CN114583135A - Spherical silicon-carbon composite material prepared by cutting waste silicon powder in one step and preparation method and application thereof - Google Patents
Spherical silicon-carbon composite material prepared by cutting waste silicon powder in one step and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the field of lithium ion batteries, and provides a spherical silicon-carbon composite material prepared by cutting waste silicon powder in one step, and a preparation method and application thereof. The preparation method can be used for preparing the spherical silicon-carbon composite material with excellent silicon-carbon binding property and uniformity, and when the spherical silicon-carbon composite material is used for a lithium ion battery cathode, high specific capacity and excellent long-cycle stability can be shown; the preparation method realizes high-valued recycling of the cut waste silicon powder in an environment-friendly manner, has short flow and high efficiency, and is suitable for large-scale industrial production.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and relates to a spherical silicon-carbon composite material prepared by cutting waste silicon powder in one step, and a preparation method and application thereof.
Background
In recent years, the photovoltaic industry has been rapidly developed, and the demand of crystalline silicon wafers as a base material of crystalline silicon solar cells has been sharply increased. Cutting waste silicon powder accounting for about 40% of the total mass of a high-purity silicon ingot (with the purity of 99.9999%) is generated in the silicon wafer cutting process, and the annual production amount of the cutting waste silicon powder exceeds 20 ten thousand tons. Due to the problems of entrainment of trace impurities, deep oxidation and the like in the cutting process, the purity of the cut waste silicon powder cannot meet the requirement of a solar cell silicon wafer. At present, the metallurgical recovery process through remelting refining can only realize the degraded utilization, and the heavy process also causes the secondary consumption of energy and a great deal of environmental pollution.
As the core power of lithium ion batteries as clean energy storage advances, a great deal of demand is focused on developing high energy density electrode materials. Silicon has an ultra-high theoretical capacity (3579mAh/g, about 10 times that of a graphite cathode) and a suitable lithium intercalation potential, and is considered as the most potential next-generation high-energy-density lithium ion battery cathode material. Among numerous silicon raw materials, the cut waste silicon powder can be a low-cost high-quality raw material for preparing the negative electrode of the lithium ion battery due to high purity (> 99.8%), fine particle size (about 1 mu m) and large yield (20 ten thousand tons/year). However, silicon itself has poor conductivity, and a large volume change (300%) occurs during the insertion and extraction of lithium, resulting in rapid degradation of cycle performance. At present, the main solution is to combine it with carbon to prepare a silicon-carbon composite material, and the modification of the silicon material by carbon coating can improve the electrical conductivity of silicon on the one hand, and can effectively isolate the interaction between silicon particles on the other hand, and buffer the huge stress generated by the volume change of silicon, thereby improving the structural stability of the material.
However, in the related field, a method for manufacturing a silicon-carbon negative electrode material of a lithium ion battery by using cut waste silicon powder as a raw material is quite lacked, and the prior art has many problems in manufacturing a spherical silicon-carbon composite material with high specific capacity and high cycling stability. CN105932245A discloses a method for preparing a silicon-carbon composite material by using a spray drying method, in the method, a carbon source, a binder and nano silicon need to be fully mixed before spray drying is carried out, carbonization treatment needs to be carried out after spray drying, the process flow is long, and the obtained silicon-carbon composite material belongs to physical mixing and has insufficient structural firmness; CN109004208A discloses a method for preparing a silicon-carbon composite material by a sol-gel method, which comprises the steps of dissolving a nitrogen-doped carbon source substance in a solution, evaporating and drying the carbon source substance, and then carbonizing the carbon source substance, wherein the uniformity of a carbon coating layer prepared by the method cannot be ensured, nano-silicon is easy to agglomerate, and further carbonization treatment is needed; CN107170979A discloses a method for preparing a silicon-carbon composite material by using a chemical vapor deposition method, in which a carbon source is added into a chemical vapor deposition apparatus for multiple times for carbonization, and each carbonization belongs to a static carbon coating process, and the obtained carbon coating layer has poor uniformity and is difficult to be applied in a large scale.
In summary, there is an urgent need to develop a new method for preparing spherical silicon-carbon composite material, which can not only make full use of the waste silicon powder, but also save time and energy consumption to meet the needs of large-scale industrial production, and the spherical silicon-carbon composite material obtained by the method has the characteristics of high carbon-silicon binding property, uniformity, excellent electrical properties, etc.
Disclosure of Invention
In view of the problems in the prior art, the invention aims to provide a spherical silicon-carbon composite material prepared by cutting waste silicon powder in one step, and a preparation method and application thereof, wherein the preparation method comprises the steps of fluidizing the cutting waste silicon powder with the particle size of 0.2-10 μm by using inert gas, then introducing carbon source gas for carbonization reaction, controlling the flow rate of the carbon source gas to account for 5-50% of the total gas flow rate, and realizing dynamic carbon coating and secondary granulation of silicon in one step. The spherical silicon-carbon composite material with excellent silicon-carbon binding property and uniformity can be prepared by the preparation method, and when the spherical silicon-carbon composite material is used for a lithium ion battery cathode, high specific capacity and excellent long-cycle stability can be shown; the preparation method can realize high-valued recycling of the cut waste silicon powder in an environment-friendly manner, has short flow and high efficiency, and is suitable for large-scale industrial production.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method for preparing a spherical silicon-carbon composite material by cutting waste silicon powder in one step, wherein the preparation method comprises the following steps:
(1) preparing cutting waste silicon powder with the particle size of 0.2-10 mu m;
(2) fluidizing the cut waste silicon powder in the step (1) by using inert gas;
(3) and (3) introducing a carbon source gas into the system obtained in the step (2) to carry out carbonization reaction, and controlling the flow of the carbon source gas to account for 5-50% of the total gas flow to obtain the spherical silicon-carbon composite material.
According to the invention, the cutting waste silicon powder with the granularity of 0.2-10 mu m is fluidized by using inert gas, then carbon source gas is introduced for carbonization reaction, the flow of the carbon source gas is controlled to account for 5-50% of the total gas flow, dynamic carbon coating and secondary granulation of silicon can be realized in one step, compared with the prior art such as spray drying and sol-gel, the carbon coating effect of the invention is better, the bonding force between the carbon coating layer and silicon is stronger, the uniformity of the carbon coating layer is greatly improved, meanwhile, the obtained silicon-carbon composite material is spherical, and the adjustment and optimization of the size and the carbon coating effect of the silicon-carbon composite material can be realized by controlling the flow of the carbon source gas, so that the key improvement effect is realized on the performance of the lithium ion battery cathode; the invention also needs to emphasize that the spherical silicon-carbon composite material of the lithium ion battery cathode with high specific capacity and excellent cycling stability can be manufactured by using the cut waste silicon powder, compared with commercial silicon powder with high purity and fine granularity used in the prior art, the invention fully expands the source range of available silicon raw materials, and meanwhile, the preparation method has the advantages of simple operation, short flow and high efficiency, is suitable for large-scale industrial production, endows extremely high additional value for secondary resource utilization of the cut waste silicon powder with huge yield, and saves huge energy and resource consumption.
The granularity of the raw materials is limited to be 0.2-10 mu m, so that fluidization, uniform carbon coating and secondary granulation in the whole process can be ensured to be in the optimal state, the three processes can be matched and connected with each other under the limited granularity of the raw materials, the process is smoothly carried out, the performance of the product prepared by using the raw materials with overlarge or undersize granularity is poor, and even the spherical carbon-returning composite material cannot be prepared; the flow of the carbon source gas in the step (3) is controlled to be 5-50% of the total gas flow, the decomposition rate of the carbon source gas can be effectively controlled, the speed and the coating amount of carbon coating are further stabilized, the carbon source gas with the excessively high concentration in unit volume can be explosively decomposed in the carbon coating process, independent nucleation is caused, carbon spheres are formed, uniform carbon coating on the surface of silicon powder is not facilitated, in addition, the residual amount of the carbon source gas with the excessively high concentration in the carbon coating process is larger, and pore channel blockage and resource waste are easily caused.
The particle size of the cutting waste silicon powder in the step (1) of the present invention is 0.2 to 10 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range of values are also applicable.
The flow rate of the carbon source gas in the step (3) of the present invention is 5 to 50% of the total gas flow rate, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.
As a preferable technical scheme of the invention, the cutting waste silicon powder in the step (1) is derived from cutting waste silicon mud in the photovoltaic industry.
Preferably, the cutting waste silicon powder in the step (1) is dried and crushed in advance to reach the target particle size.
Preferably, the purity of the cut waste silicon powder in the step (1) is more than 99.8 wt%.
Preferably, the cutting waste silicon powder in the step (1) is a flaky powder.
The cutting waste silicon powder used by the invention is derived from waste silicon sludge generated in the cutting process of crystal silicon wafers in the photovoltaic industry, the waste silicon sludge has certain granularity and shape after being processed by drying, crushing, sieving and other processing procedures, the purity of the waste silicon sludge meets the requirement of preparing a silicon-carbon cathode material of a lithium ion battery, and the waste silicon sludge can be directly used as the cutting waste silicon powder. Therefore, the high-valued cycle of secondary resources can be realized by using the cut waste silicon powder, and the green, economic and sustainable development of the photovoltaic industry and the lithium ion battery industry is effectively promoted. It should be noted that, as for the waste silicon powder from other sources, as long as the particle size and purity meet the requirements, those skilled in the art can reasonably select the waste silicon powder according to actual conditions.
As a preferred embodiment of the present invention, the inert gas in step (2) includes any one or a combination of at least two of argon, nitrogen, carbon dioxide gas or hydrogen-argon gas mixture, and typical but non-limiting examples of the combination include a combination of argon and nitrogen, a combination of argon and carbon dioxide gas, a combination of nitrogen and hydrogen-argon gas mixture or a combination of carbon dioxide gas and hydrogen-argon gas mixture.
The hydrogen-argon mixed gas in the step (2) of the invention is a commercial product and can be directly purchased, and the hydrogen content in the hydrogen-argon mixed gas provided by commercial companies is 1-10% (v/v), but those skilled in the art can reasonably select the hydrogen-argon mixed gas according to actual situations.
As a preferred embodiment of the present invention, the fluidization in step (2) is carried out in a fluidized bed reactor.
Preferably, the size of the perforated sieve plate in the fluidized bed reactor is 200 to 500 meshes, such as 200 meshes, 250 meshes, 300 meshes, 350 meshes, 400 meshes, 450 meshes or 500 meshes, but not limited to the recited values, and other values not recited in the above numerical range are also applicable.
According to the invention, the sieve plate with the air holes of a specific mesh number is selected, so that the inflow area and the flow of the inert gas can be refined, the air in the system can be fully exhausted, the cut waste silicon powder with the corresponding granularity can be fully driven by the inert gas, and the target fluidization state is further achieved.
As a preferred embodiment of the present invention, the carbon source gas in the step (3) includes any one or a combination of at least two of acetylene, methane, ethanol, ethylene or propylene, and typical but non-limiting examples of the combination include acetylene and methane, acetylene and ethanol, acetylene and ethylene, acetylene and propylene, methane and ethanol, methane and ethylene, methane and propylene, ethanol and ethylene, ethanol and propylene, or ethylene and propylene.
In a preferred embodiment of the present invention, the flow rate of the inert gas in the step (2) is set to N, and N is 500 to 2500mL/min, for example, 500mL/min, 750mL/min, 1000mL/min, 1250mL/min, 1500mL/min, 1750mL/min, 2000mL/min, 2250mL/min, 2500mL/min, or the like, but the flow rate is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable.
Preferably, after the carbon source gas is introduced in step (3), the total gas flow rate in step (3) is ensured to be 0.9-1.1N, such as 0.9N, 0.95N, 1N, 1.05N or 1.1N, but not limited to the recited values, and other values not recited in the above-mentioned range of values are also applicable.
It is worth to be noted that, the total gas flow rate in the step (3) is the sum of the inert gas flow rate and the carbon source gas flow rate; in the invention, when carbon source gas is introduced in the step (3), the flow of inert gas is properly reduced to reduce the fluctuation of the total gas flow, so that the fluidization state in the system is more stable, and the particles are gathered into spheres in the subsequent carbon coating forming process, thereby realizing secondary granulation.
Preferably, the reaction temperature of the carbonization reaction in the step (3) is 600 to 900 ℃, for example, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, or 900 ℃, but is not limited to the recited values, and other values not recited in the above numerical range are also applicable.
The method can adjust the decomposition rate of the carbon source by changing the temperature of the carbonization reaction, and optimize the uniformity of the carbon coating layer. In addition, the ordering degree of the graphite of the carbon coating layer can be adjusted by changing the carbonization reaction temperature, so that the side reaction of the silicon-carbon composite material and electrolyte in the electrochemical reaction process is weakened.
Preferably, the temperature increase rate of the carbonization reaction in step (3) is 3-15 ℃/min, such as 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, 11 ℃/min, 12 ℃/min, 13 ℃/min, 14 ℃/min or 15 ℃/min, but is not limited to the enumerated values, and other values within the above-mentioned range of values are also applicable.
Preferably, the carbonization reaction time in step (3) is 10-120 min, such as 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, but not limited to the recited values, and other values not recited in the above-mentioned range of values are also applicable.
The method can adjust the thickness of the carbon coating layer, namely the carbon content, by changing the time of the carbonization reaction, and simultaneously optimize the electrochemical performance of the spherical silicon-carbon composite material, and it needs to be noted that the temperature of the carbonization reaction is related to the time, the reaction time is shortened when the reaction is carried out at a relatively high temperature, and the reaction time is fully prolonged when the reaction is carried out at a relatively low temperature because the decomposition rate of the carbon source is reduced, so that the carbon content and the carbon coating layer reach the optimal state.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) drying and crushing the raw material of the cut waste silicon powder, and preparing the cut waste silicon powder with the particle size of 0.2-10 mu m; the cutting waste silicon powder is derived from cutting waste silicon mud in the photovoltaic industry, and the cutting waste silicon powder is flaky powder with the purity of more than 99.8 wt%;
(2) introducing inert gas with the flow rate of N into a fluidized bed reactor with a pore sieve plate of 200-500 meshes to fluidize the cut waste silicon powder in the step (1); wherein the inert gas comprises any one or combination of at least two of argon, nitrogen, carbon dioxide gas or hydrogen-argon mixed gas; n is 500-2500 mL/min;
(3) and (3) introducing a carbon source gas into the system obtained in the step (2), controlling the flow of the carbon source gas to be 5-50% of the total gas flow, ensuring that the total gas flow is 0.9-1.1N, and performing carbonization reaction at the temperature of 600-900 ℃ for 10-120 min at the heating rate of 3-15 ℃/min to obtain the spherical silicon-carbon composite material.
In a second aspect, the invention provides a spherical silicon-carbon composite material prepared by the preparation method of the first aspect.
In a third aspect, the invention provides a lithium ion battery negative electrode sheet, which contains the spherical silicon-carbon composite material according to the second aspect.
In a fourth aspect, the invention provides a lithium ion battery, wherein the lithium ion battery contains the lithium ion battery negative electrode plate.
Compared with the prior art, the invention at least has the following beneficial effects:
(1) the preparation method can realize dynamic carbon coating and secondary granulation of silicon in one step, and has the advantages of good carbon coating effect, strong binding force between the carbon coating layer and the silicon, and high uniformity of the carbon coating layer;
(2) the silicon-carbon composite material prepared by the preparation method is spherical, the size of the silicon-carbon composite material and the carbon coating effect can be adjusted and optimized by controlling the flow of carbon source gas and the temperature and time of carbonization reaction, and a lithium ion battery cathode prepared by using the spherical silicon-carbon composite material has high specific capacity and excellent cycling stability;
(3) the method can manufacture the spherical silicon-carbon composite material by using the cut waste silicon powder, fully expands the source range of available silicon raw materials, simultaneously realizes high-value secondary utilization of the cut waste silicon powder with huge yield in an environment-friendly mode, and saves huge energy and resource consumption.
Drawings
FIG. 1 is a scanning electron microscope image of cut waste silicon powders used in examples 1 to 8 of the present invention and comparative examples 1 to 2;
FIG. 2 is a graph showing the particle size distribution of cut waste silicon powders used in examples 1 to 8 of the present invention and comparative examples 1 to 2;
FIG. 3 is a scanning electron microscope image of a spherical Si-C composite material prepared in example 1 of the present invention;
FIG. 4 is a scanning electron microscope image of a spherical Si-C composite material prepared in example 2 of the present invention;
FIG. 5 is a scanning electron micrograph of a spherical silicon-carbon composite material prepared in example 3 of the present invention;
FIG. 6 is a scanning electron microscope image of a spherical Si-C composite material prepared in example 4 of the present invention;
FIG. 7 is a graph showing the charge-discharge cycle characteristics of the spherical Si-C composite material obtained in example 1 of the present invention;
FIG. 8 is a scanning electron micrograph of a spherical silicon carbon composite according to comparative example 1 of the present invention;
FIG. 9 is a scanning electron micrograph of a silicon carbon composite according to comparative example 3 of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The cutting waste silicon powders adopted in the embodiments 1 to 8 and the comparative examples 1 and 2 of the invention are dried and crushed in advance to obtain cutting waste silicon powder A with the particle size of 0.2-10 μm, the cutting waste silicon powder A is characterized by a scanning electron microscope (JSM-7800), the obtained scanning electron microscope image is shown in figure 1, the cutting waste silicon powder is shown as sheet powder, specifically sheet powder with the purity of more than 99.8 wt%, the cutting waste silicon powder A is characterized by a laser particle size analyzer (Mastersizer2000), and the obtained particle size distribution diagram is shown in figure 2, and the average particle size of the cutting waste silicon powder is shown as about 1 μm.
Example 1
The embodiment provides a preparation method for preparing a spherical silicon-carbon composite material by cutting waste silicon powder in one step, and the preparation method comprises the following steps:
(1) drying and crushing the cut waste silicon powder, and preparing cut waste silicon powder A with the particle size of 0.2-10 mu m;
(2) introducing argon with the flow rate of 1500mL/min into a fluidized bed reactor with a pore sieve plate with the size of 300 meshes to fluidize the cut waste silicon powder A in the step (1);
(3) and (3) introducing acetylene with the flow rate of 300mL/min into the system obtained in the step (2), controlling the total gas flow rate to be 1500mL/min, enabling the flow rate of the acetylene to be 20% of the total gas flow rate, and carrying out carbonization reaction at 700 ℃ for 30min at the heating rate of 10 ℃/min to obtain the spherical silicon-carbon composite material.
Example 2
The embodiment provides a preparation method for preparing a spherical silicon-carbon composite material by cutting waste silicon powder in one step, and the preparation method comprises the following steps:
(1) drying and crushing the cut waste silicon powder, and preparing cut waste silicon powder A with the particle size of 0.2-10 mu m;
(2) introducing nitrogen with the flow rate of 500mL/min into a fluidized bed reactor with an air hole sieve plate with the size of 500 meshes to fluidize the cut waste silicon powder A in the step (1);
(3) and (3) introducing methane with the flow rate of 25mL/min into the system obtained in the step (2), controlling the total gas flow rate to be 500mL/min, enabling the flow rate of the methane to be 5% of the total gas flow rate, and carrying out carbonization reaction at the temperature of 900 ℃ for 10min at the temperature rise rate of 12 ℃/min to obtain the spherical silicon-carbon composite material.
Example 3
The embodiment provides a preparation method for preparing a spherical silicon-carbon composite material by cutting waste silicon powder in one step, which comprises the following steps:
(1) drying and crushing the cut waste silicon powder, and preparing cut waste silicon powder A with the particle size of 0.2-10 mu m;
(2) introducing carbon dioxide gas with the flow rate of 2000mL/min into a fluidized bed reactor with a pore sieve plate with the size of 400 meshes to fluidize the cut waste silicon powder A in the step (1);
(3) and (3) introducing ethanol with the flow rate of 266.7mL/min into the system obtained in the step (2), controlling the total gas flow rate to be 2000mL/min, enabling the flow rate of the ethanol to be 13.3% of the total gas flow rate, and carrying out carbonization reaction at the temperature of 800 ℃ for 40min at the heating rate of 15 ℃/min to obtain the spherical silicon-carbon composite material.
Example 4
The embodiment provides a preparation method for preparing a spherical silicon-carbon composite material by cutting waste silicon powder in one step, and the preparation method comprises the following steps:
(1) drying and crushing the cut waste silicon powder, and preparing cut waste silicon powder A with the particle size of 0.2-10 mu m;
(2) introducing hydrogen-argon mixed gas with the flow rate of 2500mL/min into a fluidized bed reactor with a pore sieve plate of 200 meshes to fluidize the cut waste silicon powder A in the step (1);
(3) and (3) introducing propylene with the flow rate of 1250mL/min into the system obtained in the step (2), controlling the total gas flow rate to be 2500mL/min, enabling the flow rate of the propylene to account for 50% of the total gas flow rate, and carrying out carbonization reaction at 600 ℃ for 120min at the heating rate of 3 ℃/min to obtain the spherical silicon-carbon composite material.
Example 5
This example provides a one-step preparation method of spherical silicon-carbon composite material using cut waste silicon powder, which is identical to example 1 except that the carbonization reaction is performed at 1000 ℃ in step (3).
Example 6
This example provides a one-step preparation method of a spherical silicon-carbon composite material using cut waste silicon powder, which is identical to example 1 except that the carbonization reaction is performed at 500 ℃ in step (3).
Example 7
This example provides a one-step preparation method of spherical silicon-carbon composite material using cut waste silicon powder, which is identical to example 1 except that the carbonization reaction is performed for 150min in step (3).
Example 8
This example provides a one-step preparation method of spherical silicon-carbon composite material using cut waste silicon powder, which is identical to example 1 except that the carbonization reaction is performed for 5min in step (3).
Comparative example 1
The comparative example provides a preparation method for preparing a spherical silicon-carbon composite material by using cut waste silicon powder in one step, and the preparation method is completely the same as the preparation method in example 1 except that acetylene with the flow rate of 1250mL/min is introduced in the step (3) so that the flow rate of the acetylene accounts for 83.3% of the total gas flow rate.
Comparative example 2
The preparation method is completely the same as that in example 1 except that acetylene with the flow of 50mL/min is introduced in the step (3) so that the flow of acetylene accounts for 3.3% of the total gas flow.
Comparative example 3
The comparative example provides a preparation method for preparing a silicon-carbon composite material by using cut waste silicon powder in one step, and the preparation method comprises the following steps:
(1) drying and crushing the cut waste silicon powder, and preparing cut waste silicon powder B with the particle size of 20-30 mu m;
(2) introducing argon with the flow rate of 1500mL/min into a fluidized bed reactor with a pore sieve plate with the size of 300 meshes to fluidize the cut waste silicon powder B in the step (1);
(3) and (3) introducing acetylene with the flow rate of 300mL/min into the system obtained in the step (2), controlling the total gas flow rate to be 1500mL/min, enabling the flow rate of the acetylene to be 20% of the total gas flow rate, and carrying out carbonization reaction at 700 ℃ for 30min at the heating rate of 10 ℃/min to obtain the silicon-carbon composite material.
Comparative example 4
The comparative example provides a preparation method for preparing a spherical silicon-carbon composite material by using cut waste silicon powder in one step, and the preparation method is completely the same as the comparative example 3 except that the cut waste silicon powder C with the particle size of 0.01-0.1 mu m is prepared in the step (1) and the cut waste silicon powder C is fluidized in the step (2).
And (3) performance characterization:
(i) scanning electron microscopy: the spherical silicon-carbon composite materials obtained in the embodiments 1 to 4 are respectively characterized by a scanning electron microscope (JSM-7800) to respectively obtain scanning electron microscope images shown in figures 3 to 6, and it can be seen that the spherical silicon-carbon composite materials with higher sphericity can be obtained by the preparation method of the invention;
(ii) silicon content: silicon content of the spherical silicon-carbon composite materials obtained in the above examples and comparative examples is measured by a thermogravimetric-differential thermal analyzer, and the test results are shown in table 1;
(iii) charge-discharge cycle performance: mixing the spherical silicon-carbon composite material prepared in the example 1 with acetylene black and polyvinylidene fluoride in a nitrogen methyl pyrrolidone solution according to a mass ratio of 7:2:1 to prepare slurry, then uniformly coating the slurry on a copper current collector to obtain a negative electrode material, and taking a metal lithium sheet as a counter electrode, Celgard2325 as a diaphragm and 1mol/L LiPF6(the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1: 1) as an electrolyte, and a CR2032 type button battery case is used for assembling the button battery in an argon-protected glove box; the charge and discharge test program is set to be 500mAh/g, the voltage charge and discharge interval is 0.01-3V, the test result is shown in figure 7, and as can be seen from the figure, the coulombic efficiency of the first circle is 88.1%, and the specific capacity is more than 2104mAh/g after 300 charge and discharge cycles. The silicon-carbon composite materials prepared in other examples and comparative examples are assembled into button cells by the method and subjected to charge and discharge tests, and the test results are shown in table 1.
TABLE 1
As can be seen from table 1:
(1) the spherical silicon-carbon composite material prepared by using the cut waste silicon powder as the raw material in one step has high specific capacity and excellent long-cycle stability; the carbon coating layer is thickened, so that the silicon content in the product is gradually reduced, the specific capacity of the first circle of the battery is reduced due to the fact that the specific capacity of carbon is not high, the coulombic efficiency of the first circle of the battery is improved, the product with the silicon content being in the range of 58-81 wt% can still maintain high specific capacity after 300 times of circulation, and the excellent performance fully proves that the carbon coating effect of the preparation method is good, the binding force between the carbon layer and the silicon is high, the carbon layer is uniform and stable, the volume expansion of the silicon material in use is effectively limited, and therefore the cyclicity is improved;
the effect of carbon coating can be confirmed by fig. 3-6, and fig. 1 is a scanning electron microscope image of the spherical silicon-carbon composite material obtained in example 1, and it can be seen that the particle sizes of the spherical silicon-carbon composite material with the silicon content of 77.7 wt% obtained in example 1 are concentrated and are spherical particles, and the surface after carbon coating is uniform without obvious exposure; fig. 2 to 4 are scanning electron micrographs of the spherical silicon-carbon composites obtained in examples 2 to 4, respectively, and it can be seen that when the carbon content in the spherical silicon-carbon composite is decreased or increased relative to example 1, the surface carbon layer of the spherical silicon-carbon composite becomes rough, but the formation of spherical particles is maintained;
(2) comparing the embodiment 1 with the embodiment 5 and the embodiment 6, the embodiment 5 has a reaction temperature higher than 600-900 ℃ in the invention, which causes too fast decomposition rate of carbon source, poor uniformity and reduced ordering degree of graphite in the carbon layer, but the use requirement can still be met by controlling the silicon content to be in the range of 58-81 wt%; in example 6, because the reaction temperature of the carbonization reaction is lower than 600 to 900 ℃ in the invention, the decomposition amount of the carbon source gas is insufficient, complete and uniform coating of silicon cannot be realized, and most of silicon is directly exposed, and because the specific capacity of the silicon is high, the specific capacity of the battery obtained in example 6 is higher than that of example 1, but after circulation, the specific capacity is reduced to 11% of the original specific capacity, which indicates that the insufficient carbon coating causes severe volume expansion of the silicon material and the performance is damaged;
(3) comparing the embodiment 1 with the embodiments 7 and 8, in the embodiment 7, since the reaction time of the carbonization reaction is longer than 10-120 min in the invention, the carbon coating layer is too thick, the specific capacity of the obtained battery is obviously reduced, and the particles are easy to be bonded, in the embodiment 8, since the reaction time of the carbonization reaction is shorter than 10-120 min in the invention, the carbon coating is insufficient, the silicon can not be completely and completely protected, and the specific capacity of the obtained battery is seriously lost after the battery is cycled;
(4) comparing the embodiment 1 with the comparative example 1 and the comparative example 2, in the comparative example 1, because the flow of the introduced carbon source gas accounts for 5-50% of the total gas flow, a large amount of carbon coating layers are formed in a short time, the carbon coating layers are too thick, as shown in fig. 8, the particles are adhered, and the excessive carbon source gas can independently nucleate and form carbon spheres, so that the specific capacity of the obtained battery is greatly influenced; in comparative example 2, the flow of the introduced carbon source gas is lower than 5-50% of the total gas flow, so that effective carbon wrapping cannot be realized, most silicon is exposed outside, the flow of the carbon source gas is too low to be beneficial to forming spherical particles, and the content of silicon in the obtained product is as high as 93.8%, so that the specific capacity and the coulombic efficiency of the obtained battery cannot meet the use requirements;
(5) comparing example 1 with comparative examples 3 and 4, in comparative example 3, since the particle size of the silicon raw material is larger than 0.2 to 10 μm, although carbon coating can be performed, the coating effect is poor and secondary granulation into spherical shape cannot be realized, as shown in fig. 9, the performance of the product is rapidly deteriorated due to the non-centralized particle size distribution and irregular shape; in comparative example 4, because the granularity of the silicon raw material is less than 0.2-10 μm, part of the raw material with too small granularity directly leaks out of the sieve plate to cause waste in the preparation process, and the other part of the small-particle raw material has too much carbon coating and generates a large amount of bonding, the specific capacity of the obtained battery is obviously reduced, which is not beneficial to the application in the negative electrode of the lithium ion battery.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that, in the above embodiments, the various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, the present invention does not separately describe various possible combinations.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (10)
1. The preparation method for preparing the spherical silicon-carbon composite material by utilizing the cut waste silicon powder in one step is characterized by comprising the following steps of:
(1) preparing cutting waste silicon powder with the particle size of 0.2-10 mu m;
(2) fluidizing the cut waste silicon powder in the step (1) by using inert gas;
(3) and (3) introducing a carbon source gas into the system obtained in the step (2) to carry out carbonization reaction, and controlling the flow of the carbon source gas to account for 5-50% of the total gas flow to obtain the spherical silicon-carbon composite material.
2. The preparation method according to claim 1, wherein the cutting waste silicon powder in the step (1) is derived from cutting waste silicon sludge in photovoltaic industry;
preferably, the cutting waste silicon powder in the step (1) is dried and crushed in advance to reach the target particle size;
preferably, the purity of the cut waste silicon powder in the step (1) is more than 99.8 wt%;
preferably, the cutting waste silicon powder in the step (1) is flaky powder.
3. The production method according to claim 1 or 2, wherein the inert gas of step (2) comprises any one of argon, nitrogen, carbon dioxide gas or a hydrogen-argon mixture gas or a combination of at least two thereof.
4. The production method according to any one of claims 1 to 3, wherein the fluidization in step (2) is performed in a fluidized-bed reactor;
preferably, the size of the air hole sieve plate in the fluidized bed reactor is 200-500 meshes.
5. The production method according to any one of claims 1 to 4, wherein the carbon source gas of step (3) comprises any one or a combination of at least two of acetylene, methane, ethanol, ethylene or propylene.
6. The method according to any one of claims 1 to 5, wherein the flow rate of the inert gas in the step (2) is set to N, wherein N is 500 to 2500 mL/min;
preferably, after the carbon source gas is introduced in the step (3), the total gas flow in the step (3) is ensured to be 0.9-1.1N;
preferably, the reaction temperature of the carbonization reaction in the step (3) is 600-900 ℃;
preferably, the temperature rise rate of the carbonization reaction in the step (3) is 3-15 ℃/min;
preferably, the carbonization reaction time in the step (3) is 10-120 min.
7. The production method according to any one of claims 1 to 6, characterized by comprising the steps of:
(1) drying and crushing the cut waste silicon powder, and preparing the cut waste silicon powder with the particle size of 0.2-10 mu m; the cutting waste silicon powder is derived from cutting waste silicon mud in the photovoltaic industry, and the cutting waste silicon powder is flaky powder with the purity of more than 99.8 wt%;
(2) introducing inert gas with the flow rate of N into a fluidized bed reactor with a pore sieve plate of 200-500 meshes to fluidize the cut waste silicon powder in the step (1); wherein the inert gas comprises any one of argon, nitrogen, carbon dioxide gas or hydrogen-argon mixed gas or the combination of at least two of the argon, the nitrogen, the carbon dioxide and the hydrogen-argon mixed gas; n is 500-2500 mL/min;
(3) and (3) introducing a carbon source gas into the system obtained in the step (2), controlling the flow of the carbon source gas to account for 5-50% of the total gas flow, ensuring that the total gas flow is 0.9-1.1N, and performing carbonization reaction at 600-900 ℃ for 10-120 min at the heating rate of 3-15 ℃/min to obtain the spherical silicon-carbon composite material.
8. A spherical silicon-carbon composite material produced by the production method according to any one of claims 1 to 7.
9. A lithium ion battery negative electrode sheet, characterized in that the lithium ion battery negative electrode sheet contains the spherical silicon-carbon composite material according to claim 8.
10. A lithium ion battery, characterized in that the lithium ion battery contains the lithium ion battery negative electrode sheet according to claim 9.
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