Graphene oxide dispersion liquid, preparation method and graphene heat-conducting film

Abstract

The graphene oxide dispersion liquid is prepared from the following raw materials: a water-based organic high-molecular compound, a metal catalyst, graphene oxide, a pH regulator and deionized water, the usage amount of the water-based organic high-molecular compound is 0.03-0.8% of the mass of the graphene oxide, and the usage amount of the metal catalyst is 0.01-0.08% of the mass of the graphene oxide. The graphene oxide is modified by adopting the organic polymer-metal composite dispersion liquid, so that the graphene heat-conducting film with relatively high thickness, fewer defects, more complete crystal structure and excellent comprehensive heat-conducting property can be obtained. By adopting the ammonium lignosulfonate and the praseodymium metal salt with specific contents, the thermal dispersibility and the thermal conductivity of the heat-conducting film can be improved, the viscosity of the graphene oxide dispersion liquid is not greatly increased, and the heat-conducting film can be processed by applying a tape casting process.

Description

Technical Field

[0001] The present invention relates to the field of non-metal element compounds, and particularly to a graphene oxide dispersion liquid, a preparation method thereof, and a graphene thermal conductive film. Background Art

[0002] Graphene materials have extremely high electron mobility and excellent thermal conductivity, and have replaced traditional heat dissipation materials in the fields of mobile phones, computers, and electronic devices. However, the thermal conductivity coefficient of existing graphene thermal conductive films is lower than 1500 W / (m·K), and the further development of thermal conductivity performance is limited. The main reason is that the viscosity of high-concentration graphene dispersion liquid is relatively high, the fluidity is poor, which is not conducive to the preparation of ultra-thick GO films by the casting method. And there are defects in the crystal structure of graphene in the production process of industrial graphene dispersion liquid, resulting in serious scattering of phonons during the transmission process, leading to a decrease in the thermal conductivity performance of graphene thermal conductive films.

[0003] Chinese Patent CN117263175A discloses a high-solid graphene oxide slurry, a graphene oxide thermal conductive film and a preparation method thereof. By the mutual matching of two dispersants, the viscosity of the graphene slurry can be reduced, and the solid content can be increased. The graphene solid content can reach 6-10%, and a stable, low-viscosity, high-solid graphene oxide slurry can be prepared. However, the solid content of the graphene slurry still cannot achieve the best effect. Chinese Patent CN112794314B discloses a preparation method of a group-regulated high-density graphene thermal conductive film and the obtained product. The graphene oxide is subjected to group treatment with a group binder to complete the effective dispersion of the slurry, and a modifier is used for group repair to prepare a high-solid content slurry while controlling the dispersion uniformity and viscosity applicability of the slurry. However, it is prepared by a calendering process, and the process is relatively complex. Summary of the Invention

[0004] In order to develop a high-solid content graphene dispersion liquid, improve the film thickness of the graphene thermal conductive film formed by casting, improve the structural integrity of the graphene thermal conductive film, reduce the intrinsic defects, and improve its thermal conductivity performance. The first aspect of the present invention provides a graphene oxide dispersion liquid, and the preparation raw materials include: a water-based organic polymer compound, a metal catalyst, graphene oxide, a pH regulator, and deionized water; the usage amount of the water-based organic polymer compound is 0.03-0.8% of the mass of graphene oxide, and the usage amount of the metal catalyst is 0.01-0.08% of the mass of graphene oxide.

[0005] As an implementation manner, the water-based organic polymer compound is a lignin derivative; the lignin derivative is selected from at least one of ammonium lignosulfonate, sodium lignosulfonate, magnesium lignosulfonate, or calcium lignosulfonate.

[0006] As an implementation manner, the water-based organic polymer compound is ammonium lignosulfonate.

[0007] As an embodiment, the metal catalyst is a rare earth metal catalyst, and the rare earth metal catalyst is a praseodymium metal salt.

[0008] As an embodiment, the praseodymium metal salt is selected from at least one of praseodymium chloride, praseodymium carbonate, praseodymium sulfate or praseodymium nitrate.

[0009] As an embodiment, the praseodymium metal salt is praseodymium chloride.

[0010] As an embodiment, the pH regulator is ammonia water.

[0011] The inventor found in the experiment that by using an aqueous composite solution of ammonium lignosulfonate and praseodymium chloride to modify graphene oxide, a graphene thermal conductive film with a higher thickness and excellent comprehensive thermal conductivity can be obtained. The reason is that ammonium lignosulfonate contains a large number of phenolic hydroxyl groups, alcoholic hydroxyl groups, carboxyl groups and carbonyl groups. The unshared electron pairs on the oxygen atoms in graphene oxide can form coordination bonds with the metal ion praseodymium. At the same time, the carboxyl groups and carbonyl groups react with the oxygen-containing functional groups on the surface of graphene oxide, so that the structure with catalytic graphitization is accurately linked to the defects of graphene oxide. During the graphitization stage, the praseodymium atoms play their catalytic effect, form double bonds with carbon atoms and then form benzene rings, and then quickly detach from the benzene ring structure and continue to combine with the remaining non-benzene ring carbon atoms to produce benzene rings, thereby gradually reducing the number of defects in graphene and making the crystal structure gradually become complete.

[0012] The second aspect of the present invention provides a preparation method of a graphene oxide dispersion liquid, comprising the following steps:

[0013] S1: Prepare an aqueous solution of a water-soluble organic polymer compound;

[0014] S2: Adjust the pH of the aqueous solution of the water-soluble organic polymer compound;

[0015] S3: Add the metal catalyst to the aqueous solution of the water-soluble organic polymer compound with the pH adjusted in step S2, seal and ultrasonicate to obtain an organic polymer-metal composite dispersion liquid;

[0016] S4: Add graphene oxide to deionized water and stir to obtain a graphene oxide slurry;

[0017] S5: Add the organic polymer-metal composite dispersion liquid to the graphene oxide slurry, stir and mix, and add a pH regulator to adjust to obtain a mixture;

[0018] S6: Subject the mixture in step S5 to high-pressure homogenization to obtain a graphene oxide dispersion liquid.

[0019] As an implementation manner, the aqueous organic polymer compound solution is a solution of an aqueous organic polymer compound and deionized water, and the mass concentration of the aqueous organic polymer compound solution is 0.178 - 0.952 mg / mL.

[0020] As an implementation manner, in step S2, the pH of the aqueous organic polymer compound solution is adjusted to 9 - 9.5.

[0021] As an implementation manner, in step S2, the pH of the aqueous organic polymer compound solution is adjusted to 9.32 - 9.34.

[0022] As an implementation manner, in step S2, the pH of the aqueous organic polymer compound solution is adjusted to 9.33.

[0023] As an implementation manner, in step S3, the ultrasonic frequency is 0.3 - 1 KW, and in step S3, the ultrasonic time is 1 - 3 h.

[0024] As an implementation manner, in step S4, graphene oxide is added to deionized water in 3 - 5 times, and the addition amount of graphene oxide each time is 2 - 4% of the mass of deionized water. The solid content of the graphene oxide slurry obtained in step S4 is 10 - 15 wt%.

[0025] As an implementation manner, in step S4, graphene oxide is added to deionized water in 4 times, and the solid content of the graphene oxide slurry obtained in step S4 is 12 wt%.

[0026] As an implementation manner, in step S4, the stirring rate is 1500 - 3000 rpm.

[0027] As an implementation manner, in step S5, the stirring rate is 1500 - 3000 rpm, and in step S6, the homogenization pressure is 15 - 55 MPa.

[0028] As an implementation manner, in step S5, the pH is adjusted to 5.5 - 6.5.

[0029] The excellent thermal conductivity coefficient of the graphene thermal conductive film is mainly attributed to the long-range ordered carbon atom SP 2 hybrid aromatic ring structure, a large number of SP 2Hybrid carbon atoms form a carbon six-membered ring aromatic structure through covalent bonds, with a thermal conductivity one order of magnitude higher than that of traditional metals. Although the theoretical thermal conductivity of graphene is very high, there are defects in the crystal structure of graphene during industrial mass production, resulting in severe scattering of phonons during the transmission process, leading to a decrease in the thermal conductivity of the graphene thermal conductive film. The increase in the solid content of the GO dispersion helps to increase the thickness of the GO film, thereby increasing the thickness of the graphene thermal conductive film, so as to achieve the purpose of increasing the heat flux and further improving the heat dissipation ability of the graphene thermal conductive film. At the same time, it will also bring a reduction in production costs. However, the large specific surface area, hydrogen bonds and intermolecular forces of graphene oxide result in extremely high viscosity and almost no fluidity of the high-concentration GO dispersion, which is not conducive to the preparation of ultra-thick GO films by the casting method.

[0030] In the present invention, through the grafting and compounding between organic polymers and metal compounds, an ultra-thick and high-performance graphene thermal conductive film that can be industrially produced is developed, which increases the single film thickness of the graphene thermal conductive film and its heat flux. And the presence of praseodymium can transform non-sp2 hybrid carbon into the form of sp2 hybrid carbon, improving the crystallinity of the graphene crystal, eliminating the performance reduction caused by intrinsic defects, and improving the comprehensive thermal conductivity of the graphene thermal conductive film.

[0031] The inventors further found that along with the carbonization of ammonium lignosulfonate, lignin is cracked into carbon, providing an additional carbon source for the rearrangement and defect repair of subsequent carbon atoms, and also providing free carbon for the carbon-carrying removal of oxygen-containing functional groups, avoiding the consumption of carbon atoms on the complete six-membered ring and causing more defects to appear.

[0032] The third aspect of the present invention provides a graphene thermal conductive film prepared by using the above-mentioned graphene oxide dispersion.

[0033] The fourth aspect of the present invention provides a preparation method of the above-mentioned graphene thermal conductive film, comprising the following steps:

[0034] H1: Coating and drying the graphene oxide dispersion to obtain a graphene precursor film;

[0035] H2: Performing low-temperature heat treatment on the graphene precursor film to obtain a graphene pre-treatment film;

[0036] H3: Performing a carbonization reaction on the graphene pre-treatment film to obtain a graphene carbonization film;

[0037] H4: Performing graphitization treatment on the graphene carbonization film and rolling to obtain a graphene thermal conductive film.

[0038] As an implementation manner, in the step H1, the coating thickness is 2.5 - 5 mm, the drying temperature is 50 - 85 °C, and the drying time is 3 - 5 h.

[0039] As an implementation manner, the coating thickness in step H1 is 3 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0040] As an implementation manner, the low-temperature heat treatment temperature in step H2 is 75 - 150 °C, and the low-temperature heat treatment time is 170 - 180 h.

[0041] As an implementation manner, the low-temperature heat treatment temperature in step H2 is 150 °C, the heating rate is 0.5 °C / min, and the low-temperature heat treatment time is 172 h.

[0042] As an implementation manner, the temperature of the carbonization reaction in step H3 is 1300 - 1500 °C, the atmosphere condition is argon, the heating rate is 2 - 5 °C / min, and the carbonization reaction time is 2 - 5 h.

[0043] As an implementation manner, the temperature of the carbonization reaction in step H3 is 1400 °C, the atmosphere condition is argon, the heating rate is 2.5 °C / min, and the carbonization reaction time is 3 h.

[0044] In step H3, the oxygen-containing functional groups in the graphene carbonized film are basically removed completely. At the same time, the carbonization of ammonium lignosulfonate occurs, and a double-bond benzene ring structure is formed between praseodymium and free carbon, and the defects are repaired for the first time. The carbonized treatment film is obtained by natural cooling.

[0045] As an implementation manner, the graphitization treatment temperature in step H4 is 2600 - 3000 °C, the heating rate is 0.5 - 7 °C / min, and the heat preservation time is 3 - 4 h.

[0046] As an implementation manner, the graphitization treatment in step H4 is a stepped heating program. The stepped heating program is as follows: heating to 1000 - 1100 °C at a heating rate of 4 - 5 °C / min; then heating to 2600 - 2800 °C at a heating rate of 1 - 2 °C / min and keeping warm for 2 h; finally heating to 2600 - 3000 °C at a heating rate of 0.5 - 1 °C / min and keeping warm for 1 h. After the heat preservation is completed, it is cooled to room temperature.

[0047] As an implementation manner, the graphitization treatment in step H4 is a stepped heating program. The stepped heating program is as follows: heating to 1000 °C at a heating rate of 5 °C / min; then heating to 2600 °C at a heating rate of 2 °C / min and keeping warm for 2 h; finally heating to 2800 °C at a heating rate of 0.5 °C / min and keeping warm for 1 h. After the heat preservation is completed, it is cooled to room temperature.

[0048] As an implementation manner, the pressure of calendering in step H4 is 300 - 800 t.

[0049] As an implementation manner, the pressure of calendering in step H4 is 500t.

[0050] As an implementation manner, step H4 is specifically as follows: Stack graphene carbonized films, and intercalate graphite films between single or multiple graphene carbonized films and transfer them to a graphitization furnace. Use a 5 Kg graphite plate for natural loading, and raise the temperature to 1000 °C at a heating rate of 5 °C / min; then raise the temperature to the middle zone temperature of 2600 °C at a heating rate of 2 °C / min, and keep the temperature for 2 h; finally, raise the temperature to the graphitization temperature of 2800 °C at a heating rate of 0.5 °C, keep the temperature for 1 h, and after the heat preservation ends, cool to room temperature, and obtain a graphene thermal conductive film by calendering at 500t.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) For the graphene oxide dispersion liquid of the present invention, by using an organic polymer-metal composite dispersion liquid to modify graphene oxide, a graphene thermal conductive film with a higher thickness, fewer defects, a more complete crystal structure, and excellent comprehensive thermal conductivity can be obtained.

[0053] (2) For the graphene oxide dispersion liquid of the present invention, by using a specific content of ammonium lignosulfonate and praseodymium metal salt, the thermal dispersibility and thermal conductivity of the thermal conductive film can be improved, and the viscosity of the graphene oxide dispersion liquid will not increase significantly, and it can be processed by a casting process.

[0054] (3) For the thermal conductive film prepared from the graphene oxide dispersion liquid of the present invention, during the carbonization stage of the graphene pretreatment film, lignin is cracked into carbon, which provides an additional carbon source for the rearrangement and defect repair of subsequent carbon atoms and also provides free carbon for the carbon-carrying removal of oxygen-containing functional groups, avoiding the consumption of carbon atoms on the complete six-membered ring and causing more defects.

[0055] (4) For the thermal conductive film prepared from the graphene oxide dispersion liquid of the present invention, by using a graphitization treatment temperature of 2600 - 3000 °C, praseodymium is tightly combined with carbon. After catalyzing the formation of benzene rings between carbon-carbon double bonds, praseodymium quickly escapes and continues to bond with free carbon atoms, cyclically catalyzing graphitization, so that the crystal structure of graphene tends to be complete.

[0056] (5) For the thermal conductive film prepared from the graphene oxide dispersion liquid of the present invention, by using the casting method to prepare a thermal conductive film with a high thickness, it has a more efficient preparation efficiency and lower energy consumption. Description of the Drawings

[0057] Figure 1 Front view of the physical picture of the graphene thermal conductive film of Example 1 of the present invention;

[0058] Figure 2 Cross-sectional view of the physical picture of the graphene thermal conductive film of Example 1 of the present invention;

[0059] Figure 3 SEM micrograph of the graphene carbonized film after H3 carbonization treatment in Example 1 of the present invention;

[0060] Figure 4 SEM micrograph of the graphene thermal conductive film prepared in Example 1 of the present invention;

[0061] Figure 5 Raman diagram of the graphene thermal conductive films of Example 1 and Comparative Example 1 of the present invention;

[0062] Figure 5 In: 1. Example 1; 2. Comparative Example 1.

[0063] Figure 6 XRD diagram of the graphene thermal conductive film of Example 1 of the present invention;

[0064] Figure 7 Hot stage test diagram of the graphene thermal conductive film of Example 1 of the present invention;

[0065] Figure 8 Hot stage test diagram of the graphene thermal conductive film of Example 2 of the present invention;

[0066] Figure 9 Hot stage test diagram of the graphene thermal conductive film of Example 3 of the present invention;

[0067] Figure 10 Hot stage test diagram of the graphene thermal conductive film of Comparative Example 1 of the present invention;

[0068] Figure 11 Hot stage test diagram of the graphene thermal conductive film of Comparative Example 2 of the present invention;

[0069] Figure 12 Hot stage test diagram of the graphene thermal conductive film of Comparative Example 3 of the present invention;

[0070] Figure 13 Hot stage test diagram of the graphene thermal conductive film of Comparative Example 4 of the present invention;

[0071] Figure 14 Wide-angle X-ray scattering test diagram of the graphene thermal conductive film prepared in Example 1 of the present invention;

[0072] Figure 15 Azimuth-intensity curve diagram of the graphene thermal conductive film prepared in Example 1 of the present invention;

[0073] Figure 16 XPS peak pattern picture of the graphene thermal conductive film prepared in Example 1 of the present invention;

[0074] Figure 17The picture for testing the fluidity of the graphene oxide dispersion liquid prepared in Example 1 of the present invention;

[0075] Figure 18 The picture for testing the fluidity of the graphene oxide dispersion liquid prepared in Comparative Example 3 of the present invention. Detailed implementation manners

[0076] Example 1

[0077] A graphene oxide dispersion liquid, the preparation raw materials include: a water-based organic polymer compound, a metal catalyst, graphene oxide, a pH regulator, deionized water; the usage amount of the water-based organic polymer compound is 0.03% of the mass of graphene oxide, and the usage amount of the metal catalyst is 0.01% of the mass of graphene oxide.

[0078] The water-based organic polymer compound is ammonium lignosulfonate.

[0079] The metal catalyst is praseodymium chloride. The pH regulator is ammonia water.

[0080] A preparation method of a graphene oxide dispersion liquid, comprising the following steps:

[0081] S1: Prepare a water-based organic polymer compound solution;

[0082] S2: Adjust the pH of the water-based organic polymer compound solution;

[0083] S3: Add the metal catalyst to the water-based organic polymer compound solution after adjusting the pH in step S2, seal and ultrasonicate to obtain an organic polymer-metal composite dispersion liquid;

[0084] S4: Add graphene oxide to deionized water and stir to obtain a graphene oxide slurry;

[0085] S5: Add the organic polymer-metal composite dispersion liquid to the graphene oxide slurry, stir and mix, add a pH regulator to adjust to obtain a mixture;

[0086] S6: Subject the mixture in step S5 to high-pressure homogenization to obtain a graphene oxide dispersion liquid.

[0087] The water-based organic polymer compound solution is a solution of 0.0178 g of water-based organic polymer compound and 300 mL of deionized water.

[0088] In step S2, the pH of the water-based organic polymer compound solution is adjusted to 9.33.

[0089] In step S3, the ultrasonic frequency is 0.6 KW, and the ultrasonic time in step S3 is 1.5 h.

[0090] In step S4, graphene oxide is added to deionized water in 4 portions, and the solid content of the graphene oxide slurry obtained in step S4 is 12 wt%.

[0091] Specifically, step S4 is as follows: 160 g of graphene oxide filter cake (the solid content of graphene oxide in the graphene oxide filter cake is 37.2 wt%) is added to 500 g of deionized water in four portions. After all the additions are completed, stirring is continued for 20 min.

[0092] The graphene oxide filter cake is purchased from Baotailong New Materials Co., Ltd.

[0093] In step S4, the stirring rate is 2000 rpm.

[0094] In step S5, the pH is adjusted to 5.5. In step S5, the stirring rate is 2000 rpm, and in step S6, the homogenization pressure is 50 MPa.

[0095] A graphene thermal conductive film is prepared by using the above-mentioned graphene oxide dispersion.

[0096] A method for preparing a graphene thermal conductive film includes the following steps:

[0097] H1: Coating the graphene oxide dispersion, and drying to obtain a graphene precursor film;

[0098] H2: Performing low-temperature heat treatment on the graphene precursor film to obtain a graphene pre-treated film;

[0099] H3: Performing a carbonization reaction on the graphene pre-treated film to obtain a graphene carbonized film;

[0100] H4: Performing graphitization treatment on the graphene carbonized film, and rolling at 500 t to obtain a graphene thermal conductive film.

[0101] In step H1, the coating thickness is 3 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0102] In step H2, the low-temperature heat treatment temperature is 150 °C, the heating rate is 0.5 °C / min, and the low-temperature heat treatment time is 172 h.

[0103] In step H3, the temperature of the carbonization reaction is 1400 °C, the atmosphere condition is argon, the heating rate is 2.5 °C / min, and the carbonization reaction time is 3 h.

[0104] The graphitization treatment in step H4 is a stepped heating program, and the stepped heating program is as follows: heating at a heating rate of 5 °C / min to 1000 °C; then heating at a heating rate of 2 °C / min to 2600 °C and holding for 2 h; finally heating at a heating rate of 0.5 °C / min to 2800 °C and holding for 1 h, and cooling to room temperature after the holding ends.

[0105] The front view of the physical picture of the prepared graphene thermal conductive film is shown in Figure 1 , and the side view of the physical picture of the prepared graphene thermal conductive film is shown in Figure 2 , and the SEM micrograph of the graphene carbonized film after the H3 carbonization treatment is shown in Figure 3 ; the SEM micrograph of the prepared graphene thermal conductive film is shown in Figure 4 ; the Raman graph of the prepared graphene thermal conductive film is shown in Figure 5 ; the XRD graph of the prepared graphene thermal conductive film is shown in Figure 6 .

[0106] Example 2

[0107] A graphene oxide dispersion liquid, the preparation raw materials include: a water-based organic polymer compound, a metal catalyst, graphene oxide, a pH regulator, and deionized water; the usage amount of the water-based organic polymer compound is 0.04% of the mass of graphene oxide, and the usage amount of the metal catalyst is 0.016% of the mass of graphene oxide.

[0108] In step H1, the coating thickness is 3.5 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0109] The remaining specific implementation manners are the same as those in Example 1.

[0110] Example 3

[0111] A graphene oxide dispersion liquid, the preparation raw materials include: a water-based organic polymer compound, a metal catalyst, graphene oxide, a pH regulator, and deionized water; the usage amount of the water-based organic polymer compound is 0.06% of the mass of graphene oxide, and the usage amount of the metal catalyst is 0.023% of the mass of graphene oxide.

[0112] In step H1, the coating thickness is 3.5 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0113] The remaining specific implementation manners are the same as those in Example 1.

[0114] Comparative Example 1

[0115] A graphene oxide dispersion liquid, the preparation raw materials include: graphene oxide, a pH regulator, and deionized water.

[0116] A preparation method of a graphene oxide dispersion liquid, comprising the following steps:

[0117] S1: Add graphene oxide to deionized water and stir to obtain a graphene oxide slurry;

[0118] S2: Add a pH regulator to the graphene oxide slurry for adjustment to obtain a mixture;

[0119] S3: Subject the mixture in step S2 to high-pressure homogenization to obtain a graphene oxide dispersion liquid.

[0120] In step S1, the graphene oxide is added to the deionized water in 4 portions, and the solid content of the graphene oxide slurry obtained in step S4 is 12 wt%.

[0121] Specifically, step S1 is: Add 160 g of graphene oxide filter cake (the solid content of graphene oxide in the graphene oxide filter cake is 37.2 wt%) to 500 g of deionized water in four portions. After all are added, continue to stir for 20 min.

[0122] The stirring rate in step S1 is 2000 rpm.

[0123] In step S2, the pH is adjusted to 5.5. The stirring rate in step S2 is 2000 rpm, and the homogenization pressure in step S3 is 50 MPa.

[0124] A graphene thermal conductive film and a preparation method thereof, the specific implementation manner is the same as that in Example 1.

[0125] The Raman diagram of the prepared graphene thermal conductive film is shown in Figure 4 .

[0126] Comparative Example 2

[0127] A graphene oxide dispersion liquid and a preparation method thereof, the specific implementation manner is the same as that in Example 1.

[0128] A graphene thermal conductive film is prepared by using the above-mentioned graphene oxide dispersion liquid.

[0129] A preparation method of a graphene thermal conductive film, comprising the following steps:

[0130] H1: Coat and dry the graphene oxide dispersion liquid to obtain a graphene precursor film;

[0131] H2: Perform low-temperature heat treatment on the graphene precursor film to obtain a graphene pre-treatment film;

[0132] H3: Perform a carbonization reaction on the graphene pre-treatment film to obtain a graphene carbonization film;

[0133] H4: Graphitize the graphene carbonized film to obtain a graphene thermal conductive film.

[0134] In the step H1, the coating thickness is 3 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0135] In the step H2, the low-temperature heat treatment temperature is 150 °C, the heating rate is 0.5 °C / min, and the low-temperature heat treatment time is 172 h.

[0136] In the step H3, the temperature of the carbonization reaction is 1400 °C, the atmosphere condition is argon, the heating rate is 2.5 °C / min, and the carbonization reaction time is 3 h.

[0137] In the step H4, the graphitization treatment is a stepped heating program, and the stepped heating program is as follows: heat up to 1000 °C at a heating rate of 5 °C / min; then heat up to 2600 °C at a heating rate of 2 °C / min and hold for 2 h; finally heat up to 3050 °C at a heating rate of 0.5 °C / min and hold for 1 h, and cool to room temperature after the holding ends.

[0138] Comparative Example 3

[0139] A graphene oxide dispersion liquid, and the preparation raw materials include: a metal catalyst, graphene oxide, a pH regulator, and deionized water; the usage amount of the metal catalyst is 0.01% of the mass of the graphene oxide.

[0140] The metal catalyst is praseodymium chloride. The pH regulator is ammonia water.

[0141] A preparation method of a graphene oxide dispersion liquid, comprising the following steps:

[0142] S1: Add the metal catalyst to 300 mL of deionized water, seal and ultrasonicate to obtain a metal catalyst dispersion liquid;

[0143] S2: Add the graphene oxide to the deionized water and stir to obtain a graphene oxide slurry;

[0144] S3: Add the metal catalyst dispersion liquid to the graphene oxide slurry, stir and mix, add the pH regulator to adjust, and obtain a mixture;

[0145] S4: Subject the mixture in step S3 to high-pressure homogenization to obtain a graphene oxide dispersion liquid.

[0146] In the step S1, the ultrasonic frequency is 0.6 KW, and in the step S1, the ultrasonic time is 1.5 h.

[0147] In the step S2, the graphene oxide is added to the deionized water in 4 portions, and the solid content of the graphene oxide slurry obtained in the step S2 is 12 wt%.

[0148] Step S2 is specifically as follows: 160 g of graphene oxide filter cake (the solid content of graphene oxide in the graphene oxide filter cake is 37.2 wt%) is added into 500 g of deionized water in four portions. After all the addition is completed, stirring is continued for 20 min.

[0149] The stirring rate in step S2 is 2000 rpm.

[0150] In step S3, the pH is adjusted to 5.5. The stirring rate in step S3 is 2000 rpm, and the homogenization pressure in step S4 is 50 MPa.

[0151] A graphene thermal conductive film and a preparation method thereof, and the specific implementation manner is the same as that of Example 1.

[0152] Comparative Example 4

[0153] A graphene oxide dispersion liquid and a preparation method thereof, and the specific implementation manner is the same as that of Example 1.

[0154] A graphene thermal conductive film is prepared by using the above-mentioned graphene oxide dispersion liquid.

[0155] A preparation method of a graphene thermal conductive film includes the following steps:

[0156] H1: Coating the graphene oxide dispersion liquid, and drying to obtain a graphene precursor film;

[0157] H2: Performing low-temperature heat treatment on the graphene precursor film to obtain a graphene pre-treatment film;

[0158] H3: Performing a carbonization reaction on the graphene pre-treatment film to obtain a graphene carbonization film;

[0159] H4: Performing graphitization treatment on the graphene carbonization film to obtain a graphene thermal conductive film.

[0160] The coating thickness in step H1 is 3 mm, the drying temperature is 85 °C, and the drying time is 3.5 h.

[0161] The low-temperature heat treatment temperature in step H2 is 150 °C, the heating rate is 0.5 °C / min, and the low-temperature heat treatment time is 172 h.

[0162] The temperature of the carbonization reaction in step H3 is 1400 °C, the atmosphere condition is argon, the heating rate is 2.5 °C / min, and the carbonization reaction time is 3 h.

[0163] The graphitization treatment in step H4 is a stepped heating program, and the stepped heating program is as follows: heating at a heating rate of 10 °C / min to 1000 °C; then heating at a heating rate of 5 °C / min to 2600 °C and holding for 2 h; finally heating at a heating rate of 1 °C / min to 2800 °C and holding for 1 h, and after the holding ends, cooling to room temperature.

[0164] Performance test

[0165] The SEM micrograph of the graphene thermal conductive film prepared in Example 1 is shown in Figure 4 , from Figure 3 , it can be seen from 4 that the lamellae of the graphene oxide film after carbonization are not closely stacked between the lamellae, and there are pores between the layers; while after graphitization rolling, it can be seen that the graphene lamellae are very closely stacked between the lamellae and the degree of orientation is relatively high.

[0166] The Raman graph of the graphene thermal conductive films prepared in Example 1 and Comparative Example 1 is shown in Figure 5 , from Figure 5 it can be known that after graphitization treatment, characteristic peaks appear at the 2D peak at 2681 cm -1 , the D peak at 1350 cm -1 and the G peak at 1500 cm -1 of the sample, and the 2D peak presents a sharp and symmetric shape with a perfect single Lorentzian peak shape, which indicates that the number of graphene layers is relatively close to the state of single-layer graphene. At the same time, it can also be seen that the ratio of I D / I G of Example 1 with the addition of the organic polymer-metal composite dispersion liquid decreases significantly, which indicates that the defect density of graphene decreases significantly.

[0167] The XRD graph of the graphene thermal conductive film prepared in Example 1 is shown in Figure 6 , from Figure 6 it can be known that after graphitization treatment, the crystal structure of Example 1 tends to the crystal structure of natural graphite.

[0168] The hot stage test graph of the graphene thermal conductive film prepared in Example 1 is shown in Figure 7 , from Figure 7 it can be known that the actual heat spreading effect of the graphene thermal conductive film prepared in Example 1 is better than that of the graphene thermal conductive film of Comparative Example 1.

[0169] The hot stage test graphs of the graphene thermal conductive films prepared in Examples 2, 3, and Comparative Examples 1, 2, 3, 4 are shown in 8-13.

[0170] The wide-angle X-ray scattering test graph of the graphene thermal conductive film prepared in Example 1 is shown in Figure 14 , the azimuth-intensity curve graph of the graphene thermal conductive film prepared in Example 1 is shown in Figure 15 , fromFigure 14 , it can be seen from 15 that the wide-angle XRD diffraction spot of the graphene thermal conductive film prepared in Example 1 is small, and at the same time Figure 15 the full width at half maximum (FWHM) value in it is relatively large, being 16.1°, f = 0.91, and the peaks appearing at the azimuth angles of 0° and 180° are relatively sharp, indicating that the crystal structure orientation degree of carbon atoms in graphene is high, which provides a structural basis for the high thermal conductivity coefficient.

[0171] The XPS element peak pattern of the graphene thermal conductive film prepared in Example 1 is shown in Figure 16 , and the analysis results are shown in Table 1 below.

[0172] Table 1

[0173] Binding energy / eV Peak height / eV Peak area (cps, eV) Percentage / % C=C 283.94 1.44 13738.36 7.27 C-C 284.8 0.68 135865.4 71.92 C-O 285.8 1.34 33876.71 17.94 C=O 287.45 1.41 5408.95 2.87

[0174] It can be seen from the results that the carbon spectrum contains carbon-carbon single bonds, carbon-carbon double bonds, carbon-oxygen single bonds, and carbon-oxygen double bonds. Among them, the content of carbon-carbon bonds is 79.19%, and the high content of carbon-carbon bonds is beneficial to good thermal conductivity, and the content of carbon-oxygen bonds is 20.81%.

[0175] Drop the same amount of the graphene oxide dispersion liquids prepared in Example 1 and Comparative Example 3 at one end of a steel ruler, tilt at the same angle, and test the fluidity. The test results of Example 1 are shown in Figure 17 , and the test results of Comparative Example 3 are shown in Figure 18 .

[0176] It can be obtained from the test results that the fluidity of the graphene oxide slurry in Example 1 is better than that of Comparative Example 3, indicating that the presence of lignosulfonate greatly reduces the viscosity of the slurry and makes its fluidity better.

[0177] Thermal diffusivity performance test: Test by using LFA (laser flash method). Cut the graphene thermal conductive films of the examples and comparative examples into a certain size, with a diameter of 25.2 mm and a thickness of 0.15 mm, and conduct thermal diffusivity and thermal conductivity tests. The test results are shown in Table 2.

[0178] Table 2

[0179]

[0180]

[0181] Analysis: The viscosity of the graphene oxide dispersion prepared in Comparative Example 1 is too large to be measured (>100,000 cps). The reason is that the organic polymer-metal composite dispersion is not introduced. Compared with the graphene thermal conductive film prepared in Example 1, the efficiency of repairing defects by simply promoting carbon atom rearrangement by high temperature is low, resulting in more defects, thereby reducing the phonon transmission efficiency; secondly, due to the high concentration of the graphene oxide dispersion, the interaction between the graphene oxide sheets is strong. Simply using shear dispersion and homogenization cannot suppress and eliminate the strong interaction between the sheets, so that the actual viscosity of the slurry is too large, and the loss of fluidity is not conducive to coating.

[0182] Example 1 obtains a graphene thermal conductive film with a higher thermal conductivity than that of Comparative Example 2 at a lower graphitization temperature than Comparative Example 2. The reason is that simply increasing the graphitization temperature cannot fundamentally solve the problem of high energy barriers for carbon atom rearrangement, which leads to the existence of "diminishing marginal returns of temperature", that is, as the temperature increases, the number of defect repairs tends to be stable, the resistance to carbon atom rearrangement gradually increases, the defect repair efficiency decreases, and the thermal conductivity improvement rate decreases.

[0183] The viscosity of the graphene oxide dispersion prepared in Comparative Example 3 is too large to be measured (>100,000 cps) because ammonium lignin sulfonate is not introduced. The addition of praseodymium chloride alone will destroy the charge distribution on the surface of the graphene oxide sheet, thereby causing a surge in the absolute value of the system's Zata potential, increasing the viscosity of the system and causing a serious loss of fluidity. On the other hand, due to the serious loss of fluidity of the slurry, the self-assembly orientation of the graphene oxide sheet is reduced during coating, ultimately resulting in no significant improvement in the thermal conductivity of the graphene thermal conductive film with a single addition of praseodymium chloride.

[0184] The graphene thermal conductive film of comparative example 4 is partially broken. Due to the excessively fast temperature rise rate, the diffusion of praseodymium atoms is too fast, and there is no time to fully repair the defects, thereby reducing the defect repair efficiency, resulting in the thermal conductivity of the graphene thermal conductive film being lower than that of example 1. On the other hand, the excessively fast temperature rise rate exacerbates the stress imbalance of the film, resulting in cracking and breaking of the film.

Claims

1. A graphene oxide dispersion, characterized in that: The preparation raw materials include: aqueous organic polymer compound, metal catalyst, graphene oxide, pH regulator, and deionized water; the usage amount of the aqueous organic polymer compound is 0.03-0.8% of the mass of graphene oxide, and the usage amount of the metal catalyst is 0.01-0.08% of the mass of graphene oxide.

2. The graphene oxide dispersion according to claim 1, characterized in that: The aqueous organic polymer compound is a lignin derivative; the lignin derivative is selected from at least one of ammonium lignin sulfonate, sodium lignin sulfonate, magnesium lignin sulfonate or calcium lignin sulfonate.

3. The graphene oxide dispersion according to claim 1, characterized in that: The metal catalyst is a rare earth metal catalyst, and the rare earth metal catalyst is a praseodymium metal salt.

4. A method for preparing a graphene oxide dispersion according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: preparing an aqueous organic polymer solution; S2: adjusting the pH of the aqueous organic polymer solution; S3: adding a metal catalyst to the aqueous organic polymer compound solution after adjusting the pH in step S2, sealing and ultrasonicating, to obtain an organic polymer-metal composite dispersion; S4: adding graphene oxide to deionized water and stirring to obtain graphene oxide slurry; S5: adding the organic polymer-metal composite dispersion to the graphene oxide slurry, stirring and mixing, and adding a pH regulator to adjust the pH to obtain a mixture; S6: homogenize the mixture in step S5 under high pressure to obtain a graphene oxide dispersion.

5. The method for preparing a graphene oxide dispersion according to claim 4, characterized in that: In the step S2, the pH of the aqueous organic polymer solution is adjusted to 9-9.

5.

6. The method for preparing a graphene oxide dispersion according to claim 4, characterized in that: In step S4, graphene oxide is added to deionized water in 3-5 times, and the amount of graphene oxide added each time is 2-4% of the mass of deionized water. The solid content of the graphene oxide slurry obtained in step S4 is 10-15wt%.

7. A graphene thermally conductive film, characterized in that: The graphene oxide dispersion is prepared using the graphene oxide dispersion described in any one of claims 1 to 3.

8. A method for preparing the graphene thermally conductive film according to claim 7, characterized in that: The following steps are involved: H1: coating the graphene oxide dispersion and drying it to obtain a graphene precursor film; H2: low temperature heat treatment of the graphene precursor film to obtain a graphene pre-treated film; H3: subjecting the graphene pre-treated film to carbonization reaction to obtain a graphene carbonized film; H4: The graphene carbonized film is graphitized and rolled to obtain a graphene thermal conductive film.

9. The method for preparing the graphene thermally conductive film according to claim 8, characterized in that: In the step H4, the graphitization treatment temperature is 2600-3000° C., the heating rate is 0.5-7° C. / min, and the insulation time is 3-4 h.

10. The method for preparing the graphene thermally conductive film according to claim 8, characterized in that: The graphitization treatment in step H4 is a step-by-step heating program, which is: heating to 1000-1100°C at a heating rate of 4-5°C / min; then heating to 2600-2800°C at a heating rate of 1-2°C / min, and keeping warm for 2h; finally heating to 2600-3000°C at a heating rate of 0.5-1°C / min, keeping warm for 1h, and cooling to room temperature after the insulation is completed.

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