A method for preparing expanded graphite / silver composite materials by microwave expansion

Abstract

The present invention belongs to the field of preparation of functional composite materials, and particularly relates to a method for preparing expanded graphite / silver composite materials by microwave expansion. The method comprises the following steps: soaking graphite in an acid solution for oxidation treatment and heating, then washing the graphite with deionized water until the solution is neutral to obtain acid-treated graphite; mixing the acid-treated graphite with an AgNO3 solution, stirring evenly and then performing ultrasonic treatment to make the AgNO3 solution uniformly infiltrate the graphite, subjecting the mixture to freeze-drying treatment, placing the treated material under an infrared lamp for baking, performing microwave expansion treatment on the baked mixture, cooling the product after microwave expansion treatment, and performing pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material is obtained. The product obtained by the method of the present invention has a relatively high specific surface area and excellent electrical conductivity.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of functional composite materials, and particularly relates to a method for preparing expanded graphite / silver composite materials by microwave expansion. Background Art

[0002] Expanded graphite, as a new type of functional carbon material, is a kind of loose and porous worm-like substance obtained by processes such as intercalation, water washing, drying, and high-temperature expansion of natural graphite flakes. It not only has the excellent properties of natural graphite itself such as resistance to heat and cold, corrosion resistance, and self-lubrication, but also exhibits characteristics such as softness, compression resilience, adsorption, ecological environment compatibility, and biocompatibility that natural graphite does not have.

[0003] Although significant progress has been made in the preparation methods of expanded graphite, there are still some defects in the existing preparation methods. For example, the electrochemical method requires complex electrolysis equipment and operations, has a high cost, and consumes a large amount of electric energy during the preparation process, increasing the production cost. The mixed liquid phase method, although the reaction process is simple and the reaction speed is fast, the formed product has poor stability and is prone to structural changes during subsequent processing. With the rapid development of industries such as new energy, environmental protection, and electronic information, the demand for high-performance graphite materials is increasing day by day. Due to its unique structural and performance advantages, expanded graphite has broad application prospects in these fields. However, the limitations of the existing preparation methods restrict the further development and application of expanded graphite. Therefore, developing a preparation method of expanded graphite that can overcome the defects of the existing technology and achieve high conductivity and specific surface area is of great significance for promoting the upgrading and development of the graphite material industry. Summary of the Invention

[0004] The present invention provides a method for preparing expanded graphite / silver composite materials. The method is to acid-treat graphite, then mix it with silver nitrate solution, and use microwave expansion technology to synchronously process to obtain a composite material of expanded graphite and silver. The obtained product has a high specific surface area and excellent conductivity.

[0005] The technical solution provided by the present invention is as follows:

[0006] A method for preparing expanded graphite / silver composite materials by microwave expansion, comprising the following steps: soaking graphite in an acid solution for oxidation treatment and heating, then washing the graphite with deionized water until the solution is neutral to obtain acid-treated graphite; mixing the acid-treated graphite with AgNO3 solution, stirring evenly and then performing ultrasonic treatment to make the AgNO3 solution uniformly infiltrate the graphite, freeze-drying the mixture, baking the treated material under an infrared lamp, performing microwave expansion treatment on the baked mixture, cooling the product after microwave expansion treatment, and performing pyrolysis in a tubular furnace, and cooling to obtain expanded graphite / silver composite materials.

[0007] Further, the acid-treated graphite is mixed with an AgNO3 solution, stirred evenly, and then subjected to ultrasonic treatment. After ultrasonic treatment, the mixture is subjected to high-speed shear grinding with a colloid mill for 1 to 2 h, and the rotational speed of the colloid mill is 3500 to 5000 r / min.

[0008] Further, the pyrolysis is carried out by putting the cooled microwave-expanded product into a tubular furnace, heating it to 850 to 1000 °C at a heating rate of 6 to 9 °C / min under the protection of nitrogen, and carrying out constant-temperature pyrolysis for 1 to 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0009] Further, the acid solution is one or more of concentrated sulfuric acid, concentrated nitric acid, and perchloric acid, and the concentration of the acid solution is 70% v / v or more.

[0010] Further, the heating concentration for soaking graphite in the acid solution for oxidation treatment and heating is 100 to 200 °C, and the heating time is 10 min to 2 h.

[0011] Further, the mass ratio of silver ions in the AgNO3 solution to graphite is 2:3 to 5; the AgNO3 solution is prepared by dissolving AgNO3 in a water / ethanol mixed solution, and the volume ratio of water to ethanol is 2:1 to 3.

[0012] The baking temperature is 60 to 80 °C and the time is 2 h.

[0013] The microwave expansion treatment is intermittent microwave treatment. The power of the microwave treatment is 600 to 1000 W, the microwave treatment is 20 to 30 s, and the pause is 10 to 20 s. The total treatment time is 3 to 5 min.

[0014] A method for preparing an expanded graphite / silver composite material by microwave expansion includes the following steps:

[0015] The present invention also provides an expanded graphite / silver composite material prepared by the above method.

[0016] The present invention also provides an application of the above expanded graphite / silver composite material in the preparation of electrochemical energy storage devices.

[0017] Beneficial effects

[0018] The acid treatment method can effectively remove impurities and oxides in graphite, improve its purity, exfoliate graphite lamellae, increase its specific surface area and active sites, thereby helping to reduce electron scattering and traps in graphite and improve its electrical conductivity. The introduction of metal ions can affect the charge transfer in graphite, thus improving its electrical conductivity. Metal ions usually have a higher electrical conductivity than carbon, so their presence can form more conductive channels and promote the transport of electrons in graphite. After introducing metal ions, the thermal stability of graphite can also be enhanced, which can extend the service life of graphite.

[0019] The microwave expansion method is based on the conductive properties of graphite. Using the magnetic waves generated by a magnetron, a strong eddy current is generated inside it, and then the expandable graphite is rapidly heated from the inside out. This heating method enables the polar molecules between graphite layers to interact with microwaves, causing the compounds inserted between graphite layers to decompose and vaporize rapidly, forming expanded graphite. Due to the rapid and uniform heating, the internal structure of graphite is maintained, so its electrical conductivity is retained. Microwave expansion treatment can optimize the internal structure of graphite, making it have more conductive channels and smaller resistance, thereby improving the conduction efficiency. Microwave expansion treatment causes graphite to exfoliate along the C-axis, forming expanded graphite. This structural change makes graphite have more pores and a larger specific surface area, thus increasing the electron transport path and contact area in graphite. At the same time, the expansion treatment can also remove some impurities and defects in graphite, further reducing the resistance and improving the conduction efficiency.

[0020] After treating graphite by the method described in the present invention through acid treatment, silver particles are synchronously introduced during the microwave expansion process. By synchronously performing microwave expansion and deposition of silver particles, the preparation process of the composite material is simplified, and the complex steps in the traditional chemical reduction process are reduced. A rotating tray is used during the microwave expansion process to ensure the uniformity of the microwave field distribution and improve the uniformity and consistency of the composite powder material. The expanded graphite / silver composite material obtained by the method described in the present invention has a high specific surface area, excellent electrical conductivity and good catalytic activity, and can be widely used in fields such as electrochemical energy storage devices (such as supercapacitors, batteries), conductive coatings, conductive inks, and catalyst carriers. Description of the Drawings

[0021] Figure 1 SEM image of the expanded graphite / silver composite material obtained in Example 1 of the present invention.

[0022] Figure 2 SEM image of the expanded graphite / silver composite material obtained in Example 2 of the present invention. Detailed Description of the Invention

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1

[0025] A method for preparing expanded graphite / silver composite materials by microwave expansion includes the following steps:

[0026] 1. Graphite acid treatment: Immerse graphite in an acid solution for oxidation treatment and heating. The heating temperature is 150 °C and the heating time is 1 h to increase the graphite layer spacing and endow it with expansion characteristics. Then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite. The acid solution is a mixture of concentrated nitric acid and perchloric acid, and the volume ratio of concentrated nitric acid (70% v / v) to perchloric acid (70% v / v) is 2:1.

[0027] 2. Prepare silver nitrate (AgNO3) solution. Dissolve AgNO3 in a water / ethanol mixed solution with a volume ratio of water to ethanol of 1:1. Adjust the concentration of AgNO3 so that the mass ratio of silver ions to graphite is 1:2.

[0028] 3. Mix the acid-treated graphite with the AgNO3 solution, stir evenly and then perform ultrasonic treatment. After ultrasonic treatment, grind the mixture with a colloid mill at a high speed for 1 h. The rotation speed of the colloid mill is 3500 r / min to make the AgNO3 solution evenly infiltrate the graphite. Perform freeze-drying treatment on the mixture, and place the treated material under an infrared lamp for baking. The baking temperature is controlled at 70 °C and the time is 2 hours to ensure that the solvent in the solution is fully evaporated.

[0029] 4. Microwave expansion treatment: Transfer the baked mixture to a microwave oven for expansion treatment. The power of the microwave oven is set to 800 W and the treatment time is 4 minutes. The microwave expansion treatment is intermittent microwave treatment. The power of the microwave treatment is 800 W, the microwave treatment is 20 s, and then pause for 1 s. The total treatment time is 4 min. Use a rotating tray to keep the sample evenly heated, ensuring the rapid expansion of graphite and the uniform distribution of Ag during the microwave heating process. During the expansion process, AgNO3 is reduced to form metallic silver particles, which are distributed on the surface or inside of the expanded graphite.

[0030] 5. Cool the product after microwave expansion treatment and conduct pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material (EG / Ag) is obtained. The pyrolysis is to put the cooled microwave-expanded product into a tube furnace, heat it up to 900 °C at a heating rate of 8 °C / min under the protection of nitrogen, and carry out isothermal pyrolysis for 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0031] Example 2

[0032] A method for preparing an expanded graphite / silver composite material by microwave expansion, comprising the following steps:

[0033] 1. Graphite acid treatment: Immerse graphite in an acid solution for oxidation treatment and heating. The heating temperature is 150 °C and the heating time is 1 h to increase the graphite layer spacing and make it have expansion characteristics. Then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite. The acid solution is concentrated nitric acid (70% v / v).

[0034] 2. Prepare a silver nitrate (AgNO3) solution. Dissolve AgNO3 in a water / ethanol mixed solution with a volume ratio of water to ethanol of 1:1. Adjust the concentration of AgNO3 so that the mass ratio of silver ions to graphite is 1:2.

[0035] 3. Mix the acid-treated graphite with the AgNO3 solution, stir evenly and then carry out ultrasonic treatment. After ultrasonic treatment, grind the mixture with a colloid mill at a high speed for 1 h. The rotation speed of the colloid mill is 3500 r / min to make the AgNO3 solution uniformly infiltrate the graphite. Carry out freeze-drying treatment on the mixture, place the treated material under an infrared lamp for baking, control the baking temperature at 70 °C and the time at 2 hours to ensure that the solvent in the solution is fully evaporated.

[0036] 4. Microwave expansion treatment: Transfer the baked mixture to a microwave oven for expansion treatment. The power of the microwave oven is set at 800 W and the treatment time is 4 minutes. The microwave expansion treatment is intermittent microwave treatment. The power of the microwave treatment is 800 W, the microwave treatment is for 20 s, and then pause for 1 s. The total treatment time is 4 min. Use a rotating tray to keep the sample heated evenly to ensure the rapid expansion of graphite and the uniform distribution of Ag during the microwave heating process. During the expansion process, AgNO3 is reduced to form metal silver particles, which are distributed on the surface or inside of the expanded graphite.

[0037] 5. Cool the product after microwave expansion treatment and conduct pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material (EG / Ag) is obtained. The pyrolysis is to put the cooled microwave-expanded product into a tube furnace, heat it up to 900 °C at a heating rate of 8 °C / min under the protection of nitrogen, and carry out isothermal pyrolysis for 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0038] Example 3

[0039] A method for preparing expanded graphite / silver composite materials by microwave expansion, comprising the following steps:

[0040] 1. Graphite acid treatment: Immerse graphite in an acid solution for oxidation treatment and heating. The heating temperature is 150 °C and the heating time is 1 h to increase the graphite layer spacing and endow it with expansion characteristics. Then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite. The acid solution is concentrated sulfuric acid (70% v / v).

[0041] 2. Prepare a silver nitrate (AgNO3) solution by dissolving AgNO3 in a water / ethanol mixed solution with a volume ratio of water to ethanol of 1:1. Adjust the concentration of AgNO3 so that the mass ratio of silver ions to graphite is 1:2.

[0042] 3. Mix the acid-treated graphite with the AgNO3 solution, stir evenly and then perform ultrasonic treatment. After ultrasonic treatment, grind the mixture with a colloid mill at a high speed for 1 h. The rotation speed of the colloid mill is 3500 r / min to uniformly infiltrate the AgNO3 solution into the graphite. Freeze-dry the mixture, and place the treated material under an infrared lamp for baking. The baking temperature is controlled at 70 °C and the time is 2 hours to ensure that the solvent in the solution is fully evaporated.

[0043] 4. Microwave expansion treatment: Transfer the baked mixture to a microwave oven for expansion treatment. The power of the microwave oven is set to 800 W and the treatment time is 4 minutes. The microwave expansion treatment is intermittent microwave treatment. The power of the microwave treatment is 800 W, the microwave treatment is for 20 s, and then pause for 1 s. The total treatment time is 4 min. Use a rotating tray to keep the sample heated evenly to ensure rapid expansion of graphite and uniform distribution of Ag during the microwave heating process. During the expansion process, AgNO3 is reduced to form metal silver particles, which are distributed on the surface or inside of the expanded graphite.

[0044] 5. Cool the product after microwave expansion treatment and perform pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material (EG / Ag) is obtained. The pyrolysis is to put the cooled microwave-expanded product into a tube furnace, heat it up to 900 °C at a heating rate of 8 °C / min under the protection of nitrogen, and keep it pyrolyzed at a constant temperature for 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0045] Example 4

[0046] A method for preparing expanded graphite / silver composite materials by microwave expansion, comprising the following steps:

[0047] 1. Graphite acid treatment: Immerse graphite in an acid solution for oxidation treatment and heating. The heating temperature is 150 °C and the heating time is 1 h to increase the graphite layer spacing and endow it with expansion characteristics. Then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite. The acid solution is perchloric acid (70% v / v).

[0048] 2. Prepare a silver nitrate (AgNO3) solution by dissolving AgNO3 in a water / ethanol mixed solution with a volume ratio of water to ethanol of 1:1. Adjust the concentration of AgNO3 so that the mass ratio of silver ions to graphite is 1:2.

[0049] 3. Mix the acid-treated graphite with the AgNO3 solution, stir evenly and then perform ultrasonic treatment. After ultrasonic treatment, grind the mixture with a colloid mill at a high speed for 1 h. The rotation speed of the colloid mill is 3500 r / min to uniformly infiltrate the AgNO3 solution into the graphite. Freeze-dry the mixture and bake the treated material under an infrared lamp. Control the baking temperature at 70 °C for 2 hours to ensure that the solvent in the solution is fully evaporated.

[0050] 4. Microwave expansion treatment: Transfer the baked mixture to a microwave oven for expansion treatment. The power of the microwave oven is set at 800 W and the treatment time is 4 minutes. The microwave expansion treatment is intermittent microwave treatment. The power of the microwave treatment is 800 W, the microwave treatment is for 20 s, and then pause for 1 s. The total treatment time is 4 min. Use a rotating tray to keep the sample heated evenly to ensure rapid expansion of graphite and uniform distribution of Ag during the microwave heating process. During the expansion process, AgNO3 is reduced to form metallic silver particles, which are distributed on the surface or inside of the expanded graphite.

[0051] 5. Cool the product after microwave expansion treatment and perform pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material (EG / Ag) is obtained. The pyrolysis is to put the cooled microwave-expanded product into a tube furnace, heat it up to 900 °C at a heating rate of 8 °C / min under the protection of nitrogen, and carry out constant-temperature pyrolysis for 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0052] Example 5

[0053] A method for preparing an expanded graphite / silver composite material by microwave expansion, comprising the following steps:

[0054] 1. Graphite acid treatment: Immerse graphite in an acid solution for oxidation treatment and heating. The heating temperature is 150 °C and the heating time is 1 h to increase the graphite layer spacing and endow it with expansion characteristics. Then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite. The acid solution is a mixture of concentrated nitric acid and perchloric acid, and the volume ratio of concentrated nitric acid (70% v / v) to perchloric acid (70% v / v) is 1:2.

[0055] 2. Prepare a silver nitrate (AgNO3) solution by dissolving AgNO3 in a water / ethanol mixed solution with a volume ratio of water to ethanol of 1:1. Adjust the concentration of AgNO3 so that the mass ratio of silver ions to graphite is 1:2.

[0056] 3. Mix the acid-treated graphite with the AgNO3 solution, stir evenly and then perform ultrasonic treatment. After ultrasonic treatment, grind the mixture with a colloid mill at a high speed for 1 h. The rotation speed of the colloid mill is 3500 r / min to make the AgNO3 solution evenly infiltrate the graphite. Freeze-dry the mixture, and place the treated material under an infrared lamp for baking. The baking temperature is controlled at 70 °C for 2 hours to ensure that the solvent in the solution is fully evaporated.

[0057] 4. Microwave expansion treatment: Transfer the baked mixture to a microwave oven for expansion treatment. The power of the microwave oven is set at 800 W and the treatment time is 4 minutes. The microwave expansion treatment is intermittent microwave treatment with a microwave power of 800 W. Microwave treatment for 20 s and pause for 1 s, with a total treatment time of 4 min. Use a rotating tray to keep the sample evenly heated to ensure rapid expansion of graphite and uniform distribution of Ag during the microwave heating process. During the expansion process, AgNO3 is reduced to form metal silver particles, which are distributed on the surface or inside of the expanded graphite.

[0058] 5. Cool the product after microwave expansion treatment and perform pyrolysis in a tube furnace. After cooling, an expanded graphite / silver composite material (EG / Ag) is obtained. The pyrolysis is to put the cooled microwave-expanded product into a tube furnace, heat it up to 900 °C at a heating rate of 8 °C / min under the protection of nitrogen, and keep it pyrolyzed at a constant temperature for 2 h. After cooling, an expanded graphite / silver composite material is obtained.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that the graphite is not acid-treated, and the other conditions remain unchanged.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that the AgNO3 solution is not used, and the other conditions remain unchanged.

[0063] Comparative Example 3

[0064] In this comparative example, compared with Example 1, the difference lies in that ultrasonic treatment was not carried out, and the remaining conditions remained unchanged.

[0065] Comparative Example 4

[0066] In this comparative example, compared with Example 1, the difference lies in that colloid mill treatment was not adopted, and the remaining conditions remained unchanged.

[0067] Comparative Example 5

[0068] In this comparative example, compared with Example 1, the difference lies in that freeze-drying treatment was not adopted, and the remaining conditions remained unchanged.

[0069] Comparative Example 6

[0070] In this comparative example, compared with Example 1, the difference lies in that microwave expansion treatment was not adopted, and the remaining conditions remained unchanged.

[0071] Comparative Example 7

[0072] In this comparative example, compared with Example 1, the difference lies in that the microwave expansion treatment was carried out continuously, and intermittent microwave treatment was not adopted, and the remaining conditions remained unchanged.

[0073] Comparative Example 8

[0074] In this comparative example, compared with Example 1, the difference lies in that pyrolysis in a tubular furnace was not adopted, and the remaining conditions remained unchanged.

[0075] Test Example 1

[0076] The conductivity of the products prepared in the examples and comparative examples was tested.

[0077]

[0078] As can be seen from the above results, in the present invention, by acid-treating graphite and adding silver ions, the introduction of metal ions can affect the charge transfer in graphite, thereby improving its conductivity. Metal ions generally have higher conductivity than carbon, so their presence can form more conductive channels and promote the transmission of electrons in graphite. Then, microwave expansion treatment is carried out. By utilizing the action of high-energy microwaves, graphite is expanded. Appropriate expansion can widen the interlayer spacing of graphite, thereby improving its conductivity.

[0079] Test Example 2

[0080] The products prepared in the examples and comparative examples were subjected to performance tests. The specific test methods and test results are as follows:

[0081] The products obtained from each example or comparative example were respectively mixed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 8:1:1, and N-methylpyrrolidone was added. After grinding evenly, it was coated on the surface of a copper foil with a thickness of 6 μm, and after drying, it was used as a working electrode;

[0082] A lithium metal sheet, a working electrode, a PP separator, and an electrolyte of 1 mol / L LiPF6 were assembled into a CR2032 coin cell, and the cell assembly was carried out in a glove box filled with argon for protection;

[0083] The above coin cells were tested for charge-discharge and cycling performance using a Blue Electric test system (LAND CT2001A). The voltage test range was 0.01 - 3.0 V. For the products of the same example or comparative example, multiple groups of tests were carried out, and the charge-discharge current densities were adjusted to 0.1C and 0.3C respectively. After 40 charge-discharge cycles, the capacity retention rates of each cell were tested. The specific test results are shown in the following table:

[0084]

[0085] From the above results, it can be seen that the products obtained by the method of the present invention have good capacity retention rates during charge and discharge. In particular, when the charging rate is increased, the relative decrease in its capacity retention rate is small, which can meet the requirements of high-rate charge and discharge.

[0086] Test Example 3

[0087] The specific surface areas of the products in the examples and comparative examples were tested according to the test method in the standard GB / T - 24533 - 2019 "Graphite Anode Materials for Lithium-Ion Batteries", and the OI value and layer spacing of its powder were tested by XRD; the test results are shown in the following table:

[0088]

[0089]

[0090] As can be seen from the above table, the expanded graphite / silver composite material prepared by the method of the present invention has good specific surface area and layer spacing.

[0091] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered within the protection scope of the present invention.

[0092] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments only. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for preparing expanded graphite / silver composite materials by microwave expansion, characterized in that, It includes the following steps: Immerse graphite in an acid solution for oxidation treatment and heating, then wash the graphite with deionized water until the solution is neutral to obtain acid-treated graphite; Mix the acid-treated graphite with an AgNO₃ solution, stir evenly and then perform ultrasonic treatment. After ultrasonic treatment, subject the mixture to high-speed shear grinding with a colloid mill for 1 - 2 h, and the rotational speed of the colloid mill is 3500 - 5000 r / min to make the AgNO₃ solution uniformly infiltrate the graphite. Freeze-dry the mixture, place the treated material under an infrared lamp for baking, subject the baked mixture to microwave expansion treatment, cool the product after microwave expansion treatment, and perform pyrolysis in a tubular furnace. After cooling, an expanded graphite / silver composite material is obtained; The pyrolysis is to put the cooled microwave-expanded product into a tubular furnace, heat it at a heating rate of 6 - 9 °C / min under the protection of nitrogen to 850 - 1000 °C, and keep it at a constant temperature for pyrolysis for 1 - 2 h. After cooling, an expanded graphite / silver composite material is obtained; The microwave expansion treatment is intermittent microwave treatment. The power of microwave treatment is 600 - 1000 W, microwave treatment is carried out for 20 - 30 s, and then paused for 10 - 20 s. The total treatment time is 3 - 5 min.

2. The method for preparing expanded graphite / silver composite material by microwave expansion according to claim 1, characterized in that The acid solution is one or more of concentrated sulfuric acid, concentrated nitric acid, and perchloric acid, and the concentration of the acid solution is 70% v / v or more.

3. The method for preparing an expanded graphite / silver composite material by microwave expansion according to claim 1, characterized in that, The heating temperature for immersing graphite in the acid solution for oxidation treatment and heating is 100 - 200 °C, and the heating time is 10 min - 2 h.

4. The method for preparing an expanded graphite / silver composite material by microwave expansion according to claim 1, characterized in that, The mass ratio of silver ions in the AgNO₃ solution to graphite is 2:3 - 5; The AgNO₃ solution is prepared by dissolving AgNO₃ in a water / ethanol mixed solution, and the volume ratio of water to ethanol is 2:1 - 3.

5. The method for preparing expanded graphite / silver composite material by microwave expansion according to claim 1, characterized in that, The baking temperature is 60 - 80 °C, and the time is 2 h.

6. An expanded graphite / silver composite material, characterized in that, It is prepared by the method according to any one of claims 1 - 5.

7. Use of the expanded graphite / silver composite material according to claim 6 in the preparation of an electrochemical energy storage device.

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