Silicon-carbon composite material, preparation method thereof, negative active material, negative electrode sheet, secondary battery, and electric device

Abstract

The application relates to a silicon-carbon composite material and a preparation method thereof, a negative active material, a negative electrode sheet, a secondary battery and an electric device. The silicon-carbon composite material comprises porous carbon and a zinc silicate-silicon-oxygen-carbon composite material; at least part of the zinc silicate-silicon-oxygen-carbon composite material is filled in the pores of the porous carbon; the zinc silicate-silicon-oxygen-carbon composite material is of a porous structure; the pore diameter of the zinc silicate-silicon-oxygen-carbon composite material is 1-5 nm; and the mass content of zinc elements in the zinc silicate-silicon-oxygen-carbon composite material is 1-6%. The zinc silicate-silicon-oxygen-carbon composite material has proper pore diameter and zinc element content, is good in structural stability, and has low volume expansion rate and good conductivity. Since part of the zinc silicate-silicon-oxygen-carbon composite material is filled in the pores of the porous carbon, the volume expansion of the silicon-carbon composite material is further buffered. In the electrochemical cycle process, the silicon-carbon composite material has low volume expansion, and the cycle stability of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a silicon-carbon composite material and its preparation method, a negative electrode active material, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries and other secondary batteries have the characteristics of high energy density, long life, no memory effect, and low self-discharge rate, and are widely used in electric vehicles, large-scale energy storage equipment and other fields.

[0003] Traditional lithium-ion battery anode materials include carbon materials such as graphite, silicon-based materials, and tin-based materials. Compared to traditional graphite anodes, silicon has an extremely high theoretical specific capacity (4200 mAh / g) and a low delithiation potential (<0.5V), making it a promising option for upgrading carbon-based anodes in lithium-ion batteries. However, silicon-based materials also have drawbacks as lithium-ion battery anode materials. During electrochemical cycling, the insertion and extraction of lithium ions cause the silicon-based material to expand and contract by more than 300% in volume. The resulting mechanical forces cause the material to gradually pulverize, leading to structural collapse. Ultimately, this results in the detachment of the electrode active material from the current collector, loss of electrical contact, and a significant reduction in battery cycle performance. Summary of the Invention

[0004] Therefore, it is necessary to provide a silicon-carbon composite material with high capacity and low expansion rate and its preparation method, which can be used as a negative electrode active material to improve the cycle stability of secondary batteries.

[0005] In addition, negative electrode active materials, negative electrode sheets, secondary batteries and electrical devices including the aforementioned silicon-carbon composite materials are also provided.

[0006] One aspect of this application provides a silicon-carbon composite material, comprising porous carbon and a zinc silicate-silica-carbon composite material; at least a portion of the zinc silicate-silica-carbon composite material fills the pores of the porous carbon;

[0007] The zinc silicate-silica carbon composite material has a porous structure; the pore size of the zinc silicate-silica carbon composite material is 1 nm to 5 nm; and the mass content of zinc in the zinc silicate-silica carbon composite material is 1% to 6%.

[0008] In some embodiments, the silicon-carbon composite material satisfies at least one of the conditions (1) to (8):

[0009] (1) Part of the zinc silicate-silica carbon composite material fills the pores of the porous carbon, and part of the zinc silicate-silica carbon composite material coats the surface of the porous carbon;

[0010] (2) In the zinc silicate-silica carbon composite material, zinc silicate is dispersed in the porous framework of the silica carbon compound;

[0011] (3) In the zinc silicate-silicon-carbon composite material, the mass content of silicon element is 10% to 30%; (4) The specific surface area of ​​the porous carbon is 300 m². 2 / g~1500m 2 / g;

[0012] (5) The pore volume of the porous carbon is 0.4 cm³. 3 / g~1.2cm 3 / g;

[0013] (6) The average pore size of the porous carbon is 20 nm to 200 nm;

[0014] (7) The average particle size of the porous carbon is 5 μm to 10 μm;

[0015] (8) The porous carbon includes at least one of porous graphite, porous hard carbon, porous soft carbon, porous carbon nanotubes, porous graphene and porous carbon fiber.

[0016] Another aspect of this application provides a method for preparing the aforementioned silicon-carbon composite material, comprising the following steps:

[0017] A suspension is prepared by mixing silicone oil, zinc stearate, and porous carbon; the mass ratio of the silicone oil to the zinc stearate is (1-5):1.

[0018] The suspension was heat-treated at 0.5 MPa to 10 MPa and 300°C to 700°C under a protective atmosphere to prepare an intermediate.

[0019] The intermediate was heat-treated at 850°C to 1100°C under a protective atmosphere to prepare the silicon-carbon composite material.

[0020] In some embodiments, the preparation method satisfies at least one of the conditions in (1) to (3):

[0021] (1) The silicone oil includes at least one of methyl silicone oil, dihexyl silicone oil, benzyl silicone oil, methyl hydrogen silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil, methyl ethoxy silicone oil and hydroxyl silicone oil;

[0022] (2) The mass ratio of the silicone oil to the porous carbon is (0.2-1.5):1;

[0023] (3) In the heat treatment step of the intermediate, the heat treatment time is 2h to 4h.

[0024] In some embodiments, the step of preparing the suspension includes:

[0025] The silicone oil and the zinc stearate are dissolved in an organic solvent to prepare a silicon-containing solution;

[0026] The porous carbon is dispersed in the silicon-containing solution to prepare the suspension;

[0027] Optionally, the organic solvent includes at least one selected from benzene, toluene, cyclohexane, hexane, heptane, octane, and nonane;

[0028] Optionally, the mass ratio of the silicone oil to the organic solvent is 1:(1-3).

[0029] In some embodiments, the step of preparing the intermediate includes:

[0030] The suspension was pressurized at 0.5 MPa to 10 MPa under a protective atmosphere.

[0031] The pressurized suspension was then heat-treated at 300°C to 700°C.

[0032] Optionally, the protective atmosphere includes at least one of nitrogen, argon, helium, and neon;

[0033] Optionally, the pressurization process takes 0.5 hours to 2 hours.

[0034] Optionally, the heat treatment time is 1 hour to 3 hours.

[0035] In another aspect, this application also provides a negative electrode active material, including the silicon-carbon composite material described above or a silicon-carbon composite material prepared according to the preparation method of the silicon-carbon composite material described above.

[0036] Optionally, the negative electrode active material further includes a carbon coating layer; the carbon coating layer coats the surface of the silicon-carbon composite material;

[0037] Optionally, the mass content of the carbon coating layer in the negative electrode active material is 1% to 5%.

[0038] In another aspect of this application, a negative electrode sheet is also provided, comprising the aforementioned negative electrode active material.

[0039] Another aspect of this application provides a secondary battery, including the aforementioned negative electrode plate.

[0040] Another aspect of this application provides an electrical device including the aforementioned secondary battery.

[0041] The silicon-carbon composite material provided in this application includes porous carbon and a zinc silicate-silica-carbon composite material with a porous structure. The pore size of the zinc silicate-silica-carbon composite material is 1 nm to 5 nm, and the mass content of zinc is 1% to 6%. The above-mentioned zinc silicate-silica-carbon composite material has suitable pore size and zinc content, good structural stability, low volume expansion rate, and good conductivity. Since part of the zinc silicate-silica-carbon composite material fills the pores of the porous carbon, it further buffers the volume expansion of the silicon-carbon composite material. During electrochemical cycling, the above-mentioned silicon-carbon composite material has low volume expansion, which can improve the cycle stability of the secondary battery. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the preparation method of silicon-carbon composite material according to one embodiment of this application. Detailed Implementation

[0043] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] One embodiment of this application provides a silicon-carbon composite material, comprising porous carbon and a zinc silicate-silica-carbon composite material, wherein at least a portion of the zinc silicate-silica-carbon composite material is filled in the pores of the porous carbon.

[0046] The zinc silicate-silica-carbon composite material has a porous structure. The pore size of the zinc silicate-silica-carbon composite material ranges from 1 nm to 5 nm. Controlling the pore size within this range can effectively mitigate the volume expansion of the zinc silicate-silica-carbon composite material during electrochemical cycling. Optionally, the pore size of the zinc silicate-silica-carbon composite material can be within the range of 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any combination thereof.

[0047] In zinc silicate-silicon-carbon composite materials, the mass content of zinc is 1% to 6%. Within this range, the zinc content effectively improves the volume expansion and electrical conductivity of the silicon-carbon composite material. Optionally, the zinc content can be any combination of 1%, 2%, 3%, 4%, 5%, 6%, or any of the above values.

[0048] Zinc silicate-silicon-oxygen-carbon composite material refers to a composite material formed by zinc silicate and silicon-oxygen-carbon compounds (SiOC). Silicon-oxygen-carbon compounds are amorphous materials with Si-OC as the main component. Zinc silicate exhibits good structural stability, and its combination with silicon-oxygen-carbon compounds effectively reduces the O / Si bonding ratio in the material, improving the initial charge efficiency and enhancing the structural stability of the composite material. The zinc silicate-silicon-oxygen-carbon composite material possesses a porous structure, providing additional space for the volume changes during lithium insertion / extraction, thus reducing the volume expansion of the silicon-carbon composite material. Furthermore, at least a portion of the zinc silicate-silicon-oxygen-carbon composite material fills the pores of the porous carbon, and the abundant porous structure within the porous carbon further buffers the volume expansion of the silicon-carbon composite material. During electrochemical cycling, the aforementioned silicon-carbon composite material exhibits low volume expansion, which improves the cycle stability of the secondary battery.

[0049] In addition, the aforementioned silicon-carbon composite material also has a suitable capacity and initial charge efficiency.

[0050] In some embodiments, a portion of the zinc silicate-silica carbon composite material fills the pores of the porous carbon, and a portion of the zinc silicate-silica carbon composite material coats the surface of the porous carbon.

[0051] In some embodiments, in the zinc silicate-silica-carbon composite material, zinc silicate is dispersed within a porous framework of the silica-carbon compound. The dispersion of zinc silicate within the porous framework of the silica-carbon compound improves the structural stability of the zinc silicate-silica-carbon composite material.

[0052] In some embodiments, the silicon content in the zinc silicate-silicon-oxygen-carbon composite material is 10% to 30% by mass. Optionally, the silicon content in the zinc silicate-silicon-oxygen-carbon composite material is within the range of 10%, 15%, 20%, 25%, 30%, or any of the above values.

[0053] In some embodiments, the raw materials for preparing the zinc silicate-silica carbon composite material include silicone oil and zinc stearate.

[0054] In some embodiments, the silicone oil includes at least one of methyl silicone oil, dihexyl silicone oil, benzyl silicone oil, methyl hydrogen silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil, methyl ethoxy silicone oil, and hydroxyl silicone oil.

[0055] In some embodiments, the porous carbon has a specific surface area of ​​300 m².2 / g~1500m 2 / g. The specific surface area of ​​porous carbon is within the above range, exhibiting a rich porous structure that provides sufficient buffer volume for silicon-carbon composites. Optionally, the specific surface area of ​​porous carbon is 300 m² / g. 2 / g、500m 2 / g、600m 2 / g、800m 2 / g, 1000m 2 / g、1200m 2 / g, 1500m 2 / g or any of the above values ​​within the range.

[0056] In some embodiments, the porous carbon has a pore volume of 0.4 cm³. 3 / g~1.2cm 3 / g. Optionally, the pore volume of the porous carbon is 0.4 cm³. 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g or any of the above values ​​within the range.

[0057] In some embodiments, the average pore size of the porous carbon is 20 nm to 200 nm. Optionally, the average pore size of the porous carbon is within the range of 20 nm, 40 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, or any combination thereof.

[0058] The porous carbon has a pore volume and average pore size within the above range, and the pores can be loaded with zinc silicate-silicon oxide carbon composite material to a large extent, thereby limiting the volume expansion of silicon-based materials.

[0059] In some embodiments, the average particle size of the porous carbon is 5 μm to 10 μm. When the average particle size of the porous carbon is within this range, the silicon-carbon composite material exhibits a suitable particle size for fabricating negative electrode sheets, achieving a balance between high capacity and electrolyte wettability. Optionally, the average particle size of the porous carbon is within the range of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination thereof.

[0060] In some embodiments, porous carbon includes at least one of porous graphite, porous hard carbon, porous soft carbon, porous carbon nanotubes, porous graphene, and porous carbon fibers.

[0061] See Figure 1Another embodiment of this application also provides a method for preparing the above-mentioned silicon-carbon composite material, including the following steps S100, S200 and S300:

[0062] Step S100: Mix silicone oil, zinc stearate, and porous carbon to prepare a suspension. The mass ratio of silicone oil to zinc stearate is (1-5):1. By controlling the mass ratio of silicone oil to zinc stearate within the above range, zinc stearate and silicone oil can be pyrolyzed during subsequent preparation to form a zinc silicate-silica-carbon composite material with a porous structure.

[0063] In some embodiments, the silicone oil includes at least one of methyl silicone oil, dihexyl silicone oil, benzyl silicone oil, methyl hydrogen silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil, methyl ethoxy silicone oil, and hydroxyl silicone oil.

[0064] In some embodiments, the mass ratio of silicone oil to porous carbon is (0.2–1.5):1. When the mass ratio of silicone oil to porous carbon is within the above range, the resulting silicon-carbon composite material can achieve both high capacity and good cycle stability.

[0065] In some embodiments, step S100 includes:

[0066] Step S110: Dissolve silicone oil and zinc stearate in an organic solvent to prepare a silicon-containing solution.

[0067] In some of these embodiments, the organic solvent includes at least one selected from benzene, toluene, cyclohexane, hexane, heptane, octane, and nonane.

[0068] In some embodiments, the mass ratio of silicone oil to organic solvent is 1:(1-3).

[0069] Step S120: Disperse porous carbon in a silicon-containing solution to prepare a suspension.

[0070] Step S200: Under a protective atmosphere, the suspension is heat-treated at 0.5 MPa to 10 MPa and 300°C to 700°C to prepare an intermediate. Optionally, in step S200, the pressure is within the range of 0.5 MPa, 1 MPa, 2 MPa, 5 MPa, 8 MPa, 10 MPa, or any combination thereof.

[0071] By treating the suspension at 0.5MPa to 10MPa, the silicone oil and zinc stearate in the suspension can fill the pores of the porous carbon to a large extent, which is beneficial for loading zinc silicate-silica carbon composite materials into the pores of the porous carbon.

[0072] Optionally, in step S200, the temperature of the heat treatment is within the range of 300℃, 400℃, 500℃, 600℃, 700℃, or any combination of the above values.

[0073] In step S200, under pressure of 0.5 MPa to 10 MPa, the silicone oil and zinc stearate in the suspension can fill the pores of the porous carbon to a large extent. After heat treatment at 300℃ to 700℃, the silicone oil and zinc stearate can be cured and cross-linked in the pores and on the surface of the porous carbon. The silicone oil is cracked and polycondensed into silicon-oxygen-carbon material (Si-OC), and the zinc stearate is pyrolyzed to form ZnO@C material.

[0074] In some embodiments, the protective atmosphere includes at least one selected from nitrogen, argon, helium, and neon. Optionally, the protective atmosphere is nitrogen.

[0075] In some embodiments, step S200 includes:

[0076] Step S210: Under a protective atmosphere, the suspension is pressurized at 0.5 MPa to 10 MPa.

[0077] In some embodiments, the pressurization treatment time is 0.5h to 2h. Optionally, the pressurization treatment time is within the range of 0.5h, 1h, 1.5h, 2h, or any combination thereof.

[0078] Step S220: Heat-treat the pressurized suspension at 300℃~700℃.

[0079] In some embodiments, the heat treatment time is 1 hour to 3 hours. Optionally, the heat treatment time is within the range of 1 hour, 2 hours, 3 hours, or any combination thereof.

[0080] Step S300: Under a protective atmosphere, the intermediate is heat-treated at 850℃~1100℃ to prepare a silicon-carbon composite material. During the high-temperature heat treatment of the intermediate at 850℃~1100℃, the C encapsulated in ZnO is reduced to form Zn and CO2 gas. The CO2 gas is released from the Si-OC to form a porous structure. The Zn, upon heating, forms a highly active reducing gas and removes some of the "O" from the Si-OC. "Zn" and "O" combine to form ZnO, which further reacts with Si-O to transform into stable Zn2SiO4. A porous zinc silicate-silicon-carbon composite material is thus formed within and on the surface of the porous carbon.

[0081] In some embodiments, the protective atmosphere includes at least one selected from nitrogen, argon, helium, and neon. Optionally, the protective atmosphere is nitrogen.

[0082] In some embodiments, the heat treatment time in step S300 is 2 hours to 4 hours. Optionally, the heat treatment time is within the range of 2 hours, 3 hours, 4 hours, or any combination thereof.

[0083] The above-mentioned method for preparing silicon-carbon composite materials uses low-cost raw materials and has a simple and reliable preparation process, making it particularly suitable for large-scale industrial production.

[0084] Another embodiment of this application provides a negative electrode active material, including the silicon-carbon composite material described above or a silicon-carbon composite material prepared according to the preparation method of the silicon-carbon composite material described above.

[0085] The aforementioned negative electrode active material includes the silicon-carbon composite material provided in the embodiments of this application. The negative electrode active material has a small expansion rate, good cycle stability, and suitable capacity and first charge efficiency.

[0086] In some embodiments, the negative electrode active material further includes a carbon coating layer; the carbon coating layer is coated on the surface of the silicon-carbon composite material. The carbon coating layer on the surface of the silicon-carbon composite material can further improve the conductivity and electrochemical performance of the negative electrode active material.

[0087] In some embodiments, the mass content of the carbon coating layer in the negative electrode active material is 1% to 5%. Optionally, the mass content of the carbon coating layer in the negative electrode active material is within the range of 1%, 2%, 3%, 4%, 5%, or any of the above values.

[0088] In another embodiment of this application, a negative electrode sheet is also provided, comprising the aforementioned negative electrode active material. The negative electrode sheet comprising the aforementioned negative electrode active material has a small volume expansion rate, which can improve the cycle stability of the secondary battery.

[0089] Another embodiment of this application provides a secondary battery, including the negative electrode sheet described above.

[0090] In some embodiments, the secondary battery may include a lithium-ion battery or a sodium-ion battery.

[0091] In some embodiments, the secondary battery also includes a positive electrode, a separator, and an electrolyte.

[0092] Another embodiment of this application provides an electrical device including the aforementioned secondary battery.

[0093] The following are specific examples.

[0094] Example 1:

[0095] The preparation method of the silicon-carbon composite material in this embodiment includes:

[0096] (1) In a reactor containing 3.5 kg of benzene solvent, add 0.8 kg of polydihexylsiloxane and 0.27 kg of zinc stearate, stir thoroughly to disperse and completely dissolve, then add 1.6 kg of porous carbon (specific surface area 760 m²).2 / g, pore volume 0.6cm³ 3 / g, with an average pore size of 63.8nm and an average particle size of 6.8μm) were added to the reactor. Stirring was started and nitrogen gas was introduced to make the pressure inside the reactor reach 1.6MPa and maintain it for 1h. Then the temperature was increased to 400℃ at 1.5℃ / min and reacted for 2h. The mixture was then cooled, discharged, and screened.

[0097] (2) Using nitrogen as the carrier gas, the product obtained in step (1) was heated to 950°C for 3 hours to prepare silicon-carbon composite material.

[0098] Transmission electron microscopy revealed that the zinc silicate-silica-carbon composite material was distributed within the pores and on the surface of the porous carbon. The average pore size of the zinc silicate-silica-carbon composite material was determined to be 2.1 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silica-carbon composite material contained 1.76% Zn and 20.61% Si by mass.

[0099] Example 2:

[0100] The preparation method of the silicon-carbon composite material in this embodiment is basically the same as that in Example 1, except that the amount of zinc stearate used is 0.56 kg.

[0101] Transmission electron microscopy revealed that the zinc silicate-silicon oxide-carbon composite material was distributed within the pores and on the surface of the porous carbon. The average pore size of the zinc silicate-silicon oxide-carbon composite material was determined to be 4.5 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silicon oxide-carbon composite material contained 5.64% Zn and 18.28% Si by mass.

[0102] Example 3:

[0103] The preparation method of the silicon-carbon composite material in this embodiment is basically the same as that in Example 1, except that the amount of polydihexylsiloxane used is 1.2 kg.

[0104] Transmission electron microscopy revealed that the zinc silicate-silicon oxide-carbon composite material was distributed within the pores and on the surface of the porous carbon. The average pore size of the zinc silicate-silicon oxide-carbon composite material was determined to be 1.3 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silicon oxide-carbon composite material contained 1.45% Zn and 27.36% Si by mass.

[0105] Example 4:

[0106] The preparation method of the silicon-carbon composite material in this embodiment is basically the same as that in Example 1, except that nitrogen gas is introduced into the process until the pressure is 8.7 MPa.

[0107] Transmission electron microscopy revealed that the zinc silicate-silicon oxide-carbon composite material was distributed within the pores and on the surface of the porous carbon. The average pore size of the zinc silicate-silicon oxide-carbon composite material was determined to be 2.8 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silicon oxide-carbon composite material contained 1.78% Zn and 19.97% Si by mass.

[0108] Comparative Example 1:

[0109] The preparation method of the silicon-carbon composite material in this comparative example includes:

[0110] (1) In a reactor containing 3.5 kg of benzene solvent, add 0.8 kg of polydihexylsiloxane and 0.27 kg of zinc stearate, stir thoroughly until uniformly dispersed and completely dissolved, then add 1.6 kg of porous carbon (specific surface area 760 m2 / g, pore volume 0.6 cm3 / g, average pore diameter 63.8 nm, average particle size 6.8 μm) to the reactor and stir to disperse for 1 h, then heat to 400 °C at 1.5 °C / min and react for 2 h, cool and discharge and screen.

[0111] (2) Using nitrogen as the carrier gas, heat treatment at 950℃ for 3h was carried out to finally prepare silicon-carbon composite material.

[0112] Transmission electron microscopy revealed that the zinc silicate-silicon oxide-carbon composite material was distributed on the surface of porous carbon. The average pore size of the zinc silicate-silicon oxide-carbon composite material was determined to be 1.4 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silicon oxide-carbon composite material contained 1.78% Zn and 20.61% Si by mass.

[0113] Comparative Example 2:

[0114] The preparation method of the silicon-carbon composite material in this comparative example is basically the same as that in Example 1, except that the amount of zinc stearate used is 0.1 kg.

[0115] Transmission electron microscopy revealed that the zinc silicate-silicon oxide-carbon composite material was distributed within the pores and on the surface of the porous carbon. The average pore size of the zinc silicate-silicon oxide-carbon composite material was determined to be 1.0 nm using the BJH nitrogen adsorption-desorption method. ICP analysis showed that the zinc silicate-silicon oxide-carbon composite material contained 0.45% Zn and 18.43% Si by mass.

[0116] Comparative Example 3:

[0117] The preparation method of the silicon-carbon composite material in this comparative example is basically the same as that in Example 1, except that the heat treatment temperature in step (2) is 800℃.

[0118] Transmission electron microscopy revealed that the zinc-silicon-oxygen-carbon composite material was distributed within the pores and on the surface of the porous carbon. BJH nitrogen adsorption-desorption method confirmed that the zinc-silicon-oxygen-carbon composite material had a non-porous structure. ICP analysis showed that the zinc-silicon-oxygen-carbon composite material contained 1.89% Zn and 18.21% Si by mass.

[0119] Comparative Example 4:

[0120] The preparation method of the silicon-carbon composite material in this comparative example includes:

[0121] Porous carbon support (specific surface area 760m²) 2 / g, pore volume 0.6cm³ 3 / g, average pore size 63.8nm, average particle size 6.8μm) packed into a 2m³ container. 3 In a vacuum rotary kiln, the material was filled with 10% of the material and then heated from room temperature to 500℃ under an argon atmosphere at a rotation speed of 0.3 r / min and held for 1 h. Silane was introduced at a rate of 1.8 L / min, and after deposition for 2 h, heating was stopped, and argon was introduced to allow natural cooling to room temperature, yielding a porous carbon-supported nano-silicon precursor. Acetylene was introduced at 950℃ using nitrogen as the carrier gas for coating, ultimately preparing a silicon-carbon composite material. The carbon coating amount was 1.76%, and elemental analysis showed that the Si content of the silicon-carbon composite material was 11.32% by mass.

[0122] The preparation and product parameters of the silicon-carbon composite materials of Examples 1-4 and Comparative Examples 1-3 are recorded in Table 1.

[0123] Table 1. Preparation and product parameters of silicon-carbon composite materials in Examples 1-4 and Comparative Examples 1-3.

[0124]

[0125] Negative electrode preparation: The materials prepared in Examples 1-4 and Comparative Examples 1-4 were used as negative electrode active materials and mixed with binder CMC+SRB and conductive agent (Super-P) in a mass ratio of 80:5:5:10. An appropriate amount of deionized water was added to form a slurry, which was then coated onto a 10 μm copper foil using a coating machine and vacuum dried at 90°C for 6 hours. The slurry was then compacted by rollers to control the compaction density at 1.50 g / cm³. 3 Then, a 14mm diameter disc is obtained by a stamping machine, and dried under vacuum (-0.1MPa) at 90℃ for 5 hours. The disc is then weighed and the weight of the negative electrode active material is calculated.

[0126] Battery fabrication: CR2430 coin cells were assembled in a glove box, with lithium metal sheets as the counter electrode and polypropylene microporous membranes as the separator. 1 mol / L LiPF6 (lithium hexafluorophosphate) was dissolved in EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1, and 5.0% FEC (fluoroethylene carbonate) was added as the electrolyte.

[0127] Test section:

[0128] 0.1C First Reversible Capacity and First Efficiency Test: The battery was left to stand at room temperature for 12 hours, and then constant current charge and discharge test was performed on the Blue Electric test system. It was charged to 0.005V at 0.05C and then discharged to 1.5V at 0.1C to test the 0.1C first reversible capacity and first efficiency.

[0129] Electrode full-charge expansion rate test: Charge to 0.005V at 0.05C, then remove the electrode in the glove box and measure the full-charge expansion of the electrode with a micrometer. Measure 10 electrodes in each group, remove the highest and lowest values, and take the average of the remaining 8 as the electrode expansion thickness. Electrode full-charge expansion rate = (average expansion thickness of 8 electrodes after initial 0.05C charging to 0.005V - electrode thickness before assembly) / (electrode thickness before assembly - copper foil thickness) * 100%.

[0130] Cycle capacity retention test: The battery that has completed the first reversible capacity and first efficiency test steps is charged to 0.005V at 0.1C and then discharged to 1.5V at 0.2C. This cycle is repeated for 100 cycles. The discharge capacity after 100 cycles is measured. The cycle capacity retention rate is: (100-cycle discharge capacity - first reversible capacity) / first reversible capacity * 100%.

[0131] Cyclic electrode expansion rate (100 cycles) test: Disassemble the battery after 100 cycles in the above cycle capacity retention test and test the thickness of the negative electrode. Cyclic electrode expansion rate (100 cycles) = (electrode thickness after 100 cycles - electrode thickness before assembly) / (electrode thickness before assembly - copper foil thickness) * 100%.

[0132] The test results are recorded in Table 1.

[0133] Table 1. Performance test results of negative electrode sheets and secondary batteries in Examples 1-4 and Comparative Examples 1-4.

[0134]

[0135] As can be seen from the relevant data in Table 1, the negative electrode sheets prepared by the silicon-carbon composite materials in Examples 1 to 4 have a low expansion rate. The full-charge expansion rate of the electrode sheet is 27.4% to 35.2%, and the expansion rate of the electrode sheet after 100 cycles is 35.1% to 41.2%. The corresponding 0.1C first reversible capacity of the secondary battery is 585.7 mAh / g to 742.6 mAh / g, the first charge efficiency is 81.3% to 90.2%, and the capacity retention rate after 100 cycles is 93.8% to 96.9%. The secondary battery has better first reversible capacity, first charge efficiency, and cycle capacity retention rate.

[0136] In Comparative Example 1, since no pressurized operation was used, the benzene solution of silicone oil and zinc stearate could not fully penetrate into the porous carbon to deposit the pyrolysis load. As a result, the generated zinc silicate-silicon-carbon composite material was loaded on the outer surface of the porous carbon. Although the capacity and first-cycle efficiency were similar to those of Example 1, the silicon-based material was loaded on the outer surface of the porous carbon, which lacked the constraint of the porous inner wall on the expansion of silicon carbon. This resulted in a larger expansion rate of the electrode after full charge and cycling, and a lower cycle retention rate.

[0137] Comparative Example 2 showed a significant decrease in initial efficiency due to insufficient zinc stearate content, and the resulting pore size was also low. Although it still had good cycle performance, the full charge and cycle expansion rates were too high.

[0138] In Comparative Example 3, due to the low heat treatment temperature, the ZnO@C formed during the pyrolysis of zinc stearate could not be further reduced by carbon to form highly active Zn gas, and thus could not interact with the Si-OC formed by the cracking of silicone oil to reduce the Si-O portion and form stable zinc silicate dispersed therein. Therefore, compared with Example 1, it can be seen that the initial efficiency is low, the expansion rate is large, and the cycle capacity retention rate is low.

[0139] Comparative Example 4 uses silane as the silicon source to deposit silicon in porous carbon. Compared with Example 1, it exhibits a higher first-time efficiency at the same capacity. However, due to the absence of zinc silicate and the lack of a porous structure inside the silicon-oxygen-carbon material, it results in a high full-charge and cycle expansion rate and a poor cycle capacity retention rate.

[0140] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The embodiments described above merely illustrate several implementation methods of this application to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A silicon-carbon composite material, characterized in that, The invention includes porous carbon and zinc silicate-silica-carbon composite material; at least a portion of the zinc silicate-silica-carbon composite material fills the pores of the porous carbon. The zinc silicate-silica-carbon composite material has a porous structure; the pore size of the zinc silicate-silica-carbon composite material is 1 nm to 5 nm; and the mass content of zinc in the zinc silicate-silica-carbon composite material is 1% to 6%. The zinc silicate-silica carbon composite material refers to a composite material formed by zinc silicate and silica carbon compounds.

2. The silicon-carbon composite material according to claim 1, characterized in that, The silicon-carbon composite material satisfies at least one of the conditions in (1) to (8): (1) Part of the zinc silicate-silica carbon composite material fills the pores of the porous carbon, and part of the zinc silicate-silica carbon composite material coats the surface of the porous carbon; (2) In the zinc silicate-silica carbon composite material, zinc silicate is dispersed in the porous framework of the silica carbon compound; (3) In the zinc silicate-silicon-carbon composite material, the mass content of silicon element is 10%~30%; (4) The specific surface area of ​​the porous carbon is 300 m². 2 / g ~1500 m 2 / g; (5) The porous carbon has a pore volume of 0.4 cm³. 3 / g ~1.2 cm 3 / g; (6) The average pore size of the porous carbon is 20 nm to 200 nm; (7) The average particle size of the porous carbon is 5 μm to 10 μm; (8) The porous carbon includes at least one of porous graphite, porous hard carbon, porous soft carbon, porous carbon nanotubes, porous graphene and porous carbon fiber.

3. The method for preparing the silicon-carbon composite material according to claim 1 or 2, characterized in that, Includes the following steps: A suspension is prepared by mixing silicone oil, zinc stearate and porous carbon; the mass ratio of the silicone oil and the zinc stearate is (1~5):

1. The suspension was heat-treated at 0.5 MPa to 10 MPa and 300°C to 700°C under a protective atmosphere to prepare an intermediate. The intermediate was heat-treated at 850°C to 1100°C under a protective atmosphere to prepare the silicon-carbon composite material.

4. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, The preparation method satisfies at least one of the conditions in (1) to (3): (1) The silicone oil includes at least one of methyl silicone oil, dihexyl silicone oil, benzyl silicone oil, methyl hydrogen silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil, methyl ethoxy silicone oil and hydroxyl silicone oil; (2) The mass ratio of the silicone oil to the porous carbon is (0.2~1.5):1; (3) In the heat treatment step of the intermediate, the heat treatment time is 2 h to 4 h.

5. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, The steps for preparing the suspension include: The silicone oil and the zinc stearate are dissolved in an organic solvent to prepare a silicon-containing solution; The porous carbon is dispersed in the silicon-containing solution to prepare the suspension.

6. The method for preparing the silicon-carbon composite material according to claim 5, characterized in that, The step of preparing the suspension satisfies at least one of the conditions in (1) to (2): (1) The organic solvent includes at least one of benzene, toluene, cyclohexane, hexane, heptane, octane and nonane; (2) The mass ratio of the silicone oil to the organic solvent is 1: (1~3).

7. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that, The steps for preparing the intermediate include: The suspension was pressurized at 0.5 MPa to 10 MPa under a protective atmosphere. The pressurized suspension is then heat-treated at 300°C to 700°C.

8. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, The step of preparing the intermediate satisfies at least one of the conditions in (1) to (3): (1) The protective atmosphere includes at least one of nitrogen, argon, helium and neon; (2) The pressurization treatment time is 0.5 h to 2 h; (3) The heat treatment time is 1 h to 3 h.

9. A negative electrode active material, characterized in that, The silicon-carbon composite material includes the silicon-carbon composite material according to any one of claims 1 to 2 or the silicon-carbon composite material prepared by the method according to any one of claims 3 to 8.

10. The negative electrode active material according to claim 9, characterized in that, The negative electrode active material satisfies at least one of the conditions in (1) to (2): (1) The negative electrode active material further includes a carbon coating layer; the carbon coating layer coats the surface of the silicon-carbon composite material; (2) The mass content of the carbon coating in the negative electrode active material is 1%~5%.

11. A negative electrode sheet, characterized in that, Includes the negative electrode active material as described in claim 9 or 10.

12. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 11.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 12.

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