Silicon-carbon negative electrode material and preparation method therefor

Abstract

The present application provides a silicon-carbon negative electrode material and a preparation method therefor. The silicon-carbon negative electrode material comprises: silicon-carbon single particles, wherein the silicon-carbon single particles comprise a carbon matrix and silicon nanoclusters, the carbon matrix comprises a carbon skeleton and pores located inside the carbon skeleton, the silicon nanoclusters are loaded on the carbon skeleton and partially fill the pores, and the atoms of the silicon nanoclusters are cross-linked with each other; a first coating layer, wherein the first coating layer is a silicon-carbon layer and is coated on the surface of the silicon-carbon single particles, and silicon atoms and carbon atoms of the silicon-carbon layer are cross-linked with each other; and a second coating layer, wherein the second coating layer is a carbon layer and is coated on the surface of the first coating layer. The silicon-carbon negative electrode material and the preparation method therefor of the technical solution of the present application can improve the expansion performance when same is used.

Description

Silicon-carbon anode materials and their preparation methods Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a silicon-carbon anode material and its preparation method. Background Technology

[0002] Traditional graphite anode materials can no longer meet the demands of the electric vehicle and aerospace industries for high energy density and long cycle life in lithium-ion batteries. Silicon-based anode materials are attracting significant attention in the current battery market due to their ultra-high theoretical specific capacity and abundant reserves.

[0003] However, in silicon-based anode materials, the alloying reaction between silicon and lithium often causes large volume expansion, leading to the pulverization of the lithium-ion battery anode structure and the continuous formation of a solid electrolyte interface (SEI) on the surface of Si particles. Furthermore, the continuous consumption of lithium during the lithiation / delithiation process also reduces battery capacity. Moreover, silicon as an anode material experiences severe volume expansion and contraction during lithium insertion and extraction, making the material prone to pulverization and detachment from the current collector, resulting in loss of electrochemical performance. These factors significantly limit the practical application of silicon-based anode materials. Due to the structural stability of carbon materials, their volume change during charge and discharge is relatively small, exhibiting good cycle stability. Moreover, their chemical properties are similar to silicon, making silicon and carbon composites a common choice to mitigate the volume expansion effect of silicon and improve its electrochemical stability.

[0004] Currently, the main methods for silicon-carbon composites are: 1) grinding nano-silicon raw materials using a ball mill to form silicon grains with a particle size of about 20 nm, and then coating the surface of the silicon grains with amorphous carbon to form silicon-carbon anode materials. However, this method suffers from problems such as silicon grain agglomeration and easy oxidation of silicon grains, resulting in low initial efficiency; 2) using a chemical vapor infiltration process to decompose gaseous silanes to impregnate amorphous nano-silicon into the pores of porous carbon to generate silicon-carbon anode materials. By depositing nano-silicon in the pores of porous carbon and then adding an oxidizing gas for passivation, the activity of the nano-silicon deposited in the pores can be improved. However, when an oxidizing gas is introduced, the reaction between the nano-silicon and the oxidizing gas is rapidly exothermic, making the reaction process dangerous and difficult to control precisely. Therefore, it is necessary to develop new silicon-carbon anode materials and their preparation methods. Summary of the Invention

[0005] This application provides a silicon-carbon anode material and its preparation method that can reduce volume expansion during lithium intercalation, have low production risk, and low production cost.

[0006] One aspect of this application provides a silicon-carbon anode material, comprising: silicon-carbon single particles, the silicon-carbon single particles comprising a carbon matrix and silicon nanoclusters, the carbon matrix comprising a carbon skeleton and channels located within the carbon skeleton, the silicon nanoclusters being loaded on the carbon skeleton and partially filling the channels, and the atoms of the silicon nanoclusters being cross-linked with each other; a first coating layer, the first coating layer being a silicon-carbon layer, coating the surface of the silicon-carbon single particles, the silicon atoms and carbon atoms of the silicon-carbon layer being cross-linked with each other; and a second coating layer, the second coating layer being a carbon layer, coating the surface of the first coating layer.

[0007] In some embodiments of this application, the carbon framework comprises porous carbon, and the silicon nanoclusters are amorphous.

[0008] In some embodiments of this application, the size of the silicon nanoclusters is 0.1 nm to 5 nm.

[0009] In some embodiments of this application, the porosity of the silicon-carbon single particle is 1% to 30%, and the porosity is the ratio of the remaining volume of the pores to the total volume after silicon nanoclusters are deposited in the pores.

[0010] In some embodiments of this application, the silicon element content in the silicon-carbon anode material is 30 wt.% to 60 wt.%.

[0011] In some embodiments of this application, in the silicon-carbon anode material, the weight percentage of carbon in the second coating layer is greater than 0 wt.% and less than or equal to 10 wt.%, and the weight percentage of carbon in the first coating layer is greater than 0 wt.% and less than or equal to 5 wt.%.

[0012] In some embodiments of this application, the specific surface area of ​​the silicon-carbon anode material is 0.1 m². 2 / g~50m 2 / g. In some embodiments of this application, the median particle size Dv50 of the silicon-carbon anode material is 0.1μm to 50μm.

[0013] In some embodiments of this application, the mass of silicon atoms in the silicon-carbon layer accounts for less than or equal to 10% of the total mass of silicon atoms in the silicon-carbon anode material.

[0014] Another aspect of this application provides a method for preparing a silicon-carbon anode material, comprising: providing a carbon matrix, the carbon matrix including a carbon skeleton and channels located inside the carbon skeleton; using a silicon-containing precursor as a silicon source, depositing silicon nanoclusters by chemical vapor deposition to form silicon-carbon single particles, wherein the silicon nanoclusters are loaded on the carbon skeleton and partially fill the channels, and the atoms of the silicon nanoclusters are cross-linked; providing a first carbon source gas, causing the first carbon source gas to react with the silicon nanoclusters on the surface of the silicon-carbon single particles to form a first coating layer covering the silicon-carbon single particles, the first coating layer being a silicon-carbon layer, and the silicon atoms and carbon atoms of the silicon-carbon layer being cross-linked; and forming a second coating layer on the surface of the first coating layer, the second coating layer being a carbon layer.

[0015] In some embodiments of this application, silicon nanoclusters are deposited by chemical vapor deposition to form silicon-carbon particles at a deposition temperature of 200–700°C and a deposition time of 0.1–10 h.

[0016] In some embodiments of this application, the reaction temperature for forming the first coating layer is 200–800°C; the reaction time is 0.1–5 h.

[0017] In some embodiments of this application, the method for forming the second coating layer includes: introducing a second carbon source gas, reacting at a reaction temperature of 200–700°C for a reaction time of 0.1–5 h; and coating the surface of the first coating layer with the carbon layer.

[0018] In some embodiments of this application, the silicon source includes silane Si. n H 2n+2 At least one of the following, where n is a positive integer, and the first carbon source gas includes at least one of acetylene, methane, ethylene, propane, and propylene.

[0019] In some embodiments of this application, the carbon matrix is ​​porous carbon, and the silicon nanoclusters are amorphous; the particle size of the silicon nanoclusters is 0.1 nm to 5 nm.

[0020] In some embodiments of this application, the silicon element content in the silicon-carbon anode material is 30 wt.% to 60 wt.% by weight; in the silicon-carbon anode material, the carbon element content in the second coating layer is greater than 0 wt.% and less than or equal to 10 wt.%, and the carbon element content in the first coating layer is greater than 0 wt.% and less than or equal to 5 wt.%.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The silicon-carbon anode material provided in this application has silicon nanoclusters whose atoms are cross-linked to form an interconnected network bulk structure, and the silicon nanoclusters are uniformly loaded in the carbon skeleton. Because the bulk structure of the silicon nanoclusters is relatively stable, it is not easily crushed. A silicon-carbon layer is formed on the surface of the silicon-carbon single particles as a first coating layer. The silicon-carbon layer has high hardness, stable chemical properties, and a small coefficient of expansion, which can isolate the silicon nanoclusters from contact with air, reduce the activity of the silicon-carbon single particles, and restrict the volume expansion of the silicon nanoclusters during charge-discharge cycles, thus significantly improving the cycle performance of the silicon-carbon anode material of this application. The second coating layer improves the conductivity of the silicon-carbon anode material of this application, solving the problem of low conductivity of the silicon nanoclusters. Attached Figure Description

[0023] The following accompanying drawings describe in detail the exemplary embodiments disclosed in this application. The same reference numerals denote similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting and exemplary, and the drawings are for illustrative purposes only and are not intended to limit the scope of this application. Other embodiments may similarly fulfill the inventive intent of this application. It should be understood that the drawings are not drawn to scale. Wherein:

[0024] Figure 1 is a process flow diagram of the preparation method of silicon-carbon anode material according to an embodiment of this application;

[0025] Figure 2 is a transmission electron microscope image of the silicon nanoclusters formed in the porous carbon channels of Embodiment 1 of this application;

[0026] Figure 3 is a SEM image of the remaining components of the silicon-carbon anode material formed in Example 1 of this application after the C element is removed by combustion.

[0027] Figures 4A, 4B and 4C are XPS images of the silicon-carbon anode materials formed in Example 1, Comparative Example 2 and Comparative Example 3, respectively.

[0028] Figure 5 is the XRD pattern of the silicon-carbon anode material formed in Example 1;

[0029] Figure 6 shows the cycle performance of lithium-ion battery anodes prepared from silicon-carbon anode materials formed in Examples 1, 2 and 4.

[0030] Figure 7A is a cross-sectional view of the silicon-carbon anode material formed in Embodiment 1 of this application;

[0031] Figure 7B is a cross-sectional view of the silicon-carbon anode material formed in Comparative Example 2. Detailed Implementation

[0032] The following description provides specific application scenarios and requirements for this application, intended to enable those skilled in the art to make and use the content of this application. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0033] In the method of generating silicon-carbon anode materials by impregnating amorphous nano-silicon into the pores of porous carbon using chemical vapor infiltration, an oxidizing gas is added for passivation after the amorphous nano-silicon is deposited in the pores to improve its activity. However, due to the high activity of the amorphous nano-silicon, the reaction between the amorphous nano-silicon and the oxidizing gas after the introduction of the oxidizing gas is rapidly exothermic, making the reaction process dangerous and difficult to control precisely. Furthermore, the amorphous nano-silicon is dispersed in the pores of the porous carbon, with the silicon particles isolated from each other and not connected, resulting in poor structural stability. Therefore, there is a need to provide a silicon-carbon anode material with higher stability and a more easily controllable process, as well as a method for its preparation.

[0034] The silicon-carbon anode material and its preparation method provided in this application embodiment are characterized by the cross-linking of atoms in the silicon nanoclusters to form an interconnected network bulk structure, with the silicon nanoclusters uniformly loaded in the carbon skeleton, making the structure of the silicon-carbon anode material more stable, less prone to cracking, and easier to control the preparation process; using a silicon-carbon layer as the first coating layer, compared with the oxide layer generated by the amorphous nano-silicon and the oxidizing gas, the silicon-carbon layer has higher stability and greater strength, and also inhibits the expansion of silicon material to a certain extent.

[0035] This application provides a silicon-carbon anode material comprising: silicon-carbon single particles, each comprising a carbon matrix and silicon nanoclusters; the carbon matrix comprising a carbon skeleton and channels located within the carbon skeleton; the silicon nanoclusters being loaded on the carbon skeleton and partially filling the channels; and the atoms of the silicon nanoclusters being cross-linked; a first coating layer, which is a silicon-carbon layer coating the surface of the silicon-carbon single particles; and a second coating layer, which is a carbon layer coating the surface of the first coating layer.

[0036] In some embodiments of this application, the carbon matrix includes a carbon framework and channels located within the carbon framework. The channels include micropores with a diameter less than 2 nm, mesopores with a diameter between 2 and 50 nm, and macropores with a diameter greater than 50 nm. The carbon framework comprises porous carbon, for example, where the total volume ratio of mesopores and micropores is greater than 70%, and the surface area is greater than 500 m². 2 / g and the total volume of micropores, mesopores, and pores is greater than 0.4cm³. 3 / g of granular porous carbon.

[0037] The silicon atoms in the silicon nanoclusters are cross-linked to form an interconnected silicon network bulk phase structure. In the embodiments of this application, the silicon nanoclusters are amorphous and supported on the carbon framework of porous carbon. In some embodiments of this application, the particle size of the silicon nanoclusters is 0.1 nm to 5 nm; optionally, the particle size is 0.1 nm to 2 nm, for example, 0.5 nm, 1 nm, 1.2 nm, 1.6 nm, etc.

[0038] The silicon-carbon anode material described in this application forms an interconnected silicon network bulk structure by loading silicon nanoclusters onto the porous carbon carbon skeleton. This network bulk structure is more stable and has greater particle strength.

[0039] The silicon nanoclusters partially fill the channels. In some embodiments of this application, the porosity of the channels in the silicon-carbon single particles is 1% to 30%, where porosity is the proportion of the remaining volume of the channels after the silicon nanoclusters are deposited within them to the total volume; that is, the silicon nanoclusters fill 70% to 99% of the channels. The porosity... Where m si m c V0 and V0 represent the mass of silicon in the silicon-carbon single particle, the mass of carbon in the silicon-carbon single particle, and the pore volume of the porous carbon, respectively. The true density of carbon is 2.1, and the density of silicon is 2.33.

[0040] In this embodiment, after the silicon nanoclusters fill the channels, the channels can be completely closed, completely open, or semi-closed. The carbon framework retains a certain amount of porosity, which can significantly reduce the expansion rate of the formed silicon-carbon anode material.

[0041] In some embodiments of this application, the silicon element content in the silicon-carbon anode material is 30 wt.% to 60 wt.%, preferably 40 wt.% to 55 wt.%, such as 45 wt.%, 50 wt.%, etc.

[0042] In some embodiments of this application, the specific surface area of ​​the silicon-carbon anode material is 0.1 m². 2 / g~50m 2 / g, preferably 1m 2 / g~40m 2 / g, for example 5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、30m 2 / g etc.

[0043] In some embodiments of this application, the median particle size Dv50 of the silicon-carbon anode material is 0.1 μm to 50 μm, preferably 0.1 μm to 10 μm.

[0044] The silicon-carbon anode material described in this embodiment further includes a first coating layer, which is a silicon-carbon layer covering the surface of the silicon-carbon single particles. The silicon-carbon layer is, for example, amorphous silicon carbide cross-linked with silicon-carbon bonds. Silicon carbide has high hardness, stable chemical properties, and a small coefficient of expansion. By coating the surface of the silicon-carbon single particles with a layer of silicon carbide, the silicon nanoclusters are isolated from air, preventing the silicon atoms in the silicon nanoclusters from being oxidized and reducing the activity of the silicon-carbon single particles. Simultaneously, the silicon carbide encapsulates the silicon nanoclusters, limiting the volume expansion of silicon in the battery prepared using the silicon-carbon anode material during charge-discharge cycles, significantly improving the cycle performance of the material.

[0045] In some embodiments of this application, the percentage of silicon atoms in the silicon-carbon layer relative to the total mass of silicon atoms in the silicon-carbon anode material is less than or equal to 10%. Let the percentage of silicon atoms in the silicon-carbon layer relative to the total mass of silicon atoms in the silicon-carbon anode material be denoted as... but

[0046] in, Where m si m c p 真 V1 si V0 refers to the mass of silicon in the silicon-carbon layer, the mass of carbon in the silicon-carbon layer, the true density of the silicon-carbon anode material, the pore volume of the silicon-carbon anode material, and the pore volume of porous carbon, respectively.

[0047] The silicon-carbon anode material described in this embodiment further includes a second coating layer, which is a carbon layer covering the surface of the first coating layer. The carbon layer is, for example, amorphous carbon. Preferably, the carbon content of the second coating layer is 0 wt.% to 10 wt.%.

[0048] Referring to Figure 1, the preparation method of the silicon-carbon anode material according to an embodiment of this application includes the following steps:

[0049] Step S1: Provide a carbon matrix comprising a carbon framework and channels within the carbon framework. Using a silicon-containing precursor as the silicon source, deposit silicon nanoclusters within the channels using a chemical vapor deposition process to form silicon-carbon single particles. The silicon nanoclusters are loaded onto the carbon framework and partially fill the channels, and the atoms of the silicon nanoclusters are cross-linked. The silicon source is SinH₂n. +2(n is a positive integer) can include at least one silicon source such as silane, silane, propane, and butane. The deposition temperature for forming silicon-carbon single particles is 200–700°C, and the deposition time is 0.1–10 h.

[0050] In some embodiments of this application, the carbon matrix has a total volume ratio of mesopores and micropores greater than 70% and a surface area greater than 500 m². 2 / g and the total volume of micropores, mesopores, and pores is greater than 0.4cm³. 3 / g of granular porous carbon, wherein the silicon precursor is silane, the porous carbon is placed in the reaction chamber of a chemical deposition apparatus, silane is introduced into the reaction chamber, and the silane reacts with the porous carbon at a temperature of 650 degrees Celsius for 8 hours, thereby generating silicon nanoclusters in the pores and on the surface of the porous carbon, thus preparing the silicon-carbon single particles.

[0051] In other embodiments of this application, a mixture of silane and propane is used as the silicon source, and reacted with porous carbon at 600°C for 9 hours to generate silicon nanoclusters within the pores and on the surface of the porous carbon, thereby preparing the silicon-carbon single particles. The silicon source may also be mixed with inert gases such as nitrogen.

[0052] In some embodiments of this application, the size of the silicon nanoclusters is 0.1 nm to 5 nm. Optionally, the size of the silicon nanoclusters is 0.1 nm to 2 nm, such as 0.5 nm, 1 nm, 1.2 nm, 1.6 nm, etc. In some embodiments of this application, the porosity of the channels in the silicon-carbon single particles is 1% to 30%, and the porosity is the proportion of the remaining volume of the channels to the total volume after the silicon nanoclusters are deposited in the channels.

[0053] Step S2: A first carbon source gas is provided, which reacts with the silicon nanoclusters on the surface of the silicon-carbon single particle to form a first coating layer covering the silicon-carbon single particle. The first coating layer is a silicon-carbon layer, in which silicon atoms and carbon atoms are cross-linked. The first carbon source gas includes at least one of acetylene, methane, ethylene, propane, and propylene. The reaction temperature is 200–800°C; the reaction time is 0.1–5 hours.

[0054] In some embodiments of this application, the chemical vapor deposition equipment in step S1 is continued to be used, the first carbon source gas propylene is introduced into the reaction chamber, the temperature in the reaction chamber is adjusted to 700°C, and the reaction is carried out for 4 hours. The first carbon source gas reacts with the silicon atoms in the silicon nanoclusters on the surface of the silicon-carbon single particle to generate an amorphous silicon-carbon layer cross-linked by C-Si bonds.

[0055] In some other embodiments of this application, a mixture of ethylene and propane is used as the first carbon source gas, the temperature in the reaction chamber is adjusted to 600°C, and the reaction is carried out for 4.5 hours. The first carbon source gas reacts with silicon atoms in the silicon nanoclusters on the surface of the silicon-carbon single particle to generate an amorphous silicon-carbon layer cross-linked by C-Si bonds.

[0056] Step S3: A second coating layer, which is a carbon layer, is formed on the surface of the first coating layer. The method for forming the second coating layer includes: introducing a second carbon source gas and coating the carbon layer onto the surface of the first coating layer at a reaction temperature of 200–700°C to prepare the silicon-carbon anode material described in this application. The second carbon source gas includes at least one of acetylene, methane, ethylene, propane, and propylene.

[0057] In some embodiments of this application, a second carbon source gas, methane, is introduced into the reaction chamber, the temperature inside the reaction chamber is adjusted to 700°C, and the reaction is carried out for 3 hours, thereby coating the surface of the first coating layer with the carbon layer. In still other embodiments of this application, a second carbon source gas (a mixture of acetylene, methane, and ethylene) is introduced into the reaction chamber, the temperature inside the reaction chamber is adjusted to 700°C, and the reaction is carried out for 3 hours, thereby coating the surface of the first coating layer with the carbon layer.

[0058] In some embodiments of this application, the silicon element content in the silicon-carbon anode material is 30 wt.% to 60 wt.%, preferably 40 wt.% to 55 wt.%, such as 45 wt.%, 50 wt.%, etc.

[0059] In some embodiments of this application, the specific surface area of ​​the silicon-carbon anode material is 0.1 m². 2 / g~50m 2 / g, preferably 1m 2 / g~40m 2 / g, for example 5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、30m 2 / g etc.

[0060] In some embodiments of this application, the median particle size Dv50 of the silicon-carbon anode material is 0.1 μm to 50 μm, preferably 0.1 μm to 10 μm.

[0061] Example 1

[0062] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 550℃. Inert gas is introduced to purge air, and a mixture of silane and nitrogen (silane to nitrogen gas flow ratio of 2:8) is introduced as the silicon source for chemical vapor deposition. Silicon nanoclusters are deposited within the pores of the porous silicon for 10 hours to obtain silicon-carbon single particles. Referring to Figure 2, a transmission electron microscope image of the silicon nanoclusters formed within the pores is shown. Figure 2 shows that the silicon nanoclusters are dispersed within the carbon framework pores, and the atoms of the silicon nanoclusters are cross-linked to form an interconnected silicon network bulk phase structure.

[0063] Step S2: Control the temperature of the fluidized bed at 650℃, introduce acetylene as the first carbon source gas, and the ratio of acetylene to nitrogen is 1:100. Deposit for 1 hour to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0064] Step S3: Control the temperature of the fluidized bed at 600℃, introduce acetylene as the second carbon source gas, and the ratio of acetylene to nitrogen is 10:100. Deposit for 1 hour to form a carbon layer on the surface of the silicon-carbon layer as the second coating layer to obtain the silicon-carbon anode material.

[0065] Figure 3 is an SEM image of the remaining components of the silicon-carbon anode material formed in Example 1 of this application after the carbon element is removed by combustion. As can be seen from the figure, the entire particle still maintains its complete morphology, indicating that the silicon nanoclusters exist in a cross-linked form rather than a monodisperse state. Even if the carbon is removed by combustion, the silicon can still maintain its complete particle morphology.

[0066] Example 2

[0067] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 500°C. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition. Silicon nanoclusters are deposited in the pores of the porous silicon for 5 hours to obtain silicon-carbon single particles.

[0068] Step S2: Control the temperature of the fluidized bed at 750℃, introduce acetylene as the first carbon source gas, and the ratio of ethylene to nitrogen is 1:100. Deposition for 3 hours to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0069] Step S3: Control the temperature of the fluidized bed at 700℃, introduce acetylene as the second carbon source gas, the ratio of acetylene to nitrogen is 10:100, deposit for 3 hours, and form a carbon layer on the surface of the silicon-carbon layer as the second coating layer.

[0070] Example 3

[0071] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 600℃. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition process. Silicon nanoclusters are deposited in the pores of porous silicon for 8 hours to obtain silicon-carbon single particles.

[0072] Step S2: Control the temperature of the fluidized bed at 700℃, introduce acetylene as the first carbon source gas, and the ratio of propane to nitrogen is 1:100. Deposit for 3 hours to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0073] Step S3: Control the temperature of the fluidized bed at 650℃, introduce methane as the second carbon source gas, and the ratio of methane to nitrogen is 10:100. Deposit for 5 hours to form a carbon layer on the surface of the silicon-carbon layer as the second coating layer.

[0074] Example 4

[0075] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 400℃. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition process. Silicon nanoclusters are deposited in the pores of porous silicon for 3 hours to obtain silicon-carbon single particles.

[0076] Step S2: Control the temperature of the fluidized bed at 700℃, introduce propane as the first carbon source gas, and the ratio of propane to nitrogen is 1:100. Deposit for 1 hour to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0077] Step S3: Control the temperature of the fluidized bed at 650℃, introduce propane as the second carbon source gas, and the ratio of propane to nitrogen is 10:100. Deposit for 1 hour to form a carbon layer on the surface of the silicon-carbon layer as the second coating layer.

[0078] Example 5

[0079] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 550°C. Inert gas is introduced to remove air, and a mixture of silane and disilane in a 1:1 ratio is introduced as the silicon source (the ratio of silane to nitrogen gas flow is 2:8). Chemical vapor deposition is performed to deposit silicon nanoclusters in the pores of the porous silicon. The deposition time is 10 hours, and silicon-carbon single particles are obtained.

[0080] Step S2: Control the temperature of the fluidized bed at 600℃, introduce acetylene as the first carbon source gas, and the ratio of propylene to nitrogen is 1:100. Deposition for 5 hours to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0081] Step S3: Control the temperature of the fluidized bed at 550℃, introduce acetylene as the second carbon source gas, and the ratio of acetylene to nitrogen is 10:100. Deposit for 5 hours to form a carbon layer on the surface of the silicon-carbon layer as the second coating layer.

[0082] Comparative Example 1

[0083] Silicon-carbon anode material is prepared by performing steps S1 and S2 according to the method of Example 1, but step S3 is not performed.

[0084] Comparative Example 2

[0085] Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 550°C. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition. Silicon nanoclusters are deposited in the pores of the porous silicon for 10 hours to obtain silicon-carbon single particles.

[0086] The temperature of the fluidized bed was controlled at 550℃, and acetylene was introduced as the second carbon source gas. The ratio of acetylene to nitrogen was 10:100. After deposition for 1 hour, a carbon layer was formed on the surface of the silicon-carbon single particle as the second coating layer to obtain the silicon-carbon anode material.

[0087] Comparative Example 3

[0088] Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 550°C. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition. Silicon nanoclusters are deposited in the pores of the porous silicon for 10 hours to obtain silicon-carbon single particles.

[0089] Comparative Example 4

[0090] Step S1: Porous carbon particles are fed into a fluidized bed, the temperature of which is controlled at 550°C. Inert gas is introduced to remove air, and mixed silane is introduced as a silicon source (silane and nitrogen gas flow ratio is 2:8) to perform chemical vapor deposition process. Silicon nanoclusters are deposited in the pores of porous silicon for 15 hours to obtain silicon-carbon single particles.

[0091] Step S2: Control the temperature of the fluidized bed at 650℃, introduce acetylene as the first carbon source gas, and the ratio of acetylene to nitrogen is 1:100. Deposit for 1 hour to form a silicon carbide protective layer as the first coating layer on the surface of silicon-carbon single particles.

[0092] Step S3: Control the temperature of the fluidized bed at 600℃, introduce acetylene as the second carbon source gas, and the ratio of acetylene to nitrogen is 10:100. Deposit for 1 hour to form a carbon layer on the surface of the silicon-carbon layer as the second coating layer to obtain the silicon-carbon anode material.

[0093] Figures 4A, 4B, and 4C are XPS images of the silicon-carbon anode materials formed in Example 1, Comparative Example 2, and Comparative Example 3, respectively. The figures show that silicon in the silicon-carbon anode material formed in Example 1 mainly exists as elemental Si and Si-C-Si; while silicon in the silicon-carbon single particles formed in Comparative Example 3 mainly exists as elemental Si and Si-O, verifying the absence of a first and second coating layer; the XPS of the silicon-carbon anode material formed in Comparative Example 2 clearly shows the absence of Si-C-Si, with only elemental Si present. This is because the silicon-carbon anode material in Comparative Example 2 lacks a first coating layer. A comparison of Figures 4C and 4A reveals the difference between silicon-carbon anode materials with and without a first coating layer: silicon-carbon anode materials without a first coating layer show significant oxidation after being exposed to air for a period of time, with a noticeable increase in oxygen content.

[0094] Figure 5 shows the XRD pattern of the silicon-carbon anode material formed in Example 1. As can be seen from the figure, the silicon carbide layer exists in an amorphous form, rather than in a crystalline form.

[0095] Figure 6 shows the cycle performance of lithium-ion battery anodes prepared from silicon-carbon anode materials formed in Examples 1, 2 and 4 (where AS6-1 corresponds to Example 1, AS6-2 corresponds to Example 1, and AS6-4 corresponds to the data in Example 1). As can be seen from the figure, the cycle performance of the silicon-carbon anode material improves with the increase of the silicon carbide layer coating time, indicating that the silicon carbide layer has a significant effect on improving the overall cycle performance of the material.

[0096] Figure 7A is a cross-sectional view of the silicon-carbon anode material formed in Example 1 of this application; Figure 7B is a cross-sectional view of the silicon-carbon anode material formed in Comparative Example 2. It can be seen from the figures that the electrodes formed from the two silicon-carbon anode materials have the same compaction density (1.2 g / cm³). 3 In Comparative Example 2, no silicon carbide layer was formed on the surface of the silicon-carbon single particles, so the particles in Comparative Example 2 were more prone to cracking, with obvious cracking of multiple particles; while no particle cracking was found in Example 1 of this application, indicating that when the surface of the silicon-carbon single particles is coated with a silicon carbide layer, the silicon-carbon anode material particles have better pressure resistance.

[0097] Table 1 presents the test results of different silicon-carbon anode materials formed in Examples 1-5 and Comparative Examples 1-4 of this application. The test data includes the silicon nanocluster content in the silicon-carbon anode material, the atomic size of the silicon nanoclusters, the porosity of the silicon-carbon single particles, the weight percentage of carbon in the first and second coating layers (double-layer carbon coating amount), the specific surface area of ​​the silicon-carbon anode material, and the percentage of the mass of silicon atoms in the silicon-carbon layer to the total mass of silicon atoms in the silicon-carbon anode material. The embodiments and comparative examples of this application show the capacity, charge / discharge efficiency, and capacity retention of the silicon-carbon anode materials used to fabricate the batteries. Table 1 shows that as the deposition time for forming silicon nanoclusters increases, the weight percentage of silicon in the silicon-carbon anode material increases, and the capacity of the final silicon-carbon anode material also increases. Comparing Example 1 and Comparative Example 1 shows that without the second coating layer, the cycle performance of the silicon-carbon anode material deteriorates. Similarly, Example 1 and Comparative Example 2 show that without the first coating layer, the cycle performance of the silicon-carbon anode material deteriorates.

[0098] As can be seen from Example 1 and Comparative Example 4, the silicon deposition was excessive; the P value was too low. If the value is too high, the capacity efficiency and cycle performance of the material will be significantly reduced.

[0099] Finally, it should be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments of this application. Other modified embodiments are also within the scope of this application. Therefore, the embodiments disclosed herein are merely examples and not limitations. Those skilled in the art can implement the applications in this application by adopting alternative configurations based on the embodiments in this application. Therefore, the embodiments of this application are not limited to those embodiments precisely described in the application.

Claims

1. A silicon-carbon anode material, characterized in that, include: Silicon-carbon single particles, wherein the silicon-carbon single particles comprise a carbon matrix and silicon nanoclusters, the carbon matrix comprising a carbon skeleton and channels located within the carbon skeleton, the silicon nanoclusters being loaded on the carbon skeleton and partially filling the channels, and the atoms of the silicon nanoclusters being cross-linked with each other; The first coating layer is a silicon-carbon layer that coats the surface of the silicon-carbon single particle, and the silicon atoms and carbon atoms of the silicon-carbon layer are cross-linked with each other. The second coating layer, which is a carbon layer, covers the surface of the first coating layer.

2. The silicon-carbon anode material according to claim 1, characterized in that, The carbon matrix is ​​porous carbon, and the silicon nanoclusters are amorphous.

3. The silicon-carbon anode material according to claim 2, characterized in that, The silicon nanoclusters have a particle size of 0.1 nm to 5 nm.

4. The silicon-carbon anode material according to claim 1, characterized in that, The porosity of the silicon-carbon single particle is 1% to 30%, and the porosity is the ratio of the remaining volume of the pores to the total volume after silicon nanoclusters are deposited in the pores.

5. The silicon-carbon anode material according to claim 1, characterized in that, The silicon-carbon anode material contains 30 wt.% to 60 wt.% silicon by weight.

6. The silicon-carbon anode material according to claim 5, characterized in that, In the silicon-carbon anode material, the weight percentage of carbon in the second coating layer is greater than 0 wt.% and less than or equal to 10 wt.%, and the weight percentage of carbon in the first coating layer is greater than 0 wt.% and less than or equal to 5 wt.%.

7. The silicon-carbon anode material according to claim 1, characterized in that, The specific surface area of ​​the silicon-carbon anode material is 0.1 m². 2 / g~50m 2 / g, the median particle size of the silicon-carbon anode material is 0.1μm to 50μm.

8. The silicon-carbon anode material according to claim 1, characterized in that, The percentage of silicon atoms in the silicon-carbon layer relative to the total mass of silicon atoms in the silicon-carbon anode material is less than or equal to 10%.

9. A method for preparing a silicon-carbon anode material, characterized in that, include: A carbon matrix is ​​provided, the carbon matrix including a carbon skeleton and channels located inside the carbon skeleton. Using a silicon-containing precursor as a silicon source, silicon nanoclusters are deposited by chemical vapor deposition to form silicon-carbon single particles. The silicon nanoclusters are loaded on the carbon skeleton and partially fill the channels, and the atoms of the silicon nanoclusters are cross-linked with each other. A first carbon source gas is provided, which reacts with the silicon nanoclusters on the surface of the silicon-carbon single particle to form a first coating layer covering the silicon-carbon single particle. The first coating layer is a silicon-carbon layer, and the silicon atoms and carbon atoms of the silicon-carbon layer are cross-linked with each other. A second coating layer is formed on the surface of the first coating layer, and the second coating layer is a carbon layer.

10. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The deposition temperature for silicon nanoclusters to form silicon-carbon particles via chemical vapor deposition is 200–700°C, and the deposition time is 0.1–10 h.

11. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The reaction temperature for forming the first coating layer is 200–800°C; the reaction time is 0.1–5 h.

12. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The method for forming the second coating layer includes: introducing a second carbon source gas, reacting at a reaction temperature of 200 to 700°C for a reaction time of 0.1 to 5 hours; and coating the surface of the first coating layer with the carbon layer.

13. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The silicon source includes silane (Si). n H 2n+2 At least one of the following, where n is a positive integer.

14. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The first carbon source gas includes at least one of acetylene, methane, ethylene, propane, and propylene.

15. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The carbon matrix is ​​porous carbon, and the silicon nanoclusters are amorphous; the particle size of the silicon nanoclusters is 0.1 nm to 5 nm.

16. The method for preparing the silicon-carbon anode material according to claim 9, characterized in that, The silicon-carbon anode material has a silicon content of 30 wt.% to 60 wt.% by weight; in the silicon-carbon anode material, the carbon content in the second coating layer is greater than 0 wt.% and less than or equal to 10 wt.%, and the carbon content in the first coating layer is greater than 0 wt.% and less than or equal to 5 wt.%.

Images