CN108807948B - Graphene/nano-silicon intercalation composite material with surface coupling activity and preparation and application thereof - Google Patents
Graphene/nano-silicon intercalation composite material with surface coupling activity and preparation and application thereof Download PDFInfo
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Abstract
The graphene/nano silicon intercalation composite material with surface coupling activity provided by the invention is composed of 10-50% of nano silicon and 90-50% of graphene by mass, and the surface of the graphene/nano silicon intercalation composite material is subjected to coupling treatment by using a silane coupling agent and has a surface coupling activity functional group. The preparation method comprises the following steps: graphite powder in "(NH)4)2SO4Under the action of a ternary intercalation agent of-98% concentrated sulfuric acid-fuming sulfuric acid, obtaining the graphene nanosheet through a process of graphite-graphite intercalation compound-graphene. The specific preparation method comprises the steps of preparing the graphene/nano silicon intercalation composite material and carrying out surface coupling treatment. The method can endow the graphene/nano-silicon intercalation composite material with surface activity, is used for preparing the electrode, solves the problem of deactivation caused by falling of active substances possibly caused by volume expansion of silicon, shortens the preparation time and reduces the scale production cost.
Description
Technical Field
The invention belongs to the technical field of novel cathode materials of lithium ion batteries, and particularly relates to a graphene-based silicon-carbon composite cathode material and a preparation method thereof.
Background
The lithium ion battery is used as a power supply of portable electronic equipment, electric power and hybrid electric vehicles, and the great improvement of the energy density of the lithium ion battery is an urgent requirement for the development of a series of new technical fields of portable electronic products, electric vehicles, energy storage power stations and the like. The improvement of the power density, the energy density and the long-term endurance of the lithium ion battery mainly depends on the development of novel anode and cathode materials. The conventional commercial graphite negative electrode has the advantages of lithium dendrite generation prevention, small lithium intercalation volume change and the like, but the theoretical lithium intercalation capacity of graphite is only 372mAh/g, so that the further improvement of the energy density of a lithium ion battery is severely limited. Therefore, new high capacity, long cycle life anode materials are actively being sought to replace graphite materials.
Silicon is considered to be an ideal negative electrode for next-generation lithium ion batteries because it has a lithium storage capacity ten times that of graphite negative electrodes (4200 mAh/g). However, due to the physicochemical properties of the silicon material itself, there are some problems in lithium ion battery negative electrode applications: firstly, in the process of silicon alloying lithium storage, the volume expansion change reaches more than 300 percent, the mechanical acting force generated by the huge volume effect can gradually separate the electrode active substance from the current collector, and the silicon active phase can also be pulverized, so that the electrical contact with the current collector is lost, and the cycle performance of the electrode is rapidly reduced; secondly, silicon is a semiconductor material, the intrinsic conductivity is low, and a large amount of conductive agent is required to be added to improve the electronic conductivity of the electrode; third, silicon is in conventional LiPF due to its drastic volume effect6It is difficult to form a stable surface Solid Electrolyte Interface (SEI) film in the electrolyte, and a new SEI film is continuously formed on a newly exposed silicon surface along with the destruction of an electrode structure, resulting in a decrease in charge and discharge efficiency and an increase in capacity fading. The above problems directly restrict the practical application of silicon-based cathodes in industry.
Aiming at the problems, the conventional problems are that silicon is subjected to nanocrystallization and silicon carbon is compounded, but the existing silicon carbon composite structure has limited improvement on the cycle performance and cannot meet the current demand. Chinese patent with application number 201610914930.7 discloses a manufacturing technical method of a high-specific-capacity graphene/silicon/c-PAN/artificial graphite mixed lithium ion battery negative electrode material. The preparation method comprises the following steps: (1) by (NH)4)2S2O8Intercalating 98% concentrated sulfuric acid into graphite, and stripping liquid phase to prepare graphene; (2) mixing graphene with nano silicon (Si) powder and Polyacrylonitrile (PAN) artificial graphite, freeze drying, sintering, and pulverizingAnd carrying out chemical treatment to obtain the graphene/silicon/c-PAN/artificial graphite mixed negative electrode material. The graphene/silicon/C-PAN/artificial graphite cathode material obtained by the method has the advantages of high specific capacity, high cycle performance and the like, and is suitable for the field of consumption (3C). However, the reaction in the intercalation graphite stripping process of the method needs longer time, the whole process steps are more, the preparation period is longer, and the method is not beneficial to the consistency control of products in the industrialization process. More importantly, the problem that the adhesion between the active material and the adhesive cannot be strengthened, and the active material is likely to fall off and be inactivated due to the expansion of charge and discharge volume still remains.
Disclosure of Invention
The invention aims to provide a graphene/nano-silicon intercalation composite material with surface coupling activity and a preparation method thereof, which endow the graphene/nano-silicon intercalation composite material with surface activity and are used for preparing electrodes, solve the problem of deactivation caused by falling of active substances possibly due to volume expansion of silicon, shorten the preparation time and reduce the scale production cost.
The concept of the invention is that graphite and silicon powder which are cheap and easy to obtain are used as raw materials, a synchronous co-intercalation method (in-situ intercalation) is adopted to synthesize and prepare the graphene/nano-silicon composite material in one step, and a cheap silane coupling agent is utilized to carry out surface coupling treatment, so that the graphene/nano-silicon intercalation composite material with surface coupling activity is obtained, the negative influence of oxygen-containing functional groups on the surface of the material on the electrochemical performance of the material can be reduced, and meanwhile, a three-dimensional curing network can be formed by the cross-linking reaction of the oxygen-containing functional groups and specific functional groups in an adhesive when an electrode piece is prepared, so that the deformation tolerance of the electrode piece on the volume expansion of the silicon material is improved, and the.
The graphene/nano silicon intercalation composite material with surface coupling activity provided by the invention is composed of 10-50% of nano silicon and 90-50% of graphene by mass, and the surface of the graphene/nano silicon intercalation composite material is subjected to coupling treatment by using a silane coupling agent and has a surface coupling activity functional group.
The preparation method of the graphene/nano silicon intercalation composite material with surface coupling activity provided by the invention is characterized in that graphite powder is in the formula (NH)4)2SO4Under the action of a ternary intercalation agent of-98% concentrated sulfuric acid-fuming sulfuric acid, obtaining the graphene nanosheet through a process of graphite-graphite intercalation compound-graphene. The preparation method comprises the following steps:
(1) preparation of graphene/nano-silicon intercalation composite material
Mixing nanometer silicon powder, graphite powder and (NH)4)2S2O8Mixing 98% concentrated sulfuric acid and fuming sulfuric acid according to a certain proportion, stirring for 3-4 hours to perform intercalation reaction, filtering after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon composite material;
(2) surface coupling treatment
Hydrolyzing a silane coupling agent in a weak acid solution to obtain corresponding silanol, mixing the silanol and the graphene/silicon in-situ intercalation nano composite material, wherein the mass of the silane coupling agent is 0.1-5% of that of the graphene/nano silicon composite material, then reacting for 1-3 hours at 75-85 ℃, filtering reaction liquid after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
Further, the step (1) comprises nanometer silicon powder, graphite powder and (NH)4)2S2O8The mixing ratio of the 98 percent concentrated sulfuric acid to the fuming sulfuric acid is that the mass of the nano silicon powder is (NH) and the mass of the graphite powder is4)2S2O8The mass of the concentrated sulfuric acid is 98 percent, the volume of the fuming sulfuric acid is 1:1:10:40:40, the mass unit is g, and the volume unit is mL.
Further, the silane coupling agent in the step (2) is one of gamma-mercaptopropyltriethoxysilane (KH-580), vinyltriethoxysilane (A-151), 3-glycidoxypropyltrimethoxysilane (KH560) and 3-aminopropyltrimethoxysilane (KH-551).
Further, the silicon powder in the step (1) is 10-100 nm silicon powder, and can be a mixture with different particle sizes in the range.
Further, the graphite powder in the step (1) is at least one of natural crystalline flake graphite, artificial graphite, amorphous graphite, blocky graphite and highly oriented pyrolytic graphite.
Further, the freeze drying in the step (1) is to rapidly cool and freeze under the action of liquid nitrogen, and freeze-dry under the condition of high vacuum degree at the temperature of-50 ℃ to-30 ℃ for 22-26 h.
Further, in the step (1), when the intercalation reaction is carried out for one hour, an ultrasonic cleaning machine is utilized to carry out ultrasonic treatment on the reaction system, so that the speed of the sulfuric acid molecule intercalation entering the graphite is increased, and the ultrasonic time is 10-15 minutes each time for 2-3 times.
Further, the weak acid solution in the step (2) is an acid solution with a pH value of 5-6, such as an acetic acid solution.
Further, the hydrolysis time of the silane coupling agent in the step (2) is 20-40 min.
The novel graphene/nano-silicon intercalation composite material with surface coupling activity can be used as a negative electrode material to be applied to a lithium ion battery, namely, the composite material is used for preparing an electrode pole piece (graphene/silicon negative electrode pole piece), and the method comprises the following steps:
and mixing the graphene/nano-silicon intercalation composite material with surface coupling activity with a conductive agent, an adhesive and a solvent to obtain uniform slurry, coating the obtained slurry on a metal foil current collector, and drying to obtain the pole piece. Coupling functional groups (epoxy groups, hydroxyl groups, amino groups and the like) in the silane coupling agent are combined with the adhesive, namely, a silanol end and a coupling end of the coupling agent react with the graphene/nano silicon intercalation composite material (active substance) and the adhesive respectively, so that a good compatible interface is formed between the graphene/nano silicon intercalation composite material and the adhesive in the drying process of the pole piece, and finally the three-dimensionally cured graphene/silicon negative pole piece is obtained.
Further, the adhesive is one of polyvinylidene fluoride (PVDF), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR). In the preparation process of the composite material, the corresponding silane coupling agent with high compatibility is selected according to the type and the property of the subsequently selected adhesive.
Further, the conductive agent is acetylene black or ketjen black.
Further, the mixing mass ratio of the graphene/nano silicon intercalation composite material to the conductive agent, the adhesive and the solvent is 8:1: 1.
Further, the drying of the pole piece is constant temperature drying at 115-125 ℃.
In the actual production process, other auxiliary agents such as suspending agents, dispersing agents and the like can be added into the materials. If necessary, other fillers (such as gelatin, pre-lithiation powder and the like) which are helpful for further improving the performance of the pole piece can be added, and the additives do not influence the formation of the three-dimensional curing structure of the invention and do not have negative effects on the performance of the pole piece.
When the graphene/silicon negative electrode plate is used, the graphene/silicon negative electrode plate prepared by the method can be used as a battery negative electrode, and a lithium plate is used as a counter electrode and is installed into a button battery for further application.
Compared with the prior art, the invention has the following advantages:
1. according to the method, a good compatible interface is formed between the graphene/nano silicon intercalation composite material and the adhesive by using a cheap silane coupling agent, so that chemical bonding and adhesion between the graphene/nano silicon intercalation composite material and the adhesive are promoted, and the negative influence of oxygen-containing functional groups on the surface of the material on the electrochemical performance of the material can be reduced by surface coupling treatment, so that the tolerance of the volume expansion of the silicon-based material in the battery charging and discharging process is improved, and the electrode cycle life and the capacity retention rate of the negative electrode material are prolonged.
2. The graphene/nano silicon composite material is prepared by one-step synthesis by adopting a synchronous co-intercalation method, so that the preparation method is simplified, the preparation period is shortened, the production cost is reduced, and the large-scale production is facilitated.
3. In the method, the synchronous co-intercalation expansion preparation step of the graphene/silicon nano composite material does not involve the oxidation of graphite, does not introduce a large amount of oxygen-containing groups, and does not need a reduction process, and the carbon-oxygen ratio of the obtained graphene can reach 9: 1 or more, is a high-quality graphene material; and the in-situ co-intercalation of the nano silicon can not only effectively prevent the overlapping of the graphene, but also provide a good electronic path and a volume expansion buffer carrier for the electrochemically active silicon material.
Drawings
FIG. 1 is a scanning electron microscope atlas of the graphene/nano-silicon intercalated composite material prepared in example 2, and in FIG. 1, the ruler A is 10 μm; the scale of B is 1 μm.
Fig. 2 is a comparison graph of the charge-discharge cycle performance of the button cell prepared by using the graphene/nano-silicon intercalation composite material with surface coupling activity (mass ratio Si: C ═ 3: 7) as an electrode in example 2 and the charge-discharge cycle performance of the battery prepared by using the conventional Si/graphene composite material as an electrode for the first 100 times.
Fig. 3 is a comparison graph of the long life cycle test results of the button cell prepared from the graphene/nano-silicon intercalation composite material with surface coupling activity of example 2 and the cell prepared from the conventional Si/graphene composite material as an electrode.
Detailed Description
The following describes the graphene/nano-silicon intercalation composite material with surface coupling activity, and the preparation method and application thereof specifically by examples. It should be noted that the following examples are only intended to illustrate the present invention and should not be construed as limiting the scope of the present invention, and that those skilled in the art can make modifications and variations of the present invention without departing from the spirit and scope of the present invention.
Example 1
(1) Preparation of graphene/nano-silicon intercalation composite material
0.1g of nano silicon powder, 0.1g of graphite powder and 1g of (NH)4)2S2O84ml of 98% concentrated sulfuric acid and 4ml of fuming sulfuric acid are stirred uniformly by ultrasonic stirring, and the mixture is stirred for 4 hours by continuous magnetic stirring at room temperature. And after the reaction is finished, filtering the reaction solution, washing the solid with deionized water until the filtrate is neutral, and freeze-drying for 24 hours to obtain the graphene/nano silicon intercalation composite material.
(2) Surface coupling treatment
And selecting a corresponding silane coupling agent with high compatibility according to the type of the adhesive to be selected in the subsequent pole piece manufacturing process. Performing hydrolysis reaction on a silane coupling agent vinyl triethoxysilane (A-151) in an acetic acid solution with the pH value of 5.5 for 0.5h to obtain corresponding silanol, and immediately performing hydrolysis on the silanol and the graphene/silicon intercalation nanocomposite material according to the mass ratio of 1: 100, reacting at 80 ℃ for 2h at the same temperature, filtering the mixture obtained by the reaction, washing the solid with deionized water until the filtrate is neutral, and drying to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
Manufacturing a negative pole piece:
mixing the prepared graphene/nano silicon intercalation composite material with surface coupling activity, a bonding agent PVDF and a conductive agent acetylene black according to a mass ratio of 80: 10: 10, uniformly coating the mixture on the surface of the copper foil after ball milling, and drying the mixture at 120 ℃ to obtain the electrode plate.
The electrode plate is a lithium plate as a counter electrode, and 1mol/L LiPF is used6The Ethyl Carbonate (EC) and the dimethyl carbonate (DMC) are used as electrolyte solutions to prepare the button cell. And stopping the charge-discharge voltage by 0.001-2V, and performing charge-discharge test to actually measure reversible capacity of-1400 mAh/g and initial coulombic efficiency of 86.5%.
Example 2
(1) Preparation of graphene/nano-silicon intercalation composite material
0.3g of nano silicon powder, 0.7g of graphite powder and 7g of (NH)4)2S2O828ml of 98% concentrated sulfuric acid and 28ml of fuming sulfuric acid are stirred and mixed evenly by ultrasonic stirring, and the magnetic stirring is continued for 3 hours at room temperature. And after the reaction is finished, filtering the mixed reaction solution, washing the solid with deionized water until the filtrate is neutral, and freeze-drying for 24 hours to obtain the graphene nano/silicon intercalation composite material.
(2) Surface coupling treatment
And selecting a corresponding silane coupling agent with high compatibility according to the type of the adhesive to be selected in the subsequent pole piece manufacturing process. And (2) carrying out hydrolysis reaction on a silane coupling agent in an acetic acid solution with the pH value of 5.5 for 0.5h to obtain silanol corresponding to the silane coupling agent, and immediately carrying out hydrolysis on the silanol and the prepared graphene/silicon intercalation nano composite material according to the mass ratio of 1: 100, reacting at 80 ℃ for 2h at the same temperature, filtering the reaction solution, washing the solid with deionized water until the filtrate is neutral, and drying to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
A scanning electron microscope map of the prepared graphene/nano-silicon intercalation composite material is shown in figure 1. The figure is a representation of the product obtained in step (1) of the preparation process. In fig. 1B, the morphology of the resulting graphene/nano-silicon intercalated composite can be clearly seen. In this figure, the composite outer layer is a graphene sheet layer and the inner layer is fine silicon powder particles. The outer graphene thin layer is used for buffering the volume change of silicon particles in the charging and discharging processes, so that the cycle performance of the material applied to the battery is effectively improved.
The prepared graphene/nano silicon intercalation composite material with surface coupling activity, a bonding agent PVDF and a conductive agent acetylene black are mixed according to a mass ratio of 80: 10: 10, uniformly coating the mixture on the surface of the copper foil after ball milling, and drying the mixture at 120 ℃ to obtain the electrode plate. The electrode plate is a lithium plate as a counter electrode, and 1mol/L LiPF is used6The Ethyl Carbonate (EC) and the dimethyl carbonate (DMC) are used as electrolyte solutions to prepare the button cell.
Comparative example
For comparison, a button cell was prepared under the same conditions as in example 1, except that a conventional Si/graphene composite was used as an electrode material.
The preparation method of the conventional Si/graphene composite material comprises the following steps: graphite powder is prepared into graphene by a potassium permanganate-hydrogen peroxide oxidation reduction method, and silicon powder and the obtained graphene are mixed under the ultrasonic condition. The Si/graphene composite material obtained by the method mainly has the following problems:
(1) the silicon and the graphene are not uniformly dispersed, so that the finally prepared electrode material has great volume change in the charging and discharging processes, the battery capacity is obviously reduced along with the increase of the cycle number, and the cycle performance of the battery is seriously influenced (can be illustrated in figures 2 and 3)
(2) The conventional method for preparing the Si/graphene composite material needs to prepare graphene separately at first and then mix silicon powder and graphene, which is not beneficial to large-scale preparation and popularization.
The batteries of example 2 and comparative example were subjected to performance tests. The reversible capacity of the battery of the embodiment 2 is actually measured to be 1080mAh/g, and the first coulombic efficiency is 95.7%. The specific test results are shown in fig. 2 and 3.
Fig. 2 is a comparison of charge and discharge curves of the coupled Si/graphene composite (upper curve) and the conventional Si/graphene composite (lower curve) applied to a lithium ion battery, respectively. It can be seen from the figure that by introducing a silane coupling agent into the graphene/nano silicon intercalation composite material to perform coupling reaction, the cycle performance of the battery can be effectively improved (100 cycles, the specific capacity is kept at 1000mAh/g), and the utilization efficiency of active substances (silicon and graphene) in the electrode material is improved (the same mass ratio (Si: C ═ 3: 7), the coupled Si/graphene composite material provides more capacity than the material obtained by the conventional method)
Fig. 3 is a further illustration of fig. 2, with the comparison object also adding to a graphite negative electrode already in commercial use. Compared with the prior art, the invention further improves the two key indexes of the battery application, namely specific capacity and cycle performance. The coulombic efficiency curve refers to the ratio of the charge capacity to the discharge capacity, and the curve in the graph keeps 100 percent all the time, which proves that the invention can keep the structure of the material stable in the charge and discharge process, relieve the volume change and be beneficial to the cycle performance of the battery.
Example 3
(1) Preparation of graphene/nano-silicon intercalation composite material
0.1g of nano silicon powder, 0.9g of graphite powder and 9g of (NH)4)2S2O8Uniformly mixing 36ml of 98% concentrated sulfuric acid and 36ml of fuming sulfuric acid by ultrasonic stirring, and continuously magnetically stirring for 3-4 hours at room temperature. And after the reaction is finished, diluting and filtering the reaction liquid, washing the solid with deionized water until the filtrate is neutral, and freeze-drying for 24 hours to obtain the graphene/nano silicon intercalation composite material.
(2) Surface coupling treatment
And selecting a corresponding silane coupling agent with high compatibility according to the type of the adhesive to be selected in the subsequent pole piece manufacturing process. And (3) carrying out hydrolysis reaction on the silane coupling agent in an acetic acid solution with the pH value of 5.5 for 0.5h to obtain the silanol corresponding to the silane coupling agent. Immediately mixing the graphene/silicon intercalation nanocomposite with the prepared graphene/silicon intercalation nanocomposite according to the mass ratio of 1: 100, reacting for 2 hours at the same temperature of 80 ℃ and washing, filtering and drying the obtained mixed solution to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
The lithium ion battery preparation and the electrode electrochemical performance test were performed with reference to example 1. Lithium ion battery preparation and electrode electrochemical performance testing were performed as in example 1. The reversible capacity is measured to be 430mAh/g, and the first coulombic efficiency is 91.0%.
Claims (10)
1. The graphene/nano-silicon intercalation composite material with surface coupling activity is characterized by comprising 10-50% by mass of nano-silicon and 90-50% by mass of graphene, wherein the surface of the composite material is coupled by a silane coupling agent and has a functional group with surface coupling activity, and the composite material is prepared by the following method:
(1) preparation of graphene/nano-silicon intercalation composite material
Mixing nano silicon powder, graphite powder, (NH4)2S2O8, 98% concentrated sulfuric acid and fuming sulfuric acid according to a certain proportion, stirring for 3-4 hours to perform intercalation reaction, filtering after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon composite material;
(2) surface coupling treatment
Hydrolyzing a silane coupling agent in a weak acid solution to obtain corresponding silanol, mixing the silanol and the graphene/silicon in-situ intercalation nano composite material, wherein the mass of the silane coupling agent is 0.1-5% of that of the graphene/nano silicon composite material, then reacting for 1-3 hours at 75-85 ℃, filtering reaction liquid after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
2. The preparation method of the graphene/nano silicon intercalation composite material with surface coupling activity is characterized by comprising the following steps:
(1) preparation of graphene/nano-silicon intercalation composite material
Mixing nanometer silicon powder, graphite powder and (NH)4)2S2O8Mixing 98% concentrated sulfuric acid and fuming sulfuric acid according to a certain proportion, stirring for 3-4 hours to perform intercalation reaction, filtering after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon composite material;
(2) surface coupling treatment
Hydrolyzing a silane coupling agent in a weak acid solution to obtain corresponding silanol, mixing the silanol and the graphene/silicon in-situ intercalation nano composite material, wherein the mass of the silane coupling agent is 0.1-5% of that of the graphene/nano silicon composite material, then reacting for 1-3 hours at 75-85 ℃, filtering reaction liquid after the reaction is finished, washing the solid with deionized water until the filtrate is neutral, and freeze-drying to obtain the graphene/nano silicon intercalation composite material with surface coupling activity.
3. The preparation method of graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein the step (1) comprises nano-silicon powder, graphite powder, (NH)4)2S2O8The mixing ratio of the 98 percent concentrated sulfuric acid to the fuming sulfuric acid is that the mass of the nano silicon powder is (NH) and the mass of the graphite powder is4)2S2O8The mass of the concentrated sulfuric acid is 98 percent, the volume of the fuming sulfuric acid is 1:1:10:40:40, the mass unit is g, and the volume unit is mL.
4. The method for preparing graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein the silane coupling agent in the step (2) is one of gamma-mercaptopropyltriethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltrimethoxysilane.
5. The method for preparing the graphene/nano silicon intercalation composite material with surface coupling activity according to claim 2, wherein the silicon powder in the step (1) is 10-100 nm silicon powder, and can be a mixture of different particle sizes in the range.
6. The method for preparing graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein the graphite powder in the step (1) is at least one of natural crystalline flake graphite, artificial graphite, amorphous graphite, bulk graphite and highly oriented pyrolytic graphite.
7. The preparation method of the graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein the freeze-drying temperature is-50 ℃ to-30 ℃, and the freeze-drying time is 22-26 h.
8. The preparation method of the graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein in the step (1), every time the intercalation reaction is carried out for one hour, an ultrasonic cleaner is used for carrying out ultrasonic treatment on a reaction system, so that the speed of the sulfuric acid molecule intercalation into the graphite is increased, and the ultrasonic treatment is carried out for 10-15 minutes every time for 2-3 times.
9. The preparation method of the graphene/nano-silicon intercalation composite material with surface coupling activity according to claim 2, wherein the weak acid solution in the step (2) is an acid solution with a pH value of 5-6.
10. The application of the graphene/nano silicon intercalation composite material with surface coupling activity as a lithium ion battery negative electrode material in claim 1.
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