A negative electrode material and its preparation method and application

Abstract

This invention relates to an anode material, its preparation method, and its application. The anode material comprises carbon nanotubes and a silicon layer coating the carbon nanotubes. The anode material of this invention can reduce the resistance of the anode sheet, improve rate performance, and further alleviate the volume expansion problem. Furthermore, by combining single-walled and multi-walled carbon nanotubes, the anode material possesses a richer microporous and mesoporous structure, which can further provide a buffer gap for silicon expansion. Moreover, by configuring the carbon nanotubes to include both single-walled and multi-walled carbon nanotubes, a highly efficient conductive network can be achieved, resulting in high conductivity and further improving the rate performance of the anode sheet.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a negative electrode material, its preparation method, and its application. Background Technology

[0002] In recent years, with the large-scale application of new energy vehicles, the shortcomings of current battery technology have been exposed: range anxiety caused by low energy density. Using high-specific-capacity positive and negative electrode materials can increase battery energy while reducing material weight, significantly improving battery energy density. However, at present, the actual specific capacity of graphite anode materials commonly used in power batteries is 340-360 mAh / g, which is close to the upper limit of graphite material's specific capacity of 372 mAh / g.

[0003] Silicon anode materials are currently the most promising anode materials, with a theoretical specific capacity as high as 4200 mAh / g. By mixing with graphite, a capacity of 600-1000 mAh / g can be achieved, and the weight can be reduced by more than 50% compared to existing graphite. However, the lithium intercalation mechanism of silicon leads to a volume change rate of up to 300% during charge and discharge, making the electrode structure prone to cracking, increasing side reactions, and causing a sharp decline in battery capacity. At the same time, silicon has low electrical conductivity, resulting in slow electron conduction and poor rate performance in batteries using silicon as the anode material.

[0004] To address the aforementioned issues, methods such as optimizing the silicon anode structure and surface coating are typically employed to mitigate expansion problems and improve conductivity. For example, patent document CN112938939A discloses a method for preparing carbon-modified silicon / silica-coated acidified carbon nanotubes, including the following steps: (1) Weigh an appropriate amount of carbon nanotubes and add them to aqua regia, place them in a water bath, maintain at 2080℃ and stir at 300r / min for 4-9 hours, and dry at 60-80℃ to obtain acidified carbon nanotubes; (2) Add the acidified carbon nanotubes to anhydrous ethanol and shear at high speed for 1 hour to form a carbon nanotube dispersion; (3) Add concentrated ammonia to the carbon nanotube dispersion to adjust the pH value to 9-10, maintain the water bath temperature at 60-80℃, and simultaneously add tetraethyl orthosilicate, stir at 300r / min for 3-9 hours, filter, and dry at 60-90℃ to obtain silica-coated acidified carbon nanotubes; (4) Take the prepared silica-coated acidified carbon nanotubes, mix them with magnesium powder in a mass ratio of 5:3-4, and then mix the mixed powder with N (5) Mix aCl at a mass ratio of 1:15 until uniform. After uniform mixing, place the mixture in a tube furnace and heat it to 650°C under argon atmosphere. Hold the temperature for 3 hours and then cool to obtain mixed powder. (6) Add 10% dilute hydrochloric acid to the powder to wash away impurities. After vacuum filtration, place it in a drying oven to dry and obtain silicon / silica-coated acidified carbon nanotube material. (7) Take the dried silicon / silica-coated acidified carbon nanotube and sucrose at a mass ratio of 1:2-3. Add it to deionized water and then ultrasonically disperse it for 30-60 minutes. After filtration, obtain sucrose-attached silicon / silica-coated acidified carbon nanotube material. (8) Place the filtered sucrose-attached silicon / silica-coated acidified carbon nanotube powder in a tube furnace and heat it at 500-550°C for 12 hours under argon atmosphere. Then heat it to 800-900°C and hold it for 3 hours. Cool it with the furnace to obtain carbon-modified silicon / silica-coated acidified carbon nanotube. This method reduces some SiO2 nanotubes to Si, giving them the excellent properties of both SiO2 and Si. However, the electrodes formed by carbon-modified silicon / silica-coated acidified carbon nanotubes prepared by this method have high resistance, poor rate performance, and further improvements are needed to enhance their expansion performance. Summary of the Invention

[0005] One objective of this invention is to provide a negative electrode material to reduce the resistance of the electrode formed by the negative electrode material, improve the rate performance, and further alleviate the volume expansion problem; a second objective is to provide a method for preparing the negative electrode material as described above; a third objective is to provide an electrochemical device; and a fourth objective is to provide an electronic device.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In some embodiments, the present invention provides a negative electrode material comprising carbon nanotubes and a silicon layer coating the carbon nanotubes.

[0008] In some embodiments, the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both.

[0009] In some embodiments, the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0010] In some embodiments, the present invention also provides a method for preparing the negative electrode material as described above, the method comprising:

[0011] S1. The carbon source is soaked in an iron salt solution and then dried to obtain the precursor;

[0012] S2. The precursor is sintered under a protective gas atmosphere, then cooled and acid-washed to obtain a carbon nanotube framework;

[0013] S3. Mix carbon nanotube framework, silane coupling agent and solvent, then dry and mix with metal reducing agent, carry out reduction reaction under auxiliary gas atmosphere, then wash and dry again to obtain the negative electrode material shown.

[0014] In some embodiments, in step S1, the carbon source includes a porous sponge containing nitrogen, such as melamine sponge, polyurethane sponge, etc.

[0015] In some embodiments, in step S1, the concentration of the iron salt solution is 0.04-0.08 mg / mL, preferably 0.05-0.08 mg / mL.

[0016] In some embodiments, in step S1, the soaking time is 24-36 hours, preferably 30-36 hours.

[0017] In some embodiments, in step S1, the drying temperature is 60-75°C, preferably 65-75°C; the drying time is 10-15 hours, preferably 12-15 hours.

[0018] In some embodiments, in step S2, the sintering temperature is 500-600℃, preferably 550-600℃; and the sintering time is 0.5-1h, preferably 0.6-1h.

[0019] In some embodiments, step S2 includes a secondary sintering process after sintering and before cooling.

[0020] In some embodiments, in step S2, the temperature of the secondary sintering is 800-900℃, preferably 850-900℃; and the sintering time is 3-5h, preferably 3.5-5h.

[0021] In some embodiments, the protective gas in step S2 may include, for example, nitrogen, argon, helium, neon, etc.

[0022] In some embodiments, in step S2, the silane coupling agent includes at least one of vinyltriethoxysilane, vinyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

[0023] In some embodiments, in step S2, the mass ratio of the carbon nanotube framework to the silane coupling agent is 1:0.88-1.12.

[0024] In some embodiments, in step S2, the silane coupling agent comprises vinyltriethoxysilane and 3-aminopropyltrimethoxysilane or includes vinyltrimethoxysilane and 3-aminopropyltrimethoxysilane.

[0025] In some embodiments, in step S2, the molar ratio of vinyltriethoxysilane to 3-aminopropyltrimethoxysilane is 1:0.2-0.5.

[0026] In some embodiments, in step S2, the molar ratio of vinyltrimethoxysilane to 3-aminopropyltrimethoxysilane is 1:0.2-0.5.

[0027] In some embodiments, in step S2, the solvent includes at least one of acetone, isopropanol, and dimethyl sulfoxide.

[0028] In some embodiments, in step S3, the drying temperature is 60-75°C, preferably 65-75°C.

[0029] In some embodiments, in step S3, the metal reducing agent includes at least one of zinc, magnesium, and aluminum.

[0030] In some embodiments, in step S3, the mass ratio of the metal reducing agent to the silane coupling agent is 1:15-20, preferably 1:18-20.

[0031] In some embodiments, the auxiliary gas in step S3 may include, for example, nitrogen, argon, helium, neon, etc.

[0032] In some embodiments, in step S3, the reduction temperature is 800-1000℃, preferably 850-1000℃; the reduction duration is 2-5h, preferably 2-4h.

[0033] In some embodiments, in step S3, the temperature of the secondary drying is 60-75°C, preferably 65-75°C.

[0034] In some embodiments, the present invention also provides an electrochemical device comprising a negative electrode, the negative electrode comprising the negative electrode material as described above or a negative electrode material prepared according to the preparation method described above.

[0035] In some embodiments, the present invention also provides an electronic device comprising the electrochemical device described above.

[0036] In some embodiments, this application also provides an electrochemical device, the electrochemical device including a negative electrode sheet, the negative electrode sheet including the negative electrode material as described above or the negative electrode material prepared according to the preparation method described above.

[0037] In some embodiments, this application also provides an electronic device comprising the electrochemical device described above.

[0038] The beneficial effects of this invention are:

[0039] The negative electrode material of the present invention can reduce the resistance of the negative electrode sheet, improve the rate performance, and further alleviate the problem of volume expansion.

[0040] This invention combines single-walled carbon nanotubes with multi-walled carbon nanotubes to create a more abundant microporous and mesoporous structure in the negative electrode material, which can further provide a buffer gap for silicon expansion. Furthermore, by setting the carbon nanotubes to include both single-walled and multi-walled carbon nanotubes, it is possible to achieve a highly efficient conductive network connection with high conductivity, which can further improve the rate performance of the negative electrode sheet.

[0041] The silicon layer of the present invention is obtained by in-situ grafting of silane coupling agent and metal thermal reduction. By utilizing the polar affinity between the polar groups of silane and the acid-washed carbon nanotubes, the uniform coating effect of silane on the surface of carbon nanotubes can be guaranteed, thus ensuring the cycle performance of the negative electrode material. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the negative electrode material of the present invention;

[0043] Figure 2 Comparison of pore size distributions for single-walled carbon nanotubes, multi-walled carbon nanotubes, and single-walled carbon nanotube + multi-walled carbon nanotube composites;

[0044] Figure 3 This is a schematic flowchart illustrating the preparation process of the negative electrode material of the present invention. Detailed Implementation

[0045] The present invention will be further illustrated below through specific examples. However, it should be noted that the specific material ratios, process conditions, and results described in the embodiments of the present invention are only for illustrative purposes and should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention. It should be noted that, unless otherwise specified, "wt%" as described herein refers to "mass fraction".

[0046] like Figure 1 As shown, the present invention provides a negative electrode material comprising carbon nanotubes and a silicon layer coating the outside of the carbon nanotubes.

[0047] In this application, the negative electrode material is configured to include carbon nanotubes and a silicon layer covering the outside of the carbon nanotubes. The silicon layer covering the outside of the carbon nanotubes can serve as a reaction site for storing / releasing active lithium, participating in the charge and discharge reaction of the lithium-ion battery, reducing the resistance of the electrode sheet formed by the negative electrode material, and improving the rate performance. At the same time, the pores of the porous carbon nanotubes provide a buffer gap for the expansion of the silicon negative electrode, maintaining the overall structure of the negative electrode material, and further alleviating the volume expansion problem.

[0048] In some embodiments, carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both.

[0049] In some embodiments, carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0050] like Figure 2 As shown, the composite of single-walled carbon nanotubes and multi-walled carbon nanotubes has a richer microporous and mesoporous structure, which can further provide a buffer gap for silicon expansion. Furthermore, by setting the carbon nanotubes to include both single-walled and multi-walled carbon nanotubes, their efficient conductive network can be achieved, resulting in high conductivity and further improving the rate performance of the negative electrode.

[0051] like Figure 3 As shown, in some embodiments, the present invention also provides a method for preparing the negative electrode material as described above, comprising:

[0052] S1. The carbon source is soaked in an iron salt solution and then dried to obtain the precursor;

[0053] S2. The precursor is sintered under a protective gas atmosphere, then cooled and acid-washed to obtain a carbon nanotube framework;

[0054] S3. Mix carbon nanotube framework, silane coupling agent and solvent, then dry and mix with metal reducing agent, carry out reduction reaction under auxiliary gas atmosphere, then wash and dry again to obtain anode material (i.e. composite silicon anode).

[0055] In some embodiments, in step S1, the carbon source includes a porous sponge containing nitrogen elements, such as melamine sponge, polyurethane sponge, etc.

[0056] Specifically, porous sponges can adsorb iron salt solutions, and the nitrogen in the porous sponge can combine with iron ions to form catalytic active sites, thereby catalyzing the formation of carbon nanotubes. Iron ions in the iron salt act as catalytic sites during the sintering process, catalyzing the formation of carbon nanotubes.

[0057] Acid-washed carbon nanotubes possess a hydroxyl C-OH structure, which can serve as a polar group, improving their binding effect with silane coupling agents.

[0058] In some embodiments, in step S1, the concentration of the iron salt solution is 0.04-0.08 mg / mL, preferably 0.05-0.08 mg / mL.

[0059] In some embodiments, in step S1, the soaking time is 24-36 hours, preferably 30-36 hours.

[0060] In some embodiments, in step S1, the drying temperature is 60-75°C, preferably 65-75°C; the drying time is 10-15 hours, preferably 12-15 hours.

[0061] In some embodiments, in step S2, the sintering temperature is 500-600℃, preferably 550-600℃; the sintering time is 0.5-1h, preferably 0.6-1h.

[0062] In some embodiments, step S2, after sintering and before cooling, further includes a secondary sintering.

[0063] In some embodiments, in step S2, the temperature of the secondary sintering is 800-900℃, preferably 850-900℃; and the sintering time is 3-5h, preferably 3.5-5h.

[0064] In some embodiments, the protective gas in step S2 may include, for example, nitrogen, argon, helium, neon, etc.

[0065] In some embodiments, in step S2, the silane coupling agent includes at least one of vinyltriethoxysilane, vinyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

[0066] In some embodiments, in step S2, the silane coupling agent includes vinyltriethoxysilane and 3-aminopropyltrimethoxysilane, or includes vinyltrimethoxysilane and 3-aminopropyltrimethoxysilane.

[0067] In some embodiments, in step S2, the molar ratio of vinyltriethoxysilane to 3-aminopropyltrimethoxysilane is 1:0.2-0.5.

[0068] In some embodiments, in step S2, the molar ratio of vinyltrimethoxysilane to 3-aminopropyltrimethoxysilane is 1:0.2-0.5.

[0069] In some embodiments, in step S2, the mass ratio of the carbon nanotube framework to the silane coupling agent is 1:0.88-1.12.

[0070] In some embodiments, in step S2, the solvent includes at least one of acetone, isopropanol, and dimethyl sulfoxide.

[0071] In some embodiments, in step S3, the drying temperature is 60-75°C, preferably 65-75°C.

[0072] In some embodiments, in step S3, the metal reducing agent includes at least one of zinc, magnesium, and aluminum.

[0073] In some embodiments, in step S3, the mass ratio of the metal reducing agent to the silane coupling agent is 1:15-20.

[0074] In some embodiments, in step S3, the auxiliary gas may include, for example, nitrogen, argon, helium, neon, etc.

[0075] In some embodiments, in step S3, the reduction temperature is 800-1000℃, preferably 850-1000℃; the reduction time is 2-5h, preferably 2-4h.

[0076] In some embodiments, the temperature of the secondary drying in step S3 is 60-75°C.

[0077] In some embodiments, this application also provides an electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising the negative electrode material as described above or the negative electrode material prepared according to the preparation method described above.

[0078] It should be noted that, in this invention, the electrode assembly of the electrochemical device includes a positive electrode, a negative electrode, and a diaphragm (if necessary) disposed between the positive electrode and the negative electrode. The electrochemical device is obtained by arranging the positive electrode and the negative electrode relative to each other through the diaphragm (if necessary) and adding an electrolyte.

[0079] Regarding the positive electrode, the positive electrode may include a positive current collector and a layer of positive active material located on the positive current collector.

[0080] As for the positive electrode current collector, it can be made of aluminum, copper, nickel, titanium, etc., in the form of foil, open-cell foil, or strip material formed by mesh. It can also be a porous material, such as porous metal (e.g., foamed metal).

[0081] Regarding the positive electrode active material layer, it may be coated only on a portion of the positive electrode current collector. The positive electrode active material layer may include the positive electrode active material, a conductive agent, and a binder.

[0082] Regarding conductive agents, the conductive agents for the positive electrode sheet can include at least one of conductive carbon black, sheet graphite, graphene, and carbon nanotubes.

[0083] Regarding binders, the binders in the positive electrode sheet can include at least one of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a copolymer of styrene and acrylate, a copolymer of styrene and butadiene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0084] Regarding positive electrode active materials, examples include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide. These positive electrode active materials can be positive electrode active materials that have undergone doping or coating treatment.

[0085] Regarding the diaphragm, examples include at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid.

[0086] In some embodiments, a porous layer may also be provided on the surface of the diaphragm, the porous layer being disposed on at least one surface of the substrate of the diaphragm, and the porous layer may include inorganic particles and a binder.

[0087] Regarding inorganic particles, examples of inorganic particles in porous layers include at least one of the following: aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0088] Regarding the binder, the binder in the porous layer can be listed as at least one of the following: polyvinylidene fluoride, copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0089] It should be understood that, in this invention, the diaphragm is not a necessary component of the electrochemical device. For example, in certain types of electrochemical devices (such as structures where the positive and negative electrodes do not directly contact each other), a diaphragm may not be necessary.

[0090] In some embodiments, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.

[0091] In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be at least one of a gel electrolyte, a solid electrolyte, or an electrolyte solution.

[0092] The following example uses a lithium-ion rechargeable battery for illustration.

[0093] Regarding the electrolyte, it includes lithium salts and solvents. Examples of lithium salts include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0094] Regarding solvents, examples include at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0095] In the case of carbonate compounds, examples include at least one of chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, and other organic solvents.

[0096] Regarding chain carbonate compounds, examples include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC). Cyclic carbonate compounds include at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), and vinyl ethylene carbonate (VEC).

[0097] In the case of fluorocarbonate compounds, examples include at least one of the following: fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0098] As far as carboxylic acid ester compounds are concerned, carboxylic acid ester compounds may include at least one of the following: methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, and methyl formate.

[0099] In terms of ether compounds, examples include at least one of dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0100] Other organic solvents include, for example, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0101] In some embodiments, the electrochemical device can be prepared by sequentially winding or stacking a positive electrode, a separator, and a negative electrode into an electrode assembly, then encapsulating it in an aluminum-plastic film, adding an electrolyte, forming, and encapsulating, thus assembling a lithium-ion secondary battery.

[0102] It should be noted that the electrochemical device in this invention is not particularly limited and can be made into paper-type batteries, button-type batteries, coin-type batteries, stacked batteries, cylindrical batteries, square batteries, etc.

[0103] In some embodiments, the present invention also provides an electronic device comprising the electrochemical device described above.

[0104] It should be noted that the electronic device in this invention is not particularly limited and can be any electronic device known in the prior art.

[0105] In some embodiments, electronic devices may include, for example, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, capacitors, and other materials.

[0106] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0107] Example 1

[0108] This embodiment provides a negative electrode material, and the preparation method of the negative electrode material is as follows:

[0109] S1. Soak 500g of melamine sponge in a ferric sulfate solution with a concentration of 0.06mg / ml for 36h, and then dry it in an oven at 75℃ for 12h to obtain the precursor;

[0110] S2. The precursor is placed in a heating furnace and sintered at 500°C for 1 hour under an argon atmosphere to partially generate a single-walled carbon nanotube framework. Then, the temperature is raised to 800°C and sintered again for 3 hours to generate a multi-walled carbon nanotube framework. The precursor is then cooled to room temperature and then placed in a 1 mol / L dilute hydrochloric acid solution for 1 hour to remove excess iron and obtain the carbon nanotube framework.

[0111] S3. Place 100g of carbon nanotube framework in 5000mL of acetone, then add 88g of vinyltrimethoxysilane to the acetone and stir to allow the vinyltrimethoxysilane to undergo a coupling reaction with the carbon nanotube framework, coating the surface of the carbon nanotube framework with a silane layer. Then place it in an oven and dry at 60℃ to remove the remaining solvent. Then mix the dried solid with 4.4g of zinc powder, and then place it in a tube furnace under an argon atmosphere at 800℃ for a reduction reaction for 2h. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual zinc powder and zinc oxide, then wash with deionized water 3 times, and then dry at 75℃ to obtain the negative electrode material.

[0112] Example 2

[0113] The difference between this embodiment and Embodiment 1 is that:

[0114] S3. Take 100g of carbon nanotube framework and place it in 5000mL of acetone. Then add 88g of vinyltrimethoxysilane to the acetone and stir to allow the vinyltrimethoxysilane to undergo a coupling reaction with the carbon nanotube framework. The surface of the carbon nanotube framework is coated with a silane layer. Then place it in an oven and dry at 60℃ to remove the remaining solvent. Then mix the dried solid with 4.4g of aluminum powder. Then place it in a tube furnace and carry out a reduction reaction at 800℃ for 2h under an argon atmosphere. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual aluminum powder and alumina. Then wash with deionized water 3 times. Then dry at 75℃ to obtain the negative electrode material.

[0115] Example 3

[0116] The difference between this embodiment and Embodiment 2 is as follows:

[0117] S3. Place 100g of carbon nanotube framework in 5000mL of acetone, then add 58g of vinyltrimethoxysilane and 35g of 3-aminopropyltrimethoxysilane (molar ratio 1:0.5) to the acetone. Stir to allow the silane coupling agent to couple with the carbon nanotube framework, coating the surface of the carbon nanotube framework with a silane layer. Then place it in an oven at 60℃ to dry to remove the remaining solvent. Then mix the dried solid with 4.4g of zinc powder, and then place it in a tube furnace at 800℃ under an argon atmosphere for a reduction reaction for 2h. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual zinc powder and zinc oxide, then wash with deionized water 3 times, and then dry at 75℃ to obtain the negative electrode material.

[0118] Example 4

[0119] The difference between this embodiment and Embodiment 1 is that:

[0120] S2. The precursor was placed in a heating furnace and sintered at 500°C for 1 hour under an argon atmosphere. Then it was cooled to room temperature and washed for 15 minutes in a 1 mol / L dilute hydrochloric acid solution to remove excess iron, thus obtaining a carbon nanotube framework.

[0121] Example 5

[0122] The difference between this embodiment and Embodiment 1 is that:

[0123] S2. The precursor was placed in a heating furnace and sintered at 900°C for 4 hours under an argon atmosphere. Then it was cooled to room temperature and washed for 15 minutes in a 1 mol / L dilute hydrochloric acid solution to remove excess iron, thus obtaining a carbon nanotube framework.

[0124] Example 6

[0125] The difference between this embodiment and Embodiment 2 is as follows:

[0126] S3. Place 100g of carbon nanotube framework in 5000mL of acetone, then add 73g of vinyltrimethoxysilane and 17g of 3-aminopropyltrimethoxysilane (molar ratio 1:0.2) to the acetone. Stir to allow the silane coupling agent to couple with the carbon nanotube framework, coating the surface of the carbon nanotube framework with a silane layer. Then place it in an oven at 60℃ to dry to remove the remaining solvent. Then mix the dried solid with 4.4g of zinc powder, and then place it in a tube furnace at 800℃ under an argon atmosphere for a reduction reaction for 2h. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual zinc powder and zinc oxide, then wash with deionized water 3 times, and then dry at 75℃ to obtain the negative electrode material.

[0127] Example 7

[0128] The difference between this embodiment and Embodiment 2 is as follows:

[0129] S3. Place 100g of carbon nanotube framework in 5000mL of acetone, then add 67g of vinyltrimethoxysilane and 24g of 3-aminopropyltrimethoxysilane (molar ratio 1:0.3) to the acetone. Stir to allow the silane coupling agent to couple with the carbon nanotube framework, coating the surface of the carbon nanotube framework with a silane layer. Then place it in an oven at 60℃ to dry to remove the remaining solvent. Then mix the dried solid with 4.4g of zinc powder, and then place it in a tube furnace at 800℃ under an argon atmosphere for a reduction reaction for 2h. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual zinc powder and zinc oxide, then wash with deionized water 3 times, and then dry at 75℃ to obtain the negative electrode material.

[0130] Example 8

[0131] The difference between this embodiment and Embodiment 2 is as follows:

[0132] S3. Place 100g of carbon nanotube framework in 5000mL of acetone, then add 87g of vinyltriethoxysilane and 24g of 3-aminopropyltrimethoxysilane (molar ratio 1:0.3) to the acetone. Stir to allow the silane coupling agent to couple with the carbon nanotube framework, coating the surface of the carbon nanotube framework with a silane layer. Then place it in an oven at 60℃ to dry to remove the remaining solvent. Then mix the dried solid with 4.4g of zinc powder, and then place it in a tube furnace at 800℃ under an argon atmosphere for a reduction reaction for 2h. Then wash with a 1mol / L dilute hydrochloric acid solution for 15min to remove residual zinc powder and zinc oxide, then wash with deionized water 3 times, and then dry at 75℃ to obtain the negative electrode material.

[0133] Comparative Example 1

[0134] This comparative example provides a negative electrode material, and the preparation method of this negative electrode material is as follows:

[0135] 8.5g of silicon nanoparticles with a particle size of 100nm were mixed with 91.5g of natural graphite (the mixed specific capacity was 3400*0.085+350*0.915=609mAh / g), and added to 500mL of ethanol solvent. The mixture was ball-milled for 2h using a planetary ball mill to ensure uniform distribution of silicon nanoparticles. The ethanol solvent was removed by filtration, and then the mixture was placed in a vacuum oven and dried at 60℃ for 3h to remove residual solvent, thus obtaining the negative electrode material.

[0136] Comparative Example 2

[0137] The negative electrode material was prepared according to Example 1 of the patent document with publication number CN112938939A. The specific steps are as follows:

[0138] Weigh an appropriate amount of carbon nanotubes, add them to aqua regia, stir at 80℃ for 6 hours, and dry at 60℃ to obtain acidified carbon nanotubes; add the acidified carbon nanotubes to anhydrous ethanol for shearing and dispersion, then add concentrated ammonia to adjust the pH to 9, stir at 60℃, then add tetraethyl orthosilicate, and stir for 5 hours. Dry at 80℃ to obtain silica-coated acidified carbon nanotubes (CNTs@SiO2);

[0139] The prepared silica-coated carbon nanotubes (CNTs@SiO2) were mixed with magnesium powder at a mass ratio of 5:4. Then, the mixed powder was mixed with NaCl at a mass ratio of 1:15. The mixture was placed in a tube furnace and calcined at 650°C under an argon atmosphere. After holding at the temperature for 3 hours, the furnace was cooled.

[0140] The cooled powder was mixed with sucrose at a mass ratio of 1:2, then added to deionized water, ultrasonically dispersed for 40 minutes, and filtered. The filtered solid was kept at 500°C for 2 hours in an argon atmosphere, then heated to 800°C and kept at that temperature for 3 hours, and then cooled to room temperature to obtain the negative electrode material.

[0141] Performance testing

[0142] The negative electrode materials obtained in Examples 1-8 and Comparative Examples 1-2 were mixed with binder PAA and conductive agent SP at a mass ratio of 96:2:2, respectively. Deionized water was then added to homogenize the mixture, followed by double-sided coating with a surface density of 14.10 mg / cm². 2 It is applied to a 6µm thick copper foil and then rolled (compacted density 1.4 g / cm³). 3 ), thus obtaining the negative electrode sheet;

[0143] The sheet resistance of the negative electrode was measured using the four-probe method, and the results are shown in Table 1. Subsequently, a bare cell was obtained by stacking the cell with a high-nickel ternary positive electrode and a PE separator under low humidity conditions (dew point ≤ -40℃). An electrolyte was then injected, consisting of lithium salt (1 mol / L LiPF6 lithium hexafluorophosphate + 0.1 mol / L LiFSI lithium difluorosulfonyl imide) + solvent (20% EC ethylene carbonate + 80% EMC methyl ethyl carbonate, volume ratio) + additive (3 wt% FEC fluoroethylene carbonate). After capacity testing, a 2Ah soft-pack full cell was obtained. It was discharged at 1C to 2.5V, then charged at 1C at constant current to constant voltage to 4.2V, and cycled 500 times. The capacity retention was calculated according to the formula: capacity = 1C discharge capacity. 500cycle / 1C discharge capacity 1cycle Calculate the battery capacity retention rate and disassemble it. According to the formula, the expansion rate = (thickness of negative electrode sheet) / (expansion rate of negative electrode sheet). 500cycle -6um) / (thickness of negative electrode sheet) 辊压后 The expansion rate of the negative electrode was calculated using the formula -6um). At the same time, the rate discharge performance was tested at 3C rate (3C rate discharge to 2.5V). The 3C discharge capacity retention rate was calculated according to the formula = 3C discharge capacity / 0.33C discharge capacity. The results are shown in Table 1.

[0144] Table 1 Performance Test Results

[0145]

[0146] As shown in Table 1, compared with Comparative Examples 1 and 2, the anode sheet resistance formed by the anode materials of Examples 1-8 is significantly reduced, and the 3C discharge capacity retention rate is significantly increased. This result demonstrates that the anode material of the present invention exhibits excellent conductivity and rate performance.

[0147] As shown in Table 1, compared with Example 1, the negative electrode materials of Examples 3 and 8 have lower negative electrode sheet resistance, higher 25°C 1C / 1C cycle capacity retention rate @500 cycles, lower negative electrode expansion rate after 500 cycles, and higher 3C discharge capacity retention rate. These results indicate that compounding vinyltriethoxysilane or vinyltrimethoxysilane with 3-aminopropyltrimethoxysilane can further improve the conductivity of the negative electrode material, thereby improving the rate performance of the negative electrode material; it can further alleviate the volume expansion problem of silicon, thereby further improving the cycle performance of the electrochemical device assembled from the negative electrode sheet formed by the negative electrode material. As shown in Table 1, compared with Examples 4 and 5, the negative electrode material of Example 1 has a lower negative electrode sheet surface resistance, a higher 25℃ 1C / 1C cycle capacity retention rate @ 500 cycles, a lower negative electrode expansion rate after 500 cycles, and a higher 3C discharge capacity retention rate. These results indicate that combining single-walled carbon nanotubes and multi-walled carbon nanotubes can further improve the conductivity of the negative electrode material, reduce polarization in rate performance testing (3C discharge capacity retention rate), release more electricity, and thus improve the rate performance of the negative electrode material; it can further alleviate the volume expansion problem of silicon, and thus further improve the cycle performance of the electrochemical device assembled from the negative electrode sheet formed by the negative electrode material.

[0148] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for producing a negative electrode material, characterized by, The negative electrode material comprises carbon nanotubes and a silicon layer coating the outside of the carbon nanotubes, and the preparation method includes: S1. Immerse a carbon source in an iron salt solution, then dry it to obtain a precursor; the carbon source includes a porous sponge containing nitrogen. S2. The precursor is sintered under a protective gas atmosphere, then cooled and acid-washed to obtain a carbon nanotube framework; S3. Mix carbon nanotube framework, silane coupling agent and solvent, then dry and mix with metal reducing agent, carry out reduction reaction under auxiliary gas atmosphere, then wash and dry again to obtain the negative electrode material. The silane coupling agent includes vinyltriethoxysilane and 3-aminopropyltrimethoxysilane or includes vinyltrimethoxysilane and 3-aminopropyltrimethoxysilane.

2. The production method according to claim 1, wherein In step S2, after sintering and before cooling, a secondary sintering is also included.

3. The production method according to claim 1, wherein In step S2, the molar ratio of vinyltriethoxysilane to 3-aminopropyltrimethoxysilane is 1:0.2-0.

5.

4. The production method according to claim 1, wherein The carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both.

5. The production method according to claim 4, wherein The carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

6. An electrochemical device, characterized by, The electrochemical device includes a negative electrode sheet, which comprises a negative electrode material prepared by the preparation method according to any one of claims 1-5.

7. An electronic device, comprising: The electronic device includes the electrochemical device as described in claim 6.

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