CN113480312A - Graphene film and preparation method thereof - Google Patents

Graphene film and preparation method thereof Download PDF

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CN113480312A
CN113480312A CN202110899606.3A CN202110899606A CN113480312A CN 113480312 A CN113480312 A CN 113480312A CN 202110899606 A CN202110899606 A CN 202110899606A CN 113480312 A CN113480312 A CN 113480312A
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temperature
film
graphene
graphene oxide
oxide film
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王乾龙
陈德权
董亮亮
杨武俊
林锦盛
唐婕
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Shenzhen Shen Rui Graphene Technology Co ltd
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Shenzhen Shen Rui Graphene Technology Co ltd
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Priority to PCT/CN2022/110642 priority patent/WO2023011646A1/en
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Abstract

The application provides a graphene film and a preparation method thereof, wherein the method comprises the following steps: placing the reduced graphene oxide film into an Acheson graphitizing furnace, performing high-temperature heat treatment at different stages, and then naturally cooling to obtain a fluffy graphene film for structural defect repair and recrystallization, wherein the Acheson graphitizing furnace contains resistance heating particles, and the heating mode of the Acheson graphitizing furnace is to apply current to enable the current to flow through the resistance heating particles, so that the resistance heating particles heat and rise to the graphitization temperature to heat the reduced graphene oxide film; and compacting and densifying the fluffy graphene film to obtain the graphene film. The preparation method of the graphene film can reduce production cost, simplify preparation process and greatly improve heat conduction performance of the graphene film.

Description

Graphene film and preparation method thereof
Technical Field
The application relates to the technical field of graphite materials, in particular to a graphene film and a preparation method thereof.
Background
Graphene films are receiving increasing attention from the market due to their excellent thermal and electrical conductivity properties. Particularly, with the rapid development of the electronic industry, electronic products are increasingly highly integrated, so that heat dissipation of electrical equipment becomes an urgent problem to be solved, and the reliability of the electrical equipment is reduced along with the accumulation of heat. Therefore, in view of the excellent thermal and electrical properties of graphene, graphene is expected to be developed into a mainstream functional electronic material in the future.
At present, graphene oxide films are prepared in batches by using graphene oxide or graphite oxide as a raw material, forming the graphene oxide films by methods such as suction filtration, dip coating, spin coating, spray coating, evaporation, coating and the like, and graphitizing the graphene oxide films. Generally, the most common graphitization method is an electromagnetic induction graphitization furnace, which is also the most common graphitization method for the commercial synthetic graphite heat-conducting film at present. However, the electromagnetic induction graphitization furnace can only normally operate in the range of 2600-. And because the graphene film is obtained by carbonizing and graphitizing the graphene oxide film, a large number of oxygen-containing functional groups contained in the graphene oxide film can be decomposed along with the rise of temperature to cause the oxidation of electromagnetic induction graphitizing furnace body materials, such as a graphite crucible, a carbon felt heat preservation material, a furnace wall and the like, to further reduce the service life of the furnace body materials, and cause the increase of the integral production cost of products. In view of the situation, it is imperative to develop a low-cost large-batch graphitization preparation method which can greatly improve the performance of products.
Disclosure of Invention
In view of this, the present application provides a graphene film and a preparation method thereof, which can reduce production cost, shorten preparation process, and improve performance of the graphene film.
In a first aspect, the present application provides a method of preparing a graphene film, the method comprising the steps of:
putting the reduced graphene oxide film into an Acheson graphitizing furnace, performing high-temperature heat treatment at different stages to enable the reduced graphene oxide film to reach the graphitizing temperature, and naturally cooling to obtain a fluffy graphene film;
and compacting and densifying the fluffy graphene film to obtain the graphene film.
With reference to the first aspect, in a possible embodiment, the reduced graphene oxide film and the graphite paper are stacked and then placed in a crucible in the acheson graphitization furnace, buried resistance heating particles are laid between the crucibles and on the surface of the crucible in the acheson graphitization furnace, and the resistance heating particles heat up to a graphitization temperature; the resistance heating particles comprise calcined coke with different particle sizes, and the average particle size of the calcined coke ranges from 0mm to 30mm, and does not comprise 0 mm.
In one possible embodiment in combination with the first aspect, the volatile component in the reduced graphene oxide film is less than 10 wt%.
With reference to the first aspect, in one possible embodiment, the method satisfies at least one of the following features a to c:
a. the graphitization temperature range is 3000-3200 ℃;
b. the heat treatment period in the high-temperature heat treatment is 10 to 30 days;
c. and adopting sectional temperature rise to the graphitization temperature.
With reference to the first aspect, in one possible embodiment, the high temperature heat treatment includes:
in the first stage, the temperature of the Acheson graphitization furnace is raised to 1000-1400 ℃, and the temperature is kept for 5-10 h;
in the second stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2000-2100 ℃, and the temperature is kept for 5-10 h;
in the third stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2800-2900 ℃, the temperature is kept for 2-5 h, then the temperature is continuously increased to 3000-3200 ℃, and the temperature is kept for 5-10 h;
and stopping power transmission, and naturally cooling the Acheson graphitizing furnace to obtain the fluffy graphene film.
In one possible embodiment in combination with the first aspect, the fluffy graphene film has a compaction pressure of 2Mpa to 100 Mpa.
In combination with the first aspect, in one possible embodiment, before placing the reduced graphene oxide film in the acheson graphitization furnace, the method further comprises;
and baking the graphene oxide film prepared from the slurry containing the graphene oxide or the graphite oxide to obtain the reduced graphene oxide film.
With reference to the first aspect, in one possible embodiment, the method satisfies at least one of the following features a to f:
a. the concentration of the slurry containing graphene oxide or graphite oxide is 1 mg/mL-80 mg/mL;
b. the slurry containing the graphene oxide or the graphite oxide is obtained by mixing in any one mode of ultrasound, mechanical shearing stripping, mechanical stirring and high-pressure homogenization;
c. the preparation process of the graphene oxide film comprises any one of a suction filtration process, a dip coating process, a spin coating process, a spraying process, an evaporation process and a coating process;
d. the baking temperature is 150-550 ℃;
e. the heating rate of the baking is 0.5-10 ℃/h;
f. the heat preservation time of the baking is 5-50 h.
In a second aspect, the present application provides a graphene film obtained by the preparation method according to the first aspect, the graphene film satisfying at least one of the following characteristics a to d:
a. the thickness of the graphene film is 10-300 mu m;
b. the density of the graphene film is 1.8g/cm3~2.3g/cm3
c. The graphene film has a thermal conductivity of 1300W/mK to 1600W/mK;
d. the tensile strength of the graphene film is 50-65 MPa.
The technical scheme of the application has at least the following beneficial effects:
according to the preparation method of the graphene film, the reduced graphene oxide film is placed in a crucible of an Acheson graphite furnace, resistance heating materials with different particle sizes are paved and buried on the outer wall of the crucible, meanwhile, resistance heating particles in the Acheson graphite furnace and the reduced graphene oxide film jointly form a furnace resistor, through applying large current, current flows through the resistance heating particles in the furnace and the reduced graphene oxide film to jointly generate huge heat energy, the reduced graphene oxide film generates heat due to self resistance, meanwhile, the resistance heating particles with different particles paved and buried on the outer wall of the crucible generate heat due to self resistance, and form heat with the reduced graphene oxide film in the crucible, so that a heat sharing body is formed inside and outside the crucible, and therefore ultrahigh graphitization temperature is achieved. Meanwhile, the resistance heating particles with different particle sizes are filled around the crucible, the core graphitization temperature in the crucible is kept stable, the structural defects of the graphene film product are perfectly repaired at the ultra-high temperature graphitization temperature and in the ultra-long graphitization heat preservation process, and meanwhile, the resistance heating particles are slowly and alternately removed in the cooling process, so that the graphene film is recrystallized to generate a large area of crystal domains in the long cooling process, and the electrical, thermal and mechanical properties of the product reach unprecedented heights. Compared with the electromagnetic induction heating type graphitization furnace with a complex structure and short service life for graphitization, the method for graphitization by adopting the Acheson graphitization furnace is simpler, easy to realize, reliable in batch production and extremely low in failure rate, and most importantly, the resistance heating particles in the Acheson graphitization furnace and the partially reduced graphene oxide film in the crucible generate huge heat sharing effect due to large self resistance and then generate current so that the product reaches ultrahigh graphitization temperature, and the heating principle is different from other graphitization heating modes. And because the Acheson graphitizing furnace has strong reliability, low failure rate, high graphitization degree, simple process and the like after long-term use, the overall manufacturing cost of the graphene film is reduced, the material performance is greatly improved, and the core competitiveness of the product is enhanced.
Drawings
Fig. 1 is a flowchart of a method for preparing a graphene film according to an embodiment of the present disclosure;
fig. 2 is a schematic structural diagram of an acheson graphitization furnace provided by an embodiment of the present application;
fig. 3a is a schematic diagram of performance parameters of a graphene film prepared in example 1 of the present application;
FIG. 3b is a graph showing the performance parameters of the graphene film prepared in comparative example 1 of the present application;
fig. 3c is a graph showing the tensile strength test results of the graphene films prepared in example 1 and comparative example 1 of the present application;
fig. 3d is an SEM image of the graphene film prepared in example 1 of the present application;
fig. 3e is an SEM image of the graphene film prepared in comparative example 1 of the present application.
Detailed Description
While the following is a description of the preferred embodiments of the present invention, it should be noted that those skilled in the art can make various modifications and improvements without departing from the principle of the embodiments of the present invention, and such modifications and improvements are considered to be within the scope of the embodiments of the present invention.
The inventor finds that the graphene film is formed by stacking small-layer graphene (less than or equal to 3 microns), the highest temperature in the graphitization process is improved, the temperature reduction time is prolonged, the small-layer graphene sheets can be promoted to be crystallized and recombined into large-layer graphene sheets, and the heat conduction performance and the structural strength can be greatly improved, so that a graphitization process which can reach more than 3000 ℃ stably is needed, the slow temperature reduction rate is achieved, and the influence of volatile matters generated in the temperature rise process is avoided.
In a first aspect, the present application provides a method of preparing a graphene film, the method comprising the steps of:
baking a graphene oxide film prepared from slurry containing graphene oxide or graphite oxide to obtain a reduced graphene oxide film;
putting the reduced graphene oxide film into an Acheson graphitizing furnace, performing high-temperature heat treatment at different stages to enable the reduced graphene oxide film to reach a graphitizing temperature, and naturally cooling to obtain a fluffy graphene film;
in the scheme, a partial reduced graphene oxide film is placed in an Acheson graphitizing furnace, resistance heating particles in the Acheson graphitizing furnace and the partial reduced graphene oxide film jointly form a furnace resistance, and the current is applied to generate huge heat energy after flowing through the resistance heating particles in the furnace and the partial reduced graphene oxide film, so that the partial reduced graphene oxide film obtains heat required by graphitization, thereby realizing graphitization of the product, because the resistance heating particles and the reduced graphene oxide film generate a concurrent heating phenomenon under the application of large current, the graphitization temperature in the Acheson graphitizing furnace is kept at a very high level for a long time, the structural defects of the graphene film product can be perfectly repaired under the conditions of ultrahigh graphitization temperature and ultra-long heat preservation time, meanwhile, due to the fact that resistance heating particles with different particle sizes are filled around a crucible, the core graphitization temperature in the crucible is kept stable, by slowly and alternately removing the resistance heating particles, the graphene film is further recrystallized to generate a large-area crystal domain in a long cooling process, so that the electrical, thermal and mechanical properties of the product are improved. Compared with other graphitization heat treatment methods such as graphitization by an electromagnetic induction mode, the method for graphitizing by the Acheson graphitization furnace is simpler, easy to implement, reliable in batch production and extremely low in failure rate. And because the Acheson graphitizing furnace has strong reliability in long-term use, low failure rate, high graphitization degree, simple process and the like, the integral manufacturing cost of the graphene film is reduced, and the material performance is greatly improved.
Fig. 1 is a flowchart of a method for preparing a graphene film according to an embodiment of the present disclosure, and referring to fig. 1, the following details are introduced:
step S10, baking the graphene oxide film prepared from the slurry containing graphene oxide or graphite oxide to obtain the reduced graphene oxide film.
Specifically, graphene oxide or graphite oxide may be added to a solvent to prepare a slurry, and the slurry containing graphene oxide or graphite oxide is obtained by mixing the graphene oxide or graphite oxide in any one of ultrasonic, mechanical shear stripping, mechanical stirring and high-pressure homogenization.
The preparation process of the graphene oxide film comprises any one of a suction filtration process, a dip coating process, a spin coating process, a spraying process, an evaporation process and a coating process. Illustratively, the slurry may be coated and dried to form a graphene oxide film.
Specifically, the concentration of the slurry is 1mg/mL to 80mg/mL, specifically, the concentration of the slurry may be 1mg/mL, 5mg/mL, 10mg/mL, 15mg/mL, 20mg/mL, 30mg/mL, 40mg/mL, 50mg/mL, 60mg/mL, 70mg/mL, or 80mg/mL, or the like, and may be other values within the above range, which is not limited herein. The concentration of the slurry is the amount of solute contained in the unit solvent, and the solute may be graphene oxide and/or graphite oxide, which is not limited herein.
After the slurry is prepared, the slurry needs to be subjected to dispersion treatment, wherein the dispersion treatment comprises at least one of ultrasonic dispersion, mechanical shearing, stripping and dispersion, mechanical stirring and dispersion and high-pressure homogenizing and dispersion.
As an optional technical scheme of the application, the baking temperature is 150-550 ℃, and the heating rate is 0.5-10 ℃/h; specifically, the temperature may be 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃ or 550 ℃, and the like, and the temperature rise rate may be 0.5 ℃/h, 1 ℃/h, 1.5 ℃/h, 2 ℃/h, 2.5 ℃/h, 3 ℃/h, 3.5 ℃/h, 4 ℃/h, 4.5 ℃/h, 5 ℃/h may be other values within the above range, which is not limited herein.
It is understood that the graphene oxide film contains a large amount of moisture and oxygen-containing chemical functional groups (such as hydroxyl/carboxyl/epoxy, etc.), so that the moisture and oxygen-containing chemical functional groups need to be removed before the high-temperature graphitization treatment. Through slow baking, most of moisture and oxygen-containing chemical functional groups contained in the graphene oxide film can be removed, so that the graphene oxide film is prevented from being burst due to rapid volatilization of volatile matters such as moisture or oxygen-containing chemical functional groups in the subsequent high-temperature heat treatment process, and the subsequent graphitization treatment is facilitated.
As an alternative embodiment of the present invention, the volatile component in the baked graphene oxide film is less than 10 wt%, specifically 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, or 1 wt%, and the like, and may also be other values within the above range, which is not limited herein.
By controlling the content of volatile components in the baked graphene oxide film, the phenomenon that the graphene oxide film is cracked and damaged due to huge pressure generated by instantaneous volatilization at high temperature in the film because the volatile components such as water, hydroxyl, carboxyl, epoxy and other chemical functional groups are not completely removed in the subsequent graphitization process of the graphene oxide film can be avoided.
It is understood that this step may be omitted, and the reduced graphene oxide film satisfying the above conditions may be directly selected, that is, the reduced graphene oxide film having a volatile component of less than 10 wt% may be selected.
And step S20, putting the reduced graphene oxide film into an Acheson graphitizing furnace, performing high-temperature heat treatment at different stages to enable the reduced graphene oxide film to reach the graphitizing temperature, and naturally cooling to obtain the fluffy graphene film.
Specifically, the reduced graphene oxide film and the graphite paper may be stacked and then placed in crucibles in the acheson graphitization furnace, and the resistance heating particles are laid and buried between the crucibles and on the surface of the crucibles in the acheson graphitization furnace. The heating mode of the Acheson graphitizing furnace is that current is applied to enable the current to flow through the resistance heating particles, so that the resistance heating particles heat and rise to the graphitization temperature to heat the reduced graphene oxide film. The resistance heating particles comprise calcined coke with different particle sizes, and the average particle size of the calcined coke ranges from 0mm to 30mm, and does not comprise 0 mm.
In this embodiment, the crucible is a customized rectangular crucible, and the crucible size can be customized according to the size of the graphene film, so as to maximize the space utilization in the crucible.
Illustratively, as shown in fig. 2, before the crucible is tightly stacked in the acheson graphitization furnace, a carbon black protective layer can be laid at the bottom of the acheson graphitization furnace, wherein the thickness of the carbon black protective layer is 700mm, and the resistance value of the carbon black protective layer is more than or equal to 1000 μ Ω; and covering a first resistance heating particle layer on the carbon black protective layer, wherein the first resistance heating particle layer comprises calcined coke with the particle size of less than or equal to 2mm, and the resistance value of the first resistance heating particle layer is 450 mu omega-600 mu omega. And finally, paving a second resistance heating particle layer on the first resistance heating particle layer, wherein the second resistance heating particle layer comprises calcined coke with the particle size of 8-30 mm, and the resistance value of the second resistance heating particle layer is 450-600 [ mu ] omega.
After the crucible is tightly stacked in an Acheson graphitizing furnace, 8 mm-30 mm calcined coke is laid and buried between the outer wall of the crucible and the crucible, a layer of 8 mm-30 mm granular calcined coke is firstly covered on the upper layer of the crucible, and then a layer of 5 mm-10 mm granular calcined coke is covered on the upper layer of the crucible; then covering a layer of granular calcined coke with the grain diameter of 2 mm-4 mm, and finally covering a layer of granular calcined coke with the grain diameter of less than or equal to 2 mm. It should be noted that, the calcined cokes with different particle sizes are different in joule heat generated by electrifying in the graphitization furnace, and the calcined cokes with different particle sizes are laid, so that the resistance heating particles and the reduced graphene oxide film jointly form a furnace resistance, and current flows through the resistance heating particles and the reduced graphene oxide film in the furnace to generate co-heating, so that the reduced graphene oxide film obtains heat required by graphitization.
Understandably, during the graphitization process, the small molecular volatile matters generated by the graphene oxide film, such as carbon dioxide, carbon monoxide, nitrogen-containing compounds and the like, can be absorbed by the powdery porous resistance heating particles, do not cause any waste discharge, are low in price, and can be reused after the calcination treatment.
As an alternative embodiment of the present application, the graphitization temperature ranges from 3000 ℃ to 3200 ℃; the heat treatment period in the high-temperature heat treatment is 10 to 30 days. Understandably, due to the high graphitization temperature and the long heat preservation time, the product can realize the repair of the structural defects of the product in a longer graphitization period, and simultaneously, the internal structure of the graphene film can be recrystallized to form a large-area crystal domain, so that the electrical, thermal and mechanical properties of the product are optimal.
Specifically, the graphitization temperature may be 3000 ℃, 3050 ℃, 3100 ℃, 3150 ℃, 3200 ℃ or the like, and the heat treatment period may be 10 days, 15 days, 18 days, 20 days, 25 days, 28 days, 30 days or the like, or may be other values within the above range, which is not limited herein.
As an alternative embodiment of the present application, a stepwise temperature increase to the graphitization temperature is used.
In this embodiment, acheson graphitizing furnace includes the furnace body, and the furnace body is by the regular tetrahedron structure that stove basement, furnace end wall body, stove tail wall body and furnace wall board enclose, set up conductive electrode in furnace end wall body and the stove tail wall body, lay quartz sand and carbon black heat preservation on the furnace basement in proper order, be the wick on the heat preservation, will graphite crucible arranges the wick in and sets up along the stove direction, and the crucible gap is filled and is forged the back burnt, and landfill resistance heating particle layer is laid in turn to the upper strata, wick top and side set up the version, lay in the version and bury resistance heating particle.
Specifically, step S20 includes
In the first stage, the temperature of the Acheson graphitization furnace is raised to 1000-1400 ℃, and the temperature is kept for 5-10 h;
in the second stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2000-2100 ℃, and the temperature is kept for 5-10 h;
in the third stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2800-2900 ℃, the temperature is kept for 2-5 h, then the temperature is continuously increased to 3000-3200 ℃, and the temperature is kept for 5-10 h;
and stopping power transmission, and naturally cooling the Acheson graphitizing furnace to obtain the fluffy graphene film for structural defect repair and recrystallization.
In the third stage, when the temperature in the Acheson graphitization furnace reaches 2900 ℃, heat preservation is firstly carried out, and then the temperature is raised to the graphitization temperature of 3000-3200 ℃, so that the temperature in the furnace is uniform, the graphene film in the crucible is uniformly heated, the crystallization orientation is further improved, and the product performance is improved.
In some embodiments, the natural cooling rate is 5 ℃/h-15 ℃/h, and the cooling time is 9 days-30 days. Specifically, the cooling rate may be 5 ℃/h, 7 ℃/h, 8 ℃/h, 10 ℃/h, 12 ℃/h, 13 ℃/h, 14 ℃/h or 15 ℃/h, etc., which is not limited herein. The cooling time is 9 days, 10 days, 11 days, 12 days, 15 days, 17 days, 19 days, 20 days, 25 days or 30 days, etc., which is not limited herein. It should be noted that, in the cooling process, the cooling rate in the early stage of cooling is faster, and the cooling rate in the later stage of cooling is slower, that is, the temperature in the furnace is slower as the temperature is closer to the room temperature.
In the natural cooling process, defect repair and structural recrystallization are realized on the graphene in the slow cooling process to obtain the graphene membrane sheet, so that small-layer graphene sheets can be promoted to be crystallized and recombined into large-layer graphene sheets, and the heat conducting property and the structural strength of the graphene membrane are improved. The crystallization process usually takes place in the cooling process, and the cooling rate is slower, and the crystallization degree is better, and product property can be better, and rapid cooling can lead to crystal orientation variation, forms the micrite, and product property can descend.
And step S30, performing compaction and densification treatment on the fluffy graphene film to obtain the graphene film.
As an optional embodiment of the present application, the compaction pressure of the fluffy graphene film is 2Mpa to 100Mpa, specifically, 2Mpa, 5Mpa, 10Mpa, 20Mpa, 30Mpa, 35Mpa, 40Mpa, 50Mpa, 60Mpa, 70Mpa, 80Mpa, 90Mpa, or 100Mpa, and may be other values within the above range, which is not limited herein. Through compaction densification treatment, the graphene film has higher structural strength and higher density.
In a second aspect, the present application provides a graphene film prepared by the preparation method of the first aspect.
As an optional technical solution of the present application, the thickness of the graphene film is 10 μm to 300 μm, and specifically may be 10 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 280 μm, or 300 μm, and the like, which is not limited herein. The thickness of the graphene film can be measured by a thickness tester.
As an optional technical scheme of the application, the density of the graphene film is 1.8g/cm3~2.3g/cm3Specifically, it may be 1.8g/cm3、1.9g/cm3、2.0g/cm3、2.1g/cm3、2.2g/cm3Or 2.3g/cm3And the like, may be other values within the above range, and is not limited herein. Understandably, the improvement of the density of the graphene film is beneficial to the application of light and thin products. The density of the graphene film can be measured according to the mass m and the density ρ ═ m/v of the graphene film in a preset unit volume v.
As an optional technical solution of the present application, the thermal conductivity of the graphene film is 1300W/mK to 1600W/mK, specifically may be 1300W/mK, 1350W/mK, 1400W/mK, 1450W/mK, 1500W/mK, 1550W/mK, 1600W/mK, or the like, and may also be other values within the above range, which is not limited herein. The higher the thermal conductivity of the graphene film, the stronger the thermal conductivity of the graphene film. In particular, the thermal conductivity of graphene films can be measured by the ASTM-E1461 standard.
As an optional technical solution of the present application, the tensile strength of the graphene film is 50Mpa to 65Mpa, specifically 50Mpa, 52Mpa, 55Mpa, 58Mpa, 60Mpa, 62Mpa, or 65Mpa, or other values within the above range, which is not limited herein. The tensile strength of the graphene film is in the range, so that the mechanical property of the graphene film is improved, and the tear resistance of the graphene film can be improved. Specifically, the tensile strength of the graphene film can be measured by the GB/T1040.1-2018 standard.
In a third aspect, the present application provides an electronic device comprising the graphene film obtained by the method for preparing a graphene film according to the first aspect or the graphene film according to the second aspect.
The examples of the present application are further illustrated below in various examples. The present embodiments are not limited to the following specific examples. The present invention can be modified as appropriate within the scope of protection.
Example 1
A method for preparing a graphene film, comprising the steps of:
(1) carrying out physical crushing and high-pressure homogenization on graphene oxide with the concentration of 62gm/mL by adopting a mechanical stirring and high-pressure homogenization mode to obtain homogeneous graphene oxide slurry;
(2) coating the graphene oxide slurry in a coating mode, and drying to obtain a graphene oxide film;
(3) placing the graphene oxide film in an oven, heating to 500 ℃ at a speed of 10 ℃/h, and preserving heat for 20 hours to remove water and oxygen-containing chemical functional groups on the surface and inside of the graphene oxide film to obtain a reduced graphene oxide film, wherein the volatile component of the reduced graphene oxide film is 8 wt% when the reduced graphene oxide film is measured;
(4) and stacking the baked reduced graphene oxide film and the graphite paper, putting the stacked reduced graphene oxide film and the graphite paper into a graphite crucible, stacking the graphite crucible into an Acheson graphitization furnace, and performing graphitization treatment by adopting a sectional power transmission heating mode. In the first stage, according to the rated power and the rated voltage of the transformer, the current density in the furnace is promoted to quickly reach the temperature rise condition by adopting the maximum power output, so that the temperature of the furnace body is freely raised to 1200 ℃ and is kept for 10 hours; and in the third stage, the product is rapidly raised to 2900 ℃ under the condition of large current and is kept warm for 3 hours, the temperature is stably raised to 3200 ℃ under the condition of small current stable output power, and after the small current output power is kept warm for 5 hours, the product realizes the repair and recrystallization of structural defects in the natural cooling process lasting for 21 days to obtain the fluffy graphene film.
(5) And compacting and densifying the graphitized fluffy graphene film under the pressure of 90MPa to obtain the graphene film.
The graphene film prepared by the embodiment has the thickness of 100 mu m and the density of 2.04g/cm3The thermal conductivity coefficient is 1556.926W/mK, and the tensile strength is 62 MPa.
Example 2
(1) Carrying out ultrasonic crushing and shearing stripping on graphite oxide with the concentration of 8mg/mL by adopting an ultrasonic and mechanical shearing stripping mode to obtain homogeneous graphene oxide slurry;
(2) spraying the graphite oxide slurry on a substrate in a spraying mode, and drying to obtain a graphene oxide film;
(3) placing the graphene oxide film into an oven, heating to 430 ℃ at the speed of 5 ℃/h, and preserving the temperature for 10 hours to remove water and oxygen-containing chemical functional groups on the surface and inside of the graphene oxide film to obtain a reduced graphene oxide film, wherein the volatile component of the reduced graphene oxide film is 5 wt% when the reduced graphene oxide film is measured;
(5) and stacking the baked reduced graphene oxide film and the graphite paper, putting the stacked reduced graphene oxide film and the graphite paper into a graphite crucible, stacking the graphite crucible into an Acheson graphitization furnace, and performing graphitization treatment by adopting a sectional power transmission heating mode. In the first stage, according to the rated power and the rated voltage of the transformer, the current density in the furnace is promoted to quickly reach the temperature rise condition by adopting the maximum power output, so that the temperature of the furnace body is freely raised to 1200 ℃ and is kept for 10 hours; the second stage is to make the product raise to 2100 deg.C under the condition of full load and large current and keep the temperature for 10 hours under the condition of adjusting output power, the third stage is to make the product raise to 2900 deg.C rapidly under the condition of large current and keep the temperature for 3 hours under the condition of adjusting output power, the fourth stage is to raise the temperature to 3200 deg.C steadily under the condition of small current and stable output power and keep the small current output power and keep the temperature for 5 hours. The product realizes the repair and recrystallization of the structural defects in the natural cooling process lasting for 21 days to obtain the fluffy graphene film.
(6) And compacting and densifying the graphitized fluffy graphene film under the pressure of 65MPa to obtain the graphene film.
The graphene film prepared by the embodiment has the thickness of 65 mu m and the density of 2.056g/cm3The thermal conductivity coefficient is 1478.538W/mK, and the tensile strength is 54 MPa.
Example 3
A method for preparing a graphene film, comprising the steps of:
(1) physically crushing graphene oxide with the concentration of 12gm/mL by adopting a mechanical stirring and high-pressure homogenizing mode, and carrying out high-pressure homogenizing to obtain homogeneous graphene oxide slurry;
(2) uniformly coating a layer of slurry on a special substrate by adopting a centrifugal spin coating mode, and drying to obtain a graphene oxide film;
(3) placing the graphene oxide film in an oven, heating to 500 ℃ at the speed of 2 ℃/h, and preserving the temperature for 30 hours to remove water and oxygen-containing chemical functional groups on the surface and inside of the graphene oxide film to obtain a reduced graphene oxide film, wherein the volatile component of the reduced graphene oxide film is 10 wt% when the reduced graphene oxide film is measured;
(4) and stacking the baked reduced graphene oxide film and the graphite paper, putting the stacked reduced graphene oxide film and the graphite paper into a graphite crucible, stacking the graphite crucible into an Acheson graphitization furnace, and performing graphitization treatment by adopting a sectional power transmission heating mode. In the first stage, according to the rated power and the rated voltage of the transformer, the current density in the furnace is promoted to quickly reach the temperature rise condition by adopting the maximum power output, so that the temperature of the furnace body is freely raised to 1200 ℃ and is kept for 10 hours; and in the third stage, the product is rapidly raised to 2900 ℃ under the condition of large current and is kept warm for 3 hours, the temperature is stably raised to 3200 ℃ under the condition of small current stable output power, and after the small current output power is kept warm for 5 hours, the product realizes the repair and recrystallization of structural defects in the natural cooling process lasting for 21 days to obtain the fluffy graphene film.
(5) And compacting and densifying the graphitized fluffy graphene film under the pressure of 90MPa to obtain the graphene film.
The graphene film prepared by the embodiment has the thickness of 198 mu m and the density of 2.04g/cm3The thermal conductivity coefficient is 1309.431W/mK, and the tensile strength is 59 MPa.
Example 4
A method for preparing a graphene film, comprising the steps of:
(1) carrying out physical shearing and crushing on graphene oxide with the concentration of 2gm/mL by adopting a mechanical stirring and mechanical shearing mode to obtain homogeneous graphene oxide slurry;
(2) dipping a special substrate into the graphene oxide slurry by adopting a lifting and dip-coating mode, uniformly attaching the graphene oxide slurry to the substrate by lifting at a certain speed, drying, and demolding to obtain a graphene oxide film;
(3) putting the graphene oxide film into an oven, heating to 450 ℃ at the speed of 5 ℃/h, and preserving the temperature for 30 hours to remove water and oxygen-containing chemical functional groups on the surface and inside of the graphene oxide film, wherein the volatile component of the reduced graphene oxide is 6 wt% when the graphene oxide film is measured;
(4) and stacking the baked reduced graphene oxide film and the graphite paper, putting the stacked reduced graphene oxide film and the graphite paper into a graphite crucible, stacking the graphite crucible into an Acheson graphitization furnace, and performing graphitization treatment by adopting a sectional power transmission heating mode. In the first stage, according to the rated power and the rated voltage of the transformer, the current density in the furnace is promoted to quickly reach the temperature rise condition by adopting the maximum power output, so that the temperature of the furnace body is freely raised to 1200 ℃ and is kept for 8 hours; and in the third stage, the product is rapidly raised to 2900 ℃ under the condition of large current and is kept warm for 5 hours under the condition of small current stable output power by adjusting the output power, the temperature is stably raised to 3200 ℃, and after the small current output power is kept warm for 8 hours, the product realizes the repair and recrystallization of structural defects in the natural cooling process lasting for 21 days to obtain the fluffy graphene film.
(5) And compacting and densifying the graphitized fluffy graphene film under the pressure of 50MPa to obtain the graphene film.
The graphene film prepared by the embodiment has the thickness of 120 mu m and the density of 1.95g/cm3The thermal conductivity coefficient is 1302.86W/mK, and the tensile strength is 54 MPa.
Comparative example 1
(1) Carrying out physical crushing and high-pressure homogenization on graphene oxide with the concentration of 62gm/mL by adopting a mechanical stirring and high-pressure homogenization mode to obtain homogeneous graphene oxide slurry;
(2) coating the graphene oxide slurry in a coating mode, and drying to obtain a graphene oxide film;
(3) placing the graphene oxide film in an oven, heating to 500 ℃ at a speed of 10 ℃/h, and preserving heat for 20 hours to remove water and oxygen-containing chemical functional groups on the surface and inside of the graphene oxide film to obtain a reduced graphene oxide film, wherein the volatile component of the reduced graphene oxide film is 8 wt% when the reduced graphene oxide film is measured;
(4) and (3) laminating the baked reduced graphene oxide film and graphite paper, and putting the laminated reduced graphene oxide film and graphite paper into an electromagnetic induction type graphitization furnace for graphitization treatment. Wherein the reduced graphene oxide film is treated in an electromagnetic induction graphitization furnace at 2800 ℃ for 30min to obtain a fluffy graphene film.
(5) And compacting and densifying the graphitized fluffy graphene film under the pressure of 90MPa to obtain the graphene film.
The graphene film prepared by the comparative example has the thickness of 100 mu m and the density of 2.033g/cm3The thermal conductivity coefficient is 996.735W/mK, and the tensile strength is 45 MPa.
Comparative example 2
(1) Carrying out ultrasonic crushing and high-pressure homogenization on graphite oxide with the concentration of 62mg/mL by adopting an ultrasonic and mechanical shearing stripping mode to obtain homogeneous graphene oxide slurry;
(2) coating the graphite oxide slurry on a substrate in a coating mode, and drying to obtain a graphene oxide film, wherein the volatile component of the graphene oxide film is more than or equal to 15 wt%;
(3) and stacking the baked reduced graphene oxide film and the graphite paper, putting the stacked reduced graphene oxide film and the graphite paper into a graphite crucible, stacking the graphite crucible into an Acheson graphitization furnace, and performing graphitization treatment by adopting a sectional power transmission heating mode. In the first stage, according to the rated power and the rated voltage of the transformer, the current density in the furnace is promoted to quickly reach the temperature rise condition by adopting the maximum power output, so that the temperature of the furnace body is freely raised to 1200 ℃ and is kept for 10 hours; the second stage is to make the product raise to 2100 deg.C under the condition of full load and large current and keep the temperature for 10 hours under the condition of adjusting output power, the third stage is to make the product raise to 2900 deg.C rapidly under the condition of large current and keep the temperature for 3 hours under the condition of adjusting output power, the fourth stage is to raise the temperature to 3200 deg.C steadily under the condition of small current and stable output power and keep the small current output power and keep the temperature for 5 hours. And naturally cooling the product for 21 days to obtain the powdered graphene.
The graphene powder prepared by the comparative example cannot be pressed into a film, and the density of the graphene is 1.98g/cm3
Referring to fig. 3a to 3e, it can be seen from the test data of examples 1 to 4 that an acheson graphitization furnace is used to graphitize a reduced graphene oxide film, wherein resistive heating particles in the acheson graphitization furnace and the reduced graphene oxide film in the crucible together form a furnace resistance, and the resistive heating particles and the graphene oxide film generate co-heating to reach an extremely high graphitization temperature by applying a current, so that the resistive heating particles with different particle sizes are filled around the crucible, the core graphitization temperature in the crucible is stable, and the resistive heating particles are slowly and alternately removed to further recrystallize the graphene film in a long cooling process to generate a large area of crystal domain, so that the electrical, thermal and mechanical properties of the graphene film are improved.
The working limit of the graphitization temperature of the comparative example 1 adopting the electromagnetic induction type heating mode is 2900 ℃, the heat preservation time of the limit working temperature is short, and the graphitization temperature of the reduced graphene oxide film can not exceed 3000 ℃, so that the electrical, thermal and mechanical properties of the prepared graphene film are reduced. Due to the structural design requirement of the electromagnetic induction graphitization furnace, after heating is stopped, cooling water is needed to quickly cool the electromagnetic induction coil to avoid serious aging of core components, perfect restoration of the graphene film structure is difficult to realize in the process of accelerating cooling, and the electrical, thermal and mechanical properties of the graphene film are limited due to poor crystal orientation degree. It should be noted that, because the heating mode of the electromagnetic induction graphitization furnace is to generate a magnetic field through high-voltage current, and the magnetic field generates an induced current in the conductor, so that the conductor generates heat, in the process, the conductor must be a high-purity or isostatic pressure graphite crucible, and the graphene oxide film is placed in the crucible and is driven to reach the graphitization temperature through the self-heating of the crucible. Because the heating is realized through electromagnetic conversion, the conversion among electricity, magnetism and heat can not be stably switched, so that the temperature rise control is difficult; in addition, the electromagnetic conversion efficiency can sharply reduce the thermal efficiency along with the increase of the volume of the crucible jig, so that the higher graphitization temperature and the graphitization heat preservation time are difficult to achieve, the adoption of the electromagnetic induction type graphitization mode not only limits the productivity and increases the expensive maintenance cost, but also has the most important that the graphitization temperature cannot achieve the expected effect, so that the electrical, thermal and mechanical properties of the graphene film are influenced.
Comparative example 2 before the graphitization treatment, the graphene oxide film is not baked, and moisture and oxygen-containing chemical functional groups contained in the graphene oxide film cannot be effectively removed, so that during the graphitization treatment, volatile substances are rapidly volatilized to break the graphene film, so that the graphene is crushed into powder and cannot be pressed into a film, the mechanical properties of the graphene film are greatly reduced even if the graphene film is formed, and part of the graphene film is seriously damaged.
Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.

Claims (10)

1. A method of preparing a graphene film, the method comprising the steps of:
putting the reduced graphene oxide film into an Acheson graphitizing furnace, performing high-temperature heat treatment at different stages to enable the reduced graphene oxide film to reach the graphitizing temperature, and naturally cooling to obtain a fluffy graphene film;
and compacting and densifying the fluffy graphene film to obtain the graphene film.
2. The preparation method according to claim 1, wherein the reduced graphene oxide film and the graphite paper are stacked and then placed in crucibles in the Acheson graphitizing furnace, wherein buried resistance heating particles are paved between the crucibles in the Acheson graphitizing furnace and on the surfaces of the crucibles, and the resistance heating particles heat up to the graphitization temperature; the resistance heating particles comprise calcined coke with different particle sizes, and the average particle size of the calcined coke ranges from 0mm to 30mm, and does not comprise 0 mm.
3. The method according to claim 1, wherein the reduced graphene oxide film has a volatile component of less than 10 wt%.
4. The production method according to claim 1, wherein the method satisfies at least one of the following characteristics a to c:
a. the graphitization temperature range is 3000-3200 ℃;
b. the heat treatment period in the high-temperature heat treatment is 10 to 30 days;
c. and adopting sectional temperature rise to the graphitization temperature.
5. The method of claim 1, wherein the high temperature heat treatment comprises:
in the first stage, the temperature of the Acheson graphitization furnace is raised to 1000-1400 ℃, and the temperature is kept for 5-10 h;
in the second stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2000-2100 ℃, and the temperature is kept for 5-10 h;
in the third stage, the temperature in the Acheson graphitizing furnace is continuously increased to 2800-2900 ℃, the temperature is kept for 2-5 h, then the temperature is continuously increased to 3000-3200 ℃, and the temperature is kept for 5-10 h;
and stopping power transmission, and naturally cooling the Acheson graphitizing furnace to obtain the fluffy graphene film.
6. The method of claim 1, wherein the bulk graphene film has a compaction pressure of 2Mpa to 100 Mpa.
7. The method of manufacturing according to claim 1, wherein before placing the reduced graphene oxide film in the Acheson graphitization furnace, the method further comprises;
and baking the graphene oxide film prepared from the slurry containing the graphene oxide or the graphite oxide to obtain the reduced graphene oxide film.
8. The production method according to claim 7, wherein the method satisfies at least one of the following characteristics a to f:
a. the concentration of the slurry containing graphene oxide or graphite oxide is 1 mg/mL-80 mg/mL;
b. the slurry containing the graphene oxide or the graphite oxide is obtained by mixing in any one mode of ultrasound, mechanical shearing stripping, mechanical stirring and high-pressure homogenization;
c. the preparation process of the graphene oxide film comprises any one of a suction filtration process, a dip coating process, a spin coating process, a spraying process, an evaporation process and a coating process;
d. the baking temperature is 150-550 ℃;
e. the heating rate of the baking is 0.5-10 ℃/h;
f. the heat preservation time of the baking is 5-50 h.
9. A graphene film obtained by the production method according to any one of claims 1 to 8, wherein the graphene film satisfies at least one of the following characteristics a to d:
a. the thickness of the graphene film is 10-300 mu m;
b. the density of the graphene film is 1.8g/cm3~2.3g/cm3
c. The graphene film has a thermal conductivity of 1300W/mK to 1600W/mK;
d. the tensile strength of the graphene film is 50-65 MPa.
10. An electronic device comprising the graphene film produced by the method for producing a graphene film according to any one of claims 1 to 8.
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