CN115832259B - Silicon-carbon composite material containing nano silicon-based film and preparation method thereof - Google Patents
Silicon-carbon composite material containing nano silicon-based film and preparation method thereof Download PDFInfo
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- 239000005052 trichlorosilane Substances 0.000 claims description 2
- 239000011868 silicon-carbon composite negative electrode material Substances 0.000 claims 3
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Battery Electrode And Active Subsutance (AREA)
Abstract
本发明公开了一种含有纳米硅基薄膜的硅碳复合材料及其制备方法，主要涉及锂离子电池领域。包括多个硅碳颗粒，所述硅碳颗粒包括碳基材、嵌入碳基材中的纳米硅基薄膜以及硅碳颗粒表面的碳包覆层；所述纳米硅基薄膜厚度为0.1‑50nm，所述纳米硅基薄膜面积的中值大于10nm2；所述碳包覆层厚度为1nm‑1um。本发明的有益效果在于：含有尺寸较小、分散均匀且比表面积小的纳米硅基薄膜，有效减少负极裂纹数量，且稳定性高，使得其在首次嵌锂过程中消耗活性锂较少，首周效率较高。
The present invention discloses a silicon-carbon composite material containing a nano silicon-based film and a preparation method thereof, which mainly relates to the field of lithium-ion batteries. The present invention comprises a plurality of silicon-carbon particles, wherein the silicon-carbon particles comprise a carbon substrate, a nano silicon-based film embedded in the carbon substrate, and a carbon coating layer on the surface of the silicon-carbon particles; the thickness of the nano silicon-based film is 0.1-50nm, and the median area of the nano silicon-based film is greater than 10nm 2 ; the thickness of the carbon coating layer is 1nm-1um. The beneficial effects of the present invention are: the nano silicon-based film containing a small size, uniform dispersion and a small specific surface area effectively reduces the number of cracks in the negative electrode, and has high stability, so that it consumes less active lithium during the first lithium insertion process, and has a higher efficiency in the first week.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a silicon-carbon composite material containing a nano silicon-based film and a preparation method thereof.
Background
The lithium ion battery has the advantages of long cycle life, high working voltage, high specific energy, low self-discharge and the like, and is widely applied to the fields of electronic products, portable electric tools, electric automobiles and the like. With the rapid development of electronic technology and the increasing market of new energy automobiles, the market demand for lithium ion batteries with higher energy density is also increasing. However, the negative electrode used in the current commercial lithium ion battery is a graphite negative electrode, and the theoretical specific capacity is only 372mAh/g, so that the requirement of the high-energy-density battery cannot be met. There is thus a great need to find a negative electrode material with a high specific capacity that can replace graphite, where silicon is considered as an ideal choice for the negative electrode material of the next generation lithium ion battery due to the advantages of having a relatively high specific capacity (4200 mAh/g) and a low delithiation plateau.
However, the volume expansion and shrinkage rate of the silicon negative electrode in the lithium intercalation process is more than 300 percent, so that the cycle performance of the silicon negative electrode in a lithium battery is poor, and in addition, the electron conductivity and the ion conductivity of silicon are low, so that the rate performance of the silicon negative electrode is also poor. To solve the above problems, silicon materials are currently being composited with carbon substrates.
The traditional nano silicon-carbon composite material is prepared by mechanically grinding silicon to nano silicon, dispersing nano silicon in a carbon source, and carbonizing the nano silicon to obtain the silicon-carbon composite material, but the nano silicon in the method is difficult to uniformly disperse in the carbon source, and the nano silicon is difficult to grind to a size below 50nm by a mechanical grinding method, so that the cycle performance of the silicon-carbon composite material obtained by the method is still poor, the silicon alloy powder is washed by the CN107507972B to obtain porous silicon, then the porous silicon is coated with carbon, and finally carbonized to obtain the silicon-carbon composite material, the porous silicon has a porous structure which relieves the expansion problem of the silicon in the lithium removing process to a certain extent, the cyclic performance of the porous silicon is still poor due to the larger size of the porous silicon, the pore wall and the outer surface of the porous carbon microsphere containing through holes are covered with a plating layer containing transition elements, and then silane is decomposed on the inner surface of the pores to obtain the nano silicon-carbon composite material, the method is a better method in the market at present, the silicon decomposed silicon particles are easy to be deposited from the outer surface to the inner part, the silicon particles are not decomposed on the inner surface of the ideal silicon particles, and the silicon particles are not decomposed on the inner surface of the inner part of the ideal silicon particles, and the silicon particles are not decomposed on the inner surface of the ideal silicon particles, and the silicon particles are not decomposed on the inner surface of the porous particles.
Disclosure of Invention
The invention aims to provide a silicon-carbon composite material containing a nano silicon-based film and a preparation method thereof, wherein the nano silicon-based film has smaller size, uniform dispersion and small specific surface area, so that the number of cracks of a negative electrode is effectively reduced, the stability is high, active lithium consumption is low in the first lithium intercalation process, and the first cycle efficiency is high.
The invention aims to achieve the aim, and the aim is achieved by the following technical scheme:
a silicon-carbon composite material containing a nano silicon-based film, which comprises a plurality of silicon-carbon particles, wherein the silicon-carbon particles comprise a carbon substrate, the nano silicon-based film embedded in the carbon substrate and a carbon coating layer on the surfaces of the silicon-carbon particles;
the thickness of the nano silicon-based film is 0.1-50nm, and the median value of the area of the nano silicon-based film is larger than 10nm 2;
the thickness of the carbon coating layer is 1nm-1um.
Further, the nano silicon-based film is of a sheet structure with an irregular shape.
Further, the nano silicon-based film is at least one of a simple substance silicon material and a silicon alloy material.
Further, the carbon substrate is one or more of hard carbon and soft carbon, or is compounded with one or more of graphite, carbon nano tube, carbon fiber and graphene.
Further, the mass ratio of silicon in the silicon-carbon composite material is 0.1% -70%, and the particle size of the silicon-carbon composite material is 3-30um;
The preparation method of the silicon-carbon composite material containing the nano silicon-based film comprises the following steps:
S1, placing a solid carbon source with a softening point of 80-400 ℃ into a heating cavity with a temperature of 80-400 ℃, vacuumizing to maintain a vacuum degree of 0.1Pa-1000Pa, heating the solid carbon source to a molten state, dripping the molten solid carbon source onto a rotary disc substrate with a temperature of 150-400 ℃, spreading by using a scraper, then introducing silicon source gas, cracking the silicon source by using a plasma enhanced chemical vapor deposition method, depositing the silicon source on the surface of the molten carbon source to form a nano silicon-based film, and uniformly dispersing the formed nano silicon-based film in the molten carbon source by continuously spreading and depositing the silicon to obtain a precursor of the silicon-carbon composite material;
S2, closing the introduction of the silicon source gas after the reaction in the step S1 is finished, naturally cooling, and then transferring the rotating disc substrate loaded with the silicon-carbon composite material precursor and the silicon-carbon composite material precursor to a vacuum or inert gas atmosphere furnace for high-temperature carbonization to form the silicon-carbon composite material, wherein the carbonization temperature is 900-1200 ℃, the carbonization time is 1-6 hours, and the heating rate of the carbonization is 0.5-20 ℃ per minute;
S3, cooling to room temperature after carbonization in the step S2 is finished, and crushing and grading the silicon-carbon composite material to obtain the silicon-carbon composite anode material containing the nano silicon-based film.
Further, in the step S1, the silicon source gas is composed of silane and diluent gas, or at least one of silicon tetrachloride, dichlorosilane and trichlorosilane and the diluent gas, and the solid carbon source is selected from 1 or at least 2 of isotropic coal tar pitch, isotropic petroleum pitch, mesophase pitch or high polymer material, or the combination of the solid carbon source and one or more of graphite, carbon nano tubes, carbon fibers and graphene.
Furthermore, in the step S1, a silicon source gas may be introduced, and a non-metal element gas source may be introduced at the same time, so that the nano silicon-based film contains a silicon alloy material.
Furthermore, the silicon-carbon composite anode material obtained in the step S3 can be subjected to carbon coating by a chemical vapor deposition method or a pyrolysis method to obtain the silicon-carbon composite anode material containing the carbon coating layer.
Further, the silicon-carbon composite material is applied to a lithium ion battery cathode.
Compared with the prior art, the invention has the beneficial effects that:
1. the thickness of the nano silicon-based film is small. According to the invention, by using a plasma enhanced vapor deposition method, a nano silicon-based film with the thickness of 0.1nm-50nm can be generated, and the volume expansion effect of the silicon-carbon composite material in the anode can be effectively relieved by the inclusion of the nano silicon-based film with the small size, so that the cycle performance of the material can be improved;
2. the silicon is uniformly dispersed. Different from a method for dispersing nano silicon particles in a carbon source and then carbonizing, the method is carried out simultaneously with production and dispersion, a nano silicon-based film is generated on the surface of a molten carbon source, and the nano silicon-based film can be uniformly dispersed in the carbon source by extrusion and strickling of the nano silicon-based film and the molten carbon source, so that the nano silicon-based film in the silicon-carbon composite material obtained after carbonization of a precursor is also uniformly dispersed;
3. The overall expansion stress is uniform, the nano silicon-based film has small dispersed particles and uniform dispersion, and the cracking of the silicon-carbon composite negative electrode due to uneven stress in the circulating process is reduced;
4. The specific surface area of silicon is small. Compared with zero-dimensional nano silicon particles with the same particle size and one-dimensional nano silicon wires, the nano silicon-based film obtained by the plasma enhanced vapor deposition method has smaller specific surface area, so that active lithium consumed for generating the SEI film in the first lithium intercalation process is less, and the first cycle efficiency of the silicon-carbon composite material is higher than that of negative electrode materials with the same specific capacity in other patents.
Drawings
Fig. 1 is a schematic diagram of the structure of the present invention.
Fig. 2 is a first week charge-discharge curve of example 1 of the present invention.
FIG. 3 is a graph showing the 50-week capacity retention rate of example 1 and comparative example 1 of the present invention.
The reference numbers shown in the drawings:
1. Carbon coating layer, 2, carbon base material, 3, nano silicon-based film, 4, nano silicon-based film section.
Detailed Description
The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. Further, it will be understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the application, and equivalents thereof fall within the scope of the application as defined by the claims.
Embodiment 1 of a silicon-carbon composite material containing a nano silicon-based film comprises the nano silicon-based film uniformly embedded in a carbon substrate of hard carbon and a carbon coating layer on the surface of silicon-carbon particles, wherein the nano silicon-based film is of an irregularly-shaped sheet structure, the mass ratio of silicon in the silicon-carbon composite material is 40.7%, the particle size of the silicon-carbon composite material is 21 mu m, the thickness of the nano silicon-based film is 30.7nm, the median value of the area of the nano silicon-based film is 180nm 2, and the thickness of the carbon coating layer is 10.5nm.
The preparation method of the silicon-carbon composite material containing the nano silicon-based film comprises the following steps:
S1, placing petroleum asphalt with a softening point of 120 ℃ into a heating cavity with a temperature of 250 ℃, vacuumizing to maintain a vacuum degree of 180Pa, heating the petroleum asphalt to a molten state, adjusting the rotating speed of a rotating disc substrate to be 100rpm, dripping the molten petroleum asphalt onto the rotating disc substrate with a temperature of 270 ℃, adjusting the temperature of the rotating disc substrate to be higher than the softening point of the petroleum asphalt, adjusting the distance between a scraper and a disc to be 5um, spreading by using the scraper, depositing a nano silicon-based film on the surface of the molten petroleum asphalt, spreading by using the scraper to form an effect similar to extrusion and dispersion, uniformly dispersing the nano silicon-based film in a silicon source by continuous spreading, then introducing silane according to the flow of 35sccm and introducing hydrogen according to the flow of 4sccm, cracking a silicon source by utilizing a gas phase deposition method of plasma enhanced chemistry, turning on a radio frequency power supply of the equipment, adjusting the radio frequency power to 15w, depositing the silicon source on the surface of the molten petroleum asphalt, depositing a silicon hydride gas on the surface of the extruded and flattened molten petroleum asphalt to form a nano silicon-based film, and depositing for 3 hours, wherein in the process, the nano silicon-based film deposited on the surface of the petroleum asphalt is uniformly dispersed in the molten petroleum asphalt by continuous scraping and flattening of a scraper and silicon deposition to obtain a precursor of the silicon-carbon composite material; it is to be noted that, under the precondition of the other conditions being unchanged, the thickness of the nano silicon-based film has a certain positive correlation with the flow rate of the silane gas and the rotating speed of the rotating disc;
s2, after the reaction in the step S1 is finished, closing the introduction of the silicon source gas, stopping heating, naturally cooling, transferring the rotating disc substrate loaded with the silicon-carbon composite material precursor and the silicon-carbon composite material precursor to a box-type atmosphere furnace, heating to 900 ℃ at 2 ℃ per min under the protection of inert gas nitrogen, carbonizing for 4 hours, and cooling to room temperature to obtain a blocky silicon-carbon composite material;
s3, cooling to room temperature after carbonization in the step S2 is finished, crushing the obtained massive silicon-carbon composite material by using a jet mill, and grading to obtain the silicon-carbon composite anode material with the grain diameter of D 50 =19.6 mu m and containing the nano silicon-based film.
And (3) the silicon-carbon composite anode material obtained in the step (S3) can be subjected to carbon coating by a chemical vapor deposition method or a pyrolysis method to obtain the silicon-carbon composite anode material containing the carbon coating layer.
And C, carbon coating by a chemical vapor deposition method, namely placing the powder silicon-carbon composite material obtained in the step S3 into an intermittent CVD furnace, introducing methane and nitrogen, heating to 800 ℃ at 5 ℃ per min, preserving heat for 5 hours, and naturally cooling to obtain the silicon-carbon composite material with the carbon coating layer.
Embodiment 2A silicon-carbon composite material containing a nano silicon-based film comprises the nano silicon-based film uniformly embedded in a composite carbon substrate composed of soft carbon and carbon fibers and a carbon coating layer on the surface of silicon-carbon particles, wherein the nano silicon-based film is of an irregularly-shaped sheet structure, the mass ratio of silicon in the silicon-carbon composite material is 51.6%, the particle size of the silicon-carbon composite material is 12.7 mu m, the thickness of the nano silicon-based film is 35.6nm, the median value of the area of the nano silicon-based film is 305nm 2, and the thickness of the carbon coating layer is 20.5nm.
The preparation method of example 1 was carried out, and parameters such as temperature, material selection and equipment were adjusted selectively within the scope of the present invention.
Embodiment 3A silicon-carbon composite material containing a nano silicon-based film comprises the nano silicon-based film uniformly embedded in a carbon substrate of soft carbon and a carbon coating layer on the surface of silicon-carbon particles, wherein the nano silicon-based film is of an irregularly-shaped sheet structure, the mass ratio of silicon in the silicon-carbon composite material is 69.8%, the particle size of the silicon-carbon composite material is 7.9um, the thickness of the nano silicon-based film is 6.1nm, the median value of the area of the nano silicon-based film is 100nm 2, and the thickness of the carbon coating layer is 30.5nm.
The preparation method of example 1 was carried out, and parameters such as temperature, material selection and equipment were adjusted selectively within the scope of the present invention.
Embodiment 4. A silicon-carbon composite material containing a nano silicon-based film comprises a nano silicon-based film doped with phosphorus element uniformly embedded in a composite carbon substrate composed of hard carbon and graphite and a carbon coating layer on the surface of silicon-carbon particles, wherein the nano silicon-based film is of an irregularly-shaped sheet structure, the mass ratio of silicon in the silicon-carbon composite material is 30.4%, the mass ratio of phosphorus element is 1.1%, the particle size of the silicon-carbon composite material is 10.8um, the thickness of the nano silicon-based film is 15.1nm, the area median of the nano silicon-based film is 128nm 2, and the thickness of the carbon coating layer is 10.2nm.
The preparation method of example 1 was carried out, and parameters such as temperature, material selection and equipment were adjusted selectively within the scope of the present invention.
Comparative example 1, nano silicon of 50nm is prepared by adopting a sand milling method, then nano silicon and asphalt are dispersed and dissolved in n-hexane, spray drying is carried out, heating is carried out to 1150 ℃ for carbonization for 4 hours at 2 ℃ per min under the protection of inert gas nitrogen, then cooling is carried out to room temperature, a massive silicon-carbon composite material is obtained, crushing is carried out by a jet mill, classification is carried out, a silicon-carbon composite anode material containing nano silicon with the grain diameter of D 50 = 8um is obtained, the silicon-carbon composite anode material is put into an intermittent CVD furnace, methane and nitrogen are introduced, heating is carried out to 800 ℃ at 5 ℃ per min, heat preservation is carried out for 5 hours, and then the silicon-carbon composite material with a carbon coating layer with the thickness of 10um is obtained after natural cooling. The mass content of silicon element in the material is 41.2%.
Electrochemical testing:
(1) The silicon-carbon composite particles prepared in the above examples and comparative examples, SP and LA133 (Yindile) were prepared in a mass ratio of 70:20:10, coated on 8um copper foil, dried for 2 hours in a forced air oven at 70 ℃, then several pieces of pole pieces of phi 12mm were cut, loaded into a vacuum oven at 110 ℃, and dried for 7 hours.
(2) And (3) rapidly transferring the material to a glove box after baking, taking a metal lithium sheet with the diameter of phi 14mm as a counter electrode, using a double-sided ceramic diaphragm, adding 3% of VC and 3% of FEC as electrolyte to 1mol/L of LiPF 6/(EC+DMC) (volume ratio of 1:1), and performing button cell assembly on the glove box, wherein the water and oxygen content of the glove box is controlled below 0.1 ppm.
(3) The assembled battery is subjected to charge-discharge cycle test, the test equipment is charged and discharged, the test is carried out on a LAND battery test system (from Wuhan blue He electronic Co., ltd.) under the test conditions of room temperature, the first two weeks are discharged to 5mM according to steps of 0.1C and 0.02C, the constant current of 0.1C is charged to 1.5V, and the charge-discharge cycle of 0.1C/0.1C is carried out for 50 weeks after the second week.
The results are shown in Table 1 (specific capacity of charge of the material was calculated in such a manner that the charged capacity/mass of the negative electrode active material; the capacity retention rate at 50 weeks of the battery: specific capacity of charge at 50 weeks/specific capacity of charge at first week)
TABLE 1 results of Performance test of silicon carbon composite particles of examples 1-4 and comparative example 1
According to examples 1 to 4 in table 1, it can be found that the first efficiency and the cycle retention rate of the silicon-carbon negative electrode material prepared by the present invention are both relatively high, because the silicon material in the silicon-carbon negative electrode material of the present invention exists in the form of a nano silicon film, so that the specific surface area of the silicon material is smaller relative to zero-dimensional nano silicon particles with the same particle size and one-dimensional nano silicon wires, so that the active lithium consumed for generating an SEI film in the first lithium intercalation process is less, the first cycle efficiency is relatively high, and secondly, because the particle size of the silicon material in the silicon-carbon negative electrode material is smaller and the silicon material exists in the form of a film, the influence of small-sized silicon on the whole expansion is small during the cycle, and the nano silicon-based film dispersion particles are small, uniform in dispersion, and breakage of the silicon-carbon composite negative electrode due to uneven stress during the cycle is reduced, so that the cycle retention rate is relatively high.
As can be seen from the data of example 1 and comparative example 1 in table 1, although the content of elemental silicon of example 1 is approximately the same as that of comparative example 1, the first week charge specific capacity and the first week efficiency of comparative example 1 are lower than those of example 1, and it is apparent that the capacity retention rate of comparative example 1 is rapidly decreased, indicating that the cycle performance thereof is inferior to that of example 1, as seen from the 50 week cycle capacity retention rate graphs of example 1 and comparative example 1 of fig. 2. The reason is that the nano silicon particles in comparative example 1 are dispersed in a carbon source and then carbonized, which may cause uneven dispersion thereof, and a portion may be agglomerated together to make the capacity thereof difficult to be fully utilized, on the other hand, the nano silicon particles of 50nm per se have a larger specific surface area than a thin film composed of nano silicon of 50nm, so that more active lithium is consumed for generating an SEI film in the first lithium intercalation process, resulting in lower first efficiency of comparative example 1, and finally, the nano silicon in comparative example 1 is difficult to be uniformly dispersed, which may cause uneven stress of silicon expansion of the silicon-carbon material of comparative example 1 in the circulation process, which may cause material breakage, thereby making the circulation performance poor.
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