CN116230948A

CN116230948A - Multilayer composite current collector, preparation method thereof, battery prepared from multilayer composite current collector and electronic device

Info

Publication number: CN116230948A
Application number: CN202211612343.4A
Authority: CN
Inventors: 毛祖攀; 周健; 俞嘉杰; 夏桂玲
Original assignee: Anhui Liguang Electronic Material Co ltd
Current assignee: Anhui Liguang Electronic Material Co ltd
Priority date: 2022-12-15
Filing date: 2022-12-15
Publication date: 2023-06-06

Abstract

The invention discloses a multilayer composite current collector, a preparation method thereof, a battery and an electronic device, which relate to the technical field of secondary batteries, and the multilayer composite current collector comprises a multilayer structure, a flexible base layer, micropores, a bonding coating and a conductive layer; the flexible substrate layer is provided with a plurality of micropores, and the micropores are distributed on at least one surface of the flexible substrate layer; the bonding coating is arranged on the surface of the flexible base layer and is filled in micropores of the flexible base layer; the conductive layer is disposed on at least one surface of the flexible base layer; the bond coat is disposed between the flexible base layer and the conductive layer. According to the invention, the plurality of micropores are formed on the flexible base layer, the micropores are filled with the bonding coating and coated on the surface of the flexible base layer, the conductive layer is deposited on the surface of the bonding coating after film formation, so that the bonding strength of the conductive layer and the flexible base layer is improved, the buffering force is provided when the current collector is inevitably deformed and broken in the use process, and the service life of the current collector is prolonged. Meanwhile, the conductive layer adopts a process of magnetron sputtering and electroplating, so that the conductive layer has good conductive performance, the cost can be saved, and the adhesive force between the current collector substrate and the conductive layer can be improved.

Description

Multilayer composite current collector, preparation method thereof, battery prepared from multilayer composite current collector and electronic device

Technical Field

The present invention relates to an electrochemical product and method, and more particularly to a current collector and method of making the same.

Background

Lithium ion batteries are typical secondary batteries, which have the advantages of high energy density, low self-discharge rate, high output power, long cycle life, little environmental pollution, and the like, and are widely used.

The lithium ion battery comprises positive and negative electrodes, electrolyte, a diaphragm and other components; the positive electrode and the negative electrode are composed of a current collector and an electrode active material arranged on the current collector. The current collector is used for leading in and leading out charges generated in the process of charging and discharging the electrode material. Conventionally, current collectors have been made of metallic materials, such as aluminum alloys, copper alloys, and the like. Current collectors made of these metal materials are limited by their physical and chemical properties, for example, after metal is made into a sheet of 5-8 microns, the conductivity elongation is reduced, and the current collector is easily broken and damaged, thus resulting in reduced product performance; if thicker current collectors are used, on the one hand the costs are greatly increased, and on the other hand the greater dead weight of the current collectors leads to a reduction in the energy density.

In the prior art, the composite current collector is considered to be adopted, and a metal layer is prepared on the surface of a low-density flexible material film of the composite current collector so as to form the composite current collector, so that on one hand, the extensibility of the current collector is improved, on the other hand, the dead weight of the current collector is reduced, and the weight energy density of the lithium battery is improved. With the development of technology, the requirements of the lithium ion battery on energy density, light weight and flexible characteristic are higher and higher. At present, the copper foil is produced in a mass mode, the minimum thickness is 6 microns, and the minimum thickness of the aluminum foil is 8 microns.

Adhesion exists between the conductive metal of the composite current collector and the flexible film, and in the life cycle of preparation of the anode and the cathode and use of the battery, the conductive layer of the composite current collector has peeling-off conditions along with bending and heating, and peeling-off of the conductive layer can lead to peeling-off of the electrode active material, so that the performance and the life of the battery are seriously influenced.

In the prior art CN207097948U, the traditional aluminum foil or copper foil is changed into aluminum plating or copper plating on a high polymer film to reduce the weight of the current collector and achieve the effect of improving the energy density of the battery. The prior art CN112242527A discloses a multilayer structure lithium battery current collector, a preparation method thereof and a lithium battery. CN107123812a discloses a positive electrode current collector having a multilayer structure, comprising a plastic film, on the upper and lower surfaces of which an adhesion enhancing layer, an aluminum metal plating layer and an oxidation preventing layer are sequentially plated.

A composite current collector is disclosed in prior art CN113795954a, comprising a polymer film layer and a metal layer disposed on at least one surface of the polymer film layer. A first coating is arranged between the polymer film layer and the metal layer, and a second coating is arranged between the first coating and the metal layer. The bonding force between the first coating and the second coating is larger than the bonding force between the second coating and the metal layer and larger than the bonding force between the first coating and the polymer film layer, so that the bonding force between the metal layer and the polymer film layer is effectively improved.

In the prior art CN206849947U, a porous conductive plastic film current collector is disclosed, which has a multi-layer structure, and comprises a plastic film, wherein an adhesion enhancing layer, a metal plating layer and an oxidation preventing layer are respectively plated on the upper surface and the lower surface of the plastic film in sequence; the metal coating is a copper metal coating or an aluminum metal coating; after the plastic film is plated with an adhesion enhancing layer, a metal plating layer and an oxidation preventing layer in sequence, laser high-efficiency punching or nuclear track etching is carried out, so that micropores with the diameter of 0.1-200 mu m are distributed on the surface of the film, and the overall porosity is 0.1% -3%. Therefore, the light weight of the battery is realized, the energy density is improved, the cost is reduced, and the copper/aluminum plating layer is not easy to fall off.

The prior art focuses on the problem of improving the adhesion between the metal layer and the polymer film layer of the current collector, and also proposes to realize the weight reduction of the current collector by using a porous structure, but does not provide a composite current collector which is more durable, lower in cost and stable in performance.

Disclosure of Invention

The invention provides a composite current collector with low cost, improved service life and stable performance.

The technical scheme of the invention is as follows:

a multilayer composite current collector is provided, which is characterized by having a multilayer structure, including a flexible base layer, micropores, a bonding coating and a conductive layer; the flexible substrate layer is provided with a plurality of micropores; the bonding coating is arranged on the surface of the flexible base layer and is filled in micropores of the flexible base layer; the conductive layer is disposed on at least one surface of the flexible base layer; the bond coat is disposed between the flexible base layer and the conductive layer.

Further, the micropores are distributed on at least one surface of the flexible substrate layer.

Further, the micropores have a diameter of 0.5 to 2. Mu.m.

Further, the surface of the flexible base layer with micropores is greater than 40% of the surface area of the flexible base layer.

Further, the bonding coating forms a film in micropores and on the surface of the flexible base layer, the micropores are in a closed filling state, and the overall porosity of the flexible base layer after the bonding coating is coated is less than 0.1%.

Further, the thickness of the flexible base layer is 0.5-10 μm.

Further, the bond coat has a thickness of 0.2-2 μm.

Further, the bonding coating is coated at least twice, and the bonding coating forms a first bonding coating and a second bonding coating; a transition layer is formed between the first bonding coating and the second bonding coating.

Further, the conductive layer at least comprises two layers, wherein the first conductive layer is combined with the bonding coating, and the second conductive layer is combined with the first conductive layer; the first conductive layer is prepared by a magnetron sputtering method, the second conductive layer is prepared by an electroplating method, and the thickness of the conductive layer is 0.01-1 mu m.

Further, the peel strength between the bond coat and the flexible base layer is less than the peel strength between the bond coat and the conductive layer.

It is characterized in that the method comprises the steps of,

providing a flexible base layer;

a plurality of micropores are arranged on the flexible basic layer;

coating a bonding coating on the flexible base layer and in the micropores;

manufacturing a conductive layer on the bonding coating;

the method comprises the steps of firstly coating a first bonding coating colloid on the surface of a flexible base layer and in micropores, heating, coating a second connecting coating colloid, and heating until the solvent is completely evaporated, wherein micropores on the surface of the obtained flexible base layer are completely filled.

Further, a first conductive layer is firstly prepared on the bonding coating by adopting a magnetron sputtering method; and then preparing a second conductive layer on the first conductive layer by adopting an electroplating method.

Further, the battery comprises electrode plates and a diaphragm arranged between the two electrode plates, and is characterized in that the electrode plates comprise the multilayer composite current collector prepared by the scheme provided by the invention.

Further, the electronic device is characterized by comprising the battery prepared by the technical scheme.

Compared with the prior art, the invention has the following beneficial effects:

(1) The weight reduction is realized by taking a flexible material as a base layer, so that the energy density of the battery is improved;

(2) The flexible material is used as a base layer to increase the tensile strength of the base material, so that the tension and stress window in the current collector preparation process are increased, and the process manufacturing capacity is improved;

(3) The flexible base layer is provided with micropores, and the micropores are filled with the bonding coating, so that the deformation strength of the base material is further increased, when the bonding coating and the flexible base layer are separated to a certain extent, the bonding coating in the micropores is connected to prevent further separation, and when the current collector is peeled off, a buffer force is provided, the peeling degree is reduced, and the possibility that the electrode active substance is separated from the current collector is reduced, so that the service life of the current collector is prolonged;

(4) The bonding coating is connected with the substrate layer and the conductive layer of the current collector, so that the falling-off of the conductive metal layer is reduced, the performance stability of the current collector is improved, and the problem of performance reduction of the current collector caused by easy falling-off of the metal conductive layer is effectively prevented;

(5) The multilayer composite current collector replaces the copper foil current collector in the prior art, can realize the thinning of the traditional copper foil with the thickness of 6 mu m to 0.1 mu m, and greatly reduces the copper consumption.

(6) The invention relates to a conductive layer which is divided into at least two layers, wherein a first conductive layer is prepared by a magnetron sputtering mode, so that the adhesive force between the conductive layer and a bonding coating is increased, and the falling risk of the conductive layer is reduced; the second conductive layer is prepared in an electroplating mode, so that on one hand, the cost is saved, on the other hand, the stability of the conductive layer is improved, and the contact area of the current collector and the active substance is increased.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly explain the drawings needed to be used in the description of the embodiments of the present invention, and it should be apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the contents of the embodiments of the present invention and the drawings without inventive effort for those skilled in the art.

Fig. 1 is a schematic structural view of the present invention.

FIG. 2 is a cross-sectional view of a flexible base layer of the present invention having micro-holes.

Fig. 3 is a top view of a flexible base layer of the present invention having micro-holes.

In the figure:

1. flexible base layer

2. Adhesive coating

3. Micropores

4. A first conductive layer

5. Second conductive layer

Detailed Description

Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be understood that the process equipment or devices not specifically identified in the examples below are all conventional in the art. Furthermore, it is to be understood that the reference to one or more method steps in this disclosure does not exclude the presence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise indicated; it should also be understood that the combined connection between one or more devices/means mentioned in the present invention does not exclude that other devices/means may also be present before and after the combined device/means or that other devices/means may also be interposed between these two explicitly mentioned devices/means, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the method steps is merely a convenient tool for identifying the method steps and is not intended to limit the order of arrangement of the method steps or to limit the scope of the invention in which the invention may be practiced, as such changes or modifications in their relative relationships may be regarded as within the scope of the invention without substantial modification to the technical matter.

The product structure of the invention:

the flexible base layer may be selected from known polymeric flexible materials, which should have good physical and chemical properties. For example, polyethylene terephthalate (PET), polyimide (PI), oriented polypropylene (OPP), etc. are selected. The thickness of the polymer flexible material film is preferably 0.5 to 10. Mu.m, more preferably 1 to 3. Mu.m.

The flexible base layer is provided with micropores by adopting a laser drilling mode, and according to the light source mode, two modes of infrared (co 2) laser drilling and ultraviolet (uv) laser drilling are selected, wherein the diameter of the micropores is 0.5-2 mu m, and further preferably 1.0-1.5 mu m.

The bond coat may be at least one of epoxy resin (EPO), modified polyolefin resin (MPO), ethylene-acrylic acid copolymer (EAA), silicone resin (OS), polyacrylate (PEA), polyurethane (PU), unsaturated Polyester (UP), phenolic resin (PF), polyacrylic resin (PAA), ethylene-vinyl acetate copolymer (EVA).

The bond coat is applied twice, thereby forming a first bond coat and a second bond coat. The bonding coating is coated on the surface of the flexible base layer and in the micropore holes, preferably but not limited to, the bonding coating is coated in the micropore holes in an electrostatic spraying mode, heating is carried out between the two coating, the bonding coating is coated until the micropore holes are completely filled, drying is carried out after the second coating is finished until the solvent is completely evaporated, the bonding coating is dried to form a film, at the moment, the whole porosity of the flexible substrate filled with the bonding coating is less than 0.1%, a transition layer is formed between the first bonding coating and the second bonding coating, and the transition layer is used as an excessive interface of the bonding coating, so that the bonding coating is closely attached to the surface of the flexible base layer, the bonding coating and the micropore holes, and the bonding coating.

Tension and stress tests are carried out between the adhesive coating and the flexible base layer after coating and film forming, and density tests are carried out, so that the adhesive coating is ensured to completely fill the micropore holes.

The total thickness of the bond coat layer is preferably 0.2 to 2. Mu.m, more preferably 0.3 to 1.5. Mu.m.

The conductive layer can be a conductive layer prepared by adopting a vapor deposition method, or can be a composite conductive layer formed by preparing a first conductive layer by adopting a vapor deposition method and preparing a second conductive layer on the surface of the first conductive layer by adopting an electroplating method. The thickness of the two conductive layers is preferably 0.01 to 1. Mu.m, more preferably 0.05 to 0.1. Mu.m.

When the conductive layer is prepared by a vapor deposition method, the vapor deposition method is preferably a physical vapor deposition method. The physical vapor deposition method is preferably at least one of an evaporation method and a sputtering method, wherein the evaporation method is preferably at least one of a vacuum evaporation method, a thermal evaporation method and an electron beam evaporation method, and the sputtering method is preferably a magnetron sputtering method.

In the present invention, the conductive layer may be formed by a vacuum evaporation method, including: and placing the material subjected to surface treatment in a vacuum plating chamber, melting and evaporating metal in a metal evaporation chamber at high temperature, and finally forming a conductive layer by the evaporated metal through a cooling system in the vacuum plating chamber. The thickness of the conductive layer is preferably 0.01 to 1. Mu.m, more preferably 0.05 to 0.1. Mu.m. The conductive layer may be selected from a metal material having conductive properties such as copper, aluminum, silver, and the like.

In the present invention, the first conductive layer may be prepared by a magnetron sputtering method, and then the second conductive layer may be prepared by an electroplating method. Comprising the following steps: placing the material subjected to surface treatment in a vacuum plating chamber, introducing argon, plating a first conductive layer of 10-200nm by adopting a magnetron sputtering method, and then forming a second conductive layer on the surface of the first conductive layer by adopting electroplating, wherein the first conductive layer and the second conductive layer jointly form a composite conductive layer. The thickness of the first conductive layer is preferably 10 to 200nm, more preferably 20 to 100nm, and the first conductive layer is preferably a metal such as copper, silver, aluminum, or the like, and may be a metal oxide (nitride): in (In) ₂ O ₃ 、SnO ₂ ZnO, cdO, tiN, doped oxide: in (In) ₂ O ₃ :Sn(ITO)、ZnO:In(IZO)、ZnO:Ga(GZO)ZnO:Al(AZO)、SnO ₂ F, tiO2 Ta, mixed oxide: in (In) ₂ O ₃ -ZnO、CdIn ₂ O ₄ 、Cd ₂ SnO ₄ 、Zn ₂ SnO ₄ Etc. After the first conductive layer is prepared, a second conductive layer can be prepared on the surface of the first conductive layer by using an electroplating method, and the material of the second conductive layer is copper or aluminum. The total thickness of the first conductive layer and the second conductive layer is 0.01 to 1 μm, more preferably 0.05 to 0.1 μm.

The preparation method comprises the following steps:

step 1: a flexible base layer is selected.

For example, polyethylene terephthalate (PET), polyimide (PI), oriented polypropylene (OPP), etc. are selected. The thickness of the polymer flexible material film is preferably 0.5 to 10. Mu.m, more preferably 1 to 3. Mu.m.

Step 2: flexible base layer preamble processing: the flexible base layer is corona treated.

Step 3: and (3) carrying out laser drilling on the flexible base layer to form a plurality of micropores.

Step 4: coating a bonding coating on the surfaces of the micropore holes and the flexible base layer, and primarily coating the bonding coating according to the micropore diameter;

step 4: and uniformly coating the coating on the surface of the flexible base layer and in the micropore holes again, so that the micropore holes are completely filled with the bonding coating, and drying at 100-140 ℃.

Step 5: and (3) manufacturing a conductive layer with the thickness of 0.01-1 mu m on the surface.

Examples are magnetron sputtering and electroplating. Placing the flexible base layer coated with the bonding coating in a magnetron sputtering chamber, and reducing the vacuum degree to 3×10 under argon (and reaction gas) environment ^-1 And (3) plating a film on the nonmetallic material under Pa, wherein the argon flow is set to be 100-180Sccm, the plating time is set according to the film system and the film thickness requirement, and a copper conductive layer is plated on the surface. After the plating layer is formed, plating is performed in an electroless plating solution containing water, a copper plating material, or the like, and a plated conductive layer is formed on the surface of the copper conductive layer formed by magnetron sputtering.

The test of the invention:

porosity detection of bond coat filled microporous pores:

the pore size distribution was estimated by low temperature liquid nitrogen adsorption (LTNA) based on capillary condensation of nitrogen in the critical state. And filling the flexible base layer in the adhesive layer, drying to form a film, and obtaining the porosity of the flexible base layer with the bonding material after performing a pressure tension fixing test.

Peel strength test of bond coat:

the test was performed using the GBT 2792-2014 method.

After the surface of the flexible base layer and the microporous pores were coated, the above criteria were used to test to obtain the peel strength between the bond coating and the flexible base layer.

In the peel strength test, intermediate samples with a flexible base layer and a bond coat, and finished current collector samples were prepared.

Observation of test results:

for intermediate samples, peel strength values between the flexible base layer and the bond coat can be obtained directly.

For finished samples, peel strength values between the bond coat and the conductive layer are difficult to obtain directly. Thus, for finished samples, the bond integrity of the bond coat to the conductive layer under peel-off conditions needs to be observed.

In the invention, taking a photo of the stripped surface containing the conductive layer after stripping, and measuring the sum of the length values of the stripping surface coating; a ratio of the sum of the shed length values to the total test length of the current collector is obtained and used to characterize the ratio of shed length to total length. The ratio is a percentage ratio used to measure the bonding properties of the bond coat to the conductive layer. In the invention, binding force exists between the bonding coating and the flexible base layer and between the bonding coating and the conductive layer; in peel strength experiments, the bond coat was destroyed regardless of the amount of bond. In the invention, the service life of the conductive layer needs to be prolonged, the conductive layer is expected to be ensured to be intact as much as possible, and the bonding force between the bonding coating and the conductive layer is expected to be smaller than the bonding force between the bonding coating and the flexible base layer. The ratio of the stripped length to the total length characterizes this property to some extent. In general, a smaller ratio means that, during use, even if the conductive layer is detached, the conductive layer is separated from the flexible base layer first, so that the final detachment of the conductive layer is delayed.

Use of test

The binding force does not mean that the current collector has an excellent use effect in use under the peel test condition. The current collector manufactured according to the method of the present invention is manufactured into a lithium ion secondary electrode, and the cycle is 50 times, 100 times and 200 times.

Example 1

1. Polyethylene terephthalate is selected as the flexible base layer. The thickness of the flexible material film was 2.0 μm.

2. And arranging micropores on the surface of the flexible base layer in a laser drilling mode, wherein the diameter of the micropores is 0.5 mu m, the depth of the micropores is 1.0 mu m, and the surface area of the micropores accounts for 30% of the surface area of the flexible base layer.

2. The flexible base layer is corona treated.

3. And (3) coating polyacrylate on the surface of the flexible base layer and in the micropore pores, and drying at 125 ℃ until the solvent is completely evaporated. The polyacrylate completely fills the microporous pores, resulting in a coating thickness of 1 μm.

4. Placing the flexible base layer coated with the bonding coating in a magnetron sputtering chamber, and reducing the vacuum degree to 3×10 under argon environment ^-1 Pa or less, first, a 40nm copper conductive layer is plated on the surface. After the plating layer is formed, electroplating is performed in an electroplating solution containing water, a copper plating material, and the like, and an electroplated conductive layer is formed on the surface of the copper conductive layer formed by magnetron sputtering. The total thickness of the electroplated conductive layer was 1.2 μm.

Example 2

2. Micropores are arranged on the surface of the flexible base layer in a laser drilling mode, the diameter of each micropore is 0.5 mu m, the depth of each micropore is 2.0 mu m, each micropore penetrates through the flexible base layer, and the surface area of each micropore accounts for 40% of the surface area of the flexible base layer.

2. The flexible base layer is corona treated.

3. The surface of the flexible base layer and the inside of the micropore pores are coated with modified polyolefin resin, dried for 1min at the temperature of 100 ℃, then coated with ethylene-acrylic acid copolymer, and dried at the temperature of 120 ℃ until the solvent is completely evaporated, thus obtaining the coating with the single-layer thickness of 1 mu m. Wherein the mass ratio of the coated polyolefin resin to the ethylene-acrylic acid copolymer is 4:6.

4. placing the flexible base layer coated with the bonding coating in a magnetron sputtering chamber, and reducing the vacuum degree to 3×10 under argon environment ^-1 Pa or less, first, a 40nm copper conductive layer is plated on the surface. After the plating layer is formed, electroplating is performed in an electroplating solution containing water, a copper plating material, and the like, and an electroplated conductive layer is formed on the surface of the copper conductive layer formed by magnetron sputtering. The total thickness of the electroplated conductive layer was 1.0 μm.

Example 3

1. Polyimide is selected as the flexible base layer. The thickness of the flexible material film was 1.8 μm.

2. Micropores are arranged on the surface of the flexible base layer in a laser drilling mode, the diameter of each micropore is 2.0 mu m, the depth of each micropore is 2.0 mu m, each micropore penetrates through the flexible base layer, and the surface area of each micropore accounts for 35% of the surface area of the flexible base layer.

3. The flexible base layer is corona treated.

4. The surface of the flexible base layer and the inside of the micropore are coated with modified polyolefin resin, the modified polyolefin resin is dried at the temperature of 100 ℃ for 1min, the thickness of the bonding coating on the inner surface of the micropore is measured by a laser measurement method, then the ethylene-acrylic acid copolymer is coated in an electrostatic coating mode, so that the micropore is completely filled, then the ethylene-acrylic acid copolymer is continuously coated on the surface of the flexible base layer, and the modified polyolefin resin is dried at the temperature of 120 ℃ until the solvent is completely evaporated, thus obtaining the coating with the single-layer thickness of 1 mu m. Wherein the mass ratio of the coated polyolefin resin to the ethylene-acrylic acid copolymer is 3:7.

5. the flexible base layer coated by the bonding coating is arranged in a magnetron sputtering chamber, and the vacuum degree is reduced to 3 multiplied by 10 under the environment of argon and reaction gas ^-1 Pa or lower, plating 30nm In on the surface ₂ O ₃ Sn (ITO). After the plating layer is formed, electroplating is performed in an electroplating solution containing water, a copper plating material, and the like, and an electroplated conductive layer is formed on the surface of the copper conductive layer formed by magnetron sputtering. The total thickness of the electroplated conductive layer was 0.8 μm.

Example 4

2. Micropores are arranged on the surface of the flexible base layer in a laser drilling mode, the diameter of each micropore is 2.0 mu m, the depth of each micropore is 1.0 mu m, the upper surface of the flexible base layer is in a micropore shape, the surface area of each micropore accounts for 15% of the surface area of the flexible base layer, and the lower surface of each micropore is a smooth plane.

3. The flexible base layer is corona treated.

4. After filling the microporous pores with the polyacrylic resin, the surface of the flexible base layer is coated with the polyacrylic resin, dried for 1min at the temperature of 100 ℃, then coated with polyacrylate, and dried at the temperature of 130 ℃ until the solvent is completely evaporated, thus obtaining the coating with the single-layer thickness of 1 mu m. Wherein the mass ratio of the coated polyacrylic resin to the polyacrylate is 4:6.

5. placing the flexible base layer coated with the bonding coating in a magnetron sputtering chamber, and reducing the vacuum degree to 3×10 under the environment of argon and reaction gas ^-1 Pa or less, and plating Al of 30nm on the surface. After the plating layer is formed, electroplating is performed in an electroplating solution containing water, a copper plating material, and the like, and an electroplated conductive layer is formed on the surface of the copper conductive layer formed by magnetron sputtering. The total thickness of the electroplated conductive layer was 1.4 μm.

Example 5

3. The flexible base layer is corona treated.

4. The surface of the flexible base layer is coated with polyacrylic resin, dried for 1min at the temperature of 100 ℃, then coated with polyacrylate, and dried at the temperature of 130 ℃ until the solvent is completely evaporated, so that the coating with the single-layer thickness of 1 mu m is obtained. Wherein the mass ratio of the coated polyacrylic resin to the polyacrylate is 2:8.

5. and placing the flexible base layer coated by the bonding coating in a vacuum plating chamber, melting and evaporating Al metal in the metal evaporation chamber at high temperature, and finally forming an Al evaporation layer after the evaporated metal passes through a cooling system in the vacuum plating chamber. The total thickness of the aluminum layer was 1.2 μm.

Comparative example 1

1. Polyimide is selected as the flexible base layer. The thickness of the flexible material film was 2 μm.

2. The flexible base layer is corona treated.

3. And placing the flexible base layer coated by the bonding coating in a vacuum plating chamber, melting and evaporating Cu metal in the metal evaporation chamber at high temperature, and finally forming a Cu evaporation layer after the evaporated metal passes through a cooling system in the vacuum plating chamber. The total copper thickness was 2.0 μm.

Comparative example 2

2. The flexible base layer is corona treated.

3. The surface of the flexible basic layer is coated with polyacrylic resin, then polyacrylate is coated, and the coating is dried at 130 ℃ until the solvent is completely evaporated, so that the coating with the single-layer thickness of 1 mu m is obtained. Wherein the mass ratio of the coated polyacrylic resin to the polyacrylate is 6:4.

4. and placing the flexible base layer coated by the bonding coating in a vacuum plating chamber, melting and evaporating Cu metal in the metal evaporation chamber at high temperature, and finally forming a Cu evaporation layer after the evaporated metal passes through a cooling system in the vacuum plating chamber. The total copper thickness was 1.5 μm.

Comparative example 3

2. The flexible base layer is corona treated.

4. and placing the flexible base layer coated by the bonding coating in a vacuum plating chamber, melting and evaporating Al metal in the metal evaporation chamber at high temperature, and finally forming an Al evaporation layer after the evaporated metal passes through a cooling system in the vacuum plating chamber. The total thickness of the aluminum was 1.8. Mu.m.

The intermediate and final samples obtained in the above examples were subjected to peel tests, and the test results are shown in table 1 below:

sequence number	Intermediate sample peel force	Stripping ratio of finished sample
			Example 1	5.1	34
Example 2	6.3	17
			Example 3	5.9	23
Example 4	5.9	21
			Example 5	5.4	24
Comparative example 1	Without any means for	66
			Comparative example 2	5.1	51
Comparative example 3	5.2	63

The peel force unit in the above table is N/25mm; the peeling ratio is the ratio of the length of the separation between the adhesive layer and the conductive layer along the peeling direction after the finished sample is peeled to the total length of the finished sample, and is expressed in%. In the above table, three samples were prepared for each sample, and the average value was taken after the test.

As can be seen from the above table, the finished current collector sample prepared by the method has significantly lower stripping ratio. This means that the current collector can maintain the integrity of the conductive layer as much as possible during use; maintaining the integrity of the conductive layer prevents battery failure due to the release of the conductive layer.

It was also found that the effect of the finished test sample obtained by evaporation was inferior to the performance of the test sample obtained by electroplating after magnetron sputtering. Preliminary studies have considered that samples obtained by evaporation have poor depositability; the magnetron sputtering layer has strong bonding force on nonmetal, and the bonding force between the electroplated layer and the magnetron sputtering layer is relatively strong, so that the effect is better.

Meanwhile, the cost of the evaporation method is higher than that of the method. The raw material cost and the preparation cost are relatively high. The evaporation method needs more relatively expensive raw materials and consumes more energy; in the invention, the magnetron sputtering layer is thinner, and the electroplating method is adopted later, so that the cost is reduced and the energy consumption is lower.

After obtaining the finished samples of the above examples and comparative examples, the finished samples were made into test lithium batteries for testing. The lithium battery is provided with an anode, a cathode, a diaphragm and electrolyte which are opposite to each other; high-voltage charge and rapid discharge are adopted, and the cycle is 50 times, 100 times and 200 times; the charge-discharge efficiency was recorded. The above test cells were identical except for the current collector material.

After 200 cycles, the test lithium battery was disassembled, and after washing, the positive electrode and the negative electrode were observed.

The above test results are shown in table 2 below:

in table 2 above, efficiency refers to the ratio of output power to input power.

As can be seen from the above table, the charge and discharge efficiency of the battery significantly decreases as the number of cycles increases. In the initial stage, the difference of charge and discharge efficiency is small; the more the circulation times are, the more excellent performance can be represented by the current collector prepared by the method.

After the lithium batteries in the above examples were disassembled, the surfaces of the positive and negative electrodes were observed by washing, and it was found that the defects on the surfaces of comparative examples 1 to 3 were significantly large compared with examples 1 to 5.

The lithium battery is a device with experimental performance, and the existing secondary battery using copper foil as a current collector needs to maintain certain charge and discharge efficiency after repeated circulation (more than or equal to 500 times) and high-temperature storage (more than or equal to 85 ℃); the composite current collector has the problems that a metal layer falls off, the charge and discharge efficiency is further rapidly attenuated, and the like.

In the process of charging and discharging the battery, lithium ions are repeatedly released and intercalated from the surface of the electrode, and meanwhile, the whole battery has a thermal effect, so that the anode and the cathode can be invalid. An important aspect of failure is represented by the positive and negative electrode active materials falling off the surface of the current collector, which is unavoidable with the increase of the number of cycles. In the present invention, the falling-off condition of the comparative example was more serious.

In the invention, as the stripping percentage between the bonding coating and the conductive layer is less than 25%, the bonding coating of the current collector and the conductive layer are combined relatively well under the action of stripping force, so that the safety of the conductive layer in the subsequent use process is ensured. The reason why the percentage of peeling between the bond coat and the conductive layer is smaller is that the peeling strength between the bond coat and the flexible base layer is smaller than the peeling strength between the bond coat and the conductive layer.

In the present invention, the bond coat includes a first bond coat, a transition layer, and a second bond coat. The first bonding coating and the second bonding coating are obtained by coating gel, and after the first bonding coating gel is coated, the first bonding coating gel is dried for a short time, so that the first bonding coating forms an incompletely dried homogeneous tissue; subsequently applying a gel of a second bond coat; after the coating is completed, the solvent is dried until the solvent is completely volatilized. In this way, the first bond coat and the second bond coat have both different tissue properties and a transition layer between the two coats that is tightly fused together. The first bond coat and the second bond coat are different in terms of drying, and therefore, there is a certain force between each other, which is manifested in the second bond coat as a change in tension.

After the bonding coating is formed, the surface of the second bonding coating is subjected to magnetron sputtering to plate the first conductive layer. The first conductive layer which is plated by magnetron sputtering is combined with the surface of the second bonding coating, on one hand, the combination property is good due to the characteristic of the magnetron sputtering, and on the other hand, the tension of the second bonding coating is changed due to the acting force of the first bonding coating and the second bonding coating, so that the combination property of the whole coating and the conductive layer is more excellent.

The total thickness of the bond coat is 0.2 μm to 2 μm. The second bond coat thickness is greater than the first bond coat thickness, which is controlled by controlling the amount of applied bond material. After drying, a coating of the target thickness is formed.

In the invention, the conductive layer separation ratio is lower when the finished product sample is subjected to peeling test. A lower proportion of conductive layer separation means better retention with the bond coat. This can maintain the life of the positive and negative electrodes as long as possible during charge and discharge.

The foregoing is merely a specific embodiment of the invention and other modifications and variations can be made by those skilled in the art in light of the above teachings. It is to be understood by persons skilled in the art that the foregoing detailed description is provided for the purpose of illustrating the invention more fully, and that the scope of the invention is defined by the appended claims.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Claims

1. A multilayer composite current collector, characterized in that it has a multilayer structure comprising a flexible base layer, micropores, a bonding coating and a conductive layer; the flexible substrate layer is provided with a plurality of micropores; the bonding coating is arranged on the surface of the flexible base layer and is filled in micropores of the flexible base layer; the conductive layer is disposed on at least one surface of the flexible base layer; the bond coat is disposed between the flexible base layer and the conductive layer.

2. The multilayer composite current collector of claim 1, wherein said micropores are distributed on at least one surface of the flexible substrate layer.

3. The multilayer composite current collector of claim 1, wherein the micropores have a diameter of 0.5 to 2 μm.

4. The multilayer composite current collector of claim 1, wherein the surface of the flexible base layer with micropores has a surface area of greater than 40%, preferably greater than 35%, preferably about 30%, preferably greater than 25% of the surface area of the flexible base layer.

5. The multilayer composite current collector of claim 1, wherein the bond coating forms a film within the micropores and on the surface of the flexible base layer, the micropores are in a closed filling shape, and the overall porosity of the flexible base layer after application of the bond coating is less than 0.1%.

6. The multilayer composite current collector of claim 1, wherein the flexible base layer has a thickness of 0.5-10 μm.

7. The multilayer composite current collector of claim 1, wherein the bond coat layer has a thickness of 0.2-2 μm.

8. The multilayer composite current collector of claim 1, wherein said bond coat is applied at least twice, said bond coat forming a first bond coat, a second bond coat; a transition layer is formed between the first bonding coating and the second bonding coating.

9. The multilayer composite current collector of claim 1, wherein said conductive layer comprises at least two layers, a first conductive layer bonded to said bond coat and a second conductive layer bonded to said first conductive layer; the first conductive layer is prepared by a magnetron sputtering method, and the second conductive layer is prepared by an electroplating method; the thickness of the conductive layer is 0.01-1 μm.

10. The multilayer composite current collector of claim 1, wherein the peel strength between the bond coat and the flexible base layer is less than the peel strength between the bond coat and the conductive layer.

11. A method for producing a multilayer composite current collector according to claim 1 to 10, characterized in that,

providing a flexible base layer;

a plurality of micropores are arranged on the flexible basic layer;

coating a bonding coating on the flexible base layer and in the micropores;

manufacturing a conductive layer on the bonding coating;

12. The method for preparing a multi-layered composite current collector according to claim 11, wherein,

wherein, firstly, preparing a first conductive layer on the bonding coating by adopting a magnetron sputtering method; and then preparing a second conductive layer on the first conductive layer by adopting an electroplating method.

13. A battery comprises electrode plates and a diaphragm arranged between the two electrode plates, and is characterized in that,

the pole piece comprising a multilayer composite current collector obtained according to any one of claims 1 to 12.

14. An electronic device produced from the battery of claim 13.