CN113809306A - Method for preparing silicon-carbon nano composite material by using black talc, product and application - Google Patents
Method for preparing silicon-carbon nano composite material by using black talc, product and application Download PDFInfo
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Abstract
The invention discloses a method for preparing a silicon-carbon nano composite material by using black talc, a product and application, and relates to the technical field of preparation of inorganic nano materials. The method comprises the following steps: and carrying out a reduction reaction on the mixture of the black talc and the reducing metal under the action of a ball mill. The method utilizes black talc as raw material, and improves the utilization value of black talc. Because black talc contains two kinds of elements of silicon and carbon simultaneously, and exists with the form of silica tetrahedral sheet and class graphite alkene lamina respectively, does not contain water between the layer, and layer charge is zero, and the lamella combines with weaker van der Waals' force with the lamella, peels off the lamella through the ball-milling in this application, exposes silica tetrahedral sheet for reducing metal and silica tetrahedron fully contact, and the ball-milling is the heat energy with mechanical energy conversion, and the heat energy accumulation then triggers the metallothermic reduction reaction. The prepared silicon-carbon nano composite material has a layered morphology and a hierarchical pore structure, has good silicon-carbon interface stability, and can be widely applied to lithium electronic batteries.
Description
Technical Field
The invention relates to the technical field of inorganic nano material preparation, in particular to a method for preparing a silicon-carbon nano composite material by using black talc, a product and application.
Background
China has abundant black talc resources, and is mainly distributed in the middle and southwest areas of China, such as Jiangxi, Sichuan, Hunan, Guangxi and other provinces. Among them, the Guangfeng black talc ore deposit in Jiangxi is the black talc ore deposit with the largest reserve found in China at present, and the reserve is proved to be over 5 hundred million tons. The main mineral components of the black talc deposit comprise talc, calcite, quartz, organic carbon and the like, and the mineral forming sources comprise hydrothermal fluid substitution, regional deterioration, weathering deposition and the like. Black talc has a 2:1 type layered structure similar to talc, and the basic structural unit is composed of two silica tetrahedral sheets sandwiching one magnesium oxide octahedral sheet, and contains a certain amount of organic matter between sheets or particles, thus exhibiting a black color. The black talc contains no water between layers, has zero layer charge, and has extremely complete cleavage (001), so that it has low hardness and a slippery feel. Although the storage amount of the black talc is huge, the application field and the value of the black talc are far lower than those of the white talc due to the limitation of the color of the black talc, and the black talc is only applied to middle and low-end industries such as ceramic industrial raw materials, rubber product fillers, plastic product fillers, coating fillers and waterproof material raw materials (a director of the Chinese nonmetallic mine industry, 2014(1), 1-3). The traditional utilization mode of the black talc is to directly remove organic matters in the black talc by high-temperature calcination so as to whiten the black talc and achieve the industrial application standard of the white talc. The low-level processing not only has high energy consumption and is not friendly to the environment, but also neglects the potential application value of the black talc. Therefore, it is necessary to develop a new way for high-value utilization of the steatite to improve the application value thereof.
On the other hand, silicon is due to higher theoretical capacity (-3579 mAh g-1) And relatively low discharge voltage (0.2V), and is widely noticed as a new generation of lithium ion battery cathode material with the most application prospect. However, silicon generates huge volume change during the lithium intercalation/lithium deintercalation cycle, so that the electrode structure is cracked and pulverized, the capacity is rapidly attenuated, and the practical application of the silicon negative electrode material is seriously hindered. The compounding of nano silicon and carbon nano materials is considered as an effective strategy for improving the lithium storage stability of silicon-based negative electrode materials. The nano structure of the silicon can relieve the stress generated by volume change and accelerate the electron/ion diffusion; the carbon nano material can enhance the conductivity of the electrode material and simultaneously act as a buffer medium. However, the preparation of the silicon-carbon nano composite material still has more problems, such as non-uniform silicon-carbon composite, poor interface stability and the like; moreover, the preparation of only silicon nanomaterials and carbon nanomaterials often involves expensive raw materials, cumbersome procedures, etc.; the morphology control of silicon-carbon nanocomposites makes the above process more complicated. These have seriously hindered the scale-up and practical application of silicon-carbon nanocomposites.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a method for preparing a silicon-carbon nano composite material by using black talc, which can comprehensively utilize silicon elements and carbon elements of the black talc to prepare the silicon-carbon nano composite material and provides a new idea for high-value utilization of the black talc.
The invention aims to provide a silicon-carbon nano composite material which has a layered morphology and a hierarchical pore structure, has good silicon-carbon interface stability, is easy to be further compounded with a carbon nano material, and improves the application performance.
The invention aims to provide an application of a silicon-carbon nano composite material in a lithium ion battery.
The invention is realized by the following steps:
in a first aspect, the present invention provides a method for preparing a silicon-carbon nanocomposite using black talc, comprising: and carrying out a reduction reaction on the mixture of the black talc and the reducing metal under the action of a ball mill.
In an optional embodiment, the mass ratio of the black talc to the reducing metal is 1: 0.2-5;
preferably, the mass ratio of the black talc to the reducing metal is 1: 0.2-0.9;
preferably, the reducing metal comprises at least one of magnesium, aluminum, zinc, sodium, potassium, calcium, and iron;
preferably, the reducing metal is mixed with the black talc in a powder form.
In an alternative embodiment, the ball milling comprises placing the mixture in a ball milling tank filled with milling balls, filling an inert gas into the ball milling tank, and performing the ball milling under a sealed condition;
preferably, the material of the grinding balls comprises at least one of zirconia, stainless steel, hard alloy, corundum, agate and silicon nitride;
preferably, the mass ratio of the grinding balls to the mixture is 10-60: 1; preferably 20-50: 1;
preferably, the rotation speed of the ball mill is 300-900 rpm; the ball milling time is 1-48 h;
preferably, the rotation speed of the ball mill is 400-750 rpm; the ball milling time is 1-15 h.
In an alternative embodiment, during the ball milling, further comprising adding an inorganic salt for equalizing the reaction temperature to the mixture;
preferably, the mass ratio of the inorganic salt to the black talc is 0.1-3: 1;
preferably, the inorganic salt is NaCl, LiCl, KCl, RbCl, CsCl, CaCl2And MgCl2At least one of (1).
In an alternative embodiment, after the ball milling is finished, the method further comprises the steps of carrying out acid washing, water washing and drying on reactants;
preferably, the acid-washing acid is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid;
preferably, the volume concentration of the acid for pickling is 2-20%;
preferably, the washing time of the acid washing is 0.1-10 h.
In an alternative embodiment, after the ball milling is finished and before the reactant is subjected to acid washing, the method further comprises the steps of heating and insulating the reactant under the protection of inert gas;
preferably, the heating temperature is 500-800 ℃, and the heat preservation time is 0.5-12 h.
In an alternative embodiment, prior to subjecting the mixture to the ball milling, further comprising adding an organic or carbon material to the mixture;
preferably, the mass ratio of the black talc to the organic matter is 1: 0.1-5;
preferably, the organic matter comprises at least one of pitch, glucose, sucrose and resin;
preferably, the mass ratio of the black talc to the carbon material is 1: 0.1-2;
preferably, the carbon material includes at least one of graphite, graphene, carbon nanotubes, and carbon microspheres.
In a second aspect, the present invention provides a silicon-carbon nanocomposite material prepared by the method of preparing a silicon-carbon nanocomposite material using black talc according to any one of the preceding embodiments.
In an alternative embodiment, the silicon-carbon nanocomposite has a tap density of 0.71 to 0.85g/cm3。
In a third aspect, the present invention provides the use of a silicon-carbon nanocomposite according to the previous embodiment in a lithium ion battery.
The invention has the following beneficial effects:
the application provides a method for preparing silicon-carbon nano composite material by utilizing black talc adopts black talc as raw materials, black talc contains two kinds of elements of silicon and carbon simultaneously, can make the black talc lamella fully open through the ball-milling shearing force, the ball-milling impact can also reduce the black talc lamella to a certain extent, and then expose more surfaces and terminal surfaces, make black talc fully contact with reducing metal, the heat energy that the ball-milling produced simultaneously can promote black talc and reducing metal to take place reduction reaction, realize carbonization and reduction through a pot method and go on in step, greatly simplify silicon-carbon nano composite material's preparation process, realize the convenient regulation and control of silicon carbon proportion simultaneously. In addition, the black talc is rich in reserves and low in price, can comprehensively utilize silicon elements and carbon elements of the black talc to prepare the silicon-carbon nano composite material with irregular lamellar morphology, is different from the existing granular silicon-carbon nano composite material, and provides a new idea for high-value utilization of the black talc.
The method for preparing the silicon-carbon nano composite material by using the black talc provided by the application can easily realize large-scale preparation of the silicon-carbon nano composite material, and has great industrial application prospect. The prepared silicon-carbon nano composite material has a layered morphology and a hierarchical pore structure, has good silicon-carbon interface stability, is easy to be further compounded with a carbon nano material, and improves the application performance. The obtained silicon-carbon nano composite material is used as a lithium ion battery cathode material, has the characteristics of low tap density and fast ion/electron transmission, and the assembled battery shows good electrochemical lithium storage performance and can be widely applied to the field of lithium ion batteries.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is an X-ray diffraction pattern of a silicon-carbon nanocomposite obtained in example 1;
FIG. 2 is a Si 2p high resolution X-ray photoelectron spectrum of the silicon-carbon nanocomposite prepared in example 1;
FIG. 3 is a scanning electron microscope photograph of the silicon-carbon nanocomposite material prepared in example 1;
fig. 4 shows the cycle performance of the silicon-carbon nanocomposite prepared in example 1 as a negative electrode material for a lithium ion battery.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The invention provides a method for preparing a silicon-carbon nano composite material by using black talc, which comprises the following steps:
and S1, mixing the black talc and the reducing metal to form a mixture.
In the application, natural black talc is placed in an oven to be dried, and then the black talc is mixed with reducing metal in proportion. Wherein, the basic structural unit of the black talc is formed by two silicon-oxygen tetrahedral sheets sandwiching a magnesium-oxygen octahedral sheet, and carbon is contained in the black talc, the content of the carbon is different due to different producing areas and different samples, and the mass percent of the carbon in the black talc can reach 0.1-40%. The mass ratio of the black talc to the reducing metal is 1: 0.2-5; the mass ratio of the black talc to the reducing metal is preferably 1: 0.2-0.9; preferably, the reducing metal comprises at least one of magnesium, aluminum, zinc, sodium, potassium, calcium, and iron; in the present application, the reducing metal is mixed with the black talc in a powder form.
The inventor researches and discovers that when the mass ratio of the black talc to the reducing metal is too high, the black talc is not completely reduced, partial simple substance silicon and silicon oxide compounds are generated, and the generated silicon-carbon nano composite material is less. And when the mass ratio of the black talc to the reducing metal is too low, on the one hand, the amount of the generated silicon-carbon nanocomposite is not further increased, which may cause an increase in cost, and on the other hand, when the amount of the reducing metal is increased, the metal may be melted into a metal ingot and attached to the ball milling pot during the ball milling process, which reduces the contact between the reducing metal and the black talc. Therefore, in the present application, the silicon-carbon nanocomposite properties obtained when the mass ratio of the black talc to the reducing metal is limited to 1:0.2 to 5 are better, and specifically, the mass ratio of the black talc to the reducing metal may be, for example: any one of 1:0.2, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, and 1:5, or a range of values therebetween.
In addition, the raw material black talc is different from talc, and the black talc not only has silicon element, but also has carbon element, so that an external carbon source is not needed; and the carbon and the silicon of the black talc are uniformly distributed in an atomic scale, so that the silicon and the carbon in the obtained silicon-carbon composite material are uniformly distributed. If talc is used to prepare the silicon-carbon nanocomposite, an additional carbon source needs to be introduced, and the amount of the reducing agent and the operation steps may be different according to the carbon source. For example, when the carbon source added is pure carbon (e.g., carbon nanotubes, graphene, etc.), the reducing agent need not be in excess; if the added carbon source is an organic matter, the reducing agent does not need to be excessive, but the steps of carbonization and the like are needed; if the carbon source to be added is carbon dioxide, the reducing agent must be in excess relative to the silicon precursor, since the reducing agent needs to reduce the silicon precursor (talc) first and then the carbon source. Therefore, the cost for preparing the silicon-carbon composite material by adopting the black talc is lower. On the other hand, due to the difference of the properties of the silicon element and the carbon element, the problems of non-uniform silicon-carbon compounding and poor interface stability often occur in the direct compounding process of the silicon element and the carbon element; compared with the silicon-carbon composite material prepared directly by using the black talc, the silicon-carbon composite material prepared directly by using the black talc has uniform silicon and carbon distribution, and is easier to be compounded with other carbon materials, so that the silicon-carbon ratio is regulated and controlled.
In other embodiments, an organic or carbon material may also be added to the mixture; the organic matter or carbon material can be used for supplementing carbon and regulating the silicon-carbon ratio, thereby improving the performance of the silicon-carbon nano composite material. When organic matters are added, the mass ratio of the black talc to the organic matters is 1: 0.1-5; the organic matter comprises at least one of asphalt, glucose, sucrose and resin; when the carbon material is added, the mass ratio of the black talc to the carbon material is 1: 0.1-2; the carbon material includes at least one of graphite, graphene, carbon nanotubes, and carbon microspheres.
And S2, performing ball milling on the mixture, and performing a reduction reaction under the action of the ball milling.
Placing the mixture into a ball milling tank filled with grinding balls, filling inert gas into the ball milling tank, and carrying out ball milling under a sealed condition; the rotating speed of the ball milling is 300-900 rpm; the ball milling time is 1-48 h. Preferably, the rotation speed of the ball mill is 400-750 rpm; the ball milling time is 1-15 h.
The material of the grinding balls comprises at least one of zirconia, stainless steel, hard alloy, corundum, agate and silicon nitride. Preferably, the mass ratio of the grinding balls to the mixture is 10-60: 1. Preferably 20-50: 1; when the mass ratio of the grinding balls to the mixture is too low, the grinding cannot be sufficiently performed, and when the amount of the grinding balls is too large, the mixture added into the ball mill tank is reduced, and the generation efficiency is reduced. The inventors found that sufficient contact between the black talc and the reducing metal and reduction reaction cannot be achieved by the conventional heat treatment. This application realizes the abundant contact of reactant through the ball-milling to utilize the mechanical heat generation mode to initiate reduction reaction, need not pressurization or external heating source, the operation is simpler.
In other embodiments, inorganic salts for equalizing the reaction temperature may also be added to the mixture during ball milling; the mass ratio of the added inorganic salt to the black talc is 0.1-3: 1; the inorganic salt is NaCl, LiCl, KCl, RbCl, CsCl, CaCl2And MgCl2At least one of (1).
S3, acid washing, dry cleaning and drying.
After the ball milling is finished, the method also comprises the steps of acid washing, water washing and drying of reactants. In the present application, the acid for pickling is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; the volume concentration of the acid for pickling is 2-20%; the washing time of the acid washing is 0.1-10 h.
In other embodiments, the reactants may be heated to 500-800 ℃ under the protection of inert gas and then kept at the temperature for 0.5-12 hours before the acid washing. The heating and heat preservation treatment can ensure that the reactants after ball milling react more fully, thereby avoiding the incomplete reaction.
It should be understood that the heat-keeping step is not essential, and the pickling may be performed in combination with the preceding heat-keeping or may be performed only by pickling.
The application provides a method for preparing silicon-carbon nanocomposite by using black talc, which uses black talc as a raw material, the utilization value of the black talc is improved, the black talc contains two elements of silicon and carbon simultaneously and exists in the forms of silica tetrahedral sheet and graphene-like sheet layer respectively, no water exists between layers, the layer charge is zero, the sheet layer and the sheet layer are combined by weak van der Waals force, the black talc sheet layer is stripped through ball milling in the application, the silica tetrahedral sheet is exposed, reducing metal is fully contacted with silica tetrahedron, meanwhile, mechanical energy is converted into heat energy through ball milling, and the heat energy is accumulated to further initiate a metallothermic reduction reaction. The prepared silicon-carbon nano composite material has a layered morphology and a hierarchical pore structure, has good silicon-carbon interface stability, and can be widely applied to lithium electronic batteries.
The method skillfully utilizes the properties of the black talc lamellar structure and no ions/water between layers, and combines a ball milling method to obtain the lamellar structure with fewer nano holes. In the prior art, the material morphology is difficult to control, and very complicated steps are needed if the silicon-carbon nano composite material with the layered morphology is obtained. In addition, it should be noted that the material obtained in the prior art often contains a large number of nanopores, and when the material is used as a negative electrode of a lithium ion battery, the large number of nanopores can cause a side reaction between the negative electrode material and an electrolyte to be greatly increased, which causes a reduction in coulombic efficiency, which is also avoided in the preparation of a silicon-based negative electrode material.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in an oven at 100 ℃ for 4h, then mixing 10g of dried black talc with 6g of metal magnesium powder, putting the mixture and 320g of zirconia balls into a zirconia ball milling tank, filling inert gas into the ball milling tank, sealing, and ball milling at the rotating speed of 700rpm for 3 h. And after the reaction is finished, washing the obtained mixture with 18% hydrochloric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
FIG. 1 is an X-ray diffraction pattern of the resulting product. The results show that the product has characteristic diffraction peaks of typical crystalline silicon, which correspond to the crystal planes of (111), (220), (311), (400) and (331), respectively. No diffraction peaks of other impurity phases appeared. The raman spectrum showed that signals of silicon and carbon (D and G peaks) appeared simultaneously in the product, indicating that it is a silicon-carbon composite. The high-resolution Si 2p X photoelectron spectrum of the product presents an asymmetric characteristic (figure 2), the main peak is positioned at 99.1eV, and the main peak is attributed to simple substance silicon; two weak peak packages appear at the positions of high spectrum binding energy 100.7 and 103.1eV, and can be attributed to SiO of the surface of the simple substance siliconx. The scanning electron microscope results of the product showed (fig. 3), and the obtained silicon-carbon nanocomposite material was in a lamellar morphology and had a hierarchical pore structure. Elemental analysis results showed that the mass fraction of carbon in the silicon-carbon nanocomposite was about 4%. The tap density is 0.73g/cm3Far higher than that of the current commercial nano silicon (about 0.16 g/cm)3)。
Example 2
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in a 120 ℃ oven for 1h, then mixing 5g of dried black talc with 5g of metal magnesium powder and aluminum powder (the molar ratio of the magnesium powder to the aluminum powder is 7:3), putting the mixture and 300g of zirconia balls into a zirconia ball milling tank, filling inert gas into the ball milling tank, sealing, and ball milling at the rotating speed of 600rpm for 6 h. And after the reaction is finished, washing the obtained mixture by using 15% sulfuric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon,microcosmically presents a layered appearance, has a hierarchical pore structure and has the tap density of 0.76g/cm3。
Example 3
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in an oven at 80 ℃ for 12h, then mixing 10g of dried black talc, 10g of metal magnesium powder and 5g of sodium chloride, putting the mixture and 500g of corundum pellets into a corundum ball milling tank, filling inert gas into the corundum ball milling tank, sealing, and carrying out ball milling at the rotation speed of 550rpm for 12 h. And after the reaction is finished, washing the obtained mixture by using 10% hydrochloric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.71g/cm3。
Example 4
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in a 105 ℃ oven for 2h, then placing 4g of dried black talc, 3.2g of metal magnesium powder and 250g of hard alloy pellets into a hard alloy ball milling tank, filling inert gas into the ball milling tank, sealing, and ball milling at the rotating speed of 750rpm for 1 h. After the reaction is finished, placing the obtained mixture in a tubular furnace, and preserving the heat for 1h at 650 ℃ under the protection of inert atmosphere. And after cooling, washing the product with 8% sulfuric acid, washing the product with water for several times until the product is neutral, and drying the product to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.78g/cm3。
Example 5
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in a 90 ℃ oven for 8h, then mixing 5g of dried black talc, 2g of metal magnesium powder and 1g of graphite powder, putting the mixture and 400g of stainless steel balls into a stainless steel ball milling tank, filling inert gas into the ball milling tank, sealing, and carrying out ball milling at the rotating speed of 450rpm for 15 h. And after the reaction is finished, washing the obtained mixture by using 5% nitric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.85g/cm3。
Example 6:
the method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in an oven at 85 ℃ for 10 hours, then mixing 5g of dried black talc, 4g of metal magnesium powder and 1g of asphalt powder, putting the mixture and 500g of hard alloy balls into a hard alloy ball milling tank, filling inert gas into the ball milling tank, sealing, and carrying out ball milling at the rotating speed of 600rpm for 10 hours. And after the reaction is finished, washing the obtained mixture with 15% hydrochloric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.82g/cm3。
Example 7
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in an oven at 85 ℃ for 10 hours, then mixing 5g of dried black talc with 4g of metal magnesium powder, putting the mixture and 500g of hard alloy pellets into a hard alloy ball milling tank, filling inert gas into the ball milling tank, sealing, and ball milling at the rotating speed of 600rpm for 10 hours. And after the reaction is finished, washing the obtained mixture with 15% hydrochloric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.84g/cm3。
Example 8
The method, the product and the application for preparing the silicon-carbon nano composite material by using the black talc provided by the embodiment comprise the following steps:
placing natural black talc in an oven at 85 ℃ for 10 hours, then mixing 5g of dried black talc with 20g of metal magnesium powder, putting the mixture and 500g of hard alloy pellets into a hard alloy ball milling tank, filling inert gas into the ball milling tank, sealing, and ball milling at the rotating speed of 600rpm for 10 hours. And after the reaction is finished, washing the obtained mixture with 15% hydrochloric acid, washing the mixture for several times until the mixture is neutral, and drying the mixture to obtain the silicon-carbon nano composite material.
The obtained product consists of simple substance silicon and carbon, is microscopically layered, has a hierarchical pore structure, and has a tap density of 0.80g/cm3。
Application example:
the silicon-carbon nanocomposite obtained in example 1 was used as a negative electrode material of a lithium ion battery, and a button cell was assembled. Preparation of a working electrode: mixing an active substance (namely the obtained silicon-carbon nano negative electrode material), acetylene black and sodium alginate according to a mass ratio of 7: 1.5: 1.5, uniformly mixing, coating on a copper foil, drying in vacuum, and cutting into a circular sheet with the diameter of 12 mm. The counter electrode and the reference electrode are both metal lithium sheets. The electrolyte contains 1mol/L LiPF61:1 ethylene carbonate/dimethyl carbonate with 10 wt.% fluorinated ethylene carbonate added. The assembly process of the lithium ion battery was performed in an argon glove box (both water and oxygen concentrations were below 0.1 ppm).
The cycle performance result of the silicon-carbon nanocomposite prepared in example 1 at a current density of 1.0A/g (the first three cycles are activated at a low current density of 0.2A/g) is as shown in the figure (fig. 4), the coulombic efficiency of the first cycle of the material is 81.4%, the specific capacity is up to 2100mAh/g at the current density of 1.0A/g, the specific capacity is maintained above 81% after 50 cycles, good cycle stability is shown, and the silicon-carbon nanocomposite has good application potential in the field of lithium ion batteries.
To sum up, the method for preparing the silicon-carbon nanocomposite by using the black talc provided by the application utilizes the black talc as a raw material, the black talc is rich in reserve and low in price, a basic structural unit of the black talc is formed by two silica tetrahedron sheets sandwiching a magnesium-oxygen octahedron sheet, water is not contained between the layers, the layer charge is zero, the sheet layers and the sheet layers are combined by weak van der waals force, the sheet layers are easily opened by ball milling, the silica tetrahedron sheets are exposed, reducing metal is easily contacted with the silica tetrahedron, mechanical energy is converted into heat energy by the ball milling, and the heat energy is accumulated to further initiate a metallothermic reduction reaction.
The reason why the silicon-carbon nanocomposite material is successfully prepared is as follows:
(1) the black talc contains two elements of silicon and carbon, and exists in the forms of a silica tetrahedral sheet and a graphene-like sheet layer respectively, so that the black talc is an ideal silicon source and carbon source;
(2) the black talc lamella is not charged, is easy to peel off by mechanical force, exposes a large number of silicon-oxygen tetrahedrons, and promotes the generation of reduction reaction, and the magnesium-oxygen octahedron lamella can be used as a template and a barrier layer to induce a product to form a lamellar shape;
(3) the black talcum layer does not contain water, so that the ineffective consumption of reducing metal is avoided;
(4) the ball milling can not only strip the black talc lamella and reduce the size of reactants (black talc and reducing metal powder), so that the black talc is fully contacted with the reducing metal, but also can generate heat energy, carbonize organic matters and initiate reduction reaction, and meanwhile, the ball milling ensures the uniformity of the whole solid phase reaction;
(5) the invention realizes the synchronous carbonization and reduction by a one-pot method, greatly simplifies the preparation process of the silicon-carbon nano composite material, and simultaneously realizes the convenient regulation and control of the silicon-carbon ratio.
The method for preparing the silicon-carbon nano composite material by using the black talc provided by the application can easily realize large-scale preparation of the silicon-carbon nano composite material, and has great industrial application prospect. The prepared silicon-carbon nano composite material has irregular layered morphology and a hierarchical pore structure, has good silicon-carbon interface stability, is easy to be further compounded with the carbon nano material, and improves the application performance. The obtained silicon-carbon nano composite material is used as a lithium ion battery cathode material, has the characteristics of low tap density and fast ion/electron transmission, and the assembled battery shows good electrochemical lithium storage performance and can be widely applied to lithium ion batteries.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for preparing a silicon-carbon nanocomposite using black talc, comprising: and carrying out a reduction reaction on the mixture of the black talc and the reducing metal under the action of a ball mill.
2. The method for preparing the silicon-carbon nanocomposite material by using the black talc according to claim 1, wherein a mass ratio of the black talc to the reducing metal is 1:0.2 to 5;
preferably, the mass ratio of the black talc to the reducing metal is 1: 0.2-0.9;
preferably, the reducing metal comprises at least one of magnesium, aluminum, zinc, sodium, potassium, calcium, and iron;
preferably, the reducing metal is mixed with the black talc in a powder form.
3. The method for preparing a silicon-carbon nanocomposite using black talc according to claim 1, wherein the ball milling comprises placing the mixture in a ball milling pot filled with milling balls, filling the ball milling pot with an inert gas, and performing the ball milling under a sealed condition;
preferably, the material of the grinding balls comprises at least one of zirconia, stainless steel, hard alloy, corundum, agate and silicon nitride;
preferably, the mass ratio of the grinding balls to the mixture is 10-60: 1; preferably 20-50: 1;
preferably, the rotation speed of the ball mill is 300-900 rpm; the ball milling time is 1-48 h;
preferably, the rotation speed of the ball mill is 400-750 rpm; the ball milling time is 1-15 h.
4. The method for preparing a silicon-carbon nanocomposite using black talc according to claim 1, wherein during said ball milling, further comprising adding an inorganic salt for equalizing a reaction temperature to said mixture;
preferably, the mass ratio of the inorganic salt to the black talc is 0.1-3: 1;
preferably, the inorganic salt is NaCl, LiCl, KCl, RbCl, CsCl, CaCl2And MgCl2At least one of (1).
5. The method for preparing a silicon-carbon nanocomposite using black talc according to any one of claims 1 to 4, wherein after the ball milling is completed, further comprising acid washing, water washing and drying the reactant;
preferably, the acid-washing acid is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid;
preferably, the volume concentration of the acid for pickling is 2-20%;
preferably, the washing time of the acid washing is 0.1-10 h.
6. The method for preparing silicon-carbon nanocomposite using black talc according to claim 5, wherein after the ball milling is finished and before the acid washing is performed to the reactant, the method further comprises heating and maintaining the temperature of the reactant under the protection of inert gas;
preferably, the heating temperature is 500-800 ℃, and the heat preservation time is 0.5-12 h.
7. The method for preparing a silicon-carbon nanocomposite using black talc according to any one of claims 1 to 4, wherein before subjecting the mixture to said ball milling, further comprising adding an organic or carbon material to the mixture;
preferably, the mass ratio of the black talc to the organic matter is 1: 0.1-5;
preferably, the organic matter comprises at least one of pitch, glucose, sucrose and resin;
preferably, the mass ratio of the black talc to the carbon material is 1: 0.1-2;
preferably, the carbon material includes at least one of graphite, graphene, carbon nanotubes, and carbon microspheres.
8. A silicon-carbon nanocomposite, characterized by being produced by the method for producing a silicon-carbon nanocomposite using black talc according to any one of claims 1 to 7.
9. The silicon-carbon nanocomposite according to claim 8, wherein the silicon-carbon nanocomposite has a tap density of 0.71 to 0.85g/cm3。
10. Use of a silicon-carbon nanocomposite according to any one of claims 8 to 9 in a lithium ion battery.
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