Composite current collector, method for preparing the same, electrode sheet, and battery

Abstract

A composite current collector, its preparation method, electrode sheet, and battery are disclosed. The preparation method of the composite current collector includes: preparing a melt comprising a first molten layer and a second molten layer disposed opposite to each other, both comprising the same main polymer material and auxiliary polymer material; cooling the melt, wherein the first molten layer is cooled by an air knife, and the second molten layer is cooled by a contact chilling surface; stretching the cooled melt to form a first stretched layer and a second stretched layer, thus preparing a stretched body; and sequentially subjecting the second stretched layer and the first stretched layer of the stretched body to magnetron sputtering to deposit conductive material. Utilizing the asymmetric thermal damage during magnetron sputtering, the height of the sparse and tall roughened rings in the first stretched layer decreases under greater thermal damage, while the height of the dense and short roughened rings in the second stretched layer decreases slightly under less thermal damage, promoting a more uniform morphology of the roughened rings on both sides, thereby improving the uniformity of the bonding force between the conductive layers on both sides of the composite current collector.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to a composite current collector and its preparation method, electrode sheets, and battery. Background Technology

[0002] Composite current collectors are a key component of high-performance batteries, typically consisting of a polymer base film and a conductive layer formed on its surface. When depositing conductive materials on the polymer base film surface, the bonding strength between the conductive layer and the base film directly affects the battery's cycle life and safety. In related technologies, forming microscopic anchoring structures (such as roughening rings) on the polymer base film surface enhances the physical bonding between the conductive layer and the base film. However, during the base film preparation process, due to the asymmetry of cooling methods, the anchoring structures on both sides of the base film often exhibit different morphological characteristics: one side tends to form a denser but lower-height anchoring structure, while the other side tends to form a sparser but higher-height anchoring structure. This asymmetric anchoring structure leads to a significant difference in the bonding strength between the conductive layer and the base film after subsequent conductive layer deposition, thus affecting the overall performance consistency of the composite current collector. Furthermore, when using physical vapor deposition (such as magnetron sputtering) to deposit conductive materials on the base film surface, the thermal effects generated during deposition can cause varying degrees of damage to the anchoring structures on the base film surface. Due to the different thermal damage experienced on both sides of the base film during the deposition process, the morphology of the anchoring structures on both sides undergoes asymmetrical changes, further exacerbating the difference in bonding strength between the two sides. This non-uniformity in bifacial performance ultimately leads to uneven stress distribution in battery electrodes prepared using this composite current collector during charge and discharge, causing problems such as local delamination and inconsistent cycle expansion, severely shortening the battery's cycle life and reducing the consistency of the battery pack. Therefore, how to obtain a composite current collector with uniform bifacial performance is a technical problem that urgently needs to be solved in the current battery technology field. Summary of the Invention

[0003] In view of this, this application provides a composite current collector and its preparation method, an electrode sheet, and a battery to solve the above-mentioned technical problems.

[0004] To achieve the above objectives, in a first aspect, this application provides a method for preparing a composite current collector, comprising the following steps: preparing a melt, the melt comprising a first molten layer and a second molten layer disposed opposite to each other, the first molten layer and the second molten layer comprising the same main polymer material and the same auxiliary polymer material; cooling the melt, wherein the first molten layer is cooled by an air knife and the second molten layer is cooled by contact cooling surface; stretching the cooled melt, such that the cooled first molten layer forms a first stretched layer and the cooled second molten layer forms a second stretched layer, thereby preparing a stretched body; sequentially subjecting the second stretched layer and the first stretched layer of the stretched body to magnetron sputtering to deposit conductive material on the surfaces of the first stretched layer and the second stretched layer, thereby preparing a composite current collector.

[0005] Based on the first aspect, in some embodiments, the melt further includes a third melt layer located between the first melt layer and the second melt layer, the material of the third melt layer including the main polymer material.

[0006] Based on the first aspect, in some embodiments, the main polymeric material includes polypropylene, and the auxiliary polymeric material includes at least one of polyethylene, polyvinyl chloride, and polystyrene.

[0007] Based on the first aspect, in some embodiments, the main polymeric material includes polyphenylene sulfide, and the auxiliary polymeric material includes at least one of polyetherimide and nylon 66.

[0008] Based on the first aspect, in some embodiments, the following are defined: the temperature of the melt before cooling is T0 ℃, the temperature of the air knife is T1 ℃, the temperature of the chilled surface is T2 ℃, and the softening temperature of the main polymer material is T a ℃, the softening temperature of the auxiliary polymer material is T b ℃, the thickness percentage of the first molten layer in the melt is Th1%, the thickness percentage of the second molten layer in the melt is Th2%, the mass percentage of the auxiliary polymer material in the first molten layer is Wt1%, the mass percentage of the auxiliary polymer material in the second molten layer is Wt2%, k is a constant coefficient and k is from 2 to 20; satisfying the following equation I:

[0009] Based on the first aspect, in some embodiments, the melt further includes a third melt layer located between the first melt layer and the second melt layer, the material of the third melt layer including a main polymer material, and the main polymer material including polypropylene.

[0010] Based on the first aspect, in some implementations, Wt1 is 2 to 20.

[0011] Based on the first aspect, in some implementations, Wt2 is 2 to 20.

[0012] Based on the first aspect, in some implementations, Th1 is 5 to 30.

[0013] Based on the first aspect, in some implementations, Th2 is 5 to 30.

[0014] Based on the first aspect, in some implementations, T0 is 220 to 260.

[0015] Based on the first aspect, in some implementations, T1 is 80 to 120.

[0016] Based on the first aspect, in some implementations, T2 is 80 to 120.

[0017] Based on the first aspect, in some implementations, k is 8.

[0018] Based on the first aspect, in some embodiments, stretching includes longitudinal stretching and transverse stretching.

[0019] Based on the first aspect, in some embodiments, longitudinal stretching and transverse stretching are performed sequentially.

[0020] Based on the first aspect, in some embodiments, the stretching ratio of the longitudinal stretch is 4 to 6.

[0021] Based on the first aspect, in some embodiments, the stretching ratio of the transverse stretch is 8 to 10.

[0022] Based on the first aspect, in some embodiments, both longitudinal stretching and transverse stretching are carried out in stages, including a preheating stage, a stretching stage, and a shaping stage.

[0023] Based on the first aspect, in some embodiments, when performing longitudinal stretching, the preheating temperature is 100°C to 160°C, the stretching temperature is 150°C to 170°C, and the setting temperature is 140°C to 145°C.

[0024] Based on the first aspect, in some embodiments, when performing transverse stretching, the preheating temperature is 150°C to 180°C, the stretching temperature is 160°C to 170°C, and the setting temperature is 165°C to 170°C.

[0025] Based on the first aspect, in some embodiments, the preparation method further includes: subjecting the surfaces of the first stretching layer and the second stretching layer in the stretched body to corona treatment before magnetron sputtering.

[0026] Based on the first aspect, in some embodiments, the preparation method further includes: performing electroplating on the conductive material deposited on the surfaces of the first stretching layer and the second stretching layer after magnetron sputtering.

[0027] Secondly, this application provides a composite current collector, which is prepared according to the above-described preparation method.

[0028] Thirdly, this application provides an electrode sheet comprising the aforementioned composite current collector.

[0029] Fourthly, this application provides a battery comprising the aforementioned electrode plates.

[0030] In this application, the melt comprises a first molten layer and a second molten layer made of the same material. This helps ensure that the material properties of the two stretched layers are essentially the same after stretching, providing a material basis for obtaining a uniform anchoring structure. During the cooling step, the first molten layer is cooled using an air knife, while the second molten layer is cooled using a contact quench surface cooling method. Due to the difference in cooling rates between these two different cooling methods, a sparse but high-height coarsening ring tends to form on the first molten layer side, while a dense but low-height coarsening ring tends to form on the second molten layer side. This results in similar differences in the anchoring structures with different morphologies obtained after stretching. To address this, the asymmetric thermal damage distribution during magnetron sputtering is utilized. When sputtering the stretched body, the second stretched layer is sputtered first, followed by the first stretched layer. During the initial sputtering, the second stretched layer, as the direct deposition surface, bears the thermal damage, while the first stretched layer, due to its attachment to the cooling roller, is also affected by heat transfer. When the first stretched layer is sputtered subsequently, the second stretched layer, already coated with conductive material, is protected by its coating, reducing subsequent thermal damage. This results in the first stretched layer side experiencing relatively more thermal damage, and the second stretched layer side experiencing relatively less. Consequently, the height of the originally tall but sparse roughening ring of the first stretched layer decreases under significant thermal damage, while the height of the originally short but dense roughening ring of the second stretched layer remains constant or slightly decreases under less thermal damage. This promotes a more uniform morphology of the roughening rings on both sides, thereby improving the uniformity of the bonding force between the two conductive layers of the composite current collector. Attached Figure Description

[0031] Figure 1 The results are the test results of the roughening ring morphology of the surface of the first tensile layer in Embodiment 1 of this application.

[0032] Figure 2 The results are the test results of the roughening ring morphology of the surface of the second tensile layer in Embodiment 1 of this application. Detailed Implementation

[0033] To facilitate understanding of the technical solutions of this application, a more comprehensive description of the technical solutions of this application will be provided below with reference to the accompanying drawings, which illustrate preferred embodiments of the technical solutions of this application. However, the technical solutions of this application can be implemented in many different forms and are not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and comprehensive understanding of the disclosure of the technical solutions of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill 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 be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] One embodiment of this application provides a method for preparing a composite current collector, comprising the following steps:

[0036] Step 1: Prepare a melt, which includes a first melt layer and a second melt layer arranged opposite each other. The materials of the first melt layer and the second melt layer include the same main polymer material and the same auxiliary polymer material.

[0037] In the above steps, the melt contains a first melt layer and a second melt layer of the same material, which helps to ensure that the material properties of the two stretching layers are basically the same after stretching, providing a material basis for obtaining a uniform anchoring structure in the future.

[0038] In some embodiments, the melt further includes a third molten layer located between the first and second molten layers, the material of which comprises the host polymer material. Introducing the third molten layer as a core layer helps to reduce the overall amount of auxiliary polymer material used while maintaining the functions of the first and second molten layers (surface layers), and provides good mechanical support and dimensional stability using the core layer composed of the host polymer material. Since the core layer mainly comprises the host polymer material, its crystallization behavior and thermal shrinkage characteristics differ from those of the surface layer, which may facilitate further adjustment of the roughening ring morphology of the surface layer during stretching through the constraint effect of the core layer. Simultaneously, the presence of the core layer also helps to reduce the mutual influence between the two surface layers during cooling and stretching, facilitating more independent control of the initial morphology of the roughening rings on both sides, thereby better matching the thermal damage distribution strategy of specific sequence magnetron sputtering and achieving a balance between the control of the double-sided anchoring structure and the overall mechanical properties of the film.

[0039] In some embodiments, the host polymer material comprises polypropylene, and the auxiliary polymer material comprises at least one of polyethylene, polyvinyl chloride, and polystyrene. In other embodiments, the host polymer material comprises polyphenylene sulfide, and the auxiliary polymer material comprises at least one of polyetherimide and nylon 66. Further, using polypropylene as the host polymer material and combining it with polyethylene, polyvinyl chloride, or polystyrene as the auxiliary polymer material, or using polyphenylene sulfide as the host polymer material and combining it with polyetherimide or nylon 66 as the auxiliary polymer material, helps to utilize the difference in softening temperatures between the host and auxiliary materials to regulate crystallization behavior during cooling and stretching, ensuring that the size and distribution of the coarsening ring respond as expected to the cooling rate and subsequent thermal damage, thereby facilitating the realization of the quantitative matching relationship described in Formula I.

[0040] Step 2: Cool the melt, wherein the first molten layer is cooled by an air knife and the second molten layer is cooled by contact quenching surface.

[0041] In the above steps, the first molten layer is cooled by air knife and the second molten layer is cooled by contact quenching surface cooling. Due to the difference in cooling rate between the two different cooling methods, a sparse but high-height coarsening ring is easily formed on the first molten layer side and a dense but low-height coarsening ring is easily formed on the second molten layer side. Thus, the anchoring structure with different morphologies on both sides obtained after stretching also has similar differences.

[0042] Step 3: Stretch the cooled melt to form a first stretched layer from the first cooled molten layer and a second stretched layer from the second cooled molten layer, thus preparing a stretched body.

[0043] In some embodiments, stretching includes longitudinal stretching and transverse stretching. In some embodiments, longitudinal stretching and transverse stretching are performed sequentially. Furthermore, employing a sequential longitudinal and transverse stretching approach facilitates the formation of a biaxially oriented structure in the film, allowing the roughening rings to develop in two directions during stretching, thereby obtaining an anchoring structure with adjustable dimensions.

[0044] In some embodiments, the longitudinal stretching stretch ratio is 4 to 6. For example, the longitudinal stretching stretch ratio can be 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, or any value within the range of any two of the above values. In some embodiments, the transverse stretching stretch ratio is 8 to 10. For example, the transverse stretching stretch ratio can be 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8, 10, or any value within the range of any two of the above values. Furthermore, controlling the stretching ratios of the longitudinal and transverse stretching within the above ranges helps to develop the diameter and height of the roughened ring to the desired range during the stretching process, promotes the full development of the roughened ring morphology, and reduces the risk of over-deformation, thereby providing a suitable initial morphological basis for the control of the roughened ring height by thermal damage in the subsequent magnetron sputtering step.

[0045] In some embodiments, longitudinal stretching is performed in stages, including a preheating stage, a stretching stage, and a setting stage. In some embodiments, during longitudinal stretching, the preheating temperature is 100°C to 160°C, the stretching temperature is 150°C to 170°C, and the setting temperature is 140°C to 145°C. For example, during longitudinal stretching, the preheating temperature can be 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, or any value within the range of any two of the above values; the stretching temperature can be 150 ℃, 152 ℃, 154 ℃, 156 ℃, 158 ℃, 160 ℃, 162 ℃, 164 ℃, 166 ℃, 168 ℃, 170 ℃, or any value within the range of any two of the above values; and the setting temperature can be 140 ℃, 141 ℃, 142 ℃, 143 ℃, 144 ℃, 145 ℃, or any value within the range of any two of the above values. Furthermore, for example, when the main polymer material is polypropylene, preheating the film to the above-mentioned temperature range before longitudinal stretching helps to promote the softening of the cooled melt and reduce the stretching resistance; then longitudinal stretching is performed within the above-mentioned temperature range to orient the polymer chains along the stretching direction, while causing the roughening ring to undergo plastic deformation; then shaping is performed within the above-mentioned temperature range to help stabilize the orientation structure and reduce internal stress, thereby fixing the morphology of the roughening ring.

[0046] In some embodiments, the transverse stretching is performed in stages, including a preheating stage, a stretching stage, and a setting stage. In some embodiments, when performing transverse stretching, the preheating temperature is 150°C to 180°C, the stretching temperature is 160°C to 170°C, and the setting temperature is 165°C to 170°C. For example, when performing transverse stretching, the preheating temperature can be 150 ℃, 153 ℃, 156 ℃, 159 ℃, 162 ℃, 165 ℃, 168 ℃, 171 ℃, 174 ℃, 177 ℃, 180 ℃, or any value within the range of any two of the above values; the stretching temperature can be 160 ℃, 161 ℃, 162 ℃, 163 ℃, 164 ℃, 165 ℃, 166 ℃, 167 ℃, 168 ℃, 169 ℃, 170 ℃, or any value within the range of any two of the above values; and the setting temperature can be 165 ℃, 166 ℃, 167 ℃, 168 ℃, 169 ℃, 170 ℃, or any value within the range of any two of the above values. Furthermore, during lateral stretching, preheating to the aforementioned temperature range helps to fully soften the film, providing a uniform temperature field for lateral stretching. Then, lateral stretching within this temperature range forms a uniform lateral orientation and helps to control the diameter of the roughening ring. Finally, sizing within the aforementioned temperature range helps maintain dimensional stability after stretching, while keeping the height and density of the roughening ring within the range required for subsequent magnetron sputtering. By controlling the temperature at each stage within the aforementioned range, it is beneficial to match the initial morphology of the roughening ring with the differences formed during the cooling steps, thereby synergizing with the thermal damage effect of sequential magnetron sputtering to promote a more consistent morphology on both sides.

[0047] Step 4: The second and first stretched layers of the stretched body are sequentially subjected to magnetron sputtering to deposit conductive materials on the surfaces of the first and second stretched layers, thereby preparing a composite current collector.

[0048] In the above steps, utilizing the asymmetric thermal damage distribution during magnetron sputtering, the second stretched layer is sputtered first, followed by the first stretched layer, during the initial sputtering process. In the first sputtering, the second stretched layer, as the direct deposition surface, bears the thermal damage, while the first stretched layer, due to its attachment to the cooling roller, is also affected by heat transfer. Subsequently, when the first stretched layer is sputtered, the second stretched layer, already coated with conductive material, is protected by the coating, reducing subsequent thermal damage. This results in the first stretched layer side experiencing relatively more thermal damage, and the second stretched layer side experiencing relatively less. Consequently, the height of the originally high but sparse roughening ring of the first stretched layer decreases under significant thermal damage, while the height of the originally low but dense roughening ring of the second stretched layer remains constant or slightly decreases under less thermal damage. This promotes a more uniform morphology of the roughening rings on both sides, thereby improving the uniformity of the bonding force between the two conductive layers of the composite current collector.

[0049] In some embodiments, before magnetron sputtering, the surfaces of the first and second stretched layers in the stretched body are subjected to corona treatment. Furthermore, the corona treatment performed during magnetron sputtering helps to increase the polarity of the stretched layer surface and increase its surface energy, thereby enhancing the initial adhesion between the conductive material subsequently deposited by magnetron sputtering and the base film, which is beneficial for further improving the adhesion of the composite current collector double-sided conductive layer.

[0050] In some embodiments, after magnetron sputtering, the conductive material deposited on the surfaces of the first and second stretching layers is subjected to electroplating. Furthermore, the electroplating process after magnetron sputtering helps to further thicken the conductive layer on the deposited conductive seed layer, helps to reduce the resistivity of the conductive layer and meet the high current transmission requirements of the battery electrodes. Simultaneously, the electroplating process has a lower thermal effect, which helps to maintain the roughened ring morphology after magnetron sputtering thermal damage control and avoids additional thermal damage that could disrupt the consistency of the double-sided morphology.

[0051] Based on the aforementioned preparation method, this application further discovered that there is a quantifiable correlation between the morphology (including height and diameter) of the roughened rings on both sides of the stretched body and specific process and material parameters. Furthermore, the height and diameter of the roughened rings on both sides of the stretched body satisfy specific proportional relationships before and after magnetron sputtering thermal damage, and these proportional coefficients are related to the number of thermal damages the roughened rings endure. Based on this, this application derives the matching process parameters required to achieve a consistent theoretical morphology of the final double-sided roughened rings by constructing a relational formula encompassing the aforementioned variables, thereby providing a quantitative basis for optimizing process conditions.

[0052] In some embodiments, the following are defined: the temperature of the melt before cooling is T0 ℃, the temperature of the air knife is T1 ℃, the temperature of the chilled surface is T2 ℃, and the softening temperature of the main polymer material is T a ℃, the softening temperature of the auxiliary polymer material is T b ℃, the thickness percentage of the first molten layer in the melt is Th1%, the thickness percentage of the second molten layer in the melt is Th2%, the mass percentage of the auxiliary polymer material in the first molten layer is Wt1%, the mass percentage of the auxiliary polymer material in the second molten layer is Wt2%, k is a constant coefficient and k is from 2 to 20; satisfying the following equation I:

[0053]

[0054] This application finds that by limiting the melt temperature, air knife temperature, quench surface temperature, softening temperature of the main body and auxiliary materials, the thickness ratio of each layer, and the mass ratio of auxiliary materials to satisfy Equation I above, it is helpful to establish a quantitative matching relationship between process parameters and material parameters. This allows the height and diameter of the roughened rings on both sides to undergo relative deformation after cooling, stretching, and sequential magnetron sputtering, ultimately achieving a more consistent morphology of the double-sided anchored structure. This, in turn, helps to improve the uniformity of the bonding force of the double-sided conductive layers of the composite current collector.

[0055] It should be noted that, when the main polymer material is polypropylene, this application first constructs the relationship between the height and diameter of the roughening rings on both sides of the stretched body and specific process parameters and material parameters as follows:

[0056] Formula II:

[0057]

[0058] Formula III:

[0059]

[0060] Formula IV:

[0061]

[0062] Formula V:

[0063]

[0064] In equations II to V above, h1 represents the average height of the roughened rings on the surface of the first stretched layer (in μm), d1 represents the average diameter of the roughened rings on the surface of the first stretched layer (in μm), T0 represents the temperature of the melt (in °C), T1 represents the temperature of the air knife (in °C), T2 represents the temperature of the chilled surface (in °C), Th represents the total thickness of the stretched body (in μm), Th0 represents the total thickness of the melt (in μm), Th1% represents the thickness percentage of the first molten layer in the melt, Th2% represents the thickness percentage of the second molten layer in the melt, Wt1% represents the mass percentage of the auxiliary polymer material in the first molten layer, Wt2% represents the mass percentage of the auxiliary polymer material in the second molten layer, and T a The softening temperature (in °C) of the main polymer material and the softening temperature T of the auxiliary polymer material are indicated. b Indicated (unit: °C).

[0065] In Equations II and III above, when the air knife temperature T1 increases, the cooling effect of the melt deteriorates, the crystallization rate of the main polymer material decreases, thus reducing the formation of fine crystalline rings, ultimately leading to an increase in the height and diameter of the coarsening ring. Therefore, T1 has a positive proportional relationship with both h1 and d1. When the difference between the melt temperature T0 and the air knife temperature T1 increases, the cooling effect of the melt is relatively enhanced, the crystallization rate of the main polymer material increases, thus promoting the formation of finer crystalline rings, ultimately leading to a decrease in the height and diameter of the coarsening ring. Therefore, (T0-T1) has an inverse proportional relationship with both h1 and d1. The addition of auxiliary materials also plays a role in inhibiting the crystal growth of the main material. Therefore, when the mass proportion of auxiliary polymer materials in the melt layer increases, the final height and diameter of the coarsening ring decrease. Thus, Th1% and Wt1% have an inverse proportional relationship with both h1 and d1. Based on the same principle, it is inferred that the other parameters have a positive and inverse proportional relationship with h1 and d1. Meanwhile, the power values ​​of the temperature coefficients in Equations II and III are chosen to satisfy fundamental principles of quantum statistics and solid-state physics, conforming to the Debye model and the Bloch-Grundsen model. The power value of the total melt thickness Th0 is chosen to conform to the thin-walled cylinder model in heat conduction. Furthermore, the constant terms in Equations II and III are constant coefficients characteristic of the substrate, related to the choice of the host polymer material. Similarly, Equations IV and V can be derived according to the above logical relationships.

[0066] This application also determines the average height (h1, h2) and average diameter (d1, d2) of the roughened rings on both sides of the body before magnetron sputtering, and the deformation coefficients of the height and diameter of the roughened rings due to magnetron sputtering thermal damage. Therefore, the theoretical expressions for the final double-sided roughened rings are constructed as follows:

[0067] Formula VI:

[0068]

[0069] Formula VII:

[0070]

[0071] Formula VIII:

[0072]

[0073] Formula IX:

[0074]

[0075] In equations VI to IX above, H1 represents the average height (in μm) of the roughened ring after deformation of the first tensile layer surface, H2 represents the average height (in μm) of the roughened ring after deformation of the second tensile layer surface, D1 represents the average diameter (in μm) of the roughened ring after deformation of the first tensile layer surface, and D2 represents the average diameter (in μm) of the roughened ring after deformation of the second tensile layer surface. R h1 R represents the loss deformation coefficient representing the height of the roughened ring of the first tensile layer. d1 R represents the loss deformation coefficient representing the diameter of the roughened ring in the first stretching layer. h2 R represents the loss deformation coefficient representing the height of the roughened ring of the second tensile layer. d1 This represents the loss deformation coefficient of the roughening ring diameter of the second stretching layer.

[0076] In equations VI to IX above, the deflection coefficient is obtained from the measured data after equivalent heat baking.

[0077] Based on this, since the physical anchoring force of the roughened ring on the base film to the copper layer mainly comes from the height of the roughened ring, and the raised roughened ring provides an attachment anchor point for the metal plating layer, in order to control the final double-sided anchoring structure morphology to be more consistent, thereby improving the uniformity of the bonding force of the double-sided conductive layer of the composite current collector, this application introduces the following conditional constraint:

[0078] Formula X:

[0079]

[0080] Then, by relating Equations II, IV, VI, and VIII and performing mathematical transformations, Equation I is obtained. It is understandable that in the preparation method of this application, when the specified parameters further satisfy Equation I, a composite current collector with a theoretically consistent final double-sided roughening ring can be constructed. This is beneficial for further promoting the uniformity of the roughening ring morphology on both sides of the obtained composite current collector, thereby improving the uniformity of the bonding force of the double-sided conductive layers of the composite current collector.

[0081] Understandably, to construct a composite current collector with consistent performance across both roughened rings, priority should be given to ensuring the consistent height of the roughened rings. Therefore, provided that the internal relationships of the process parameters conform to Equation X, the diameter of the roughened rings only needs to satisfy D1 / D2 being 0.5 to 2.

[0082] In some embodiments, T0 is between 220 and 260. For example, T0 can be 220, 224, 228, 232, 236, 240, 244, 248, 252, 256, 260, or any value within the range of any two of the above values. Furthermore, controlling the melt temperature T0 within the above range helps to obtain suitable melt flowability, avoids uneven melting at lower temperatures or material degradation at higher temperatures, thereby providing a stable melt state for the formation of the desired coarsening ring difference in subsequent cooling steps.

[0083] In some embodiments, T1 is 80 to 120. For example, T1 can be 80, 84, 88, 92, 96, 100, 104, 108, 112, 116, 120, or any value within the range of any two of the above values. In some embodiments, T2 is 80 to 120. For example, T2 can be 80, 84, 88, 92, 96, 100, 104, 108, 112, 116, 120, or any value within the range of any two of the above values. Furthermore, controlling the air knife temperature T1 and the quench surface temperature T2 within the above ranges is beneficial for creating an appropriate cooling rate difference between the air knife surface and the quench surface, keeping the initial height and density difference of the roughened rings on both sides within a controllable range, thereby achieving a more consistent morphology in conjunction with the thermal damage distribution of sequential magnetron sputtering.

[0084] In some embodiments, Wt1 is 2 to 20. For example, Wt1 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any value within the range of any two of the above values. In some embodiments, Wt2 is 2 to 20. For example, Wt2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any value within the range of any two of the above values. Furthermore, controlling the mass ratios of the auxiliary polymer materials Wt1 and Wt2 within the above ranges is beneficial for introducing an appropriate amount of auxiliary polymer material into the surface layer to regulate the rheological properties and crystallization kinetics of the surface layer. It also helps to reduce the risk of decreased material compatibility or impact on the mechanical properties of the film when there is excessive doping, thereby providing a material basis for the synergistic regulation of the morphology of the roughening rings on both sides.

[0085] In some embodiments, Th1 is 5 to 30. For example, the thickness percentage of the first molten layer Th1 can be 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, or any value within the range of any two of the above values. In some embodiments, Th2 is 5 to 30. For example, the thickness percentage of the second molten layer Th2 can be 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, or any value within the range of any two of the above values. Furthermore, when a third molten layer is provided, controlling the thickness percentages of the first and second molten layers in the total thickness of the melt within the above range helps ensure that the surface layer has sufficient thickness during cooling and stretching to form an effective roughening ring, reducing the risk that the roughening ring is difficult to form or easily damaged excessively by heat when the surface layer is thin, and maintaining sufficient thickness of the core layer formed by the third molten layer, thereby improving the overall mechanical properties of the film. Adjusting the surface thickness ratio within the above range also helps to optimize the morphological consistency of the double-sided anchoring structure in conjunction with the parameters in Equation I. For example, a thicker surface layer can accommodate a larger difference in the height of the roughening rings, while a thinner surface layer is more sensitive to thermal damage. Therefore, by selecting an appropriate thickness ratio, it is beneficial to ensure that the roughening rings on both sides reach the required height ratio range after sequential magnetron sputtering.

[0086] Secondly, this application provides a composite current collector, which is prepared according to the above-described preparation method.

[0087] In this application, during the preparation of the composite current collector, asymmetric cooling using an air knife and a chiller roller during the cooling stage creates a difference in the initial roughening ring morphology on both sides (one side is tall and sparse, the other side is short and dense). Combined with sequential magnetron sputtering of the second stretching layer followed by the first stretching layer during the sputtering stage to achieve asymmetric thermal damage distribution (the side with the first stretching layer suffers more thermal damage, and the side with the second stretching layer suffers less thermal damage), the resulting composite current collector exhibits a more uniform morphology on both sides of the polymer base film after thermal damage. The side with the higher initial roughening ring experiences a decrease in height due to more thermal damage, while the side with the lower initial height maintains its height or slightly decreases due to less thermal damage. This results in a higher uniformity of the bonding force between the conductive layers and the base film. When this composite current collector is subsequently used in electrode sheets, it helps reduce the risk of local delamination caused by differences in bonding force on both sides. Furthermore, due to the mechanical support of the core layer (when present), the overall mechanical properties of the film are maintained.

[0088] Thirdly, this application provides an electrode sheet comprising the aforementioned composite current collector.

[0089] In this application, due to the uniform bonding force of the conductive layers on both sides of the composite current collector, the stress distribution at the interface on both sides is more balanced during the coating of active material and subsequent rolling and stacking processes when using this composite current collector to prepare the electrode sheet. When the active material slurry is coated on both sides of the composite current collector, the uniform bonding force helps to form a stable interface between the active material layer and the conductive layer, reducing the shedding of active material due to insufficient local bonding force. In the rolling process, the uniform double-sided bonding force helps to maintain consistent compaction density on both sides of the electrode sheet, avoiding wrinkles or cracks caused by weaker bonding force on one side. In the stacking or winding process, the comparable stability of the interfaces on both sides helps to reduce the expansion difference of the electrode sheet caused by uneven interface bonding force during charge and discharge cycles, which helps to extend the service life of the electrode sheet.

[0090] Fourthly, this application provides a battery comprising the aforementioned electrode plates.

[0091] In this application, the use of a composite current collector with uniform performance on both sides of the electrode sheet helps improve the interfacial stability between the positive and negative electrodes and the current collector during multiple charge-discharge cycles. During charge and discharge, the insertion and extraction of lithium ions between the positive and negative electrodes causes volume changes in the electrode materials. If the bonding force of the current collector is uneven on both sides, the volume change will cause local stress concentration on the side with weaker bonding force, leading to interface cracking or delamination of the active material layer, thereby increasing the interfacial resistance and accelerating capacity decay. Batteries using the electrode sheet described in this application have a more uniform bonding force on both sides of the current collector, which helps to disperse the volume change stress during cycling, reducing capacity decay caused by local delamination or increased interfacial resistance, and thus improving the cycle life and battery pack consistency. Furthermore, since the mechanical properties of the composite current collector itself are guaranteed by the core layer (when present), the battery is less prone to current collector breakage during cycling, further improving battery reliability.

[0092] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0093] Example 1:

[0094] A composite current collector, the preparation method of which is as follows:

[0095] Phase 1: Base Film Preparation

[0096] (1) Particle melt co-extrusion: A two-layer co-extrusion process is adopted, with two extruders. The first extruder is used for the first melt layer (upper surface layer), and the second extruder is used for the second melt layer (lower surface layer); the materials for both the first and second melt layers are polypropylene (PP), the main polymer material, with a softening temperature of T. a=150 ℃) and auxiliary polymer material polyethylene (PE, softening temperature T b =120 ℃), where the mass percentage of auxiliary polymer materials is Wt1%=9% and Wt2%=5%; the extruder barrel temperature is set to 250 ℃, and the die head pressure is controlled at 20 MPa. The proportion of the first melt layer and the second melt layer in the total thickness is controlled to be 50% by the flow rate of the split channel.

[0097] (2) Cooling the casting sheet: The multi-layer molten sheet (molten body) is extruded from the composite die head. The composite die head is set to a temperature of T0 = 250 ℃ and a pressure of 15 MPa to cast the sheet. The total thickness of the molten body is Th0 = 200 μm. Then, the molten sheet is tightly bonded to the surface of the chilling roller for cooling by a high-pressure airflow (air knife and edge blowing nozzle). Specifically, the first molten layer is cooled by air knife, and the gas temperature of the air knife and edge blowing nozzle is T1 = 100 ℃. The second molten layer is cooled by contact chilling surface, and the surface temperature of the chilling roller is T2 = 105 ℃. The air knife pressure is set to 14 MPa, and the edge blowing nozzle pressure is set to 0.2 MPa.

[0098] (3) Biaxial stretching: The cooled cast sheet was subjected to longitudinal and transverse stretching sequentially, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 9 times. The longitudinal stretching was carried out in stages: preheating temperature 130 ℃, stretching temperature 160 ℃, and setting temperature 142 ℃; the transverse stretching was carried out in stages: preheating temperature 165 ℃, stretching temperature 165 ℃, and setting temperature 168 ℃. A film with a total thickness Th=4.5 μm was obtained after stretching, and the stretched body was prepared.

[0099] Phase Two: Preparation of Composite Current Collectors

[0100] (1) Corona treatment: The surfaces of the first and second stretching layers of the stretch body are subjected to corona treatment with a power of 3 kW and a speed of 10 m / min.

[0101] (2) Magnetron sputtering: A roll-to-roll double-sided magnetron sputtering device was used. First, a copper seed layer was deposited by magnetron sputtering on the second stretched layer (corresponding to the quenching surface during casting cooling), while the first stretched layer was attached to the cooling main roller. Sputtering parameters: working vacuum degree 0.3 Pa, argon flow rate 150 sccm, target power 7 kW, main roller temperature -20 ℃, and belt speed 10 m / min. Then, the film was flipped over, and a copper seed layer was deposited by magnetron sputtering on the first stretched layer (corresponding to the air knife surface during casting cooling) with the same parameters. The thickness of the copper seed layer on both sides was 30 nm.

[0102] (3) Electroplating: The thin film with deposited copper seed layer is thickened by electroplating to achieve a copper layer thickness of 1 μm on both sides. Electroplating adopts a side-clamp type winding and unwinding structure with a winding speed of 5 m / min and a winding and unwinding tension of 65 N. The copper plating solution composition is: copper sulfate 130 g / L, sulfuric acid 90 g / L, chloride ion 50 ppm, brightener sodium polydisulfide dipropane sulfonate 0.4 mL / L, and carrier agent polyethylene glycol 3 mL / L.

[0103] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0104] Example 2:

[0105] The difference from Example 1 is that the particle melt co-extrusion was adjusted to use three extruders. The added third extruder was used for the third melt layer (core layer), and the material was a single main polymer material, PP, forming a three-layer co-extrusion structure. The proportion of auxiliary polymer materials in the first and second melt layers was adjusted to Wt1%=10% and Wt2%=12%. The thickness proportions of the first and second melt layers were also adjusted: Th1%=10% for the first melt layer, Th2%=8% for the second melt layer, and the thickness proportion of the third melt layer was 82%. T1 was adjusted to 85°C and T2 was adjusted to 90°C. The composite current collector was prepared according to the method of Example 1 using the above parameters.

[0106] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0107] Example 3:

[0108] The difference from Example 2 is that Th1% is adjusted to 25%, Th2% is adjusted to 20%, and the thickness ratio of the third molten layer is correspondingly changed to 55%. The composite current collector is prepared according to the method of Example 2 with the above parameters.

[0109] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0110] Example 4:

[0111] The difference from Example 2 is that Wt1% was adjusted to 7.5% and Wt2% was adjusted to 9%. The composite current collector was prepared according to the method of Example 2 with the above parameters.

[0112] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0113] Example 5:

[0114] The difference from Example 2 is that the auxiliary polymer materials for the first and second molten layers are changed to polyvinyl chloride (PVC, softening temperature T). b =85 ℃), T0 is adjusted to 220 ℃, Th0 is adjusted to 250 μm, T1 is adjusted to 95 ℃, T2 is adjusted to 100 ℃, Th1% is adjusted to 15%, Th2% is adjusted to 10%, Wt2% is adjusted to 13.5%, and Th is adjusted to 5.0 μm (the transverse stretching ratio needs to be 10 times). The composite current collector is prepared according to the method of Example 2 with the above parameters.

[0115] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0116] Example 6:

[0117] The difference from Example 2 is that the auxiliary polymer material for the first and second molten layers is changed to polystyrene (PS, softening temperature T). b =100 ℃), T0 is adjusted to 230 ℃, T1 is adjusted to 95 ℃, Th1% is adjusted to 25%, Th2% is adjusted to 7.5%, Wt1% is adjusted to 8.5%, and Wt2% is adjusted to 12.5%. The composite current collector is prepared according to the method of Example 2 with the above parameters.

[0118] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 8, but not exactly equal.

[0119] Example 7:

[0120] For production scenarios where the main polymer material is polypropylene, the gas temperature T1 of the air knife and edge blowing nozzle and the surface temperature T2 of the chilling roller are usually the same, both being 90 ℃. The above conditions can be correlated with Equation I, and the simplified Equation I' is (T1 is retained for both T1 and T2): .

[0121] The difference between this embodiment and Embodiment 1 is that Wt1% is adjusted to 5% and Wt2% is adjusted to 3%. The composite current collector is prepared according to the method of Embodiment 1 using the above parameters.

[0122] All parameters in the above embodiments satisfy Equation I'. Due to issues such as the need to round the parameters, the actual calculated value of k is close to 8, but not exactly equal to it.

[0123] Example 8:

[0124] Similarly, in this embodiment, T1 and T2 are the same, both being 90 °C, and the relevant parameters are selected according to the simplified formula I' in Embodiment 7.

[0125] The difference between this embodiment and Embodiment 2 is that Th1% is adjusted to 15%, Th2% is adjusted to 13.5%, Wt1% is adjusted to 15%, and Wt2% is adjusted to 10%. The composite current collector is prepared according to the method of Embodiment 2 with the above parameters.

[0126] All parameters in the above embodiments satisfy Equation I'. Due to issues such as the need to round the parameters, the actual calculated value of k is close to 8, but not exactly equal to it.

[0127] Example 9:

[0128] The difference from Example 2 is that the materials of the first and second molten layers are polyphenylene sulfide (PPS), the main polymer material, with a softening temperature of T. a =270 ℃) and auxiliary polymer material polyetherimide (PEI, softening temperature T b =210℃).

[0129] The constant coefficients of the substrate characteristics in the corresponding equations II-V, 1 / 20000, 1 / 40, 3 / 800000, and 3 / 1600, are adjusted to 1 / 300, 10, 1 / 6000, and 1 / 2, respectively. Based on the same derivation conditions, equation I is obtained when the main polymer material is polyphenylene sulfide: .

[0130] The difference between this embodiment and Embodiment 2 is that T0 is adjusted to 360 ℃, T1 is adjusted to 100 ℃, T2 is adjusted to 100 ℃, Th0 is adjusted to 28 μm, Th2% is adjusted to 7.5%, Wt2% is adjusted to 10%, the longitudinal stretching ratio is adjusted to 2.5, the preheating temperature is 90 ℃, the stretching temperature is 130 ℃, and the setting temperature is 120 ℃; the transverse stretching ratio is adjusted to 2.5, the preheating temperature is 95 ℃, the stretching temperature is 110 ℃, and the setting temperature is 113 ℃.

[0131] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 15, but not exactly equal.

[0132] Example 10:

[0133] The difference from Example 9 is that the auxiliary polymer materials for the first and second molten layers are changed to Nylon 66 (PA66, softening temperature T). b =170 ℃). Th1% was adjusted to 5%, Th2% to 5%, Wt1% to 8%, and Wt2% to 9%. The composite current collector was prepared according to the method of Example 9 with the above parameters.

[0134] All parameters in the above embodiments satisfy Equation I. Due to issues such as the need for parameter rounding, the actual calculated value of k is close to 15, but not exactly equal.

[0135] Comparative Example 1:

[0136] The difference from Example 2 is that (2) in magnetron sputtering, the first stretching layer is first magnetron sputtered to deposit a copper seed layer, and at this time the second stretching layer is attached to the cooling main roller; then it is flipped and the second stretching layer is magnetron sputtered.

[0137] Comparative Example 2:

[0138] The difference from Example 10 is that (2) in magnetron sputtering, the first stretching layer is first magnetron sputtered to deposit a copper seed layer, and at this time the second stretching layer is attached to the cooling main roller; then it is flipped and the second stretching layer is magnetron sputtered.

[0139] This application uses an optical microscope to analyze the morphology of the thin film surface after stretching (before magnetron sputtering) in Example 2. Please refer to [link to relevant documentation]. Figure 1 The surface of the first stretching layer (corresponding to the air knife surface during casting cooling) has sparse but large-diameter roughened rings, with an average roughened ring diameter of approximately 300 μm; please refer to Figure 2 The surface of the second stretching layer (corresponding to the quenching surface during casting cooling) has dense but small-diameter roughening rings, with an average roughening ring diameter of approximately 100 μm. Please refer to [reference needed]. Figure 1 and Figure 2 Under the same brightness window, Figure 1 The deeper roughening ring lines indicate a higher roughening ring height on the surface of the first stretched layer. Air knife cooling and quench surface cooling produce different roughening morphologies. After magnetron sputtering, the roughening rings of the aforementioned film undergo further thermal damage deformation.

[0140] The testing method for this application is as follows:

[0141] 1. Single-sided physical peel strength test: Performed according to Method 1 of GB / T 2792-2014. The composite current collector sample was adhered to a stainless steel plate, and tests were conducted on both the first tensile layer side (referred to as side A) and the second tensile layer side (referred to as side B). A 20 mm wide adhesive tape with a viscosity ≥0.8 N / m was used, and the test was conducted at a 180° peel angle with a peel speed of 100 mm / min. Fifty different locations across the entire width of each sample were selected for testing, and the average peel strength (unit: kN / m) was calculated.

[0142] 2. Single-sided physical peel strength consistency test: The relative dispersion (RSD) is calculated by measuring the peel strength at each point on one side of A or B.

[0143] Please refer to Table 1 for the test results above.

[0144] Table 1. Performance test results of the composite current collectors in Examples 1-10 and Comparative Examples 1-2 of this application.

[0145]

[0146] In the preparation process of Examples 1-10 of this application, during the cooling step, the first molten layer is cooled by an air knife, and the second molten layer is cooled by contact quenching surface cooling. Due to the difference in cooling rate between the two different cooling methods, a sparse but high-height roughening ring is easily formed on the first molten layer side, while a dense but low-height roughening ring is easily formed on the second molten layer side. This results in a similar difference in the anchoring structure with different morphologies on both sides after stretching. To address this, the asymmetric thermal damage distribution during magnetron sputtering is utilized. When magnetron sputtering the stretched body, the second stretched layer is sputtered first, followed by the first stretched layer. During the initial sputtering, the second stretched layer, as the direct deposition surface, bears the thermal damage, while the first stretched layer is also affected by heat transfer due to its attachment to the cooling roller. Then, during the subsequent sputtering of the first stretched layer, the second stretched layer, already coated with conductive material, is protected by the coating, reducing subsequent thermal damage. This results in the first stretched layer side bearing relatively more thermal damage, and the second stretched layer side bearing relatively less thermal damage. In view of this, the height of the roughening ring of the first stretching layer, which was originally high but sparse, is reduced under the influence of more thermal damage, while the height of the roughening ring of the second stretching layer, which was originally low but dense, is maintained or slightly reduced under the influence of less thermal damage. This promotes the uniformity of the morphology of the roughening rings on both sides, which in turn helps to improve the uniformity of the bonding force of the double-sided conductive layer of the composite current collector.

[0147] Compared to the embodiments of this application, Comparative Examples 1 and 2 first perform magnetron sputtering on the first stretched layer and then on the second stretched layer. This asymmetric magnetron sputtering thermal damage further exacerbates the structural differences in the roughening rings on the surfaces of the first and second stretched layers, resulting in poor uniformity of the bonding force between the resulting composite current collector and the conductive layer on both sides.

[0148] 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.

[0149] The embodiments described above are merely illustrative of several implementations of the technical solution of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the technical solution of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing a composite current collector, characterized in that, Includes the following steps: A melt is prepared, the melt comprising a first melt layer and a second melt layer disposed opposite to each other, wherein the materials of the first melt layer and the second melt layer comprise the same main polymer material and the same auxiliary polymer material; The melt is cooled, wherein the first molten layer is cooled by an air knife, and the second molten layer is cooled by contact cooling surface; The cooled melt is stretched to form a first stretched layer from the first cooled melt layer and a second stretched layer from the second cooled melt layer, thus preparing a stretched body. The second stretched layer and the first stretched layer of the stretched body are sequentially subjected to magnetron sputtering to deposit conductive materials on the surfaces of the first stretched layer and the second stretched layer, thereby preparing the composite current collector.

2. The preparation method according to claim 1, characterized in that, The melt further includes a third melt layer located between the first melt layer and the second melt layer, the material of the third melt layer including the main polymer material.

3. The preparation method according to claim 1, characterized in that, The preparation method satisfies one of the following conditions: (1) The main polymer material includes polypropylene, and the auxiliary polymer material includes at least one of polyethylene, polyvinyl chloride and polystyrene; (2) The main polymer material includes polyphenylene sulfide, and the auxiliary polymer material includes at least one of polyetherimide and nylon 66.

4. The preparation method according to any one of claims 1-3, characterized in that, Definitions: The temperature of the melt before cooling is T0 ℃, the temperature of the air knife is T1 ℃, the temperature of the chilled surface is T2 ℃, and the softening temperature of the main polymer material is T a The softening temperature of the auxiliary polymer material is T. b ℃, the thickness percentage of the first molten layer in the melt is Th1%, the thickness percentage of the second molten layer in the melt is Th2%, the mass percentage of the auxiliary polymer material in the first molten layer is Wt1%, the mass percentage of the auxiliary polymer material in the second molten layer is Wt2%, k is a constant coefficient and k is from 2 to 20; satisfying the following equation I: 。 5. The preparation method according to claim 4, characterized in that, The melt further includes a third melt layer located between the first melt layer and the second melt layer, the material of the third melt layer including the host polymer material, and the host polymer material including polypropylene, and the preparation method further satisfies at least one of the following conditions: (1) Wt1 is 2 to 20; (2) Wt2 is 2 to 20; (3) Th1 ranges from 5 to 30; (4) Th2 ranges from 5 to 30; (5) T0 is between 220 and 260; (6) T1 is 80 to 120; (7) T2 is 80 to 120; (8) k is 8.

6. The preparation method according to claim 5, characterized in that, The stretching includes longitudinal stretching and transverse stretching, and the stretching also satisfies at least one of the following conditions: (1) The longitudinal stretching and the transverse stretching are performed sequentially; (2) The stretching ratio of the longitudinal stretch is 4 to 6; (3) The stretching ratio of the transverse stretching is 8 to 10.

7. The preparation method according to claim 6, characterized in that, Both the longitudinal stretching and the transverse stretching are performed in stages, including a preheating stage, a stretching stage, and a setting stage. The stretching also satisfies at least one of the following conditions: (1) When performing the longitudinal stretching, the preheating temperature is 100 ℃ to 160 ℃, the stretching temperature is 150 ℃ to 170 ℃, and the setting temperature is 140 ℃ to 145 ℃; (2) When performing the transverse stretching, the preheating temperature is 150 ℃ to 180 ℃, the stretching temperature is 160 ℃ to 170 ℃, and the setting temperature is 165 ℃ to 170 ℃.

8. The preparation method according to claim 1, characterized in that, The preparation method further includes at least one of the following steps: (1) Before performing the magnetron sputtering, the surfaces of the first stretching layer and the second stretching layer in the stretched body are subjected to corona treatment; (2) After the magnetron sputtering is performed, the conductive material deposited on the surfaces of the first stretching layer and the second stretching layer is subjected to electroplating.

9. A composite current collector, characterized in that, The composite current collector is prepared according to the preparation method described in any one of claims 1-8.

10. An electrode sheet, characterized in that, The electrode sheet includes the composite current collector as described in claim 9.

11. A battery, characterized in that, The battery includes the electrode plates as described in claim 10.

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