CN117577819A - Silicon-carbon composite anode material and preparation method and application thereof - Google Patents

Silicon-carbon composite anode material and preparation method and application thereof Download PDF

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Publication number
CN117577819A
CN117577819A CN202311556912.2A CN202311556912A CN117577819A CN 117577819 A CN117577819 A CN 117577819A CN 202311556912 A CN202311556912 A CN 202311556912A CN 117577819 A CN117577819 A CN 117577819A
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silicon
nano silicon
carbon
nano
composite anode
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成文博
殷营营
刘柏男
罗飞
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Tianmulake Excellent Anode Materials Co Ltd
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Tianmulake Excellent Anode Materials Co Ltd
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    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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    • B22F1/054—Nanosized particles
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    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/12—Metallic powder containing non-metallic particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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    • C01B33/00—Silicon; Compounds thereof
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    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
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    • C01B33/00—Silicon; Compounds thereof
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    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • C01B33/029—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition of monosilane
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a silicon-carbon composite anode material, a preparation method and application thereof, wherein the silicon-carbon composite anode material comprises an inner core and an outer shell; wherein the shell is an amorphous carbon layer; the inner core comprises nano silicon, nano silicon lithium alloy and a porous carbon material; the nano silicon and nano silicon lithium alloy are deposited in the pores of the porous carbon material, the nano silicon lithium alloy supports the skeleton structure of the porous carbon material, and the volume expansion caused by nano silicon is restrained in the charge and discharge process. The nano silicon-lithium alloy can support the skeleton structure of the porous carbon material, so that the skeleton structure of the porous carbon material is not obviously changed in the charge-discharge process, the volume expansion problem caused by nano silicon in the reaction is effectively reduced, and the cycling stability of the lithium ion battery is improved; the coated amorphous carbon layer further slows down the volume expansion of the silicon-carbon composite anode material in the charging and discharging process of the lithium ion battery, thereby further improving the cycling stability of the lithium ion battery.

Description

Silicon-carbon composite anode material and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium ion anode materials, in particular to a silicon-carbon composite anode material and a preparation method and application thereof.
Background
The transformation of energy sources has become a trend that people living irreversibly in the transformation, and lithium ion batteries are a device in the energy storage field, and are attracting attention because of high energy density and multiple charge and discharge. Among them, the negative electrode, which is one of the core materials of the lithium ion battery, is important for improving the performance of the entire device, and therefore, development of a negative electrode material for the lithium ion battery having a high gram capacity and high cycle stability has been a trend.
Traditional carbon materials (such as graphite) are still mainstream lithium ion battery cathode materials in the market at present, and have low gram capacity and cannot meet the requirements of the current lithium ion batteries with high energy density although the traditional carbon materials have good stability.
The silicon-based material is used as a large-class lithium ion battery anode material, has outstanding advantages, not only has high gram capacity, can meet the requirement of high capacity density, but also has rich energy storage, lower price and low cost, and can be used as an important break for replacing a carbon material as an anode material. However, silicon-based anode materials have hindered their large-scale application due to the volumetric expansion effect itself. At present, a coating mode is generally adopted to enhance the interface stability of the silicon-based material, such as coating an amorphous carbon layer on the surface of the silicon-based material, but the volume change rate of the silicon-based material is relatively large, the long-term integrity of the coating layer structure is difficult to maintain, and the silicon-based material still cannot meet the application requirements.
Therefore, the synthesis of a novel silicon-carbon composite anode material with high gram capacity and low volume expansion is urgent to solve the problem of volume expansion of a silicon-based material in the lithium ion electrochemical reaction process.
Disclosure of Invention
The embodiment of the invention provides a silicon-carbon composite anode material, a preparation method and application thereof, wherein the silicon-carbon composite anode material is used for an anode material of a lithium ion battery, so that the problem of volume expansion of a silicon-based material is solved to a certain extent, and the cycling stability of the lithium ion battery is improved.
To this end, in a first aspect, the present invention provides a silicon-carbon composite anode material, the silicon-carbon composite anode material comprising an inner core and an outer shell; wherein the shell is an amorphous carbon layer;
the inner core comprises nano silicon, nano silicon-lithium alloy and a porous carbon material; the nano silicon and the nano silicon lithium alloy are deposited in the pores of the porous carbon material, the nano silicon lithium alloy supports the skeleton structure of the porous carbon material, and the volume expansion caused by the nano silicon is restrained in the charging and discharging process.
Preferably, the mass of the inner core accounts for 90-95% of the mass of the silicon-carbon composite anode material;
the mass of the shell accounts for 5-10% of the mass of the silicon-carbon composite anode material.
Preferably, the particle diameter D50 of the silicon-carbon composite anode material is 4-10 mu m;
the pore diameter of the porous carbon material is 2nm-20nm;
the grain diameter of the nano silicon is 1nm-10nm;
the particle size of the nano silicon lithium alloy is 1nm-10nm;
the amorphous carbon layer has a thickness of 8nm to 12nm.
Preferably, the total mass of the nano silicon and the nano silicon lithium alloy accounts for 30-60% of the mass of the silicon-carbon composite anode material.
In a second aspect, the present invention provides a method for preparing the silicon-carbon composite anode material according to the first aspect, where the preparation method includes:
under the protective atmosphere, placing a porous carbon material and lithium hydride in a reaction furnace, uniformly mixing under the protective atmosphere, heating to a first temperature, and preserving heat for a first time to decompose the lithium hydride to obtain nano lithium, and depositing the nano lithium in pores of the porous carbon material;
under the protective atmosphere, introducing silicon source gas into the reaction furnace at a second temperature, and preserving heat for a second time to decompose the silicon source gas to obtain nano silicon, depositing the nano silicon in pores of the porous carbon material, and performing alloying reaction with nano lithium to generate nano silicon lithium alloy, so as to obtain a porous carbon material loaded with nano silicon and silicon lithium alloy;
and under the protective atmosphere, introducing carbon source gas into the reaction furnace at a third temperature, and preserving heat for a third time to decompose the carbon source gas to obtain carbon, and depositing the carbon source gas on the porous carbon material loaded with nano silicon and nano silicon lithium alloy to obtain the silicon-carbon composite anode material.
Preferably, the mass ratio of the porous carbon material to the lithium hydride is 100:1-10:1.
Preferably, the gas forming the protective atmosphere is one or more of nitrogen and argon;
the silicon source gas comprises one or more of monosilane and disilane;
the carbon source gas comprises one or more of methane, acetylene, ethylene and propylene.
Preferably, the first temperature is 850-1200 ℃, and the first time is 10-50 min;
the second temperature is 200-800 ℃, and the second time is 3-8 h;
the third temperature is 600-1800 ℃, and the third time is 6-15 h.
In a third aspect, the invention provides a negative electrode piece, which comprises the silicon-carbon composite negative electrode material in the first aspect or the silicon-carbon composite negative electrode material prepared by the preparation method in the second aspect.
In a fourth aspect, the invention provides a lithium ion battery, which comprises the negative electrode plate in the third aspect.
The silicon-carbon composite anode material maintains the structural characteristics of a core shell, the inner core is a porous carbon material deposited with nano silicon and nano silicon-lithium alloy, the nano silicon-lithium alloy can support the skeleton structure of the porous carbon material, the skeleton structure of the porous carbon material is ensured not to be obviously changed in the charge-discharge process, the volume expansion problem caused by nano silicon in the reaction is effectively reduced, and the cycling stability of the lithium ion battery is improved; the shell is an amorphous carbon layer, so that the volume expansion of the silicon-carbon composite anode material in the charging and discharging process of the lithium ion battery is further slowed down, and the cycling stability of the lithium ion battery is further improved.
Drawings
The technical scheme of the embodiment of the invention is further described in detail through the drawings and the embodiments.
Fig. 1 is a flowchart of a preparation method of a silicon-carbon composite anode material according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the drawings and the specific examples, which are to be understood as being for the purpose of more detailed description only and are not to be construed as limiting the invention in any way, i.e. not intended to limit the scope of the invention.
The invention provides a silicon-carbon composite anode material, which comprises an inner core and a shell, wherein the shell is amorphous carbon;
the inner core comprises nano silicon, nano silicon lithium alloy and a porous carbon material; the nano silicon and nano silicon lithium alloy are deposited in the pores of the porous carbon material, the nano silicon lithium alloy supports the skeleton structure of the porous carbon material, and the volume expansion caused by nano silicon is restrained in the charging process.
Wherein the mass of the inner core accounts for 90-95% of the mass of the silicon-carbon composite anode material; the mass of the shell accounts for 5-10% of the mass of the silicon-carbon composite anode material; the total mass of the nano silicon and nano silicon lithium alloy accounts for 36-60% of the mass of the silicon-carbon composite anode material.
The particle diameter D50 of the prepared silicon-carbon composite anode material is 4-10 mu m; the pore diameter of the porous carbon material is 2nm-20nm; the particle size of the nano silicon is 1nm-10nm, and the particle size of the nano silicon lithium alloy is 1nm-10nm; the amorphous carbon has a thickness of 8nm to 12nm.
The invention also provides a preparation method of the silicon-carbon composite anode material, which comprises the following steps as shown in figure 1:
step 110, under the protective atmosphere, placing the porous carbon material and lithium hydride in a reaction furnace, uniformly mixing the materials under the protective atmosphere, heating the materials to a first temperature, and preserving the heat for a first time to decompose the lithium hydride to obtain nano lithium, and depositing the nano lithium in pores of the porous carbon material;
wherein the porous carbon material is biomass porous carbon, resin-based porous carbon and the like, and the mass ratio of the porous carbon material to lithium hydride is 100:1-10:1.
The method mainly comprises the steps of chemical vapor deposition, lithium hydride is heated and decomposed to obtain nanoparticles, the nanoparticles are deposited in pores of a porous carbon material, and the specific reaction is as follows:
2LiH(s)→2Li(s)+H 2 (g)。
the gas forming the protective atmosphere is one or more of nitrogen and argon, the flow rate of the gas introduced into the reaction furnace is 10L/min-80L/min, wherein the mixing time is 0.5-2h, the purpose of the gas is to remove oxygen in the raw materials, avoid reaction with hydrogen generated after decomposition of lithium hydride, and the purpose of uniform mixing is to enable nano lithium generated by decomposition of lithium hydride to be uniformly deposited in pores of the porous carbon material.
In the step, the heating rate is 2 ℃/min-8 ℃/min, the first temperature is 850 ℃ -1200 ℃, the first time of heat preservation is 10min-50min, and the purpose of heat preservation is to enable lithium hydride to be fully decomposed.
Step 120, under a protective atmosphere, introducing a silicon source gas into the reaction furnace at a second temperature, and preserving heat for a second time to decompose the silicon source gas to obtain nano silicon, depositing the nano silicon in pores of a porous carbon material, and performing alloying reaction with nano lithium to generate nano silicon lithium alloy, thereby obtaining the porous carbon material loaded with nano silicon and silicon lithium alloy;
in the step, the reaction furnace is cooled in a protective atmosphere, the first temperature of the reaction furnace is reduced to the second temperature, then the silicon source gas is introduced, and the heat preservation is carried out, so that the introduced silicon source gas is heated and fully decomposed to generate nano silicon, and the nano lithium and the nano silicon are subjected to alloying reaction to generate nano silicon lithium alloy. Wherein the second temperature is 200-800 ℃, the cooling rate is 2-8 ℃/min, the second time of heat preservation is 3-8 h, the silicon source gas comprises one or more of monosilane and disilane, and the flow rate ratio of the silicon source gas to the gas forming the protective atmosphere is 10L/min 40L/min, 25L/min 35L/min or 35L/min 25L/min.
The step mainly involves chemical vapor deposition, firstly, the silicon source gas is heated and decomposed to generate nano silicon, and the nano silicon is deposited in the pores of the porous carbon material, and the specific reaction is as follows:
SiH 4 (s)→Si(s)+2H 2 (g)；
Si 2 H 6 (s)→2Si(s)+3H 2 (g)。
and (3) carrying out alloying reaction on nano-lithium in the pores of the nano-silicon and porous carbon material under the heating condition to generate the nano-silicon lithium alloy.
And 130, under a protective atmosphere and at a third temperature, introducing carbon source gas into the reaction furnace, and preserving heat for a third time to decompose the carbon source gas to obtain carbon, and depositing the carbon source gas on a porous carbon material loaded with nano silicon and nano silicon lithium alloy to obtain the silicon-carbon composite anode material.
Wherein the carbon source gas comprises one or more of methane, acetylene, ethylene and propylene, and the flow rate ratio of the gas forming the protective atmosphere to the carbon source gas is 10L/min, 20L/min, 15L/min or 20L/min, 10L/min.
The step also mainly relates to chemical vapor deposition, and is mainly used for realizing carbon coating, specifically, in the step, the temperature of the reaction furnace is firstly reduced or continuously increased under the protection atmosphere, so that the reaction furnace is reduced from the second temperature to the third temperature or increased to the third temperature, then carbon source gas is introduced, and heat preservation is carried out. Wherein the heating rate is 2 ℃/min-8 ℃/min, the cooling rate is 2 ℃/min-8 ℃/min, the third temperature is 600 ℃ to 1800 ℃, the third time of heat preservation is 6h-15h, the purpose of heat preservation is to decompose carbon source gas to generate carbon, and deposit the carbon on a porous carbon material loaded with nano silicon and nano silicon lithium alloy to form an amorphous carbon layer, namely, the porous carbon material loaded with nano silicon and nano silicon lithium alloy is subjected to carbon coating to obtain a silicon-carbon composite anode material, and the specific reaction is as follows:
CH 4 (g)→C(s)+H 2 (g)；
C 2 H 2 (g)→2C(s)+H 2 (g)；
C 2 H 4 (g)→2C(s)+2H 2 (g)；
C 3 H 6 (g)→3C(s)+3H 2 (g)。
in step 120 and step 130, the second temperature and the third temperature are selected according to the actually selected silicon source gas and carbon source gas, respectively.
The silicon-carbon composite anode material prepared by the invention maintains the structural characteristics of a core shell, the core is a porous carbon material deposited with nano silicon and nano silicon-lithium alloy, the nano silicon-lithium alloy can support the skeleton structure of the porous carbon material, the skeleton structure of the porous carbon material is ensured not to be obviously changed in the charge-discharge process, the volume expansion problem caused by nano silicon in the reaction is effectively reduced, and the cycling stability of the lithium ion battery is improved; the shell is an amorphous carbon layer, so that the volume expansion of the silicon-carbon composite anode material in the charging and discharging process of the lithium ion battery is further slowed down, and the cycling stability of the lithium ion battery is further improved.
The silicon-carbon composite anode material provided by the invention can be used for an anode piece and further used in a lithium ion battery.
In order to better understand the technical scheme provided by the invention, the specific process of preparing the silicon-carbon composite anode material by applying the method provided by the embodiment of the invention and the characteristics of the prepared silicon-carbon composite anode material are respectively described in the following specific examples.
First, an embodiment of the present invention is described.
Example 1
Firstly, introducing 40L/min of nitrogen into a reaction furnace for protection, then adding 15kg of porous carbon material and 300g of LiH powder material, and fully mixing the two raw materials for 1h; after 1h, heating is started, the temperature of the reaction furnace is raised to 850 ℃ at a heating rate of 4 ℃/min, and then the reaction furnace is kept for 30min.
Secondly, under the protection of nitrogen, the temperature of the reaction furnace is reduced to 500 ℃ at a cooling rate of 4 ℃/min, monosilane and nitrogen are introduced into the reaction furnace at a gas flow rate of 25L/min to 35L/min, and the heat preservation time is 6h, so that the porous carbon material loaded with nano silicon and nano silicon lithium alloy is obtained.
And thirdly, continuously placing the porous carbon material loaded with the nano silicon and nano silicon lithium alloy in a reaction furnace, heating to 1800 ℃ at a heating rate of 4 ℃/min under the protection of nitrogen, and then introducing acetylene to ensure that the gas flow rate ratio of the nitrogen to the acetylene is 10L/min to 20L/min and the heat preservation time is 7 hours, thereby obtaining the required silicon-carbon composite anode material.
The silicon-carbon composite anode material prepared by the embodiment is used as an anode active material to prepare an anode piece, and the anode piece is assembled into a button cell in a box, and then tested, and the specific process is as follows:
the silicon-carbon composite anode material obtained in the embodiment, acetylene black and carboxymethyl cellulose (CMC) are fully ground in a mortar according to the mass ratio of 9:0.5:0.5, deionized water is added, and then the mixture is pulped in a pulping machine to form slurry, coated on a copper foil current collector and baked in a vacuum oven at 85 ℃ for 10 hours. And then cutting the dried pole piece into a wafer with the diameter of 14mm to be used as a negative pole piece of the lithium ion battery.
Wherein the aqueous electrolyte of the assembled lithium ion battery is 1mol/L lithium hexafluorophosphate (LiPF) 6 ) The solvent of the electrolyte is Ethylene Carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, DMC, DEC is 1:1:1. The diaphragm is a polyethylene diaphragm, and the opposite electrode of the button half cell is a lithium sheet.
Finally, the electrochemical performance of the blue cell was evaluated by performing a test on a blue cell test system. The test conditions were: voltage window: 0.01V-2V; discharge rate: 0.1C; lower limit of discharge voltage window: 0.01V; the instrument used is as follows: scanning electron microscope.
The testing method comprises the following steps: at normal temperature, cutting the prepared negative electrode plate by an ion beam, shooting a Scanning Electron Microscope (SEM) image on a cross section, measuring the thickness of the negative electrode plate, marking as T1, measuring the thickness of a copper foil current collector substrate, marking as T2, under the condition of 0.1C current density, charging a cut-off voltage of 2V, fully charging a button half battery, then disassembling the battery in a glove box, taking out the negative electrode plate, shooting the SEM image again on the cross section after cutting by the ion beam, and measuring the thickness of the negative electrode plate at the moment, marking as T3. Then the first expansion rate is calculated as follows:
the first expansion ratio= (T3-T1)/(T1-T2) ×100%.
The first expansion ratio and the capacity retention ratio of 200 cycles of the prepared coin cell were obtained, and the results are shown in table 1.
Example 2
This example differs from example 1 in that the raw materials charged into the reaction furnace were 15kg of a porous carbon material and 750g of LiH powder material.
The negative electrode sheet was prepared using the silicon carbon composite negative electrode material prepared in this example and assembled into a button cell for testing, and the specific procedure was the same as in example 1, and the results of the initial expansion rate and the capacity retention rate of 200 cycles are shown in table 1.
Example 3
The difference between the examples and example 1 is that the raw materials charged into the reaction furnace were 15kg of a porous carbon material and 1.5kg of LiH powder material.
The silicon-carbon composite anode material prepared in this example was used to prepare an anode sheet and assembled into a button cell for testing, and the specific procedure was the same as in example 1, and the results of the initial expansion rate and the capacity retention rate of 200 cycles are shown in Table 1
Example 4
Firstly, introducing 10L/min of nitrogen into a reaction furnace for protection, then adding 15kg of porous carbon material and 150g of LiH powder material, and fully mixing the two raw materials for 2 hours; after 2 hours, the temperature is raised, the temperature of the reaction furnace is raised to 1200 ℃ at a heating rate of 4 ℃/min, and then the reaction furnace is kept for 10 minutes.
Secondly, under the protection of nitrogen, the temperature of the reaction furnace is reduced to 800 ℃ at a cooling rate of 4 ℃/min, monosilane and nitrogen are introduced into the reaction furnace at a gas flow rate ratio of 10L/min to 40L/min, and the heat preservation time is 3h, so that the porous carbon material loaded with nano silicon and nano silicon lithium alloy is obtained.
And thirdly, continuously placing the porous carbon material loaded with the nano silicon and nano silicon lithium alloy in a reaction furnace, heating to 1800 ℃ at a heating rate of 4 ℃/min under the protection of nitrogen, and introducing acetylene to ensure that the gas flow rate ratio of the nitrogen to the acetylene is 15L/min to 15L/min and the heat preservation time is 15h, so as to obtain the required silicon-carbon composite anode material.
Example 5
Firstly, introducing 80L/min of nitrogen into a reaction furnace for protection, then adding 15kg of porous carbon material and 375g of LiH powder material, and fully mixing the two raw materials for 0.5h; after 0.5h, the temperature is raised, the temperature of the reaction furnace is raised to 900 ℃ at a heating rate of 8 ℃/min, and then the reaction furnace is kept for 50min.
Secondly, under the protection of nitrogen, the temperature of the reaction furnace is reduced to 200 ℃ at a cooling rate of 6 ℃/min, disilane and nitrogen are introduced into the reaction furnace at a gas flow rate of 25L/min to 35L/min, and the heat preservation time is 8 hours, so that the porous carbon material loaded with nano silicon and nano silicon lithium alloy is obtained.
And thirdly, continuously placing the porous carbon material loaded with the nano silicon and nano silicon lithium alloy in a reaction furnace, heating to 1500 ℃ at a heating rate of 8 ℃/min under the protection of nitrogen, and introducing methane to ensure that the gas flow rate ratio of the nitrogen to the acetylene is 20L/min to 10L/min and the heat preservation time is 6h, so as to obtain the required silicon-carbon composite anode material.
Example 6
Firstly, introducing 50L/min of nitrogen into a reaction furnace for protection, then adding 15kg of porous carbon material and 250g of LiH powder material, and fully mixing the two raw materials for 1h; after 1h, heating is started, the temperature of the reaction furnace is raised to 1000 ℃ at a heating rate of 6 ℃/min, and then the temperature is kept for 20min.
Secondly, under the protection of nitrogen, the temperature of the reaction furnace is reduced to 450 ℃ at a cooling rate of 6 ℃/min, monosilane and nitrogen are introduced into the reaction furnace at a gas flow rate of 25L/min to 35L/min, and the heat preservation time is 6h, so that the porous carbon material loaded with nano silicon and nano silicon lithium alloy is obtained.
And thirdly, continuously placing the porous carbon material loaded with the nano silicon and nano silicon lithium alloy in a reaction furnace, heating to 600 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen, and then introducing ethylene to ensure that the gas flow rate ratio of the nitrogen to the acetylene is 10L/min to 20L/min and the heat preservation time is 7 hours, thereby obtaining the required silicon-carbon composite anode material.
Example 7
Firstly, introducing 80L/min of nitrogen into a reaction furnace for protection, then adding 15kg of porous carbon material and 375g of LiH powder material, and fully mixing the two raw materials for 0.5h; after 0.5h, the temperature is raised, the temperature of the reaction furnace is raised to 1100 ℃ at a heating rate of 8 ℃/min, and then the reaction furnace is kept for 10min.
Secondly, under the protection of nitrogen, the temperature of the reaction furnace is reduced to 400 ℃ at a cooling rate of 8 ℃/min, the gas flow rate ratio is 35L/min and 25L/min, disilane and nitrogen are then introduced into the reaction furnace, and the heat preservation time is 5h, so that the porous carbon material loaded with nano silicon and nano silicon lithium alloy is obtained.
And thirdly, continuously placing the porous carbon material loaded with the nano silicon and nano silicon lithium alloy in a reaction furnace, heating to 1000 ℃ at a heating rate of 8 ℃/min under the protection of nitrogen, and introducing propylene to ensure that the gas flow rate ratio of the nitrogen to the acetylene is 20L/min to 10L/min and the heat preservation time is 6h, so as to obtain the required silicon-carbon composite anode material.
The following provides comparative examples for comparison with the examples of the present invention.
Comparative example 1
This comparative example differs from example 1 in that no LiH was used.
The negative electrode tab was prepared using the material prepared in this example and assembled into a button cell for testing, and the specific procedure was the same as in example 1, and the results of the first expansion rate and the capacity retention rate at 200 cycles are shown in table 1.
Comparative example 2
The comparative example differs from example 1 in that no LiH was used, the carbon source gas used in the carbon coating was propylene, and the holding temperature was 1200 ℃.
The negative electrode tab was prepared using the material prepared in this example and assembled into a button cell for testing, and the specific procedure was the same as in example 1, and the results of the first expansion rate and the capacity retention rate at 200 cycles are shown in table 1.
TABLE 1
As can be seen from the data in table 1, the first expansion rate and the capacity retention rate of examples 1-3 are far better than those of comparative examples 1-2, by introducing LiH powder, then depositing nano silicon and nano silicon lithium alloy in pores of a porous carbon material through a chemical vapor deposition technology, and then carbon-coating the porous carbon material loaded with nano silicon and nano silicon lithium alloy to form an amorphous carbon layer, on one hand, the nano silicon lithium alloy can support a skeleton structure of the porous carbon material, so that the skeleton structure of the porous carbon material is not obviously changed any more in the charging and discharging process, the volume expansion problem caused by nano silicon in the reaction is effectively reduced, and the cycling stability of the lithium ion battery is improved; on the other hand, the coated amorphous carbon layer further slows down the volume expansion of the silicon-carbon composite anode material in the charging and discharging process of the lithium ion battery, so that the cycling stability of the lithium ion battery is further improved.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (10)

1. The silicon-carbon composite anode material is characterized by comprising an inner core and an outer shell; wherein the shell is an amorphous carbon layer;
the inner core comprises nano silicon, nano silicon-lithium alloy and a porous carbon material; the nano silicon and the nano silicon lithium alloy are deposited in the pores of the porous carbon material, the nano silicon lithium alloy supports the skeleton structure of the porous carbon material, and the volume expansion caused by the nano silicon is restrained in the charging and discharging process.
2. The silicon-carbon composite anode material according to claim 1, wherein the mass of the inner core is 90% -95% of the mass of the silicon-carbon composite anode material;
the mass of the shell accounts for 5-10% of the mass of the silicon-carbon composite anode material.
3. The silicon-carbon composite anode material according to claim 1, wherein the particle diameter D50 of the silicon-carbon composite anode material is 4 μm to 10 μm;
the pore diameter of the porous carbon material is 2nm-20nm;
the grain diameter of the nano silicon is 1nm-10nm;
the particle size of the nano silicon lithium alloy is 1nm-10nm;
the amorphous carbon layer has a thickness of 8nm to 12nm.
4. The silicon-carbon composite anode material according to claim 1, wherein the total mass of the nano silicon and the nano silicon-lithium alloy is 30% -60% of the mass of the silicon-carbon composite anode material.
5. A method for preparing the silicon-carbon composite anode material according to any one of claims 1 to 4, comprising the steps of:
under the protective atmosphere, placing a porous carbon material and lithium hydride in a reaction furnace, uniformly mixing under the protective atmosphere, heating to a first temperature, and preserving heat for a first time to decompose the lithium hydride to obtain nano lithium, and depositing the nano lithium in pores of the porous carbon material;
under the protective atmosphere, introducing silicon source gas into the reaction furnace at a second temperature, and preserving heat for a second time to decompose the silicon source gas to obtain nano silicon, depositing the nano silicon in pores of the porous carbon material, and performing alloying reaction with nano lithium to generate nano silicon lithium alloy, so as to obtain a porous carbon material loaded with nano silicon and silicon lithium alloy;
and under the protective atmosphere, introducing carbon source gas into the reaction furnace at a third temperature, and preserving heat for a third time to decompose the carbon source gas to obtain carbon, and depositing the carbon source gas on the porous carbon material loaded with the nano silicon and the silicon-lithium alloy to obtain the silicon-carbon composite anode material.
6. The method according to claim 5, wherein the mass ratio of the porous carbon material to the lithium hydride is 100:1 to 10:1.
7. The method according to claim 5, wherein the gas forming the protective atmosphere is one or more of nitrogen and argon;
the silicon source gas comprises one or more of monosilane and disilane;
the carbon source gas comprises one or more of methane, acetylene, ethylene and propylene.
8. The method of claim 5, wherein the first temperature is 850 ℃ to 1200 ℃ and the first time is 10min to 50min;
the second temperature is 200-800 ℃, and the second time is 3-8 h;
the third temperature is 600-1800 ℃, and the third time is 6-15 h.
9. The negative electrode plate is characterized by comprising the silicon-carbon composite negative electrode material according to any one of claims 1-4 or the silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 5-8.
10. A lithium ion battery comprising the negative electrode tab of claim 9.
CN202311556912.2A 2023-11-20 2023-11-20 Silicon-carbon composite anode material and preparation method and application thereof Pending CN117577819A (en)

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