Disclosure of Invention
Aiming at the problems, the invention provides carbon-coated two-dimensional silicon and a preparation method and application thereof. The method can prepare the carbon-coated two-dimensional silicon material to overcome the problems caused by the silicon cathode in the circulating process; in addition, the invention integrates the synthesis of the two-dimensional silicon and the carbon coating, thereby effectively simplifying the preparation process of the carbon-coated two-dimensional silicon and reducing the preparation cost of the carbon-coated two-dimensional silicon.
The first object of the present invention: a carbon-coated two-dimensional silicon is provided.
The second object of the present invention: provides a preparation method of carbon-coated two-dimensional silicon.
The third object of the present invention: provides the carbon-coated two-dimensional silicon and the application of the preparation method thereof.
In order to achieve the purpose, the invention adopts the following technical means:
the invention discloses a carbon-coated two-dimensional silicon, which consists of a layered silicon material with a porous structure and a carbon layer coated on the surface of the silicon material.
The preparation of the silicon material into the layered structure is an effective way for solving the problems that the silicon cathode can generate volume expansion in the circulating process and the electronic conductivity of the silicon is poor, and the silicon cathode with the layered structure can effectively shorten the ion transmission path, enlarge the contact interface of an electrode and electrolyte and improve the charge transmission rate, so that the electrochemical performance is improved. And secondly, the expansion generated in the circulation process is accommodated by the gaps of the laminated structure, so that the expansion of the whole volume of the silicon cathode is not caused. In addition, the electron conductivity of the silicon negative electrode can be further improved and the rate capability of the silicon negative electrode can be improved by coating the two-dimensional silicon with carbon.
Furthermore, the carbon layer has higher graphitization degree, and the carbon layer with the high graphitization degree has higher electronic conductivity, so that the transmission rate of ions can be promoted, and the rate capability of the material can be improved.
Further, the thickness of the carbon layer is between 1 nm and 200 nm; for example between 8-12 nm.
Secondly, a method for preparing carbon-coated two-dimensional silicon is disclosed, which comprises the steps ofThe following steps: with ASi2The carbon-coated two-dimensional silicon is prepared by the steps of taking the type alloy as a precursor, carrying out heating reaction on the precursor in carbon dioxide and/or hydrocarbon atmosphere, and carrying out acid washing treatment on the obtained solid product after the reaction is finished.
Further, the precursor includes: CaSi2、NiSi2、FeSi2、TiSi2、CoSi2、CrSi2、NbSi2、ZrSi2、MoSi2、LiSi2Any one or a mixture of two or more of them.
Further, the carbon dioxide or/and hydrocarbon atmosphere also contains inert gas, so that the obtained two-dimensional silicon surface is prevented from being oxidized, and the formed oxide layer can influence the charge transmission performance of the two-dimensional silicon.
Alternatively, the hydrocarbon gas includes any one or a mixture of two or more of methane, ethane, propane, ethylene, propylene, acetylene, propyne, and the like. Active carbon atoms formed after the gases are decomposed in a high-temperature environment can grow in situ on the surface of the precursor to form the carbon coating layer, and the carbon coating layer and the two-dimensional silicon surface are strong in binding force and not easy to fall off.
Further, the temperature of the heating reaction is 600-1500 ℃, and the time is 1-20 h. By heating, not only the carbon coating layer is grown in situ on the surface of the precursor, but also the ASi2The A element in the type alloy forms a product that is easily removed by some acid (e.g., CaSi)2Formation of CaCO under carbon dioxide atmosphere3Etc.) are removed after the acid wash treatment, while silicon remains, i.e. ASi2The type alloy is transformed into two-dimensional silicon after retaining its specific layered structure. At the same time, due to ASi2The element A in the alloy is removed, and the two-dimensional silicon prepared by the invention also has certain porous characteristic, so that the contact interface with electrolyte is further increased, the charge transmission rate is improved, and the electrochemical performance is improved.
Optionally, the acid used in the acid washing treatment comprises: hydrochloric acid, sulfuric acid, acetic acid, oxalic acid, citric acid, phosphoric acid, sulfurous acid, phosphoric acid, hydrofluoric acid, formic acid, benzoic acid, acetic acid, propionic acid, stearic acid, carbonic acid, hydrosulfuric acid, hypochlorous acid, boric acid, silicic acid, or a mixture of two or more thereof.
Further, the product obtained after the acid washing is sequentially filtered, washed and dried. So as to remove residual acid solution on the surface of the product. Preferably, the drying is vacuum drying; the temperature of vacuum drying is 70-150 ℃, and the surface of the two-dimensional silicon is prevented from being oxidized at high temperature.
Finally, the invention discloses the carbon-coated two-dimensional silicon and application of the carbon-coated two-dimensional silicon obtained by the preparation method in the fields of energy storage and the like. For example, when the lithium ion battery is used as a negative electrode material of a lithium ion battery, the performance of the battery can be effectively improved.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) the invention carries out carbon coating and ASi2The A element in the type alloy is converted into carbonate which can be easily removed, the carbonate can be easily removed through subsequent acid washing to obtain the carbon-coated two-dimensional silicon, namely the carbon-coated two-dimensional silicon is prepared and integrated with the carbon coating process by the market, the technical scheme greatly simplifies the preparation process of the carbon-coated two-dimensional silicon, and because of the ASi2Type alloys have been commercialized and are of many types, enabling the large-scale, low-cost preparation of carbon-coated silicon.
(2) Compared with the traditional carbon coating material, the carbon coating is carried out in gas, the generated carbon coating layer is more uniform, and the in-situ generated carbon coating structure has strong binding force with the two-dimensional silicon and is not easy to fall off in the use process.
(3) The carbon is coated by heating the precursor (such as asphalt, glucose and the like) for producing carbon, the method generates a large amount of gases such as carbon dioxide and the like in the heating process and pollutes the environment, and compared with the traditional method, the carbon coating method disclosed by the invention has the advantages that the generation of greenhouse gases can be effectively reduced, and the environment is more environment-friendly.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As described above, the commercial development of silicon cathodes is limited by the problems of volume expansion, poor electronic conductivity, complex preparation method, high preparation cost, etc. of the silicon cathodes during the cycling process. Thus, the invention is based on ASi2The type alloy provides a method for preparing carbon-coated alloy II on a large scaleA method of vitamin silicon; the invention will now be further described with reference to the drawings and detailed description.
First embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial CaSi was taken2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing carbon dioxide gas, heating to 900 ℃, preserving the temperature for 20 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 1M hydrochloric acid solution for 2h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 100 ℃ to obtain the carbon-coated two-dimensional silicon.
Second embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial CaSi was taken2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing methane gas, heating to 1100 ℃, preserving the temperature for 18 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 2M sulfuric acid solution for 0.6h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 120 ℃ to obtain the carbon-coated two-dimensional silicon.
Third embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial TiSi was taken2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing ethylene gas, heating to 700 ℃, preserving the temperature for 20 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 5M formic acid solution for 8h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 70 ℃ to obtain the carbon-coated two-dimensional silicon.
Fourth embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial FeSi was taken2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing acetylene gas, heating to 1400 ℃, preserving heat for 2 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 3M acetic acid solution for 4h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 150 ℃ to obtain the carbon-coated two-dimensional silicon.
Fifth embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial FeSi was taken2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing mixed gas of carbon dioxide and argon, heating to 1000 ℃, preserving the temperature for 20 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 5M hydrochloric acid solution for 2h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 130 ℃ to obtain the carbon-coated two-dimensional silicon.
Sixth embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial CaSi was taken2And 0.2g of TiSi2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing carbon dioxide gas, heating to 1400 ℃, preserving the temperature for 1h, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 0.8M hydrochloric acid solution for 5h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 90 ℃ to obtain the carbon-coated two-dimensional silicon.
Seventh embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial CaSi was taken2And 0.8g NbSi2Putting the powder into a magnetic boat, placing the magnetic boat into a tube furnace, and introducing carbon dioxide gasHeating to 800 ℃, preserving the heat for 10h, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 1.4M hydrochloric acid and 0.4M sulfuric acid solution for 2 hours, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 80 ℃ to obtain the carbon-coated two-dimensional silicon.
Eighth embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.4g of commercial MoSi was taken2And 0.9g ZrSi2Putting the powder into a magnetic boat, placing the magnetic boat into a tubular furnace, introducing carbon dioxide gas, heating to 1500 ℃, preserving the temperature for 2 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 1.8M acetic acid and 0.2M sulfuric acid solution for 4 hours, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 100 ℃ to obtain the carbon-coated two-dimensional silicon.
Ninth embodiment
A preparation method of carbon-coated two-dimensional silicon comprises the following steps:
(1) 0.5g of commercial CaSi was taken2And 0.1g LiSi2Putting the powder into a magnetic boat, putting the magnetic boat into a tubular furnace, introducing carbon dioxide gas, heating to 600 ℃, preserving the temperature for 20 hours, and cooling to room temperature to obtain an intermediate product.
(2) And (3) treating the intermediate product with 2.1M sulfuric acid solution for 6h, filtering out a solid product in the reaction solution after the treatment, washing, and drying in vacuum at 950 ℃ to obtain the carbon-coated two-dimensional silicon.
Performance testing
FIG. 1 is an XRD pattern of an intermediate product (not subjected to acid washing) prepared according to a first embodiment of the present invention, and it can be seen that CaSi appears therein2、CaCO3Characteristic peaks of Si, which indicate carbon dioxide and part of CaSi2Reaction to form CaCO3And a carbon-coated two-dimensional silicon composite.
FIG. 2 shows a carbon-coated carbon film prepared according to the first embodiment of the present inventionThe XRD pattern of the vitamin silicon shows that the characteristic peak of the silicon appears in the pattern, which indicates that CaSi2Precursor and reaction to CaCO3Has been successfully removed, and high purity carbon-coated two-dimensional silicon is synthesized.
Fig. 3 is a raman diagram of carbon-coated two-dimensional silicon prepared according to the first embodiment of the present invention, in which characteristic raman peaks of silicon and carbon appear without other miscellaneous peaks, further illustrating that high-purity carbon-coated two-dimensional silicon is synthesized and the coated carbon has a high graphitization degree.
Fig. 4 is a scanning electron micrograph of the carbon-coated two-dimensional silicon prepared according to the first embodiment of the present invention, which shows that the product synthesized in this embodiment has an obvious two-dimensional layered structure, and it can be determined that the material prepared in this embodiment is a material prepared by coating carbon on the surface of the two-dimensional layered silicon by combining the XRD and the raman mapping.
Fig. 5 is a transmission electron micrograph (low magnification) of the carbon-coated two-dimensional silicon prepared according to the first embodiment of the present invention, which further demonstrates that the synthesized product has a two-dimensional layered structure, and the surface of the product is obviously coated with a carbon layer.
Fig. 6 is a transmission electron micrograph (high magnification) of the carbon-coated two-dimensional silicon prepared according to the first embodiment of the present invention, and it can be seen that: the carbon in the product is coated on the surface of the two-dimensional silicon, the graphitization degree of the carbon is higher and is consistent with the Raman detection result, and the thickness of the highly graphitized carbon layer is between 8 and 12 nm.
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.