Lithium-free negative electrode plate containing carbon nanotube coating, preparation method and lithium-free negative electrode battery

Abstract

The invention discloses a lithium-free negative electrode plate containing a carbon nanotube coating, a preparation method and a lithium-free negative electrode battery, and relates to the field of lithium-free negative electrode plates. The lithium-free negative electrode plate comprises a negative electrode current collector and a carbon nanotube coating, the carbon nanotube coating is formed by sequentially coating, drying, calcining and rolling transfer printing slurry, the calcining temperature is 300-500 DEG C, and the mass fraction of carbon nanotubes in the slurry is 1-10 wt%. The uniform and flat carbon nanotube coating is introduced on the lithium-free negative electrode plate, so that the conductivity and the lithium affinity of the negative electrode plate are improved, more lithium deposition active sites are introduced, uniform deposition of lithium is promoted, meanwhile, the structural stability of the negative electrode plate can be enhanced due to the high mechanical strength of the carbon nanotubes, and the service life of the negative electrode plate is prolonged. The volume expansion and deformation in the circulation process are effectively relieved, and the energy density and the cycle life of the lithium-free negative electrode battery are both improved and prolonged.

Description

Technical Field

[0001] The present invention relates to the field of lithium-free negative electrode sheets, and in particular to a lithium-free negative electrode sheet containing a carbon nanotube coating, a preparation method thereof, and a lithium-free negative electrode battery. Background Art

[0002] Lithium metal, with its exceptional theoretical specific capacity of 3860 mAh / g, far exceeding that of conventional graphite anodes, has become a research hotspot for next-generation lithium battery anode materials, demonstrating broad application potential. However, practical applications of lithium metal anodes face significant challenges, particularly the uncontrolled growth of lithium dendrites and volume expansion of the lithium metal during cycling. These issues not only reduce the battery's cycle life and stability but also pose serious safety risks, significantly limiting its commercialization.

[0003] To this end, a lithium-free negative electrode battery system has emerged. This system abandons the excessive lithium storage method in the negative electrode and relies on the positive electrode material as the only lithium source. This design fundamentally reduces the total amount of lithium inside the battery and significantly improves the safety of the battery. However, in the current development of lithium-free negative electrode battery technology, there are three key challenges that need to be overcome: first, the scarcity of nucleation sites on the negative electrode surface leads to uneven lithium deposition, and new strategies need to be developed to promote uniform deposition; second, the electrode sheet has poor conductivity, and lithium is more likely to form dead lithium under shallow charge and discharge conditions, resulting in irreversible capacity loss, and the electrode sheet conductivity needs to be improved; third, the negative electrode structure is prone to volume expansion and deformation after long-term cycling, and it should be ensured that the negative electrode structure remains highly stable during frequent charge and discharge processes to extend the overall battery life. Summary of the Invention

[0004] The present invention provides a lithium-free negative electrode plate containing a carbon nanotube coating, a preparation method, and a lithium-free negative electrode battery. By introducing a carbon nanotube coating on the lithium-free negative electrode plate, the conductivity and lithium affinity are improved, the uniform deposition of lithium is promoted, the stability of the negative electrode structure is enhanced, and the energy density and cycle life of the lithium-free negative electrode battery are both improved.

[0005] In order to solve the above technical problems, one of the purposes of the present invention is to provide a lithium-free negative electrode plate containing a carbon nanotube coating, including a negative electrode current collector and a carbon nanotube coating, wherein the carbon nanotube coating is formed by sequentially coating, drying, calcining and roller transfer of a slurry, the calcination temperature is 300-500°C, and the mass fraction of the carbon nanotubes in the slurry is 1wt%-10wt%.

[0006] In this application, a calcined carbon nanotube coating is roller-transferred onto the lithium-free negative electrode sheet. Carbon nanotubes (CNTs) have excellent electrical conductivity, chemical stability and mechanical strength. The high conductivity and lithium affinity of carbon nanotubes are utilized to introduce more lithium deposition active sites on the negative electrode sheet, promote the uniform deposition of lithium, improve the conductivity of the electrode sheet, avoid the formation of dead lithium in shallow charge and discharge states, and ensure the capacity retention rate of the cycle. At the same time, the carbon nanotube coating can also enhance the mechanical strength of the negative electrode sheet, improve the stability of the negative electrode structure, effectively alleviate the volume expansion and deformation that occur during the cycle, and achieve a dual increase in the energy density and cycle life of the lithium-free negative electrode battery.

[0007] As a preferred solution, the mass fraction of the carbon nanotubes in the slurry is 2 wt%-5 wt%.

[0008] The present application controls the carbon nanotube content in the carbon nanotube coating on the lithium-free negative electrode plate to be low, which can meet the higher energy density requirements of the lithium-free negative electrode battery. At the same time, it can also maximize the introduction of lithium deposition active sites to ensure uniform deposition of lithium and avoid affecting the energy density of the battery due to excessive carbon nanotube content in the coating.

[0009] As a preferred solution, the mass fraction of the carbon nanotubes in the slurry is within the range of any one or any two of 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, and 5wt%.

[0010] As a preferred solution, the slurry further includes a binder with a mass fraction of 1wt%-10wt%.

[0011] As a preferred solution, the mass fraction of the binder in the slurry is 1wt%-5wt%.

[0012] As a preferred embodiment, the mass fraction of the binder in the slurry is within the range of any one or any two of 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, and 5wt%.

[0013] As a preferred solution, the slurry further comprises a solvent with a mass fraction of 80 wt% to 98 wt%.

[0014] As a preferred solution, the binder is at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0015] As a preferred embodiment, the solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0016] As a preferred embodiment, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes, preferably single-walled carbon nanotubes.

[0017] As a preferred embodiment, the negative electrode current collector is any one of copper foil, carbon-coated copper foil, copper-based lithium tape, aluminum foil, silver-plated copper foil, nickel-plated copper foil, and tin-plated copper foil, preferably aluminum foil.

[0018] As a preferred solution, the thickness of the carbon nanotube coating is 5-50 μm.

[0019] As a preferred solution, the thickness of the carbon nanotube coating is 10-30 μm.

[0020] As a preferred solution, the thickness of the carbon nanotube coating is within the range of any one or any two of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm.

[0021] In order to solve the above technical problems, the second object of the present invention is to provide a method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating, comprising the following steps:

[0022] (1) uniformly coating the slurry on a carrier foil, drying the slurry, and calcining the slurry at 300-500° C. to obtain a carrier foil containing a carbon nanotube coating;

[0023] (2) The carbon nanotube coating is slightly peeled off from the carrier foil, and the carrier foil is placed on the negative electrode current collector for roller pressing. The carbon nanotube coating is located between the carrier foil and the negative electrode current collector, and the distance between the two rollers during rolling is 60-120 μm. After rolling, the carrier foil is separated, and the carbon nanotube coating is transferred to the negative electrode current collector. The negative electrode current collector is dried and cut to obtain a lithium-free negative electrode sheet.

[0024] This application first applies a carbon nanotube coating on a specific carrier foil, removes organic components during the calcination process to avoid interference with the subsequent lithium deposition active sites. The calcined carbon nanotube coating can be stably attached to the carrier foil, and the calcined coating is smooth and wrinkle-free, avoiding affecting the deposition of lithium in the subsequent cyclic charge and discharge process. The carbon nanotube coating is transferred to the surface of the negative electrode current collector by rolling to fix the carbon nanotube coating, thereby improving the conductivity and lithium affinity of the lithium-free negative electrode sheet, improving the mechanical strength of the negative electrode structure, and making the assembled lithium-free negative electrode battery have high energy density and cycle life.

[0025] As a preferred embodiment, in step (1), the calcination temperature is within the range of any one or any two of 300°C, 350°C, 400°C, 450°C, and 500°C.

[0026] As a preferred embodiment, in step (1), the calcination time is 4-12 hours.

[0027] As a preferred embodiment, in step (1), the calcination time is within the range of any one or any two of 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, and 12 h.

[0028] As a preferred solution, in step (1), the heating rate of the calcination process is 3-8°C / min.

[0029] As a preferred embodiment, in step (1), calcination is carried out in nitrogen or an inert gas.

[0030] As a preferred solution, in step (1), the drying temperature is 35-150° C., and the drying time is 1-8 hours.

[0031] As a preferred solution, in step (1), the drying temperature is 20-120° C., and the drying time is 2-5 h.

[0032] As a preferred solution, in step (1), the carrier foil is any one of copper foil and stainless steel foil.

[0033] As a preferred embodiment, in step (2), the temperature of the roller pressing is 20-100°C.

[0034] As a preferred embodiment, in step (2), the temperature of the roller pressing is 40-80°C.

[0035] As a preferred embodiment, in step (2), the rolling temperature is within the range of any one or any two of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, and 80°C.

[0036] In order to solve the above technical problems, the third object of the present invention is to provide a lithium-free negative electrode battery, including a lithium-free negative electrode plate containing a carbon nanotube coating.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] In this application, the calcined carbon nanotube coating is transferred to the surface of the negative electrode current collector by roller pressing. The high conductivity and lithium affinity of carbon nanotubes are used to introduce more lithium deposition active sites on the negative electrode plate to promote the uniform deposition of lithium. The pre-calcination treatment of the carbon nanotube coating can prevent organic components from interfering with the lithium deposition active sites. At the same time, the high mechanical strength of carbon nanotubes can also enhance the structural stability of the negative electrode plate, effectively alleviate the volume expansion and deformation that occur during the cycle, and achieve a dual increase in the energy density and cycle life of lithium-free negative electrode batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : It is a schematic flow chart of a method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0041] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0043] As used herein:

[0044] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0045] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0046] In these examples, parts and percentages are by mass unless otherwise indicated.

[0047] "Parts by mass" is a basic unit of measurement that indicates the mass ratio of multiple components. 1 part can represent any unit of mass. It should be noted that, unlike parts by mass, the sum of all parts by mass of all components is not limited to 100 parts.

[0048] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0049] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "top", "bottom", etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0050] To further illustrate the present invention, the present invention is described in detail below with reference to the following examples, but they should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following examples and comparative examples of the present application are all commercially available, and the same raw materials are used in parallel experiments.

[0051] Example 1

[0052] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating, such as Figure 1 As shown, the following steps are included:

[0053] (1) 6 g of single-walled carbon nanotube slurry with a solid content of 3 wt% and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 99:1 to prepare a slurry, wherein the single-walled carbon nanotube slurry also included 97 wt% of N-methylpyrrolidone. The mixed slurry was evenly coated on an aluminum foil, and then the aluminum foil was placed in an oven at 100°C for 3 h. After drying, a carbon nanotube coating with a thickness of about 10 μm was formed. The aluminum foil was then placed in a muffle furnace and calcined at 400°C for 6 h to remove part of the organic binder and reduce subsequent interference with the active sites of lithium deposition. The heating rate was 5°C / min, and nitrogen protection was introduced throughout the process to obtain an aluminum foil containing a carbon nanotube coating;

[0054] (2) After calcination, the carbon nanotube coating and the aluminum foil peeled off slightly, but not completely. The aluminum foil was placed on the bare copper foil and rolled relative to each other. The distance between the two rollers was about 120 μm and the rolling temperature was 60 ° C. The two foils were separated after rolling. At this time, most of the carbon nanotube coating on the aluminum foil was successfully transferred to the bare copper foil. A small amount of carbon nanotube coating remained on the corners of the aluminum foil due to the uneven pressure of the roller press. The carbon nanotube coating on the bare copper foil was flat and smooth. After the bare copper foil was dried and cut, a flat and smooth lithium-free negative electrode sheet was obtained by screening.

[0055] Example 2

[0056] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating comprises the following steps:

[0057] (1) 6 g of single-walled carbon nanotube slurry with a solid content of 3 wt% was mixed with PVDF in a mass ratio of 99:1 to prepare a slurry, wherein the single-walled carbon nanotube slurry also included 97 wt% of N-methylpyrrolidone. The mixed slurry was evenly coated on an aluminum foil, and then the aluminum foil was placed in an oven at 100°C for 3 h. After drying, a carbon nanotube coating with a thickness of about 10 μm was formed. The aluminum foil was then placed in a muffle furnace and calcined at 450°C for 8 h to remove part of the organic binder and reduce subsequent interference with the active sites of lithium deposition. The heating rate was 5°C / min, and nitrogen protection was introduced throughout the process to obtain an aluminum foil containing a carbon nanotube coating;

[0058] (2) After calcination, the carbon nanotube coating and the aluminum foil peeled off slightly, but not completely. The aluminum foil was placed on the bare copper foil and rolled relative to each other. The distance between the two rollers was about 120 μm, and the rolling temperature was 80 ° C. The two foils were separated after rolling. At this time, most of the carbon nanotube coating on the aluminum foil was successfully transferred to the bare copper foil. A small amount of carbon nanotube coating remained on the corners of the aluminum foil due to the uneven pressure of the roller press. The carbon nanotube coating on the bare copper foil was flat and smooth. After the bare copper foil was dried and cut, it was screened to obtain a flat and smooth lithium-free negative electrode sheet.

[0059] Example 3

[0060] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (2), the roller spacing is about 80 μm.

[0061] Example 4

[0062] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating comprises the following steps:

[0063] (1) 6 g of single-walled carbon nanotube slurry with a solid content of 3 wt% was mixed with PVDF in a mass ratio of 98.5:1.5 to prepare a slurry, wherein the single-walled carbon nanotube slurry also included 97 wt% of N-methylpyrrolidone. The mixed slurry was evenly coated on an aluminum foil, and then the aluminum foil was placed in an oven at 100°C for 3 h. After drying, a carbon nanotube coating with a thickness of about 10 μm was formed. The aluminum foil was then placed in a muffle furnace and calcined at 400°C for 6 h to remove part of the organic binder and reduce subsequent interference with the active sites of lithium deposition. The heating rate was 5°C / min, and nitrogen protection was introduced throughout the process to obtain an aluminum foil containing a carbon nanotube coating;

[0064] (2) After calcination, the carbon nanotube coating and the aluminum foil peeled off slightly, but not completely. The aluminum foil was placed on the bare copper foil and rolled relative to each other. The distance between the two rollers was about 120 μm, and the rolling temperature was 80 ° C. The two foils were separated after rolling. At this time, most of the carbon nanotube coating on the aluminum foil was successfully transferred to the bare copper foil. A small amount of carbon nanotube coating remained on the corners of the aluminum foil due to the uneven pressure of the roller press. The carbon nanotube coating on the bare copper foil was flat and smooth. After the bare copper foil was dried and cut, it was screened to obtain a flat and smooth lithium-free negative electrode sheet.

[0065] Example 5

[0066] A method for preparing a lithium-free negative electrode plate containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (1), the aluminum foil calcination temperature is 500°C.

[0067] Example 6

[0068] A method for preparing a lithium-free negative electrode plate containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (1), the aluminum foil calcination temperature is 350°C.

[0069] Comparative Example 1

[0070] A method for preparing a lithium-free negative electrode plate containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (1), the aluminum foil calcination temperature is 600°C.

[0071] Comparative Example 2

[0072] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (2), the distance between the two rollers in the rolling process is about 150 μm.

[0073] Comparative Example 3

[0074] A method for preparing a lithium-free negative electrode plate containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that, in step (1), 6 g of a single-walled carbon nanotube slurry having a solid content of 3 wt% is mixed with PVDF in a mass ratio of 99:1 to prepare a slurry, wherein the single-walled carbon nanotube slurry further comprises 97 wt% of N-methylpyrrolidone, the mixed slurry is evenly and evenly coated on an aluminum foil, and the aluminum foil is then placed in an oven at 100°C and baked for 3 h. After drying, a carbon nanotube coating having a thickness of about 10 μm is formed, thereby obtaining an aluminum foil containing a carbon nanotube coating.

[0075] Comparative Example 4

[0076] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating comprises the following steps:

[0077] (1) 6 g of single-walled carbon nanotube slurry with a solid content of 3 wt% and PVDF were mixed in a mass ratio of 99:1 to prepare a slurry, wherein the single-walled carbon nanotube slurry also included 97 wt% of N-methylpyrrolidone. The mixed slurry was evenly coated on a bare copper foil, and then the bare copper foil was placed in an oven at 100° C. and baked for 3 h. After drying, a carbon nanotube coating with a thickness of about 10 μm was formed. Subsequently, the bare copper foil was placed in a muffle furnace and calcined at 400° C. for 6 h to remove part of the organic binder and reduce subsequent interference with the active sites of lithium deposition. The heating rate was 5° C. / min, and nitrogen protection was introduced throughout the process to obtain a bare copper foil containing a carbon nanotube coating;

[0078] (2) After calcination, most of the copper foil and the carbon nanotube coating are separated, and the unseparated part is severely wrinkled, which affects the uniformity of subsequent lithium deposition. The bare copper foil without the separated carbon nanotube coating is dried and cut to obtain a lithium-free negative electrode.

[0079] Comparative Example 5

[0080] A method for preparing a lithium-free negative electrode plate containing a graphite coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (1), single-walled carbon nanotubes are replaced by an equal amount of graphite.

[0081] Comparative Example 6

[0082] A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating comprises the following steps: drying and cutting a bare copper foil, and then screening to obtain a flat and smooth lithium-free negative electrode sheet.

[0083] Comparative Example 7

[0084] A method for preparing a lithium-free negative electrode plate containing a carbon nanotube coating, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (1), the solid content of the single-walled carbon nanotube slurry is 15 wt%.

[0085] Performance testing

[0086] The full battery was assembled using the eight-series ternary material as the positive electrode, the lithium-free negative electrode plate as the negative electrode, and a polyethylene-based film coated with ceramic on one side as the separator. After injection of a dual-salt electrolyte containing 1 mol / L LiDFOB and 0.7 mol / L LiBF4 and a balance of FEC:DEC=7:3, it was placed at room temperature for 24 hours. After formation, degassing, and trimming, a lithium-ion full battery was obtained. Thereafter, constant current charge and discharge cycles were carried out at a current density of 0.2C and a voltage window of 3.5-4.5V. The energy density after the cycle, the first-cycle coulomb efficiency, and the number of cycles with 80% capacity retention were tested. The test results are shown in Table 1 below.

[0087] Table 1 - Charge and discharge cycle test results of full batteries prepared from lithium-free negative electrode sheets in the present embodiment and comparative example

[0088]

[0089] As shown in Table 1, compared with Comparative Example 6 which uses bare copper foil as the lithium-free negative electrode plate, Example 1 of the present application introduces a uniform and flat carbon nanotube protective coating on the lithium-free negative electrode plate, which not only improves the conductivity of the negative electrode, but also introduces more lithium deposition active sites to achieve uniform lithium deposition, and can also enhance structural stability, effectively alleviate the volume change during the charge and discharge process, so that the lithium-free negative electrode battery can achieve a dual improvement in high energy density and cycle life. The number of cycles with 80% capacity retention of the assembled battery is increased, and the cycle stability is good.

[0090] As shown in Table 1, the carbon nanotube-coated aluminum foil in Examples 1, 6-7 was calcined at 350-500°C, while the carbon nanotube-coated aluminum foil in Comparative Example 1 was calcined at 600°C. This excessively high calcination temperature caused the carbon nanotube coating to completely separate from the current collector, increasing the difficulty of the subsequent transfer step. Furthermore, the excessively high temperature caused the carbon nanotubes to almost completely carbonize, rendering them unable to perform their original lithium storage and structural protection functions. Consequently, the cycle capacity retention rate of the resulting lithium-free negative electrode assembled battery was low, resulting in a sharp drop in capacity. The carbon nanotube-coated aluminum foil in Comparative Example 3 was not calcined, and most of the organic functional groups remained at the current collector-electrolyte interface, interfering with the normal deposition of lithium on the current collector. This easily led to the growth of lithium dendrites during cycling, thus affecting the cycle life. Its cycle capacity dropped sharply, with only 18 cycles achieving 80% capacity retention.

[0091] As shown in Table 1, during the rolling process of the aluminum foil and the bare copper foil in Examples 1 and 3, the distance between the two rollers was 80-120 μm, while the distance between the two rollers in Comparative Example 2 was 150 μm. The excessive distance between the two rollers resulted in a loose adhesion of the carbon nanotube coating on the bare copper foil, which was prone to wrinkling or detachment during the charge and discharge cycle, affecting the cycle capacity retention of the battery and reducing the cycle stability.

[0092] As shown in Table 1, in Example 1 of the present application, a carbon nanotube coating is pre-coated on an aluminum foil for calcination. After calcination, the coating and the aluminum foil are not easily separated, and the coating is subsequently transferred to a bare copper foil by roller pressing to prepare a lithium-free negative electrode sheet. In Comparative Example 4, a carbon nanotube coating is coated on a bare copper foil and calcined. After calcination, the coating has weak adhesion to the bare copper foil and is prone to wrinkling or peeling, affecting the uniformity of lithium deposition in the subsequent battery cycle process, causing a sharp drop in capacity during the cycle process, and affecting the cycle stability.

[0093] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A lithium-free negative electrode plate containing a carbon nanotube coating, characterized in that: The invention comprises a negative electrode current collector and a carbon nanotube coating. The carbon nanotube coating is formed by coating, drying, calcining and roller transfer of slurry in sequence. The calcination temperature is 300-500°C. The mass fraction of carbon nanotubes in the slurry is 1wt%-10wt%.

2. The lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 1, wherein: The slurry further includes a binder with a mass fraction of 1wt%-10wt%; And / or, the slurry further comprises a solvent with a mass fraction of 80 wt% to 98 wt%.

3. The lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 2, wherein: The binder is at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber; and / or, the solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; And / or, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes.

4. The lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 1, wherein: The negative electrode current collector is any one of copper foil, carbon-coated copper foil, copper-based lithium tape, aluminum foil, silver-plated copper foil, nickel-plated copper foil, and tin-plated copper foil.

5. The lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 1, wherein: The thickness of the carbon nanotube coating is 5-50 μm.

6. A method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) uniformly coating the slurry on a carrier foil, drying the slurry, and calcining the slurry at 300-500° C. to obtain a carrier foil containing a carbon nanotube coating; (2) The carbon nanotube coating is slightly peeled off from the carrier foil, and the carrier foil is placed on the negative electrode current collector for roller pressing. The carbon nanotube coating is located between the carrier foil and the negative electrode current collector, and the distance between the two rollers during rolling is 60-120 μm. After rolling, the carrier foil is separated, and the carbon nanotube coating is transferred to the negative electrode current collector. The negative electrode current collector is dried and cut to obtain a lithium-free negative electrode sheet.

7. The method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 6, wherein: In step (1), the calcination time is 4-12 hours; and / or, in step (1), the heating rate during the calcination process is 3-8°C / min; And / or, in step (1), calcination is carried out in nitrogen or an inert gas.

8. The method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 6, wherein: In step (1), the drying temperature is 35-150° C. and the drying time is 1-8 h; And / or, in step (1), the carrier foil is any one of copper foil and stainless steel foil.

9. The method for preparing a lithium-free negative electrode sheet containing a carbon nanotube coating according to claim 6, wherein: In step (2), the temperature of the roller pressing is 20-100°C.

10. A lithium-free negative electrode battery, characterized in that: A lithium-free negative electrode sheet comprising a carbon nanotube-coated lithium-free negative electrode sheet as claimed in any one of claims 1 to 5 or a lithium-free negative electrode sheet prepared according to the preparation method of a carbon nanotube-coated lithium-free negative electrode sheet as claimed in any one of claims 6 to 9.

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