Multilayer current collector and preparation method thereof

Abstract

The invention discloses a multi-layer current collector and a preparation method thereof, and the multi-layer current collector comprises a base film which is made of a polymer material; the first aluminum layer is arranged on the base film; the second aluminum layer is arranged on the surface, away from the base film, of the first aluminum layer, and the grain size of the first aluminum layer is larger than that of the second aluminum layer. According to the metal aluminum functional layer with the grain gradient, the residual stress caused in the process of manufacturing the current collector can be relieved, the binding force between plating layers can be increased, and the service life of the multi-layer aluminum current collector is further prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically relates to a multi-layer current collector and a preparation method thereof. Background Art

[0002] In the application of lithium-ion batteries, the current collector is a key component, mainly serving to carry the electrode material and conduct electrons. Reasonably selecting the current collector is a prerequisite for the successful operation of lithium-ion batteries. An ideal current collector needs to meet the characteristics of high electrical conductivity, good flexibility, strong stability, light weight, good compatibility and binding force with battery active materials, and being cheap and easily available. Against this background, the multi-layer current collector came into being. The multi-layer current collector adopts a three-layer composite structure of "metal - polymer material - metal", which is a new composite material made by using polymer materials such as PET / PP as the base film and forming nano-scale metals on the surface of the polymer base film through methods such as vacuum evaporation coating and magnetron sputtering.

[0003] The superiority of the multi-layer current collector material itself has been verified, but due to the immaturity of equipment and process, there are still some problems at present, such as the warping problem of multi-layer aluminum current collector products. One of the reasons may be that currently, most of the preparation of multi-layer aluminum current collectors is to prepare an aluminum metal layer on a polymer film by vacuum evaporation coating. The performance of the metal layer is closely related to its microstructure, and this deposition method is the rapid stacking of a large number of metal atoms, which will cause a large number of lattice defects and holes at the microscopic level inside the prepared metal film during the deposition process. Under the action of external forces, these defects may cause stress concentration, thus generating residual stress; on the other hand, during the vacuum evaporation coating process, the temperature of aluminum vapor is relatively high, and the temperature change will cause the volume change of the material, thus generating thermal stress. If these stresses cannot be released in a short time, it will lead to the warping of the product, affecting the product quality and product yield. Summary of the Invention

[0004] In order to reduce the defects of the aluminum layer of the multi-layer current collector, reduce the residual stress of the multi-layer current collector, and improve the performance of the current collector, the present invention proposes a multi-layer current collector and a preparation method thereof. The above object can be achieved through the following implementation manners of technical solutions:

[0005] A multi-layer current collector, comprising:

[0006] A base film made of a polymer material;

[0007] A first aluminum layer disposed on the base film;

[0008] A second aluminum layer disposed on the surface of the first aluminum layer away from the base film, and the grain size of the first aluminum layer is larger than that of the second aluminum layer.

[0009] Optionally, the grain size of the first aluminum layer is 500 - 1500 nm, and the grain size of the second aluminum layer is 50 - 200 nm.

[0010] Optionally, at least one aluminum layer is further stacked on the surface of the second aluminum layer away from the first aluminum layer; and the grain size of the aluminum layer stacked on the second aluminum layer increases as the distance between the aluminum layer and the base film increases.

[0011] Optionally, a second aluminum layer to an Nth aluminum layer are sequentially stacked on the surface of the first aluminum layer away from the base film; among the second aluminum layer to the Nth aluminum layer, the ratio of the grain size of the Nth aluminum layer to the grain size of the (N - 1)th aluminum layer is 1.4 - 2.3:1.

[0012] Optionally, N is 3, 4 or 5.

[0013] Optionally, the thickness of the first aluminum layer is 100 - 500 nm; the thickness of the second aluminum layer to the Nth aluminum layer is 50 - 400 nm; the total thickness of the first aluminum layer and the second aluminum layer to the Nth aluminum layer is 0.6 - 1.5 μm.

[0014] Optionally, an underlayer is provided between the base film and the first aluminum layer.

[0015] Preferably, the thickness of the underlayer is 2 - 20 nm.

[0016] Preferably, the underlayer is made of aluminum oxide or aluminum alloy.

[0017] Optionally, the base film layer is selected from at least one of PET (polyethylene terephthalate), PE (polyethylene), PP (polypropylene), PEN (polyethylene naphthalate), PPTA (poly-m-phenylene isophthalamide), PI (polyimide), PC (polycarbonate), PEEK (polyetheretherketone), POM (polyoxymethylene), PPS (polyphenylene sulfide), PPO (polyphenylene oxide), PVC (polyvinyl chloride), PA (nylon), PTFE (polytetrafluoroethylene).

[0018] The preparation method of the above multi-layer current collector includes:

[0019] Depositing aluminum on the base film to form a first aluminum layer, and then depositing aluminum on the first aluminum layer to form a second aluminum layer; the grain size of the first aluminum layer is larger than that of the second aluminum layer.

[0020] Optionally, the method further includes depositing at least one aluminum layer on the second aluminum layer, and the grain size of the aluminum layer deposited on the second aluminum layer increases as the distance between the aluminum layer and the base film increases;

[0021] Preferably, the method further includes depositing a primer layer on the base film first, and then depositing aluminum on the primer layer to form a first aluminum layer;

[0022] Optionally, the deposition method is vacuum evaporation coating; during the deposition process, the grain size of the aluminum layer is adjusted by adjusting the ion source flow rate, the wire feeding speed of the evaporation boat, the winding speed, and the cooling temperature;

[0023] Optionally, the method further includes removing oxides and moisture on the surface of the base film before the deposition process.

[0024] The application of the above multi-layer current collector in the preparation of a battery.

[0025] The technical solution of the present invention has the following advantages:

[0026] A multi-layer current collector and a preparation method thereof provided by the present invention achieve the purpose of regulating the grain size of the metal layer by adding an ion source and combining the adjustment of the cooling temperature during the process of preparing the metal aluminum functional layer. The metal aluminum functional layer is composed of multiple aluminum layers with different grain sizes. The bottom aluminum layer is a large-grain layer, and the upper aluminum layer is a multi-layer small-grain layer with different film thicknesses. As the distance between the upper aluminum layer and the bottom aluminum layer increases, the grains gradually become larger, but the grain size of the upper aluminum layer is always smaller than that of the bottom aluminum layer. In this way, a metal aluminum functional layer with a grain gradient of "large-grain layer + small-grain layer + metal layer with gradually increasing grains" is obtained. By adopting the metal aluminum functional layer with such a grain distribution, on the one hand, the bottom aluminum layer is a relatively thin large-grain layer, which can achieve rapid heat dissipation of the base film and is beneficial to the release of the thermal stress of the base film; the distribution of small grains in the upper layer can fill defects such as holes in the large-grain film layer, improve the denseness of the film layer, and further improve the corrosion resistance of the current collector to the electrolyte; on the other hand, the grains of the upper film layer gradually become larger, which can prevent the problem of winding adhesion during the manufacturing process due to too small grains. This metal aluminum functional layer with a grain gradient can not only relieve the residual stress brought during the current collector manufacturing process, but also increase the bonding force between the coating layers, and further improve the service life of the multi-layer aluminum current collector. Detailed Embodiments

[0027] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation embodiments and are not used to limit the present invention.

[0028] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Intermediate values within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, are also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0030] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0031] The present invention provides a multi-layer current collector, which includes a flexible polymer base film layer and metal aluminum layers deposited on both sides of the flexible polymer base film layer; the metal aluminum layer is composed of at least two aluminum layers with different grain sizes, wherein the first aluminum layer at the bottom layer is a large-grain layer, and the second aluminum layer above the first aluminum layer is a small-grain layer.

[0032] Furthermore, at least one aluminum layer is further stacked on the surface of the second aluminum layer away from the first aluminum layer; and the grain size of the aluminum layer stacked on the second aluminum layer increases with the increase of the distance between the aluminum layer and the base film.

[0033] Furthermore, a second aluminum layer to an Nth aluminum layer are sequentially stacked on the surface of the first aluminum layer away from the base film; among the second aluminum layer to the Nth aluminum layer, the ratio of the grain size of the Nth aluminum layer to the grain size of the (N - 1)th aluminum layer is 1.4 to 2.3:1; N is 3, 4, or 5. The grain size of the first aluminum layer is 500 - 1500 nm, and the minimum grain size of the upper aluminum layer is 50 - 200 nm.

[0034] Furthermore, the flexible polymer base film layer is selected from at least one of PET, PE, PP, PEN, PPTA, PI, PC, PEEK, POM, PPS, PPO, PVC, PA, or PTFE.

[0035] An underlayer is provided between the base film and the first aluminum layer; the thickness of the underlayer is 2 - 20 nm; the underlayer is made of alumina or aluminum alloy

[0036] Furthermore, the total thickness of the multi-layer metal aluminum layer is 0.6 - 1.5 μm,

[0037] The present invention also provides a method for preparing a multi-layer current collector, including the following steps:

[0038] 1) Pretreatment of the flexible polymer-based film layer: In the vacuum chamber of the vacuum evaporation equipment, through the winding system, the flexible polymer-based film layer is pretreated with argon gas to remove oxides and moisture on the surface of the base film, reduce the defect generation sites, and the argon gas flow rate is set to 50 - 200 sccm.

[0039] 2) Preparation of the underlayer: The underlayer is prepared by vacuum evaporation coating, preferably alumina, and the oxygen flow rate is set to 500 - 1500 sccm.

[0040] 3) Preparation of the aluminum metal functional layer: On the basis of the underlayer, first, the bottom aluminum metal layer is prepared by vacuum evaporation coating, where the cooling temperature is 0 - 50 °C.

[0041] 4) Repeat step 3), add an Ar ion source, use argon gas molecules to buffer the metal atoms, and with the cooling effect of the cooling drum, rapidly cool the argon gas molecules and aluminum metal atoms, reduce the kinetic energy of the aluminum vapor before depositing on the sample, reduce the possibility of a large amount of aluminum vapor stacking and depositing rapidly, and refine the deposited aluminum metal particles; for the subsequent preparation of metal layers, adjust the process parameters on this basis in turn: the ion source flow rate gradually decreases, the wire feeding speed of the evaporation boat decreases, the winding speed increases, and the cooling temperature gradually increases, but does not exceed 50 °C.

[0042] Example 1:

[0043] The preparation of the multi-layer aluminum current collector includes the following steps:

[0044] Step 1: Select a PET film with a thickness of 6 μm as the substrate, place it in the winding system of the vacuum evaporation equipment, thread the base film in the correct direction, and then evacuate the evaporation chamber to ≤ 9.0×10 -1 Pa. Open the Ar ion source and the winding system switch respectively, and perform plasma surface pretreatment on the base film. Among them, the Ar ion source flow rate is set to 100 sccm;

[0045] Step 2: Prepare the underlayer on the above base film by vacuum evaporation coating. Open the oxygen source switch, set the oxygen flow rate to 1000 sccm, maintain the wire feeding amount at 50 mm / min, the winding speed at 550 m / min, and the cooling temperature at 30 °C to prepare an alumina underlayer;

[0046] Step 3: Prepare the bottom aluminum layer on the above underlayer by vacuum evaporation coating. Among them, maintain the wire feeding amount at 400 mm / min, the winding speed at 250 m / min, and the cooling temperature at 40 °C;

[0047] Step 4: Inject Ar ions into the evaporation chamber through the ion source of the vacuum ion evaporation equipment, and then repeat the vacuum evaporation coating 4 times to prepare the aluminum layer. During each vacuum evaporation coating process, adjust process parameters such as the Ar ion source flow rate and the cooling temperature to sequentially achieve the deposition of multiple aluminum metal layers with different film thicknesses, forming the aluminum metal functional layer, and finally prepare the multi-layer aluminum current collector. Among them, the Ar ion flow rates during the 4 times of vacuum evaporation coating are sequentially adjusted to: 200 sccm, 150 sccm, 100 sccm, 50 sccm; the cooling temperatures are sequentially adjusted to: 0 °C, 10 °C, 20 °C, 30 °C; the wire feeding amounts are sequentially adjusted to: 300 mm / min, 250 mm / min, 200 mm / min, 150 mm / min; the winding speeds are sequentially adjusted to: 50 m / min, 100 m / min, 150 m / min, 200 m / min.

[0048] Finally, an aluminum metal functional layer with a total film thickness of 1 μm is obtained. There are 5 layers in the obtained aluminum metal functional layer. The thicknesses of the aluminum layers of the 1st to 5th layers are sequentially 300 nm, 250 nm, 200 nm, 150 nm, and 100 nm.

[0049] Example 2:

[0050] Compared with Example 1, the difference in this example is that: in Step 3, the wire feeding amount is maintained at 450 mm / min, the winding speed is 260 m / min, and the cooling temperature is 45 °C; in Step 4, the vacuum evaporation coating is repeated 3 times to prepare the aluminum layer. The Ar ion flow rates are sequentially adjusted to: 200 sccm, 150 sccm, 100 sccm; the cooling temperatures are sequentially adjusted to: 0 °C, 10 °C, 20 °C; the wire feeding amounts are sequentially adjusted to: 350 mm / min, 300 mm / min, 250 mm / min; the winding speeds are sequentially adjusted to: 50 m / min, 100 m / min, 150 m / min. The remaining steps are the same as those in Example 1. Finally, an aluminum metal functional layer with a total film thickness of 1 μm is obtained. There are 4 layers in the obtained aluminum metal functional layer. The thicknesses of the aluminum layers of the 1st to 4th layers are sequentially 330 nm, 270 nm, 230 nm, and 170 nm.

[0051] Example 3:

[0052] Compared with Example 1, the differences in this example are as follows: the wire feeding amount in Step 3 is maintained at 450 mm / min, the winding speed is 200 m / min, and the cooling temperature is 40°C; in Step 4, vacuum evaporation coating is repeated twice to prepare the aluminum layer, and the Ar ion flow rates are adjusted to 200 sccm and 150 sccm respectively, the cooling temperatures are adjusted to 0°C and 10°C respectively, the wire feeding amounts are adjusted to 350 mm / min and 300 mm / min respectively, and the winding speeds are adjusted to 50 m / min and 100 m / min respectively. The remaining steps are the same as those in Example 1. Finally, a metal aluminum functional layer with a total film thickness of 1 μm is obtained. The obtained metal aluminum functional layer has 3 layers, and the thicknesses of the aluminum layers of the 1st to 3rd layers are 500 nm, 270 nm, and 230 nm in sequence.

[0053] Example 4:

[0054] Compared with Example 1, the differences in this example are as follows: a total of 2 metal aluminum layers are prepared. In Step 4, only one vacuum evaporation coating is performed to prepare the aluminum layer, the Ar ion flow rate is 200 sccm, the cooling temperature is 0°C, the wire feeding amount is 400 mm / min, and the winding speed is 250 m / min. The remaining steps are the same as those in Example 1. Finally, a metal aluminum functional layer with a total film thickness of 1 μm is obtained. The obtained metal aluminum functional layer has 2 layers, and the thicknesses are 500 nm and 500 nm in sequence. Comparative Example 1:

[0055] Compared with Example 1, the differences in this example are as follows: in Steps 3 and 4, the preparation of the metal aluminum functional layer is a single film formation. Among them, the Ar ion flow rate is 150 sccm, the wire feeding amount is maintained at 800 mm / min, the winding speed is 30 m / min, and the cooling temperature is 40°C. The remaining steps are the same as those in Example 1. Finally, a metal aluminum functional layer with a total film thickness of 1 μm is obtained.

[0056] Comparative Example 2:

[0057] Compared with Example 1, the differences in this example are as follows: in Steps 3 and 4, the same parameters are used each time for vacuum evaporation coating to prepare the metal aluminum functional layer. Among them, the wire feeding amount is maintained at 250 mm / min, the winding speed is 100 m / min, and the cooling temperature is 40°C. The remaining steps are the same as those in Example 1. Finally, a metal aluminum functional layer with a total film thickness of 1 μm is obtained. The thicknesses of the aluminum layers of the 1st to 5th layers are 200 nm, 200 nm, 200 nm, 200 nm, and 200 nm in sequence.

[0058] Performance tests were carried out on each example and comparative example, and the test methods are as follows

[0059] Grain size: SEM morphology tests were respectively performed on each aluminized layer to obtain the grain size.

[0060] Product edge warping height: Cut the coated film into A4 paper size, place it on a horizontal table, and measure the distance the film edge is warped relative to the horizontal table;

[0061] The bonding strength is measured by an electronic peeling force tester (model BLD-200H): cut a 120×50mm sample, stick the sample on a steel plate with 3M double-sided tape, roll it, and then stick 3M transparent tape on the sample. After rolling again, place the sample on the fixture of the electronic peeling force tester to test and obtain the sample bonding strength value.

[0062] The test results are shown in Table 1:

[0063] Table 1

[0064]

[0065] By comparing the various embodiments with comparative example 1, it can be seen that when only one large-grain aluminum layer is used, the effect of reducing stress cannot be achieved, and by comparing the embodiment with comparative example 2, it can be seen that the stress problem in the obtained multi-layer current collector cannot be alleviated by using multiple layers of aluminum layers with the same grain size. At least one layer of small-grain layer must be prepared on the large-grain layer to achieve the effect of reducing stress.

[0066] Based on the test results of the embodiments and comparative examples in Table 1, it can be seen that the multi-layer current collector structure of "large grain layer + small grain layer + metal layer with gradually increasing grains" of the present invention can not only alleviate the residual stress caused by the current collector manufacturing process and significantly reduce product warping, but also increase the bonding force between the coatings, further improving the life of the multi-layer aluminum current collector. Moreover, as the number of aluminum layers increases, the effect of improving bonding force and reducing stress is better.

[0067] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A multi-layer current collector, characterized in that, Comprising: A base film, which is made of a polymer material; A first aluminum layer, which is disposed on the base film; A second aluminum layer, which is disposed on the surface of the first aluminum layer away from the base film, and the grain size of the first aluminum layer is larger than that of the second aluminum layer.

2. The multi-layer current collector according to claim 1, wherein The grain size of the first aluminum layer is 500 - 1500 nm, and the grain size of the second aluminum layer is 50 - 200 nm.

3. The multi-layer current collector according to claim 1, wherein At least one aluminum layer is further stacked on the surface of the second aluminum layer away from the first aluminum layer; and the grain size of the aluminum layer stacked on the second aluminum layer increases with the increase of the distance between the aluminum layer and the base film.

4. The multi-layer current collector according to claim 3, wherein A second aluminum layer to an Nth aluminum layer are sequentially stacked on the surface of the first aluminum layer away from the base film; among the second aluminum layer to the Nth aluminum layer, the ratio of the grain size of the Nth aluminum layer to the grain size of the (N - 1)th aluminum layer is 1.4 - 2.3:1; Preferably, N is 3, 4 or 5.

5. The multi-layer current collector according to claim 4, wherein The thickness of the first aluminum layer is 100 - 500 nm; the thickness of the second aluminum layer to the Nth aluminum layer is 50 - 400 nm; The total thickness of the first aluminum layer and the second aluminum layer to the Nth aluminum layer is 0.6 - 1.5 μm.

6. The multi-layer current collector according to claim 1, wherein An underlayer is provided between the base film and the first aluminum layer; preferably, the thickness of the underlayer is 2 - 20 nm; Preferably, the underlayer is made of alumina or aluminum alloy.

7. The multi-layer current collector according to claim 1, wherein The base film layer is selected from at least one of PET, PE, PP, PEN, PPTA, PI, PC, PEEK, POM, PPS, PPO, PVC, PA, PTFE.

8. The preparation method of the multi-layer current collector according to any one of claims 1 to 7, characterized in that, Comprising: Depositing aluminum on the base film to form a first aluminum layer, and then depositing aluminum on the first aluminum layer to form a second aluminum layer; the grain size of the first aluminum layer is larger than that of the second aluminum layer.

9. The preparation method of the multi-layer current collector according to claim 8, characterized in that, The method further includes depositing at least one aluminum layer on the second aluminum layer, and the grain size of the aluminum layer deposited on the second aluminum layer increases with the increase of the distance between the aluminum layer and the base film; Preferably, the method further includes first depositing an underlayer on the base film, and then depositing aluminum on the underlayer to form a first aluminum layer; Preferably, the deposition method is vacuum evaporation coating; During the deposition process, the grain size of the aluminum layer is adjusted by adjusting the ion source flow rate, the wire feeding speed of the evaporation boat, the winding speed and the cooling temperature; Preferably, the method further includes removing oxides and moisture on the surface of the base film before the deposition process.

10. Use of the multi-layer current collector according to any one of claims 1 - 7 in the preparation of a battery.

Images