CN114975959A - Method for preparing silicon/carbon composite anode material by utilizing photovoltaic industry line cutting waste silicon - Google Patents
Method for preparing silicon/carbon composite anode material by utilizing photovoltaic industry line cutting waste silicon Download PDFInfo
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- 239000010703 silicon Substances 0.000 title claims abstract description 94
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- 239000002699 waste material Substances 0.000 title claims abstract description 45
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 38
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- 238000005520 cutting process Methods 0.000 title claims abstract description 22
- 239000010405 anode material Substances 0.000 title claims abstract description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 100
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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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
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
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- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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 technical field of cutting waste silicon recycling, and particularly relates to a method for preparing a silicon/carbon composite anode material by utilizing photovoltaic industry linear cutting waste silicon, which comprises the following steps: 1) reducing the micron-sized waste silicon to submicron by mechanical sanding; 2) pre-oxidizing and chemically purifying the thinned silicon particles to obtain purified silicon particles; 3) and carrying out hydrothermal reaction on sucrose serving as a carbon source and purified silicon to obtain a precursor of the polymer-coated silicon particles, centrifugally washing to complete solid-liquid separation, and finally pyrolyzing the precursor under argon to obtain the silicon/carbon composite material. According to the method, the waste silicon and cane sugar are cut by a photovoltaic industry line with low cost and the surface of the waste silicon is coated with a conductive amorphous carbon layer by taking the raw materials. The coating of the carbon layer can improve the conductivity of the waste silicon, effectively relieve the internal stress generated by the volume change of the waste silicon in the lithium desorption process and improve the electrochemical stability of the composite material. Realizes the recycling of waste silicon and is suitable for further popularization and application.
Description
Technical Field
The invention belongs to the technical field of cutting waste silicon recycling, and particularly relates to a method for preparing a silicon/carbon composite anode material by utilizing photovoltaic industry linear cutting waste silicon.
Background
The current commercialized lithium ion battery cathode material mainly uses graphite, but the theoretical specific capacity of the graphite is only 370mAh/g, and the development requirement of the high-capacity lithium ion battery can not be met gradually. The silicon-based negative electrode is the material with the highest theoretical specific capacity (about 4200mAh/g) at present and is about 11 times of the theoretical specific capacity of the graphite negative electrode. On the other hand, silicon has a low intercalation potential (about 0.2V vs Li/Li +) and can output a higher voltage when matched to the positive electrode. In addition, the silicon is abundant and is the second element in the earth crust, and the silicon has very low toxicity and is environment-friendly. In conclusion, silicon is the most promising new generation of high specific capacity lithium ion battery anode material to replace graphite anode at present. The problem of exposure of the silicon negative electrode is also very significant. 1. As a semiconductor, the intrinsic conductivity of silicon is low, which directly affects the activity of the electrochemical reaction, reducing the cell's capacity output capability. 2. The silicon negative electrode is accompanied by severe volume expansion (300%) during the cycling process, which causes the material to crack, pulverize, and fall off from the surface of the current collector, resulting in severe capacity fade 3. the price of the commercially available nano silicon is expensive, which is not good for commercialization of the silicon negative electrode.
In recent years, the photovoltaic industry is rapidly developed, great loss is caused in the actual processing process of online cutting, about 40% of crystalline silicon is lost in the form of micron-sized silicon powder, and the waste silicon generated in the photovoltaic industry is nearly 20 ten thousand tons per year at present. There is therefore a need for an efficient way of recycling scrap silicon from line cutting in the photovoltaic industry.
Disclosure of Invention
Aiming at the problems, the invention provides a method for preparing a silicon/carbon composite cathode material by utilizing photovoltaic industry wire-electrode cutting waste silicon.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method for preparing a silicon/carbon composite anode material by utilizing photovoltaic industry wire-electrode cutting waste silicon comprises the following steps:
1) reducing the micron-sized waste silicon to submicron by mechanical sanding;
2) pre-oxidizing and chemically purifying the thinned silicon particles to obtain purified silicon particles;
3) and carrying out hydrothermal reaction on sucrose serving as a carbon source and purified silicon to obtain a precursor of the polymer-coated silicon particles, centrifugally washing to complete solid-liquid separation, and finally pyrolyzing the precursor under inert gas to obtain the silicon/carbon composite material.
Further, the step 1) is specifically as follows:
adding initial waste silicon and deionized water into a sand mill to grind to submicron.
Preferably, the rotation speed of the sand mill in the step 1) is 1500r/min, and the grinding time is 1 h.
Further, the step 2) specifically comprises:
2.1) heating and pre-oxidizing the sanded silicon powder in a muffle furnace;
2.2) adding the pre-oxidized silicon powder into HF solution, (NH) in sequence 3 ·H 2 O+H 2 O 2 ) Solution, (HCl + H) 2 O 2 ) Purifying the solution, filtering and washing the product, and drying to obtain purified silicon particles.
Preferably, the heating temperature in the step 2.1) is 850 ℃, and the oxidation time is 1 h.
Further, the step 2.2) specifically comprises:
slowly adding the oxidized silicon powder into 10 wt% of HF, stirring for 1h, filtering and washing;
then adding into the reaction solution containing NH 3 ·H 2 O、H 2 O 2 Treating the mixture with deionized water in a solution prepared according to the volume ratio of 1:1:5 at room temperature for 15min, filtering and washing;
finally adding HCl and H 2 O 2 And deionized water in a solution prepared according to the volume ratio of 1:1:5, treating at the temperature of 80 ℃ for 15min, filtering, washing, and drying in a vacuum drying oven at the temperature of 80 ℃ to obtain purified silicon particles.
Further, the step 3) specifically comprises:
3.1) mixing and stirring the solution 1 and the solution 2, and then pouring the mixture into a high-pressure kettle for heating reaction to obtain a precursor of the polymer-coated silicon particles;
3.2) cooling the reaction product at room temperature, then carrying out centrifugal filtration to obtain a precipitate, rinsing the precipitate with deionized water and ethanol successively for three times, then drying, and finally carrying out high-temperature carbonization on the dried precipitate in Ar atmosphere to obtain a silicon/carbon composite material;
wherein the solution 1 is prepared by adding 3.75g of sucrose, 1.75g of oxalic acid and 0.75g of hexadecyl trimethyl ammonium bromide into 20ml of deionized water under stirring;
the solution 2 was prepared from 20ml of deionized water with stirring and 0.5g of purified silicon particles, 0.75g of polyvinylpyrrolidone.
Preferably, the mixing and stirring time in the step 3.1) is 60min, the heating temperature is 200 ℃, and the heating time is 12 h;
drying the rinsed precipitate in the step 3.2) in a vacuum drying oven at 80 ℃; the carbonization temperature is 700 ℃, and the carbonization time is 6 h.
According to the method, sucrose is used as a carbon source in the hydrothermal reaction process, oxalic acid with the same molar ratio is added into a sucrose solution, the sucrose is hydrolyzed in one step to obtain glucose, and the glucose obtained by hydrolysis is more active than the glucose directly added at the beginning, so that the coating of carbon source polymers on silicon particles is facilitated.
In the invention, a layer of film can be formed on the surface of irregular waste silicon by adding PVP, active sites on the surface are increased, the combination of cetyl trimethyl ammonium bromide and waste silicon is facilitated, and a polymer can grow on the surface of the waste silicon along the direction of the cetyl trimethyl ammonium bromide in the hydrothermal reaction process; the effective combination of the hexadecyl trimethyl ammonium bromide and the waste silicon is beneficial to coating the silicon particles by the polymer in the hydrothermal reaction process.
The traditional purification scheme uses hydrochloric acid for soaking, and organic pollution liquid and impurity ions cannot be well removed. The invention adopts a one-step pre-oxidation method to remove organic pollution liquid (polyethylene glycol) at 850 ℃, and simultaneously generates an oxide film on the surface of the waste silicon. Subsequent removal of oxygen with hydrofluoric acidAnd (5) film formation, and further material size reduction. Then alkaline cleaning solution (mixed solution of ammonia water and hydrogen peroxide, wherein H is 2 O 2 Can form a natural oxide layer on the surface of the silicon to make the surface hydrophilic, the cleaning solution can wet the surface, the ammonia water can corrode the natural oxide layer on the surface subsequently, therefore, the particles adsorbed on the surface of the waste silicon can fall into the cleaning solution to be removed, such as Ni 2+ 、Ca 2+ ) Mixing with acidic cleaning solution (mixed solution of hydrochloric acid and hydrogen peroxide solution, and capable of dissolving multiple metal ions not complexed by ammonia such as Al 3+ ，Fe 3+ ) And removing metal ions on the surface of the waste silicon.
The traditional size reduction scheme is that mechanical ball milling needs a long time for achieving the size reduction effect, and the size of the material can be reduced more quickly by adopting sand milling.
The invention also provides a negative electrode plate, which comprises the prepared silicon/carbon composite negative electrode material, and the preparation method of the negative electrode plate comprises the following steps:
s1: mixing a silicon/carbon composite material, acetylene black and PAA-Li according to a mass ratio of 7: 2: 1, then uniformly mixing, then adding 70ul of deionized water and 30ul of absolute ethyl alcohol to prepare slurry, and stirring for not less than 12 hours;
in the mixing process, lithiated PAA is used for replacing the traditional CMC to be used as a binder, and the lithiated PAA serving as a flexible polymer can better adapt to the volume expansion of a silicon negative electrode in the charging and discharging processes, so that the electrochemical cycle stability of the material can be improved.
S2: coating the uniformly mixed slurry on a Cu foil by using a film drawing device, drying for more than 12h at 70 ℃ in a vacuum drying oven, rolling the pole piece by using a roller after drying, punching the pole piece into an electrode piece with the diameter of 12mm by using a slicing machine, and screening out the electrode piece which is complete and has no crease on the surface.
A film drawing device is selected for preparing the pole piece to replace the traditional scraper for coating, and the prepared pole piece is controllable and more uniform in thickness. The material on the pole piece can be more compact by the rolling of the roller machine, and good contact is beneficial to the conduction of ions.
The invention further provides a lithium ion battery which comprises the negative electrode plate.
Has the advantages that:
according to the invention, the surface of the waste silicon is coated with a conductive amorphous carbon layer by using low-cost photovoltaic industry line cutting waste silicon (purity is less than 2N) and cane sugar as raw materials. The coating of the carbon layer can improve the conductivity of the waste silicon, effectively relieve the internal stress generated by the volume change of the waste silicon in the lithium desorption process and improve the electrochemical stability of the composite material. The capacity of the composite material is still 1579mAh/g after the composite material is circulated for 150 cycles under the current density of 0.5A/g. The method reduces the cost of the silicon cathode material and provides a recovery way for the waste silicon of the photovoltaic industry by wire cutting.
Drawings
FIG. 1 is an SEM image of W-Si;
FIG. 2 is an SEM image of P-Si;
FIG. 3 is an SEM image of P-Si/C;
FIG. 4 is a graph of W-Si grit-sanding time variation;
FIG. 5 is an XRD pattern of W-Si, P-Si/C;
FIG. 6 is a TEM image of P-Si/C;
FIG. 7 is a graph showing the cycle performance of W-Si, P-Si/C (0.5A/g).
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The method for preparing the silicon/carbon composite cathode material by utilizing the photovoltaic industry line cutting waste silicon comprises the following steps:
1. the initial scrap silicon is denoted as W-Si. 10g W-Si and 500ml deionized water are added into a sand mill for grinding for 1h at 1500 r/min.
2. Sanded siliconThe powder was oxidized in a muffle furnace at 850 ℃ for 1 h. Then, 10g of oxidized silicon powder was slowly added to 10 wt% HF (prepared from 25ml of 40 wt% HF and 75ml of deionized water), stirred for 1 hour, filtered and washed. Is then added to NH 3 ·H 2 O、H 2 O 2 Treating with deionized water (volume ratio of 1:1:5) at room temperature for 15min, filtering, and washing. Finally adding HCl and H 2 O 2 And treating the second liquid prepared by deionized water (the volume ratio is 1:1:5) at the temperature of 80 ℃ for 15min, filtering, washing, and drying in a vacuum drying oven at the temperature of 80 ℃ to obtain a purified silicon particle product, which is marked as P-Si.
(1) preparing solution 1: to 20ml of deionized water were added 3.75g of sucrose, 1.75g of oxalic acid, and 0.75g of cetyltrimethylammonium bromide with stirring.
(2) Preparing a solution 2: to 20ml of deionized water, 0.5g of P-Si and 0.75g of polyvinylpyrrolidone were added with stirring.
(3) Solution 1 was mixed with solution 2 and stirred vigorously for 60 minutes. The mixed solution was poured into a Teflon-lined stainless steel autoclave and maintained at 200 ℃ for 12 hours. Cooling at room temperature, centrifuging to obtain precipitate, and rinsing with deionized water and ethanol successively for three times. And drying the final product in a vacuum drying oven at 80 ℃, and finally carbonizing the final product for 6 hours at 700 ℃ in Ar atmosphere. The powder obtained (rate of temperature rise 5 ℃/min) was noted as P-Si/C. Wherein Si/C is 1: 7.5.
(1) slurry preparation: the method comprises the following steps of (1) mixing an active material, acetylene black and PAA-Li according to the mass percentage of 7: 2: 1, then adding 70ul of deionized water and 30ul of absolute ethyl alcohol into the mixture by using a liquid-transferring gun to prepare slurry with moderate viscosity, and stirring for not less than 12 hours.
(2) Preparing a pole piece: and (3) coating the uniformly mixed slurry on a Cu foil by using a film drawing device, and drying for more than 12 hours in a vacuum drying oven at 70 ℃. After drying, rolling the pole piece by a roller machine, punching the pole piece into an electrode piece with the diameter of 12mm by a slicer, screening out the complete electrode piece without crease on the surface, and finally weighing the mass of the pole piece and the blank Cu foil.
(3) Assembling half cell in glove box with 2025 battery case, 1.5mm lithium sheet, 0.8mm gasket, and Polyethylene (PE) as separatorElectrolyte LiPF 6 (1mol/L)/EC + DEC + EMC, and assembling the button half cell. Standing at room temperature for more than 24h to allow the electrolyte to infiltrate the diaphragm, and waiting for electrochemical test and analysis.
Changing the mass of P-Si to be 0.75g and the other experimental conditions to be 0.375g, respectively carrying out experiments to obtain P-Si/C1: 5. P-Si/C1: 10.
characterization and testing
As can be seen from fig. 1, the original silicon scrap has an irregular shape, mostly in the form of sheet, layer or strip, with the size varying from several micrometers to several hundred nanometers. It can be seen from fig. 2 that the material after sanding and chemical purification has a significant reduction in size and an increase in size uniformity.
As shown in FIG. 4, the grain size median diameter (D50) of the waste silicon after sanding for 60min, 120min, 180min and 240min is respectively 0.445um, 0.381um, 0.348um and 0.286um at the rotating speed of 1500 r/min. As sanding time increases, the particle size of the waste silicon decreases significantly, appearing flocculent. The sanding treatment condition at 1500r/min for 60min was most effective in reducing the size (48.8% reduction in product size).
As can be seen from fig. 3, the surface of the waste silicon is still sheet-like after being coated with the sucrose-derived carbon layer, and an uneven amorphous carbon layer appears on the surface.
From FIG. 5, it can be seen that the P-Si after sand grinding and chemical purification corresponds to the characteristic peaks of silicon on the standard PDF #27-1402 one by one, indicating that no other impurities are brought in by the sand grinding and chemical purification steps, and the main phase of P-Si is still Si. P-Si/C1 after carbon coating treatment: 5. P-Si/C1: 7.5, P-Si/C1: 10 show a broad peak around 23 deg., corresponding to amorphous carbon, and the characteristic peaks of silicon still correspond one-to-one to the standard PDF cards. The method shows that the hydrothermal carbon-coating method using sucrose as a carbon source can introduce amorphous carbon without damaging the silicon phase of the material main body.
As shown in FIG. 6, FIG. 6a shows that the P-Si/C composite material prepared exhibits a sheet-like structure, and the sheets are combined into islands. The lattice fringes at a pitch of 0.31nm in fig. 6C correspond to the (111) lattice plane of Si. Further illustrating the existence of the carbon layer and the main phase crystalline silicon, the feasibility of the sucrose hydrothermal carbon coating method is shown.
As shown in FIG. 7, the specific discharge capacity of W-Si in the first turn is up to about 3600mAh/g, but the capacity after 25 turns is suddenly reduced to 300mAh/g, and the electrochemical performance of W-Si is extremely unstable. Compared with W-Si, the cycle performance of the three modified P-Si/C samples is improved. P-Si/C1: the initial discharge specific capacity of 5 reaches 3000mAh/g, but the rapid capacity attenuation occurs after 10 circles, and the discharge specific capacity is about 1200mAh/g after 150 circles of circulation. The reason is that the silicon occupies a relatively large amount, and the volume expansion of the silicon cannot be well inhibited in the thin cyclic process of the carbon layer, so that the specific capacity of the first ring is high but the cyclic performance is poor. P-SI/C1: the first discharge specific capacity of 10 is 1824mAh/g, and the capacity after 150 cycles is 940 mAh/g. The higher carbon ratio, although the cycle performance is improved, the lower silicon content does not take advantage of the high capacity of silicon. The first discharge specific capacity of P-Si/C1: 7.5 reaches 2682mAh/g, and the capacity still reaches 1579mAh/g after the circulation is carried out for 150 circles under the current density of 0.5A/g.
Therefore, compared with other two modified samples, the P-Si/C1: 7.5 optimizes the cycle stability performance while ensuring the discharge specific capacity, and is a preferred scheme of the scheme. On one hand, the reduction of the size and the removal of organic dirt and an oxide layer on the surface of the waste silicon improve the lithium ion transmission performance. On the other hand, although a part of the first-turn specific discharge capacity is lost by the introduction of the amorphous carbon layer, the cycle stability performance of the material is improved. Therefore, the invention can actually improve the electrochemical cycle performance of the linear cutting waste silicon in the photovoltaic industry as the lithium ion battery cathode material.
The above embodiments are further described in detail for illustrating the objects, technical solutions and advantages of the present invention, it should be understood that the above embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for preparing a silicon/carbon composite anode material by utilizing photovoltaic industry wire-electrode cutting waste silicon is characterized by comprising the following steps:
1) reducing the micron-sized waste silicon to submicron by mechanical sanding;
2) pre-oxidizing and chemically purifying the thinned silicon particles to obtain purified silicon particles;
3) and carrying out hydrothermal reaction on sucrose serving as a carbon source and purified silicon to obtain a precursor of the polymer-coated silicon particles, centrifugally washing to complete solid-liquid separation, and finally pyrolyzing the precursor under inert gas to obtain the silicon/carbon composite material.
2. The method for preparing the silicon/carbon composite anode material by utilizing the photovoltaic industry wire-electrode cutting waste silicon according to claim 1, wherein the step 1) is as follows:
adding initial waste silicon and deionized water into a sand mill to grind to submicron.
3. The method for preparing the silicon/carbon composite anode material by utilizing the photovoltaic industry wire-electrode cutting waste silicon as claimed in claim 2, wherein the rotation speed of the sand mill in the step 1) is 1500r/min, and the grinding time is 1 h.
4. The method for preparing the silicon/carbon composite anode material by using the photovoltaic industry wire-electrode cutting waste silicon as claimed in claim 1, wherein the step 2) specifically comprises:
2.1) heating and pre-oxidizing the sanded silicon powder in a muffle furnace;
2.2) adding the pre-oxidized silicon powder into HF solution, (NH) in sequence 3 ·H 2 O+H 2 O 2 ) Solution, (HCl + H) 2 O 2 ) Purifying the solution, filtering and washing the product, and drying to obtain purified silicon particles.
5. The method for preparing the silicon/carbon composite anode material by utilizing the photovoltaic industry wire-electrode cutting waste silicon as claimed in claim 4, wherein the heating temperature in the step 2.1) is 850 ℃, and the oxidation time is 1 h.
6. The method for preparing the silicon/carbon composite anode material by utilizing the photovoltaic industry wire-electrode cutting waste silicon as claimed in claim 4, wherein the step 2.2) specifically comprises the following steps:
slowly adding the oxidized silicon powder into 10 wt% of HF, stirring for 1h, filtering and washing;
then adding into the reaction solution containing NH 3 ·H 2 O、H 2 O 2 Treating the mixture with deionized water in a solution prepared according to the volume ratio of 1:1:5 at room temperature for 15min, filtering and washing;
finally adding HCl and H 2 O 2 And deionized water in a solution prepared according to the volume ratio of 1:1:5, treating at the temperature of 80 ℃ for 15min, filtering, washing, and drying in a vacuum drying oven at the temperature of 80 ℃ to obtain purified silicon particles.
7. The method for preparing the silicon/carbon composite anode material by using the photovoltaic industry wire-electrode cutting waste silicon as claimed in claim 1, wherein the step 3) specifically comprises:
3.1) mixing and stirring the solution 1 and the solution 2, and then pouring the mixture into a high-pressure kettle for heating reaction to obtain a precursor of the polymer-coated silicon particles;
3.2) cooling the reaction product at room temperature, then carrying out centrifugal filtration to obtain a precipitate, rinsing the precipitate with deionized water and ethanol for three times in sequence, then drying, and finally carrying out high-temperature carbonization on the dried precipitate in Ar atmosphere to obtain the silicon/carbon composite material;
wherein the solution 1 is prepared by adding 3.75g of sucrose, 1.75g of oxalic acid and 0.75g of hexadecyl trimethyl ammonium bromide into 20ml of deionized water under stirring;
the solution 2 was prepared from 20ml of deionized water with stirring and 0.5g of purified silicon particles, 0.75g of polyvinylpyrrolidone.
8. The method for preparing the silicon/carbon composite anode material by utilizing the photovoltaic industry wire-electrode cutting waste silicon is characterized in that in the step 3.1), the mixing and stirring time is 60min, the heating temperature is 200 ℃, and the heating time is 12 h;
drying the rinsed precipitate in the step 3.2) in a vacuum drying oven at 80 ℃; the carbonization temperature is 700 ℃, and the carbonization time is 6 h.
9. A negative electrode sheet comprising the silicon/carbon composite negative electrode material according to any one of claims 1 to 8, the method for producing the negative electrode sheet comprising the steps of:
s1: mixing a silicon/carbon composite material, acetylene black and PAA-Li according to a mass ratio of 7: 2: 1, then adding 70ul of deionized water and 30ul of absolute ethyl alcohol to prepare slurry, and stirring for not less than 12 hours;
s2: coating the uniformly mixed slurry on a Cu foil by using a film drawing device, drying for more than 12h at 70 ℃ in a vacuum drying oven, rolling the pole piece by using a roller after drying, punching the pole piece into an electrode piece with the diameter of 12mm by using a slicing machine, and screening out the electrode piece which is complete and has no crease on the surface.
10. A lithium ion battery comprising the negative electrode sheet according to claim 9.
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