Preparation method of graphene film with high thermal conductivity in Z-axis direction, graphene film with high thermal conductivity in Z-axis direction and application of graphene film

Abstract

The invention provides a preparation method of a graphene film with high thermal conductivity in a Z-axis direction, the graphene film with high thermal conductivity in the Z-axis direction and application of the graphene film, and relates to the technical field of graphene. The preparation method comprises the following steps: carrying out air crushing treatment on low-solid-content graphene oxide slurry to enable micron-sized air bubbles to be attached to the surface of a sheet layer of graphene oxide, so as to obtain low-solid-content gas-dissolved graphene oxide slurry; preparing the low-solid-content dissolved gas graphene oxide slurry into high-solid-content dissolved gas graphene oxide slurry; carrying out homogenizing and stripping treatment on the high-solid-content gas-dissolved graphene oxide slurry to obtain homogenized graphene oxide slurry; the homogenized graphene oxide slurry is subjected to coating, drying and heat treatment in sequence, and the graphene film with the high thermal conductivity in the Z-axis direction is obtained. According to the preparation method disclosed by the invention, the tiling order of the graphene sheet layers in the X-Y direction is broken, and the cardinal number of the graphene sheet layers arranged in the Z-axis direction is increased, so that the heat-conducting property in the Z-axis direction is improved.

Description

Technical Field

[0001] This invention relates to the field of graphene technology, specifically to a method for preparing a graphene film with high thermal conductivity in the Z-axis direction, the graphene film with high thermal conductivity in the Z-axis direction and its application, and in particular to a method for preparing a graphene thermally conductive film with improved thermal conductivity in the Z-axis direction based on a disordered system constructed from micron-sized air bubbles, the graphene thermally conductive film and its application. Background Technology

[0002] Graphene boasts the highest theoretical thermal conductivity of any known material, holding immense market potential in thermal management materials for new energy technologies, 5G technology, and highly integrated electronics. Currently, graphene and graphene-based thermal conductive films are widely used in devices with high thermal management requirements, such as mobile phones, computers, and new energy vehicles. Graphene and graphene-based thermal conductive films exhibit excellent planar thermal diffusion performance in the XY direction, primarily attributed to the highly ordered and flat distribution of graphene sheets on the XY plane. However, research on thermal conductivity in the Z-axis direction lags behind, with few reports on high Z-axis thermal conductivity. Conventional graphene or graphene-based thermal conductive films exhibit XY-axis thermal conductivity ≥1300 W / mK, reaching a maximum of 2400 W / mK, which generally meets most conventional XY-planar thermal diffusion applications. Currently, research on Z-axis thermal conductivity remains at a low level, with the Z-axis thermal conductivity being approximately two orders of magnitude lower than that in the XY direction.

[0003] The research and development of improving the thermal conductivity of graphene and graphene-based thermal conductive films in the Z-axis direction can be divided into three strategies: first, improving the planar order of graphene sheets in the Z-axis direction; second, improving the thermal conductivity in the Z-axis direction by filling the graphene film with a thermally conductive medium; and third, constructing a chaotic system by sacrificing the planar order of graphene sheets in the XY direction to increase the number of graphene sheets in the Z-axis direction and thus improve the thermal conductivity in the Z-axis direction.

[0004] Due to the two-dimensional nature of graphene, the widespread use of planar coating technology, and the objective influence of gravity during the coating process, the first strategy for improving the planar orderliness of graphene sheets in the Z-axis direction is quite difficult to implement. The second method, filling the graphene thermal conductive film with a thermally conductive medium, often requires physical or chemical expansion of the graphene thermal conductive film to fill the pores. This often significantly disrupts the self-assembled structure within the graphene film. Moreover, because the pores of the expanded graphene film are still relatively small, there are significant limitations on the filling medium. The filling medium must be a highly fluid liquid or other thermally conductive filler, such as paraffin wax. However, such thermally conductive fillers often lack high thermal conductivity, making it impossible to achieve a breakthrough in the thermal conductivity of the graphene film in the Z-axis direction. The third approach, constructing a chaotic system to improve the thermal conductivity in the Z-axis direction, has a clearer research direction. It mainly involves disrupting the ordered arrangement in the XY directions, increasing the number of graphene sheets in the Z-axis direction, thereby improving the thermal conductivity in the Z-axis direction.

[0005] Currently, research on strategies for constructing chaotic systems mainly focuses on disrupting the ordered self-assembly of graphene sheets on the XY plane by adding organic and inorganic auxiliary materials, thereby achieving the goal of constructing chaotic systems. Although this method can achieve the goal of constructing chaotic systems, the added organic and inorganic auxiliary materials and their pyrolysis byproducts will seriously affect the overall performance of the graphene film.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a graphene film with high thermal conductivity in the Z-axis direction, the graphene film itself, and its applications. The preparation method of this invention utilizes micron-sized air bubbles to construct a chaotic system, breaking the planar order of graphene sheets in the XY directions and increasing the number of graphene sheets arranged in the Z-axis direction, thereby improving the thermal conductivity in the Z-axis direction. While traditional strategies involving the addition of organic or inorganic heterogeneous materials can achieve the goal of constructing a chaotic system, the added organic or inorganic auxiliary materials and their pyrolysis byproducts can severely affect the overall performance of the graphene film. The method provided by this invention for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed using micron-sized air bubbles utilizes micron-sized air bubbles as a heterogeneous material to hinder the planar order of graphene sheets. Micron-sized air bubbles are a green, cost-effective, and non-productive filler material that can maximize the release of the intrinsic thermal conductivity of graphene.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a graphene film with high thermal conductivity in the Z-axis direction, the method comprising: Low-solids graphene oxide slurry is subjected to air-breaking treatment to allow micron-sized air bubbles to adhere to the surface of graphene oxide sheets, thus obtaining low-solids dissolved gas graphene oxide slurry. The low-solids-content dissolved gas graphene oxide slurry was formulated into a high-solids-content dissolved gas graphene oxide slurry. The high-solids-content dissolved gas graphene oxide slurry was subjected to homogenization and exfoliation treatment to obtain a homogenized graphene oxide slurry. The homogenized graphene oxide slurry was sequentially coated, dried, and heat-treated to obtain the graphene film with high thermal conductivity in the Z-axis direction.

[0009] Furthermore, the air abrasion process is performed using an air abrasion apparatus; wherein the air abrasion apparatus includes: An ultrasonic transducer head is provided, wherein the ultrasonic transducer heads are arranged in an array and fixed inside a sealed box, and the working surface of the ultrasonic transducer head is exposed on the surface of the sealed box. Each aeration head is vertically mounted above the corresponding ultrasonic transducer head via a metal frame, and each aeration head is provided with an air inlet. An external air source is provided, with each air inlet connected to the external air source via an air guide pipe, and the air guide pipe is equipped with a throttle valve for adjusting the gas flow rate. Furthermore, the sealing box is a square sealing metal box.

[0010] Furthermore, the ultrasonic transducer heads are arranged in at least two rows, with more than three in each row.

[0011] Furthermore, the individual power of each ultrasonic transducer head is independently 10~100 W, and the individual vibration frequency of each ultrasonic transducer head is independently 10~100 kHz.

[0012] Furthermore, the aeration head is a porous metal aeration head made of sintered stainless steel powder.

[0013] Furthermore, the stainless steel powder sintered porous metal aerator head has a mesh size of 200 mesh or higher.

[0014] Furthermore, the distance between the bottom of the aeration head and the working surface of the ultrasonic transducer head is 5~15 mm.

[0015] Furthermore, the sealing box is mounted on a supporting base; and the bottom of the supporting base is provided with four sets of rubber discs.

[0016] Furthermore, the air abrasion process specifically includes the following steps: The air-breaking instrument is immersed in the bottom of the low-solids-content graphene oxide slurry. Under stirring conditions, air is introduced into the slurry through the aeration head, and the ultrasonic transducer head is activated to break up the introduced air and integrate it into the slurry, so that micron-sized air bubbles are attached to the surface of the graphene oxide sheets, thus obtaining a low-solids-content dissolved air graphene oxide slurry.

[0017] Furthermore, the stirring speed is 50~200 r / min.

[0018] Furthermore, the air injection flow rate is 1~3 L / min.

[0019] Furthermore, the start-up time for the ultrasonic transducer head is 20-40 minutes.

[0020] Furthermore, the method for preparing the low-solids-content graphene oxide slurry includes: Graphene oxide, pH adjuster and water are mixed and stirred and dispersed to obtain the low-solids-content graphene oxide slurry.

[0021] Furthermore, in the process of preparing the low-solids graphene oxide slurry, the stirring and dispersion treatment is carried out using a dual planetary mixer; wherein, the stirring speed is 30~100 rpm, the dispersion speed is 500~3000 rpm, the dispersion time is 30~180 min, and the dispersion temperature is below 10℃.

[0022] Furthermore, the viscosity of the low-solids graphene oxide slurry is below 8000 MPa·s.

[0023] Furthermore, the solid content of the low-solids graphene oxide slurry does not exceed 2.5 wt%.

[0024] Furthermore, the preparation method of the high-solids-content dissolved gas graphene oxide slurry includes: Graphene oxide and a pH adjuster are added to the low-solids-content dissolved gas graphene oxide slurry, and the mixture is stirred and dispersed to obtain the high-solids-content dissolved gas graphene oxide slurry.

[0025] Furthermore, in the process of preparing the high solids content dissolved gas graphene oxide slurry, the stirring and dispersion treatment adopts a double planetary mixer; wherein, the stirring speed is 30~100 rpm, the dispersion treatment speed is 500~3000 rpm, the dispersion treatment time is 30~180 min, and the dispersion treatment temperature is below 10℃.

[0026] Furthermore, the solid content of the high-solids dissolved graphene oxide slurry is 2.5 wt% or more, preferably 3 to 8 wt%.

[0027] Furthermore, the pH adjuster is ammonia.

[0028] Furthermore, the pH of the low-solids-content graphene oxide slurry or the high-solids-content dissolved gas graphene oxide slurry is independently 6.6~7.0.

[0029] Furthermore, the pressure of the homogenization stripping process is 1000~1500 bar.

[0030] Furthermore, the temperature of the homogenization stripping process is below 10°C.

[0031] Furthermore, the homogenization stripping process is performed more than twice.

[0032] Furthermore, the coating thickness is 2000~8000 μm.

[0033] Furthermore, the drying temperature is 40~50℃, and the drying vacuum degree is 10~100 Pa.

[0034] Furthermore, the heat treatment sequentially includes: pretreatment, carbonization treatment, and graphitization treatment.

[0035] Furthermore, the pretreatment temperature is 220~260℃, and the pretreatment time is 1~3 h.

[0036] Furthermore, the carbonization temperature is 1100~1300℃, and the carbonization time is 1~3 h.

[0037] Furthermore, the graphitization treatment temperature is 3100~3200℃, and the graphitization treatment time is 1~3h.

[0038] In a second aspect, the present invention provides a graphene film with high thermal conductivity in the Z-axis direction, wherein the graphene film with high thermal conductivity in the Z-axis direction is prepared by the preparation method of the graphene film with high thermal conductivity in the Z-axis direction as described in the first aspect.

[0039] Furthermore, the thermal diffusivity of the graphene film with high thermal conductivity in the Z-axis direction is 80 mm. 2 / s or higher, preferably 150 mm 2 / s or higher, more preferably 450 mm 2 / s or more.

[0040] Thirdly, the present invention provides an application of a graphene film with high thermal conductivity in the Z-axis direction as described in the second aspect in the preparation of thermal management materials.

[0041] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method described in this invention constructs a chaotic system by micron-level air bubbles, which breaks the planar order of graphene sheets in the XY direction and increases the number of graphene sheets arranged in the Z-axis direction, thereby improving the thermal conductivity in the Z-axis direction. (2) Compared with the traditional strategy of constructing a chaotic system by adding organic and inorganic heterogeneous materials, the added organic and inorganic auxiliary materials and their pyrolysis byproducts will seriously affect the overall performance of the graphene film; while the preparation method proposed in this invention uses micron-sized air bubbles as heterogeneous materials to hinder the orderly spread of graphene sheets. Micron-sized air bubbles are a green, cost-effective filling material that does not produce any byproducts or residues, and can release the intrinsic thermal conductivity of graphene to the greatest extent. (3) The preparation method provided by the present invention introduces a large number of micron-sized air bubbles into the graphene oxide slurry through a simple low-temperature ultrasonic crushing method, thereby achieving the purpose of introducing a large number of micron-sized air bubble heterogeneous material into the graphene oxide slurry. (4) Unlike the traditional atmospheric pressure forced-air drying oven, the preparation method provided by the present invention dries the coating film in a micro-low pressure environment during the coating drying stage. The purpose is to use the micro-low pressure environment to maintain the heterogeneous barrier effect of micron-sized air bubbles in the film, disrupt the orderly arrangement of graphene sheets in the coating film, and realize the construction of a chaotic system. (5) The preparation method provided by the present invention utilizes the large specific surface area of ​​exfoliated graphene oxide and the easy adhesion of micro air bubbles to achieve stable carrying of micron-sized air bubbles in the exfoliated graphene oxide sheets. (6) The preparation method provided by the present invention uses low-temperature ultrasonic crushing to solve the problem of air bubble escape and successfully realizes the attachment and carrying of air bubbles on graphene oxide sheets; (7) The preparation method provided by the present invention is a structural control strategy with air bubbles as heterogeneous or framework, which has reference value for the research and development of homogeneous chaotic structural systems. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a three-dimensional structural diagram of the air-breaking instrument provided by the present invention.

[0044] Figure 2 A top view of the air-breaking instrument provided by the present invention.

[0045] Figure 3 A plan view of the air-breaking instrument provided by the present invention.

[0046] Among them, 100 is the aeration head, 200 is the air inlet, 300 is the ultrasonic transducer head, 400 is the sealing box, and 500 is the voltage interface.

[0047] Figure 4 The particle size distribution of the slurry after the first homogenization in step S3 of the preparation method provided in Example 1 is shown in the figure.

[0048] Figure 5 The particle size distribution of the slurry after the second homogenization in step S3 of the preparation method provided in Example 1.

[0049] Figure 6 The graph shows the test results of the Z-axis thermal conductivity of the graphene film with high thermal conductivity in Example 1.

[0050] Figure 7 The particle size distribution of the slurry after the first homogenization in step S3 of the preparation method provided for Comparative Example 1.

[0051] Figure 8 The particle size distribution of the slurry after the second homogenization in step S3 of the preparation method provided for Comparative Example 1.

[0052] Figure 9 The graph shows the test results of the thermal conductivity of the graphene thermal conductive film provided in Comparative Example 1 in the Z-axis direction.

[0053] Figure 10 The graph shows the test results of the thermal conductivity of the graphene thermal conductive film provided in Comparative Example 2 in the Z-axis direction. Detailed Implementation

[0054] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0055] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0056] In a first aspect, the present invention provides a method for preparing a graphene film with high thermal conductivity in the Z-axis direction, the method comprising: Low-solids graphene oxide slurry is subjected to air-breaking treatment to allow micron-sized air bubbles to adhere to the surface of graphene oxide sheets, thus obtaining low-solids dissolved gas graphene oxide slurry. The low-solids-content dissolved gas graphene oxide slurry was formulated into a high-solids-content dissolved gas graphene oxide slurry. The high-solids-content dissolved gas graphene oxide slurry was subjected to homogenization and exfoliation treatment to obtain a homogenized graphene oxide slurry. The homogenized graphene oxide slurry was sequentially coated, dried, and heat-treated to obtain the graphene film with high thermal conductivity in the Z-axis direction.

[0057] It should be noted that in the method for preparing a graphene film with high thermal conductivity in the Z-axis direction provided by this invention, the low-solids-content graphene oxide slurry is first subjected to air-breaking treatment. The injected air is broken up and incorporated into the low-solids-content graphene oxide slurry. This step utilizes the low-solids-content characteristics of the slurry and the high specific surface area characteristics of the graphene oxide sheets, which is conducive to the adhesion of micron-sized air bubbles to the surface of the graphene oxide sheets. This allows the graphene oxide sheets to carry a sufficient number of micron-sized air bubbles, thus obtaining a low-solids-content dissolved air graphene oxide slurry. Next, the low-solids-content dissolved air graphene oxide slurry is transferred again, and a certain amount of graphene oxide raw material is added again. A high-solids-content dissolved gas graphene oxide slurry was obtained; subsequently, a homogenization exfoliation process was performed, utilizing the large specific surface area of ​​the exfoliated graphene oxide and the ease with which tiny air bubbles adhered, to achieve stable carrying of micron-sized air bubbles in the exfoliated graphene oxide sheets; finally, coating, drying, and heat treatment were performed sequentially; among them, the advantage of using micro-low pressure drying is that, while ensuring that the micron-sized air bubbles do not over-expand and burst, the micron-sized air bubbles carried by the graphene oxide sheets are appropriately expanded in a micro-low pressure environment, which strengthens the obstruction effect of the micron-sized air bubbles and improves the degree of disordered arrangement of the graphene oxide sheets in the graphene oxide coating film system.

[0058] It is important to note that the solid content is a key factor affecting the effectiveness of the air breaker in the preparation of graphene oxide slurry. In slurries with low solid content, the graphene sheets are loosely distributed with large interlayer gaps. In this case, the airflow introduced by the air breaker can easily penetrate into the gaps between the sheets, forming uniformly dispersed micron-sized bubbles on the surface of individual sheets. However, if high-solid-content slurries are directly subjected to air breaker treatment, the airflow penetration resistance is significantly increased due to the dense arrangement and high degree of stacking of the sheets, resulting in a significant reduction in the efficiency of micron-sized bubble generation, or even the inability to form an effective bubble structure, thus affecting the subsequent process results. The two-step configuration process effectively solves the technical bottlenecks of low air breaker efficiency and difficult sheet dispersion in high-solid-content systems by segmentally controlling the solid content and bubble structure, while taking into account both the rheological properties of the slurry and the quality of the film forming. This process design follows the basic principles of colloidal dispersion systems and fully considers the material characteristics of graphene oxide, providing reliable process support for the large-scale preparation of high-performance graphene films.

[0059] As an optional implementation, the air-breaking process is carried out using an air-breaking instrument.

[0060] As an optional implementation method, such as Figures 1-3 As shown, the air-breaking instrument includes: An ultrasonic transducer head 300 is arranged in an array and fixed inside a sealed box 400, with the working surface of the ultrasonic transducer head exposed on the surface of the sealed box 400. Aeration head 100, each of the aeration heads 100 is vertically mounted above the corresponding ultrasonic transducer head 300 by means of a metal frame, and each of the aeration heads 100 is provided with an air inlet 200. An external air source is provided, with each air inlet 200 connected to the external air source via an air guide pipe, and the air guide pipe is equipped with a throttle valve for adjusting the gas flow rate.

[0061] As an optional implementation, the sealing box 400 is a square sealing metal box.

[0062] As an optional implementation, the sealed box 400 is also provided with a voltage interface 500.

[0063] As an optional implementation, the ultrasonic transducer heads 300 are arranged in at least two rows, such as two rows, three rows, four rows, five rows, etc.

[0064] As an optional implementation, the ultrasonic transducer heads 300 are provided in more than 3 rows, for example, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0065] As an optional implementation, the ultrasonic transducer heads 300 are connected in parallel.

[0066] As an optional implementation, the exposed circuitry in the air-breaking instrument is protected with adhesive to prevent short circuits in water.

[0067] As an optional implementation, the power of each individual ultrasonic transducer head 300 is independently 10~100 W, for example, it can be 10 W, 20 W, 30 W, 40 W, 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, etc.

[0068] As an optional implementation, the individual vibration frequencies of the ultrasonic transducer head 300 are each independently 10~100 kHz, for example, 10 kHz, 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, etc.

[0069] As an optional implementation, the aeration head 100 is a porous metal aeration head made of sintered stainless steel powder.

[0070] As an optional implementation, the stainless steel powder sintered porous metal aerator head has a mesh size of 200 mesh or more, such as 200 mesh, 300 mesh, 400 mesh, 500 mesh, 600 mesh, 700 mesh, 800 mesh, 900 mesh, 1000 mesh, etc.

[0071] As an optional implementation, the distance between the bottom of the aeration head 100 and the working surface of the ultrasonic transducer head 300 is 5 to 15 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, etc.

[0072] As an optional implementation, the sealing box 400 is mounted on a support base.

[0073] As an optional implementation, the bottom of the supporting base is provided with four sets of rubber discs, the purpose of which is to bear the weight and prevent it from tipping over and moving during vibration.

[0074] As an optional implementation, the preparation method includes the step of assembling an air breaker, specifically: It provides 10 ultrasonic transducer heads with a power of 50 W and a vibration frequency of 40 kHz, and 10 200-mesh stainless steel powder sintered porous metal aeration heads with air inlets, such as... Figure 1The designed structure is assembled into an air breaker. The ultrasonic transducer heads are distributed in two rows, with five transducers in each row. The transducers are embedded in a square sealed metal box, with the transducers exposed on the surface of the sealed metal box. Ten 200-mesh stainless steel powder sintered porous aeration heads with air inlets are vertically set above the transducers through a metal frame. The distance between the bottom of the aeration head and the surface of the transducer head is designed to be 10 mm. The air guide pipe is connected to the air inlet of the aeration head. The gas flow rate through the aeration head is regulated by a throttle valve on the air guide pipe. The exposed circuit is protected with glue to prevent short circuits in water. Four sets of rubber discs are installed on the supporting base to bear the weight and prevent tipping and movement during vibration, thus completing the air breaker assembly.

[0075] As an optional implementation, the air ablation process specifically includes the following steps: The air-breaking instrument is immersed in the bottom of the low-solids-content graphene oxide slurry. Under stirring conditions, air is introduced into the slurry through the aeration head, and the ultrasonic transducer head is activated to break up the introduced air and integrate it into the slurry, so that micron-sized air bubbles are attached to the surface of the graphene oxide sheets, thus obtaining a low-solids-content dissolved air graphene oxide slurry.

[0076] As an optional implementation, during the air crushing process, the stirring speed is 50~200 r / min, for example, it can be 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, etc.

[0077] As an optional implementation, during the air crushing process, the air injection flow rate is 1~3L / min, for example, it can be 1 L / min, 1.2 L / min, 1.4 L / min, 1.6 L / min, 1.8 L / min, 2 L / min, 2.2 L / min, 2.4 L / min, 2.6 L / min, 2.8 L / min, 3 L / min, etc.

[0078] As an optional implementation, the start-up time of the ultrasonic transducer head is 20~40 min, for example, it can be 200 min, 22 min, 24 min, 25 min, 26 min, 28 min, 30 min, 32 min, 34 min, 35 min, 36 min, 38 min, 40 min, etc.

[0079] As an optional implementation, the method for preparing the low-solids-content graphene oxide slurry includes: Graphene oxide, pH adjuster and water are mixed and stirred and dispersed to obtain the low-solids-content graphene oxide slurry.

[0080] As an optional implementation, in the process of preparing the low-solids-content graphene oxide slurry, the stirring and dispersion treatment adopts a dual planetary mixer; wherein, the stirring speed is 30~100 rpm, for example, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, etc., and the dispersion treatment speed is 500~3000 rpm, for example, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2500 rpm, 3000 rpm, etc., and the dispersion treatment time is 30~180 min, for example, 30 min, 40 min, 50 min, 60 min, 80 min, 100 min, 120 min, 140 min, 150 min, 160 min, 180 min, etc.

[0081] As an optional implementation, during the preparation of the low-solids-content graphene oxide slurry, the dispersion treatment temperature is below 10°C, for example, it can be 10°C, 9°C, 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, 1°C, etc.

[0082] As an optional implementation, the viscosity of the low-solids graphene oxide slurry is below 8000 MPa·s, for example, it can be 8000 MPa·s, 7000 MPa·s, 6000 MPa·s, 5000 MPa·s, 4000 MPa·s, 3000 MPa·s, 2000 MPa·s, 1000 MPa·s, etc.

[0083] As an optional implementation, the solid content of the low-solids graphene oxide slurry does not exceed 2.5 wt%, for example, it can be 2.49 wt%, 2.45 wt%, 2.4 wt%, 2.3 wt%, 2.2 wt%, 2.1 wt%, 2 wt%, 1.8 wt%, 1.6 wt%, 1.5 wt%, 1.4 wt%, 1.2 wt%, 1 wt%, 0.9 wt%, 0.5 wt%, 0.1 wt%, 0.05 wt%, 0.01 wt%, etc.

[0084] It should be noted that the first step requires air ablation in a low-solids-content system (defined in this process as solids content < 2.5%). In this stage, by precisely controlling the airflow rate and pressure, air molecules are allowed to fully penetrate the surface of the loose graphene sheets. The adsorption between the sheets fixes the micron-sized bubbles, forming a pre-dispersion system with a stable gas-liquid interface. The introduction of bubbles not only optimizes the rheological properties of the slurry but also provides spatial support for the subsequent sheet dispersion in the high-solids-content system, preventing excessive sheet stacking.

[0085] As an optional implementation, the method for preparing the high-solids-content dissolved gas graphene oxide slurry includes: Graphene oxide and a pH adjuster are added to the low-solids-content dissolved gas graphene oxide slurry, and the mixture is stirred and dispersed to obtain the high-solids-content dissolved gas graphene oxide slurry.

[0086] As an optional implementation, in the process of preparing the high-solids-content dissolved gas graphene oxide slurry, the stirring and dispersion treatment is carried out using a dual planetary mixer; wherein, the stirring speed is 30~100 rpm, for example, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, etc., and the dispersion treatment speed is 500~3000 rpm, for example, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2500 rpm, 3000 rpm, etc., and the dispersion treatment time is 30~180 min, for example, 30 min, 40 min, 50 min, 60 min, 80 min, 100 min, 120 min, 140 min, 150 min, 160 min, 180 min. min etc.

[0087] As an optional implementation, during the preparation of the high solids content dissolved gas graphene oxide slurry, the dispersion treatment temperature is below 10°C, for example, it can be 10°C, 9°C, 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, 1°C, etc.

[0088] As an optional implementation, the high-solids-content dissolved gas graphene oxide slurry has a solids content of 2.5 wt% or more, for example, it can be 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, etc.

[0089] As an optional implementation, the solid content of the high-solids dissolved graphene oxide slurry is 3-8 wt%.

[0090] It should be noted that after introducing the bubbles, the second step requires adjusting the solid content by adding graphene oxide cake (the main raw material), and deionized water and pH adjusters (such as ammonia) can also be added as needed. The core objective of this stage is to increase the solid content of the slurry to the range required by the process while retaining the bubble structure: on the one hand, by increasing the concentration of effective components, it is ensured that the graphene sheets remaining after solvent evaporation can form a film of sufficient thickness in the subsequent coating and drying stages; on the other hand, by using the spacing effect of the bubbles, it is promoted that the sheets form a uniformly overlapping network structure during the drying process, avoiding film defects caused by uneven sheet distribution (such as local excessive thinness, abnormal porosity, etc.), thereby ensuring the mechanical properties and structural integrity of the final film.

[0091] As an optional implementation, in the process of preparing the low-solids-content graphene oxide slurry and the high-solids-content dissolved gas graphene oxide slurry, the pH adjuster is ammonia water.

[0092] It should be noted that the role of ammonia is twofold: firstly, to adjust the pH value of the graphene oxide slurry to a certain range; and secondly, to remove residual sulfate ions in the thermally conductive film during the carbonization stage using volatile ammonium sulfate.

[0093] As an optional implementation, the pH of the low-solids-content graphene oxide slurry or the high-solids-content dissolved gas graphene oxide slurry is independently 6.6 to 7.0, for example, it can be 6.6, 6.7, 6.8, 6.9, 7.0, etc.

[0094] As an optional implementation, the pressure of the homogenization stripping process is 1000~1500 bar, for example, it can be 1000 bar, 1100 bar, 1200 bar, 1300 bar, 1400 bar, 1500 bar, etc.

[0095] As an optional implementation, the temperature of the homogenization stripping process is below 10°C, for example, it can be 10°C, 9°C, 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, 1°C, etc.

[0096] As an optional implementation, the homogenization stripping process is performed more than twice, for example, twice, three times, four times, five times, etc.

[0097] As an optional implementation, the coating thickness is 2000~8000 μm, for example, it can be 2000 μm, 2500 μm, 3000 μm, 3500 μm, 4000 μm, 4500 μm, 5000 μm, 5500 μm, 6000 μm, 6500 μm, 7000 μm, 7500 μm, 8000 μm, etc.

[0098] As an optional implementation, the drying temperature is 40~50℃, for example, it can be 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, etc.

[0099] As an optional implementation, the vacuum degree of the drying process is 10~100 Pa, for example, it can be 10 Pa, 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 100 Pa, etc.

[0100] As an optional implementation, the heat treatment includes, in sequence, pretreatment, carbonization treatment and graphitization treatment.

[0101] As an optional implementation, the pretreatment temperature is 220~260℃, for example, it can be 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, etc.

[0102] As an optional implementation, the pretreatment time is 1 to 3 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, etc.

[0103] As an optional implementation, the carbonization temperature is 1100~1300℃, for example, it can be 1100℃, 1120℃, 1140℃, 1150℃, 1180℃, 1200℃, 1220℃, 1240℃, 1250℃, 1260℃, 1280℃, 1300℃, etc.

[0104] As an optional implementation, the carbonization treatment time is 1 to 3 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, etc.

[0105] As an optional implementation, the graphitization treatment temperature is 3100~3200℃, for example, it can be 3110℃, 3120℃, 3130℃, 3140℃, 3150℃, 3160℃, 3170℃, 3180℃, 3190℃, 3200℃, etc.

[0106] As an optional implementation, the graphitization treatment time is 1 to 3 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, etc.

[0107] In a second aspect, the present invention provides a graphene film with high thermal conductivity in the Z-axis direction, wherein the graphene film with high thermal conductivity in the Z-axis direction is prepared by the preparation method of the graphene film with high thermal conductivity in the Z-axis direction as described in the first aspect.

[0108] As an optional implementation, the thermal diffusivity of the graphene film with high thermal conductivity in the Z-axis direction is 80 mm. 2 / s or higher, for example, 80 mm 2 / s, 90 mm 2 / s, 100 mm 2 / s, 110 mm 2 / s, 120 mm 2 / s, 130 mm 2 / s, 140mm 2 / s, 150 mm 2 / s, 160 mm 2 / s, 170 mm 2 / s, 180 mm 2 / s, 190 mm 2 / s, 200 mm 2 / s, 250 mm 2 / s, 300mm 2 / s, 350 mm 2 / s, 400 mm 2 / s, 450 mm 2 / s, 460 mm 2 / s, 470 mm 2 / s, 480 mm 2 / s, 490 mm 2 / s, 492mm 2 / s, 494 mm 2 / s, 495 mm 2 / s, 496 mm 2 / s, 498 mm 2 / s, 500 mm2 / s, 502 mm 2 / s, 505 mm 2 / s, 510mm 2 / s, 520 mm 2 / s etc.

[0109] In a preferred embodiment, the thermal diffusivity of the graphene film with high thermal conductivity in the Z-axis direction is 150 mm. 2 / s or more.

[0110] In a more preferred embodiment, the thermal diffusivity of the graphene film with high thermal conductivity in the Z-axis direction is 450 mm. 2 / s or more.

[0111] Thirdly, the present invention provides an application of a graphene film with high thermal conductivity in the Z-axis direction as described in the second aspect in the preparation of thermal management materials.

[0112] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0113] In the following examples and comparative examples, the graphene oxide cake was purchased from the A52 model cake of Yuntian Morui Technology Co., Ltd., and the ammonia water was purchased from the Aladdin test machine website.

[0114] Example 1 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles, specifically including the following steps: S1. Assemble the air breaker: Ten 50 W ultrasonic transducers with a vibration frequency of 40 kHz and ten porous metal aeration heads made of 200-mesh stainless steel powder with air inlets were sintered together. Figure 1 The design structure shown is assembled into an air breaker; the ultrasonic transducer heads are distributed in two rows, with five transducers in each row. The transducers are embedded in a square sealed metal box, with the transducers exposed on the surface of the sealed metal box; ten 200-mesh stainless steel powder sintered porous aeration heads with air inlets are vertically set above the transducers through a metal frame. The distance between the bottom of the aeration head and the surface of the transducer head is designed to be 10 mm. The air guide pipe is connected to the air inlet of the aeration head. The gas flow rate through the aeration head is regulated by a throttle valve on the air guide pipe. The exposed circuit is protected with glue to prevent short circuits in water; four sets of rubber discs are installed on the supporting base to bear the weight and prevent tipping and movement during vibration, thus completing the air breaker assembly; S2, Preparation of graphene oxide slurry and low-temperature ultrasonic air injection: S2-1, Preparation of low-solids dissolved gas graphene oxide slurry: Deionized water, ammonia water, and graphene oxide cake were added to a double planetary mixer in a certain proportion and stirred and dispersed at a stirring speed of 80 rpm and a dispersion speed of 2500 rpm for 60 min to disperse the graphene oxide slurry. A low solid content graphene oxide slurry with a solid content of 2 wt% and a viscosity of 6202 MPa·s was prepared, and the slurry had good fluidity. During the preparation of the graphene oxide slurry, a chiller was used to maintain the slurry temperature below 10°C. The air-breaking instrument assembled in step S1 was immersed in the bottom of the low-solids graphene oxide slurry. The instrument was slowly stirred at 100 r / min using a stirring rod, and air was introduced through the metal aerator. The air injection flow rate was designed to be 2 L / min. The ultrasonic transducer was started for 30 min to break up the injected air and integrate it into the low-solids graphene oxide slurry. Utilizing the low-solids content of the slurry and the high specific surface area of ​​the graphene oxide sheets, it is beneficial for micron-sized air bubbles to adhere to the surface of the graphene oxide sheets, allowing the graphene oxide sheets to carry a sufficient amount of micron-sized air bubbles, thus obtaining a low-solids dissolved gas graphene oxide slurry. S2-2, Preparation of high-solids-content dissolved gas graphene oxide slurry: The low-solids dissolved gas graphene oxide slurry was transferred to a dual planetary mixer, and ammonia water and graphene oxide cake were added in sequence. The mixture was stirred and dispersed at a stirring speed of 90 rpm and a dispersion speed of 3000 rpm for 180 min until it was uniformly dispersed, thus preparing a high-solids dissolved gas graphene oxide slurry with a solids content of 5 wt%. In S2-1 and S2-2, the role of ammonia is twofold: first, to adjust the pH value of the graphene oxide slurry to 6.8; and second, to remove residual sulfate ions in the thermally conductive film in the carbonization stage using volatile ammonium sulfate. S3. Homogenized stripping process: The 5 wt% high solids dissolved gas graphene oxide slurry obtained in step S2 was subjected to high-pressure homogenization and exfoliation using a high-pressure homogenizer. The homogenization pressure was 1200 bar, and a water-cooled heat exchanger was used to cool the slurry outlet to keep the temperature of the homogenized slurry below 10°C. The homogenization was performed twice to obtain the homogenized graphene oxide slurry. S4. Coating and drying: S4-1, Coating: The homogenized graphene oxide slurry obtained in step S3 was directly coated onto the breathable substrate using a flat blade coater to obtain a graphene oxide coating film with a thickness of 5 mm. S4-2, Low-pressure drying treatment: The graphene oxide coating film was transferred to a CNC vacuum oven. The oven temperature was set at 45°C, and the vacuum level was maintained at a low pressure of 50 Pa. The purpose of maintaining the low pressure atmosphere was to appropriately expand the micron-sized air bubbles carried by the graphene oxide sheets under the premise of ensuring that the micron-sized air bubbles did not expand and burst excessively. This enhanced the obstructive effect of the micron-sized air bubbles and improved the disordered arrangement of the graphene oxide sheets in the graphene oxide coating film system. After drying, a GO dry film was obtained.

[0115] S5. Heat treatment: S5-1, Pretreatment: The GO dry film obtained in step S4 is transferred to a forced-air drying oven. The film is stacked with 304 stainless steel plates and graphite paper, and a 20 kg load is applied to the surface. The temperature in the forced-air drying oven is raised to 240℃ at a heating rate of 0.5℃ / min. During this period, the temperature is maintained at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, and 200℃ for 30 min. When the temperature rises from 200℃ to the target 240℃ and is maintained for 2 h, the heating is stopped and the film is allowed to cool naturally to room temperature. This completes the pretreatment of the GO dry film and yields the pretreated film. S5-2, Carbonization treatment: The pretreated membrane obtained in the previous stage is loaded into a graphite fixture and transferred to a carbonization furnace. The carbonization furnace raises the temperature to 500°C at a heating rate of 5°C / min, and then reduces the heating rate to 0.5°C / min. When the temperature rises from 500°C to the target 1200°C and is held for 2 hours, the heating is stopped. After the temperature naturally cools down to room temperature, the carbonization treatment of the pretreated membrane is completed. S5-3, Graphitization treatment: The carbonized film, along with the graphite fixture, was transferred to a graphitization furnace after carbonization. The graphitization process was carried out under an argon atmosphere at a flow rate of 5 L / min. The graphitization furnace was heated at a rate of 10℃ / min up to 1200℃, 5℃ / min in the 1200–2000℃ range, 2.5℃ / min in the 2000–2500℃ range, 1℃ / min in the 2500–3000℃ range, and 0.5℃ / min in the 3000–3150℃ range. Temperatures at 1200℃, 2000℃, 2500℃, and 3000℃ were held for 30 min to reduce temperature fluctuations, and the target temperature of 3150℃ was held for 2 minutes. After h, the heating is stopped, and the material is allowed to cool naturally to room temperature, thus completing the graphitization process and obtaining a graphitized film, namely the graphene film with high thermal conductivity in the Z-axis direction.

[0116] Example 2 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles, specifically including the following steps: S1. Assemble the air breaker: An air breaker is assembled by combining six 60 W ultrasonic transducers with a vibration frequency of 80 kHz and six 300-mesh stainless steel powder sintered porous metal aerators with air inlets. The ultrasonic transducers are arranged in two rows of three, embedded in a square sealed metal box with the transducers exposed on the surface of the box. The six 300-mesh stainless steel powder sintered porous aerators with air inlets are vertically mounted above the transducers via a metal frame. The distance between the bottom of the aerator and the surface of the transducer is designed to be 6 mm. An air guide pipe connects to the air inlet of the aerator, and the gas flow through the aerator is regulated by a throttle valve on the air guide pipe. Exposed circuits are protected with adhesive to prevent short circuits in water. Four sets of rubber discs are installed on the supporting base to support the weight and prevent tipping and movement during vibration, thus completing the air breaker assembly. S2, Preparation of graphene oxide slurry and low-temperature ultrasonic air injection: S2-1, Preparation of low-solids dissolved gas graphene oxide slurry: Deionized water, ammonia water, and graphene oxide cake were added to a double planetary mixer in a certain proportion and stirred and dispersed at a stirring speed of 50 rpm and a dispersion speed of 2000 rpm for 60 min to disperse the graphene oxide slurry. A low solid content graphene oxide slurry with a solid content of 2 wt% and a viscosity of 5480 MPa·s was prepared, and the slurry had good fluidity. During the preparation of the graphene oxide slurry, a chiller was used to maintain the slurry temperature below 10°C. The air-breaking instrument assembled in step S1 was immersed in the bottom of the low-solids graphene oxide slurry. The instrument was slowly stirred at 200 r / min using a stirring rod, and air was introduced through the metal aerator. The air injection flow rate was designed to be 2.5 L / min. The ultrasonic transducer was started for 20 min to break up the injected air and integrate it into the low-solids graphene oxide slurry. Utilizing the low-solids content of the slurry and the high specific surface area of ​​the graphene oxide sheets, it is beneficial for micron-sized air bubbles to adhere to the surface of the graphene oxide sheets, allowing the graphene oxide sheets to carry a sufficient amount of micron-sized air bubbles, thus obtaining a low-solids dissolved gas graphene oxide slurry. S2-2, Preparation of high-solids-content dissolved gas graphene oxide slurry: The low-solids dissolved gas graphene oxide slurry was transferred to a dual planetary mixer, and ammonia water and graphene oxide cake were added in sequence. The mixture was stirred and dispersed at a stirring speed of 100 rpm and a dispersion speed of 3000 rpm for 150 min until it was uniformly dispersed, thus preparing a high-solids dissolved gas graphene oxide slurry with a solids content of 6 wt%. In S2-1 and S2-2, the role of ammonia is twofold: first, to adjust the pH value of the graphene oxide slurry to 7.0; and second, to remove residual sulfate ions in the thermally conductive film in the carbonization stage using volatile ammonium sulfate. Steps S3 to S5 are completely consistent with those in Example 1.

[0117] Example 3 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles, specifically including the following steps: S1. Assemble the air breaker: An air breaker is assembled by combining twelve 30 W ultrasonic transducers with a vibration frequency of 20 kHz and twelve 350-mesh stainless steel powder sintered porous metal aerators with air inlets. The ultrasonic transducers are arranged in three rows of four, embedded in a square sealed metal box with the transducers exposed on the surface of the box. The twelve 350-mesh stainless steel powder sintered porous aerators with air inlets are vertically mounted above the transducers via a metal frame. The distance between the bottom of the aerator and the surface of the transducer is designed to be 15 mm. An air guide pipe connects to the air inlet of the aerator, and the gas flow through the aerator is regulated by a throttle valve on the air guide pipe. Exposed circuits are protected with adhesive to prevent short circuits in water. Four sets of rubber discs are installed on the support base to support the weight and prevent tipping and movement during vibration, thus completing the air breaker assembly. S2, Preparation of graphene oxide slurry and low-temperature ultrasonic air injection: S2-1, Preparation of low-solids dissolved gas graphene oxide slurry: Deionized water, ammonia water, and graphene oxide cake were added to a double planetary mixer in a certain proportion and stirred and dispersed at a stirring speed of 30 rpm and a dispersion speed of 1500 rpm for 180 min to disperse the graphene oxide slurry. A low solid content graphene oxide slurry with a solid content of 2 wt% and a viscosity of 4638 MPa·s was prepared, and the slurry had good fluidity. During the preparation of the graphene oxide slurry, a chiller was used to maintain the slurry temperature below 10°C. The air-breaking instrument assembled in step S1 was immersed in the bottom of the low-solids graphene oxide slurry. The instrument was slowly stirred at 60 r / min using a stirring rod, and air was introduced through the metal aerator. The air injection flow rate was designed to be 3.0 L / min. The ultrasonic transducer was started for 40 min to break up the injected air and integrate it into the low-solids graphene oxide slurry. Utilizing the low-solids content of the slurry and the high specific surface area of ​​the graphene oxide sheets, it is beneficial for micron-sized air bubbles to adhere to the surface of the graphene oxide sheets, allowing the graphene oxide sheets to carry a sufficient amount of micron-sized air bubbles, thus obtaining a low-solids dissolved gas graphene oxide slurry. S2-2, Preparation of high-solids-content dissolved gas graphene oxide slurry: The low-solids dissolved gas graphene oxide slurry was transferred to a dual planetary mixer, and ammonia water and graphene oxide cake were added in sequence. The mixture was stirred and dispersed at a stirring speed of 100 rpm and a dispersion speed of 2800 rpm for 180 min until it was uniformly dispersed, thus preparing a high-solids dissolved gas graphene oxide slurry with a solids content of 5 wt%. In S2-1 and S2-2, the role of ammonia is twofold: first, to adjust the pH value of the graphene oxide slurry to 6.8; and second, to remove residual sulfate ions in the thermally conductive film in the carbonization stage using volatile ammonium sulfate. Steps S3 to S5 are completely consistent with those in Example 1.

[0118] Example 4 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles. The only difference from Embodiment 1 is that in S2-1, a low-solid-content graphene oxide slurry with a solid content of 1 wt% is prepared; in S2-2, a high-solid-content dissolved gas graphene oxide slurry with a solid content of 6 wt% is prepared; the other steps are the same as in Embodiment 1.

[0119] Example 5 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity by constructing a chaotic system based on micron-sized air bubbles. The only difference from Embodiment 1 is that in S4-2, the vacuum degree of the oven is maintained at a micro-low pressure range of 10 Pa; the other steps are the same as in Embodiment 1.

[0120] Example 6 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles. The only difference from Embodiment 1 is that in S4-2, the vacuum degree of the oven is maintained at a micro-low pressure range of 100 Pa; the other steps are the same as in Embodiment 1.

[0121] Example 7 This embodiment provides a method for preparing a graphene thermally conductive film based on a chaotic system constructed from micron-sized air bubbles to improve thermal conductivity in the Z-axis direction. The only difference from Embodiment 1 is that in step S3, during the homogenization process of the graphene oxide slurry, the temperature of the water chiller is adjusted to control the discharge temperature of the homogenized graphene oxide slurry. It was found that the temperature of the graphene oxide slurry reached as high as 48°C after two homogenization treatments. The other steps are the same as in Embodiment 1.

[0122] Note: The purpose of this embodiment is to investigate the effect of adjusting the temperature of homogenized graphene oxide slurry on the thermal conductivity of graphene film in the Z-axis direction.

[0123] Example 8 This embodiment provides a method for preparing a graphene thermally conductive film based on a chaotic system constructed from micron-sized air bubbles to improve thermal conductivity in the Z-axis direction. The only difference from Embodiment 1 is that in step S3, during the homogenization process of the graphene oxide slurry, a water-cooled heat exchanger is not used to control the discharge temperature of the homogenized graphene oxide slurry. It was found that the temperature of the graphene oxide slurry reached as high as 63°C after two homogenization treatments. The other steps are the same as in Embodiment 1.

[0124] Note: The purpose of this embodiment is to investigate the effect of adjusting the temperature of homogenized graphene oxide slurry on the thermal conductivity of graphene film in the Z-axis direction.

[0125] Example 9 This embodiment provides a method for preparing a graphene thermally conductive film with improved Z-axis thermal conductivity based on a chaotic system constructed from micron-sized air bubbles. The only difference from Embodiment 1 is that step S4 uses a normal pressure forced-air oven to dry the graphene oxide coating film, and no micro-low pressure control is performed during the drying process; the other steps are the same as in Embodiment 1.

[0126] Note: The purpose of this embodiment is to investigate the effect of micro-low pressure atmosphere control on the thermal conductivity of graphene film in the Z-axis direction.

[0127] Comparative Example 1 The comparative example describes a method for preparing a graphene thermally conductive film. The only difference between this method and Example 1 is that air is not introduced into the aeration head air duct in step S2, i.e., air is not injected into the graphene oxide slurry through low-temperature ultrasonic crushing; the other steps are the same as in Example 1.

[0128] Note: The purpose of this comparative example is to investigate the effect of air dissolved in ionized water carried by deoxidized graphene slurry under normal conditions on the thermal conductivity of graphene film in the Z-axis direction.

[0129] Comparative Example 2 This comparative example describes a method for preparing a graphene thermal conductive film. The only difference between this method and Example 1 is that in step S2, the graphene oxide slurry is not prepared in two steps with low and high solid content, but is directly prepared with a designed high solid content of 5 wt%. It was found that the slurry prepared with the designed 5 wt% solid content has a solid content as high as 26000 MPa·s. The other steps are the same as in Example 1.

[0130] Note: The purpose of this comparative example is to investigate the effect of the viscosity of graphene oxide slurry on the thermal conductivity of graphene film in the Z-axis direction.

[0131] Test Example 1 Test samples: graphene films with high thermal conductivity in the Z-axis direction provided in Examples 1-9, and graphene thermal conductive films provided in Comparative Examples 1-2.

[0132] Test method: The thermal conductivity in the Z-axis direction was tested using the LFA467 laser thermal conductivity meter with 4 sample rounds.

[0133] The test results are shown in Table 1 below, and Figure 6 , Figures 9-10 As shown: Table 1

[0134] As shown in Table 1, the thermal diffusivity of the graphene film with high thermal conductivity in the Z-axis direction is 80 mm. 2 / s or higher, preferably 450 mm 2 / s or more. This fully demonstrates that the preparation method of the present invention constructs a chaotic system through micron-level air bubbles, breaking the planar order of graphene sheets in the XY direction and increasing the number of graphene sheets arranged in the Z-axis direction, thereby improving the thermal conductivity in the Z-axis direction.

[0135] The comparison between Example 1 and Example 7 shows that after two homogenization treatments, the temperature of the graphene oxide slurry reached as high as 48°C, and the thermal conductivity in the Z-axis direction decreased, but it was still better than Comparative Example 1 without air breakup treatment. This can be attributed to the fact that the slurry temperature was too high, causing some air bubbles to escape and the chaotic arrangement effect in the Z-axis direction to deteriorate.

[0136] The comparison between Example 1 and Example 8 shows that after two homogenization treatments, the thermal conductivity of graphene oxide in the Z-axis direction is significantly reduced when the temperature reaches 63°C. However, it is still better than Comparative Example 1 without air-breaking treatment. This can be attributed to the fact that the slurry is overheated, causing a large number of air bubbles to expand and escape due to heat, resulting in a poor chaotic arrangement in the Z-axis direction.

[0137] The comparison between Examples 1 and 9 shows that the thermal conductivity in the Z-axis direction of graphene oxide coating film is reduced when dried using a normal pressure forced-air oven, but it is still better than that of Comparative Example 1 without air breakup treatment. This can be attributed to the small size of the air bubbles in the slurry. Without low-pressure expansion and amplification, it is difficult to achieve the longitudinal alignment of large air bubbles with graphene oxide sheets. At the same time, the effect of hindering the orderly arrangement of graphene oxide sheets in the XY direction is limited, resulting in its lower thermal conductivity in the Z-axis direction.

[0138] A comparison between Example 1 and Comparative Example 1 shows that the graphene thermally conductive film prepared without air-breaking treatment has a performance one order of magnitude lower than that of the sample in Example 1. This is mainly attributed to the absence of micro / nano air bubbles; the graphene oxide sheets exhibit a highly ordered liquid crystal arrangement in the XY direction during self-assembly, and this arrangement does not contribute to thermal conductivity in the Z-axis direction. Figure 7 , 8It is also easy to see that the particle size distribution decreases significantly and becomes more concentrated with the number of homogenization processes, which is consistent with the particle size distribution of slurry prepared by conventional degassing process, indicating that Comparative Example 1 did not introduce micro-nano air bubbles.

[0139] The comparison between Comparative Example 1 and Comparative Example 2 shows that although Comparative Example 2 underwent air ablation treatment, it was a direct treatment of the high solids content slurry. Obviously, the thermal conductivity improvement effect in the Z-axis direction of Comparative Example 2 was not significant compared to that of Comparative Example 1. This is mainly due to the excessively high initial viscosity of the slurry, which made it difficult for the ablated air bubbles to adhere to the surface of the graphene oxide sheets, resulting in the failure to introduce micro-nano air bubbles into the slurry.

[0140] Test Example 2 Test samples: Slurry after two homogenization processes following step S3 of the preparation method provided in Example 1, and slurry after two homogenization processes following step S3 of the preparation method provided in Comparative Example 1.

[0141] Test results: like Figure 4 As shown, the particle size distribution of the slurry after the first homogenization in Example 1 is as follows: D10, D50, and D90 are 0.244 μm, 0.529 μm, and 0.991 μm, respectively; Figure 5 As shown, the particle size distribution of the slurry after the second homogenization in Example 1 is as follows: D10, D50, and D90 are 1.352 μm, 4.462 μm, and 8.751 μm, respectively. It can be seen that the particle size distribution of the slurry increases anomalously with the number of homogenization passes. This is mainly attributed to the low-pressure expansion of micron-sized air bubbles attached to the graphene oxide sheets under the cavity effect of the homogenizer's working chamber.

[0142] like Figure 7 As shown, the particle size distribution of the slurry after the first homogenization in Comparative Example 1 is as follows: D10, D50, and D90 are 0.238 μm, 0.371 μm, and 0.593 μm, respectively. Compared to Example 1, the particle size of the slurry in Comparative Example 2, which did not introduce micron-sized air bubbles, is smaller after the first homogenization. Figure 8 As shown, the particle size distribution of the slurry after the second homogenization in Comparative Example 2 is 0.151 μm, 0.263 μm, and 0.448 μm, respectively. Unlike Example 1, without the introduction of micron-sized air bubbles, the particle size of the slurry decreases with the increase of the number of homogenization passes.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a graphene film with high thermal conductivity in the Z-axis direction, characterized in that, The preparation method comprises: air breaking treatment is performed on the low solid content oxidized graphene slurry, so that micron-sized air bubbles are attached to the surface of the oxidized graphene sheets, to obtain a low solid content gas-dissolved oxidized graphene slurry; the low solid content gas-dissolved oxidized graphene slurry is prepared into a high solid content gas-dissolved oxidized graphene slurry; homogenization and exfoliation treatment is performed on the high solid content gas-dissolved oxidized graphene slurry, to obtain a homogenized oxidized graphene slurry; the homogenized oxidized graphene slurry is sequentially subjected to coating, drying and heat treatment, to obtain the graphene film with high thermal conductivity in the Z-axis direction.

2. The method of claim 1, wherein the graphene film has a thermal conductivity of 1,000 W / mK or more in the Z-axis direction. The air breaking treatment is performed by using an air breaking instrument; wherein the air breaking instrument comprises: ultrasonic transducer vibration heads, which are arranged in an array distribution manner and are fixed in a sealed box, and the working surfaces of the ultrasonic transducer vibration heads are exposed to the surface of the sealed box; aeration heads, each of which is vertically arranged above the corresponding ultrasonic transducer vibration head through a metal framework, and each of the aeration heads is provided with a gas inlet; an external gas source, each gas inlet is connected to the external gas source through a gas guide pipe, and a throttle valve for adjusting the gas flow is arranged on the gas guide pipe; Preferably, the sealed box is a square sealed metal box. Preferably, the ultrasonic transducer vibration heads are arranged in at least two rows, each row having more than 3. Preferably, the power of each ultrasonic transducer vibration head is independently 10-100 W, and the vibration frequency of each ultrasonic transducer vibration head is independently 10-100 kHz. Preferably, the aeration head is a stainless steel powder sintered porous metal aeration head. Preferably, the mesh number of the stainless steel powder sintered porous metal aeration head is more than 200. Preferably, the distance between the bottom of the aeration head and the working surface of the ultrasonic transducer vibration head is 5-15 mm. Preferably, the sealed box is mounted on a bearing substrate, and the bottom of the bearing substrate is provided with four groups of rubber discs.

3. The method of claim 1, wherein the graphene film has a thermal conductivity of 5,000 W / mK or more in the Z-axis direction. The air breaking treatment specifically comprises the following steps: The air breaking instrument is immersed into the bottom of the low solid content oxidized graphene slurry, under stirring, air is introduced into the slurry through the aeration head, and the ultrasonic transducer vibration head is started to break and mix the introduced air into the slurry, so that micron-sized air bubbles are attached to the surface of the oxidized graphene sheets, to obtain a low solid content gas-dissolved oxidized graphene slurry. Preferably, the stirring speed is 50-200 r / min. Preferably, the injection flow rate of the air is 1-3 L / min. Preferably, the starting time of the ultrasonic transducer vibration head is 20-40 min.

4. The method of claim 1, wherein the graphene film has a thermal conductivity of 5,000 W / mK or more in the Z-axis direction. The preparation method of the low solid content oxidized graphene slurry comprises: mixing the oxidized graphene, the pH adjuster and water, and performing stirring and dispersion treatment, to obtain the low solid content oxidized graphene slurry. Preferably, in the process of preparing the low solid content graphene oxide slurry, the stirring and dispersion treatment is performed by a double planetary mixer; wherein the stirring speed is 30-100 rpm, the dispersion treatment speed is 500-3000 rpm, the dispersion treatment time is 30-180 min, and the dispersion treatment temperature is below 10°C; Preferably, the viscosity of the low solid content graphene oxide slurry is below 8000 MPa·s; Preferably, the solid content of the low solid content graphene oxide slurry is no more than 2.5 wt%; Preferably, the process of preparing the high solid content gas-solubilized graphene oxide slurry comprises: adding graphene oxide and a pH adjusting agent to the low solid content gas-solubilized graphene oxide slurry, and performing stirring and dispersion treatment to obtain the high solid content gas-solubilized graphene oxide slurry; Preferably, in the process of preparing the high solid content gas-solubilized graphene oxide slurry, the stirring and dispersion treatment is performed by a double planetary mixer; wherein the stirring speed is 30-100 rpm, the dispersion treatment speed is 500-3000 rpm, the dispersion treatment time is 30-180 min, and the dispersion treatment temperature is below 10°C; Preferably, the solid content of the high solid content gas-solubilized graphene oxide slurry is above 2.5 wt%, preferably 3-8 wt%; Preferably, the pH adjusting agent is ammonia water; Preferably, the pH of the low solid content graphene oxide slurry or the high solid content gas-solubilized graphene oxide slurry is independently 6.6-7.

0.

5. The method of claim 1, wherein the graphene film has a thermal conductivity of 5,000 W / mK or more in the Z-axis direction. The pressure of the homogenization and exfoliation treatment is 1000-1500 bar; Preferably, the temperature of the homogenization and exfoliation treatment is below 10°C; Preferably, the number of times of the homogenization and exfoliation treatment is above 2.

6. The method of claim 1, wherein the graphene film has a thermal conductivity of 5,000 W / mK or more in the Z-axis direction. The thickness of the coating is 2000-8000 μm; Preferably, the temperature of the drying is 40-50°C, and the vacuum degree of the drying is 10-100 Pa.

7. The method of claim 1, wherein the graphene film has a thermal conductivity of 5,000 W / mK or more in the Z-axis direction. The heat treatment comprises, in sequence, a pre-treatment, a carbonization treatment, and a graphitization treatment; Preferably, the temperature of the pre-treatment is 220-260°C, and the time of the pre-treatment is 1-3 h; Preferably, the temperature of the carbonization treatment is 1100-1300°C, and the time of the carbonization treatment is 1-3 h; Preferably, the temperature of the graphitization treatment is 3100-3200°C, and the time of the graphitization treatment is 1-3 h.

8. A graphene film having a high thermal conductivity in the Z-axis direction, characterized by The Z-axis direction high thermal conductivity graphene film is prepared by the method of preparing a Z-axis direction high thermal conductivity graphene film according to any one of claims 1-7.

9. The Z-axis direction high thermal conductivity graphene film according to claim 8, characterized in that, The thermal diffusivity of the graphene film having high thermal conductivity in the Z-axis direction is 80 mm 2 / s or more, preferably 150 mm 2 / s or more, further preferably 450 mm 2 / s or more.

10. Use of the Z-axis direction high thermal conductivity graphene film according to claim 8 or 9 in preparing a thermal management material.

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