CN117374239A - Silicon-carbon negative electrode material, battery negative electrode, battery and preparation method thereof - Google Patents
Silicon-carbon negative electrode material, battery negative electrode, battery and preparation method thereof Download PDFInfo
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- CN117374239A CN117374239A CN202311246513.6A CN202311246513A CN117374239A CN 117374239 A CN117374239 A CN 117374239A CN 202311246513 A CN202311246513 A CN 202311246513A CN 117374239 A CN117374239 A CN 117374239A
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- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 title claims abstract description 100
- 239000007773 negative electrode material Substances 0.000 title claims abstract description 78
- 238000002360 preparation method Methods 0.000 title claims abstract description 30
- 239000011148 porous material Substances 0.000 claims abstract description 143
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 94
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 88
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 79
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 79
- 239000010703 silicon Substances 0.000 claims abstract description 79
- 230000008021 deposition Effects 0.000 claims abstract description 73
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/24—Deposition of silicon only
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
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- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- 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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- H—ELECTRICITY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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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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- 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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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a preparation method of a silicon-carbon negative electrode material, which uses a porous carbon material as a substrate, and carries out surface carbon coating after staged silicon source deposition; staged silicon source deposition includes: in the first stage, the temperature in the reactor is controlled to be 300-800 ℃, the initial pressure is controlled to be 10-30 Kpa, and the flow rate of the introduced feed gas is controlled to be 2-10L/min; when the pressure in the reactor starts to drop to enter the next stage; in the second stage, the initial pressure in the reactor is adjusted to 5-8 Kpa, and the flow rate of the introduced feed gas is adjusted to 8-20L/min; the deposition ends when the pressure in the reactor begins to rise. The invention obviously improves the utilization rate of the pore structure of the porous carbon substrate by carrying out the staged silicon deposition process and accurately regulating and controlling the deposition process parameters of each stage, so that the prepared negative plate prepared by the silicon-carbon negative electrode material is assembled into the battery, and the battery has excellent initial capacity, initial efficiency and cycle stability.
Description
Technical Field
The invention relates to the technical field of negative electrode materials, in particular to a silicon-carbon negative electrode material, a battery negative electrode, a battery and a preparation method thereof.
Background
Silicon is the anode material with the maximum theoretical capacity at present, the specific capacity is up to 4200mAh/g, which is far higher than the theoretical capacity of graphite (the theoretical capacity of graphite anode material is only 372 mAh/g), and silicon has the advantages of low lithium intercalation potential and low cost, and is expected to replace graphite to become the anode material of next generation lithium ion battery. However, silicon as a negative electrode material undergoes serious volume expansion and shrinkage during lithium intercalation and deintercalation, which results in easy pulverization and stripping of the material from a current collector, and loss of electrochemical performance.
Because of the structural stability of the carbon material, the volume change is relatively small in the charge and discharge process, the carbon material has better circulation stability, and is similar to silicon in chemical property, and silicon and carbon are often compounded, so that the purposes of improving the volume expansion effect of the silicon and improving the electrochemical stability of the silicon are achieved. The method for preparing the silicon-carbon composite material is that silicon is deposited on a porous carbon material by chemical vapor deposition. However, in the chemical vapor deposition process, if fine regulation and control of the process are not performed, a large amount of silicon is deposited on the surface of the porous carbon, the pore structure of the porous carbon has low utilization rate, so that the surface of the porous carbon has a silicon-rich phenomenon, and the permeation of electrolyte and the diffusion of lithium ions are seriously hindered, thereby influencing the electrochemical performance of the battery; the nano silicon enriched on the surface reacts with lithium to generate alloy, so that the volume of the material is expanded, the porous carbon structure is damaged and destabilized, particles of the electrode material are aggregated and disintegrated, and the cycle stability and capacity retention rate of the electrode are greatly reduced. In addition, the enrichment of silicon may also lead to uneven charge distribution on the surface of the material, increasing the interface impedance between the electrode and the electrolyte, further affecting the electrochemical performance of the cell.
A silicon carbon composite material comprising ultra low Z and a process related thereto is disclosed in US patent No. US20230219819 A1. The scheme is selected and optimized from the aspects of preparation and selection of the porous support, doping and modification of the porous support, a composite mode of nano silicon and the porous support and the like, and the silicon-carbon anode material with high stability is prepared. The technical scheme takes the selection of process raw materials and a composite mode as a main starting point, ensures that silicon is deposited into porous carbon, effectively avoids enrichment of silicon on the surface of the porous carbon, and provides a method for indirectly judging the deposition position of the silicon through thermal gravimetric analysis quality change, wherein the judgment formula is Z=1.875× [ (M1100-M800)/M1100 ] ×100%.
The application publication number CN116111065A discloses a silicon-carbon negative electrode material, a preparation method of the silicon-carbon negative electrode material and a lithium ion battery, wherein nano silicon is deposited in holes of porous carbon under the action of inorganic salt and cannot fall on the surface of the porous carbon material, so that the volume expansion of the silicon in the lithium storage process is greatly reduced; and the nano silicon is not deposited on the surface of the porous carbon, so that the carbon coating layer is more uniform, and the cycle performance and the rate capability of the anode material are improved.
The two preparation methods are used for controlling the deposition of the nano silicon from the aspects of raw material selection, substrate modification and the like, and other hetero atoms except silicon and carbon are required to be introduced, so that the precise deposition of the nano silicon cannot be realized directly from the process angle; the introduction of the hetero atoms can improve the silicon-carbon binding capacity or the conductivity and simultaneously cause the structural damage of the silicon-carbon negative electrode, so that the silicon-carbon negative electrode does not have long-term circulation stability. And even if more silicon is deposited into the porous carbon, uniform distribution of the deposition cannot be achieved, which results in a decrease in the cycle stability.
Therefore, how to effectively control the deposition position of nano silicon from the process angle, ensure the utilization rate of the pore structure of the porous carbon substrate, improve the uniformity of silicon deposition and prepare the high-performance silicon-carbon anode material is a technical problem which needs to be solved urgently.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a preparation method of a silicon-carbon anode material, which is used for remarkably improving the utilization rate of the pore structure of a porous carbon substrate by carrying out staged silicon deposition process and accurately regulating and controlling deposition process parameters of each stage so as to prepare a lithium ion battery assembled by the silicon-carbon anode material, and has excellent initial capacity, initial efficiency and cycle stability.
The specific technical scheme is as follows:
the preparation method of the silicon-carbon anode material comprises the following steps:
taking a porous carbon material as a substrate, depositing nano silicon particles in holes of the porous carbon material after staged silicon source deposition, and coating surface carbon to obtain the high-performance silicon-carbon negative electrode material;
the staged silicon source deposition uses silicon source gas as raw material gas for vapor deposition, and comprises the following steps:
in the first stage, the temperature in the reactor is controlled to be 300-800 ℃, the initial pressure is controlled to be 10-30 Kpa, and the flow rate of the introduced feed gas is controlled to be 2-10L/min; when the pressure in the reactor starts to drop and the pressure change value is 10-70% of the initial pressure, entering the next stage;
in the second stage, the initial pressure in the reactor is adjusted to 5-8 Kpa, and the flow rate of the introduced feed gas is adjusted to 8-20L/min; ending the deposition when the pressure in the reactor starts to rise and the pressure change value is 10-70% of the initial pressure.
According to the preparation method disclosed by the invention, the silicon deposition process is carried out in stages and the deposition process parameters of each stage are accurately regulated and controlled, so that the efficient deposition of nano silicon can be carried out in pore structures with different sizes in the porous carbon material, the utilization rate of the pore structure of the porous carbon material is improved, the nano silicon is ensured to be uniformly deposited in the pores of the porous carbon material and not to fall on the surface of the porous carbon material, the domain limiting effect of the porous carbon is fully exerted, and the electrochemical performance of a silicon carbon negative electrode is improved; meanwhile, the high-efficiency deposition can effectively avoid the gas production phenomenon in the subsequent process, and ensure the safety of the whole process.
Experiments show that compared with the traditional one-time deposition, the staged silicon source deposition disclosed by the invention can enable the deposited nano silicon particles to be distributed more uniformly under the condition of a corresponding deposition amount, and the utilization rate of a pore structure is obviously improved; the lithium ion battery assembled by the silicon-carbon negative electrode material prepared by the preparation method disclosed by the invention has more excellent cycling stability, reversible specific capacity and initial effect.
It has also been found through experiments that if the two-stage deposition sequence is exchanged, or the regulation of the process parameters in each stage of deposition is no longer within the above-defined range, the electrochemical performance of the lithium ion battery assembled by the prepared silicon-carbon negative electrode material can be degraded, including the influence on capacity, initial efficiency and cycle stability. The above-mentioned effects may be due to poor control of deposition parameters, resulting in low utilization of pore structures or uneven deposition of nano-silicon, even enrichment on porous carbon surfaces, etc. Therefore, only by adopting the staged deposition sequence disclosed by the invention and accurately regulating and controlling the deposition process parameters of each stage, the pore structure utilization rate of the porous carbon substrate can be remarkably improved, and the lithium ion battery with excellent initial capacity, initial efficiency and cycle stability can be assembled.
Preferably:
the SPAN value of the porous carbon material is less than 1.5, and the D50 value is 4-10 mu m;
the specific surface area of the porous carbon material is 1200-2000 m 2 Per gram, the average pore diameter is 1.5-5.0 nm, the pore volume is 0.6-2.0 cm 3 And/g, wherein the aperture concentration is 0.03-1.0, and the calculation formula is as follows:
p: pore volume;
P all : total pore volume;
d max* ：P>a maximum pore diameter of 0.005;
d min* ：P>a minimum pore size of 0.005.
Experiments show that the preparation process disclosed by the invention has good adaptability to porous carbon materials with different specific surface areas, average pore diameters, pore volumes and pore concentration, the purpose of improving the pore structure utilization rate of the porous carbon materials to the greatest extent can be achieved by accurately controlling the parameters of two-stage deposition in the sectional deposition mode disclosed by the invention, and the pore structure utilization rate can reach more than 98%.
However, based on the volume expansion rate at different silicon deposition amounts and different influences on the initial specific capacity and initial efficiency of the assembled battery, it is preferable to use a specific surface area of 1500 to 2000m 2 Per gram, the average pore diameter is 1.5-3.0 nm, and the pore volume is 0.8-1.6 cm 3 The porous carbon material per gram is used as a substrate. Experiments show that the porous carbon material with the apparent parameters is used as a substrate, and under the condition of ensuring the utilization rate of a pore structure of more than 98%, the silicon deposition amount in the prepared silicon-carbon composite material can be controlled to be 50-55wt%, and the assembled lithium ion battery has high specific capacity, high initial efficiency and high cycle stability.
The preparation method comprises the following steps:
the silicon source gas is selected from one or more of monosilane, disilane, dichlorosilane and trichlorosilane;
the raw material gas is a mixed gas comprising silicon source gas and inert gas, wherein the silicon source gas accounts for 70-99 vol% in the mixed gas; preferably 70 to 85vol%.
The inert gas is selected from the conventional species in the art, such as nitrogen, neon, argon, krypton, xenon, radon, and the like;
preferably:
the first stage, the initial pressure is 10-25 Kpa, and the flow rate of the introduced raw material gas is 3-10L/min;
the initial pressure is 6-8 Kpa, and the flow rate of the introduced raw material gas is 8-18L/min.
Preferably:
the first stage is performed, and when the pressure change value in the reactor is 20-67% of the initial pressure, the next stage is performed;
and in the second stage, when the pressure change value in the reactor is 15-50% of the initial pressure, ending the deposition.
Further preferred is:
the first stage is performed, and when the pressure change value in the reactor is 20-50% of the initial pressure, the next stage is performed;
and in the second stage, when the pressure change value in the reactor is 15-30% of the initial pressure, ending the deposition.
Experiments show that with further optimization of the deposition process parameters, the assembled lithium ion battery has more excellent electrochemical performance.
In the preparation method, the surface carbon coating is carried out by taking a mixed gas consisting of carbon source gas and inert gas as raw material gas and carrying out vapor deposition at 400-1000 ℃.
The carbon source gas is selected from alkane gas with a cracking temperature of 400-1200 ℃, and is specifically selected from common types such as acetylene, ethylene and the like.
In the mixed gas, the volume ratio of the carbon source gas is 60-99 vol%.
The flow rate of the mixed gas is 0.1-50L/min; preferably 0.1 to 10L/min.
Preferably, the temperature of the vapor deposition is 400-600 ℃.
The invention also discloses the silicon-carbon negative electrode material prepared by the method, and the silicon-carbon negative electrode material prepared by the method has the advantages that the pore structure utilization rate is more than 98%, the nano silicon particles are uniformly distributed and mostly exist in pore channels of the porous carbon material and are not deposited on the surface, the normal-temperature gas production amount is less, and the safety performance is better.
According to the test, in the silicon-carbon anode material prepared in the embodiment, the mass ratio of the content of deposited silicon to the content of porous carbon is (0.5-1.4) P all ：1。
The invention also discloses a negative electrode plate, which comprises a negative electrode current collector and a negative electrode active material layer deposited on the negative electrode current collector; the negative electrode active material layer contains the silicon-carbon negative electrode material.
The invention also discloses a battery, which comprises the negative electrode plate. The silicon-carbon negative electrode material is used for preparing a negative electrode plate, and the negative electrode plate is assembled to obtain the lithium ion battery, so that the lithium ion battery has excellent cycling stability, high reversible specific capacity and first coulombic efficiency.
Compared with the prior art, the invention has the following advantages:
according to the preparation method of the silicon-carbon anode material, different deposition environments are adopted for pore structures with different sizes in the porous carbon material, so that the transmission and diffusion of gas molecules in the pore structures are guaranteed, the utilization rate of the pore structures, especially micropores (less than 2 nm), is improved, agglomeration blocking channels of nano silicon in the porous carbon are reduced, nano silicon particles are uniformly dispersed in a porous substrate, enrichment of nano silicon on the surface of the porous carbon is reduced, the limit effect of the pore structures on volume expansion of the nano silicon during lithium intercalation is fully exerted, and the porous substrate structure with uniformly concentrated pore diameters is prevented from being damaged due to stress concentration caused by agglomeration, so that the circulation stability of the final anode material is greatly improved.
The silicon-carbon anode material prepared by the method has the advantages that the utilization rate of the pore structure is more than 98%, no obvious gas is generated, and the lithium ion battery assembled by the lithium ion battery has excellent cycling stability, and the capacity retention rate after 100 times of cycling is up to more than 90%, and can be up to 96%; the capacity retention rate after 500 times of circulation is up to more than 85 percent and the highest capacity retention rate can be up to 90 percent; the powder resistance is low, and the reversible specific capacity and the first coulombic efficiency are high.
Drawings
FIG. 1 is a graph showing pore size distribution of the porous carbon material used in example 1;
FIG. 2 is a graph showing pore size distribution of the porous carbon material used in comparative example 3;
fig. 3 is a raman spectrum of the silicon carbon negative electrode material prepared in example 1 and comparative example 13, respectively.
Detailed Description
The following examples are provided to further illustrate the present invention and should not be construed as limiting the scope of the invention.
Example 1
(1) 100g of a porous carbon material was used as a substrate (d50=6 μm, span value<1.5 Placing in a thermal deposition furnace with the temperature of 500 ℃ and the specific surface area of the porous carbon material of 1800m 2 Per g, average pore diameter of 2nm and pore volume of 1.2cm 3 /g；
FIG. 1 is a graph showing pore size distribution of a porous carbon material used in the present example, wherein the porous carbon material has a pore volume distribution of 10.64% of very micro pores (< 1nm fraction), 11.71% of micro pores (1-2 nm fraction), 62.77% of meso pores (2-10 nm fraction), 13.32% of meso pores (10-50 nm fraction) and 1.56% of macro pores (> 50 nm) according to the test; the pore size concentration of the porous carbon material used in this example was 0.092, as calculated from the following pore size concentration calculation formula.
P: pore volume;
P all : total pore volume;
d max* ：P>a maximum pore diameter of 0.005;
d min* ：P>a minimum pore size of 0.005.
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 5L/min, and keeping the pressure in the furnace at 15Kpa to enable the inside of the porous carbon cavity to be continuously nucleated and deposited to form silicon particles, and continuously introducing air until the pressure in the furnace changes;
and a second stage:
when the pressure in the furnace changes to 8Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace increases to 8Kpa, deposition is finished;
(3) After the silicon deposition is finished, introducing a mixed gas consisting of 70vol% of acetylene and 30vol% of argon at a flow rate of 1L/min, coating at high temperature, continuously introducing air for 2 hours to control the mass of the carbon coating to account for 5wt% of the mass of the finally prepared silicon-carbon negative electrode material, cooling to room temperature, and scattering, sieving, demagnetizing and the like to obtain the silicon-carbon negative electrode material.
The silicon-carbon negative electrode material with the deposited silicon content of 53.7wt%, the porous carbon content of 41.3wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area and pore volume data of the finished silicon-carbon negative electrode material prepared in this example are shown in table 1 below, and the pore structure utilization data of the finished silicon-carbon negative electrode material prepared in this example are calculated according to the following calculation formula, and are also shown in table 1.
P1: pore volume of the raw material porous carbon material;
p2: pore volume of the finished silicon-carbon anode material.
Example 2
(1) 100g of a porous carbon material was used as a substrate (d50=6 μm, span value<1.5 Placing in a thermal deposition furnace with a temperature of 500 ℃, wherein the specific surface area of the porous carbon material is 2000m 2 Per g, average pore diameter of 1.5nm and pore volume of 1.6cm 3 /g, pore size concentration of 0.076;
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 10L/min, and keeping the pressure in the furnace at 20Kpa to enable the inside of the porous carbon cavity to be continuously nucleated and deposited to form silicon particles, and continuously introducing air until the pressure in the furnace changes;
and a second stage:
when the pressure in the furnace changes to 12Kpa, the flow rate of the mixed gas is adjusted to 18L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace increases to 8Kpa, deposition is finished;
step (3) is exactly the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 54.2wt%, the porous carbon content of 40.8wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Example 3
(1) 100g of a porous carbon material was used as a substrate (d50=6 μm, span value<1.5 Placing in a thermal deposition furnace with a temperature of 500 ℃, the specific surface area of the porous carbon material is 1500m 2 Per g, average pore diameter of 3nm and pore volume of 0.8cm 3 /g, pore size concentration of 0.094;
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 3L/min, and keeping the pressure in the furnace at 12Kpa to enable the inside of the porous carbon cavity to be continuously nucleated and deposited to form silicon particles, and continuously introducing air until the pressure in the furnace changes;
and a second stage:
when the pressure in the furnace changes to 7Kpa, the flow rate of the mixed gas is adjusted to 8L/min, ventilation is continuously carried out, and when the pressure in the furnace increases to 9Kpa, deposition is finished;
step (3) is exactly the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 51.9wt%, the porous carbon content of 43.1wt% and the surface carbon coating layer content of 5wt% was prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Comparative example 1
(1) 100g of a porous carbon material was used as a substrate (d50=6 μm, span value<1.5 Placing in a thermal deposition furnace with a temperature of 500 ℃, wherein the specific surface area of the porous carbon material is 2400m 2 Per g, average pore diameter of 1nm, pore volume of 2.0cm 3 /g, pore size concentration of 0.087;
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 5L/min, and keeping the pressure in the furnace at 25Kpa to enable the inside of the porous carbon cavity to be continuously nucleated and deposited to form silicon particles, and continuously introducing air until the pressure in the furnace changes;
and a second stage:
when the pressure in the furnace changes to 15Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace increases to 8Kpa, deposition is finished;
step (3) is exactly the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 58.1wt%, the porous carbon content of 36.9wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 2
(1) 100g of a porous carbon material was used as a substrate (d50=6 μm, span value<1.5 Placing in a thermal deposition furnace with a temperature of 500 ℃, the specific surface area of the porous carbon material is 1000m 2 Per g, average pore diameter of 10nm and pore volume of 0.6cm 3 /g, pore size concentration of 0.095;
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 5L/min, and keeping the pressure in the furnace at 10Kpa to enable the inside of the porous carbon cavity to be continuously nucleated and deposited to form silicon particles, and continuously introducing air until the pressure in the furnace changes;
and a second stage:
when the pressure in the furnace changes to 7Kpa, the flow rate of the mixed gas is adjusted to be 12L/min, ventilation is continuously carried out, and when the pressure in the furnace increases to 10Kpa, deposition is finished;
step (3) is exactly the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 43.7wt%, the porous carbon content of 51.3wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 3
The preparation process was substantially the same as in example 1, except that the porous carbon material selected in step (1) had a pore size concentration of 0.025 and a specific surface area of 1852m 2 Per gram, average pore diameter of 1.9nm and pore volume of 1.2cm 3 And/g. FIG. 2 is a graph showing pore size distribution of the porous carbon material used in the comparative example.
The silicon-carbon negative electrode material with the deposited silicon content of 52.1wt%, the porous carbon content of 42.9wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 4
Step (1) is the same as in example 1;
(2) Introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 10L/min, and keeping the pressure in the furnace at 8Kpa for 10 hours;
step (3) is the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 50.8wt%, the porous carbon content of 44.2wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 5
Step (1) is the same as in example 1;
(2) The first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 12L/min, keeping the pressure in the furnace at 6Kpa, continuously nucleating and depositing the inside of the porous carbon holes to form silicon particles, and continuously introducing the gas for 7h;
and a second stage:
adjusting the flow rate of the mixed gas to 5L/min, adjusting the pressure in the furnace to 12Kpa, continuously ventilating for 3h, and ending the deposition;
step (3) is the same as in example 1.
The silicon-carbon negative electrode material with the deposited silicon content of 45.7wt%, the porous carbon content of 49.3wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 6
The preparation process was substantially the same as in example 1, except that the flow rate of the mixture gas in the first stage in step (2) was replaced with 12L/min.
The silicon-carbon negative electrode material with the deposited silicon content of 44.9wt%, the porous carbon content of 50.1wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 7
The preparation process was substantially the same as in example 1, except that the flow rate of the mixture gas in the second stage in step (2) was replaced with 3L/min.
The silicon-carbon composite material with the deposited silicon content of 52.7wt%, the porous carbon content of 42.3wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 8
The preparation process was essentially the same as in example 1, except that the furnace pressure in the first stage in step (2) was replaced with 32Kpa.
The silicon-carbon negative electrode material with the deposited silicon content of 51.9wt%, the porous carbon content of 43.1wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 9
The preparation process was essentially the same as in example 1, except that the furnace pressure in the first stage in step (2) was replaced with 5Kpa.
The silicon-carbon negative electrode material with 48.5wt% of deposited silicon, 46.5wt% of porous carbon and 5wt% of surface carbon coating layer was prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 10
The preparation process was essentially the same as in example 1, except that the furnace pressure in the second stage in step (2) was replaced with 12Kpa.
The silicon-carbon negative electrode material with the deposited silicon content of 54.3wt%, the porous carbon content of 40.7wt% and the surface carbon coating layer content of 5wt% is prepared in the comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Example 4
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 12Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 8Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 51.3wt%, the porous carbon content of 43.7wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Example 5
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 5Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 8Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 53.1wt%, the porous carbon content of 41.9wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Comparative example 11
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 14Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 8Kpa, deposition is ended.
The silicon-carbon negative electrode material with 48.9wt% of deposited silicon, 46.1wt% of porous carbon and 5wt% of surface carbon coating layer was prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Comparative example 12
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 3Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 8Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 53.8wt%, the porous carbon content of 41.2wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Example 6
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 8Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 7Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 52.8wt%, the porous carbon content of 42.2wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Example 7
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 8Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 9Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 55.1wt%, the porous carbon content of 39.9wt% and the surface carbon coating layer content of 5wt% is prepared in this example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this example are shown in table 1 below.
Comparative example 13
The preparation process is basically the same as that in example 1, except that in the second stage of step (2), when the pressure in the furnace is changed to 8Kpa, the flow rate of the mixed gas is adjusted to 12L/min, the pressure in the furnace is adjusted to 6Kpa, ventilation is continued, and when the pressure in the furnace is increased to 11Kpa, deposition is ended.
The silicon-carbon negative electrode material with the deposited silicon content of 58.4wt%, the porous carbon content of 36.6wt% and the surface carbon coating layer content of 5wt% is prepared in this comparative example.
The specific surface area, pore volume and pore structure utilization data of the finished silicon carbon negative electrode material prepared in this comparative example are shown in table 1 below.
Fig. 3 is a raman spectrum of the silicon carbon negative electrode material prepared in example 1 and comparative example 13, respectively. At 480cm -1 The silicon characteristic peak at the position is more remarkable in strength due to accumulation and enrichment of silicon particles, and the higher the accumulation and enrichment degree of the silicon particles is, the higher the strength of the silicon peak is; based on this, the raman spectrum curves of comparative example 1 and comparative example 13 are clearly known, and the raman spectrum curve of comparative example 13 shows a silicon-rich condition at 480cm -1 The characteristic peak intensity of the silicon at the position is obviously increased, which indicates that if the process parameters are improperly regulated in the silicon deposition process, silicon particles are seriously accumulated, and the silicon-rich condition appears on the surface of the porous carbon material.
Test case
To verify the accuracy of the conclusion that the first stage was used to deposit the microporous portion of the porous carbon material and the second stage was used to deposit the mesoporous portion of the porous carbon material in the staged deposition disclosed above, the following verification was performed:
the preparation process was essentially the same as in example 1, except that in step (2):
the first stage:
introducing a mixed gas consisting of 80vol% of monosilane and 20vol% of argon into the thermal deposition furnace at a flow rate of 5L/min, and keeping the pressure in the furnace at 15Kpa;
and a second stage:
when the pressure in the furnace changes to 8Kpa, introducing a mixed gas consisting of 80vol% of acetylene and 20vol% of argon into the thermal deposition furnace at a flow rate of 12L/min, adjusting the pressure in the furnace to 6Kpa, continuously introducing until the pressure in the furnace increases to 8Kpa, and ending deposition.
Through testing, the silicon-carbon anode material with the deposited silicon content of 12.7 weight percent, the deposited carbon content of 42.1 weight percent, the porous carbon content of 40.2 weight percent and the surface carbon coating layer content of 5 weight percent is finally prepared.
As is clear from the parameters of the porous carbon material in example 1, the ratio of the mesoporous portion (2 to 50 nm) to the microporous portion (. Ltoreq.2 nm) was about 3.404, and the mass ratio of the deposited carbon to the deposited silicon obtained according to the above-described test was about 3.314, which were equivalent in value. From this, it is inferred that the judgment basis of the segmentation section of the segmentation process satisfies the actual porous carbon pore structure distribution.
Performance test:
1. the specific surface area and pore volume data of the finished silicon-carbon anode material prepared in each example and each comparative example were tested, and the pore structure utilization ratio was calculated using the above formula (1), which are shown in table 1 below.
TABLE 1
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2. And (3) normal temperature gas production test: adding 300mL of deionized water into a bottle with good sealing performance, adding 1g of the silicon-carbon anode material prepared in each example or each comparative example respectively, covering the bottle cap, ensuring no air leakage, standing for 10min after shaking uniformly, quickly unscrewing the bottle cap, extending an instrument for detecting the gas concentration into the bottle, and reading the indication of the instrument to obtain the initial gas production value of the silicon-carbon anode material; opening and waiting for a period of time, putting the gas detection instrument into a bottle, screwing the bottle cap again when the reading is 0, uniformly shaking after 24 hours, and repeating the test operation; the 24h test procedure was repeated for 48h and 72h and the initial, 24h, 48h, 72h gas production values were recorded, with the test results shown in Table 2 below.
TABLE 2
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In the silicon carbon deposition process, if the silicon nano-particles are well deposited in the porous carbon, namely: even distribution, no obvious channel blocking, high utilization rate of pore structure, low porosity, good gas production data, and no obvious change of 24h, 48h or even 72h gas production data compared with the initial value. If the conditions of uneven deposition, agglomeration and the like occur, the initial gas production value is obviously increased, and the gas production rate is rapidly increased along with the time extension. Therefore, the normal temperature gas production test can indirectly judge the silicon deposition state. The gas yield can effectively indicate the safety of related materials, and the larger the gas yield is, the worse the safety of the product is.
Application example
The silicon carbon negative electrode materials prepared in each example and each comparative example were assembled into batteries as follows.
(1) Preparing a positive electrode plate: the positive electrode active material nickel cobalt lithium manganate (NCM 811), a conductive agent SuperP, a carbon nano tube and a binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 97:1:0.5:1.5 and N-methyl pyrrolidone (NMP) are uniformly mixed to prepare positive electrode slurry (the solid content is 70wt percent), the positive electrode slurry is coated on the front and back surfaces of a current collector aluminum foil, the positive electrode slurry is dried at 100 ℃ and then subjected to cold pressing at room temperature by 4Kpa, and then subjected to trimming, cutting, slitting and welding of tabs to prepare the positive electrode plate.
(2) Preparing a negative electrode plate: under the protection of nitrogen, the solvent NMP and the binder PVDF are stirred and mixed uniformly, then the conductive agent SuperP is added and mixed uniformly, and then the negative electrode active material is added and mixed uniformly by full stirring, so as to prepare the negative electrode slurry (the solid content is 50 wt%).
The negative electrode active material was obtained by sufficiently mixing the silicon carbon negative electrode materials prepared in the above examples and comparative examples, respectively, with graphite so that the gram capacity of the prepared negative electrode material was 450 mAh/g.
The negative electrode slurry is coated on the front and back surfaces of a current collector copper foil, dried at 100 ℃, cold-pressed at room temperature by 4Kpa, cut, sliced and striped, and electrode lugs are welded to prepare the negative electrode plate.
(3) Assembly of lithium ion batteries
Sequentially stacking the prepared positive plate, the membrane and the negative plate by taking the PE porous polymeric film as the membrane, enabling the membrane to be positioned between the positive plate and the negative plate, and winding to obtain a bare cell; and (3) placing the bare cell in an aluminum plastic shell package, and drying at 100 ℃ under the relative vacuum pressure of-0.95 multiplied by 105Pa until the moisture is below 100 ppm. Injecting an electrolyte into the dried bare cell, wherein the electrolyte is composed of Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC)
(EC: EMC: DEC volume ratio = 1:1:1) LiPF 6 (1.0M), packaging, standing, forming (0.02C constant current charging for 2h and 0.1C constant current charging for 2 h), shaping, and testing capacity (capacity division) to obtain soft-package liquid lithium ion battery.
When the batteries are assembled, five batteries are prepared in each group of tests, five groups of data are tested together, and the average value of the five groups of data is taken as the final performance.
The battery cycle performance was tested on a new power plant, specifically:
at 25 ℃,0.1C to 0.005V, then 0.08C to 0.001V, 0.05C to 0.001V, 0.02C to 0.001V, and standing for 10min; charging to 1.5V at 0.1C, standing for 10min, recording the charge-discharge capacity after the first cycle, and calculating the first coulomb efficiency; cycling for 100 times according to the mode, recording the charge and discharge capacity after 100 times, and calculating to obtain the capacity retention rate after 100 times of cycling, wherein the test of the capacity retention rate after 500 times of cycling and the calculation process adopt the same mode; the powder resistance was measured by a semiconductor powder resistivity tester (30 MPa four-probe V1.4), and the test results are shown in table 3 below.
TABLE 3 Table 3
Data analysis:
the comprehensive performance analysis of the silicon-carbon negative electrode material is carried out by combining the data in tables 1 to 3, and the specific analysis is as follows:
as can be seen from the data of comparative examples 1 to 3 and comparative examples 1 to 3, when porous carbon materials with different specific surface areas, average pore diameters, pore volumes and pore concentration ratios are used as substrates, the purpose of maximally improving the pore structure utilization rate of the porous carbon substrates can be achieved by precisely controlling the parameters of the two-stage deposition in the staged deposition manner disclosed by the invention. However, if a porous carbon material with too small average pore diameter is selected as a substrate (comparative example 1), the deposition amount of silicon is too large under the condition of high pore structure utilization rate, the cycle stability of the silicon-carbon anode material is seriously affected by silicon expansion, the performance degradation is accelerated, and the cycle stability is poor; when a porous carbon material having an excessively large average pore diameter is selected as the substrate (comparative example 2), the amount of silicon deposition is low due to the limited pore volume, the reversible specific capacity is lowered, and the initial coulombic efficiency is lowered. When the average pore size and pore volume of the selected porous carbon material are suitable, but the pore size concentration is too low (comparative example 3), the uniformity of the deposited silicon is poor, and local stress concentration occurs upon expansion, resulting in a decrease in the overall electrochemical performance.
The data of comparative example 1 and comparative examples 4 and 5 are compared with the conventional one-time deposition (comparative example 4, i.e. no segmentation process), and under the condition of equivalent deposition amount, the segmented deposition in example 1 can lead the nano silicon particles to be distributed more uniformly, the utilization rate of the pore structure is higher, and the cyclic stability is more excellent; according to the data of comparative example 5, the battery assembled by the silicon-carbon negative electrode materials prepared by exchanging the sectional deposition sequence has limited cycle stability and greatly increased surface resistance, which is possibly caused by phenomena of hole blocking, silicon surface deposition and the like due to unreasonable design of deposition process parameters, and is unfavorable for the cycle application of the subsequent battery.
In comparative example 1 and comparative examples 6 and 7, if a faster gas flow rate is used in the first stage, the utilization rate of the pore structure is significantly reduced, possibly due to blocking of the pore channels caused by too fast deposition, and the utilization rate of the pore structure, especially the microporous part is significantly reduced; the gas production is obviously increased, and the safety and the circulation stability are affected; if the second stage adopts a lower gas flow rate, the gas production is obviously increased; this may be due to the lower gas flow rate coupled with lower furnace pressure, lower deposition efficiency, resulting in uneven deposition distribution of nano silicon particles and significant increase in gas production.
In comparative example 1 and comparative examples 8 to 10, if excessive reaction pressure (comparative example 8) is adopted in the first stage, the pore structure utilization rate of the prepared silicon-carbon negative electrode material is reduced, and meanwhile, the gas production is obviously increased, which is probably because the deposition speed is too high, the nano silicon is extremely unevenly distributed, a large number of pore channels are blocked, and the cycle performance and the safety performance of the silicon-carbon negative electrode are seriously affected; if the excessive reaction pressure (comparative example 10) is adopted in the second stage, the gas production is also increased obviously, and the deposition speed is too high, so that the nano silicon is distributed unevenly, and the cycle performance and the safety performance of the silicon-carbon cathode are seriously affected. If too small reaction pressure is adopted in the first stage (comparative example 9), the utilization rate of micropores is reduced, so that the utilization rate of a pore structure is obviously reduced, and the gas production is obviously increased; the low utilization rate of the pore structure can lead to the relative reduction of deposition quantity, and the capacity and first effect are reduced.
As can be seen from comparative examples 1, 4 to 5 and comparative examples 11 to 12, the pressure change occurs in the first stage, and if the ratio of the pressure change value to the initial pressure is too small (comparative example 11), the pore structure utilization rate of the prepared silicon-carbon negative electrode material is reduced, and the capacity and the initial efficiency of the assembled battery are both reduced, possibly because: the micropore part is not fully filled, so that the micropore utilization rate is reduced, the deposited silicon content is reduced, and the capacity and the first effect are slightly reduced; if the ratio of the pressure variation value to the initial pressure is too large (comparative example 12), the pore structure utilization ratio of the prepared silicon-carbon anode material is not greatly changed, but the cycle stability of the assembled battery is significantly deteriorated, possibly because: and after the microporous deposition is finished, mesoporous partial deposition is carried out under a larger pressure, and the partial deposition amount of the mesoporous part is overlarge, the distribution is uneven, the gas yield is increased, and the cycle performance is obviously deteriorated in combination with the subsequent deposition process.
As can be seen from comparative examples 1, 6 and 7 and comparative example 13, the second stage judges whether to end the deposition by pressure variation, and the appropriate pressure variation ensures higher utilization rate of the pore structure and higher deposition amount of silicon, and ensures excellent electrochemical performance of the finally assembled battery; however, if the ratio of the pressure variation value to the initial pressure is too large, the deposition of silicon on the surface of the porous carbon is increased, the resistance is obviously increased, the gas yield is increased, and the cycle performance is obviously deteriorated.
The foregoing is merely a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and the present invention is described by using the specific examples, which are only for aiding in understanding the present invention, and are not limited thereto. Several simple deductions, variations, substitutions or combinations may also be made by those skilled in the art to which the invention pertains based on the inventive concept. Such deductions, modifications, substitutions or combinations are also within the scope of the claims of the present invention.
Claims (12)
1. The preparation method of the silicon-carbon anode material is characterized by comprising the following steps of:
taking a porous carbon material as a substrate, depositing nano silicon particles in holes of the porous carbon material after staged silicon source deposition, and coating surface carbon to obtain the high-performance silicon-carbon negative electrode material;
the staged silicon source deposition uses silicon source gas as raw material gas for vapor deposition, and comprises the following steps:
in the first stage, the temperature in the reactor is controlled to be 300-800 ℃, the initial pressure is controlled to be 10-30 Kpa, and the flow rate of the introduced feed gas is controlled to be 2-10L/min; when the pressure in the reactor starts to drop and the pressure change value is 10-70% of the initial pressure, entering the next stage;
in the second stage, the initial pressure in the reactor is adjusted to 5-8 Kpa, and the flow rate of the introduced feed gas is adjusted to 8-20L/min; ending the deposition when the pressure in the reactor starts to rise and the pressure change value is 10-70% of the initial pressure.
2. The method for preparing the silicon-carbon anode material according to claim 1, wherein:
the SPAN value of the porous carbon material is lower than 1.5, and the D50 value is 4-10 mu m;
the porous carbon materialHas a specific surface area of 1200 to 2000m 2 Per gram, the average pore diameter is 1.5-5.0 nm, the pore volume is 0.6-2.0 cm 3 And/g, wherein the aperture concentration is 0.03-1.0, and the calculation formula is as follows:
p: pore volume;
P all : total pore volume;
d max* ：P>a maximum pore diameter of 0.005;
d min* ：P>a minimum pore size of 0.005.
3. The method for preparing the silicon-carbon anode material according to claim 1, wherein:
the silicon source gas is selected from one or more of monosilane, disilane, dichlorosilane and trichlorosilane;
the raw material gas is a mixed gas comprising silicon source gas and inert gas, wherein the silicon source gas accounts for 70-99 vol%.
4. The method for preparing the silicon-carbon anode material according to claim 1, wherein:
the first stage is performed, and when the pressure change value in the reactor is 20-67% of the initial pressure, the next stage is performed;
and in the second stage, when the pressure change value in the reactor is 15-50% of the initial pressure, ending the deposition.
5. The method for producing a silicon-carbon negative electrode material according to claim 1, wherein the porous carbon material has a specific surface area of 1500 to 2000m 2 Per gram, the average pore diameter is 1.5-3.0 nm, and the pore volume is 0.8-1.6 cm 3 /g。
6. The method for preparing the silicon-carbon anode material according to claim 1, wherein:
the first stage is performed, and when the pressure change value in the reactor is 20-50% of the initial pressure, the next stage is performed;
and in the second stage, when the pressure change value in the reactor is 15-30% of the initial pressure, ending the deposition.
7. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein the surface carbon coating is carried out by vapor deposition at 400-1000 ℃ by using a mixed gas of a carbon source gas and an inert gas as a raw material gas.
8. The method for preparing a silicon-carbon negative electrode material according to claim 7, wherein the surface carbon is coated with:
the carbon source gas is selected from alkane gas with the cracking temperature of 400-1200 ℃;
in the mixed gas, the volume ratio of the carbon source gas is 60-99 vol%;
the flow rate of the mixed gas is 0.1-50L/min;
the temperature of the vapor deposition is 400-600 ℃.
9. A silicon-carbon negative electrode material prepared according to the method of any one of claims 1 to 8, characterized in that:
the silicon-carbon anode material has a deposited silicon content of 40-60 wt% and a specific surface area of<25m 2 /g, pore structure utilization>96%, powder resistance<Gas production value of 35 Ω cm for 72 hours<110ppm。
10. The silicon-carbon negative electrode material according to claim 9, wherein:
the silicon-carbon anode material has a deposited silicon content of 50-55wt% and a specific surface area of<5.0m 2 /g, pore structure utilization>98%, powder resistance<Gas production value of 5 Ω·cm for 72 hours<90ppm。
11. The negative electrode plate is characterized by comprising a negative electrode current collector and a negative electrode active material layer deposited on the negative electrode current collector;
the silicon carbon anode material according to claim 9 or 10 is contained in the anode active material layer.
12. A battery comprising the negative electrode tab of claim 11.
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