CN112382748B - Graphene/silicon composite microsphere and preparation method thereof - Google Patents
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Abstract
The invention provides a graphene/silicon composite microsphere and a preparation method thereof, belonging to the technical field of battery materials. The graphene/silicon composite microspheres are of a core-shell structure in which silicon particles are coated by graphene, the graphene shell layer is of a central control fold structure, and the graphene shell layer is attached to the silicon particles. In the preparation process, the reduced graphene microspheres are obtained firstly, and are developed in hydrogen peroxide and concentrated sulfuric acid solution after heat treatment to form a larger hollow structure. Dispersing the graphene/silicon composite microspheres with silicon and the like, controlling the heating rate, and heating in sections to obtain the graphene/silicon composite microspheres. According to the invention, the hollow folded graphene microspheres wrap silicon nano and micro particles, and high filling ensures high capacity of the battery material; obtain the relative confined graphite alkene interior fold space through quick thermal response, graphite alkene fold microballon has certain elasticity, can tolerate the charge and discharge that the silicon particle relapse, and can not take place the breakage phenomenon, very big assurance battery charge and discharge's stability.
Description
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a graphene/silicon battery anode composite material and a preparation method thereof.
Background
The lithium battery market is developed vigorously at present, and the lithium battery has ultra-light weight and relatively high capacity, so that the lithium battery becomes the mainstream of the modern battery market. However, further improvement of the lithium battery capacity is a hot point problem in the lithium battery industry and is also a key problem of the next generation of energy.
In recent years, the extremely high capacity of silicon-based materials has received much attention from scientists and is considered as the future of next-generation high capacity batteries. However, silicon-based batteries have a great risk: high expansion ratio. During the charging and discharging processes, volume expansion occurs, and the stability, the service life and the capacity retention rate of the battery are seriously influenced.
Graphene is the most popular material in the 21 st century, and has high specific surface area, excellent conductivity and modifiable characteristics, so that the graphene also has a huge application share in the field of batteries. However, the capacity of the pure graphene-based battery has not made a great breakthrough over the existing batteries because the intercalation property determines the upper limit of the capacity. The graphene and silicon are compounded in the scientific community to obtain the high-capacity high-density battery material, but the use method is only limited to laboratory preparation, the cost is high, and the battery material is not suitable for civil production.
Therefore, a new generation of battery structure design scheme with high density and high capacity is urgently needed, and the advantages of graphene and silicon can be simultaneously exerted, so that a foundation is laid for the next generation of batteries.
Disclosure of Invention
Aiming at the problems in the prior art, the technical problems to be solved by the invention are as follows: provides a graphene/silicon composite microsphere and a preparation method and application thereof.
The solution of the invention is realized by the following steps:
a graphene/silicon composite microsphere is a core-shell structure of graphene coated silicon particles; the graphene shell layer is of a hollow fold structure, and the thickness of the graphene shell layer is 1-10 nm; the diameter of the silicon particles is 10 nm-3 um; the graphene shell layer is attached to the silicon particles; the graphene shell layer has elasticity and can expand and contract to adapt to the volume expansion of the silicon particles.
Further, a graphene shell layer in the graphene/silicon composite microsphere has a pore structure.
The invention also provides a preparation method of the graphene/silicon composite microsphere, which comprises the following steps:
step S1, fumigating the graphene oxide folded microspheres with hydrazine hydrate steam, and then transferring the graphene oxide folded microspheres into hydrazine hydrate solution for reduction to obtain reduced graphene microspheres;
step S2, carrying out heat treatment on the reduced graphene microspheres obtained in the step S1;
step S3, dispersing the graphene microspheres subjected to heat treatment in the step S2 in a mixed solution composed of hydrogen peroxide and concentrated sulfuric acid, standing, filtering, cleaning, and then dispersing in a composite solution composed of deionized water and a hydrophobic organic solvent together with silicon powder and a dispersing agent; taking out the graphene composite microspheres suspended on the upper layer of the composite solution, and then dehydrating and drying;
step S4, heating the graphene composite microspheres dehydrated and dried in the step S3 to 300-600 ℃ in a reaction furnace at a speed of 2-10 ℃/min; and then heating to 1300-1450 ℃ at a speed of less than 10 ℃/min, preserving the temperature for a period of time, and heating to more than 2000 ℃ at a speed of 500-2000 ℃/min to obtain the closed graphene/silicon composite microspheres.
Preferably, the fumigating temperature in the step S1 is 10-120 ℃, and the fumigating time is 1-12 h; the volume fraction of the hydrazine hydrate solution is 10-60%, and the reduction time is 1-12 h.
Further, the heat treatment process in step S2 is as follows: rapidly heating to 300-400 ℃ at the speed of 10-50 ℃/min, then slowly heating to 1600-1800 ℃ at the speed of less than 10 ℃/min, and preserving heat for a certain time.
Preferably, the mass fraction of the hydrogen peroxide solution in the step S3 is 30 to 50%, and the mass fraction of the concentrated sulfuric acid is 98%.
Preferably, the volume ratio of hydrogen peroxide to concentrated sulfuric acid in step S3 is 1-4: 10.
preferably, the standing time in step S3 is 10-60 min.
Preferably, the filtering step in step S3 screens out graphene spheres having a size of 1 to 10 um.
Preferably, in step S3, the graphene microspheres, the silicon powder, and the dispersing agent are mixed according to a mass ratio of 1: 2-20: 0.1-0.5, dispersing in a composite solution consisting of deionized water and a hydrophobic organic solvent, and stirring for more than 0.1 h. The hydrophobic organic solvent is preferably ethyl acetate.
Preferably, the dispersant in step S3 is one or more selected from lignin, water-soluble polyimide, and graphene oxide.
Further, the method also comprises the following steps: and removing the low-density graphene/silicon composite microspheres by using a differential centrifugation method.
Further, the method also comprises the following steps: and placing the graphene/silicon composite microspheres in a hydrogen peroxide solution for a period of time to obtain a graphene shell layer with nano holes.
Preferably, the weight percentage of the hydrogen peroxide solution is 20-30%, the temperature is 50-70 ℃, and the hydrogen peroxide solution is kept for 4-8 hours.
Based on the same inventive concept, the invention provides a battery anode comprising the graphene/silicon composite microspheres.
Based on the same inventive concept, the present invention provides a battery including the above battery positive electrode.
Compared with the prior art, the invention has the following beneficial effects:
1. the composite material is prepared by wrapping silicon nano-particles and micro-particles with hollow folded graphene microspheres, and ensures high capacity of the battery material through high filling.
2. According to the preparation method, the relatively closed graphene inner fold space is obtained through rapid thermal response, so that on one hand, silicon particles are closed, the phenomena of powder falling and performance reduction of the battery are avoided, and on the other hand, the cost is greatly saved through rapid thermal treatment.
3. The closed folded graphene microspheres can expand and contract to adapt to the volume expansion of silicon particles. Due to the concept of rapid thermal treatment, the defects of the graphene folded microspheres are not healed in a large amount, so that the graphene folded microspheres have certain elasticity, can resist repeated charge and discharge of silicon particles, cannot be damaged, and greatly ensure the charge and discharge stability of the battery.
4. The good adjustment of the graphene defects and the crystal ensures the capacity on one hand and the charging and discharging speed on the other hand.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.
Fig. 1 is an SEM image of the graphene oxide-pleated microspheres prepared in example 1.
Fig. 2 is a diagram of graphene microspheres having a hollow structure prepared in example 1.
Fig. 3 is a TEM image of the charged graphene/silicon composite microsphere prepared in example 1.
Fig. 4 is a TEM image of the internal nano silicon of the charged graphene/silicon composite microsphere prepared in example 1.
Fig. 5 is a TEM image of the graphene/silicon composite microsphere prepared in example 1.
Fig. 6 is an SEM image of the expanded and silicon-filled graphene composite microspheres prepared in example 1.
Fig. 7 is an SEM image of a cross section of the graphene/silicon composite microsphere prepared in example 1.
Fig. 8 is a raman spectrum of the graphene/silicon composite microsphere prepared in example 1.
Fig. 9 is an SEM image of the etched surface of graphene prepared in example 1.
FIG. 10 shows the coexistence state of charged and uncharged composite microspheres during the charge and discharge processes of example 1.
Detailed Description
The present invention will now be described in detail with reference to the drawings, which are given by way of illustration and explanation only and should not be construed to limit the scope of the present invention in any way.
Example 1:
the preparation of the graphene/silicon composite microsphere in the embodiment includes the following steps:
(1) adopting single-layer graphene oxide with the size of 60-100um to prepare a graphene oxide solution with the concentration of 0.1mg/mL, and carrying out spray drying at 200 ℃ to obtain the graphene oxide folded microsphere with the size of about 2-5um, as shown in figure 1.
(2) Fumigating the graphene oxide folded microspheres with hydrazine hydrate steam for 1h at the fumigating temperature of 120 ℃, and then transferring the graphene oxide folded microspheres into hydrazine hydrate aqueous solution with the volume fraction of 10% for reduction for 12h to obtain the reduced graphene microspheres.
(3) Carrying out the following heat treatment on the reduced graphene microspheres obtained in the step (2): the temperature is rapidly increased to 300 ℃ at the speed of 10 ℃/min, and then the temperature is slowly increased to 1600 ℃ at the speed of 10 ℃/min.
(4) Dispersing the thermally treated graphene microspheres in 30% of hydrogen peroxide and 98% of concentrated sulfuric acid according to a volume ratio of 4: 10 for 10 min.
Through the steps (3) and (4), the graphene microspheres are unfolded to form a larger hollow structure, as shown in fig. 2.
(5) Screening out graphene microspheres with the size of 6-10um by a filter screen; after being cleaned by deionized water, the silicon powder (with the particle size of 200 nm) and lignin are mixed according to the mass ratio of 1: 2: 0.1 is dispersed in the compound solution of deionized water and ethyl acetate and stirred for 1 hour.
(6) And standing, and layering the graphene balls and the silicon powder. And taking out the graphene composite microspheres suspended on the upper layer of the obtained solution, and then dehydrating and drying.
(7) Heating the dehydrated and dried graphene composite microspheres to 300 ℃ at a speed of 2 ℃/min; then heating to 1300 ℃ at the speed of 10 ℃/min, and keeping for 60 min; and then heating to 2000 ℃ at a speed of 500 ℃/min and maintaining for 1s to obtain the closed graphene/silicon composite microsphere.
(8) And (3) removing the graphene/silicon composite microspheres with low density (no coating or few coating silicon particles) by using a differential centrifugation method.
As shown in fig. 3, 4 and 5, the diameter of the silicon particle is 200nm, and the thickness of the shell graphene is 1-4 nm; the microspheres close.
As can be seen from fig. 6 and 7, the graphene spherical wall has a large number of folds, and the graphene spherical wall and the inner core of the silicon particle are tightly attached. The raman spectra before and after closing of the closed cell in fig. 8 also demonstrate a good combination of the two.
(9) And placing the graphene/silicon composite microspheres in a hydrogen peroxide solution with the temperature of 60 ℃ and the mass fraction of 20% for 4 hours to obtain a graphene shell with nano holes. As shown in fig. 9, the pore structure of the graphene surface is confirmed by a scanning electron microscope, and a good substance transport channel is constructed on the surface, so as to provide a channel for the ingress and egress of an electrolyte.
The graphene/silicon composite microsphere prepared in the embodiment is placed in a lithium particle electrolyte, the composite microsphere expands, the expanded microsphere is further characterized, as shown in fig. 10, the microsphere is kept closed, the graphene sphere wall and the silicon particle inner core are kept in close fit, and the folding density of the graphene sphere wall is reduced. Finally, the specific mass capacity of the composite material is determined to be 800 mAh/g.
Example 2:
the preparation of the graphene/silicon composite microsphere in the embodiment includes the following steps:
(1) adopting single-layer graphene oxide with the size of 60-100um to prepare a graphene oxide solution with the concentration of 0.01mg/mL, and spray-drying at 280 ℃ to obtain the graphene oxide folded microsphere with the size of 1-2 um.
(2) Fumigating the graphene oxide folded microspheres with hydrazine hydrate steam for 12h at the fumigating temperature of 10 ℃, and then transferring the graphene oxide folded microspheres into 60% hydrazine hydrate aqueous solution by volume fraction for reduction for 1h to obtain the reduced graphene microspheres.
(3) Carrying out the following heat treatment on the reduced graphene microspheres obtained in the step (2): rapidly heating to 400 ℃ at the speed of 50 ℃/min, and then slowly heating to 1800 ℃ at the speed of 5 ℃/min;
(4) dispersing the thermally treated graphene microspheres in 50% of hydrogen peroxide and 98% of concentrated sulfuric acid according to a volume ratio of 1: 10 for 60 min.
Through the steps (3) and (4), the graphene spheres are unfolded to form a larger hollow structure.
(5) Filtering and screening out graphene microspheres with the size of 1-2 um; after deionized water cleaning, mixing the graphene microspheres, silicon powder (particle size of 10 nm) and graphene oxide according to a mass ratio of 1: 20: 0.5 is dispersed in the compound solution of deionized water and ethyl acetate and stirred for 0.1 h.
(6) And standing, and layering the graphene microspheres and the silicon powder. Taking out the graphene composite microspheres suspended on the upper layer of the obtained solution, and then dehydrating and drying;
(7) heating the dehydrated and dried graphene composite microspheres to 600 ℃ at a speed of 10 ℃/min; then raising the temperature to 1450 ℃ at the speed of 5 ℃/min, and preserving the temperature for 30 min; and then heating to 2000 ℃ at a speed of 600 ℃/min and maintaining for 5s to obtain the closed graphene/silicon composite microsphere.
(8) And (3) removing the graphene/silicon composite microspheres with low density (no coating or few coating silicon particles) by using a differential centrifugation method.
Finally, the specific mass capacity of the composite material is 1300 mAh/g.
Example 3:
the preparation of the porous graphene/silicon composite microsphere in this embodiment includes the following steps:
(1) preparing a graphene oxide solution with the concentration of 1mg/mL by using single-layer graphene oxide with the size of 40-200um, and carrying out spray drying at 240 ℃ to obtain the graphene oxide folded microsphere with the size of 8-10 um.
(2) Fumigating the graphene oxide folded microspheres with hydrazine hydrate steam for 6h at the fumigating temperature of 60 ℃, and then transferring the graphene oxide folded microspheres into hydrazine hydrate aqueous solution with the volume fraction of 40% for reduction for 6h to obtain the reduced graphene microspheres.
(3) Carrying out the following heat treatment on the reduced graphene microspheres obtained in the step (2): rapidly heating to 400 ℃ at the speed of 40 ℃/min, and then slowly heating to 1800 ℃ at the speed of 5 ℃/min;
(4) dispersing the thermally treated graphene microspheres in 50% of hydrogen peroxide and 98% of concentrated sulfuric acid according to a volume ratio of 1: 30, standing for 30 min.
Through the steps (3) and (4), the graphene microspheres are unfolded to form a larger hollow structure.
(5) Screening out graphene microspheres with the size of 6-10um by a filter screen; after being cleaned by deionized water, the silicon powder (with the particle size of 2-3 um) and water-soluble polyimide are mixed according to the mass ratio of 1: 10: 0.4 is dispersed in the compound solution of deionized water and ethyl acetate and stirred for 0.1 h;
(6) and standing, and layering the graphene balls and the silicon powder. Taking out the graphene composite microspheres suspended on the upper layer of the obtained solution, and then dehydrating and drying;
(7) heating the dehydrated and dried graphene composite microspheres to 400 ℃ at a speed of 5 ℃/min; then heating to 1300 ℃ at the speed of 10 ℃/min, and preserving the heat for 30 min; and then heating to 2000 ℃ at the speed of 1000 ℃/min and maintaining for 5s to obtain the closed graphene/silicon composite microsphere.
(8) Removing the graphene/silicon composite microspheres with low density (no coating or few coating silicon particles) by a differential centrifugation method, placing the obtained graphene/silicon composite microspheres in hydrogen peroxide solution with the temperature of 70 ℃ and the mass concentration of 30% for keeping for 4 hours, and etching the surfaces and the internal sp3 structures of the microspheres to obtain the graphene microsphere silicon-coated core-shell composite material with nano holes.
Finally, the specific mass capacity of the composite material is determined to be 800 mAh/g.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (12)
1. A preparation method of graphene/silicon composite microspheres is characterized by comprising the following steps:
step S1, fumigating the graphene oxide folded microspheres with hydrazine hydrate steam, and then transferring the graphene oxide folded microspheres into hydrazine hydrate solution for reduction to obtain reduced graphene microspheres;
step S2, carrying out heat treatment on the reduced graphene microspheres obtained in the step S1;
step S3, dispersing the graphene microspheres subjected to heat treatment in the step S2 in a mixed solution composed of hydrogen peroxide and concentrated sulfuric acid, standing, filtering, cleaning, and then dispersing in a composite solution composed of deionized water and a hydrophobic organic solvent together with silicon powder and a dispersing agent; taking out the graphene composite microspheres suspended on the upper layer of the composite solution, and then dehydrating and drying;
step S4, heating the graphene composite microspheres dehydrated and dried in the step S3 to 300-600 ℃ in a reaction furnace at a speed of 2-10 ℃/min; then heating to 1300-1450 ℃ at the speed of less than 10 ℃/min, keeping the temperature for a period of time, and heating to more than 2000 ℃ at the speed of 500-2000 ℃/min to obtain closed graphene/silicon composite microspheres;
the graphene/silicon composite microspheres are of a core-shell structure in which a graphene shell layer coats silicon particles; the graphene shell layer is of a hollow fold structure, and the thickness of the graphene shell layer is 1-10 nm; the diameter of the silicon particles is 10 nm-3 um; the graphene shell layer is attached to the silicon particles; the graphene shell layer has elasticity and can expand and contract to adapt to the volume expansion of the silicon particles.
2. The method for preparing the graphene/silicon composite microsphere according to claim 1, wherein a graphene shell layer in the graphene/silicon composite microsphere has a pore structure.
3. The preparation method of the graphene/silicon composite microsphere as claimed in claim 1, wherein the fumigating temperature in the step S1 is 10-120 ℃, and the fumigating time is 1-12 h; the volume fraction of the hydrazine hydrate solution is 10-60%, and the reduction time is 1-12 h.
4. The method for preparing graphene/silicon composite microspheres according to claim 1, wherein the heat treatment process of step S2 is as follows: rapidly heating to 300-400 ℃ at the speed of 10-50 ℃/min, then slowly heating to 1600-1800 ℃ at the speed of less than 10 ℃/min, and preserving heat for a certain time.
5. The preparation method of the graphene/silicon composite microsphere as claimed in claim 1, wherein in step S3, the mass fraction of the hydrogen peroxide is 30-50%, and the mass fraction of the concentrated sulfuric acid is 98%; the volume ratio of the hydrogen peroxide to the concentrated sulfuric acid is 1-4: 10; and in the filtering step, the graphene microspheres with the size of 1-10um are screened out.
6. The preparation method of the graphene/silicon composite microsphere according to claim 1, wherein in step S3, the graphene microsphere, the silicon powder and the dispersing agent are mixed according to a mass ratio of 1: 2-20: 0.1-0.5, dispersing in a composite solution consisting of deionized water and a hydrophobic organic solvent, and stirring for more than 0.1 h.
7. The method for preparing the graphene/silicon composite microsphere as claimed in claim 1 or 6, wherein the dispersant is one or more selected from lignin, water-soluble polyimide and graphene oxide; the hydrophobic organic solvent is ethyl acetate.
8. The method for preparing graphene/silicon composite microspheres according to claim 1, further comprising the steps of: and removing the low-density graphene/silicon composite microspheres by using a differential centrifugation method.
9. The method for preparing graphene/silicon composite microspheres according to claim 1, further comprising the steps of: and placing the graphene/silicon composite microspheres in a hydrogen peroxide solution for a period of time to obtain a graphene shell layer with nano holes.
10. The preparation method of the graphene/silicon composite microsphere according to claim 9, wherein the mass fraction of the hydrogen peroxide solution is 20-30%, the temperature is 50-70 ℃, and the temperature is maintained for 4-8 hours.
11. A battery positive electrode comprising the graphene/silicon composite microspheres prepared by the method for preparing graphene/silicon composite microspheres according to any one of claims 1 to 10.
12. A battery comprising the positive electrode for a battery according to claim 11.
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| CN106241778A (en) * | 2016-07-15 | 2016-12-21 | 浙江大学 | A kind of high-specific surface area many folds hollow graphite alkene microsphere and preparation method thereof |
| CN109309222A (en) * | 2018-09-29 | 2019-02-05 | 盐城师范学院 | A kind of preparation method of nano-silicon/fold graphene core-shell structure |
| CN110752363A (en) * | 2019-11-16 | 2020-02-04 | 昝武 | Preparation method of composite negative electrode material |
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