Negative electrode material based on magnetic field treatment and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery material preparation, and particularly relates to a negative electrode material based on magnetic field treatment and a preparation method and application thereof. Mixing a binder, a conductive agent and an active substance to prepare slurry; wherein the active substance comprises a silicon negative electrode material, a magnetic layer coated on the surface of the silicon negative electrode material and a carbon nanotube coated on the surface of the magnetic layer; and coating a current collector with the slurry, and then drying in the presence of a magnetic field to obtain the negative electrode material. The carbon nanotubes are directionally arranged through the magnetic field and the magnetic layer, the three-dimensional connectivity of an electrode conductive network is remarkably improved, and the lithium ion transmission dynamics and the electrode structure stability can be effectively enhanced in combination with an interface modification effect brought by element doping. The lithium ion battery designed based on the negative electrode has remarkable advantages in the aspects of energy density, rate capability and cycle life, and is suitable for various mobile electronic equipment, electric vehicles and other electric devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a negative electrode material based on magnetic field treatment, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are key energy storage devices in electric vehicles and consumer electronics, and improving their performance is crucial to meeting the growing energy demand. Silicon-based materials are considered promising anode materials for next-generation lithium-ion batteries due to their high theoretical specific capacity (4200 mAh / g) and suitable operating voltage (0.4 V). However, silicon-based materials suffer from significant volume expansion during charge and discharge, which not only leads to unstable electrode structures but also causes rapid battery capacity degradation, severely limiting their practical applications.

[0003] At present, researchers have developed a variety of strategies, such as: one-dimensional carbon nanotube (CNTs) conductive network construction, two-dimensional graphene coating technology, and three-dimensional porous carbon skeleton confined structure to deal with the volume expansion and low conductivity problems of silicon-based negative electrode materials. However, existing technologies still have significant limitations: in terms of composite structure, even advanced metal organic framework (MOFs) derived carbon has an energy consumption of more than 800 ° C for preparation, and the cost is 200% higher than that of graphite negative electrode. At present, breakthroughs in expansion rate and conductivity after 1500 cycles have been achieved, but its large-scale production still faces technical bottlenecks in nano-silicon dispersion and electrode slurry stability, resulting in low cycle stability and energy density. Therefore, the development of a mass-producible composite negative electrode system with low expansion, high conductivity, high cycle stability and low cost is still a common problem that needs to be broken through in the lithium battery field. Summary of the Invention

[0004] The purpose of the present invention is to provide a negative electrode material based on magnetic field treatment, its preparation method and application, and through magnetic field regulation, the magnetic layer on the surface of the silicon negative electrode material drives the carbon nanotubes to form a gradient orientation arrangement along the vertical direction, effectively improving the coulombic efficiency, cycle stability and energy density.

[0005] To achieve the above object, the present invention provides a first aspect of a method for preparing a negative electrode material, comprising the following steps:

[0006] S1. Mixing a binder, a conductive agent, and an active material to form a slurry; wherein the active material includes a silicon negative electrode material, a magnetic layer coated on the surface of the silicon negative electrode material, and carbon nanotubes coated on the surface of the magnetic layer;

[0007] S2. Coating the slurry on a current collector, and then drying it in a magnetic field to obtain a negative electrode material.

[0008] Furthermore, the magnetic layer contains one or more elements among iron, cobalt, and nickel.

[0009] Furthermore, the carbon nanotubes are doped with nitrogen or boron elements, and the content of nitrogen or boron elements in the carbon nanotubes is 2% - 30%. The carbon nanotubes include at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibers, and / or their mixtures. The axial length of the carbon nanotube particle chain is 1 mm - 5 mm, and the tube diameter is 1 - 5 nm. Through the action of the magnetic field and the magnetic layer, a specific spatial arrangement is presented in-situ, and the spatial arrangement has a strong vertical orientation. For example, the length can be 1 mm, 2 mm, … or the range composed of any two of the above values, and the orientation includes from small to large or from large to small.

[0010] Furthermore, the silicon negative electrode material is one or more of silicon powder, silicon monoxide, silicon powder coated with a carbon layer on the surface, and silicon monoxide coated with a carbon layer on the surface.

[0011] Furthermore, the preparation method of the active material includes: mixing the silicon negative electrode material evenly in a solution containing a metal salt and an organic ligand, then standing for reaction, and then centrifuging, separating, and drying to obtain a powdery premixed material;

[0012] Heat-treating the powdery premixed material and a carbon source under an inert gas to obtain an active material with a magnetic layer and carbon nanotubes coated on the surface in sequence.

[0013] Furthermore, the mass ratio of the silicon negative electrode material to the organic ligand is 1:(8 - 15), and the molar ratio of the organic ligand to the metal salt is (5 - 8):1;

[0014] The mass ratio of the carbon source to the silicon negative electrode material is (8 - 12):1.

[0015] Furthermore, the metal salt is one or more of cobalt salts, nickel salts, and iron salts; the organic ligand is dimethylimidazole or dicyandiamide.

[0016] Furthermore, the carbon source is one or more of melamine, cyanuric acid, dopamine hydrochloride, chitosan, and polyaniline.

[0017] Furthermore, the temperature of the heat treatment is 650°C - 850°C, and the heat preservation time is 1 - 3 hours.

[0018] Furthermore, in the mixture composed of the binder, the conductive agent, and the active material, the mass content of the active material is 90% - 99%, the mass content of the binder is 0.5% - 10%, and the mass content of the conductive agent is 0.5% - 10%.

[0019] The conductive agent includes at least one of conductive carbon black, acetylene black, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, etc.; the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0020] Furthermore, the intensity of the magnetic field is 0.01T - 5T; preferably 0.05 - 0.5T, more preferably 0.05 - 0.2T.

[0021] The drying temperature is 70 - 90°C.

[0022] The first aspect of the present invention provides a negative electrode material prepared by the preparation method described in any one of the above. Specifically, it includes a negative electrode current collector and a negative electrode active layer coated outwardly on at least one side of the negative electrode current collector; the negative electrode active layer includes a binder, a conductive agent, and an active material; the surface of the active material includes carbon nanotubes presenting a special spatial arrangement; the proportion of the carbon nanotubes in the total mass of the electrode sheet is 0.02% - 2%, having magnetism or magnetic modification, and the spatial arrangement in situ is that the geometric mass center of the carbon nanotubes presents an oriented arrangement in the vertical direction, preferably containing nitrogen or boron elements.

[0023] The third aspect of the present invention provides an application of the above-mentioned negative electrode material in a lithium-ion battery or an electrical device containing a lithium-ion battery. The electrical device includes mobile phones, computers, mobile power supplies, electric vehicles, energy storage devices, etc.

[0024] The lithium-ion battery includes a positive electrode sheet, an electrolyte, a separator, and the above-mentioned negative electrode material (electrode sheet). The separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet and the negative electrode sheet and infiltrates the separator.

[0025] Optionally, the separator includes at least one of polyethylene, polypropylene, ceramic-coated separator, cellulose separator, polyimide, sodium polystyrene sulfonate, polyvinylidene fluoride, polytetrafluoroethylene, etc.

[0026] Optionally, the electrolyte includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, silyl lithium salt, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, silicon-based electrolyte additive, etc.

[0027] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface thereof. For example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode active material layer can be laminated on either one of these two surfaces of the positive electrode current collector, or laminated on both surfaces.

[0028] The positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a positive electrode current collector.

[0029] Optionally, the positive electrode active material includes lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium cobalt oxide, etc., and other conventional recognized positive electrode active materials can also be selected, including LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, LiMnPO4, LiNi 0.8 Fe 0.1 Mn 0.1 O2, lithium-rich manganese-based oxides, cobalt-free nickel-based oxides, etc., at least one of them.

[0030] Optionally, the conductive agent includes at least one of carbon black, conductive graphite, carbon nanotubes, graphene, reduced graphene oxide, liquid metal, conductive carbon fiber, graphene nanosheets, etc.

[0031] Optionally, the binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid, polytetrafluoroethylene, polymethyl methacrylate, polyvinyl alcohol, sodium alginate, β-cyclodextrin polymer, polypropylene emulsion, etc. When the binder is CMC and SBR, the preferred ratio of the two is 55:45 to 65:35.

[0032] Optionally, the positive electrode current collector includes copper foil, aluminum foil, stainless steel current collector, titanium current collector, etc.

[0033] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0034] 1. For the negative electrode material provided by the present invention, the active material with a multi-layer structure design effectively improves the electrical performance. Among them, the magnetic layer can enhance the structural stability, and the carbon nanotube layer further strengthens and improves the conductivity. At the same time, through magnetic field regulation, the magnetic layer on the surface of the silicon negative electrode material drives the carbon nanotubes to form a gradient-oriented arrangement in the vertical direction, significantly improving the three-dimensional penetration of the electrode conductive network, and can effectively improve the Coulomb efficiency, cycle stability and energy density of the lithium-ion battery.

[0035] 2. The present invention combines the interfacial modification effect brought by the doping of nitrogen and / or boron elements in the carbon nanotubes, which can further enhance the lithium-ion transport kinetics and the electrode structure stability, promote the adsorption and diffusion of lithium ions, enhance the interfacial compatibility, and reduce the stress concentration. The lithium-ion battery designed based on this negative electrode has significant advantages in terms of energy density, rate performance and cycle life, and is suitable for various power-consuming devices such as mobile electronic devices and electric vehicles. Description of the Drawings

[0036] Figure 1It is a graph showing the rate performance test of the non-magnetic-field-induced negative electrode sheet prepared in Comparative Example 1 and the magnetic-field-induced negative electrode sheet prepared in Example 1 in a coin cell.

[0037] Figure 2 It is a graph showing the impedance test of the non-magnetic-field-induced negative electrode sheet prepared in Comparative Example 1 and the magnetic-field-induced negative electrode sheet prepared in Example 1 in a coin cell. Detailed implementation manners

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in the art can be followed. For the reagents or instruments not indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0040] Example 1

[0041] This example provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer provided on one side of the negative electrode current collector. The negative electrode active layer includes a conductive agent, a binder, and an active material composite.

[0042] The preparation method of the negative electrode sheet is as follows:

[0043] (1) Dissolve the binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone, and make a uniform slurry with the ground conductive carbon black and the active material composite. The mass percentages of PVDF, conductive carbon black, and the active material composite are 5%, 5%, and 90% respectively.

[0044] Among them, the preparation method of the active material composite is as follows:

[0045] (1-1) Place 0.02 g of polyvinylpyrrolidone in 50 ml of deionized water, and let it stand and disperse evenly to obtain a first solution;

[0046] (1-2) Add 0.325 g of dimethylimidazole and 0.03 g of a silicon-based material with a carbon layer on the surface to the first solution obtained in operation (1) in sequence. After stirring, a second solution is obtained;

[0047] (1-3) Add 0.145 g of cobalt nitrate hexahydrate to the second solution obtained in operation (2), and stir for 3 min to obtain a third solution;

[0048] (1-4) Seal the container of the third solution and let it stand for reaction for 24 hours to obtain the fourth solution;

[0049] (1-5) Centrifuge the fourth solution at 8000 rpm for the first time. After the solid obtained from the first centrifugation is fully resuspended with deionized water, centrifuge it at 8000 rpm for the second time. After the solid obtained from the second centrifugation is fully resuspended with ethanol, centrifuge it at 8000 rpm for the third time. After the solid obtained from the third centrifugation is fully resuspended with deionized water, centrifuge it at 8000 rpm for the fourth time. After the solid obtained from the fourth centrifugation is fully resuspended with ethanol, centrifuge it at 8000 rpm for the fifth time. After the solid obtained from the fifth centrifugation is fully resuspended with deionized water, the premixed material is obtained;

[0050] (1-6) Place the premixed material obtained in operation (1-5) in a low-temperature freezer and freeze it at -26 °C for 24 hours to obtain the solid premixed material;

[0051] (1-7) Place the solid frozen premixed material in a freeze-dryer and obtain the powdered premixed material after freeze-drying;

[0052] (1-8) Place the powdered premixed material and 0.3 g of melamine in a porcelain boat, and place the porcelain boat in a tube furnace. In an argon atmosphere, heat it to 800 °C at a heating rate of 5 °C / min and hold for 2 h. After the holding is completed, cool it to room temperature in an argon atmosphere and then take it out to obtain a silicon-carbon negative electrode material with carbon nanotubes on the surface, and the carbon nanotubes contain nitrogen elements, which is the active substance complex.

[0053] (2) Evenly coat the above-mentioned slurry on the copper foil with a coater, place it in a drying oven and dry it completely at 80 °C. Place the magnetic field device in the drying oven so that there is a specific magnetic field in the drying oven, and the magnetic field intensity on the surface of the electrode is 0.05 T.

[0054] (3) After rolling and slicing the dried electrode, place it in a drying oven for standby.

[0055] Example 2

[0056] This example provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer provided on one side of the negative electrode current collector. The negative electrode active layer includes a conductive agent, a binder, and an active substance complex.

[0057] The preparation method of the negative electrode sheet is as follows:

[0058] (1) Dissolve the binder pre-lithiated polyacrylic acid (PAA-Li) in deionized water, and make a uniform slurry with the ground conductive carbon black and the active substance complex. The mass percentages of PAA-Li, conductive carbon black, and the active substance complex are 5%, 5%, and 90% respectively.

[0059] The preparation method of the active material composite is the same as that of Example 1.

[0060] (2) The above-mentioned slurry was evenly coated on the copper foil with a coater, placed in a drying oven and completely dried at 80 °C. A magnetic field generating device was placed in the drying oven so that a specific magnetic field existed in the drying oven, and the magnetic field strength on the surface of the electrode was 0.10 T.

[0061] (3) After the dried electrode was roll-pressed and sliced, it was placed in a drying oven for standby.

[0062] Example 3

[0063] This example provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer provided on one side of the negative electrode current collector. The negative electrode active layer includes a conductive agent, a binder, and an active material composite.

[0064] The preparation method of the negative electrode sheet is as follows:

[0065] (1) The binder CMC (sodium carboxymethyl cellulose) + SBR (styrene-butadiene rubber) (the mass ratio of CMC and SBR is 65:35) was dissolved in deionized water, and was made into a uniform slurry with the ground conductive carbon black and the active material composite. The mass percentages of CMC+SBR, conductive carbon black, and the active material composite are 5%, 5%, and 90% respectively.

[0066] (2) The above-mentioned slurry was evenly coated on the copper foil with a coater, placed in a drying oven and completely dried at 80 °C. A magnet was placed in the drying oven so that a specific magnetic field existed in the drying oven, and the magnetic field strength on the surface of the electrode was 0.10 T.

[0067] (3) After the dried electrode was roll-pressed and sliced, it was placed in a drying oven for standby.

[0068] Example 4

[0069] The negative electrode sheet was prepared according to the method of Example 1, except that in operation (1) of this example, the mass percentages of PAA-Li, conductive carbon black, and the active material composite are 10%, 10%, and 80% respectively.

[0070] Example 5

[0071] The negative electrode sheet was prepared according to the method of Example 1, except that in operation (2) of this example, the magnetic field strength on the surface of the electrode was 0.20 T.

[0072] Example 6

[0073] The negative electrode sheet was prepared according to the method of Example 2, except that in operation (1) of this example, the mass percentages of PAA-Li, conductive carbon black, and the active material composite are 5%, 15%, and 80% respectively.

[0074] Example 7

[0075] The negative electrode sheet was prepared according to the method of Example 2, except that in operation (2) of this example, the magnetic field strength on the surface of the sheet was 0.30 T.

[0076] Example 8

[0077] The negative electrode sheet was prepared according to the method of Example 3, except that in operation (1) of this example, the mass percentages of CMC+SBR, conductive carbon black, and the active material complex were 2.5%, 2.5%, and 95% respectively.

[0078] Example 9

[0079] The negative electrode sheet was prepared according to the method of Example 3, except that in operation (2) of this example, the magnetic field strength on the surface of the sheet was 0.45 T.

[0080] Example 10

[0081] The negative electrode sheet was prepared according to the method of Example 1, except that in operation (1) of this example, polyvinylidene fluoride was replaced equally with CMC and SBR (the mass ratio of the two was 25:75).

[0082] Comparative Example 1

[0083] The negative electrode sheet was prepared according to the method of Example 1, except that in this example, the magnetic field treatment in step (2) was omitted. After operation (1) was completed, the above slurry was evenly coated on the copper foil with a coater, placed in a drying oven and completely dried at 80 °C, and then operation (3) was carried out.

[0084] Comparative Example 2

[0085] The negative electrode sheet was prepared according to the method of Example 6, except that in this example, the magnetic field treatment in operation (2) was omitted. After operation (1) was completed, the above slurry was evenly coated on the copper foil with a coater, placed in a drying oven and completely dried at 80 °C, and then operation (3) was carried out.

[0086] Comparative Example 3

[0087] The negative electrode sheet was prepared according to the method of Example 8, except that in this example, the magnetic field treatment in operation (2) was omitted. After operation (1) was completed, the above slurry was evenly coated on the copper foil with a coater, placed in a drying oven and completely dried at 80 °C, and then operation (3) was carried out.

[0088] Experimental Example

[0089] Button cells and 3 Ah soft-pack batteries were prepared using the anode materials of Examples 1-10 and Comparative Examples 1-3, respectively, and the electrical properties of each battery were tested.

[0090] Among them, the composition of the button cell is as follows:

[0091] Anode: The anode sheet prepared according to the conditions of the above-mentioned examples or comparative examples was used.

[0092] Cathode: Lithium metal.

[0093] Electrolyte: 1.2 mol / L LiPF6, and the solvent is EC / DMC with a molar ratio of 1:1 plus 10 wt% FEC (EC: ethylene carbonate, DMC: dimethyl carbonate, FEC: fluoroethylene carbonate).

[0094] Separator: Celgard 2500.

[0095] The composition of the soft-pack battery is as follows:

[0096] Anode: The anode sheet prepared according to the conditions of the above-mentioned examples or comparative examples was used.

[0097] Cathode: Lithium nickel cobalt manganese oxide NCM811 was used as the cathode material, and a slurry was prepared according to the weight ratio of cathode material, conductive agent SP and PVDF of 97:2:1, and coated on an aluminum foil current collector to prepare the cathode.

[0098] Electrolyte: 1.2 mol / L LiPF6, and the solvent is EC / DMC with a molar ratio of 1:1 plus 10 wt% FEC (EC: ethylene carbonate, DMC: dimethyl carbonate, FEC: fluoroethylene carbonate).

[0099] Separator: Celgard 2500.

[0100] The method for testing the electrical properties is as follows:

[0101] (1) First-cycle anode specific capacity utilization test: First-cycle discharge capacity mAh / mass of anode active material g;

[0102] (2) First-cycle Coulombic efficiency: First-cycle charge capacity / first-cycle discharge capacity * 100%;

[0103] (3) First-cycle charge specific capacity: First-cycle charge capacity / mass of active material (mAh / g);

[0104] (4) 4C rate discharge capacity retention test: 4C discharge capacity / 1C discharge capacity;

[0105] (5) DC internal resistance DCR test: Divide the battery capacity for grading and adjust it to 50% SOC, discharge at 5C for 10s, and test the discharge resistance. The resistance DCR = (V0 - V10) / I, where V0 is the potential before discharge, V10 is the potential at the 10th second of discharge, and I is the discharge current of 5C;

[0106] (6) Capacity retention rate test: ① Charging: Constant current charge at a current density of 1C until 4.2V and then stand for 10 min; ② Discharging: Constant current discharge at a current density of 1C until 2.5V, stand for 0 min, and record the discharge capacity as Qn (n = 1, 2, 3... 400); ③ Repeat "①, ②" 400 cycles; The capacity retention rate of the soft-pack battery after 400 cycles is: Q400 / Q1;

[0107] (7) Volume expansion rate test: After 400 cycles, disassemble the battery when it is fully charged. Use a micrometer to measure the thickness as d2, and the thickness of the fresh electrode sheet after rolling is d1. The calculation formula for the full charge expansion rate of the soft-pack battery after 400 cycles is: (d2 - d1) / (d1 - 8), where the thickness of the copper foil is 8μm;

[0108] (8) Lithium plating test: ① Charging: Constant current charge at a current density of 2.4C until 4.2V and then stand for 10 min; ② Discharging: Constant current discharge at a current density of 1C until 2.5V and then stand for 10 min; After 10 cycles, charge at a current density of 1.6C until fully charged to 4.2V and then disassemble to observe the negative electrode interface.

[0109] (9) Electrochemical impedance spectroscopy (EIS) test: The EIS measurement is carried out before the charge-discharge cycle, and the frequency range is from 1 MHz to 0.01 Hz.

[0110] The test results are shown in Table 1 and Table 2.

[0111] Table 1 Detection results of the electrical performance of each button cell

[0112]

[0113] As can be seen from Table 1, in the magnetic regulation, the PAA-Li system has better comprehensive performance. Too strong or too weak magnetic field is not conducive to optimizing the conductive network arrangement of the material, and too high magnetic field will deteriorate the overall electrochemical performance of the electrode sheet in terms of specific capacity and Coulomb efficiency.

[0114] Table 2 Detection results of the electrical performance of each soft-pack battery

[0115]

[0116]

[0117] As can be seen from Table 2, for the binder, the electrochemical performance of PVDF is weaker than that of CMC+SBR, and CMC+SBR is weaker than PAA-Li. Generally speaking, the PAA-Li system currently shows better comprehensive performance in magnetic regulation. Too strong or too weak a magnetic field is not conducive to optimizing the arrangement of the conductive network of the material, which will weaken the overall conductivity of the electrode sheet and deteriorate the electrochemical performance in terms of capacity retention, volume expansion, and rate performance.

[0118] As Figure 1 can be seen, the specific capacity in the coin cell assembled with the negative electrode sheet induced by the magnetic field is larger. As Figure 2 can be seen, the impedance of the coin cell assembled with the negative electrode sheet induced by the magnetic field is significantly reduced.

[0119] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode material, characterized in that, It includes the following steps: S1. Mix a binder, a conductive agent and an active material to form a slurry; wherein, the active material includes a silicon negative electrode material, a magnetic layer coated on the surface of the silicon negative electrode material, and a carbon nanotube coated on the surface of the magnetic layer; S2. Coat the slurry on a current collector, and then dry it under the condition of a magnetic field to obtain a negative electrode material.

2. The preparation method of the negative electrode material according to claim 1, wherein The magnetic layer contains one or more elements of iron, cobalt, and nickel; and / or, the carbon nanotube is doped with nitrogen or boron element; and / or, the silicon negative electrode material is one or more of silicon powder, silicon monoxide, silicon powder coated with a carbon layer, and silicon monoxide coated with a carbon layer; 3. The preparation method of the negative electrode material according to claim 1, wherein The preparation method of the active material includes: mixing the silicon negative electrode material evenly in a solution containing a metal salt and an organic ligand, then standing for reaction, and then centrifuging, separating and drying to obtain a powdery premixed material; Heat-treat the powdery premixed material and a carbon source under an inert gas to obtain an active material with a magnetic layer and a carbon nanotube coated on the surface in sequence.

4. The preparation method of the negative electrode material according to claim 3, wherein, The mass ratio of the silicon negative electrode material to the organic ligand is 1:(8 - 15), and the molar ratio of the organic ligand to the metal salt is (5 - 8):1; The mass ratio of the carbon source to the silicon negative electrode material is (8 - 12):

1.

5. The preparation method of the negative electrode material according to claim 3, characterized in that, The metal salt is one or more of cobalt salt, nickel salt, and iron salt; the organic ligand is dimethylimidazole or dicyandiamide; and / or, the carbon source is one or more of melamine, cyanuric acid, dopamine hydrochloride, chitosan, and polyaniline.

6. The preparation method of the negative electrode material according to claim 3, wherein, The temperature of the heat treatment is 650°C to 850°C, and the heat preservation time is 1 - 3 hours.

7. The method for preparing the negative electrode material according to claim 1, characterized in that, In the mixture composed of the binder, the conductive agent and the active material, the mass content of the active material is 80% - 99%, the mass content of the binder is 0.5% - 10%, and the mass content of the conductive agent is 0.5% - 10%.

8. The preparation method of the negative electrode material according to any one of claims 1-7, characterized in that, The intensity of the magnetic field is 0.05 - 5T; The temperature of the drying is 70 - 90°C.

9. A negative electrode material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the negative electrode material according to claim 9 in a lithium-ion battery or an electrical device including a lithium-ion battery.

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