A graphene porous membrane and a method for preparing the same

Abstract

The application provides a preparation method of a graphene porous membrane. Through process improvement and control of different process parameters, a porous graphene oxide is formed by hole etching on a raw material graphene oxide cake, and then the porous graphene oxide is pulped and coated to form a membrane to form a nanopore surface. After chemical reduction and foaming, exhaust passages are formed on the surface and the edge, the problem of bulging and delamination caused by untimely exhaust during industrial production is solved, and the interlayer bonding force is improved.

Description

Technical Field

[0001] This application relates to the field of thermal management, specifically to a graphene porous membrane and its preparation method. Background Technology

[0002] With the increasing multifunctionality, high integration, and algorithm complexity of electronic products, chip power density continues to rise. If the resulting heat cannot be dissipated in time, it will cause product malfunctions or failures. Therefore, integrating highly thermally conductive and stable heat dissipation materials into electronic products to achieve efficient thermal management is crucial. A wide variety of thermal interface materials are available on the market, such as silicone grease, gaskets, thermal adhesives, and phase change materials (PCMs). While silicone grease and thermal adhesives have good flowability and can fully fill the gaps between heat-generating components and heat sinks, effectively reducing interfacial thermal resistance, their thermal conductivity is generally <5 W / (m·K). PCMs combine thermal conductivity and heat storage, but they suffer from interfacial thermal resistance issues due to uneven thickness, and their thermal conductivity is also relatively low. Furthermore, PCMs pose risks of phase separation and leakage. Metal gaskets can achieve thermal conductivity of over 10 W / (m·K), but they are dense and easily oxidized, lacking compressive resilience, and cannot solve the problem of increased interfacial thermal resistance caused by thermal stress leading to new interfaces after long-term product use.

[0003] Graphene porous membranes possess numerous excellent properties, including stable performance, high strength, light weight, high thermal conductivity, and compression resilience. As a thermal management material, they can compensate for the shortcomings of the aforementioned materials. However, during the preparation process, problems such as bulging and poor interlayer bonding are prone to occur. Based on these issues, this invention is proposed. Summary of the Invention

[0004] This invention provides a method for preparing a graphene porous membrane, as detailed below:

[0005] The process involves etching graphene oxide cakes to obtain porous graphene oxide, preparing a slurry to obtain porous graphene oxide slurry, coating it into a primary film, chemically reducing and foaming it, and then heat-treating it to obtain a porous graphene membrane.

[0006] During the chemical reduction foaming and heat treatment processes of graphene, gases are generated. If these gases are not released in time, they accumulate between the film layers, causing bulging and affecting product quality. A solution is to etch pores into a porous graphene oxide cake to form a porous graphene oxide, which is then slurryed and coated to form a nanoporous surface. After chemical reduction foaming, venting channels are formed on the surface and edges, solving the bulging and delamination problem caused by untimely venting and improving interlayer bonding.

[0007] Furthermore, the etching step of the graphene oxide cake is as follows: the etchant, the catalyst and the graphene oxide cake are mixed and reacted in a certain proportion, the mass ratio of the etchant to the graphene oxide cake is 7-10:1, and the mass ratio of the catalyst to the etchant is 0.7-1:1.

[0008] Typical, but not limiting, mass ratios of etchant to graphene oxide cake are 7:1, 8:1, 9:1, and 10:1. When the mass ratio of etchant to graphene oxide cake B is <7:1, the reaction is slow and the etched pore density is low. The small pore size is not conducive to foaming and venting, and bulging or internal delamination is still highly likely. When the mass ratio of etchant to graphene oxide cake B is >10:1, the reaction is fast and the etched pores are large. The large pore size makes high-temperature repair during graphitization difficult, thus affecting the thermal conductivity of the graphene film. The catalyst's role is to catalyze and promote the reaction. Typical, but not limiting, mass ratios of catalyst to etchant are 0.7:1, 0.8:1, 0.9:1, and 1:1.

[0009] Furthermore, the etchant is hydrogen peroxide, which can etch graphene oxide sheets in solution and is more likely to damage graphene oxide sp in an alkaline environment. 3 The hybridization region breaks the C-C and CO bonds, forming pores. Therefore, the catalyst is selected as an alkaline reagent. Furthermore, the catalyst is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0010] Furthermore, the etching reaction time is 2-5 hours, typically but not limitingly 2 hours, 3 hours, 4 hours, and 5 hours. The etching pore size can be controlled by adjusting the reaction time. If the etching pore size is too small, it is not conducive to foaming and venting, and there is still a high probability of bulging or internal delamination. When the etching pore size is too large, it is difficult to repair at high temperatures during graphitization, which will affect the thermal conductivity of the graphene film.

[0011] Preferably, the pore size of the porous graphene oxide obtained by etching is 1-2.5 nm, and typically, but not limitingly, the pore size is 1 nm, 1.5 nm, 2 nm, or 2.5 nm.

[0012] Furthermore, the median sheet diameter of the porous graphene oxide in the porous graphene oxide slurry is 4-12 μm. High-pressure homogenization is required when preparing the porous graphene oxide slurry. Homogenization ensures stable and uniform dispersion, which is more conducive to the coating of the original film. However, the shear force, cavitation, and impact during homogenization can cause the porous graphene oxide sheets to open up, and its sheet structure is inevitably partially damaged, thus affecting the thermal conductivity of the film material. The applicant discovered that when the porous graphene sheet diameter is maintained at 4-12 μm, the porous graphene oxide can be uniformly dispersed without damaging the sheet structure.

[0013] Furthermore, a foaming agent is used in the chemical reduction foaming process. Chemical reduction foaming is a crucial step in enabling graphene porous membranes to possess compression resilience. Through the action of the foaming agent, cavities are formed within the original membrane, creating a stable three-dimensional porous structure similar to a honeycomb. When subjected to external compressive stress, this three-dimensional porous structure can quickly disperse the stress, allowing the membrane to be compressed without damaging its structure. When no longer subjected to external forces, the membrane rebounds. Typical, but not limiting, foaming agents include at least one of hydrazine hydrate, ascorbic acid, sodium hydroxide, sodium borate, dimethylhydrazine, and thiourea.

[0014] Furthermore, the chemical reduction foaming time is 30s-10min. A foaming time <30s results in poor foaming uniformity and effect, while a foaming time >10min leads to an overly fluffy film, weakened interlayer bonding, and powder shedding. Preferably, the chemical reduction foaming time is 30s-5min. Typical but not limiting foaming times are 30s, 60s, 90s, 120s, 150s, 180s, 210s, 240s, 270s, and 300s.

[0015] Furthermore, the concentration of the foaming agent is 10%-30%. If the concentration of the foaming agent is too low, the reaction is mild and a honeycomb-like structure cannot be formed inside the membrane, resulting in poor compression resilience. If the foaming agent concentration is too high, the reaction is violent, gas production is too fast, the internal pressure of the membrane rises sharply and cannot be released in time, and the probability of surface bubbling and internal delamination is high.

[0016] Furthermore, the heat treatment includes a pretreatment process at 150-380℃, a carbonization process at 900-1400℃, and a graphitization process at 2000-3300℃. This segmented heat treatment further avoids rapid thermal reduction of the membrane, which can lead to blistering, delamination, breakage, or burning. The pretreatment stage primarily removes moisture and a small amount of oxygen-containing functional groups; the carbonization stage removes most of the oxygen-containing functional groups; and the graphitization stage removes almost all of the oxygen-containing functional groups. Simultaneously, various defects such as pores are repaired, and the intrinsic thermal conductivity of graphene is improved.

[0017] Furthermore, the carbonization and graphitization stages are protected with an inert gas, typically but not limitingly, which is one or more of argon, helium, and neon.

[0018] Furthermore, after heat treatment, a calendering step is also included. Calendering makes the surface of the graphitized film smoother, the thickness more uniform, and the internal structure more orderly and dense, thus resulting in better adhesion.

[0019] The graphene porous membrane prepared by the method described in this invention has a Z thermal conductivity of 5-11 W / mK, an in-plane thermal conductivity of 80-120 W / mK, an interlayer separation force of >4 N / cm², and a recovery of >95% after 20 cycles of 50% compression.

[0020] The beneficial effects of this invention are as follows:

[0021] In the preparation of graphene porous membranes, through process improvement and control of different process parameters, porous graphene oxide is formed by etching holes on the raw material graphene oxide cake. Then, it is slurryed and coated into a film to form a nanoporous surface. After chemical reduction and foaming, exhaust channels are formed on the surface and edges, which solves the problem of bulging and delamination caused by untimely exhaust in industrial production and improves the interlayer bonding force.

[0022] The porous graphene oxide sheets are flexible and can be tightly and continuously stacked during the coating and assembly process, improving interlayer interaction. After foaming, the interlayers are intertwined, and the gas generated during foaming can be discharged from the side of the membrane and multiple channels on the porous surface, effectively preventing the foamed membrane from bubbling and delamination. At the same time, the porous graphene oxide sheets are repaired after high-temperature heat treatment, improving intrinsic thermal conductivity. In addition, the strong interlayer connections promote phonon transfer, giving the graphene porous membrane excellent Z-axis thermal conductivity. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Comparative images of the foamed and dried reduced graphene oxide porous membranes provided in Example 1 (left) and Comparative Example 1 (right) of the present invention;

[0025] Figure 2 SEM comparison images of the cross-sections of graphene porous membranes provided in Example 1 (left) and Comparative Example 1 (right) of the present invention;

[0026] Figure 3 This is a SEM image of the cross-section of the graphene porous membrane provided in Comparative Example 4 of the present invention;

[0027] Figure 4 The stress-strain curve of the graphene porous membrane provided in Embodiment 1 of the present invention after 20 cycles of 50% compression.

[0028] Figure 5 The graph shows the interlayer separation force test process of the graphene porous membrane provided in Example 1 of the present invention. Detailed Implementation

[0029] The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form part of the description, illustrating exemplary embodiments in which the invention may be practiced, wherein features of the invention are identified by reference numerals. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not to limit the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings should be considered illustrative only and not restrictive, and any such modifications and variations will fall within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit the invention or the application field of the invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0032] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0033] Graphene porous membranes, as a novel thermally conductive and heat-dissipating material, are widely used in 3C electronic products, new energy battery packs, and other fields due to their excellent properties such as stable use, high strength, light weight, high thermal conductivity, and compression resilience. However, the applicant discovered that during the industrial production of this new material, the large amount of gas generated during thermal reduction can easily cause defects such as bulging and delamination, and even pose a risk of breakage or burning. To solve these problems, the applicant, through extensive process verification, found that chemical foaming and reduction treatment before heat treatment of the coated original membrane can create pores on the membrane side, giving the membrane a "honeycomb"-like structure. Gas molecules can partially escape from the membrane side, thereby alleviating the bulging problem. However, the concentration of the foaming agent and the foaming time need to be precisely controlled; otherwise, problems such as unsuccessful foaming, an overly fluffy membrane, weakened interlayer bonding, and powder shedding may occur.

[0034] Meanwhile, the applicant also discovered through extensive process verification that if holes could be created at both ends of the membrane surface, the problems of membrane foaming and bonding strength could be solved to a great extent.

[0035] The following are specific embodiments and comparative examples of the present invention: Example 1

[0036] (1) Preparation of porous graphene oxide by etching graphene oxide cake:

[0037] 100g of graphene oxide cake (purchased from Yunnan Yuntian Morui Technology Co., Ltd.) was mixed with deionized water and 28% ammonia at a mass ratio of 6:50:1 and added to a planetary mixer for dispersion for 4 hours. After dispersion, etching was performed by adding 900g of 30% hydrogen peroxide and 800g of 28% ammonia and stirring at 55℃ for 2 hours to etch pores in the graphene oxide sheets, obtaining a porous graphene oxide mixture. The porous graphene oxide mixture was purified three times with deionized water to obtain a porous graphene oxide cake. The average pore size of the porous graphene oxide was 1.5nm.

[0038] (2) Pulping to obtain porous graphene oxide slurry:

[0039] The porous graphene oxide material obtained in step (1) and 960 ml of deionized water were added to a planetary mixer and stirred for 2 hours. The resulting porous graphene dispersion was then passed through a homogenizer for gradient homogenization. In this embodiment, six pressure gradients were set for homogenization: 160, 360, 450, 550, 660, and 780 mBr. The homogenization time for each gradient was 18 minutes. After homogenization, a porous graphene oxide slurry was obtained, which was then further defoamed. At this point, the median diameter of the porous graphene oxide in the slurry was 7.3 μm.

[0040] (3) Coating to form the original film:

[0041] The defoamed porous graphene oxide slurry was coated onto a PP substrate using a coating machine to a thickness of 1.8 mm. After natural drying, the graphene oxide film was obtained by separation.

[0042] (4) Chemical reduction foaming:

[0043] The original graphene oxide membrane was immersed in 15% hydrazine hydrate for 3 minutes and then dried to obtain a reduced graphene oxide porous membrane.

[0044] (5) Heat treatment:

[0045] Reduced graphene oxide porous membranes were pretreated, carbonized, and graphitized to obtain graphene porous membranes. In this embodiment, the maximum processing temperatures for pretreatment, carbonization, and graphitization were 250℃, 1000℃, and 2850℃, respectively, to obtain graphene porous membranes.

[0046] (6) Rolling:

[0047] The heat-treated graphene porous membrane was rolled at a pressure of 2 MPa, a roller spacing of 300 μm, and a rolling speed of 5 m / min.

[0048] The obtained graphene porous membrane was subjected to Z-axis and in-plane thermal conductivity, compression, and interlayer separation force tests. Specifically, Z-axis and in-plane thermal conductivity were tested using the LFA-467 laser scintillation thermal conductivity meter, referencing the standard "Q / GDMR 04-2023 Thermal Conductivity Test by Laser Flash Method". Compression was tested using the CTM2050 microcomputer-controlled electronic universal testing machine, referencing the standard "Q / GDMR 06-2023 Compression Performance Test of Graphene Film". The recovery amount after compression cycles was also calculated, i.e., the ratio of the compressed thickness to the original thickness. Interlayer separation force was tested by fixing one side of a 15*15mm sample on the sample stage of the universal testing machine and vertically pulling the other side of the sample at a rate of 5mm / min until the sample was completely delaminated. The maximum force for delamination was obtained, and the maximum delamination force per unit area was calculated. The testing equipment was the CTM2050 microcomputer-controlled electronic universal testing machine.

[0049] Example 2-3

[0050] Unlike Example 1, in step (1), the etching and pore-forming time for the graphene oxide cake was adjusted to 4 hours and 5 hours, while the other steps were the same as in Example 1. In these two examples, the average pore sizes of the porous graphene oxide sheets in the final slurry were 2.1 nm and 2.4 nm, respectively.

[0051] Examples 4-5

[0052] Unlike Example 1, in step (1), the amount of etchant hydrogen peroxide was adjusted from 900g to 700g and 1000g respectively, while the other steps were the same as in Example 1. In these two examples, the average pore sizes of the porous graphene oxide in the final slurry were 1.0nm and 1.9nm, respectively.

[0053] Examples 6-7

[0054] Unlike Example 1, in step (1), the reagent type of the catalyst was adjusted to 650g of sodium hydroxide solution and 900g of potassium hydroxide solution, respectively; the other steps were the same as in Example 1. In both examples, the average pore sizes of the porous graphene oxide in the final slurry were 1.3nm and 1.7nm, respectively. Example 8

[0055] Unlike Example 1, the homogenization process was adjusted in step (2) during the preparation of the porous graphene oxide slurry. In this example, six pressure gradients were set for homogenization: 200, 360, 450, 600, 680, and 800 mBr, respectively. The homogenization time for each gradient was 20 min. After homogenization, a porous graphene oxide slurry was obtained, which was then further defoamed. At this point, the median diameter of the porous graphene oxide in the slurry was 4.2 μm. Example 9

[0056] Unlike Example 1, the homogenization process was adjusted in step (2) during the preparation of the porous graphene oxide slurry. In this example, six pressure gradients were set for homogenization: 160, 360, 450, 550, 660, and 780 mbr. The homogenization time for each gradient was 13 min. After homogenization, a porous graphene oxide slurry was obtained, which was then further defoamed. At this point, the median diameter of the porous graphene oxide in the slurry was 11.7 μm. Example 10

[0057] Unlike Example 1, the concentration of the foaming agent hydrazine hydrate and the foaming time were adjusted from 15% and 3 min to 10% and 5 min, while the other steps remained the same as in Example 1. Example 11

[0058] Unlike Example 1, the concentration of the foaming agent hydrazine hydrate and the foaming time were adjusted from 15% and 3 min to 30% and 30 s, while the other steps remained the same as in Example 1. Example 12

[0059] Unlike Example 1, the graphene porous membrane obtained in step (5) is not subjected to calendering, while the other steps are consistent with those in Example 1. Comparative Example 1

[0060] Unlike Example 1, after the graphene oxide cake was dispersed for 4 hours, it was directly subjected to subsequent operations such as homogenization to prepare a slurry, and finally a porous graphene membrane was obtained. In this comparative example, the graphene oxide sheet was not etched to create pores. Comparative Example 2

[0061] Unlike Example 1, in step (1), the chemical etching time for creating pores was adjusted from 2 hours to 8 hours, while the other steps remained the same as in Example 1. In this comparative example, the average pore size of the porous graphene oxide in the final slurry was 5.8 nm. Comparative Example 3

[0062] Unlike Example 1, in step (1), the chemical etching time for creating pores was adjusted from 2 hours to 10 minutes, while other steps remained unchanged. In this comparative example, the average pore size of the porous graphene oxide sheets in the final slurry was 0.3 nm. Comparative Example 4

[0063] Unlike Example 1, the concentration of the foaming agent hydrazine hydrate was adjusted from 15% to 0.5%, while the other steps remained unchanged. Comparative Example 5

[0064] Unlike Example 1, the foaming time of hydrazine hydrate was adjusted from 3 minutes to 50 minutes, while other steps remained unchanged. Comparative Example 6

[0065] Unlike Example 1, in step (5), the reduced graphene oxide porous membrane is directly graphitized at 2850°C.

[0066] The test results of Examples 1-12 and Comparative Examples 1-6 are summarized in Table 1:

[0067] Table 1:

[0068]

[0069] As can be seen from Table 1, the graphene porous membranes provided in Examples 1-12 have excellent Z-direction and in-plane thermal conductivity, high interlayer bonding strength, and good compression resilience. Specifically, their Z-direction thermal conductivity is 5-11 W / (m·K), their in-plane thermal conductivity is 80-120 W / (m·K), their interlayer separation force is >4 N / cm², and their recovery after 20 cycles of 50% compression is >95%.

[0070] The graphene porous membranes provided in Examples 1-12 exhibit significantly better performance parameters than the graphene porous membrane prepared without chemical etching in Comparative Example 1. The graphene oxide membrane in Comparative Example 1 lacks a nanoporous surface, allowing foaming gas to escape primarily from the side, resulting in obstructed surface venting, surface bubbling, and internal stratification. Furthermore, the presence of bubbling and stratification disrupts the thermal conductivity path of the graphene porous membrane, negatively impacting its Z-axis thermal conductivity and in-plane thermal conductivity. Comparative Example 2, with its long chemical etching time and excessively large pores, also lacks [specific performance characteristics] after graphitization. The main drawback of the method of repair is its adverse effect on thermal conductivity; Comparative Example 3 has a short chemical etching time, resulting in small pores that prevent the foaming gas from effectively escaping from the surface, and the situation and test results are similar to those of Comparative Example 1; Comparative Example 4 has a low foaming agent concentration and a mild reaction, which fails to form a honeycomb structure, resulting in low interlayer cross-linking, low Z-direction thermal conductivity, low interlayer bonding force, and poor compression resilience; Comparative Example 5 has a structure that collapses during the preparation process due to excessively long chemical reduction foaming time; Comparative Example 6 has a graphene film that is burned due to the lack of segmented heat treatment and the instantaneous large amount of gas exhaust during the heat treatment process.

[0071] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0072] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a graphene porous membrane, characterized in that, Includes the following steps: Etching agent, catalyst, and graphene oxide cake are mixed and reacted in a certain proportion, wherein the mass ratio of etching agent to graphene oxide cake is 7-10:1, and the mass ratio of catalyst to etching agent is 0.7-1:1, to obtain porous graphene oxide with a pore size of 1-2.5 nm. The porous graphene oxide is then slurried to obtain porous graphene oxide slurry, coated into a primary film, chemically reduced and foamed, and heat-treated to obtain a porous graphene membrane.

2. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, The etching agent is hydrogen peroxide, and the catalyst is an alkaline reagent.

3. A method for preparing a graphene porous membrane as described in claim 2, characterized in that, The catalyst is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

4. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, The reaction time is 2-5 hours.

5. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, The median sheet diameter of the porous graphene oxide in the porous graphene oxide slurry is 4-12 μm.

6. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, The chemical reduction foaming process uses a foaming agent, which is at least one of hydrazine hydrate, ascorbic acid, sodium hydroxide, sodium borate, dimethylhydrazine, and thiourea. The chemical reduction foaming time is 30s-10min.

7. A method for preparing a graphene porous membrane as described in claim 5, characterized in that, The chemical reduction foaming time is 30s-5min.

8. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, The heat treatment includes a pretreatment process at 150-380℃, a carbonization process at 900-1400℃, and a graphitization process at 2000-3300℃.

9. A method for preparing a graphene porous membrane as described in claim 1, characterized in that, After the heat treatment, a calendering step is also included, wherein the calendering is either roll pressing or flat pressing.

10. A graphene porous membrane, prepared by the method according to any one of claims 1-9, wherein the graphene porous membrane has a longitudinal thermal conductivity of 5-11 W / (m·K), an in-plane thermal conductivity of 80-120 W / (m·K), an interlayer separation force >4 N / cm², and a recovery amount >95% after 20 cycles of 50% compression.

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