CN109273675B - Graphene composite material, preparation method thereof and lithium ion battery cathode - Google Patents
Graphene composite material, preparation method thereof and lithium ion battery cathode Download PDFInfo
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Abstract
The invention discloses a graphene composite material, a preparation method thereof and application thereof to a lithium ion battery cathode. Further ball milling with SnO through high energy2Mixing the/SiO powder, and calcining at high temperature to obtain the graphene/SnO2the/SiO composite material. The composite material prepared by the invention effectively reduces the agglomeration degree of graphene, and has large specific surface area and high conductivity. In addition, the lithium ion battery cathode prepared by the composite material is also disclosed, and the cycle performance of the lithium ion battery can be greatly improved.
Description
Technical Field
The invention relates to the technical field of graphene preparation, in particular to a graphene composite material, a preparation method thereof and application thereof in a lithium ion battery cathode technology.
Background
Graphene is a novel material having a unique structure and excellent properties, is a monoatomic layer two-dimensional honeycomb structure, and is considered as a basic structural unit of fullerene, carbon nanotube and graphite. The zero-dimensional fullerene is obtained by bending graphene into a football shape, the one-dimensional carbon nanotube is formed by curling the graphene, and the graphite with a three-dimensional structure is considered to be tightly stacked graphene sheet layers. In recent years, theoretical research, experimental preparation, application and other aspects of graphene have become hot spots of domestic and foreign research. Due to the excellent characteristics of high electrical conductivity, high thermal conductivity, high specific surface area, high strength, rigidity and the like, the graphene is widely applied to the fields of energy storage, photoelectric devices, chemical catalysis and the like, wherein the graphene is particularly prominent in the field of lithium ion batteries. The lithium ion battery is the secondary battery with the highest specific energy so far, has the best comprehensive performance, and has become the first choice of portable electronic equipment and power sources, and particularly the latter places higher requirements on the energy density and the power density of the lithium ion battery. Graphite is mostly adopted as a negative electrode of the current commercial lithium ion battery, but poor rate capability and lower theoretical capacity (372mAh/g) of the graphite are one of the main bottlenecks restricting the lithium ion battery to be used as a future large-scale energy storage device. Therefore, the development of new high-energy anode materials is urgent.
The appearance of the graphene brings possibility for breakthrough of high performance of the lithium ion battery, so that a new round of research heat tide is brought for research of high-capacity, high-rate and long-service-life lithium ion battery materials.
The prior art CN106960959A discloses a lithium ion battery cathode and a lithium ion battery, which are composed of a current collector and a cathode material coated on the current collector, wherein the cathode material is composed of graphite active substances, a conductive agent, a binder and an additive; the lithium ion receiving capacity of the additive for first charging is 0.2-4 wt% of the graphite active material. The lithium ion battery cathode directly selects graphite as an active substance of a cathode material, and the capacity of the cathode obtained from the graphite is limited due to low theoretical capacity and conductivity of the graphite.
The prior art CN107359308A discloses a preparation device and a preparation method of a graphene silicon lithium battery cathode material, wherein the preparation method mainly comprises the steps of preparing graphene oxide by a Hummers method, and then compounding the graphene oxide with nano silicon and commercial carbon nanotubes under a certain condition to obtain the graphene/carbon nanotube/silicon cathode material. In the invention, the obtained negative electrode material has low dispersibility and is easy to be aggregated again, thereby influencing the cycle performance of the lithium ion battery.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a method for preparing a graphene composite material, and the graphene composite material obtained by the method can effectively reduce the agglomeration degree of graphene, and has a large specific surface area and high conductivity.
Meanwhile, the invention also aims to solve the technical problem of providing the lithium ion battery cathode, which can effectively inhibit the formation of an SEI film and greatly improve the cycle performance of the lithium ion battery.
In order to solve the technical problem, the invention provides a preparation method of a graphene composite material, which comprises the following steps:
A. preparation of graphene by oxidation-reduction method
(1) H is to be3PO4、H2SO4Stirring and mixing the mixed solution and graphite powder at the stirring speed of 400-600r/min for 0.5-1.5h, adding potassium permanganate in batches, and keeping the temperature below 30 ℃ in the reaction;
(2) heating to 30-40 deg.C, adding deionized water, heating to 50-60 deg.C, and reacting for 0.5-1 h;
(3) cooling to 35-45 ℃, and dropwise adding hydrogen peroxide to obtain a mixed solution, wherein the mass fraction of the hydrogen peroxide is 20-40%;
(4) centrifuging the obtained mixed solution, removing supernatant, and washing the obtained solid with hydrochloric acid and distilled water respectively;
(5) repeating the centrifugation and the washing twice to obtain a lower-layer solid, adding distilled water and yellow dextrin, and ultrasonically mixing to obtain a stable graphene oxide aqueous solution;
(6) adjusting the pH value of the graphene oxide aqueous solution to 10-11, controlling the temperature to be 30-35 ℃, adding alanine and hydrazine hydrate, reacting for 3-6h, centrifugally separating to obtain lower-layer solid, washing with methanol and water respectively, filtering, and drying to obtain graphene;
B. preparation of SnO2SiO mixed powder
Adding ethanol into SnCl2.2H2Ultrasonic treating in O water solution for 1-2 hr, adding ammonia water to precipitate completely, filtering to obtain precipitate, washing with ethanol and water respectively, vacuum drying, and grinding into SnO2Powder, mixing the obtained powder with SiO in proportion to obtain SnO2SiO mixed powder;
C. preparation of graphene/SnO2SiO composite material
(1) Mixing the graphene in the step A and the SnO in the step B2Placing the/SiO mixed powder in a ball milling tank, and carrying out ball milling in an inert gas environment;
(2) and placing the ball-milled mixture in a tube furnace filled with inert gas for calcining for 4-6h, wherein the calcining temperature is 500-900 ℃.
The preparation method of graphene comprises mechanical stripping method, epitaxial growth method and chemical vapor phaseDeposition, liquid phase stripping, chemical synthesis, chemical stripping, and the like. Among them, the chemical stripping method is an extremely simple production process and is considered as one of the most industrially valuable methods. At present, a Brodie method, a Standmaier method and a Hummers method are commonly used for producing graphene, and the invention utilizes the improved Hummers method, namely H in the preparation process3PO4、H2SO4The mixed acid system can obviously reduce the high-temperature reaction of the conventional Hummers method, thereby reducing the production energy consumption, generating no toxic gas in the reaction process, and obtaining the graphene oxide with regular structure.
Preferred is H3PO4And H2SO4The molar ratio is 1: 7-9.
In addition, distilled water and yellow dextrin are added in the step A (5) at the same time, wherein the yellow dextrin mainly plays a role of a stabilizer, the addition of the yellow dextrin greatly increases the stability of the graphene oxide in an aqueous solution, and the obtained graphene oxide has good dispersibility, so that the agglomeration degree of the graphene composite material is also improved. And C, simultaneously adding alanine in the step A (6) to obtain part of amino acid functionalized graphene, so that the conductivity of the graphene is improved to a certain extent.
In a plurality of material research systems, Sn and Si can respectively release 994 mA.h.g-1And 4200mA · h · g-1However, Sn and Si based materials have a large volume effect when used in the negative electrode of a lithium ion battery, which in turn causes a rapid decay of the capacity. To improve this property, the invention selects SnO2The composite material is compounded with SiO and graphene, so that the volume effect of Sn and Si-based materials is improved, and the conductivity of the composite material is greatly improved.
Preferably, in the step A (1), potassium permanganate is added in batches to control the feeding time to be 20-30min, and the graphite powder can be completely oxidized by slowly adding the potassium permanganate in batches.
Preferably, the mass ratio of the distilled water to the yellow dextrin in the step A (5) is 30-60:1, the ultrasonic mixing process is 200-400W, and the ultrasonic time is 2-5 h.
Further, in the centrifugation process involved in the step A, the centrifugation rotating speed is 5000-.
Preferably, the mass ratio of alanine to hydrazine hydrate in the step A (6) is 1-2: 5-10.
Preferably, the ratio in step B is SnO2The mass ratio of the silicon dioxide to SiO is 1-2: 7-10. Selecting SiO and SnO with proper proportion2The conductivity and the cycling stability of the composite material can be improved.
Preferably, the ball milling in the step C is specifically: the grinding balls are ceramic balls, the grinding rotating speed is 300-. Ball milling to make graphene and SnO2Fully mixing with SiO to obtain uniformly distributed graphene/SnO2The mixed powder of/SiO.
The second purpose of the present invention is to provide a graphene composite material obtained by the preparation method of the graphene composite material.
The invention also aims to provide a lithium ion battery negative electrode which comprises a negative electrode current collector and a negative electrode material coated on the current collector, wherein the negative electrode material is prepared by mixing the graphene composite material, a conductive agent, a binder and a dispersing agent.
Preferably, the graphene composite material accounts for 93-95%, the conductive agent accounts for 2-4%, the binder accounts for 1.5-3.5%, and the dispersant accounts for 0.2-1% of the total weight of the negative electrode material.
Further, the conductive agent is acetylene black; the binder is any one of styrene butadiene rubber, polyacrylate and polyimide; the dispersant is sodium carboxymethyl cellulose.
The invention has the beneficial effects that:
1) the invention provides a graphene composite material, which is prepared from graphene and SnO by an improved Hummers method2The obtained material can effectively reduce the agglomeration degree of graphene and has large specific surface area and high conductivity.
2) The invention also provides a lithium ion battery cathode which can effectively inhibit the formation of an SEI film and greatly improve the cycle performance of the lithium ion battery.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1 preparation of graphene composite
A. Preparation of graphene
500ml of H with a molar ratio of 1:83PO4/H2SO4Adding the potassium permanganate into 5g of graphite powder, magnetically stirring for 1.5h at the stirring speed of 400r/min and the temperature of less than 30 ℃, adding 20g of potassium permanganate into a reaction system in batches, and controlling the charging time of the potassium permanganate to be 30 min. Heating to 40 ℃, adding 100ml of deionized water, continuously heating to 60 ℃, and reacting for 0.5 h. Adjusting the temperature to 45 ℃, dropwise adding 5ml of hydrogen peroxide with the mass fraction of 40% to obtain a mixed solution, centrifuging and washing the obtained mixed solution for 3 times, and washing with hydrochloric acid and distilled water in sequence during washing. Adding 300ml of distilled water and 10g of yellow dextrin into the lower-layer solid, carrying out ultrasonic treatment for 5h under the power of 200W, then adjusting the pH value of the solution to 11, adding 0.5g of alanine and 5g of hydrazine hydrate at the temperature of 35 ℃, stirring for reaction for 3h, centrifuging, washing with methanol and water respectively, filtering and drying to obtain the graphene. The centrifugal rotation speed is 5000r/min, and the centrifugal time is 30 min.
B. Preparation of SnO2SiO mixed powder
Adding 20ml ethanol slowly into 50ml SnCl2··2H2Ultrasonic treating in O water solution for 1 hr, adding ammonia water to precipitate completely, filtering to obtain precipitate, washing with ethanol and water respectively, and vacuum drying 4Grinding for 5min to obtain SnO2Powder of SnO2Mixing the powder and SiO according to the ratio of 1:7 to obtain SnO2The mixed powder of/SiO.
C. Preparation of graphene/SnO2SiO composite material
Mixing the graphene obtained in the step A with SnO2Mixing the/SiO mixed powder to obtain a mixed material, placing the mixed material and ceramic balls in a ball milling tank filled with Ar gas according to the ratio of 1:10, performing ball milling at the ball milling rotation speed of 300r/min for 9 hours to obtain graphene/SnO2Mixing powder of/SiO, and then mixing graphene/SnO2Calcining the/SiO mixed powder in a tubular furnace filled with Ar gas for 4 hours at the calcining temperature of 900 ℃ to obtain the graphene/SnO2the/SiO composite material.
And performing electrical detection on the obtained graphene composite material, wherein the conductivity is 6700S/m.
Example 2 preparation of graphene composite
A. Preparation of graphene
500ml of H with a molar ratio of 1:73PO4/H2SO4Adding the potassium permanganate into 5g of graphite powder, mechanically stirring for 0.5h at the stirring speed of 600r/min and the temperature of less than 30 ℃, adding 20g of potassium permanganate into a reaction system in batches, and controlling the charging time of the potassium permanganate to be 20 min. Heating to 30 ℃, adding 100ml of deionized water, continuously heating to 50 ℃, and reacting for 1 h. Adjusting the temperature to 35 ℃, dropwise adding 5ml of hydrogen peroxide with the mass fraction of 20% to obtain a mixed solution, centrifuging and washing the obtained mixed solution for 3 times, and washing with hydrochloric acid and distilled water in sequence during washing. Adding 600ml of distilled water and 10g of yellow dextrin into the lower-layer solid, carrying out ultrasonic treatment for 2h under the power of 400W, then adjusting the pH value of the solution to 10, adding 1g of alanine and 5g of hydrazine hydrate at the temperature of 30 ℃, stirring for reaction for 6h, centrifuging, washing with methanol and water respectively, filtering and drying to obtain the graphene. 7000r/min is selected as the centrifugal rotating speed, and the centrifugal time is 25 min.
B. Preparation of SnO2SiO mixed powder
Adding 20ml ethanol slowly into 50ml SnCl2··2H2Ultrasonic treating in O water solution for 2 hr, adding ammonia water to precipitate completely, filtering to obtain precipitate, and separatingWashing with ethanol and water, vacuum drying for 1 hr, grinding into SnO2Powder of SnO2Mixing the powder and SiO according to the ratio of 1:10 to obtain SnO2The mixed powder of/SiO.
C. Preparation of graphene/SnO2SiO composite material
Mixing the graphene obtained in the step A with SnO2Mixing the/SiO mixed powder to obtain a mixed material, placing the mixed material and ceramic balls in a ball milling tank filled with helium according to the proportion of 1:20, performing ball milling at the ball milling rotation speed of 500r/min for 6 hours to obtain graphene/SnO2Mixing powder of/SiO, and then mixing graphene/SnO2Calcining the/SiO mixed powder in a helium-filled tubular furnace for 5 hours at the calcining temperature of 700 ℃ to obtain the graphene/SnO2the/SiO composite material.
And performing electrical detection on the obtained graphene composite material, wherein the electric conductivity is 7100S/m.
Example 3 preparation of graphene composite
A. Preparation of graphene
800ml of H with a molar ratio of 1:93PO4/H2SO4Adding the mixture into 10g of graphite powder, magnetically stirring for 1h at the stirring speed of 600r/min at the temperature of lower than 30 ℃, adding 30g of potassium permanganate into a reaction system in batches, and controlling the charging time of the potassium permanganate to be 28 min. The temperature is increased to 35 ℃, 200ml of deionized water is added, the temperature is continuously increased to 55 ℃, and the reaction is carried out for 1 h. Adjusting the temperature to 40 ℃, dropwise adding 10ml of hydrogen peroxide with the mass fraction of 30% to obtain a mixed solution, centrifuging and washing the obtained mixed solution for 3 times, and washing with hydrochloric acid and distilled water in sequence during washing. And adding 600ml of distilled water and 15g of yellow dextrin into the lower-layer solid, carrying out ultrasonic treatment for 4h under the power of 300W, then adjusting the pH value of the solution to 10, adding 1g of alanine and 9g of hydrazine hydrate at the temperature of 33 ℃, stirring for reaction for 5h, centrifuging, washing with methanol and water respectively, filtering, and drying to obtain the graphene. The centrifugal rotation speed is 8000r/min, and the centrifugal time is 20 min.
B. Preparation of SnO2SiO mixed powder
30ml of ethanol is slowly added into 80ml of SnCl2··2H2Ultrasonic treating in O water solution for 2 hr, adding ammonia water to precipitatePrecipitating completely, filtering to obtain precipitate, washing with ethanol and water, vacuum drying for 1 hr, grinding into SnO2Powder of SnO2Mixing the powder and SiO according to the ratio of 2:7 to obtain SnO2The mixed powder of/SiO.
C. Preparation of graphene/SnO2SiO composite material
Mixing the graphene obtained in the step A with SnO2Mixing the/SiO mixed powder to obtain a mixed material, placing the mixed material and ceramic balls in a ball milling tank filled with nitrogen according to the proportion of 1:15, performing ball milling at the ball milling rotation speed of 500r/min for 8 hours to obtain graphene/SnO2Mixing powder of/SiO, and then mixing graphene/SnO2Calcining the/SiO mixed powder in a nitrogen-filled tubular furnace for 6 hours at the calcining temperature of 500 ℃ to obtain the graphene/SnO2the/SiO composite material.
And performing electrical detection on the obtained graphene composite material, wherein the conductivity is 6500S/m.
EXAMPLE 4 comparative example (without addition of yellow dextrin and alanine)
A. Preparation of graphene
800ml of H with a molar ratio of 1:93PO4/H2SO4Adding the mixture into 10g of graphite powder, mechanically stirring for 1h at the stirring speed of 500r/min at the temperature of lower than 30 ℃, adding 30g of potassium permanganate into a reaction system in batches, and controlling the charging time of the potassium permanganate to be 25 min. Heating to 40 ℃, adding 200ml of deionized water, continuously heating to 60 ℃, and reacting for 1 h. Adjusting the temperature to 45 ℃, dropwise adding 10ml of hydrogen peroxide with the mass fraction of 30% to obtain a mixed solution, centrifuging and washing the obtained mixed solution for 3 times, and washing with hydrochloric acid and distilled water in sequence during washing. And (3) adding 500ml of distilled water into the lower-layer solid, carrying out ultrasonic treatment for 3h under the power of 400W, adjusting the pH value of the solution to 10, adding 5g of hydrazine hydrate at the temperature of 35 ℃, carrying out stirring reaction for 4h, centrifuging, washing with methanol and water respectively, filtering and drying to obtain the graphene. The centrifugal rotation speed is 8000r/min, and the centrifugal time is 25 min.
B. Preparation of SnO2SiO mixed powder
40ml of 0.4mol/L ethanol are slowly added into 80ml of SnCl2··2H2O aqueous solutionPerforming medium ultrasonic treatment for 1.5h, adding ammonia water until the precipitate is completely precipitated, filtering to obtain precipitate, washing with ethanol and water respectively, vacuum drying for 1h, grinding into SnO2Powder of SnO2Mixing the powder and SiO according to the ratio of 1:8 to obtain SnO2The mixed powder of/SiO.
C. Preparation of graphene/SnO2SiO composite material
Mixing the graphene obtained in the step A with SnO2Mixing the/SiO mixed powder to obtain a mixed material, placing the mixed material and ceramic balls in a ball milling tank filled with nitrogen according to the proportion of 1:10, performing ball milling at the ball milling rotation speed of 450r/min for 7 hours to obtain graphene/SnO2Mixing powder of/SiO, and then mixing graphene/SnO2Calcining the/SiO mixed powder in a nitrogen-filled tubular furnace for 6 hours at the calcining temperature of 800 ℃ to obtain the graphene/SnO2the/SiO composite material.
And performing electrical detection on the obtained graphene composite material, wherein the electric conductivity is 5800S/m.
Example 5 lithium ion Battery negative electrode
The cathode material comprises the following components by taking the total weight of the cathode material as a reference: 93% of the graphene composite material prepared in the embodiment 1, 4% of acetylene black, 2.8% of styrene butadiene rubber and 0.2% of sodium methyl cellulose are mixed to prepare a negative electrode material, the obtained material is coated on a current collector copper foil, and the negative electrode of the lithium ion battery is obtained by drying.
Example 6 lithium ion Battery negative electrode
The cathode material comprises the following components by taking the total weight of the cathode material as a reference: the graphene composite material prepared in the embodiment 2 is prepared by mixing 94% of acetylene black, 3% of polyacrylate and 0.5% of sodium methyl cellulose to prepare a negative electrode material, and the obtained material is coated on a current collector copper foil and dried to obtain the lithium ion battery negative electrode.
Example 7 lithium ion Battery negative electrode
The cathode material comprises the following components by taking the total weight of the cathode material as a reference: the graphene composite material prepared in the embodiment 3, acetylene black 2%, polyimide 3.5% and sodium methyl cellulose 0.5% are mixed to prepare a negative electrode material, and the obtained material is coated on a current collector copper foil and dried to obtain a lithium ion battery negative electrode.
Example 8 lithium ion Battery negative electrode
The cathode material comprises the following components by taking the total weight of the cathode material as a reference: 95% of the graphene composite material prepared in example 4, 2.5% of acetylene black, 1.5% of styrene butadiene rubber and 1% of sodium methyl cellulose are mixed to prepare a negative electrode material, the obtained material is coated on a current collector copper foil, and the negative electrode of the lithium ion battery is obtained by drying.
Example 9 testing of the Performance of the negative electrode of a lithium ion Battery
Under the condition of room temperature, 100mA/g 3.5V charging and 100mA/g 2.7V discharging are carried out, and a battery A, B, C, D is assembled by the same positive electrode and electrolyte and the negative electrode of the lithium ion battery obtained in the above examples 5-8 respectively to carry out cycle performance test. The results are as follows:
| battery with a battery cell | First cycle efficiency | 50 cycle specific capacity retention | Cyclic 100 cycle specific capacity retention |
| A | 95％ | 632.9mA/g | 613.5mA/g |
| B | 96.2％ | 647.3mA/g | 621.4mA/g |
| C | 94.3％ | 628.8mA/g | 610.7mA/g |
| D | 89％ | 607.1mA/g | 526.8mA/g |
As can be seen from the above table, battery D obtained by using the graphene composite material obtained in comparative example 4 as the negative electrode material of the lithium ion battery has lower first cycle efficiency and poorer cycle performance than batteries A, B and C. The lithium ion battery cathode prepared from the graphene composite material provided by the invention has greatly improved cycle performance and certain improved specific capacity.
In the description herein, references to the description of the term "one embodiment," "another embodiment," or "first through xth embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, method steps, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (8)
1. The preparation method of the graphene composite material is characterized by comprising the following steps:
A. preparation of graphene by oxidation-reduction method
(1) Stirring and mixing the mixed solution of H3 PO 4 and H2 SO 4 and graphite powder at the stirring speed of 400-600r/min for 0.5-1.5H, adding potassium permanganate in batches, wherein the feeding time is controlled to be 20-30min, and keeping the temperature below 30 ℃ in the reaction;
(2) heating to 30-40 deg.C, adding deionized water, heating to 50-60 deg.C, and reacting for 0.5-1 h;
(3) cooling to 35-45 ℃, and dropwise adding hydrogen peroxide to obtain a mixed solution, wherein the mass fraction of the hydrogen peroxide is 20-40%;
(4) centrifuging the obtained mixed solution, removing supernatant, and washing the obtained solid with hydrochloric acid and distilled water respectively;
(5) repeating the centrifugation and the washing twice to obtain a lower-layer solid, adding distilled water and yellow dextrin, and ultrasonically mixing to obtain a stable graphene oxide aqueous solution;
(6) adjusting the pH value of the graphene oxide aqueous solution to 10-11, controlling the temperature to be 30-35 ℃, adding alanine and hydrazine hydrate, reacting for 3-6h, centrifugally separating to obtain lower-layer solid, washing with methanol and water respectively, filtering, and drying to obtain graphene;
B. preparation of SnO 2/SiO mixed powder
Adding ethanol into an aqueous solution of SnCl 2.2H 2O, performing ultrasonic treatment for 1-2H, adding ammonia water until the precipitate is completely precipitated, filtering to obtain a precipitate, washing with ethanol and water respectively, performing vacuum drying, grinding into SnO 2 powder, and mixing the obtained powder with SiO in proportion to obtain SnO 2/SiO mixed powder;
C. preparation of graphene/SnO 2/SiO composite material
(1) B, placing the graphene in the step A and the SnO 2/SiO mixed powder in the step B into a ball milling tank, and carrying out ball milling in an inert gas environment;
the ball milling in the step C is specifically as follows: the grinding balls are ceramic balls, the grinding rotating speed is 300-;
(2) and placing the ball-milled mixture in a tube furnace filled with inert gas for calcining for 4-6h, wherein the calcining temperature is 500-900 ℃.
2. The preparation method of the graphene composite material as claimed in claim 1, wherein the mass ratio of the distilled water to the yellow dextrin in the step A (5) is 30-60:1, the ultrasonic mixing process is performed at a power of 200-400W, and the ultrasonic time is 2-5 h.
3. The method for preparing the graphene composite material according to claim 1, wherein the mass ratio of alanine to hydrazine hydrate in the step A (6) is 1-2: 5-10.
4. The preparation method of the graphene composite material according to claim 1, wherein the ratio in the step B is a mass ratio of SnO 2 to SiO of 1-2: 7-10.
5. A graphene composite material prepared by the method of any one of claims 1 to 4.
6. A negative electrode of a lithium ion battery comprises a negative electrode current collector and a negative electrode material coated on the current collector, and is characterized in that the negative electrode material is prepared by mixing the graphene composite material, a conductive agent, a binder and a dispersing agent according to claim 5.
7. The lithium ion battery negative electrode of claim 6, wherein the graphene composite material accounts for 93-95%, the conductive agent accounts for 2-4%, the binder accounts for 1.5-3.5%, and the dispersant accounts for 0.2-0.8% of the total weight of the negative electrode material.
8. The lithium ion battery negative electrode of any one of claims 6 to 7, wherein the conductive agent is acetylene black; the binder is any one of styrene butadiene rubber, polyacrylate and polyimide; the dispersant is sodium carboxymethyl cellulose.
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