CN114864887A - Modification method for fluidity of silicon monoxide - Google Patents

Modification method for fluidity of silicon monoxide Download PDF

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CN114864887A
CN114864887A CN202210361616.6A CN202210361616A CN114864887A CN 114864887 A CN114864887 A CN 114864887A CN 202210361616 A CN202210361616 A CN 202210361616A CN 114864887 A CN114864887 A CN 114864887A
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silica
flowability
amino acid
silicon oxide
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CN114864887B (en
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易旭
廖寄乔
戴朝晖
李鑫
曾鹏
卢治斌
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Hunan Jinsi Technology Co ltd
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    • H01M4/00—Electrodes
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    • H01M4/0421—Methods of deposition of the material involving vapour deposition
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
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    • H—ELECTRICITY
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    • 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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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a modification method of fluidity of silica, which is characterized in that hydrophobic amino acid and silica powder are uniformly mixed and then calcined to obtain modified silica powder; the method comprises the steps of generating a carbon coating layer on the surface of modified silicon oxide powder through high-temperature vapor deposition to obtain the carbon-coated silicon oxide negative electrode material, wherein hydrophobic amino acid is used for forming a hydrophobic and anti-static coating layer on the surface of silicon oxide particles, the agglomeration of the silicon oxide particles can be effectively prevented, the phenomenon that materials are stuck to walls and retained is reduced, after the hydrophobic amino acid is pyrolyzed, an even thin carbon layer can be formed on the surface of the silicon oxide particles, an even CVD pyrolytic carbon layer can be obtained, the flowability of the silicon oxide material can be increased, the problems of low yield, poor consistency and the like in the production process of the silicon oxide negative electrode are solved, the method is simple in process and free of safety risk, and the large-scale industrial production requirements can be met.

Description

Modification method for fluidity of silicon monoxide
Technical Field
The invention relates to a modification method of a silicon oxide material, in particular to a modification method of the fluidity of the silicon oxide material, belonging to the technical field of preparation of the silicon oxide material.
Background
With the development of society and the advancement of science and technology, the energy consumption is increasingly intensified, the environmental pollution is also increasingly serious, and the future survival of human beings is seriously threatened. 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, environmental friendliness and the like. The carbon-based graphite negative electrode material is most commonly used in a plurality of negative electrode materials of the lithium ion battery, but the material has low specific capacity (372mAh/g) and large irreversible capacity loss, so that the lithium ion battery is difficult to meet the service performance requirement, and the development space is difficult to break through. In all the known negative electrode materials, the specific capacity of the silicon-based material is the highest and reaches 4200 mAh/g. Is one of the next generation lithium ion battery cathode materials with the most potential to replace graphite cathodes, and has excellent market prospect.
Silica-based materials of silicon monoxide (SiO) are distinguished from a plurality of silicon-based negative electrode materials because of higher theoretical specific capacity (2680mAh/g) and smaller volume expansion rate (160%). But the powder has poor flowability, so that on one hand, the materials are stuck to the wall and are retained in 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 and detention of the material can cause that the carbon coating effect is not ideal in the continuous production process, and the problems of inconsistent carbon coating amount, poor consistency in product batches and the like are caused; therefore, solving the powder fluidity becomes a critical problem to be solved urgently in the processing production of the silicon oxide. The main reason for influencing the flowability of the silica powder is the poor hydrophobicity and antistatic property of the material. Chinese patent (publication No. CN 112289999A) discloses a silicon oxide/carbon composite material and a preparation method and application thereof, the patent technology improves the problem of poor powder flowability to a certain extent, but oxygen-containing waste gas generated in the preparation process easily reacts with pyrolysis gas and hydrogen generated after pyrolysis gas is decomposed, the consumption of the pyrolysis gas is increased, and the cost is increased; and the oxygen-containing waste gas and hydrogen are interacted at high temperature, so that serious potential safety hazard exists, the preparation difficulty is high, the amplification is difficult, and the method is not suitable for large-scale industrial production in practice.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a modification method of the flowability of the silicon oxide, the method utilizes hydrophobic amino acid to form a coating layer with hydrophobic property and antistatic property on the surface of silicon oxide particles, can effectively improve the surface adsorption of water molecules and the mutual adsorption among particles caused by static electricity, reduce the agglomeration of silicon oxide powder, reduce the phenomenon of material wall sticking and detention, can 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 flowability of the silicon oxide material, solves the problems of low yield and poor consistency in the production process of a silicon oxide cathode, has simple process and no safety risk, and can meet the requirement of large-scale industrial production.
In order to realize the technical purpose, the invention provides a modification method of the fluidity of silica, 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 used for coating the surface of the silica powder to form a protective film with hydrophobicity and antistatic property, agglomeration can be effectively prevented, uniform coating is formed, and after the hydrophobic amino acid is calcined, a uniform thin carbon layer can be formed on the surface of the silica powder, so that a uniform CVD carbon coating layer can be obtained, and the flowability of the silica material is improved.
In 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 silicon oxide from absorbing water, so that agglomeration can be effectively prevented, if the hydrophilic amino acid is adopted, a hydrophilic layer can be formed on the surface of the silicon oxide after mixing, the agglomeration of materials can be increased in the mixing process, the coating is not uniform, the coating uniformity of the calcined carbon layer is reduced, and the aim of improving the flowability of the silicon oxide is difficult to achieve.
Preferably, the mass ratio of the hydrophobic amino acid to the silica fume is 1 (1-10). The mass ratio of the hydrophobic amino acid to the silica fume is preferably 1 (2.5-10); the mass ratio of the hydrophobic amino acid to the silica fume is more preferably 1:5 to 10. If the proportion of the hydrophobic amino acid is too low, the surface of the mixed silica powder can not form a uniform hydrophobic and antistatic coating layer, and the surface can not form a uniform thin carbon layer after calcination.
Preferably, the median value of the silica fume is 4.0-7.0 μm in the D50. More preferably, the median value of D50 is 5.5. + -. 0.5. mu.m.
Preferably, the mixing is performed in a stirring manner, the stirring speed is 300-1000 rpm, and the stirring time is 1-5 hours. Under proper high-speed stirring conditions, the uniform adsorption of the hydrophobic amino acid on the surface of the silicon oxide is facilitated.
As a preferred embodiment, the conditions of the calcination treatment are: the heating 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. And in the calcining process, the protective atmosphere is at least one of nitrogen, helium, argon and argon-hydrogen mixed gas. If the calcination temperature is too low and the calcination time is too short, the hydrophobic amino acid is not sufficiently pyrolyzed, and the coated carbon layer is not uniform enough, so that the modification efficiency is too low. If the calcination temperature is too high and the calcination time is too long, the disproportionation reaction of the silicon monoxide can be caused, silicon crystal grains grow, and the cycle performance of the silicon monoxide is reduced.
As a preferable scheme, the high-temperature vapor deposition is realized by a continuous rotary furnace, the frequency conversion of a main machine of the continuous rotary furnace is 5-50 Hz, and the frequency conversion of lower feeding is 5-50 Hz. The frequency conversion of the main machine of the continuous rotary furnace is 20-30 Hz, and the frequency conversion of the lower feeding material is 20-30 Hz.
As a preferred scheme, the conditions of the high-temperature vapor deposition are as follows: at least one of methane, acetylene and propylene is used as cracking gas, the flow rate of the cracking gas is controlled to be 2.0-5.0L/min, the vapor deposition temperature is 800-1050 ℃, and the time is 1-4 h. During vapor deposition, when the gas flow is too low, the carbon source required by carbon coating is insufficient, and the coating effect is seriously influenced; the gas flow is too high, the carbon source provided far exceeds the required carbon source, although the carbon coating effect is not influenced, most of the carbon source cannot participate in vapor deposition to cause the loss of the carbon source of natural gas, the natural gas belongs to combustible and explosive gas, the potential safety hazard of the natural gas is greatly improved due to too high flow, and the sufficient cracking of cracked gas can be ensured under proper temperature conditions. The flow rate of the cracking gas is more preferably 2.0-4.0L/min.
The modification method of the fluidity of the silicon oxide also has the following alternative schemes, for example, the silicon oxide can be replaced by simple substance silicon, carbon silicon material, silicon dioxide material and the like.
The invention provides a modification method of fluidity of silica powder, which comprises the following steps:
step 1): placing hydrophobic amino acid powder and silica powder with the particle size median D50 of 4.0-7.0 mu m in a stirrer according to the mass ratio of 1 (2.5-10), and stirring for 1-5 hours at the 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, etc.;
step 2): placing the material in the step 1) into a box-type furnace, heating to 600-800 ℃ at a speed of 2-15 ℃/min under the atmosphere protection of nitrogen, helium, argon or argon-hydrogen mixed gas, keeping the temperature for 4-6 hours, and naturally cooling to obtain modified silica fume;
and 3) placing the modified silica fume obtained in the step 2) into a rotary furnace with a main machine frequency conversion of 5-50 Hz and a lower feeding frequency conversion of 5-50 Hz, and carrying out vapor deposition at 800-1050 ℃ for 1-4 hours under the conditions of a nitrogen, helium, argon or argon-hydrogen mixed gas shielding gas and at least one cracking gas of methane, acetylene and propylene at 2-5L/min 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 silica powder fluidity modification process, the adopted hydrophobic amino acid belongs to a common biological material, the acquisition way is wide, the cost is low, and no toxic substance is generated, so that the silica powder fluidity modification process is environment-friendly;
2. in the fluidity modification process of the silica powder, hydrophobic amino acid is used for coating a layer with a hydrophobic and antistatic modification layer on the surface of the silica powder, so that the surface adsorption of water molecules and the mutual adsorption among particles caused by static electricity can be effectively improved, the agglomeration among silica particles is prevented, the phenomenon that materials are stuck to walls and retained is reduced, after the hydrophobic amino acid is carbonized, an even thin carbon layer can be formed on the surface of the silica powder, the even CVD carbon coating layer can be 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 preparation process of the fluidity modification process of the silica powder is simple, has no safety risk, and can meet the requirement of large-scale industrial production.
4. The method has the advantages of high product yield and good consistency of carbon coating in the fluidity modification process of the silica powder.
Drawings
Fig. 1 is an SEM image of the carbon-coated silica negative electrode material prepared in example 1.
Detailed Description
The following specific examples are intended to illustrate the invention in further detail, but not to limit the scope of the claims.
The following provides definitions of some of the academic terms used in the present invention, and other non-described academic terms have definitions and meanings well known in the art:
the modified silica powder material can be used as a precursor material to carry 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 particle size median D50 being 5.5 mu m in a stirrer, and stirring for 2h at the rotating speed of 600rpm to obtain a uniform mixed material;
step 2) placing the material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 3L/min methane to finally obtain the carbon-coated silica negative electrode material.
Example 2
Step 1) placing 7.5kg of alanine powder and 50kg of silica powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 3L/min methane to finally obtain the carbon-coated silica negative electrode material.
Example 3
Step 1) putting 10kg of alanine powder and 50kg of silica powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 3L/min methane to finally obtain the carbon-coated silica negative electrode material.
Example 4
Step 1) putting 7.5kg of leucine powder and 50kg of silica powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing 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 (using hydrophilic amino acids as control)
Step 1) placing 7.5kg of glycine powder and 50kg of silica fume powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 3L/min methane to finally obtain the carbon-coated silica negative electrode material.
Comparative example 2 (calcination conditions as control)
Step 1) placing 7.5kg of alanine powder and 50kg of silica powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 3L/min methane to finally obtain the carbon-coated silica negative electrode material.
Comparative example 3 (vapor deposition conditions as control)
Step 1) placing 7.5kg of alanine powder and 50kg of silica powder with the particle size median D50 being 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 material in the step 1 into a box-type 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 fume;
and 3) placing the modified silica powder obtained in the step 2 in a rotary furnace with a main machine frequency conversion of 25Hz and a lower feeding frequency conversion of 25Hz, and performing vapor deposition for 2 hours at 980 ℃ under the atmosphere of nitrogen protection gas and 1L/min methane to finally obtain the carbon-coated silica negative electrode material.
Comparative example 4
The only differences from example 1 are: and (3) eliminating 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 cathode material.
Application example 1
The performance test of the button cell is carried out on the modified and unmodified silicon monoxide negative electrode materials prepared in the embodiments 1-4 and the comparative example 4, and the button cell manufacturing steps are as follows: mixing the negative electrode material, carbon black, carboxymethyl cellulose and styrene butadiene rubber prepared under the conditions according to a mass ratio of 90: 5: 4: 1, adding deionized water with solid content of 50% to prepare slurry, then uniformly coating the slurry on a copper foil on a coating machine, and finally baking for 4 hours at 100 ℃ in a vacuum chamber to prepare the working electrode. A lithium sheet is taken as a counter electrode, a diaphragm of 25umPP and 1mol/l LiPF6 (the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1: 1) are taken as electrolyte, and the button cell is assembled in a glove box under the protection of argon to complete the manufacture of the button cell.
Application example 2
The modified and unmodified silica negative electrode materials prepared in examples 1 to 4 and comparative example 4 were subjected to a repose angle test, which specifically includes the following steps: and three support legs on the bottom plate are adjusted by the level gauge to enable the device to be in a horizontal state.
The hopper feed opening is adjusted with the height gauge to just touch the height gauge plane, at which point the hopper is screwed in place and the height gauge is removed.
The prepared modified and unmodified silica negative electrode materials were fed from about 40mm height into the center of the funnel without shaking the experimental setup. 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 screen can be lightly swept by a soft brush, and the experimental device can not be vibrated. The addition of material was stopped when the tip of the cone of sample reached the funnel outlet. Eight radii of the circumference of the cone bottom are scribed on the bottom plate, the sample is removed, and the four marked diameters in the radial direction are measured.
Application example 3
The carbon content of the modified silicon monoxide negative electrode materials prepared in examples 1-4 and comparative example 4 was tested by a carbon sulfur analyzer, and the obtained test results were compared and analyzed.
Experimental conditions:
the modified silica fume powders prepared in examples 1 to 4 and comparative examples 1 to 3 and the unmodified silica fume powder prepared in comparative example 1 were tested according to the detection method of application examples 1 to 3, and table 1 shows the test data of repose angle of the mixture in step 1, and the content is as follows:
case(s) 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 addition of the hydrophobic amino acid mixture reduces the repose angle of the material; when the proportion of the hydrophobic amino acid to the silica fume is increased, the effect of improving the fluidity of the silica fume is also increased; the improvement effect of the alanine is slightly better than that of the leucine; the use of hydrophilic amino acid mixtures did not significantly improve the angle of repose; the calcination temperature and time also have obvious influence on the fluidity, and when the calcination temperature is too low and the calcination time is too short, the modification effect on the fluidity of the silica powder is not good.
Table 2 shows the data of the discharge amount and carbon content of the carbon-coated silica discharged at different time periods after the discharge of the material in step 3, the contents are as follows:
Figure BDA0003585521870000091
as can be seen from Table 2, the addition of the hydrophobic amino acid significantly improves the discharge amount of the carbon-coated silica and the stability of the carbon content, as compared with comparative example 4; the yield of the material modified by the hydrophobic amino acid is basically more than 80 percent, and is higher than that of the material without the hydrophobic amino acid modification (the total yield of the material is 60.0 percent). In comparison with example 2, the gas flow rate in the vapor deposition in comparative example 3 was too low, and the carbon content and the tapping amount were reduced.
Table 3 shows electrochemical test data of button cells prepared according to application example 1 for the modified silica negative electrode materials prepared in examples 1 to 4 and comparative examples 1 to 4, which are as follows:
Figure BDA0003585521870000101
as can be seen from Table 3, the addition of the hydrophobic amino acid significantly improves the cycle performance of the material, as compared to comparative example 4, 50 th The capacity retention rate is between 87 and 90 percent (forComparative example 4: 50 th Capacity retention rate of about 80%). Comparative example 1 compared to example 2, the modification effect of the hydrophilic amino acid was much less than that of 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 method for modifying the flowability of silica is characterized in that: uniformly mixing hydrophobic amino acid and silica powder, and then placing the mixture in a protective atmosphere to carry out calcination treatment 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 flowability 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. A method for modifying the flowability of silica according to claim 1 or 2, wherein: the mass ratio of the hydrophobic amino acid to the silica fume is 1 (1-10).
4. The method for modifying the flowability of silica according to claim 3, wherein: the median value of the silica fume powder D50 is 4.0-7.0 μm.
5. The method for modifying the flowability of silica according to claim 1, wherein: the mixing adopts a stirring mode, the stirring speed is 300-1000 rpm, and the stirring time is 1-5 h.
6. The method for modifying the flowability of silica according to claim 1, wherein: the conditions of the calcination treatment are as follows: the heating 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 flowability of silica according to claim 1, wherein: the high-temperature vapor deposition is realized through a continuous rotary furnace, the frequency conversion of a main machine of the continuous rotary furnace is 5-50 Hz, and the frequency conversion of lower feeding is 5-50 Hz.
8. The method for modifying the flowability 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 cracking gas, the flow rate of the cracking 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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