Double-sided evaporation was carried out sequentially, and a vacuum environment was maintained during the interval to avoid oxidation contamination, resulting in a composite current collector.

[0094] Example 2 This embodiment provides a base film and a composite current collector, which differ from Embodiment 1 in that: in step 2.2, the pulse frequency is 100Hz and the pulse width is 10μs; during high-energy injection, the bias amplitude is -30kV, the injection energy is 30keV, and the dose is 5×10⁻⁶. 15 ions / cm 2 During medium-energy injection, the bias amplitude is -20kV, the injected energy is 20keV, and the dose is 1×10⁻⁶. 16 ions / cm 2 At low energy injection, the bias amplitude is -10kV, the injection energy is 10keV, and the dose is 2×10⁻⁶. 16 ions / cm 2 The entire process was completed in an argon inert atmosphere. After injection, the mixture was allowed to cool naturally to room temperature to obtain a 100 nm thick hybrid transition layer, thus obtaining a double-sided hybrid transition layer PET substrate film. The remaining steps were the same as in Example 1 and will not be repeated here.

[0095] Example 3 This embodiment provides a base film and a composite current collector, which differ from Embodiment 1 in that: in step 2.2, the pulse frequency is 1000Hz and the pulse width is 100μs; during high-energy injection, the bias amplitude is -40kV, the injection energy is 40keV, and the dose is 1×10⁻⁶. 16 ions / cm 2 During medium-energy injection, the bias amplitude is -30kV, the injected energy is 30keV, and the dose is 2×10⁻⁶. 16 ions / cm 2 At low energy injection, the bias amplitude is -20kV, the injection energy is 20keV, and the dose is 5×10⁻⁶. 16 ions / cm 2The entire process was completed in an argon inert atmosphere. After injection, the mixture was allowed to cool naturally to room temperature to obtain a 500 nm thick hybrid transition layer, thus obtaining a double-sided hybrid transition layer PET substrate film. The remaining steps were the same as in Example 1 and will not be repeated here.

[0096] Example 4 This embodiment provides a base film and a composite current collector. The difference from Embodiment 1 is that in step 2.2, a metal vapor vacuum arc (MEVVA) ion source is activated to extract Al. + Al 2+ Al 3+ Three charge states of aluminum ion beams; bias voltage amplitude of -12kV, Al + The injection energy was 12 keV, and the injection dose was 3.5 × 10⁻⁶. 16 ions / cm 2 Al 2+ The injection energy was 24 keV, and the injection dose was 1.5 × 10⁻⁶. 16 ions / cm 2 Al 3+ The injection energy was 36 keV, and the injection dose was 7.5 × 10⁻⁶. 15 ions / cm 2 The entire process was completed in an inert argon atmosphere, and the film was naturally cooled to room temperature after injection to obtain a double-sided hybrid transition layer PET base film.

[0097] Example 5 This embodiment provides a base film and a composite current collector, which differs from Embodiment 1 in that: during energy injection, the bias amplitude is -8kV, the injected energy is 8keV, and the dose is 2×10⁻⁶. 16 ions / cm 2 The thickness of the mixed transition layer is 70 nm. The remaining steps are the same as in Example 1 and will not be repeated here.

[0098] Example 6 This embodiment provides a base film and a composite current collector, which differ from Embodiment 1 in that the polymer matrix is ​​a 3 μm thick biaxially oriented polypropylene (PP) film, and the evaporated aluminum layer has a thickness of 0.5 μm. The remaining steps are the same as in Embodiment 1, and will not be repeated here.

[0099] Example 7 This embodiment provides a base film and a composite current collector, which differ from Embodiment 1 in that the polymer matrix is ​​a 10 μm thick biaxially oriented polyimide (PI) film, and the evaporated aluminum layer has a thickness of 2 μm. The remaining steps are the same as in Embodiment 1, and will not be repeated here.

[0100] Example 8 This embodiment provides a base film and a composite current collector, which differs from Embodiment 1 in that: monovalent copper ions (Cu) are implanted. + The copper metal layer is formed on the prepared base film, and the remaining steps are the same as in Example 1, and will not be repeated here.

[0101] Comparative Example 1 This comparative example provides a base film and a composite current collector. The difference from Example 1 is that step 2 is omitted. The base film is a 6μm thick biaxially oriented polyethylene terephthalate (PET) film. Aluminum is directly vacuum-deposited on both sides of the base film. The remaining steps are the same as in Example 1 and will not be repeated here.

[0102] Test Example 1 The composite current collectors obtained in the examples and comparative examples were subjected to performance tests, including interfacial bonding strength tests and electrolyte resistance tests.

[0103] The interface bonding strength test was conducted using the tape peeling method: the sample was cut into strips 20mm wide and longer than 100mm. One side of the strip was attached to the SUS steel plate with double-sided PET tape. Then, commercially available standard 20mm wide tape (Nitto tape) was attached to the side of the strip to be tested (the length should be longer than the strip). A 2kg rubber roller was used to roll and press the strip back and forth three times. Finally, a 180° peel test (bonding force) was performed on the peel tester. The test conditions were 300mm / min.

[0104] Electrolyte resistance test: The sample was cut into 50mm×100mm pieces. The pieces were placed in a plastic test box in a glove box, and approximately 61g of electrolyte was poured into the test box to immerse the pieces. The sealed plastic test box was then placed in an 85℃ oven. After immersion, the sample was removed in a fume hood and rinsed with water and alcohol sequentially to remove any electrolyte residue. After the sample dried, the bonding strength was tested using the same method as above. The specific formulation of the electrolyte was: 1 mol / L LiPF6 (lithium hexafluorophosphate) dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), with a volume ratio of EC:DMC:EMC = 1:1:1.

[0105] The test data is recorded in Table 1.

[0106] Table 1

[0107] As can be seen from Table 1, the initial interfacial bonding strength of Examples 1-8 is significantly higher than that of Comparative Example 1. After soaking in electrolyte at 85°C for 12 hours, the bonding strength retention rate of each example is much better than that of Comparative Example 1. Comparative Example 1 not only has a lower initial bonding strength, but also shows a significant decrease in interfacial bonding strength after soaking.

[0108] The above comparison clearly demonstrates that the gradient hybrid transition layer constructed by ion implantation is key to performance improvement. It enhances the initial binding strength through molecular-scale interlocking and chemical bonding, and effectively blocks the capillary penetration path of the electrolyte with its continuously varying composition, thereby significantly inhibiting the erosion of the interface by HF and solvent molecules and significantly enhancing resistance to electrolyte aging. It is worth noting that while Examples 5 and 8 are still superior to the comparative examples, their binding strength retention rates are relatively low, suggesting that insufficient transition layer thickness or metal type / valence state matching may affect gradient stability. Example 7, however, performs best, confirming the decisive role of material thermal stability, gradient structure integrity, and synergistic optimization of process parameters in overall performance.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A base film, characterized in that, It includes a polymer matrix and a hybrid transition layer disposed on at least one surface of the polymer matrix; The materials of the hybrid transition layer include polymers and metals; In the hybrid transition layer, the content of the polymer decreases and the content of the metal increases along the thickness direction away from the polymer matrix.

2. The base film according to claim 1, characterized in that, In the hybrid transition layer, the metal content gradually increases from 0% to 100% from the inner surface in contact with the polymer matrix to the outer surface of the hybrid transition layer.

3. The base film according to claim 1 or 2, characterized in that, The thickness of the polymer matrix is ​​3μm~10μm; Preferably, the thickness of the hybrid transition layer is 100nm~500nm.

4. The base film according to claim 1 or 2, characterized in that, The polymer includes at least one of polyimide, polyethylene terephthalate, polypropylene, polyethylene, and polyetheretherketone; Preferably, the metal includes copper or aluminum.

5. A method for preparing the base film according to any one of claims 1 to 4, characterized in that, The pretreated polymer matrix is ​​fixed in an ion implantation device, and after vacuuming and plasma excitation, ion implantation is performed to obtain the base film.

6. The preparation method according to claim 5, characterized in that, The ion implantation includes multi-energy state metal ion implantation or multi-charge state metal ion implantation; In the ion implantation, the pulse frequency is 100Hz~1000Hz and the pulse width is 10μs~100μs; Preferably, in the multi-energy-state metal ion implantation, the bias voltage amplitude is -10 kV to -40 kV, and the implantation energy is 10 keV to 40 keV; Preferably, in the multi-charged metal ion implantation, at least two types of metal ions, including monovalent, divalent, and trivalent metal ions, are implanted simultaneously.

7. The preparation method according to claim 6, characterized in that, The multi-energy state metal ion implantation includes sequential high-energy implantation, medium-energy implantation, and low-energy implantation. Preferably, during the high-energy injection process, the bias voltage amplitude is -30 kV to -40 kV, the injection energy is 30 keV to 40 keV, and the dose is 5 × 10⁻⁶ kV. 15 ions / cm 2 ~1×10 16 ions / cm 2 ; Preferably, during the medium-energy injection process, the bias voltage amplitude is -20 kV to -30 kV, the injected energy is 20 keV to 30 keV, and the dose is 1×10⁻⁶. 16 ions / cm 2 ~2×10 16 ions / cm 2 ; Preferably, during the low-energy injection process, the bias voltage amplitude is -10 kV to -20 kV, the injection energy is 10 keV to 20 keV, and the dose is 2 × 10⁻⁶ kV. 16 ions / cm 2 ~5×10 16 ions / cm 2 .

8. The preparation method according to any one of claims 5 to 7, characterized in that, The plasma excitation is performed in an inert atmosphere; Preferably, the gas used in the inert atmosphere includes argon; Preferably, during the plasma excitation process, the working gas pressure is 0.1 Pa to 0.5 Pa, and the power of the radio frequency power supply is 100 W to 500 W, thereby generating argon plasma; Preferably, after the vacuuming process, the background vacuum level is ≤5×10⁻⁶. -4 Pa; Preferably, the pretreatment includes cleaning and drying the polymer matrix.

9. A composite current collector, characterized in that, It includes a base film and a metal layer disposed on at least one side of the base film; The metal layer is disposed on the side of the hybrid transition layer away from the polymer matrix; The base film is the base film according to any one of claims 1 to 4 or the base film prepared by the preparation method according to any one of claims 5 to 8.

10. The composite current collector according to claim 9, characterized in that, The metal layer is made of copper or aluminum; Preferably, the thickness of the metal layer is 0.5μm to 2μm.

11. An electrode sheet, characterized in that, Includes the composite current collector as described in claim 9 or 10.

12. An electrochemical device, characterized in that, Includes the electrode sheet as described in claim 11.

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