Manufacturing method of lithium battery negative electrode composite current collector

Abstract

The invention discloses a manufacturing method of a lithium battery negative electrode composite current collector, which comprises the following steps: (1) preparing a carrier film: selecting a BOPET (Biaxially Oriented Polyethylene Terephthalate) protective film with proper thickness, and coating a release agent on the surface of the protective film, so that the surface stripping force is 10-20g / cm; (2) generating a copper layer: generating an ultra-thin copper foil on the surface of the cathode roller in an electroplating manner on the surface of the cathode roller with the surface roughness of less than 0.1 mu m and ultra-smooth finish; (3) stripping a copper layer: continuously stripping the ultrathin copper foil from the cathode roller through a carrier film; (4) generating a high-molecular material core layer: generating the high-molecular material core layer by adopting a precise crack coating mode; and (5) compounding and curing: simultaneously compounding the copper layers on the two carrier films and the two sides of the core layer material, curing, shaping, stripping the carrier films on the two sides, and trimming to obtain the composite current collector. The high-quality composite current collector is produced with high efficiency by selecting a proper process, the high-quality composite current collector is high in peel strength, excellent in mechanical property, good in toughness and ductility, high in safety and thinner in copper foil, and a battery using the high-quality composite current collector has higher energy density.

Description

Technical Field

[0001] The present invention relates to a battery current collector, and in particular to the production of a lithium battery negative electrode composite current collector. Background Art

[0002] The current collector is a crucial component of new energy batteries. Currently, higher performance, especially energy density, is being demanded of new energy batteries. Higher energy density translates to lighter batteries, necessitating a reduction in the thickness and weight of the current collector.

[0003] Composite copper foil current collectors are currently the mainstream. There are two methods for manufacturing composite copper foil current collectors: a one-step method and a two-step method. The one-step method uses a pre-made BOPP (biaxially oriented polypropylene film) / BOPET (biaxially oriented polyester film) substrate and gradually forms a 1μm thick copper foil on both sides of the substrate through chemical water electroplating. The two-step method uses an existing BOPP / BOPET substrate and thickens it through magnetron sputtering followed by water electroplating, forming a 1μm thick copper foil on both sides of the substrate.

[0004] Existing methods rely solely on existing ultra-thin BOPP or BOPET substrates. Copper foil layers are formed on both sides of the substrate through various processes, creating a composite current collector with a "metal-PP / PET-metal" sandwich structure. In this case, the thickness uniformity and mechanical properties of the core material significantly impact the mechanical properties of the resulting composite current collector.

[0005] In addition, the existing methods have the following shortcomings:

[0006] (1) The core layer material has few surface functional groups, the bonding strength between the metal layer and the substrate (BOPP / BOPET) is insufficient, and the copper layer is prone to falling off during use;

[0007] (2) The existing route requires a vacuum environment, and the product must be repeatedly coated, plated, wound, conveyed and stretched, and dried at high temperature in an acidic or alkaline environment, resulting in low production efficiency (speed), yield (trimming) and yield rate;

[0008] (3) The thickness of the core layer substrate (BOPP / BOPET) is limited. The thickness of the intermediate substrate currently used is above 4μm, and there are many suppliers. It is difficult to reduce the cost when further thinning.

[0009] (4) The electrochemical properties and acid and alkali corrosion resistance of the core layer substrate BOPET film need to be improved, while the high temperature resistance of the substrate BOPP film needs to be improved. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for manufacturing a composite current collector for the negative electrode of a lithium battery. By designing a suitable process and selecting a suitable polymer material core layer, a high-density ultra-thin copper layer is obtained on both sides of the core layer through a one-step method, thereby efficiently producing high-quality composite current collectors.

[0011] The method provided by the present invention comprises the following steps:

[0012] (1) Prepare the carrier film: Select a BOPET protective film of appropriate thickness and apply a release agent on the surface of the protective film to make the surface peeling force between 10 and 20 g / cm;

[0013] (2) Generating a copper layer: generating an ultra-thin copper foil on the surface of a cathode roller having an ultra-smooth finish and a surface roughness of less than 0.1 μm by electroplating;

[0014] (3) Stripping the copper layer: Continuously peeling the ultra-thin copper foil from the cathode roller through the carrier film;

[0015] (4) Generating a polymer core layer: using a precise gap coating method to generate a polymer core layer;

[0016] (5) Composite curing: The copper layers on the two carrier films are composited with both sides of the core layer material at the same time, cured and solidified, and the carrier films on both sides are peeled off and trimmed to obtain a composite current collector.

[0017] The present invention also aims to provide a lithium battery negative electrode composite current collector, which includes a core layer as an intermediate layer and ultra-thin copper foil on both sides of the core layer, wherein the core layer has a thickness of 4 to 6 μm and the ultra-thin copper foil has a thickness of 1 to 2 μm.

[0018] The method for manufacturing a composite current collector for a lithium battery negative electrode provided by the present invention has the following beneficial effects:

[0019] (1) The requirements for the carrier film are reduced, and a relatively thick carrier film can be used, which reduces production requirements and costs;

[0020] (2) The release agent requirement is low, and the surface peeling force can be 10-20g / cm, which further reduces the production requirements;

[0021] (3) The core layer material selection range is wider, such as polyester, polyurethane, polyolefin, epoxy or various modified polymer materials;

[0022] (4) Due to the use of a precise gap coating method, the core layer material can be customized. The core layer material of the obtained current collector has good adhesion to the copper foil layer, and the core layer and the copper foil are not easy to peel off. At the same time, the current collector has excellent electrolyte resistance and stable electrochemical properties, and the battery using it has good cycle performance;

[0023] (5) By adopting a precise gap coating method, the core layer thickness can be precisely controlled within 4-6 μm, with a thickness tolerance within the range of + / - 5%, uniform thickness, and stable mechanical properties, especially good toughness and ductility, can be provided at the lowest possible thickness;

[0024] (6) The production process of the composite current collector is simple. The copper foil is generated in one step by electroplating, and the core layer is generated in one step by precision gap coating. The production process is continuous, the electroplating process and equipment are simplified, the yield and yield of the product are significantly improved, and the product quality consistency and stability are significantly improved;

[0025] (7) The carrier film can be reused multiple times, reducing production costs;

[0026] (8) By selecting a suitable process, high-quality composite current collectors can be produced with high efficiency, which have high peel strength, excellent mechanical properties, good toughness and ductility, high safety, thinner copper foil, and batteries using them have higher energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1(A) shows a preferred embodiment of a method for manufacturing a composite current collector for a negative electrode of a lithium battery according to the present invention;

[0028] FIG1(B) shows a preferred embodiment of the method for manufacturing a composite current collector for a negative electrode of a lithium battery according to the present invention;

[0029] Figure 2 A schematic structural diagram of the composite current collector of the present invention is shown. DETAILED DESCRIPTION

[0030] The present invention will be further described below through specific embodiments to make the features and advantages of the present invention more clear. However, these specific embodiments are only non-limiting descriptions and explanations of the present invention and do not constitute any limitation on the scope of protection of the present invention.

[0031] In a preferred embodiment of the present invention, a BOPET protective film of suitable thickness, such as a BOPET protective film of about 25 μm in thickness, can be selected as the carrier film. Such a protective film is sufficient to provide appropriate protection and subsequent desired peelability after the release agent is coated on the surface.

[0032] Furthermore, there is no particular restriction on the release agent, and a component-free migration release agent, such as an alkyl or polyethyleneimine modified polymer copolymer, can be used to make the surface peeling force between 10 and 20 g / cm, which enables the carrier film to continuously and stably peel the ultra-thin copper foil from the cathode roller, and easily separate the carrier film after subsequent curing and solidification with the core layer without causing separation of the copper foil from the core layer.

[0033] There is no particular limitation on the coating process of the release agent, and any of slit coating, blade coating, micro-gap coating, and roller transfer coating can be used.

[0034] In a preferred embodiment of the present invention, an ultra-thin copper foil is electroplated onto the surface of a cathode roller with an ultra-smooth surface roughness of less than 0.1 μm. This ultra-thin copper foil can be easily peeled off the carrier film without damage during the subsequent stripping process and can be easily bonded and cured onto the core layer.

[0035] The thickness of the resulting copper layer is preferably 1 to 2 μm. Within this thickness range, the copper foil can maintain ideal ductility and strength while providing higher energy density and significantly reducing production costs.

[0036] For electroplating, a copper sulfate solution is preferably used as the plating solution, and more preferably, an appropriate amount of sulfuric acid, a chloride such as hydrochloric acid, and additives such as polyethylene glycol (PEG), sulfonates, and / or polyether thiols are added thereto. Alternatively, an appropriate amount of sulfuric acid, a chloride such as hydrochloric acid, and additives such as polyethylene glycol, collagen, and / or sulfonates are added thereto. The ultra-thin copper foil formed by electroplating has a uniform and stable metal crystal structure, high density, uniform thickness, high tensile strength, high elongation, and stable electrochemical properties.

[0037] In a preferred embodiment of the present invention, an ultra-thin copper foil with a thickness of 1 to 2 μm is continuously and completely peeled off from the cathode roller through a carrier film, and the copper layer is pasted together with the carrier film and subjected to cleaning, anti-oxidation and passivation treatments in a post-processing machine.

[0038] In a more preferred embodiment, the carrier film has a running speed of 1 to 5 m / min.

[0039] Next, on the laminating machine, the two copper layers and carrier films are pasted together, with the copper layer facing the core layer, and compounded at the same time. Then they are put into the oven for curing and solidification. After peeling off the carrier film and cutting the edges, the composite current collector can be obtained.

[0040] In the present invention, a polymer core layer is formed as the core layer by a precision slit coating method.

[0041] In a preferred embodiment, at least one of epoxies, polyolefins, polyesters, or polyurethanes having stable electrochemical properties, resistance to electrolyte corrosion, and strong bonding with metal materials is used as the core layer material. Examples of epoxy core layer materials include glycidyl ether epoxy resins, such as glycidyl diether epoxy resin (EGDE), propylene glycol glycidyl diether epoxy resin (PGDE), and bisether glycidyl diether epoxy resin (BDGE).

[0042] The core layer material is precisely controlled to have a width of 2 to 6 μm, especially 4 to 6 μm, through a precision slit coating method to generate a core layer with a thickness of 2 to 6 μm, especially 4 to 6 μm. The obtained core layer has stable electrochemical properties, resistance to electrolyte corrosion, and strong bonding with metal materials. It not only provides the composite current collector with stable electrolyte resistance, stable electrochemical properties, and higher bonding with copper foil, thereby providing high safety, but also has high peel strength.

[0043] At the same time, since the composite current collector of the present invention has good electrolyte resistance, the service life of the battery can be increased.

[0044] Example

[0045] Example 1

[0046] (1) A 25 μm thick general-purpose BOPET protective film was selected and polyethyleneimine was coated on its surface to obtain a carrier film;

[0047] (2) A copper foil layer with a thickness of 2 μm was prepared by electroplating on an ultra-smooth cathode roller (surface roughness Ra of 0.08-0.1 μm); the plating solution formula was as follows: copper ions at a concentration of 30 g / L, hydrochloric acid at a concentration of 20 ppm, sulfate ions at a concentration of 200 g / L, collagen at a concentration of 100 ppm, PEG-600 at a concentration of 30 ppm, and sodium sulfonate at a concentration of 30 ppm; the plating solution temperature was 50 °C; the electroplating parameters were set as follows: current density of 30 A / dm 2 ; Line speed is 2.6m / min; The diameter of the titanium roller is 500mm and the roller surface width is 350mm;

[0048] (3) After the carrier film is pressed by the pressure roller, the copper foil is taken away from the cathode roller. The thickness of the copper foil is about 2 μm. The carrier film travel speed is consistent with the linear speed of step (2), which is 2.6 m / min.

[0049] (4) Using a precise gap extrusion lamination method on a laminating machine with a pressure of 0.5 MPa, two layers of carrier films with copper layers are laminated together through glycidyl diether epoxy resin (EGDE);

[0050] (5) The composite film enters the oven and is cured and shaped at 150°C for 40 seconds, with the core layer being approximately 4 μm;

[0051] (6) On a stripping machine, the carrier film is stripped and then trimmed to obtain a composite current collector.

[0052] Example 2

[0053] The composite current collector was obtained in a similar manner to Example 1, except that the current density in step (2) was 36 A / dm 2; Line speed is 3.1m / min.

[0054] Example 3

[0055] A composite current collector was obtained in a manner similar to Example 1, except that in step (4), the amount of glycidyl ether epoxy resin was reduced, and in step (5), a core layer of about 3 μm was obtained.

[0056] Example 4

[0057] A composite current collector was obtained in a manner similar to Example 1, except that in step (4), the amount of glycidyl ether epoxy resin was increased, and in step (5), a core layer of about 5 μm was obtained.

[0058] Example 5

[0059] A composite current collector was obtained in a manner similar to Example 1, except that in step (2), the electroplating solution formula was: copper ions at a concentration of 30 g / L, hydrochloric acid at a concentration of 20 ppm, sulfate ions at a concentration of 200 g / L, trithiopolythiol at a concentration of 100 ppm, PEG-600 at a concentration of 30 ppm, and sodium sulfonate at a concentration of 30 ppm.

[0060] Test example

[0061] 1. Mechanical properties test: The results are shown in Table 1 below:

[0062] Room temperature tensile strength (MPa) Elongation at room temperature Example 1 211 8.6％ Example 2 206 8.2％ Example 3 200 7.1％ Example 4 208 7.0％ Example 5 209 8.3％

[0063] 2. Composite current collector test: Test of the bonding strength between the copper foil and the core layer: According to GB / T 3923.1-1997, the composite current collectors of Examples 1-5 and the commercially available composite current collectors as a control were cut into small strips 1 cm wide. The bonding strength between the copper foil and the core layer was tested using a tensile composite current collector tester. The results are shown in the following table:

[0064] 3. Density reduction rate: Regarding the density reduction rate of the composite current collectors 1 to 5 and the control composite current collector sample examples, the density reduction rate of Examples 1 to 5 and the control sample was calculated using a single layer of copper foil with a thickness of 8 μm as the reference current collector. The density of copper is 8.9 g / cm 3 , the core density is 1.3g / cm 3 .

[0065] Composite current collector density reduction rate = (density of reference copper foil current collector - density of composite current collector in example or control) / density of reference copper foil current collector × 100%

[0066] For example, in Example 1, the density reduction rate is: [8.9-(2*8.9*2+4*1.3) / 8] / 8.9*100%=42%. The results are shown in the following table:

[0067]

[0068] It can be seen that the density of the composite current collector of the present invention is much smaller than that of the copper foil current collector. When the current collector has the same mass, the composite current collector of the present invention has a larger volume and more units that can store charge, which is beneficial to improving the energy density of the battery and has good safety.

[0069] The present invention has been described in detail above with reference to specific embodiments. However, these descriptions are not to be construed as limiting the present invention. It will be appreciated by those skilled in the art that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, and all of these fall within the scope of the present invention.

Claims

1. A method for manufacturing a composite current collector for a lithium battery negative electrode, comprising the following steps: (1) Prepare the carrier film: Select a BOPET protective film of appropriate thickness and apply a release agent on the surface of the protective film to make the surface peeling force between 10 and 20 g / cm; (2) Generating a copper layer: generating an ultra-thin copper foil on the surface of a cathode roller having an ultra-smooth finish and a surface roughness of less than 0.1 μm by electroplating; (3) Stripping the copper layer: Continuously peeling the ultra-thin copper foil from the cathode roller through the carrier film; (4) Generating a polymer core layer: using a precise gap coating method to generate a polymer core layer; (5) Composite curing: The copper layers on the two carrier films are composited with both sides of the core layer material at the same time, cured and solidified, and the carrier films on both sides are peeled off and trimmed to obtain a composite current collector.

2. The method according to claim 1, wherein As the carrier film, a BOPET protective film having a thickness of 25 μm was used.

3. The method according to claim 1, wherein As the release agent, a non-component migration type release agent, such as an alkyl or polyethyleneimine modified high molecular copolymer, is used.

4. The method according to claim 1, wherein In (2) generating the copper layer, the thickness of the generated ultra-thin copper foil is 1 to 2 μm.

5. The method according to claim 1, wherein In (2) forming the copper layer, the electroplating solution is a copper sulfate solution to which sulfuric acid, chlorides such as hydrochloric acid, and additives such as polyethylene glycol (PEG), sulfonates and / or polyether thiols are added, or the electroplating solution is a copper sulfate solution to which sulfuric acid, chlorides such as hydrochloric acid, and additives such as polyethylene glycol, collagen, and / or sulfonates are added.

6. The method of claim 1, wherein: In (3) stripping the copper layer, the carrier film has a film travel speed of 1 to 5 m / min.

7. The method of claim 1, wherein: In (4) forming the polymer material core layer, the precision slit width is 2 to 6 μm, preferably 4 to 6 μm.

8. The method of claim 1, wherein: In (5) composite curing, two copper layers and carrier films are pasted together on a laminating machine, with the copper layer facing the core layer, and composited at the same time. Then, they are put into an oven for curing and shaping. After the carrier film is peeled off and the edges are cut, a composite current collector is obtained.

9. A lithium battery negative electrode composite current collector comprising a core layer as an intermediate layer and ultra-thin copper foils on both sides of the core layer, wherein: The thickness of the core layer is 2 to 6 μm, preferably 4 to 6 μm, and the thickness of the ultra-thin copper foil is 1 to 2 μm.

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