CN110556528A - Porous silicon/carbon shell composite material and preparation method and application thereof - Google Patents
Porous silicon/carbon shell composite material and preparation method and application thereof Download PDFInfo
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Abstract
the invention discloses a porous silicon/carbon shell composite material and a preparation method thereof. The preparation method of the porous silicon/carbon shell composite material comprises the steps of 1) mixing magnesium silicide, a carbon source and an organic solvent, uniformly dispersing, and heating until the organic solvent is completely volatilized to obtain an intermediate product; 2) carrying out heat treatment on the intermediate product prepared in the step 1) in a nitrogen atmosphere, and carrying out post-treatment to obtain the porous silicon/carbon shell composite material. The invention discloses a porous silicon/carbon shell composite material with a novel structure and a preparation method thereof.
Description
Technical Field
The invention relates to the technical field of composite materials, in particular to a porous silicon/carbon shell composite material and a preparation method and application thereof.
Background
Lithium ion batteries are currently the most important rechargeable batteries, and are widely applied to consumer electronics such as mobile phones, notebook computers and the like, pure electric vehicles and hybrid electric vehicles, and other various military and aerospace fields. While lithium ion batteries have been used in these areas on a large scale, with the rapid development of these industries, it is increasingly difficult for current lithium ion batteries to satisfy their performance requirements. In particular, in the field of electric automobiles and electronic consumers, the appearance of batteries with smaller weight and volume and higher energy density, i.e., batteries with higher specific capacity, is urgently desired.
In order to prepare a lithium ion battery with higher capacity, a positive electrode material and a negative electrode material with higher capacity are firstly developed. Silicon is used as a negative electrode material with high theoretical specific capacity, and has ultrahigh theoretical specific capacity (4200mAh/g) and lower lithium intercalation potential, so that silicon is one of the materials which have the highest potential to become the negative electrode of the next-generation lithium ion battery.
Although silicon has the above advantages, when used as a negative electrode material, it undergoes volume expansion of up to 400% after intercalation of lithium ions, and undergoes volume re-contraction after deintercalation of lithium ions. Therefore, after many cycles, the silicon active material may crack, pulverize, and even fall off the current collector due to continuous and drastic volume changes, resulting in capacity degradation. Therefore, the most important problem hindering the application of silicon anodes is the rapid decay of the cycling capacity due to the large volume change.
In addition, the current lithium ion battery has low rate capability besides the specific capacity which can not completely meet the requirements of people, which is also an urgent problem to be solved. For example, even if the electric vehicle is in the fast charge mode, at least 30 minutes are required for charging to 80% of the electric quantity, which is completely incomparable with the conventional refueling experience. Although silicon has the highest theoretical specific capacity, silicon is a semiconductor material, and poor conductivity makes it easy to generate surface polarization during rapid charge and discharge, and hinders further rapid charge transmission, so to improve the rate capability of the silicon cathode, the silicon cathode needs to be compounded with a material with better conductivity and combined with further structural optimization to realize the purpose.
In response to the above problems, researchers have proposed many solutions. Among them, the recombination with carbon is one of the most important solutions. This is because carbon has higher electron conductivity than silicon of a semiconductor, and recombination with carbon can improve conductivity of the entire system. Then, the carbon has certain mechanical properties, and can buffer the volume expansion effect of the silicon to a certain extent, reduce internal stress caused by volume change and reduce the possibility of fracture and inactivation of the silicon active material.
Jinhui Zhu et al (Zhu J, Yang J, Xu Z, et al, silicon antibodies protected by a nitrile-treated porous carbon shell for high-performance magnesium-ion batteries [ J ]. nanoscales, 2017,9.) propose a method of coating nitrogen-doped porous carbon on the surface of silicon particles. The conductivity and the mechanical property of the carbon are enhanced after the nitrogen atoms are doped, so that the effects of enhancing the conductivity and buffering the mechanical stress of the carbon layer can be better exerted. However, based on theoretical modeling and in situ TEM observation, it was found that carbon layers tightly coated with nano-silicon particles limit the displacement of silicon when the silicon undergoes volume expansion, resulting in failure to release internal stress of silicon and, in turn, silicon is more likely to crack. It follows that a simple silicon/carbon core-shell structure does not completely solve the problem of silicon.
Chengmao Xiao et al (Chengmao Xiao, Ning Du, Xianxin Shi, Hui Zhang and Deren Yang. Large-Scale synthesis of Si @ C three-dimensional structures as high-performance and materials for performance and materials J. Material. chem. A.2014,2,20494) propose a scheme of obtaining porous silicon by thermally decomposing magnesium silicide in air to obtain a mixture of magnesium oxide and silicon, and then removing the magnesium oxide by acid washing. The scheme realizes large-scale preparation of the porous silicon by a quick and simple method. The network-shaped porous structure reduces the charge transmission distance, is beneficial to promoting charge transport and improves the multiplying power performance. However, the obtained porous silicon/carbon composite material is still in a traditional core-shell structure. Thus, the tightly coated carbon layer still remains unstable and even accelerates the cracking of the silicon itself. Thus, there is still room for improvement in this solution.
To further optimize silicon carbon structures, the stand topic group of stanford university in the united states proposed a silicon/carbon composite of yolk/eggshell structure (Liu N, Wu H, Mcdowell M T, et al. a yolk-shell design for stabilized and scalable li-ion clay alloys [ J ]. Nano Letters,2012,12(6): 3315.). A silicon oxide layer is coated on the surface of the nano silicon particle, a carbon layer is coated outside the silicon oxide layer, and then the silicon oxide template is removed by acid cleaning, so that a pore is introduced between the silicon and the carbon layer, and a space is provided for the free volume expansion of the silicon. Due to the existence of the pores, the silicon does not cause pressure on the carbon layer when expanding, so that the carbon layer can be stable, and the stress of the silicon can be released in time. The structure obtains excellent cycling stability, but the outer diameter of the silicon particles designed by the structure is far smaller than the inner diameter of the carbon shell, silicon used as 'yolk' can only keep single-point contact with a carbon layer used as 'eggshell', electron and lithium ion transmission sites are too few, rapid charge transmission cannot be realized, and therefore the rate performance is poor.
Therefore, the preparation of silicon/carbon composite materials with excellent rate capability and cycle performance is still the focus of current research.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a porous silicon/carbon shell composite material with a novel structure and a preparation method thereof.
The specific technical scheme is as follows:
a porous silicon/carbon shell composite material comprises a porous silicon inner core and a carbon shell, wherein the outer wall of the porous silicon inner core is attached to the inner wall of the carbon shell, and discrete pores are reserved between the outer wall of the porous silicon inner core and the inner wall of the carbon shell.
According to the porous silicon/carbon shell composite material prepared by the invention, the outer diameter of the porous silicon core is equivalent to the inner diameter of the carbon shell so as to ensure that the outer wall of the porous silicon core is attached to the inner wall of the carbon shell; discrete pores and the porous structure of the silicon inner core are kept between the outer wall of the porous silicon inner core and the inner wall of the carbon shell, and a space is provided for the volume expansion of silicon.
Preferably:
The particle size of the porous silicon/carbon shell composite material is 1-10 mu m;
The thickness of the carbon shell is 5-30 nm;
The content of the carbon shell is 5-30% of the total weight of the porous silicon/carbon shell composite material.
The invention also discloses a preparation method of the porous silicon/carbon shell composite material, which comprises the following steps:
1) mixing magnesium silicide, a carbon source and an organic solvent, uniformly dispersing, and heating until the organic solvent is completely volatilized to obtain an intermediate product;
2) Carrying out heat treatment on the intermediate product prepared in the step 1) in a nitrogen atmosphere, and carrying out post-treatment to obtain the porous silicon/carbon shell composite material.
In the invention, magnesium silicide is used as a silicon source, and is mixed with a carbon source, then through a heat treatment process in a nitrogen atmosphere, an organic carbon source is gradually cracked to generate carbon, meanwhile, a decomposition reaction (Mg 2 Si is 2Mg + Si) of the magnesium silicide is also synchronously carried out, a generated carbon layer can be attached to an outer skeleton of the silicon, so that a carbon shell can be tightly contacted with the silicon, after the reaction, another product, namely magnesium nitride (3Mg + N 2 is Mg 3 N 2) is removed through acid treatment, the position of the original magnesium nitride is left out to enable the silicon to be in a porous structure, wherein discrete pores between the silicon and the carbon shell are formed by the exposed pores, and thus the porous silicon/carbon shell composite material with the novel microstructure is formed.
In addition, tests also unexpectedly find that the magnesium silicide is used as a silicon source, gaseous magnesium element decomposed in the heat treatment is very active and has great activity, carbon can be rapidly reduced by catalysis, and generated carbon atoms are promoted to be arranged orderly to form a carbon layer with higher graphitization degree.
Most of the traditional preparation processes firstly prepare porous silicon and then coat a carbon layer on the surface of the porous silicon, and the preparation processes can cause the prepared carbon layer to enter pores of the porous silicon and coat the carbon layer along the outline of the porous silicon, so that a core-shell structure with the carbon layer tightly attached to the porous silicon is formed, and the expansion of the silicon is not facilitated.
In step 1):
The carbon source is at least one selected from asphalt, phenolic resin and polyvinylidene fluoride.
the organic solvent is used for swelling the carbon source, so that the organic solvent suitable for the carbon source can be selected according to different carbon sources, but the organic solvent is ensured not to react with the magnesium silicide.
the mass ratio of the magnesium silicide to the carbon source to the organic solvent is 1: 0.1-1: 5 to 50.
Experiments show that different carbon sources and different mass ratios of magnesium silicide to the carbon sources have influence on the graphitization degree of the carbon shell in the product.
preferably:
The mass ratio of the magnesium silicide to the carbon source to the organic solvent is 1: 0.1-1: 8-12; further preferably, the mass ratio of the magnesium silicide to the carbon source is 1: 0.1 to 0.2.
Further preferably:
The carbon source is selected from polyvinylidene fluoride, and further preferably, the mass ratio of the magnesium silicide to the polyvinylidene fluoride is 10: 1. tests show that when the preferred carbon source is matched with magnesium silicide in the above dosage, the prepared carbon shell has higher graphitization degree.
In step 2):
In the heat treatment process, carbon source organic matters are carbonized into carbon shells, and the magnesium silicide reacts with nitrogen to generate silicon and magnesium nitride. The temperature of the heat treatment is 200-1000 ℃, and the time is 0.5-30 h.
Preferably, the temperature of the heat treatment is 500-900 ℃, and the time is 2-24 h. Under the preferred heat treatment conditions, the carbon source can be completely decomposed into carbon, and the magnesium element decomposed from the magnesium silicide completely reacts with nitrogen. More preferably, the temperature of the heat treatment is 700 ℃ and the time is 10 h.
The post-treatment comprises pickling, washing and drying.
preferably, the acid washing is a hydrochloric acid solution which is cheap and easily available and has no environmental pollution pressure, and more preferably, the hydrochloric acid solution has a concentration of 0.5-5 mol/L.
The invention also discloses application of the porous silicon/carbon shell composite material in a lithium ion battery.
Compared with the prior art, the invention has the following advantages:
The invention discloses a preparation method of a porous silicon/carbon shell composite material, which takes magnesium silicide as a silicon source to prepare the porous silicon/carbon shell composite material in situ.
The composite material prepared by the process has the advantages that the silicon and the carbon shell are in multipoint close contact, and the silicon is in a porous structure, so that an internal and external through three-dimensional network structure is formed, the transmission distance of electrons and lithium ions is shortened, transmission channels are increased, particularly the transmission channels of a silicon/carbon interface are greatly increased, the rapid transmission of the lithium ions and the charges can be promoted, and the rapid charging and discharging capacity of an electrode is enhanced.
The lithium ion battery assembled by taking the composite material as the electrode material has excellent rate performance and cycle stability, and is expected to be prepared into the lithium ion battery with more excellent performance.
Drawings
FIG. 1 is a Scanning Electron Micrograph (SEM) of the porous silicon/carbon shell composite prepared in example 1 at different magnifications;
FIG. 2 is a Raman spectrum of the porous silicon/carbon shell composite prepared in example 1, and a Raman spectrum of a product prepared in comparative example is given as a comparison;
Fig. 3 is a comparison of rate performance curves for lithium ion batteries assembled with products prepared from example 1 and comparative example, respectively.
Detailed Description
the present invention is further illustrated by the following specific examples, but the scope of the present invention is not limited to the following examples.
Example 1
1) 1g of phenol resin (alatin) was dissolved in 100mL of toluene, and then magnesium silicide powder was dispersed in the solution, the mass ratio of magnesium silicide to phenol resin being 10: 1. after stirring well, toluene was completely volatilized at 120 ℃ to obtain a mixture of magnesium silicide/phenol resin.
2) carrying out heat treatment on the mixture obtained in the step 1) in a nitrogen atmosphere, wherein the heat treatment temperature is 700 ℃ and the time is 10 h.
3) Carrying out acid washing treatment on the product obtained in the step 2). And (3) carrying out acid washing by using excessive dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 1mol/L, washing for 5 times by using deionized water after washing, and drying to obtain the porous silicon/carbon shell composite material.
through tests, the particle size of the porous silicon/carbon shell composite material prepared in the embodiment is 1-5 μm, the thickness of the carbon layer is about 12-15 nm, and the carbon content is 13%.
Fig. 1 is an SEM photograph of the porous silicon/carbon shell composite material prepared in this example, and it can be observed that the carbon layer is in a self-supporting shell-like structure, the silicon inside the carbon layer is in a porous structure, the carbon layer is tightly connected with the skeleton of the porous silicon, and the exposed pores of the porous silicon form discrete pores between the silicon and the carbon shell.
Fig. 2 is a Raman spectrum of the porous silicon/carbon shell composite material prepared in this example, and the ratio I D/I G of the amorphous carbon peak to the graphitized carbon peak is calculated to be 0.91.
Example 2
The same raw materials and preparation process as those in example 1 were used except that the mass ratio of magnesium silicide to phenolic resin was 5: 1.
Through raman test, the ratio I D/I G of the amorphous carbon peak to the graphitized carbon peak of the porous silicon/carbon shell composite material prepared in the present example is 0.99.
Example 3
the same raw materials and preparation process as those in example 1 were used except that the mass ratio of magnesium silicide to phenolic resin was 1: 1.
through raman test, the ratio I D/I G of the amorphous carbon peak to the graphitized carbon peak of the porous silicon/carbon shell composite material prepared in the present example is 1.06.
Comparative example
1) The magnesium silicide is heat treated for 10 hours at 700 ℃ in the nitrogen atmosphere.
2) carrying out acid washing treatment on the product obtained in the step 1). And (3) carrying out acid washing by using excessive dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 2.5mol/L, washing for 5 times by using deionized water after washing, and drying to obtain the porous silicon.
3) adding the porous silicon obtained in the step 2) into a phenolic resin/toluene solution (the concentration of the porous silicon is the same as that of the porous silicon obtained in the step 1), stirring and uniformly dispersing the porous silicon into the phenolic resin/toluene solution, wherein in order to ensure the same silicon-carbon ratio of the product and the porous silicon obtained in the step 1, the mass ratio of the porous silicon to the phenolic resin in the comparative example is 3.33: 1 (magnesium silicide: phenol resin 10: 1 in example 1, the amount of silicon in magnesium silicide is about 1/3). Volatilizing the solvent at 120 ℃, and then carrying out heat treatment in a nitrogen atmosphere at 700 ℃ for 10 h.
fig. 2 also shows a Raman spectrum of the porous silicon/carbon shell composite material prepared by the comparative example, and the ratio I D/I G of the amorphous carbon peak to the graphitized carbon peak is calculated to be 1.15, which is higher than that of example 1.
Observing fig. 2, it is found that the D peak representing amorphous carbon and the G peak representing graphitized carbon appear in the products prepared in example 1 and comparative example 1, respectively, and the ratio of the intensities of the two peaks is I D/I G, and the lower the value of I D/I G, the higher the degree of graphitization representing carbon, further comparison can find that the degree of graphitization of carbon is significantly higher in the composite material prepared in example 1 than in comparative example 1.
Example 4
1) 1g of pitch (ba ling petrochemical) was dissolved in 100mL of tetrahydrofuran, and then magnesium silicide powder was dispersed in the solution, the mass ratio of magnesium silicide to pitch being 10: 1. after stirring well, tetrahydrofuran was completely evaporated to dryness at 80 ℃ to obtain a magnesium silicide/pitch mixture.
2) Carrying out heat treatment on the mixture obtained in the step 1) in a nitrogen atmosphere, wherein the heat treatment temperature is 700 ℃ and the time is 10 h.
3) Carrying out acid washing treatment on the product obtained in the step 2). And (3) carrying out acid washing by using excessive dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 2mol/L, washing for 5 times by using deionized water after washing, and drying to obtain the porous silicon/carbon shell composite material.
Tests prove that the particle size of the composite material prepared by the method is 1-5 mu m, the carbon content is 17 wt%, the thickness of the carbon layer is 17-19 nm, and the ratio of the amorphous carbon peak to the graphitized carbon peak, namely I D/I G, is 0.95.
Example 5
1) 1g of polyvinylidene fluoride (alatin) was dissolved in 100ml of n-methylpyrrolidone, and then a magnesium silicide powder was dispersed in the solution, the mass ratio of magnesium silicide to polyvinylidene fluoride being 10: 1. after stirring well, the N-methylpyrrolidone was completely volatilized at 210 ℃ to obtain a mixture of magnesium silicide/polyvinylidene fluoride.
2) Carrying out heat treatment on the mixture obtained in the step 1) in a nitrogen atmosphere, wherein the heat treatment temperature is 700 ℃ and the time is 10 h.
3) Carrying out acid washing treatment on the product obtained in the step 2). And (3) carrying out acid washing by using excessive dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 4mol/L, washing for 5 times by using deionized water after washing, and drying to obtain the porous silicon/carbon shell composite material to be prepared.
The particle size of the composite material prepared by the embodiment is 1-5 mu m, the carbon content is 8 wt%, the thickness of the carbon layer is 8-10 nm, and the ratio of the amorphous carbon peak to the graphitized carbon peak, I D/I G, is 0.87.
Performance testing
the lithium ion battery porous silicon/carbon shell composite material is tested by adopting a half-cell testing method. The adopted slurry mixture ratio is as follows: active material (porous silicon/carbon shell composite prepared in example 1 and product prepared in comparative example): super P (conductive agent): CMC (binder) ═ 7: 2: 1.
The method comprises the following specific steps:
Firstly, CMC is dissolved in deionized water, the solubility of the prepared solution is 5%, and then a conductive agent (SP) and an active substance are sequentially added and stirred to form slurry. Then coating the copper foil on the cleaned copper foil, drying the copper foil in vacuum for 12h, and then blanking and weighing a negative plate with the diameter of 12 mm. We used a lithium metal sheet as the counter electrode of the cell, and the electrolyte was a 1M solution of LiPF6 in a mixed solution of DMC and EC, where DMC: EC 1: 1 (volume ratio). And assembling the button cell in the glove box, standing for 12h, and then carrying out performance test on the button cell.
Fig. 3 is a comparison of rate performance of assembled batteries when the products prepared in example 1 and comparative example, respectively, were used as negative electrodes of lithium ion batteries. It can be seen that at a current density of 0.5A/g, the initial capacity of the two materials is comparable. As the current density increased, it is apparent that example 1 can maintain a higher capacity and keep the capacity stable. At a high current density of 8.0A/g, example 1 still maintained a capacity of 710mAh/g and stable cycling, while the comparative example only had a capacity of 310 mAh/g. When the current density returns to 0.5A/g again, the capacity of the capacitor in example 1 can still return to 1600mAh/g, which shows that the structure and the capacity can still be kept stable after large-current charging and discharging. While the comparative example only left 800mAh/g and continued to decay.
In conclusion, it can be seen that the rate performance of the battery assembled by the porous silicon/carbon shell composite material prepared by the invention is significantly better than that of the comparative example, which represents the superiority of the structural design and method of the material of the invention.
Claims (8)
1. the porous silicon/carbon shell composite material is characterized by comprising a porous silicon inner core and a carbon shell, wherein the outer wall of the porous silicon inner core is attached to the inner wall of the carbon shell, and discrete pores are reserved between the outer wall of the porous silicon inner core and the inner wall of the carbon shell.
2. The porous silicon/carbon shell composite material according to claim 1, characterized in that:
The particle size of the porous silicon/carbon shell composite material is 1-10 mu m;
The thickness of the carbon shell is 5-30 nm;
The content of the carbon shell is 5-30% of the total weight of the porous silicon/carbon shell composite material.
3. A method for preparing a porous silicon/carbon shell composite material according to claim 1 or 2, comprising:
1) Mixing magnesium silicide, a carbon source and an organic solvent, uniformly dispersing, and heating until the organic solvent is completely volatilized to obtain an intermediate product;
2) Carrying out heat treatment on the intermediate product prepared in the step 1) in a nitrogen atmosphere, and carrying out post-treatment to obtain the porous silicon/carbon shell composite material.
4. The method for preparing a porous silicon/carbon shell composite material according to claim 3, wherein in step 1), the carbon source is selected from at least one of pitch, phenolic resin, polyvinylidene fluoride;
The organic solvent may swell the carbon source.
5. the method for preparing a porous silicon/carbon shell composite material according to claim 3, wherein in the step 1), the mass ratio of the magnesium silicide, the carbon source and the organic solvent is 1: 0.1-1: 5 to 50.
6. The preparation method of the porous silicon/carbon shell composite material according to claim 3, wherein in the step 2), the temperature of the heat treatment is 200-1000 ℃ and the time is 0.5-30 h.
7. the method for preparing a porous silicon/carbon shell composite material according to claim 3, wherein in step 2), the post-treatment comprises acid washing, washing and drying.
8. Use of a porous silicon/carbon shell composite material according to claim 1 or 2 in a lithium ion battery.
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| CN113206231A (en) * | 2021-04-25 | 2021-08-03 | 浙江锂宸新材料科技有限公司 | Silicon-carbon-cobalt composite material and preparation method and application thereof |
| CN115312775A (en) * | 2022-07-27 | 2022-11-08 | 江西盛源新材料有限公司 | Carbon nanotube composite conductive slurry and preparation method thereof |
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| 张亚光: "多孔硅基复合材料的制备及作为锂离子电池负极材料的应用", 《中国博士学位论文全文数据库 工程科技Ⅱ辑》 * |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111370663B (en) * | 2020-03-18 | 2021-05-25 | 浙江锂宸新材料科技有限公司 | Porous silicon @ amorphous carbon/carbon nanotube composite material and preparation method and application thereof |
| CN113206231A (en) * | 2021-04-25 | 2021-08-03 | 浙江锂宸新材料科技有限公司 | Silicon-carbon-cobalt composite material and preparation method and application thereof |
| CN113206231B (en) * | 2021-04-25 | 2022-06-10 | 浙江锂宸新材料科技有限公司 | Silicon-carbon-cobalt composite material and preparation method and application thereof |
| CN115312775A (en) * | 2022-07-27 | 2022-11-08 | 江西盛源新材料有限公司 | Carbon nanotube composite conductive slurry and preparation method thereof |
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| CN110556528B (en) | 2021-08-17 |
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