Silicon-carbon negative electrode material and preparation and application thereof

Abstract

The invention relates to a silicon-carbon negative electrode material and preparation and application thereof.The preparation method of the silicon-carbon negative electrode material comprises the following steps that 1, zinc salt and 2-methylimidazole are weighed to react in a solvent, a zeolite imidazole framework substance ZIF-8 is prepared, then centrifugation, washing, drying and grinding are conducted, and a powdery carbon source precursor is obtained; (2) carrying out high-temperature calcination treatment on the obtained carbon source precursor to obtain a porous carbon material; and (3) taking a porous carbon material as a substrate bed layer in a fixed bed reactor, sequentially introducing silicon source gas and carbon source gas at high temperature to perform chemical vapor deposition, filling nano silicon into pore channels of the substrate material, and coating a carbon layer outside to enhance the silicon-carbon bonding strength, thereby obtaining a target product. Compared with the prior art, the silicon-carbon negative electrode material prepared by the method has excellent capacity performance and cycle performance, the production scale is easy to amplify, the cost is controllable, and the method has a wide commercial prospect.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material preparation technology, and relates to a silicon-carbon anode material and its preparation and application. Background Technology

[0002] Lithium-ion batteries have been commercially deployed on a large scale in the electric vehicle sector. Improving the energy density of lithium-ion batteries is crucial for extending the driving range of electric vehicles, and developing high-specific-capacity electrode materials has become a key core of technological development in this industry. Graphite is currently a widely used anode material, with a theoretical specific capacity of 372 mAh·g. -1 Silicon has a theoretical specific capacity of up to 4200 mAh·g. -1 Silicon is a highly promising high-capacity lithium-ion battery anode material. However, silicon undergoes a volume change of approximately 300% during charging and discharging, which causes a series of problems such as the pulverization and shedding of the anode active components, the continuous breakage and formation of the SEI film, and ultimately leads to a rapid and irreversible decay of battery capacity.

[0003] Depositing elemental silicon within the pores of specific porous carbon materials, thereby limiting the characteristic size of silicon through the carbon pore confinement effect and buffering the volume changes of silicon during charging and discharging, while utilizing the carbon material to form a stable SEI film, is considered one of the best solutions to the aforementioned problems. Currently, the cost of preparing porous carbon materials with suitable pore structures remains high, failing to meet industrialization requirements; the overall process route for producing silicon-carbon composite materials is not yet mature, and the properties of the prepared silicon-carbon materials are not stable.

[0004] For example, Chinese patent application CN202410399437.0 discloses a silicon-carbon material, its preparation method, and a lithium battery anode material. This includes silicon deposition and carbon coating of large-particle porous carbon, with the material particles being crushed after any step of silicon deposition or carbon coating. The particle size of the large-particle porous carbon ranges from 0 to 150 μm, and the average particle size of the crushed material particles is no greater than 20 μm. Carbon coating is performed using a one-step or two-step method. The mass of the coating layer formed during carbon coating accounts for 0.01% to 10% of the total mass of the silicon-carbon material. However, the porous carbon used in this patent experiences a significant reduction in specific surface area during deposition, resulting in a low theoretical upper limit for silicon deposition.

[0005] Therefore, it is necessary to develop a stable and efficient preparation process for silicon-carbon composite materials based on carbon substrates. Summary of the Invention

[0006] The purpose of this invention is to provide a silicon-carbon anode material and its preparation and application, which has excellent capacity and cycle performance, and is easy to scale up in production, with controllable cost and broad commercial prospects.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] In one aspect, the present invention provides a method for preparing a silicon-carbon anode material, comprising the following steps:

[0009] (1) Weigh out zinc salt and react it with 2-methylimidazole in a solvent to prepare zeolite imidazole framework material ZIF-8, and then centrifuge, wash, dry and grind to obtain powdered carbon source precursor;

[0010] (2) The obtained carbon source precursor is subjected to high-temperature calcination to obtain porous carbon material;

[0011] (3) In a fixed-bed reactor, porous carbon material is used as the substrate bed. Silicon source gas and carbon source gas are sequentially introduced at high temperature to carry out chemical vapor deposition, so that nano-silicon is filled into the pores of the substrate material, and a carbon layer is coated on the outside to enhance the silicon-carbon bonding strength, thus obtaining the target product.

[0012] Furthermore, in step (1), the zinc salt is selected from any one or a combination of zinc nitrate, zinc sulfate, zinc acetate or their hydrates.

[0013] Furthermore, in step (1), the solvent is selected from any one or a combination of several of deionized water, methanol, ethanol and N,N-dimethylformamide.

[0014] Furthermore, in step (1), the ratio of the amount of zinc salt, 2-methylimidazole, and solvent added is 1 mmol: (3-5) mmol: (60-100) mL.

[0015] Furthermore, in step (1), the reaction temperature is 80–120°C and the time is 2–4 h.

[0016] Furthermore, the pore size distribution of the prepared carbon source precursor is mainly concentrated in the range of 1–1.5 nm, and the specific surface area is 700–1500 m². 2 ·g -1 Specific pore volume is 0.4–0.8 cc·g -1 .

[0017] Furthermore, the pore size distribution of the prepared porous carbon is mainly concentrated in the range of 1–5 nm, and the specific surface area is 700–1800 m². 2 ·g -1 Specific pore volume is 0.7–1.3 cc·g -1 Typically, but not limitingly, the pore size of porous carbon can be a range of 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any combination thereof; the specific surface area can be 700 m². 2 ·g -1 1000m 2·g -1 1300m 2 ·g -1 1600m 2 ·g -1 1800m 2 ·g -1 Or a range of values ​​consisting of any two of them.

[0018] Furthermore, in step (2), the high-temperature calcination treatment is carried out at a temperature of 700–1200°C under an inert atmosphere for 1–5 hours. Preferably, the inert atmosphere is argon.

[0019] Furthermore, before chemical vapor deposition, the substrate material is subjected to acid washing and water washing to remove impurities from the porous carbon, and then further dried.

[0020] Furthermore, in step (3), the chemical vapor deposition reaction uses a fixed bed as the reactor and a porous carbon material as the substrate bed, through which the gas passes and reacts.

[0021] Furthermore, in step (3), the silicon source gas is selected from one or more combinations of silane, ethyl silane and propane.

[0022] Furthermore, in step (3), the carbon source gas is selected from one or a combination of several of acetylene, ethylene, propylene, and butene.

[0023] Furthermore, in step (3), the temperature for chemical vapor deposition of silicon source gas is 350℃~700℃, the volume ratio of silicon source gas to carrier gas is 1:(18~22), and the gas introduction time is 20~25min. Specifically, the carrier gas can be nitrogen.

[0024] Furthermore, in step (3), the temperature for introducing carbon source gas for chemical vapor deposition is 450℃~800℃, the volume ratio of carbon source gas to carrier gas is 1:(18~22), and the gas introduction time is 8~12min. Specifically, the carrier gas can be nitrogen.

[0025] Furthermore, through chemical vapor deposition, the specific surface area and specific pore volume of the material are significantly reduced, while the pore size distribution remains largely unchanged.

[0026] In a second aspect, the present invention provides a silicon-carbon anode material prepared according to the preparation method described in any of the preceding claims.

[0027] In a third aspect, the present invention provides an application of silicon-carbon anode material as an anode in lithium-ion batteries.

[0028] In a fourth aspect, the present invention provides a lithium-ion battery that uses the silicon-carbon anode material as described above as the anode.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) Porous carbon was prepared by using zeolite imidazole framework material ZIF-8 as a precursor. The pore size distribution of the product is relatively concentrated and the technical route is relatively simple, which can effectively reduce the equipment cost and raw material cost of production. The porous carbon has a rich pore structure and there is still room for pore space after silicon deposition, which can provide a buffer for the volume expansion of silicon and prevent the electrode material from cracking and breaking due to excessive internal stress.

[0031] (2) Using a fixed-bed reactor for chemical vapor deposition ensures uniform and sufficient contact between the gas source and the substrate, allowing nano-silicon to be dispersedly deposited into the pores of the carbon substrate. This results in high substrate utilization and can improve the silicon content and uniformity of silicon-carbon materials. The aforementioned silicon-carbon composite material can improve the specific capacity and cycle stability of lithium-ion batteries when used as a negative electrode. Attached Figure Description

[0032] Figure 1 This is a flowchart of the process flow of the present invention;

[0033] Figure 2 This is a SEM image of the silicon-carbon composite material of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0036] Example 1

[0037] Weigh 3.512 g of zinc acetate dihydrate and 3.941 g of 2-methylimidazole, dissolve them separately in 80 mL of DMF, and pour the two solutions into a round-bottom flask and mix. Then add 20 mL of DMF. Place the flask in an oil bath, stir magnetically, and heat to 100 °C for about 3 h. Separate the solid phase using a centrifuge, and wash thoroughly three times with methanol. Place the washed product in an oven at 65 °C and dry overnight. After drying, grind it in an agate mortar to obtain a powdered precursor. Place the powdered precursor in an oven at 120 °C under vacuum for about 10 h for activation. Place 2 g of the precursor sample in a crucible in the center of a tube furnace, seal the tube furnace with a cap, and place the exhaust pipe into an absorption water bottle to ensure a complete gas passage. Adjust the Ar flow rate to approximately 20 mL / min, set the tube furnace program, purge at room temperature for 1 hour, then increase the temperature to 900°C at a rate of 5°C / min and hold for 5 hours to allow the material to fully carbonize. After the temperature drops to room temperature, close the gas cylinder and remove the black carbonized product. Soak the product in 0.5M hydrochloric acid for 10 minutes to remove impurities generated during carbonization, filter, and then wash with deionized water to remove hydrochloric acid. Place the product in an oven to dry and remove moisture to obtain the final carbonized product.

[0038] Quartz wool was inserted into the predetermined position in the center of the fixed-bed reaction tube to support the carbon substrate. 0.20 g of the carbon substrate (i.e., the carbonized product obtained above) was weighed and added to the reaction tube. The fixed-bed heating program was set, heating to 520°C at a rate of 5°C / min. The tube was purged with N2 for 2 hours. After purging and heating were completed, SiH4 gas was introduced (the pipeline was pre-emptively purged with N2). The flow rates of N2 and SiH4 were 530 mL / min and 28 mL / min, respectively, with SiH4 purging time approximately 23 minutes. The SiH4 passage ball valve was closed, and the pipeline was continued to be purged with N2, with the temperature increased to 600°C at a rate of 5°C / min. Then, C2H2 was introduced, with the flow rates of N2 and SiH4 being 480 mL / min and 25 mL / min, respectively, with C2H2 purging time approximately 10 minutes. After the reaction was complete, the tube was cooled and the gas in the pipeline was thoroughly purged to obtain the silicon-carbon product.

[0039] Prepare coin cell half-cells. Weigh out the active components: conductive agent Super P: binder CMC = 8:1:1 (mass ratio), mix them, add an appropriate amount of deionized water and stir. Use a four-sided slurry spreader to evenly coat the slurry onto copper foil, dry at 65℃ for 12h, slice, use lithium foil as counter electrode, use 1mol / L LiPF6 solution (solvent components volume ratio EC:DMC:DEC = 1:1:1) as electrolyte, and use a polypropylene membrane Celgard2500 as separator, assemble coin cell half-cells in a glove box.

[0040] Instruments used for battery assembly and testing: The LG1200 / 750TS glove box of Suzhou Weige Technology Co., Ltd. was used to assemble the batteries, and the battery constant temperature test chamber of Shenzhen Xinwei Electronics Co., Ltd. was used to test the battery performance.

[0041] Battery testing conditions: voltage range 0.01~1.5V, charge / discharge current for the first three cycles 0.200A·g -1 The circulating current thereafter is 0.500 A·g -1 Let it rest for 4 hours before the first discharge, and rest for 10 minutes after each charge and discharge.

[0042] Example 2

[0043] It is largely the same as Example 1, except that the carbon source gas is replaced with ethylene.

[0044] Example 3

[0045] The process is largely the same as in Example 1, except that the carbon source gas is replaced with propylene.

[0046] Comparative Example 1

[0047] Compared to Example 1, the carbon substrate was directly used for battery testing.

[0048] Comparative Example 2

[0049] The two examples are largely the same as in Example 1, except that the carbon substrate is replaced with conductive carbon black commercially available from Cabot Corporation of the United States.

[0050] The material test data for each case are listed in Table 1.

[0051] Table 1

[0052]

[0053] Table 1 shows that, compared with Comparative Example 1, the silicon deposition process causes silicon to occupy the pore space of the carbon substrate, and the specific surface area and specific pore volume of the material are significantly reduced, which is beneficial to provide an effective buffer for the volume change of silicon during charging and discharging.

[0054] As shown in Table 1, the changes in the carbon source gas in Examples 1, 2, and 3 did not significantly affect the electrochemical performance of the materials, and the material manufacturing process exhibits excellent stability and adaptability. The specific capacity of the silicon-carbon composite material prepared in this invention is greatly improved on the basis of a carbon substrate, and the initial coulombic efficiency is not high due to the properties of the carbon substrate; it also maintains a high specific capacity after 100 cycles. Comparative Example 2, using commercial porous conductive carbon black as a carbon substrate, showed significantly worse electrochemical cycling performance with a similar amount of silicon deposition as the porous carbon prepared in this invention, indicating that the product prepared in this invention has good silicon-carbon bonding performance and possesses high specific capacity and cycling stability.

[0055] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: (1) Weigh out zinc salt and react it with 2-methylimidazole in a solvent to prepare zeolite imidazole framework material ZIF-8, and then centrifuge, wash, dry and grind to obtain powdered carbon source precursor; (2) The obtained carbon source precursor is subjected to high-temperature calcination to obtain porous carbon material; (3) In a fixed-bed reactor, porous carbon material is used as the substrate bed. Silicon source gas and carbon source gas are sequentially introduced at high temperature to carry out chemical vapor deposition, so that nano-silicon is filled into the pores of the substrate material, and a carbon layer is coated on the outside to enhance the silicon-carbon bonding strength, thus obtaining the target product.

2. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (1), the zinc salt is selected from any one or a combination of zinc nitrate, zinc sulfate, zinc acetate or their hydrates; The solvent is selected from any one or a combination of several of deionized water, methanol, ethanol and N,N-dimethylformamide.

3. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (1), the ratio of the amount of zinc salt, 2-methylimidazole and solvent added is 1 mmol: (3-5) mmol: (60-100) mL.

4. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (1), the reaction temperature is 80-120℃ and the time is 2-4h.

5. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (2), the high-temperature calcination treatment is carried out at a temperature of 700–1200℃ for 1–5 hours.

6. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (3), the silicon source gas is selected from one or more combinations of silane, ethyl silane and propane; The carbon source gas is selected from one or a combination of several of acetylene, ethylene, propylene, and butene.

7. The method for preparing a silicon-carbon anode material according to claim 1, characterized in that, In step (3), the temperature for chemical vapor deposition of silicon source gas is 400-1000℃, the volume ratio of silicon source gas to carrier gas is 1:(18-22), and the gas transmission time is 20-25 min. The temperature for chemical vapor deposition by introducing carbon source gas is 400–1000℃, the volume ratio of carbon source gas to carrier gas is 1:18–22, and the gas introduction time is 8–12 min.

8. A silicon-carbon anode material, prepared according to the preparation method described in any one of claims 1-7.

9. The application of the silicon-carbon anode material as described in claim 8 as an anode in lithium-ion batteries.

10. A lithium-ion battery that uses the silicon-carbon anode material as described in claim 8 as the anode.

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