CN117117159A - Silicon-carbon negative electrode material and preparation method and application thereof - Google Patents
Silicon-carbon negative electrode material and preparation method and application thereof Download PDFInfo
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- CN117117159A CN117117159A CN202311376909.2A CN202311376909A CN117117159A CN 117117159 A CN117117159 A CN 117117159A CN 202311376909 A CN202311376909 A CN 202311376909A CN 117117159 A CN117117159 A CN 117117159A
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- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 title claims abstract description 158
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 239000007773 negative electrode material Substances 0.000 title claims description 46
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 182
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 165
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 76
- 239000010405 anode material Substances 0.000 claims abstract description 59
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Classifications
-
- 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
- H01M4/366—Composites as layered products
-
- 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
-
- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- 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
- H01M4/386—Silicon or alloys based on silicon
-
- 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
- H01M4/58—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
-
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
-
- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a silicon-carbon anode material and a preparation method and application thereof, wherein the preparation method comprises the following steps: adding silicon powder, a first carbon source and polyvinylidene fluoride into an organic solvent, and mixing to obtain a first slurry; spray drying the first slurry to obtain a first silicon-carbon precursor; melting the silicon-carbon precursor and a second carbon source to obtain a second silicon-carbon precursor, placing the second silicon-carbon precursor in an atmosphere furnace, introducing a first inert gas into the atmosphere furnace, heating the atmosphere furnace to 350-550 ℃, and keeping the temperature constant for 5-30 min; and continuously introducing a first inert gas into the atmosphere furnace, heating the atmosphere furnace to 800-900 ℃, and keeping the temperature for 2-6 hours to obtain the silicon-carbon anode material. The silicon-carbon anode material has a silicon core with a porous structure and a compact carbon layer surface, and is beneficial to improving the cycle life and capacity retention rate of a battery assembled by the anode material.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-carbon anode material and a preparation method and application thereof.
Background
The lithium ion battery is a battery type widely applied to the fields of electric automobiles, mobile communication, household appliances and the like, and the cathode material is taken as an important component of the lithium ion battery, so that the performance and the service life of the battery are directly affected. Silicon has great potential for improving battery capacity as a cathode material with high specific capacity. However, the silicon negative electrode material expands in volume during the charge and discharge cycle of the lithium ion battery, resulting in damage to the electrode structure and serious impact on the cycle life of the battery.
In order to solve the problem of the silicon cathode material, the volume effect of silicon is effectively relieved by a carbon-coated silicon method at present, and the cycle life and capacity retention rate of the battery are improved. However, the bonding strength between the carbon coating layer and the silicon is poor, so that firm interface bonding cannot be formed, the carbon coating layer is easy to separate or peel off in the charge and discharge process, and part of the silicon still easily generates volume effect in the charge process, so that the cycle life and capacity retention rate of the battery are affected. Therefore, how to improve the bonding strength between silicon and carbon, thereby further improving the cycle life of the battery, is a technical problem to be solved in the art.
Disclosure of Invention
The invention provides a preparation method of a silicon-carbon negative electrode material, which can form the silicon-carbon negative electrode material with a specific structure, wherein the silicon-carbon negative electrode material is provided with a silicon core with a porous structure and a compact carbon layer surface, which is beneficial to enhancing the bonding strength of silicon and carbon, and can improve the volume expansion of the silicon-carbon negative electrode material, thereby improving the cycle life of a battery assembled by the silicon-carbon negative electrode material.
The invention also provides a silicon-carbon negative electrode material, which is high in bonding strength between silicon and carbon and beneficial to prolonging the cycle life of a battery due to the adoption of the method.
The invention also provides a negative electrode plate, and the battery assembled by the negative electrode plate has excellent cycle life due to the silicon-carbon negative electrode material.
The invention also provides a battery which has excellent cycle life due to the inclusion of the negative electrode sheet.
In a first aspect of the present invention, a method for preparing a silicon-carbon anode material is provided, comprising the steps of: adding silicon powder, a first carbon source and polyvinylidene fluoride into an organic solvent, and mixing to obtain a first slurry; the first carbon source is at least one of carbon nano tube, graphene, graphite sheet and amorphous carbon;
spray drying the first slurry to coat a first carbon source on the surface of a mixture comprising polyvinylidene fluoride and silicon powder particles to obtain a first silicon-carbon precursor; wherein the centrifugal linear speed of spray drying is 15-22 m/s, the temperature of hot air is 260-320 ℃, and the flow rate is 60-100L/min;
melting the first silicon-carbon precursor and the second carbon source to enable the second carbon source to be filled in the pores of the first silicon-carbon precursor in a melting way, so as to obtain a second silicon-carbon precursor; the second carbon source is selected from at least one of asphalt and resin; the melting treatment is carried out in a nitrogen atmosphere, the temperature is 300-450 ℃, and the time is 2-5 hours;
placing the second silicon-carbon precursor in an atmosphere furnace, introducing a first protective gas into the atmosphere furnace, heating the atmosphere furnace to 350-550 ℃, stopping introducing the first protective gas, keeping the temperature constant for 5-30 min, and enabling polyvinylidene fluoride to undergo a cracking reaction to form hydrofluoric acid, wherein the hydrofluoric acid and silicon undergo an etching reaction to form porous silicon; continuously introducing a first protective gas into the atmosphere furnace, heating the atmosphere furnace to 800-900 ℃, and keeping the temperature constant for 2-6 hours;
the silicon-carbon anode material at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon.
The preparation method comprises the steps of heating the inside of the atmosphere furnace to 800-900 ℃, keeping the temperature constant for 2-6 hours to obtain a primary carbon-coated silicon material, stirring and dispersing the primary carbon-coated silicon material at 500-600 rpm for 5-10 minutes, sieving the primary carbon-coated silicon material by a 325-mesh sieve, placing the primary carbon-coated silicon material in a rotary furnace, introducing a second protective gas into the rotary furnace, heating the inside of the rotary furnace to 800-900 ℃, keeping the temperature constant for 15-90 minutes, then introducing an organic carbon source gas and a third protective gas for 5-70 minutes, and coating the surface of the primary carbon-coated silicon material with a second carbon coating layer to obtain a silicon carbon anode material; wherein, the flow ratio of the third shielding gas to the organic carbon source gas is 10: (1-2);
the silicon-carbon anode material comprises a filling body, a first carbon coating layer positioned on the surface of the filling body, and a second carbon coating layer positioned on the surface of the first carbon coating layer far away from the filling body.
The preparation method as described above, wherein the organic carbon source gas is at least one selected from methane and acetylene; and/or the number of the groups of groups,
the organic solvent is at least one selected from N-methyl pyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide; and/or the number of the groups of groups,
the first protective gas, the second protective gas and the third protective gas are respectively and independently selected from at least one of nitrogen and argon.
The preparation method comprises the steps of, by mass, 10: (10-65): (0.5 to 6.5): (250-400).
The preparation method comprises the following steps of: (5-20).
According to the preparation method, the organic carbon source gas is introduced in an amount of 2-5wt% of the primary carbon-coated silicon material.
According to a second aspect of the invention, there is provided a silicon-carbon negative electrode material prepared by the preparation method according to the first aspect, the silicon-carbon negative electrode material at least comprises a filler and a first carbon coating layer positioned on the surface of the filler, wherein the filler comprises porous silicon and carbon filled in a pore structure of the porous silicon; the porous silicon has a pore structure, the pore diameter of the pore structure is 0.1-0.3 mu m, and the pore depth is 0.2-0.3 mu m.
The silicon-carbon anode material as described above, wherein the silicon-carbon anode material further comprises a second carbon coating layer located on the surface of the first carbon coating layer away from the filler.
The silicon-carbon anode material is characterized in that the specific surface area of the silicon-carbon anode material is 4.56-6.58 m 2 /g; and/or the number of the groups of groups,
the compaction density of the silicon-carbon anode material is 1.12-1.34 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the number of the groups of groups,
the silicon-carbon anode material is subjected to positive pressure treatment under 20MPa, and the change rate of the specific surface area before and after the positive pressure treatment is not more than 6%.
The silicon-carbon anode material is characterized in that the initial coulomb efficiency of the silicon-carbon anode material under the conditions of 5-2V and 0.05C is not lower than 85.2%; and/or the number of the groups of groups,
the capacity retention rate of the silicon-carbon anode material is not lower than 84.2% after the material is cycled for 200 circles under the conditions of 5-2V and 0.05C.
In a third aspect of the present invention, there is provided a negative electrode sheet comprising the silicon-carbon negative electrode material produced by the production method described in the first aspect or the silicon-carbon negative electrode material described in the second aspect.
In a fourth aspect of the present invention, a lithium ion battery is provided, including the negative electrode sheet according to the third aspect.
The implementation of the invention has at least the following beneficial effects:
according to the preparation method of the silicon-carbon anode material, the silicon-carbon anode material with a specific structure can be prepared, the silicon-carbon anode material is provided with the silicon inner core with a porous structure and the surface of the compact carbon layer, the silicon inner core with the porous structure can buffer the problem of volume expansion in the charge-discharge process, meanwhile, the porous structure increases the contact area between the carbon layer and the silicon inner core, the bonding strength of the silicon and the carbon layer is favorably improved, the defect that the carbon layer is easy to peel off is avoided, the carbon layer can isolate the contact between the silicon inner core and electrolyte, and the cycle life of a battery assembled by the silicon-carbon anode material is favorably prolonged.
Drawings
FIG. 1 is an SEM image of a silicon-carbon anode material according to one embodiment of the invention;
fig. 2 is an SEM image of a silicon-carbon anode material heated at 600 ℃ for 4-5 hours according to an embodiment of the invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In a first aspect of the present invention, a method for preparing a silicon-carbon anode material is provided, comprising the steps of: adding silicon powder, a first carbon source and polyvinylidene fluoride into an organic solvent, and mixing to obtain a first slurry; the first carbon source is at least one of carbon nano tube, graphene, graphite flake and amorphous carbon; spray drying the first slurry to coat a first carbon source on the surface of a mixture comprising polyvinylidene fluoride and silicon powder to obtain a first silicon-carbon precursor; wherein the centrifugal linear speed of spray drying is 15-22 m/s, the temperature of hot air is 260-320 ℃, and the flow speed is 60-100L/min; melting the first silicon-carbon precursor and the second carbon source to enable the second carbon source to be filled in the pores of the first silicon-carbon precursor in a melting way, so as to obtain a second silicon-carbon precursor; the second carbon source is selected from at least one of asphalt and resin; the melting treatment is carried out in the atmosphere of nitrogen, the temperature is 300-450 ℃, and the time is 2-5 h; placing a second silicon-carbon precursor in an atmosphere furnace, introducing a first protective gas into the atmosphere furnace, heating the atmosphere furnace to 350-550 ℃, stopping introducing the first protective gas, keeping the temperature constant for 5-30 min, and enabling polyvinylidene fluoride to undergo a cracking reaction to form hydrofluoric acid, and enabling the hydrofluoric acid and silicon to undergo an etching reaction to form porous silicon; continuously introducing a first protective gas, heating the interior of the atmosphere furnace to 800-900 ℃, and keeping the temperature for 2-6 hours to obtain a silicon-carbon anode material; the silicon-carbon anode material at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon.
The process of adding silicon powder, a first carbon source and polyvinylidene fluoride into an organic solvent for mixing can be carried out by mixing polyvinylidene fluoride (PVDF) with the organic solvent to obtain PVDF solution, adding silicon powder and the first carbon source into PVDF solution, and fully stirring and mixing to form stable first slurry.
The first carbon source is essentially elemental carbon, for example, at least one selected from carbon nanotubes, graphene, graphite flakes and amorphous carbon, and the first carbon source has excellent conductivity and structural stability, which is beneficial to alleviating the volume effect of silicon.
Spray drying can rapidly convert the slurry into solid particles and volatilize the organic solvent. According to the invention, the first slurry is subjected to spray drying, and the first carbon source is coated with the silicon and PVDF particle material by controlling the parameters of spray drying, so that the first silicon-carbon precursor is obtained.
For example, spray drying may be performed in a spray dryer, and the first carbon source coated silicon and PVDF may be obtained by controlling the centrifugal linear velocity of the spray dryer to 15 to 22m/s, the temperature of hot air to 260 to 320℃and the flow rate to 60 to 100L/min. The spray dryer may employ equipment conventional in the art, such as a spray dryer comprising at least a drying chamber provided with a hot air inlet connected to a hot air supply and a slurry inlet connected to the centrifugal atomizer, a centrifugal atomizer through which the first slurry is fed, and a hot air supply through which the hot air is fed. Wherein the centrifugal linear speed of the centrifugal atomizer is 15-22 m/s, the temperature of hot air supplied by the hot air supply device is 260-320 ℃, and the flow rate is 60-100L/min.
After spray drying, the first carbon source is coated on the surface of the silicon powder, and as the shape and the size of the first carbon source are different and are mostly granular, tiny holes may still exist in the inner part and the surface of the first silicon carbon precursor.
The second carbon source is a meltable carbon material, such as at least one of pitch, resin. The second carbon source is enabled to be in a flowing state through mixing the silicon carbon precursor and the second carbon source, and the second carbon source is filled in pores (holes) of the first silicon carbon precursor, so that the purpose of plugging the holes is achieved, and the surface of particles is enabled to form a compact state, namely the second silicon carbon precursor with a compact surface structure is obtained, and the surface of the mixture containing silicon powder and PVDF is substantially coated with the first carbon source and the second carbon source.
And placing the second silicon-carbon precursor in an atmosphere furnace, introducing a first inert gas, raising the temperature to 350-550 ℃, closing the first inert gas to enable the gas in the atmosphere furnace to be static, and keeping the constant temperature for 5-30 min. And after the end, continuously introducing the first inert gas, and discharging redundant tail gas. This process is essentially a process in which polyvinylidene fluoride in the second silicon-carbon precursor is subjected to a cleavage reaction to form hydrofluoric acid, which reacts with silicon to form porous silicon, causing the silicon to form a porous structure. At this time, the residual carbonaceous matter after the cleavage reaction of polyvinylidene fluoride fills the pore structure of the porous silicon.
And after the redundant tail gas is discharged, continuously introducing a first inert gas into the atmosphere furnace, heating the atmosphere furnace to 800-900 ℃, and keeping the temperature constant for 2-6 hours. The process is essentially to promote the carbonization of the residual carbon-containing substances to form carbon after the cracking reaction of the first carbon source, the second carbon source and the polyvinylidene fluoride, form carbon at the pore structure of the porous silicon, and form a first carbon coating layer on the surface of the filling body to obtain the silicon-carbon anode material. The silicon-carbon anode material at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon.
In the constant temperature process of keeping 350-550 ℃, PVDF can be subjected to cracking reaction to decompose and release hydrofluoric acid, and as the second silicon-carbon precursor has a densified surface structure, the effect of preventing a large amount of hydrofluoric acid gas from escaping from the inside to the outside is achieved, at the moment, hydrofluoric acid is fully contacted with silicon in the inside, and the hydrofluoric acid preferentially performs etching reaction with the silicon in the inside, so that the silicon in the inside forms a porous structure, more specific surfaces are exposed, and the silicon core of the porous structure can buffer the volume expansion problem in the charge-discharge process; the PVDF after the cracking reaction is remained in the porous structure of the porous structure silicon, the PVDF after the cracking reaction, the first carbon source and the second carbon source are subjected to carbonization reaction at the subsequent temperature of 800-900 ℃, carbon materials formed by the PVDF after the cracking reaction can be wrapped in the porous structure in the carbonization process to form more anchor points, most of carbon materials formed by the PVDF after the cracking reaction are amorphous carbon, the amorphous carbon is combined with the porous structure of the silicon to generate silicon-carbon Van der Waals bonds, the effect of bonding and combining the silicon and the carbon is achieved, meanwhile, the amorphous carbon can be combined with the carbon formed by the first carbon source and the second carbon source to generate covalent bonds, the covalent bonds have very firm physical strength, and the bridge structure between the silicon and the carbon can be achieved, so that the bonding strength between the silicon and the carbon is improved from the two aspects of enhancing the silicon-carbon Van der Waals bonds and the covalent bonds between the amorphous carbon and the carbon.
According to the research of the invention, the silicon-carbon negative electrode material prepared by the preparation method has high bonding strength of the silicon and the carbon layer, and is beneficial to prolonging the cycle life of a battery assembled by the silicon-carbon negative electrode material. This is because the melting characteristics of the second carbon source can be filled in the pores of the particles to ensure densification of the particle surfaces, and simultaneously by introducing PVDF, PVDF can not only undergo an etching reaction with the silicon core to form a silicon core in a porous structure, but also can be carbonized to form amorphous carbon and carbon to form a covalent bond, enhancing the bonding strength of silicon and carbon, and the silicon core in the porous structure can buffer the problem of volume expansion in the charge-discharge process, and at the same time, the porous structure increases the contact area of the carbon layer and the silicon core, thereby being beneficial to further improving the bonding strength of the silicon and the carbon layer, avoiding the defect that the carbon layer is easily peeled off, and the carbon layer can isolate the contact of the silicon core and the electrolyte, thereby being beneficial to improving the cycle life of a battery assembled from the silicon-carbon negative electrode material.
And heating the atmosphere furnace to 800-900 ℃, keeping the temperature for 2-6 hours to obtain the primary carbon-coated silicon material, wherein particles of the primary carbon-coated silicon material can be adhered together, and the primary carbon-coated silicon material is subjected to deagglomeration and screening, so that adhered particles can be separated. Depolymerization can be achieved by using a V-shaped dispersing mixer to stir and disperse for 5-10 min at a low rotation speed, such as 500-600 rpm. Screening may be accomplished using standard test screens, such as 325 mesh screens. The particle size of the material after depolymerization and screening is changed from the original large particle size (sub-millimeter level) to micron level.
And (3) depolymerizing the primary carbon-coated silicon material, screening, and placing the obtained solid particles into a rotary furnace for secondary carbon coating. At the moment, introducing a second inert gas into the rotary furnace, heating the rotary furnace to 800-900 ℃, and keeping the temperature for 15-90 min to ensure that the rotary furnace is in an inert atmosphere. And then, simultaneously introducing an organic carbon source gas and a third protective gas for 5-70 min, wherein at the moment, the organic carbon source gas undergoes a cracking reaction, and the gas phase has good diffusivity and can fully contact with solid particles, so that the uniformity and effectiveness of carbon distribution on the surfaces of the solid particles are greatly improved, a second carbon coating layer is formed on the surfaces of the solid particles by deposition, and the solid particles can be well coated to obtain the silicon-carbon anode material. The specific surface area of the anode material is further reduced and the conductivity is improved by secondary coating.
And (3) after introducing the organic carbon source gas and the third protective gas for 5-70 min, cooling, stopping introducing the organic carbon source gas in the cooling process, and continuing introducing the third protective gas until the temperature is reduced to room temperature, thereby obtaining the silicon-carbon anode material. At this time, the silicon-carbon anode material comprises a filler, a first carbon coating layer located on the surface of the filler, and a second carbon coating layer located on the surface of the first carbon coating layer away from the filler, wherein the filler comprises porous silicon and carbon filled in a pore structure of the porous silicon.
Wherein, the flow ratio of the third shielding gas to the organic carbon source gas is 10: (1-2), for example, the flow rate of the third shielding gas is 15L/min, and the flow rate of the organic carbon source gas is 1.5L/min.
The present invention is not limited to the specific selection of each raw material, and may be according to the actual situation. For example, in some embodiments, the organic carbon source gas is selected from at least one of methane, acetylene; and/or the organic solvent is at least one selected from N-methyl pyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide; and/or, the first inert gas, the second inert gas and the third inert gas are respectively and independently selected from at least one of nitrogen and argon.
The addition amount of each raw material is controlled, so that the silicon-carbon content in the silicon-carbon anode material can be adjusted, and different requirements can be met. In some embodiments, the mass ratio of silicon powder, the first carbon source, polyvinylidene fluoride, and the organic solvent is 10: (10-65): (0.5 to 6.5): (250-400); the mass ratio of the first silicon carbon precursor to the second carbon source is 100: (5-20); the inlet amount of the organic carbon source gas is 2-5wt% of the primary carbon-coated silicon material.
In a second aspect of the present invention, there is provided a silicon carbon negative electrode material prepared by the preparation method provided in the first aspect. The silicon-carbon anode material prepared by the preparation method has a porous silicon core and a compact carbon layer surface, and is used as an anode material in a battery, so that the cycle life of the battery is prolonged.
Specifically, the silicon-carbon anode material at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon. Wherein the porous silicon has a pore structure, the pore diameter of the pore structure is 0.1-0.3 μm, and the pore depth is 0.2-0.3 μm.
Through the secondary cladding, the silicon carbon negative electrode material further comprises a second carbon cladding layer which is positioned on the surface of the first carbon cladding layer far away from the filler, and the cycle life of the battery is further prolonged.
In some embodiments, the specific surface area of the silicon-carbon anode material is 4.56-6.58 m 2 /g; and/or the compaction density of the silicon-carbon anode material is 1.12-1.34 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the silicon-carbon anode material is subjected to positive pressure treatment of 20MPa, and the change rate of the specific surface area before and after the positive pressure treatment is not more than 6%. If the specific surface area change rate is small, the bonding strength between silicon and carbon is high, ifThe larger the rate of change of the specific surface area, the lower the bonding strength of silicon and carbon. The specific surface area change rate of the silicon-carbon anode material is not more than 6%, which shows that the bonding strength of silicon and carbon is high.
In some embodiments, the first coulombic efficiency of the silicon-carbon negative electrode material under the conditions of 5-2V and 0.05C is not lower than 85.2%; and/or the capacity retention rate of the silicon-carbon anode material is not lower than 84.2% after the material is cycled for 200 circles under the condition of 5-2V and 0.05C.
In a third aspect of the present invention, there is provided a negative electrode sheet comprising the silicon-carbon negative electrode material produced by the production method provided in the first aspect or the silicon-carbon negative electrode material provided in the second aspect.
The negative electrode plate can also be prepared by adopting the conventional technical means in the art, specifically, the silicon-carbon negative electrode material, the conductive agent and the binder can be uniformly dispersed in a solvent to obtain negative electrode active layer slurry, then the negative electrode active layer slurry is coated on at least one functional surface of a negative electrode current collector, and the negative electrode plate can be obtained after drying.
In a fourth aspect of the present invention, there is provided a lithium ion battery including the negative electrode sheet provided in the third aspect.
The lithium ion battery comprises a diaphragm, a positive plate and electrolyte besides the negative plate. The composition of the positive electrode sheet can be referred to as a conventional positive electrode sheet in the art, and the separator can also be a separator conventionally used in the art, such as a PP film, a PE film, and the like. The lithium ion battery can be prepared by adopting a conventional method in the art, specifically, the positive plate, the diaphragm and the negative plate are sequentially stacked and placed, the battery core is obtained through lamination or winding process, and then the lithium ion battery is obtained through the procedures of baking, liquid injection, formation, encapsulation and the like.
The present invention will be further illustrated by the following specific examples and comparative examples. The reagents, materials and instruments used in the following are all conventional reagents, conventional materials and conventional instruments, which are commercially available, and the reagents and materials involved can be synthesized by conventional synthesis methods, unless otherwise specified. The reaction materials used are shown in Table 1:
TABLE 1
The amorphous carbon is obtained by carbonizing glucose or sucrose at 800-900 ℃ in an inert atmosphere.
Example 1
The preparation method of the silicon-carbon anode material of the embodiment comprises the following steps:
after 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 300 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 10 parts by mass of graphite flakes are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
using a spray dryer to spray-dry the first slurry, wherein the centrifugal linear speed is 15m/s, the hot air temperature is 300 ℃, and the hot air flow rate is 60L/min to obtain a first silicon-carbon precursor;
mixing 100 parts by mass of a first silicon-carbon precursor with 5 parts by mass of asphalt, and melting and filling the asphalt into pores of the first silicon-carbon precursor in a high-temperature melting cladding machine by using technological parameters of 300 ℃ and nitrogen protection for 2 hours to obtain a second silicon-carbon precursor;
placing the second silicon-carbon precursor in an atmosphere furnace, heating to 350 ℃ under the protection of nitrogen, closing the nitrogen atmosphere, keeping the constant temperature for 10min, and cracking PVDF to release hydrofluoric acid and etch silicon; after the end, continuing to introduce nitrogen, heating to 850 ℃ and preserving heat for 3 hours, and after the end, taking out after cooling to obtain a primary carbon-coated silicon material;
and depolymerizing and sieving the primary carbon-coated silicon material, putting 100 parts by mass of the material into a rotary furnace, introducing nitrogen for protection, heating to 800 ℃, and continuously introducing 3 parts by mass of methane gas to crack the material into a carbon material, and depositing the carbon material on the surface of the primary carbon-coated silicon material to obtain the target silicon-carbon negative electrode material.
Example 2
After 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 280 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 20 parts by mass of graphene are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
using a spray dryer to spray-dry the first slurry, wherein the centrifugal linear speed is 15m/s, the hot air temperature is 300 ℃, and the hot air flow rate is 60L/min to obtain a first silicon-carbon precursor;
mixing 100 parts by mass of a first silicon-carbon precursor with 8 parts by mass of asphalt, and melting and filling the asphalt into pores of the first silicon-carbon precursor in a high-temperature melting cladding machine by using technological parameters of 300 ℃ and nitrogen protection for 2 hours to obtain a second silicon-carbon precursor;
placing the second silicon-carbon precursor in an atmosphere furnace, heating to 400 ℃ under the protection of nitrogen, closing the nitrogen atmosphere, keeping the constant temperature for 10min, and cracking PVDF to release hydrofluoric acid and etch silicon; after the end, continuing to introduce nitrogen, heating to 850 ℃ and preserving heat for 3 hours, and after the end, taking out after cooling to obtain a primary carbon-coated silicon material;
and depolymerizing and sieving the primary carbon-coated silicon material, taking 100 parts by mass of the material, placing the material into a rotary furnace, introducing nitrogen for protection, heating to 850 ℃, and continuously introducing 4 parts by mass of methane gas to crack the material into a carbon material, and depositing the carbon material on the surface of the primary carbon-coated silicon material to obtain the target silicon-carbon negative electrode material.
Example 3
After 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 350 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 40 parts by mass of multi-wall carbon nano tubes are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
using a spray dryer to spray-dry the first slurry, wherein the centrifugal linear speed is 15m/s, the hot air temperature is 300 ℃, and the hot air flow rate is 60L/min to obtain a first silicon-carbon precursor;
mixing 100 parts by mass of a first silicon-carbon precursor with 10 parts by mass of resin, and filling the resin into pores of the first silicon-carbon precursor in a high-temperature melting cladding machine by using technological parameters of 350 ℃ and nitrogen protection for 2 hours to obtain a second silicon-carbon precursor;
placing the second silicon-carbon precursor in an atmosphere furnace, heating to 500 ℃ under the protection of nitrogen, closing the nitrogen atmosphere, keeping the constant temperature for 20min, and cracking PVDF to release hydrofluoric acid and etch silicon; after the end, continuing to introduce nitrogen, heating to 850 ℃ and preserving heat for 3 hours, and after the end, taking out after cooling to obtain a primary carbon-coated silicon material;
and depolymerizing and sieving the primary carbon-coated silicon material, putting 100 parts by mass of the material into a rotary furnace, introducing nitrogen for protection, heating to 850 ℃, and continuously introducing 4 parts by mass of acetylene gas to crack the material into a carbon material, and depositing the carbon material on the surface of the primary carbon-coated silicon material to obtain the target silicon-carbon negative electrode material.
Example 4
After 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 350 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 30 parts by mass of amorphous carbon are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
using a spray dryer to spray-dry the first slurry, wherein the centrifugal linear speed is 15m/s, the hot air temperature is 300 ℃, and the hot air flow rate is 60L/min to obtain a first silicon-carbon precursor;
mixing 100 parts by mass of a first silicon-carbon precursor with 8 parts by mass of resin, and melting and filling the resin into pores of the first silicon-carbon precursor in a high-temperature melting and coating machine by using technological parameters of 350 ℃ and nitrogen protection for 2 hours to obtain a second silicon-carbon precursor;
placing the second silicon-carbon precursor in an atmosphere furnace, heating to 550 ℃ under the protection of nitrogen, closing the nitrogen atmosphere, keeping the constant temperature for 30min, and cracking PVDF to release hydrofluoric acid and etch silicon; after the end, continuing to introduce nitrogen, heating to 850 ℃ and preserving heat for 4 hours, and after the end, taking out after cooling to obtain a primary carbon-coated silicon material;
and depolymerizing and sieving the primary carbon-coated silicon material, putting 100 parts by mass of the material into a rotary furnace, introducing nitrogen for protection, heating to 850 ℃, and continuously introducing 5 parts by mass of methane gas to crack the material into a carbon material, and depositing the carbon material on the surface of the primary carbon-coated silicon material to obtain the target silicon-carbon negative electrode material.
Example 5
The same procedure as in example 1 was followed except that no secondary carbon coating was performed, and the other conditions were unchanged, with the primary carbon-coated silicon material being directly used as the silicon carbon negative electrode material.
Comparative example 1
After 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 350 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 30 parts by mass of graphite are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
using a spray dryer to spray-dry the first slurry, wherein the centrifugal linear speed is 15m/s, the hot air temperature is 300 ℃, and the hot air flow rate is 60L/min to obtain a first silicon-carbon precursor;
mixing 100 parts by mass of a first silicon-carbon precursor with 8 parts by mass of asphalt, and melting and coating the asphalt on the surface of a material in a high-temperature melting coating machine by using technological parameters of 350 ℃ and nitrogen protection for 2 hours to obtain a second silicon-carbon precursor;
and (3) placing the second silicon-carbon precursor in an atmosphere furnace, introducing nitrogen, heating to 850 ℃, preserving heat for 4 hours, cooling, taking out for depolymerization, and sieving to obtain the silicon-carbon anode material.
Comparative example 2
After 1 part by mass of polyvinylidene fluoride (PVDF) is dissolved in 350 parts by mass of NMP (N-methylpyrrolidone), 10 parts by mass of 3-10 micrometer silicon powder and 30 parts by mass of graphite are added, and the mixture is fully and uniformly dispersed to obtain first slurry;
spraying the first slurry in a spray dryer at a centrifugal linear speed of 15m/s and a hot air temperature of 300 ℃ and a hot air flow rate of 60L/min to obtain a first silicon-carbon precursor;
and mixing 100 parts by mass of the first silicon-carbon precursor with 8 parts by mass of resin, placing in an atmosphere furnace, directly heating to 950 ℃ for carbonization by using nitrogen protection, cooling, depolymerizing and sieving to obtain the silicon-carbon anode material.
Comparative example 3
Adding 3-10 microns of silicon powder and a dispersing agent accounting for 5% of the total weight of silicon carbon into an isopropanol solvent by using a grinder to grind to obtain nano silicon slurry containing nano silicon particles with the particle diameter D50 of 40-50 nm, wherein the solid content of the slurry is 15%;
weighing 1kg of isopropanol by using a clean container, adding 0.2kg of graphite with the particle size of 15 mu m, stirring for 10min at the rotation speed of 1000rpm/min, adding 3kg of nano silicon slurry with the solid content of 15% obtained in the previous step, stirring for 15min at the rotation speed of 2000rpm/min, adding a citric acid binder, wherein citric acid accounts for 2% of the total weight of silicon carbon, and stirring for 2 hours at the rotation speed of 2000rpm/min to form a mixed solution; spray drying the mixed solution, wherein the temperature of hot air is 300 ℃, the centrifugal speed of an atomizer is 15m/s, the flow rate of hot air is 60L/min, and spray drying is carried out to obtain a precursor A;
the mass ratio of the precursor A to the pyrolytic carbon precursor-sucrose is 100:3, uniformly mixing, and then adding the mixture into a fusion machine for fusion for 30min to obtain a precursor B;
carbonizing the precursor B in a tube furnace at a high temperature under the gas protection, wherein the heating rate is 5 ℃ per minute, the carbonization temperature is 900 ℃, and the carbonization time is 4 hours; and finally, sieving the carbonized product with a 325-mesh screen to obtain the silicon-carbon anode material.
Test examples
The following tests were performed on the anode materials of examples and comparative examples:
1. specific surface area and compaction density measuring method
The specific surface area test method is carried out according to the standard GB/T19587; the powder compacted density was measured using a compacted densitometer.
2. Method for measuring bonding strength of silicon and carbon
After positive pressure is carried out on the negative electrode material by using the positive pressure of 20MPa of the compaction densitometer, the specific surface area of the negative electrode material is retested, and the change rate of the specific surface area of the negative electrode material before and after the positive pressure is compared, and the change rate of the specific surface area is multiplied by 100 according to the ratio of the specific surface area = (specific surface area after positive pressure-specific surface area before positive pressure)/specific surface area before positive pressure.
3. Method for measuring cycle life
Silicon-carbon negative electrode material: carboxymethyl cellulose (CMC): styrene Butadiene Rubber (SBR) is prepared by mixing conductive carbon black (SP) according to a mass ratio of 80:4:6:10, adding deionized water to prepare slurry, uniformly coating on copper foil, vacuum drying at 120 ℃ for 24 hours,obtaining a battery pole piece, and using a lithium sheet as a counter electrode by using 1.1mol/L LiPF 6 The mass ratio of the Ethylene Carbonate (EC): vinylene Carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) =1:1:1:1 mixed electrolyte, a polypropylene microporous film is adopted as a diaphragm, a CR2032 type button half cell is assembled in a vacuum glove box, and is discharged to 5mV at constant 0.05C, discharged to 5mV at constant 0.05mA, and charged to 2.0V at constant 0.05C.
The test results are shown in tables 2 and 3.
TABLE 2
TABLE 3 Table 3
Fig. 1 is an SEM image of the silicon-carbon negative electrode material in example 1, and fig. 2 is an SEM image of the silicon-carbon negative electrode material in example 1 after being heated to 600 ℃ in air for 4 to 5 hours, and as can be seen from fig. 2, carbon is removed by changing carbon to carbon dioxide after the heating treatment, and the remaining silicon is changed to silicon dioxide, but the shape of the silicon is not changed during the silicon changing to silicon dioxide, and the shape of the silicon in the silicon-carbon can be reversely deduced from the shape of the silicon dioxide to be a porous structure.
As can be seen from tables 2 and 3, the specific surface area of the silicon-carbon negative electrode material of the example of the present invention is smaller than that of the comparative example, indicating that the surface is more dense; the specific surface area of the silicon-carbon anode material of the embodiment of the invention is far smaller than that of the comparative example in the rate of change before and after positive pressure, which shows that the bonding strength of silicon and carbon in the silicon-carbon anode material of the embodiment is far greater than that of the comparative example; as can be seen from table 2, the initial coulombic efficiency of the battery assembled by the silicon-carbon negative electrode material of the example is not lower than 85.2%, and the capacity retention rate after 200 cycles is not lower than 84.2%, which is far higher than that of the comparative example, which indicates that the silicon-carbon negative electrode material provided by the invention can remarkably improve the cycle life of the battery.
Preferred embodiments of the present invention and experimental verification are described in detail above. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention without requiring creative effort by one of ordinary skill in the art. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (10)
1. The preparation method of the silicon-carbon anode material is characterized by comprising the following steps of: adding silicon powder, a first carbon source and polyvinylidene fluoride into an organic solvent, and mixing to obtain a first slurry; wherein the first carbon source is selected from at least one of carbon nanotubes, graphene, graphite flakes and amorphous carbon;
spray drying the first slurry to coat a first carbon source on the surface of a mixture comprising polyvinylidene fluoride and silicon powder to obtain a first silicon-carbon precursor; wherein the centrifugal linear speed of spray drying is 15-22 m/s, the temperature of hot air is 260-320 ℃, and the flow rate is 60-100L/min;
carrying out melting treatment on the first silicon-carbon precursor and a second carbon source to enable the second carbon source to be filled in the pores of the first silicon-carbon precursor in a melting way, so as to obtain a second silicon-carbon precursor; wherein the second carbon source is selected from at least one of asphalt and resin; the melting treatment is carried out in a nitrogen atmosphere, the temperature is 300-450 ℃, and the time is 2-5 hours;
placing the second silicon-carbon precursor in an atmosphere furnace, introducing a first protective gas into the atmosphere furnace, heating the atmosphere furnace to 350-550 ℃, stopping introducing the first protective gas, keeping the temperature constant for 5-30 min, and enabling polyvinylidene fluoride to undergo a cracking reaction to form hydrofluoric acid, wherein the hydrofluoric acid and silicon powder undergo an etching reaction to form porous silicon; continuously introducing a first protective gas into the atmosphere furnace, heating the atmosphere furnace to 800-900 ℃, and keeping the temperature for 2-6 hours to obtain a silicon-carbon anode material;
the silicon-carbon anode material at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon.
2. The preparation method of the silicon-carbon anode material is characterized in that the temperature in the atmosphere furnace is increased to 800-900 ℃ and kept constant for 2-6 hours to obtain a primary carbon-coated silicon material, the silicon-carbon anode material is further prepared by stirring and dispersing the primary carbon-coated silicon material at 500-600 rpm for 5-10 minutes, sieving the primary carbon-coated silicon material by a 325-mesh sieve, placing the primary carbon-coated silicon material in a rotary furnace, introducing a second protective gas into the rotary furnace, heating the rotary furnace to 800-900 ℃ and keeping constant for 15-90 minutes, introducing an organic carbon source gas and a third protective gas for 5-70 minutes, and coating the surface of the primary carbon-coated silicon material with a second carbon coating layer to obtain the silicon-carbon anode material; wherein, the flow ratio of the third shielding gas to the organic carbon source gas is 10: (1-2);
the silicon-carbon anode material comprises a filling body, a first carbon coating layer positioned on the surface of the filling body, and a second carbon coating layer positioned on the surface of the first carbon coating layer far away from the filling body.
3. The production method according to claim 2, wherein the organic carbon source gas is at least one selected from methane and acetylene; and/or the number of the groups of groups,
the organic solvent is at least one selected from N-methyl pyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide; and/or the number of the groups of groups,
the first protective gas, the second protective gas and the third protective gas are respectively and independently selected from at least one of nitrogen and argon.
4. The preparation method according to claim 2, wherein the mass ratio of the silicon powder, the first carbon source, the polyvinylidene fluoride and the organic solvent is 10: (10-65): (0.5 to 6.5): (250-400); and/or the number of the groups of groups,
the mass ratio of the first silicon carbon precursor to the second carbon source is 100: (5-20); and/or the number of the groups of groups,
the amount of the organic carbon source gas is 2-5wt% of the primary carbon-coated silicon material.
5. A silicon-carbon negative electrode material, characterized in that the silicon-carbon negative electrode material is prepared by adopting the preparation method of any one of claims 1-4, and at least comprises a filling body and a first carbon coating layer positioned on the surface of the filling body, wherein the filling body comprises porous silicon and carbon filled in a pore structure of the porous silicon;
the porous silicon has a pore structure, wherein the pore diameter of the pore structure is 0.1-0.3 mu m, and the pore depth is 0.2-0.3 mu m.
6. The silicon-carbon negative electrode material of claim 5, further comprising a second carbon cladding layer located on a surface of the first carbon cladding layer remote from the filler.
7. The silicon-carbon negative electrode material according to claim 6, wherein the specific surface area of the silicon-carbon negative electrode material is 4.56-6.58 m 2 /g; and/or the number of the groups of groups,
the compaction density of the silicon-carbon anode material is 1.12-1.34 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the number of the groups of groups,
the silicon-carbon anode material is subjected to positive pressure treatment under 20MPa, and the change rate of the specific surface area before and after the positive pressure treatment is not more than 6%.
8. The silicon-carbon negative electrode material according to claim 7, wherein the initial coulombic efficiency of the silicon-carbon negative electrode material under the conditions of 5 v-2 v and 0.05C is not lower than 85.2%; and/or the number of the groups of groups,
the capacity retention rate of the silicon-carbon anode material is not lower than 84.2% after the material is cycled for 200 circles under the conditions of 5-2V and 0.05C.
9. A negative electrode sheet comprising the silicon-carbon negative electrode material produced by the production method according to any one of claims 1 to 4 or the silicon-carbon negative electrode material according to any one of claims 5 to 8.
10. A lithium ion battery comprising the negative electrode sheet of claim 9.
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