CN114864887B - Modification method for fluidity of silicon oxide - Google Patents
Modification method for fluidity of silicon oxide Download PDFInfo
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Abstract
The invention discloses a modification method of silica fluidity, which comprises the steps of uniformly mixing hydrophobic amino acid and silica powder, and then calcining to obtain modified silica powder; the method utilizes hydrophobic amino acid to form a hydrophobic and antistatic coating layer on the surface of the silica particles, can effectively prevent the silica particles from agglomerating and reduce the phenomenon of material wall sticking retention, can form a uniform thin carbon layer on the surface of the silica after the hydrophobic amino acid is pyrolyzed, is favorable for obtaining a uniform CVD pyrolytic carbon layer, can increase the fluidity of the silica material, solves the problems of low yield, poor consistency and the like in the production process of the silica negative electrode, has simple process, has no safety risk, and can meet the requirement of large-scale industrial production.
Description
Technical Field
The invention relates to a modification method of a silicon oxide material, in particular to a modification method of fluidity of the silicon oxide material, and belongs to the technical field of preparation of the silicon oxide material.
Background
With the development of society and the progress of technology, energy consumption is increased, environmental pollution is also increased, and future survival of human beings is threatened seriously. Under the background of urgent need of developing clean and environment-friendly renewable energy sources, lithium ion batteries are rapidly developed due to the advantages of high energy density, long cycle life, environment friendliness and the like. Among the negative electrode materials of the lithium ion batteries, carbon-based graphite negative electrode materials are most commonly used, but the materials have lower specific capacity (372 mAh/g) and larger irreversible capacity loss, so that the lithium ion batteries are difficult to meet the use performance requirements, and the development space is difficult to break through. The specific capacity of the silicon-based material is highest among all the currently known anode materials, reaching 4200mAh/g. Is one of the next generation lithium ion battery anode materials with the highest potential for replacing graphite anode, and has excellent market prospect.
Silicon oxide (SiO) silicon-based materials are distinguished from numerous silicon-based negative electrode materials by having a relatively high theoretical specific capacity (2680 mAh/g) and a relatively low volume expansion rate (160%). However, the powder has poor fluidity, so that on one hand, the materials are stuck to the wall and retained in the places such as a collecting barrel, a baffle plate and the like, the yield is reduced, and the production cost is increased; on the other hand, the wall sticking retention of the materials can cause the problems of unsatisfactory carbon coating effect in the continuous production process, inconsistent carbon coating amount, poor consistency in product batches and the like; therefore, the solution of powder flowability has become a critical issue to be resolved in the processing and production of silica. The main reason for influencing the fluidity of the silica powder is that the hydrophobicity and antistatic property of the material are poor. Chinese patent (publication No. CN 112289999A) discloses a silicon oxide/carbon composite material and a preparation method and application thereof, and the patent technology improves the problem of poor powder flowability to a certain extent, but oxygen-containing waste gas generated in the preparation is easy to react with pyrolysis gas and hydrogen generated after the pyrolysis gas is decomposed, so that the consumption of the pyrolysis gas is increased, and the cost is increased; the oxygen-containing waste gas and the hydrogen are interacted at high temperature, so that serious potential safety hazards exist, the preparation difficulty is high, the amplification is difficult, the method is not suitable for large-scale industrial production in practice, the improvement effect of the method on the flowability of materials is not obvious, and the carbon coating stability and the yield are still to be further improved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a modification method for the fluidity of the silicon oxide, which utilizes hydrophobic amino acid to form a layer of coating layer with hydrophobicity and antistatic property on the surface of silicon oxide particles, can effectively improve the mutual adsorption caused by static electricity between water molecule surface adsorption and particles, reduce the agglomeration of silicon oxide powder, reduce the phenomenon of material wall sticking retention, form a uniform thin carbon layer on the surface of the silicon oxide after the hydrophobic amino acid is pyrolyzed, is favorable for obtaining a uniform CVD carbon coating layer, can increase the fluidity of the silicon oxide material, solves the problems of low yield and poor consistency in the production process of the silicon oxide cathode, has simple process, has no safety risk, and can meet the requirement of large-scale industrial production.
In order to achieve the technical aim, the invention provides a modification method of silica fluidity, which comprises the steps of uniformly mixing hydrophobic amino acid and silica powder, placing the mixture in a protective atmosphere, and calcining the mixture to obtain modified silica powder; and generating a carbon coating layer on the surface of the modified silica powder through high-temperature vapor deposition to obtain the carbon-coated silica negative electrode material.
After the hydrophobic amino acid and the silica powder are fully and uniformly mixed, the hydrophobic amino acid can be coated on the surface of the silica powder to form a protective film with hydrophobicity and antistatic property, so that agglomeration can be effectively prevented, uniform coating is formed, a uniform thin carbon layer can be formed on the surface of the silica powder after the hydrophobic amino acid is calcined, uniform CVD carbon coating can be obtained, and the fluidity of the silica material is increased.
As a preferred embodiment, the hydrophobic amino acid is at least one of alanine, valine, leucine, phenylalanine, tryptophan, methionine, and proline. The hydrophobic amino acid can prevent the surface of the silica from absorbing water, so that agglomeration can be effectively prevented, if the hydrophilic amino acid is adopted, a layer of hydrophilic layer is formed on the surface of the silica after mixing, agglomeration of materials can be increased in the mixing process, uneven coating is caused, uniformity of carbon layer coating after calcination is reduced, and the aim of improving the fluidity of the silica is difficult to achieve.
As a preferable mode, the mass ratio of the hydrophobic amino acid to the silica powder is 1 (1-10). The mass ratio of the hydrophobic amino acid to the silica powder is preferably 1 (2.5-10); the mass ratio of the hydrophobic amino acid to the silica powder is more preferably 1:5 to 10. If the proportion of hydrophobic amino acid is too low, the surface of the mixed silica powder cannot form a uniform hydrophobic and antistatic coating layer, and the surface of the mixed silica powder cannot form a uniform thin carbon layer after calcination, if the proportion of hydrophobic amino acid is too high, the redundant amino acid material does not participate in the coating process any more, so that unnecessary waste is caused, and the meaning is not great.
As a preferable mode, the silica powder has a D50 median value of 4.0-7.0 μm. More preferred median D50 values are 5.5±0.5 μm.
As a preferable mode, the mixing adopts a stirring mode, the stirring speed is 300-1000 rpm, and the stirring time is 1-5 h. The uniform adsorption of hydrophobic amino acid on the surface of silicon oxide is facilitated under the condition of proper high-speed stirring.
As a preferable embodiment, the conditions of the calcination treatment are as follows: the temperature rising rate is 2.0-15.0 ℃/min, the calcining temperature is 600-800 ℃, and the calcining time is 4-6 h. The heating rate is more preferably 5 to 10 ℃/min. The protective atmosphere in the calcination process is at least one of nitrogen, helium, argon and argon-hydrogen mixed gas. Too low a calcination temperature and too short a calcination time may result in insufficient pyrolysis of the hydrophobic amino acid, and insufficient uniformity of the coated carbon layer, resulting in too low modification efficiency. If the calcination temperature is too high and the calcination time is too long, disproportionation reaction of the silicon oxide occurs, silicon grains grow, and the cycle performance of the silicon oxide is reduced.
As a preferable scheme, the high-temperature vapor deposition is realized by a continuous rotary furnace, the main machine of the continuous rotary furnace rotates at 5-50 Hz, and the lower feeding rotates at 5-50 Hz. The main machine of the continuous rotary furnace rotates at 20-30 Hz, and the lower feeding rotates at 20-30 Hz.
As a preferable scheme, the conditions of the high temperature vapor deposition are as follows: at least one of methane, acetylene and propylene is used as pyrolysis gas, the flow rate of the pyrolysis gas is controlled to be 2.0-5.0L/min, the vapor deposition temperature is 800-1050 ℃, and the time is 1-4 h. When the gas flow rate is too low in vapor deposition, the carbon source required by carbon coating is insufficient, and the coating effect is seriously affected; the gas flow is too high, the carbon source is provided far exceeding the required carbon source, the carbon source is not influenced but most of the carbon source cannot participate in vapor deposition to cause the loss of the natural gas carbon source, the natural gas belongs to inflammable and explosive gas, the potential safety hazard is greatly improved due to the too high flow, and the adequate temperature condition can ensure the sufficient cracking of the cracking gas. The amount of the cleavage gas flow is more preferably 2.0 to 4.0L/min.
The modification method of the fluidity of the silica of the present invention also has an alternative scheme in which the silica may be replaced with elemental silicon, a silicon carbide material, a silicon dioxide material, or the like.
The invention provides a modification method of silica powder fluidity, which comprises the following steps:
step 1): placing hydrophobic amino acid powder and silica powder with particle size median D50=4.0-7.0 μm according to mass ratio of 1 (2.5-10) into a stirrer, stirring for 1-5 h at a rotating speed of 300-1000 rpm to obtain a uniform mixed material; the hydrophobic amino acid material is crystalline powdery hydrophobic amino acid such as alanine, valine, leucine, phenylalanine, tryptophan, methionine, proline and the like;
step 2): placing the materials in the step 1) into a box furnace, heating to 600-800 ℃ at a speed of 2-15 ℃/min under the atmosphere protection gas of nitrogen, helium, argon or argon-hydrogen mixed gas, keeping the temperature for 4-6 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2) into a rotary furnace with a main machine rotating frequency of 5-50 Hz and a lower feeding rotating frequency of 5-50 Hz, and carrying out vapor deposition for 1-4 hours at 800-1050 ℃ under the conditions of nitrogen, helium, argon or argon-hydrogen mixed gas shielding gas and at least one cracking gas of 2-5L/min methane, acetylene and propylene to finally obtain the carbon-coated silica cathode material.
Compared with the prior art, the technical scheme of the invention has the following advantages:
1. in the fluidity modification process of the silica powder, the adopted hydrophobic amino acid belongs to common biological materials, has wide acquisition path and low cost, does not generate toxic substances and is friendly to the environment;
2. in the silica powder fluidity modification process, the hydrophobic amino acid is used for coating the silica powder surface with the hydrophobic and antistatic modification layer, so that the mutual adsorption caused by the static electricity between water molecule surface adsorption and particles can be effectively improved, the aggregation among silica particles is prevented, the phenomenon of wall sticking retention of materials is reduced, a uniform thin carbon layer can be formed on the silica surface after carbonization of the hydrophobic amino acid, the uniform CVD carbon coating layer is favorably obtained, the fluidity of the silica material can be increased, and the problems of low yield and poor consistency in the production process of the silica negative electrode are solved.
3. The silica powder fluidity modification process has the advantages of simple preparation process and no safety risk, and can meet the requirement of large-scale industrial production.
4. The silica powder has high product yield and good consistency of carbon coating in the fluidity modification process.
Drawings
Fig. 1 is an SEM image of the carbon-coated silica anode material prepared in example 1.
Detailed Description
The following specific examples are intended to illustrate the present invention in further detail, but are not intended to limit the scope of the claims.
The definitions of some of the academic terms used in the present invention are given below, and other unrecited academic terms have definitions and meanings well known in the art:
the modified silica powder material can be used as a precursor material for carrying out subsequent preparation processes such as carbon coating, pre-lithiation, battery preparation and the like.
Example 1
Step 1), placing 5kg of alanine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotation speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 750 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 5 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica anode material.
Example 2
Step 1), placing 7.5kg of alanine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 750 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 5 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica anode material.
Example 3
Step 1), placing 10kg of alanine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotation speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 750 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 5 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica anode material.
Example 4
Step 1) placing 7.5kg of leucine powder and 50kg of silica powder with the median particle size d50=5.5 mu m in a stirrer, and stirring for 2 hours at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 650 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 6 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 3 hours at 850 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica negative electrode material.
Comparative example 1 (hydrophilic amino acids were used as controls)
Step 1) placing 7.5kg of glycine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 750 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 5 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica anode material.
Comparative example 2 (calcination conditions were used as control)
Step 1), placing 7.5kg of alanine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 400 ℃ at a speed of 2 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 2 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and 3L/min methane atmosphere to finally obtain the carbon-coated silica anode material.
Comparative example 3 (control with vapor deposition conditions)
Step 1), placing 7.5kg of alanine powder and 50kg of silica powder with the median particle size d50=5.5 mu m into a stirrer, and stirring for 2 hours at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the materials in the step 1 into a box furnace, heating to 750 ℃ at a speed of 8 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 5 hours, and naturally cooling to obtain modified silica powder;
and 3) placing the modified silica powder in the step 2 into a rotary furnace with a main machine rotating frequency of 25Hz and a lower feeding rotating frequency of 25Hz, and carrying out vapor deposition for 2 hours at 980 ℃ under the conditions of nitrogen protection gas and methane atmosphere of 1L/min to finally obtain the carbon-coated silica anode material.
Comparative example 4
The only difference from example 1 is that: and (3) canceling the step (1) and the step (2), and directly carrying out high-temperature vapor deposition in the step (3) by using the silica powder to obtain the carbon-coated silica negative electrode material.
Application example 1
The modified and unmodified silicon oxide anode materials prepared in examples 1 to 4 and comparative example 4 were subjected to button cell performance test, and the button cell was fabricated as follows: the anode material, carbon black, carboxymethyl cellulose and styrene butadiene rubber prepared under the conditions are mixed according to the mass ratio of 90:5:4:1, adding deionized water with the solid content of 50% after uniformly mixing to prepare slurry, uniformly coating the slurry on copper foil on a coating machine, and finally baking for 4 hours at 100 ℃ in a vacuum empty box to prepare the working electrode. The lithium sheet is used as a counter electrode, a 25umPP diaphragm and 1mol/l LiPF6 (the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1:1) are used as electrolyte, and the button cell is assembled in a glove box under the protection of argon.
Application example 2
The modified and unmodified silicon oxide anode materials prepared in examples 1 to 4 and comparative example 4 were subjected to a repose angle test, which specifically comprises the following steps: with the help of the level gauge, three supporting feet on the bottom plate are adjusted to enable the device to be in a horizontal state.
The hopper blanking opening is adjusted by the height gauge to be just contacted with the plane of the height gauge, the hopper is fixed at the position by a screw, and the height gauge is removed.
The prepared modified and unmodified silicon oxide negative electrode materials were added to the center of the funnel from a height of about 40mm, and the experimental apparatus was not vibrated. The feeding amount is controlled to be 20 g/min-60 g/min, and the feeding is uniform and continuous as much as possible. When the screen is blocked, the experimental device can be gently swept by a soft brush, and the experimental device cannot be vibrated. When the top of the sample cone reaches the funnel outlet, the addition of material is stopped. Eight radii of the cone bottom circumference were marked on the bottom plate, the sample was removed, and four diameters marked in the radial radiation direction were measured.
Application example 3
The modified silicon oxide anode materials prepared in examples 1 to 4 and comparative example 4 were subjected to carbon content testing by using a carbon-sulfur analyzer, and the obtained test results were subjected to comparative analysis.
Experimental conditions:
the modified silica powders prepared in examples 1 to 4 and comparative examples 1 to 3 and the unmodified silica powders prepared in comparative example 1 were tested according to the test methods of application examples 1 to 3, and table 1 is the blend repose angle test data of step 1, the contents of which are as follows:
| case (B) | Angle of repose/° |
| Example 1 | 50 |
| Example 2 | 47 |
| Example 3 | 47 |
| Example 4 | 48 |
| Comparative example 1 | 51 |
| Comparative example 2 | 49 |
| Comparative example 3 | 47 |
| Comparative example 4 | 52 |
As can be seen from table 1, the mixed addition of hydrophobic amino acids can reduce the repose angle of the material; when the proportion of the hydrophobic amino acid to the silica powder is increased, the fluidity improving effect is also increased; the improvement effect of the alanine is slightly better than that of leucine; the use of hydrophilic amino acid mixtures does not significantly improve the angle of repose; the calcination temperature and time also have obvious influence on fluidity, and when the calcination temperature is too low and the time is too short, the modification effect of fluidity of the silica powder is not efficient.
Table 2 is the data of the discharge amount and carbon content test of the carbon-coated silica discharged in different time periods after the material discharged in step 3, and the contents are as follows:
as can be seen from table 2, the addition of the hydrophobic amino acid can significantly improve the discharge amount of the carbon-coated silica and the stability of the carbon content, compared with comparative example 4; the yield of the material modified by the hydrophobic amino acid is basically more than 80 percent, and the material is higher than the material without the hydrophobic amino acid modification (the total yield of the material is 60.0 percent). Compared with example 2, the gas flow rate at the time of vapor deposition in comparative example 3 was too low, and both the carbon content and the tapping amount were reduced.
Table 3 is electrochemical test data of the button cell prepared according to application example 1 for the modified silicon oxide anode materials prepared in examples 1 to 4 and comparative examples 1 to 4, and the contents are as follows:
as can be seen from Table 3, the addition of the hydrophobic amino acid significantly improves the cycle performance of the material, 50, compared with comparative example 4 th The capacity retention was between 87 and 90% (comparative example 4: 50) th The capacity retention rate was about 80%). Comparative example 1 compared to example 2, the hydrophilic amino acid was much less effective in modifying than the hydrophobic amino acid; when the calcination temperature is too low, the modification effect of the silica powder is poor, and the electrochemical performance is reduced.
Claims (8)
1. A modification method of the fluidity of silicon oxide is characterized in that: uniformly mixing hydrophobic amino acid and silica powder, and placing the mixture in a protective atmosphere for calcining treatment to carbonize the hydrophobic amino acid to obtain modified silica powder; and generating a carbon coating layer on the surface of the modified silica powder through high-temperature vapor deposition to obtain the carbon-coated silica negative electrode material.
2. The method for modifying the fluidity of silica according to claim 1, wherein: the hydrophobic amino acid is at least one of alanine, valine, leucine, phenylalanine, tryptophan, methionine and proline.
3. The method for modifying the fluidity of silica according to claim 1 or 2, characterized in that: the mass ratio of the hydrophobic amino acid to the silica powder is 1 (1-10).
4. A method for modifying the flowability of silica according to claim 3, characterized in that: the silica powder has a D50 median value of 4.0-7.0 mu m.
5. The method for modifying the fluidity of silica according to claim 1, wherein: the mixing is performed in a stirring mode, the stirring speed is 300-1000 rpm, and the stirring time is 1-5 h.
6. The method for modifying the fluidity of silica according to claim 1, wherein: the conditions of the calcination treatment are as follows: the temperature rising rate is 2.0-15.0 ℃/min, the calcining temperature is 600-800 ℃, and the calcining time is 4-6 h.
7. The method for modifying the fluidity of silica according to claim 1, wherein: the high-temperature gas phase deposition is realized through a continuous rotary furnace, the main machine rotation frequency of the continuous rotary furnace is 5-50 Hz, and the lower feeding rotation frequency is 5-50 Hz.
8. The method for modifying the fluidity of silica according to claim 1, wherein: the conditions of the high-temperature vapor deposition are as follows: at least one of methane, acetylene and propylene is used as pyrolysis gas, the flow rate of the pyrolysis gas is controlled to be 2.0-5.0L/min, the vapor deposition temperature is 800-1050 ℃, and the time is 1-4 h.
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