A method for preparing high expansion volume expanded graphite by activation or pretreatment

Abstract

The present application relates to the technical field of graphite material, and provides a method for preparing high-expansion-volume expanded graphite by activation or pretreatment. In the method, natural flake graphite, potassium permanganate, concentrated sulfuric acid and an activating agent are mixed to perform an oxidation intercalation reaction, and then high-expansion-volume expanded graphite is obtained by high-temperature expansion. Alternatively, in the method, natural flake graphite is pretreated by a pretreatment agent, and then an oxidation intercalation reaction and high-temperature expansion are performed to obtain high-expansion-volume expanded graphite. By activation or pretreatment, the method can improve the expansion volume of expanded graphite. In particular, when the pretreatment method is used, the method can prepare expanded graphite with significantly increased expansion volume on the basis of reduced use of oxidizing agent and intercalating agent, and the expansion effect is more significant.

Description

Technical Field

[0001] This invention relates to the field of graphite materials technology, and in particular to a method for preparing high-expansion volume expanded graphite by activation or pretreatment. Background Technology

[0002] Expanded graphite is a carbon material with high expansion volume obtained by oxidative intercalation of flake graphite. It has a loose and porous worm-like structure, good electrical and thermal conductivity, high chemical stability, and large specific surface area, and has broad application prospects in many fields.

[0003] The traditional method for preparing expanded graphite involves using chemical reagents such as concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide to oxidize and intercalate flake graphite, forming graphite with intercalation materials, which is called expanded graphite. At high temperatures, the intercalation materials of expanded graphite rapidly vaporize under high heat, and the resulting gas exerts a huge tensile force on the graphite flakes, causing the graphite flakes to open and form expanded graphite.

[0004] Currently, expanded graphite prepared by traditional methods has a low expansion volume. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing high-expansion-volume expanded graphite through activation or pretreatment. The expanded graphite prepared by the method of the present invention has a high expansion volume, and the operation steps are simple and the cost is low.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for preparing highly expanded volumetric graphite by activation includes the following steps:

[0008] Natural flake graphite, potassium permanganate, concentrated sulfuric acid, and an activator are mixed and subjected to an oxidative intercalation reaction to obtain expandable graphite; the activator is phosphoric acid, phosphate, or an organic solvent; the organic solvent is one or more of carboxylic acids and alcohols.

[0009] The expandable graphite is subjected to high-temperature expansion to obtain the high-expansion volume expanded graphite; the high-temperature expansion temperature is 800-900℃.

[0010] Preferably, the mass ratio of natural flake graphite to potassium permanganate is 1:(0.08-0.4); the volume ratio of natural flake graphite to concentrated sulfuric acid is 1g:(2-6)mL; when the activator is phosphoric acid or an organic solvent, the volume ratio of natural flake graphite to activator is 1g:(0.5-2)mL; when the activator is phosphate, the mass ratio of natural flake graphite to activator is 1:(1-4).

[0011] The concentration of the phosphoric acid is 83-88 wt%; the carboxylic acid is formic acid and / or acetic acid; the alcohol is ethanol; and the phosphate is dihydrogen phosphate.

[0012] Preferably, the mixing of natural flake graphite, potassium permanganate, concentrated sulfuric acid and activator includes: first mixing natural flake graphite and potassium permanganate and heating to 73-75°C, and then adding concentrated sulfuric acid and activator;

[0013] The oxidation intercalation reaction is carried out at a temperature of 75–80°C for 10–60 min.

[0014] Preferably, after the oxidation intercalation reaction, the resulting reaction solution is washed with water until the pH value is 3-7, then filtered and dried to obtain the expandable graphite; the drying temperature is 40-80℃ and the time is 2-5h.

[0015] Preferably, the high-temperature expansion time is 3 to 5 seconds.

[0016] The present invention also provides a method for preparing high-expansion volume expanded graphite through pretreatment, comprising the following steps:

[0017] Natural flake graphite is pretreated by immersing it in a pretreatment agent to obtain pretreated natural flake graphite; the pretreatment agent is phosphoric acid, phosphate solution, hot water or organic solvent; the temperature of the hot water is 60-90℃; the organic solvent is carboxylic acid or alcohol;

[0018] The pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid were mixed and subjected to an oxidation intercalation reaction to obtain expandable graphite.

[0019] The expandable graphite is subjected to high-temperature expansion to obtain the high-expansion volume expanded graphite; the high-temperature expansion temperature is 800-900℃.

[0020] Preferably, the pretreatment time is 1 to 4 hours.

[0021] Preferably, the mass ratio of the natural flake graphite to potassium permanganate is 1:(0.03-0.1); the volume ratio of the natural flake graphite to concentrated sulfuric acid is 1g:(1.5-4)mL.

[0022] The concentration of the phosphoric acid is 83-88 wt%; the concentration of the phosphate solution is 0.375-0.425 g / mL; the carboxylic acid is formic acid and / or acetic acid; the alcohol is ethanol; and the phosphate is dihydrogen phosphate.

[0023] Preferably, after the oxidation intercalation reaction, the resulting reaction solution is washed with water until the pH value is 3-7, then filtered and dried to obtain the expandable graphite; the drying temperature is 40-80℃ and the time is 2-5h.

[0024] Preferably, the high-temperature expansion time is 3 to 5 seconds.

[0025] This invention provides a method for preparing high-expansion-volume expanded graphite through activation, comprising the following steps: mixing natural flake graphite, potassium permanganate, concentrated sulfuric acid, and an activator to perform an oxidative intercalation reaction to obtain expandable graphite; wherein the activator is phosphoric acid, phosphate, or an organic solvent; wherein the organic solvent is one or more of carboxylic acids and alcohols; and subjecting the expandable graphite to high-temperature expansion to obtain the high-expansion-volume expanded graphite; wherein the high-temperature expansion temperature is 800–900°C. This invention, by adding an activator to the intercalator, utilizes the swelling effect of the activator to allow the graphite flakes to open more fully during the oxidative intercalation stage, enabling more intercalator to enter. Simultaneously, during the high-temperature expansion stage, the activator can protect the graphite carbon layer, reducing carbon loss at high temperatures, thereby increasing the impact force of the intercalator decomposition and vaporization on the flakes, thus preparing expanded graphite with increased expansion volume. Example results show that the average expansion volume of the expanded graphite obtained by this method reaches 400 mL / g.

[0026] This invention also provides a method for preparing high-expansion-volume expanded graphite through pretreatment, comprising the following steps: pretreating natural flake graphite by immersing it in a pretreatment agent to obtain pretreated natural flake graphite; the pretreatment agent is phosphoric acid, phosphate solution, hot water, or an organic solvent; the temperature of the hot water is 60–90°C; the organic solvent is a carboxylic acid or an alcohol; mixing the pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid to perform an oxidation intercalation reaction to obtain expandable graphite; and subjecting the expandable graphite to high-temperature expansion to obtain the high-expansion-volume expanded graphite; the high-temperature expansion temperature is 800–900°C. This invention uses a pretreatment agent with swelling properties to pretreat natural flake graphite, opening the flakes before subsequent oxidation intercalation. This method can prepare expanded graphite with a significantly increased expansion volume while reducing the amount of oxidant and intercalating agent used. The average expansion volume of the expanded graphite obtained by this method reaches 450 mL / g, demonstrating a more significant expansion effect. Furthermore, the pretreatment agent used in this method can be hot water, which is inexpensive and recyclable after use, thus solving the problems of high cost and environmental pollution associated with traditional preparation methods. Attached Figure Description

[0027] Figure 1 The XRD patterns of the expanded graphite prepared in Comparative Example 1 and the commercially available expanded graphite in Comparative Example 2 are shown.

[0028] Figure 2 SEM image of the expanded graphite prepared in Comparative Example 1;

[0029] Figure 3 Here is a SEM image of the expanded graphite prepared in Example 3;

[0030] Figure 4 SEM image of the expanded graphite prepared in Example 10;

[0031] Figure 5 This is a SEM image of commercially available expanded graphite. Detailed Implementation

[0032] This invention provides a method for preparing highly expanded volume graphite by activation (hereinafter referred to as the activation method), comprising the following steps:

[0033] Natural flake graphite, potassium permanganate, concentrated sulfuric acid, and an activator are mixed and subjected to an oxidative intercalation reaction to obtain expandable graphite; the activator is phosphoric acid, phosphate, or an organic solvent; the organic solvent is one or more of carboxylic acids and alcohols.

[0034] The expandable graphite is subjected to high-temperature expansion to obtain the high-expansion volume expanded graphite; the high-temperature expansion temperature is 800-900℃.

[0035] This invention involves mixing natural flake graphite, potassium permanganate, concentrated sulfuric acid, and an activator to perform an oxidative intercalation reaction to obtain expandable graphite. In this invention, the preferred mass ratio of natural flake graphite to potassium permanganate is 1:(0.08–0.4), more preferably 1:(0.08–0.2); the preferred molar ratio of natural flake graphite to concentrated sulfuric acid is 1 g:(2–6) mL, more preferably 1 g:(3–5) mL; the concentration of the concentrated sulfuric acid is specifically 98 wt%; in this invention, potassium permanganate is the oxidant, and the concentrated sulfuric acid is the intercalating agent.

[0036] In this invention, the activator is phosphoric acid, a phosphate, or an organic solvent; the organic solvent is one or more of a carboxylic acid and an alcohol; the concentration of the phosphoric acid is preferably 83-88 wt%, more preferably 85 wt%; the phosphate is dihydrogen phosphate, more preferably sodium dihydrogen phosphate; the carboxylic acid is preferably formic acid and / or acetic acid; the alcohol is preferably ethanol; in specific embodiments of this invention, the activator is most preferably phosphoric acid; when the activator is phosphoric acid or an organic solvent, the ratio of the amount of natural flake graphite to the activator is preferably 1 g:(0.5-2) mL, more preferably 1 g:(1-1.5) mL; when the activator is a phosphate, the mass ratio of the natural flake graphite to the activator is 1:(1-4), preferably 1:(2-3).

[0037] In this invention, the mixing of natural flake graphite, potassium permanganate, concentrated sulfuric acid and activator preferably includes: first mixing natural flake graphite and potassium permanganate and heating to 73-75°C, and then adding concentrated sulfuric acid and activator; this invention does not have special requirements on the order of adding concentrated sulfuric acid and activator, as long as they can be added immediately when the system temperature is reached.

[0038] In this invention, the temperature of the oxidation intercalation reaction is preferably 75-80°C, and the reaction time is preferably 10-60 min, more preferably 20-40 min; the oxidation intercalation reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 250-350 r / min, more preferably 290-330 r / min; in a specific embodiment of this invention, stirring is preferably started immediately after the addition of concentrated sulfuric acid and activator.

[0039] This invention enables natural flake graphite to undergo a full oxidation and intercalation process by controlling the system temperature and rotation speed. Potassium permanganate acts as an oxidant to open the graphite flakes, while the swelling effect of the activator helps the graphite flakes open more fully. More intercalating agent, sulfuric acid, is inserted into the graphite flakes to form graphite interlayer compounds. The system after the reaction is completed is a brownish-brown slurry.

[0040] In this invention, after the oxidation intercalation reaction, it is preferable to further wash the resulting reaction solution with water until the pH value is 3-7, preferably 6-7, and then filter and dry it to obtain the expandable graphite; this invention removes excess activator, oxidant and other impurities by washing with water; the drying temperature is preferably 40-80℃, more preferably 50-70℃, and the drying time is preferably 2-5 hours; this invention has a short drying time and low temperature, reducing energy consumption; in a specific embodiment of this invention, a silver-black powder is obtained after drying, which is the expandable graphite.

[0041] After obtaining expandable graphite, the present invention further expands the expandable graphite at high temperature to obtain high-expansion-volume expanded graphite. In the present invention, the high-temperature expansion temperature is 800-900℃, preferably 890-900℃, and the high-temperature expansion time is preferably 3-5s. The present invention obtains black worm-like expanded graphite by high-temperature expansion of expandable graphite. This process involves decomposing the intercalating agent sulfuric acid at high temperature to generate gas, which impacts the graphite sheets, thereby increasing the interlayer spacing and transforming it into expanded graphite. When phosphoric acid is used as an activator, its presence generates polyphosphate at high temperature to protect the graphite carbon layer. As is well known, carbon is also lost at high temperatures, resulting in pores in the carbon layer. This change of phosphoric acid precisely compensates for the pores caused by carbon loss, increases the impact force of sulfuric acid decomposition on the graphite sheets, and, in addition, more intercalating agent is inserted into the graphite sheets, thus obtaining expanded graphite with a significantly increased expansion volume. In the present invention, the average expansion volume of the high-expansion-volume expanded graphite obtained by the activation method reaches 400mL / g.

[0042] This invention also provides a method for preparing high-expansion volume expanded graphite through pretreatment (hereinafter referred to as the pretreatment method), comprising the following steps:

[0043] Natural flake graphite is pretreated by immersing it in a pretreatment agent to obtain pretreated natural flake graphite; the pretreatment agent is phosphoric acid, phosphate solution, hot water or organic solvent; the temperature of the hot water is 60-90℃; the organic solvent is carboxylic acid or alcohol;

[0044] The pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid were mixed and subjected to an oxidation intercalation reaction to obtain expandable graphite.

[0045] The expandable graphite is subjected to high-temperature expansion to obtain the high-expansion volume expanded graphite; the high-temperature expansion temperature is 800-900℃.

[0046] This invention involves pretreating natural flake graphite by immersing it in a pretreatment agent to obtain pretreated natural flake graphite. In this invention, the pretreatment agent is phosphoric acid, a phosphate solution, hot water, or an organic solvent; the concentration of the phosphoric acid is preferably 83-88 wt%, more preferably 85 wt%; the concentration of the phosphate solution is preferably 0.375-0.425 g / mL, more preferably 0.4 g / mL; the phosphate is preferably dihydrogen phosphate, more preferably sodium dihydrogen phosphate; the organic solvent is a carboxylic acid or an alcohol; the carboxylic acid is preferably formic acid and / or acetic acid; the alcohol is preferably ethanol; the temperature of the hot water is preferably 60-90°C, specifically 60°C, 70°C, 80°C, or 90°C; in a specific embodiment of this invention, the pretreatment agent is most preferably hot water, as hot water is inexpensive and easy to process, and the increase in the volume of the expanded graphite increases more significantly with increasing hot water temperature.

[0047] In this invention, the pretreatment time is preferably 1-4 hours, more preferably 1 hour, 2 hours, or 3 hours. When using phosphoric acid, phosphate solution, or organic solvent as the pretreatment agent, the pretreatment can be carried out at room temperature or under conditions of heating and stirring, with the latter being more effective. The heating temperature is preferably 50-70°C, and the stirring speed is preferably 250-350 r / min, more preferably 290-330 r / min. This invention does not have special requirements for the amount of the pretreatment agent, as long as it can completely immerse the natural flake graphite. After the pretreatment, this invention preferably performs solid-liquid separation, and the obtained solid is the pretreated natural flake graphite. This invention preferably recycles the liquid obtained from the solid-liquid separation. This invention uses a pretreatment agent to pretreat natural flake graphite, which can swell the graphite flakes, reduce the amount of oxidant and intercalating agent used in subsequent oxidation intercalation, and shorten the reaction time. At the same time, the pretreatment agent can be recycled, saving the cost of the entire preparation process.

[0048] After obtaining the pretreated natural flake graphite, the present invention mixes the pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid to carry out an oxidative intercalation reaction to obtain expandable graphite. In the present invention, the mass ratio of the natural flake graphite to potassium permanganate is preferably 1:(0.03-0.1), more preferably 1:0.04, 1:0.06, or 1:0.08; the volume ratio of the natural flake graphite to concentrated sulfuric acid is preferably 1g:(1.5-4)mL, more preferably 1g:1.5mL, 1g:2mL, or 1g:3mL; the concentration of the concentrated sulfuric acid is specifically 98wt%.

[0049] In this invention, the mixing of pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid preferably includes: first mixing natural flake graphite and potassium permanganate and heating to 73-75°C, and then adding concentrated sulfuric acid.

[0050] In this invention, the temperature of the oxidation intercalation reaction is preferably 75-80°C, and the reaction time is preferably 10-40 min, more preferably 10-30 min; the oxidation intercalation reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 250-350 r / min, more preferably 290-330 r / min; in a specific embodiment of this invention, stirring is preferably started immediately after the addition of concentrated sulfuric acid.

[0051] This invention utilizes the swelling effect of a pretreatment agent to slightly open the graphite flakes, thereby reducing the use of oxidants and intercalators, lowering costs and reducing environmental pollution. Alternatively, under the same conditions of oxidant and intercalator dosage, pretreatment allows more intercalator to enter the graphite flakes. Then, by controlling the system temperature and rotation speed, the natural flake graphite undergoes a full oxidation and intercalation process to form graphite interlayer compounds. The system after the reaction is completed is a brownish-brown slurry.

[0052] In this invention, after the oxidation intercalation reaction, it is preferable to further wash the resulting reaction solution with water until the pH value is 3-7, preferably 6-7, and then filter and dry it to obtain the expandable graphite; the drying temperature is 40-80°C, more preferably 50-70°C, and the drying time is preferably 2-5 hours, more preferably 3-4 hours.

[0053] After obtaining expandable graphite, the present invention subjectes the expandable graphite to high-temperature expansion to obtain high-expansion-volume expanded graphite. In the present invention, the high-temperature expansion temperature is 800-900℃, preferably 890-900℃, and the high-temperature expansion time is preferably 3-5s. In the present invention, the high-temperature expansion of expandable graphite yields black worm-like expanded graphite. This process involves decomposing the intercalating agent sulfuric acid at high temperature to generate gas, which impacts the graphite flakes, thereby increasing the interlayer spacing and transforming it into expanded graphite. Because the pretreatment slightly opens the graphite flakes, more intercalating agent can enter the graphite flakes under the same conditions. Therefore, the high-temperature decomposition will result in more intercalating agent vaporization, yielding expanded graphite with a significantly increased expansion volume.

[0054] In this invention, the high expansion volume expanded graphite prepared by the pretreatment method has an average expansion volume of 450 mL / g; at the same time, compared with the aforementioned activation method, the pretreatment method has lower cost, is more environmentally friendly, and has a more significant expansion effect.

[0055] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0056] Comparative Example 1

[0057] Weigh 2g of natural flake graphite and 0.2g of potassium permanganate into a beaker in a water bath. Turn on the heating power and when the temperature reaches 73℃, add 8mL of 98wt% concentrated sulfuric acid to the system. Turn on the magnetic stirring at 300r / min and react for 30min, controlling the temperature at 75℃ throughout the reaction. After the reaction, pour the mixture into deionized water and wash until the pH reaches 6-7. Filter and dry at 60℃ for 3h to obtain expandable graphite. Take 0.1g of expandable graphite and expand it in a muffle furnace at 900℃ for 3s to obtain expanded graphite. Measure its volume in a graduated cylinder and calculate the expanded volume of the graphite.

[0058] Example 1

[0059] Expanded graphite was prepared according to the method of Comparative Example 1, except that 1 mL of 85 wt% phosphoric acid was added immediately after concentrated sulfuric acid was added to the system.

[0060] Example 2

[0061] Expanded graphite was prepared according to the method of Comparative Example 1, except that 2 mL of 85 wt% phosphoric acid was added immediately after adding concentrated sulfuric acid to the system.

[0062] Example 3

[0063] Expanded graphite was prepared according to the method of Comparative Example 1, except that 3 mL of 85 wt% phosphoric acid was added immediately after adding concentrated sulfuric acid to the system.

[0064] Example 4

[0065] Expanded graphite was prepared according to the method of Comparative Example 1, except that 4 mL of 85% phosphoric acid was added immediately after concentrated sulfuric acid was added to the system.

[0066] Example 5

[0067] Expanded graphite was prepared according to the method of Comparative Example 1, except that 2g of sodium dihydrogen phosphate was added immediately after concentrated sulfuric acid was added to the system.

[0068] Example 6

[0069] Expanded graphite was prepared according to the method of Comparative Example 1, except that 4g of sodium dihydrogen phosphate was added immediately after concentrated sulfuric acid was added to the system.

[0070] Example 7

[0071] Expanded graphite was prepared according to the method of Comparative Example 1, except that 6g of sodium dihydrogen phosphate was added immediately after concentrated sulfuric acid was added to the system.

[0072] Example 8

[0073] Expanded graphite was prepared according to the method of Comparative Example 1, except that 8g of sodium dihydrogen phosphate was added immediately after concentrated sulfuric acid was added to the system.

[0074] Example 9

[0075] Expanded graphite was prepared according to the method of Comparative Example 1, except that before the reaction, natural flake graphite was soaked in 4 mL of 85 wt% phosphoric acid, and magnetic stirring at 290 r / min was turned on during the soaking process for 1 h.

[0076] Example 10

[0077] Expanded graphite was prepared according to the method of Example 9, except that the oxidation intercalation reaction time was 10 min, that is, the oxidant and intercalating agent were added to the system, and after magnetic stirring was turned on, the reaction was allowed to proceed for 10 min.

[0078] Example 11

[0079] Expanded graphite was prepared according to the method of Example 9, except that the oxidation intercalation reaction time was 20 min, that is, the oxidant intercalator was added to the system, magnetic stirring was turned on, and the reaction was carried out for 20 min.

[0080] Example 12

[0081] Expanded graphite was prepared according to the method of Example 9, except that the oxidation intercalation reaction time was 40 min, that is, the oxidant intercalator was added to the system, and after magnetic stirring was turned on, the reaction was carried out for 40 min.

[0082] Example 13

[0083] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to concentrated sulfuric acid was C(g):H2SO4(mL)=1:3. Specifically, 6mL of 98% concentrated sulfuric acid was added to 2g of natural flake graphite and 0.2g of potassium permanganate to obtain a mixed system.

[0084] Example 14

[0085] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to concentrated sulfuric acid was C(g):H2SO4(mL)=1:2.

[0086] Example 15

[0087] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to concentrated sulfuric acid was C(g):H2SO4(mL)=1:1.5.

[0088] Example 16

[0089] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to potassium permanganate was C(g):KMnO4(g)=1:0.08, that is, 0.16g of potassium permanganate was weighed and placed into a beaker for reaction.

[0090] Example 17

[0091] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to potassium permanganate was C(g):KMnO4(g)=1:0.06.

[0092] Example 18

[0093] Expanded graphite was prepared according to the method of Example 10, except that the ratio of natural flake graphite to potassium permanganate was C(g):KMnO4(g)=1:0.04.

[0094] Example 19

[0095] Expanded graphite was prepared according to the method of Comparative Example 1, except that before the reaction, natural flake graphite was soaked in hot water at 60°C, and magnetic stirring at 290 r / min was turned on during the soaking process for 1 hour.

[0096] Example 20

[0097] Expanded graphite was prepared according to the method of Comparative Example 1, except that before the reaction, natural flake graphite was soaked in hot water at 75°C, and magnetic stirring at 290 r / min was turned on during the soaking process for 1 hour.

[0098] Example 21

[0099] Expanded graphite was prepared according to the method of Comparative Example 1, except that natural flake graphite was soaked in 90°C hot water before the reaction, and magnetic stirring at 290 r / min was turned on during the soaking process for 1 hour.

[0100] Example 22

[0101] Expanded graphite was prepared according to the method of Comparative Example 1, except that before the reaction, natural flake graphite was soaked in 20 mL of sodium dihydrogen phosphate solution (0.4 g / mL), and magnetic stirring at 290 r / min was turned on during the soaking process for 1 h.

[0102] Example 23

[0103] Expanded graphite was prepared according to the method of Comparative Example 1, except that before the reaction, natural flake graphite was soaked in 10 mL of formic acid, and magnetic stirring at 290 r / min was turned on during the soaking process for 1 h.

[0104] Comparative Example 2

[0105] Commercially available expanded graphite was used as a comparative example 2.

[0106] Test case

[0107] 1. Characterization and morphology testing

[0108] Figure 1 The XRD patterns of commercially available expanded graphite in Comparative Examples 1 and 2 are shown below. Figure 1 It can be seen that the (002) diffraction peak of graphite appears at 26.6° and the (004) diffraction peak of graphite appears at 54.4°, indicating that the self-made expanded graphite has no impurities and has no difference in crystal structure compared with commercially available expanded graphite.

[0109] Figure 2 This is a SEM image of the expanded graphite prepared in Comparative Example 1. According to... Figure 2 It can be seen that, compared with commercially available expanded graphite ( Figure 5 In contrast, most graphite sheets have expanded, with a more pronounced worm-like structure, a more porous graphite sheet structure, and a larger expansion volume.

[0110] Figure 3 This is a SEM image of the expanded graphite prepared in Example 3. Figure 3 It can be seen that, compared with Comparative Example 1, the expanded graphite obtained in Example 3 has a larger expansion volume.

[0111] Figure 4 This is a SEM image of the expanded graphite prepared in Example 10. Figure 4 It can be seen that, compared with Comparative Example 1 and Example 3, the expanded graphite obtained in Example 10 has a larger expansion volume.

[0112] Figure 5 This is a SEM image of commercially available expanded graphite. Based on... Figure 5 It can be seen that the expansion volume of commercially available expanded graphite is relatively small.

[0113] 2. Expansion Volume Test

[0114] The expansion volume of expanded graphite in Comparative Example 1 and Examples 1-23 was obtained by weighing and calculation, and the results are listed in Table 1.

[0115] Table 1 shows the expansion volumes of expanded graphite in Comparative Example 1 and Examples 1-23, and the expansion volume values ​​of the comparative examples.

[0116]

[0117]

[0118] As shown in Table 1, adding phosphoric acid as an activator significantly increases the expansion volume of expanded graphite. According to Examples 1-4, the expansion volume first increases and then decreases with increasing phosphoric acid content. This is mainly because the presence of phosphoric acid allows the graphite flakes to open more fully, allowing more intercalating agent to enter the graphite flakes. This results in more intercalating agent being decomposed and vaporized during subsequent high-temperature expansion, leading to a greater impact on the carbon layers and a larger expansion volume. However, as the phosphoric acid content continues to increase, the oxidant concentration decreases, weakening the oxidizing ability of the graphite flakes, reducing the degree of flake opening, and decreasing the amount of intercalating agent entering, thus reducing the expansion volume. When the ratio of natural flake graphite to phosphoric acid is 1g:1.5mL, the expansion volume of the obtained expanded graphite reaches 450mL / g, which is 90mL / g higher than that of Comparative Example 1. To investigate whether the action of phosphoric acid is caused by hydrogen ions or phosphate ions, the phosphoric acid in the system was replaced with an equal amount of sodium dihydrogen phosphate. According to Examples 5 to 8, it can be seen that when the phosphate content in the system is the same, the volume of expanded graphite is the same, indicating that this activation process is caused by phosphate ions.

[0119] As shown in Table 1, using phosphoric acid as a pretreatment agent to first soak natural flake graphite before proceeding with the subsequent oxidation and intercalation reaction can produce expanded graphite with a larger expansion volume. Importantly, compared to Comparative Example 1, this preparation method can shorten the reaction time, reduce the amount of oxidant and intercalator, and achieve a better expansion effect. Furthermore, the pretreatment solvent used can be recovered and recycled. According to Examples 9-12, with the same amount of oxidant and intercalator, pretreatment can shorten the reaction time. According to Examples 13-18, after reducing the amount of oxidant and intercalator, the expansion volume of the obtained expanded graphite is comparable to or higher than that of Comparative Example 1, indicating that pretreatment can reduce the amount of oxidant and intercalator.

[0120] As can be seen from the data in Examples 19 to 21 in Table 1, expanding graphite with a significantly increased expansion volume can also be prepared by replacing phosphoric acid with hot water at different temperatures, which has a swelling effect. This preparation method is low in cost, environmentally friendly, and effective.

[0121] As can be seen from the data in Examples 22 to 23 in Table 1, expanded graphite with a significantly increased expansion volume can also be obtained by using phosphate solution and formic acid as pretreatment agents.

[0122] In summary, as shown in Table 1, the expansion volume of the expanded graphite prepared by the activation method or pretreatment method of the present invention is much higher than that of traditional methods and commercially available expanded graphite.

[0123] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-expansion volumetric graphite through pretreatment, characterized in that, Includes the following steps: Natural flake graphite is pretreated by immersing it in a pretreatment agent to obtain pretreated natural flake graphite; the pretreatment agent is phosphoric acid, phosphate solution or hot water; the temperature of the hot water is 60~90℃; the pretreatment time is 1~4h. The pretreated natural flake graphite, potassium permanganate, and concentrated sulfuric acid are mixed and subjected to an oxidation intercalation reaction to obtain expandable graphite; the mass ratio of natural flake graphite to potassium permanganate is 1:0.1; the volume ratio of natural flake graphite to concentrated sulfuric acid is 1g:4mL; the temperature of the oxidation intercalation reaction is 75~80℃, and the time is 10~30min. The expandable graphite is subjected to high-temperature expansion to obtain the high-expansion volume expanded graphite; the high-temperature expansion temperature is 800~900℃.

2. The method according to claim 1, characterized in that, The concentration of the phosphoric acid is 83-88 wt%; the concentration of the phosphate solution is 0.375-0.425 g / mL; and the phosphate is dihydrogen phosphate.

3. The method according to claim 1, characterized in that, After the oxidation intercalation reaction, the reaction solution is washed with water until the pH value is 3-7, then filtered and dried to obtain the expandable graphite; the drying temperature is 40-80℃ and the time is 2-5h.

4. The method according to claim 1, characterized in that, The high-temperature expansion time is 3~5 seconds.

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