Preparation method of graphene-based composite film for heat dissipation of lithium-sulfur battery

Abstract

The application discloses a preparation method of a graphene-based composite film for heat dissipation of a lithium-sulfur battery. The preparation method uses polyethylene imine solidification as a connecting piece between graphene contact layers, ensures heat conduction performance, and enhances the tensile property of the composite film. The molar mass ratio between pyromellitic dianhydride and diaminodiphenyl ether is reasonably controlled, so that the graphitization degree of the PI base film is improved.

Description

Technical Field

[0001] This invention relates to the field of graphene-based composite film technology, specifically to a method for preparing a graphene-based composite film for heat dissipation in lithium-sulfur batteries. Background Technology

[0002] In recent years, with the rapid development of lithium-sulfur battery technology, lithium-sulfur batteries have been moving towards thinner and more integrated designs. However, this often leads to higher heating temperatures, and overheating can significantly reduce the lifespan and operational stability of internal components in lithium-sulfur batteries. Polymer materials, due to their advantages such as light weight, excellent insulation, ease of processing, and low price, have been widely used in electronic devices. As an important component of battery packaging systems and the component closest to the heat source, they mainly serve to mount, support, and fix electronic components, playing a crucial role in the rapid heat dissipation of chips. However, due to the severe phonon scattering of polymer polymer chains, the intrinsic thermal conductivity is too low, which is far from meeting the rapid heat dissipation requirements of electronic devices. Graphene films can be used as heat sinks in electronic components. Heat sinks are usually attached to the surface of electronic components that are prone to heat generation and have been the ideal choice for thermal conductive films for a long time.

[0003] Graphene heat dissipation film is a highly oriented thermally conductive film made of graphene as raw material and stacked with multiple layers of graphene. It includes a protective film, single-sided adhesive, graphene film, double-sided adhesive and release film. Graphene thermal conductive film has a wide range of applications. With the upgrading and iteration of graphene preparation technology, the performance of graphene thermal conductive film has been continuously improved. In the preparation of graphene thermal conductive film, natural graphite is first oxidized to synthesize graphene oxide, and then it is assembled into graphene oxide film. After thermal stabilization and graphitization, graphene oxide film must be graded and densified to make a highly flexible and high-density thermal conductive film.

[0004] The biggest advantage of the graphene film preparation method using graphene dispersion is that it preserves the planar structure of graphene, resulting in a relatively high intrinsic thermal conductivity. However, since the preparation of graphene dispersion often requires the application of strong mechanical force, the sheet size in the graphene dispersion is usually small. Moreover, due to the lack of oxygen-containing functional groups, the interaction between graphene sheets is weak, and there is a possibility that the advantages and disadvantages cancel each other out. Therefore, the tensile strength of the graphene film is poor, which is not conducive to its large-area use in lithium-sulfur batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a graphene-based composite film for heat dissipation in lithium-sulfur batteries, so as to solve the problem of poor connection stability between graphene film sheets mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a graphene-based composite film for heat dissipation in lithium-sulfur batteries, comprising the following steps:

[0007] S1. Polyamic acid is synthesized by adding dimethylacetamide to pyromellitic anhydride and diaminodiphenyl ether and then polyimide fiber is prepared by thermal imidization of the obtained polyamic acid;

[0008] S2. The fully degassed polyimide fiber slurry is evenly coated onto a clean mirror steel plate. The steel plate is placed in an oven at 80°C and baked for 1 hour to evaporate most of the solvent. Then it is transferred to an oven at 120°C and baked for 30 minutes; then to an oven at 150°C and baked for 30 minutes; then to an oven at 200°C and baked for 10 minutes; then to an oven at 250°C and baked for 10 minutes; then to an oven at 350°C and baked for 5 minutes; finally, it is transferred to an oven at 430°C and baked for 3 minutes. After the mirror steel plate cools down, the film is removed to obtain the PI substrate film.

[0009] S3. The PI base film prepared in S2 is laid flat on the carrier, so that the PI base film is stably placed by being supported by the lattice pillars on the carrier.

[0010] S4. Add water and stabilizer to powdered graphene oxide material to prepare graphene oxide dispersion;

[0011] S5. Pour the graphene oxide dispersion obtained in S4 evenly onto the surface of the PI substrate film. Use a round rod to roll and coat the graphene oxide dispersion on the surface of the PI substrate film, so that excess water in the graphene oxide dispersion can seep down through the PI substrate film, and the graphene oxide material accumulates on the surface of the PI substrate film to form a graphene oxide contact layer.

[0012] S6. The PI substrate film and graphene oxide contact layer obtained in S5 are simultaneously sintered to graphitize them to obtain a graphite film and a graphene contact layer.

[0013] S7. The graphite film and graphene contact layer obtained in S6 are laid flat on the worktable in a rectangular array. The spacing between the graphene contact layers is fixed by inserting a cross-shaped shaping tool between the graphene contact layers.

[0014] S8. Remove the cross-shaped shaping fixture in S7 and apply polyethyleneimine evenly between the graphene contact layers using a low-pressure spray method through an atomizing nozzle.

[0015] S9. After the polyethyleneimine has cured, remove the polyethyleneimine from the surface of the graphene contact layer to expose the graphene contact layer, forming a complete cured polyethyleneimine bonding thin layer and a composite film formed by the graphite film and the graphene contact layer.

[0016] Preferably, the molar ratio between pyromellitic anhydride and diaminodiphenyl ether in S1 is 7:3.

[0017] By adopting the above technical solution, the PI substrate film can maintain a good balance between thermal conductivity and mechanical properties, achieving optimal performance.

[0018] Preferably, calcium carbonate solution is also added in step S1, and the proportion of calcium carbonate solution added is 1.5%.

[0019] By adopting the above technical solution, the PI substrate film can maintain high thermal conductivity and good flexibility.

[0020] Preferably, the polyimide fiber in S1 is cured after passing through a coagulation bath.

[0021] By adopting the above technical solution, polyimide fibers can obtain good strength through the coagulation bath.

[0022] Preferably, the powdered graphene oxide in step S4 is prepared using an oxidant method.

[0023] The above technical solution is used to obtain graphene oxide powder.

[0024] Compared with the prior art, the beneficial effects of the present invention are: the preparation method of the graphene-based composite film for heat dissipation in lithium-sulfur batteries:

[0025] 1. By using polyethyleneimine curing as a connector between graphene contact layers, the tensile strength of the small graphene-based composite film can be enhanced while ensuring thermal conductivity during connection.

[0026] 2. Furthermore, by rationally controlling the molar ratio between pyromellitic anhydride and diaminodiphenyl ether, the rigid symmetrical structure of pyromellitic anhydride increases the in-plane orientation of the molecular chains during the thermal imidization process of the graphene-based composite film. This reduces the difficulty for disordered carbon atoms to form ordered graphite crystals during the graphitization process, decreases the carbon atom rearrangement amplitude, and makes it easier to form a uniform graphite crystal structure, thus increasing the degree of graphitization and exhibiting a higher thermal conductivity.

[0027] 3. Furthermore, by adding micron-sized calcium carbonate during the preparation of the PI substrate film, the calcium carbonate particles in the film sublimate during the graphitization process, generating a large number of bubbles in the PI substrate film. This results in a honeycomb-like structure inside the PI substrate film. Through this structure, the PI substrate film forms a large number of thermally conductive pathways inside. After calendering, the graphene-based composite film exhibits high thermal conductivity and good flexibility. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall preparation process of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a technical solution: a method for preparing a graphene-based composite film for heat dissipation in lithium-sulfur batteries, comprising the following steps:

[0031] S1. Polyamic acid is synthesized by adding dimethylacetamide to pyromellitic anhydride and diaminodiphenyl ether and then polyimide fiber is prepared by thermal imidization of the obtained polyamic acid;

[0032] S2. The fully degassed polyimide fiber slurry is evenly coated onto a clean mirror steel plate. The steel plate is placed in an oven at 80°C and baked for 1 hour to evaporate most of the solvent. Then it is transferred to an oven at 120°C and baked for 30 minutes; then to an oven at 150°C and baked for 30 minutes; then to an oven at 200°C and baked for 10 minutes; then to an oven at 250°C and baked for 10 minutes; then to an oven at 350°C and baked for 5 minutes; finally, it is transferred to an oven at 430°C and baked for 3 minutes. After the mirror steel plate cools down, the film is removed to obtain the PI substrate film.

[0033] S3. The PI base film prepared in S2 is laid flat on the carrier, so that the PI base film is stably placed by being supported by the lattice pillars on the carrier.

[0034] S4. Add water and stabilizer to powdered graphene oxide material to prepare graphene oxide dispersion;

[0035] S5. Pour the graphene oxide dispersion obtained in S4 evenly onto the surface of the PI substrate film. Use a round rod to roll and coat the graphene oxide dispersion on the surface of the PI substrate film, so that excess water in the graphene oxide dispersion can seep down through the PI substrate film, and the graphene oxide material accumulates on the surface of the PI substrate film to form a graphene oxide contact layer.

[0036] S6. The PI substrate film and graphene oxide contact layer obtained in S5 are simultaneously sintered to graphitize them to obtain a graphite film and a graphene contact layer.

[0037] S7. The graphite film and graphene contact layer obtained in S6 are laid flat on the worktable in a rectangular array. The spacing between the graphene contact layers is fixed by inserting a cross-shaped shaping tool between the graphene contact layers.

[0038] S8. Remove the cross-shaped shaping fixture in S7 and apply polyethyleneimine evenly between the graphene contact layers using a low-pressure spray method through an atomizing nozzle.

[0039] S9. After the polyethyleneimine has cured, remove the polyethyleneimine from the surface of the graphene contact layer to expose the graphene contact layer, forming a complete cured polyethyleneimine bonding thin layer and a composite film formed by the graphite film and the graphene contact layer.

[0040] The molar ratio between pyromellitic anhydride and diaminodiphenyl ether in S1 is 7:3. When the molar ratio of diaminodiphenyl ether is 0, the tensile strength of the PI base film is low, but the elongation at break is high. This is because pyromellitic anhydride contains ether bonds -O-, which allows the polyimide molecular chains to rotate and become more flexible, resulting in lower tensile strength and higher elongation at break.

[0041] With the addition of diaminodiphenyl ether, the tensile strength of the PI base film gradually increases, but the elongation at break gradually decreases. This is because diaminodiphenyl ether is a rigid monomer, and its addition increases the rigidity of the polyimide molecular chain, thereby increasing the tensile strength of the PI base film. However, due to the increase in molecular chain rigidity, its elongation at break decreases accordingly. When the molar content of diaminodiphenyl ether is greater than 50%, although the tensile strength of the PI base film is high due to the addition of too much diaminodiphenyl ether, the excessive rigidity makes the PI base film hard and brittle, and the film-forming properties of the PI base film are poor. According to the needs of the production process, the molar amount of diaminodiphenyl ether is 30%, that is, the optimal molar ratio of pyromellitic anhydride to diaminodiphenyl ether is 70:30.

[0042] When the content of diaminodiphenyl ether is 0, the CTE of the PI substrate film is relatively high. This is because the ether bonds -O- in the large amount of pyromellitic anhydride in the system give the polyimide molecular chain greater free rotation and greater chain flexibility. The PI substrate film has a large degree of chain stretching after heating, thus exhibiting a high coefficient of thermal expansion. With the addition of diaminodiphenyl ether, the CTE of the PI substrate film gradually decreases. This is because the rigid diaminodiphenyl ether increases the rigidity of the polyimide molecular chain, which restricts the free stretching after heating, thus exhibiting a lower coefficient of thermal expansion.

[0043] After carbonization and graphitization, a PI substrate film is obtained to form a graphite film. When the content of diaminodiphenyl ether is 0, the thermal conductivity of the graphite film is low. This is because the in-plane orientation of the PI substrate film is low in the p-phenylene tetracarboxylic anhydride system, which leads to a longer path required for the disordered carbon atoms to transform into an ordered graphite crystal structure during the graphitization process. This results in a larger carbon atom rearrangement, making graphitization difficult and resulting in a low degree of graphitization, thus leading to a low thermal conductivity of the graphite film. The addition of diaminodiphenyl ether, with its rigid symmetrical structure, increases the in-plane orientation of the molecular chains during the thermal imidization process of the PI substrate film, improving the thermal conductivity of the graphite film. During the graphitization process, the difficulty of disordered carbon atoms forming ordered graphite crystals decreases, the rearrangement of carbon atoms is reduced, and it is easier to form a uniform graphite crystal structure, thus increasing the degree of graphitization and exhibiting a higher thermal conductivity. It is also noted that when the molar content of diaminodiphenyl ether exceeds 30%, the increase in the thermal conductivity of the graphite film slows down. This is because the effect of the increased in-plane orientation of the molecular chain brought about by diaminodiphenyl ether reaches saturation, and its effect on increasing the degree of graphitization of the film also gradually reaches saturation. Considering the mechanical properties of the PI substrate film and the thermal conductivity of the graphite film, a molar content of 30% for diaminodiphenyl ether is most appropriate.

[0044] S1 also contains a calcium carbonate solution at a concentration of 1.5%. With the addition of micron-sized calcium carbonate, the tensile strength of the PI substrate film gradually decreases. This is because calcium carbonate is inorganic, while diaminodiphenyl ether is organic; when they are compatible, they cannot form a completely homogeneous system, resulting in defects at the phase interface. Simultaneously, the inorganic particles also affect the adhesion between polyimide molecular chains, leading to a decrease in the tensile strength of the PI substrate film. Regarding the thermal conductivity of the graphite film, it can be seen that the thermal conductivity gradually increases with the increase of calcium carbonate content. When the content exceeds 1.5%, the thermal conductivity shows a decreasing trend. This is because the addition of high-melting-point calcium carbonate makes the PI... During the graphitization process of the PI base film, calcium carbonate particles sublimate within the film, generating numerous bubbles that create a honeycomb-like structure, known as "foaming." Graphite films with this structure form numerous internal thermal conductivity pathways. After calendering, these films exhibit high thermal conductivity and good flexibility. However, when the calcium carbonate content is too high, excessive inorganic particles during PI base film graphitization can create too many pores, leading to over-foaming. This lengthens the internal thermal conductivity pathways, thus reducing the thermal conductivity of the graphite film. Overall, a calcium carbonate addition of 1.5% results in the best PI base film graphitization effect.

[0045] The polyimide fiber in S1 is cured after passing through a coagulation bath. The coagulation bath is a mixture of deionized water and ethanol. The first coagulation bath is kept at 0°C and 50% ethanol content, the second coagulation bath is kept at 20°C and 20% ethanol content, and the third coagulation bath is kept at 40°C and 10% ethanol content.

[0046] In S4, powdered graphene oxide is prepared by an oxidant method. First, graphite powder is added to nitric acid, and an appropriate amount of sulfuric acid is added as a catalyst. Then, the temperature is raised to 80-100℃ under stirring, and the reaction time is 4-6 hours. Then, the graphene oxide is obtained by filtration, washing and drying.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a graphene-based composite film for heat dissipation in lithium-sulfur batteries, characterized in that: Includes the following steps: S1. Polyamic acid is synthesized by adding dimethylacetamide to pyromellitic anhydride and diaminodiphenyl ether and then polyimide fiber is prepared by thermal imidization of the obtained polyamic acid; S2. The fully degassed polyimide fiber slurry is evenly coated onto a clean mirror steel plate. The steel plate is placed in an oven at 80°C and baked for 1 hour to evaporate most of the solvent. Then it is transferred to an oven at 120°C and baked for 30 minutes; then to an oven at 150°C and baked for 30 minutes; then to an oven at 200°C and baked for 10 minutes; then to an oven at 250°C and baked for 10 minutes; then to an oven at 350°C and baked for 5 minutes; finally, it is transferred to an oven at 430°C and baked for 3 minutes. After the mirror steel plate cools down, the film is removed to obtain the PI substrate film. S3. The PI base film prepared in S2 is laid flat on the carrier, so that the PI base film is stably placed by being supported by the lattice pillars on the carrier. S4. Add water and stabilizer to powdered graphene oxide material to prepare graphene oxide dispersion; S5. Pour the graphene oxide dispersion obtained in S4 evenly onto the surface of the PI substrate film. Use a round rod to roll and coat the graphene oxide dispersion on the surface of the PI substrate film, so that excess water in the graphene oxide dispersion can seep down through the PI substrate film, and the graphene oxide material accumulates on the surface of the PI substrate film to form a graphene oxide contact layer. S6. The PI substrate film and graphene oxide contact layer obtained in S5 are simultaneously sintered to graphitize them to obtain a graphite film and a graphene contact layer. S7. The graphite film and graphene contact layer obtained in S6 are laid flat on the worktable in a rectangular array. The spacing between the graphene contact layers is fixed by inserting a cross-shaped shaping tool between the graphene contact layers. S8. Remove the cross-shaped shaping fixture in S7 and apply polyethyleneimine evenly between the graphene contact layers using a low-pressure spray method through an atomizing nozzle. S9. After the polyethyleneimine has cured, remove the polyethyleneimine from the surface of the graphene contact layer to expose the graphene contact layer, forming a complete cured polyethyleneimine bonding thin layer and a composite film formed by the graphite film and the graphene contact layer.

2. The method for preparing a graphene-based composite film for heat dissipation in a lithium-sulfur battery according to claim 1, characterized in that: The molar ratio between pyromellitic anhydride and diaminodiphenyl ether in S1 is 7:

3.

3. The method for preparing a graphene-based composite film for heat dissipation in a lithium-sulfur battery according to claim 1, characterized in that: Calcium carbonate solution was also added to S1, and the proportion of calcium carbonate solution added was 1.5%.

4. The method for preparing a graphene-based composite film for heat dissipation in a lithium-sulfur battery according to claim 1, characterized in that: The polyimide fiber in S1 is cured after passing through a coagulation bath.

5. The method for preparing a graphene-based composite film for heat dissipation in a lithium-sulfur battery according to claim 1, characterized in that: The powdered graphene oxide in S4 is prepared using an oxidant method.

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