CN113023731A - Method for preparing silicon powder - Google Patents
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- CN113023731A CN113023731A CN202110389273.XA CN202110389273A CN113023731A CN 113023731 A CN113023731 A CN 113023731A CN 202110389273 A CN202110389273 A CN 202110389273A CN 113023731 A CN113023731 A CN 113023731A
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 126
- 239000011863 silicon-based powder Substances 0.000 title claims abstract description 107
- 238000000034 method Methods 0.000 title claims abstract description 39
- 239000002245 particle Substances 0.000 claims abstract description 56
- 239000004570 mortar (masonry) Substances 0.000 claims abstract description 44
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- 238000005520 cutting process Methods 0.000 claims abstract description 25
- 238000009826 distribution Methods 0.000 claims abstract description 25
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- 239000010432 diamond Substances 0.000 claims abstract description 23
- 238000001694 spray drying Methods 0.000 claims abstract description 20
- 239000007788 liquid Substances 0.000 claims abstract description 19
- 239000007787 solid Substances 0.000 claims abstract description 14
- 238000010902 jet-milling Methods 0.000 claims abstract description 8
- 229910052710 silicon Inorganic materials 0.000 claims description 21
- 239000010703 silicon Substances 0.000 claims description 21
- 239000012535 impurity Substances 0.000 claims description 8
- 229910021645 metal ion Inorganic materials 0.000 claims description 5
- 238000003756 stirring Methods 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 abstract description 11
- 238000004064 recycling Methods 0.000 abstract description 4
- 238000011031 large-scale manufacturing process Methods 0.000 abstract description 3
- 238000007599 discharging Methods 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 19
- 238000001514 detection method Methods 0.000 description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
- 239000001301 oxygen Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 229910021419 crystalline silicon Inorganic materials 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
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- 230000008901 benefit Effects 0.000 description 5
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 230000005284 excitation Effects 0.000 description 4
- 229910052744 lithium Inorganic materials 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000000498 ball milling Methods 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
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- 238000001228 spectrum Methods 0.000 description 3
- 235000012431 wafers Nutrition 0.000 description 3
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 238000005119 centrifugation Methods 0.000 description 2
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- 239000011248 coating agent Substances 0.000 description 2
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- NYQDCVLCJXRDSK-UHFFFAOYSA-N Bromofos Chemical compound COP(=S)(OC)OC1=CC(Cl)=C(Br)C=C1Cl NYQDCVLCJXRDSK-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 229920002125 Sokalan® Polymers 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- OLBVUFHMDRJKTK-UHFFFAOYSA-N [N].[O] Chemical compound [N].[O] OLBVUFHMDRJKTK-UHFFFAOYSA-N 0.000 description 1
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 description 1
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- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000005049 silicon tetrachloride Substances 0.000 description 1
- 239000011856 silicon-based particle Substances 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
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- ZSDSQXJSNMTJDA-UHFFFAOYSA-N trifluralin Chemical compound CCCN(CCC)C1=C([N+]([O-])=O)C=C(C(F)(F)F)C=C1[N+]([O-])=O ZSDSQXJSNMTJDA-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
-
- 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
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Silicon Compounds (AREA)
Abstract
The application provides a method for preparing silicon powder, which comprises the following steps: carrying out spray drying on the mortar; performing jet milling on a product obtained by spray drying to prepare silicon powder; wherein the solid content of the diamond wire cutting waste liquid is 3.5-45.0% by mass percent; the particle size distribution D90 of the silicon 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 diamond wire cutting waste liquid, reduces the resource waste, has low three-waste discharge amount in the production process, is environment-friendly, has low silicon powder production cost, is easy for large-scale production, and has high charging and discharging capacity and high first coulombic efficiency of the battery prepared from the silicon powder produced by the method.
Description
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 rapid development of economy, the energy crisis and environmental problems are increasingly aggravated, and the lithium ion battery has been widely applied to the fields of portable consumer electronics, electric tools, medical electronics and the like due to 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 energy density of batteries has been rapidly increasing in various fields, and development of lithium ion batteries with 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 promotion space of the energy density of the corresponding lithium ion battery is quite limited.
Under the background, the silicon-based negative electrode material is considered to be the next generation high energy density lithium ion battery negative electrode material with great potential due to the advantages of higher theoretical specific capacity (4200 mAh/g at high temperature, 3580mAh/g at room temperature), low lithium removal potential (< 0.5V), environmental friendliness, abundant storage capacity, lower cost and the like. However, the silicon material has 300% volume expansion in the process of lithium extraction, and repeated expansion and contraction can cause the negative electrode material to be pulverized and fall off, and finally cause the negative electrode material to lose electric contact, so that the battery completely fails. The nano-crystallization of the silicon material can effectively solve the problems.
The preparation method of industrially produced silicon particles mainly comprises a ball milling method and chemical vapor deposition, wherein the ball milling method is used for crushing bulk silicon into silicon nanoparticles by utilizing rolling mechanical force and has the advantages of high yield, low cost and easiness in doping, but the ball milling method has the defects of long production process, long time, contact of silicon materials and grinding media, more impurities, high surface oxidation degree, wide particle size distribution range, larger particle size, easiness in agglomeration and the like. The chemical vapor deposition method usually forms spheroidal nano-silicon particles with controllable particle size and narrow particle size distribution range by pyrolyzing, condensing and depositing a gas-phase silicon source such as silane or silicon tetrachloride, but the CVD gas-phase silicon source is dangerous, low in yield, high in equipment cost and the like, and the scale of the CVD gas-phase silicon source is limited.
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 easy mass production, and the battery prepared from the silicon powder obtained by the production has high charge and discharge capacity and high first coulombic efficiency.
The specific technical scheme comprises the following steps:
1. a method for preparing silicon powder comprises the following steps:
carrying out spray drying on the mortar;
performing jet milling on a product obtained by spray drying to prepare silicon powder;
wherein the solid content of the mortar is 3.5-45.0% by mass percent;
the particle size distribution D90 of the silicon powder particles in the mortar is less than or equal to 2.20 mu m.
2. The process for producing silicon powder according to item 1, wherein,
the air inlet temperature of the spray drying is 200-230 ℃, specifically 210 ℃ and 220 ℃, and preferably 200-210 ℃; the air outlet temperature is 80-110 ℃, specifically 90 ℃ and 100 ℃, and preferably 85-90 ℃.
3. The method for preparing silicon powder according to item 1, wherein the airflow pressure of the airflow pulverization is 0.2-0.7 MPa, specifically 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, and preferably 0.2-0.4 MPa; the rotation speed of the grading wheel is 2500-4500 rpm, specifically 3000rpm, 3500rpm and 4000rpm, preferably 4000-4500 rpm.
4. The method for preparing silicon powder according to item 1, wherein the total content of metal ion impurities in the silicon powder is less than or equal to 500ppm by mass.
5. The method for preparing silicon powder according to item 1, wherein the mortar is prepared by adding silicon mud into diamond wire cutting waste liquid.
6. The method for preparing silicon powder according to item 1, further comprising a step of stirring the mortar before the spray drying treatment.
The method for preparing the silicon powder realizes the recycling of the diamond wire cutting waste liquid, the three wastes discharge amount in the production process is low, the environment is friendly, the cost for producing the silicon powder is low, the large-scale production is easy, and the battery prepared by using the silicon powder produced by the method has high charge and discharge capacity and high first coulombic efficiency.
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 by a laser particle size distribution meter. The graph output by the laser particle size distribution instrument for detecting the particle size volume distribution of the silicon powder is a particle size distribution graph. The volume ratio of the silicon powder in different particle size range distributions can be calculated through the integral area of the peaks in different particle size distribution.
The particle size distribution diagram of the silicon powder of example 1 was measured by using a betersize 2600 laser particle size distribution instrument manufactured by dandongbott instruments ltd as shown in fig. 1.
Diamond wire cutting waste liquid:
when a diamond wire cutting method is used for producing silicon wafers, a surfactant and cooling water are used as cooling and lubricating media, a high-speed running steel wire with electroplated diamond particles is used for cutting crystalline silicon, and the surfactant and the cooling water bring out cut silicon powder to form diamond wire cutting waste liquid. Because the crystalline silicon has anisotropy, the crystalline silicon can be cut from a specific cleavage plane in the cutting process, so that particles with a specific shape are formed.
Silicon sludge:
in the production process, because the mortar cannot be directly discharged and can meet the discharge requirement only through sewage treatment, the mortar is subjected to the procedures of centrifugation, filtration, filter pressing and the like to reduce water content, and a semi-solid paste is produced, namely the silicon mud in the application.
Mortar:
the diamond wire cutting waste liquid can be directly used as mortar, or silicon mud is added into the diamond wire cutting waste liquid to form high-solid-content mortar for subsequent treatment.
The flake size of the silicon powder particles:
the sheet size of the silicon powder particles refers to the maximum value of any two line segments passing through the geometric center of the sheet surface of the silicon powder particles detected by using a scanning electron microscope.
In addition, the average flake size in the present invention refers to the arithmetic mean of the flake sizes of any number of silicon powder particles. In the examples and comparative examples, 5 regions were randomly selected to photograph silicon powder using a U.S. FEI cold field emission scanning electron microscope Quanta SEM scanning electron microscope at a magnification of 50000 times, and the average flake size was obtained by counting the flake sizes of all silicon powder particles in the photographing field and taking the arithmetic mean.
Thickness of the silicon powder particles:
the thickness of the silicon powder particles refers to the smallest dimension of the silicon powder particles in a direction perpendicular to the sheet-shaped surface through the geometric center of the silicon powder particles detected by a scanning electron microscope.
In addition, the average thickness in the present invention refers to the arithmetic mean of the thicknesses of any number of silicon powder particles. In the examples and comparative examples, the invention uses a U.S. FEI cold field emission scanning electron microscope Quanta SEM scanning electron microscope to randomly select 5 regions to shoot silicon powder under the condition of a magnification of 50000 times, and counts the thicknesses of all silicon powder particles in the shooting field and takes the arithmetic mean value to obtain the average thickness.
The above description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly apparent, and to make the implementation of the content of the description possible for those skilled in the art, and to make the above and other objects, features and advantages of the present invention more obvious, the following description is given by way of example of the specific embodiments of the present invention.
Drawings
FIG. 1: the particle size distribution detection result of the silicon powder obtained in example 1;
FIG. 2: a scanning electron microscope picture of the silicon powder obtained in example 1 is taken;
FIG. 3: the nitrogen isothermal adsorption and desorption curve of the silicon powder obtained in example 1;
FIG. 4: FIG. 4-1: peak separation diagram of oxygen element excitation peak in 524-540 electron volt interval; FIG. 4-2: an X-ray photoelectron spectroscopy (XPS) total spectrum of the silicon powder obtained in example 1; FIGS. 4-3: a peak separation chart of silicon element excitation peaks in a 95-107 electron volt interval;
FIG. 5: a transmission electron microscope picture of the silicon powder obtained in example 1 is taken;
FIG. 6: the X-ray diffraction pattern (XRD) of the silicon powder obtained in example 1;
FIG. 7: a first charge-discharge curve of the button cell prepared from the silicon powder obtained in example 1;
FIG. 8: the results of particle size distribution measurement of silica powder particles in the mortar raw material of example 1.
Detailed Description
The following embodiments of the present invention are merely illustrative of specific embodiments for carrying out the present invention and should not be construed as limiting the present invention. Other changes, modifications, substitutions, combinations, and simplifications which may be made without departing from the spirit and principles of the invention are intended to be equivalents thereof and to fall within the scope of the invention.
In one particular embodiment, a method for preparing silicon powder includes the steps of:
carrying out spray drying on the mortar;
performing jet milling on a product obtained by spray drying to prepare silicon powder;
wherein the solid content of the mortar is 3.5-45.0% by mass percent;
the particle size distribution D90 of the silicon powder particles in the mortar is less than or equal to 2.20 mu m.
In a specific embodiment, the inlet air temperature of the spray drying is 200-230 ℃, preferably 200-210 ℃; the air outlet temperature is 80-110 ℃, and preferably 85-90 ℃.
In a specific embodiment, the airflow pressure of the airflow pulverization is 0.2-0.7 MPa, preferably 0.2-0.4 MPa; the rotation speed of the grading 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 mud into diamond wire cutting waste 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 before the spray drying treatment.
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 diamond wire cutting waste liquid, reduces the resource waste, has low three-waste discharge amount in the production process, is environment-friendly, has low silicon powder production cost, is easy for large-scale production, and the battery prepared from the silicon powder produced by the method has high charge and discharge capacity and high first coulombic efficiency.
Examples
The experimental methods used in the following examples are all conventional methods, unless otherwise specified.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
The source of the mortar is as follows:
the mortar used in the following examples is waste diamond wire cutting liquid generated when the applicant cuts crystalline silicon by diamond wire in the production process of silicon wafers and silicon mud mixed in the waste diamond wire cutting liquid. The solid content of the silicon powder in the diamond wire cutting waste liquid is 3.5 to 6.5 percent. Unless otherwise specified in the following procedures, the mortars used were all from the mortars produced by the applicant. Because the current processes for cutting silicon wafers by diamond wires are similar, the compositions of the generated diamond wire cutting waste liquid and the characteristics of silicon powder particles in the diamond wire cutting waste liquid are also similar, so that the technical personnel in the field know that the diamond wire cutting waste liquid produced by other companies is used as the mortar in the embodiment of the application.
In addition, the mortar may be stirred in order to prevent the silicon powder from agglomerating before the preparation of the silicon powder.
And (3) detecting the solid content of the mortar:
in the following examples and comparative examples, the solid content of the mortar was measured by centrifugation and drying, specifically, a quantitative mortar was taken and centrifuged at high speed until the supernatant was transparent (the centrifuge was a Thermo Fisher Scientific brand Sorvall MTX 150 desk-top micro ultracentrifuge); and discharging the supernatant, drying the solid slag in vacuum to constant weight, and calculating the solid content of the mortar according to the weight of the solid slag.
Spray drying:
in the following examples and comparative examples, 8LPG-50 type spray dryer, Gannan forest drying engineering Co., Ltd. of Changzhou city, was used for spray drying.
Airflow crushing:
in the following examples and comparative examples, jet milling was carried out using a JSDL-Q jet mill, a Sichuan ultra-fast kinetic ultrafine powder manufacturing facility Co.
Example 1
(1) Detecting mortar:
the mortar used in this example was diamond wire cutting waste liquid.
Taking the mortar, and measuring the solid content of the mortar to be 4.2%;
(2) carrying out spray drying on the mortar:
the air inlet temperature of spray drying is 210 ℃, and the air outlet temperature is 85 ℃;
(3) then, carrying out jet milling:
the air flow pressure: 0.3MPa, and the rotating speed of the grading wheel is 4500 rpm.
Thereby producing silicon powder.
Examples 2 to 7 differ from example 1 in the solids content of the mortar and in the parameters of spray drying and jet milling. In addition, in example 7, a silicon sludge was added to the diamond wire cutting waste liquid to form a mortar.
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 detailed in Table 1.
Table 1:
the following tests were carried out on the silicon powders obtained in examples 1 to 7 and comparative examples 1 to 6. The method and results of testing the silicon powder obtained in example 1 are given as an example, and the methods of testing other examples and comparative examples are the same as example 1. The results of the measurements obtained are shown in Table 2 (tables 2-1 and 2-2).
(1) Measurement of particle size distribution of silicon powder
The particle size distribution was measured using a betersize 2600 manufactured by dandongbott instruments ltd.
As shown in fig. 1, the particle size volume distribution detection result of the silicon powder obtained in example 1 includes 3 peaks, which are sequentially from small to large according to the peak position order: 0.13 μm (first peak position), 0.52 μm (second peak position), 1.55 μm (third peak position); the particle size is D10:0.242 μm, D50:0.745 μm, D90:2.049 μm. The volume ratio of the silicon powder in different particle size range distributions can be calculated through the integral area of the peaks in different particle size distribution.
(2) Determination of sample state of silicon powder particles
Silicon powder is shot by using a Quanta SEM scanning electron microscope of an FEI cold field emission scanning electron microscope.
FIG. 2 (FIG. 2-1, FIG. 2-2) shows a scanning electron micrograph of the silicon powder of example 1, wherein the silicon powder particles have a lamellar nanostructure and an average thickness of 60 nm; the average platelet size was: 0.792 μm, so its average platelet size to average thickness ratio is 13.2.
The average flake size and average thickness are obtained by randomly selecting 5 regions to shoot the silicon powder under the condition of magnification of 50000 times by using a scanning electron microscope, counting the flake sizes and thicknesses of all silicon powder particles in a shooting field, and taking an arithmetic mean value, namely the average flake size and average thickness of the embodiment 1. The average plate-like size and average thickness were obtained in the same manner in the following examples and comparative examples.
(3) Determination of tap density of silicon powder
According to GB/T243360, the test was carried out using an HY-100 tap density tester from Haoyu technologies, Inc., Dandong.
Wherein, the detection result of the embodiment 1 is 0.1123g/cm3。
(4) Determination of specific surface area of silicon powder
According to GB/T19587, the measurements were carried out using a Tristar model 3020 specific surface area and porosity analyzer, manufactured by Micromeritics, USA.
As shown in FIG. 3, the nitrogen isothermal adsorption and desorption curves of the silicon powder of example 1 are shown. According to the calculation of a BET equation, the specific surface area of the silicon powder is as follows: 15.95m2/g。
(5) Surface chemical bond detection
Detection was carried out using X-ray photoelectron spectroscopy (XPS) model K-Alpha from Thermo Fisher Scientific, USA.
In examples 1 to 7 and comparative examples 1 to 6, the surface of the nano silicon mainly contains three elements, i.e., silicon, oxygen, and carbon. According to the peak separation result, the silicon surface is completely oxidized, and no other impurities except carbon exist; meanwhile, the presence of silicon-silicon bonds indicates that the thickness of the silicon oxide layer is less than 10nm (XPS ray detection depth), which is not shown in table 2.
The detection diagram of the embodiment 1 is shown in the attached figure 4 (figures 4-1-4-3) in detail.
Wherein: FIG. 4-1 is a peak-separation diagram of the oxygen excitation peak in the range of 524 to 540 electron volts;
FIG. 4-2 is a total X-ray photoelectron spectroscopy (XPS) spectrum of silicon powder;
FIG. 4-3 is a peak separation diagram of the silicon excitation peak in the interval of 95 to 107 electron volts.
(6) Thickness of surface oxide layer
Detecting with Theris type TEM transmission electron microscope of Thermo Fisher Scientific, USA, and analyzing the surface state of the material by high power transmission electron microscope;
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 an amorphous state of 2-5 nm exists on the surface; the thickness of the oxide layer on the surface of the silicon powder is about 2-5 nm, and the oxidation degree is smaller.
(7) Crystal form detection
And (3) crystal form detection: and performing product crystal form detection by using a BRUKER (Bruker) D8 ADVANCE type X-ray polycrystalline diffractometer.
FIG. 6 is a detection spectrum of the silicon powder particles of example 1.
Wherein an X-ray diffraction pattern (XRD) indicates 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 map (JCPDS card No.01-0787), and no obvious impurity peak exists; indicating that the silicon powder is a crystalline silicon material.
The results of the tests in examples 1 to 7 and comparative examples 1 to 6 are similar to those in the above examples, and the test 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 high-frequency infrared carbon-sulfur instrument of Chongqing research instrument Co;
the oxygen content of the silicon powder was measured using an ONH-330 model oxygen nitrogen hydrogen tester from Chongqing research instruments, Inc.
Wherein the detection result of the embodiment 1 is as follows:
carbon content: 3.13 percent;
oxygen content: 4.76 percent.
(9) Metal ion impurity detection
Detection was performed using ICPMS model NexiON 2000 from Perkin Elmer PE.
Example 1 the test results are: the total content of total metal ion impurities in the silicon powder is 132 ppm.
Table 2-1:
tables 2 to 2:
in addition, the silicon powder in the prior art is used as comparative examples 7 to 8.
Of these, comparative example 7, which was a silicon powder having a particle size D50 of 0.811 μm obtained by milling from Ishikaki technologies, Inc. of Beijing Deke, was close to the particle size D50 of the silicon powder of example 1, and it was found that the particles of the silicon powder of comparative example 7 were spherical.
Comparative example 8, which was a silicon powder having a particle size D50 of 0.765 μm obtained by milling from Shanghai Chaowei nanotechnology Co., Ltd, was close to the particle size D50 of the silicon powder of example 1, and it was found that the silicon powder of comparative example 8 had a spherical particle shape.
Experimental example:
in the art, the product is usually made into a CR2016 button cell to simulate the full cell reaction, and the specific capacity and coulombic efficiency of the product are detected.
The silicon powders prepared in examples 1-7 and comparative examples 1-8 are respectively prepared into 8 CR2016 button cells, and the preparation method of the cell comprises the following steps:
(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 in a water system to prepare electrode slurry;
(2) coating the electrode slurry on copper foil for a lithium battery negative electrode, wherein the coating thickness is 150 micrometers, and then drying the coated copper foil in a vacuum oven to constant weight to obtain a battery pole piece;
(3) cutting the pole piece into small round pieces by using a cutting machine with the diameter of 12mm, then placing the small round pieces in a glove box, and assembling the button cell under the environment that the water oxygen value is less than 0.1 ppm;
(4) and (3) selecting a CR2016 button cell case, assembling by adopting the sequence of a positive electrode case, a pole piece, a diaphragm, a metal lithium piece, a gasket and a negative electrode case, and then injecting electrolyte for packaging to obtain the assembled button cell.
The average number of the detected specific discharge capacity, the detected charge capacity and the detected first coulombic efficiency of the corresponding batteries prepared in the examples and the comparative examples is recorded in table 3.
Table 3:
the specific measurement method comprises the following steps:
according to GB/T38823-.
Wherein fig. 7 shows the first charge-discharge curve 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 embodiments and application fields, and the above-described embodiments are illustrative, instructive, and not restrictive. Those skilled in the art, having the benefit of this disclosure, may effect numerous modifications thereto without departing from the scope of the invention as defined by the appended claims.
Claims (6)
1. A method for preparing silicon powder comprises the following steps:
carrying out spray drying on the mortar;
performing jet milling on a product obtained by spray drying to prepare silicon powder;
wherein the solid content of the mortar is 3.5-45.0% by mass percent;
the particle size distribution D90 of the silicon powder particles in the mortar is less than or equal to 2.20 mu m.
2. The method for preparing silicon powder according to claim 1,
the air inlet temperature of the spray drying is 200-230 ℃, and preferably 200-210 ℃;
the air outlet temperature is 80-110 ℃, and preferably 85-90 ℃.
3. The method according to claim 1, wherein the silicon powder is prepared by a method comprising the steps of,
the airflow pressure of the airflow crushing is 0.2-0.7 MPa, and preferably 0.2-0.4 MPa;
the rotation speed of the classification wheel is 2500-4500 rpm, preferably 4000-4500 rpm.
4. The method for preparing silicon powder according to claim 1, wherein the total content of metal ion impurities in the silicon powder is 500ppm or less by mass ratio.
5. The method for preparing silicon powder according to claim 1, wherein the mortar is prepared by adding silicon mud to diamond wire cutting waste liquid.
6. The method for preparing silicon powder according to claim 1,
the method also comprises the step of stirring the mortar before the spray drying treatment.
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