CN113023731B

CN113023731B - Method for preparing silicon powder

Info

Publication number: CN113023731B
Application number: CN202110389273.XA
Authority: CN
Inventors: 王晓哲; 韩昀钊
Original assignee: Longi Green Energy Technology Co Ltd
Current assignee: Longi Green Energy Technology Co Ltd
Filing date: 2021-04-12
Publication date: 2024-05-03
Anticipated expiration: 2041-04-12

Abstract

The application provides a method for preparing silicon powder, which comprises the following steps: spray drying the mortar; jet milling is carried out on the product obtained by spray drying, thereby obtaining silicon powder; wherein, the solid content in the diamond wire cutting waste liquid is 3.5 to 45.0 percent according to the mass percentage; the grain size distribution D90 of silica powder particles in the mortar is less than or equal to 2.20 mu m. The method for preparing the silicon powder realizes the recycling of the waste liquid of the diamond wire cutting, reduces the resource waste, has low discharge amount of three wastes in the production process, is environment-friendly, has low cost for producing the silicon powder and is easy for mass production, and the battery prepared from the silicon powder produced by the method has high charge and discharge capacity and high initial coulombic efficiency.

Description

Method for preparing silicon powder

Technical Field

The invention relates to the technical field of silicon materials, in particular to a method for preparing silicon powder.

Background

Along with the high-speed development of economy, the energy crisis and the environmental problems are increasingly aggravated, and the lithium ion battery has been widely applied in the fields of portable consumer electronics, electric tools, medical electronics and the like because of the advantages of high energy density, high power density, long cycle life, no memory effect, low self-discharge rate, wide working temperature range, safety, reliability, environmental friendliness and the like; meanwhile, the method has good application prospect in the fields of pure electric vehicles, hybrid electric vehicles, energy storage and the like.

However, in recent years, the demand for battery energy density has rapidly increased in various fields, and development of lithium ion batteries having higher energy density has been strongly demanded. At present, the commercial lithium ion battery mainly uses graphite as a negative electrode material, the theoretical specific capacity of the graphite is 372mAh/g, and the high-end graphite material on the market can reach 360-365 mAh/g, so that the improvement space of the energy density of the corresponding lithium ion battery is quite limited.

Under the background, the silicon-based anode material is considered to be a potential anode material of a next-generation high-energy-density lithium ion battery because of the advantages of higher theoretical specific capacity (high temperature 4200mAh/g, room temperature 3580 mAh/g), low delithiation potential (< 0.5V), environmental friendliness, abundant reserves, lower cost and the like. However, the silicon material has volume expansion of 300% in the lithium intercalation process, and repeated expansion and contraction can lead to pulverization and falling of the anode material, and finally lead to loss of electrical contact of the anode material, so that the battery is completely failed. Nanocrystallization of silicon materials can effectively solve the above-described problems.

The preparation method of the industrial silicon particles mainly comprises a ball milling method and chemical vapor deposition, wherein the ball milling method is used for crushing massive silicon into silicon nano particles by utilizing rolling mechanical force, and has the advantages of high yield, low cost and easy doping, but the ball milling method has the defects of long production process, long time, more impurities, high surface oxidation degree, wide particle size distribution range, larger particle size, easy agglomeration and the like when the silicon material is contacted with a grinding medium. Chemical vapor deposition is usually carried out by pyrolyzing, condensing and depositing a gas-phase silicon source such as silane or silicon tetrachloride to form spheroid-like nano silicon particles with controllable particle size and narrower particle size distribution range, but the gas-phase silicon source of the CVD is dangerous, has lower yield, has higher equipment cost and the like, and limits the scale.

Disclosure of Invention

Aiming at the problems, the invention provides the method for preparing the silicon powder, which can realize the recycling of wastes, reduce the resource waste, has low cost for producing the silicon powder and is easy for mass production, and the battery prepared from the silicon powder obtained by the production has high charge and discharge capacity and high initial coulombic efficiency.

The specific technical scheme comprises the following steps:

1. A method for preparing silicon powder, comprising the following steps:

spray drying the mortar;

jet milling is carried out on the product obtained by spray drying, thereby obtaining silicon powder;

Wherein, the solid content in the mortar is 3.5 to 45.0 percent according to the mass percentage;

the grain size distribution D90 of silica powder particles in the mortar is less than or equal to 2.20 mu m.

2. A process for producing silicon powder according to claim 1, wherein,

The air inlet temperature of the spray drying is 200-230 ℃, specifically 210 ℃, 220 ℃ and preferably 200-210 ℃; the air outlet temperature is 80-110 ℃, specifically 90 ℃, 100 ℃, preferably 85-90 ℃.

3. The process for producing silicon powder according to item 1, wherein the jet-milling has a jet pressure of 0.2 to 0.7MPa, specifically 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, preferably 0.2 to 0.4MPa; the rotation speed of the classifier wheel is 2500 to 4500rpm, specifically 3000rpm, 3500rpm, 4000rpm, preferably 4000 to 4500rpm.

4. The method for producing silicon powder according to item 1, wherein the total content of metal ion impurities in the silicon powder is 500ppm or less in terms of mass ratio.

5. The method for producing silicon powder according to item 1, wherein the mortar is produced by adding silicon paste to a waste diamond wire cutting liquid.

6. A method of preparing silicon powder according to item 1, further comprising the step of stirring the mortar before the spray-drying treatment.

The method for preparing the silicon powder realizes the recycling of the waste liquid of the diamond wire cutting, has low discharge amount of three wastes in the production process, is environment-friendly, has low cost for producing the silicon powder, is easy for mass production, and has high charge and discharge capacity and high initial coulombic efficiency of a battery prepared from the silicon powder obtained by using the method.

Noun interpretation

Particle size distribution and particle size distribution diagram:

In the present invention, the particle size distribution of the silicon powder refers to the particle size volume distribution of the silicon powder detected using a laser particle size distribution meter. The graph of the particle size and volume distribution output of the laser particle size distribution instrument for detecting the silicon powder is the particle size distribution graph. The volume ratio of the silicon powder distributed in different particle size ranges can be calculated through the integral areas of the peaks with different particle sizes.

FIG. 1 is a distribution diagram of the grain size of silicon powder according to example 1, using a bettersize laser grain size distribution instrument manufactured by Dandong Baite instruments Co., ltd.

Diamond wire cutting waste liquid:

When the diamond wire cutting method is used for producing the silicon wafer, the surfactant and the cooling water are used as cooling and lubricating media, the high-speed running steel wire for electroplating diamond particles is used for cutting the silicon wafer, and the surfactant and the cooling water carry out the cut silicon powder to form the diamond wire cutting waste liquid. Since the crystalline silicon has anisotropy, the crystalline silicon is cut from a specific cleavage plane during the cutting process, thereby forming particles having a specific morphology.

Silicon mud:

In the production process, because the mortar cannot be directly discharged and the discharge requirement can be met by sewage treatment, the mortar is subjected to procedures such as centrifugation, filtration, filter pressing and the like to reduce the water content, so that the semi-solid paste is produced, namely the silicon mud in the application.

And (3) mortar:

The waste diamond wire cutting liquid can be directly used as mortar, or silicon mud is added into the waste diamond wire cutting liquid to form high-solid-content mortar for subsequent treatment.

Sheet size of silicon powder particles:

The sheet-like size of the silicon powder particles refers to the maximum value of any two-point line segments passing through the geometric center of the sheet-like surface of the silicon powder particles detected by using a scanning electron microscope.

In addition, the average flake size of the present invention refers to the arithmetic average of the flake sizes of any number of silicon powder particles. In the examples and comparative examples, 5 areas are randomly selected to shoot silicon powder by using an American FEI cold field emission scanning electron microscope Quanta SEM scanning electron microscope under the condition that the magnification is 50000 times, and the sheet sizes of all silicon powder particles in the shooting view are counted and arithmetic average is taken to obtain the average sheet size.

Thickness of silicon powder particles:

The thickness of the silicon powder particles refers to the minimum dimension of the silicon powder particles in the direction perpendicular to the sheet-shaped surface through the geometric center of the silicon powder particles by using a scanning electron microscope.

In addition, the average thickness of the present invention refers to the arithmetic average of the thickness of any number of silicon powder particles. In the embodiment and the comparative example, the invention uses an American FEI cold field emission scanning electron microscope Quanta SEM scanning electron microscope to randomly select 5 areas to shoot silicon powder under the condition that the magnification is 50000 times, and the thickness of all silicon powder particles in the shooting view field is counted and the arithmetic average value is taken, so that the average thickness is obtained.

The foregoing description is only an overview of the technical solutions of the present invention, to the extent that it can be implemented according to the content of the specification by those skilled in the art, and to make the above-mentioned and other objects, features and advantages of the present invention more obvious, the following description is given by way of example of the present invention.

Drawings

Fig. 1: the particle size distribution detection result of the silicon powder obtained in example 1;

Fig. 2: scanning electron microscope pictures of the silicon powder obtained in the embodiment 1;

fig. 3: nitrogen isothermal adsorption and desorption curves of the silicon powder obtained in the example 1;

fig. 4: fig. 4-1: peak splitting diagram of oxygen element excitation peak in 524-540 electron volt interval; fig. 4-2: x-ray photoelectron spectroscopy (XPS) total spectrum of the silicon powder obtained in example 1; fig. 4-3: peak splitting diagram of silicon element excitation peak in 95-107 electron volt interval;

fig. 5: a transmission electron microscope picture of the silicon powder obtained in example 1;

fig. 6: x-ray diffraction pattern (XRD) of the silicon powder obtained in example 1;

Fig. 7: a first charge-discharge curve of a button cell prepared from the silicon powder obtained in example 1;

Fig. 8: the particle size distribution of silica powder particles in the mortar raw material of example 1 was measured.

Detailed Description

The following embodiments of the invention are merely illustrative of specific embodiments for carrying out the invention and are not to be construed as limiting the invention. Any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the invention are intended to be equivalent arrangements which are within the scope of the invention.

In one specific embodiment, a method of preparing silicon powder is provided, comprising the steps of:

spray drying the mortar;

In a specific embodiment, the air inlet temperature of the spray drying is 200-230 ℃, preferably 200-210 ℃; the temperature of the air outlet is 80-110 ℃, preferably 85-90 ℃.

In a specific embodiment, the jet mill has a jet pressure of 0.2 to 0.7MPa, preferably 0.2 to 0.4MPa; the rotation speed of the classifying wheel is 2500-4500 rpm, preferably 4000-4500 rpm.

In a specific embodiment, the total content of metal ion impurities in the silicon powder is less than or equal to 500ppm by mass ratio.

In a specific embodiment, the mortar is prepared by adding silicon sludge to waste diamond wire cutting liquid.

The solid content of the mortar can be increased by adding the silicon mud, so that the preparation efficiency of the silicon powder is improved.

In a specific embodiment, the method further comprises the step of stirring the mortar prior to the spray drying process.

And stirring the mortar to prevent silicon powder in the mortar from agglomerating.

The method for preparing the silicon powder realizes the recycling of the waste liquid of the diamond wire cutting, reduces the resource waste, has low discharge amount of three wastes in the production process, is environment-friendly, has low cost for producing the silicon powder, is easy for mass production, and has high charge and discharge capacity and high initial coulombic efficiency for the battery prepared by the silicon powder obtained by the production.

Examples

The experimental methods used in the following examples are conventional methods, if no special requirements are imposed.

Materials, reagents and the like used in the examples described below are commercially available unless otherwise specified.

Mortar source:

The mortar used in the following examples was a waste solution of wire cutting of diamond generated by the applicant in wire cutting of crystalline silicon during production of silicon wafers, and silicon sludge was mixed in the waste solution of wire cutting of diamond. The solid content of the silicon powder in the diamond wire cutting waste liquid is 3.5 to 6.5 percent. Unless otherwise specified, the mortar used in the following processes was from that produced by the applicant. Since the current process of diamond wire cutting silicon wafers is similar, the composition of the generated diamond wire cutting waste liquid and the characteristics of silicon powder particles therein are similar, and therefore, those skilled in the art know to use the diamond wire cutting waste liquid produced by other companies as the mortar in the embodiment of the application.

In addition, to prevent agglomeration of the silicon powder before preparation of the silicon powder, the mortar may be stirred.

And (3) detecting the solid content of the mortar:

In the following examples and comparative examples, the solid content of mortar was measured by centrifugation and drying, specifically, quantitative mortar was taken and centrifuged at high speed to give clear supernatant (the centrifuge was a Sorvall MTX 150 desktop micro ultracentrifuge, brand name of Thermo FISHER SCIENTIFIC, U.S.); and discharging supernatant, vacuum drying the solid slag to constant weight, and calculating the solid content of the mortar through the weight of the solid slag.

Spray drying:

in the following examples and comparative examples, 8LPG-50 type spray dryer, ganlin drying engineering Co., ltd. In Changzhou was used for spray drying.

Jet milling:

In the following examples and comparative examples, a Sichuan ultra-fine powder apparatus manufacturing Co.Ltd. JSDL-Q type jet mill was used for jet milling.

Example 1

(1) And (3) detecting mortar:

the mortar used in this example was a waste diamond wire cutting liquid.

Taking mortar, and measuring the solid content of the mortar to be 4.2%;

(2) Spray drying the mortar:

the air inlet temperature of spray drying is 210 ℃, and the air outlet temperature is 85 ℃;

(3) Then carrying out jet milling:

airflow pressure: 0.3MPa, and the rotation speed of the classifying wheel is 4500rpm.

Thereby preparing silicon powder.

Examples 2 to 7 differ from example 1 in the solids content of the mortar, as well as in the parameters of spray drying and jet milling. In addition, example 7 was a mortar formed by adding silicon sludge to a waste diamond wire cutting liquid.

Comparative examples 1 to 7 differ from example 1 in the parameters of spray drying and jet milling.

The mortar treatment parameters of examples 1 to 7 and comparative examples 1 to 6 are specifically shown in Table 1.

Table 1:

The silicon powders obtained in examples 1 to 7 and comparative examples 1 to 6 were subjected to the following tests. The method and results for detecting the silicon powder obtained in example 1 are shown below by way of example, and the method for detecting other examples and comparative examples are the same as in example 1. The obtained test results are shown in Table 2 (Table 2-1 and Table 2-2).

(1) Silica powder particle size distribution determination

Particle size distribution was measured using bettersize2600 manufactured by dandong baud instruments.

The result of the particle size volume distribution test of the silicon powder obtained in example 1 is shown in fig. 1, which includes 3 peaks, in order from small to large: 0.13 μm (first peak position), 0.52 μm (second peak position), 1.55 μm (third peak position); the particle size was D10:0.242. Mu.m, D50:0.745. Mu.m, D90:2.049. Mu.m. The volume ratio of the silicon powder distributed in different particle size ranges can be calculated through the integral areas of the peaks with different particle sizes.

(2) Silica powder particle morphology determination

Silicon powder was photographed using a FEI cold field emission scanning electron microscope Quanta SEM.

As shown in fig. 2 (fig. 2-1, fig. 2-2), a scanning electron microscope image of the silicon powder of example 1 is shown, wherein the silicon powder particles are in a sheet-like nano structure, and the average thickness of the particles is 60nm; the average sheet size is: 0.792 μm, so that the ratio of the average sheet size to the average thickness was 13.2.

The average sheet size and average thickness are the average sheet size and average thickness of example 1, in which 5 regions are randomly selected to photograph silicon powder by using a scanning electron microscope under the condition that the magnification is 50000 times, and the sheet size and thickness of all silicon powder particles in the photographed field of view are counted and the arithmetic average is taken. In the following examples and comparative examples, average sheet sizes and average thicknesses were obtained by the same methods.

(3) Silica powder tap density determination

According to GB/T24533, detection is carried out by using an HY-100 tap density tester of Dendong Haoyu science and technology Co.

Wherein, the detection result of the example 1 is 0.1123g/cm ³.

(4) Determination of specific surface area of silica powder

The detection was carried out according to GB/T19587 using a Tristar 3020 specific surface area and porosity analyzer manufactured by Micromeritics, inc.

The isothermal adsorption and desorption curves of nitrogen of the silicon powder of example 1 are shown in fig. 3. The specific surface area of the silicon powder is calculated according to the BET equation to be: 15.95m ²/g.

(5) Surface chemical bond detection

Detection was performed using a K-Alpha type X-ray photoelectron spectrometer (XPS) from Thermo FISHER SCIENTIFIC, U.S.

The nano-silicon surfaces in examples 1 to 7 and comparative examples 1 to 6 mainly contain three elements such as silicon, oxygen, and carbon. The peak separation result shows that the silicon surface is completely oxidized, and no other impurities except carbon exist; meanwhile, the presence of the si—si bond indicates that the thickness of the si oxide layer is less than 10nm (XPS radiation detection depth), and the detection result is not shown in table 2.

The detection diagram of example 1 is shown in detail in FIG. 4 (FIGS. 4-1 to 4-3).

Wherein: FIG. 4-1 is a peak separation diagram of oxygen element excitation peaks in the 524-540 electron volt interval;

FIG. 4-2 is an X-ray photoelectron spectroscopy (XPS) total spectrum of silicon powder;

FIG. 4-3 is a peak separation diagram of the Si element excitation peak in the 95-107 eV interval.

(6) Thickness of surface oxide layer

Detection was performed using a Themis TEM transmission electron microscope of Thermo FISHER SCIENTIFIC, usa, and the material surface state was analyzed by high power transmission electron microscopy;

FIG. 5 (5-1, 5-2) is a transmission electron microscope photograph of the silicon powder of example 1.

The high-power transmission electron microscope photo shows that the material matrix is in a crystalline state, and the surface of the material matrix is in an amorphous state with the wavelength of 2-5 nm; the thickness of the oxide layer on the surface of the silicon powder is about 2-5 nm, and the oxidation degree is small.

(7) Crystal form detection

And (3) detecting a crystal form: and (3) detecting the crystal form of the product by using a BRUKER D8 ADVANCE X-ray polycrystalline diffractometer.

FIG. 6 is a graph of the test pattern of the silica fume particles of example 1.

Among them, X-ray diffraction pattern (XRD) shows that: the diffraction peak intensity of the silicon powder is high, the background noise is low, all peak positions can be well matched with a crystalline silicon standard spectrum (JCPCDS card No. 01-0787), and no obvious impurity peak exists; indicating that the silicon powder is a crystalline silicon material.

The detection results in examples 1 to 7 and comparative examples 1 to 6 are similar to each other, and the detection results are not shown in Table 2.

(8) Oxygen and carbon content detection

Detecting the carbon content of the silicon powder by using a CS320 type high-frequency infrared carbon-sulfur instrument of Chongqing Sharey instruments Co;

the oxygen content of the silicon powder was measured using an ONH-330 oxygen-nitrogen-hydrogen tester from Chongqing Ministry of instruments.

Wherein the test results of example 1 are:

Carbon content: 3.13%;

oxygen content: 4.76%.

(9) Metal ion impurity detection

Detection was performed using ICPMS model NexION from perkin elmer PE company.

The test results of example 1 were: the total content of total metal ion impurities in the silicon powder is 132ppm.

Table 2-1:

Table 2-2:

In addition, silicon powder in the prior art was used as comparative examples 7 to 8.

Among them, comparative example 7 was a silicon powder obtained from Beijing island gold technology Co., ltd, and was ground to obtain a silicon powder having a particle size D50 of 0.811 μm, which was close to the silicon powder particle size D50 of example 1, and it was found that the silicon powder particles of comparative example 7 were spherical.

Comparative example 8 is silicon powder obtained from Shanghai super-Wired nanotechnology Co., ltd. And ground to a particle size D50 of 0.765 μm, which is close to the particle size D50 of the silicon powder of example 1, it is known that the silicon powder of comparative example 8 is spherical.

Experimental example:

In the art, products are typically fabricated into CR2016 button cells to simulate full cell reactions, and the specific capacity and coulombic efficiency of the products are measured.

The silicon powders prepared in examples 1 to 7 and comparative examples 1 to 8 were prepared into 8 CR2016 button cells, respectively, and the preparation method of the cells was as follows:

(1) Weighing and mixing silicon powder, conductive carbon black and lithiated polyacrylic acid according to the mass ratio of 7:2:1, and uniformly stirring under a water system to prepare electrode slurry;

(2) Coating electrode slurry on a copper foil for a lithium battery negative electrode, wherein the coating thickness is 150 mu m, and then drying the coated copper foil to constant weight in a vacuum oven to prepare a battery pole piece;

(3) Cutting the pole piece into small wafers by adopting a cutting machine with the diameter of 12mm, then placing the small wafers in a glove box, and assembling the button cell under the environment that the water oxygen values are less than 0.1 ppm;

(4) And (3) selecting a CR2016 button cell shell, assembling by adopting the sequence of a positive electrode shell, a pole piece, a diaphragm, a metal lithium piece, a gasket and a negative electrode shell, and then injecting electrolyte and packaging to obtain the assembled button cell.

The specific discharge capacity, the charging capacity and the first coulombic efficiency of the corresponding batteries prepared in each example and comparative example are detected, and the average numbers are respectively recorded in a table 3.

Table 3:

the specific measuring method comprises the following steps:

According to GB/T38823-2020, a Wuhan blue electric constant current battery tester is selected to perform charge and discharge test on the assembled button battery, a first discharge capacity divided by the mass of silicon powder in a pole piece is the specific discharge capacity (lithium intercalation), and the same time, the first charge capacity divided by the mass of silicon powder in the pole piece is the charge capacity (lithium deintercalation), and the charge capacity divided by the discharge capacity multiplied by 100% is the first coulombic efficiency.

Wherein fig. 7 shows the first charge and discharge curves of the battery prepared from the silicon powder of example 1.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described specific embodiments and application fields, and the above-described specific embodiments are merely illustrative, and not restrictive. Those skilled in the art, having the benefit of this disclosure, may effect numerous forms of the invention without departing from the scope of the invention as claimed.

Claims

1. A method for preparing silicon powder, comprising the following steps:

spray drying the mortar;

wherein, the solid content in the mortar is 3.5-45.0% by mass percent;

the grain size distribution D90 of silica powder particles in the mortar is less than or equal to 2.20 mu m;

The air inlet temperature of the spray drying is 200-230 ℃;

the air outlet temperature is 80-110 ℃;

the air flow pressure of the air flow crushing is 0.2-0.7 MPa;

the rotating speed of the classifying wheel is 2500-4500 rpm.

2. A method for preparing silicon powder as defined in claim 1,

The air inlet temperature of the spray drying is 200-210 ℃; the air outlet temperature is 85-90 ℃.

3. A method for preparing silicon powder as defined in claim 1,

The air flow pressure of the air flow crushing is 0.2-0.4 MPa; the rotating speed of the classifying wheel is 4000-4500 rpm.

4. A method for producing silicon powder according to claim 1, wherein the total content of metal ion impurities in the silicon powder is 500ppm or less in terms of mass ratio.

5. A method for producing silicon powder according to claim 1, wherein the mortar is produced by adding silicon paste to a waste diamond wire cutting liquid.

6. A method for preparing silicon powder as defined in claim 1,

The method further comprises the step of stirring the mortar before the spray drying treatment.