A metal lithium negative electrode and a preparation method thereof

Abstract

The application discloses a metal lithium negative electrode and a preparation method thereof. The metal lithium negative electrode comprises a lithium-containing substrate and a carbon layer arranged on the surface of the lithium-containing substrate, and the roughness of the surface of the carbon layer is 0.4-0.8 nm. By arranging the carbon layer on the surface of the lithium-containing substrate, the metal lithium negative electrode can not only isolate the metal lithium from air and water, protect the lithium-containing substrate and inhibit lithium dendrites, but also form intermetallic compounds between the carbon layer and the lithium-containing substrate, so that the mechanical adhesion is strong, the carbon layer is not easy to fall off, the metal lithium negative electrode has good electrical conductivity and high lithium ion transmission rate, and the electrochemical performance of the battery is improved. Moreover, the roughness of the suitable carbon layer can effectively reduce the interface impedance between the metal lithium negative electrode and the electrolyte, and improve the rate performance of the lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a metal lithium negative electrode and a preparation method thereof. BACKGROUND

[0002] In recent years, lithium ion batteries are widely used in mobile phones, computers and electric vehicles due to high energy and power density, no pollution and other advantages.

[0003] Metal lithium is a commonly used negative electrode material of lithium ion batteries, which has a very high specific capacity. However, since the activity of metal lithium is very high, it is easy to react with oxygen and water in the air for a long time. When a negative electrode containing a lithium metal layer is used in the production process of lithium batteries, coating, baking, lamination and other production processes cannot be completed in the air, resulting in a decrease in battery performance.

[0004] In view of the problem that lithium metal is easily oxidized, some studies have adopted a surface protection method to form a polymer layer on the lithium metal to isolate the lithium metal from the oxygen and water in the air. However, the mechanical strength and lithium ion transmission rate of the metal lithium negative electrode prepared by this method are low. SUMMARY

[0005] The purpose of the present application is to provide a metal lithium negative electrode and a preparation method thereof.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a metal lithium negative electrode, which comprises a lithium-containing substrate and a carbon layer arranged on the surface of the lithium-containing substrate, wherein the roughness of the surface of the carbon layer is 0.4-0.8 nm, for example, 0.8 nm, 0.6 nm, 0.5 nm or 0.4 nm, etc.

[0008] Preferably, the sp 3 The proportion of the sp3 hybrid structure is greater than or equal to 50%, preferably 50%-80%.

[0009] Preferably, the lithium-containing substrate is selected from any one of a lithium alloy or a lithium foil. The lithium alloy may be, for example, a lithium-copper alloy.

[0010] Preferably, the thickness of the lithium-containing substrate is 40-400 pm.

[0011] Preferably, the thickness of the carbon layer is 1-200 nm, preferably 1-100 nm, further preferably 1-54 nm, and more preferably 10-54 nm.

[0012] In a second aspect, the present invention provides a method for preparing a lithium metal anode as described in the first aspect, using a carbon source as a target material and a lithium-containing substrate as a base, and performing vacuum carbon deposition on the surface of the lithium-containing substrate to obtain the lithium metal anode.

[0013] During the vacuum carbon plating process, the temperature of the substrate is 1℃ to 180℃, but does not exceed 180℃.

[0014] In this invention, during the vacuum carbon plating process, a carbon source is used as a target to bombard the substrate.

[0015] Preferably, the vacuum carbon plating method is selected from at least one of magnetron sputtering, laser sputtering, or arc ion plating.

[0016] Preferably, during the vacuum carburizing process, the pressure inside the vacuum chamber is ≤10. -2 Pa.

[0017] Preferably, the carbon source is selected from at least one of graphite and carbon nanotube-containing substances, or the carbon source is acetylene.

[0018] Preferably, the carbon nanotube-containing material is carbon nanotubes or a mixture of carbon nanotubes.

[0019] Preferably, the carbon nanotube-containing mixture is a mixture of carbon nanotubes and polypropylene.

[0020] Preferably, in the mixture of carbon nanotubes and polypropylene, the mass fraction of carbon nanotubes is 15% to 20%.

[0021] As a preferred embodiment of the method described in this invention, in the magnetron sputtering method, the distance between the target and the substrate is 40mm to 150mm.

[0022] Preferably, in the magnetron sputtering method, the working gas is a protective gas, and the flow rate of the working gas is 10 cm³. 3 / min~30cm 3 / min, the working gas pressure is 0.1Pa to 1Pa.

[0023] Preferably, in the magnetron sputtering method, the sputtering time is 20 min to 180 min.

[0024] Preferably, in the magnetron sputtering method, the sputtering power is 50W to 300W.

[0025] Preferably, in the magnetron sputtering method, the temperature of the substrate is 50℃~175℃.

[0026] Preferably, in the magnetron sputtering method, the duty cycle is 20% to 60%.

[0027] Preferably, in the magnetron sputtering method, the substrate bias is -100 V to -300 V.

[0028] As a preferred technical solution of the method of the present application, in the laser sputtering method, the distance between the target and the substrate is 4 cm to 15 cm.

[0029] Preferably, in the laser sputtering method, the frequency of the laser is 4 Hz to 30 Hz.

[0030] Preferably, in the laser sputtering method, the energy density is 0.15 J cm -2 ~ 1.2 J cm -2 .

[0031] Preferably, in the laser sputtering method, the temperature of the substrate is room temperature to 120°C.

[0032] In the present application, "room temperature" refers to 20°C to 25°C.

[0033] Preferably, in the laser sputtering method, the sputtering time is 1 min to 120 min.

[0034] Preferably, in the laser sputtering method, the angle between the laser incidence direction and the surface of the target is 40° to 60°.

[0035] Preferably, in the laser sputtering method, the rotation speed of the target is 0.5 rpm to 15 rpm.

[0036] Preferably, in the laser sputtering method, the substrate bias is -100 V to -300 V.

[0037] Preferably, in the laser sputtering method, the partial pressure of the inert gas is maintained at 0.1 Pa to 10 Pa.

[0038] As a preferred technical solution of the method of the present application, in the arc ion plating method, when the carbon source is selected from at least one of graphite and a substance containing carbon nanotubes, at least one of the following conditions is met:

[0039] (a) The arc source current is 10 A to 100 A.

[0040] (b) The substrate bias is -200 V to -750 V.

[0041] (c) The duty cycle is 10% to 70%.

[0042] (d) The working voltage is 20 V to 50 V.

[0043] (e) The distance between the target and the substrate is 10 cm to 30 cm.

[0044] (f) the argon gas flow rate is 10-110 seem.

[0045] (g) in the process of the arc ion plating method, the temperature of the substrate is room temperature-120℃.

[0046] As a preferred technical solution of the method of the present application, in the arc ion plating method, when the carbon source is acetylene, at least one of the following conditions is met:

[0047] (h) the flow rate of acetylene gas is 30-200 seem.

[0048] (i) the evaporation time is 20-100 min.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] (1) The present application provides a metal lithium negative electrode, which has a carbon layer on the surface of a lithium-containing substrate. The carbon layer not only isolates the metal lithium from contact with air and water, protects the lithium-containing substrate, and inhibits lithium dendrites, but also forms intermetallic compounds between the carbon layer and the lithium-containing substrate, has strong mechanical adhesion, and the carbon layer is not easy to fall off. The metal lithium negative electrode also has good electrical conductivity and high lithium ion transmission rate, which improves the electrochemical performance of the battery. Moreover, the appropriate roughness of the carbon layer can effectively reduce the interfacial impedance between the metal lithium negative electrode and the electrolyte, and improve the rate performance of the lithium metal battery.

[0051] (2) The present application can improve the compactness and uniformity of the carbon layer by controlling the proportion of sp 3 Hybrid structure, thereby better protecting the metal lithium negative electrode and inhibiting the formation of lithium dendrites.

[0052] (3) The method of the present application is simple to operate and can be used for large-scale production. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be further described below through specific embodiments.

[0054] One embodiment of the present application provides a metal lithium negative electrode, which comprises a lithium-containing substrate and a carbon layer disposed on the surface of the lithium-containing substrate. The roughness of the surface of the carbon layer is 0.4-0.8 nm, for example, it can be 0.8 nm, 0.6 nm, 0.5 nm or 0.4 nm, etc.

[0055] In one embodiment, the present application provides a metal lithium negative electrode, a carbon layer is arranged on the surface of a lithium-containing substrate, which can not only isolate the metal lithium from contacting with air and water, protect the lithium-containing substrate and inhibit lithium dendrite, but also form intermetallic compounds between the carbon layer and the lithium-containing substrate, so that the mechanical adhesion is strong, the carbon layer is not easy to fall off, the metal lithium negative electrode also has good electrical conductivity and high lithium ion transmission rate, and the electrochemical performance of the battery is improved. In addition, the appropriate roughness can effectively reduce the interfacial impedance between the metal lithium negative electrode and the electrolyte, and improve the rate performance of the lithium metal battery.

[0056] In one embodiment, the sp 3 The proportion of the sp

[0057] Generally, the structure of carbon atoms in the carbon layer is divided into sp 2 hybrid structure and sp 3 hybrid structure, and the composition of the carbon atoms of the two structures is the main factor affecting the performance of the carbon layer. For a single carbon film, the sp 2 hybrid structure is more similar to graphite, and the carbon film at this time shows good electrochemical performance. However, the present application is different from this. The present application uses the carbon layer to protect the lithium-containing substrate, and the sp 3 hybrid structure accounts for more than or equal to 50%, the carbon layer is more dense and uniform, which can effectively protect the metal lithium negative electrode and inhibit the formation of lithium dendrites.

[0058] In one embodiment, the lithium-containing substrate is selected from any one of a lithium alloy or a lithium foil. The lithium alloy may, for example, be a lithium-copper alloy.

[0059] In one embodiment, the lithium-copper alloy can be a foil or a substrate made of a lithium-copper alloy, or a composite foil or a composite substrate formed by combining a lithium sheet and a copper sheet.

[0060] In one embodiment, the thickness of the lithium-containing substrate is 40 μm to 400 μm, for example, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 185 μm, 200 μm, 210 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm, 360 μm, 380 μm or 400 μm, etc.

[0061] In one embodiment, the thickness of the carbon layer is 1 nm to 200 nm, such as 1 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm or 200 nm, preferably 1 nm to 100 nm, further preferably 1 nm to 54 nm, and more preferably 10 nm to 54 nm. In the present application, the carbon layer is thin, which can protect the lithium-containing substrate and ensure high energy density of the lithium metal anode. In addition, the thickness of the carbon layer affects the modification effect on the lithium-containing substrate. If the carbon layer is too thin, the protective effect of the carbon layer will be weakened, and it is difficult to ensure that the lithium metal is not oxidized. If the carbon layer is too thick, not only the energy density of the lithium metal anode is reduced, but also the carbon layer is more likely to fall off, and the mechanical properties are poor.

[0062] In another embodiment, the present application provides a method for preparing the above-mentioned lithium metal anode. A carbon source is used as a target material, and a lithium-containing substrate is used as a substrate. The surface of the lithium-containing substrate is coated with carbon by vacuum plating to obtain the lithium metal anode.

[0063] In one embodiment, the temperature of the substrate during the vacuum plating of carbon is 1°C to 180°C, such as 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 175°C.

[0064] In one embodiment, the carbon source is used as a target material to bombard the substrate during the vacuum plating of carbon.

[0065] In one embodiment, the method provided by the present application uses a carbon source as a target material to bombard the lithium-containing substrate to achieve surface modification. A carbon layer is introduced on the surface of the lithium-containing substrate, which can not only isolate the lithium metal from air and water, protect the lithium-containing substrate and inhibit lithium dendrites, but also improve the electrical conductivity and lithium ion transmission rate of the modified lithium metal anode, thereby improving the electrochemical performance of the battery. It should be noted that the temperature of the lithium-containing substrate during the formation of the carbon layer should be less than 180°C, otherwise the morphology of the lithium metal will be affected, the introduction and uniformity of the carbon layer will be affected, and thus an effective carbon layer cannot be formed on the lithium-containing substrate, and the lithium dendrites cannot be inhibited and the electrochemical performance cannot be improved.

[0066] In one embodiment, the method for vacuum plating of carbon is selected from at least one of a magnetron sputtering method, a laser sputtering method or an arc ion plating method.

[0067] In one embodiment, the pressure in the vacuum chamber during the vacuum carbon plating process is ≤ 10 -2 Pa.

[0068] In one embodiment, the carbon source is selected from at least one of graphite, a carbon nanotube-containing substance, or the carbon source is acetylene.

[0069] In one embodiment, the carbon nanotube-containing substance is carbon nanotubes or a carbon nanotube-containing mixture.

[0070] In one embodiment, the carbon nanotube-containing mixture is a mixture of carbon nanotubes and polypropylene.

[0071] In one embodiment, the mixture of carbon nanotubes and polypropylene has a mass fraction of carbon nanotubes of 15% to 20%, such as 15%, 16%, 16.5%, 17%, 18%, 18.5%, 19%, or 20%, etc.

[0072] In one embodiment, the magnetron sputtering method has a target-to-substrate distance of 40 mm to 150 mm, such as 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, or 150 mm, etc.

[0073] In one embodiment, the magnetron sputtering method has a working gas that is a protective gas, the working gas has a flow rate of 10 cm 3 / min to 30 cm 3 / min, and the working gas has a pressure of 0.1 Pa to 1 Pa, such as 0.1 Pa, 0.3 Pa, 0.5 Pa, 0.6 Pa, 0.8 Pa, or 1 Pa, etc.

[0074] In one embodiment, the magnetron sputtering method has a sputtering time of 20 min to 180 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, or 180 min, etc.

[0075] In one embodiment, in the magnetron sputtering method, the sputtering power is 50 W to 300 W, for example, 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, 110 W, 120 W, 140 W, 160 W, 180 W, 200 W, 220 W, 240 W, 260 W, 280 W, or 300 W, etc. The sputtering power affects the energy of carbon ions. With the increase of the sputtering power, the sp 3 Hybrid structure carbon atom ratio increases, which is conducive to the formation of a carbon film with compact and uniform structure, but the sputtering power should not be too high, because under the condition of too high sputtering power, the sp 3 Hybrid structure carbon atom ratio decreases, which reduces the compactness and uniformity of the carbon film.

[0076] In one embodiment, in the magnetron sputtering method, the temperature of the substrate is 50°C to 175°C. The temperature of the substrate affects the sp 2 Hybrid structure and sp 3 Hybrid structure ratio, if the temperature of the substrate is too low, the sp 3 Hybrid ratio in the carbon layer decreases, and the surface roughness of the carbon layer increases, affecting the morphology; if the temperature of the substrate is too high, the lithium metal will melt.

[0077] In one embodiment, in the magnetron sputtering method, the duty cycle is 20% to 60%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%, etc. The higher the duty cycle, the higher the pulse frequency in the same time, and the frequency of carbon ions excited from the target bombarding the substrate is also higher. A higher duty cycle is conducive to the formation of sp 3 Hybrid structure ratio increases, which generates a film layer structure with higher compactness, achieving the purpose of effectively protecting the metal lithium, but too high duty cycle will make the sp 3 Hybrid structure ratio decreases.

[0078] In one embodiment, in the magnetron sputtering method, the substrate bias is -100 V to -300 V. In the magnetron sputtering method, the substrate bias has an important influence on the structure and properties of the carbon layer. The substrate bias not only affects the compactness of the carbon layer, but also affects the roughness and thickness of the carbon layer. Specifically, first, with the increase of the substrate bias, the compactness of the carbon layer first increases and then decreases, because when the substrate bias is low, the energy of carbon ions is small, which is not enough to inject into the film layer or migrate to the surrounding, but only adsorbed on the surface of the film layer; when the substrate bias increases, the energy increases, which can inject into the film layer or migrate to the surrounding, carbon ions inject into the subsurface, forming stable sp 3The hybrid structure is formed, and the compactness is improved. With the increase of the substrate bias, the bombardment energy on the substrate is too large, and the compact structure formed is destroyed, resulting in a decrease in compactness. Second, with the increase of the substrate bias, the surface roughness of the carbon layer shows a trend of first decreasing and then increasing. The reason is that a proper substrate bias will make the energized ions have a higher energy, realize surface ion migration and diffusion to remove large particles, so that the surface roughness decreases, and both insufficient and excessive energy will increase the surface roughness. Third, with the increase of the substrate bias, the film thickness shows a trend of first increasing and then decreasing. When the substrate bias is controlled in the range of -100V to -300V, the higher compactness, lower roughness and appropriate thickness can be considered.

[0079] In an embodiment, in the laser sputtering method, the distance between the target and the substrate is 4cm to 15cm, such as 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm, 11cm, 13cm or 15cm, etc. The distance between the target and the substrate will affect the deposition rate, but has little effect on the structure of the carbon layer.

[0080] In an embodiment, in the laser sputtering method, the frequency of the laser is 4Hz to 30Hz, such as 4Hz, 6Hz, 8Hz, 10Hz, 12Hz, 15Hz, 17Hz, 20Hz, 22Hz, 24Hz, 25Hz, 28Hz or 30Hz, etc. Reducing the wavelength, increasing the frequency of the laser, and improving the energy are generally beneficial to the sp 3 The formation of the hybrid structure, and the frequency of the laser is too small or too high, which will lead to a decrease in sp 3 structure in the carbon film, thereby reducing the compactness and uniformity of the carbon film, and thus reducing the protection of the carbon film on the metal lithium.

[0081] In an embodiment, in the laser sputtering method, the energy density is 0.15J cm -2 to 1.2J cm -2 , such as 0.15J cm -2 , 0.2J cm -2 , 0.25J cm -2 , 0.3J cm -2 , 0.35J cm -2 , 0.4J cm -2 , 0.45J cm -2 , 0.5J cm -2 , 0.55J cm -2 , 0.6J cm -2 , 0.65J cm -2 , 0.7J cm -2 , 0.8J cm -20.9 J / cm2 -2 or 1.0 J / cm2 -2 1.1 J / cm2 -2 or 1.2 J / cm2 -2 etc. If the sputtering energy is too small, the film thickness will be reduced, and the sp 3 hybrid ratio will be reduced, the film density will be reduced, and the protection of lithium metal will be reduced.

[0082] In an embodiment, the temperature of the substrate in the laser sputtering method is room temperature to 120°C. In the laser sputtering method, a lower substrate temperature is not conducive to the formation of sp 3 hybrid structure in the carbon layer, although a higher temperature is conducive to the formation of sp 3 hybrid structure, but a too high substrate temperature is not conducive to the formation of sp 3 hybrid structure in the carbon film, thereby reducing the density and uniformity of the film layer.

[0083] In an embodiment of the present application, "room temperature" refers to 20°C to 25°C, for example, it can be 20°C, 22°C, 23°C, 24°C or 25°C, etc.

[0084] In an embodiment, the sputtering time in the laser sputtering method is 1 min to 120 min, for example, 1 min, 3 min, 6 min, 8 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc.

[0085] In an embodiment, the angle between the laser incidence direction and the target surface in the laser sputtering method is 40° to 60°, for example, 40°, 45°, 50°, 55° or 60°, etc. When the angle is smaller, the sp 2 hybrid ratio in the carbon film will increase, thereby reducing the density and uniformity of the carbon film material.

[0086] In an embodiment, the rotation speed of the target in the laser sputtering method is 0.5 rpm to 15 rpm, for example, 0.5 rpm, 1 rpm, 2 rpm, 3 rpm, 4 rpm, 5 rpm, 7 rpm, 8 rpm, 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm, etc.

[0087] In an embodiment, the substrate bias in the laser sputtering method is -100 V to -300 V. Too low and too high substrate bias will reduce the sp 3 hybrid ratio, thereby affecting the film density and uniformity.

[0088] In one embodiment, in the laser sputtering method, the partial pressure of inert gas is kept at 0.1 Pa to 10 Pa, such as 0.1 Pa, 0.3 Pa, 0.5 Pa, 0.6 Pa, 0.8 Pa, 1 Pa, 2 Pa, 3 Pa, 4 Pa, 5 Pa, 6 Pa, 7 Pa, 8 Pa or 10 Pa, etc. Inert gas can hinder the formation of carbon particles, reduce their kinetic energy, so relatively large inert gas pressure is not conducive to the formation of sp 3 Hybrid structure.

[0089] In one embodiment, in the arc ion plating method, when the carbon source is selected from at least one of graphite, carbon nanotube-containing substance, at least one of the following conditions is met:

[0090] (a) Arc source current is 10 A to 100 A, such as 10 A, 15 A, 20 A, 25 A, 30 A, 35 A, 40 A, 45 A, 50 A, 55 A, 60 A, 65 A, 70 A, 75 A, 80 A, 90 A or 100 A, etc. Within this preferred range, it is more conducive to the formation of sp3 hybrid structure, thereby improving the density and uniformity of the carbon layer.

[0091] (b) Substrate bias is -200 V to -750 V, such as -200 V, -250 V, -300 V, -350 V, -400 V, -450 V, -500 V, -550 V, -600 V, -650 V, -700 V or -750 V, etc. The effect of substrate bias on the structure of carbon layer is more complex. Generally speaking, the sp 3 Hybrid structure accounts for a rising trend first and then a falling trend as the substrate bias rises. Within the above preferred range, it is conducive to the formation of a higher proportion of sp 3 Hybrid structure.

[0092] (c) Duty cycle is 10% to 70%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%, etc. Higher duty cycle is conducive to the formation of sp 3 Hybrid, too low or too high duty cycle will lead to sp 3 Hybrid structure accounts for a falling trend, and the density and uniformity of the carbon film decrease.

[0093] (d) Working voltage is 20 V to 50 V, such as 20 V, 25 V, 30 V, 35 V, 40 V, 45 V or 50 V, etc.

[0094] (e) The distance between the target and the substrate is 10 cm to 30 cm, such as 10 cm, 12 cm, 15 cm, 18 cm, 20 cm, 23 cm, 26 cm, 28 cm or 30 cm, etc.

[0095] (f) the flow rate of argon gas is 10-110sccm, for example, 10sccm, 20sccm, 30sccm, 40sccm, 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, 100sccm or 110sccm, etc.

[0096] (g) the temperature of the substrate during the arc ion plating process is room temperature-120°C. Appropriate reduction of the temperature of the substrate is conducive to the formation of sp 3 The formation of the hybrid structure, and considering the properties of lithium metal, the temperature of the substrate should not be too high.

[0097] In one embodiment, when the carbon source in the arc ion plating process is acetylene, at least one of the following conditions is met:

[0098] (h) the flow rate of acetylene gas is 30-200sccm, for example, 30sccm, 40sccm, 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, 100sccm, 110sccm, 120sccm, 130sccm, 140sccm, 150sccm, 160sccm, 180sccm or 200sccm, etc.

[0099] (i) the evaporation time is 20-100min, for example, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 60min, 70min, 80min, 90min or 100min, etc.

[0100] When acetylene is used as the carbon source, the flow rate of acetylene gas and the evaporation time are the main factors affecting the structure of the carbon layer. In order to form more sp 3 hybrid structures in the carbon layer to improve the density and uniformity of the carbon layer, the flow rate of acetylene gas should not be too slow, and the deposition time should not be too long. Preferably, the flow rate of acetylene gas is 100-180sccm, and the deposition time is preferably 30-60min.

[0101] Example 1

[0102] The present embodiment provides a preparation method of a lithium metal negative electrode, comprising the following steps:

[0103] (1) Pretreatment: Firstly, the lithium-copper alloy with a thickness of 250 μm (wherein the lithium-copper alloy is composed of a copper foil and lithium sheets arranged on both sides of the copper foil, the thickness of the copper foil is 5 μm, and the thickness of the lithium sheets on both sides of the copper foil is 100 μm respectively) is soaked in acetone for a period of time, and then is naturally dried in a drying room (dew point ≤ 50℃).

[0104] (2) Magnetron sputtering: the dried lithium-copper alloy is placed in the cavity of a magnetron sputtering device, a graphite sheet with a purity of 99.9% is used as the target material, the lithium-copper alloy is used as the substrate, a molecular pump is used to control the vacuum degree to 1×10 -3 Pa, the target-substrate distance (the distance between the target material and the lithium-copper alloy) is fixed at 50 mm, argon gas is used as the working gas, the argon gas flow is 20 cm 3 / min, the argon partial pressure is 0.9 Pa, the duty cycle is 30%, the sputtering power is 100 W, the sputtering time is 30 min, the temperature of the substrate is 50℃, a carbon layer is formed, and after the sputtering is completed, the surface-modified copper-lithium alloy substrate is taken out, the thickness of the carbon layer is 50 nm, the sp 3 hybrid structure in the carbon layer accounts for 50.8%, that is, a metal lithium negative electrode is obtained.

[0105] Example 2

[0106] Different from Example 1, the temperature of the substrate is adjusted to 70℃.

[0107] Example 3

[0108] Different from Example 1, the temperature of the substrate is adjusted to 90℃.

[0109] Example 4

[0110] Different from Example 1, the temperature of the substrate is adjusted to 110℃.

[0111] Example 5

[0112] Different from Example 1, the temperature of the substrate is adjusted to 130℃.

[0113] Example 6

[0114] Different from Example 1, the temperature of the substrate is adjusted to 170℃.

[0115] Example 7

[0116] Different from Example 1, the duty cycle is adjusted to 40%.

[0117] Example 8

[0118] Different from Example 1, the duty cycle is adjusted to 50%. Example 9

[0119] Unlike Example 1, the duty cycle was adjusted to 20%.

[0120] Example 10

[0121] Unlike Example 1, the duty cycle was adjusted to 60%.

[0122] Example 11

[0123] The embodiment provides a preparation method of a metal lithium negative electrode, comprising the following steps:

[0124] (1) Pretreatment: first, a lithium foil with a thickness of 200 μm is soaked in acetone for a period of time, and then is naturally dried in a drying room (dew point ≤ 50℃).

[0125] (2) Laser sputtering: a carbon nanotube / polypropylene mixture (wherein the mass fraction of carbon nanotube is 15%) is used as a target material, and the dried lithium foil is used as a substrate, the target material and the substrate are placed in a vacuum chamber, the distance between the target material and the substrate is adjusted to 8 cm, the vacuum degree of the chamber is pumped to less than 1 × 10 -3 Pa by a pump, the temperature of the substrate is raised to 60℃, the frequency of the laser is 20 Hz, the energy density is set to 0.4 J cm -2 , the sputtering time is 80 min, the angle between the laser and the target material is 60°, the rotating speed of the target material is 10 rpm, the partial pressure of the inert gas is kept at 7 Pa, a carbon layer is formed, the thickness of the carbon layer is 59 nm, and the metal lithium negative electrode is obtained.

[0126] Example 12

[0127] Unlike Example 10, the temperature of the substrate is adjusted to 80℃.

[0128] Example 13

[0129] Unlike Example 10, the temperature of the substrate is adjusted to 100℃.

[0130] Example 14

[0131] Unlike Example 10, the temperature of the substrate is adjusted to 40℃.

[0132] Example 15

[0133] Unlike Example 10, the temperature of the substrate is adjusted to 120℃.

[0134] Example 16

[0135] Unlike Example 10, the energy density is adjusted to 0.2 J cm -2 .

[0136] Example 17

[0137] Unlike Example 10, the energy density was adjusted to 0.6 J cm -2 .

[0138] Example 18

[0139] Unlike Example 10, the energy density was adjusted to 0.8 J cm -2 .

[0140] Example 19

[0141] Unlike Example 10, the energy density was adjusted to 1.0 J cm -2 .

[0142] Example 20

[0143] Unlike Example 10, the energy density was adjusted to 1.2 J cm -2 .

[0144] Example 21

[0145] (1) Pretreatment: First, a lithium-copper alloy (in which the lithium-copper alloy is composed of a copper foil and lithium sheets disposed on both sides of the copper foil, the thickness of the copper foil is 5 μm, and the thickness of the lithium sheets on both sides of the copper foil is 100 μm) having a thickness of 250 μm was immersed in acetone for a period of time, and then was placed in a drying chamber to air dry (dew point ≤ 50 °C).

[0146] (2) Arc ion plating method: Using graphite having a purity of 99.9% as a target material and the lithium-copper alloy after air drying as a substrate, the arc ion plating equipment cavity was first evacuated to 1 x 10 -3 Pa, the distance between the target material and the substrate was fixed at 200 mm, the argon partial pressure was 0.1 Pa, the arc source current was 20 A, the substrate bias was -200 V, the duty cycle was adjusted to 20%, the working voltage was 30 V, the plating time was 20 min, the substrate temperature was adjusted to 50 °C, and the negative electrode sheet was removed after the plating was completed.

[0147] Example 22

[0148] Unlike Example 18, the temperature of the substrate was adjusted to 60 °C.

[0149] Example 23

[0150] Unlike Example 18, the temperature of the substrate was adjusted to 70 °C.

[0151] Example 24

[0152] Unlike Example 18, the temperature of the substrate was adjusted to 80 °C.

[0153] Example 25

[0154] Unlike Example 18, the temperature of the substrate was adjusted to 90°C.

[0155] Example 26

[0156] Unlike Example 18, the temperature of the substrate was adjusted to 100°C.

[0157] Example 27

[0158] Unlike Example 18, the temperature of the substrate was adjusted to 120°C.

[0159] Example 28

[0160] Unlike Example 18, the duty cycle was adjusted to 30%.

[0161] Example 29

[0162] Unlike Example 18, the duty cycle was adjusted to 40%.

[0163] Example 30

[0164] Unlike Example 18, the duty cycle was adjusted to 50%.

[0165] Example 31

[0166] Unlike Example 18, the duty cycle was adjusted to 60%.

[0167] Example 32

[0168] Unlike Example 18, the duty cycle was adjusted to 70%.

[0169] Comparative Example 1

[0170] Unlike Example 1, the temperature of the substrate was 200°C or more.

[0171] When the temperature was 180°C or more, the metal lithium was molten and film deposition could not be performed.

[0172] Comparative Example 2

[0173] Unlike Example 1, a lithium-copper alloy was directly used as the metal lithium negative electrode without forming a carbon layer on the surface thereof.

[0174] Comparative Example 3

[0175] Unlike Example 1, the duty cycle was adjusted to 10%.

[0176] Comparative Example 4

[0177] Unlike Example 10, the sputtering energy was adjusted to 0.1 J cm -2 .

[0178] The structural parameters of the metal lithium negative electrode of Examples 1-27 and Comparative Examples 1-9 were tested by the same method. The roughness of the carbon layer was tested by using a Taylor Hobson profilometer. The sp 3 hybrid structure was tested by using Raman spectroscopy. The asymmetric peak of the sample was divided into two peaks by using a Gaussian function. One was a D peak, which was generated by a T2g symmetric vibration mode, proving the existence of sp 3 hybrid structure. The G peak was generated by a D2g symmetric vibration mode, proving the existence of sp 2 hybrid structure. The ratio of sp 3 hybrid structure was calculated by comparing the peak intensities of the two peaks.

[0179] Table 1

[0180]

[0181]

[0182] Note: Comparative Example 2 does not contain a carbon layer, so there is no corresponding data in the table, replaced by “—”.

[0183] It can be known from Examples 1-32 that the carbon layer with a certain roughness and a certain ratio of sp 3 hybrid can be obtained by using a magnetron sputtering method, a laser sputtering method or an arc ion plating method. Comparative Example 1 will cause the lithium metal to melt due to the too high substrate temperature. Comparative Example 3 will cause the ratio of sp 3 hybrid in the carbon layer formed by magnetron sputtering to be too low, which is not conducive to the densification of the film. Comparative Example 4 will cause the ratio of sp 3 hybrid in the carbon layer formed by laser sputtering to be too low and the roughness to be small.

[0184] Meanwhile, it can be known from the comparison between Example 1 and Example 10 that, in the magnetron sputtering method, when the duty ratio is 60%, the ratio of sp 3 hybrid structure can be increased to a certain extent compared with the duty ratio of 30% in Example 1, and the energy consumed is larger. Moreover, compared with the duty ratio of 50% in Example 8, the ratio of sp 3 hybrid structure decreases instead, so it can be known that the duty ratio is not the higher the better.

[0185] It can be known from the comparison between Example 10 and Example 15 that, in the laser sputtering method, when the temperature of the substrate is 120°C, the ratio of sp 3 hybrid structure can be increased to a certain extent compared with 60°C in Example 10, and the energy consumed is larger. Moreover, compared with 100°C in Example 13, the ratio of sp3 The hybrid structure actually decreased, which shows that the higher the temperature of the substrate, the better.

[0186] A comparison between Example 10 and Example 20 shows that the sputtering energy in the laser sputtering method is 1.2 J / cm². -2 At that time, compared to 0.4 J cm in Example 10 -2 It can improve sp to a certain extent 3 The proportion of hybrid structures is higher, and the energy consumption is also greater. Meanwhile, compared to 0.6-1.0 J / cm² in Examples 17-19... -2 sp 3 The hybrid structure actually decreases, which shows that higher sputtering energy is not necessarily better.

[0187] A comparison between Examples 18 and 27 shows that in the arc ion plating method, a substrate temperature of 120°C, compared to 50°C in Example 18, can improve the performance of sp to a certain extent. 3 The proportion of hybrid structures is higher, and the energy consumption is also greater. Furthermore, compared to the 80-100°C in Examples 24-26, sp 3 The hybrid structure actually decreased, which shows that the higher the temperature of the substrate, the better.

[0188] A comparison between Examples 18 and 32 shows that in the arc ion plating method, a duty cycle of 70% can improve the performance of sp to a certain extent compared to the duty cycle of 20% in Example 1. 3 The proportion of hybrid structures is higher, and the energy consumption is also greater. Furthermore, compared to the 40-60% in Examples 29-31, sp... 3 The hybridization structure actually decreases, which shows that a higher duty cycle is not necessarily better.

[0189] Performance testing:

[0190] (a) Using the lithium metal anodes of Examples 1-32 and Comparative Examples 1-4, lithium metal batteries were assembled, and the electrochemical performance of the batteries was tested:

[0191] Using the aforementioned lithium metal anode as the anode, and employing ternary material LiNi 0.8 Co 0.1 Mn 0.1O2 is a ternary active material for making a positive electrode, and the process for making the positive electrode material is as follows: the mass ratio of the ternary active material is 95%, the mass ratio of the adhesive PVDF is 5%, the mass ratio of the conductive agent Super P is 5%, and the dispersing agent is selected as N-methyl pyrrolidone (NMP); first, the NMP solution (mass fraction of 6%) of PVDF is placed in a stirrer, then the corresponding proportion of the conductive agent is added, and after stirring for a period of time, the ternary active material is added, and then a certain amount of dispersing agent NMP is added, so that the solid content of the whole system is maintained at 60%, and a coating machine is used to coat to prepare a positive electrode sheet, and the surface density of the positive electrode sheet is 35 mg / cm 2 , and a plurality of soft package batteries are assembled, and the cycle and rate performance thereof is tested.

[0192] The test conditions of the cycle performance are as follows: at room temperature, 1C charging and discharging, and the capacity and energy retention rate after 200 cycles are calculated.

[0193] The test conditions of the rate performance are as follows: at room temperature, 0.5C, 1C, 3C and 5C charging and discharging tests are carried out, the capacity under different rate performance is calculated, and by comparing the capacity under 1C, 3C and 5C conditions with the capacity under 0.5C condition, the rate performance can be evaluated. The results are shown in Table 2.

[0194] Table 2

[0195]

[0196]

[0197]

[0198] As can be seen from the above, by arranging the carbon layer on the surface of the substrate, the metal lithium can be isolated from the contact with air and water, the substrate can be protected, the lithium dendrite can be inhibited, the intermetallic compound is formed between the carbon layer and the substrate, the mechanical adhesion is strong, the carbon layer is not easy to fall off, the modified metal lithium negative electrode prepared has good conductivity and high lithium ion transmission rate, and the electrochemical performance of the battery is improved.

[0199] By comparing the embodiment with Comparative Examples 1 and 2, it can be illustrated that the carbon layer can be effectively formed below the temperature of 200 DEG C, the metal lithium can be protected from oxidation, and the lithium ion transmission performance is good.

[0200] By comparing Example 1 with Comparative Example 3 and comparing Example 10 with Comparative Example 4, it can be known that the ratio of sp 3 Hybridization is too low and the roughness is small, which is not conducive to the improvement of electrochemical performance.

[0201] Applicants declare that the detailed method of the present application is illustrated by the above-mentioned examples, but the present application is not limited to the above-mentioned detailed method, i.e. it does not mean that the present application must rely on the above-mentioned detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A metal lithium negative electrode, characterized by, The metal lithium negative electrode comprises a lithium-containing substrate and a carbon layer disposed on the surface of the lithium-containing substrate, wherein the roughness of the surface of the carbon layer is 0.4-0.8 nm. sp 3 The proportion of the hybrid structure is greater than or equal to 50%.

2. The lithium metal anode of claim 1, wherein, sp 3 The proportion of the hybrid structure is 50% to 80%.

3. The lithium metal anode of claim 1, wherein, The lithium-containing substrate is selected from any one of lithium alloy or lithium foil.

4. The lithium metal anode of claim 1, wherein, The thickness of the lithium-containing substrate is 40 μm-400 μm.

5. The lithium metal anode of claim 1, wherein, The thickness of the carbon layer is 1 nm-200 nm.

6. The lithium metal anode of claim 5, wherein, The thickness of the carbon layer is 1 nm-100 nm.

7. The lithium metal anode of claim 6, wherein, The thickness of the carbon layer is 1 nm-54 nm.

8. The lithium metal anode of claim 7, wherein, The thickness of the carbon layer is 10 nm-54 nm.

9. A method of producing a metal lithium negative electrode as claimed in any one of claims 1 to 8, characterized in that, The metal lithium negative electrode is obtained by vacuum carbon plating on the surface of the lithium-containing substrate with the carbon source as the target material and the lithium-containing substrate as the substrate. In the process of the vacuum carbon plating, the temperature of the substrate is 1 ℃-180 ℃ and does not contain 180 ℃.

10. The preparation method according to claim 9, characterized in that, The method of the vacuum carbon plating is selected from at least one of magnetron sputtering, laser sputtering or arc ion plating.

11. The preparation method according to claim 9, characterized in that, The pressure in the vacuum chamber during the vacuum carbon coating process is ≤ 10 -2 Pa.

12. The method of claim 9, wherein, The carbon source is selected from at least one of graphite or carbon nanotube-containing substance, or the carbon source is acetylene.

13. The method of claim 12, wherein, The carbon nanotube-containing substance is carbon nanotube or carbon nanotube-containing mixture.

14. The method of claim 13, wherein, The carbon nanotube-containing mixture is a mixture of carbon nanotube and polypropylene.

15. The preparation method according to claim 14, characterized in that, In the mixture of carbon nanotube and polypropylene, the mass fraction of carbon nanotube is 15%-20%.

16. The method of claim 10, wherein, In the magnetron sputtering, the distance between the target material and the substrate is 40 mm-150 mm.

17. The method of claim 10, wherein, In the magnetron sputtering method, the working gas is a protective gas, the flow rate of the working gas is 10 cm 3 / min~30 cm 3 / min, and the gas pressure of the working gas is 0.1 Pa~1 Pa.

18. The method of claim 10, wherein, In the magnetron sputtering, the sputtering time is 20 min-180 min.

19. The method of claim 10, wherein, In the magnetron sputtering, the sputtering power is 50 W-300 W.

20. The method of claim 10, wherein, In the magnetron sputtering, the temperature of the substrate is 50 ℃-175 ℃.

21. The method of claim 10, wherein, In the magnetron sputtering, the duty cycle is 20%-60%.

22. The method of claim 10, wherein, In the magnetron sputtering, the substrate bias is -100 V--300 V.

23. The method of claim 10, wherein, In the laser sputtering, the distance between the target material and the substrate is 4 cm-15 cm.

24. The method of claim 10, wherein, In the laser sputtering, the frequency of the laser is 4 Hz-30 Hz.

25. The method of claim 10, wherein, In the laser sputtering method, the energy density is 0.15 Jcm -2 ~ 1.2 Jcm -2 .

26. The method of claim 10, wherein, In the laser sputtering, the temperature of the substrate is room temperature-120 ℃.

27. The method of claim 10, wherein, In the laser sputtering, the sputtering time is 1 min-120 min.

28. The method of claim 10, wherein, In the laser sputtering, the angle between the laser incidence direction and the surface of the target material is 40°-60°.

29. The method of claim 10, wherein, In the laser sputtering, the rotation speed of the target material is 0.5 rpm-15 rpm.

30. The method of claim 10, wherein, In the laser sputtering, the substrate bias is -100 V--300 V.

31. The method of claim 10, wherein, In the laser sputtering, the partial pressure of the inert gas is kept at 0.1 Pa-10 Pa.

32. The method of claim 10, wherein, In the arc ion plating, when the carbon source is selected from at least one of graphite or carbon nanotube-containing substance, at least one of the following conditions is met: (a) the arc source current is 10 A-100 A; (b) the substrate bias is -200 V--750 V; (c) the duty cycle is 10%-70%; (d) the working voltage is 20 V-50 V; (e) the distance between the target material and the substrate is 10 cm-30 cm; (f) the flow rate of the protective gas is 10 sccm-110 sccm; (g) in the process of the arc ion plating, the temperature of the substrate is room temperature-120 ℃.

33. The method of claim 10, wherein, In the arc ion plating method, when the carbon source is acetylene, at least one of the following conditions is satisfied: (h) the flow rate of acetylene gas is 30 sccm to 200 sccm; (i) the deposition time is 20 min to 100 min.

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