Graphite felt having flow channels and method for producing the same

Abstract

This invention provides a graphite felt with flow channels and its preparation method, comprising the following steps: fixing a fiber felt, constructing and shaping macroscopic flow channels on the fiber felt to obtain a preform; carbonizing the preform under inert gas protection, removing the fiber felt to obtain a carbonized fiber felt; immersing the carbonized fiber felt in liquid nitrogen to obtain a fiber felt with microscopic flow channels; heat-treating the fiber felt with microscopic flow channels, followed by activation and wettability treatment to obtain a graphite felt with flow channels. The graphite felt obtained by the preparation method of this invention provides more reaction sites, higher activity, and lower flow resistance, which can reduce resistivity. When used as an electrode material in a flow battery energy storage system, it can greatly improve the performance of the battery stack and the energy conversion efficiency based on pump consumption.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a graphite felt with flow channels and its preparation method. Background Technology

[0002] With the continuous development of renewable energy application technologies such as solar and wind power, electrochemical energy storage technology has received increasing attention in order to address the impact of the discontinuity and instability of these energy sources on the power grid. Flow batteries, as a type of electrochemical energy storage technology, have become a research hotspot due to their advantages such as high capacity, wide range of applications, and long cycle life.

[0003] In flow batteries, the stack is the core functional component for energy conversion. It mainly includes a frame, bipolar plates, electrodes, ion exchange membranes, current collectors, and end plates. The conversion of electrical energy into chemical energy is achieved through chemical reactions between ions of different valence states in the electrolyte at the electrode surfaces, thus enabling energy storage and release. Among these, the electrodes, as the site of electrochemical reactions in the flow battery, have a significant impact on the battery's performance.

[0004] Currently, carbon-based electrodes are the most widely used, but their limited number of reaction sites and high flow resistance restricts the potential for improving the electrochemical performance of fuel cell stacks. Reducing the length of the electrolyte flow through the electrodes can effectively lower the flow resistance, but this leads to low utilization of core materials, large stack size, low power density, and consequently increased cost. To improve the utilization of core materials, existing technologies typically construct flow channels on bipolar plates to increase the flow rate of the electrolyte electrodes within the stack. However, constructing flow channels on bipolar plates results in high material costs, and the bipolar plates are prone to erosion and swelling under the combined effects of high-velocity electrolyte flow and side reactions in the flow channels, significantly reducing the stack's lifespan. Summary of the Invention

[0005] The purpose of this invention is to provide a graphite felt with flow channels and its preparation method, so as to solve the problems of few reaction sites and high flow resistance in carbon electrodes in the prior art.

[0006] This invention provides the following technical solution:

[0007] A method for preparing a graphite felt with flow channels includes the following steps:

[0008] (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform;

[0009] (2) The preform obtained in step (1) is carbonized under inert gas protection, and the fiber felt is taken out to obtain the carbonized fiber felt.

[0010] (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen to obtain a fiber felt with micro-channels.

[0011] (4) The fiber felt with microchannels obtained in step (3) is heat-treated and then activated and wettable to obtain graphite felt with channels.

[0012] Preferably, in step (1), the fiber felt is a polyacrylonitrile-based fiber felt;

[0013] Preferably, the polyacrylonitrile-based fiber felt is a pre-oxidized fiber felt;

[0014] Optionally, the fiber diameter of the fiber felt is 3-20 μm;

[0015] Optionally, the thickness of the fiber felt is 0.3 mm to 10 mm;

[0016] Optionally, the length of the fiber felt is 150-1400 mm;

[0017] Optionally, the width of the fiber felt is 100-700 mm.

[0018] Preferably, in step (1), the macroscopic flow channels are constructed and shaped on the fiber felt using the following method: insert rows of needles into both sides of the fiber felt along a direction parallel to the plane of the fiber felt. Inside the fiber felt, the rows of needles on both sides form intersecting flow channels, and the rows of needles are fixed inside the fiber felt.

[0019] Preferably, the needle row consists of a plurality of needles arranged in a row at equal intervals;

[0020] Optionally, the spacing between two adjacent needles in the needle array is 10-40 mm;

[0021] Optionally, the diameter of the needles in the needle array is 0.15mm-7mm;

[0022] Optionally, the needles of the needle array are inserted into the fiber felt to a depth of 50-680 mm;

[0023] Optionally, the pin header is made of one of the following materials: metal alloy, ceramic, or graphite.

[0024] Optionally, the metal alloy is a molybdenum-based alloy; the ceramic is one of oxide ceramics, carbide ceramics, and nitride ceramics; and the graphite is sintered graphite.

[0025] Optionally, the nitride ceramic is one of silicon carbide and boron carbide; the oxide ceramic is one of zirconium oxide and aluminum oxide; and the nitride ceramic is one of silicon nitride, aluminum nitride, and boron nitride.

[0026] Preferably, in step (2), the carbonization temperature is 300-800℃ and the time is 5-30 min;

[0027] Optionally, the carbonization is performed using a microwave oven or a carbonization furnace.

[0028] Preferably, in step (3), the immersion time in the liquid nitrogen is 10-20 seconds.

[0029] Preferably, in step (4), the heat treatment includes high-temperature carbonization and high-temperature graphitization.

[0030] Preferably, the high-temperature carbonization temperature is 1000-1400℃ and the time is 0.08-6h;

[0031] Optionally, the high-temperature graphitization temperature is 1800-3000℃ and the time is 0.08-3h.

[0032] Preferably, in step (4), the activation and wetting treatment involves mixing water vapor and nitrogen at a volume ratio of 1:(2-5) and activating at a temperature of 800-1200℃ for 30-180 minutes.

[0033] Preferably, step (4) further includes immersing the fiber felt with microchannels obtained in step (3) in a toluene solution of ferric naphthenate and / or ferric oleate for 10-20 minutes before the heat treatment, and then drying it.

[0034] Preferably, the concentration of the ferric naphthenate in toluene is 3-8 wt%.

[0035] Preferably, the concentration of ferric oleate in toluene is 0.5-1.2 wt%.

[0036] The present invention also provides a method for preparing graphite felt with flow channels as described above.

[0037] The above-described solution of the present invention has at least the following beneficial effects:

[0038] (1) The preparation method of the graphite felt with flow channels of the present invention includes the following steps: fixing the fiber felt, constructing and shaping macroscopic flow channels on the fiber felt to obtain a preform; carbonizing the preform under inert gas protection, removing the fiber felt to obtain carbonized fiber felt; immersing the carbonized fiber felt in liquid nitrogen to obtain fiber felt with microscopic flow channels; heat-treating the fiber felt with microscopic flow channels, and then performing activation and wettability treatment to obtain graphite felt with flow channels. The graphite felt obtained by the preparation method of the present invention provides more reaction sites, has higher activity, and has lower flow resistance, which can reduce resistivity. When used as an electrode material in a flow battery energy storage system, it can greatly improve the performance of the stack and the energy conversion efficiency based on pump consumption.

[0039] The present invention discloses a method for preparing graphite felt with flow channels. First, macroscopic flow channels are constructed on the fiber felt. Then, after carbonization and liquid nitrogen cooling, thermal stress is used to induce the formation of collapsed grooves on its surface, giving it a wrinkled appearance. These microscopic and macroscopic structural changes increase the specific surface area of ​​the fiber felt by 2-5 times. Finally, the fiber felt undergoes heat treatment and activation wettability treatment. The high specific surface area of ​​the fiber felt provides more interfaces for electrochemical activation, allowing the resulting graphite felt to provide more reaction sites. Furthermore, the construction of macroscopic flow channels allows the electrolyte to flow freely through these channels on its surface, significantly reducing flow resistance.

[0040] (2) In the preparation method of the graphite felt with flow channels according to the present invention, in step (1), the macroscopic flow channels are constructed and shaped on the fiber felt using the following method: along a direction parallel to the plane of the fiber felt, rows of needles are inserted into both sides of the fiber felt. Inside the fiber felt, the rows of needles on both sides form staggered flow channels, and the rows of needles are fixed inside the fiber felt. The rows of needles consist of several needles arranged in a row at equal intervals. The macroscopic flow channels constructed in this way ensure that the flow path is consistent and the pressure drop is consistent, which satisfies the uniform flow of electrolyte. When the graphite felt obtained in this way is used as an electrode, the electrochemical reaction at each point can be carried out sufficiently and uniformly, which not only satisfies the potential balance at each point, but also greatly improves the mass transfer efficiency.

[0041] (3) In the preparation method of the graphite felt with flow channels described in this invention, in step (2), the carbonization temperature is 300-800℃ and the time is 5-30min. After the above carbonization treatment, the surface of the fiber felt is carbonized, while the core is not carbonized. Immersing it in liquid nitrogen can achieve rapid cooling. Under the rapid change of temperature difference, the instantaneous internal stress generated by the thermal expansion and contraction of the material will cause the material to shrink and collapse rapidly. However, due to the structure of the surface carbonization and the uncarbonized core, the high temperature difference generates interlaced internal stress, which can form regular and disordered collapse grooves on the surface of the material without destroying the fiber filament characteristics of the material itself, thereby obtaining a material with a high specific surface area.

[0042] (4) The method for preparing graphite felt with flow channels according to the present invention further includes, in step (4), immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric naphthenate and / or ferric oleate for 10-20 min before the heat treatment, and then drying it.

[0043] During heat treatment, the carbonization of the naphthenic acid ligands in the ferric naphthenate forms a cyclic carbon structure, enhancing the stability of the carbon skeleton and reducing the shrinkage and cracking of the collapsed grooves and other wrinkles formed in the fiber felt after immersion in liquid nitrogen at high temperatures. The carbon defects remaining from the decomposition of the double bonds in the ferric oleate increase active sites and improve electrochemical performance. Simultaneously, the thermal decomposition of ferric naphthenate and ferric oleate forms Fe3O4 or FeO particles, which are uniformly distributed on the fiber felt. This lowers the activation energy for carbon atom rearrangement, promotes the transformation of disordered carbon into a graphite layered structure, and increases the number of oxygen-containing functional groups on the material surface, increasing the reaction sites of the graphite felt after active wettability treatment. In particular, when ferric naphthenate and ferric oleate are used together, the ferric oleate decomposes first to form small-sized iron cores, and the iron particles from the subsequent decomposition of the ferric naphthenate fill the gaps, thereby better inducing the formation of a hierarchical porous structure during the carbonization-graphitization process, resulting in a graphite felt with a rich pore structure. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the process of constructing and shaping macroscopic flow channels on fiber felt in Example 1;

[0045] Among them, 1. Fiber felt; 2. Needle row. Detailed Implementation

[0046] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products; different manufacturers and models of raw materials do not affect the implementation of the technical solution or the achievement of the technical effect of this invention.

[0047] Example 1

[0048] The method for preparing the graphite felt with flow channels in this embodiment includes the following steps:

[0049] (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform;

[0050] The fiber felt is a pre-oxidized polyacrylonitrile-based fiber felt; the fiber diameter of the fiber felt is 3 μm; the thickness of the fiber felt is 10 mm; the length of the fiber felt is 800 mm; and the width of the fiber felt is 100 mm.

[0051] In this embodiment, the macroscopic flow channels are constructed and shaped on the fiber felt as follows: (e.g.) Figure 1 As shown, rows of needles 2 are inserted into both sides of the fiber felt 1 along a direction parallel to the plane of the fiber felt 1. Inside the fiber felt, the rows of needles on both sides form staggered flow channels, thus fixing the needles inside the fiber felt. The rows of needles consist of several needles arranged in a row at equal intervals.

[0052] The spacing between two adjacent needles in the needle array is 10 mm; the diameter of the needles in the needle array is 3 mm; the depth to which the needles of the needle array insert into the fiber felt is 50 mm; the material of the needle array is ceramic; the ceramic includes, but is not limited to, oxide ceramics, carbide ceramics, and nitride ceramics; the nitride ceramic can be silicon carbide or boron carbide; the oxide ceramic can be zirconium oxide or alumina; the nitride ceramic can be silicon nitride, aluminum nitride, or boron nitride. In this embodiment, the ceramic is silicon nitride nitride.

[0053] (2) The preform obtained in step (1) is carbonized in a carbonization furnace for 20 minutes under inert gas protection and at a temperature of 300°C. The fiber felt is then removed to obtain the carbonized fiber felt.

[0054] (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen for 10 seconds to obtain a fiber felt with micro-channels.

[0055] (4) The fiber felt with micro-channels obtained in step (3) is subjected to high-temperature carbonization and high-temperature graphitization, and then activated and wettable treatment to obtain graphite felt with channels.

[0056] The high-temperature carbonization is carried out at 1200℃ for 0.08 hours; the high-temperature graphitization is carried out at 3000℃ for 1 hour. The activation and wettability treatment involves mixing water vapor and nitrogen at a volume ratio of 1:2 and activating at 1000℃ for 30 minutes.

[0057] The graphite felt obtained in this embodiment can be used as an all-carbon electrode in various types of flow batteries, including but not limited to all-vanadium redox flow batteries and all-iron redox flow batteries.

[0058] It should be noted that, Figure 1 (a) shows a schematic diagram of the state before the needle row 2 is inserted into the fiber felt 1. Figure 1 (b) shows a schematic diagram of the state in which the pin 2 is inserted into the fiber felt 1. This state is the preform, which is then subjected to the carbonization treatment in step (2). Figure 1 As shown in (c), the carbonized fiber felt is obtained after removing the pin 2 following the carbonization treatment in step (2). During the carbonization process, the molecular chains of the fiber break and rearrange, accompanied by volume shrinkage. The macroscopic shape of the fiber felt changes due to the decomposition of some organic matter, but the basic morphology of the carbon skeleton is initially fixed. That is, the macroscopic flow channels inside the carbonized fiber felt are initially fixed. Figure 1 The macroscopic flow channels of the fiber felt shown in (c) are represented by dashed lines, indicating that the flow channels are structures that allow visibility into the interior of the fiber felt, rather than representing that the flow channels themselves are discontinuous structures. The same applies below, and will not be repeated hereafter.

[0059] Example 2

[0060] The method for preparing the graphite felt with flow channels in this embodiment includes the following steps:

[0061] (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform;

[0062] The fiber felt is a pre-oxidized polyacrylonitrile-based fiber felt; the fiber diameter of the fiber felt is 20 μm; the thickness of the fiber felt is 5 mm; the length of the fiber felt is 1400 mm; and the width of the fiber felt is 700 mm.

[0063] In this embodiment, the macroscopic flow channels are constructed and shaped on the fiber felt as follows: (e.g.) Figure 1 As shown, rows of needles 2 are inserted into both sides of the fiber felt 1 along a direction parallel to the plane of the fiber felt 1. Inside the fiber felt, the rows of needles on both sides form staggered flow channels, thus fixing the needles inside the fiber felt. The rows of needles consist of several needles arranged in a row at equal intervals.

[0064] The spacing between two adjacent needles in the needle array is 40 mm; the diameter of the needles in the needle array is 0.15 mm; the depth to which the needles of the needle array insert into the fiber felt is 680 mm; the material of the needle array is ceramic; the ceramic includes, but is not limited to, oxide ceramics, carbide ceramics, and nitride ceramics; the nitride ceramic can be silicon carbide or boron carbide; the oxide ceramic can be zirconium oxide or alumina; the nitride ceramic can be silicon nitride, aluminum nitride, or boron nitride. In this embodiment, the ceramic is oxide ceramic alumina.

[0065] (2) The preform obtained in step (1) is carbonized in an inert gas environment at a temperature of 800°C for 5 minutes using a microwave oven. The fiber felt is then removed to obtain the carbonized fiber felt.

[0066] (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen for 20 seconds to obtain a fiber felt with micro-channels.

[0067] (4) The fiber felt with micro-channels obtained in step (3) is subjected to high-temperature carbonization and high-temperature graphitization, and then activated and wettable treatment to obtain graphite felt with channels.

[0068] The high-temperature carbonization is carried out at 1400℃ for 6 hours; the high-temperature graphitization is carried out at 2400℃ for 3 hours. The activation and wetting treatment involves mixing water vapor and nitrogen at a volume ratio of 1:5 and activating at 1200℃ for 180 minutes.

[0069] The graphite felt obtained in this embodiment can be used as an all-carbon electrode in various types of flow batteries, including but not limited to all-vanadium redox flow batteries and all-iron redox flow batteries.

[0070] Example 3

[0071] The method for preparing the graphite felt with flow channels in this embodiment includes the following steps:

[0072] (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform;

[0073] The fiber felt is a pre-oxidized polyacrylonitrile-based fiber felt; the fiber diameter of the fiber felt is 10 μm; the thickness of the fiber felt is 10 mm; the length of the fiber felt is 150 mm; and the width of the fiber felt is 600 mm.

[0074] In this embodiment, the macroscopic flow channels are constructed and shaped on the fiber felt as follows: (e.g.) Figure 1As shown, rows of needles 2 are inserted into both sides of the fiber felt 1 along a direction parallel to the plane of the fiber felt 1. Inside the fiber felt, the rows of needles on both sides form staggered flow channels, thus fixing the needles inside the fiber felt. The rows of needles consist of several needles arranged in a row at equal intervals.

[0075] The spacing between two adjacent needles in the needle array is 25mm; the diameter of the needles in the needle array is 7mm; the depth to which the needles of the needle array are inserted into the fiber felt is 360mm; the material of the needle array is a metal alloy; the metal alloy is a molybdenum-based alloy.

[0076] (2) The preform obtained in step (1) is carbonized in a carbonization furnace for 30 minutes under inert gas protection and at a temperature of 500°C. The fiber felt is then removed to obtain the carbonized fiber felt.

[0077] (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen for 15s to obtain a fiber felt with micro-channels.

[0078] (4) The fiber felt with micro-channels obtained in step (3) is subjected to high-temperature carbonization and high-temperature graphitization, and then activated and wettable treatment to obtain graphite felt with channels.

[0079] The high-temperature carbonization is carried out at 1000℃ for 3 hours; the high-temperature graphitization is carried out at 1800℃ for 0.08 hours. The activation and wetting treatment involves mixing water vapor and nitrogen at a volume ratio of 1:3 and activating at 800℃ for 100 minutes.

[0080] The graphite felt obtained in this embodiment can be used as an all-carbon electrode in various types of flow batteries, including but not limited to all-vanadium redox flow batteries and all-iron redox flow batteries.

[0081] Example 4

[0082] The method for preparing the graphite felt with flow channels in this embodiment includes the following steps:

[0083] (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform;

[0084] The fiber felt is a pre-oxidized polyacrylonitrile-based fiber felt; the fiber diameter of the fiber felt is 15 μm; the thickness of the fiber felt is 5 mm; the length of the fiber felt is 800 mm; and the width of the fiber felt is 600 mm.

[0085] In this embodiment, the macroscopic flow channels are constructed and shaped on the fiber felt as follows: (e.g.) Figure 1As shown, rows of needles 2 are inserted into both sides of the fiber felt 1 along a direction parallel to the plane of the fiber felt 1. Inside the fiber felt, the rows of needles on both sides form staggered flow channels, thus fixing the needles inside the fiber felt. The rows of needles consist of several needles arranged in a row at equal intervals.

[0086] The spacing between two adjacent needles in the needle array is 30mm; the diameter of the needles in the needle array is 3mm; the depth to which the needles of the needle array are inserted into the fiber felt is 400mm; the material of the needle array is graphite; and the graphite is sintered graphite.

[0087] (2) The preform obtained in step (1) is carbonized for 20 minutes under inert gas protection and at a temperature of 600°C. The fiber felt is then removed to obtain the carbonized fiber felt.

[0088] The carbonization is carried out using a microwave oven or a carbonization furnace.

[0089] (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen for 20 seconds to obtain a fiber felt with micro-channels.

[0090] (4) The fiber felt with micro-channels obtained in step (3) is subjected to high-temperature carbonization and high-temperature graphitization, and then activated and wettable treatment to obtain graphite felt with channels.

[0091] The high-temperature carbonization is carried out at 1200℃ for 1 hour; the high-temperature graphitization is carried out at 2400℃ for 1 hour. The activation and wetting treatment involves mixing water vapor and nitrogen at a volume ratio of 1:3 and activating at 1000℃ for 120 minutes.

[0092] The graphite felt obtained in this embodiment can be used as an all-carbon electrode in various types of flow batteries, including but not limited to all-vanadium redox flow batteries and all-iron redox flow batteries.

[0093] Example 5

[0094] The graphite felt with flow channels in this embodiment uses the same raw materials and the same amount of each raw material as in Example 4, and is obtained by the same preparation method. The only difference is that step (4) also includes the step of immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric naphthenate.

[0095] In this embodiment, step (4) is as follows:

[0096] The fiber felt with microchannels obtained in step (3) was immersed in a toluene solution of ferric naphthenate for 15 minutes and dried. Then, it was subjected to high-temperature carbonization, high-temperature graphitization, and activation wettability treatment to obtain graphite felt with channels.

[0097] The concentration of the ferric naphthenate in toluene is 3 wt%.

[0098] The graphite felt obtained in this embodiment can be used as an electrode in an all-ferrofluid flow battery.

[0099] Example 6

[0100] The graphite felt with flow channels in this embodiment uses the same raw materials and the same amount of each raw material as in Example 4, and is obtained by the same preparation method. The only difference is that step (4) also includes the step of immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric naphthenate.

[0101] In this embodiment, step (4) is as follows:

[0102] The fiber felt with microchannels obtained in step (3) was immersed in a toluene solution of ferric naphthenate for 15 minutes and dried. Then, it was subjected to high-temperature carbonization, high-temperature graphitization, and activation wettability treatment to obtain graphite felt with channels.

[0103] The concentration of the ferric naphthenate in toluene is 5 wt%.

[0104] The graphite felt obtained in this embodiment can be used as an electrode in an all-ferrofluid flow battery.

[0105] Example 7

[0106] The graphite felt with flow channels in this embodiment uses the same raw materials and the same amount of each raw material as in Example 4, and is obtained by the same preparation method. The only difference is that step (4) also includes the step of immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric naphthenate.

[0107] In this embodiment, step (4) is as follows:

[0108] The fiber felt with microchannels obtained in step (3) was immersed in a toluene solution of ferric naphthenate for 15 minutes and dried. Then, it was subjected to high-temperature carbonization, high-temperature graphitization, and activation wettability treatment to obtain graphite felt with channels.

[0109] The concentration of the ferric naphthenate in toluene is 8 wt%.

[0110] The graphite felt obtained in this embodiment can be used as an electrode in an all-ferrofluid flow battery.

[0111] Example 8

[0112] The graphite felt with flow channels in this embodiment uses the same raw materials and the same amount of each raw material as in embodiment 4, and is prepared using the same method. The only difference is that step (4) also includes immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric oleate.

[0113] In this embodiment, step (4) is as follows:

[0114] The fiber felt with microchannels obtained in step (3) was immersed in a toluene solution of ferric oleate for 15 minutes and dried. Then, it was subjected to high-temperature carbonization, high-temperature graphitization, and activation wettability treatment to obtain graphite felt with channels.

[0115] The concentration of ferric oleate in toluene is 0.8 wt%.

[0116] The graphite felt obtained in this embodiment can be used as an electrode in an all-ferrofluid flow battery.

[0117] Example 9

[0118] The graphite felt with flow channels in this embodiment uses the same raw materials and the same amount of each raw material as in Example 4, and is obtained by the same preparation method. The only difference is that step (4) also includes the step of immersing the fiber felt with micro-flow channels obtained in step (3) in a toluene solution of ferric naphthenate and ferric oleate.

[0119] In this embodiment, step (4) is as follows:

[0120] The fiber felt with microchannels obtained in step (3) was immersed in a toluene solution of ferric naphthenate and ferric oleate for 15 minutes and dried. Then, it was subjected to high-temperature carbonization, high-temperature graphitization, and activation wettability treatment to obtain graphite felt with channels.

[0121] The concentration of the ferric naphthenate in toluene is 6 wt%. The concentration of the ferric oleate in toluene is 0.8 wt%.

[0122] The graphite felt obtained in this embodiment can be used as an electrode in an all-ferrofluid flow battery.

[0123] Comparative Example 1

[0124] The graphite felt of this comparative example uses the same raw materials and the same amount of each raw material as that of Example 4, and is prepared using the same method. The only difference is that step (1) is not included, that is, macroscopic flow channels are not constructed, but the fiber felt is directly carbonized.

[0125] Comparative Example 2

[0126] The graphite felt of this comparative example uses the same raw materials and the same amount of each raw material as that used in Example 4, and is prepared using the same method. The only difference is that step (3) is not included, that is, it does not go through soaking in liquid nitrogen, but directly undergoes high-temperature carbonization, high-temperature graphitization, and activation wettability treatment.

[0127] Effect Experiment Example

[0128] To verify the technical effect of the graphite felt with flow channels described in this invention, the following experiments were conducted:

[0129] The graphite felts obtained in Examples 1-4 and Comparative Examples 1-2 were used as positive electrode materials. A fuel cell assembly test was conducted on these materials. The charge / discharge instrument's cutoff voltage was set to a charging cutoff voltage of 1.55V and a discharging initiation voltage of 1V. The effective electrode area was 0.22 × 0.22 m². 2 A 1.7 mol / L vanadium sulfate electrolyte was used; the electrolyte was supplied by a peristaltic pump with adjustable positive and negative electrode flow rates; before operation, the internal gas of the system was purged with inert nitrogen. The DC-side energy conversion efficiency based on pump consumption, the flow resistance at a flow length of 220 mm, and the flow rate per unit area were measured for each group at current densities of 150 mA / cm², 250 mA / cm², and 350 mA / cm², respectively. The specific surface area of ​​the graphite felt for each group was also measured.

[0130] The results of the experiment are as follows:

[0131]

[0132]

[0133] The vanadium sulfate electrolyte in the above-mentioned stack assembly test was replaced with the electrolyte in the all-iron flow battery disclosed in Chinese patent document CN112467179B. Stack assembly tests were performed on the graphite felts obtained in Examples 1-9 and Comparative Examples 1-2, respectively. The DC-side energy conversion efficiency based on pump consumption, the flow resistance at a flow length of 220 mm, and the flow rate per unit area were measured at a current density of 100 mA / cm². The specific surface area of ​​the graphite felts in Examples 5-9 was also measured.

[0134] The results of the experiment are as follows:

[0135]

[0136] Based on the results of Examples 1-9 and Comparative Examples 1-2, it can be seen that the graphite felt with flow channels described in this invention has a higher specific surface area, can provide more reaction sites, and has lower flow resistance, which can reduce resistivity. When used as an electrode material in a flow battery energy storage system, it can greatly improve the performance of the stack and the energy conversion efficiency based on pump consumption.

[0137] Based on the results of Examples 1-4 and Comparative Examples 1-2, it can be seen that, regardless of whether it is used in an all-vanadium redox flow battery or an all-iron redox flow battery, the flow resistance of Comparative Example 1, which did not construct a macroscopic flow channel, was significantly higher than that of Examples 1-4 and Comparative Example 2, resulting in a lower DC-side energy conversion efficiency based on pump consumption. Comparative Example 2, which did not undergo liquid nitrogen immersion to construct a microscopic flow channel, had a significantly lower specific surface area than Examples 1-4 and Comparative Example 1, resulting in fewer reaction sites and a poorer DC-side energy conversion efficiency based on pump consumption.

[0138] Based on the results of Examples 1-4 and Examples 5-9, it can be seen that in Examples 5-7, soaking in ferric naphthenate before heat treatment slightly increased the specific surface area. When applied in an all-iron flow battery, the DC-side energy conversion efficiency based on pump loss was significantly improved at the same current density. However, in Example 8, soaking in ferric oleate before heat treatment, compared to Example 4, although it increased the active sites, it led to increased flow resistance, thus failing to improve the DC-side energy conversion efficiency based on pump loss. Therefore, soaking in ferric oleate alone cannot effectively improve the DC-side energy conversion efficiency based on pump loss. When soaking in a mixture of ferric naphthenate and ferric oleate, the specific surface area increased, the flow resistance did not increase significantly, and the DC-side energy conversion efficiency based on pump loss was significantly improved. Therefore, the graphite felt obtained when both are used synergistically yields the best overall performance.

[0139] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are encompassed by this invention.

Claims

1. A method for preparing a graphite felt with flow channels, characterized in that, Includes the following steps: (1) Fix the fiber felt, construct macroscopic flow channels on the fiber felt and shape it to obtain a preform; The macroscopic flow channels and shaping on the fiber felt are constructed using the following method: needles are inserted into both sides of the fiber felt along a direction parallel to the plane of the fiber felt. Inside the fiber felt, the needles on both sides form intersecting flow channels, and the needles are fixed inside the fiber felt. The pin header is made of one of the following materials: metal alloy, ceramic, or graphite; the metal alloy is a molybdenum-based alloy; the ceramic is one of oxide ceramic, carbide ceramic, or nitride ceramic; the graphite is sintered graphite; the carbide ceramic is one of silicon carbide or boron carbide; the oxide ceramic is one of zirconium oxide or alumina; and the nitride ceramic is one of silicon nitride, aluminum nitride, or boron nitride. (2) The preform obtained in step (1) is carbonized under inert gas protection, the pins are removed, and the fiber felt is taken out to obtain the carbonized fiber felt. The carbonization temperature is 300-800℃, and the time is 5-30 minutes; (3) Immerse the carbonized fiber felt obtained in step (2) in liquid nitrogen to obtain a fiber felt with micro-channels; (4) The fiber felt with microchannels obtained in step (3) is immersed in a toluene solution of ferric naphthenate and ferric oleate for 10-20 minutes, dried, then heat-treated, and then activated and wettable to obtain graphite felt with channels. The concentration of the ferric naphthenate in toluene is 3-8 wt%; the concentration of the ferric oleate in toluene is 0.5-1.2 wt%.

2. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (1), the fiber felt is a polyacrylonitrile-based fiber felt; The fiber diameter of the fiber felt is 3-20 μm; The thickness of the fiber felt is 0.3mm-10mm; The length of the fiber felt is 150-1400 mm; The width of the fiber felt is 100-700mm.

3. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, The needle row consists of several needles arranged in a row at equal intervals; The spacing between two adjacent needles in the needle array is 10-40mm; The diameter of the needles in the needle array is 0.15mm-7mm; The needles of the needle array are inserted into the fiber felt to a depth of 50-680 mm.

4. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (2), the carbonization is carried out using a microwave oven or a carbonization furnace.

5. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (3), the immersion time in the liquid nitrogen is 10-20 seconds.

6. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (4), the heat treatment includes high-temperature carbonization and high-temperature graphitization.

7. The method for preparing graphite felt with flow channels according to claim 6, characterized in that, The high-temperature carbonization is carried out at a temperature of 1000-1400℃ for a time of 0.08-6 hours. The high-temperature graphitization is carried out at a temperature of 1800-3000℃ for a time of 0.08-3h.

8. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (4), the activation and wetting treatment involves mixing water vapor and nitrogen at a volume ratio of 1:(2-5) and activating at a temperature of 800-1200℃ for 30-180 minutes.

9. A method for preparing graphite felt with flow channels according to any one of claims 1-8.

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