Silicon-carbon negative electrode material with closed pore structure, preparation method, application and battery

Abstract

The application provides a silicon-carbon negative electrode material with a closed pore structure, a preparation method, application and battery. The preparation method comprises the following steps: (1) performing silane gas phase deposition on a porous carbon material to obtain a silicon-carbon intermediate; the deposition amount of silicon in the silicon-carbon intermediate is less than 60%; (2) performing plasma chemical vapor deposition on the silicon-carbon intermediate first, and then performing chemical vapor deposition on the silicon-carbon intermediate without plasma assistance. The silicon-carbon negative electrode material prepared by the application has low true density and expansion rate on the basis of excellent cycle performance, specific capacity and initial efficiency.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a silicon-carbon anode material with a closed-pore structure, its preparation method, application, and battery. Background Technology

[0002] Silicon boasts a theoretical specific capacity as high as 4200 mAh / g, making it a hot research topic for next-generation high-energy-density lithium-ion battery anode materials. However, silicon undergoes a volume expansion of over 300% during lithium insertion / extraction, leading to problems such as particle pulverization, repeated rupture and regeneration of the solid electrolyte interfacial film, and loss of electrical contact in active materials, severely hindering its commercial application.

[0003] The mainstream approach for industrialization is to deposit nano-silicon within the pores of a porous carbon framework, followed by secondary carbon coating. The porous carbon framework provides a buffer for the volume expansion of silicon, while the secondary carbon coating layer performs crucial functions such as isolating the electrolyte, stabilizing the solid electrolyte interface film, and improving conductivity. Currently, secondary carbon coating commonly employs thermochemical vapor deposition using a single carbon source gas (such as acetylene), resulting in a uniform and dense carbon layer.

[0004] However, this dense carbon coating lacks compressible space. When the internal silicon expands, the carbon layer directly bears all the expansion stress, easily leading to cracks and eventual rupture during repeated cycles, causing material failure. To solve this problem, the ideal solution is to introduce closed pores within the secondary carbon coating to provide internal buffer space for silicon expansion. However, the pore-forming process of the porous carbon framework (such as chemical activation) occurs before silicon deposition, and the resulting pores belong to the framework itself, unable to create new closed pores in the carbon coating layer outside the already deposited silicon composite particles. Furthermore, conventional thermochemical vapor deposition (TCV) carbon coating processes can only form a uniform, dense carbon layer, lacking the ability to create and seal pores in situ during deposition.

[0005] Plasma-assisted chemical vapor deposition (PCVD) utilizes an electromagnetic field to excite gas and generate plasma, which contains high-energy reactive species such as electrons, ions, and free radicals, enabling rapid deposition of carbon thin films at relatively low temperatures. However, conventional PCVD carbon coating aims to improve film density and uniformity, but the process cannot create closed pores. Therefore, how to achieve closed pores during the secondary carbon coating process remains an unsolved technical problem in this field. Summary of the Invention

[0006] To address the technical problem of existing technologies failing to effectively construct closed-pore structures within the secondary carbon coating layer after silicon deposition, this invention provides a silicon-carbon anode material with a closed-pore structure, its preparation method, applications, and batteries. The silicon-carbon anode material prepared by this invention possesses abundant closed-pore structures, which are entirely formed within the secondary carbon coating layer. This not only provides a buffer space for the volume expansion of silicon but also ensures conductivity and interface stability through the dense outer carbon shell. Furthermore, in addition to excellent cycle performance, specific capacity, and initial efficiency, it also exhibits low true density and expansion rate.

[0007] This invention utilizes plasma-assisted chemical vapor deposition (PCVD) and thermochemical vapor deposition (TCVD) in a stepwise synergistic manner, completing pore-closure and coating sequentially within the same secondary carbon coating process to form a closed-pore structure. After nano-silicon is deposited onto a porous carbon framework, the resulting composite particles undergo stepwise secondary carbon coating: First, a gaseous carbon source is used for plasma-assisted chemical vapor deposition (CVD). Highly active carbon groups in the plasma preferentially nucleate and grow on the surface of the silicon-carbon intermediate and at the pore edges, selectively epitaxially sealing the pores and gradually forming a carbon "cap" that ultimately closes them. Subsequently, the plasma is turned off, and thermochemical vapor deposition (TCVD) is performed. The high deposition rate and density of the gaseous carbon source (alkyne) are used for further coating, isolating silicon from direct contact with the electrolyte and reducing the specific surface area of ​​silicon-carbon. This closed-pore structure is entirely formed within the carbon coating layer, providing a buffer space for silicon volume expansion, while the dense outer carbon shell ensures conductivity and interface stability.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions: This invention provides a method for preparing a silicon-carbon anode material with a closed-pore structure, comprising the following steps: (1) A porous carbon material is subjected to silane vapor deposition to obtain a silicon-carbon intermediate; the silicon deposition content in the silicon-carbon intermediate is less than 60%; (2) The silicon-carbon intermediate is first subjected to plasma chemical vapor deposition, and then chemical vapor deposition is performed without plasma assistance.

[0009] In this invention, the porous carbon material can be one or more of resin-based porous carbon, petroleum coke-based porous carbon, and biomass-based porous carbon. The morphology of the porous carbon material can be non-spherical, spherical, or near-spherical. The pore volume of the porous carbon material can be 0.5-1.5 cm³. 3 / g, for example, 0.8cm 3 / g, 1.1cm 3 / g or 1.3cm 3 / g; the specific surface area of ​​the porous carbon material can be 1500-3000 m². 2 / g, for example 2000 m 2 / g、2400 m 2 / g、2450 m 2 / g、2500 m 2 / g or 2800 m 2 / g; the microporosity of the porous carbon material can be above 80%, preferably above 90%, for example 92%, 95%, 97% or 99%. The particle size D of the porous carbon material 50 It can be 4-12 micrometers, such as 6 micrometers, 8 micrometers or 10 micrometers.

[0010] In this invention, the temperature for silane vapor deposition can be 400-550℃, for example, 420℃, 450℃, 480℃, or 500℃; the deposition time can be 1-12 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or 10 hours. The silane vapor deposition is generally performed using a plasma-free vapor deposition method. During the silane vapor deposition process, silane undergoes pyrolysis within porous carbon channels to generate nano-silicon particles.

[0011] In this invention, the silane vapor deposition is preferably carried out in a mixture of silane and inert gas.

[0012] The inert gas can be conventional in the art, such as argon and / or nitrogen. The volume ratio of the silane to the inert gas can be 1:(5-15), for example 1:6, 1:8, 1:9, 1:10 or 1:12. The flow rate of the silane can be 1-10 L / min, preferably 1-5 L / min, for example 2 L / min, 3 L / min or 4 L / min.

[0013] In this invention, the silane vapor deposition preferably includes the following process: vapor deposition of porous carbon material in a mixed atmosphere of silane and inert gas.

[0014] In this invention, the amount of silicon deposited in the silicon-carbon intermediate is preferably 20%-55%, for example 20%, 24%, 28%, 30%, 32%, 40%, 45%, 48%, 50% or 55%, more preferably 35%-55%; the amount of silicon deposited refers to the percentage of silicon mass to porous carbon mass; generally, the mass of the silicon-carbon intermediate before and after treatment is determined by thermogravimetric analysis, the mass difference is the mass of porous carbon, and the mass after treatment is the mass of silicon, and the mass of silicon / mass of porous carbon is the amount of silicon deposited.

[0015] In this invention, plasma chemical vapor deposition refers to a reaction method in which high-energy electrons in plasma are used to activate the reactive gas through a plasma excitation device, thereby activating and decomposing the gaseous carbon source and depositing it onto the substrate.

[0016] In the present invention, the carbon source used in the plasma chemical vapor deposition process is preferably a gaseous carbon source, and more preferably an alkane and / or olefin, such as methane and / or ethylene.

[0017] In this invention, during the plasma chemical vapor deposition process, under plasma assistance, the gaseous carbon source is decomposed into highly active free radicals and deposited on the surface of silicon-carbon intermediate particles; the highly active carbon groups in the plasma grow epitaxially at the outer edge of the pore opening, sealing the pore like a lid to form a closed pore.

[0018] In this invention, the power and / or frequency of the plasma excitation device used in the plasma chemical vapor deposition process are adjustable. The power of the plasma excitation device in the plasma chemical vapor deposition process can be 100-250W, for example, 120W, 150W, 180W, or 200W; the frequency of the plasma excitation device can be conventional in the art, generally 12-14 MHz, for example, 13.56MHz.

[0019] In this invention, the plasma chemical vapor deposition is generally carried out in a mixed gas atmosphere of gaseous carbon source and inert gas.

[0020] The inert gas can be conventional in the art, such as argon. The volume ratio of the gaseous carbon source to the inert gas can be 1:(3-6), for example, 1:4, 1:5 or 1:6. The flow rate of the gaseous carbon source can be 0.2-4 L / min, for example, 0.5 L / min, 1 L / min, 1.5 L / min or 2 L / min.

[0021] In this invention, the temperature of the plasma chemical vapor deposition can be 500-620℃, for example 500℃, 530℃, 550℃, 560℃, 580℃, 600℃ or 620℃; the time of the plasma chemical vapor deposition can be 1-6 h, for example 1h, 1.5h, 2h, 3h or 4h.

[0022] In one specific implementation, during the plasma chemical vapor deposition process, the power of the plasma excitation device is 150W and the frequency is 13.56MHz.

[0023] In this invention, pulsed plasma mode can also be used in the plasma chemical vapor deposition process.

[0024] In the pulsed plasma mode, "pulse" refers to the periodic switching of the plasma generation power supply on and off, causing the plasma to exist in a discontinuous and intermittent state over time. This mode adjusts the physical and chemical properties of the plasma by controlling the pulse frequency and duty cycle of the power supply (i.e., the ratio of pulse on-time to the total period).

[0025] In the pulsed plasma mode, the pulse frequency can be 500Hz-2000Hz, for example 800 Hz, 1000 Hz or 1500 Hz; the duty cycle can be 30%-70%, for example 40%, 50% or 60%; and the peak power can be 200-300W, for example 225W or 250W, where the peak power refers to the maximum power that the power supply can reach in a short time.

[0026] In this invention, during the chemical vapor deposition process without plasma assistance, the high deposition rate and high density of the gaseous carbon source are utilized to form a dense carbon shell on the silicon-carbon surface that has been coated with closed pores in a single step, thereby further reducing the specific surface area of ​​silicon-carbon.

[0027] In the present invention, the carbon source used in the plasma-free chemical vapor deposition process is preferably a gaseous carbon source, and more preferably an alkyne, such as acetylene and / or phenylacetylene.

[0028] In this invention, the chemical vapor deposition without plasma assistance is generally carried out in a mixed gas atmosphere of gaseous carbon source and inert gas.

[0029] The inert gas can be conventional in the art, such as argon. The volume ratio of the gaseous carbon source to the inert gas can be 1:(3-7), for example, 1:4, 1:5 or 1:6. The flow rate of the gaseous carbon source can be 0.5-4 L / min, for example, 1 L / min, 2 L / min or 3 L / min.

[0030] In this invention, the temperature for performing chemical vapor deposition without plasma assistance can be 500-620℃, for example 550℃, 580℃, 600℃, 610℃ or 620℃; the time for performing chemical vapor deposition without plasma assistance can be 45-300min, for example 60min, 80min, 100min, 120min, 150min or 200min.

[0031] In this invention, after the plasma chemical vapor deposition is completed, it is generally not necessary to cool down to room temperature. Instead, the temperature is directly increased or decreased from the plasma chemical vapor deposition temperature to the temperature at which chemical vapor deposition is performed without plasma assistance.

[0032] In this invention, the plasma chemical vapor deposition and the chemical vapor deposition without plasma assistance can be performed in the same chemical vapor deposition furnace. However, the plasma generator needs to be turned off when performing chemical vapor deposition without plasma assistance. The transition between the two steps can be achieved by switching the type of gas introduced and / or adjusting the reaction temperature.

[0033] The present invention also provides a silicon-carbon anode material with a closed-pore structure prepared by the preparation method described above.

[0034] The present invention also provides an application of the silicon-carbon anode material with a closed-pore structure as described above in a battery.

[0035] The present invention also provides a battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises the silicon-carbon negative electrode material having a closed-pore structure.

[0036] In this invention, the battery is preferably a lithium-ion battery.

[0037] This invention utilizes a step-by-step synergistic process of "plasma-assisted formation of closed pores + secondary carbon coating" to construct a composite carbon shell containing closed pores on the outermost layer of porous carbon composite particles deposited on silicon. The inner closed pores provide an internal buffer space for the volume expansion of silicon, while the outer dense carbon shell ensures electronic conductivity and isolation from the electrolyte. Specifically, the following process occurs: The first stage involves plasma-assisted coating to form closed pores: Carbon source gas is introduced onto the surface of porous carbon / silicon composite particles where silicon deposition has already been completed, while a plasma generator is simultaneously activated. The introduction of plasma serves two purposes: first, the high-energy electrons in the plasma break down carbon source gas molecules into various highly reactive free radicals, accelerating the carbon deposition process; second, plasma-assisted carbon groups can grow epitaxially along the pore openings. The resulting carbon layer acts like a "lid," sealing the pores. The second stage involves thermochemical vapor deposition for dense coating: after the formation of closed pores, the plasma generator is shut down, switching to a pure thermochemical vapor deposition mode without plasma assistance. When alkynes are used as the carbon source gas, their molecules contain carbon-carbon triple bonds, and their pyrolysis activation energy is significantly lower than that of alkanes and alkenes. Therefore, at the same deposition temperature, they exhibit a higher thermal deposition rate, and the degree of cross-linking and density of the deposited carbon layer are higher. The pyrolytic carbon from alkynes rapidly deposits on the outer surface of the loose carbon layer, forming a dense carbon shell. Since the pyrolysis of alkynes is an exothermic reaction, the heat released during deposition has a local heating effect on the inner wall of the loose carbon layer, which helps to relax the local structure of carbon atoms on the inner surface of the pores, making the pore morphology more stable.

[0038] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0039] The reagents and raw materials used in this invention are all commercially available.

[0040] The positive and progressive effects of this invention are as follows: (1) In this invention, a composite carbon coating shell with an inner porous layer and an outer sealed layer is constructed on the outermost layer of porous carbon / silicon composite particles that have completed silicon deposition; the inner closed pores provide an internal buffer space for the volume expansion of silicon, and the outer dense carbon shell ensures electronic conductivity and the isolation effect on the electrolyte. (2) The silicon-carbon anode material prepared by the present invention has excellent cycle performance, specific capacity and first efficiency, as well as low true density and expansion rate. Attached Figure Description

[0041] Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1; Figure 2 The XRD pattern of the silicon-carbon anode material prepared in Example 1; Figure 3 The charge-discharge curve of the silicon-carbon anode material prepared in Example 1 at 0.1C is shown. Figure 4 The figures show the cycling stability curves of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 at 1C. Detailed Implementation

[0042] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0043] The porous carbon used in the following examples and comparative examples is spherical resin-based porous carbon, purchased from Shengquan, model ZMC-4, with a microporosity of 97% and a pore volume of 1.1 cm³. 3 / g, specific surface area 2450 m² 2 / g. Example 1

[0044] Step (1): 1 kg of porous carbon was placed in a chemical vapor deposition furnace (Shanghai Jinghong SK2-4-10TP dual-gas-path tube furnace) and heated to 450℃ under argon protection. A mixture of silane and argon gas (silane gas accounted for 10% of the volume in the mixture, and the silane flow rate was 3 L / min) was introduced, and the deposition time was 6 hours, resulting in a silicon-carbon intermediate with nano-silicon deposited in the pores of the porous carbon framework. The amount of silicon deposited was 48% of the mass of the porous carbon.

[0045] Step (2): Place the silicon-carbon intermediate obtained in step (1) into a chemical vapor deposition furnace equipped with a plasma generator.

[0046] Stage 1 (Plasma-Assisted Carbon Coating to Form Closed Pores): The furnace body is heated to 560℃ and stabilized. A mixture of methane and argon is introduced, with a volume ratio of methane to argon of 1:5 and a methane flow rate of 1L / min. The radio frequency plasma generator (Tektronix) is turned on at a frequency of 13.56 MHz and a power of 150W, with a deposition time of 2 hours, forming a carbon "cap" with a thickness of 2-10 nanometers.

[0047] The second stage (thermochemical vapor deposition for dense carbon coating): The plasma generator was shut off, and the methane supply was stopped. The temperature was then raised to 600°C, and a mixture of acetylene and argon gas was introduced at a volume ratio of 1:5, an acetylene flow rate of 2 L / min, and a deposition time of 100 minutes, forming a dense carbon shell with a thickness of 3-6 nanometers. After deposition, the carbon source gas supply was stopped, and the material was allowed to cool naturally to room temperature under an inert atmosphere, thus obtaining a silicon-carbon anode material with a closed-pore structure within the secondary carbon coating layer. Example 2

[0048] Step (1): Same as in Example 1; Step (2): Phase 1: Compared with Example 1, except that the deposition temperature was adjusted to 500°C, the other operations and conditions were the same as in Example 1; Second stage: Same as Example 1. Example 3

[0049] Step (1): Same as in Example 1; Step (2): Phase 1: Compared with Example 1, except that the deposition temperature was adjusted to 600°C, the other operations and conditions were the same as in Example 1; Second stage: Same as Example 1. Example 4

[0050] Step (1): Same as in Example 1; Step (2): Phase 1: Compared with Example 1, except that the deposition time was adjusted to 1 hour, the other operations and conditions were the same as in Example 1; Second stage: Same as Example 1. Example 5

[0051] Step (1): Same as in Example 1; Step (2): Phase 1: Compared with Example 1, except that the deposition time was adjusted to 4 hours, the other operations and conditions were the same as in Example 1; Second stage: Same as Example 1. Example 6

[0052] Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Second stage: Compared with Example 1, except that the deposition temperature was adjusted to 550°C, the other operations and conditions were the same as in Example 1. Example 7

[0053] Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Second stage: Compared with Example 1, except that the deposition temperature was adjusted to 620°C, the other operations and conditions were the same as in Example 1. Example 8

[0054] Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Second stage: Compared with Example 1, except that the deposition time was adjusted to 60 min, the other operations and conditions were the same as in Example 1. Example 9

[0055] Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Second stage: Compared with Example 1, except that the deposition time was adjusted to 150 min, the other operations and conditions were the same as in Example 1. Example 10

[0056] Step (1): Same as in Example 1; Step (2): Phase 1: Compared with Example 1, except that methane is replaced with ethylene, the other operations and conditions are the same as in Example 1; Second stage: Same as Example 1. Example 11

[0057] Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Phase 2: Compared with Example 1, except that acetylene is replaced with phenylacetylene, the other operations and conditions are the same as in Example 1. Example 12

[0058] Compared with Example 1, except that the pulsed plasma mode is used in the first stage of step (2) to adjust the ion bombardment intensity and pore distribution, the other operations and conditions are the same as in Example 1; The pulse parameters were: pulse frequency 1 kHz, duty cycle 50%, and peak power 225 W. The defect density of the carbon layer was controlled through periodic plasma bombardment. The remaining process steps were the same as in Example 1. Example 13

[0059] Step (1): Except for adjusting the silane vapor deposition time to 3h, the other operations and conditions are the same as in Example 1; the amount of silicon deposited is 24% of the porous carbon mass.

[0060] Step (2): Same as in Example 1. Example 14

[0061] Step (1): Except for adjusting the silane vapor deposition time to 4h, the other operations and conditions are the same as in Example 1; the amount of silicon deposited is 32% of the porous carbon mass.

[0062] Step (2): Same as in Example 1.

[0063] Comparative Example 1: Two-step plasma-assisted pure thermochemical vapor deposition stepwise coating Step (1): Same as in Example 1; Step (2): Phase 1: Same as Example 1; Second stage: Except for keeping the plasma generator on during the preparation process, all other operations and conditions are the same as in Example 1.

[0064] Comparative Example 2 Compared with Example 1, except that step (2) adopts the following operation (no step-by-step hole making and sealing, and no plasma is used), the remaining process steps are the same as in Example 1: Step (1): Same as in Example 1; Step (2): After turning off the plasma generator and continuing to heat up to 600℃, switch to a mixed gas of acetylene and argon. The volume ratio of acetylene to argon is 1:5, the acetylene gas flow rate is 2L / min, and the deposition time is 100 minutes to obtain a dense carbon coating without closed pore structure.

[0065] Comparative Example 3 Step (1): 1 kg of porous carbon was placed in a chemical vapor deposition furnace (Shanghai Jinghong SK2-4-10TP dual-gas-path tube furnace), and heated to 450℃ under argon protection. A mixture of silane and argon gas (silane gas accounted for 10% of the volume in the mixture, and the silane flow rate was 3 L / min) was introduced, and the deposition time was 8 hours, resulting in a silicon-carbon intermediate with nano-silicon deposited in the pores of the porous carbon framework. The amount of silicon deposited was 48% of the mass of the porous carbon.

[0066] Step (2): Place the silicon-carbon intermediate obtained in step (1) into a chemical vapor deposition furnace equipped with a plasma generator.

[0067] First stage (thermochemical vapor deposition sealing): After turning off the plasma generator and heating the furnace to 600°C, switch to a mixed gas of acetylene and argon with a volume ratio of 1:5 and an acetylene gas flow rate of 2L / min. The deposition time is 100 minutes to form a dense carbon shell with a thickness of 3-6 nanometers.

[0068] The second stage (plasma-assisted construction of a loose carbon layer): Acetylene supply was stopped, and the furnace was cooled to 560℃ and stabilized. A mixture of methane and argon was introduced, with a volume ratio of methane to argon of 1:5 and a methane flow rate of 1 L / min. The radio frequency plasma generator (Taikeri) was turned on at a frequency of 13.56 MHz and a power of 150 W, with a deposition time of 2 hours. After deposition, the carbon source gas supply was stopped, and the material was allowed to cool naturally to room temperature under an inert atmosphere, thus obtaining a silicon-carbon anode material with a closed-pore structure within the secondary carbon coating layer.

[0069] Comparative Example 4 Step (1): Except for adjusting the silane deposition time to 15h, the other process steps are the same as in Example 1; the amount of silicon deposited is 60% of the porous carbon mass.

[0070] Step (2): Same as in Example 1. Effect Example

[0071] (1) Characterization of material properties Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1; Figure 2 The image shows the XRD pattern of the silicon-carbon anode material prepared in Example 1.

[0072] In the above embodiments and comparative examples, the thickness of the coating layer was obtained by TEM observation; the amount of silicon deposited was obtained by thermogravimetric analysis.

[0073] The silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-4 were tested using an ASAP2020 surface area and pore size analyzer. The test results are shown in Table 1.

[0074] True density testing of silicon carbide materials: During sample preparation, approximately 5-6.5g of sample is placed in a pre-weighed 10cc sample cup, and the sample mass is recorded. The test uses a helium true density meter, based on the gas displacement method. First, 30 purging cycles are set to remove adsorbed gases from the sample. Then, 5 tests are performed, and the average value is taken. The instrument automatically calculates the true volume of the sample based on Boyle's law and pressure changes, finally outputting the true density value (unit: g / cm³). 3 Preheating and calibration are required before testing. High-purity helium is used. After the test, the average value and standard deviation are recorded. The results are judged according to the standard. The daily testing volume is flexibly arranged, and the samples are kept dry.

[0075] (2) Electrochemical performance testing The silicon-carbon anode materials prepared in Examples 1-14 and Comparative Examples 1-4 were subjected to half-cell tests. The test method was as follows: the above-mentioned test materials were uniformly mixed with binder CMC (sodium carboxymethyl cellulose) and conductive carbon black in a mass ratio of 80:10:10 to form a slurry. This slurry was then coated onto copper foil to a thickness of 100 micrometers and dried under vacuum at 90°C for 12 hours to prepare lithium-ion battery anode sheets. Simulated battery assembly was conducted in an argon-filled glove box using a 1 mol / L LiPF6 electrolyte (solvents were EC, EMC, and DMC, EC: EMC: DMC = 1:1:1 (volume ratio)). A polypropylene microporous membrane was used as the separator, and a lithium metal sheet was used as the counter electrode. Electrochemical performance tests were performed on a Land CT2001A battery tester at 25°C, with a charge / discharge voltage range of 0.01 to 1.5V (1 C = 1000V). (mAh / g). Select qualified electrode sheets and weigh the active material. Measure the thickness of each electrode sheet three times in the center area using a micrometer and take the average value. After assembling the battery, mark it. The battery testing procedure is as follows: let it stand for 8 hours, then discharge at a constant current rate of 0.1C to the cutoff potential of 1.5V, and then discharge at a constant current rate of 0.05C to the cutoff potential of 1.5V. After the test, disassemble the battery in a fume hood. Prepare a beaker containing alcohol, remove the electrode sheets, and blot off any residual electrolyte on their surface with a paper towel. Then, use a micrometer to measure the thickness of the electrode sheet in the center area, measuring three times and taking the average value. Finally, place the disassembled electrode sheets and battery casing together in the alcohol beaker. The expansion rate = (thickness of the negative electrode sheet after the first discharge - thickness of the negative electrode sheet before discharge) / thickness of the negative electrode sheet before discharge * 100%. Relevant test results are shown in Table 1 and... Figures 3-4 .

[0076] Table 1

[0077] Based on the experimental data above, it can be seen that by reserving space and then using plasma-assisted "carbon cap" coating, the expansion rate of silicon carbon can be reduced. Furthermore, the true density test proves that the silicon carbon samples prepared in Examples 1-14 have a low true density, indicating that closed pores do exist in the silicon carbon samples.

[0078] pass Figure 4 The cycling comparison between Example 1 and Comparative Example 1 shows that if plasma-assisted deposition is chosen for secondary carbon coating, the carbon activity of the outer layer will be too high and the reaction of the electrolyte will be intensified, resulting in a decrease in cycling performance.

[0079] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material with a closed-pore structure, characterized in that, Includes the following steps: (1) A porous carbon material is subjected to silane vapor deposition to obtain a silicon-carbon intermediate; the silicon deposition content in the silicon-carbon intermediate is less than 60%; (2) The silicon-carbon intermediate is first subjected to plasma chemical vapor deposition, and then chemical vapor deposition is performed without plasma assistance.

2. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, Step (1) satisfies one or more of the following conditions: (1) The porous carbon material is one or more of resin-based porous carbon, petroleum coke-based porous carbon and biomass-based porous carbon; (2) The pore volume of the porous carbon material is 0.5-1.5 cm. 3 / g; (3) The specific surface area of ​​the porous carbon material is 1500-3000 m². 2 / g; (4) The microporosity of the porous carbon material is above 80%; (5) The amount of silicon deposited in the silicon-carbon intermediate is 20%-55%, for example 20%, 24%, 28%, 30%, 32%, 40%, 45%, 48%, 50% or 55%, preferably 35%-55%.

3. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, The temperature for silane vapor deposition is 400-550°C, for example 420°C, 450°C, 480°C or 500°C; And / or, the silane vapor deposition time is 1-12h, for example 2h, 3h, 4h, 5h, 6h, 7h, 8h or 10h.

4. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, During the plasma chemical vapor deposition process, the power of the plasma excitation device is 100-250W, for example, 120W, 150W, 180W or 200W. And / or, during the plasma chemical vapor deposition process, the frequency of the plasma excitation device is 12-14 MHz.

5. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, The plasma chemical vapor deposition of carbon satisfies one or more of the following conditions: (1) In the process of plasma chemical vapor deposition, the carbon source used is a gaseous carbon source, preferably an alkane and / or olefin, such as methane and / or ethylene; (2) The temperature of the plasma chemical vapor deposition is 500-620℃, for example 500℃, 530℃, 550℃, 560℃, 580℃, 600℃ or 620℃; (3) The plasma chemical vapor deposition time is 1-6 h, for example 1h, 1.5h, 2h, 3h or 4h.

6. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, The chemical vapor deposition of carbon without plasma assistance shall meet one or more of the following conditions: (1) In the plasma-free chemical vapor deposition process, the carbon source used is a gaseous carbon source, preferably an alkyne, such as acetylene and / or phenylacetylene; (2) The temperature for chemical vapor deposition without plasma assistance is 500-650℃, for example 500℃, 550℃, 580℃, 600℃, 610℃ or 620℃. (3) The time for chemical vapor deposition without plasma assistance is 45-300 min, for example 60 min, 80 min, 100 min, 120 min, 150 min or 200 min.

7. The method for preparing the silicon-carbon anode material with a closed-pore structure as described in claim 1, characterized in that, The plasma chemical vapor deposition is performed in a mixed gas atmosphere of gaseous carbon source and inert gas; The volume ratio of the gaseous carbon source to the inert gas is preferably 1:(3-6); the flow rate of the gaseous carbon source is preferably 0.2-4 L / min. And / or, the chemical vapor deposition without plasma assistance is performed in a mixed gas atmosphere of gaseous carbon source and inert gas; The volume ratio of the gaseous carbon source to the inert gas is preferably 1:(3-7); the flow rate of the gaseous carbon source is preferably 0.5-4 L / min.

8. A silicon-carbon anode material with a closed-cell structure prepared by the method for preparing a silicon-carbon anode material with a closed-cell structure as described in any one of claims 1-7.

9. The application of a silicon-carbon anode material with a closed-pore structure as described in claim 8 in a battery.

10. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a silicon-carbon negative electrode material with a closed-pore structure as described in claim 8.

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