Silicon-based negative electrode material and preparation method thereof, lithium battery and electric equipment

Abstract

The invention provides a silicon-based negative electrode material and a preparation method thereof, a lithium battery and electric equipment, and relates to the field of lithium batteries. The preparation method of the silicon-based negative electrode material comprises the following steps: carrying out first mixing on various carbon-containing high polymer materials and silicon powder, and then carrying out high-temperature self-propagating reaction to obtain a nanoscale precursor; and carrying out second mixing on the nanoscale precursor and graphite to obtain the silicon-based negative electrode material. According to the silicon-based negative electrode material provided by the invention, through the high-temperature self-propagating reaction of the silicon powder and the carbon-containing high polymer material, the surface of the silicon can be uniformly coated with the graphene, finally, the silicon with the surface uniformly coated with the graphene is obtained, and the silicon-based negative electrode with the structure greatly inhibits volume expansion of the silicon in the charging and discharging process; and meanwhile, after compounding with graphite, the conductivity of the material is improved, so that the material has relatively good cycling stability.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and particularly to a silicon-based anode material, a preparation method thereof, a lithium battery, and an electric device. Background Art

[0002] The development of anode active materials is an important part of the development of lithium batteries.

[0003] As a key link in the battery industry chain, silicon-carbon anodes have the advantages of good safety, high energy density, and fast charge and discharge capabilities.

[0004] However, due to the large volume expansion of silicon during charge and discharge, its cycling performance is poor.

[0005] Therefore, it is necessary to develop a silicon-carbon anode material with long cycling performance for use in lithium-ion batteries, especially in solid-state lithium-ion batteries. Summary of the Invention

[0006] The purpose of this application is to provide a silicon-based anode material, a preparation method thereof, a lithium battery, and an electric device to solve the above problems.

[0007] To achieve the above purpose, the following technical solutions are adopted in this application:

[0008] A preparation method of a silicon-based anode material, comprising:

[0009] Performing a first mixing on a variety of carbon-containing polymer materials and silicon powder, and then performing a high-temperature self-propagating reaction to obtain a nanoscale precursor;

[0010] Performing a second mixing on the nanoscale precursor and graphite to obtain the silicon-based anode material.

[0011] Preferably, the carbon-containing polymer materials include multiple ones among polyethylene, polypropylene, polyvinyl chloride, ethylene-vinyl acetate copolymer, polyethylene terephthalate, polybutylene terephthalate, polytetrafluoroethylene, polystyrene, polycarbonate, polyvinylidene fluoride, polyfluoropropylene, polyvinylpyrrolidone, polyperfluoroacrylate;

[0012] Preferably, the carbon-containing polymer materials are a mixture of polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene with a mass ratio of (1.5 - 3):(5 - 7):(1 - 3), or the carbon-containing polymer materials are a mixture of polytetrafluoroethylene and polyvinylpyrrolidone with a mass ratio of (7:3)-(9:1);

[0013] Preferably, the mass ratio of the silicon powder to the carbon-containing polymer materials is (0.001 - 50):1, and more preferably (0.01 - 20.5):1.

[0014] Preferably, the first mixing method includes one or more of mechanical stirring, vibration ball milling, and ultrasonic compounding.

[0015] Preferably, a solvent is also added during the first mixing;

[0016] Preferably, the solvent includes one or more of ethanol, water, isopropanol, ether, methyl acetate, and acetone;

[0017] Preferably, the time for the first mixing is 0.1 - 36 h.

[0018] Preferably, the temperature of the high-temperature self-propagating reaction is 1000 - 2800 °C, and the time is 0.05 - 6 h;

[0019] Preferably, the atmosphere of the high-temperature self-propagating reaction includes one or more of air, oxygen, nitrogen, and argon.

[0020] Preferably, the graphite includes natural graphite and / or artificial graphite;

[0021] Preferably, the particle size D50 of the graphite is 5 - 30 μm, and the tapped density is not less than 1.2 g / cm 3 , and the purity is not less than 99.95%.

[0022] Preferably, the mass ratio of the nanoscale precursor to the graphite is (0.01 - 0.8):1;

[0023] Preferably, the second mixing method includes one or more of mechanical stirring, mechanical ball milling, and ultrasonic mixing.

[0024] This application also provides a silicon-based anode material prepared by using the preparation method of the silicon-based anode material described above.

[0025] This application also provides a lithium battery, the raw materials of which include the silicon-based anode material described above.

[0026] Preferably, the lithium battery is a all-solid-state lithium battery.

[0027] This application also provides an electricity-related device including the lithium battery described above.

[0028] Compared with the prior art, the beneficial effects of this application include:

[0029] The silicon-based anode material provided by this application can uniformly coat graphene on the surface of silicon through the high-temperature self-propagating reaction of silicon powder and carbon-containing polymer materials, and finally obtain silicon with graphene uniformly coated on the surface. The silicon-based anode with such a structure greatly inhibits the volume expansion of silicon during charge and discharge. At the same time, after being compounded with graphite, the conductivity of the material is improved. Therefore, this material has good cycle stability. Brief Description of the Drawings

[0030] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0031] Figure 1 It is the cyclic performance curve of the silicon-carbon negative electrode material obtained in Example 3;

[0032] Figure 2 It is the scanning electron microscope image of Product C obtained in Example 6;

[0033] Figure 3 It is the scanning electron microscope image of the silicon-based negative electrode material obtained in Example 6. Detailed Embodiments

[0034] To better explain the technical solutions provided by the present application, before the embodiments, the technical solutions will be presented as a whole, as follows:

[0035] A preparation method of a silicon-based negative electrode material, comprising:

[0036] Performing a first mixing of a variety of carbon-containing polymer materials and silicon powder, and then performing a high-temperature self-propagating reaction to obtain a nanoscale precursor;

[0037] Performing a second mixing of the nanoscale precursor and graphite to obtain the silicon-based negative electrode material.

[0038] In an optional embodiment, the carbon-containing polymer materials include multiple ones among polyethylene, polypropylene, polyvinyl chloride, ethylene-vinyl acetate copolymer, polyethylene terephthalate, polybutylene terephthalate, polytetrafluoroethylene, polystyrene, polycarbonate, polyvinylidene fluoride, polyfluoropropylene, polyvinylpyrrolidone, and polyperfluoroacrylate;

[0039] When the carbon-containing polymer materials are composed of multiple substances, they are compounded according to the following principle:

[0040] Using high-carbon-yield materials (polytetrafluoroethylene, polyvinylidene fluoride, polyfluoropropylene, polyperfluoroacrylate, polyethylene terephthalate, polybutylene terephthalate) as the main components, and using high-adhesion materials (polyvinylpyrrolidone, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, polycarbonate) as the auxiliary, and the mass ratio of the two is (6-9):(1-4), so as to ensure that the pyrolytic carbon layer has both conductivity and mechanical strength.

[0041] In addition, it is also necessary to consider the balance of conductivity (such as polytetrafluoroethylene), film-forming property (such as polyvinylidene fluoride), and dispersibility (such as polypropylene) to reduce the uneven coating caused by the performance overload provided by a single component. The mass ratio is generally (3-7):(1-5):(1-3).

[0042] In an alternative embodiment, the carbon-containing polymer material is a mixture of polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene with a mass ratio of (3-7):(1-5):(1-3), or the carbon-containing polymer material is a mixture of polytetrafluoroethylene and polyvinylpyrrolidone with a mass ratio of (6-9):(1-4);

[0043] In an alternative embodiment, the carbon-containing polymer material is a mixture of polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene with a mass ratio of 2:6:2, or the carbon-containing polymer material is a mixture of polytetrafluoroethylene and polyvinylpyrrolidone with a mass ratio of 8:2;

[0044] In addition to the above considerations, for the polyvinylidene fluoride (PVDF) / polytetrafluoroethylene (PTFE) / polypropylene (PP) ternary system with a mass ratio of 2:6:2: The high-temperature pyrolysis characteristics of polytetrafluoroethylene (400-500 °C) and the medium-temperature carbonization of polyvinylidene fluoride (300-400 °C) form a gradient carbon layer. 6 parts of polytetrafluoroethylene can construct a continuous conductive network. Adding 2 parts of polypropylene decomposes first to generate micropores in the low-temperature section (200-300 °C), and cooperates with the carbonization products of 2 parts of polyvinylidene fluoride to form a multi-stage buffer structure.

[0045] For the polytetrafluoroethylene / polyvinylpyrrolidone binary system with a mass ratio of 8:2: The nitrogen-containing functional groups of polyvinylpyrrolidone can induce the formation of a stable SEI film rich in LiF. 8 parts of polytetrafluoroethylene provide a rigid skeleton to inhibit the expansion of silicon particles, and 2 parts of polyvinylpyrrolidone form a three-dimensional winding structure after carbonization.

[0046] In an alternative embodiment, the mass ratio of the silicon powder to the carbon-containing polymer material is (0.001-50):1, and more preferably (0.01-20.5):1.

[0047] Optionally, the mass ratio of the silicon powder to the carbon-containing polymer material can be 0.001:1, 0.005:1, 0.01:1, 0.05:1, 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 20.5:1, or any value between (0.001-50):1.

[0048] In an alternative embodiment, the first mixing method includes one or more of mechanical stirring, vibration ball milling, and ultrasonic compounding.

[0049] In an alternative embodiment, a solvent is also added during the first mixing;

[0050] In an alternative embodiment, the solvent includes one or more of ethanol, water, isopropanol, ether, methyl acetate, and acetone;

[0051] In an alternative embodiment, the time for the first mixing is 0.1 - 36 h.

[0052] Optionally, the time for the first mixing can be 0.1 h, 1 h, 6 h, 12 h, 18 h, 24 h, 30 h, 36 h, or any value between 0.1 - 36 h.

[0053] In an alternative embodiment, the temperature of the high - temperature self - propagating reaction is 1000 - 2800 °C, and the time is 0.05 - 6 h;

[0054] Optionally, the temperature of the high - temperature self - propagating reaction can be 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, 1500 °C, 1600 °C, 1700 °C, 1800 °C, 1900 °C, 2000 °C, 2100 °C, 2200 °C, 2300 °C, 2400 °C, 2500 °C, 2600 °C, 2700 °C, 2800 °C, or any value between 1000 - 2800 °C, and the time can be 0.05 h, 0.1 h, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, or any value between 0.05 - 6 h;

[0055] In an alternative embodiment, the atmosphere of the high - temperature self - propagating reaction includes one or more of air, oxygen, nitrogen, and argon.

[0056] In an alternative embodiment, the graphite includes natural graphite and / or artificial graphite;

[0057] The artificial graphite is a product that meets the detection standard of GB / T 3521. Among them, the specific capacity of the graphite negative electrode is ≥355 mAh / g.

[0058] In an alternative embodiment, the D50 particle size of the graphite is 5 - 30 μm, the tapped density is not less than 1.2 g / cm 3 , and the purity is not less than 99.95%.

[0059] In an alternative embodiment, the mass ratio of the nanoscale precursor to the graphite is (0.01 - 0.8):1;

[0060] Optionally, the mass ratio of the nanoscale precursor to the graphite may be 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 or any value between (0.01-0.8):1;

[0061] In an alternative embodiment, the second mixing method includes one or more of mechanical stirring, mechanical ball milling, and ultrasonic mixing.

[0062] The present application also provides a silicon-based anode material prepared by using the preparation method of the silicon-based anode material.

[0063] The present application also provides a lithium battery, the raw materials of which include the silicon-based anode material.

[0064] In an alternative embodiment, the lithium battery is a all-solid-state lithium battery.

[0065] The silicon-based anode material provided by the present application is particularly suitable for the all-solid-state lithium battery system. Its special structure and preparation process solve key problems such as the interfacial compatibility between the anode material and the solid electrolyte, volume expansion suppression, and ion / electron transport efficiency in all-solid-state batteries. Specifically, it is embodied as follows: 1. Interface stability optimization. The graphene coating layer (nanoscale precursor) generated by the high-temperature self-propagating reaction has excellent mechanical flexibility and chemical stability, and can form a tight and low-impedance interfacial contact with the solid electrolyte (such as sulfide and oxide solid electrolytes). The high toughness and ductility of graphene can buffer the volume expansion of the silicon core during charge and discharge, avoiding the rupture of the solid electrolyte or interfacial peeling caused by volume changes, thereby improving the cycle life of the all-solid-state battery. 2. The graphene network uniformly coated on the surface of the nanoscale precursor and the subsequent composite graphite matrix jointly construct a continuous electron conduction path, solving the problem of low electron transport efficiency caused by the lack of liquid electrolyte infiltration in all-solid-state batteries. 3. The selection of the preferred high-temperature self-propagating reaction atmosphere (such as nitrogen and argon) and carbon-containing polymer materials (such as polytetrafluoroethylene and polyvinylidene fluoride) in the present application avoids the generation of side reaction products, ensures the cleanliness of the surface of the graphene coating layer, and reduces the side reaction with the sulfide solid electrolyte (such as Li 3 PS 4 )

[0066] The present application also provides an electricity-related device including the lithium battery.

[0067] The implementation scheme of the present application will be described in detail below in combination with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained by purchasing in the market.

[0068] Example 1

[0069] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0070] Polytetrafluoroethylene, polypropylene, and polyvinyl chloride are uniformly mixed in a mass ratio of 8:1.5:1 to obtain mixture A. Silicon powder (with a particle size of 5 - 15 μm) and mixture A are placed in ethanol in a mass ratio of 8:1 and ultrasonicated for 1 h, and product B is obtained after pressure filtration. Then, product B is placed in a nitrogen atmosphere at 1100 °C for a high-temperature self-propagating reaction for 3 h to obtain product C. Product C and graphite (type: artificial graphite, source: Luoyang Yuexing New Energy Technology Co., Ltd., model GS16-S, D50 particle size 15 μm, tapped density 1.5 g / cm 3 , purity ≥ 99.99%)) are placed in ethanol in a mass ratio of 0.02:0.98 and stirred to obtain a silicon-carbon anode material with long cycle performance.

[0071] Example 2

[0072] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0073] Polystyrene and polybutylene terephthalate are uniformly mixed in a mass ratio of 15:9:1 to obtain mixture A. Silicon powder (with a particle size of 500 nm - 1000 nm) and mixture A are placed in pure water in a mass ratio of 0.6:1 and mechanically stirred for 1 h, and product B is obtained after pressure filtration and drying. Then, product B is placed in a nitrogen atmosphere at 2000 °C for a high-temperature self-propagating reaction for 2 h to obtain product C. Product C and graphite are placed in pure water in a mass ratio of 0.08:0.92 and stirred to obtain a silicon-carbon anode material with long cycle performance.

[0074] Example 3

[0075] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0076] Polybutylene terephthalate and styrene are uniformly mixed in a mass ratio of 9:1 to obtain mixture A. Silicon powder (with a particle size of 200 nm - 400 nm) and mixture A are vibrationally ball-milled for 3 h in a mass ratio of 15:1. After centrifugation and drying, product B is obtained. Then, product B is subjected to a high-temperature self-propagating reaction at 1300 °C for 4 h under an argon atmosphere to obtain product C. Product C and graphite are placed in pure water in a mass ratio of 0.11:0.89 and stirred to obtain a silicon-carbon anode material with long cycle performance.

[0077] The cycle performance curve of the obtained silicon-carbon anode material is as Figure 1 shown, indicating that after 571 cycles of the obtained silicon-carbon anode material, the capacity retention rate of the material is 82.69%, indicating that the material has good cycle stability.

[0078] Example 4

[0079] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0080] Polybutylene terephthalate and styrene are uniformly mixed in a mass ratio of 9:1 to obtain mixture A. Silicon powder (with a particle size of 800 nm - 1000 nm) and mixture A are vibrationally ball-milled for 3 h in a mass ratio of 15:1. After centrifugation and drying, product B is obtained. Then, product B is subjected to a high-temperature self-propagating reaction at 2600 °C for 0.5 h under an argon atmosphere to obtain product C. Product C and graphite are ball-milled in a mass ratio of 0.17:0.83 to obtain a silicon-carbon anode material with long cycle performance.

[0081] Example 5

[0082] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0083] Polypropylene, polyethylene terephthalate, and polybutylene terephthalate are uniformly mixed in a mass ratio of 4:7:1 to obtain mixture A. Silicon powder (with a particle size of 1 μm - 5 μm) and mixture A are mechanically stirred in acetone for 12 h in a mass ratio of 1:1. After centrifugation and drying, product B is obtained. Then, product B is subjected to a high-temperature self-propagating reaction at 1350 °C for 4 h under a mixed atmosphere of oxygen and argon in a ratio of 1:1 to obtain product C. Product C and graphite are placed in pure water in a mass ratio of 0.25:0.75 and sonicated to obtain a silicon-carbon anode material with long cycle performance.

[0084] Example 6

[0085] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0086] Mix polytetrafluoroethylene, polypropylene, and polybutylene terephthalate evenly at a mass ratio of 9:2:5 to obtain mixture A. Mix silicon powder (with a particle size of 400 nm - 500 nm) and mixture A by ball milling at a mass ratio of 1:8 for 2 h to obtain product B. Then place product B in an atmosphere where oxygen and argon are mixed at a ratio of 1:2 and carry out a high-temperature self-propagating reaction at 1200 °C for 2 h to obtain product C (the scanning electron microscope image is as shown in Figure 2 ), and place product C and graphite in pure water at a mass ratio of 0.52:0.48 and perform ultrasonic treatment to obtain a silicon-carbon anode material with long cycle performance.

[0087] The scanning electron microscope image of the obtained silicon-carbon anode material is as shown in Figure 3 .

[0088] Example 7

[0089] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0090] Mix polyvinylidene fluoride, polyethylene, and polypropylene evenly at a mass ratio of 6:5:5 to obtain mixture A. Mix silicon powder (with a particle size of 200 nm - 300 nm) and mixture A by ball milling at a mass ratio of 1:8 for 2 h to obtain product B. Then place product B in a nitrogen atmosphere and carry out a high-temperature self-propagating reaction at 2100 °C for 1 h to obtain product C. Place product C and graphite in pure water at a mass ratio of 0.66:0.34 and perform ultrasonic treatment to obtain a silicon-carbon anode material with long cycle performance.

[0091] Example 8

[0092] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0093] Mix polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene evenly at a mass ratio of 2:6:2 to obtain mixture A. Mix silicon powder (with a particle size of 100 nm - 200 nm) and mixture A by ball milling at a mass ratio of 1:8 for 2 h to obtain product B. Then place product B in an air atmosphere and carry out a high-temperature self-propagating reaction at 2000 °C for 3 h to obtain product C. Place product C and graphite in pure water at a mass ratio of 0.66:0.34 and perform ultrasonic treatment to obtain a silicon-carbon anode material with long cycle performance.

[0094] Example 9

[0095] This example provides a silicon-based anode material, and its preparation method includes the following steps:

[0096] Polytetrafluoroethylene and polyvinylpyrrolidone were uniformly mixed at a mass ratio of 8:2 to obtain mixture A. Silicon powder (with a particle size of 80 nm - 150 nm) and mixture A were ball-milled and mixed at a mass ratio of 1:8 for 2 h to obtain product B. Then, product B was placed in an air atmosphere at 2100 °C for high-temperature self-propagating reaction for 1 h to obtain product C. Product C and graphite were placed in pure water at a mass ratio of 0.66:0.34 and ultrasonically treated to obtain a silicon-carbon anode material with long cycle performance.

[0097] Comparative Example 1

[0098] Compared with Example 8, the difference lies in that the polymer only uses polytetrafluoroethylene.

[0099] Polytetrafluoroethylene (without adding polyvinylidene fluoride and polypropylene) was used as mixture A at a mass ratio of 100%. Silicon powder (with a particle size of 50 - 200 nm) and mixture A were ball-milled and mixed at a mass ratio of 1:8 for 2 h to obtain product B. Then, product B was placed in an air atmosphere at 1700 °C for high-temperature self-propagating reaction for 3 h to obtain product C. Product C and graphite were placed in pure water at a mass ratio of 0.66:0.34 and ultrasonically treated to obtain a comparative silicon-carbon anode material.

[0100] Comparative Example 2

[0101] Compared with Example 4, the difference lies in that the high-temperature self-propagating reaction temperature is 800 °C.

[0102] Polybutylene terephthalate and styrene were uniformly mixed at a mass ratio of 9:1 to obtain mixture A. Silicon powder (with a particle size of 50 - 200 nm) and mixture A were vibration ball-milled at a mass ratio of 15:1 for 3 h, and after centrifugation and drying, product B was obtained. Then, product B was placed in an argon atmosphere at 800 °C (1000 °C lower than the lower limit of this application) for high-temperature self-propagating reaction for 3 h to obtain product C. Product C and graphite were ball-milled at a mass ratio of 0.17:0.83 to obtain a comparative material.

[0103] Comparative Example 3

[0104] Compared with Example 3, product C was directly used as the anode material.

[0105] Polybutylene terephthalate and styrene were uniformly mixed at a mass ratio of 9:1 to obtain mixture A. Silicon powder (with a particle size of 100 - 300 nm) and mixture A were vibration ball-milled at a mass ratio of 15:1 for 3 h, and after centrifugation and drying, product B was obtained. Product B was placed in an argon atmosphere at 2200 °C for high-temperature self-propagating reaction for 4 h to obtain product C (not compounded with graphite), which was directly used as the anode material.

[0106] Comparative Example 4

[0107] Compared with Example 8, carbon nanotubes are used to replace graphite.

[0108] Polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene are uniformly mixed in a mass ratio of 2:6:2 to obtain mixture A. Silicon powder (with a particle size of 50 - 200 nm) and mixture A are ball-milled and mixed in a mass ratio of 1:8 for 2 h to obtain product B. Product B is placed in an air atmosphere and subjected to a high-temperature self-propagating reaction at 1700 °C for 3 h to obtain product C. Product C is compounded with carbon nanotubes (with a diameter of 20 - 30 nm, a length of 10 - 20 μm, and a purity of ≥98%) in a mass ratio of 0.66:0.34 to prepare a comparative material.

[0109] Electrochemical performance test

[0110] Using the silicon-based anode materials prepared in Examples 1 - 10 above as the active material, a metal rod that can apply pressure is used as the current collector, and a solid-state mold battery is assembled with the active material: electrolyte: conductive carbon in a ratio of 70:25:5.

[0111] The results of the electrochemical performance test are shown in Table 1.

[0112] Table 1 Electrochemical performance

[0113]

[0114] From the comparison between Comparative Example 1 and Example 8, it can be seen that the capacity retention rate of Comparative Example 1 after 300 cycles is only 62.4%, while that of Example 8 is 85.1%. The reason is that the pyrolytic carbon layer structure of single polytetrafluoroethylene is loose and cannot uniformly coat the silicon particles (scanning electron microscopy shows that there are cracks in the coating layer), resulting in a significant decline in the cycling performance.

[0115] From the comparison between Comparative Example 2 and Example 4, it can be seen that the initial Coulombic efficiency of Comparative Example 2 is 85.5%, while that of Example 4 is 92.5%; the capacity retention rate of Comparative Example 2 after 300 cycles is only 58.5%, while that of Example 4 is 85.24%. The reason is that low temperature causes the carbon-containing polymer not to be fully pyrolyzed into graphene, and a large amount of amorphous carbon remains in product C, resulting in poor electron conductivity; and the electrode swelling rate after cycling is as high as 45% (≤30% in Example 4).

[0116] From the comparison between Comparative Example 3 and Example 3, it can be seen that the capacity retention rate of Comparative Example 3 after 300 cycles is only 55.8%, while that of Example 3 is 84.46%. The reason is that the non-composite graphite leads to discontinuous conductive network of the material, increased interfacial impedance, and the volume expansion is not buffered by the graphite matrix, resulting in cracking after 300 cycles.

[0117] From the comparison between Comparative Example 4 and Example 8, it can be seen that the capacity retention rate of Comparative Example 4 after 300 cycles is only 68.9%, while that of Example 8 is 85.1%. The reason is that the carbon nanotubes have a high specific surface area (≥250 m2 / g) and low tap density (0.2 g / cm 3 ), resulting in an electrode compaction density of only 2.1 g / cm 3 (the density of the graphite composite electrode in Example 8 is 3.2 g / cm 3 ), and the contact between CNTs and silicon particles is point contact rather than surface contact, which cannot effectively inhibit expansion.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a silicon-based negative electrode material, characterized in that: include: A plurality of carbon-containing polymer materials and silicon powder are first mixed, and then subjected to a high-temperature self-propagating reaction to obtain a nano-scale precursor; The nanoscale precursor is mixed with graphite for a second time to obtain the silicon-based negative electrode material.

2. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The carbon-containing polymer material includes multiple types of polyethylene, polypropylene, polyvinyl chloride, ethylene-vinyl acetate copolymer, polyethylene terephthalate, polybutylene terephthalate, polytetrafluoroethylene, polystyrene, polycarbonate, polyvinylidene fluoride, polyfluoropropylene, polyvinyl pyrrolidone, and polyperfluoroacrylate; Preferably, the carbon-containing polymer material is a mixture of polyvinylidene fluoride, polytetrafluoroethylene, and polypropylene in a mass ratio of (1.5-3):(5-7):(1-3), or the carbon-containing polymer material is a mixture of polytetrafluoroethylene and polyvinyl pyrrolidone in a mass ratio of (7:3)-(9:1); Preferably, the mass ratio of the silicon powder to the carbon-containing polymer material is (0.001-50):1, and more preferably (0.01-20.5):1; Preferably, the first mixing method includes one or more of mechanical stirring, vibration ball milling, and ultrasonic compounding.

3. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: A solvent is also added during the first mixing; Preferably, the solvent includes one or more of ethanol, water, isopropanol, ether, methyl acetate, and acetone; Preferably, the first mixing time is 0.1-36h.

4. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The temperature of the high temperature self-propagating reaction is 1000-2800°C and the time is 0.05-6h; Preferably, the atmosphere of the high temperature self-propagating reaction includes one or more of air, oxygen, nitrogen and argon.

5. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The graphite includes natural graphite and / or artificial graphite; Preferably, the graphite has a particle size D50 of 5-30 μm and a tap density of not less than 1.2 g / cm 3 , purity not less than 99.95%.

6. The method for preparing a silicon-based negative electrode material according to any one of claims 1 to 5, characterized in that: The mass ratio of the nanoscale precursor to the graphite is (0.01-0.8):1; Preferably, the second mixing method includes one or more of mechanical stirring, mechanical ball milling, and ultrasonic mixing.

7. A silicon-based negative electrode material, characterized in that: The method for preparing the silicon-based negative electrode material according to any one of claims 1 to 6 is used to prepare the silicon-based negative electrode material.

8. A lithium battery, characterized in that: The raw materials include the silicon-based negative electrode material as described in claim 7.

9. The lithium battery according to claim 8, characterized in that: The lithium battery is an all-solid-state lithium battery.

10. An electrical equipment, characterized in that: Including the lithium battery as described in claim 8 or 9.

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