Growth method and growth apparatus for graphene powder loaded with nanoscale spherical pyrolytic carbon

Abstract

The present application relates to the technical field of carbon materials, and in particular, to a growth method for graphene powder loaded with nanoscale spherical pyrolytic carbon. The method comprises: providing a reaction furnace, the reaction furnace being provided with a reaction container capable of accommodating molten metal, the reaction container being provided with a gas inlet pipe inlet and a discharging port located above the molten metal, the gas inlet pipe inlet being used for passing of a carbon source gas inlet pipe that can extend into the molten metal, the discharging port being used for being in communication with a powder collecting apparatus, and an empty cavity being present between the molten metal and the discharging port and being heated to a preset reaction temperature; introducing a mixed gas comprising a carbon source gas and an auxiliary gas into the molten metal from the carbon source gas inlet pipe so as to form bubbles in the molten metal; and in the rising process of the bubbles, heating and catalytically cracking the carbon source gas to partially grow into graphene, part of the carbon source gas rising to be separated from the molten metal along with the bubbles, and at least part of the carbon source gas growing into nanoscale spherical pyrolytic carbon loaded on the surface of the graphene in the empty cavity. According to the present application, the dispersity of the graphene product can be significantly improved.

Description

Method and apparatus for growing graphene powder loaded with nanoscale spherical pyrolytic carbon

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. CN202410480134.1, filed on April 22, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of carbon materials technology, and in particular to a method and apparatus for growing graphene powder loaded with nanoscale spherical pyrolytic carbon. Background Technology

[0004] Graphene, due to its excellent electrical and physicochemical properties, is widely used in optoelectronics, energy, and many other fields. For example, graphene can be added as a conductive agent to the cathode material of energy batteries, such as to cathode materials with low conductivity like LiCoO2, LiMn2O4, and LiFePO4, to improve the conductivity of the cathode material, effectively reduce the battery's internal resistance, improve the specific capacity of the active material, and thus enhance the rate performance, cycle life, and charging rate of lithium batteries. However, in the current preparation process of conductive slurries for batteries with added graphene, the graphene powder exhibits a sheet-like, near-planar structure in the slurry. Furthermore, because the graphene flakes are very thin, they are prone to agglomeration under the influence of interfacial molecular forces, which severely affects the high conductivity of graphene.

[0005] In related technologies, researchers from the University of California published an article titled "Catalytic methane pyrolysis in molten MnCl2-KCl" in Applied Catalysis in May 2019, proposing that methane is introduced into a molten salt mixture of MnCl2-KCl to generate bubbles. The methane then undergoes a pyrolysis reaction in the molten salt to produce carbon powder. Patent application CN202210528819.X discloses a method for preparing a graphene / carbon black mixture using molten salt. This method involves first placing solid salt in a reaction vessel for dehydration, then heating the dehydrated solid salt to a molten state and reaching a target temperature. Hydrocarbon gas is then introduced into the molten salt, forming hydrocarbon bubbles in the molten solid salt. These hydrocarbon bubbles then react in the molten solid salt to generate the graphene / carbon black mixture. However, the above technology uses molten salt as a catalyst, which has very poor catalytic activity. The conversion rate of carbon materials generated by the pyrolysis reaction of hydrocarbon gases is very low (≤8%), and the quality of the grown graphene is also very poor. In addition, carbon black with even worse conductivity is generated at the same time and mixed into the product in a non-adhesive form, resulting in poor conductivity of the product. Furthermore, when the product is mixed with conductive slurry, the graphene and carbon black particles are prone to separation due to the density difference, which further seriously affects the conductivity of carbon material powder in the slurry and limits its application in graphene-based conductive slurries. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this application provides a method and apparatus for growing graphene powder loaded with nanoscale spherical pyrolytic carbon, the specific technical solution of which is as follows.

[0007] On one hand, this application provides a method for growing graphene powder loaded with nanoscale spherical pyrolytic carbon, comprising:

[0008] A reactor is provided, wherein a reaction vessel capable of containing molten metal is provided inside the reactor, the reaction vessel having an inlet gas inlet and an outlet located above the molten metal, the inlet gas inlet being used to pass through a carbon source gas inlet pipe that can extend into the molten metal, and the outlet being used to connect to a powder collection device; a cavity exists between the molten metal and the outlet, and the molten metal is heated to a preset reaction temperature;

[0009] A mixture of carbon source gas and auxiliary gas is introduced into the molten metal through the carbon source inlet pipe to form bubbles in the molten metal. During the rising process of the bubbles, the carbon source gas is heated and catalytically decomposed, partially growing into graphene, and partially rising with the bubbles to exit the molten metal, where it at least partially grows into nanoscale spherical pyrolytic carbon loaded with graphene powder in the cavity, thereby forming graphene powder loaded with nanoscale spherical pyrolytic carbon, which is collected in the powder collection device through the outlet.

[0010] The distance between the outlet of the carbon source inlet pipe and the liquid surface of the molten metal is such that some of the unpyrolyzed carbon source and some of the carbon source pyrolysis intermediates in the bubbles can be retained and rise into the cavity; in the reaction vessel, the gas pressure in the cavity above the molten metal is a slightly positive pressure.

[0011] In some embodiments, the preset reaction temperature is 1090℃-1400℃.

[0012] In some embodiments, the preset reaction temperature is 1120℃-1220℃.

[0013] In some embodiments, the temperature inside the cavity above the molten metal surface is 1050°C-1150°C.

[0014] In some embodiments, the distance between the outlet of the carbon source inlet pipe and the liquid surface of the molten metal is 10cm-15cm.

[0015] In some embodiments, the distance between the molten metal surface and the discharge port is 30 cm or more.

[0016] In some embodiments, the distance between the molten metal surface and the discharge port is 30cm-50cm.

[0017] In some embodiments, the pressure in the space outside the reaction vessel in the reactor is atmospheric pressure.

[0018] In some embodiments, the gas pressure in the cavity above the molten metal is 106 kPa-115 kPa.

[0019] In some embodiments, the flow rate of the mixed gas introduced into the carbon source inlet pipe is 120 L / min to 180 L / min.

[0020] In some embodiments, the flow rate ratio between the auxiliary gas and the carbon source gas forming the mixture is 1:0.5 to 1:1.5.

[0021] In some embodiments, the intake pressure of the mixed gas in the carbon source intake pipe is 0.12 MPa-0.18 MPa.

[0022] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is n times the inner diameter of the carbon source inlet pipe, where 1 < n ≤ 3.

[0023] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is n times the inner diameter of the carbon source inlet pipe, where 1.5 < n ≤ 2.5.

[0024] In some embodiments, the inner diameter of the carbon source intake pipe is 7mm-10mm.

[0025] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is 15mm-18mm.

[0026] In some embodiments, the exhaust pipe connected to the discharge port has a double-layer water-cooled structure to prevent carbon deposition from the pyrolysis reaction at the exhaust port and to prevent pipe blockage.

[0027] In some embodiments, the reaction vessel includes a sealed container body and a container cover, the gas inlet is disposed on the container cover, and the carbon source gas inlet is sealed to the gas inlet.

[0028] The carbon source inlet pipe is introduced after the container cap and the container body are sealed together and the metal catalyst in the container body forms the molten metal.

[0029] In some embodiments, the molten metal is copper, or an alloy of one or more of iron, nickel, cobalt, gallium, tin, chromium, lead, germanium, antimony, bismuth, silver, and palladium with copper.

[0030] On the other hand, this application provides a growth apparatus for graphene powder loaded with nanoscale spherical pyrolytic carbon, applied to the growth method described in the first aspect, wherein the growth apparatus includes a reactor, a reaction vessel, and a powder collection device:

[0031] The reactor is equipped with a reaction vessel capable of holding molten metal. The reaction vessel has an inlet pipe and an outlet located above the molten metal. The inlet pipe is used to pass through a carbon source inlet pipe that can extend into the molten metal. The outlet is used to connect to a powder collection device. There is a cavity between the molten metal and the outlet.

[0032] In some embodiments, the distance between the outlet of the carbon source inlet pipe and the liquid surface of the molten metal is 10cm-15cm.

[0033] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is n times the inner diameter of the carbon source inlet pipe, where 1 < n ≤ 3.

[0034] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is n times the inner diameter of the carbon source inlet pipe, where 1.5 < n ≤ 2.5.

[0035] In some embodiments, the inner diameter of the carbon source intake pipe is 7mm-10mm.

[0036] In some embodiments, the inner diameter of the exhaust pipe connected to the discharge port is 15mm-18mm.

[0037] In some embodiments, the reaction vessel includes a sealed container body and a container cover, the gas inlet is disposed on the container cover, and the carbon source gas inlet is sealed to the gas inlet.

[0038] Furthermore, after the container lid is sealed to the container body, the carbon source inlet pipe can enter the inner cavity of the reaction vessel from the inlet pipe inlet.

[0039] In some embodiments, the container body and the container cap are threadedly sealed together; the carbon source inlet pipe is threadedly sealed to the inlet pipe passage.

[0040] This application also provides a graphene powder loaded with nanoscale spherical pyrolytic carbon, which is prepared by the graphene powder growth method of the first aspect loaded with nanoscale spherical pyrolytic carbon.

[0041] This application also provides the application of the above-mentioned graphene powder loaded with nanoscale spherical pyrolytic carbon in conductive pastes.

[0042] Based on the above technical solution, this application has the following beneficial effects.

[0043] In the technical solution of this application, the provided reactor is equipped with a reaction vessel capable of containing molten metal. The reaction vessel has an inlet gas inlet and an outlet located above the molten metal. The inlet gas inlet is used to pass through a carbon source gas inlet pipe that can extend into the molten metal, and the outlet is used to connect to a powder collection device. A cavity exists between the molten metal and the outlet, and the molten metal is heated to a preset reaction temperature. In the growth method provided in this application, a mixture of carbon source gas and auxiliary gas is introduced from the carbon source gas inlet pipe into the molten metal contained in the reaction vessel to form bubbles in the molten metal. During the rising process of the bubbles, the carbon source gas is heated and catalytically decomposed, partially growing into graphene, and partially rising with the bubbles to escape from the molten metal, and at least partially growing in the cavity into nanoscale spherical pyrolytic carbon loaded with graphene, thereby forming graphene powder loaded with nanoscale spherical pyrolytic carbon. This powder is collected in the powder collection device through the outlet. Furthermore, the distance between the outlet of the carbon source gas inlet pipe and the liquid surface of the molten metal is such that the gas... The method involves a distance during which some unpyrolyzed carbon source and some carbon source pyrolysis intermediates remain and rise into the cavity, while the gas pressure in the cavity above the molten metal in the reaction vessel is slightly positive. Thus, using the molten metal as a heating carrier and catalyst, high-quality graphene growth can be achieved. Simultaneously, by controlling the reaction distance, some of the carbon source gas, after catalytic decomposition, remains and rises to the surface of the liquid metal (i.e., the molten metal). The hydrocarbon components remaining in the upper cavity, under the catalytic action of the graphene powder rising with the gas flow, grow into nanoscale spherical pyrolytic carbon on the graphene powder surface, firmly adhering to the high-quality graphene powder. This method is not only simple to operate and has controllable processes, but also produces high-quality graphene products with high carbon conversion rates. Furthermore, the slightly positive pressure setting in the cavity increases the concentration of unpyrolyzed carbon source and some carbon source pyrolysis intermediate hydrocarbon components, thereby improving the growth efficiency of nanoscale spherical pyrolytic carbon on the graphene powder surface. Furthermore, the nanoscale spherical pyrolytic carbon loaded on the surface of the graphene microsheets in this application makes them easy to disperse during the preparation of conductive paste. Adding the graphene powder loaded with nanoscale spherical pyrolytic carbon in this application is beneficial to obtaining high-performance graphene conductive paste. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0045] Figure 1: Schematic diagram of the structure of the graphene powder growth device loaded with nanoscale spherical pyrolytic carbon provided in the embodiments of this application;

[0046] Figure 2: Schematic diagram of the structure after the carbon source inlet pipe in Figure 1 extends into the molten metal;

[0047] Figure 3: A magnified view of the area enclosed by the dashed box in Figure 1;

[0048] Figure 4: SEM image of graphene powder loaded with nanoscale spherical pyrolytic carbon provided in the embodiments of this application;

[0049] Figures 5 and 6: Raman images of graphene powder loaded with nanoscale spherical pyrolytic carbon provided in the embodiments of this application;

[0050] Figure 7: Raman diagram of graphene powder provided in the comparative example of this application;

[0051] Figure 8: SEM image of the graphene powder provided in the comparative example.

[0052] Explanation of reference numerals in the attached drawings: 1-Reactor, 2-Induction heating device, 3-Refractory packing, 4-Base, 5-Reaction vessel, 6-Molten metal, 7-Temperature measuring device, 8-Container cover, 9-Inlet pipe, 10-Exhaust pipe, 11-Exhaust pipe boss, 12-Heat insulation cover, 13-Carbon source inlet pipe, 14-Inlet pipe boss, 15-First interface, 16-Third interface, 17-Fifth interface, 18-Fourth interface, 19-Second interface, 20-Valve, 21-Powder collecting device, 22-Collector exhaust port, 23-Cavity, 24-Upper boss, 25-Sealing joint. Detailed Implementation

[0053] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0054] For the terms defined below, unless a different definition is given elsewhere in the claims or this specification, these definitions shall apply. All numerical values, whether explicitly indicated or not, are defined herein as being modified by the term "about." The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​included within that range and all subranges included within that range.

[0055] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0056] The following describes the graphene powder growth apparatus for loading nanoscale spherical pyrolytic carbon provided in the embodiments of this application. Please refer to Figures 1 to 3, which are schematic diagrams of the structure of the graphene powder growth apparatus for loading nanoscale spherical pyrolytic carbon. It is understood that the method structure in the figures is only a technical solution of one specific embodiment of this application, and the method of this application may include fewer or more structural features, and is not limited to the apparatus structure described in the figures.

[0057] The growth apparatus includes a reactor 1, a reaction vessel 5, and a powder collection device 21. The reactor 1 is equipped with a reaction vessel 5 that can hold molten metal 6. The reaction vessel 5 has an inlet 9 and an outlet located above the molten metal 6. The inlet 9 is used to pass through a carbon source inlet pipe 13 that can extend into the molten metal 6. The outlet is used to connect to the powder collection device 21. There is a cavity 23 between the molten metal 6 and the outlet.

[0058] Specifically, reactor 1 is a heating furnace with a heating device, including a furnace cover and a furnace body. The furnace cover and furnace body are sealed and fastened together by a sealing element, such as a sealing gasket and fastening bolts. The furnace cover and furnace body of reactor 1 are also provided with a first interface 15, a second interface 19, a third interface 16, a fourth interface 18, and a fifth interface 17. The first interface 15 is used to introduce carbon source gas inlet pipe 13, the fourth interface 18 is used to connect the discharge port of reaction vessel 5 and the inlet of powder collection device 21, the third interface 16 is used to connect to the gas inlet device, and the fifth interface 17 is used for exhaust. Inert gas can be introduced through the third interface 16 and discharged through the fifth interface 17, which can realize gas replacement in the inner cavity of the growth device and maintain the inert environment in the furnace cavity during the reaction process. The introduction of mixed gas through the carbon source gas inlet pipe 13 through the first interface 15 and the collection of products through the connection of the fourth interface 18 can realize the collection of products. The second interface 19 can be connected to a vacuum pump. Preferably, the fifth interface 17 connects the inner cavity of the reactor 1 and the powder collection device 21 so as to introduce inert gas into the powder collection device 21 during gas replacement.

[0059] Preferably, the first interface 15 is provided with an upper boss 24 and a sealing joint 25, and a sealing gasket is provided between the sealing joint 25 and the upper boss 24. More preferably, the sealing joint 25 can be threadedly connected to the first interface 15 provided on the furnace cover.

[0060] Specifically, the reaction vessel 5 is placed inside the furnace 1, preferably in the middle of the horizontal direction. The reaction vessel 5 can be a crucible. A base 4 can also be provided at the bottom of the reaction vessel 5 for heat insulation.

[0061] Specifically, an induction heating device 2 is provided on the outside of the reactor vessel (i.e., reaction container 5), and the induction heating device 2 is located inside the heating furnace (i.e., reaction furnace 1). Refractory filler 3, such as refractory sand, is provided between the reactor vessel and the induction heating device 2 for heat insulation. The base 4 mentioned above is provided at the bottom of the induction heating device 2, and a bottom heat insulation component, such as a ceramic plate, is provided between the reactor vessel and the base 4. The ceramic plate not only provides heat insulation but also has excellent compressive strength.

[0062] In some embodiments, the material of the reaction vessel 5 may include one or more of graphite, silicon carbide, silicon carbide / graphite (i.e., silicon carbide-graphite composite material), and corundum.

[0063] Specifically, the reaction vessel 5 includes a sealed container body and a container lid 8; the container lid 8 is provided with a heat insulation cover 12, preferably a composite ceramic heat insulation cover, and the specific materials may include silica composite ceramic, alumina composite ceramic, aluminum silicate composite ceramic, or silicon carbide composite ceramic, etc. Preferably, a sealing gasket is provided at the connection between the container body and the container lid 8.

[0064] Specifically, the inlet 9 is located on the container cover 8, and the carbon source inlet pipe 13 is sealed to the inlet 9. With the container cover 8 sealed to the container body, the carbon source inlet pipe 13 can enter the inner cavity of the reaction vessel 5 through the inlet 9. The carbon source inlet pipe 13 can pass through the first interface 15 of the reactor 1 to enter the furnace cavity and then through the inlet 9 on the container cover 8 to enter the inner cavity of the reaction vessel 5. Furthermore, the carbon source inlet pipe 13 is a high-temperature resistant pipe, specifically a graphite pipe, silicon carbide pipe, silicon carbide / graphite pipe, corundum pipe, carbon-carbon composite pipe, etc.

[0065] Preferably, the container body and container cap 8 are connected by a threaded seal; the carbon source inlet pipe 13 is connected by a threaded seal to the inlet pipe inlet 9. Accordingly, the inlet pipe inlet 9 can be a threaded through hole, and the carbon source inlet pipe 13 is provided with a matching external thread, thereby achieving a sealed connection through pipe rotation to improve sealing performance.

[0066] In some embodiments, an inlet pipe boss 14 is also fitted onto the carbon source inlet pipe 13, with a sealing gasket on the side facing the container cover 8. After the carbon source inlet pipe 13 enters the inner cavity of the reaction vessel 5, the inlet pipe boss 14 can abut against the container cover 8 and seal the inlet pipe inlet 9. Preferably, the position of the inlet pipe boss 14 on the carbon source inlet pipe 13 is adjustable.

[0067] Preferably, a sealing joint 25 is also provided at the first interface 15 of the reactor 1. After the carbon source inlet pipe 13 passes through the first interface 15, the sealing joint 25 further seals the connection between the carbon source inlet pipe 13 and the reactor 1.

[0068] Specifically, the carbon source inlet pipe 13 can also be connected to a drive device to move it into and out of the reaction vessel 5.

[0069] The discharge port is located on the container cover 8 and is connected to the fourth interface 18 of the reactor 1 via the exhaust pipe 10. Preferably, the container cover 8 and the exhaust pipe 10 are integrated into one structure.

[0070] Preferably, an exhaust pipe boss 11 is provided at the inlet of the exhaust pipe 10, with a sealing gasket between it and the top surface of the container cover 8. The upper part of the exhaust pipe 10 is connected to the fourth interface 18 via a metal flexible hose. This not only facilitates the connection between the two but also avoids loosening of the interface due to vibrations when venting into the liquid metal. Furthermore, it facilitates the assembly and disassembly of the container cover 8 and the reaction vessel 5. The exhaust pipe 10 can be a tungsten tube or a tungsten steel tube. The exhaust pipe 10 can be a double-layer water-cooled structure. The inlet and outlet of the exhaust pipe 10 are connected to the water-cooled circulation interface of the reactor 1 via metal flexible hoses. This avoids loosening of the interface and leakage of cooling water due to vibrations when venting into the liquid metal, and also prevents carbon buildup and blockage at the inlet of the exhaust pipe 10 during the reaction in the cavity 23.

[0071] Specifically, an appropriate amount of metal catalyst can be placed inside the reaction vessel 5, and heated to melt it to form molten metal 6. The liquid surface of molten metal 6 and the outlet form a cavity 23 inside the reaction vessel 5.

[0072] In some embodiments, the growth apparatus is further provided with a temperature measuring device 7, specifically including at least one first temperature measuring element and at least one second temperature measuring element. The temperature measuring point of the first temperature measuring element is located in the molten metal 6 to detect the temperature of the metal, preferably located in the middle of the longitudinal direction of the molten metal 6; the temperature measuring point of the second temperature measuring element is located in the cavity 23 to detect the temperature inside the cavity 23, preferably located in the middle of the longitudinal direction between the liquid surface of the molten metal 6 and the discharge port.

[0073] In some embodiments, the powder collecting device 21 is provided with a collector exhaust port 22 to achieve gas replacement and exhaust gas discharge.

[0074] In some embodiments, a valve 20 is provided on the connecting pipe between the powder collecting device 21 and the reactor 1 to facilitate the evacuation of the reactor cavity.

[0075] In some embodiments, the powder collecting device 21 includes a powder collecting vessel and a filter element. The filter element is sealed to the inner wall of the powder collecting vessel and is located between the inlet and the outlet 22 of the collector of the powder collecting device 21. It is used to separate the powder from the exhaust gas. The exhaust gas can pass through the filter element and be discharged from the outlet 22 of the collector. The graphene powder cannot pass through the filter element and remains in the powder collecting device 21. Specifically, the filter element can be a dust filter equipped with a backflushing device. The filter element is tightly fixed to the inner wall of the powder collecting vessel without gaps. The backflushing device is located above the filter element and is used to blow away the dust adhering to the dust filter to prevent clogging of the filter pores. The backflushing pressure is 0.3MPa to 0.5MPa, and the backflushing frequency is 1 time / 5s to 1 time / 10s.

[0076] Preferably, the bottom of the powder collection container is conical to facilitate the discharge of graphene powder.

[0077] According to this application, the preparation process of graphene powder loaded with nanoscale spherical pyrolytic carbon includes:

[0078] First, the metal catalyst is placed inside the reaction vessel 5. After sealing the furnace body and furnace cover, a vacuum is drawn through the second port 19, and an inert gas is introduced through the third port 16 to replace the air in all the internal cavities of the growth device, including the furnace cavity and the inner cavity of the vessel. The container cover 8 is then placed on top to seal the connection. The metal catalyst is heated until it melts and reaches the preset reaction temperature.

[0079] Then, the carbon source inlet pipe 13 is inserted into the inlet pipe 9 on the container cover 8 and extends to the bottom of the molten metal 6; a mixture of carbon source gas and auxiliary gas is introduced to allow it to grow in the cavity 23 below and above the liquid metal surface, thereby growing into graphene (powder product) loaded with nanoscale spherical pyrolytic carbon. The powder enters the powder collection device 21 through the outlet pipe, and the powder product is retained in the powder collection device 21, while the exhaust gas is discharged.

[0080] The distance between the outlet of the carbon source inlet pipe 13 and the liquid surface of the molten metal 6 is such that some of the un-cracked carbon source and some of the carbon source cracking intermediate products in the bubble can be retained and rise into the cavity 23. This allows the carbon source gas to be heated in the molten metal 6, partially cracking to form graphene, while part of it rises with the bubble into the cavity 23, where it continues to react to form nanoscale carbon spheres and attach to the graphene.

[0081] In some embodiments, the distance between the outlet of the carbon source inlet pipe 13 and the liquid surface of the molten metal 6 is 10cm-15cm.

[0082] In some embodiments, the distance between the surface of the molten metal 6 and the outlet is greater than 30 cm. Preferably, the distance between the surface of the molten metal 6 and the outlet is 30 cm-50 cm, meaning that after the bubbles rise to the surface and burst, the maximum rising distance of the carbon source pyrolysis products that have not formed graphene is 30 cm-50 cm. During this stage, graphene powder is present in the cavity 23, rising with the airflow. Under the catalytic action of the graphene powder, the carbon source pyrolysis products can grow into nanoscale spherical pyrolytic carbon on the surface of the graphene powder and adhere to the surface of the graphene powder. By setting the above distance, sufficient reaction time can be ensured to form loaded nanoscale spherical pyrolytic carbon of suitable quality and size.

[0083] In some embodiments, the inner diameter of the exhaust pipe 10 connected to the discharge port is n times the inner diameter of the carbon source inlet pipe 13, where 1 < n ≤ 3. Thus, by setting the inner diameter ratio between the inlet pipe and the exhaust pipe 10, it is possible to ensure the smooth discharge of the powder product and to achieve a slight positive pressure setting within the cavity 23. This increases the concentration of carbon source that has not been cracked in the molten metal and the hydrocarbon components of some carbon source cracking intermediates, thereby improving the growth efficiency of nanoscale spherical pyrolytic carbon on the graphene powder surface.

[0084] Preferably, the inner diameter of the exhaust pipe 10 connected to the discharge port is n times the inner diameter of the carbon source inlet pipe 13, where 1.5 < n ≤ 2.5. Through the above preferred range, the micro-positive pressure range is optimized while ensuring the smooth discharge of powder products.

[0085] In some embodiments, the inner diameter of the carbon source inlet pipe 13 is 7mm-10mm. By controlling the inner diameter of the inlet pipe to the above range, it is convenient to regulate the airflow velocity of the mixed gas, thereby controlling the degree of carbon source gas decomposition in the molten metal, i.e., the growth efficiency of graphene powder.

[0086] In some embodiments, the inner diameter of the exhaust pipe 10 connected to the discharge port is 15mm-18mm. By controlling the inner diameter of the exhaust pipe 10 to the above range, it is convenient to collect the powder product smoothly.

[0087] According to this application, the growth apparatus described herein can controllably grow graphene powder loaded with nanoscale spherical pyrolytic carbon. In this product, the nanoscale spherical pyrolytic carbon loaded on the surface of the graphene powder is tightly bonded to the graphene carrier interface. During its ascent within the cavity with the airflow, the high-temperature environment inside the cavity allows for carbon atom rearrangement, which welds the two together. Experimental verification shows that when the obtained graphene powder loaded with nanoscale spherical pyrolytic carbon is added to a slurry, the nanoscale spherical pyrolytic carbon is not easily detached during mixing. Furthermore, the graphene powder loaded with nanoscale spherical pyrolytic carbon disperses well in the slurry as an additive, preventing aggregation due to van der Waals adsorption and improving the conductive properties of the slurry.

[0088] The following describes a method for preparing graphene powder loaded with nanoscale spherical pyrolytic carbon, as provided in the embodiments of this application, in conjunction with the aforementioned growth apparatus. This specification provides the method operation steps as shown in the embodiments or flowcharts, but based on conventional or non-inventive methods, more or fewer operation steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible execution order. In actual preparation, the method can be executed in the order shown in the embodiments or accompanying drawings, or in parallel.

[0089] The method for preparing graphene powder loaded with nanoscale spherical pyrolytic carbon according to the embodiments of this application includes:

[0090] S1, a reactor 1 is provided, and a reaction vessel 5 capable of containing molten metal 6 is provided inside the reactor 1. The reaction vessel 5 has an inlet 9 and an outlet located above the molten metal 6. The inlet 9 is used to pass through a carbon source inlet pipe 13 that can extend into the molten metal 6, and the outlet is used to connect to a powder collection device 21. There is a cavity 23 between the molten metal 6 and the outlet, and the molten metal 6 is heated to a preset reaction temperature.

[0091] S2, a mixture of carbon source gas and auxiliary gas is introduced into the molten metal 6 through the carbon source inlet pipe 13 to form bubbles in the molten metal 6. During the rising process of the bubbles, the carbon source gas is heated and catalytically decomposed, and partially and completely dehydrogenated to grow into graphene. Part of the carbon source and the hydrocarbon components of the decomposition intermediate products rise with the bubbles and are removed from the molten metal 6. In the cavity 23, due to the presence of graphene powder rising with the airflow, at least part of the hydrocarbon components grow into nano-sized spherical pyrolytic carbon on the surface of the graphene powder under the catalytic action of the graphene powder, and adhere to the surface of the graphene powder, thereby forming graphene powder loaded with nano-sized spherical pyrolytic carbon, which is collected in the powder collection device 21 through the discharge port. The distance between the outlet of the carbon source inlet pipe 13 and the liquid surface of the molten metal 6 is such that part of the undecomposed carbon source and part of the carbon source decomposition intermediate products in the bubbles are retained and rise into the cavity 23.

[0092] Optionally, the molten metal 6 is copper, or an alloy of one or more of iron, nickel, cobalt, gallium, tin, chromium, lead, germanium, antimony, bismuth, silver, and palladium with copper. Alternatively, the molten metal 6 can also be other metals capable of catalytic cracking of carbon source gases.

[0093] Optionally, the carbon source gas is selected from at least one of methane, natural gas, ethane, propane, butane, ethylene, propylene, acetylene, liquefied petroleum gas, coalbed methane, and biogas. Alternatively, the carbon source gas can be any other gaseous substance capable of achieving graphene growth.

[0094] Optionally, the auxiliary gas includes, but is not limited to, at least one of nitrogen, helium, and hydrogen. The auxiliary gas can also be other gases that can assist in graphene growth.

[0095] Specifically, a metal catalyst (e.g., copper or copper alloy) is added to the inner cavity of the reaction vessel 5. Under an inert atmosphere, the induction heating device 2 is turned on to heat the metal catalyst to a molten state (forming molten metal 6) and reach a preset reaction temperature to facilitate subsequent graphene growth. Then, the carbon source inlet pipe 13 is introduced from the inlet pipe inlet 9 on the container cover 8 and extends to the bottom of the molten metal 6. The other end of the carbon source inlet pipe 13 is connected to an external ventilation pipe. A mixed gas is introduced into the molten metal 6 through the carbon source inlet pipe 13, and the formed bubbles contain carbon source gas and auxiliary gas. Inside the bubble beneath the molten metal surface, due to interfacial metal catalysis, as the bubble rises within the molten metal, the carbon source gas undergoes dehydrogenation. Part of it dehydrogenates on the bubble surface to grow into graphene, while the remaining undehydrogenated and incompletely dehydrogenated hydrocarbon components rise with the bubble to the surface of the molten metal 6. The bubble then bursts and enters the cavity 23 above the liquid surface. By controlling the temperature and pressure of the cavity, and considering the presence of graphene powder rising with the airflow within the cavity, the high concentration of hydrocarbon components undergoes decomposition on the graphene powder surface under the catalytic action of the graphene powder, forming nanoscale spherical pyrolytic carbon loaded on the graphene powder surface. This carbon firmly adheres to the high-quality graphene powder. Simultaneously, in the higher space and temperature above the liquid surface, as the carbon rises with the airflow, structural defects in the nanoscale spherical pyrolytic carbon on the graphene powder surface are repaired to some extent, thus forming graphene powder loaded with nanoscale spherical pyrolytic carbon with good electrical conductivity. Furthermore, the graphene powder loaded with nano-sized spherical pyrolytic carbon rises with the airflow to the discharge port and enters the powder collection device 21 through the pipeline.

[0096] In summary, high-quality graphene growth is achieved using molten metal 6 as a heating carrier and catalyst. Simultaneously, the carbon source gas is controlled to partially remain after catalytic decomposition and rise to the surface of the liquid metal. The hydrocarbon components remaining in the cavity 23 then grow into nanoscale spherical pyrolytic carbon on the graphene powder surface under the catalytic action of the rising graphene powder, firmly adhering to the high-quality graphene powder. This method is not only simple to operate and has controllable processes, but also produces high-quality graphene products with high carbon conversion rates. Furthermore, in the product of this application, the nanoscale spherical pyrolytic carbon supported on the graphene powder surface is tightly bonded to the carrier graphene powder at the interface: during the upward flow of air in the cavity, the high-temperature environment inside the cavity causes carbon atom rearrangement, welding the two together at high temperature. Experiments have verified that when this graphene powder loaded with nanoscale spherical pyrolytic carbon is added to conductive slurry, the nanoscale spherical pyrolytic carbon is not easily detached during the stirring and mixing process. At the same time, the graphene powder loaded with nanoscale spherical pyrolytic carbon is easy to disperse in the slurry as an additive, avoiding the aggregation caused by the adsorption of graphene sheet structure under van der Waals forces. The addition of the graphene powder loaded with nanoscale spherical pyrolytic carbon of this application is beneficial to obtaining high-performance graphene conductive slurry.

[0097] Understandably, during the insertion of molten metal 6 into the carbon source inlet pipe 13, the valve on the pipeline connected to the carbon source inlet pipe 13 is closed. The gas introduced into the furnace cavity from the third port 16 is discharged through the gap between the carbon source inlet pipe 13 and the hole in the outer wall of the furnace cavity, ensuring that an inert atmosphere is maintained inside the furnace cavity during this process, and the pressure is slightly positive, preventing air leakage. Even if part of the molten metal 6 enters the carbon source inlet pipe 13, the gas remaining in the pipeline has a certain pressure after the external pipeline valve is closed, and the molten metal 6 will not be drawn back. When the external valve connected to the carbon source inlet pipe 13 is opened, the molten metal 6 in the pipeline can be blown out by the introduced mixed gas.

[0098] In some embodiments, the preset reaction temperature is 1090℃-1400℃. This relatively low growth temperature can slow down the catalytic cracking reaction of the carbon source gas in the liquid metal, allowing some of the carbon source to be completely dehydrogenated to form graphene. The remaining uncracked carbon source and incompletely dehydrogenated hydrocarbons react on the surface of the graphene powder above the liquid surface under the catalytic action of the graphene powder rising with the gas flow, forming nanoscale spherical pyrolytic carbon. Preferably, the preset reaction temperature is 1120℃-1220℃. Experiments have verified that this preferred temperature range ensures the quality of graphene growth while optimizing the quality of nanoscale spherical pyrolytic carbon growth.

[0099] In some embodiments, the temperature inside the cavity 23 above the molten metal 6 is 1050℃-1150℃. By controlling the temperature inside the cavity 23 to the above range, the uncatalyzed carbon source and the carbon source cracking intermediate products (hydrocarbon components) can form nanoscale spherical pyrolytic carbon on the surface of graphene powder, and the structural defects can be repaired by carbon atom rearrangement, thereby obtaining nanoscale spherical pyrolytic carbon with a certain degree of crystallinity.

[0100] In this embodiment, the distance between the outlet of the carbon source inlet pipe 13 and the liquid surface of the molten metal 6 is such that some of the unpyrolyzed carbon source and some of the carbon source pyrolysis intermediates in the bubble are retained and rise into the cavity 23. This allows the carbon source gas to be partially pyrolyzed in the molten metal 6 to form graphene, while some of it rises with the bubble into the cavity 23, where it continues to react and generate nanoscale carbon spheres that attach to the graphene.

[0101] In some embodiments, the distance between the outlet of the carbon source inlet pipe 13 and the liquid surface of the molten metal 6 is 10cm-15cm, that is, the depth from the liquid surface to the outlet is 10cm-15cm. This depth, as set in this application, is approximately 1 / 2-2 / 3 lower than the height of a preparation process based on complete graphene growth using liquid metal (i.e., approximately 1 / 3-1 / 2 of the liquid surface depth in a process based on complete graphene growth using liquid metal), preferably 1 / 3. Understandably, as the carbon source gas is introduced into the molten metal 6, the bubbles formed during their ascent experience a decrease in pressure and continuous heating, resulting in an increase in bubble surface area, i.e., a gradual expansion of the growth substrate. As the pyrolysis reaction continues, the liquid level depth in this application is lower than that of normal graphene growth (where the product is only graphene). The reduced liquid level depth means that the graphene growth inside the bubbles in the molten metal 6 is terminated midway, in order to control the graphene conversion rate of the carbon source gas in the liquid metal. This further ensures and regulates the quality of the residual hydrocarbon components, thereby controlling the amount of nanoscale spherical pyrolytic carbon growth on the surface of the graphene powder in the cavity.

[0102] In some embodiments, the distance between the surface of the molten metal 6 and the outlet is more than 30 cm. Preferably, the distance between the surface of the molten metal 6 and the outlet is 30 cm-50 cm; this ensures that the cavity 23 has sufficient height for the reaction process of growing nanoscale spherical pyrolytic carbon on the surface of the graphene powder, so that the residual hydrocarbon components, under the catalysis of the graphene powder, have sufficient time for the formation and carbonization of nanoscale spherical pyrolytic carbon on the surface of the graphene powder, thereby achieving the growth of high-quality graphene powder loaded with nanoscale spherical pyrolytic carbon.

[0103] In some embodiments, the gas pressure in the external space of the reaction vessel 5 in the reactor 1 is atmospheric pressure. This is beneficial for maintaining an inert environment both outside and inside the reaction vessel 5, and reduces the difficulty of controlling the maintenance of the inert environment.

[0104] In some embodiments, the gas pressure in the cavity 23 above the molten metal 6 in the reaction vessel 5 is slightly positive, thereby increasing the pressure above the liquid surface. Since graphene has weak catalytic properties, increasing the pressure above the liquid surface helps to increase the concentration of hydrocarbon components in the cavity, enabling them to grow into nanoscale spherical pyrolytic carbon on the surface of the graphene powder under the catalytic action of the graphene powder rising with the airflow, and attach to the surface of the graphene powder. Understandably, after the bubbles burst, the higher pressure on the molten metal surface increases the concentration of un-cracked carbon sources and incompletely dehydrogenated hydrocarbon components. Simultaneously, graphene powder rises with the airflow within the cavity. When the hydrocarbon components in the cavity come into contact with the graphene powder, they undergo a cracking reaction under the catalysis of the graphene powder, forming nanoscale spherical pyrolytic carbon loaded on the surface of the graphene powder. This carbon is firmly attached to the high-quality graphene powder. Furthermore, in the higher space and temperature above the liquid surface, the structural defects of the nanoscale spherical pyrolytic carbon on the surface of the graphene powder are repaired to some extent during the upward flow of airflow, thus forming graphene powder loaded with nanoscale spherical pyrolytic carbon with good electrical conductivity.

[0105] In some embodiments, the gas pressure in the cavity 23 above the molten metal 6 is 106 kPa to 115 kPa. Controlling the pressure within this range can, on the one hand, satisfy the growth of nanoscale spherical pyrolytic carbon loaded on the surface of graphene powder in the cavity 23, and on the other hand, avoid affecting the stability of the system structure due to excessive pressure.

[0106] In some embodiments, the flow rate ratio between the auxiliary gas and the carbon source gas forming the mixed gas is 1:0.5 to 1:1.5. By setting a higher carbon source gas concentration, the graphene powder yield per unit time can be ensured at a lower growth temperature. At the same time, for the growth of spherical pyrolytic carbon loaded on the surface of graphene powder, when the catalyst is graphene powder, sufficient residual hydrocarbon component concentration is ensured after the bubbles rise to the upper part of the liquid surface and rupture.

[0107] In some embodiments, the flow rate of the mixed gas introduced into the carbon source inlet pipe 13 is 120 L / min-180 L / min. This allows the bubbles to have a suitable rising speed in the liquid metal, enabling controllable growth of graphene in the molten metal and maintaining pressure control above the liquid metal surface to achieve a micro-positive pressure environment in the cavity 23.

[0108] In some embodiments, the intake pressure of the mixed gas in the carbon source intake pipe 13 is 0.12MPa-0.18MPa.

[0109] Experiments have verified that the size of the nanoscale spherical pyrolytic carbon in the graphene powder loaded with nanoscale spherical pyrolytic carbon prepared in this application is related to the temperature of the cavity 23 above the liquid surface. If the temperature is too high, the size of the nanoscale spherical pyrolytic carbon will increase, and vice versa.

[0110] By controlling growth conditions such as the depth of the molten metal surface from the outlet, the preset reaction temperature, the cavity temperature, or the cavity pressure, it is possible to control the conversion rate of graphene powder in liquid metal, as well as the concentration of hydrocarbon components, reaction efficiency, and degree of carbonization of nanoscale spherical pyrolytic carbon growth on the surface of graphene powder, thereby achieving the regulation of carbon sphere size, content, and quality.

[0111] In some embodiments, the reaction vessel 5 includes a sealed container body and a container lid 8. An inlet 9 is disposed on the container lid 8, and a carbon source inlet pipe 13 is sealed to the inlet 9. The container lid 8 is sealed at the port of the container body, and the connection between the carbon source inlet pipe 13 and the container lid 8 is also sealed. Preferably, the connection between the exhaust pipe 10 and the container lid 8 is sealed. This sealed connection facilitates the control of the gas pressure above the liquid surface.

[0112] In some embodiments, the carbon source inlet pipe 13 is introduced after the container cover 8 is sealed to the container body and the metal catalyst in the container body forms molten metal 6. Specifically, the carbon source inlet pipe 13 and the container cover 8 can be a separate structure. Before heating, the container cover 8 is fastened to seal the container body, and then the air inside the reaction chamber is replaced. During the air replacement process, the carbon source inlet pipe 13 and the container cover 8 are separated to facilitate the exhaust of air and the inert gas inflow into the reaction container 5. After the air replacement is completed, inert gas is introduced through the third port 16 to heat the metal in the container body to molten state, and then the carbon source inlet pipe 13 is inserted through the inlet pipe inlet 9. This allows for precise control of the insertion position and depth of the inlet pipe, thereby ensuring that the inlet pipe is accurately positioned in the preset position and ensuring the sealing of the inner cavity of the reaction container 5.

[0113] In some cases, the pressure in the cavity 23 above the liquid surface is controlled at atmospheric pressure. If the carbon source inlet pipe 13 in the device needs to be inserted into the inner cavity of the reaction vessel 5 before the container cover 8 is closed, or if the carbon source inlet pipe 13 and the container cover 8 move together until the inlet pipe is inserted into the molten metal 6, in these operating methods, the container cover 8 is not sealed to the container body. Because the pressure in the cavity above the liquid surface is low, the concentration of residual hydrocarbon components is low. In addition, the catalytic activity of graphene powder in the cavity is very weak, which is insufficient to cause the residual hydrocarbon components to undergo pyrolysis reaction in the cavity above the liquid surface. Therefore, when the cavity pressure is atmospheric pressure, it is impossible to achieve the growth of nanoscale spherical pyrolytic carbon loaded on the graphene surface in the reaction vessel 5 with molten metal as catalyst, or the production efficiency is extremely low (negligible), which ultimately affects its performance as a conductive additive in conductive slurry.

[0114] In some embodiments, the inner diameter of the carbon source inlet pipe 13 is 7mm-10mm, and the inner diameter of the exhaust pipe 10 connected to the outlet is 15mm-18mm. Combined with the aforementioned airflow setting, by setting the above-mentioned inner diameter dimensions, a positive pressure setting for the cavity 23 can be ensured, allowing the cavity 23 to obtain higher pressure. This increases the concentration of residual hydrocarbon components after the molten metal bubbles burst, which is beneficial for the growth of nanoscale spherical pyrolytic carbon on the surface of graphene powder. It also facilitates the smooth discharge of the graphene powder loaded with nanoscale spherical pyrolytic carbon from the exhaust pipe.

[0115] Understandably, the diameter of the exhaust pipe 10 will affect the internal pressure of the cavity, thereby affecting the concentration of hydrocarbon components in the cavity and the growth efficiency and quality of nanoscale spherical pyrolytic carbon loaded on the surface of graphene powder. In addition, the exhaust pipe 10 can be designed as a double-layer water-cooled structure, which can prevent carbon buildup and blockage at the exhaust pipe opening during the decomposition and growth of hydrocarbon components under high pressure.

[0116] The embodiments of this application are described below in conjunction with the above technical solutions. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0117] Example 1

[0118] This embodiment provides a method for growing graphene powder loaded with nanoscale spherical pyrolytic carbon, specifically including:

[0119] 1. Add copper to the crucible, and then cover it with the crucible lid and the composite ceramic heat insulation cover in sequence. The crucible lid is threaded to the crucible opening, and a sealing gasket is installed at the contact position between the crucible and the top surface of the crucible opening. The crucible lid and the exhaust pipe 10 are connected as an integral structure, and there is a sealing gasket between the exhaust pipe protrusion 11 and the top surface of the crucible lid. The upper part of the exhaust pipe 10 is connected to the fourth interface 18 through a metal flexible tube.

[0120] 2. Under an inert atmosphere, the metal in the crucible is heated and melted to a temperature of 1200℃, and the temperature in the cavity above the liquid surface is 1100℃. Then, the carbon source inlet pipe 13 is inserted from the inlet pipe inlet 9 on the crucible lid. After melting, the depth from the liquid metal surface to the outlet is 15cm. The carbon source inlet pipe 13 is threaded to the crucible lid, and there is a sealing gasket between the inlet pipe boss 14 and the top surface of the crucible lid. At the same time, the upper part of the inlet pipe is connected to the external ventilation pipe. The inner diameter of the ventilation pipe of the carbon source inlet pipe 13 is 7mm, and the inner diameter of the exhaust pipe 10 is 15mm. The inlet pressure is 0.12MPa (Note: This can be tested using a digital pressure gauge that displays a value of 0 at atmospheric pressure. This digital pressure gauge displays a negative value when the pressure is below atmospheric pressure and a positive value when the pressure is above atmospheric pressure). The space pressure in the cavity 23 above the liquid surface is 106kPa (Note: This can be tested using a digital pressure gauge that displays 101kPa at atmospheric pressure).

[0121] 3. A mixture of carbon source gas is introduced into the crucible through the carbon source inlet pipe 13. The ratio of nitrogen to methane flow rate is 1:0.5, and the total flow rate of the mixture is 120 L / min. The graphene powder loaded with nanoscale spherical pyrolytic carbon is grown and enters the powder collection device 21 through the exhaust pipe 10. The graphene powder product loaded with nanoscale spherical pyrolytic carbon is obtained in the powder collection device 21.

[0122] Figure 4 shows a SEM image of graphene powder loaded with nanoscale spherical pyrolytic carbon, which shows that nanoscale spherical pyrolytic carbon is attached to the surface of the graphene powder.

[0123] Figure 5 shows the Raman spectra of graphene positions on the surface of graphene powder loaded with nanoscale spherical pyrolytic carbon. D / I G The value ≈0.162 indicates that the graphene powder grown in liquid metal is of good quality; Figure 6 shows the Raman spectra of the positions of the nano-sized pyrolytic carbon on the graphene powder loaded with nano-sized spherical pyrolytic carbon, I D / I G The value is approximately 0.714, and a distinct 2D peak graphene characteristic signal can be observed, indicating that the defects in the nanoscale spherical pyrolytic carbon structure on the surface of the graphene powder grown on the metal liquid surface are repaired to a certain extent, giving it a certain degree of crystallinity.

[0124] The grown graphene powder product was etched with H2O2 / HCl solution (molar concentration ratio of 2:1) to remove metal impurities, and then washed with high-purity water, centrifuged and filtered, and dried to obtain pure graphene powder loaded with nano-sized spherical pyrolytic carbon. Its mass was weighed and the ratio of its mass to the carbon atoms in the carbon source gas introduced at the corresponding time was calculated, and the carbon conversion rate was calculated to be 92.8%.

[0125] Electrochemical performance testing: Purified graphene powder loaded with nanoscale spherical pyrolytic carbon was pulverized and mixed with LiFePO4, dispersant PVP, and binder PVDF. The mass ratio of LiFePO4, graphene powder loaded with nanoscale spherical pyrolytic carbon, PVP, and PVDF was 94.3:3:0.2:2.5. Using NMP as solvent, a positive electrode slurry was prepared. The graphene powder was well dispersed in the slurry and no obvious agglomeration occurred. A coin cell was fabricated using lithium foil as the counter electrode, Celgard 2500 polyethylene porous membrane as the separator, and a 1 mol / L LiPF6 / EC-EMC-DMC (volume ratio 1:1:1) solution electrolyte. The electrochemical performance of the battery was then tested using a battery testing system. The results showed that the battery impedance was 12 Ω, the initial discharge specific capacity at 0.2C was 228 mAh / g, the initial discharge efficiency was 97.6%, and the capacity retention rate after 150 charge-discharge cycles at 1C was 92%, indicating that the positive electrode slurry performed well.

[0126] Comparative Example 1

[0127] This comparative example provides a method for growing graphene powder loaded with nanoscale spherical pyrolytic carbon, specifically including:

[0128] 1. Add copper to a crucible and heat the metal in the crucible to a molten state and reach 1200°C under an inert atmosphere. The temperature in the cavity above the liquid surface is 1100°C. Then, insert the carbon source inlet pipe 13 from the inlet pipe inlet 9 on the crucible lid. After melting, the depth from the liquid surface to the outlet is 15cm. The inner diameter of the vent of the carbon source inlet pipe 13 is 7mm, the inner diameter of the vent of the exhaust pipe 10 is 45mm, the inlet pressure is 0.12MPa, and the pressure in the space above the liquid surface is 103kPa.

[0129] 2. A mixture of methane-containing gas is introduced into the crucible through a carbon source tube, wherein the flow rate ratio of nitrogen to methane is 1:0.5 and the total flow rate of the mixture is 120 L / min. The graphene powder loaded with nanoscale spherical pyrolytic carbon is grown and enters the powder collection device 21 through the exhaust pipe 10. The graphene powder product is obtained in the powder collection device 21.

[0130] The Raman spectrum of the grown graphene powder product is shown in Figure 7. D / I G The value is approximately 0.171, indicating good quality. Figure 8 shows the SEM image of the grown graphene. No carbon spheres were found, indicating that the formation of nanoscale spherical pyrolytic carbon supported on the surface of the graphene powder is related to the pressure of the cavity above the liquid surface. At lower pressures, the concentration of residual hydrocarbon components in the cavity is lower. At the same time, the catalytic activity of the graphene powder rising with the airflow in the cavity is very weak, insufficient to cause the residual hydrocarbon components to undergo pyrolysis in the cavity above the liquid surface. Therefore, no nanoscale spherical pyrolytic carbon was observed in the SEM image of the graphene powder in this comparative example.

[0131] The grown graphene powder product was etched with H2O2 / HCl solution (molar concentration ratio of 2:1) to remove metal impurities, and then washed with high-purity water, centrifuged and filtered, and dried to obtain pure graphene powder loaded with nano-sized spherical pyrolytic carbon. Its mass was weighed and the ratio of its mass to the carbon atoms in the carbon source gas introduced at the corresponding time was calculated. The carbon conversion rate was calculated to be 76%.

[0132] Based on the results of carbon conversion calculations from Example 1 and Comparative Example 1, the mass percentage of carbon nanospheres pyrolytic carbon loaded on the surface of graphene powder in Example 1 is 19.8%.

[0133] Electrochemical performance testing: Purified graphene powder was pulverized and mixed with LiFePO4, dispersant PVP, and binder PVDF, with a mass ratio of LiFePO4, graphene powder, PVP, and PVDF of 94.3:3:0.2:2.5. NMP was used as the solvent to prepare the positive electrode slurry. A coin cell was fabricated using a lithium sheet as the counter electrode, a Celgard 2500 polyethylene porous membrane as the separator, and a 1 mol / L LiPF6 / EC-EMC-DMC solution (volume ratio 1:1:1) as the electrolyte. The electrochemical performance of the battery was then tested using a battery testing system. The results showed that the battery impedance was 38Ω, the initial discharge specific capacity at 0.2C was 158 mAh / g, the initial discharge efficiency was 88%, and the capacity retention rate after 150 charge-discharge cycles at 1C was 82%. The performance of the positive electrode slurry was significantly reduced.

[0134] The foregoing description has fully disclosed the specific embodiments of this application. It should be noted that any modifications made by those skilled in the art to the specific embodiments of this application do not depart from the scope of the claims. Accordingly, the scope of the claims of this application is not limited to the foregoing specific embodiments.

Claims

1. A method for growing graphene powder loaded with nanoscale spherical pyrolytic carbon, characterized in that, The growth method includes: A reactor (1) is provided, wherein a reaction vessel (5) capable of containing molten metal (6) is provided inside the reactor (1). The reaction vessel (5) has an inlet pipe (9) and an outlet located above the molten metal (6). The inlet pipe (9) is used to pass through a carbon source inlet pipe (13) that can extend into the molten metal (6). The outlet is used to connect to a powder collection device (21). There is a cavity (23) between the molten metal (6) and the outlet, and the molten metal (6) is heated to a preset reaction temperature. A mixture of carbon source gas and auxiliary gas is introduced into the molten metal (6) through the carbon source inlet pipe (13) to form bubbles in the molten metal (6). During the rising process of the bubbles, the carbon source gas is heated and catalytically decomposed, partially growing into graphene, and partially rising with the bubbles to exit the molten metal (6), and at least partially growing into nanoscale spherical pyrolytic carbon loaded with graphene powder in the cavity (23), thereby forming graphene powder loaded with nanoscale spherical pyrolytic carbon, which is collected in the powder collection device (21) through the outlet; wherein, The distance between the outlet of the carbon source inlet pipe (13) and the liquid surface of the molten metal (6) is such that some of the unpyrolyzed carbon source and some of the carbon source pyrolysis intermediate products in the bubble can be retained and rise into the cavity (23); in the reaction vessel (5), the gas pressure in the cavity (23) above the molten metal (6) is a slightly positive pressure.

2. The growth method according to claim 1, characterized in that, The growth method satisfies at least one of the following characteristics: The preset reaction temperature is 1090℃-1400℃; The temperature inside the cavity (23) above the surface of the molten metal (6) is 1050℃-1150℃.

3. The growth method according to claim 1, characterized in that, The growth method satisfies at least one of the following characteristics: The distance between the outlet of the carbon source inlet pipe (13) and the liquid surface of the molten metal (6) is 10cm-15cm; The distance between the liquid surface of the molten metal (6) and the discharge port is more than 30 cm.

4. The growth method according to claim 1, characterized in that, The growth method satisfies at least one of the following characteristics: The preset reaction temperature is 1120℃-1220℃; The distance between the liquid surface of the molten metal (6) and the discharge port is 30cm-50cm.

5. The growth method according to claim 1, characterized in that, The gas pressure in the external space of the reaction vessel (5) in the reactor (1) is atmospheric pressure; and / or The air pressure in the cavity (23) above the molten metal (6) is 106 kPa-115 kPa.

6. The growth method according to claim 1, characterized in that, The growth method satisfies at least one of the following characteristics: The flow rate of the mixed gas introduced into the carbon source inlet pipe (13) is 120L / min-180L / min; The flow rate ratio between the auxiliary gas and the carbon source gas forming the mixture is 1:0.5 to 1:1.5; The intake pressure of the mixed gas in the carbon source intake pipe (13) is 0.12MPa-0.18MPa; The inner diameter of the exhaust pipe (10) connected to the discharge port is n times the inner diameter of the carbon source inlet pipe (13), where 1 < n ≤ 3.

7. The growth method according to claim 1, characterized in that, The growth method satisfies at least one of the following characteristics: The inner diameter of the exhaust pipe (10) connected to the discharge port is n times the inner diameter of the carbon source inlet pipe (13), where 1.5 < n ≤ 2.5; The inner diameter of the carbon source inlet pipe (13) is 7mm-10mm; The inner diameter of the exhaust pipe (10) connected to the discharge port is 15mm-18mm.

8. The growth method according to claim 1, characterized in that, The reaction vessel (5) includes a sealed container body and a container cover (8), the inlet pipe (9) is provided on the container cover (8), and the carbon source inlet pipe (13) is sealed to the inlet pipe (9). The carbon source inlet pipe (13) is introduced after the container cover (8) is sealed to the container body and the metal catalyst in the container body forms the molten metal (6).

9. The growth method according to claim 1, characterized in that, The molten metal (6) is copper, or an alloy of one or more of iron, nickel, cobalt, gallium, tin, chromium, lead, germanium, antimony, bismuth, silver, and palladium with copper.

10. A growth apparatus for graphene powder loaded with nanoscale spherical pyrolytic carbon, applied to the growth method according to any one of claims 1-9, characterized in that, The growth apparatus includes a reactor (1), a reaction vessel (5), and a powder collection device (21): The reactor (1) is provided with a reaction vessel (5) capable of containing molten metal (6). The reaction vessel (5) has an air inlet (9) and a discharge port located above the molten metal (6). The air inlet (9) is used to pass through a carbon source air inlet pipe (13) that can extend into the molten metal (6). The discharge port is used to connect to a powder collection device (21). There is a cavity (23) between the molten metal (6) and the discharge port.

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