CN110061198B - Silicon-carbon composite negative electrode material and preparation method and application thereof - Google Patents

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

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CN110061198B
CN110061198B CN201810057246.0A CN201810057246A CN110061198B CN 110061198 B CN110061198 B CN 110061198B CN 201810057246 A CN201810057246 A CN 201810057246A CN 110061198 B CN110061198 B CN 110061198B
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silicon
bituminous coal
carbon composite
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coal
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CN110061198A (en
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杨娟
孙安涛
唐晶晶
周向阳
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Hunan Chenxing New Material Research Institute Co.,Ltd.
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Central South University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • H01M4/362—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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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 belongs to the field of battery material preparation, and particularly discloses a preparation method of a silicon-carbon composite negative electrode material, which is characterized in that bituminous coal and nano silicon particles subjected to oxidation treatment are mixed to obtain a mixture; the mixture is firstly sintered at the temperature of 400 ℃ and 500 ℃ for the first time and then sintered at the temperature of 700 ℃ and 1000 ℃ for the second time; and obtaining the silicon-carbon composite negative electrode material. The invention also discloses a silicon-carbon composite cathode material prepared by the preparation method, and the silicon-carbon composite cathode material is already applied to lithium ion batteries. The invention adopts bituminous coal as raw material; the raw material is matched with nano-scale silicon particles subjected to surface oxidation treatment, and the battery cathode material with excellent electrical properties can be prepared under the specific two-stage sintering mechanism.

Description

Silicon-carbon composite negative electrode material and preparation method and application thereof
Technical Field
The invention relates to a silicon-carbon composite negative electrode material of a lithium ion battery and a preparation method thereof, belonging to the field of battery negative electrode materials.
Background
The lithium ion battery has the advantages of high energy density, high open circuit voltage, good cycle performance, no memory effect, environmental protection, small self-discharge and the like, and is widely applied to the fields of mobile phones, game machines, notebook computers, electric vehicles, aerospace, new energy power grids and the like. The cathode material is one of the key factors influencing the comprehensive electrochemical performance of the lithium ion battery.
At present, the most widely commercialized carbon negative electrode material comprises natural graphite and artificial graphite, the theoretical specific capacity of the graphite is 372mAh/g, the actual capacity of the commercialized graphite negative electrode is close to the theoretical value, and the improvement space is very limited. The development of a novel anode material with high capacity is one of the important directions of research in the field of lithium ion batteries at present. The silicon has the highest theoretical specific capacity of 4200mAh/g, a lower lithium removal potential platform, good safety performance and high storage capacity in the earth crust, and is a new generation of lithium ion battery cathode material which has development prospect and can replace carbon. However, the huge volume expansion of about 300% of silicon during charging and discharging easily causes pulverization of material particles and destruction of conductive network inside the electrode, so that the cycle performance is poor, and commercial application of silicon is limited.
In order to solve the problems of the silicon cathode, the existing technical scheme generally uses conductive carbon as a buffer framework to compound silicon carbon, so that the volume expansion of silicon is effectively buffered, the conductivity is increased, the electrode polarization is reduced, and the charge-discharge cycling stability is improved. For example, patent CN200510030785.8 discloses mixing and ball-milling silicon powder and graphite, adding a carbohydrate solution, drying, adding concentrated sulfuric acid, dehydrating, carbonizing, washing, and drying to obtain a composite negative electrode material composed of silicon, graphite, and amorphous carbon. Patent CN102496701A uses nano silicon powder particles as matrix, and uses carbon nanotube and amorphous carbon to perform surface coating, so as to obtain carbon-silicon composite negative electrode material.
In the prior art, the conductive carbon used in the prior art mainly includes graphite, graphene, carbon nanotubes, amorphous carbon, and the like. Wherein, graphite itself is used as bulk phase particles, and the volume expansion of silicon is difficult to be effectively inhibited after the graphite is physically mixed with the silicon; the modification of silicon by using graphene or carbon nanotubes has the problems of expensive raw materials and poor dispersibility of nanocarbon; when amorphous carbon coating is carried out on silicon by using carbon-containing raw materials such as resin and the like, the problems of complex process, poor controllability and the like exist, and after multiple cycles, the materials are still pulverized, and the capacity is rapidly attenuated.
Disclosure of Invention
The first purpose of the invention is to provide a preparation method of a silicon-carbon composite negative electrode material.
The second purpose of the invention is to provide the silicon-carbon composite negative electrode material prepared by the preparation method.
The third purpose of the invention is to provide the application of the silicon-carbon composite negative electrode material.
A preparation method of a silicon-carbon composite negative electrode material comprises the steps of mixing bituminous coal with nano silicon particles subjected to oxidation treatment to obtain a mixture; the mixture is firstly sintered at the temperature of 400 ℃ and 500 ℃ for the first time and then sintered at the temperature of 700 ℃ and 1000 ℃ for the second time; and obtaining the silicon-carbon composite negative electrode material.
The invention adopts bituminous coal as raw material; the raw material is matched with nano-scale silicon particles subjected to surface oxidation treatment, and the battery cathode material with excellent electrical properties can be prepared under the specific two-stage sintering mechanism.
Preferably, the bituminous coal is coking coal and/or fat coal.
The bituminous coal is preferably coking coal and/or fat coal in the Chinese coal classification (GB/T5751-2009). Research shows that the electrical property of the prepared negative electrode material is more excellent by adopting the preferred bituminous coal.
Preferably, the ash-free base volatile component content of the coking coal is 10-28%, the caking index is 50-65%, and the maximum thickness of the colloidal layer is less than or equal to 25%. The preferred degree of expansion of Aoau is less than or equal to 150%.
Further preferably, the ash-free base volatile component content of the coking coal is 15% -25%, the caking index is 55% -60%, and the maximum thickness of the colloidal layer is 15% -20%.
Preferably, the components of the fat coal are that the ash-free base volatile component content is 10-37%, the caking index is more than or equal to 85%, and the maximum thickness of the colloidal layer is more than 25%.
Further preferably, the ash-free base volatile component content of the fat coal is 20% -30%, the caking index is 90% -95%, and the maximum thickness of the colloidal layer is 30% -40%.
Preferably, the bituminous coal contains at least one of nitrogen, sulfur and phosphorus; the total content of the miscellaneous elements in the bituminous coal is not less than 2 wt%;
further preferably 4% to 10%. The use of bituminous coal containing the heteroatoms helps to produce more excellent negative electrode materials.
Preferably, the bituminous coal is purified prior to sintering. Through purification treatment, metal impurities in the bituminous coal can be further removed, and the electrical properties of the prepared negative electrode material are further improved.
Preferably, the ash content of the bituminous coal after the purification treatment is controlled to be less than or equal to 0.5%. And mixing the purified bituminous coal with the nano silicon particles and then performing the two-stage sintering, which is favorable for further improving the performance of the prepared cathode material.
In the invention, the existing method can be adopted for the purification treatment of the bituminous coal, and the acid method or the alkali method is preferably adopted for the purification treatment of the bituminous coal.
Preferably, the acid process step is: adding the dried, crushed and screened bituminous coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid of 10:1-1:10, adjusting the total acid concentration to 3-4, stirring and reacting for 2-5 hours at room temperature, filtering and washing to be neutral, and obtaining the bituminous coal purified by an acid method.
Preferably, the alkaline process step is: adding the dried, crushed and screened bituminous coal into an alkali metal hydroxide aqueous solution with the mass concentration of 7.5-17.5%, uniformly mixing, controlling the liquid-solid ratio to be 4-8, standing for 2-5 hours, drying in a drying box with the temperature of 105-550 ℃, roasting for 1-3 hours at the temperature of 450-550 ℃ in an inert atmosphere, filtering and washing the roasted product to be neutral, and obtaining the bituminous coal purified by an alkali method.
In the alkaline purification process, the aqueous solution of the alkali metal hydroxide is preferably an aqueous solution of sodium hydroxide.
The bituminous coal or purified bituminous coal and the nano-silicon particles are mixed by conventional methods, such as ball milling, mechanical stirring, etc.
Preferably, the nano-silicon particles may be general commercially available nano-silicon, which may be obtained by using a ball milling method, chemical vapor deposition, thermal reduction method.
Preferably, the particle size of the nano silicon particles is 5-100 nm. The use of nanoscale silicon at this preferred particle size helps to further enhance the properties of the resulting material.
Preferably, the shape of the nano silicon particles is at least one of spherical, spheroidal, linear, tubular and flaky.
The inventor finds that the oxidation treatment of the nano silicon particles is helpful for further improving the electrical properties of the finally compounded material.
The method for carrying out oxidation treatment on the nano silicon particles can adopt the existing method, and the invention preferably puts the nano silicon particles into a solution containing an oxidant for carrying out surface oxidation treatment to obtain the nano silicon particles after oxidation treatment.
The oxidizing agent may be a compound known in the art to be useful for silicon surface oxidation modification.
Preferably, the oxidant is hydrogen peroxide (NH)4)2S2O8Concentrated nitric acid or Ce (SO)4)2At least one of (1).
Preferably, the temperature of the surface oxidation treatment is 25-90 ℃; the reaction time is 1-72 h.
Through the surface oxidation treatment, the treated nano silicon particles react with water and an oxidant to form a silicon oxide layer on the surfaces of the nano silicon particles.
Preferably, the oxygen content in the nano silicon particles after oxidation treatment is 5-20 wt%; further preferably 10 to 20 wt%.
In the present invention, the mixing of the bituminous coal and the oxidized nano-silicon particles may be performed by a conventional method.
Such as mixing with stirring, ball milling; the ball milling mixing is preferably wet ball milling mixing.
Preferably, the mass ratio of the bituminous coal to the oxidized nano-silicon particles is 1:5 to 20: 1.
Further preferably, the mass ratio of the bituminous coal to the nano silicon particles subjected to oxidation treatment is 1: 1-5; more preferably 1: 2-5.
In the present invention, preferably, the bituminous coal and the oxidized nano-silicon particles are sufficiently mixed in a solvent, and the mixed solution is dried to obtain the mixture.
Preferably, the solvent is at least one of water, methanol, ethanol, propanol, toluene and diethyl ether, and the mixing mode comprises any one or more of mechanical stirring, mechanical ball milling and ultrasonic dispersion.
In the present invention, the drying is preferably spray drying.
In the present invention, the mixed solution may be subjected to spray drying granulation in a spray dryer under an inert atmosphere.
Preferably, the spray granulation is performed by a peristaltic pump spray dryer.
Preferably, in the spray drying process, the feeding speed is 0.5-4L/h, the air inlet temperature range is 180-200 ℃, and the air outlet temperature range is 50-80 ℃.
Further preferably, in the spray drying process, the feeding speed is 0.5-2L/h, the air inlet temperature range is 180-200 ℃, and the air outlet temperature range is 50-80 ℃.
Preferably, the inert atmosphere is at least one of helium, argon, neon and nitrogen.
In the invention, the sintering process is carried out in a protective atmosphere; preferably, the protective atmosphere is, for example, nitrogen and/or an inert gas; the inert gas is at least one of helium, argon and neon.
In the invention, the secondary calcination at the temperature is beneficial to obviously improving the electrical property of the material prepared from the material.
Preferably, the temperature of the one-stage sintering is 450-500 ℃.
Preferably, the sintering is carried out for 1 to 3 hours under the condition of heat preservation at the first-stage sintering temperature.
Preferably, the temperature of the second-stage sintering is 800-1000 ℃; further preferably 900-1000 ℃.
Preferably, the sintering is carried out for 1 to 3 hours under the temperature of the second-stage sintering.
The heating rates of the first-stage sintering and the second-stage sintering are both 1-10 ℃/min.
Preferably, the sintered material is crushed and sieved to obtain the battery negative electrode material.
The invention relates to a more preferable preparation method of a lithium ion battery silicon-carbon composite negative electrode material, which comprises the following steps:
the first step is as follows: drying, crushing and screening bituminous coal serving as a raw material to obtain coal powder particles with the particle size of less than 20 microns;
the second step is that: purifying the bituminous coal particles obtained in the step one by an acid method or an alkaline method, removing metal impurities in the bituminous coal, and obtaining the purified bituminous coal with ash content of less than 0.5%;
the third step: carrying out mild oxidation treatment on the surface of the nano silicon by using an oxidant, and then mechanically mixing the purified bituminous coal obtained in the step two and the nano silicon subjected to oxidation treatment in a solvent according to the proportion of 1:5-20:1 for more than 12 hours;
the fourth step: carrying out spray granulation on the uniformly mixed bituminous coal and nano-silicon mixture in a spray dryer under the protection of inert gas to obtain composite particles;
the fifth step: carrying out primary sintering on the composite particles obtained by spray granulation at the temperature of 400-500 ℃ in an inert atmosphere, and then carrying out secondary sintering at the temperature of 700-1000 ℃; and cooling to room temperature after sintering, taking out the sintering material, and crushing and grading the sintering material to obtain the carbon-silicon composite lithium ion battery cathode material.
Preferably, in the first step, the drying temperature is 105-120 ℃, the drying time is 10-12h, the crushing mode is preferably a vibration crusher for crushing for 1-10min, a planetary ball mill for ball milling for 6-10h or a combination of the two.
Preferably, in the fifth step, the inert atmosphere is selected from at least one of helium, argon, neon and nitrogen, the temperature of the heat treatment is raised to 400-1000 ℃ at a temperature raising rate of 1-10 ℃/min, and the temperature is maintained for 1-3 hours, and then the sintering is carried out for 1-3 hours at a temperature raising rate of 1-5 ℃/min.
The invention provides a silicon-carbon composite negative electrode material prepared by the preparation method, which comprises nano silicon particles and bituminous coal pyrolytic carbon compounded on the surface of the nano silicon particles in situ.
Preferably, the silicon-carbon composite negative electrode material consists of bituminous coal pyrolytic carbon and modified nano silicon particles (also referred to as nano silicon for short) which are uniformly dispersed in the bituminous coal pyrolytic carbon, a large number of pore channels and gaps exist in the bituminous coal pyrolytic carbon, and the mass ratio of the bituminous coal pyrolytic carbon to the nano silicon is 1: 10-10: 1.
Preferably, the particle size of the silicon-carbon composite negative electrode material is 5-25 microns.
The silicon-carbon composite negative electrode material is preferably a lithium ion battery negative electrode material.
The invention also provides application of the battery cathode material to preparation of a cathode of a lithium ion battery.
In the invention, the battery cathode material can be used as a cathode active component to be assembled into a cathode of a lithium ion battery by adopting the existing method.
The principle and the characteristics of the invention are as follows: the carbon content of bituminous coal is 74-92%, the volatile component content is 18-26%, the content of colloidal matter is moderate, a viscous gas-liquid-solid three-phase coexisting mixture can be formed at a certain temperature (about 500 ℃), at the moment, the added modified nano-silicon is easily and uniformly dispersed in the liquid phase of the colloidal matter, and micron-sized silicon-carbon secondary composite particles with uniform appearance and particle size can be obtained by spray granulation in an inert atmosphere. Thermal polymerization of bituminous coal can be carried out by heat treatment at a higher temperature (above 700 ℃), forming a carbon shell layer with a porous structure around the nano-silicon.
The invention has the following beneficial effects:
(1) the carbon shell layer is formed around the nano-silicon in situ, and the nano-silicon is uniformly dispersed and tightly combined with the carbon shell layer; the protective layer formed by bituminous coal pyrolytic carbon can effectively improve the conductivity of the material and avoid the large amount of SEI (solid electrolyte interface) films generated due to the direct contact of internal nano silicon particles and electrolyte; in addition, the bituminous coal contains a certain amount of nitrogen, sulfur and phosphorus elements, and in-situ doping is realized in the pyrolysis process, so that the conductivity is further improved.
(2) In the process of bituminous coal pyrolysis, volatile matters (high molecular organic matters) contained in the bituminous coal are violently decomposed at high temperature to generate and discharge a large amount of gaseous volatile matters, and a porous structure with a large number of apertures and gaps can be formed in bituminous coal pyrolytic carbon, and the apertures and the gaps provide a storage space for electrolyte, shorten an ion transmission path and improve the rate capability on one hand; on the other hand, the space capable of accommodating the nano silicon charging expansion is provided, the structural stability is maintained, and the cycle stability is improved.
(3) The obtained silicon-carbon composite negative electrode material has high capacity, good rate capability and long cycle life; the soft coal has wide raw material source and low cost; the process is simple, the flow is short, and the control is easy.
Drawings
Fig. 1 is an SEM image of a silicon-carbon composite anode material prepared in example 1 of the present invention;
FIG. 2 is an XRD pattern of a silicon-carbon composite anode material prepared in example 1 of the present invention;
as can be seen from the attached figure 1, the nano silicon is uniformly dispersed in the bituminous coal pyrolytic carbon and is tightly combined with the carbon shell layer; and a large number of pores and voids are formed in the bituminous coal pyrolytic carbon as a matrix.
It can be seen from fig. 2 that the silicon-carbon composite negative electrode material contains two phases of silicon and amorphous carbon, and does not contain other impurities.
Detailed description of the preferred embodiments
Example 1:
(1) selecting coking coal with ash-free base volatile component content of 15%, bonding index of 62%, colloidal layer maximum thickness of 25%, contained heteroatom N, S, P and heteroatom content of 4% as raw materials, placing 100g of coking coal raw material dried at 120 ℃ for 10h into a vibration pulverizer, crushing for 1min, ball-milling for 6 h by a planetary ball mill, sieving with a 500-mesh sieve, and taking undersize.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 4, the total acid concentration is adjusted to be 3, stirring and reacting for 2 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.32%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 1 hour at the temperature of 25 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 5 wt%.
(4) And (3) taking 40g of purified coking coal and 20g of oxidized nano-silicon, mechanically stirring and mixing in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 0.5L/h, air inlet temperature of 180 ℃ and air outlet temperature of 50 ℃ to obtain the composite particles.
(5) And (2) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 450 ℃ at a heating rate of 1 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving the heat for 1 hour, heating to 800 ℃ at a heating rate of 1 ℃/min, sintering for 1 hour, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Example 2:
(1) selecting coking coal with ash-free base volatile component content of 25%, bonding index of 62%, maximum thickness of colloidal layer of 25%, contained heteroatom N, S, P and heteroatom content of 10% as raw materials, putting 100g of coking coal raw material dried at 105 ℃ for 12h into a vibration pulverizer, crushing for 3min, ball-milling for 7 h by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened bituminous coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 2: 1, wherein the liquid-solid ratio is 6, the total acid concentration is adjusted to be 4, stirring and reacting for 5 hours at room temperature, filtering and washing to be neutral to obtain acid-purified coking coal, and the ash content of the purified coking coal is 0.43%.
(3) Selecting a spherical and linear mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 72 hours at the temperature of 90 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 20 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 40g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 2L/h, air inlet temperature of 200 ℃ and air outlet temperature of 80 ℃ to obtain the composite particles.
(5) And (2) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 1000 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Example 3:
(1) selecting coking coal with ash-free base volatile component content of 20%, bonding index of 58%, maximum colloidal layer thickness of 18%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, placing 100g of coking coal raw material dried at 105 ℃ for 12h into a vibration pulverizer, crushing for 5min, ball-milling for 8 h by a planetary ball mill, sieving with a 500-mesh sieve, and taking undersize.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 2: 1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.4%.
(3) Selecting a spherical and tubular mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 50 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 12 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(5) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 3 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving the heat for 2 hours, heating to 900 ℃ at a heating rate of 3 ℃/min, sintering for 2 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Example 4:
(1) selecting fat coal with ash-free base volatile component content of 25%, caking index of 95%, colloid layer maximum thickness of 35%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, putting 100g of the fat coal raw material dried at 105 ℃ for 12h into a vibration pulverizer, crushing for 5min, then ball-milling for 8 h by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened fat coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 6, the total acid concentration is adjusted to be 3, stirring and reacting for 4 hours at room temperature, filtering and washing to be neutral to obtain the fertilizer coal purified by an acid method, and the ash content of the purified fertilizer coal is 0.23%.
(3) Selecting a spherical and flaky nano silicon raw material with the particle size of D50 being 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 48 hours at the temperature of 70 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 20 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified fat coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed fat coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas under the conditions of a feeding speed of 2L/h, an air inlet temperature of 180 ℃ and an air outlet temperature of 80 ℃ to obtain the composite particles.
(5) And (2) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 1000 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Example 5:
(1) selecting coking coal with ash-free base volatile component content of 20%, bonding index of 58%, maximum colloidal layer thickness of 18%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, placing 100g of coking coal raw material dried at 105 ℃ for 12h into a vibration pulverizer, crushing for 5min, ball-milling for 8 h by a planetary ball mill, sieving with a 500-mesh sieve, and taking undersize.
(2) Adding 50g of dried, crushed and screened coking coal into a sodium hydroxide aqueous solution with the mass concentration of 15%, uniformly dispersing, controlling the liquid-solid ratio to be 5, standing for 3 hours, drying in a drying oven at 120 ℃, roasting for 3 hours at 500 ℃ in an argon atmosphere, filtering and washing a roasting product to be neutral to obtain the coking coal purified by an alkaline method, wherein the ash content of the bituminous coal after purification is 0.48%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 90 ℃, enabling silicon particles in the slurry to react with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 18 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 0.5L/h, air inlet temperature of 180 ℃ and air outlet temperature of 80 ℃ to obtain the composite particles.
(5) And (2) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 1000 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Example 6:
(1) selecting coking coal with ash-free base volatile component content of 15%, bonding index of 52%, colloid layer maximum thickness of 25%, contained heteroatom N, S, P and heteroatom content of 2% as raw materials, placing 100g of coking coal raw material dried at 120 ℃ for 12h into a vibration pulverizer, crushing for 4min, ball-milling for 8 h by a planetary ball mill, sieving with a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.33%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 50 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 12 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(5) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 900 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Comparative example 1:
the comparison example discusses the use of anthracite, and comprises the following specific steps:
(1) taking anthracite with 3.5 percent of dry ashless-based volatile component and 2 percent of dry ashless-based hydrogen as a raw material, putting 100g of the anthracite raw material which is dried for 12 hours at 120 ℃ into a vibration crusher to be crushed for 4 minutes, then ball-milling the crushed anthracite raw material for 8 hours by a planetary ball mill, sieving the crushed anthracite raw material by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened bituminous coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the bituminous coal purified by an acid method, and the ash content of the purified bituminous coal is 0.2%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 50 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 12 wt%.
(4) And (2) mechanically stirring and mixing 40g of purified anthracite and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed bituminous coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas under the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(5) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 900 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Comparative example 2:
the comparison example discusses the use of lignite, and the specific steps are as follows:
(1) selecting lignite with 40% of ash-free base volatile content and 6% of heteroatom N, S, P as raw materials, putting 100g of lignite raw material dried at 120 ℃ for 10 hours into a vibration crusher, crushing for 4min, then ball milling for 8 hours by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize.
(2) Adding 50g of dried, crushed and screened lignite into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 6, the total acid concentration is adjusted to be 3, stirring and reacting for 4 hours at room temperature, filtering and washing to be neutral to obtain the lignite purified by an acid method, and the content of the purified lignite ash is 0.22%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 90 ℃, enabling silicon particles in the slurry to react with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 18 wt%.
(4) Taking 40g of purified lignite and 80g of oxidized nano-silicon, mechanically stirring and mixing in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed lignite and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas under the conditions of feeding speed of 0.5L/h, air inlet temperature of 180 ℃ and air outlet temperature of 80 ℃ to obtain the composite particles.
(5) And (2) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 1000 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Comparative example 3:
this comparative example discusses that the following details are used, not with nano-silicon, but with micro-silicon:
(1) selecting coking coal with ash-free base volatile component content of 20%, bonding index of 58%, maximum colloidal layer thickness of 18%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, putting 100g of coking coal raw material dried at 120 ℃ for 12h into a vibration pulverizer, crushing for 4min, ball-milling for 8 h by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.32%.
(3) Selecting a silicon raw material with silicon particles of which the size D50 is about 20 mu m and which is a mixture of spherical and spheroidal silicon, adding the micron silicon raw material into 20 mass percent aqueous hydrogen peroxide, stirring for 36 hours at the temperature of 50 ℃ to enable the silicon particles in the slurry to react with water and hydrogen peroxide to form a silicon dioxide layer on the surface, wherein the oxygen content in the micron silicon after the oxidation treatment is about 12 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and micron silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(5) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 900 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Comparative example 4:
the comparative example discusses that the oxidation pretreatment is not carried out on the nano silicon, and the specific steps are as follows:
(1) selecting coking coal with ash-free base volatile component content of 20%, bonding index of 58%, maximum colloidal layer thickness of 18%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, putting 100g of coking coal raw material dried at 120 ℃ for 12h into a vibration pulverizer, crushing for 4min, ball-milling for 8 h by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.33%.
(3) Taking 40g of purified coking coal and 80g of spherical and spheroidal mixed nano-silicon with the particle size of D50 being 40nm, mechanically stirring and mixing in an ethanol solution for 12 hours, carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(4) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 500 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, preserving heat for 3 hours, heating to 900 ℃ at a heating rate of 5 ℃/min, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
Comparative example 5:
the comparison example discusses that the once calcining process is adopted, and the specific steps are as follows:
(1) selecting coking coal with ash-free base volatile component content of 20%, bonding index of 58%, maximum colloidal layer thickness of 18%, contained heteroatom N, S, P and heteroatom content of 8% as raw materials, putting 100g of coking coal raw material dried at 120 ℃ for 12h into a vibration pulverizer, crushing for 4min, ball-milling for 8 h by a planetary ball mill, sieving by a 500-mesh sieve, and taking undersize products.
(2) Adding 50g of dried, crushed and screened coking coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid being 10:1, wherein the liquid-solid ratio is 5, the total acid concentration is adjusted to be 3, stirring and reacting for 3 hours at room temperature, filtering and washing to be neutral to obtain the coking coal purified by an acid method, and the ash content of the purified coking coal is 0.33%.
(3) Selecting a spherical and spheroidal mixed nano silicon raw material with the particle size D50 of 40nm, adding the nano silicon raw material into a 20% hydrogen peroxide aqueous solution by mass, stirring for 36 hours at the temperature of 50 ℃, reacting silicon particles in the slurry with water and hydrogen peroxide to form a silicon oxide layer on the surface, wherein the oxygen content in the nano silicon after the oxidation treatment is about 12 wt%.
(4) And (3) mechanically stirring and mixing 40g of purified coking coal and 80g of oxidized nano-silicon in an ethanol solution for 12 hours, and carrying out spray granulation on the uniformly mixed coking coal and nano-silicon mixture in a peristaltic pump spray dryer under the protection of inert gas at the conditions of feed speed of 1L/h, air inlet temperature of 190 ℃ and air outlet temperature of 70 ℃ to obtain the composite particles.
(5) And (3) putting 10g of the uniformly mixed mixture into a graphite boat, heating to 900 ℃ at a heating rate of 5 ℃/min in a muffle furnace protected by nitrogen atmosphere, sintering for 3 hours, cooling to room temperature, and taking out to obtain the silicon-carbon composite negative electrode material of the lithium ion battery.
The electrochemical performance of the negative electrode materials prepared in each example and each comparative example in a lithium half cell is tested; the test method is as follows:
(1) the preparation process of the electrode comprises the following steps: mixing the prepared active material, PVDF and conductive carbon black (acetylene black) in a mass ratio of 8: 1, adding a certain amount of N-methylpyrrolidone (NMP), and fully and uniformly mixing in an agate mortar. And uniformly coating the uniformly mixed slurry on a copper foil, and drying the copper foil coated with the slurry in a vacuum drying oven at 120 ℃ for 12 hours after the coating is finished. And after drying, cutting the electrode plate into 12mm round pieces, weighing and marking the electrode plate, drying and placing the electrode plate in a glove box for later use.
(2) The assembling process of the battery comprises the following steps: in the experiment, a button type half cell is adopted to test the electrochemical performance of the material, all the cell assemblies are carried out in a glove box under the argon atmosphere, the water oxygen value detection is required to be always less than 0.1ppm in the assembly process, and the electrolyte adopts commercial 1mol L in the assembly process-1The lithium hexafluorophosphate electrolyte is used as the lithium ion battery electrolyte, a polypropylene (PP) diaphragm is used as the diaphragm of the lithium ion battery, and the lithium ion battery takes a lithium sheet as a counter electrode; all cells were assembled into 2025 type button cells and sealed in a glove box with a cell packaging machine. The battery assembly is assembled according to the sequence of negative electrode shell, pole piece electrolyte, diaphragm, electrolyte, lithium piece, nickel piece and positive electrode shell.
Table 1 shows the results of the electrochemical performance tests on lithium half-cells of examples 1 to 5 and comparative examples 1 to 3
TABLE 1
Figure BDA0001553701600000141
Figure BDA0001553701600000151
As can be seen from the electrochemical performance test results, examples 1 to 6 all have good comprehensive electrochemical performance in the lithium ion half cell.
In the comparative example 1, because the anthracite is adopted as the raw material, the volatile component is too low, the number of the colloidal substances is small, the fluidity is poor in the high-temperature heat treatment process, and the binding does not occur, so that the added nano silicon cannot be dispersed in the anthracite, an effective conductive framework cannot be formed, and the electrochemical performance is poor.
In the comparative example 2, because the lignite is used as the raw material, the volatile component is too high, the lignite expands in the high-temperature heat treatment process, the coking performance of the material is poor, and the uniform silicon-carbon composite negative electrode material cannot be formed, so that the electrochemical performance is influenced.
In comparative example 3, the bituminous coal is difficult to completely coat silicon due to the adoption of micron silicon instead of nano silicon, and the electrochemical performance is poor due to the poor electrochemical activity of the micron silicon.
In comparative example 4, the nano silicon surface modification is not performed, so that the dispersibility of the nano silicon is poor, and the bonding force between the nano silicon and the bituminous coal pyrolytic carbon is reduced, so that the electrochemical performance is poor.
In comparative example 5, only one calcination was performed, so that the dispersibility of the nano-silicon in the pyrolytic carbon was not good, and the bonding force with the pyrolytic carbon of bituminous coal was not uniform, thereby the electrochemical performance was poor.

Claims (9)

1. A preparation method of a silicon-carbon composite negative electrode material is characterized in that bituminous coal and nano silicon particles subjected to oxidation treatment are mixed to obtain a mixture; the mixture is firstly sintered at the temperature of 400 ℃ and 500 ℃ for the first time and then sintered at the temperature of 700 ℃ and 1000 ℃ for the second time; obtaining the silicon-carbon composite negative electrode material;
the bituminous coal is coking coal and/or fat coal;
the ash-free base volatile component content of the coking coal is 10-28%, the caking index is 50-65%, and the maximum thickness of the colloidal layer is less than or equal to 25%;
the components of the fat coal are that the ash-free base volatile component content is 10-37%, the caking index is more than or equal to 85%, and the maximum thickness of the colloidal layer is more than 25%;
the bituminous coal contains at least one miscellaneous element of nitrogen, sulfur and phosphorus; the total content of the miscellaneous elements in the bituminous coal is not less than 2 wt%;
the bituminous coal is purified before sintering, and the ash content of the purified bituminous coal is controlled to be less than or equal to 0.5%;
the oxygen content in the nano silicon particles after oxidation treatment is 5-20 wt%.
2. The method for preparing the silicon-carbon composite anode material according to claim 1, wherein the purification treatment method is an acid method or an alkali method; wherein the content of the first and second substances,
the acid method comprises the following steps: adding the dried, crushed and screened bituminous coal into a mixed acid solution with the mass ratio of hydrofluoric acid to sulfuric acid of 10:1-1:10, adjusting the total acid concentration to 3-4, stirring and reacting at room temperature for 2-5 hours, filtering and washing to be neutral to obtain the bituminous coal purified by an acid method;
the alkaline method comprises the following steps: adding the dried, crushed and screened bituminous coal into an alkali metal hydroxide solution with the mass concentration of 7.5-17.5%, uniformly mixing, controlling the liquid-solid ratio to be 4-8, standing for 2-5 hours, drying in a drying box with the temperature of 105-550 ℃, roasting for 1-3 hours at the temperature of 550-450 ℃ in an inert atmosphere, filtering and washing the roasted product to be neutral, and obtaining the bituminous coal purified by an alkali method.
3. The method for preparing the silicon-carbon composite anode material as claimed in claim 1, wherein the nano silicon particles are subjected to surface oxidation treatment in a solution containing an oxidant to obtain the oxidized nano silicon particles.
4. The method for preparing the silicon-carbon composite anode material as claimed in claim 1, wherein the particle size of the nano silicon particles is 5-100 nm.
5. The method for preparing a silicon-carbon composite anode material according to claim 1, wherein the mass ratio of the bituminous coal to the oxidized nano-silicon particles is 1:5 to 20: 1.
6. The method for preparing a silicon-carbon composite anode material according to claim 1, wherein bituminous coal and the nano-silicon particles subjected to oxidation treatment are mixed in a solvent to obtain a mixed solution; carrying out spray drying granulation on the mixed solution in a spray dryer to obtain a mixed material;
the solvent is at least one of water, methanol, ethanol, propanol, toluene and diethyl ether;
in the spray drying process, the feeding speed is 0.5-4L/h, the air inlet temperature range is 180-200 ℃, and the air outlet temperature range is 50-80 ℃.
7. The preparation method of the silicon-carbon composite anode material as claimed in claim 1, wherein the heat preservation sintering is carried out for 1-3h at the first-stage sintering temperature; and carrying out heat preservation sintering for 1-3h at the second-stage sintering temperature.
8. A silicon-carbon composite anode material prepared by the preparation method of any one of claims 1 to 7; the bituminous coal pyrolysis carbon composite material is characterized by comprising nano silicon particles and bituminous coal pyrolysis carbon compounded on the surfaces of the nano silicon particles in situ.
9. The use of the silicon-carbon composite anode material of claim 8 for the preparation of lithium ion batteries.
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