阅读说明：本技术 一种无硫膨胀石墨的电化学制备方法 (Electrochemical preparation method of sulfur-free expanded graphite ) 是由 贺君 袁梦 武振兴 刘光武 崔恩铭 任浩冬 于 2021-10-14 设计创作，主要内容包括：本发明公开了一种无硫膨胀石墨的电化学制备方法,包括如下步骤：对天然鳞片石墨进行电化学氧化插层反应制备无硫可膨胀石墨,其中电化学氧化插层反应的电解液为高氯酸钠和草酸的混合水溶液；然后对上述无硫可膨胀石墨进行膨化处理即可得到无硫膨胀石墨。本发明提供的无硫可膨胀石墨具有良好的可膨胀特性,其制备的无硫膨胀石墨的膨胀容积为260～290mL/g。本发明能充分利用电能,实现天然鳞片石墨常温条件下的电化学氧化插层,本发明以草酸和高氯酸钠为电解液,其为无毒无害的环境友好型电解液,可循环使用,无插层废液的产生,从源头上避免危险废物的产生,消除了环境危害。(The invention discloses an electrochemical preparation method of sulfur-free expanded graphite, which comprises the following steps: carrying out electrochemical oxidation intercalation reaction on natural flake graphite to prepare sulfur-free expandable graphite, wherein electrolyte of the electrochemical oxidation intercalation reaction is mixed aqueous solution of sodium perchlorate and oxalic acid; and then carrying out puffing treatment on the sulfur-free expandable graphite to obtain the sulfur-free expandable graphite. The sulfur-free expandable graphite provided by the invention has good expandable characteristics, and the expansion volume of the prepared sulfur-free expandable graphite is 260-290 mL/g. The invention can fully utilize electric energy to realize the electrochemical oxidation intercalation of natural crystalline flake graphite under the normal temperature condition, and the invention takes oxalic acid and sodium perchlorate as electrolyte, which is nontoxic and harmless environment-friendly electrolyte, can be recycled, does not generate intercalation waste liquid, avoids the generation of hazardous waste from the source and eliminates the environmental hazard.)

1. The electrochemical preparation method of the sulfur-free expanded graphite is characterized by comprising the following steps:

(1) carrying out electrochemical oxidation intercalation reaction on natural flake graphite to prepare sulfur-free expandable graphite, wherein electrolyte of the electrochemical oxidation intercalation reaction is mixed aqueous solution of sodium perchlorate and oxalic acid;

(2) and (2) carrying out expansion treatment on the sulfur-free expandable graphite obtained in the step (1).

2. The electrochemical preparation method according to claim 1, wherein the mass ratio of the natural crystalline flake graphite to the sodium perchlorate and oxalic acid in the electrolyte in step (1) is natural crystalline flake graphite: sodium perchlorate and oxalic acid are 1: 5-8: 0.5-3.5.

3. The electrochemical preparation method according to claim 1, wherein in the step (1), the electrochemical oxidation intercalation reaction is a constant current reaction, and the constant current is 25-65 mA/cm²。

4. The electrochemical preparation method according to claim 3, wherein the reaction time of the electrochemical oxidation intercalation reaction is 40-100 min.

5. The electrochemical preparation method according to claim 1, wherein in step (1), the anode of the electrochemical oxidation intercalation reaction is a composite anode of stainless steel and natural crystalline flake graphite, and the cathode of the electrochemical oxidation intercalation reaction is a stainless steel double cathode.

6. The electrochemical preparation method of claim 1, wherein the step (1) further comprises post-treatment, wherein the post-treatment comprises washing, suction filtration and drying;

preferably, the washing is carried out until the pH value of the filtrate is 5-7.

7. The electrochemical production method according to claim 1, wherein the puffing process in the step (2) is a microwave puffing process;

preferably, the power of the microwave is 700-900W;

preferably, the time length of the puffing treatment is 10-20 s.

8. Sulfur-free expanded graphite obtainable by the electrochemical preparation process according to any one of claims 1 to 7.

9. The sulfur-free expanded graphite according to claim 8, wherein the expanded volume of the sulfur-free expanded graphite is 260 to 290 mL/g.

Technical Field

The invention relates to the technical field of expanded graphite preparation, in particular to an electrochemical preparation method of sulfur-free expanded graphite.

Background

Expanded graphite was first discovered in 1841 by Shafautl in germany when immersing graphite in concentrated sulfuric acid and concentrated nitric acid, and the expanded graphite sealing material was first patented by united states co-carbonization until 1963 and was commercially produced since 1968.

Graphite crystals are a typical layered structure carbon material, and other heterogeneous particles such as atoms, molecules, ions or even atomic groups are physically or chemically inserted into the graphite layers of the crystal to form a new layered compound, which is called a graphite intercalation compound. Up to now, more than 200 kinds of graphite intercalation compounds have been found. Some of these graphite intercalation compounds (expandable graphite) are capable of expanding rapidly at high temperatures to form expanded graphite which is vermiform.

In the preparation method of the expanded graphite, a traditional chemical oxidation method is mostly adopted, not only high-temperature conditions are required, but also a large amount of strong acid and strong oxidant are required to be used as an intercalation agent and an oxidant, so a large amount of waste liquid is generated in the preparation and production processes, and a large amount of waste gas is generated to pollute air and cause great harm to the health of operators in the process of producing the expanded graphite by high-temperature or microwave puffing of the expandable graphite. People hope to explore a safe and environment-friendly preparation method through technical innovation, because natural crystalline flake graphite has excellent conductivity, an electrochemical method becomes a potential method for preparing expandable graphite, the electrochemical method can fully utilize electric energy to oxidize the natural crystalline flake graphite, the opening of the edge of a graphite layer is realized, and then an intercalation agent is adopted to insert the opened graphite layer to realize the preparation of the expandable graphite. The process reduces the addition of strong acid and strong oxidant, and is an excellent and new method for preparing the expanded graphite. Mixing sulfuric acid and acetic acid to prepare electrolyte by people of Shanghai et al, wherein the volume fraction of the sulfuric acid in the electrolyte is controlled to be 40-80%, and the current density is 15-20 mA/cm²The reaction time is 8-12h, the puffing temperature is 600-800 ℃, and the expanded graphite with the expansion volume of 200-300 mL/g is obtained. Kang F et al use natural crystalline flake graphite as an anode and platinum gold plate as a cathode, and the electrolyte uses 98-100% formic acid by mass and has a current density of 10mA/cm²And the electrolysis time is 10 h. And washing with water after treatment, drying at 60-70 ℃ for 1h, and performing swelling treatment, wherein the swelling volume is 270 mL/g. Yangxiang et al use potassium permanganate as oxidation medium to prepare expanded graphite, and obtain the appropriate conditions for preparing expanded graphite by electrolyzing sulfuric acid and potassium permanganate: h₂SO₄(90％):KMnO₄Adding 0.1g of graphite into each milliliter of electrolyte according to the mass ratio of 22:1, wherein the current density is 22-25 mA/cm²And electrolyzing for 5 hours at room temperature to obtain the expanded graphite, wherein the expanded graphite is expanded at about 800 ℃, and the measured expansion volume is 248 mL/g. Yangyongqing et al use acid-proof stainless steel plate and graphite plate as polar plates, respectively adopt 50-80% sulfuric acid solution and 25-40% nitric acid solution, and current density is 50-500 mA/cm²And controlling the oxidation time to be about 2-8 h according to the weight of the graphite, and treating the flake graphite with about 80 meshes to obtain the expanded volume of 200 mL/g. H for Cheng-G₂SO₄And H₃PO₄As electrolyte, adding small amount of oxidant K₂Cr₂O₇The anode and the cathode are made of stainless steel plates and assist ultrasonic oscillation to prepare the expandable graphite. The results show that: at V (H)₂SO₄):V(H₃PO₄) 1:1, m (graphite) 1:0.02, current density 20mA/cm²And under the condition of 3h of electrolysis, the expansion volume of the expanded graphite obtained by the ultrasonic oscillation assisted by electrochemical oxidation can reach 350 mL/g. Zhou Jiang et al mix perchloric acid and glacial acetic acid, use this mixed acid as electrolyte, Ti metal sheet is regarded as negative and positive plate. The optimal preparation conditions of the sulfur-free expandable graphite are as follows: the ratio of graphite (g) to electrolyte (ml) is 1:7, HClO₄(mL) with CH₃(COOH ml) volume ratio of 4:1, current density of 0.06A/cm²The reaction time is 60min, and the mass fraction of the electrolyte is 70%. The expansion volume of the prepared sulfur-free expandable graphite is 150 mL/g.

Therefore, in the beginning of research on the preparation of the expanded graphite by an electrochemical method, sulfuric acid is mostly used as an oxidation intercalation substance, and the prepared expanded graphite has high sulfur content and great harm to the environment. Meanwhile, some of the electric energy generating device can also be added with oxidants such as potassium dichromate or potassium permanganate, so that the electric energy oxidation effect is not fully exerted, and heavy metal ions can be generated to harm the environment. Later, research on the preparation of sulfur-free expanded graphite has been carried out, and although sulfuric acid or sulfur-containing substances are not used, the sulfur-free expanded graphite is replaced by oxidized intercalation substances such as nitric acid, perchloric acid, glacial acetic acid and the like, which still cause the harm of nitrogen oxide, and the acids have strong volatility and also cause the harm to human bodies. In the background of the research, the invention mainly considers the preparation of the environment-friendly electrolyte which is non-volatile, non-sulfur, non-toxic and harmless.

Disclosure of Invention

In view of the above technical problems, the present invention aims to provide an electrochemical preparation method of sulfur-free expanded graphite, which does not require strong acid or strong oxidant containing heavy metals, is operated at room temperature and has a simple process, and can prepare sulfur-free expanded graphite having no sulfur, large expansion volume and good adsorption performance.

In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides a first aspect of a method for electrochemically preparing sulfur-free expanded graphite, which comprises the following steps:

(1) carrying out electrochemical oxidation intercalation reaction on natural flake graphite to prepare sulfur-free expandable graphite, wherein electrolyte of the electrochemical oxidation intercalation reaction is mixed aqueous solution of sodium perchlorate and oxalic acid;

(2) and (2) carrying out expansion treatment on the sulfur-free expandable graphite obtained in the step (1).

As a preferable embodiment, in the step (1), the mass ratio of the natural crystalline flake graphite to the sodium perchlorate and the oxalic acid in the electrolyte is natural crystalline flake graphite: sodium perchlorate: oxalic acid is 1: 5-8: 0.5-3.5.

In the technical scheme of the invention, the natural crystalline flake graphite: sodium perchlorate: when the mass ratio of the oxalic acid is 1: 5-8: 0.5-3.5, the prepared sulfur-free expanded graphite has the best expansion effect.

In a preferable embodiment, in the step (1), the electrochemical oxidation intercalation reaction is a constant current reaction, and the constant current is 25 to 65mA/cm²E.g. 25mA/cm²、30mA/cm²、35mA/cm²、40mA/cm²、45mA/cm²、50mA/cm²、55mA/cm²、60mA/cm²、65mA/cm²Or any constant current between them.

In a preferred embodiment, in step (1), the reaction time of the electrochemical oxidation intercalation reaction is 40-100 min, for example, 40min, 50min, 60min, 70min, 80min, 90min, 100min or any reaction time therebetween.

As a preferable embodiment, in step (1), the anode of the electrochemical oxidation intercalation reaction is a composite anode of stainless steel and natural flake graphite, and the cathode of the electrochemical oxidation intercalation reaction is a stainless steel double-cathode, and the double-cathodes are respectively disposed on two sides of the anode. The double-cathode mode is adopted, and double cathodes are respectively arranged on two sides of the composite anode, so that constant and stable current electric fields exist on two sides of the anode, and the effect of graphite oxidation intercalation is improved.

Further, the step (1) further comprises post-treatment, wherein the post-treatment comprises washing, suction filtration and drying, and the washing is carried out until the pH value of the filtrate is 5-7.

In a preferred embodiment, the puffing treatment in step (2) is microwave puffing treatment, and the power of the microwave is 700-900W, such as 700W, 750W, 800W, 850W, 900W or any power therebetween; the duration of the puffing treatment is 10-20 s.

The second aspect of the present invention provides sulfur-free expanded graphite obtained by the above-mentioned production method.

In the technical scheme of the invention, the expansion volume of the sulfur-free expanded graphite is 260-290 mL/g, such as 260mL/g, 265mL/g, 270mL/g, 275mL/g, 280mL/g, 285mL/g, 290mL/g or any expansion volume therebetween, wherein the calculation formula of the expansion volume is as follows: expanded volume (mL/g) volume of sulfur-free expanded graphite (mL)/mass of sulfur-free expandable graphite (g).

The technical scheme has the following advantages or beneficial effects:

1. the invention adopts the electrochemical method to prepare the sulfur-free expanded graphite, does not need high-temperature operation, has simple installation of the device, can be recycled for a plurality of times, fully utilizes electric energy to realize the electrochemical intercalation of the natural crystalline flake graphite, and has outstanding environmental benefit, economic benefit and social benefit. The prepared non-toxic and harmless environment-friendly electrolyte does not generate intercalation waste liquid, fundamentally avoids the generation of dangerous waste from the source and also fundamentally eliminates the environmental hazard.

2. The invention adopts the mixed solution of oxalic acid and sodium perchlorate as the electrolyte of the electrochemical preparation method, and the sodium perchlorate is used as the oxidation intercalation agent, under the action of the directional current, the opening of the edge of the graphite layer and the entering of the intercalation agent can be realized, while the oxalic acid is matched with the sodium perchlorate to generate a small amount of intercalation, and simultaneously the invention plays a role of reducing the corrosion of the electrolyte to the stainless steel electrode, if the oxalic acid is removed, the preparation of the sulfur-free expandable graphite can be still realized, but the corrosion can be caused to the reaction electrode. Therefore, the electrochemical method provided by the invention can be recycled, strong acid and strong oxidant containing heavy metal are not needed, no pollutants such as sulfur dioxide and nitrogen oxide are generated in the preparation process, no volatile gas is generated, the harm to human bodies is small, the operation is safe, the generation of dangerous waste is avoided from the source, and the harm to the environment is also eliminated fundamentally. The expanded graphite product prepared by the method does not contain sulfur, and the corrosion resistance of the expanded graphite is improved.

3. The sulfur-free expandable graphite prepared by the invention has no smoke, no irritant gas escaping, environmental protection and no pollution in the microwave expanding process, and the expansion volume of the prepared sulfur-free expandable graphite can reach 260-290 mL/g, so that the sulfur-free expandable graphite has a wide application prospect.

Drawings

FIG. 1 is a diagram showing an apparatus for producing sulfur-free expanded graphite in example 1 of the present invention.

Fig. 2 is an X-ray diffraction analysis (XRD) pattern of natural flake graphite, sulfur-free expandable graphite, and sulfur-free expanded graphite in example 1 of the present invention.

Fig. 3a is a Scanning Electron Microscope (SEM) image of natural flake graphite used in example 1 of the present invention.

FIG. 3b is a Scanning Electron Microscope (SEM) image of sulfur-free expandable graphite prepared in example 1 of the present invention.

FIG. 3c is a Scanning Electron Microscope (SEM) image of sulfur-free expanded graphite obtained in example 1 of the present invention.

FIG. 4a is an energy spectrum analysis (EDS) chart of natural flake graphite used in example 1 of the present invention.

FIG. 4b is an energy spectrum analysis (EDS) chart of the sulfur-free expandable graphite prepared in example 1 of the present invention.

FIG. 4c is an energy spectrum analysis (EDS) chart of the sulfur-free expanded graphite obtained in example 1 of the present invention.

FIG. 5 is a Fourier transform Infrared Spectroscopy (FTIR) plot of sulfur-free expandable graphite prepared in example 1 of the present invention.

Detailed Description

The following examples are only a part of the present invention, and not all of them. Thus, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention without making creative efforts, belong to the protection scope of the invention.

Example 1

The preparation process of the sulfur-free expanded graphite in the present example was as follows:

1. assembling electrodes and preparing electrochemical intercalation:

the device diagram is shown in figure 1: a direct current stabilized power supply 1 is used as an output device of constant current, and the positive electrode and the negative electrode of the direct current stabilized power supply are respectively connected with a positive electrode 7 and a negative electrode through leads 2. The anode 7 is a stainless steel plate-natural crystalline flake graphite composite anode, and 1.5g of natural crystalline flake graphite with the granularity of 32 meshes and the carbon content of 99.9 percent is uniformly coated around the stainless steel plate by a non-woven cloth bag and is placed in the middle. The cathode adopts a stainless steel plate and comprises a stainless steel plate 5 and a stainless steel plate 6 in a double-cathode mode, the stainless steel plate 5 and the stainless steel plate 6 are respectively arranged on two sides of the anode 7, the distance is 2.5cm, the two sides are equidistant and are just opposite to the anode plate, the length of the stainless steel plate in the anode 7 and the length of the stainless steel plate 5 and the stainless steel plate 6 in the double-cathode are 12mm, the width is 4mm, and the height is 80 mm.

2. Preparing chemical electrolyte for electrochemical intercalation of natural crystalline flake graphite:

the anode 7, the stainless steel plate 5 and the stainless steel plate 6 were placed in the electrolyte 4, and fixed with the position-limiting plate 3 according to the step 1. The electrolyte 4 was prepared by dissolving 10g of sodium perchlorate and 2g of oxalic acid in 100mL of deionized water and stirring to dissolve them sufficiently. Then the DC regulated power supply is regulated to 47mA/cm²The reaction time is 60min at normal temperature.

3. Treatment of flake graphite intercalation compounds

And washing the reacted flake graphite intercalation compound with water until the supernatant is clear, and then carrying out repeated suction filtration and dehydration to fully wash off acid liquor on the surface, wherein the pH value is about 5-7. And (3) putting the intercalated compound after suction filtration into an oven, drying at 80 ℃, and taking out the intercalated compound after complete drying to obtain a product, namely the sulfur-free expandable graphite prepared by an electrochemical method.

4. Measurement of expansion ratio of Sulfur-free Expandable graphite, i.e., expansion volume of Sulfur-free Expandable graphite

Weighing 0.3g of sulfur-free expandable graphite, placing the crucible into a microwave oven, operating for 15s at the power of 720W, taking out the crucible to obtain the sulfur-free expandable graphite, pouring the obtained sulfur-free expandable graphite into a measuring cylinder, slightly shaking to uniformly distribute the sulfur-free expandable graphite in the measuring cylinder, looking up the highest scale mark of the sulfur-free expandable graphite in the measuring cylinder, reading the volume of the sulfur-free expandable graphite, repeating the operation for three times, averaging the volume numbers read out three times, and calculating according to the formula of expanded volume (mL/g)/sample mass (g). The expansion ratio of the sulfur-free expandable graphite, namely the expansion volume of the sulfur-free expandable graphite, is 290mL/g, which proves that the sulfur-free expandable graphite prepared in the step 3 has good expandable characteristics.

Fig. 2 is an X-ray diffraction analysis chart of the natural crystalline flake graphite used in example 1, the prepared sulfur-free expandable graphite, and the sulfur-free expandable graphite, and it can be seen that two characteristic peaks corresponding to (002) and (004) crystal planes appear at 2 θ of 26.62 ° and 2 θ of 54.78 ° in the XRD spectrum of the natural crystalline flake graphite. Because the crystal face of the natural crystalline flake graphite is complete and the particles are regularly distributed, the diffraction peak intensity is large, the peak width is narrow, and the peak shape is sharp. The characteristic peaks of the sulfur-free expandable graphite appear at 26.58 ° 2 θ and 54.70 ° 2 θ, both shifted to the left, and the intensity of the diffraction peak is much smaller than that of the natural crystalline flake graphite, and the peak width is broadened. This is because the intercalation of natural crystalline flake graphite is oxidized and intercalated, resulting in increased interlayer spacing, destruction of original crystal structure, increased defects, and reduced crystallinity, and thus shift of characteristic peak. But the offset position is small, so that the original characteristic peak of the graphite is not damaged by the electrochemical oxidation intercalation reaction. The characteristic peaks of the sulfur-free expanded graphite appear at 26.64 degrees 2 theta and 54.78 degrees 2 theta, and the diffraction peak intensity of the sulfur-free expanded graphite is obviously smaller than that of natural crystalline flake graphite. This is because, in the process of preparing sulfur-free expanded graphite by microwave expansion of sulfur-free expandable graphite, the interlayer intercalates of sulfur-free expandable graphite are vaporized at high temperature and released along the C-axis, resulting in an increase in the graphite layer spacing. Because the graphite interlayer of the sulfur-free expandable graphite after the intercalation material is released does not contain other materials, the crystal structure of the sulfur-free expandable graphite is more complete than that of the sulfur-free expandable graphite.

Fig. 3a, b, c are field emission scanning electron microscope analysis diagrams of the natural crystalline flake graphite, the sulfur-free expandable graphite, and the sulfur-free expandable graphite used in example 1, respectively, and it is obvious that the natural crystalline flake graphite and the sulfur-free expandable graphite are both in lamellar structures, the natural crystalline flake graphite has flat surfaces and are arranged tightly between layers, and the separation between the sheets of the sulfur-free expandable graphite intercalated by electrochemical oxidation is obvious, which indicates that the graphite layers are fully opened, and the interlayer spacing is increased, so that under the interaction of current and electrolyte, the intermolecular force of the graphite layers is destroyed, and the intercalated substance enters the graphite layers and causes the change of the graphite layer structure. As can be seen from fig. 3C, the morphology of the sulfur-free expanded graphite is greatly changed, the original structure is destroyed, and the graphite is in a worm-like structure, because in the microwave heating process, the intercalation between the sulfur-free expandable graphite layers is vaporized to generate thrust, so that the graphite is rapidly expanded along the C axis, and thus the sulfur-free expanded graphite with larger volume is generated.

Fig. 4a, b, c are the energy spectrum analysis diagrams of the natural flake graphite, the sulfur-free expandable graphite, and the sulfur-free expanded graphite used in example 1, respectively, and the elemental compositions of each substance can be understood more intuitively, and fig. 4a shows that the carbon content of the natural flake graphite is almost close to 100%, indicating that the purity thereof is very high. Fig. 4b shows that the sulfur-free expandable graphite also contains O, Na, and Cl elements, because graphite layers and surfaces have oxygen-containing functional groups such as hydroxyl groups and carboxyl groups after being oxidized and intercalated, and because sodium perchlorate is used as an oxidizing agent, perchlorate is intercalated between the layers, so Na and Cl elements are contained, but the content is small, and C, O elements are mainly contained. Fig. 4C shows that the sulfur-free expanded graphite contains O, Cl elements in addition to C elements, which is different from sulfur-free expandable graphite in that Na elements are reduced because Na elements are extremely trace, and in that the intercalant is decomposed by heat during the high-temperature expansion of the sulfur-free expandable graphite and escapes from the graphite layers in the form of gas, so that only C, O, Cl elements are contained. As can be seen from the energy spectrum, the sulfur-free expanded graphite prepared by the electrochemical oxidation method does not contain other impurities and has very high purity.

FIG. 5 is a Fourier transform infrared spectrum of the sulfur-free expandable graphite of example 1, as seen at 630cm^-1、1130cm^-1、1635cm^-1、2360cm^-1And 3440cm^-1Has a significant absorption peak of 630cm^-1Is treated as an absorption peak generated by Cl-O bonds in sodium perchlorate serving as an intercalating agent, and is 1130cm^-1Is ClO in sodium perchlorate as an intercalant in a graphite intercalation compound₄ ^-The vibration causes, the peak can be seen, and the peak is sharp and has high strength, which indicates that the intercalation material has more content and good intercalation effect and is the main intercalation agent. 1635cm^-1Caused by-COOH vibration in oxalic acid as intercalation agent in graphite intercalation compound, and its peak is sharp but intensity is inferior to that of ClO₄ ^-Absorption peak of (A) toThe carboxyl in the amine oxalic acid also plays a role in intercalation, but the content of intercalation substances is less than that of sodium perchlorate. 2360cm^-1Two nearby splitting peaks are the residual CO part in the air₂And (4) forming. 3440cm^-1The absorption peak is formed by water molecules absorbed by the graphite intercalation compound, and the sample itself is not completely dried with trace moisture. The presence of peaks characteristic of each intercalant indicates successful intercalation of the intercalant into the graphite interlayer.

Example 2

In this example, the preparation process of the sulfur-free expanded graphite was as follows:

1. electrode assembly and electrochemical intercalation preparation as in example 1;

2. preparing chemical electrolyte for electrochemical intercalation of natural crystalline flake graphite:

the electrolyte in the embodiment is prepared by dissolving 12g of sodium perchlorate and 5.25g of oxalic acid in 100mL of deionized water, stirring to fully dissolve the sodium perchlorate and the oxalic acid, and the constant current of a direct current stabilized power supply is 65mA/cm²The reaction time at room temperature was 100min, as in example 1

3. Treatment of flake graphite intercalation compounds

The same as in example 1.

4. Determination of bulking rate of sulfur-free expandable graphite

Weighing 0.3g of sulfur-free expandable graphite, placing the crucible into a microwave oven, operating the microwave oven at 900W for 10s, taking out the crucible, pouring the obtained expanded graphite into a measuring cylinder, slightly shaking the measuring cylinder to uniformly distribute the expanded graphite in the measuring cylinder, looking up the highest scale mark of the expanded graphite in the measuring cylinder, reading the volume of the expanded graphite, repeating the operation for three times, averaging the volume numbers read out three times, and calculating according to the formula of expanded volume (mL/g) to sample mass (g). The expansion ratio of the sulfur-free expandable graphite is 275mL/g, which proves that the prepared sulfur-free expandable graphite prepared in the step 3 has good expandable characteristics.

Example 3

In this example, the preparation process of the sulfur-free expanded graphite was as follows:

1. electrode assembly and electrochemical intercalation preparation as in example 1;

2. preparing chemical electrolyte for electrochemical intercalation of natural crystalline flake graphite:

the electrolyte in this example was prepared by dissolving 7.5g of sodium perchlorate and 0.75g of oxalic acid in 100mL of deionized water, stirring and dissolving them thoroughly, and the constant current of a DC regulated power supply was 25mA/cm²The reaction time at room temperature was 40min, as in example 1.

3. Treatment of flake graphite intercalation compounds

The same as in example 1.

4. Measurement of expansion ratio of Sulfur-free Expandable graphite, i.e., expansion volume of Sulfur-free Expandable graphite

Weighing 0.3g of sulfur-free expandable graphite, placing the crucible into a microwave oven, operating the microwave oven at 700W for 20s, taking out the crucible, pouring the obtained sulfur-free expandable graphite into a measuring cylinder, slightly shaking to uniformly distribute the sulfur-free expandable graphite in the measuring cylinder, looking up the highest scale line of the sulfur-free expandable graphite in the measuring cylinder, reading the volume of the sulfur-free expandable graphite, repeating the operation for three times, averaging the volume numbers read out three times, and calculating according to the formula of expanded volume (mL/g)/sample mass (g). The expansion ratio (i.e., the expansion volume of the sulfur-free expandable graphite) of the sulfur-free expandable graphite was calculated to be 260mL/g, which confirmed that the sulfur-free expandable graphite prepared in step 3 had good expandable characteristics.

The above description is only for the preferred embodiment of the present invention and is not intended to limit the scope of the present invention, and all equivalent modifications made by the contents of the present specification and the drawings, or applied directly or indirectly to other related technical fields, are included in the scope of the present invention.