Lithium composite negative electrode and preparation method and application thereof

Abstract

The invention provides a lithium composite negative electrode and a preparation method and application thereof. The lithium composite electrode comprises a current collector membrane material and an active substance layer attached to at least one surface of the current collector membrane material, an active substance in the active substance layer is metal lithium or lithium alloy, and the current collector membrane material is a carbon nanotube membrane meeting the following conditions: the content of catalyst metal is 0.1 wt% or less; the thickness of the film is 5-20 microns; the tensile strength of the film is greater than 20 MPa and less than or equal to 200 MPa; and the sheet resistance of the film is 0.1-100 omega / cm < 2 >. The negative electrode formed by combining the carbon nanotube film and the metal lithium can well replace an existing lithium-copper composite product, and by using the negative electrode, the specific energy of the battery can exceed 400 wh / kg.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a lithium composite negative electrode for a lithium ion battery, and a preparation method and application thereof. Background Art

[0002] The lithium negative electrode commonly used at present is mainly a lithium-copper composite tape with copper foil as the supporting material. The thinnest copper foil available is 4um thick. It is too thin and is easy to break and wrinkle during use, making it difficult to apply in batches. In addition, the density of metallic copper is 8.96g / cm 3 Currently, the thinnest 4um thick copper foil is equivalent to 67um thick lithium metal, and copper foil accounts for a large proportion of the weight of the entire battery cell. Some people also consider using pure metal lithium strips (without support) directly as negative electrodes. The thickness of metal lithium is about 70um, and the tensile strength is less than 1MPa. Currently, they are all hand-cut and hand-made battery cells. Metal lithium strips are easily torn and deformed during industrial production and cannot be used as batteries. Currently, the positive electrode in the battery uses lithium iron phosphate or ternary nickel-cobalt-manganese materials. The positive electrode itself already contains lithium ions, so the amount of metal lithium used in the negative electrode is very small. The thinner the lithium is, the weaker the strength is. Support materials are required to scale up industrial production applications. However, most materials are not suitable for use as support materials for metal lithium because of the following problems: some membrane materials do not have sufficient tensile strength and are easily deformed by stress during industrial applications; some membrane materials contain components that react with metal lithium, resulting in the loss of active lithium; some membrane materials have poor conductivity, and the battery cycle performance is poor when the battery is charged and discharged at a high rate.

[0003] In view of this, there is a need to develop a lightweight and high-strength conductive film material suitable for supporting metallic lithium strips. Summary of the Invention

[0004] In response to the above problems, the present invention prepares a lightweight, high-strength conductive film material suitable for supporting thin lithium strips, and the lightweight, high-strength conductive film material is a treated carbon nanotube film. The inventors of this application found that the carbon nanotube film prepared by the vapor phase method is very light and thin, and has a certain strength and conductivity. It is one of the candidate materials for the support material of metallic lithium. However, in the process of using the carbon nanotube film as the negative electrode support material of metallic lithium, there is a problem that the metallic lithium will react and turn black, resulting in the loss of active lithium. The composition of the blackened area was tested and it was found that it contained nitrogen. However, in the process of manufacturing the carbon nanofilm, no N component was introduced. It is speculated that the catalyst metal component present in the carbon nanotube film (the residue of the catalyst in the vapor phase method) catalyzes the reaction between metallic lithium and air. Further research found that this metal component not only exists inside the amorphous carbon particles that do not form carbon nanotubes during the vapor phase reaction, but also exists in part at the ends of the carbon nanotubes. Faced with the challenge of removing the catalyst while minimizing damage to the carbon nanotube film's original state, the inventors devised a treatment process to completely remove the metal component without substantially compromising the film's mechanical properties (such as tensile strength) or electrical properties. This resulted in a carbon nanotube film with moderate tensile strength and electrical conductivity that does not discolor the lithium metal when combined with it. This led to the completion of the present invention.

[0005] Specifically, one aspect of the present invention relates to a lithium composite negative electrode, comprising: a current collector film and an active material layer attached to at least one surface of the current collector film, wherein the active material in the active material layer is metallic lithium or a lithium alloy, and the current collector film is a carbon nanotube film that meets the following conditions:

[0006] The content of catalyst metal is below 0.1wt%;

[0007] The thickness of the membrane is 5-20um;

[0008] The tensile strength of the membrane is greater than 20 MPa and less than or equal to 200 MPa;

[0009] The sheet resistance of the film is 0.1-100Ω / cm 2 .

[0010] In the present invention, the catalyst metal in the carbon nanotube film is the catalyst residue when the carbon nanotube film is prepared by the vapor phase method. The carbon nanotube film used as the current collector film is obtained by removing the catalyst metal from the carbon nanotube film prepared by the vapor phase method.

[0011] According to certain embodiments, the catalyst metal includes at least one of iron, cobalt, and nickel.

[0012] According to certain embodiments, the catalyst metal content is less than 0.01wt%.

[0013] According to certain embodiments, the active material layer has a thickness of 1-100 um, preferably 1-20 um; and a width of 50-1400 mm, preferably 200-700 mm.

[0014] According to certain embodiments, the lithium alloy is formed by a combination of metallic lithium and any one or at least two elements of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, C, V, Cu, Fe or Ti. Preferably, the mass percentage of metallic lithium in the lithium alloy is greater than 90%.

[0015] According to certain embodiments, the carbon nanotube film is a carbon nanotube film with iron removed.

[0016] According to some embodiments, the density of the carbon nanotube film is 0.5-0.6 g / cm 3 .

[0017] Another aspect of the present invention relates to a method for preparing the above-mentioned lithium composite negative electrode, the method comprising:

[0018] preparing a carbon nanotube film from which catalyst metals have been removed;

[0019] Applying active material to at least one surface of the carbon nanotube film from which the metal has been removed by coating, pressure lamination or vapor deposition process to obtain a lithium composite negative electrode,

[0020] The preparation of the carbon nanotube film from which the catalyst metal has been removed includes the steps of subjecting the carbon nanotube film prepared by the vapor phase method to a two-step heat treatment, wherein the first heat treatment step is: subjecting the carbon nanotube film to a high temperature treatment in air for 2-6 hours at a temperature of 400-500°C; the second heat treatment step is: subjecting the carbon nanotube film to a vacuum heat treatment at a temperature of 1800-2000°C and a vacuum degree of 10 -2 Below Pa, the processing time is 30min-60min.

[0021] According to some embodiments, the method further comprises: soaking the carbon nanotube film in dilute acid between the first heat treatment and the second heat treatment, or after the two heat treatments, wherein the concentration of the dilute acid is 0.005-0.1 mol / L, washing with deionized water after soaking, and drying.

[0022] According to certain embodiments, the dilute acid includes dilute nitric acid, dilute hydrochloric acid, dilute sulfuric acid, etc.; the concentration may be 0.005-0.05 mol / L; and the soaking time may be 2-12 hours.

[0023] According to some embodiments, the method further comprises:

[0024] Before the heat treatment, the carbon nanotube film prepared by the vapor phase method is cleaned and dried to remove the oil on the surface of the carbon nanotube film; and

[0025] Optionally, after the two-step heat treatment step and the dilute acid soaking step, the surface of the obtained carbon nanotube film is moistened and then rolled with a hot roller to make the surface flat.

[0026] According to certain embodiments, cleaning the carbon nanotube film prepared by the vapor phase method includes: first cleaning the carbon nanotube film with an ethanol-water solution, and then cleaning it with deionized water.

[0027] According to certain embodiments, after the two-step heat treatment step and the dilute acid soaking step, wetting the surface of the obtained carbon nanotube film comprises: spraying an ethanol solution onto the surface of the carbon nanotube film.

[0028] According to certain embodiments, the temperature of the hot roller pressing is 40-100° C., and the pressure is 1-10 MPa.

[0029] According to certain embodiments, the carbon nanotube film prepared by the gas phase method includes: using a carbon source of benzene / toluene / ethanol / methanol, a catalyst of ferrocene, and a promoter of thiophene, the reaction solution (e.g., benzene + ferrocene + thiophene) is introduced into the reactor at a rate of 0.5-1 mL / min, and the gas flow is selected as an argon-hydrogen mixed gas, and the gas flow rate is controlled at 100-300 cm 3 / min; the part before the reaction is the low temperature zone, and the part after the reaction is the high temperature zone. The temperature of the low temperature zone is 600-700℃, and the temperature of the high temperature zone is 1100-1300℃.

[0030] According to certain embodiments, a method for preparing a lithium composite negative electrode comprises:

[0031] (1) washing the carbon nanotube film prepared by the gas phase method with an ethanol aqueous solution, then washing with deionized water, and drying for use;

[0032] (2) treating the carbon nanotube film obtained in step (1) in air at a high temperature of 400-500° C. for 2-6 h;

[0033] (3) soaking the carbon nanotube film obtained in step (2) in dilute nitric acid for 2-12 hours, wherein the concentration of the dilute nitric acid is 0.005-0.05 mol / L, washing the film with deionized water after soaking, and drying the film for later use;

[0034] (4) The carbon nanotube film obtained in step (3) is subjected to vacuum heat treatment at a temperature of 1800-2000°C and a vacuum degree of 10 -2 Pa or less (pressure less than 10 -2 Pa), the processing time is 30min-60min;

[0035] (5) Spraying ethanol solution on the surface of the carbon nanotube film in step (4), and further rolling it into a film material with a smooth surface using a hot roller to obtain a carbon nanotube film with the catalyst metal removed.

[0036] The present invention addresses the distribution characteristics of catalyst metals in carbon nanotube films produced by a vapor phase method and takes into account the inherent characteristics of the carbon nanotube films. A two-step heat treatment process is designed. The catalyst metals present within amorphous carbon particles that have not yet formed into carbon nanotubes are exposed through air calcination (high-temperature heating in air) (and subsequently removed by washing with dilute acid). Subsequently, the catalyst metals present at the ends of the carbon nanotubes are removed through vacuum heat treatment. This allows the catalyst metals to be completely removed while minimizing damage to the carbon nanotube film's structure.

[0037] Another aspect of the present invention relates to the use of the above-mentioned lithium composite electrode, wherein the lithium composite electrode is directly used as the negative electrode of a lithium battery.

[0038] According to certain embodiments, the positive electrode of the lithium battery uses nickel-cobalt-manganese ternary, nickel-cobalt-aluminum ternary, lithium-rich manganese-based positive electrode material, lithium iron phosphate, sulfur-based positive electrode material, and lithium cobalt oxide positive electrode material.

[0039] According to certain embodiments, the lithium battery is a liquid lithium ion battery or a solid lithium ion battery.

[0040] According to certain embodiments, the electrolyte of the lithium battery can be a liquid electrolyte or a solid electrolyte; the liquid electrolyte can be an ester or an ether; the solid electrolyte can be an oxide solid electrolyte, a halide solid electrolyte, a sulfide solid electrolyte or a polymer electrolyte, such as PEO, PVDF (mixed oxide, halide, sulfide powder) electrolyte.

[0041] According to certain embodiments, the diaphragm of the liquid battery is selected from PP, PE, or a three-layer laminated diaphragm of PP and PE, and the diaphragm may be provided with a ceramic coating.

[0042] According to certain embodiments, the battery can be configured as a prismatic, pouch, or cylindrical battery.

[0043] The present invention has at least one of the following advantages:

[0044] 1. The treated carbon nanotube film does not contain substances that catalyze the reaction between metallic lithium and air. The density of the carbon nanotube film is 0.5-0.6g / cm 3 , can be used as a preferred lightweight supporting material for metallic lithium.

[0045] 2. The process of removing the catalyst metal does not substantially affect (weaken) the mechanical properties of the carbon nanotube film;

[0046] 3. The negative electrode combined with the treated carbon nanotube film and metallic lithium can well replace the existing lithium-copper composite products. Using this negative electrode, the battery's specific energy can exceed 400wh / kg. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The lithium composite electrode prepared in Comparative Example 2 is shown.

[0048] Figure 2 The transmission electron microscope image of the carbon nanotube film prepared in Example 1 is shown.

[0049] Figure 3 The lithium composite electrode prepared in Example 1 is shown. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0051] Furthermore, the various product structural parameters, various reaction participants and process conditions used in the following embodiments are all relatively typical examples. However, after a large number of experiments and verifications by the inventors of this case, other different structural parameters, other types of reaction participants and other process conditions listed above are also applicable and can also achieve the technical effects claimed in the present invention.

[0052] Comparative Example 1: Benzene was used as the carbon source, ferrocene was used as the catalyst, and thiophene was added as the promoter. After passing through two temperature ranges of low temperature 600°C and high temperature 1200°C, the gas flow was a hydrogen / argon mixture to obtain a carbon nanotube film 1 (thickness 8um), and the tensile strength of the film 1 was 68.9MPa.

[0053] The tensile strength was measured as follows: a 1.5 cm wide x 8 cm long carbon nanotube film 1 was cut and placed on a universal material testing machine (BT-P-50). The two ends of the test material were first clamped to ensure the flatness of the material. The test speed was 30 mm / min, and the test data was recorded when the film broke.

[0054] This membrane material was pressure-compounded with a lithium membrane (lithium thickness was 10 μm). The upper and lower rolls of lithium membrane and the processed membrane material in the middle were unwound separately to obtain a product with lithium coating on both sides. The product was placed in a drying workshop with a dew point of -45°C for two days, and it was found that the lithium in most areas had reacted and turned black.

[0055] After testing, it was found that the blackened area contained nitrogen. It is speculated that the metal components in the carbon nanotube film catalyzed the reaction between metallic lithium and air, resulting in the formation of the blackened area.

[0056] Comparative Example 2

[0057] The carbon nanotube film material 1 prepared in Comparative Example 1 was treated by soaking it in 0.02 mol / L nitric acid for four hours and then washing it three times with deionized water to obtain a treated carbon nanotube film material.

[0058] This membrane material was used to perform pressure lamination with a lithium membrane (lithium thickness of 10 μm). The upper and lower rolls of lithium membrane and the processed membrane material in the middle were unwound to obtain a product with lithium coating on both sides. The product was placed in a drying room with a dew point of -45°C for two days. It was found that the lithium in some areas had reacted and turned black, as shown in the real thing. Figure 1 shown.

[0059] Comparative Example 3

[0060] The carbon nanotube film material 1 prepared in comparative example 1 was treated by soaking it in 1 mol / L nitric acid for six hours and then washing it three times with deionized water to obtain the treated carbon nanotube film material. It was found that there were many holes on the treated film material, the strength of the film material was reduced (less than 20 MPa), the film material was easily torn, and it was not easy to use as a supporting material.

[0061] Comparative Example 4

[0062] The carbon nanotube film 1 prepared in Comparative Example 1 was treated by first performing air firing (high-temperature heating in air) in a muffle furnace for 3 hours at a temperature of 400° C. to obtain a treated carbon nanotube film.

[0063] This membrane material was pressure-compounded with a lithium membrane (lithium thickness of 10 μm). The upper and lower rolls of lithium membrane and the processed membrane material in the middle were unwound separately to obtain a product with lithium coating on both sides. The product was placed in a drying workshop with a dew point of -45°C for two days, and it was found that the lithium in some areas had reacted and turned black.

[0064] Comparative Example 5

[0065] The carbon nanotube film 1 prepared in Comparative Example 1 was treated at a temperature of 2000°C and a pressure of 10 - 3 Pa, the treatment time is 2h, and the treated carbon nanotube film is obtained. The carbon nanotube film becomes brittle and the tensile strength changes from 68.9MPa to 20.6MPa.

[0066] This membrane material and lithium membrane (lithium thickness is 10um) are pressure-compounded. The upper and lower rolls of lithium membrane and the processed membrane material in the middle are unwound separately to obtain a product with lithium coating on both sides. The product is placed in a drying workshop with a dew point of -45℃ for two days, and it is found that the lithium in some areas will react and turn black.

[0067] Comparative Example 6

[0068] The carbon nanotube film material 1 prepared in Comparative Example 1 was treated by first performing air firing in a muffle furnace for 3 hours at a temperature of 400° C. to obtain a preliminarily treated carbon nanotube film material.

[0069] The carbon nanotube film material after the preliminary treatment was further treated with dilute nitric acid, the concentration of the nitric acid was 0.02 mol / L, and the soaking time was 4 hours to obtain a further treated carbon nanotube film material.

[0070] This membrane material and lithium membrane (lithium thickness is 10um) are pressure-compounded. The upper and lower rolls of lithium membrane and the processed membrane material in the middle are unwound separately to obtain a product with lithium coating on both sides. The product is placed in a drying workshop with a dew point of -45℃ for two days, and it is found that the lithium in some areas will react and turn black.

[0071] Comparative Example 7

[0072] The carbon nanotube film material 1 prepared in Comparative Example 1 was treated by first performing air firing in a muffle furnace for three hours at a temperature of 400° C. to obtain a preliminarily treated carbon nanotube film material.

[0073] The carbon nanotube film after preliminary treatment is further treated with high temperature negative pressure, the temperature is 2000℃, the pressure is 10 -3 Pa, the treatment time is 1 hour, and the carbon nanotube film material after further treatment is obtained.

[0074] This membrane material and lithium membrane (lithium thickness is 10um) are pressure-compounded. The upper and lower rolls of lithium membrane and the processed membrane material in the middle are unwound separately to obtain a product with lithium coating on both sides. The product is placed in a drying workshop with a dew point of -45℃ for two days, and it is found that the lithium in some areas will react and turn black.

[0075] Comparative Example 8

[0076] The carbon nanotube film 1 prepared in comparative example 1 was first subjected to high temperature negative pressure treatment at a temperature of 2000°C and a pressure of 10 - 3 Pa, the treatment time is 1 hour, and the carbon nanotube film material after preliminary treatment is obtained.

[0077] The carbon nanotube film after the preliminary treatment was further soaked in 0.02 mol / L nitric acid for four hours to obtain a further treated carbon nanotube film.

[0078] This membrane material and lithium membrane (lithium thickness is 10um) are pressure-compounded. The upper and lower rolls of lithium membrane and the processed membrane material in the middle are unwound separately to obtain a product with lithium coating on both sides. The product is placed in a drying workshop with a dew point of -45℃ for two days, and it is found that the lithium in some areas will react and turn black.

[0079] Comparative Example 9

[0080] The carbon nanotube film 1 prepared in Comparative Example 1 was treated by first soaking it in 0.02 mol / L nitric acid for four hours and then washing it three times with deionized water to obtain a preliminarily treated carbon nanotube film.

[0081] The carbon nanotube film after preliminary treatment was further subjected to vacuum heat treatment at a temperature of 2000°C and a pressure of 10 - 3 Pa, the treatment time is 1 hour, and the carbon nanotube film material after further treatment is obtained.

[0082] This membrane material and lithium membrane (lithium thickness is 10um) are pressure-compounded. The upper and lower rolls of lithium membrane and the processed membrane material in the middle are unwound separately to obtain a product with lithium coating on both sides. The product is placed in a drying workshop with a dew point of -45℃ for two days, and it is found that the lithium in some areas will react and turn black.

[0083] Example 1

[0084] The carbon nanotube film material 1 prepared in Comparative Example 1 was treated by first performing air firing in a muffle furnace for three hours at a temperature of 400° C. to obtain a preliminarily treated carbon nanotube film material.

[0085] The carbon nanotube film material after the preliminary treatment was soaked in 0.02 mol / L nitric acid for four hours, and then washed three times with deionized water to obtain the carbon nanotube film material after further treatment.

[0086] The carbon nanotube film was further treated with high temperature negative pressure treatment at a temperature of 2000°C and a pressure of 10 - 3 Pa, the treatment time is 30min, and a clean carbon nanotube film is obtained. The transmission electron microscope image is as follows Figure 2 As shown, no iron particles were observed.

[0087] The cleaned carbon nanotube film and lithium film (lithium thickness is 10um) are pressure-compounded, and the upper and lower rolls of lithium film and the cleaned film in the middle are unwound to obtain a double-sided lithium-coated product. The product is placed in a drying workshop with a dew point of -45℃ for two days or even a month, and it is found that there is no black area of ​​the metallic lithium, as shown in the actual product. Figure 3 As shown, it shows that the carbon nanotube film has completely removed iron.

[0088] Table 1: Content values ​​excluding iron

[0089]

[0090] The iron content in the carbon nanotube film prepared by the vapor phase method is about 8 wt%. As can be seen from the values ​​in Table 1, when only acid treatment is used on the original carbon nanotube film, such as in Comparative Examples 2 and 3, very little iron is removed. Therefore, when compounded with metallic lithium, the metallic lithium will react and turn black.

[0091] The carbon nanotube film is first calcined and then acid treated. A lot of iron is removed, such as in Comparative Example 6, but not all of it is removed. Further vacuum heat treatment is required. Figure 2 It can be seen from the transmission electron microscope image that the iron impurities have been completely removed after the above treatment.

[0092] The present invention first adopts empty burning, and the carbon that does not form carbon tube is burned off, and the catalyst of iron is leaked out, and then dilute acid treatment is carried out, and most of iron can be slowly removed, and the intrinsic structure of carbon nanotube film is not destroyed as far as possible. Because some iron catalysts are present in the tube end inside of carbon nanotube, there will be a small amount of iron catalyst that can not be thoroughly removed, and it is necessary to further remove deeply in a short time by vacuum heat treatment. Because only adopting one-step vacuum heat treatment such as comparative example 5, catalyst iron is still not completely removed, and the temperature and time of another vacuum heat treatment are longer, and the carbon nanotube film after treatment can become more brittle, and tensile strength decreases (film material cannot be used as the supporting material of metallic lithium), so vacuum heat treatment is carried out in the last step as far as possible, and is equivalent to most of catalyst iron and has been removed, and a small amount of iron catalyst can be removed in a very short time, and the intensity and the apparent morphology of carbon nanotube film itself are destroyed minimum, and the carbon nanotube film with the iron catalyst removed can be obtained.

[0093] It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium composite negative electrode, characterized in that The lithium composite negative electrode comprises: a current collector film and an active material layer attached to at least one surface of the current collector film, wherein the active material in the active material layer is metallic lithium or a lithium alloy, and the current collector film is a carbon nanotube film that meets the following conditions: The content of catalyst metal is below 0.1wt%; The thickness of the membrane is 5-20um; The tensile strength of the membrane is greater than 20 MPa and less than or equal to 200 MPa; The sheet resistance of the film is 0.1-100Ω / cm 2 .

2. The lithium composite negative electrode according to claim 1, characterized in that The catalyst metal includes at least one of iron, cobalt, and nickel.

3. The lithium composite negative electrode according to claim 1, characterized in that The thickness of the active material layer is 1-100 μm, preferably 1-20 μm; the width is 50-1400 mm, preferably 200-700 mm; The lithium alloy is formed by combining metallic lithium with any one or at least two elements of Ag, Au, Sn, Si, Zn, Al, Mg, In, Ga, B, Mn, Sb, Cr, C, V, Cu, Fe or Ti. Preferably, the mass percentage of metallic lithium in the lithium alloy is above 90%.

4. The lithium composite negative electrode according to claim 1, characterized in that The carbon nanotube film is a carbon nanotube film prepared by a gas phase method, from which iron elements are removed.

5. A method for preparing a lithium composite negative electrode according to any one of claims 1 to 4, characterized in that: The method comprises: preparing a carbon nanotube film from which catalyst metals have been removed; Applying active material to at least one surface of the carbon nanotube film from which the metal has been removed by coating, pressure lamination or vapor deposition process to obtain a lithium composite negative electrode, The preparation of the carbon nanotube film from which the catalyst metal has been removed includes the steps of subjecting the carbon nanotube film prepared by the vapor phase method to a two-step heat treatment, wherein the first heat treatment step is: subjecting the carbon nanotube film to a high temperature treatment in air for 2-6 hours at a temperature of 400-500°C; the second heat treatment step is: subjecting the carbon nanotube film to a vacuum heat treatment at a temperature of 1800-2000°C and a vacuum degree of 10 -2 Below Pa, the processing time is 30min-60min.

6. The method according to claim 5, characterized in that The method further comprises: soaking the carbon nanotube film in dilute acid between the first heat treatment and the second heat treatment, or after the two heat treatments, wherein the concentration of the dilute acid is 0.005-0.1 mol / L, washing with deionized water after soaking, and drying.

7. The method according to claim 6, characterized in that The method further comprises: Before the heat treatment, the carbon nanotube film prepared by the vapor phase method is cleaned and dried to remove the oil on the surface of the carbon nanotube film; and Optionally, after the two-step heat treatment step and the dilute acid soaking step, the surface of the obtained carbon nanotube film is moistened and then rolled with a hot roller to make the surface flat.

8. The use of the lithium composite negative electrode according to any one of claims 1 to 4, characterized in that: The lithium composite negative electrode is directly used as the negative electrode of the lithium battery.

9. The use according to claim 8, characterized in that The positive electrode of the lithium battery uses nickel-cobalt-manganese ternary, nickel-cobalt-aluminum ternary, lithium-rich manganese-based positive electrode material, lithium iron phosphate, sulfur-based positive electrode material, and lithium cobalt oxide positive electrode material.

10. The use according to claim 8, characterized in that The lithium battery is a liquid lithium ion battery or a solid lithium ion battery.

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