Preparation method of lithium-copper composite foil

Abstract

The invention discloses a preparation method of a lithium-copper composite foil, which comprises the following steps: S1, a lithium-based alloy is selected and rolled to form a lithium alloy foil, and the alloy element in the lithium-based alloy is at least one of magnesium, zinc or aluminum; s2, selecting a piece of copper foil as a supporting framework; and S3, the two pieces of lithium alloy foil and copper foil are stacked together according to the sequence of lithium alloy foil-copper foil-lithium alloy foil, the stacked pieces of lithium alloy foil and copper foil are placed in a roller press to be rolled, metallurgical bonding is formed between the copper foil and the lithium alloy foil, and the lithium-copper composite foil is obtained. The invention adopts release-film-free rolling preparation, aims to solve the problem that lithium metal is easy to stick to a roller due to high viscosity and needs to depend on a high-cost release film in the prior art, simplifies the preparation process of the composite foil, reduces the manufacturing cost, increases the mechanical strength of the lithium-copper alloy foil, reduces the thickness, improves the energy density of the battery, and further improves the product quality and reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery negative electrode materials, and particularly relates to a preparation process of a lithium-copper composite foil. BACKGROUND

[0002] With higher requirements for batteries in energy density and power density, use safety and portability, etc. Lithium metal is expected to be used as a negative electrode material for the next generation of high specific energy secondary batteries due to its high theoretical mass specific capacity, low electrochemical potential, close to the lowest solid density (light weight), and small atomic radius. Using an ultrathin lithium metal negative electrode to reduce the thickness of the lithium metal negative electrode can effectively improve the energy density of the battery, and among them, the lithium-copper composite foil has been widely used in the field of lithium metal batteries due to its stable electrode structure.

[0003] At present, in order to make the lithium-copper composite foil reach the target thickness, the mechanical rolling method is generally used in the production process. In the rolling process, due to the high adhesion of lithium metal, it is easy to adhere to the surface of the roller, and a release film needs to be wrapped to prevent adhesion. However, the use of the release film leads to the following problems: 1. The material cost of the release film is high, which significantly increases the production cost; 2. Additional steps of covering and uncovering the release film are needed in the preparation process, which increases the equipment investment and operation time; 3. In order to realize the smooth separation of the lithium-copper composite foil, a release film treated with silicone oil is usually used. Although silicone oil has low surface energy and good release performance, it can realize complete and damage-free peeling of the lithium-copper composite foil, but the residual silicone oil composition will adversely affect the battery performance, such as affecting the wettability of the electrolyte, the electrode contact resistance and the cycle stability, etc.

[0004] Therefore, how to solve the problem of sticking to the roller in the production and preparation of the lithium-copper composite foil, simplify the process flow and reduce the manufacturing cost is imminent. SUMMARY

[0005] The present application provides a preparation method of a lithium-copper composite foil, which is prepared by rolling without a release film, aiming to solve the problem in the prior art that lithium metal is easy to stick to the roller due to its high adhesion, and needs to rely on high-cost release film, simplify the preparation process of the composite foil, reduce the manufacturing cost, increase the mechanical strength of the lithium-copper alloy foil, reduce the thickness, improve the energy density of the battery, and further improve the product quality and reliability.

[0006] The technical scheme adopted by the present application to solve the above technical problems is as follows:

[0007] A preparation method of a lithium-copper composite foil, comprising the following steps:

[0008] S1, selecting a lithium-based alloy to be rolled into a lithium alloy foil, wherein the alloying element in the lithium-based alloy is at least one of magnesium, zinc or aluminum;

[0009] S2, selecting a copper foil as a supporting framework;

[0010] S3, stacking the two lithium alloy foils and the copper foil together in the order of lithium alloy foil-copper foil-lithium alloy foil, and placing them in a rolling machine for rolling, so that the copper foil and the lithium alloy foil form a metallurgical bond, thereby obtaining a lithium-copper composite foil.

[0011] Preferably, in the step S1, the mass percentage of the alloying element in the lithium-based alloy is 1-30wt%, preferably 5wt%, 8wt%, 10wt%, 15wt%, 20wt%.

[0012] Preferably, the lithium alloy foil prepared in the step S1 has a thickness of 10-40μm, preferably 15μm, 20μm, 25μm, 30μm, 35μm.

[0013] Preferably, the copper foil in the step S2 has a thickness of 5-20μm, preferably 5μm, 8μm, 10μm, 15μm.

[0014] Preferably, the copper foil in the step S2 is subjected to surface roughening or punching treatment.

[0015] Preferably, the copper foil in the step S2 is subjected to annealing treatment at 200-400℃, preferably 220℃, 250℃, 300℃, 350℃, before being stacked and rolled.

[0016] Preferably, in the step S3, the rolling conditions are as follows: temperature: 20-80℃, preferably 20℃, 25℃, 30℃, 40℃, 50℃, 60℃; pressure: 100-200MPa, preferably 120MPa, 150MPa, 180MPa; speed: 8-15m / min, preferably 10m / min, 12m / min, in an inert atmosphere or vacuum environment.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] 1. The present application uses low-viscosity lithium-based alloy (such as Li-Mg, Li-Zn, Li-Al, etc.) to replace traditional high-viscosity pure lithium material, and the alloying element content is 1-30wt%, which ensures that the alloy has low adhesion and high ionic conductivity, significantly reduces the adhesion tendency of the material to the roll surface, and reduces the dependence on release film from the source.

[0019] 2, The intermediate copper foil layer serves as a support framework to improve mechanical strength and provides an electronic conduction path, then the lithium alloy foil and the copper foil are stacked in a structure of "lithium alloy foil-copper foil-lithium alloy foil", and then metallurgical bonding is realized at the interface by controlling the pressure and the rolling speed at room temperature or medium temperature, that is, a firm connection is formed between the lithium alloy and the copper through interatomic diffusion and interface metal bonding, which not only improves the interface bonding strength, but also reduces the interface resistance, which is beneficial to the improvement of the rate performance and the cycle life of the subsequent battery.

[0020] 3, The lithium-copper composite foil obtained by the application has the advantages of smooth surface, high peeling strength and good electrical contact performance, the lithium alloy layer of the lithium-copper composite foil can inhibit dendrite growth, effectively improve the cycle performance and energy density, and is suitable for integrated application of current collector and negative material of the next generation high-energy-density battery (such as negative electrode-free lithium metal battery).

[0021] 4, The process of the application is simple, and the release film wrapping and peeling steps are omitted, which reduces equipment investment and working hours, and significantly improves production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0023] Figure 1 The macroscopic morphology of the lithium-copper composite foil in Example 2 of the present application;

[0024] Figure 2 The macroscopic morphology of the lithium-copper composite foil in Comparative Example 1 of the present application;

[0025] Figure 3 The bar chart of the peeling force between the lithium foil and the copper foil in Example 2 and Comparative Example 1 of the present application.

[0026] Figure 4 The charge-discharge cycle curve of the solid-state battery prepared by using the lithium-copper composite foil prepared in Example 2 and Comparative Example 1 of the present application as the negative electrode. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be described in detail below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, not all embodiments.

[0028] Example 1,

[0029] A preparation method of lithium-copper composite foil, comprising the following specific steps:

[0030] Lithium alloy foil preparation: high-purity lithium ingot and magnesium metal particles are mixed and smelted to obtain Li-5wt% Mg alloy, which is rolled into an upper lithium alloy foil (thickness 25 μm) and a lower lithium alloy foil (thickness 25 μm) after cooling;

[0031] Copper foil treatment: 5 μm copper foil is selected, first annealed at 300 ℃, then rough etched by HCl and nano-laser punched, with a pore diameter of about 20 μm and a pore density of about 104 / cm 2 ;

[0032] Laminate assembly and rolling process: stacked in the mode of "lithium alloy foil-punched copper foil-lithium alloy foil", loaded into a rolling cavity, rolled in an argon protection environment, with a temperature of 30 ℃, a pressure of 150 MPa and a speed of 10 m / min, the obtained composite foil has a total thickness of about 45 μm, a smooth surface and a peel strength of ≥20 N / cm, and SEM test shows that an obvious intermetallic diffusion zone has been formed at the copper-lithium interface.

[0033] Example 2,

[0034] A preparation method of lithium-copper composite foil, comprising the following specific steps:

[0035] Lithium alloy foil preparation: high-purity lithium ingot and magnesium metal particles are mixed and smelted to obtain Li-5wt% Mg alloy, which is rolled into an upper lithium alloy foil (thickness 20 μm) and a lower lithium alloy foil (thickness 20 μm) after cooling;

[0036] Copper foil treatment: 5 μm copper foil is selected, first annealed at 300 ℃, then rough etched by HCl and nano-laser punched, with a pore diameter of about 20 μm and a pore density of about 104 / cm 2 ;

[0037] Laminate assembly and rolling process: stacked in the mode of "lithium alloy foil-punched copper foil-lithium alloy foil", loaded into a rolling cavity, rolled in an argon protection environment, with a temperature of 30 ℃, a pressure of 150 MPa and a speed of 10 m / min, the obtained composite foil has a total thickness of about 40 μm, a smooth surface and a peel strength of ≥20 N / cm, and SEM test shows that an obvious intermetallic diffusion zone has been formed at the copper-lithium interface.

[0038] Example 3,

[0039] A preparation method of lithium-copper composite foil, comprising the following specific steps:

[0040] Lithium alloy foil preparation: high-purity lithium ingot and magnesium metal particles were mixed and smelted to obtain Li-5wt% Mg alloy, which was rolled into an upper lithium alloy foil (thickness 30 pm) and a lower lithium alloy foil (thickness 30 pm) after cooling;

[0041] Copper foil treatment: 5 pm copper foil was selected, first annealed at 300°C, then rough etched with HCl, and then nano-laser punched with a pore size of about 20 pm and a pore density of about 104 / cm 2 ;

[0042] Laminate assembly and rolling process: stacked in the order of "lithium alloy foil-punched copper foil-lithium alloy foil", and rolled into a rolling cavity, rolled at a temperature of 30°C, a pressure of 150 MPa, and a speed of 10 m / min in an argon protection environment, the total thickness of the composite foil was about 60 pm, the surface was flat, the peel strength was increased to ≥20 N / cm, and SEM test showed that a clear intermetallic diffusion zone had been formed at the copper-lithium interface.

[0043] Example 4,

[0044] A preparation method of a lithium-copper composite foil, comprising the following specific steps:

[0045] Lithium alloy foil preparation: high-purity lithium ingot and magnesium metal particles were mixed and smelted to obtain Li-5wt% Mg alloy, which was rolled into an upper lithium alloy foil (thickness 40 pm) and a lower lithium alloy foil (thickness 40 pm) after cooling;

[0046] Copper foil treatment: 5 pm copper foil was selected, first annealed at 300°C, then rough etched with HCl, and then nano-laser punched with a pore size of about 20 pm and a pore density of about 104 / cm 2 ;

[0047] Laminate assembly and rolling process: stacked in the order of "lithium alloy foil-punched copper foil-lithium alloy foil", and rolled into a rolling cavity, rolled at a temperature of 20°C, a pressure of 150 MPa, and a speed of 10 m / min in an argon protection environment, the total thickness of the composite foil was about 80 pm, the surface was flat, the peel strength was increased to ≥20 N / cm, and SEM test showed that a clear intermetallic diffusion zone had been formed at the copper-lithium interface.

[0048] Comparative Example 1,

[0049] A pure lithium foil with a thickness of 25 pm and a 5 pm copper foil were stacked together in the order of lithium foil-copper foil-lithium foil, wrapped with a release film, and then rolled to obtain a lithium-copper composite foil with a thickness of 40 pm.

[0050] Peeling strength test: the lithium copper composite foil prepared from example 2 and comparative example 1 was cut to a fixed size, a high-tack paper tape was adhered to the surface of the sample, and a roller was rolled back and forth for 10 times, and after the same time, the peeling force test was carried out at the tensile machine.

[0051] Cycling test: PEO-based solid-state batteries were prepared with the lithium copper composite foil prepared from example 2 and comparative example 1 as the negative electrode and LFP as the positive electrode, and constant current charge-discharge test was carried out at 0.33C rate.

[0052] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a lithium-copper composite foil, characterized in that, Includes the following steps: S1. Select a lithium-based alloy and roll it to form a lithium alloy foil, wherein the alloying element in the lithium-based alloy is at least one of magnesium, zinc or aluminum. S2. Select a copper foil as the supporting frame; S3. Stack two lithium alloy foils and copper foil together in the order of lithium alloy foil-copper foil-lithium alloy foil, and place them in a roller press for rolling to form a metallurgical bond between the copper foil and the lithium alloy foil, thus obtaining a lithium-copper composite foil.

2. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, In step S1, the mass percentage of alloying elements in the lithium-based alloy is 1 to 30 wt%.

3. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, The thickness of the lithium alloy foil prepared in step S1 is 10 μm to 40 μm.

4. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, The thickness of the copper foil in step S2 is 5μm to 20μm.

5. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, In step S2, the copper foil undergoes surface roughening or perforation treatment.

6. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, In step S2, the copper foil undergoes annealing treatment at 200℃ to 400℃ before being stacked and rolled.

7. The method for preparing a lithium-copper composite foil according to claim 1, characterized in that, In step S3, the rolling conditions are as follows: in an inert atmosphere or vacuum environment, the temperature is 20℃~80℃, the pressure is 100MPa~200MPa, and the speed is 8m / min~15m / min.

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