Silicon-carbon negative electrode material and preparation method and application thereof
High-performance silicon-carbon anode materials were prepared by coating a porous silicon framework with metals, graphene, and composite coatings, which solved the problems of volume expansion and conductivity of lithium-ion battery anode materials during charging and discharging, and achieved high-capacity, fast-charging and long-life battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-13
AI Technical Summary
Existing lithium-ion battery anode materials such as graphite cannot meet the requirements for high capacity, fast charging performance and cycle stability. Silicon-based materials experience severe volume expansion during charging and discharging, leading to electrode structure breakage and material detachment.
A silicon-carbon anode material is prepared by using a porous silicon framework as the core and coating it with metal, graphene, and composite coatings, including amorphous carbon and lithium-containing compounds, through deposition and carbonization reactions, thereby improving the material's conductivity and structural stability.
It achieves high capacity, low full-charge expansion, high initial efficiency and excellent cycle performance, improves the rate performance and fast charging capability of the material, and extends battery life.
Smart Images
Figure CN121662783A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of secondary battery technology, specifically to a silicon-carbon anode material, its preparation method, and its applications. Background Technology
[0002] Lithium-ion batteries, as promising rechargeable batteries, have been widely used in mobile phones, computers, new energy vehicles, and many other fields. However, as people place higher demands on battery capacity and fast-charging performance, traditional negative electrode materials used in lithium-ion batteries, such as graphite, can no longer meet these evolving needs. Silicon-based materials possess a higher theoretical specific capacity (4200 mAh·g). -1 Silicon, with its low lithium intercalation potential and abundant reserves, is considered a promising anode material for next-generation lithium-ion batteries. However, pure silicon itself has low conductivity and undergoes massive volume expansion (300%) during charge and discharge, leading to electrode structure fracture, material shedding, and further capacity decay. While existing technologies employ methods to mitigate the volume expansion of silicon-based materials during charge and discharge, such as depositing nano-silicon into the pores of porous carbon, this method suffers from poor bonding between silicon and carbon, failing to effectively reduce full-charge expansion. Furthermore, the porous structure of porous carbon itself causes deviations in electronic conductivity, reducing rate performance. Moreover, after depositing nano-silicon, surface oxidation and passivation are required, affecting the material's initial efficiency. Summary of the Invention
[0003] This invention provides a silicon-carbon anode material, its preparation method, and its applications, in order to solve the problems of low conductivity, poor rate performance, poor initial efficiency, high full-charge expansion, and poor cycle performance of existing silicon-carbon materials.
[0004] In a first aspect, the present invention provides a silicon-carbon anode material, comprising a porous silicon framework as a core, a metal cladding layer covering at least a portion of the surface of the porous silicon framework, a graphene cladding layer covering at least a portion of the surface of the metal cladding layer, and a composite cladding layer covering at least a portion of the surface of the graphene cladding layer. The composite coating layer comprises amorphous carbon and lithium-containing compounds; The thickness of the metal cladding layer is 2~50 nm; The thickness of the graphene coating layer is 2~50nm; The thickness of the composite coating layer is 20~100nm.
[0005] In one optional embodiment, the porous silicon framework has a particle size of 50-500 nm and a porosity of 30%-70%.
[0006] In one alternative embodiment, the metal cladding layer comprises at least one of antimony, cerium, indium, and bismuth.
[0007] In one alternative embodiment, the lithium-containing compound includes at least one of lithium oxide, lithium phosphate, lithium carbonate, lithium fluoride, lithium niobate, and lithium citrate.
[0008] In one optional embodiment, the mass ratio of lithium to carbon in the composite coating layer is 0.03 to 3:1.
[0009] Secondly, the present invention provides a method for preparing the above-mentioned silicon-carbon anode material, comprising the following steps: S1: Mix silica spheres and reducing agent, carry out reduction reaction, and acid wash to obtain porous silicon framework; S2: Deposit a metal coating layer on a porous silicon framework to obtain the first intermediate product; S3: Deposit a graphene coating layer on the first intermediate product to obtain the second intermediate product; S4: Mix the second intermediate product, carbon source, lithium-containing compound, and solvent to obtain a spray slurry, and spray dry to obtain the third intermediate product; S5: Take the third intermediate product and carry out a carbonization reaction to obtain silicon-carbon anode material.
[0010] In one optional embodiment, in S1, the mass ratio of silica spheres to reducing agent is 1:0.5~2.
[0011] In one optional embodiment, in step S1, the reduction reaction is carried out in a protective gas atmosphere at a temperature of 550~800℃, a holding time of 1~6h, and a heating rate of 1~10℃ / min.
[0012] In one optional embodiment, in step S1, pickling includes sequential pickling with a strong acid and a weak acid, wherein the pickling time with the strong acid is 2-12 hours and the pickling time with the weak acid is 2-12 hours; optionally, the strong acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; optionally, the weak acid includes hydrofluoric acid; further optionally, the concentration of the strong acid is 1-4M; further optionally, the concentration of the weak acid is 2-8M.
[0013] In one optional embodiment, the pickling temperature in S1 is 25~80°C.
[0014] In one optional embodiment, in step S4, the mass ratio of the second intermediate product, the carbon source, and the lithium-containing compound is 1:0.05~0.5:0.05~0.5. In the carbon source, the mass percentage of amorphous carbon is approximately 10%~70%, so a carbon source and lithium-containing compound with a mass ratio of 0.05~0.5:0.05~0.5 essentially corresponds to a lithium element to carbon element mass ratio of 0.03~3:1 in the composite coating layer.
[0015] In one optional embodiment, the solid content of the spray slurry is 10% to 50%, and the viscosity is 50 to 500 cp.
[0016] In one optional embodiment, spray drying is carried out under a protective gas atmosphere, with an inlet temperature of 180~300℃, an outlet temperature of 80~120℃, a rotation speed of 10000~30000rpm, and a feed rate of 5~20mL / min.
[0017] In one optional embodiment, in step S5, the carbonization reaction is carried out under a protective gas atmosphere at a temperature of 600~1000℃, a holding time of 2~6h, and a heating rate of 1~10℃ / min.
[0018] In one optional implementation, step S2 includes the following steps: S201: Preheating; S202: Heat up, introduce metal-organic vapor, and purge with protective gas; S203: Introduce the reaction gas and purge with the protective gas; S204: Repeat steps S202 and S203; S205: Introduce the reaction gas, anneal, and obtain the first intermediate product.
[0019] In one optional embodiment, S3 includes the following steps: introducing a carbon source gas and a hydrogen-argon mixture, depositing a graphene coating layer, and obtaining a second intermediate product.
[0020] In one optional implementation, in step S201, the preheating temperature is 100~200℃ and the time is 1~2h.
[0021] In one optional embodiment, in S202, the pressure is 0.1~10 Torr, the temperature is 200~450℃, the flow rate of the metal-organic vapor is 10~100mL / min, and the pulse time is 0.1~1.5s.
[0022] In one optional embodiment, in S203, the pressure is 0.1~10 Torr, the flow rate of the introduced reaction gas is 10~100 mL / min, and the pulse time is 0.5~2 s.
[0023] In one optional embodiment, in step S202, the flow rate of the protective gas is 20-200 mL / min, and the purging time is 5-10 s.
[0024] In one optional embodiment, in step S203, the flow rate of the protective gas is 20~200 mL / min, and the purging time is 5~20 s.
[0025] In one optional implementation, the number of cycles in S204 is 50 to 500.
[0026] In one optional embodiment, in step S205, the flow rate of the reaction gas is 10~100 mL / min, the annealing temperature is 200~450℃, and the time is 1~2 h.
[0027] In one optional embodiment, in step S3, the pressure for depositing the graphene coating is 0.1~10 Torr, the temperature is 700~1000℃, and the holding time is 0.5~8h.
[0028] In one optional embodiment, in step S3, the flow rate of the carbon source gas and the hydrogen-argon mixture is 5~50 mL / min, and the volume ratio of the carbon source gas and the hydrogen-argon mixture is 1:1~10; optionally, in the hydrogen-argon mixture, the volume ratio of hydrogen to argon is 2~10:90~98.
[0029] In one optional embodiment, the silica spheres have a particle size of 50~500nm.
[0030] In one optional embodiment, the reducing agent includes at least one of aluminum powder and magnesium powder.
[0031] In one alternative embodiment, the organometallic compound includes at least one of trimethylantimony, triethylantimony, antimony trichloride, antimony pentachloride, tetra(2,2,6,6-tetramethyl-3,5-heptadecyl)cerium, cerium acetylacetonate, trimethylindium, triethylindium, trimethylbismuth, triethylbismuth, and triphenylbismuth.
[0032] In one alternative embodiment, the reactant gas includes at least one of hydrogen and hydrogen plasma.
[0033] In one optional embodiment, the carbon source gas includes at least one of methane, ethane, ethylene, and acetylene.
[0034] In one alternative embodiment, the carbon source includes at least one of glucose, sucrose, pitch, polyvinylpyrrolidone, and polyacrylonitrile.
[0035] In one alternative embodiment, the solvent includes at least one of water, ethanol, and isopropanol.
[0036] In one alternative embodiment, the protective gas includes at least one of nitrogen and rare gases.
[0037] Thirdly, the present invention provides a negative electrode sheet comprising the above-mentioned silicon-carbon negative electrode material, or the silicon-carbon negative electrode material prepared by the above-mentioned preparation method.
[0038] Fourthly, the present invention provides a secondary battery, including the above-mentioned negative electrode, a positive electrode, a separator, and an electrolyte.
[0039] The technical solution of this invention has the following advantages: 1. The silicon-carbon anode material provided by this invention comprises a porous silicon framework as a core, a metal coating layer covering at least a portion of the surface of the porous silicon framework, a graphene coating layer covering at least a portion of the surface of the metal coating layer, and a composite coating layer covering at least a portion of the surface of the graphene coating layer; the composite coating layer comprises amorphous carbon and a lithium-containing compound; the thickness of the metal coating layer is 2-50 nm; the thickness of the graphene coating layer is 2-50 nm; and the thickness of the composite coating layer is 20-100 nm. It exhibits high capacity, low full-charge expansion, high initial efficiency, high rate performance, excellent cycle performance, and fast charging capability. Specifically, the porous silicon framework, as a core, can provide buffer space, effectively mitigating the volume expansion of silicon; it can also improve the material's wettability to the electrolyte, shortening the migration path of lithium ions. Metal coatings can significantly improve the conductivity of materials, ensuring rapid charge transport and enhancing rate performance. Simultaneously, the weak alloying of metals and silicon can reduce stress concentration, enhance structural stability, and help improve the cycling stability of the material. Graphene coatings can provide flexible support and a conductive network, effectively improving the ionic conductivity of the material, enhancing rate performance, and helping to mitigate the volume expansion of silicon. The amorphous carbon in the composite coatings possesses a certain degree of mechanical flexibility, further providing a flexible buffer for expansion. It can also provide fast lithium-ion channels, and the lithium-containing compounds have a certain SEI regulation capability. Their combination can synergistically improve cycle life, effectively increase the first coulombic efficiency, reduce the lithium-ion diffusion barrier, and help improve rate performance.
[0040] 2. The preparation method of the silicon-carbon anode material provided by the present invention includes the following steps: mixing silica spheres and a reducing agent, performing a reduction reaction, and acid washing to obtain a porous silicon framework; depositing a metal coating layer on the porous silicon framework to obtain a first intermediate product; depositing a graphene coating layer on the first intermediate product to obtain a second intermediate product; mixing the second intermediate product, a carbon source, a lithium-containing compound, and a solvent to obtain a spray slurry, spray drying to obtain a third intermediate product; taking the third intermediate product and performing a carbonization reaction to obtain the silicon-carbon anode material. In the preparation method provided by the present invention, the metal coating layer is prepared by deposition, which can achieve precise and uniform coating at the nanoscale. Further deposition of a graphene coating layer on the metal coating layer allows the metal in the metal coating layer to act as a catalyst, assisting in the better growth of the graphene coating layer. Attached Figure Description
[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0042] Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention. Detailed Implementation
[0043] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.
[0044] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.
[0045] Example 1 This embodiment provides a silicon-carbon anode material and its preparation method, wherein the average particle size of the silica spheres used is 100 nm, and the method includes the following steps: (1) Mix silica spheres and magnesium powder at a mass ratio of 1:1, transfer to a sealed container, and react in an inert atmosphere in a tube furnace at a rate of 2℃ / min to 700℃ for 4h. After natural cooling to room temperature, the reduced silica spheres are obtained. The reduced silica spheres are then acid-washed at 50℃ in 100mL hydrochloric acid solution (2M) and 50mL hydrofluoric acid solution (4M) for 2h each to remove magnesium oxide byproducts. After washing until neutral, a porous silica framework is obtained. The obtained porous silica framework has the same particle size as the silica spheres, and the porosity of the porous silica framework is 39.6%. The method for determining the porosity of the porous silica framework is based on GB / T19587-2017, and the same applies below.
[0046] (2) The porous silicon framework was placed in an atomic layer deposition reactor and allowed to stand at 180°C for 1.5 h, then heated to 350°C. Under a pressure of 5 Torr, trimethylantimony vapor was introduced at a flow rate of 50 mL / min with a pulse duration of 0.5 s; nitrogen gas was introduced at a flow rate of 100 mL / min for 8 s; hydrogen gas was introduced at a flow rate of 80 mL / min with a pulse duration of 1 s; nitrogen gas was introduced at a flow rate of 100 mL / min for 10 s. This process, from the introduction of organometallic compound vapor to the last nitrogen purging, constituted one cycle, which was repeated 100 times. Finally, hydrogen gas was introduced at a flow rate of 50 mL / min, and the mixture was annealed at 350°C for 1.5 h to obtain the first intermediate product.
[0047] (3) The first intermediate product was placed in a CVD (chemical vapor deposition) furnace, the air in the furnace was vented, and methane gas and hydrogen-argon mixture (H2:Ar volume ratio of 5:95, the same below) were introduced at a flow rate of 20 mL / min under a pressure of 2 Torr. The volume ratio of methane to hydrogen-argon mixture was 1:4. The mixture was kept at 800℃ for 1 h to deposit a graphene coating layer and obtain the second intermediate product.
[0048] (4) The second intermediate product, glucose and lithium oxide are mixed in a mass ratio of 1:0.2:0.1 and uniformly dispersed in ethanol to prepare a spray slurry with a solid content of 30% and a viscosity of 200cp. The spray slurry is placed in a spray dryer, and the inlet temperature is set to 200℃, the outlet temperature to 100℃, the rotation speed to 20000rpm, the feed rate to 10mL / min, and spray dried under a nitrogen atmosphere to obtain the third intermediate product.
[0049] (5) The third intermediate product is placed in a tube furnace and heated to 700°C at a rate of 2°C / min under a nitrogen atmosphere. The temperature is maintained for 2 hours to carry out the carbonization reaction. After the reaction is completed, the product is naturally cooled to room temperature to obtain silicon-carbon anode material.
[0050] The obtained silicon-carbon anode material has a metal coating thickness of 10.5 nm, a graphene coating thickness of 11.3 nm, and a composite coating thickness of 50.9 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.58.
[0051] The mass ratio test method for amorphous carbon and lithium-containing compounds is as follows: the Li content is determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the carbon content is determined by a carbon-sulfur analyzer; the coating thickness test method is in accordance with GB / T 6462-2005. The obtained silicon-carbon anode material is polished in powder cross-section and measured by scanning electron microscopy, and the same applies below.
[0052] Example 2 This embodiment provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that: in step (1), silica balls and magnesium powder are mixed evenly at a mass ratio of 1:1.5, the reaction temperature is 750℃, the time is 5h, and the porosity of the resulting porous silicon skeleton is 62.5%; in step (2), tetra(2,2,6,6-tetramethyl-3,5-heptadecyl)cerium vapor is used for the organometallic compound vapor; in step (3), the temperature for depositing the graphene coating layer is 900℃; in step (4), sucrose is used as the carbon source, lithium phosphate is used as the lithium-containing compound, the solid content of the spray slurry is 40%, and the viscosity is 300cp.
[0053] The obtained silicon-carbon anode material has a metal coating thickness of 9.3 nm, a graphene coating thickness of 13.8 nm, and a composite coating thickness of 48.3 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.21.
[0054] Example 3 This embodiment provides a silicon-carbon anode material and its preparation method. Compared with Embodiment 1, the difference is that in step (1), silicon dioxide spheres and magnesium powder are mixed evenly at a mass ratio of 1:1.5, the reaction temperature is 750℃, the time is 5h, and sulfuric acid solution of equal concentration is used instead of hydrochloric acid solution in acid washing, resulting in a porous silicon framework with a porosity of 62.5%; in step (2), antimony pentachloride vapor is used for organometallic compound vapor, the pulse time of antimony pentachloride vapor is 0.8s, and it is circulated 200 times; in step ( In step (3), the carbon source gas used is acetylene, the flow rate of the acetylene and hydrogen-argon mixture is 60 mL / min, the temperature for depositing the graphene coating is 900℃, and the holding time is 2 h; in step (4), polyacrylonitrile is used as the carbon source, lithium carbonate is used as the lithium-containing compound, the mass ratio of the second intermediate product, polyacrylonitrile, and lithium carbonate is 1:0.3:0.1, the solid content of the spray slurry is 45%, the viscosity is 360 cp, the spray drying speed is 25000 rpm, and the feed rate is 20 mL / min.
[0055] The obtained silicon-carbon anode material has a metal coating thickness of 22.6 nm, a graphene coating thickness of 39.3 nm, and a composite coating thickness of 53.2 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.09.
[0056] Example 4 This embodiment provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is as follows: In step (1), aluminum powder is used as the reducing agent. Silica balls and aluminum powder are mixed evenly at a mass ratio of 1:1.5. The reaction temperature is 650℃ and the time is 5h. The porosity of the resulting porous silicon framework is 56.1%. In step (2), trimethylindium vapor is used as the organometallic compound vapor. The flow rate of trimethylindium vapor is 80mL / min, the pulse time is 0.8s, and the cycle is 400 times. In step (3), ethylene is used as the carbon source gas. The flow rate of the ethylene and hydrogen-argon mixture was 60 mL / min, the temperature for depositing the graphene coating was 900℃, and the holding time was 2 h. In step (4), polyvinylpyrrolidone was used as the carbon source, lithium citrate was used as the lithium-containing compound, the mass ratio of the second intermediate product, polyvinylpyrrolidone, and lithium citrate was 1:0.3:0.2, the solid content of the spray slurry was 45%, the viscosity was 360 cp, the spray drying speed was 25000 rpm, and the feed rate was 20 mL / min. In step (5), the carbonization reaction temperature was 600℃.
[0057] The obtained silicon-carbon anode material has a metal coating thickness of 42.7 nm, a graphene coating thickness of 43.1 nm, and a composite coating thickness of 78.9 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.10.
[0058] Example 5 This embodiment provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that: the average particle size of the silica spheres used is 200 nm; in step (1), aluminum powder is used as the reducing agent, and the silica spheres and aluminum powder are mixed evenly at a mass ratio of 1:0.5, the reaction temperature is 600℃, the time is 3h, and the porosity of the resulting porous silicon framework is 33.7%; in step (2), the flow rate of trimethylantimony vapor is 10 mL / min, the pulse time is 0.2 s, and the pulse time of hydrogen gas during the circulation process is... The interval is 0.5s, and the cycle is repeated 50 times. In step (3), the carbon source gas used is ethylene, the flow rate of the ethylene and hydrogen-argon mixture is 5mL / min, and the heat preservation time for depositing the graphene coating is 2h. In step (4), lithium citrate is used as the lithium-containing compound, the mass ratio of the second intermediate product, glucose and lithium citrate is 1:0.1:0.1, the solid content of the spray slurry is 15%, the viscosity is 100cp, and the spray drying speed is 25000rpm. In step (5), the carbonization reaction temperature is 600℃.
[0059] The obtained silicon-carbon anode material has a metal coating thickness of 2.6 nm, a graphene coating thickness of 2.9 nm, and a composite coating thickness of 24.3 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.15.
[0060] Example 6 This embodiment provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that the average particle size of the silica spheres used is 500 nm; in step (1), silica spheres and magnesium powder are mixed evenly at a mass ratio of 1:2, the reaction temperature is 800℃, the time is 6h, and the porosity of the resulting porous silicon framework is 72.1%; in step (2), the flow rate of trimethylantimony vapor is 100 mL / min, the pulse time is 1.5s, and the cycle is repeated 500 times; in step (3) In step (4), the carbon source gas used is ethylene, the flow rate of the ethylene and hydrogen-argon mixture is 70 mL / min, the temperature for depositing the graphene coating is 1000℃, and the holding time is 2 h; in step (5), lithium citrate is used as the lithium-containing compound, the mass ratio of the second intermediate product, glucose and lithium citrate is 1:0.4:0.5, the solid content of the spray slurry is 15%, the viscosity is 100 cp, and the spray drying speed is 25000 rpm; in step (5), the carbonization reaction temperature is 600℃.
[0061] The obtained silicon-carbon anode material has a metal coating thickness of 46.9 nm, a graphene coating thickness of 48.5 nm, and a composite coating thickness of 96.8 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.19.
[0062] Example 7 This embodiment provides a silicon-carbon anode material and its preparation method, wherein the average particle size of the silica spheres used is 50 nm, and the method includes the following steps: (1) Mix silica balls and magnesium powder at a mass ratio of 1:0.5, transfer to a sealed container, and heat to 550°C for 6 hours in a tube furnace under an inert atmosphere at a rate of 1°C / min. Then, cool naturally to room temperature to obtain the reduction product of silica balls. Wash the reduction product of silica balls in 100 mL hydrochloric acid solution (1 M) for 12 hours and in 50 mL hydrofluoric acid solution (8 M) for 2 hours at 50°C to remove magnesium oxide byproducts. Wash until neutral to obtain a porous silicon framework. The obtained porous silicon framework has the same particle size as silica balls and a porosity of 28.6%.
[0063] (2) The porous silicon framework was placed in an atomic layer deposition reactor and allowed to stand at 100°C for 2 hours, then heated to 200°C. At a pressure of 10 Torr, cerium acetylacetone vapor was introduced at a flow rate of 10 mL / min with a pulse duration of 1 s; nitrogen gas was introduced at a flow rate of 20 mL / min for 10 s; hydrogen gas was introduced at a flow rate of 10 mL / min with a pulse duration of 2 s; nitrogen gas was introduced at a flow rate of 20 mL / min for 20 s. This process, from the introduction of organometallic compound vapor to the final nitrogen purging, constituted one cycle, which was repeated 300 times. Finally, hydrogen gas was introduced at a flow rate of 10 mL / min, and the mixture was annealed at 200°C for 2 hours to obtain the first intermediate product.
[0064] (3) The first intermediate product was placed in a CVD (chemical vapor deposition) furnace, the air in the furnace was vented, and ethane gas and hydrogen-argon mixture (H2:Ar volume ratio of 5:95, the same below) were introduced at a pressure of 0.1 Torr at a flow rate of 50 mL / min. The volume ratio of ethane and hydrogen-argon mixture was 1:1. The mixture was kept at 700℃ for 8 h to deposit a graphene coating layer and obtain the second intermediate product.
[0065] (4) The second intermediate product, polyacrylonitrile, and lithium phosphate are mixed in a mass ratio of 1:0.05:0.5 and uniformly dispersed in isopropanol to prepare a spray slurry with a solid content of 50% and a viscosity of 450cp. The spray slurry is placed in a spray dryer, and the inlet temperature is set to 300℃, the outlet temperature to 120℃, the rotation speed to 10000rpm, the feed rate to 5mL / min, and spray dried under a nitrogen atmosphere to obtain the third intermediate product.
[0066] (5) The third intermediate product is placed in a tube furnace and heated to 600°C at a rate of 1°C / min under a nitrogen atmosphere. The temperature is maintained for 6 hours to carry out the carbonization reaction. After the reaction is completed, the product is naturally cooled to room temperature to obtain silicon-carbon anode material.
[0067] The obtained silicon-carbon anode material has a metal coating thickness of 32.2 nm, a graphene coating thickness of 26.4 nm, and a composite coating thickness of 82.3 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 2.7.
[0068] Example 8 This embodiment provides a silicon-carbon anode material and its preparation method, wherein the average particle size of the silica spheres used is 500 nm, and the method includes the following steps: (1) Mix silica balls and aluminum powder at a mass ratio of 1:2, transfer to a sealed container, and heat to 800℃ for 5h in a tube furnace at a rate of 10℃ / min under an inert atmosphere. Then, cool naturally to room temperature to obtain the reduction product of silica balls. Wash the reduction product of silica balls in 100mL hydrochloric acid solution (4 M) for 2h and in 50mL hydrofluoric acid solution (2M) for 12h at 50℃ to remove alumina byproducts. Wash until neutral to obtain a porous silicon framework. The obtained porous silicon framework has the same particle size as silica balls and a porosity of 69.4%.
[0069] (2) The porous silicon framework was placed in an atomic layer deposition reactor and allowed to stand at 200°C for 1 h, then heated to 450°C. Triethylbismuth vapor was introduced at a pressure of 0.1 Torr at a flow rate of 100 mL / min with a pulse duration of 0.1 s; nitrogen gas was introduced at a flow rate of 200 mL / min for 5 s purging; hydrogen gas was introduced at a flow rate of 100 mL / min with a pulse duration of 0.5 s; nitrogen gas was introduced at a flow rate of 200 mL / min for 5 s purging. This process, from the introduction of organometallic compound vapor to the final nitrogen purging, constituted one cycle, which was repeated 400 times. Finally, hydrogen gas was introduced at a flow rate of 100 mL / min, and the mixture was annealed at 450°C for 1 h to obtain the first intermediate product.
[0070] (3) The first intermediate product was placed in a CVD (chemical vapor deposition) furnace, the air in the furnace was vented, and acetylene gas and hydrogen-argon mixture (H2:Ar volume ratio of 5:95, the same below) were introduced at a pressure of 10 Torr at a flow rate of 5 mL / min. The volume ratio of acetylene to hydrogen-argon mixture was 1:10. The mixture was kept at 1000℃ for 0.5 h to deposit a graphene coating layer and obtain the second intermediate product.
[0071] (4) The second intermediate product, sucrose, and lithium phosphate are mixed in a mass ratio of 1:0.5:0.05 and uniformly dispersed in ethanol to prepare a spray slurry with a solid content of 10% and a viscosity of 70cp. The spray slurry is placed in a spray dryer, and the inlet temperature is set to 180℃, the outlet temperature to 80℃, the rotation speed to 30000rpm, the feed rate to 20mL / min, and spray dried under a nitrogen atmosphere to obtain the third intermediate product.
[0072] (5) The third intermediate product is placed in a tube furnace and heated to 1000°C at a rate of 10°C / min under a nitrogen atmosphere. The temperature is maintained for 2 hours to carry out the carbonization reaction. After the reaction is completed, the product is naturally cooled to room temperature to obtain silicon-carbon anode material.
[0073] The obtained silicon-carbon anode material has a metal coating thickness of 40.7 nm, a graphene coating thickness of 47.3 nm, and a composite coating thickness of 66.9 nm composed of amorphous carbon and lithium-containing compounds; in the composite coating, the mass ratio of lithium to carbon is 0.04.
[0074] Comparative Example 1 This comparative example provides a porous silicon anode material and its preparation method, wherein the average particle size of the silica spheres used is 100 nm, and the method includes the following steps: Silica spheres and magnesium powder were mixed evenly at a mass ratio of 1:0.3, transferred to a sealed container, and reacted in a tube furnace under an inert atmosphere at a rate of 2℃ / min to 600℃ for 2 hours. After natural cooling to room temperature, the reduced product of silica spheres was obtained. The reduced product of silica spheres was then acid-washed at 50℃ in 100mL hydrochloric acid solution (2 M) and 50mL hydrofluoric acid solution (4 M) for 2 hours each to remove magnesium oxide byproducts. After washing until neutral, a porous silicon anode material with a porosity of 10.6% was obtained.
[0075] Comparative Example 2 This comparative example provides a silicon / metal anode material and its preparation method. Compared with Example 1, the difference is that step (3) is not performed, and the first intermediate product obtained in step (2) is used instead of the second intermediate product to participate in the preparation of the composite coating layer in step (4).
[0076] Comparative Example 3 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that steps (4) and (5) are not performed, and the second intermediate product obtained in step (3) is used as the silicon-carbon anode material.
[0077] Comparative Example 4 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that in step (4), an equal mass of glucose is used instead of lithium oxide.
[0078] Comparative Example 5 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that step (2) is not performed, and the porous silicon framework obtained in step (1) is directly used to replace the first intermediate product to participate in the graphene deposition in step (3).
[0079] Comparative Example 6 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that the porous silicon skeleton obtained in step (1) is used to replace the first intermediate product for graphene coating in step (3), and the obtained graphene-coated porous silicon skeleton is used to replace the porous silicon skeleton for metal layer coating in step (2).
[0080] Comparative Example 7 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that steps (1) and (2) are not performed, and the first intermediate product is prepared by the following method: 3g of F127 (polyethylene glycol) is added to the anode material. Polypropylene glycol Polyethylene glycol), 6g CTAB (hexadecyltrimethylammonium bromide) and 75g water were mixed evenly, and 75mL HCl (4mol / L) solution was added dropwise. Then, 2g antimony chloride was added, and 6g TEOS (tetraethyl orthosilicate) was added dropwise while stirring. After stirring at room temperature for 24h, the mixture was transferred to a reaction vessel and hydrothermally reacted at 80℃ for 24h. The product was obtained by washing with deionized water and ethanol alternately and then drying. The product was placed in a tube furnace and heated to 1000℃ at a heating rate of 2℃. It was kept at this temperature for 8h in a hydrogen-argon mixture to obtain a niobium-doped silicon framework, where the flow rate of the hydrogen-argon mixture was 20mL / min. The obtained niobium-doped silicon framework was used as the first intermediate product in step (3).
[0081] Comparative Example 8 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is that in step (4), lithium metal of equal mass is used instead of lithium oxide, and isopropanol of equal mass is used instead of ethanol.
[0082] Comparative Example 9 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is as follows: In step (1), silica spheres and magnesium powder are mixed evenly at a mass ratio of 1:3, and the reaction time is 12h to obtain a porous silicon skeleton with a porosity of 81.6%; In step (2), the flow rate of trimethylantimony vapor is 10mL / min, the pulse time is 1s, and it is circulated twice; In step (3), the flow rate of methane and hydrogen-argon mixture is 50mL / min, and the heat preservation time for depositing the graphene coating is 5h; In step (4), the second intermediate product, glucose, and lithium oxide are mixed at a mass ratio of 1:0.01:0.01, and the solid content of the spray slurry is 30%.
[0083] The obtained silicon-carbon anode material has a metal coating thickness of 1.3 nm, a graphene coating thickness of 63.4 nm, and a composite coating thickness of 13.1 nm composed of amorphous carbon and lithium-containing compounds. In the composite coating, the mass ratio of lithium to carbon is 1.11.
[0084] Comparative Example 10 This comparative example provides a silicon-carbon anode material and its preparation method. Compared with Example 1, the difference is as follows: In step (1), silica spheres and magnesium powder are mixed evenly at a mass ratio of 1:0.3, the reaction temperature is 600℃, and the time is 2h, resulting in a porous silicon skeleton with a porosity of 10.6%; In step (2), the flow rate of trimethylantimony vapor is 50mL / min, the pulse time is 0.8s, and the cycle is repeated 200 times; In step (3), the flow rate of methane and hydrogen-argon mixture is 5mL / min, and the heat preservation time for depositing the graphene coating is 0.5h; In step (4), the second intermediate product, glucose, and lithium oxide are mixed at a mass ratio of 1:0.5:0.5, and the solid content of the spray slurry is 30%.
[0085] The obtained silicon-carbon anode material has a metal coating thickness of 19.5 nm, a graphene coating thickness of 0.8 nm, and a composite coating thickness of 118.5 nm composed of amorphous carbon and lithium-containing compounds. In the composite coating, the mass ratio of lithium to carbon is 1.11.
[0086] Experimental Example 1 The silicon-carbon anode material obtained in Example 1 was observed using a scanning electron microscope (SEM), and its SEM image is shown below. Figure 1 It can be seen that the material is in the form of nanoparticles after spray drying.
[0087] Experiment Example 2 The resistivity of the negative electrode materials prepared in the examples and comparative examples was tested using a four-probe tester. The test results are shown in Table 1.
[0088] Table 1
[0089] As can be seen from Table 1, the conductivity of the anode material powder obtained in the comparative examples is worse than that in the examples. This indicates that the silicon-carbon anode material provided in this application can effectively improve the conductivity of the material powder by sequentially coating a porous silicon framework with a metal coating layer, a graphene coating layer, an amorphous carbon and lithium-containing compound composite coating layer, and by appropriately adjusting the coating layer thicknesses. Analysis of the data between the examples also shows that appropriately increasing the coating thickness is beneficial to improving the powder conductivity.
[0090] Experimental Example 3 The negative electrode materials obtained in the examples and comparative examples were used to assemble CR2032 coin cells according to the following steps.
[0091] A negative electrode slurry was prepared by mixing negative electrode material, binder polyacrylic acid, conductive carbon black, and dispersant sodium carboxymethyl cellulose in a mass ratio of 95:1:2:2 and then mixing with water. The slurry was then coated onto copper foil and dried to a thickness of 100 μm, and cut to obtain the negative electrode sheet. The electrolyte was a 1.5 mol / L LiPF6 solution, with the solvent being a 1:1 volume ratio mixture of EC (ethylene carbonate) and DEC (diethyl carbonate). A lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. Battery assembly was performed in an argon-filled glove box.
[0092] Electrical performance was tested using a blue electric tester.
[0093] The initial discharge capacity and first efficiency were tested within the 0–2V voltage range at 200 mA·g. -1 Charge and discharge tests were conducted at a current density of , and the discharge capacity of the first cycle (as the first discharge capacity) and the charging capacity were measured. The first efficiency was calculated as follows: First efficiency = (first discharge capacity / first charging capacity) × 100%. The test results are shown in Table 2.
[0094] The electrode expansion rate was tested at 100% SOC after full charge. The specific method was as follows: the electrode thickness D1 after rolling was tested, and the electrode thickness D2 was tested after full charge to 100% SOC. The full charge expansion = (D2-D1) / D1×100%. The test results are shown in Table 2.
[0095] The diffusion coefficient was tested using the GITT (Gentian-Gentian Intermittent Titration) method. The coin cell was discharged at 0.1C, and a cycle was performed with ① discharge time of 2 min and ② resting time of 30 min. The cycle was repeated until the voltage was less than 0.005V. The voltage at each step was recorded, and the diffusion coefficient LogD of lithium ions before and after cycling was calculated. The test results are shown in Table 2.
[0096] Cycle capacity retention was tested: the battery was tested at 200 mA·g in the voltage range of 0~2V. -1 The capacity retention rate after 500 cycles of charge-discharge cycling at a current density of and at 5 A·g -1 The capacity retention rate after 500 cycles of charge and discharge at the specified current density is shown in Table 3.
[0097] Table 2
[0098] Table 3
[0099] As can be seen from Tables 2 and 3, compared with the negative electrode materials provided in the embodiments, the negative electrode materials provided in the comparative examples of this application have lower initial discharge capacity, lower initial efficiency, and lower lithium-ion diffusion coefficient, higher full-charge expansion, and poor 500-cycle capacity retention at both low and high current densities. Furthermore, comparing the data between the embodiments of this application also shows that appropriately increasing the porosity of the porous silicon framework can reduce material expansion.
[0100] Experiment Example 4 The button cell prepared in Experiment 3 was used to measure the capacity retention rate of the cell after 100 charge-discharge cycles at different current densities within the voltage range of 0 to 2V. The test current densities were 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, and 3A / g, respectively. The results are shown in Table 4.
[0101] Table 4
[0102] As can be seen from Table 4, the negative electrode material provided in the embodiments of this application still has excellent cycle capacity retention rate at high current density and has excellent fast charging capability.
[0103] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A silicon-carbon anode material, characterized in that, It includes a porous silicon framework as the core, a metal cladding layer covering at least a portion of the surface of the porous silicon framework, a graphene cladding layer covering at least a portion of the surface of the metal cladding layer, and a composite cladding layer covering at least a portion of the surface of the graphene cladding layer. The composite coating layer comprises amorphous carbon and lithium-containing compounds; The thickness of the metal cladding layer is 2~50 nm; The thickness of the graphene coating layer is 2~50nm; The thickness of the composite coating layer is 20~100nm.
2. The silicon-carbon anode material according to claim 1, characterized in that, The porous silicon framework has a particle size of 50~500nm and a porosity of 30%~70%.
3. The silicon-carbon anode material according to claim 1, characterized in that, The metal cladding layer contains at least one of antimony, cerium, indium, and bismuth. And / or, the lithium-containing compound includes at least one of lithium oxide, lithium phosphate, lithium carbonate, lithium fluoride, lithium niobate, and lithium citrate; And / or, in the composite coating layer, the mass ratio of lithium to carbon is 0.03 to 3:
1.
4. A method for preparing a silicon-carbon anode material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Mix silica spheres and reducing agent, carry out reduction reaction, and acid wash to obtain porous silicon framework; S2: Deposit a metal coating layer on a porous silicon framework to obtain the first intermediate product; S3: Deposit a graphene coating layer on the first intermediate product to obtain the second intermediate product; S4: Mix the second intermediate product, carbon source, lithium-containing compound, and solvent to obtain a spray slurry, and spray dry to obtain the third intermediate product; S5: Take the third intermediate product and carry out a carbonization reaction to obtain silicon-carbon anode material.
5. The preparation method according to claim 4, characterized in that, In S1, the mass ratio of silica spheres to reducing agent is 1:0.5~2; And / or, in S1, the reduction reaction is carried out in a protective gas atmosphere at a temperature of 550~800℃, a holding time of 1~6h, and a heating rate of 1~10℃ / min. And / or, in S1, pickling includes sequential pickling with a strong acid and a weak acid, wherein the pickling time with the strong acid is 2-12 hours, and the pickling time with the weak acid is 2-12 hours; optionally, the strong acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; optionally, the weak acid includes hydrofluoric acid; further optionally, the concentration of the strong acid is 1-4M; further optionally, the concentration of the weak acid is 2-8M; And / or, in S1, the pickling temperature is 25~80℃; And / or, in S4, the mass ratio of the second intermediate product, the carbon source, and the lithium-containing compound is 1:0.05~0.5:0.05~0.5; And / or, the solid content of the spray slurry is 10%~50%, and the viscosity is 50~500cp; And / or, spray drying is carried out under a protective gas atmosphere, with an inlet temperature of 180~300℃, an outlet temperature of 80~120℃, a rotation speed of 10000~30000rpm, and a feed rate of 5~20mL / min; And / or, in S5, the carbonization reaction is carried out under a protective gas atmosphere at a temperature of 600~1000℃, a holding time of 2~6h, and a heating rate of 1~10℃ / min.
6. The preparation method according to claim 4 or 5, characterized in that, S2 includes the following steps: S201: Preheating; S202: Heat up, introduce metal-organic vapor, and purge with protective gas; S203: Introduce the reaction gas and purge with the protective gas; S204: Repeat steps S202 and S203; S205: Introduce the reaction gas, anneal, and obtain the first intermediate product; And / or, S3 includes the following steps: introducing a carbon source gas and a hydrogen-argon mixture, depositing a graphene coating layer, and obtaining a second intermediate product.
7. The preparation method according to claim 6, characterized in that, In step S201, the preheating temperature is 100~200℃ and the time is 1~2h; And / or, in S202, the pressure is 0.1~10 Torr, the temperature is 200~450℃, the flow rate of the metal-organic vapor is 10~100mL / min, and the pulse time is 0.1~1.5s; And / or, in S203, the pressure is 0.1~10 Torr, the flow rate of the introduced reaction gas is 10~100 mL / min, and the pulse time is 0.5~2 s; And / or, in S202, the flow rate of the protective gas is 20~200 mL / min, and the purging time is 5~10s; And / or, in S203, the flow rate of the protective gas is 20~200 mL / min, and the purging time is 5~20s; And / or, in S204, the number of cycles is 50 to 500; And / or, in S205, the flow rate of the reaction gas is 10~100mL / min, the annealing temperature is 200~450℃, and the time is 1~2h; And / or, in S3, the pressure for depositing the graphene coating is 0.1~10 Torr, the temperature is 700~1000℃, and the holding time is 0.5~8h; And / or, in S3, the flow rate of the carbon source gas and the hydrogen-argon mixture is 5~50 mL / min, and the volume ratio of the carbon source gas and the hydrogen-argon mixture is 1:1~10; optionally, in the hydrogen-argon mixture, the volume ratio of hydrogen to argon is 2~10:90~98.
8. The preparation method according to claim 6 or 7, characterized in that, The particle size of the silica spheres is 50~500nm; And / or, the reducing agent includes at least one of aluminum powder and magnesium powder; And / or, the organometallic compound includes at least one of trimethylantimony, triethylantimony, antimony trichloride, antimony pentachloride, tetra(2,2,6,6-tetramethyl-3,5-heptadecyl)cerium, cerium acetylacetonate, trimethylindium, triethylindium, trimethylbismuth, triethylbismuth, and triphenylbismuth. And / or, the reactant gas includes at least one of hydrogen and hydrogen plasma; And / or, the carbon source gas includes at least one of methane, ethane, ethylene, and acetylene; And / or, the carbon source includes at least one of glucose, sucrose, pitch, polyvinylpyrrolidone, and polyacrylonitrile; And / or, the solvent includes at least one of water, ethanol, and isopropanol; And / or, the protective gas includes at least one of nitrogen and rare gases.
9. A negative electrode sheet, characterized in that, Includes the silicon-carbon anode material as described in any one of claims 1 to 3, or the silicon-carbon anode material prepared by the preparation method as described in any one of claims 4 to 8.
10. A secondary battery, characterized in that, It includes the negative electrode as described in claim 9, and also includes a positive electrode, a separator, and an electrolyte.