CN116895747A - Phosphorus-doped silicon-carbon composite material, preparation method thereof and secondary battery - Google Patents

Phosphorus-doped silicon-carbon composite material, preparation method thereof and secondary battery Download PDF

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Publication number
CN116895747A
CN116895747A CN202310849365.0A CN202310849365A CN116895747A CN 116895747 A CN116895747 A CN 116895747A CN 202310849365 A CN202310849365 A CN 202310849365A CN 116895747 A CN116895747 A CN 116895747A
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phosphorus
carbon
silicon
composite material
carbon composite
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傅拽
郑安华
余德馨
傅儒生
仰韻霖
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Guangdong Kaijin New Energy Technology Co Ltd
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Guangdong Kaijin New Energy Technology Co Ltd
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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
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/02—Preparation of phosphorus
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • 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
    • H01M4/36—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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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

Abstract

The invention relates to the technical field of material preparation, and discloses a phosphorus-doped silicon-carbon composite material, a preparation method thereof and a secondary battery. The phosphorus doped silicon carbon composite material comprises an inner core and an outer layer. The inner core comprises phosphorus doped nano silicon particles and a carbon skeleton with a pore structure, and at least part of the pore structure is provided with the phosphorus doped nano silicon particles. The outer layer includes a carbon coating. The preparation method comprises the following steps: and (3) placing the carbon skeleton with the pore structure in a vapor deposition reactor, introducing protective gas, maintaining a stirring state and heating, and introducing a gaseous phosphorus source and a gaseous silicon source into the vapor deposition reactor and the carbon skeleton for vapor deposition reaction to obtain the composite particles. Step (II): the composite particles are carbon coated. The phosphorus-doped silicon-carbon composite material has excellent electrochemical performance, can relieve the volume expansion of silicon, and reduces the damage of stress to the material and the electrode structure.

Description

Phosphorus-doped silicon-carbon composite material, preparation method thereof and secondary battery
Technical Field
The invention relates to the technical field of material preparation, in particular to a phosphorus-doped silicon-carbon composite material, a preparation method thereof and a secondary battery.
Background
In recent years, lithium ion batteries have been widely used in the fields of portable electronic devices, electric vehicles, and smart grids. With the continued development of manufacturing processes and material science associated with battery technology, the energy density of lithium ion batteries has been surprisingly increased. However, lithium ion battery systems having carbon-based materials as the negative electrode composition have now approached the theoretical limit of energy density, and therefore it is critical to develop higher capacity negative electrode materials. In alloy type negative electrodes, silicon is considered as one of the most promising active materials due to the characteristics of high theoretical capacity, moderate reaction potential, rich raw materials, and the like. However, the serious volume effect and poor intrinsic electron conductivity of silicon in the lithium alloying/dealloying process lead to problems of capacity fading, poor rate capability and cycle performance and the like, and prevent commercial application of silicon-based materials.
At present, the silicon material is nanocrystallized, so that the absolute expansion of the volume of the material in the charge-discharge process can be reduced, the damage of stress to the material and the electrode structure is reduced, and the cycle performance is further improved. However, nano silicon particles have large surface energy, so that the coulombic efficiency of a battery is extremely low, agglomeration is easy to occur, capacity is attenuated, and the problem that the intrinsic electronic conductivity of a silicon material is poor cannot be improved due to nano. In the modification research of the silicon-based material, the silicon-carbon composite material prepared by compounding silicon with carbon materials such as graphite, hard carbon, soft carbon, carbon nano tubes, graphene and the like can give consideration to the high capacity of the silicon and the cycle performance of the carbon material. In such materials, too high a carbon content is advantageous for improvement of cycle performance but results in lower practical capacity, while the conductivity of the material is mainly derived from the carbon material, whereas the intrinsic electron conductivity of silicon is not improved. In addition, on the one hand, the intrinsic electron conductivity of the silicon material is difficult to improve, and the problem of polarization after the battery is manufactured is serious. On the other hand, even though the intrinsic electronic conductivity of the silicon material is improved, a complex synthesis process is needed, for example, secondary spray sintering is needed, the sintering temperature is high, the energy consumption is extremely high, and the energy conservation and the environmental protection are not facilitated. Therefore, the problems of large battery polarization, poor multiplying power performance and poor cycle performance caused by serious expansion and poor intrinsic electronic conductivity of the silicon-based material are solved, the preparation process is energy-saving and efficient, large-scale production is facilitated, and the method is a current key research direction and is a technical problem in the technical field.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a phosphorus-doped silicon-carbon composite material, a method for preparing the same, and a secondary battery. The phosphorus doped silicon-carbon composite material adopted by the invention has excellent electrochemical performance, and can obviously relieve the volume expansion of silicon and reduce the damage of stress to the material and the electrode structure.
To achieve the above object, a first aspect of the present invention provides a phosphorus doped silicon carbon composite material. The phosphorus doped silicon carbon composite material comprises an inner core and an outer layer. The inner core comprises phosphorus doped nano silicon particles and a carbon skeleton with a pore structure, and at least part of the pore structure is provided with the phosphorus doped nano silicon particles. The outer layer includes a carbon coating.
The phosphorus doped nano silicon particles are nano silicon particles formed by substitution doping of phosphorus elements on silicon elements, phosphorus atoms replace silicon atoms and are located at lattice points, four valence electrons of phosphorus form covalent bonds with silicon, redundant donor electrons are easy to break loose and bind, free electrons capable of freely moving in the lattice are changed into carriers, and the intrinsic electronic conductivity of the nano silicon particles is further improved.
The phosphorus-doped silicon-carbon composite material has at least the following technical effects.
(1) The inner core comprises phosphorus doped nano silicon particles and a carbon skeleton with a pore structure, the porous structure of the carbon skeleton can provide a reserved space for the volume expansion of the nano silicon particles and is beneficial to the nanocrystallization of silicon, the volume expansion of the nano silicon particles can be remarkably relieved, the damage of stress to materials and electrode structures is reduced, and the cycle performance of the materials is further improved.
(2) The nano silicon particles of the inner core are doped with phosphorus, and the substitution doping of phosphorus element can improve the lone pair electron concentration in the nano silicon particles, so that the intrinsic electron conductivity of the silicon material is improved, the internal resistance is reduced, and the multiplying power performance and the cycle performance of the silicon-carbon composite material are improved.
(3) The carbon coating layer on the outer layer can reduce the specific surface area of the silicon-carbon composite material, and meanwhile, side reactions caused by the subsequent contact of nano silicon with electrolyte are avoided, so that the first coulomb efficiency and the structural stability of the silicon-carbon composite material are improved.
Therefore, the phosphorus doped silicon carbon composite material has better electrochemical performance, the reversible capacity is more than or equal to 2000mAh/g, the first coulomb efficiency is more than or equal to 90%, the multiplying power discharge 2C/0.1C is more than or equal to 94.0%, and the capacity retention rate in 300 cycles is more than or equal to 88.0%.
In some embodiments, the phosphorus doped nano-silicon particles are also distributed on the surface of the carbon skeleton.
In some embodiments, the phosphorus doped nano-silicon particles are distributed on the surface of the carbon skeleton and in part of the pore structure.
In some embodiments, the phosphorus doped nano-silicon particles are distributed in the surface and pore structure of the carbon backbone.
In some embodiments, the phosphorus element has a dispersion in the phosphorus doped silicon carbon composite of 0.25 or less.
In some embodiments, the nano-silicon particles comprise at least amorphous silicon, the amorphous silicon has a ratio of greater than or equal to 99.5wt.% to the nano-silicon particles, and the amorphous silicon has a grain size of less than or equal to 3nm.
In some embodiments, the 2 theta diffraction angle of the phosphorus doped silicon carbon composite is less than 50 ° ± 0.5 ° peak intensity at a peak intensity maximum of 46.0 ° to 48.0 ° as measured by XRD, and the 2 theta diffraction angle of the phosphorus doped silicon carbon composite is less than 50 ° ± 0.5 ° peak intensity at a peak intensity maximum of 54.0 ° to 58.0 °.
In some embodiments, the phosphorus doped silicon carbon composite has a peak intensity maximum of I at a 2 theta diffraction angle of 26.0 DEG to 30.0 DEG as measured by XRD 1 The peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon carbon composite material between 18.0 and 24.0 degrees is I 2 ，0.90≤I 1 /I 2 ≤1.09。
In some embodiments, the median particle diameter of the carbon skeleton is from 0.5 μm to 40.0 μm.
In some embodiments, the phosphorus doped silicon carbon composite has a median particle size of from 1 μm to 50 μm.
In some embodiments, the phosphorus doped silicon carbon composite has a content of elemental silicon of from 35wt.% to 75wt.%.
In some embodiments, the phosphorus element content in the phosphorus doped silicon carbon composite is from 0.01wt.% to 5.00wt.%.
In some embodiments, the phosphorus doped silicon carbon composite has a specific surface area of 1m 2 /g to 10m 2 /g。
In a second aspect, the invention provides a method for preparing a phosphorus doped silicon carbon composite material, comprising the steps (I) and (II).
Step (I): the carbon skeleton with the pore structure is placed in a vapor deposition reactor. And (3) introducing protective gas into the vapor deposition reactor, maintaining the stirring state and heating, and introducing a gaseous phosphorus source and a gaseous silicon source into the vapor deposition reactor and the carbon skeleton for vapor deposition reaction to obtain the composite particles. Wherein at least part of the pore structure is filled with a gaseous silicon source and a gaseous phosphorus source.
Step (II): the composite particles are carbon coated.
In combination with the second aspect, the invention provides the phosphorus-doped silicon-carbon composite material prepared by the preparation method of the phosphorus-doped silicon-carbon composite material.
In the preparation method of the phosphorus doped silicon-carbon composite material, in the step (I), the stirring state and the heating are maintained, so that the carbon skeleton, the phosphorus source steam and the silicon source steam are fully mixed, the vapor phase phosphorus doping is carried out while the silicon is deposited, and the uniformity degree and the doping depth of the doped phosphorus element in the silicon-carbon composite material are higher. The substitution doping of phosphorus element can raise the lone pair electron concentration in nanometer silicon particle to raise the intrinsic electron conductivity of silicon material, lower internal resistance and improve the rate performance and circulation performance of silicon-carbon composite material. Carbon coating the composite particles can inhibit side reactions caused by subsequent contact of nano silicon in the composite particles with electrolyte.
In some embodiments, the oxygen content is less than 50ppm after the protective gas is introduced into the vapor deposition reactor.
In some embodiments, the carbon skeleton comprises at least one of activated carbon, capacitive carbon, and carbon molecular sieves.
In some embodiments, the median particle diameter of the carbon skeleton is from 0.5 μm to 40.0 μm.
In some embodiments, the pore volume of the carbon skeleton is 0.2cm 3 /g to 1.2cm 3 /g。
In some embodiments, the carbon skeleton has a true density of 1.6g/cm 3 To 2.4g/cm 3 。
In some embodiments, the average pore size of the carbon skeleton is from 1.0nm to 20.0nm.
In some embodiments, the linear velocity of the agitation is from 0.05m/s to 1.00m/s.
In some embodiments, the gaseous phosphorus source is obtainable by heating the phosphorus source material at 20 ℃ to 650 ℃. The phosphorus source substance is solid phase and comprises at least one of red phosphorus, phosphorus pentoxide, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, tributyl phosphate, sodium metaphosphate and sodium hypophosphite.
In some embodiments, the gaseous phosphorus source is phosphine.
In some embodiments, the gaseous phosphorus source is present in the gas of the vapor deposition reactor at a volume concentration of 0.5% to 30.0%.
In some embodiments, the gaseous silicon source is obtainable by heating the silicon source material at 40 ℃ to 650 ℃. The silicon source material is in a liquid phase and comprises at least one of trisilane, butanosilane, trichlorosilane, methyltrichlorosilane and dimethyldichlorosilane.
In some embodiments, the gaseous silicon source is at least one of monosilane, disilane, monochlorosilane, and dichlorosilane.
In some embodiments, the gaseous silicon source is present in the gas of the vapor deposition reactor at a volume concentration of 1% to 60%.
In some embodiments, the heating is at a ramp rate of 1 ℃/min to 10 ℃/min.
In some embodiments, the temperature of heating is 400 ℃ to 700 ℃.
In some embodiments, the vapor deposition reaction time is from 1h to 20h.
In some embodiments, the vapor deposition reactor is a chamber furnace, rotary furnace, tube furnace, vacuum furnace, roller kiln, fluidized bed, or plasma enhanced chemical vapor deposition apparatus.
In some embodiments, the protective gas comprises at least one of nitrogen, helium, neon, argon, krypton, and xenon.
In some embodiments, the reaction temperature of the carbon coating is 400 ℃ to 700 ℃.
In some embodiments, the reaction time for the carbon coating is from 1h to 20h.
In some embodiments, the carbon-coated temperature ramp rate is from 1 ℃/min to 10 ℃/min.
In some embodiments, the carbon coating is performed under an inert atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon.
In some embodiments, the carbon source employed for the carbon coating is in the gas phase and the carbon source comprises at least one of methane, ethane, propane, isopropyl alcohol, butane, isobutane, ethylene, propylene, acetylene, butene, vinyl chloride, vinyl fluoride, 1-difluoroethylene, ethyl chloride, pentachloromonofluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, methylamine, and formaldehyde.
In some embodiments, the carbon source employed for carbon coating is in the gas phase and the carbon source is in a gas from the coating apparatus at a volume concentration of 1% to 50%.
In some embodiments, the carbon source employed for the carbon coating is in a liquid phase and the carbon source comprises at least one of acetone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, toluene, xylene, styrene, cyclohexane, n-hexane, isoheptane, 3-dimethylpentane, 3-methylhexane, and liquefied petroleum gas.
In some embodiments, the reaction temperature in both step (I) and step (II) is below 700 ℃.
The invention also provides a secondary battery, which comprises a positive electrode material and a negative electrode material, wherein the negative electrode material comprises the phosphorus-doped silicon-carbon composite material or the phosphorus-doped silicon-carbon composite material prepared by the preparation method of the phosphorus-doped silicon-carbon composite material.
In some embodiments, the positive electrode material includes at least one of a lithium iron phosphate-based material, a lithium cobalt oxide-based material, a lithium nickel cobalt manganese oxide-based material, and a lithium nickel cobalt aluminate-based material.
Drawings
FIG. 1 is a schematic structural diagram of a phosphorus doped silicon carbon composite material of the present invention;
FIG. 2 is a schematic structural view of individual particles in the phosphorus doped silicon carbon composite of the present invention;
FIG. 3 is an XRD pattern for the phosphorus doped silicon carbon composite of example 1;
FIG. 4 is a scanning electron microscope image of the phosphorus doped silicon carbon composite material of example 1;
fig. 5 is an XRD pattern of the phosphorus doped silicon carbon composite of comparative example 4.
Detailed Description
The phosphorus doped silicon-carbon composite material can be used as a cathode active material to be applied to secondary batteries, and can also be applied to the fields of solar devices, light-emitting devices, sensor devices and the like. As an example, the phosphorus-doped silicon carbon composite material is applied to a secondary battery as a negative electrode active material.
The secondary battery includes a positive electrode material and a negative electrode material. The positive electrode material includes at least one of a lithium iron phosphate material, a lithium cobalt oxide material, a lithium nickel cobalt manganese oxide material, and a lithium nickel cobalt aluminate material. The phosphorus doped silicon carbon composite material can be used as a cathode active material singly or in combination with other cathode active materials (such as natural graphite, artificial graphite, soft carbon, hard carbon and the like).
The phosphorus-doped silicon-carbon composite material comprises an inner core and an outer layer.
The specific surface area of the phosphorus doped silicon carbon composite material is 1m 2 /g to 10m 2 /g, e.g. 1m 2 /g to 5m 2 /g, which may be, but is not limited to, 1m 2 /g、2m 2 /g、3m 2 /g、4m 2 /g、5m 2 /g、6m 2 /g、7m 2 /g、8m 2 /g、9m 2 /g、10m 2 And/g. The reversible capacity of the phosphorus doped silicon carbon composite material is more than or equal to 2000mAh/g, can be more than or equal to 2000mAh/g, more than or equal to 2030mAh/g, more than or equal to 2060mAh/g, more than or equal to 2090mAh/g, more than or equal to 2100mAh/g, more than or equal to 2130mAh/g, more than or equal to 2160mAh/g, more than or equal to 2190mAh/g, and more than or equal to 2220mAh/g. The first coulomb efficiency of the phosphorus doped silicon carbon composite material is more than or equal to 90 percent, can be more than or equal to 90 percent, more than or equal to 92 percent, more than or equal to 93 percent, more than or equal to 94 percent, more than or equal to 95 percent, more than or equal to 96 percent, more than or equal to 97 percent, more than or equal to 98 percent and more than or equal to 99 percent. The multiplying power discharge 2C/0.1C of the phosphorus doped silicon carbon composite material is more than or equal to 94.0 percent, can be more than or equal to 94.0 percent, more than or equal to 95.0 percent, more than or equal to 96.0 percent and more than or equal to 97.0 percent, but is not limited to the following. The 300-week capacity retention rate of the phosphorus-doped silicon-carbon composite material is more than or equal to 88.0 percent, can be more than or equal to 88.0 percent, more than or equal to 89.0 percent, more than or equal to 90.0 percent, more than or equal to 91.0 percent, more than or equal to 92.0 percent, more than or equal to 93.0 percent, more than or equal to 94.0 percent, more than or equal to 95.0 percent, more than or equal to 96.0 percent, more than or equal to 97.0 percent and more than or equal to 98.0 percent. The content of elemental silicon in the phosphorus doped silicon carbon composite is 35wt.% to 75wt.%, e.g., 35wt.% to 55wt.%, and may be, but is not limited to, 35wt.%, 40wt.%, 45wt.%, 50wt.%, 55wt.%, 60wt.%, 65wt.%, 70wt.%, 75wt.%. The phosphorus element content in the phosphorus doped silicon carbon composite is 0.01wt.% to 5.00wt.%, e.g., 0.50wt.% to 2.50wt.%, and may be, but is not limited to, 0.01wt.%, 0.05wt.%, 0.10wt.%, 0.50wt.%, 1.00wt.%, 2.00wt.%, 3.00wt.%, 4.00wt.%, 5.00wt.%. The median particle diameter of the phosphorus doped silicon carbon composite material is 1 μm to 50 μm, for example 2 μm to 15 μm, or 3 μm to 10 μm, or 4 μm to 8 μm, may be, but is not limited to, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm.
The inner core comprises phosphorus doped nano silicon particles and a carbon skeleton with a pore structure. Alternatively, the inner core comprises phosphorus, nano-silicon, phosphorus doped nano-silicon particles and a carbon skeleton having a pore structure.
The median particle diameter of the carbon skeleton is 0.5 μm to 40.0 μm, for example 2.0 μm to 15.0 μm, or 3.0 μm to 10.0 μm, or 4.0 μm to 8.0 μm, and may be, but is not limited to, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 5.0 μm, 10.0 μm, 15.0 μm, 20.0 μm, 25.0 μm, 30.0 μm, 35.0 μm, 40.0 μm.
The pore structure of the carbon skeleton has certain average pore diameter and pore volume, so that at least part of the pore structure is provided with phosphorus doped nano silicon particles. The distribution of the phosphorus doped nano-silicon particles on the carbon skeleton has various forms, for example, the phosphorus doped nano-silicon particles only fill all pore structures; the phosphorus doped nano silicon particles only fill part of the pore structure; the phosphorus doped nano silicon particles fill all pore structures and are also distributed on the surface of the carbon skeleton; the phosphorus doped nano silicon particles fill part of the pore structure and are also distributed on the surface of the carbon skeleton. The distribution form of the phosphorus doped nano-silicon particles on the carbon skeleton is influenced by the pore size of the pore structure of the carbon skeleton, the uniformity of pore size distribution, the content of the phosphorus doped nano-silicon particles and the like.
The nano silicon particles at least comprise amorphous silicon, and the ratio of the amorphous silicon to the nano silicon particles is more than or equal to 99.5 wt%. As an example, the amorphous silicon to nano-silicon particles may be present at 99.5wt.%, 99.6wt.%, 99.7wt.%, 99.8wt.%, 99.9wt.%, 100.0wt.%. When the amorphous silicon is not 100%, the nano silicon particles include amorphous silicon and crystalline silicon. As an example, the nano-silicon particles are all amorphous silicon. The grain size of the amorphous silicon is not more than 3nm, and may be not more than 3nm, not more than 2nm, or not more than 1nm. XRD tests prove that the maximum value of the peak intensity of the 2 theta diffraction angle of the phosphorus doped silicon-carbon composite material between 46.0 and 48.0 degrees is smaller than 50 degrees+/-0.5 degrees, and the maximum value of the peak intensity of the phosphorus doped silicon-carbon composite material between 54.0 and 58.0 degrees is smaller than 50 degrees+/-0 degrees.Peak intensity of 5 °. XRD tests prove that the peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon carbon composite material between 26.0 and 30.0 degrees is I 1 The peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon carbon composite material between 18.0 and 24.0 degrees is I 2 ，0.90≤I 1 /I 2 And is less than or equal to 1.09. By way of example, I 1 /I 2 The values of (c) may be, but are not limited to, 0.90, 0.91, 0.93, 0.95, 0.97, 0.99, 1.01, 1.03, 1.05, 1.07, 1.09.
The phosphorus element is deposited together with the silicon element when being deposited on the carbon skeleton, so that phosphorus doping is carried out, and the dispersion degree of the phosphorus element in the phosphorus doped silicon-carbon composite material is less than or equal to 0.25. As an example, the dispersion may be, but is not limited to being, 0.25 or less, 0.24 or less, 0.23 or less, 0.22 or less, 0.21 or less, 0.20 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less.
The calculation formula for the phosphor element dispersion (D) is described by means of a schematic structure of the phosphor-doped silicon-carbon composite. As shown in fig. 1 and 2, the phosphorus doped silicon carbon composite material 100 includes a plurality of phosphorus doped silicon carbon composite particles 10. The phosphorus doped silicon carbon composite particle 10 includes an inner core 11 and an outer layer 13. The inner core 11 includes phosphorus doped nano-silicon particles 111 and a carbon skeleton 113 having a pore structure, at least a portion of which is provided with the phosphorus doped nano-silicon particles 111. The calculating method of the dispersion degree comprises the following steps: the method comprises the steps of performing element surface scanning on any internal section of the phosphorus-doped silicon-carbon composite material by adopting energy dispersion X-ray spectroscopy (EDS) to obtain the phosphorus element content of the section, wherein the surface scanning area is more than or equal to pi D50 2 And/16, D50 is the median particle diameter of the phosphorus doped silicon carbon composite material. Continuing to show as 2, defining the phosphorus element content of the arbitrary cross-section surface scanning area A1 as X, and defining the phosphorus element content of the arbitrary cross-section surface scanning area A2 as Y, wherein the calculation formula of the dispersion degree (D) of the phosphorus element in the phosphorus-doped silicon-carbon composite material is as follows:
D＝Max|X-Y|/(X+Y)
the larger the D value is, the worse the uniformity of the phosphorus element in the phosphorus-doped silicon-carbon composite material is, and the smaller the D value is, the better the uniformity of the phosphorus element in the phosphorus-doped silicon-carbon composite material is.
The outer layer includes a carbon coating layer having a thickness of 10nm to 1 μm. The carbon coating layer is formed by sintering a carbon source, and the carbon coating layer can be one layer, two layers, three layers and the like.
The preparation method of the phosphorus-doped silicon-carbon composite material comprises the steps of (I) and (II).
Step (I): placing a carbon skeleton with a pore structure in a vapor deposition reactor, introducing protective gas into the vapor deposition reactor, maintaining a stirring state and heating, introducing a gaseous phosphorus source and a gaseous silicon source into the vapor deposition reactor and performing vapor deposition reaction on the carbon skeleton to obtain composite particles, wherein at least part of the pore structure is filled with the gaseous silicon source and the gaseous phosphorus source.
Wherein the carbon skeleton comprises at least one of active carbon, capacitance carbon and carbon molecular sieve. The median particle diameter of the carbon skeleton is 0.5 μm to 40.0 μm, for example 2.0 μm to 15.0 μm, or 3.0 μm to 10.0 μm, or 4.0 μm to 8.0 μm, and may be, but is not limited to, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 5.0 μm, 10.0 μm, 15.0 μm, 20.0 μm, 25.0 μm, 30.0 μm, 35.0 μm, 40.0 μm. Pore structure parameters of the carbon skeleton can be tested by mercury intrusion, nitrogen adsorption or carbon dioxide adsorption. Pore volume of the carbon skeleton is 0.2cm 3 /g to 1.2cm 3 /g, e.g. 0.4cm 3 /g to 1.2cm 3 /g, or 0.5cm 3 /g to 1.2cm 3 Per g, may be, but is not limited to, 0.2cm 3 /g、0.3cm 3 /g、0.4cm 3 /g、0.5cm 3 /g、0.6cm 3 /g、0.7cm 3 /g、0.8cm 3 /g、0.9cm 3 /g、1.0cm 3 /g、1.1cm 3 /g、1.2cm 3 And/g. The average pore size of the carbon skeleton is 1.0nm to 20.0nm, for example 1.0nm to 10.0nm, or 1.5nm to 5.0nm, and may be, but is not limited to, 1.0nm, 2.0nm, 4.0nm, 6.0nm, 8.0nm, 10.0nm, 12.0nm, 14.0nm, 16.0nm, 18.0nm, 20.0nm. The true density of the carbon skeleton is 1.6g/cm 3 To 2.4g/cm 3 For example 1.8g/cm 3 To 2.2g/cm 3 Can be, but is not limited to, 1.6g/cm 3 、1.7g/cm 3 、1.8g/cm 3 、1.9g/cm 3 、2.0g/cm 3 、2.1g/cm 3 、2.2g/cm 3 、2.3g/cm 3 、2.4g/cm 3 。
The gaseous phosphorus source is phosphine, or the gaseous phosphorus source is obtainable by heating a phosphorus source substance at 20 ℃ to 650 ℃. As an example, the heating temperature of the phosphorus source material may be, but not limited to, 20 ℃, 50 ℃, 80 ℃, 100 ℃, 120 ℃, 150 ℃, 180 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃. The phosphorus source substance is solid phase and comprises at least one of red phosphorus, phosphorus pentoxide, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, tributyl phosphate, sodium metaphosphate and sodium hypophosphite. Therefore, the heating temperature of the phosphorus source material is not lower than the sublimation temperature or the decomposition temperature of the corresponding material. The gaseous phosphorus source is present in the gas of the vapor deposition reactor in a concentration of 0.5% to 30.0% by volume, i.e. the gaseous phosphorus source is present in a ratio of 0.5% to 30.0%, such as 1.0% to 20.0%, or 2.0% to 15.0% by volume of the sum of the volumes of the gaseous phosphorus source, the gaseous silicon source and the protective gas. By way of example, the gaseous phosphorus source may have a duty cycle of, but is not limited to, 0.5%, 1.0%, 5.0%, 10.0%, 15.0%, 20.0%, 25.0%, 30.0%.
The gaseous silicon source is at least one of monosilane, disilane, monochlorosilane, and dichlorosilane, and as an example, the gaseous silicon source is monosilane. Alternatively, gaseous silicon sources may be obtained by heating the silicon source material at 40 ℃ to 650 ℃. As an example, the heating temperature of the silicon source material may be, but is not limited to, 40 ℃, 50 ℃, 80 ℃, 100 ℃, 120 ℃, 150 ℃, 180 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃. The silicon source material is in a liquid phase and comprises at least one of trisilane, butanosilane, trichlorosilane, methyltrichlorosilane and dimethyldichlorosilane. Therefore, the heating temperature of the silicon source material is not lower than the boiling point of the corresponding material. The gaseous silicon source in the gas of the vapor deposition reactor has a volume concentration of 1 to 60%, i.e. the gaseous silicon source is present in a ratio of 1 to 60% of the sum of the volumes of the gaseous phosphorus source, the gaseous silicon source and the protective gas. As an example, the gaseous silicon source may have a duty cycle of, but is not limited to, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, such as 5% to 50%, or 10% to 40%.
In the invention, the gaseous phosphorus source and the gaseous silicon source are introduced into the vapor deposition reactor, and the gaseous phosphorus source and the gaseous silicon source can be mixed first and then introduced into the vapor deposition reactor, or can be sequentially introduced into the vapor deposition reactor, so long as the two sources can be introduced. The oxygen content of the vapor deposition reactor after the protective gas is introduced is less than 50ppm, and can be, but is not limited to, less than 50ppm, < 45ppm, < 40ppm, < 35ppm, < 30ppm, < 25ppm, < 20ppm, < 15ppm, < 10ppm, < 5ppm, which is equivalent to the introduction of the protective gas to exclude air. The protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.
The linear speed of stirring is 0.05m/s to 1.00m/s, and may be, but is not limited to, 0.05m/s, 0.06m/s, 0.07m/s, 0.08m/s, 0.09m/s, 0.10m/s, 0.20m/s, 0.30m/s, 0.40m/s, 0.50m/s, 0.60m/s, 0.70m/s, 0.80m/s, 0.90m/s, 1.00m/s. The heating rate is 1 to 10 c/min, e.g., 1 to 3 c/min, and may be, but is not limited to, 1 c/min, 2 c/min, 3 c/min, 4 c/min, 5 c/min, 6 c/min, 7 c/min, 8 c/min, 9 c/min, 10 c/min. The heating temperature is 400 to 700 ℃, for example 400 to 650 ℃, and may be, but not limited to, 400 ℃, 430 ℃, 450 ℃, 480 ℃, 500 ℃, 530 ℃, 550 ℃, 580 ℃, 600 ℃, 630 ℃, 660 ℃, 700 ℃. The time of the vapor deposition reaction is 1h to 20h, for example, 2h to 10h, or 2h to 5h, and may be, but not limited to, 1h, 3h, 5h, 7h, 9h, 11h, 13h, 15h, 17h, 19h, 20h. The vapor deposition reactor adopts a box-type furnace, a rotary furnace, a tubular furnace, a vacuum furnace, a roller kiln, a fluidized bed or plasma enhanced chemical vapor deposition equipment.
Step (II): the composite particles are carbon coated.
Wherein the reaction temperature of the carbon coating is 400 ℃ to 700 ℃, for example 400 ℃ to 680 ℃, and can be, but not limited to, 400 ℃, 430 ℃, 470 ℃, 500 ℃, 520 ℃, 550 ℃, 580 ℃, 600 ℃, 630 ℃, 650 ℃, 680 ℃, 700 ℃. The reaction time for carbon coating is 1h to 20h, such as 1h to 5h, or 1h to 3h, and may be, but is not limited to, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h. The carbon-coated heating rate is 1 to 10 c/min, e.g., 1 to 3 c/min, and may be, but is not limited to, 1 c/min, 2 c/min, 3 c/min, 4 c/min, 5 c/min, 6 c/min, 7 c/min, 8 c/min, 9 c/min, 10 c/min. The carbon coating is performed in an inert atmosphere comprising at least one of nitrogen, helium, neon, argon, krypton, and xenon.
The carbon source used for the carbon coating is in a gas phase, and the carbon source includes at least one of methane, ethane, propane, isopropyl alcohol, butane, isobutane, ethylene, propylene, acetylene, butylene, vinyl chloride, vinyl fluoride, 1-difluoroethylene, ethyl chloride, pentachloromonofluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, methylamine, and formaldehyde. The volume concentration of carbon in the gas originating from the cladding apparatus is 1% to 50%, i.e. the ratio of the gas phase carbon originating from the gas phase carbon source to the sum of the volumes of the inert atmosphere is 1% to 50%. As an example, the gas phase carbon source may have a duty cycle of, but is not limited to, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, such as 5% to 40%, or 10% to 30%. In addition, the carbon source used for the carbon coating may be a liquid phase, and the carbon source may include at least one of acetone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, toluene, xylene, styrene, cyclohexane, n-hexane, isoheptane, 3-dimethylpentane, 3-methylhexane, and liquefied petroleum gas. Of course, it may be solid phase, plasma, or other coating methods, as long as the coating forms a carbon-coated outer layer. The carbon-coated outer layer formed by the method can be one layer, two layers, three layers and the like.
The reaction temperatures in both step (I) and step (II) above are below 700 ℃, e.g., below 690 ℃, below 680 ℃, below 670 ℃, below 660 ℃, below 650 ℃, below 640 ℃, below 630 ℃, below 620 ℃, below 610 ℃, or below 600 ℃. All reactions are carried out at the temperature lower than 700 ℃, so that the method is efficient and energy-saving, and is suitable for industrial production.
For a better description of the objects, technical solutions and advantageous effects of the present invention, the present invention will be further described with reference to specific examples. It should be noted that the following implementation of the method is a further explanation of the present invention and should not be taken as limiting the present invention.
Example 1
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm), and argon is introduced to remove air until the oxygen content is lower than 50ppm, the stirring linear speed is started and maintained at 0.5m/s, and the mixture is heated at a heating rate of 3 ℃/min and the temperature is maintained at 470 ℃. Monosilane (28% by volume of the mixed gas in the reactor) was introduced into the reactor, and phosphine (2.4% by volume of the mixed gas in the reactor) was slowly introduced. The active carbon, the monosilane and the phosphine are fully mixed under the stirring action and are subjected to vapor deposition reaction for 5 hours at 470 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
The crystal structure of the phosphorus-doped silicon-carbon composite material obtained in example 1 was measured by an X-ray diffractometer, and the result is shown in FIG. 3. The surface morphology of the phosphorus-doped silicon-carbon composite material obtained in example 1 was observed by using a field emission scanning electron microscope, and the result is shown in fig. 4. As can be seen from the results of fig. 3 and 4, the phosphorus-doped silicon-carbon composite material exhibits an irregular morphology. The deposited nano silicon particles are all amorphous silicon. Peak intensity maximum of 2 theta diffraction angle of 46.0 degree to 48.0 degree is smaller than peak intensity of 50 degree plus or minus 0.5 degree, peak intensity maximum of 2 theta diffraction angle of 54.0 degree to 58.0 degree is smaller than peak intensity of 50 degree plus or minus 0.5 degree, I 1 /I 2 1.01.
Example 2
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm), and argon is introduced to remove air until the oxygen content is lower than 50ppm, the stirring linear speed is started and maintained at 0.5m/s, and the mixture is heated at a heating rate of 3 ℃/min and the temperature is maintained at 470 ℃. Monosilane (28% by volume of the mixed gas in the reactor) was introduced into the reactor, and phosphine (4.8% by volume of the mixed gas in the reactor) was slowly introduced. The active carbon, the monosilane and the phosphine are fully mixed under the stirring action and are subjected to vapor deposition reaction for 5 hours at 470 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 3
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm) was placed in a vapor deposition reactor, argon was introduced to remove air until the oxygen content was less than 50ppm, the stirring was started and maintained at a linear speed of 0.5m/s, and the reactor was heated at a heating rate of 3 c/min and maintained at a temperature of 550 c. Monosilane (28% by volume of the mixed gas in the reactor) was introduced into the reactor, and phosphine (2.4% by volume of the mixed gas in the reactor) was slowly introduced. The active carbon, the monosilane and the phosphine are fully mixed under the stirring action and are subjected to vapor deposition reaction for 5 hours at 550 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 4
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1.2kg of a carbon molecular sieve having a pore structure (median particle diameter of 7.0 μm, pore volume of 0.8 cm) 3 Per gram, true density of 1.8g/cm 3 Average pore diameter of 3.0 nm) was placed in a vapor deposition reactor, argon was introduced to remove air until the oxygen content was less than 50ppm, the stirring was started and maintained at a linear speed of 0.5m/s, and the mixture was heated at a heating rate of 3 c/min and maintained at a temperature of 500 c. Monosilane (the volume ratio of the mixed gas in the reactor is 32%) was introduced into the reactor, and then vapor generated after decomposition of sodium hypophosphite (400 g of sodium hypophosphite was heated to 500 ℃ to decompose to form vapor) was slowly introduced. The vapor generated after the decomposition of the carbon molecular sieve, the monosilane and the sodium hypophosphite is fully mixed under the stirring action and is subjected to vapor deposition reaction for 5 hours at 500 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 20%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 5
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1.2kg of a carbon molecular sieve having a pore structure (median particle diameter of 7.0 μm, pore volume of 0.8 cm) 3 Per gram, true density of 1.8g/cm 3 Average pore diameter of 3.0 nm) was placed in a vapor deposition reactor, argon was introduced to remove air until the oxygen content was less than 50ppm, the stirring was started and maintained at a linear speed of 0.5m/s, and the mixture was heated at a heating rate of 3 c/min and maintained at a temperature of 500 c. Monosilane (the volume ratio of the mixed gas in the reactor is 32%) was introduced into the reactor, and then vapor generated after decomposition of sodium hypophosphite (600 g of sodium hypophosphite was heated to 500 ℃ to decompose to form vapor) was slowly introduced. Carbon molecular sieve and monosilaneAnd vapor generated after decomposing sodium hypophosphite is fully mixed under the stirring action and is subjected to vapor deposition reaction for 5 hours at 500 ℃ to obtain composite particles.
Step (II): heating the composite particles to 650 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 20%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 2.0h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 6
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1.2kg of a carbon molecular sieve having a pore structure (median particle diameter of 7.0 μm, pore volume of 0.8 cm) 3 Per gram, true density of 1.8g/cm 3 Average pore diameter of 3.0 nm) was placed in a vapor deposition reactor, argon was introduced to remove air until the oxygen content was less than 50ppm, the stirring was started and maintained at a linear speed of 0.5m/s, and the mixture was heated at a heating rate of 3 c/min and maintained at a temperature of 500 c. Monosilane (the volume ratio of the mixed gas in the reactor is 32%) was introduced into the reactor, and then vapor generated after decomposition of sodium hypophosphite (400 g of sodium hypophosphite was heated to 500 ℃ to decompose to form vapor) was slowly introduced. The vapor generated after the decomposition of the carbon molecular sieve, the monosilane and the sodium hypophosphite is fully mixed under the stirring action and is subjected to vapor deposition reaction for 5 hours at 500 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, slowly introducing 0.6L of acetone under an inert atmosphere of nitrogen, preserving heat for 3 hours for reaction, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 7
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm) is placed in a vapor deposition reactor, argon is introduced to remove air until the oxygen content is lower than 50ppm, and the stirring linear speed is started and maintained0.7m/s, heated at a heating rate of 5 ℃ per minute and maintained at a temperature of 470 ℃. Disilane and phosphine are simultaneously introduced into the reactor (the volume ratio of disilane is 12.5% and the volume ratio of phosphine is 2.0% in the mixed gas in the reactor). The active carbon, the disilane and the phosphine are fully mixed under the stirring action and are subjected to vapor deposition reaction for 6 hours at 470 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 5 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under an inert atmosphere of argon, performing heat preservation reaction for 1.5 hours, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Example 8
The embodiment is a preparation method of a phosphorus-doped silicon-carbon composite material, which comprises the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm), nitrogen was introduced to exclude air until the oxygen content was less than 50ppm, the stirring was started and maintained at a linear speed of 0.7m/s, and the reactor was heated at a heating rate of 3 c/min and maintained at a temperature of 470 c. Trisilane vapor (1500 g trisilane heated to 60 ℃ C. To form vapor) was introduced into the reactor, followed by phosphine (2.4% by volume of the mixture gas in the reactor). The active carbon, trisilane vapor and phosphine are fully mixed under the stirring action and are subjected to vapor deposition reaction at 470 ℃ for 5 hours to obtain composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Comparative example 1
The comparative example is a method for preparing a phosphorus doped silicon carbon composite material, comprising the following steps.
Step (I): 1kg of activated carbon having a pore structure(median particle diameter of 7.5 μm and pore volume of 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm), and argon is introduced to remove air until the oxygen content is lower than 50ppm, the stirring linear speed is started and maintained at 0.5m/s, and the mixture is heated at a heating rate of 3 ℃/min and the temperature is maintained at 470 ℃. Monosilane was introduced into the reactor (the volume ratio of the mixed gas in the reactor was 28%). The active carbon and monosilane are fully mixed under the stirring action and are subjected to vapor deposition reaction for 5 hours at 470 ℃ to obtain composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, reacting for 1.5 hours at a temperature, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the silicon-carbon composite material.
Comparative example 2
The comparative example is a method for preparing a phosphorus doped silicon carbon composite material, comprising the following steps.
Step (I): 1.2kg of a carbon molecular sieve having a pore structure (median particle diameter of 7.0 μm, pore volume of 0.8 cm) 3 Per gram, true density of 1.8g/cm 3 Average pore diameter of 3.0 nm) and 400g of sodium hypophosphite in a solid state are mechanically mixed and then placed in a vapor deposition reactor, argon is introduced to remove air until the oxygen content is lower than 50ppm, the stirring linear speed is started and maintained at 0.5m/s, and the mixture is heated at a heating rate of 3 ℃/min and the temperature is maintained at 500 ℃. Monosilane was introduced into the reactor (the volume ratio of the mixed gas in the reactor was 32%). The carbon molecular sieve, the monosilane and the sodium hypophosphite are fully mixed under the stirring action and are subjected to vapor deposition reaction for 5 hours at 500 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 20%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Comparative example 3
The comparative example is a method for preparing a phosphorus doped silicon carbon composite material, comprising the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 5.0 nm), and argon is introduced to remove air until the oxygen content is lower than 50ppm, the stirring linear speed is started and maintained at 0.5m/s, and the mixture is heated at a heating rate of 3 ℃/min and the temperature is maintained at 470 ℃. And (3) introducing monosilane (the volume ratio of the mixed gas in the reactor is 28%) into the reactor, fully mixing the activated carbon and the monosilane under the stirring effect, and carrying out vapor deposition reaction at 470 ℃ for 5 hours to obtain the composite particles. Under the protection of argon, phosphine (the volume ratio of the mixed gas in the reactor is 2.4%) is slowly introduced, the phosphine and the composite particles are fully mixed, and the doping reaction of phosphorus is carried out for 5 hours at 470 ℃ to obtain the dopant.
Step (II): heating the dopant to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
Comparative example 4
The comparative example is a method for preparing a phosphorus doped silicon carbon composite material, comprising the following steps.
Step (I): 1kg of activated carbon having a pore structure (median particle diameter: 7.5 μm, pore volume: 0.7 cm) 3 Per gram, true density of 1.9g/cm 3 Average pore diameter of 15.0 nm) and 1.1g of silicon powder are placed in a vapor deposition reactor, argon is introduced to remove air until the oxygen content is lower than 50ppm, the silicon powder is heated at a heating rate of 3 ℃/min and maintained at a temperature of 1300 ℃, the silicon powder is changed into a vapor state, and phosphine is slowly introduced (the volume ratio of mixed gas in the reactor is 2.4%) under the protection of the argon. The active carbon, the silicon powder vapor and the phosphine are fully mixed and are subjected to vapor deposition reaction for 5 hours at 1300 ℃ to obtain the composite particles.
Step (II): heating the composite particles to 680 ℃ at a heating rate of 3 ℃/min, introducing acetylene (the volume concentration of the acetylene in the gas of the coating equipment is 16%) under the inert atmosphere of nitrogen, performing heat preservation reaction for 1.5h, closing the introduction of the acetylene, and naturally cooling to room temperature to obtain the phosphorus-doped silicon-carbon composite material.
The crystal structure of the phosphorus-doped silicon-carbon composite material obtained in comparative example 4 was measured by an X-ray diffractometer, and the result is shown in fig. 5. As can be seen from the results of fig. 5, the nano-silicon in the composite material is crystalline silicon.
The silicon carbon composites prepared in examples 1 to 8 and comparative examples 1 to 4 were subjected to physical properties and chemical composition tests under the following conditions, and the results are shown in table 1.
The silicon carbon composite materials prepared in examples 1 to 8 and comparative examples 1 to 4 were respectively prepared into button cells for electrochemical performance test, the button cell preparation process and test conditions thereof were as follows, and the test results are shown in table 2.
(1) Physical Properties
And testing the particle size distribution of the silicon-carbon composite material by adopting a laser particle sizer.
And testing the specific surface area of the silicon-carbon composite material by adopting a nitrogen isothermal adsorption-desorption curve.
And testing the conductivity of the silicon-carbon composite material by adopting a conductivity tester.
Testing the crystal form structure of the silicon-carbon composite material by adopting an X-ray diffractometer to obtain the grain size of the nano silicon, and calculating I 1 /I 2 Values.
(2) Chemical composition testing
And testing the phosphorus element and silicon element content of the silicon-carbon composite material by adopting an inductively coupled plasma atomic emission spectrometry.
The cross section of the material is observed by adopting an argon ion polishing technology and a field emission scanning electron microscope, the cross section phosphorus element surface scanning of the material is tested by utilizing energy dispersion X-ray spectrum analysis, and the dispersion degree (D) of the phosphorus element is calculated.
(3) Electrochemical performance test
The silicon carbon composites prepared in examples 1 to 8 and comparative examples 1 to 4 were used as active materials, respectively, and were used as an aqueous dispersion of a binder acrylonitrile copolymer (LA 132, solids content 15%) And the conductive agent (Super-P) is mixed according to the mass ratio of 92:6:2, a proper amount of water is added as a solvent to adjust the solid content of the slurry to 55%, the slurry is coated on a copper foil, and the negative plate is prepared by vacuum drying and rolling. A1 mol/L LiPF was used as a counter electrode using a metallic lithium sheet 6 And mixing the three components of mixed solvents according to the ratio of EC to DMC to emc=1:1:1 (v/v/v) to form an electrolyte, and adopting a polypropylene microporous membrane as a diaphragm to assemble the CR2032 button cell in a glove box filled with inert gas. The charge and discharge test of the button cell was performed on the LANHE cell test system of blue electronics inc.
First charge and discharge performance test: under normal temperature conditions, the first reversible specific capacity and the first coulombic efficiency are obtained by discharging with a constant current of 0.1C to a voltage of 0.01V, then discharging with a constant current of 0.02C to a voltage of 0.005V, and charging with a constant current of 0.1C to a voltage of 1.5V.
And (3) multiplying power performance test: at normal temperature, the current of 0.1C is circulated for 5 weeks, then the current of 0.2C is circulated for 5 weeks, the current of 0.5C is circulated for 5 weeks, the current of 1C is circulated for 5 weeks, the current of 2C is circulated for 5 weeks, and finally the current of 0.1C is circulated for 5 weeks.
And (3) testing the cycle performance: under normal temperature, 1C constant current charge and discharge is carried out to 0.01V, then 0.05C constant current discharge is carried out to 0.005V, and finally 1C constant current charge is carried out to 1.5V, thereby obtaining the lithium removal specific capacity, and the cycle is carried out 300 times, and the capacity retention rate of 300 weeks of the cycle is calculated. The capacity retention rate at 300 weeks was a ratio of the lithium removal specific capacity at 300 weeks to the lithium removal specific capacity at 1 week.
Table 1 physical properties and chemical composition test results of the silicon carbon composite materials prepared in each example and comparative example
Table 2 results of electrochemical performance tests of the silicon carbon composite materials prepared in examples and comparative examples
As can be seen from the results in table 1, the Si grains of the silicon-carbon composite materials prepared in examples 1 to 8 of the present invention are small, and the nano-silicon in the silicon-carbon composite materials is mainly amorphous silicon. The silicon-carbon composite material has a certain amount of phosphorus elements, and the dispersion degree of the phosphorus elements is low, so that the doped phosphorus elements are uniformly distributed, and the conductivity of the material is improved by the doping of the phosphorus elements. The median particle diameter and specific surface area of the silicon-carbon composite material are also low, and the silicon element content is high. Therefore, from the physical properties and chemical components of the materials, the electrochemical properties of the silicon-carbon composite materials prepared in examples 1 to 8 are better, and the results in Table 2 also prove that the reversible capacity of the silicon-carbon composite materials prepared in examples 1 to 8 is more than or equal to 2000mAh/g, the initial coulomb efficiency is more than or equal to 90%, the rate discharge 2C/0.1C is more than or equal to 94.0%, and the capacity retention rate at 300 weeks is more than or equal to 88.0%. This is mainly because the carbon skeleton, the phosphorus source vapor and the silicon source vapor can be sufficiently mixed by maintaining the stirring state and heating when the silicon-carbon composite material is prepared, so that the silicon is deposited and the uniform gas phase phosphorus doping is performed.
Comparative example 1 and comparative examples 1, 3 and 4 show that comparative example 1 is not doped with phosphorus element, and thus has low conductivity, resulting in poor rate and cycle performance. In the comparison document 3, silicon element is deposited first and then phosphorus element is deposited, and the phosphorus element cannot be uniformly doped in the material, so that the improvement of multiplying power and cycle performance is limited. In comparative example 4, silicon powder is directly added into a reactor and heated at high temperature to form vapor, which is mainly deposited on the surface of activated carbon, but not in the pores of activated carbon, and the deposited nano-silicon is crystalline silicon, the Si grain size is larger, and I 1 /I 2 The value is far greater than 1.09, which indicates that the proportion of crystalline silicon is large, so the electrochemical performance of the material is poor.
As is clear from comparative examples 4 and 2, the silicon-carbon composite material prepared by solid phase doping of phosphorus element has high dispersion of phosphorus element, which means that uniform doping cannot be performed by solid phase, and thus the electrochemical performance of the prepared silicon-carbon composite material is also poor.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the present invention can be modified or substituted without departing from the spirit and scope of the technical solution of the present invention.

Claims (10)

1. The phosphorus-doped silicon-carbon composite material is characterized by comprising an inner core and an outer layer, wherein the inner core comprises phosphorus-doped nano silicon particles and a carbon skeleton with a pore structure, at least part of the pore structure is provided with the phosphorus-doped nano silicon particles, and the outer layer comprises a carbon coating layer.
2. The phosphorus-doped silicon-carbon composite of claim 1, wherein the phosphorus-doped nano-silicon particles are also distributed on the surface of the carbon skeleton.
3. The phosphorus-doped silicon-carbon composite of claim 1, wherein the phosphorus-doped nano-silicon particles are distributed on the surface of the carbon skeleton and in a portion of the pore structure.
4. The phosphorus-doped silicon-carbon composite of claim 1, wherein the phosphorus-doped nano-silicon particles are distributed on the surface of the carbon skeleton and in the pore structure.
5. The phosphorus-doped silicon-carbon composite of claim 1, wherein the dispersion of phosphorus element in the phosphorus-doped silicon-carbon composite is less than or equal to 0.25.
6. The phosphorus-doped silicon-carbon composite of claim 1, comprising at least one of the following features (one) to (twelve):
the nano silicon particles at least comprise amorphous silicon, the ratio of the amorphous silicon to the nano silicon particles is more than or equal to 99.5 wt%, and the grain size of the amorphous silicon is less than or equal to 3nm;
(II) through XRD test, the peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon-carbon composite material between 46.0 and 48.0 degrees is smaller than 50 degrees+/-0.5 degrees, and the peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon-carbon composite material between 54.0 and 58.0 degrees is smaller than 50 degrees+/-0.5 degrees;
(III) according to XRD test, the peak intensity maximum value of 2 theta diffraction angle of the phosphorus doped silicon carbon composite material between 26.0 and 30.0 degrees is I 1 The peak intensity maximum value of the 2 theta diffraction angle of the phosphorus doped silicon carbon composite material between 18.0 and 24.0 degrees is I 2 ，0.90≤I 1 /I 2 ≤1.09；
(IV) the median particle diameter of the carbon skeleton is 0.5 μm to 40.0 μm;
(fifth), the median particle diameter of the phosphorus doped silicon carbon composite material is 1 μm to 50 μm;
(six) the phosphorus doped silicon carbon composite material has a silicon element content of 35wt.% to 75wt.%;
(seventh), the phosphorus doped silicon carbon composite material has a content of phosphorus element of 0.01wt.% to 5.00wt.%;
(eighth) the specific surface area of the phosphorus-doped silicon-carbon composite material is 1m 2 /g to 10m 2 /g；
(nine) the reversible capacity of the phosphorus-doped silicon-carbon composite material is more than or equal to 2000mAh/g;
(ten) the first coulomb efficiency of the phosphorus doped silicon carbon composite material is more than or equal to 90%;
(eleventh), the multiplying power discharge 2C/0.1C of the phosphorus doped silicon carbon composite material is more than or equal to 94.0%;
(twelve) the cycle 300 weeks capacity retention rate of the phosphorus doped silicon carbon composite material is more than or equal to 88.0 percent.
7. The preparation method of the phosphorus-doped silicon-carbon composite material is characterized by comprising the following steps:
(I) Placing a carbon skeleton with a pore structure in a vapor deposition reactor, introducing protective gas into the vapor deposition reactor, maintaining a stirring state and heating, introducing a gaseous phosphorus source and a gaseous silicon source into the vapor deposition reactor and performing vapor deposition reaction on the carbon skeleton to obtain composite particles, wherein at least part of the pore structure is filled with the gaseous silicon source and the gaseous phosphorus source;
(II) carbon coating the composite particles.
8. The method of producing a phosphorus-doped silicon-carbon composite according to claim 7, comprising at least one of the following features (1) to (26):
(1) The oxygen content of the gas phase deposition reactor after protective gas is introduced is lower than 50ppm;
(2) The carbon skeleton comprises at least one of active carbon, capacitance carbon and carbon molecular sieve;
(3) The median particle diameter of the carbon skeleton is 0.5 μm to 40.0 μm;
(4) The pore volume of the carbon skeleton is 0.2cm 3 /g to 1.2cm 3 /g；
(5) The true density of the carbon skeleton is 1.6g/cm 3 To 2.4g/cm 3 ；
(6) The average pore diameter of the carbon skeleton is 1.0nm to 20.0nm;
(7) The linear speed of the stirring is 0.05m/s to 1.00m/s;
(8) The gaseous phosphorus source is obtained by heating a phosphorus source substance at 20-650 ℃, wherein the phosphorus source substance is a solid phase and comprises at least one of red phosphorus, phosphorus pentoxide, potassium dihydrogen phosphate, monoamine phosphate, tributyl phosphate, sodium metaphosphate and sodium hypophosphite;
(9) The gaseous phosphorus source is phosphine;
(10) The volume concentration of the gaseous phosphorus source in the gas of the vapor deposition reactor is 0.5 to 30.0%;
(11) The gaseous silicon source is obtained by heating a silicon source substance at 40-650 ℃, wherein the silicon source substance is in a liquid phase and comprises at least one of trisilane, butylsilane, trichlorosilane, methyltrichlorosilane and dimethyldichlorosilane;
(12) The gaseous silicon source is at least one of monosilane, disilane, monochlorosilane and dichlorosilane;
(13) The volume concentration of the gaseous silicon source in the gas of the vapor deposition reactor is 1% to 60%;
(14) The heating rate of the heating is 1 ℃/min to 10 ℃/min;
(15) The heating temperature is 400 ℃ to 700 ℃;
(16) The time of the vapor deposition reaction is 1h to 20h;
(17) The vapor deposition reactor adopts a box-type furnace, a rotary furnace, a tube furnace, a vacuum furnace, a roller kiln, a fluidized bed or plasma enhanced chemical vapor deposition equipment;
(18) The protective gas includes at least one of nitrogen, helium, neon, argon, krypton, and xenon;
(19) The reaction temperature of the carbon coating is 400-700 ℃;
(20) The reaction time of the carbon coating is 1h to 20h;
(21) The heating rate of the carbon coating is 1 ℃/min to 10 ℃/min;
(22) The carbon coating is performed in an inert atmosphere, and the inert atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton and xenon;
(23) The carbon source adopted by the carbon coating is in a gas phase, and the carbon source comprises at least one of methane, ethane, propane, isopropyl alcohol, butane, isobutane, ethylene, propylene, acetylene, butylene, vinyl chloride, vinyl fluoride, 1-difluoroethylene, vinyl chloride, pentachloro-fluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, methylamine and formaldehyde;
(24) The carbon source adopted by the carbon coating is in a gas phase, and the volume concentration of the carbon source in the gas of the coating equipment is 1-50%;
(25) The carbon source adopted by the carbon coating is liquid phase, and the carbon source comprises at least one of acetone, methyl butanone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, toluene, xylene, styrene, cyclohexane, n-hexane, isoheptane, 3-dimethylpentane, 3-methylhexane and liquefied petroleum gas;
(26) The reaction temperature in step (I) and step (II) is lower than 700 ℃.
9. A secondary battery comprising a positive electrode material and a negative electrode material, wherein the negative electrode material comprises the phosphorus-doped silicon-carbon composite material according to any one of claims 1 to 6, or the phosphorus-doped silicon-carbon composite material produced by the method for producing the phosphorus-doped silicon-carbon composite material according to claims 8 and 9.
10. The secondary battery according to claim 9, wherein the positive electrode material includes at least one of a lithium iron phosphate-based material, a lithium cobalt oxide-based material, a lithium nickel cobalt manganese oxide-based material, and a lithium nickel cobalt aluminate-based material.
CN202310849365.0A 2023-07-11 2023-07-11 Phosphorus-doped silicon-carbon composite material, preparation method thereof and secondary battery Pending CN116895747A (en)

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