Flexible negative electrode material based on conductive network and preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of negative electrode materials, and particularly relates to a flexible negative electrode material based on a conductive network and a preparation method and application thereof. The preparation method comprises the following steps: adding a silicon negative electrode material, metal salt and an organic ligand into deionized water to obtain a mixed solution; dipping and adsorbing three-dimensional foam in the mixed solution, and then taking out and freezing to obtain pretreated foam; the pretreated foam and a carbon source are subjected to heat treatment in inert gas, carbon foam with the silicon-carbon negative electrode material attached to the surface is obtained, and carbon nanotubes grow on the surface of the silicon-carbon negative electrode material. The obtained flexible negative electrode material can be used as an independent current collector, and the mass energy density of the battery is improved; and the material can serve as a buffer matrix of a silicon-based material to adapt to volume expansion and shrinkage of silicon in the lithiation process, so that the structural stability is enhanced, and the problem of capacity fading is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery negative electrode material preparation, and specifically relates to a flexible negative electrode material based on a conductive network, and a preparation method and application thereof. Background Art

[0002] With the rapid development of electric vehicles and energy storage technologies, the theoretical specific capacity of existing lithium-ion battery graphite anodes (372 mAh / g) is no longer sufficient to meet high energy density demands. Silicon-based materials have become a research hotspot due to their ultra-high theoretical capacity of 4200 mAh / g, but their approximately 300% volume expansion during charge and discharge can lead to electrode pulverization, SEI membrane rupture, and capacity decay. While traditional solutions such as nano-processing, carbon coating, and graphene composites can partially mitigate the volume effect, structural designs that rely on two-dimensional copper foil current collectors and polymer binders still present challenges such as fragility of the conductive network and high interfacial impedance.

[0003] Foam materials, with their three-dimensional network structure, are characterized by low density, high porosity, excellent elasticity, and thermal insulation. These properties have led to their widespread application in a variety of fields, including packaging, thermal insulation, sound absorption, and filtration. In recent years, with the continuous advancement of materials science, the research and application of foam materials has also made significant progress. The development of new foam materials not only focuses on improving their basic performance but also strives to expand their application potential in areas such as new energy and environmental protection.

[0004] Researchers utilized a novel foam material: three-dimensional nickel foam. Three-dimensional carbon foam has a unique three-dimensional network structure, providing an ideal support platform for loading silicon nanoparticles. Compared to traditional copper ribbon current collectors, three-dimensional nickel foam has significantly enhanced porosity and mechanical strength, effectively accommodating the over 300% volume expansion of silicon during lithiation, preventing electrode structural collapse and active material shedding caused by volume changes. Its highly conductive metal skeleton not only reduces charge transfer impedance but also forms a stable conductive network through close contact with silicon particles, significantly enhancing the electrode's electrochemical activity. This structural design creates an adaptive buffer space during cycling, evenly distributing the expansion and contraction of silicon nanoparticles, reducing local stress concentrations and significantly improving battery capacity fading. Although three-dimensional nickel foam exhibits significant performance advantages among silicon-based anode materials, its large-scale commercialization still faces the following challenges: the complex production process leads to high manufacturing costs; the good compatibility with silicon nanoparticles has not yet been fully extended to other battery components; and the high density of three-dimensional nickel foam may increase battery weight, thereby affecting energy density. Therefore, developing a three-dimensional foam silicon negative electrode material with both low cost and excellent performance has become a key issue that needs to be urgently addressed in this field. Summary of the Invention

[0005] The object of the present invention is to provide a flexible anode material based on a conductive network, its preparation method and application. With a three-dimensional foam as the substrate, a flexible freestanding three-dimensional conductive network is formed through in-situ growth, which not only enhances the structural stability but also improves the problem of capacity attenuation.

[0006] To achieve the above object, the present invention provides a preparation method of a flexible anode material based on a conductive network, comprising the following steps:

[0007] S1. Add a silicon anode material, a metal salt, and an organic ligand to deionized water to obtain a mixed solution;

[0008] S2. Immerse and adsorb a three-dimensional foam in the mixed solution, and then take it out and freeze it to obtain a pretreated foam; the volume mass ratio of the three-dimensional foam to the silicon anode material is 1 cm 3 :(0.1 - 2) g;

[0009] S3. Heat-treat the pretreated foam and a carbon source under an inert gas to obtain a carbon foam with a silicon-carbon anode material attached to the surface, and carbon nanotubes grow on the surface of the silicon-carbon anode material; the temperature of the heat treatment is 600°C to 900°C.

[0010] Further, in step S1, the silicon anode material is nano-silicon or nano-silicon monoxide with a particle size of 20 - 200 nm. The silicon-based anode material particles contain silicon nanocrystalline domains, and the average particle size of the silicon nanocrystalline domains is less than or equal to 10 nm. Optionally, in the silicon-based anode material particles, the average particle size of the silicon monoxide nanocrystalline domains is 2 nm to 10 nm. For example, the average particle size of the silicon nanocrystalline domains can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or a range composed of any two of the above values.

[0011] Further, in step S1, the metal salt is one or more of cobalt salts, nickel salts, and aluminum salts; the organic ligand is dimethylimidazole or dicyandiamide.

[0012] Further, in step S3, the carbon source is one or more of melamine, cyanuric acid, dopamine hydrochloride, chitosan, and polyaniline, so that the grown carbon nanotubes are doped with nitrogen elements. The tube diameter of the carbon nanotube layer is 1 - 5 nm, and the aspect ratio is (2 - 50):1. The thickness of the carbon layer grown on the surface of the silicon anode material is 1 - 20 nm, and the ID / IG in the Raman spectrum is 0.5 - 1.2. The carbon layer includes a carbon layer jointly formed by the organic ligand, the binder, and the carbon source.

[0013] Further, in step S1, the mass ratio of the silicon negative electrode material to the organic ligand is (10-20):1, the silicon content in the obtained flexible negative electrode material is 20-65 wt%, and the molar ratio of the organic ligand to the metal salt is (5-8):1;

[0014] The concentration of the silicon negative electrode material in the mixed solution is 50-120 g / L.

[0015] Further, a binder is added to the mixed solution in step S1, and the binder includes one or more of polyvinylpyrrolidone, polyacrylonitrile, polydopamine, and carboxymethyl cellulose; the addition amount of the binder is 0.1%-1% of the mass of the silicon negative electrode material.

[0016] Further, in step S2, the three-dimensional foam is melamine foam; the pore structure of the three-dimensional foam is a pore structure with interconnected pores having a pore diameter of 20-100 μm.

[0017] The volume-mass ratio of the melamine foam to the silicon negative electrode material is 1 cm 3 :(0.1-2) g, more preferably 1 cm 3 :(0.5-1.5) g.

[0018] Further, in step S2, the impregnation adsorption time is 6-36 h; the freezing is to freeze the three-dimensional foam after impregnation adsorption in liquid nitrogen.

[0019] Further, in step S3, the heat treatment time is 1-3 hours;

[0020] The mass ratio of the carbon source to the silicon negative electrode material in step S1 is (0.01-0.1):1.

[0021] The flexible negative electrode material based on the conductive network obtained by the present invention is a carbon foam with a silicon-carbon negative electrode material containing carbon nanotubes attached to the surface, and the mass of cobalt element accounts for 0.001%-2.3% of the total mass of the active material (containing the silicon-carbon negative electrode material containing carbon nanotubes), and the nitrogen element content in the carbon nanotubes is 0.1%-45%.

[0022] Compared with the conventional silicon-carbon composite material, the above preparation method of the present invention uses a three-dimensional foam, coats a silicon-carbon material on its surface, introduces a solid product containing a cobalt or nickel compound, and uses a carbon and nitrogen compound under high temperature and argon atmosphere to grow carbon nanotubes and dope nitrogen elements, obtaining a carbon foam (Carbon Foam@Si@C@CNT) with a silicon-carbon negative electrode material containing carbon nanotubes attached to the surface.

[0023] The present invention also provides a flexible negative electrode material based on a conductive network, which is prepared by using the preparation method described in any one of the above.

[0024] The present invention also provides an application of the above-mentioned flexible anode material based on a conductive network in a lithium-ion battery. The lithium-ion battery can be used in electric vehicles, energy storage devices, etc.

[0025] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0026] 1. The flexible anode material based on a conductive network provided by the present invention constructs a three-dimensional conductive network through a multi-layer structure design and a composite of various materials, significantly improving the electrode performance. Specifically, silicon particles are loaded on the surface of the carbon foam, a compound layer containing cobalt, nickel or aluminum is further introduced, and carbon nanotubes are in-situ grown on the composite material, forming a flexible freestanding three-dimensional conductive network. The three-dimensional conductive network has a hierarchical porous structure, constructing interconnected pores and intertwining with a uniformly distributed carbon nanotube conductive framework. This design not only enhances the electrical conductivity and mechanical stability of the electrode, but also optimizes the lithium-ion diffusion path, shortens the diffusion distance, and improves the rate performance.

[0027] 2. The doped elements improve the electronic structure of the carbon nanotubes, enhance the interfacial compatibility, reduce the stress concentration caused by the volume expansion of silicon, thereby maintaining the structural integrity of the anode material during charge and discharge, significantly improving the cycle stability and rate performance of the battery, extending the cycle life of the battery, and the used foam has a low cost, effectively reducing the technical cost.

[0028] 3. The present invention optimizes the loading amount of nanosilicon on the three-dimensional foam, regulates the hierarchical porous structure of the three-dimensional conductive network, and further enables the flexible anode material to have better cycle stability and rate performance.

[0029] 4. The flexible anode material based on a conductive network provided by the present invention can not only serve as a freestanding current collector to improve the mass energy density of the battery, but also act as a buffer matrix for the silicon-based material to adapt to the volume expansion and contraction of silicon during lithiation, not only enhancing the structural stability, but also improving the problem of capacity decay. Description of the Drawings

[0030] Figure 1 It is an impedance test chart of the anode sheet with in-situ growth of CNT prepared in Example 1 and the carbon foam anode without in-situ growth of CNT in Comparative Example 1 in a button cell.

[0031] Figure 2 It is a rate test chart of the anode sheet with in-situ growth of CNT prepared in Example 1 and the carbon foam anode sheet without in-situ growth of CNT in Comparative Example 1 in a button cell. Detailed Embodiments

[0032] 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.

[0033] 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 this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0034] Example 1

[0035] This example provides a negative electrode material, which is prepared by the following method:

[0036] (1) Place 0.02 g of polyvinylpyrrolidone and 5 g of nano-silicon (100 nm) in 50 mL of deionized water, and let it stand still to disperse evenly to obtain a first solution;

[0037] (2) Add 0.325 g of dimethylimidazole to the first solution obtained in operation (1), and stir to obtain a second solution;

[0038] (3) Add 0.145 g of cobalt (II) nitrate hexahydrate to the second solution obtained in operation (2), and stir for 3 min to obtain a third solution;

[0039] (4) Immerse the melamine foam (3 cm × 3 cm × 0.5 cm) in the third solution. After it is completely immersed and the foam has absorbed evenly and completely, let it stand and react for 24 hours to obtain a reacted melamine foam A;

[0040] (5) Take out foam A and place it in a clean beaker, pour liquid nitrogen into the beaker to quickly freeze foam A to obtain foam B;

[0041] (6) Place foam B 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 at a heating rate of 5 °C / min to 800 °C and keep it warm for 2 h. After the heat preservation is completed, cool it to room temperature in an argon atmosphere and then take it out to obtain a carbon foam (Carbon Foam@Si@C@CNT) with a silicon-carbon negative electrode material containing carbon nanotubes attached to the surface, and the carbon nanotubes contain nitrogen elements.

[0042] The negative electrode material provided in this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and a 10-nm-thick carbon coating layer obtained by heat treatment. After calculation, the mass of silicon element in the composite carbon foam accounts for 35% of the total composite material. The diameter of the carbon nanotube layer is 1 - 5 nm, and the aspect ratio is 3:1 - 60:1.

[0043] Example 2

[0044] The negative electrode material was prepared according to the method of Example 1, except that in operation (4) of this example, the static reaction was carried out for 12 hours.

[0045] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and a carbon coating layer with a thickness of 5 nm obtained by heat treatment. After calculation, the mass of silicon element in the composite carbon foam accounts for 35% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 6:1 - 27:1.

[0046] Example 3

[0047] The negative electrode material was prepared according to the method of Example 1, except that in operation (4) of this example, the static reaction was carried out for 20 hours.

[0048] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and a carbon coating layer with a thickness of 8 nm obtained by heat treatment. After calculation, the mass of silicon element in the composite carbon foam accounts for 35% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 7:1 - 23:1.

[0049] Example 4

[0050] The negative electrode material was prepared according to the method of Example 1, except that in operation (4) of this example, the static reaction was carried out for 28 hours.

[0051] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and a carbon coating layer with a thickness of 16 nm obtained by heat treatment. After calculation, the mass of silicon element in the composite carbon foam accounts for 35% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 9:1 - 46:1.

[0052] Example 5

[0053] The negative electrode material was prepared according to the method of Example 1, except that in operation (6) of this example, 0.4 g of melamine was added.

[0054] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and a carbon coating layer with a thickness of 17 nm obtained by heat treatment. After calculation, the mass of silicon element in the composite carbon foam accounts for 33% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 13:1 - 60:1.

[0055] Example 6

[0056] The negative electrode material was prepared according to the method of Example 1, except that in operation (6) of this example, the heat preservation temperature was 900 °C.

[0057] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 8 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 32% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 3:1 - 26:1.

[0058] Example 7

[0059] The negative electrode material was prepared according to the method of Example 1, except that in operation (6) of this example, the heat preservation time was 1 hour.

[0060] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 4 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 30% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 6:1 - 19:1.

[0061] Example 8

[0062] The negative electrode material was prepared according to the method of Example 1, except that in operation (6) of this example, the heat preservation time was 3 hours.

[0063] The negative electrode material of this example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 18 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 37% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 16:1 - 90:1.

[0064] Comparative Example 1

[0065] The negative electrode material was prepared according to the method of Example 1, except that in operation (3) of this example, 0 g of cobalt nitrate hexahydrate was added.

[0066] The negative electrode material of this comparative example includes a foam with a pore size of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 11 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 37% of the total composite material, and basically no carbon nanotubes are formed on the surface of Si by coating.

[0067] Comparative Example 2

[0068] The negative electrode material was prepared according to the method of Example 1, except that in operation (6) of this example, the heat preservation temperature was 550 °C.

[0069] In the negative electrode material of this embodiment, it includes a foam with a pore diameter of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 10 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 35% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 3:1 - 18:1.

[0070] Comparative Example 3

[0071] The negative electrode material was prepared according to the method of Example 1, except that in operation (1) of this example, 10 g of nano-silicon (100 nm) was added.

[0072] In the negative electrode material of this comparative example, it includes a foam with a pore diameter of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 9 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 62% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 5:1 - 35:1.

[0073] Comparative Example 4

[0074] The negative electrode material was prepared according to the method of Example 1, except that in operation (1) of this example, 15 g of nano-silicon (100 nm) was added.

[0075] In the negative electrode material of this comparative example, it includes a foam with a pore diameter of 40 μm, silicon with a particle size of 100 nm, and the thickness of the carbon coating layer obtained by heat treatment is 9 nm. After calculation, the mass of silicon element in the composite carbon foam accounts for 80% of the total composite material, the diameter of the carbon nanotube layer is 1 - 3 nm, and the aspect ratio is 5:1 - 35:1.

[0076] Experimental Example

[0077] Button cells and CR2032 and 3 Ah soft-pack batteries were respectively prepared using the negative electrode materials of Examples 1 - 8 and Comparative Examples 1 - 4, and the electrical performance of each battery was detected.

[0078] Among them, the composition of the button cell is as follows:

[0079] Negative electrode: The carbon foam (Carbon Foam@Si@C@CNT) containing the carbon nanotube silicon-carbon negative electrode material obtained directly was used as the negative electrode material.

[0080] Positive electrode: Lithium metal.

[0081] 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).

[0082] Separator: Celgard 2500.

[0083] The pouch cell is composed as follows:

[0084] Negative electrode: Directly use the obtained carbon foam (Carbon Foam@Si@C@CNT) containing silicon-carbon negative electrode material with carbon nanotubes as the negative electrode material.

[0085] Positive electrode: Lithium nickel cobalt manganese oxide NCM811 is used as the positive electrode material. A slurry is prepared according to the weight ratio of 97:2:1 of the positive electrode material, conductive agent SP, and PVDF (binder), and is coated on a carbon-coated aluminum foil current collector to prepare the positive electrode.

[0086] 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).

[0087] Separator: Celgard 2500.

[0088] The method for testing the electrical performance is as follows:

[0089] (1) Initial cycle negative electrode specific capacity utilization test: Initial discharge capacity mAh / mass of negative electrode active material g;

[0090] (2) Initial cycle Coulombic efficiency: Initial charge capacity / initial discharge capacity * 100%;

[0091] (3) Initial charge specific capacity: Initial charge capacity / mass of active material (mAh / g);

[0092] (4) 4C rate discharge capacity retention test: 4C discharge capacity / 1C discharge capacity;

[0093] (5) DC internal resistance DCR test: Divide the battery capacity and adjust it to 50% SOC, discharge at 5C for 10s, test the discharge resistance, and 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 5C;

[0094] (6) Capacity retention test: ① Charging: Constant current charge at a current density of 1C to 4.2V and then stand for 10 min; ② Discharging: Constant current discharge at a current density of 1C to 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 400-cycle capacity retention rate of the pouch cell is: Q400 / Q1;

[0095] (7) Volume expansion rate test: After 400 cycles, fully charged and disassembled, the thickness measured by a micrometer is d2, and the thickness of the fresh electrode after rolling is d1. The calculation formula for the expansion rate of the soft-pack battery after 400 full charges is: (d2 - d1) / (d1 - 8), where the thickness of the copper foil is 8 μm;

[0096] (8) Lithium plating test: ① Charging: Constant current charging at a current density of 2.4C until 4.2V, then standing for 10 min; ② Discharging: Constant current discharging at a current density of 1C until 2.5V, then standing for 10 min; After 10 cycles, constant current charging at a current density of 1.6C until full charge at 4.2V and then disassembled to observe the negative electrode interface.

[0097] (9) Electrochemical impedance spectroscopy (EIS) test: The EIS measurement was carried out before the charge-discharge cycle, and the frequency range was from 1 MHz to 0.01 Hz.

[0098] The test results are shown in Table 1 and Table 2.

[0099] Table 1 Detection results of the electrical properties of each button cell

[0100]

[0101] As can be seen from Table 1, in Comparative Example 1, due to the absence of cobalt nitrate, it is difficult for the carbon source to be catalytically in-situ formed into carbon nanotubes, so the first-cycle Coulombic efficiency is relatively low. The button cell prepared with the negative electrode material of the present invention that generates a comprehensive conductive network of CNT, C, and carbon foam has an obvious first-cycle Coulombic efficiency advantage compared with the negative electrode material (Comparative Example 1) that does not generate a comprehensive conductive network of CNT, C, and carbon foam. However, when the silicon content is too high, the first-cycle specific capacity of the negative electrode increases significantly, but the first-cycle Coulombic efficiency decreases.

[0102] Table 2 Detection results of the electrical properties of each soft-pack battery

[0103]

[0104]

[0105] As can be seen from Table 2, too high heat treatment temperature (Example 6) will affect the aspect ratio of CNTs after growth, thus affecting the comprehensive effect of its conductive network. The overall conductivity and lithium ion transport ability of the material both decrease, and the volume expansion of the electrode increases, so the capacity retention rate during long cycling decreases.

[0106] As Figure 1 and 2 shown, no in-situ CNT growth - foam in the figure refers to the negative electrode material prepared in Comparative Example 1, and in-situ CNT growth - foam refers to the negative electrode material prepared in Example 1. From Figure 1It can be seen that the negative electrode material prepared in Example 1 has a smaller Ohmic impedance and has obvious advantages in the lithium ion transmission rate.

[0107] From Figure 2 It can be seen that the negative electrode material prepared in Example 1 has stronger conductivity, better discharge specific capacity performance under battery rate charge and discharge, and higher capacity retention rate after high-rate current. The in-situ grown CNT-foam conductive network significantly promotes the rate performance of the material.

[0108] In summary, the flexible negative electrode material provided by the present invention forms a flexible freestanding three-dimensional conductive network by means of an in-situ growth process on the material surface. The three-dimensional conductive network is hierarchically porous, constructs interconnected pores, and interweaves with a uniformly distributed carbon nanotube conductive framework. This structure can not only serve as a freestanding current collector to improve the mass energy density of the battery, but also act as a buffer matrix for the silicon-based material to adapt to the volume expansion and contraction of silicon during the lithiation process, which not only enhances the structural stability but also improves the problem of capacity decay. Through the synergistic effect between the cobalt, nickel, aluminum compound layer and carbon nanotubes (CNTs), and the optimization strategy of nitrogen / boron doping on the interface characteristics of CNTs, the novel negative electrode material shows a significant enhancement in conductivity, mechanical stability and lithium ion diffusion efficiency in the lithium ion battery system. The lithium ion battery using this material can achieve low cost, high capacity and long cycle life.

[0109] Those skilled in the art can easily understand that the above are only 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 preparation method of a flexible anode material based on a conductive network, characterized in that, It includes the following steps: S1. Add a silicon negative electrode material, a metal salt, and an organic ligand to deionized water to obtain a mixed solution; S2. Immerse and adsorb the three-dimensional foam in the mixed solution, and then take it out and freeze it to obtain a pretreated foam; the volume mass ratio of the three-dimensional foam to the silicon negative electrode material is 1 cm 3 :(0.1 - 2) g; S3. Heat-treat the pretreated foam and a carbon source under an inert gas to obtain a carbon foam with a silicon-carbon negative electrode material attached to the surface, and carbon nanotubes grow on the surface of the silicon-carbon negative electrode material; the temperature of the heat treatment is 600°C to 900°C.

2. The preparation method according to claim 1, wherein In step S1, the silicon negative electrode material is nano-silicon or nano-silicon monoxide with a particle size of 20 - 200 nm.

3. The preparation method according to claim 1, characterized in that, In step S1, the metal salt is one or more of cobalt salts, nickel salts, and aluminum salts; the organic ligand is dimethylimidazole or dicyandiamide; And / or, in step S3, the carbon source is one or more of melamine, cyanuric acid, dopamine hydrochloride, chitosan, and polyaniline.

4. The preparation method according to claim 1, wherein, In step S1, the mass ratio of the silicon negative electrode material to the organic ligand is (10 - 20):1, and the molar ratio of the organic ligand to the metal salt is (5 - 8):1; The concentration of the silicon negative electrode material in the mixed solution is 50 - 120 g / L.

5. The preparation method according to claim 1, wherein In the mixed solution of step S1, a binder is further added, and the binder includes one or more of polyvinylpyrrolidone, polyacrylonitrile, polydopamine, and carboxymethyl cellulose; the addition amount of the binder is 0.1% - 1% of the mass of the silicon negative electrode material.

6. The preparation method according to claim 1, characterized in that, In step S2, the three-dimensional foam is a melamine foam.

7. The preparation method according to claim 1, characterized in that, In step S2, the time for impregnation and adsorption is 6 - 36 h; the freezing is to put the three-dimensional foam after impregnation and adsorption into liquid nitrogen for freezing.

8. The preparation method according to claim 1, characterized in that, In step S3, the time for the heat treatment is 1 - 3 hours; The mass ratio of the carbon source to the silicon negative electrode material in step S1 is (0.01 - 0.1):

1.

9. A flexible anode material based on a conductive network, characterized in that Prepared by using the preparation method according to any one of claims 1 - 8.

10. An application of the flexible negative electrode material based on a conductive network according to claim 9 in a lithium-ion battery.

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