Silicon carbon material and preparation method thereof, secondary battery and electronic device

Abstract

The invention provides a silicon-carbon material and a preparation method thereof, a secondary battery and an electronic device. The silicon-carbon material comprises a carbon skeleton and silicon particles, the carbon skeleton comprises amorphous carbon and carbon nanotubes, the elasticity modulus of the silicon-carbon material is E, and E is larger than or equal to 50 Gpa and smaller than or equal to 200 Gpa. The silicon-carbon material provided by the invention has relatively good expansion performance and good silicon-carbon material particle stability in the cycle process, and the rate capability, the expansion performance and the cycle performance of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of batteries. Specifically, this application relates to a silicon-carbon material, a preparation method thereof, a secondary battery, and an electronic device. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high working voltage, good safety, and environmental friendliness, and are widely used in consumer electronics fields such as mobile phones and laptop computers. Among them, silicon, as the anode material of lithium-ion batteries, has a theoretical specific capacity of up to 4200 mAh / g and is considered to be the next-generation lithium-ion anode material that is most likely to replace traditional graphite anode materials and thus improve the energy density of lithium-ion batteries. However, during the charge and discharge process of silicon particles, the insertion process of lithium ions leads to a phase change, which will cause serious particle volume expansion. For conventional silicon-carbon prepared by sanding method, the expansion of silicon still cannot be avoided. The proposed new type of silicon-carbon provides an effective solution to the problem of silicon expansion. However, the reserved pore structure in the new type of silicon-carbon makes the internal electrical contact poor, which is not conducive to meeting the requirements of kinetic improvement and fast charging performance, and it is difficult to further improve the cycle and expansion performance. Summary of the Invention

[0003] This application provides a silicon-carbon material, a preparation method thereof, a secondary battery, and an electronic device.

[0004] In the first aspect of this application, a silicon-carbon material is provided. The silicon-carbon material includes a carbon skeleton and silicon particles. The carbon skeleton includes amorphous carbon and carbon nanotubes. The elastic modulus of the silicon-carbon material is E, and 50 GPa ≤ E ≤ 200 GPa.

[0005] In this application, carbon nanotubes are in-situ compounded inside the silicon-carbon material particles. Carbon nanotubes have good electrical conductivity, which can compensate for the kinetic performance of the deposited silicon-carbon material. At the same time, the good mechanical properties of carbon nanotubes can effectively improve the expansion performance of the silicon-carbon material and the stability of the silicon-carbon material particles during the cycling process, so as to obtain better rate performance, expansion performance, and cycling performance. The elastic modulus of the silicon-carbon material can reflect the stress that the silicon-carbon material can buffer. When the elastic modulus of the silicon-carbon material is within the above suitable range, the silicon-carbon material is not easily deformed, the shedding of active substances is reduced, and the silicon in the silicon-carbon material can effectively buffer the expansion stress of silicon, reducing the rupture of the silicon material under large stress and resulting in the exposure of nanosilicon in the electrolyte to accelerate the consumption of the electrolyte, thereby improving the cycling performance of the silicon-carbon material.

[0006] Based on the first aspect, in some embodiments, 70 GPa ≤ E ≤ 150 GPa. This is beneficial to further improve the cycling performance of the secondary battery.

[0007] Based on the first aspect, in some embodiments, the ratio of the outer diameter to the inner diameter of the carbon nanotube is L, where 1.0 ≤ L ≤ 10.0. This is beneficial for improving the dispersibility of the carbon nanotube, achieving good close contact between the carbon nanotube and the amorphous carbon, and at the same time can fully exert the electrical conductivity and mechanical properties of the carbon nanotube to improve the cycle performance, expansion performance, and kinetic performance of the silicon-carbon material. The inventors found that when the tube diameter ratio of the carbon nanotube is within the above suitable range, while maintaining good rigidity of the carbon nanotube, the dispersibility of the carbon nanotube inside the silicon-carbon material particles can be improved, making the carbon nanotubes evenly distributed, reducing agglomeration, improving the overall mechanical strength and electrical conductivity of the negative electrode sheet, and also being beneficial for improving the flexibility of the carbon nanotube inside the silicon-carbon material particles, which is conducive to buffering the volume expansion and contraction of the silicon material during charge and discharge, fully exerting the capacity of the silicon-carbon material and releasing the expansion stress of silicon, and improving the cycle performance of the silicon-carbon material.

[0008] Based on the first aspect, in some embodiments, the average circularity of the silicon-carbon material is from 0.65 to 0.8. This is beneficial for exerting the pressure resistance, uniform stress release, and uniform internal structure of the silicon-carbon material, and at the same time is also beneficial for improving the problem of reducing the adhesive force of the binder during the preparation of the negative electrode slurry due to the increase in the average circularity, thereby being conducive to improving the kinetic performance of the secondary battery. And within the above range, it is also beneficial for improving the pressure resistance of the silicon-carbon material, thereby being conducive to improving the long-term cycle stability of the secondary battery.

[0009] Based on the first aspect, in some embodiments, the powder conductivity of the silicon-carbon material is from 0.1 S / cm to 20 S / cm. Carbon nanotubes are in-situ introduced on the amorphous carbon to improve the electrical conductivity and mechanical properties of the silicon-carbon material. When the powder conductivity of the silicon-carbon material is within the above range, it is beneficial to have an appropriate content of carbon nanotubes in the silicon-carbon material, which is conducive to improving the close contact between the amorphous carbon and the carbon nanotube, and is also beneficial for the silicon material to release the expansion stress and exert the capacity contribution, being conducive to improving the kinetic performance and capacity exertion of the silicon-carbon material, and improving the cycle performance of the silicon-carbon material.

[0010] Based on the first aspect, in some embodiments, the cross-section of the silicon-carbon material includes a first test area with an area of 1000 nm 2 and a second test area with an area of 1000 nm 2In the second test area, the first test area and the second test area do not overlap. Based on the area of the first test area, the area ratio of carbon nanotubes is S1%, and based on the area of the second test area, the area ratio of carbon nanotubes is S2%. |S1 - S2| ≤ 0.093. This indicates that the carbon nanotubes in the silicon-carbon material have better dispersion uniformity, reducing the agglomeration of carbon nanotubes in the silicon-carbon material, forming an effective conductive network with amorphous carbon and nanosilicon, and giving full play to the better conductivity and excellent mechanical properties of the carbon nanotubes in the silicon-carbon material composite with carbon nanotubes, thereby improving the mass energy density and cycle performance of the secondary battery.

[0011] The second aspect of the present application provides a preparation method of a silicon-carbon material, including the following steps: S1. Add carbon nanotubes, a carbon precursor, a curing agent, and a surfactant into an organic solvent, and grind and stir to obtain a suspension, where the mass ratio of carbon nanotubes to the surfactant is (0.005 - 0.1):1; S2. Granulate the suspension by spray drying to obtain mixed particles; S3. Carbonize and activate the mixed particles to obtain porous carbon; S4. Use chemical vapor deposition to deposit silicon and carbon coat on the porous carbon to obtain a silicon-carbon material. By mixing carbon nanotubes, a carbon precursor, a curing agent, and a surfactant in an organic solvent, through solid-liquid mixing, the carbon nanotubes, carbon precursor, curing agent, and surfactant are mixed and dispersed uniformly, improving the uniformity of the distribution of carbon nanotubes and the carbon precursor, and facilitating the reduction of the agglomeration of some carbon nanotubes in the subsequent preparation process; in the above preparation method, the elastic modulus of the silicon-carbon material is also regulated by controlling the mass ratio of carbon nanotubes to the surfactant and the rotation speed and time of grinding and stirring the suspension, and the elastic modulus of the silicon-carbon material is designed to meet a specific range, thereby improving the cycle performance and rate performance of the silicon-carbon material.

[0012] The third aspect of the present application provides a secondary battery, including a negative electrode sheet, a positive electrode sheet, and an electrolyte. The negative electrode sheet includes the silicon-carbon material or the silicon-carbon material obtained by the preparation method passed through.

[0013] Based on the third aspect, in some embodiments, the electrolyte includes ethyl propionate and propyl propionate. Based on the mass of the electrolyte, the mass ratio of ethyl propionate is A1%, and the mass ratio of propyl propionate is A2%. 2 ≤ A2 / A1 ≤ 6. This is beneficial to further improve the rate performance and cycle performance of the secondary battery.

[0014] Based on the third aspect, in some embodiments, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass ratio of fluoroethylene carbonate is F%. 5 ≤ F ≤ 20. This is beneficial to further improve the rate performance, cycle performance, and swelling performance of the secondary battery.

[0015] Based on the third aspect, in some embodiments, 3.5 ≤ E / F ≤ 18.75, which is beneficial to further improve the rate performance, cycle performance, and swelling performance of the secondary battery.

[0016] The fourth aspect of the present application provides an electronic device including the secondary battery described above. The silicon-carbon material included in the secondary battery has excellent rate performance, cycle performance, and swelling performance, which is beneficial to improving the service life of the electronic device. Specific Embodiments

[0017] For the sake of brevity, the present application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0018] In the description of the present application, unless otherwise specified, "above" and "below" include the corresponding numbers.

[0019] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0020] The list of items connected by the terms "at least one of", "at least one in", "at least one kind in", or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0021] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0022] An embodiment of the present application provides a secondary battery, which includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing.

[0023] The outer casing can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film). For example, if the secondary battery is a soft-pack battery. In some other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0024] The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate. The electrode assembly can be a stacked structure, which is formed by laminating the positive electrode plate, the separator, and the negative electrode plate. In some other embodiments, the electrode assembly can also be a wound structure, which is formed by laminating and then winding the positive electrode plate, the separator, and the negative electrode plate.

[0025] Negative electrode plate

[0026] The negative electrode plate includes a negative current collector and a negative active layer located on the surface of the negative current collector. The negative current collector includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof, and can also be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and polymer substrate. In the negative electrode plate, the negative active layer includes a silicon-carbon material.

[0027] The present application provides a silicon-carbon material. The silicon-carbon material includes a carbon skeleton and silicon particles. The carbon skeleton includes amorphous carbon and carbon nanotubes. The elastic modulus of the silicon-carbon material is E, and 50 GPa ≤ E ≤ 200 GPa.

[0028] In the present application, carbon nanotubes are in-situ composite inside the silicon-carbon material particles. The carbon nanotubes have good electrical conductivity, which can make up for the kinetic performance of the deposited silicon-carbon material. At the same time, the good mechanical properties of the carbon nanotubes can effectively improve the expansion performance of the silicon-carbon material and the stability of the silicon-carbon material particles during the cycling process, so as to obtain better rate performance, expansion performance, and cycling performance. The elastic modulus of the silicon-carbon material can reflect the stress that the silicon-carbon material can buffer. When the elastic modulus of the silicon-carbon material is within the above suitable range, the silicon-carbon material is not easily deformed, the shedding of the active material is reduced, and the silicon in the silicon-carbon material can effectively buffer the expansion stress of silicon, reducing the rupture of the silicon material under large stress and resulting in the exposure of nano-silicon in the electrolyte to accelerate the consumption of the electrolyte, thereby improving the cycling performance of the silicon-carbon material.

[0029] When the elastic modulus E of the silicon-carbon material is small, such as less than 50 GPa, the silicon-carbon material may be easily deformed, causing the active material on the negative electrode plate to be easily shed. When applied to a secondary battery, the secondary battery will have poor expansion performance; when the elastic modulus E of the silicon-carbon material is large, such as greater than 200 GPa, the silicon-carbon material has a large stiffness, and it is not conducive to effectively buffering the change of the expansion stress of silicon during expansion, and it is easy to cause the silicon-carbon material particles to break, reducing the cycling performance of the silicon-carbon material.

[0030] In some embodiments, the elastic modulus E of the silicon-carbon material can be 50 GPa, 70 GPa, 80 GPa, 90 GPa, 100 GPa, 120 GPa, 130 GPa, 150 GPa, 170 GPa, 190 GPa, 200 GPa or any value within the range formed by any two of the above values.

[0031] In some embodiments, 70 GPa ≤ E ≤ 150 GPa, which is beneficial to further improve the cycling performance of the secondary battery.

[0032] In some embodiments, the ratio of the outer diameter to the inner diameter of the carbon nanotube is L, and 1.0 ≤ L ≤ 10.0. When the carbon nanotube is compounded inside the silicon-carbon material particles as an additive, the tube diameter ratio (the ratio of the outer diameter to the inner diameter) of the carbon nanotube is within a reasonable range, which can facilitate the dispersion of the carbon nanotube, achieve good close contact between the carbon nanotube and the amorphous carbon, and at the same time can give full play to the conductivity and mechanical properties of the carbon nanotube to improve the cycling performance, expansion performance and kinetic performance of the silicon-carbon material. The inventors found that when the tube diameter ratio of the carbon nanotube is within the above suitable range, while maintaining good rigidity of the carbon nanotube, the dispersibility of the carbon nanotube inside the silicon-carbon material particles can be improved, so that the carbon nanotubes are evenly distributed, agglomeration is reduced, the overall mechanical strength and conductivity of the negative electrode sheet are improved, and it is also beneficial to improve the flexibility of the carbon nanotube inside the silicon-carbon material particles, which is conducive to buffering the volume expansion and contraction of the silicon material during charge and discharge, giving full play to the capacity of the silicon-carbon material and releasing the expansion stress of silicon, and improving the high-temperature cycling performance of the silicon-carbon material. In some embodiments, the ratio L of the outer diameter to the inner diameter of the carbon nanotube can be 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 or any value within the range formed by any two of the above values.

[0033] In some embodiments, the average circularity of the silicon-carbon material is 0.65 to 0.8. When the average circularity of the silicon-carbon material is within the above suitable range and the silicon-carbon material is used as the negative electrode material in the secondary battery, it is beneficial to exert the characteristics of the silicon-carbon material such as pressure resistance, uniform stress release, and uniform internal structure of the silicon material. At the same time, it is also beneficial to improve the problem of reducing the bonding force of the binder during the preparation of the negative electrode slurry due to the increase in the average circularity, thereby facilitating the improvement of the kinetic performance of the secondary battery. And within the above range, it is also beneficial to improve the pressure resistance of the silicon-carbon material, thereby facilitating the improvement of the long-term cycling stability of the secondary battery. In some embodiments, the average circularity of the silicon-carbon material can be 0.65, 0.68, 0.7, 0.75, 0.8 or any value within the range formed by any two of the above values.

[0034] In some embodiments, the powder conductivity of the silicon-carbon material is 0.1 S / cm to 20 S / cm. During the preparation of the silicon-carbon material, carbon nanotubes are in-situ introduced onto the amorphous carbon to improve the conductivity and mechanical properties of the silicon-carbon material. When the powder conductivity of the silicon-carbon material is within the above range, it is beneficial to have an appropriate content of carbon nanotubes in the silicon-carbon material, thereby facilitating the improvement of the contact tightness between the amorphous carbon and the carbon nanotubes, also facilitating the release of expansion stress by the silicon material and the exertion of capacity contribution, and also facilitating the improvement of the kinetic performance and capacity exertion of the silicon-carbon material, and enhancing the cycling performance of the silicon-carbon material. In some embodiments, the powder conductivity of the silicon-carbon material can be 0.1 S / cm, 0.5 S / cm, 1 S / cm, 1.5 S / cm, 2 S / cm, 3 S / cm, 5 S / cm, 8 S / cm, 10 S / cm, 13 S / cm, 15 S / cm, 18 S / cm, 20 S / cm or any value within the range formed by any two of the above values.

[0035] In some embodiments, the cross-section of the silicon-carbon material includes a first test area with an area of 1000 nm 2 and a second test area with an area of 1000 nm 2 The first test area and the second test area do not overlap. Based on the area of the first test area, the area proportion of the carbon nanotubes is S1%, and based on the area of the second test area, the area proportion of the carbon nanotubes is S2%, and |S1 - S2| ≤ 0.093. Carbon nanotubes (CNT) are in-situ compounded inside the silicon-carbon material particles. The inventors found that when the ratio of the proportion of carbon nanotubes in the first test area and the second test area satisfies the above relationship, the carbon nanotubes in the silicon-carbon material have better dispersion uniformity, reduce the agglomeration of carbon nanotubes in the silicon-carbon material, and form an effective conductive network with the amorphous carbon and nano-silicon, giving full play to the advantages of the better conductivity and excellent mechanical properties of the carbon nanotubes in the silicon-carbon material composite with carbon nanotubes, and enhancing the mass energy density and cycling performance of the secondary battery. In some embodiments, the difference of |S1 - S2| ≤ 0.093 can be 0, 0.012, 0.016, 0.02, 0.03, 0.039, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.093 or any value within the range formed by any two of the above values. Preferably, |S1 - S2| ≤ 0.039.

[0036] The present application provides a method for preparing a silicon-carbon material, comprising the following steps:

[0037] S1. Adding carbon nanotubes, a carbon precursor, a curing agent, and a surfactant into an organic solvent, and obtaining a suspension through sand grinding and stirring, wherein the mass ratio of the carbon nanotubes to the surfactant is (0.005 - 0.1):1.

[0038] In this step, the carbon precursor can be a linear resin, the curing agent can be hexamine, and the surfactant can be at least one of polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC), or cetyltrimethylammonium bromide (CTAB). Ethanol is selected as the organic solvent.

[0039] In this step, the addition amount of carbon nanotubes, the addition amount of surfactant, the mixing and grinding time, and the rotation speed of the grinding and stirring will all affect the composition of the silicon-carbon material, or affect the composite content of carbon nanotubes on amorphous carbon or the composite uniformity of carbon nanotubes on amorphous carbon, thereby affecting the magnitude of the elastic modulus of the silicon-carbon material.

[0040] Among them, the mass ratios of carbon nanotubes to the carbon precursor and the curing agent are (0.000125 - 0.0075):1 and (0.005 - 0.1):1 respectively. The mass ratio of carbon nanotubes to the surfactant is (0.005 - 0.1):1. Within this range, it is beneficial to disperse carbon nanotubes, improve the dispersion uniformity of carbon nanotubes, and is conducive to increasing the elastic modulus of the silicon-carbon material. When the mass ratio of carbon nanotubes to the surfactant is within the above range, it is also conducive to increasing the elastic modulus of the silicon-carbon material. In some embodiments, the mass ratio value of carbon nanotubes to the carbon precursor can be 0.000125, 0.000150, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0075, or any value within the range composed of any two of the above values. In some embodiments, the mass ratio of carbon nanotubes to the surfactant can be 0.005:1, 0.007:1, 0.008:1, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, or any ratio within the range composed of any two of the above ratios. The rotation speed of the grinding and stirring is 200 r / min - 2000 r / min, and the grinding and stirring time is 0.1 h - 6 h to make the carbon nanotubes in the suspension evenly dispersed. When in the above mixing process, the mixing and grinding time and the grinding rotation speed are within the appropriate range, it is beneficial to make the carbon nanotubes have good dispersion uniformity in the suspension, thereby being conducive to increasing the elastic modulus of the silicon-carbon material. In some embodiments, the grinding rotation speed can be 200 r / min, 300 r / min, 500 r / min, 700 r / min, 1000 r / min, 1200 r / min, 1500 r / min, 1700 r / min, 2000 r / min, or any value within the range composed of any two of the above values; the grinding time can be 0.1 h, 0.5 h, 1 h, 2 h, 3 h, 5 h, 6 h, or any value within the range composed of any two of the above values.

[0041] S2. Granulate the suspension by spray drying to obtain mixed particles.

[0042] During the spray drying process, the inlet air temperature for spray drying is 200°C to 260°C, the outlet air temperature is 80°C to 100°C, the atomization pressure is 0.3 MPa, and the feeding rate is 0.03 L / min to 0.1 L / min. Granulate the suspension under the above conditions to obtain mixed particles containing carbon nanotubes with a diameter of 5 μm to 10 μm. Then dry under vacuum for 24 h to remove the solvent, and the drying temperature is 80°C. During the spray drying process, the feeding rate can adjust the average particle size of the mixed particles. When the feeding rate is larger, the average particle size of the mixed particles can be increased. In some embodiments, the inlet air temperature can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C or any value within the range composed of any two of the above values; the outlet air temperature can be 80°C, 90°C, 100°C or any value within the range composed of any two of the above values; the feeding rate can be 0.03 L / min, 0.05 L / min, 0.08 L / min, 0.1 L / min or any value within the range composed of any two of the above values.

[0043] S3. Carbonize and activate the mixed particles in an inert gas atmosphere to obtain porous carbon.

[0044] In the carbonization stage: In an inert gas (such as nitrogen or argon) atmosphere, the carbonization temperature is 550°C to 1500°C, and the carbonization time is 2 h to 6 h. In the activation stage: In an atmosphere of a mixed gas of water and carbon dioxide, the activation temperature is 700°C to 1000°C, and the activation time is 2 h to 20 h. Under the above conditions, the carbon in the mixed particles is fully carbonized and activated, so as to facilitate the obtaining of porous carbon with a more stable structure. In some embodiments, the carbonization temperature can be 550°C, 600°C, 800°C, 900°C, 1000°C, 1200°C, 1400°C, 1500°C or any value within the range composed of any two of the above values; the carbonization time can be 2 h, 3 h, 4 h, 5 h, 6 h or any value within the range composed of any two of the above values; the activation temperature can be 700°C, 800°C, 900°C, 1000°C or any value within the range composed of any two of the above values; the activation time can be 2 h, 5 h, 10 h, 15 h, 20 h or any value within the range composed of any two of the above values.

[0045] S4. Use chemical vapor deposition to deposit silicon and coat carbon on the porous carbon to obtain a silicon-carbon material.

[0046] Using chemical vapor deposition, silicon is deposited on porous carbon containing carbon nanotubes in a silicon-containing atmosphere (such as silane, SiH4). The flow rate of the silicon-containing gas introduced is 5 to 100 L / min, the deposition temperature is 400°C to 600°C, and the deposition time is 2 h to 20 h. Then, the porous carbon with silicon particles deposited thereon is carbon-coated. In a carbon-containing gas such as acetylene atmosphere, the flow rate of the carbon-containing gas introduced is 10 to 120 L / min, the carbon coating temperature is 500°C to 900°C, and the carbon coating time is 0.1 h to 6 h to further stabilize the structure of the porous carbon and obtain a silicon-carbon material. In some embodiments, the deposition temperature can be 400°C, 500°C, 600°C, or any value within the range formed by any two of the above values; the deposition time can be 2 h, 5 h, 10 h, 15 h, 20 h, or any value within the range formed by any two of the above values. The carbon coating temperature can be 500°C, 600°C, 700°C, 800°C, 900°C, or any value within the range formed by any two of the above values; the carbon coating time can be 0.1 h, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, or any value within the range formed by any two of the above values; the flow rate of the silicon-containing gas introduced can be 5 L / min, 10 L / min, 20 L / min, 25 L / min, 30 L / min, 40 L / min, 50 L / min, 60 L / min, 70 L / min, 80 L / min, 90 L / min, 100 L / min, 110 L / min, 120 L / min, or any value within the range formed by any two of the above values; the flow rate of the carbon-containing gas introduced can be 10 L / min, 20 L / min, 25 L / min, 30 L / min, 40 L / min, 50 L / min, 60 L / min, 70 L / min, 80 L / min, 90 L / min, 100 L / min, 110 L / min, 120 L / min, or any value within the range formed by any two of the above values.

[0047] In the preparation method of the silicon-carbon material provided by this application, carbon nanotubes, a carbon precursor, a curing agent, and a surfactant are in an organic solvent, and through solid-liquid mixing, the carbon nanotubes, the carbon precursor, the curing agent, and the surfactant are mixed and dispersed evenly, improving the uniformity of the distribution of the carbon nanotubes and the carbon precursor, which is beneficial to reducing the agglomeration of some carbon nanotubes in the subsequent preparation process; in the above preparation method, the elastic modulus of the silicon-carbon material is also regulated by controlling the mass ratio of the carbon nanotubes and the surfactant and the rotation speed and time of sanding and stirring of the suspension, and the elastic modulus of the designed silicon-carbon material is satisfied within a specific range, thereby improving the cycling performance and rate performance of the silicon-carbon material.

[0048] In some embodiments, the negative electrode active layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0049] In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0050] In some embodiments, the electrolyte includes ethyl propionate and propyl propionate. Based on the mass of the electrolyte, the mass percentage of ethyl propionate is A1%, and the mass percentage of propyl propionate is A2%, where 2 ≤ A2 / A1 ≤ 6. The inclusion of ethyl propionate and propyl propionate in the electrolyte and the mass ratio of the two satisfying the above conditions are beneficial to further improving the rate performance and cycle performance of the secondary battery. In some embodiments, the ratio of A2 / A1 can be 2, 3, 4, 5, 6, or any value within the range formed by any two of the above values.

[0051] In some embodiments, 3 ≤ A2 / A1 ≤ 5. This can further improve the rate performance and cycle performance of the secondary battery.

[0052] In some embodiments, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is F%, where 5 ≤ F ≤ 20. The inclusion of fluoroethylene carbonate in the electrolyte and within the above mass percentage range is beneficial to further improving the rate performance, cycle performance, and swelling performance of the secondary battery. In some embodiments, F can be 5, 8, 10, 12, 14, 15, 17, 18, 20, or any value within the range formed by any two of the above values. In some embodiments, 8 ≤ F ≤ 14.

[0053] In some embodiments, 3.5 ≤ E / F ≤ 18.75. When the elastic modulus of the silicon-carbon material in the secondary battery and the mass percentage of fluoroethylene carbonate in the electrolyte satisfy the above conditions, it is beneficial to further improve the rate performance, cycle performance, and swelling performance of the secondary battery. In some embodiments, the ratio of E / F can be 3.5, 4, 5, 8, 10, 12, 13, 14, 15, 16, 17, 18, 18.75, or any value within the range formed by any two of the above values. In some embodiments, 7.5 ≤ E / F ≤ 15.

[0054] Separator

[0055] There are no particular limitations on the material and shape of the separator used in the secondary battery of the present application, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application.

[0056] For example, the separator may include a base layer and a surface treatment layer. The base layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0057] A surface treatment layer is provided on at least one surface of the base layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0058] Electrolyte

[0059] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and an optional additive. The organic solvent in the electrolyte of the present application can be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no limitation on the electrolyte used in the electrolyte according to the present application, and it can be any electrolyte known in the prior art. The additive of the electrolyte according to the present application can be any additive known in the prior art that can be used as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, such as including at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0060] Positive electrode sheet

[0061] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on the positive electrode current collector. The positive electrode current collector can use aluminum foil, nickel foil, etc., or can also be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly intercalate and deintercalate lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material can include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganate, spinel-type lithium nickel manganate, and lithium titanate.

[0062] The positive electrode active layer further includes a binder for bonding the positive electrode active material particles to facilitate the formation of a film layer, and at the same time can also improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the binder may include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0063] The positive electrode active layer may further include a conductive material, and the conductive material includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials may include but are not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0064] The above secondary battery is applied to an electronic device to supply power to a load in the electronic device. Moreover, the silicon-carbon material in the above secondary battery has excellent structural stability, which is beneficial to improving the cycle performance and rate performance of the secondary battery, and is conducive to improving the service life of the electronic device. Among them, the electronic device may include but is not limited to laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0065] The present application will be described below through specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0066] In the following examples and comparative examples, the reagents, materials, and instruments used, unless otherwise specified, can be obtained commercially.

[0067] Example 1-1

[0068] First, dissolve 2 grams of carbon nanotubes, 500 grams of linear resin, 150 grams of hexamethylenetetramine (HMT), and 200 g of polyvinylpyrrolidone (PVP) in 5000 milliliters of ethanol solution. Under a sand grinding and stirring rate of 1200 r / min, after sand grinding and stirring for 3 h, a uniform suspension containing carbon nanotubes is formed. Subsequently, granulate the suspension by spray drying. The inlet air temperature of the spray drying is 200 °C, the outlet air temperature is 80 °C, the atomization pressure is 0.3 MPa, and the feeding rate is 0.03 L / min to obtain mixed particles containing carbon nanotubes with a diameter of about 10 μm, and vacuum dry the mixed particles at 80 °C for 24 hours to remove the solvent.

[0069] Then, carbonize and activate the dried mixed particles in sequence. Carbonization stage: Under an argon atmosphere, the carbonization temperature is 550 °C and the carbonization time is 2 h; activation stage: Under a mixed gas atmosphere of water and carbon dioxide, the activation temperature is 850 °C and the activation time is 4 h to obtain porous carbon containing carbon nanotubes.

[0070] Deposit silicon on the porous carbon containing carbon nanotubes and perform carbon coating by chemical vapor deposition. During the silicon deposition process, use a silicon-containing gas (such as silane, SiH4), the flow rate of the silane gas introduced is 8 L / min, the deposition temperature is 550 °C, and the deposition time is 6 h. Then, perform carbon coating on the porous carbon after silicon deposition. During the carbon coating process, use a carbon-containing gas (such as acetylene, C2H2) for coating, the flow rate of the acetylene gas introduced is 10 L / min, the carbon coating temperature is 600 °C, and the carbon coating time is 0.5 h to obtain a silicon-carbon material.

[0071] Preparation of lithium-ion battery:

[0072] Preparation of the positive electrode: Mix lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) evenly by fully stirring in an N-methylpyrrolidone solvent system according to a weight ratio of 95%:2.5%:2.5% to prepare a positive electrode slurry. Coating the prepared positive electrode slurry on the positive electrode current collector aluminum foil, drying, cold pressing, cutting, and welding the tab to obtain a positive electrode plate.

[0073] Preparation of the negative electrode: Mix graphite, silicon-carbon material, conductive agent carbon nanotubes, and binder polymethyl acrylate according to a solid mass ratio of about 88.4%, 9.8%, 0.1%, and 1.7%, and knead and disperse at a solid content of about 38% - 50 wt% to prepare a negative electrode slurry. Coating the prepared negative electrode slurry on the negative electrode current collector copper foil, drying, cold pressing, cutting, and welding the tab to obtain a negative electrode.

[0074] Preparation of the electrolyte:

[0075] Under a dry argon atmosphere, LiPF6, lithium tetrafluoroborate, lithium difluorophosphate, and 1,3 - propane sultone were added to a mixed solution of propyl propionate (PP), ethyl propionate (EP), fluoroethylene carbonate (FEC), propylene carbonate (PC), and ethylene carbonate (EC). Among them, based on the mass of the electrolyte, the mass ratio of LiPF6 was 12.5%, the mass ratio of PP was 45%, the mass ratio of EP was 15%, the mass ratio of FEC was 10%, the mass ratio of lithium tetrafluoroborate was 1%, the mass ratio of lithium difluorophosphate was 0.5%, and the mass ratio of 1,3 - propane sultone was 2.5%. The balance was PC and EC. The mass ratio of PC to EC was 1:1.

[0076] Preparation of the separator: A PE composite film was used as the separator.

[0077] Preparation of the lithium - ion battery: The positive electrode, separator, and negative electrode were stacked in sequence, with the separator placed between the positive and negative electrodes to play a separating role. The electrode assembly was wound. The electrode assembly was placed in an aluminum - plastic film packaging bag, dried at 80 °C, and then injected with the electrolyte. After vacuum packaging, standing, forming, shaping, and capacity testing processes, a soft - package lithium - ion battery was obtained.

[0078] Comparative Example 1

[0079] First, 0.3 grams of carbon nanotubes, 60 grams of linear resin, 100 grams of hexamethylenetetramine (HMT), and 300 g of polyvinylpyrrolidone (PVP) were dissolved in 5000 milliliters of ethanol solution. Under a sand - grinding stirring rate of 2200 r / min, after sand - grinding and stirring for 0.3 h, a uniform suspension containing carbon nanotubes was formed. The suspension was granulated by spray - drying. The inlet air temperature of the spray - drying was 200 °C, the outlet air temperature was 80 °C, the atomization pressure was 0.3 MPa, and the feeding rate was 0.03 L / min to obtain carbon - tube - containing organic particles with a diameter of about 10 microns, and they were vacuum - dried at 80 °C for 24 hours to remove the solvent.

[0080] The dried mixed particles were carbonized and activated in sequence. Carbonization stage: Under an argon atmosphere, the carbonization temperature was 600 °C and the carbonization time was 2 h; Activation stage: Under a mixed gas atmosphere of water and carbon dioxide, the activation temperature was 900 °C and the activation time was 4 h to obtain carbon - nanotube - containing porous carbon.

[0081] By chemical vapor deposition, silicon is deposited on porous carbon containing carbon nanotubes and carbon coating is carried out. During the silicon deposition process, a silicon-containing gas (such as silane, SiH4) is used. The flow rate of the silane gas introduced is 1 L / min, the deposition temperature is 550 °C, and the deposition time is 6 h. Then, carbon coating is carried out on the porous carbon after silicon deposition. During the carbon coating process, a carbon-containing gas (such as acetylene, C2H2) is used for coating. The flow rate of the acetylene gas introduced is 3 L / min, the carbon coating temperature is 600 °C, and the carbon coating time is 0.5 h to obtain a silicon-carbon material.

[0082] Comparative Example 2

[0083] First, 7.0 grams of carbon nanotubes, 777.8 grams of linear resin, 100 grams of hexamethylenetetramine (HMT), and 23.3 g of polyvinylpyrrolidone (PVP) are dissolved in 5000 milliliters of ethanol solution. Under a sand grinding and stirring rate of 90 r / min, after sand grinding and stirring for 8.0 hours, a uniform carbon nanotube-containing organic solution is formed. Subsequently, the suspension is granulated by spray drying. The inlet air temperature of the spray drying is 200 °C, the outlet air temperature is 80 °C, the atomization pressure is 0.3 MPa, and the feeding rate is 0.03 L / min to obtain carbon nanotube-containing organic particles with a diameter of about 10 microns, and they are vacuum dried at 80 °C for 24 hours to remove the solvent.

[0084] The dried mixed particles are carbonized and activated in sequence. Carbonization stage: Under an argon atmosphere, the carbonization temperature is 600 °C and the carbonization time is 2 h; activation stage: Under a mixed gas atmosphere of water and carbon dioxide, the activation temperature is 900 °C and the activation time is 4 h to obtain porous carbon containing carbon nanotubes.

[0085] By chemical vapor deposition, silicon is deposited on porous carbon containing carbon nanotubes and carbon coating is carried out. During the silicon deposition process, a silicon-containing gas (such as silane, SiH4) is used. The flow rate of the silane gas introduced is 200 L / min, the deposition temperature is 550 °C, and the deposition time is 6 h. Then, carbon coating is carried out on the porous carbon after silicon deposition. During the carbon coating process, a carbon-containing gas (such as acetylene, C2H2) is used for coating. The flow rate of the acetylene gas introduced is 170 L / min, the carbon coating temperature is 600 °C, and the carbon coating time is 0.5 h to obtain a silicon-carbon material.

[0086] Examples 1-2 to 1-11

[0087] The differences between Examples 1-2 to 1-11 and Example 1-1 are that the mass ratio of carbon nanotubes and surfactants, the rotation speed and time of sand grinding in the preparation of the silicon-carbon material are changed in the preparation condition parameters, and the remaining steps are the same as those in Example 1-1. The specific preparation parameters can be referred to in Tables 1 and 2.

[0088] Examples 2-1 to 2-11

[0089] Examples 2-1 to 2-11 are different from Example 1-1 in that the diameter ratio of carbon nanotubes or the average circularity of the silicon-carbon material is changed (for example, the spray drying conditions can be changed to obtain particles with appropriate circularity), and the remaining steps are the same as those in Example 1-1. The specific preparation parameters can be referred to Table 3.

[0090] Examples 3-1 to 3-13

[0091] Examples 3-1 to 3-13 are different from Example 2-1 in that the components of the electrolyte in the lithium-ion battery and the mass ratio of some components are adjusted. Except for adjusting the parameters of the relevant electrolyte components according to Table 4, the rest are the same as those in Example 2-1.

[0092] The prepared silicon-carbon materials and assembled lithium-ion batteries in each example and comparative example were tested.

[0093] Testing method for silicon-carbon materials:

[0094] (1) Testing method for the elastic modulus of silicon-carbon materials:

[0095] Using a Shimadzu single-particle crushing instrument (FLAT50), randomly select 10 silicon-carbon material particles for crushing force testing, minimum / maximum pressure: 0.02 / 10 mN; calculate the elastic modulus of each silicon-carbon material particle according to the deformation amount and approximate contact surface corresponding to the maximum pressure, and using Hooke's law and pressure formula, and obtain the arithmetic mean value as the elastic modulus of the silicon-carbon material.

[0096] (2) Testing method for the diameter ratio of carbon nanotubes:

[0097] First, disperse the carbon nanotubes in an appropriate solvent to ensure uniform dispersion. Then, use a transmission electron microscope (TEM) to observe the structure of the carbon nanotubes and take high-resolution images. Next, measure the outer diameter and inner diameter of the carbon nanotubes through image processing software, and calculate the diameter ratio (outer diameter / inner diameter). Finally, statistically analyze the diameter ratios of more than 10 carbon nanotubes to obtain the average value.

[0098] (3) Testing method for the average circularity of silicon-carbon materials:

[0099] Use a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe the particle samples of the negative electrode active material. Randomly select 20 silicon-carbon material particles and calculate their perimeter equivalent diameter and area equivalent diameter. The sphericity of each silicon-carbon material = perimeter equivalent diameter / area equivalent diameter, and calculate the arithmetic mean value of the sphericity of 20 silicon-carbon materials as the average circularity of the silicon-carbon materials.

[0100] (4) Test method for the powder conductivity of silicon carbide materials:

[0101] Use a conductivity tester (instrument model: Suzhou Jingge Electronics ST-2255A) to test the powder conductivity of silicon carbide materials. Take 5 g of silicon carbide material powder sample, press and form a sample with an electronic press, apply pressure up to 5000 kg ± 2 kg, and maintain for 20 s to obtain a silicon carbide material test sample. Place the above test sample between the electrodes of the conductivity tester, and obtain the resistance R (unit: Ω) through the voltage U and current I at both ends. The height of the test sample is h (unit: cm), and the area of the test sample S = 3.14 cm 2 , and calculate the powder conductivity of silicon carbide materials according to the formula powder conductivity δ = h / (S×R), with the unit of S / cm.

[0102] (5) Test method for |S1 - S2| of silicon carbide materials:

[0103] Thin the silicon carbide material particles containing carbon nanotubes by ion thinning to make a thin slice with a thickness of about 80 nm. Place the prepared sample on the sample stage of the TEM, and observe the distribution of carbon nanotubes inside the particles and collect images in the high-resolution TEM mode. Use image analysis software to process the collected images, and randomly select a cross-section including a first test area and a second test area with an area of 1000 nm 2 . Since carbon nanotubes have obvious TEM lattice fringes, and other regions of the carbon skeleton except the regions containing carbon nanotubes and silicon particles are amorphous, measure the areas of the regions with obvious lattice fringes in the first test area and the second test area, and then the proportion of the distribution area of carbon nanotubes in the two test areas S1 and S2 can be obtained, and the value of |S1 - S2| can be calculated.

[0104] Test method for the performance of lithium-ion batteries:

[0105] (1) Cycle performance test

[0106] The test temperature is 45 °C. The lithium-ion battery is charged at a constant current of 0.7C to 4.4V, then charged at a constant voltage to 0.025C, left to stand for 5 minutes, and then discharged at 0.5C to 3.0V. The capacity obtained by this step is the initial capacity. Perform a cycle test with 0.7C charge / 0.5C discharge, and take the ratio of the capacity of each step to the initial capacity to obtain the capacity decay curve. Record the number of cycles when the capacity retention rate reaches 80% at 45 °C as the high-temperature cycle performance of the secondary battery. Capacity retention rate = remaining discharge capacity / initial discharge capacity × 100%.

[0107] (2) Discharge rate test

[0108] At 25 °C, the lithium-ion battery is discharged to 3.0 V at 0.2 C, left standing for 5 min, charged to 4.45 V at 0.5 C, charged at a constant voltage until 0.05 C and then left standing for 5 min. The discharge rate is adjusted and discharge tests are carried out at 0.2 C, 0.5 C, 1 C, 1.5 C, and 2.0 C respectively to obtain the discharge capacities. The capacity obtained at each rate is compared with the capacity obtained at 0.2 C, and the rate performance is compared by comparing the ratio of 2 C to 0.2 C.

[0109] Table 1

[0110]

[0111] Table 2

[0112]

[0113] Combining Table 1 and Table 2, compared with the comparative examples, in Examples 1-1 to 1-11, during the preparation of the negative electrode active silicon-carbon material, by changing the mass ratio of carbon nanotubes and surfactant in the preparation of the silicon-carbon material and the rotation speed and time of sanding in the preparation conditions parameters, when the elastic modulus of the silicon-carbon material meets a specific range, the high-temperature cycle performance and rate performance of the silicon-carbon material can be improved.

[0114] In Table 1 and Table 2, during the preparation of the silicon-carbon material, when the difference between |S1 - S2| and the powder conductivity of the silicon-carbon material are respectively within specific ranges, the high-temperature cycle performance and rate performance of the silicon-carbon material can be further improved.

[0115] Table 3

[0116]

[0117] In Table 3, during the preparation of the silicon-carbon material, when the diameter ratio of carbon nanotubes or the average circularity of the silicon-carbon material are respectively within specific ranges, the high-temperature cycle performance and rate performance of the silicon-carbon material can be further improved.

[0118] Table 4

[0119]

[0120] Combining Table 4, in the lithium-ion battery, by changing the components of the electrolyte, when the electrolyte contains ethyl propionate and propyl propionate and within a suitable mass percentage range, and the mass percentage of fluoroethylene carbonate and the ratio of E / F are maintained within specific ranges, the high-temperature cycle performance and rate performance of the silicon-carbon material can be further improved.

[0121] The above-disclosed is only the preferred embodiment of the present application, and of course, it cannot be used to limit the present application. Therefore, the equivalent changes made according to the present application still fall within the scope covered by the present application.

Claims

1. A silicon-carbon material, characterized in that: The silicon-carbon material comprises a carbon skeleton and silicon particles, the carbon skeleton comprises amorphous carbon and carbon nanotubes, and the elastic modulus of the silicon-carbon material is E, 50 Gpa≤E≤200 Gpa.

2. The silicon-carbon material according to claim 1, characterized in that 70Gpa≤E≤150Gpa.

3. The silicon-carbon material according to claim 1, characterized in that: The silicon-carbon material satisfies at least one of the following conditions: (1) The ratio of the outer diameter to the inner diameter of the carbon nanotube is L, 1.0≤L≤10.0; (2) The average circularity of the silicon-carbon material is 0.65 to 0.8; (3) The powder conductivity of the silicon-carbon material is 0.1 S / cm to 20 S / cm.

4. The silicon-carbon material according to any one of claims 1 to 3, characterized in that The cross section of the silicon carbon material includes an area of ​​1000nm 2 A first test area and a second test area, the first test area and the second test area do not overlap, based on the area of ​​the first test area, the area of ​​the carbon nanotubes accounts for S1%, based on the area of ​​the second test area, the area of ​​the carbon nanotubes accounts for S2%, |S1-S2|≤0.093, preferably, |S1-S2|≤0.

039.

5. A method for preparing a silicon-carbon material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Add carbon nanotubes, carbon precursor, curing agent and surfactant into an organic solvent, sand grind and stir to obtain a suspension, wherein the mass ratio of the carbon nanotubes to the surfactant is (0.005-0.1):1; S2. granulating the suspension by spray drying to obtain mixed particles; S3. Carbonizing and activating the mixed particles to obtain porous carbon; S4. Using chemical vapor deposition, silicon is deposited on the porous carbon and carbon is coated to obtain the silicon-carbon material.

6. A secondary battery comprising a negative electrode sheet, a positive electrode sheet and an electrolyte, characterized in that: The negative electrode plate comprises the silicon-carbon material according to any one of claims 1 to 4 or the silicon-carbon material obtained by the preparation method according to claim 5.

7. The secondary battery according to claim 6, characterized in that: The electrolyte includes ethyl propionate and propyl propionate. Based on the mass of the electrolyte, the mass proportion of ethyl propionate is A1%, the mass proportion of propyl propionate is A2%, 2≤A2 / A1≤6, preferably, 3≤A2 / A1≤5.

8. The secondary battery according to claim 6 or 7, characterized in that: The electrolyte includes fluoroethylene carbonate, and based on the mass of the electrolyte, the mass proportion of the fluoroethylene carbonate is F%, 5≤F≤20, preferably, 8≤F≤14.

9. The secondary battery according to claim 8, characterized in that 3.5≤E / F≤18.75, preferably, 7.5≤E / F≤15.

10. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 6 to 9.

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