Expanded graphite, preparation method thereof, composite phase change material and preparation method thereof

Abstract

The application belongs to the technical field of phase change materials, and particularly relates to expanded graphite, a preparation method thereof, and a composite phase change material and a preparation method thereof. The expanded graphite obtained by the preparation method has a high expansion volume, can be applied to a phase change material, can further improve heat transfer performance, can improve a thermal conductivity coefficient, and can lose less phase change latent heat. Further, the application provides a composite phase change material. The application directly mixes beef tallow, high-melting-point paraffin and expanded graphite, controls different proportions of the three, is beneficial to improving the utilization rate of biomass resources, can greatly reduce a melting point, and can improve phase change latent heat of the phase change material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of phase change materials, and particularly relates to expanded graphite and a preparation method thereof, and a composite phase change material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy vehicles, power batteries as one of the core components have become the focus of research and attention. The endurance mileage and safety of power batteries have also become the main problems restricting the development of new energy vehicles. At present, lithium ion power batteries are widely used in electric vehicles. Compared with other rechargeable batteries, lithium ion batteries have the advantages of high energy density, low self-discharge rate, low maintenance requirement, long cycle life, light weight, compactness and the like. However, the operating performance of lithium ion batteries is greatly affected by the environmental temperature, and the safe and efficient operation of the battery can only be realized within a relatively narrow temperature range. At low temperature, the internal resistance of the lithium ion battery will rapidly increase, the charge and discharge capacity will be significantly reduced, and the charge and discharge cycle number will also be greatly reduced. High-speed charging and discharging of the battery at too low temperature will also cause internal short circuit and other safety problems. In a high-temperature environment, if the battery temperature is not effectively controlled, the high temperature will cause the internal SEI film and the positive and negative active materials to decompose in turn, and the separator to melt, thereby causing internal chain chemical reactions and generating a large amount of heat, leading to battery thermal runaway and other safety accidents.

[0003] In order to ensure the working performance and thermal safety of lithium ion batteries, the battery must be maintained in a suitable temperature range. However, due to the large temperature difference between the north and south in winter, the cold climate in the north may cause the performance of the battery to decrease during high-speed charging and discharging, shorten the service life, and even cause thermal runaway and other safety problems. Phase change material (PCM) cooling technology can maintain the working temperature of the battery within a relatively constant temperature range, and absorb / release a large amount of heat during the phase change process. This solution can keep the temperature within the optimal range, manage uniform temperature distribution, especially in extreme environments. With the in-depth study of phase change materials, the PCM-based structure is simple, has strong shape adaptability and does not increase additional energy consumption, and therefore has attracted widespread attention.

[0004] Expanded graphite (EG) is a commonly used material, which has the advantages of rich pores, low chemical activity, strong adsorption and low density compared with metals, and most importantly, it has high thermal conductivity and is widely used to enhance the thermal performance of phase change materials. However, the existing expanded graphite has a small expansion volume, which limits the application of expanded graphite in phase change materials. SUMMARY

[0005] The application aims to provide an expanded graphite and a preparation method thereof, and a composite phase change material and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0007] The application provides a preparation method of expanded graphite, comprising the following steps.

[0008] Mixing hydrogen peroxide, concentrated sulfuric acid and flake graphite to perform oxidation intercalation to obtain intercalated graphite;

[0009] Mixing the intercalated graphite and an auxiliary intercalation agent to perform auxiliary intercalation to obtain expandable graphite; the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate;

[0010] Expanding the expandable graphite to obtain expanded graphite.

[0011] Preferably, the mass concentration of the hydrogen peroxide is 30%; the mass concentration of the concentrated sulfuric acid is 98%;

[0012] The volume ratio of the hydrogen peroxide and the concentrated sulfuric acid is 0.25:5.5-7;

[0013] The dosage ratio of the concentrated sulfuric acid and the flake graphite is 5.5-7 mL:2 g.

[0014] Preferably, the temperature of the oxidation intercalation is 35-45 DEG C, and the time is 25-45 min.

[0015] Preferably, the mass ratio of the flake graphite and the auxiliary intercalation agent is 2:0.24-0.3;

[0016] The temperature of the auxiliary intercalation is 35-45 DEG C, and the time is 25-45 min.

[0017] Preferably, the expansion temperature is 900-1000 DEG C.

[0018] The application further provides the expanded graphite prepared by the preparation method.

[0019] The application further provides a composite phase change material comprising paraffin, beef tallow and expanded graphite.

[0020] The expanded graphite is the expanded graphite according to the above-mentioned technical scheme.

[0021] Preferably, the melting point of the paraffin is 100-107 DEG C.

[0022] The mass ratio of the paraffin and the beef tallow is 1-9:1-9; the mass percentage of the expanded graphite in the composite phase change material is 4.5-5.5%.

[0023] Preferably, the melting point of the composite phase change material is 70-80 DEG C, and the phase change latent heat is 54.55-202.8 J / g.

[0024] The application further provides a preparation method of the composite phase change material, comprising the following steps: mixing paraffin, beef tallow and expanded graphite to obtain the composite phase change material.

[0025] The application provides a preparation method of expanded graphite, comprising the following steps: mixing hydrogen peroxide, concentrated sulfuric acid and flake graphite to perform oxidation intercalation, to obtain intercalated graphite; mixing the intercalated graphite and an auxiliary intercalation agent to perform auxiliary intercalation, to obtain expandable graphite; the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate; expanding the expandable graphite to obtain expanded graphite.

[0026] The application further provides a composite phase change material, comprising paraffin, beef tallow and expanded graphite; the expanded graphite is the expanded graphite provided in the above technical solution. In the application, beef tallow has a wide source of raw materials and a low production cost, and has a significant economic advantage compared with synthetic materials which need complex chemical synthesis. Meanwhile, compared with synthetic phase change materials such as organic waxes or polymers, beef tallow has a relatively high melting point (usually between 30-40 DEG C). In addition, the good heat storage capacity and low thermal conductivity of beef tallow make it competitive in heat management. Meanwhile, as a bio-based material, beef tallow has a smaller impact on the environment and meets the current demand for sustainable materials. The application directly mixes beef tallow, high-melting-point paraffin and expanded graphite, controls different proportions of the three, improves the utilization rate of biomass resources, and can greatly reduce the melting point while improving the phase change latent heat of the phase change material. DETAILED DESCRIPTION

[0027] The application provides a preparation method of expanded graphite, comprising the following steps:

[0028] Mixing hydrogen peroxide, concentrated sulfuric acid and flake graphite to perform oxidation intercalation, to obtain intercalated graphite;

[0029] Mixing the intercalated graphite and an auxiliary intercalation agent to perform auxiliary intercalation, to obtain expandable graphite; the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate;

[0030] Expanding the expandable graphite to obtain expanded graphite.

[0031] The present application mixes hydrogen peroxide, concentrated sulfuric acid and flake graphite, carries out oxidative intercalation, and obtains intercalated graphite.

[0032] In the present application, the mass concentration of the hydrogen peroxide is preferably 30%; the mass concentration of the concentrated sulfuric acid is preferably 98%; the volume ratio of the hydrogen peroxide and the concentrated sulfuric acid is preferably 0.25:5.5-7, and specifically can be 0.25:5.5, 0.25:6, 0.25:6.5 or 0.25:7; and the dosage ratio of the concentrated sulfuric acid and the flake graphite is preferably 5.5-7 mL:2 g, and specifically can be 5.5 mL:2 g, 6 mL:2 g or 7 mL:2 g.

[0033] In the present application, the mixing process preferably comprises: mixing the hydrogen peroxide and the concentrated sulfuric acid uniformly, and then adding the flake graphite. In the present application, the temperature of the oxidative intercalation is preferably 35-45℃, and specifically can be 30℃, 35℃ or 40℃; and the time is preferably 25-45 min, and specifically can be 25 min, 30 min, 35 min, 40 min or 45 min. In the present application, the oxidative intercalation is preferably carried out under stirring, and the stirring speed is preferably 200 rpm. After the oxidative intercalation, no subsequent treatment is preferably carried out, and the subsequent auxiliary intercalation is directly carried out.

[0034] In the present application, the process of the oxidative intercalation comprises an oxidation reaction and an intercalation reaction, the equation of the oxidation reaction is shown as formula 1, and the equation of the intercalation reaction is shown as formula 2:

[0035]

[0036] After obtaining the intercalated graphite, the present application mixes the intercalated graphite and an auxiliary intercalation agent, carries out auxiliary intercalation, and obtains expandable graphite; and the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate.

[0037] In the present application, the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate, and is preferably ammonium nitrate. In the present application, the mass ratio of the flake graphite and the auxiliary intercalation agent is preferably 2:0.24-0.3, and specifically can be 2:0.24, 2:0.27 or 2:0.30; the temperature of the auxiliary intercalation is preferably 35-45℃, and specifically can be 30℃, 35℃ or 40℃; and the time is preferably 25-45 min, and specifically can be 25 min, 30 min, 35 min, 40 min or 45 min. In the present application, the auxiliary intercalation is preferably carried out under stirring, and the stirring speed is preferably 200 rpm.

[0038] In the present application, the reaction equation in the process of the auxiliary intercalation is shown as formula 3;

[0039]

[0040] In the present application, the auxiliary intercalation agent is used on the basis of the preparation of low-sulfur expandable graphite by the sulfuric acid-nitric acid mixed method, according to the reaction that nitrate and concentrated sulfuric acid generate nitric acid and bisulfate, so that they generate nitric acid in concentrated sulfuric acid. The natural flake graphite is subjected to an oxidation intercalation reaction under the joint action of nitric acid, sulfuric acid and nitrate, so that the flake graphite is moderately oxidized and sufficient intercalation is obtained, and the expandable graphite with good quality is obtained.

[0041] In the present application, the temperature of the oxidation intercalation is preferably the same as that of the auxiliary intercalation; the time of the oxidation intercalation is preferably the same as that of the auxiliary intercalation.

[0042] After the auxiliary intercalation, the present application further preferably comprises filtering the obtained system, washing the obtained precipitate to neutral, and then drying; the temperature of the drying is preferably 60-90℃, and specifically can be 60℃, 70℃, 80℃ or 90℃; the time is preferably 4h.

[0043] After the expandable graphite is obtained, the present application expands the expandable graphite to obtain expanded graphite.

[0044] In the present application, the expansion temperature is preferably 900-1000℃.

[0045] The present application further provides the expanded graphite prepared by the preparation method described in the above technical solution. In the present application, the collision volume of the expanded graphite is preferably 310-380mL / g.

[0046] The present application further provides a composite phase change material comprising paraffin, butter and expanded graphite.

[0047] The expanded graphite is the expanded graphite described in the above technical solution.

[0048] In the present application, the melting point of the paraffin is preferably 100-107℃, and specifically can be 100℃, 103℃, 105℃ or 107℃. In the present application, the mass ratio of the paraffin and butter is preferably 1-9:1-9, and specifically can be 1:1, 3:7, 7:3, 1:9 or 9:1. In the present application, the mass percentage content of the expanded graphite in the composite phase change material is preferably 4.5-5.5%, and specifically can be 4.5%, 5.0% or 5.5%.

[0049] In the present application, the melting point of the composite phase change material is preferably 70-80℃, and the latent heat of phase change is preferably 54.55-202.8J / g.

[0050] The application further provides a preparation method of the composite phase change material.

[0051] The paraffin wax, the beef tallow and the expanded graphite are mixed to obtain the composite phase change material.

[0052] In the application, the mixing process preferably comprises:

[0053] The paraffin wax and the beef tallow are heated and melted, and a solid mixture is obtained after condensation;

[0054] The solid mixture and the expanded graphite are stirred and mixed.

[0055] In the application, the temperature of the heating and melting is preferably 120 DEG C. In the application, the stirring and mixing speed is preferably 200-400 rpm, and the time is preferably 1-3 h.

[0056] After the mixing, the application further preferably comprises condensing and compacting the obtained mixed system at room temperature.

[0057] Unless otherwise specified, the materials and devices used in the application are commercially available in the art.

[0058] The technical solutions in the application will be described clearly and completely in the application with reference to the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the application.

[0059] Embodiment 1

[0060] 0.25 mL of oxidant hydrogen peroxide with a mass concentration of 30% and 5.5 mL of intercalation agent concentrated sulfuric acid with a mass concentration of 98% are mixed uniformly, 2 g of flake graphite is added to mix and perform oxidation intercalation reaction, the water bath temperature is 40 DEG C, and the reaction time is 30 min (with stirring at a speed of 200 rpm); 0.24 g of auxiliary intercalation agent ammonium nitrate is added to the mixed system to perform auxiliary intercalation, the water bath temperature is 40 DEG C, the reaction time is 30 min (with stirring at a speed of 200 rpm), and then the product is extracted and washed to be neutral; the product is dried at 80 DEG C for 4 h to obtain expandable graphite; the expandable graphite is expanded at 900 DEG C to obtain expanded graphite.

[0061] Embodiment 2

[0062] The expanded graphite is prepared in the manner of embodiment 1, wherein the addition amount of ammonium nitrate is 0.27 g.

[0063] Embodiment 3

[0064] Expanded graphite was prepared in the manner of Example 1, wherein the amount of ammonium nitrate added was 0.30 g.

[0065] Example 4

[0066] Expanded graphite was prepared in the manner of Example 2, wherein the time for oxidative intercalation was 25 min and the time for auxiliary intercalation was 25 min.

[0067] Example 5

[0068] Expanded graphite was prepared in the manner of Example 2, wherein the time for oxidative intercalation was 35 min and the time for auxiliary intercalation was 35 min.

[0069] Example 6

[0070] Expanded graphite was prepared in the manner of Example 2, wherein the time for oxidative intercalation was 40 min and the time for auxiliary intercalation was 40 min.

[0071] Example 7

[0072] Expanded graphite was prepared in the manner of Example 2, wherein the time for oxidative intercalation was 45 min and the time for auxiliary intercalation was 45 min.

[0073] Example 8

[0074] Expanded graphite was prepared in the manner of Example 2, wherein the amount of concentrated sulfuric acid used was 6 mL.

[0075] Example 9

[0076] Expanded graphite was prepared in the manner of Example 2, wherein the amount of concentrated sulfuric acid used was 6.5 mL.

[0077] Example 10

[0078] Expanded graphite was prepared in the manner of Example 2, wherein the amount of concentrated sulfuric acid used was 7 mL.

[0079] Example 11

[0080] Expanded graphite was prepared in the manner of Example 2, wherein the temperature for drying was 60°C.

[0081] Example 12

[0082] Expanded graphite was prepared in the manner of Example 2, wherein the temperature for drying was 70°C.

[0083] Comparative Example 1

[0084] Expanded graphite was prepared in the manner of Example 2, wherein the amount of ammonium nitrate added was 0.21 g

[0085] Comparative Example 2

[0086] The expanded graphite was prepared in the same manner as in Example 2, except that the amount of concentrated sulfuric acid was 4.5 mL.

[0087] Comparative Example 3

[0088] The expanded graphite was prepared in the same manner as in Example 2, except that the amount of concentrated sulfuric acid was 5 mL.

[0089] Comparative Example 4

[0090] The expanded graphite was prepared in the same manner as in Example 2, except that the temperature of the oxidation intercalation and the temperature of the auxiliary intercalation were 30°C.

[0091] Comparative Example 5

[0092] The expanded graphite was prepared in the same manner as in Example 2, except that the temperature of the oxidation intercalation and the temperature of the auxiliary intercalation were 50°C.

[0093] Comparative Example 6

[0094] The expanded graphite was prepared in the same manner as in Example 2, except that the temperature of the drying was 50°C.

[0095] Comparative Example 7

[0096] The expanded graphite was prepared in the same manner as in Example 2, except that the temperature of the drying was 90°C.

[0097] Comparative Example 8

[0098] A commercially available expanded graphite was used as a comparative example.

[0099] Test Example 1

[0100] The expanded volumes of the expanded graphites obtained in Examples 1 to 12 and Comparative Examples 1 to 8 were tested by the national standard GB 10698-1989, and the results are shown in Table 1.

[0101] Table 1 Expanded Volumes of Expanded Graphites of Examples and Comparative Examples

[0102] Example 1 Example 2 Example 3 Example 4 Example 5 Swelling volume (mL / g) 330 380 310 330 350 Example 6 Example 7 Example 8 Example 9 Example 1 Swelling volume (mL / g) 350 350 330 330 330 Example 11 Example 12 Comparative Example 1 Comparative Example 2 Comparative Example 3 Swelling volume (mL / g) 350 380 290 260 300 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Swelling volume (mL / g) 300 300 300 260 300

[0103] As can be seen from Table 1, the preparation conditions of the expanded graphite are closely related to the expanded volume thereof, and by comparison, it can be shown that the expanded volume of the expanded graphite prepared according to the present application is greater than that of the conventional expanded graphite on the market.

[0104] Example 13

[0105] 1 g of beef tallow and 9 g of high-melting-point paraffin (melting point: 105°C) were heated and melted, and the mixture was heated and stirred at a constant temperature to obtain a mixed system, the temperature of the system being controlled at 120°C during the mixing process; the mixed system was condensed at room temperature to obtain a solid mixture;

[0106] The solid mixture was mixed with the expanded graphite prepared in Example 2 for 2 h at 200 rpm, and the resulting mixture was solidified and compacted at room temperature to obtain a composite phase change material in which the mass percentage of the expanded graphite in the composite phase change material was 5%.

[0107] Example 14

[0108] A composite phase change material was prepared in the same manner as in Example 13, in which 3 g of beef tallow and 7 g of high-melting-point paraffin were added.

[0109] Example 15

[0110] A composite phase change material was prepared in the same manner as in Example 13, in which 5 g of beef tallow and 5 g of high-melting-point paraffin were added.

[0111] Example 16

[0112] A composite phase change material was prepared in the same manner as in Example 13, in which 7 g of beef tallow and 3 g of high-melting-point paraffin were added.

[0113] Example 17

[0114] A composite phase change material was prepared in the same manner as in Example 13, in which 9 g of beef tallow and 1 g of high-melting-point paraffin were added.

[0115] Example 18

[0116] A composite phase change material was prepared in the same manner as in Example 13, in which the mixing time of the solid mixture and the expanded graphite was 1 h.

[0117] Example 19

[0118] A composite phase change material was prepared in the same manner as in Example 13, in which the mixing time of the solid mixture and the expanded graphite was 3 h.

[0119] Comparative Example 9

[0120] A commercially available high-melting-point paraffin material was used as a comparative example.

[0121] Comparative Example 10

[0122] A commercially available beef tallow material was used as a comparative example.

[0123] Comparative Example 11

[0124] A commercially available paraffin-based phase change material was used as a comparative example.

[0125] Test Example 2

[0126] The melting points of the composite phase change materials of Examples 13-17 and the products of Comparative Examples 9-10 were tested by a melting point tester, and the latent heat of phase change of the composite phase change materials of Examples 13-17 and the products of Comparative Examples 9-10 were tested by a differential scanning calorimeter, and the test results are shown in Table 2.

[0127] Table 2 Performance parameters of phase change materials of examples and comparative examples

[0128]

[0129]

[0130] As shown in Table 2, a small amount of beef tallow can be added to high-melting-point paraffin with a melting point of 107℃ to reduce the melting point, and the loss of latent heat of phase change is small, and the latent heat of phase change is much higher than that of beef tallow itself, which shows that the paraffin / beef tallow-based phase change material provided by the application has good heat storage performance and low cost.

[0131] Test Example 2

[0132] The thermal stability of the products of Examples 13, 18-19 and Comparative Example 11 as phase change materials was detected by the following method: 10g of the phase change material was formed by compression at the same pressure, and was placed in an oven at 90℃ for constant temperature heating for 1h, the mass of the phase change material before and after heating was weighed and the weight loss rate was calculated, and the results are shown in Table 3.

[0133] Table 3 Weight loss rate of products of examples and comparative examples

[0134] Example Before heating (g) After heating (g) Weight loss rate (%) Example 13 9.645 9.638 0.07 Example 18 9.704 9.670 0.35 Example 19 9.690 9.680 0.10 Comparative Example 11 9.776 9.741 0.36

[0135] To further detect the thermal stability of the products of Examples 13, 18-19 and Comparative Example 11 as phase change materials; 10g of the phase change material was formed by compression at the same pressure, and was placed in an oven at 90℃ for constant temperature heating for 1h, and the sample was cooled with the furnace, and the mass of the sample was weighed, and the temperature was repeatedly cycled for 30 times, and the mass change was recorded and the weight loss rate was calculated, and the results are shown in Table 4.

[0136] Table 4 Weight loss rate of products of examples and comparative examples

[0137] Example Before cycling (g) After cycling (g) Weight loss rate (%) Example 13 9.638 9.565 0.76 Example 18 9.670 9.581 0.92 Example 19 9.680 9.595 0.88 Comparative Example 11 9.741 9.650 0.93

[0138] As shown in Tables 3 and 4, the infiltration time of the paraffin / beef tallow-based phase change material directly affects the thermal stability of the phase change material, and only the paraffin / beef tallow-based phase change material prepared under the best reaction conditions has the best stability, and through the comparative examples, it can be seen that the stability of the paraffin / beef tallow-based phase change material prepared by the application is higher than that of the conventional phase change material on the market.

[0139] Comprehensively, the method provided by the application has high utilization rate for tallow and flaky graphite, and the prepared paraffin / tallow-based phase change material has excellent heat storage performance.

[0140] Although the above embodiment has made a detailed description of the application, it is only a part of the embodiment of the application, not all the embodiments, and other embodiments can be obtained according to the embodiment without creativity, and these embodiments all belong to the protection scope of the application.

Claims

1. A composite phase change material, characterized in that, The paraffin, the beef tallow and the expanded graphite; The melting point of the paraffin is 100-107℃; The preparation method of the expanded graphite comprises the following steps: The hydrogen peroxide, the concentrated sulfuric acid and the flake graphite are mixed to perform oxidation intercalation, so as to obtain intercalated graphite; the dosage ratio of the concentrated sulfuric acid and the flake graphite is 5.5-7mL:2g; the temperature of the oxidation intercalation is 35-45℃, and the time is 25-45min; The intercalated graphite and an auxiliary intercalation agent are mixed to perform auxiliary intercalation, so as to obtain expandable graphite; the auxiliary intercalation agent comprises copper nitrate, ammonium nitrate or zinc nitrate; the mass ratio of the flake graphite and the auxiliary intercalation agent is 2:0.24-0.3; the temperature of the auxiliary intercalation is 35-45℃, and the time is 25-45min; The expandable graphite is expanded to obtain expanded graphite.

2. The composite phase change material of claim 1, wherein, The mass concentration of the hydrogen peroxide is 30%; the mass concentration of the concentrated sulfuric acid is 98%; The volume ratio of the hydrogen peroxide and the concentrated sulfuric acid is 0.25:5.5-7.

3. The composite phase change material of claim 1, wherein, The expansion temperature is 900-1000℃.

4. The composite phase change material of claim 1, wherein, The mass ratio of the paraffin and the beef tallow is 1-9:1-9; the mass percentage content of the expanded graphite in the composite phase change material is 4.5-5.5%.

5. The composite phase change material of claim 1, wherein, The melting point of the composite phase change material is 70-80℃, and the phase change latent heat is 54.55-202.8J / g.

6. The method of producing a composite phase change material according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: The paraffin, the beef tallow and the expanded graphite are mixed to obtain the composite phase change material.

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