High-strength composite current collector and preparation method thereof

Abstract

The invention relates to the technical field of battery current collectors, in particular to a high-strength composite current collector and a preparation method thereof.The preparation method of the composite aluminum foil current collector comprises the following steps that S1, a base material roll film is modified on a film stretching line so as to improve the tensile strength and reduce the ductility; the base material roll film is a polymer base material roll film for preparing the composite current collector; s2, copper plating or aluminum plating is conducted on the surface of the modified base material roll film; and S3, forming the high-strength composite current collector coiled material. Through base material modification, compared with a composite current collector in the prior art, the composite current collector is higher in strength and lower in total elongation under low elongation, the problem that the compactness of a metal layer becomes poor under high elongation is effectively solved, the modified composite current collector is not prone to being excessively stretched during subsequent procedure operation, and if the modified composite current collector is excessively stretched, the modified composite current collector can be directly fractured, so that the service life of the composite current collector is prolonged. The problem that the compactness of the metal layer is poor but not easy to find due to excessive stretching and non-fracture is solved, and the operation difficulty of procedures such as downstream coating is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery current collectors, and particularly to a high-strength composite current collector and a preparation method thereof. Background Art

[0002] With the wide application of lithium batteries in the new energy field, the requirements for battery performance are continuously increasing. As an important part of lithium batteries, the performance of the current collector directly affects the overall performance of the battery.

[0003] Traditional electrolytic copper foils and electrolytic aluminum foils have certain limitations in meeting the requirements of battery lightweight and high energy density. Composite copper foils and composite aluminum foils, as a new generation of current collectors, have emerged. They have advantages such as reducing the weight of the battery, increasing the energy density of the battery, enhancing the safety of the battery, and reducing the cost of the battery. However, the overall composite current collector has a sandwich structure, and the middle polymer substrate has problems of low tensile strength and extremely high elongation rate. Compared with pure metal foils, in the subsequent coating process, the metal layer of the composite current collector is more likely to have a fault, and the concealment of the fault is relatively high, seriously affecting the performance of the final lithium battery.

[0004] At present, the composite current collectors in the prior art cannot well meet the operation requirements of downstream processes in terms of strength and elongation rate. For example, for a 6.5μm BOPP substrate composite copper foil (1μm copper + 4.5μm BOPP + 1μm copper), the maximum tensile strength in the MD direction is 212MPa, the total elongation rate is 16%, and the strength within an elongation rate of 8% does not exceed 190MPa; for a 6.5μm BOPP substrate composite aluminum foil (1μm aluminum + 4.5μm BOPP + 1μm aluminum), the maximum tensile strength in the MD direction is 200MPa, the total elongation rate is 17%, and the strength within an elongation rate of 8% does not exceed 170MPa. When the tensile exceeds a certain proportion, the compactness of the metal layer deteriorates, affecting properties such as sheet resistance and adhesion, and further affecting the performance of lithium batteries. Therefore, it is of great significance to develop a high-strength composite current collector that can optimize performance and reduce the operation difficulty of downstream processes. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem in the prior art that when the tensile exceeds a certain proportion, the compactness of the metal layer deteriorates, affecting properties such as sheet resistance and adhesion, and further affecting the performance of lithium batteries. A high-strength composite current collector and a preparation method thereof are provided. By modifying the substrate, the strength of the composite current collector at low elongation rates is increased, the total elongation rate is reduced, thereby optimizing the performance of the composite current collector, reducing the operation difficulty of downstream processes, and enhancing the stability of lithium batteries.

[0006] To achieve the above object, a method for preparing a high-strength composite current collector proposed by the present invention includes the following steps: S1. Modify the base material roll film on a film stretching line to improve the tensile strength and reduce the elongation rate; the base material roll film is a polymer base material roll film for preparing a composite current collector; S2. Copper plating or aluminum plating is performed on the surface of the modified base material roll film; S3. A high-strength composite current collector roll material is formed.

[0007] As a further description of the above technical solution: In step S1, the base material roll film is made of PET, PP, PI, PE or PPS material. When it is loaded onto the winding film stretching line for modification, it is first longitudinally stretched on the stretching roller, and then transversely stretched in the stretching oven.

[0008] As a further description of the above technical solution: In step S1, the composite current collector is a composite copper foil, and copper plating is performed on the surface of the composite current collector.

[0009] As a further description of the above technical solution: In step S1, the composite current collector is a composite aluminum foil, and aluminum plating is performed on the surface of the composite current collector.

[0010] As a further description of the above technical solution: In step S2, the modified base material roll film is loaded onto a winding magnetron sputtering coater to perform copper plating on the A / B sides for a primer, and then the roll film with the copper plating primer is loaded onto a water plating line to perform water plating on the A / B sides to quickly thicken the copper layer.

[0011] As a further description of the above technical solution: In step S2, the modified base material roll film is loaded onto a winding evaporation coater. First, an aluminum layer is plated on the A side, and after the aluminum plating on the A side is completed, an aluminum layer is plated on the B side.

[0012] A high-strength composite current collector includes a modified base material layer, and plating layers are provided on both the upper surface and the lower surface of the modified base material layer.

[0013] As a further description of the above technical solution: The plating layer includes an upper copper plating layer and a lower copper plating layer. The upper copper plating layer is provided on the upper surface of the modified base material layer, and the lower copper plating layer is provided on the lower surface of the modified base material layer.

[0014] As a further description of the above technical solution: The plating layer includes an upper evaporated aluminum layer and a lower evaporated aluminum layer. The upper evaporated aluminum layer is provided on the upper surface of the modified base material layer, and the lower evaporated aluminum layer is provided on the lower surface of the modified base material layer.

[0015] As a further description of the above technical solution: Both the upper copper plating layer and the lower copper plating layer are composed of a magnetron sputtered copper plating layer and a water-plated thickened copper layer.

[0016] The above technical solution has the following advantages or beneficial effects:

[0017] 1. Through the modification of the substrate, the maximum strength of the high-strength composite copper foil within an elongation of 8% reaches 240 MPa, and the total elongation is about 10%; the maximum strength of the high-strength composite aluminum foil within an elongation of 8% reaches 213 MPa, and the total elongation is about 10%. Compared with the composite current collectors in the prior art, it has higher strength and lower total elongation at low elongation, effectively improving the problem of poor densification of the metal layer at high elongation.

[0018] 2. The modified composite current collector of the present invention is not easily over-stretched during the subsequent process operations. If it is over-stretched, it will also break directly at about 10%, avoiding the problem of poor densification of the metal layer caused by over-stretching without breaking, which is not easily detected, and reducing the operation difficulty of downstream coating and other processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flowchart of the preparation method of the high-strength composite current collector in an embodiment of the present invention;

[0020] Figure 2 It is a comparison diagram of the composite copper foil before and after stretching in an embodiment of the present invention;

[0021] Figure 3 It is a comparison diagram of the composite aluminum foil before and after stretching in an embodiment of the present invention;

[0022] Figure 4 It is a comparison diagram of the tensile strength of the composite copper foil base film before and after modification in an embodiment of the present invention;

[0023] Figure 5 It is a comparison diagram of the tensile strength of the composite copper foil before and after modification of the base film in an embodiment of the present invention;

[0024] Figure 6 It is a comparison diagram of the tensile strength of the composite aluminum foil base film before and after modification in an embodiment of the present invention;

[0025] [[ID=३२]] Figure 7 It is a comparison diagram of the tensile strength of the composite aluminum foil before and after modification of the base film in an embodiment of the present invention;

[0026] Figure 8 It is a schematic structural diagram of the high-strength composite current collector in an embodiment of the present invention;

[0027] Figure 9 It is Figure 8 a schematic structural diagram of the copper plating layer in

[0028] Figure 10 It is Figure 8 a schematic structural diagram of the aluminum plating layer in.

[0029] Legend Explanation:

[0030] 1. Modified substrate layer; 2. Coating layer; 201. Upper copper plating layer; 202. Lower copper plating layer; 203. Upper aluminum evaporation plating layer; 204. Lower aluminum evaporation plating layer; 2011. Magnetron sputtering copper plating layer; 2012. Electroplated thickened copper layer. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0032] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "vertical", "upper", "lower", "horizontal", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0033] Please refer to Figures 1-7 , the present invention provides a technical solution: A preparation method of a high-strength composite current collector of the present invention includes the following steps: S1. The substrate roll film is modified on a film stretching line to improve the tensile strength and reduce the elongation; the substrate roll film is a polymer substrate roll film for preparing a composite current collector; S2. Copper plating or aluminum plating is performed on the surface of the modified substrate roll film; S3. A high-strength composite current collector roll material is formed.

[0034] In the technical solution of the present invention, through substrate modification, the highest strength of the high-strength composite copper foil within 8% elongation reaches 240 MPa, and the total elongation is about 10%; the highest strength of the high-strength composite aluminum foil within 8% elongation reaches 213 MPa, and the total elongation is about 10%. Compared with the composite current collectors in the prior art, the strength is higher at low elongation, and the total elongation is lower, effectively improving the problem that the compactness of the metal layer becomes poor at high elongation. The modified composite current collector is not easily over-stretched during the subsequent process operations. If it is over-stretched, it will also break directly at about 10%, avoiding the problem that the metal layer has poor compactness but is not easily detected due to over-stretching without breaking, and reducing the operation difficulty of downstream coating and other processes. At the same time, the optimized performance of the composite current collector makes the performance of the lithium battery, such as sheet resistance and adhesion, more stable, thereby improving the overall stability and performance of the lithium battery.

[0035] Such as Figure 1 and Figure 2As shown, in step S1, the base material winding film is made of PET, PP, PI, PE or PPS. When it is fed onto the winding film stretching line for modification, it is first longitudinally stretched on the stretching roller and then transversely stretched in the stretching oven. The base material winding film is placed on the film stretching line for modification, and by adjusting the process parameters, the tensile strength is increased and the elongation rate is reduced. Specifically, a 6-μm-thick BOPP base film is fed onto the winding film stretching line, the unwinding tension is controlled at 200 ± 20 N, the winding tension is controlled at 180 ± 20 N, the line speed is 30 ± 2 m / min. It is first longitudinally stretched on the stretching roller at 100 - 140 °C, and the total stretching ratio is 5 - 20 times. Then it is transversely stretched in the stretching oven at 110 - 150 °C, and the stretching ratio is 5 - 20 times, obtaining a BOPP base film with high resistance and low elongation.

[0036] As Figure 1 and Figure 2 shown, in step S1, the composite current collector is a composite copper foil, and the surface of the composite current collector is copper-plated. The modified base material winding film is fed onto the winding magnetron sputtering coater for copper plating on sides A / B as a primer, and then the copper-plated winding film is fed onto the electroplating line to electroplate sides A / B to quickly thicken the copper layer. The modified base film is magnetron copper-plated as a primer with a thickness of 80 nm. For example, the modified 4.5-μm-thick BOPP winding film is fed onto the winding magnetron sputtering coater for copper plating on sides A / B as a primer, and 80 ± 10 nm thick copper is plated on each of sides A / B. The unwinding tension is 100 ± 5 N, the winding tension is adaptive, the running speed is 20 m / min, there are 14 copper targets on each side, the total power is controlled at 120 ± 5 kw, and the ion source cleaning voltage is 700 V. The primed material is fed onto the electroplating line to thicken the copper layer to 1000 nm. If the unwinding tension is 95 ± 10 N, the winding tension is 85 ± 10 N, the speed is 14 ± 2 m / min, and the total current of the rectifier is 6000 ± 500 A, a high-strength composite copper foil with a thickness of 6.5 μm (4.5 μm base material + 2 μm copper layer) is obtained at this time.

[0037] As Figure 1 and Figure 2 shown, in step S1, the composite current collector is a composite aluminum foil, and the surface of the composite current collector is aluminum-plated. The modified base material winding film is fed onto the winding evaporation coater. First, an aluminum layer is plated on side A. After the aluminum plating on side A is completed, an aluminum layer is then plated on side B. The modified 4.5-μm-thick BOPP winding film is fed onto the winding evaporation coater, and a 1000 ± 50 nm aluminum layer is plated on side A, with a speed of 20 ± 2 m / min, a wire feeding speed of 300 ± 50 mm / min, an unwinding tension of 250 ± 50 N, and an adaptive winding tension. After the aluminum plating on side A is completed, 1000 ± 50 nm of aluminum is plated on side B, with a speed of 20 ± 2 m / min, a wire feeding speed of 300 ± 50 mm / min, an unwinding tension of 250 ± 50 N, and an adaptive winding tension, obtaining a high-strength composite aluminum foil with a thickness of 6.5 μm.

[0038] Example 1:

[0039] Example of preparing high-strength composite copper foil:

[0040] As Figure 4 and Figure 5 shown, substrate modification: Take a roll of 6-μm-thick BOPP base film and load it onto the winding film stretching line. According to the set parameters, the unwinding tension is adjusted to 200 N, the winding tension is adjusted to 180 N, and the line speed is set to 30 m / min. Longitudinal stretching is carried out on the stretching roller at 120 °C, and then transverse stretching is carried out in the stretching oven at 130 °C. After this process, the strength of the obtained BOPP base film is significantly improved, and the elongation is significantly reduced. The highest strength before modification is 217 MPa, and the elongation is 84%. After modification, the highest strength is 240 MPa, and the elongation is 30%.

[0041] Magnetron copper plating for primer: Load the modified 4.5-μm-thick BOPP roll film onto the winding magnetron coating machine. Set the unwinding tension to 100 N, and the winding tension is adaptive. The running speed is set to 20 m / min, 14 copper targets are arranged on each side, the total power is controlled at 120 kw, and the ion source cleaning voltage is 700 V. Copper with a thickness of 80 nm is plated on both sides A / B.

[0042] Electroplating for thickening: Load the roll film plated with copper primer onto the electroplating line. Set the unwinding tension to 95 N, the winding tension to 85 N, the speed to 14 m / min, and the total current of the rectifier to 6000 A. The copper layer on both sides A / B is thickened to 1000 nm. At this time, the thickness of the obtained high-strength composite copper foil is 6.5 μm (4.5 μm substrate + 2 μm copper layer). The strength curve of the composite copper foil finished product is as shown in the figure. The highest strength before modification is 212 MPa, and the elongation is 16%. After modification, the highest strength is 250 MPa, and the elongation is 10%. When the elongation is 8%, the strength is about 240 MPa.

[0043] Example 2:

[0044] Example of preparing high-strength composite aluminum foil:

[0045] As Figure 6 and Figure 7 shown, substrate modification: Similarly, take a roll of 6-μm-thick BOPP base film and process it according to the same equipment parameters and process conditions as those for the substrate modification of the composite copper foil. That is, the unwinding tension is 200 N, the winding tension is 180 N, the line speed is 30 m / min, longitudinal stretching is carried out on the stretching roller at 120 °C, and transverse stretching is carried out in the stretching oven at 130 °C. The highest strength before modification is 223 MPa, and the elongation is 92%. After modification, the highest strength is 247 MPa, and the elongation is 38%.

[0046] Aluminum evaporation coating on side A: Feed the modified 4.5-μm-thick BOPP wound film onto the winding evaporation coating machine. Set the speed at 20 m / min, the wire feeding speed at 300 mm / min, the unwind tension at 250 N, and the rewind tension to be adaptive. Coat a 1000-nm aluminum layer on side A.

[0047] Aluminum evaporation coating on side B: After the aluminum coating on side A is completed, keep the same equipment parameters and coat a 1000-nm aluminum layer on side B. The finally obtained high-strength composite aluminum foil with a thickness of 6.5 μm. The strength curve of the composite aluminum foil finished product shows that before modification, the maximum strength is 200 MPa and the elongation is 17.5%; after modification, the maximum strength is 220 MPa and the elongation is 10%. When the elongation is 8%, the strength is about 214 MPa.

[0048] A high-strength composite current collector includes a modified substrate layer 1, and coating layers 2 are provided on both the upper and lower surfaces of the modified substrate layer 1; the modified substrate layer 1 serves as the core support structure of the high-strength composite current collector. After special treatment on the film stretching line, its molecular chain structure has changed significantly. The longitudinal and transverse stretching causes the molecular chains to reorient and closely arrange in two directions, thereby significantly improving the tensile strength of the substrate and reducing the elongation. This modified substrate can not only provide stable support for the coating layers on the upper and lower surfaces, but also buffer the influence of external stress on the coating layers to a certain extent, preventing problems such as faults in the coating layers due to substrate deformation during subsequent processing or use.

[0049] Among them, the thickness range of the modified substrate layer 1 is 2.5 - 8 μm, the thickness range of the increased copper layer is 600 nm - 2000 nm, and the thickness range of the increased aluminum layer is 6000 nm - 3000 nm.

[0050] As Figure 8 and Figure 9 shown, the coating layer 2 includes an upper copper coating layer 201 and a lower copper coating layer 202. The upper copper coating layer 201 is provided on the upper surface of the modified substrate layer 1, and the lower copper coating layer 202 is provided on the lower surface of the modified substrate layer 1. Both the upper copper coating layer 201 and the lower copper coating layer 202 are composed of a magnetron sputtering copper coating layer 2011 and a water plating thickened copper layer 2012. Both the upper copper coating layer 201 and the lower copper coating layer 202 are composed of a magnetron sputtering copper coating layer 2011 and a water plating thickened copper layer 2012. The magnetron sputtering copper coating layer 2011 serves as the bottom layer, having good crystal orientation and adhesion to the substrate. Its uniform microstructure provides an ideal template for the growth of the subsequent water plating thickened copper layer 2012. The water plating thickened copper layer 2012 further increases the thickness of the copper layer to meet the requirements of the lithium battery current collector for electrical conductivity. This double-layer copper layer structure can effectively improve the electrical conductivity of the composite copper foil, reduce the resistance, and improve the charge and discharge efficiency of the battery. For example, during the charge and discharge process of the lithium battery, the current can pass more smoothly through the copper layer of the composite copper foil, reducing energy loss and increasing the energy density of the battery.

[0051] As Figure 8 and Figure 10 shown, the coating layer 2 includes an upper vapor-deposited aluminum layer 203 and a lower vapor-deposited aluminum layer 204. The upper vapor-deposited aluminum layer 203 is disposed on the upper surface of the modified substrate layer 1, and the lower vapor-deposited aluminum layer 204 is disposed on the lower surface of the modified substrate layer 1. The upper vapor-deposited aluminum layer 203 and the lower vapor-deposited aluminum layer 204 are formed on the upper and lower surfaces of the modified substrate layer 1 by a winding evaporation coating machine. The vapor-deposited aluminum layer has good compactness and purity, and can effectively improve the electrical conductivity and chemical stability of the composite aluminum foil. In the working environment of a lithium battery, the aluminum layer can stably conduct current, and at the same time, the oxide film formed on its surface can protect the aluminum layer from further corrosion, extend the service life of the composite aluminum foil, and improve the safety and stability of the lithium battery. For example, in harsh environments such as high temperature or high humidity, the vapor-deposited aluminum layer can maintain good performance to ensure the normal operation of the lithium battery.

[0052] It should be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0053] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation method of a high-strength composite current collector, characterized in that, It includes the following steps: S1. The base material roll film is modified on the film stretching line to improve the tensile strength and reduce the elongation rate; the base material roll film is a polymer base material roll film for preparing a composite current collector. S2. Copper or aluminum is plated on the surface of the modified base material roll film. S3. A high-strength composite current collector roll material is formed.

2. The preparation method of the high-strength composite current collector according to claim 1, wherein: In step S1, the base material roll film is made of PET, PP, PI, PE or PPS. When it is loaded onto the winding film stretching line for modification, it is first longitudinally stretched on the stretching roller, and then transversely stretched in the stretching oven.

3. The preparation method of the high-strength composite current collector according to claim 1, characterized in that: In step S1, the composite current collector is a composite copper foil, and copper is plated on the surface of the composite current collector.

4. The preparation method of the high-strength composite current collector according to claim 1, characterized in that: In step S1, the composite current collector is a composite aluminum foil, and aluminum is plated on the surface of the composite current collector.

5. The preparation method of the high-strength composite current collector according to claim 3, wherein: In step S2, the modified base material roll film is loaded onto the winding magnetron sputtering coater for copper plating on the A / B sides as a primer, and then the roll film with copper plating primer is loaded onto the aqueous plating line to perform aqueous plating on the A / B sides to quickly thicken the copper layer.

6. The preparation method of the high-strength composite current collector according to claim 4, characterized in that: In step S2, the modified base material roll film is loaded onto the winding evaporation coater. First, an aluminum layer is plated on the A side, and after the aluminum plating on the A side is completed, an aluminum layer is plated on the B side.

7. A high-strength composite current collector, characterized in that, The high-strength composite current collector is prepared by the preparation method according to any one of claims 1-6.

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