A method for preparing continuous graphite films using small molecule carbohydrates

Abstract

A method for preparing continuous graphite films using small molecule carbohydrates belongs to the field of carbon material preparation, and specifically relates to a method for preparing continuous graphite films using small molecule carbohydrates. The purpose of the present invention is to solve the problems of high difficulty in preparing continuous graphite films, high production costs, and large environmental pollution. The present invention uses small molecule carbohydrates as the carbon source, sodium carboxymethyl cellulose as the thickener, acrylic acid and N,N'-methylenebisacrylamide as the gel system, and deionized water as the solvent of the gel system. The continuous hydrogel film is prepared between the polyimide film and the PET film by the casting method, and the continuous graphite film is obtained after pre-carbonization, carbonization, and graphitization. The present invention pioneers the preparation of continuous graphite films using small molecule carbohydrates, breaks the limitation of preparing continuous graphite films by polymers such as polyimide, and the prepared continuous graphite film has a high crystallization quality and few defects.

Description

Technical Field

[0001] The present invention belongs to the field of carbon material preparation, and particularly relates to a method for preparing continuous graphite films using small molecule carbohydrates. Background Art

[0002] Continuous graphite films have good electrical conductivity, thermal conductivity and mechanical properties. At the same time, due to the excellent chemical stability and high temperature resistance of the graphite film itself, they have a wide range of applications in flexible electronic devices, efficient thermal management, energy, aerospace and other fields. At present, the commercially available continuous graphite films are mainly obtained by subjecting polyimide films to high temperature heat treatment at 3000 °C or above under the action of biaxial stress. However, the production raw materials of polyimide films with high cross-linking degree are expensive, the preparation process is complex, and the production equipment is expensive. At present, only a few countries such as the United States and Japan have relatively complete high-quality polyimide film production lines, and most of the production raw materials of polyimide are derived from petrochemical industry, which is not only difficult to regenerate but also causes great environmental pollution. The graphite films prepared by rolling expanded graphite have a high cost advantage, but the high defect content and low structural integrity of such graphite films only enable them to be used in low-end applications. Although the graphite films prepared by high-purity hydrocarbon chemical vapor deposition method, epitaxial growth method and graphene layer-by-layer stacking method can have complete structures and good properties, these methods have low production efficiency, complex and harsh production processes, and are difficult to achieve continuous batch production, and only exist in the laboratory research stage. In summary, it is very necessary to develop green, environmentally friendly and renewable continuous graphite films, which can not only solve the environmental pollution problem, but also effectively reduce the production cost of continuous graphite films.

[0003] Carbohydrates are an important class of carbohydrates widely distributed in nature. They can be extracted from plants in nature, belong to a renewable resource, and have low prices and are relatively easy to purify, making them an ideal carbon raw material. It has been reported that small molecule carbohydrates such as glucose, fructose, sucrose and maltose can obtain dense carbon (graphite) materials by introducing a macromolecular gel system into their aqueous solutions to inhibit the uncontrollable foaming during their carbonization process. However, the high reaction activity and large volume shrinkage rate during the carbonization and graphitization of carbohydrates make it difficult to process them into uniform and continuous films. At present, there are no relevant reports on preparing high-quality continuous graphite films using small molecule carbohydrates. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing continuous graphite films using small molecule carbohydrates in order to solve the problems of difficult preparation, high production cost and large environmental pollution of continuous graphite films.

[0005] The present invention first uses small - molecule carbohydrates as carbon sources to prepare continuous graphite films. The prepared graphite films have a length exceeding 10 cm, a relatively high crystallization quality, a low defect degree, and a high graphitization degree. Almost all raw materials used in this method are low - cost organic compounds, which are not only rich in sources, simple in production process, but also simple in preparation process, have low equipment requirements, and high production efficiency, greatly reducing the production cost of continuous graphite films and providing a new and efficient idea for the preparation of high - performance continuous graphite films.

[0006] The present invention adopts the following technical scheme: using small - molecule carbohydrates with good water solubility such as glucose, fructose, sucrose, and maltose as carbon sources, acrylic acid and N,N’ - methylenebisacrylamide as the gel system, α - ketoglutaric acid as the photo - initiator, sodium carboxymethyl cellulose as the thickener, and polyimide film as the gel substrate, and preparing a continuous hydrogel film by the casting method; the hydrogel film is pre - carbonized to obtain a carbon precursor film with a stable morphological structure. The carbon precursor film separated from the polyimide substrate is transferred between isostatic graphite sheets for carbonization and graphitization treatment, and finally a graphite film with a low defect degree is obtained. The specific steps are as follows:

[0007] A method for preparing continuous graphite films using small - molecule carbohydrates is realized according to the following steps:

[0008] I. Preparation of hydrogel solution:

[0009] Mix deionized water, water - soluble sugars, acrylic acid, N,N’ - methylenebisacrylamide, α - ketoglutaric acid, and sodium carboxymethyl cellulose in a certain proportion and stir to obtain a hydrogel solution;

[0010] The mass ratio of the water - soluble sugars to deionized water in step I is (1 - 4):1;

[0011] The mass ratio of the sodium carboxymethyl cellulose to deionized water in step I is (0.001 - 0.05):1;

[0012] The mass ratio of the acrylic acid to the water - soluble sugars in step I is (0.1 - 0.5):1;

[0013] The mass ratio of N,N’ - methylenebisacrylamide to acrylic acid in step I is (0.01 - 0.1):1;

[0014] The mass ratio of α - ketoglutaric acid to acrylic acid in step I is (0.001 - 0.01):1;

[0015] II. Casting into film and gelation:

[0016] Drop the hydrogel solution onto a clean polyimide film, then cover the liquid surface with a clean PET film, and then continuously spread the liquid droplets between the two films into a film with a certain thickness using a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for gelation to finally obtain a continuous hydrogel film;

[0017] III. Pre-carbonization:

[0018] Separate the hydrogel film obtained in Step II from the PET film, attach the hydrogel film to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0019] IV. Carbonization and graphitization:

[0020] Carry out carbonization and graphitization on the carbon precursor film obtained in Step III to obtain a continuous graphite film derived from small molecule carbohydrates.

[0021] Advantages of the present invention:

[0022] (1). The present invention creates a precedent for preparing continuous graphite films from small molecule carbohydrates. The prepared graphite film has a length exceeding 10 cm, good crystallization quality, high graphitization degree, and high practical application and scientific research value;

[0023] (2). The main raw materials used for the continuous graphite film provided by the present invention are green, environmentally friendly, non-toxic, harmless and inexpensive. It transforms the preparation process of complex high-polymerization-degree polymer precursors into a simple purification process of small molecule carbohydrates, providing a new solution for commercial preparation of continuous graphite films;

[0024] (3). The preparation process of the continuous graphite film provided by the present invention is simple, the graphite film has good structural integrity, and has excellent electrical conductivity, thermal conductivity and mechanical properties. It is expected to be used as a high-performance graphite material in fields such as communication, electronics, aerospace, etc., and has broad market prospects. Description of the drawings

[0025] Figure 1 Is a physical diagram of the graphite film prepared in Example 1;

[0026] Figure 2 Is a cross-sectional microscopic morphology diagram of the graphite film prepared in Example 1;

[0027] Figure 3 Is an XRD pattern of the graphite film prepared in Example 1;

[0028] Figure 4 Is a Raman spectrum of the graphite film prepared in Example 1;

[0029] Figure 5 The physical diagram of the graphite film prepared for Example 2. Specific implementation mode

[0030] Specific implementation mode 1: A method for preparing a continuous graphite film by using small molecule carbohydrates is realized according to the following steps:

[0031] 1. Prepare a hydrogel solution:

[0032] Mix deionized water, water-soluble saccharides, acrylic acid, N,N'-methylenebisacrylamide, α-ketoglutaric acid and sodium carboxymethylcellulose in a certain proportion and stir to obtain a hydrogel solution;

[0033] In step 1, the mass ratio of the water-soluble saccharides to the deionized water is (1-4):1;

[0034] In step 1, the mass ratio of the sodium carboxymethylcellulose to the deionized water is (0.001-0.05):1;

[0035] In step 1, the mass ratio of the acrylic acid to the water-soluble saccharides is (0.1-0.5):1;

[0036] In step 1, the mass ratio of the N,N'-methylenebisacrylamide to the acrylic acid is (0.01-0.1):1;

[0037] In step 1, the mass ratio of the α-ketoglutaric acid to the acrylic acid is (0.001-0.01):1;

[0038] 2. Cast into a film and gelation:

[0039] Drop the hydrogel solution on a clean polyimide film, then cover a clean PET film on the liquid surface, and then continuously spread the liquid droplets in the two films into a film with a certain thickness by a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for gelation to finally obtain a continuous hydrogel film;

[0040] 3. Pre-carbonization:

[0041] Separate the hydrogel film obtained in step 2 from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0042] 4. Carbonization and graphitization:

[0043] Carry out carbonization and graphitization on the carbon precursor film obtained in step 3 to obtain a continuous graphite film derived from small molecule carbohydrates.

[0044] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the water-soluble saccharide described in Step 1 is one or a mixture of several of analytical pure or chemically pure water-soluble glucose, water-soluble fructose, water-soluble sucrose, and water-soluble maltose. Other steps are the same as those in Specific Embodiment 1.

[0045] Specific Embodiment 3: The difference between this embodiment and either Specific Embodiment 1 or 2 is that the thickness of the hydrogel film described in Step 2 is 20 μm to 200 μm, and the length is 10 cm to 20 cm. Other steps are the same as those in Specific Embodiment 1 or 2.

[0046] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the gelation time described in Step 2 is 5 min to 30 min. Other steps are the same as those in Specific Embodiments 1 to 3.

[0047] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the low-temperature pre-carbonization process described in Step 3 is: heating at a heating rate of 1 °C / min to 2 °C / min to 150 °C to 300 °C, and carbonizing at 150 °C to 300 °C for 1 h to 24 h. Other steps are the same as those in Specific Embodiments 1 to 4.

[0048] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that the carbonization temperature described in Step 4 is 800 °C to 1400 °C, the carbonization atmosphere is vacuum or inert gas, and the carbonization time is 0.5 h to 6 h. Other steps are the same as those in Specific Embodiments 1 to 5.

[0049] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that the inert gas is argon. Other steps are the same as those in Specific Embodiments 1 to 6.

[0050] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that the graphitization temperature described in Step 4 is 2400 °C to 3000 °C, the graphitization atmosphere is vacuum or inert gas, and the graphitization time is 1 h to 6 h. Other steps are the same as those in Specific Embodiments 1 to 7.

[0051] Specific Embodiment 9: The difference between this embodiment and any one of Specific Embodiments 1 to 8 is that the inert gas is argon. Other steps are the same as those in Specific Embodiments 1 to 8.

[0052] Specific Embodiment 10: The difference between this embodiment and any one of Specific Embodiments 1 to 9 is that the thickness of the continuous graphite film described in Step 4 is 15 μm to 150 μm, and the length is 10 cm to 16 cm. Other steps are the same as those in Specific Embodiments 1 to 9.

[0053] The beneficial effects of the present invention are verified by the following examples:

[0054] Example 1: A method for preparing continuous graphite film using small molecule carbohydrates is realized according to the following steps:

[0055] I. Prepare a hydrogel solution:

[0056] Mix 30 g of deionized water, 70 g of analytical pure glucose, 14 g of acrylic acid, 0.7 g of N,N'-methylenebisacrylamide, 0.8 g of α-ketoglutaric acid, and 0.21 g of sodium carboxymethyl cellulose in a certain proportion and stir until fully dissolved to obtain a clear hydrogel solution;

[0057] II. Cast film and gelation:

[0058] Drop the hydrogel solution onto a polyimide film with a thickness of 100 μm, then cover a PET film with a thickness of 100 μm on the liquid surface, and then the casting blade continuously spreads the liquid droplets in the two films into a film with a certain thickness at a speed of 200 mm / min. Transfer the cast liquid film together with the polyimide film to ultraviolet light for 20 min of gelation to finally obtain a continuous hydrogel film;

[0059] III. Pre-carbonization:

[0060] Separate the hydrogel film obtained in step II from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0061] The process of the low-temperature pre-carbonization described in step III is: heat up at a heating rate of 2 °C / min to 200 °C and carbonize at 200 °C for 6 h;

[0062] IV. Carbonization and graphitization:

[0063] Carry out carbonization and graphitization on the carbon precursor film obtained in step III to obtain a large-size graphite film with high crystallinity;

[0064] The temperature of the carbonization described in step IV is 1200 °C, the atmosphere of the carbonization is vacuum, and the time of the carbonization is 1 h;

[0065] The temperature of the graphitization described in step IV is 2800 °C, the atmosphere of the graphitization is argon, and the time of the graphitization is 3 h.

[0066] Figure 1 It is a physical picture of the graphite film prepared in Example 1;

[0067] FromFigure 1 It can be seen that the length of the continuous graphite film exceeds 10 cm.

[0068] Figure 2 It is the cross-sectional microscopic morphology diagram of the graphite film prepared in Example 1;

[0069] From Figure 2 An obvious graphite sheet layer structure can be observed.

[0070] Figure 3 It is the XRD pattern of the graphite film prepared in Example 1;

[0071] Figure 3 It proves that the prepared continuous graphite film has good crystallization quality.

[0072] Figure 4 It is the Raman spectrum of the graphite film prepared in Example 1.

[0073] Figure 4 It shows that the prepared continuous graphite film has less defect content and higher quality.

[0074] Example 2: A method for preparing a continuous graphite film using small molecule carbohydrates is realized according to the following steps:

[0075] I. Prepare a hydrogel solution:

[0076] Mix 30 g of deionized water, 70 g of analytical pure fructose, 14 g of acrylic acid, 0.7 g of N,N'-methylenebisacrylamide, 0.8 g of α-ketoglutaric acid and 0.21 g of sodium carboxymethyl cellulose in a certain proportion and stir until fully dissolved to obtain a clear hydrogel solution;

[0077] II. Cast film and gelation:

[0078] Drop the hydrogel solution onto a polyimide film with a thickness of 100 μm, then cover a PET film with a thickness of 100 μm on the liquid surface, and then continuously spread the liquid droplets in the two films into a film with a certain thickness at a speed of 200 mm / min by a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for 20 min of gelation to finally obtain a continuous hydrogel film;

[0079] III. Pre-carbonization:

[0080] Separate the hydrogel film obtained in step II from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0081] The process of low-temperature pre-carbonization described in Step 3 is as follows: heating up to 200°C at a heating rate of 2°C / min and carbonizing at 200°C for 6 hours;

[0082] IV. Carbonization and graphitization:

[0083] Carbonize and graphitize the carbon precursor film obtained in Step 3 to obtain a large-size graphite film with high crystallinity;

[0084] The temperature of carbonization described in Step 4 is 1400°C, the atmosphere of carbonization is vacuum, and the time of carbonization is 1 hour;

[0085] The temperature of graphitization described in Step 4 is 2800°C, the atmosphere of graphitization is argon, and the time of graphitization is 3 hours.

[0086] Figure 5 It is a physical picture of the graphite film prepared in Example 2;

[0087] From Figure 5 it can be seen that the length of the continuous graphite film exceeds 15 cm.

[0088] Example 3: A method for preparing a continuous graphite film using small molecule carbohydrates is realized according to the following steps:

[0089] I. Prepare a hydrogel solution:

[0090] Mix 15 g of deionized water, 45 g of analytical pure glucose, 9 g of acrylic acid, 0.45 g of N,N'-methylenebisacrylamide, 0.4 g of α-ketoglutaric acid, and 0.105 g of sodium carboxymethyl cellulose in a certain proportion and stir until fully dissolved to obtain a clear hydrogel solution;

[0091] II. Casting into film and gelation:

[0092] Drop the hydrogel solution onto a polyimide film with a thickness of 100 μm, then cover a PET film with a thickness of 100 μm on the liquid surface, and then continuously spread the liquid droplets in the two films into a film with a certain thickness at a speed of 200 mm / min by a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for 15 minutes of gelation to finally obtain a continuous hydrogel film;

[0093] III. Pre-carbonization:

[0094] Separate the hydrogel film obtained in Step II from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0095] The process of low-temperature pre-carbonization described in Step 3 is as follows: heating at a rate of 1 °C / min to 200 °C and carbonizing at 200 °C for 6 h;

[0096] IV. Carbonization and graphitization:

[0097] Carbonize and graphitize the carbon precursor film obtained in Step 3 to obtain a large-sized graphite film with high crystallinity;

[0098] The temperature of carbonization described in Step 4 is 1200 °C, the atmosphere of carbonization is vacuum, and the time of carbonization is 1 h;

[0099] The temperature of graphitization described in Step 4 is 2800 °C, the atmosphere of graphitization is argon, and the time of graphitization is 3 h.

[0100] Example 4: A method for preparing a continuous graphite film using small molecule carbohydrates is implemented according to the following steps:

[0101] I. Preparation of hydrogel solution:

[0102] Mix 30 g of deionized water, 70 g of analytical pure glucose, 14 g of acrylic acid, 0.7 g of N,N'-methylenebisacrylamide, 0.8 g of α-ketoglutaric acid, and 0.63 g of sodium carboxymethyl cellulose in a certain proportion and stir until fully dissolved to obtain a clear hydrogel solution;

[0103] II. Casting into film and gelation:

[0104] Drop the hydrogel solution onto a polyimide film with a thickness of 100 μm, then cover a PET film with a thickness of 100 μm on the liquid surface, and then continuously spread the liquid droplets in the two films into a film with a certain thickness at a speed of 200 mm / min by a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for 20 min of gelation to finally obtain a continuous hydrogel film;

[0105] III. Pre-carbonization:

[0106] Separate the hydrogel film obtained in Step 2 from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film;

[0107] The process of low-temperature pre-carbonization described in Step 3 is as follows: heating at a rate of 2 °C / min to 200 °C and carbonizing at 200 °C for 6 h;

[0108] IV. Carbonization and graphitization:

[0109] Carbonize and graphitize the carbon precursor film obtained in Step 3 to obtain a large-sized graphite film with high crystallinity;

[0110] In Step 4, the temperature of carbonization is 1200 °C, the atmosphere of carbonization is vacuum, and the time of carbonization is 1 h;

[0111] In Step 4, the temperature of graphitization is 3000 °C, the atmosphere of graphitization is argon, and the time of graphitization is 3 h.

Claims

1. A method for preparing continuous graphite film using small molecule carbohydrates, characterized in that the preparation method is realized according to the following steps: I. Prepare a hydrogel solution: Mix deionized water, water-soluble saccharides, acrylic acid, N,N'-methylenebisacrylamide, α-ketoglutaric acid and sodium carboxymethylcellulose in a certain proportion and stir to obtain a hydrogel solution; In step I, the mass ratio of the water-soluble saccharides to deionized water is (1-4):1; In step I, the mass ratio of the sodium carboxymethylcellulose to deionized water is (0.001-0.05):1; In step I, the mass ratio of the acrylic acid to the water-soluble saccharides is (0.1-0.5):1; In step I, the mass ratio of the N,N'-methylenebisacrylamide to the acrylic acid is (0.01-0.1):1; In step I, the mass ratio of the α-ketoglutaric acid to the acrylic acid is (0.01-0.1):1; II. Cast film and gelation: Drop the hydrogel solution on a clean polyimide film, then cover a clean PET film on the liquid surface, and then continuously spread the liquid droplets between the two films into a film with a certain thickness by a casting knife. Transfer the cast liquid film together with the polyimide film to ultraviolet light for gelation to finally obtain a continuous hydrogel film; III. Pre-carbonization: Separate the hydrogel film obtained in step II from the PET film, make the hydrogel film adhere to the surface of the polyimide film on one side, and perform low-temperature pre-carbonization on the separated hydrogel film. The hydrogel film undergoes a polymerization reaction and transforms into a carbon precursor film; IV. Carbonization and graphitization: Perform carbonization and graphitization on the carbon precursor film obtained in step III to obtain a continuous graphite film derived from small molecule carbohydrates.

2. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the water-soluble saccharides described in step I are one or a mixture of several of analytically pure or chemically pure water-soluble glucose, water-soluble fructose, water-soluble sucrose and water-soluble maltose.

3. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the thickness of the hydrogel film described in step II is 20μm-200μm, and the length is 10cm-20cm.

4. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the gelation time described in step II is 5min-30min.

5. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the low-temperature pre-carbonization process described in step III is: heating at a heating rate of 1°C / min-2°C / min to 150°C-300°C, and carbonizing at 150°C-300°C for 1h-24h.

6. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that The temperature of carbonization described in Step 4 is 800°C to 1400°C, the atmosphere of carbonization is vacuum or inert gas, and the time of carbonization is 0.5 h to 6 h.

7. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 6, characterized in that the inert gas is argon.

8. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the temperature of graphitization described in Step 4 is 2400°C to 3000°C, the atmosphere of graphitization is vacuum or inert gas, and the time of graphitization is 1 h to 6 h.

9. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 8, characterized in that the inert gas is argon.

10. A method for preparing continuous graphite film using small molecule carbohydrates according to claim 1, characterized in that the thickness of the continuous graphite film described in Step 4 is 15 μm to 150 μm, and the length is 10 cm to 16 cm.

Images