Preparation method of modified carbon-coated silicon / scale graphite nanocomposite

Abstract

This invention discloses a method for preparing modified carbon-coated silicon / flake graphite nanocomposite materials. The first part of the method involves preparing thin-layer graphite nanosheets (G-NPS) through three-roll milling; the second part involves preparing the modified carbon-coated silicon / flake graphite nanocomposite materials using dopamine hydrochloride. In the first part, the three-roll milling completely removes the flake graphite, and the suspension is centrifuged and washed with ethanol to obtain thin-layer graphite nanosheets. The second part involves the following steps: first, ultrasonically dispersing a mixed solution of silicon powder and flake graphite nanosheets, and freeze-drying the suspension; second, preparing the silicon / flake graphite nanocomposite material through heat treatment; third, preparing a mixture of the silicon / flake graphite nanocomposite material and dopamine hydrochloride, repeatedly filtering and washing it, and vacuum drying it; fourth, heating the prepared sample under a nitrogen-hydrogen mixture to obtain the modified carbon-coated silicon / flake graphite nanocomposite material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material preparation technology, and more particularly to a method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material. Background Technology

[0002] Lithium-ion batteries have been widely used in electric vehicles, large-scale energy storage systems, and portable electronic products due to their advantages such as high specific energy, high specific power, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. However, the performance of lithium-ion batteries degrades significantly with repeated charge and discharge cycles. Therefore, researching lithium-ion battery recycling technologies is essential to improve their performance.

[0003] Silicon-based anode materials are a type of lithium-ion anode material. In recent years, silicon-based anodes have attracted increasing attention from researchers due to their extremely high specific capacity and are considered one of the most promising materials to replace graphite anodes. This patent mainly studies silicon anode materials.

[0004] Silicon (Si) possesses an extremely high theoretical specific capacity (4200 mAh / g), approximately 11 times that of graphite anodes (372.0 mAh / g). Simultaneously, Si exhibits a low lithium intercalation potential (<0.5V vs. Li+ / Li), ensuring high energy density in batteries. Furthermore, Si is the second most abundant element in the Earth's crust and is environmentally friendly, laying a solid foundation for the large-scale commercial application of Si anodes. Despite these advantages, Si anodes also face some challenges in practical applications: ① Lithium intercalation volume expansion can reach up to 300%. After continuous deintercalation / intercalation, the Si anode cracks and pulverizes, losing electrochemical contact with the conductive network and current collector, ultimately leading to rapid capacity decay; ② An unstable SEI film forms on the surface of the Si anode. With cycling, the SEI film continuously breaks down and reforms, irreversibly consuming the lithium source in the electrolyte. Moreover, the continuously forming SEI film becomes increasingly thick, resulting in poor lithium-ion diffusion kinetics; ③ The intrinsic conductivity and lithium-ion diffusion coefficient of Si are ~10⁻⁶. -3 S / cm and ~10 -12 cm 2 / S, poor electron / ion conductivity hinders the full utilization of active materials.

[0005] This invention proposes a method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material to address the problems of volume expansion, poor conductivity, and low lithium-ion diffusion rate of silicon anode materials. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a method for preparing modified carbon-coated silicon / flake graphite nanocomposite materials.

[0007] To achieve the above objectives, the technical solution provided by the present invention is: a method for preparing modified carbon-coated silicon / flake graphite nanocomposite material, the method comprising two parts: the first part: preparing thin-layer flake graphite nanosheets (G-NPS) by three-roll milling; the second part: preparing modified carbon-coated silicon / flake graphite nanocomposite material by using dopamine hydrochloride.

[0008] The method specifically includes the following steps:

[0009] Step (1): Three-roll milling to remove flake graphite: Mix 20g of flake graphite with 300mL of phenolic resin and stir to form suspension 1; mill suspension 1 with three rollers and ensure that the flake graphite is completely removed; centrifuge and wash the milled suspension 1 with ethanol to obtain solid 1 after removal.

[0010] Step (2): Preparation of silicon / flake graphite nanosheet mixed solution: 0.2g silicon powder, 0.2g solid 1 and 0.2g citric acid monohydrate were dispersed in 100mL of anhydrous ethanol and deionized water mixed solution to obtain mixed solution 1; mixed solution 1 was ultrasonicated at 100W ultrasonic power for 20 minutes.

[0011] Step (3): Freeze-drying silicon / flake graphite nanosheets: Place the ultrasonically treated mixture 1 in a refrigerator and freeze for 12 hours, then place it in a freeze dryer at -40°C to freeze-dry and obtain solid 2;

[0012] Step (4): Prepare silicon / flake graphite nanosheet composite material: Heat solid 2 to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixed atmosphere and keep it at that temperature for 2h to obtain solid 3;

[0013] Step (5): Preparation of silicon / flake graphite nanocomposite material and dopamine hydrochloride mixed solution: Solid 3 and dopamine hydrochloride were ultrasonically treated in 100 ml of 0.01 mol / L tromethamine aqueous solution and magnetically stirred at 60 °C for 5 h to obtain mixed solution 2; Ultrasonic treatment: ultrasonic power 100 W, ultrasonic time 20 minutes;

[0014] Step (6): Silicon / flake graphite / dopamine hydrochloride composite material: The solid in the mixture 2 was separated by filtration and washed with deionized water, repeated 3 times; then dried in a vacuum dryer at 110°C for 10 h to obtain solid 4;

[0015] Step (7): High-temperature solid-phase synthesis of modified carbon-coated silicon / flake graphite nanocomposite material: The prepared solid 4 is heated to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixture and held at that temperature for a certain time to obtain the final product: modified carbon-coated silicon / flake graphite nanocomposite material.

[0016] Preferably, in step (1), the mass ratio of flake graphite to phenolic resin is 1:15, and the three-roll milling process is divided into four segments: 12μm-6μm-3μm-1μm, with each segment requiring 5 peelings.

[0017] Preferably, in step (2), the ratio of silicon powder, solid 1 and citric acid monohydrate is 1:1:1 by mass, and the volume ratio of anhydrous ethanol and deionized water is 1:4.

[0018] Preferably, in step (3), the freeze dryer freeze-dries the mixture 1 to obtain a composite material with uniformly dispersed silicon particles. The freeze-drying temperature is less than -30°C and the freeze-drying time is greater than 24 hours.

[0019] Preferably, in step (4), solid 2 is heated to 300-500°C in a nitrogen-hydrogen mixed atmosphere.

[0020] Preferably, in step (5), dopamine hydrochloride is used as the carbon source for carbon coating; tromethamine aqueous solution is used as a buffer; and the mass ratio of solid 3 to dopamine hydrochloride is between 5:1 and 2:1.

[0021] Preferably, in step (6), the solids in the mixture 2 are separated by centrifugation, settling, or filtration.

[0022] Preferably, in step (7), solid 4 is heated to 750-900°C under a nitrogen-hydrogen mixture and kept at that temperature for 3-5 hours.

[0023] Beneficial effects of this invention:

[0024] This invention features low cost, easy production and implementation. Compared with other methods, three-roll milling can prepare a large number of graphite nanosheets in a shorter time, improve production efficiency, and is relatively simple to operate, making it easy to achieve large-scale industrial production. Attached Figure Description

[0025] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0026] Figure 1 This is the XRD pattern of Embodiment 1 in this invention;

[0027] Figure 2This is a TEM image of Example 1 in this invention;

[0028] Figure 3 This is a rate performance diagram of Example 1 in this invention. Detailed Implementation

[0029] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0030] A preferred embodiment of the present invention provides a method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material. The method comprises two parts: the first part is to prepare thin-layer graphite nanosheets (G-NPS) by three-roll milling; the second part is to prepare the modified carbon-coated silicon / flake graphite nanocomposite material by using dopamine hydrochloride.

[0031] The first part consists of two steps: the first step is to completely peel off the flake graphite by three-roll milling; the second step is to centrifuge the suspension with ethanol to obtain thin-layer graphite nanosheets.

[0032] The second part consists of four steps: The first step is to ultrasonically disperse a mixed solution of silicon powder and flake graphite nanosheets, and then freeze-dry the suspension; the second step is to prepare silicon / flake graphite nanocomposites through heat treatment; the third step is to prepare a mixture of silicon / flake graphite nanocomposites and dopamine hydrochloride, and then repeatedly filter, wash, and vacuum dry it; the fourth step is to heat the prepared sample under a nitrogen-hydrogen mixture to obtain modified carbon-coated silicon / flake graphite (Si / G-NPs@MC) nanocomposites.

[0033] The specific steps are as follows:

[0034] Step (1): Three-roll milling to remove flake graphite: Mix 20g of flake graphite with 300mL of phenolic resin and stir to form suspension 1; mill suspension 1 with three rollers and ensure that the flake graphite is completely removed; centrifuge and wash the milled suspension 1 with ethanol to obtain solid 1 after removal.

[0035] Step (2): Preparation of silicon / flake graphite nanosheet mixed solution: 0.2g silicon powder, 0.2g solid 1 and 0.2g citric acid monohydrate were dispersed in 100mL of anhydrous ethanol and deionized water mixed solution to obtain mixed solution 1; mixed solution 1 was ultrasonicated at 100W ultrasonic power for 20 minutes.

[0036] Step (3): Freeze-drying silicon / flake graphite nanosheets: Place the ultrasonically treated mixture 1 in a refrigerator and freeze for 12 hours, then place it in a freeze dryer at -40°C to freeze-dry and obtain solid 2;

[0037] Step (4): Prepare silicon / flake graphite nanosheet composite material: Heat solid 2 to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixed atmosphere and keep it at that temperature for 2h to obtain solid 3;

[0038] Step (5): Preparation of silicon / flake graphite nanocomposite material and dopamine hydrochloride mixed solution: Solid 3 and dopamine hydrochloride were ultrasonically treated in 100 ml of 0.01 mol / L tromethamine aqueous solution and magnetically stirred at 60 °C for 5 h to obtain mixed solution 2; Ultrasonic treatment: ultrasonic power 100 W, ultrasonic time 20 minutes;

[0039] Step (6): Silicon / flake graphite / dopamine hydrochloride composite material: Filter to separate the solid in the mixture 2 and wash with deionized water, repeat 3 times; then dry in a vacuum dryer at 110°C for 10 h to obtain solid 4;

[0040] Step (7): High-temperature solid-phase synthesis of modified carbon-coated silicon / flake graphite nanocomposite material: The prepared solid 4 is heated to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixture and held at that temperature for a certain time to obtain the final product: modified carbon-coated silicon / flake graphite nanocomposite material.

[0041] This invention effectively suppresses the volume expansion of silicon anodes by modifying carbon coating, thereby improving their cycle stability and service life, and reducing costs.

[0042] Example 1

[0043] Step (1): Three-roll milling to remove flake graphite: Mix 20g of flake graphite with 300mL of phenolic resin and stir to form suspension 1; mill suspension 1 with three rollers and ensure that the flake graphite is completely removed; centrifuge and wash the milled suspension 1 with ethanol to obtain solid 1 after removal.

[0044] Step (2): Preparation of silicon / flake graphite nanosheet mixed solution: 0.2g silicon powder, 0.2g solid 1 and 0.2g citric acid monohydrate were dispersed in 100mL of anhydrous ethanol and deionized water mixed solution to obtain mixed solution 1; mixed solution 1 was ultrasonicated at 100W ultrasonic power for 20 minutes.

[0045] Step (3): Freeze-drying silicon / flake graphite nanosheets: Freeze-dry silicon / flake graphite nanosheets: Place the ultrasonically treated mixture 1 in a refrigerator and freeze for 12 hours, then place it in a freeze dryer at -40°C to freeze-dry, and obtain solid 2;

[0046] Step (4): Prepare silicon / flake graphite nanosheet composite material: Heat solid 2 to 400℃ at a heating rate of 5℃ / min and hold for 2h in a nitrogen-hydrogen mixed atmosphere to obtain solid 3;

[0047] Step (5): Preparation of silicon / flake graphite nanocomposite material and dopamine hydrochloride mixed solution: Solid 3 and dopamine hydrochloride were ultrasonically treated in 100 ml of 0.01 mol / L tromethamine aqueous solution and magnetically stirred at 60 °C for 5 h to obtain mixed solution 2; Ultrasonic treatment: ultrasonic power 100 W, ultrasonic time 20 minutes;

[0048] Step (6): Silicon / flake graphite / dopamine hydrochloride composite material: Filter to separate the solid in the mixture 2 and wash with deionized water, repeat 3 times; then dry in a vacuum dryer at 110°C for 10 h to obtain solid 4;

[0049] Step (7): High-temperature solid-phase synthesis of modified carbon-coated silicon / flake graphite nanocomposite material: The prepared solid 4 was heated to 800℃ and held for 4h under a nitrogen-hydrogen mixed gas at a heating rate of 5℃ / min to obtain the final product: modified carbon-coated silicon / flake graphite nanocomposite material.

[0050] Step (8): Assemble half-cells and test electrochemical performance: Mix the final product with carbon black and CMC in a mass ratio of 7:1.5:1.5 to prepare a uniform slurry, assemble the cell, and test the electrochemical performance of the product.

[0051] The XRD pattern of the product in this embodiment is shown below. Figure 1 ; TEM image of the product in this embodiment is shown below Figure 2 The electrochemical performance diagram of the product in this embodiment is shown below. Figure 3 .

[0052] This invention employs a three-roll milling method to prepare low-cost thin-layer flake graphite nanosheets. Si / G-NPs are prepared via freeze-drying and heat treatment; and the composite material is then carbon-encapsulated to prepare a modified carbon-encapsulated silicon / flake graphite nanocomposite material (Si / G-NPs@MC). Three-roll milling can grind graphite raw materials into thinner nanosheets, reducing layer thickness, increasing specific surface area, and improving the performance of the graphite nanosheets.

[0053] The materials used in this invention include: silicon powder, flake graphite, phenolic resin, anhydrous ethanol, deionized water, hydrated citric acid, dopamine hydrochloride, and tromethorphan. These materials are safe and inexpensive. The solid waste generated, such as residual byproducts, is harmless to the environment and is easily recyclable. The amount of gas generated is small and pollution-free. This experiment does not produce excessive impurities and precipitates, making it convenient for cleaning and requiring minimal reagents. The entire process is green and environmentally friendly.

[0054] This invention features low cost, easy production and implementation. Compared with other methods, three-roll milling can prepare a large number of graphite nanosheets in a shorter time, improve production efficiency, and is relatively simple to operate, making it easy to achieve large-scale industrial production.

[0055] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0056] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means is within the protection scope of the present invention.

Claims

1. A method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material, characterized in that: The preparation method consists of two parts: the first part is to prepare thin-layer flake graphite nanosheets by three-roll milling; the second part is to prepare modified carbon-coated silicon / flake graphite nanocomposite material by using dopamine hydrochloride. The method specifically includes the following steps: Step (1): Three-roll milling to remove flake graphite: Mix 20g of flake graphite with 300mL of phenolic resin and stir to form suspension 1; mill suspension 1 with three rollers and ensure that the flake graphite is completely removed; centrifuge and wash the milled suspension 1 with ethanol to obtain solid 1 after removal. Step (2): Preparation of silicon / flake graphite nanosheet mixed solution: 0.2g silicon powder, 0.2g solid 1 and 0.2g citric acid monohydrate were dispersed in 100mL of anhydrous ethanol and deionized water mixed solution to obtain mixed solution 1; mixed solution 1 was ultrasonicated at 100W ultrasonic power for 20 minutes. Step (3): Freeze-drying silicon / flake graphite nanosheets: Place the ultrasonically treated mixture 1 in a refrigerator and freeze for 12 hours, then place it in a freeze dryer and freeze-dry at less than -30°C to obtain solid 2; Step (4): Prepare silicon / flake graphite nanosheet composite material: Heat solid 2 to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixed atmosphere and keep it at that temperature for 2h to obtain solid 3; Step (5): Preparation of silicon / flake graphite nanocomposite material and dopamine hydrochloride mixed solution: Solid 3 and dopamine hydrochloride were ultrasonically treated in 100 ml of 0.01 mol / L tromethamine aqueous solution and magnetically stirred at 60 °C for 5 h to obtain mixed solution 2; Ultrasonic treatment: ultrasonic power 100 W, ultrasonic time 20 minutes; Step (6): Silicon / flake graphite / dopamine hydrochloride composite material: Filter to separate the solid in the mixture 2 and wash with deionized water, repeat 3 times; then dry in a vacuum dryer at 110℃ for 10h to obtain solid 4; Step (7): High-temperature solid-phase synthesis of modified carbon-coated silicon / flake graphite nanocomposite material: The prepared solid 4 is heated to a certain temperature at a heating rate of 5℃ / min under a nitrogen-hydrogen mixture and held at that temperature for a certain time to obtain the final product: modified carbon-coated silicon / flake graphite nanocomposite material.

2. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (1), the three-roll milling process consists of four segments: 12μm-6μm-3μm-1μm, and each segment requires five peelings.

3. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (2), the mass ratio of silicon powder, solid 1 and citric acid monohydrate is 1:1:1, and the volume ratio of anhydrous ethanol and deionized water is 1:

4.

4. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (3), the freeze dryer freeze-dries the mixture 1 to obtain a composite material with uniformly dispersed silicon particles. The freeze-drying temperature is -40℃ and the freeze-drying time is greater than 24 hours.

5. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (4), solid 2 is heated to 300-500℃ in a nitrogen-hydrogen mixed atmosphere.

6. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (5), dopamine hydrochloride is used as the carbon source for carbon coating; tromethamine aqueous solution is used as a buffer, and the mass ratio of solid 3 to dopamine hydrochloride is between 5:1 and 2:

1.

7. The method for preparing a modified carbon-coated silicon / flake graphite nanocomposite material according to claim 1, characterized in that: In step (7), solid 4 is heated to 750-900℃ under a nitrogen-hydrogen mixture and kept at that temperature for 3-5 hours.

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