A three-dimensional graphene / SiO composite material and its preparation method and application

Abstract

The present invention discloses a three-dimensional graphene / SiO composite material and a preparation method and application thereof. The preparation method comprises the following steps: mixing, stirring, standing, washing and drying three-dimensional graphene oxide, water, potassium sulfide and potassium ferrate to obtain reduced three-dimensional graphene, and then mixing with SiO, drying and laser processing to obtain a three-dimensional graphene / SiO composite material. The present invention uses a combined method of multi-step hydrothermal-laser etching to dope the combined element to synthesize the three-dimensional graphene / SiO composite material, and the lithium ion battery prepared with the material has the characteristics of coulombic efficiency, cycle life and reversible capacity under high load.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for lithium-ion batteries, and specifically relates to a three-dimensional graphene / SiO composite material and a preparation method and application thereof. Background Art

[0002] Developing low-cost, long-cycle, high-energy-density energy storage devices to make full use of green energy is the key to solving current environmental and resource problems. Lithium-ion batteries have the advantages of high energy density, long life, and environmental friendliness, and are widely used in portable electronic products, power vehicles, large-scale energy storage devices, etc. Within a certain range, the higher the loading of lithium-ion battery electrodes, the higher the surface capacity, and it is easier to build high-energy-density energy storage devices. Traditional commercial lithium-ion batteries with graphite as the negative electrode material can have a loading of up to 10 mg cm -2 , but its theoretical specific capacity is only 372 mAh g -1 , which makes it increasingly difficult for currently commercialized lithium-ion batteries to meet the requirements of high energy density energy storage devices. Therefore, developing lithium-ion battery anode materials with excellent performance under high loading is a top priority for realizing high-performance energy storage devices.

[0003] Alloy negative electrode materials with high theoretical capacity such as Si (3579 mAh g -1 )、Sn(990mAh·g -1 )、P(2596mAh·g -1 ) and Ge(1600mAh·g -1 ) are considered to be very promising negative electrode materials for the next generation of lithium batteries. Among them, silicon negative electrode materials are the most attractive, with a theoretical capacity of about 372mAh g -1 ) is 10 times that of silicon, and has great application prospects in the field of high energy density lithium batteries. However, the huge volume expansion of silicon negative electrode materials leads to a rapid decrease in capacity and poor cycle performance. Compared with silicon, silicon monoxide (SiO, 2680mAh·g -1 , assuming that all Si can be converted into Li during lithiation 4.4 Si) has a smaller volume change (Si>400%, SiO is about 220%), and the cost is lower. In addition, the lithium silicates (such as Li2Si2O5) and Li2O generated during the charge and discharge process are beneficial to Li + In Li x The migration between Si alloys makes SiO exhibit excellent rate performance and cycle stability. Therefore, alloy SiO is considered to be a more ideal negative electrode for future commercial lithium-ion batteries. However, the low coulombic efficiency and poor cycle stability seriously hinder the large-scale commercial application of SiO. The key scientific problem lies in the large volume expansion and inherent poor electronic or ionic conductivity of SiO-based negative electrodes.

[0004] Therefore, the present invention provides a three-dimensional graphene / SiO composite material to solve the problems raised in the above background technology. Summary of the invention

[0005] The object of the present invention is to provide a three-dimensional graphene / SiO composite material to solve at least one aspect of the problems and defects raised in the above background technology.

[0006] The present invention also provides a three-dimensional graphene / SiO composite material prepared by the above preparation method.

[0007] The present invention also provides applications of the three-dimensional graphene / SiO composite material.

[0008] Specifically, the first aspect of the present invention provides a method for preparing a three-dimensional graphene / SiO composite material, comprising the following steps:

[0009] S1. Preparation of three-dimensional graphene oxide: mixing graphite, water, concentrated sulfuric acid and sodium vanadate, and then sequentially performing hydrothermal treatment, ultrasonic treatment and impurity removal to obtain a mixed dispersion, and finally drying to obtain three-dimensional graphene oxide;

[0010] S2. Preparation of three-dimensional graphene / SiO composite materials:

[0011] S21, mixing the three-dimensional graphene oxide, water, potassium sulfide and potassium ferrate to obtain a reduced three-dimensional graphene dispersion, and then stirring, ultrasonicating, standing and drying to obtain reduced three-dimensional graphene;

[0012] S22, mixing the reduced three-dimensional graphene, SiO powder and water, and then performing ultrasound and drying to obtain a mixed material;

[0013] S23, laser processing the mixed material to obtain a three-dimensional graphene / SiO composite material.

[0014] According to one technical solution of the high-binding phase cemented carbide technical solution of the present invention, at least the following beneficial effects are achieved:

[0015] The present invention intends to obtain a three-dimensional graphene / SiO2 negative electrode material by doping a combined element into a synthetic lithium-ion battery negative electrode through a multi-step hydrothermal-laser etching combined method.

[0016] When preparing three-dimensional graphene, no cross-linking agent is needed. The cross-linking agent is obtained after the transition metal oxidant is reduced by graphene. The cross-linking agent can enhance the π-π interaction between graphene sheets and is conducive to the formation of a stable three-dimensional structure.

[0017] The present invention adopts sodium vanadate as an oxidant, which can avoid excessive damage to the graphene structure. The electrical conductivity after oxidation is significantly higher than that of general graphene oxide. After reduction, the mechanical strength is significantly improved due to fewer structural defects, three-dimensionality and dispersed force.

[0018] The present invention adopts laser processing to make the three-dimensional graphene / SiO2 negative electrode material have a large number of laser-etched holes, which can be more easily infiltrated by the electrolyte, reduce the resistivity, and improve the cycle life.

[0019] In some specific embodiments of the present invention, the drying in S21 is freeze-drying.

[0020] In some specific embodiments of the present invention, the median particle size of the graphite is 4 μm to 8 μm.

[0021] In some specific embodiments of the present invention, the median particle size of the graphite is 5 μm to 7 μm.

[0022] In some specific embodiments of the present invention, the mass ratio of graphite to sodium vanadate is 1:1-6.

[0023] In some specific embodiments of the present invention, the mass ratio of the graphite to concentrated sulfuric acid is 1:1-3.

[0024] In some specific embodiments of the present invention, the mass ratio of graphite to water in S1 is 1:20-30.

[0025] In some specific embodiments of the present invention, the mass ratio of the three-dimensional graphene oxide to water in S21 is 1:80-120.

[0026] In some specific embodiments of the present invention, the mass ratio of reduced three-dimensional graphene to water in S22 is 1:30-40.

[0027] In some specific embodiments of the present invention, the hydrothermal temperature is 100°C to 160°C;

[0028] The hydrothermal time is 2h to 6h.

[0029] In some specific embodiments of the present invention, the hydrothermal temperature is 110°C to 160°C.

[0030] In some specific embodiments of the present invention, the hydrothermal time is 3 h to 6 h.

[0031] In some specific embodiments of the present invention, the redox potential value of the mixed dispersion is below 150 mV.

[0032] In some specific embodiments of the present invention, the mass ratio of the three-dimensional graphite oxide, potassium sulfide and potassium ferrate in step S21 is 1:3-9:1-8.

[0033] In some specific embodiments of the present invention, the mass ratio of the reduced three-dimensional graphene to SiO powder is 1:2-5.

[0034] In some specific embodiments of the present invention, the output pulse width of the laser treatment is 500fs to 600fs;

[0035] The pulse frequency of the laser treatment is 0.9kHz to 1.1kHz;

[0036] The spot diameter of the laser treatment is 0.9 μm to 1.1 μm;

[0037] The scanning speed of the laser processing is 0.8 mm / s to 2.2 mm / s.

[0038] A second aspect of the present invention provides a three-dimensional graphene / SiO composite material obtained by the above preparation method.

[0039] A third aspect of the present invention provides an application of a three-dimensional graphene / SiO composite material in the preparation of an electrode material.

[0040] In some specific embodiments of the present invention, the steps of making a battery from the three-dimensional graphene / SiO composite material are:

[0041] The first step is to mix the three-dimensional graphene / SiO composite material, acetylene black and ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0042] Step 2: Slice the negative electrode material and dry it to obtain a negative electrode sheet;

[0043] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into a battery shell to obtain a battery;

[0044] The mass ratio of the three-dimensional graphene / SiO composite material, acetylene black and ethanol is 3-10:1:3-10.

[0045] The slice thickness is 80 mg / cm 2 ~100mg / cm 2 .

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The present invention does not require the use of a crosslinking agent when preparing three-dimensional graphene. The crosslinking agent is obtained after the transition metal oxidant is reduced by graphene. The crosslinking agent can enhance the π-π interaction between graphene sheets and is conducive to the formation of a stable three-dimensional structure.

[0048] 2. The present invention uses a medium-strength oxidant to produce graphene oxide, which can avoid excessive damage to the graphene structure, and its conductivity after oxidation is significantly higher than that of general graphene oxide. In this way, after reduction, due to fewer structural defects, three-dimensionality, and dispersed force, its mechanical strength is significantly improved.

[0049] 3. The graphite raw material used is ultrafine graphite powder, and its median particle size measured by a laser particle size analyzer is between 4 μm and 8 μm. The fineness of the graphite powder determines that even if the oxidizing agent has poor oxidizing properties, the graphite powder can still be fully oxidized. At the same time, the present invention reasonably selects the graphite particle size. If the graphite particle size is less than 4 μm, the prepared graphene area is small and it is difficult to embed SiO particles well; if it is greater than 8 μm, it is difficult to be fully oxidized.

[0050] 4. The laser-treated three-dimensional graphene / SiO composite material has a large number of laser-etched holes, which can be more easily wetted by the electrolyte, reduce the resistivity, alleviate the SiO volume number, and thus improve the cycle life.

[0051] 5. The high mechanical strength, conductivity and wettability of graphene determine that this material can be coated on the current collector with a loading amount far exceeding that of the current products on the market. The capacity per unit area can reach that of the commercially available products (loading amount of about 10mg / cm 2 )5 to 10 times.

[0052] 6. The three-dimensional graphene itself has thickness and mechanical strength, and does not need to be coated on the current collector. It can be used directly as an electrode sheet, saving metal copper and reducing the manufacturing cost of lithium battery negative electrode sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0054] Figure 1 TEM image (high magnification) of the three-dimensional graphene / SiO composite material prepared in Example 1;

[0055] Figure 2 TEM image (low magnification) of the three-dimensional graphene / SiO composite material prepared in Example 1;

[0056] Figure 3 A comparison chart of the number of cycles of batteries made from the composite materials of Examples 1 to 3 and Comparative Examples 1 to 3;

[0057] Figure 4 This is the particle size distribution diagram of the ultrafine graphite powder in Example 1 measured using a laser particle size analyzer. DETAILED DESCRIPTION

[0058] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0059] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0060] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0061] Specific embodiments of the present invention are described in detail below.

[0062] The mechanical strength in this embodiment is a uniaxial compression test to measure the mechanical strength when the repeatable strain reaches 90%.

[0063] Specific embodiments of the present invention are described in detail below.

[0064] Example 1

[0065] This embodiment is a method for preparing a three-dimensional graphene / SiO composite material.

[0066] A preparation step of a three-dimensional graphene / SiO composite material is as follows:

[0067] S1. Preparation of three-dimensional graphene oxide:

[0068] 10g of graphite was ultrafinely ground to a median particle size of 5.22μm, 25g of water and 25g of concentrated sulfuric acid were added, and after ultrasonic dispersion, 10g of sodium vanadate was added for hydrothermal reaction at 150°C for 4h. After being taken out, it was kept sealed and stirred for 8 hours at 80°C under ultrasonic conditions. Then, it was removed from the mixture with an ion exchange resin to obtain a mixed dispersion. The redox potential of the dispersion after removal of impurities was 130mV and the pH was 5.5. It was then freeze-dried to obtain three-dimensional graphene oxide.

[0069] S2. Preparation of three-dimensional graphene / SiO composite materials:

[0070] S21. Add 1 g of three-dimensional graphene oxide to 100 g of deionized water, disperse it sufficiently by ultrasound, then add 6 g of potassium sulfide and 2 g of potassium ferrate to mix to obtain a reduced three-dimensional graphene dispersion, the pH value of the dispersion is 9.5, stir for 5 minutes, ultrasound for 15 minutes, let stand in a water bath at 85°C for 30 minutes, and then freeze-dry to obtain the reduced three-dimensional graphene.

[0071] S22, 2.5 g of reduced three-dimensional graphene was mixed with 7.5 g of nano-SiO powder (average particle size of 700 nm), 90 g of deionized water was added, and the mixture was fully dispersed by ultrasound. The ultrasound treatment was maintained for 2 h, and a mixed material was obtained after freeze-drying.

[0072] S23, spreading the dried mixed material in a laser container, and performing laser patterning treatment using an ultraviolet femtosecond laser to obtain a three-dimensional graphene / SiO composite material. The laser treatment conditions are shown in Table 1.

[0073] The obtained three-dimensional graphene / SiO composite material was observed by transmission electron microscopy. Figure 1 and Figure 2 .

[0074] Depend on Figure 1 and Figure 2 visible:

[0075] 1. The SiO nanoparticles are well embedded in the graphene flakes, and almost all visible SiO particles are embedded in the graphene.

[0076] 2. The laser etching points are evenly distributed on the material.

[0077] 3. The electron diffraction pattern confirms that the material obtained in this example is a non-crystalline material.

[0078] 4. The graphene is three-dimensional, that is, even in the position where SiO is not embedded, there are still a large number of graphene stacks with different shades of color, which confirms that graphene exists in a three-dimensional form with different numbers of layers and different structures, and is not a simple two-dimensional single-layer graphene.

[0079] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0080] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0081] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0082] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0083] Example 2

[0084] This embodiment is a method for preparing a three-dimensional graphene / SiO composite material, which is different from Embodiment 1 in that the median particle size of the graphite powder used is 8.0 μm.

[0085] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0086] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0087] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0088] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0089] Example 3

[0090] This embodiment is a method for preparing a three-dimensional graphene / SiO composite material. The difference from Embodiment 1 is that potassium sulfide and potassium ferrate are replaced by sodium pyrosulfite and potassium permanganate.

[0091] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0092] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0093] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0094] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0095] Comparative Example 1

[0096] This comparative example is a method for preparing a three-dimensional graphene / SiO composite material, which differs from Example 1 in that sodium vanadate is replaced by potassium permanganate.

[0097] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0098] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0099] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0100] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0101] Comparative Example 2

[0102] This comparative example is a method for preparing a three-dimensional graphene / SiO composite material, which differs from Example 1 in that no laser treatment is performed.

[0103] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0104] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0105] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0106] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0107] Comparative Example 3

[0108] This comparative example is a method for preparing a three-dimensional graphene / SiO composite material. The difference from Example 1 is that the median particle size of the graphite powder is 13 μm (about 1000 mesh).

[0109] The following is the preparation of a battery using the obtained three-dimensional graphene / SiO composite material:

[0110] The first step is to mix 7.5 g of the three-dimensional graphene / SiO composite material, 2.5 g of acetylene black and 10 g of ethanol to obtain a three-dimensional graphene / SiO negative electrode material;

[0111] The second step is to coat the negative electrode material with a thickness of 90 mg / cm 2 Cut into slices and dry at 60℃ for 2h to obtain the negative electrode sheet;

[0112] The third step is to combine the negative electrode sheet with the lithium iron phosphate positive electrode sheet and the separator, add the electrolyte, and assemble them into the battery casing to obtain the battery.

[0113] The three-dimensional graphene oxides and reduced three-dimensional graphene oxides obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to conductivity tests, and the three-dimensional graphene oxides after reduction were subjected to mechanical strength tests. The results are shown in Table 2.

[0114] The batteries obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were tested for the number of cycles used. The results are shown in Tables 3 and Figure 3 .

[0115] The ultrafine graphite powder obtained by grinding Example 1 was tested for particle size distribution using a laser particle size analyzer. The results are shown in Tables 4 and Figure 4 .

[0116] Table 1 Laser treatment conditions

[0117]

[0118] Table 2 Conductivity test and mechanical strength test of Examples 1 to 3 and Comparative Examples 1 to 3

[0119]

[0120]

[0121] Table 3 Battery cycle test

[0122]

[0123] Table 4 Particle size values ​​of graphite powder at various levels measured by laser particle size analyzer

[0124]

[0125] It can be seen from Table 4 that the median particle size of graphite powder is 5.22 μm.

[0126] In summary, the three-dimensional graphene / SiO composite material provided in the present invention has the following characteristics: the present invention does not need to use a crosslinking agent when manufacturing three-dimensional graphene, and the crosslinking agent is obtained after the transition metal oxidant is reduced by graphene. The crosslinking agent can enhance the π-π interaction between graphene sheets and is conducive to forming a stable three-dimensional structure; the present invention uses a medium-strength oxidant to prepare graphene oxide, which can avoid excessive damage to the graphene structure. The conductivity after oxidation is significantly higher than that of ordinary graphene oxide, and the conductivity after reduction is also much higher than that of ordinary graphene oxide. In this way, after reduction, its mechanical strength is significantly improved due to its fewer structural defects, three-dimensionality and dispersed force. The graphite raw material used is ultrafine graphite powder, which determines that even if the oxidant has poor oxidizing property, the graphite powder can still be fully oxidized. The three-dimensional graphene / SiO composite material treated with laser has a large number of laser-etched holes, which can be more easily infiltrated by electrolyte, reduce resistivity and increase cycle life. The high mechanical strength, conductivity and wettability of graphene determine that this material can be coated on the current collector with a loading amount far exceeding that of the current market products, and the capacity per unit area can reach the commercially available products (loading amount of about 10mg / cm 2 )5-10 times.

[0127] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional graphene / SiO composite material, characterized in that: The following steps are involved: S1. Preparation of three-dimensional graphene oxide: mixing graphite, water, concentrated sulfuric acid and sodium vanadate, and then sequentially performing hydrothermal treatment, ultrasonic treatment and impurity removal to obtain a mixed dispersion, and finally drying to obtain three-dimensional graphene oxide; S2. Preparation of three-dimensional graphene / SiO composite materials: S21, mixing the three-dimensional graphene oxide, water, potassium sulfide and potassium ferrate to obtain a reduced three-dimensional graphene dispersion, and then stirring, ultrasonicating, standing and drying to obtain reduced three-dimensional graphene; S22, mixing the reduced three-dimensional graphene, SiO powder and water, and then performing ultrasound and drying to obtain a mixed material; S23, laser processing the mixed material to obtain a three-dimensional graphene / SiO composite material; The median particle size of the graphite is 4 μm to 8 μm.

2. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The mass ratio of graphite to sodium vanadate is 1:1-6.

3. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The hydrothermal temperature is 100°C to 160°C; The hydrothermal time is 2h~6h.

4. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The redox potential value of the mixed dispersion is below 150 mV.

5. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The mass ratio of the three-dimensional graphite oxide, potassium sulfide and potassium ferrate in step S21 is 1:3-6:2-9.

6. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The mass ratio of the reduced three-dimensional graphene to SiO powder is 1:2-5.

7. The method for preparing the three-dimensional graphene / SiO composite material according to claim 1, characterized in that: The output pulse width of the laser treatment is 500fs~600fs; The pulse frequency of the laser treatment is 0.9kHz~1.1kHz; The spot diameter of the laser treatment is 0.9 μm~1.1 μm; The scanning speed of the laser processing is 0.8 mm / s to 2.2 mm / s.

8. A three-dimensional graphene / SiO composite material, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the three-dimensional graphene / SiO composite material as claimed in claim 8 in the preparation of electrode materials.

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