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 located in holes of the carbon skeleton, the silicon-carbon material comprises first silicon-carbon particles and second silicon-carbon particles, the silicon-carbon material with the particle size of R1 is the first silicon-carbon particles, R1 is greater than or equal to 3 microns and less than or equal to 6 microns, and R2 is greater than or equal to 3 microns and less than or equal to 6 microns. The average elastic modulus E1 of the first silicon carbon particles is greater than or equal to 30GPa and less than or equal to 65GPa; the silicon-carbon material with the particle size of R2 is second silicon-carbon particles, R2 is more than 6 microns and less than or equal to 15 microns, the average elastic modulus of the second silicon-carbon particles is E2, and E2 is more than or equal to 68 GPa and less than or equal to 168 GPa. The silicon-carbon material provided by the invention can improve the cycle performance of the secondary battery and improve the expansion of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a silicon-carbon material, a method for preparing the silicon-carbon material, a secondary battery using the silicon-carbon material, and an electronic device using the secondary battery. Background Art

[0002] Lithium-ion batteries, with their high energy density, high operating voltage, excellent safety, and environmental friendliness, have been widely used in consumer electronics such as mobile phones and laptops. Silicon-carbon materials, due to their high theoretical specific capacity (approximately 4200 mAh / g), are considered ideal anode materials for next-generation lithium-ion batteries. However, in practical applications, silicon-carbon materials still face two major challenges: poor rate performance and poor structural stability. Poor rate performance is primarily due to the slow lithium-ion diffusion kinetics of silicon-carbon materials during charge and discharge, resulting in rapid capacity decay at high current densities. Furthermore, silicon-carbon materials undergo significant volume expansion during charge and discharge (up to 300% or more), leading to particle breakage, active material shedding, and electrode structural damage, severely impacting the battery's cycle stability and service life. Summary of the Invention

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

[0004] In a first aspect, the present application provides a silicon-carbon material, which includes a carbon skeleton and silicon particles located in the pores of the carbon skeleton. The silicon-carbon material includes first silicon-carbon particles and second silicon-carbon particles. The silicon-carbon material with a particle size of R1 is the first silicon-carbon particle, 3μm≤R1≤6μm, and the average elastic modulus of the first silicon-carbon particle is E1, 30GPa≤E1≤65GPa; the silicon-carbon material with a particle size of R2 is the second silicon-carbon particle, 6 μm<R2≤15μm, and the average elastic modulus of the second silicon-carbon particle is E2, 68GPa≤E2≤168GPa.

[0005] In this application, by tailoring the elastic modulus of silicon-carbon materials of different particle sizes, it is possible to improve the overall elastic modulus of the silicon-carbon material while also enabling the silicon-carbon material as a whole and the negative electrode sheet containing the silicon-carbon material to have a higher deformation rate and stability, thereby improving the initial efficiency of the silicon-carbon material, the cycling performance and initial efficiency of the secondary battery, and reducing the expansion of the secondary battery. In the negative electrode sheet, the first silicon-carbon particles have a smaller particle size and tend to be distributed in the pores formed by the accumulation of the second silicon-carbon particles. The first silicon-carbon particles have a lower elastic modulus, which is beneficial for them to serve as a rigid skeleton in the negative electrode sheet to maintain the basic structure of the negative electrode sheet. When the silicon-carbon particles change in volume due to charging and discharging, the skeleton structure formed by the first silicon-carbon particles has a certain rigidity, which is beneficial for maintaining the structural stability of the negative electrode sheet. The second silicon-carbon particles are distributed on the outside of the skeleton formed by the first silicon-carbon particles. When the negative electrode sheet is squeezed by external force, such as cold pressing, the second silicon-carbon particles in the negative electrode sheet tend to contact the cold pressing roller before the first silicon-carbon particles. The second silicon-carbon particles with a higher elastic modulus are beneficial for acting as a buffer structure, reducing the rupture of the silicon-carbon material, thereby reducing the oxygen introduced into the silicon-carbon particles due to the rupture of the material, and thereby improving the first efficiency of the silicon-carbon material. At the same time, silicon-carbon materials and negative electrode sheets with higher deformation rates and stability are beneficial for improving the cycle performance of secondary batteries and improving the expansion of secondary batteries.

[0006] Based on the first aspect, in some embodiments, 10 GPa ≤ E2-E1 ≤ 120 GPa. This can enable the second silicon-carbon particles to have a higher load-bearing capacity, and also facilitate the first silicon-carbon particles to play a skeletal role, reducing the breakage of the silicon-carbon material particles during the charge and discharge process of the silicon-carbon material, while also improving the structural stability of the negative electrode sheet, improving the structural stability of the silicon-carbon material, and improving the cycle performance of the secondary battery.

[0007] Based on the first aspect, in some embodiments, the carbon skeleton comprises amorphous carbon and carbon nanotubes. The inclusion of carbon nanotubes in the carbon skeleton can improve the conductivity and mechanical stability of the carbon skeleton, thereby improving the cycle performance of the silicon-carbon material and improving the expansion performance of the secondary battery.

[0008] Based on the first aspect, in some embodiments, the diameter ratio of the carbon nanotubes, L, is 1.1≤L≤2.3. This can effectively improve the electrical conductivity and mechanical properties of the silicon-carbon material while also maintaining the structural stability of the silicon-carbon material and improving the cycle performance of the secondary battery. Preferably, 1.2≤L≤2.

[0009] Based on the first aspect, in some embodiments, the powder conductivity of the silicon-carbon material is 0.1 S / cm to 10 S / cm. The combination of the first silicon-carbon particles and the second silicon-carbon particles in the silicon-carbon material is designed so that the powder conductivity of the silicon-carbon material is maintained within the above-mentioned suitable range, so as to maintain the silicon-carbon material with good electrical conductivity, improve the charge and discharge efficiency of the secondary battery, reduce capacity attenuation, and increase the cycle life of the secondary battery. A second aspect of the present application provides a method for preparing a silicon-carbon material, comprising the following steps: S1. dissolving carbon nanotubes, a carbon precursor, a curing agent, and a surfactant in an organic solvent to obtain a first mixed liquid, and granulating the first mixed liquid by spray drying to obtain first organic particles, wherein the mass ratio of the carbon nanotubes to the surfactant is (1:1) to (1:190); S2. carbonizing and activating the first organic particles in sequence to obtain first porous carbon; S3. depositing silicon gas and coating the first porous carbon by chemical vapor deposition to obtain first silicon-carbon particles; S4. Dissolve carbon nanotubes, carbon precursor, curing agent and surfactant in an organic solvent to obtain a second mixed liquid, granulate the second mixed liquid by spray drying to obtain second organic particles, wherein the mass ratio of carbon nanotubes to surfactant is (1:200) to (1:400); S5. Carbonize and activate the second organic particles in sequence to obtain second porous carbon; S6. Perform silicon gas deposition and carbon coating on the second porous carbon by chemical vapor deposition to obtain second silicon-carbon particles; S7. Mix the first silicon-carbon particles and the second silicon-carbon particles to obtain a silicon-carbon material.

[0010] A third aspect of the present application provides a secondary battery, comprising a negative electrode plate, a positive electrode plate and an electrolyte, wherein the negative electrode plate comprises a silicon-carbon material or a silicon-carbon material obtained by a preparation method.

[0011] 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 proportion of ethyl propionate is A1%, the mass proportion of propyl propionate is A2%, and 2≤A2 / A1≤6. This facilitates the uniformity of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles, further improving the cycle performance and expansion performance of the secondary battery.

[0012] Based on the third aspect, in some embodiments, the electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is F%, based on the mass of the electrolyte, with 5≤F≤20. This improves the conductivity and rigidity of the SEI film on the surfaces of the first and second silicon-carbon particles, further leveraging the enhanced conductivity brought about by the inclusion of carbon nanotubes in the carbon framework, and further improving the cycling performance and expansion performance of the secondary battery. Preferably, 10≤F≤16.

[0013] A fourth aspect of the present application provides an electronic device comprising the aforementioned secondary battery. The secondary battery has excellent cycle performance and low expansion rate, which is beneficial for increasing the service life of the electronic device. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0015] In order to solve the problem of rapid volume expansion and rate reduction of silicon-carbon materials during the charge and discharge process, researchers have proposed a variety of modification strategies, including nano-sizing, carbon coating, introduction of conductive additives, and design of porous structures. However, these methods still have certain limitations in practical applications. For example, nano-sizing may lead to an increase in the surface area of ​​the material and an increase in side reactions; carbon coating may limit the diffusion channels of lithium ions and affect the rate performance. Therefore, the development of a silicon-carbon material that can improve the rate performance and enhance the structural stability remains the focus and difficulty of current research. Future research directions may include the development of new nanostructures, optimization of the conductivity and stability of the carbon matrix, and exploration of new synthesis methods to achieve efficient preparation and performance improvement of silicon-carbon materials.

[0016] One 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 in the housing.

[0017] The outer shell can be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0018] The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, with the separator being disposed between the positive and negative electrode sheets. The electrode assembly can be a laminated structure, formed by stacking the positive electrode sheet, separator, and negative electrode sheet. In other embodiments, the electrode assembly can also be a wound structure, formed by stacking the positive electrode sheet, separator, and negative electrode sheet and then winding them.

[0019] Negative electrode The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the surface of the negative electrode current collector. The negative electrode 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. It may also be any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and polymer substrate. In the negative electrode sheet, the negative electrode active layer includes a silicon-carbon material.

[0020] The present application provides a silicon-carbon material, which includes a carbon skeleton and silicon particles located in the pores of the carbon skeleton. The silicon-carbon material includes first silicon-carbon particles and second silicon-carbon particles. The silicon-carbon material with a particle size of R1 is the first silicon-carbon particle, 3μm≤R1≤6 μm, and the average elastic modulus of the first silicon-carbon particle is E1, 30GPa≤E1≤65GPa; the silicon-carbon material with a particle size of R2 is the second silicon-carbon particle, 6 μm<R2≤15 μm, and the average elastic modulus of the second silicon-carbon particle is E2, 68GPa≤E2≤168GPa.

[0021] In this application, by tailoring the elastic modulus of silicon-carbon materials of different particle sizes, it is possible to improve the overall elastic modulus of the silicon-carbon material while also enabling the silicon-carbon material as a whole and the negative electrode sheet containing the silicon-carbon material to have a higher deformation rate and stability, thereby improving the initial efficiency of the silicon-carbon material, the cycling performance and initial efficiency of the secondary battery, and reducing the expansion of the secondary battery. In the negative electrode sheet, the first silicon-carbon particles have a smaller particle size and tend to be distributed in the pores formed by the accumulation of the second silicon-carbon particles. The first silicon-carbon particles have a lower elastic modulus, which is beneficial for them to serve as a rigid skeleton in the negative electrode sheet to maintain the basic structure of the negative electrode sheet. When the silicon-carbon particles change in volume due to charging and discharging, the skeleton structure formed by the first silicon-carbon particles has a certain rigidity, which is beneficial for maintaining the structural stability of the negative electrode sheet. The second silicon-carbon particles are distributed on the outside of the skeleton formed by the first silicon-carbon particles. When the negative electrode sheet is squeezed by external force, such as cold pressing, the second silicon-carbon particles in the negative electrode sheet tend to contact the cold pressing roller before the first silicon-carbon particles. The second silicon-carbon particles with a higher elastic modulus are beneficial for acting as a buffer structure, reducing the rupture of the silicon-carbon material, thereby reducing the oxygen introduced into the silicon-carbon particles due to the rupture of the material, and thereby improving the first efficiency of the silicon-carbon material. At the same time, silicon-carbon materials and negative electrode sheets with higher deformation rates and stability are beneficial for improving the cycle performance of secondary batteries and improving the expansion of secondary batteries.

[0022] In some embodiments, the average particle size R1 of the first silicon-carbon particles may be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or any value within a range formed by any two of the above values.

[0023] In some embodiments, the average elastic modulus E1 of the first silicon-carbon particles can be 30 GPa, 35 GPa, 40 GPa, 45 GPa, 50 GPa, 55 GPa, 60 GPa, 65 GPa, or any value within the range formed by any two of the foregoing values.

[0024] In some embodiments, the average particle size R2 of the second silicon-carbon particles may be 7 μm, 8 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value within a range formed by any two of the foregoing values.

[0025] In some embodiments, the average elastic modulus E2 of the second silicon-carbon particles can be 68 GPa, 70 GPa, 72 GPa, 75 GPa, 80 GPa, 85 GPa, 90 GPa, 95 GPa, 100 GPa, 110 GPa, 120 GPa, 130 GPa, 140 GPa, 150 GPa, 160 GPa, 168 GPa, or any value within the range formed by any two of the above values.

[0026] In some embodiments, 10GPa≤E2-E1≤120GPa. In the silicon-carbon material, the difference in the average elastic modulus between the first silicon-carbon particles and the second silicon-carbon particles within the above range can enable the second silicon-carbon particles to have a higher load-bearing capacity, and also help the first silicon-carbon particles to play their skeleton role, reduce the breakage of the silicon-carbon material particles during the charge and discharge process of the silicon-carbon material, and at the same time improve the structural stability of the negative electrode sheet, thereby improving the structural stability and cycle performance of the silicon-carbon material. In some embodiments, the difference E2-E1 can be 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, 60GPa, 70GPa, 80GPa, 90GPa, 100GPa, 110GPa, 120GPa, or any value within the range formed by any two of the above values.

[0027] In some embodiments, the carbon skeleton comprises amorphous carbon and carbon nanotubes. The inclusion of carbon nanotubes in the carbon skeleton can improve the electrical conductivity and mechanical stability of the carbon skeleton, thereby improving the cycling performance of the silicon-carbon material and improving the expansion performance of the secondary battery. In some embodiments, the carbon nanotubes are uniformly dispersed on the amorphous carbon, further improving the electrical conductivity and mechanical stability of the carbon skeleton, thereby improving the cycling performance of the silicon-carbon material and improving the expansion performance of the secondary battery.

[0028] In some embodiments, the diameter ratio of the carbon nanotubes is L, 1.1≤L≤2.3. Preferably, 1.2≤L≤2. The diameter ratio of the carbon nanotubes refers to the ratio of the outer diameter to the inner diameter of the carbon nanotubes. The diameter ratio of the carbon nanotubes within the above range can effectively improve the electrical conductivity and mechanical properties of the silicon-carbon material, while also helping to maintain the structural stability and cycle performance of the silicon-carbon material. And the diameter ratio of the carbon nanotubes within the above range is conducive to making the silicon-carbon material have a suitable specific surface area, improving the dispersion and uniformity of the carbon nanotubes, improving the mechanical properties and stability of the silicon-carbon material, and improving the overall electrical conductivity and electrochemical properties of the silicon-carbon material. In some embodiments, the diameter ratio L of the carbon nanotubes can be 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.1, 2.3 or any value within the range formed by any two of the above values.

[0029] In some embodiments, the powder conductivity of the silicon-carbon material is 0.1S / cm to 10S / cm. The combination design of the first silicon-carbon particles and the second silicon-carbon particles in the silicon-carbon material is such that the powder conductivity of the silicon-carbon material is maintained within the above-mentioned suitable range, the silicon-carbon material is kept with good electrical conductivity, the charge and discharge efficiency of the secondary battery is improved, the capacity attenuation is reduced, and the cycle life of the secondary battery is increased; and it is also beneficial to maintain a suitable current during the charge and discharge process of the secondary battery, improve the thermal stability of the silicon-carbon material, and reduce the risk of thermal runaway or instability of the secondary battery. In some embodiments, the powder conductivity of the silicon-carbon material is 0.1S / cm, 0.5S / cm, 1S / cm, 2S / cm, 3S / cm, 4S / cm, 5S / cm, 6S / cm, 7S / cm, 8S / cm, 9S / cm, 10S / cm or any value within the range formed by any two of the above values.

[0030] In some embodiments, 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%, and 2≤A2 / A1≤6. When A2 / A1 satisfies the above relationship, it is beneficial to take into account the uniformity of the SEI film on the surface of the first silicon-carbon particles and the second silicon-carbon particles, and to further improve the cycle performance of the secondary battery and improve the expansion 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 of any two of the above values. Preferably, 3≤A2 / A1≤5.

[0031] In some embodiments, the electrolyte includes fluoroethylene carbonate, and the mass proportion of fluoroethylene carbonate based on the mass of the electrolyte is F%, and 5≤F≤20. It is beneficial to improve the conductivity and rigidity of the SEI film on the surface of the first silicon-carbon particles and the second silicon-carbon particles, and it is beneficial to further take advantage of the improved conductivity brought about by the inclusion of carbon nanotubes in the carbon skeleton, and it is beneficial to further improve the cycle performance of the secondary battery and improve the expansion performance of the secondary battery. In some embodiments, F can be 5, 8, 10, 12, 15, 17, 18, 20 or any value within the range of any two of the above values. Preferably, 10≤F≤16.

[0032] 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0033] 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 material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0034] The present application also provides a method for preparing a silicon-carbon material, comprising the following steps: S1. dissolving carbon nanotubes, a carbon precursor, a curing agent, and a surfactant in an organic solvent to obtain a first mixed solution, and granulating the first mixed solution by spray drying to obtain first organic particles.

[0035] In the above steps, the carbon precursor can be a linear resin, the curing agent can be hexamethylenetetramine, and the organic solvent can be an alcohol such as ethanol or methanol. The surfactant includes at least one of polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (CMC), or cetyltrimethylammonium bromide (CTAB). The mass ratio of carbon nanotubes, carbon precursor, and curing agent can range from 1:350 to 900:100. The mass ratio of carbon nanotubes to surfactant ranges from 1:1 to 1:190.

[0036] During the spray drying step, the air inlet temperature is 200°C to 260°C, the air outlet temperature is 80°C to 100°C, the atomization pressure is 0.3 MPa, and the feed rate is 0.03 L / min to 0.1 L / min. During the spray drying process, the feed rate can adjust the average particle size of the first organic particles. A higher feed rate can increase the average particle size of the first organic particles.

[0037] S2. Carbonizing and activating the first organic particles in sequence to obtain first porous carbon.

[0038] In this step, the first organic particles undergo a carbonization stage and an activation stage in sequence. Carbonization stage: In an inert gas (such as nitrogen or argon), the carbonization temperature is 600°C to 1500°C, and the carbonization time is 2h to 6h. Activation stage: In a mixed gas atmosphere of water and carbon dioxide, the activation temperature is 700°C to 1000°C, and the activation time is 2h to 20h. In this step, the first organic particles undergo the above-mentioned carbonization and activation, thereby facilitating the production of a first porous carbon with a more stable structure.

[0039] In some embodiments, the carbonization temperature can be 600°C, 800°C, 900°C, 1000°C, 1200°C, 1400°C, 1500°C, or any value within the range formed by any two of the above values; the carbonization time can be 2h, 3h, 4h, 5h, 6h, or any value within the range formed by 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 formed by any two of the above values; the activation time can be 2h, 5h, 10h, 15h, 20h, or any value within the range formed by any two of the above values.

[0040] S3. Perform silicon gas deposition and carbon coating on the first porous carbon through chemical vapor deposition to obtain first silicon-carbon particles.

[0041] Chemical vapor deposition is used to deposit a silicon-containing gas on a first porous carbon containing carbon nanotubes in a silane atmosphere at a temperature of 400°C to 600°C for 2 to 20 hours. The first porous carbon with deposited silicon particles is then carbon-coated in a carbon-containing gas atmosphere, such as acetylene, at a temperature of 500°C to 900°C for 0.1 to 6 hours to further stabilize the porous carbon structure, thereby obtaining first silicon-carbon particles.

[0042] In some embodiments, the deposition temperature in this step 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 hours, 5 hours, 10 hours, 15 hours, 20 hours, 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 hour, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value within the range formed by any two of the above values.

[0043] S4. Dissolving the carbon nanotubes, the carbon precursor, and the curing agent in an organic solvent to obtain a second mixed solution, and granulating the second mixed solution by spray drying to obtain second organic particles.

[0044] The carbon precursor can be a linear resin, the curing agent can be hexamethylenetetramine, and the organic solvent can be an alcohol such as ethanol or methanol. The surfactant includes at least one of polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (CMC), or cetyltrimethylammonium bromide (CTAB). The mass ratio of carbon nanotubes, carbon precursor, and curing agent can range from 1:350 to 900:100. The mass ratio of carbon nanotubes to surfactant ranges from 1:200 to 1:400.

[0045] During the spray drying step, the air inlet temperature is 200°C to 260°C, the air outlet temperature is 80°C to 100°C, the atomization pressure is 0.3 MPa, and the feed rate is 0.06 L / min to 0.1 L / min. During the spray drying process, the feed rate can adjust the average particle size of the second organic particles.

[0046] S5. Carbonizing and activating the second organic particles in sequence to obtain second porous carbon.

[0047] The second organic particles undergo a carbonization and activation phase. The carbonization phase is performed in an inert gas (such as nitrogen or argon) at a temperature of 600°C to 1500°C for a period of 2 to 6 hours. The activation phase is performed in a mixed gas atmosphere of water and carbon dioxide at a temperature of 700°C to 1000°C for a period of 2 to 20 hours. During this step, the mixed particles undergo the aforementioned carbonization and activation, thereby producing a more structurally stable second porous carbon. In some embodiments, the carbonization temperature can be 600°C, 800°C, 900°C, 1000°C, 1200°C, 1400°C, 1500°C, or any value within the range formed by any two of the above values; the carbonization time can be 2h, 3h, 4h, 5h, 6h, or any value within the range formed by 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 formed by any two of the above values; the activation time can be 2h, 5h, 10h, 15h, 20h, or any value within the range formed by any two of the above values. S6. Silicon gas deposition and carbon coating are performed on the second porous carbon by chemical vapor deposition to obtain second silicon-carbon particles.

[0048] Chemical vapor deposition is used to deposit a silicon-containing gas on a second porous carbon containing carbon nanotubes in a silane atmosphere at a temperature of 400°C to 600°C for 2 to 20 hours. The second porous carbon with the deposited silicon particles is then carbon-coated in a carbon-containing gas atmosphere, such as acetylene, at a temperature of 500°C to 900°C for 0.1 to 6 hours to further stabilize the structure of the second porous carbon and obtain second silicon-carbon particles.

[0049] In some embodiments, the deposition temperature in this step 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 hours, 5 hours, 10 hours, 15 hours, 20 hours, 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 hour, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value within the range formed by any two of the above values.

[0050] S7. Mix the first silicon-carbon particles and the second silicon-carbon particles in proportion to obtain a silicon-carbon material.

[0051] In the silicon-carbon material, the mass ratio of the second silicon-carbon particles to the first silicon-carbon particles may be (10:1) to (1:10).

[0052] In the above-mentioned method for preparing silicon-carbon materials, the carbon nanotubes, carbon precursors, curing agents and surfactants are mixed and dispersed evenly by solid-liquid phase mixing, thereby improving the uniformity of the distribution of carbon nanotubes and carbon precursors, which is beneficial to reducing the agglomeration of some carbon nanotubes in the subsequent preparation process. The mass ratio of carbon nanotubes and surfactants is controlled to regulate the average elastic modulus of the first silicon-carbon particles and the second silicon-carbon particles respectively, and the first silicon-carbon particles and the second silicon-carbon particles with different particle sizes and different average elastic moduli are mixed, thereby improving the overall elastic modulus of the silicon-carbon material and also helping to improve the overall deformation rate of the silicon-carbon material, improving the cycle performance and first efficiency of the silicon-carbon material, and improving the expansion performance of the secondary battery.

[0053] In the present application, first silicon-carbon particles with a particle size of 3 μm to 6 μm and second silicon-carbon particles with a particle size of 6 μm to 15 μm can be obtained by sieving through a sieve.

[0054] Within the above-mentioned suitable range, the average elastic modulus of the first or second silicon-carbon particles can be increased by reducing the mass ratio of carbon nanotubes to surfactant. When preparing the first or second silicon-carbon particles, the average elastic modulus of the corresponding silicon-carbon particles can also be increased simply by increasing the carbon nanotube content within a suitable range.

[0055] Isolation film The material and shape of the separator used in the secondary battery of the present application are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

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

[0057] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, 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, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer. The polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0058] electrolyte According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of the present application can be any organic solvent known in the art as a solvent for an electrolyte. The electrolyte used in the electrolyte of the present application is not limited and can be any electrolyte known in the art. The additive in the electrolyte of the present application can be any additive known in the art 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, for example, at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (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(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0059] Positive electrode The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. The positive electrode current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide containing lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, 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 lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0060] The positive electrode active layer also includes a binder to bond the positive electrode active material particles to facilitate film formation and improve the bonding strength 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0061] The positive electrode active layer may further comprise a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include, but is 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 material may include, but is 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.

[0062] The secondary battery is applied to an electronic device to power a load in the electronic device. Moreover, the silicon-carbon material in the secondary battery has excellent structural stability and electrical conductivity, which is beneficial to improving the cycle performance and expansion performance of the secondary battery, and is beneficial to improving the service life of the electronic device. Among them, the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0063] The present application is described below by way of specific examples and comparative examples. It should be understood by those skilled in the art that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0064] Example 1-1 Preparation of silicon-carbon materials: Preparation of the first silicon-carbon particle: 0.5 g of carbon nanotubes, 500 g of linear resin, 100 g of hexamethylenetetramine (HMT), and 50 g of polyvinylpyrrolidone (PVP) were dissolved in 5000 ml of ethanol and stirred for 2 hours to form an organic solution containing carbon nanotubes. The organic solution was then granulated by spray drying at an inlet air temperature of 200°C, an outlet air temperature of 80°C, an atomization pressure of 0.3 MPa, and a feed rate of 0.03 L / min. Organic particles containing carbon nanotubes with an average particle size of approximately 5 μm were obtained. The organic particles were then vacuum dried at 80°C for 24 hours to remove the organic solvent.

[0065] Then, the dried organic particles are carbonized and activated in sequence. In the carbonization stage, the carbonization temperature is 600°C and the carbonization time is 2 hours under an argon atmosphere; in the activation stage, the activation temperature is 900°C and the activation time is 4 hours under a mixed gas atmosphere of water and carbon dioxide, thereby obtaining the first porous carbon containing carbon nanotubes.

[0066] Finally, silicon-containing gas (silane, SiH4) was deposited on the first porous carbon containing carbon nanotubes by chemical vapor deposition. The deposition temperature was 550°C and the deposition time was 6 hours. Then, carbon-containing gas (acetylene, C2H2) was coated at a coating temperature of 600°C and a coating time of 0.5 hours. The first silicon-carbon particle material was obtained by screening through a sieve.

[0067] Preparation of the second silicon-carbon particle: 5 g of carbon nanotubes, 500 g of linear resin, 100 g of hexamethylenetetramine (HMT), and 1150 g of polyvinylpyrrolidone (PVP) were dissolved in 5000 ml of ethanol and stirred for 2 hours to form a uniform organic solution containing carbon nanotubes. Subsequently, the organic solution was granulated by spray drying at an inlet air temperature of 200°C, an outlet air temperature of 80°C, an atomization pressure of 0.3 MPa, and a feed rate of 0.06 L / min. Organic particles containing carbon nanotubes with an average particle size of approximately 10 μm were obtained. The organic particles were then vacuum dried at 80°C for 24 hours to remove the solvent.

[0068] Then, the dried organic particles are carbonized and activated in sequence. In the carbonization stage, the carbonization temperature is 600°C and the carbonization time is 2 hours under an argon atmosphere. In the activation stage, the activation temperature is 900°C and the activation time is 4 hours under a mixed gas atmosphere of water and carbon dioxide to obtain a second porous carbon containing carbon nanotubes.

[0069] Finally, silicon-containing gas (silane, SiH4) was deposited on the second porous carbon containing carbon nanotubes by chemical vapor deposition. The deposition temperature was 550°C and the deposition time was 6 hours. Carbon-containing gas (acetylene, C2H2) was then coated at a coating temperature of 600°C and a coating time of 0.5 hours. The second silicon-carbon particle material was obtained by sieving through a sieve.

[0070] The first silicon-carbon particles and the second silicon-carbon particles are mixed, with the mass ratio of the second silicon-carbon particles to the first silicon-carbon particles being 1:1, to obtain a silicon-carbon material.

[0071] Preparation method of lithium-ion button half-cell: Preparation of the negative electrode sheet: A mixture of graphite and the aforementioned silicon-carbon material in a weight ratio of 90:10 was used as the negative electrode active material. The negative electrode active material, polymethyl acrylate, and sodium carboxymethyl cellulose were thoroughly stirred in a weight ratio of 97:2:1 in deionized water to form a uniform negative electrode slurry with a solids content of 40 wt%. This slurry was coated onto the negative electrode current collector copper foil, dried at 85°C, cold pressed, cut, and slit, and then dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0072] A 7 μm polyethylene separator was used, and lithium sheets were used as counter electrodes to assemble button-type half-cells in a glove box. The button-type cells used the same electrolyte as the lithium-ion battery in the same embodiment.

[0073] Preparation method of lithium-ion battery: Positive electrode preparation: Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a weight ratio of 95%:2.5%:2.5% to prepare a positive electrode slurry. The slurry was coated onto the positive electrode current collector aluminum foil, dried, cold-pressed, cut, and the tabs were welded to form the positive electrode sheets.

[0074] Preparation of the negative electrode: Graphite, silicon-carbon material, carbon nanotubes, and polymethyl acrylate are mixed in a solid mass ratio of 88.4%:9.8%:0.1%:1.7%, kneaded and dispersed at a solid content of about 38%~50wt% to form a negative electrode slurry. The prepared negative electrode slurry is coated on the negative electrode current collector copper foil, dried, cold pressed, cut, and welded to the pole ear to obtain the negative electrode.

[0075] Preparation of the electrolyte: Under a dry argon atmosphere, LiPF6 was added to a mixture of 1,3-propane sultone (1,3-PS), propyl propionate (PP), ethyl propionate (EP), fluoroethylene carbonate (FEC), propylene carbonate (PC), and ethylene carbonate (EC). Based on the mass of the electrolyte, the weight proportion of LiPF6 was 12.5%, the weight proportion of 1,3-PS was 3.5%, the weight proportion of PP was 45%, the weight proportion of EP was 15%, the weight proportion of FEC was 10%, and the weight proportion of PC and EC was the remainder. The weight ratio of PC to EC was 1:1.

[0076] Preparation of isolation membrane: PE composite film is used as isolation membrane.

[0077] Preparation of a lithium-ion battery: The positive electrode, separator, and negative electrode are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. Winding is performed to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film bag, dried at 80°C, and then injected with electrolyte. The soft-pack lithium-ion battery is produced through vacuum packaging, resting, formation, shaping, and capacity testing.

[0078] Example 1-2 to Example 1-9 Examples 1-2 through 1-9 differ from Example 1-1 in that the mass ratio of carbon nanotubes to surfactant in the first silicon-carbon particles and the mass ratio of carbon nanotubes to surfactant in the second silicon-carbon particles were varied to adjust the average elastic modulus of the first and second silicon-carbon particles, respectively. The remaining steps were the same as in Example 1-1. See Tables 1 and 2.

[0079] Example 2-1 to Example 2-4 The difference between Examples 2-1 to 2-4 and Example 1-1 is that the diameter ratio of the carbon nanotubes in the first and second silicon-carbon particles is changed. The remaining steps are the same as Example 1-1. See Table 3.

[0080] Example 3-1 to Example 3-6 The difference between Examples 3-1 to 3-6 and Example 1-1 is that the mass ratios of the components of the electrolyte in the lithium-ion battery are adjusted. Except for adjusting the parameters of the relevant electrolyte components according to Table 3, the rest are the same as Example 1-1, see Table 4.

[0081] Comparative Examples 1 to 4 Comparative Examples 1 to 4 differ from Example 1-1 in that the mass ratio of carbon nanotubes to surfactant in the first silicon-carbon particles and the mass ratio of carbon nanotubes to surfactant in the second silicon-carbon particles were varied to adjust the average elastic modulus of the first and second silicon-carbon particles, respectively. The remaining steps were the same as in Example 1-1. See Tables 1 and 2.

[0082] The silicon-carbon materials prepared in various embodiments and comparative examples and the assembled lithium-ion batteries were tested.

[0083] Silicon carbon material related test methods: (1) Elastic modulus test method The crushing force test was performed using a Shimadzu single particle crusher (FLAT50) with a minimum / maximum pressure of 0.02 / 10 mN. The elastic modulus of the silicon-carbon particles was calculated based on the deformation and contact area corresponding to the maximum pressure, combined with Hooke's law and the pressure formula. Ten first silicon-carbon particles and ten second silicon-carbon particles were selected for testing, and their respective average elastic moduli were calculated.

[0084] (2) Testing method for carbon nanotube diameter ratio The structure of carbon nanotubes was observed using a transmission electron microscope (TEM), capturing high-resolution images. The outer and inner diameters of the carbon nanotubes were then measured using image processing software, and the diameter ratio (outer diameter / inner diameter) was calculated. The above method was repeated for 20 carbon nanotubes. The average diameter ratio, L, was calculated.

[0085] (3) Test method for powder conductivity The conductivity of silicon-carbon material powder was tested using a conductivity tester (model: Suzhou Jingge Electronics ST-2255A). A 5g sample of silicon-carbon material powder was taken and pressed into a pellet using an electronic press. The pellet was pressed to 5000kg ± 2kg and maintained for 20s to prepare a test sample. The test sample was placed between the electrodes of the conductivity tester. The resistance R (unit: Ω) was obtained by measuring the voltage U and current I across the two terminals. The height of the test sample was h (unit: cm) and the area of ​​the test sample was S = 3.14cm. 2 The powder conductivity of the silicon-carbon material is calculated according to the formula powder conductivity δ = h / (S×R) and the unit is S / cm.

[0086] Performance test method for lithium-ion batteries: (1) First efficiency test (after cold pressing) At 25°C, the electrode was cold-pressed at 15t and then installed into a lithium-ion button half-cell. The button half-cell was then left to rest for 4 hours, discharged at 0.02C to 5 mV, and then charged at 0.02C to 2.0V after resting for 5 minutes. The charge and discharge capacities were recorded, and the charge / discharge capacity value of the first cycle was calculated as the first efficiency. The charging capacity was based on 0.8V, so the first efficiency was the first efficiency after cold pressing at 0.8V.

[0087] (2) Expansion rate test The test temperature is 45°C. A flat-plate thickness gauge (load of 600g) is used to measure the thickness M of the lithium-ion battery at the second half charge (50% SOC). When the above charge and discharge process is cycled for 10 cycles, the lithium-ion battery is in a fully charged state (100% SOC). The thickness N of the lithium-ion battery at this time is measured again using a flat-plate thickness gauge (load of 600g). The expansion rate of the lithium-ion battery after 500 cycles at 45°C is L = (NM) / M×100%. Among them, the thickness of the lithium-ion battery is tested cold, that is, the lithium-ion battery is taken back and placed in a normal temperature test room for testing.

[0088] (4) Cyclic performance test At 25°C, the lithium-ion battery was charged to 4.53V at a constant current of 0.8C, charged to 0.05C at a constant voltage of 4.53V, and after standing for 5 minutes, discharged to 3.0V at a constant current of 0.8C. The discharge capacity obtained in this step is the initial capacity. Carry out charge and discharge cycle tests according to the above steps, and make a ratio of the discharge capacity of each step to the initial capacity to obtain the discharge capacity retention rate of each step, and record the number of cycles of the lithium-ion battery at 25°C until the discharge capacity retention rate is 80%. The cycle performance of the lithium-ion battery is characterized by the number of cycles at 25°C until the discharge capacity retention rate is 80%. The higher the number of cycles of the lithium-ion battery at 25°C until the discharge capacity retention rate is 80%, the better the cycle performance of the lithium-ion battery.

[0089] Table 1 Table 2 In Table 1 and Table 2 above, compared with Comparative Examples 1 to 4, in the process of preparing the first silicon-carbon particles and the second silicon-carbon particles, the mass ratio of the carbon nanotubes and the surfactant is controlled to regulate the average elastic modulus of the first silicon-carbon particles and the second silicon-carbon particles, respectively. When the first silicon-carbon particles and the second silicon-carbon particles respectively meet the specific average elastic modulus range, after the first silicon-carbon particles and the second silicon-carbon particles are mixed, the overall elastic modulus of the silicon-carbon material is improved and the overall deformation rate of the silicon-carbon material is also improved, thereby improving the cycle performance, initial efficiency and expansion performance of the silicon-carbon material.

[0090] When the difference (E2-E1) between the average elastic modulus of the first silicon-carbon particles and the second silicon-carbon particles meets a specific range, the cycle performance, initial efficiency and expansion performance of the silicon-carbon material can be further improved.

[0091] Table 3 In Table 3, during the preparation of the silicon-carbon material, the diameter ratio of the carbon nanotubes of the first silicon-carbon particles and the second silicon-carbon particles was changed. When the diameter ratio of the carbon nanotubes was within a specific range of 1.2 to 2, the cycle performance, first efficiency and expansion performance of the silicon-carbon material were further improved.

[0092] Table 4 Combined with Table 4, in lithium-ion batteries, changing the mass ratio of the components of the electrolyte, when the electrolyte contains ethyl propionate and propyl propionate and is within an appropriate mass ratio range, and the mass ratio of fluoroethylene carbonate is maintained within a specific range, can further improve the cycle performance, initial efficiency and expansion performance of the silicon-carbon material.

[0093] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the present application. Therefore, equivalent changes made based on the present application are still within the scope covered by the present application.

Claims

1. A silicon-carbon material, characterized in that: The silicon-carbon material includes a carbon skeleton and silicon particles located in the pores of the carbon skeleton, and the silicon-carbon material includes first silicon-carbon particles and second silicon-carbon particles. The silicon-carbon material with a particle size of R1 is the first silicon-carbon particle, 3μm≤R1≤6μm, and the average elastic modulus of the first silicon-carbon particle is E1, 30GPa≤E1≤65GPa; the silicon-carbon material with a particle size of R2 is the second silicon-carbon particle, 6 μm<R2≤15 μm, and the average elastic modulus of the second silicon-carbon particle is E2, 68GPa≤E2≤168GPa.

2. The silicon-carbon material according to claim 1, wherein 10 GPa≤E2-E1≤120Gpa.

3. The silicon-carbon material according to claim 1, wherein The carbon skeleton includes amorphous carbon and carbon nanotubes.

4. The silicon-carbon material according to claim 3, wherein The carbon nanotubes have a diameter ratio L, 1.1≤L≤2.

3.

5. The silicon-carbon material according to claim 4, wherein 1.2≤L≤2。 6. A method for preparing a silicon-carbon material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. dissolving carbon nanotubes, a carbon precursor, a curing agent, and a surfactant in an organic solvent to obtain a first mixed solution, and granulating the first mixed solution by spray drying to obtain first organic particles, wherein the mass ratio of the carbon nanotubes to the surfactant is (1:1) to (1:190); S2. The first organic particles are sequentially carbonized and activated to obtain a first porous carbon; S3. silicon gas deposition and carbon coating are performed on the first porous carbon by chemical vapor deposition to obtain first silicon-carbon particles; S4. dissolving carbon nanotubes, a carbon precursor, a curing agent, and a surfactant in an organic solvent to obtain a second mixed solution, and granulating the second mixed solution by spray drying to obtain second organic particles, wherein the mass ratio of the carbon nanotubes to the surfactant is (1:200) to (1:400); S5. The second organic particles are sequentially carbonized and activated to obtain a second porous carbon; S6. performing silicon gas deposition and carbon coating on the second porous carbon by chemical vapor deposition to obtain second silicon-carbon particles; S7. Mixing the first silicon-carbon particles and the second silicon-carbon particles to obtain the silicon-carbon material.

7. 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 5 or the silicon-carbon material obtained by the preparation method according to claim 6.

8. The secondary battery according to claim 7, wherein 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%, and 2≤A2 / A1≤6.

9. The secondary battery according to claim 7 or 8, wherein The electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass proportion of the fluoroethylene carbonate is F%, 5≤F≤20, preferably, 10≤F≤16.

10. An electronic device, characterized in that: The secondary battery according to any one of claims 7 to 9 is included.

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