Graphite felt with runner and preparation method thereof

Abstract

The invention provides a graphite felt with a runner and a preparation method thereof, and the preparation method comprises the following steps: fixing a fiber felt, constructing a macroscopic runner on the fiber felt, and shaping to obtain a preform; performing carbonization treatment on the preform under the protection of inert gas, and taking out the fiber felt to obtain carbonized fiber felt; the carbonized fiber felt is soaked in liquid nitrogen, and a fiber felt with a micro flow channel is obtained; and carrying out heat treatment on the fiber felt with the microcosmic flow channel, and then carrying out activation wettability treatment to obtain the graphite felt with the flow channel. The graphite felt obtained by the preparation method provided by the invention provides more reaction sites, has higher activity and lower flow resistance, can reduce the resistivity, and can greatly improve the stack performance and the energy conversion efficiency of energy storage based on pump consumption when being applied to a flow battery energy storage system as an electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage technology, and particularly relates to a graphite felt with flow channels and a preparation method thereof. BACKGROUND

[0002] With the development of application technologies of renewable energy such as solar energy and wind energy, in order to solve the impact on the power grid caused by the discontinuity and instability of these energy, electrochemical energy storage technology has been increasingly concerned. As one of the electrochemical energy storage technologies, the flow battery has become one of the research focuses due to its advantages of high capacity, wide application field and long cycle service life.

[0003] In the flow battery, the electric pile is a core functional component for realizing energy conversion, which mainly includes a frame, a bipolar plate, an electrode, an ion exchange membrane, a current collector and an end plate, and the transformation between electric energy and chemical energy is completed through chemical reactions of ions with different valence states in the electrolyte on the surface of the electrode, so that the energy storage and release are realized. Among them, the electrode is the place for electrochemical reaction of the flow battery, and the performance of the electrode has a great influence on the performance of the battery.

[0004] At present, carbon electrodes are the most widely used, but due to the few reaction sites and large flow resistance, the electrochemical performance of the electric pile is limited. By reducing the length of the electrolyte flowing through the electrode, the flow resistance can be effectively reduced, but it will lead to low utilization rate of the core material of the electric pile, large size of the electric pile structure, small power density of the electric pile, and further increase the cost of the electric pile. In order to improve the utilization rate of the core material of the electric pile, the existing technology usually constructs flow channels on the bipolar plate to improve the flow of the electrolyte in the electric pile, but the construction of flow channels on the bipolar plate will lead to high cost of electric pile materials, and under the combined action of high flow rate electrolyte flushing and flow channel side reactions, the bipolar plate is prone to flushing and swelling, which greatly reduces the service life of the electric pile. SUMMARY

[0005] The purpose of the present application is to provide a graphite felt with flow channels and a preparation method thereof, in order to solve the problem of few reaction sites and large flow resistance of the carbon electrode in the prior art.

[0006] The present application provides the following technical solutions:

[0007] A preparation method of a graphite felt with flow channels, comprising the following steps:

[0008] (1) fixing a fiber felt, constructing a macroscopic flow channel on the fiber felt and shaping to obtain a preform;

[0009] (2) performing carbonization treatment on the preform obtained in step (1) under the protection of inert gas, taking out the fiber felt, and obtaining the carbonized fiber felt;

[0010] (3) soaking the carbonized fiber felt obtained in step (2) in liquid nitrogen to obtain a fiber felt with micro flow channels;

[0011] (4) heat treating the fiber felt with micro flow channels obtained in step (3) and then performing activation wetting treatment to obtain a graphite felt with flow 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 um;

[0015] Optionally, the thickness of the fiber felt is 0.3 mm-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 macro flow channels are constructed on the fiber felt and shaped by inserting pins into both sides of the fiber felt along a direction parallel to the plane on which the fiber felt lies, the pins on both sides form staggered flow channels inside the fiber felt, and the pins are fixed in the fiber felt.

[0019] Preferably, the pins are composed of a plurality of pins equidistantly arranged in a row;

[0020] Optionally, the distance between two adjacent pins is 10-40 mm;

[0021] Optionally, the diameter of the pins is 0.15 mm-7 mm;

[0022] Optionally, the depth of the pins inserted into the fiber felt is 50-680 mm;

[0023] Optionally, the material of the pins is one of a metal alloy, a ceramic, and graphite;

[0024] Optionally, the metal alloy is a molybdenum-based alloy; the ceramic is one of an oxide ceramic, a carbide ceramic, and a nitride ceramic; 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 zirconia and alumina; 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 5-30min.

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

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

[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 wetting treatment is mixing water vapor and nitrogen in a volume ratio of 1:(2-5), and activating at a temperature of 800-1200℃ for 30-180min.

[0033] Preferably, step (4) further includes soaking the fiber mat with micro-channels obtained in step (3) in a toluene solution of iron naphthenate and / or iron oleate for 10-20min, and drying.

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

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

[0036] The present application also provides a graphite mat with micro-channels prepared by the above method.

[0037] The above scheme of the present application at least has the following advantages:

[0038] (1) The preparation method of the graphite felt with flow channels of the present application comprises the following steps: fixing a fiber felt, constructing macroscopic flow channels on the fiber felt and shaping to obtain a preform; performing carbonization treatment on the preform under inert gas protection, taking out the fiber felt to obtain carbonized fiber felt; soaking the carbonized fiber felt in liquid nitrogen to obtain fiber felt with microscopic flow channels; performing heat treatment on the fiber felt with microscopic flow channels, and then performing activation wettability treatment to obtain graphite felt with flow channels. The graphite felt obtained by the preparation method of the present application provides more reaction sites, has higher activity, and has lower flow resistance, which can reduce the resistivity. As an electrode material applied in a liquid flow battery energy storage system, it can greatly improve the performance of the electric pile and the energy conversion efficiency based on the pump consumption.

[0039] The preparation method of the graphite felt with flow channels of the present application first constructs macroscopic flow channels on the fiber felt, and then performs liquid nitrogen cooling after carbonization to induce the formation of collapsed gullies on the surface by thermal stress, so that the fiber felt has a wrinkled appearance. The specific surface area of the fiber felt is increased by 2-5 times through the change of microstructure and macrostructure. Finally, the fiber felt is subjected to heat treatment and activation wettability treatment. The fiber felt with high specific surface area can provide more interfaces for electrochemical activation, so that the obtained graphite felt can provide more reaction sites. In addition, the construction of macroscopic flow channels enables the electrolyte to flow through the macroscopic flow channels when flowing on the surface, thereby greatly reducing the flow resistance.

[0040] (2) The preparation method of the graphite felt with flow channels of the present application adopts the following method for constructing macroscopic flow channels on the fiber felt and shaping in step (1): along the direction parallel to the plane where the fiber felt is located, a row of pins are inserted into both sides of the fiber felt, the pins on both sides form staggered flow channels inside the fiber felt, and the pins are fixed in the fiber felt. The pins are composed of a row of equidistant pins. The macroscopic flow channels constructed in this way ensure that the flow paths and pressure drops are consistent everywhere, which meets the uniform flow of the electrolyte. When the graphite felt obtained in this way is used as an electrode, the electrochemical reactions at different positions can be fully and uniformly carried out, which not only balances the electric potential at different positions, but also greatly improves the mass transfer efficiency.

[0041] (3) The preparation method of the graphite felt with flow channel, in step (2), the temperature of carbonization is 300-800℃, and the time is 5-30 min. After the above carbonization treatment, the surface of the fiber filaments of the fiber felt is carbonized, while the core is not carbonized. By immersing in liquid nitrogen, rapid cooling can be achieved. Under the rapid change of the temperature difference in this range, the instantaneous internal stress generated by the thermal expansion and cold contraction of the material will make the material rapidly shrink and collapse. However, due to the structure of the carbonized surface and the non-carbonized core, the high temperature difference generates staggered internal stress, which can form regular and irregular collapsed gullies on the surface of the material without damaging the characteristics of the fiber filaments of the material itself, thereby obtaining a material with high specific surface area.

[0042] (4) The preparation method of the graphite felt with flow channel, in step (4), further comprises immersing the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron naphthenate and / or iron oleate for 10-20 min before the heat treatment, and drying.

[0043] When the heat treatment is performed, the naphthenate ligand of the iron naphthenate can form a ring-shaped carbon structure during carbonization, enhancing the stability of the carbon skeleton and reducing the shrinkage and cracking of the collapsed gullies and other wrinkle morphologies of the fiber felt formed by immersion in liquid nitrogen at high temperatures. The double bond of the iron oleate can decompose and leave carbon defects, which can increase the active sites and improve the electrochemical performance. At the same time, the thermal decomposition of the iron naphthenate and the iron oleate forms Fe3O4 or FeO particles, which are uniformly distributed on the fiber felt, can reduce the activation energy of carbon atom rearrangement, promote the transformation of disordered carbon to graphite layered structure, and also can increase the oxygen-containing functional groups on the surface of the material, increase the reaction sites of the graphite felt after active wetting treatment. Especially, when the iron naphthenate and the iron oleate are used together, the iron oleate is first decomposed to form small-sized iron nuclei, and the iron naphthenate is then decomposed to fill the gaps, thereby better inducing the formation of multi-level pore structure during carbonization-graphitization, so that the obtained graphite felt has a rich pore structure. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a flowchart of constructing macro flow channels on the fiber felt and shaping in Example 1;

[0045] Wherein, 1, fiber felt; 2, needle bar. DETAILED DESCRIPTION

[0046] In the embodiments of the present application, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by market purchase. Different manufacturers and models of raw materials do not affect the implementation and technical effect realization of the technical solutions of the present application.

[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 distance between two adjacent pins of the pin array is 40 mm; the diameter of the pins of the pin array is 0.15 mm; the depth of the pins of the pin array inserted into the fiber felt is 680 mm; the material of the pin array is ceramic; the ceramic includes but is not limited to one of oxide ceramic, carbide ceramic, nitride ceramic; the nitride ceramic can be one of silicon carbide and boron carbide; the oxide ceramic can be one of zirconium oxide and aluminum oxide; the nitride ceramic can be one of silicon nitride, aluminum nitride and boron nitride. In this embodiment, the ceramic is oxide ceramic aluminum oxide.

[0065] (2) The preform obtained in step (1) is carbonized at a temperature of 800 ℃ for 5 min under the protection of inert gas by using a microwave oven, and the fiber felt is taken out to obtain the carbonized fiber felt;

[0066] (3) The carbonized fiber felt obtained in step (2) is soaked in liquid nitrogen for 20 s to obtain the fiber felt with micro flow channels;

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

[0068] The temperature of the high-temperature carbonization is 1400 ℃, and the time is 6 h; the temperature of the high-temperature graphitization is 2400 ℃, and the time is 3 h. The activated wetting treatment is to mix water vapor and nitrogen according to a volume ratio of 1:5, and activate at a temperature of 1200 ℃ for 180 min.

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

[0070] Embodiment 3

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

[0072] (1) The fiber felt is fixed, a macro flow channel is constructed on the fiber felt, and the fiber felt is shaped to obtain a preform;

[0073] The fiber felt is pre-oxidized polyacrylonitrile-based fiber felt; the fiber filament diameter of the fiber felt is 10 um; 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 macro flow channel is constructed on the fiber felt and shaped as follows: as shown in Figure 1As shown, along the direction parallel to the plane where the fiber felt 1 is located, the pin array 2 is inserted into both sides of the fiber felt, and the pin arrays on both sides form staggered flow channels inside the fiber felt and fix the pin array in the fiber felt.

[0075] The distance between the adjacent two pins of the pin array is 25 mm; the diameter of the pin of the pin array is 7 mm; the depth of the pin of the pin array inserted into the fiber felt is 360 mm; the material of the pin array is metal alloy; and the metal alloy is molybdenum-based alloy.

[0076] (2) The preform obtained in step (1) is carbonized in a carbonization furnace under the protection of inert gas at a temperature of 500℃ for 30 min, and the fiber felt is taken out to obtain the carbonized fiber felt;

[0077] (3) The carbonized fiber felt obtained in step (2) is soaked in liquid nitrogen for 15 s to obtain the fiber felt with micro flow channels;

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

[0079] The temperature of the high-temperature carbonization is 1000℃, and the time is 3 h; the temperature of the high-temperature graphitization is 1800℃, and the time is 0.08 h. The activated wetting treatment is to mix water vapor and nitrogen according to a volume ratio of 1:3, and activate at a temperature of 800℃ for 100 min.

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

[0081] Embodiment 4

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

[0083] (1) The fiber felt is fixed, a macro flow channel is constructed on the fiber felt, and the fiber felt is shaped to obtain a preform;

[0084] The fiber felt is pre-oxidized polyacrylonitrile-based fiber felt; the fiber filament diameter of the fiber felt is 15 um; 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 macro flow channel is constructed on the fiber felt and shaped as follows: as shown in Figure 1As shown, along the direction parallel to the plane where the fiber felt 1 is located, the pin array 2 is inserted into both sides of the fiber felt, and the pin arrays on both sides form staggered flow channels inside the fiber felt and fix the pin arrays in the fiber felt. The pin array is composed of a plurality of pins arranged equidistantly in a row;

[0086] The distance between the adjacent two pins of the pin array is 30 mm; the diameter of the pin of the pin array is 3 mm; the depth of the pin of the pin array inserted into the fiber felt is 400 mm; the material of the pin array is graphite; and the graphite is sintered graphite.

[0087] (2) The preform obtained in step (1) is carbonized at a temperature of 600°C for 20 min under the protection of inert gas, and the fiber felt is taken out to obtain the carbonized fiber felt;

[0088] The carbonization is performed by using a microwave oven or a carbonization furnace.

[0089] (3) The carbonized fiber felt obtained in step (2) is soaked in liquid nitrogen for 20 s to obtain the fiber felt with micro flow channels;

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

[0091] The temperature of the high-temperature carbonization is 1200°C, and the time is 1 h; the temperature of the high-temperature graphitization is 2400°C, and the time is 1 h. The activated wetting treatment is to mix water vapor and nitrogen according to a volume ratio of 1:3, and activate at a temperature of 1000°C for 120 min.

[0092] The graphite felt obtained in the embodiment can be used as a full-carbon electrode in various types of flow batteries, including but not limited to a full-vanadium flow battery and a full-iron flow battery.

[0093] Embodiment 5

[0094] The graphite felt with flow channels of the embodiment has the same raw materials and the same amount of each raw material as those used in Embodiment 4, and is obtained by using the same preparation method. The only difference is that step (4) further includes the step of soaking the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron naphthenate.

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

[0096] The fiber felt with micro flow channels obtained in step (3) is soaked in a toluene solution of iron naphthenate for 15 min and dried, and then subjected to high-temperature carbonization, high-temperature graphitization, and then activated wetting treatment to obtain the graphite felt with flow channels.

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

[0098] The graphite felt obtained in this embodiment can be used as an electrode for a full-iron flow battery.

[0099] Example 6

[0100] The graphite felt with flow channels in this embodiment is obtained by using the same raw materials and in the same amounts as in Example 4 and by using the same preparation method, except that step (4) further comprises a step of immersing the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron naphthenate.

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

[0102] The fiber felt with micro flow channels obtained in step (3) is immersed in a toluene solution of iron naphthenate for 15 min and dried, and then high-temperature carbonization, high-temperature graphitization, and activation and wettability treatment are performed to obtain the graphite felt with flow channels.

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

[0104] The graphite felt obtained in this embodiment can be used as an electrode for a full-iron flow battery.

[0105] Example 7

[0106] The graphite felt with flow channels in this embodiment is obtained by using the same raw materials and in the same amounts as in Example 4 and by using the same preparation method, except that step (4) further comprises a step of immersing the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron naphthenate.

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

[0108] The fiber felt with micro flow channels obtained in step (3) is immersed in a toluene solution of iron naphthenate for 15 min and dried, and then high-temperature carbonization, high-temperature graphitization, and activation and wettability treatment are performed to obtain the graphite felt with flow channels.

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

[0110] The graphite felt obtained in this embodiment can be used as an electrode for a full-iron flow battery.

[0111] Example 8

[0112] The graphite felt with flow channels of the present example was prepared using the same raw materials and in the same amounts as in Example 4, and using the same preparation method, except that step (4) further included the step of immersing the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron oleate for 15 min, and then drying.

[0113] In the present example, step (4) was performed as follows:

[0114] The fiber felt with micro flow channels obtained in step (3) was immersed in a toluene solution of iron oleate for 15 min, and then dried, and then subjected to high-temperature carbonization, high-temperature graphitization, and then activation and wettability treatment, to obtain the graphite felt with flow channels.

[0115] The concentration of the iron oleate in the toluene was 0.8 wt%.

[0116] The graphite felt obtained in the present example can be used as an electrode for a full-iron flow battery.

[0117] Example 9

[0118] The graphite felt with flow channels of the present example was prepared using the same raw materials and in the same amounts as in Example 4, and using the same preparation method, except that step (4) further included the step of immersing the fiber felt with micro flow channels obtained in step (3) in a toluene solution of iron naphthenate and iron oleate.

[0119] In the present example, step (4) was performed as follows:

[0120] The fiber felt with micro flow channels obtained in step (3) was immersed in a toluene solution of iron naphthenate and iron oleate for 15 min, and then dried, and then subjected to high-temperature carbonization, high-temperature graphitization, and then activation and wettability treatment, to obtain the graphite felt with flow channels.

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

[0122] The graphite felt obtained in the present example can be used as an electrode for a full-iron flow battery.

[0123] Comparative Example 1

[0124] The graphite felt of the present comparative example was prepared using the same raw materials and in the same amounts as in Example 4, and using the same preparation method, except that step (1) was not included, i.e., the macro flow channels were not constructed, but the fiber felt was directly subjected to carbonization treatment.

[0125] Comparative Example 2

[0126] The graphite felt of the present comparative example, which is the same as the raw materials used in Example 4, has the same amount of each raw material, and is obtained by using the same preparation method, the only difference being that step (3) is not included, that is, without soaking in liquid nitrogen, but directly high-temperature carbonization, high-temperature graphitization, and activation wetting treatment.

[0127] Effect experimental examples

[0128] In order to verify the technical effect of the graphite felt with flow channel described in the present application, the following tests were carried out:

[0129] The graphite felt obtained in Examples 1-4 and Comparative Examples 1-2 was taken as the positive electrode material, and the material was subjected to stack assembly test, with the charge cut-off voltage set to 1.55V and the discharge starting voltage set to 1V; the effective area of the electrode was 0.22x0.22m 2 , and 1.7mol / L vanadium sulfate electrolyte was used; the electrolyte used a positive and negative electrode flow adjustable peristaltic pump; before running, the system internal gas was replaced by inert gas nitrogen. The direct current side energy conversion efficiency based on pump consumption, the flow resistance when the length of flow was 220mm, and the unit area flow rate of each group were measured at a current density of 150mA / c㎡, 250mA / c㎡, and 350mA / c㎡, respectively, and the specific surface area of the graphite felt of each group was measured.

[0130] Through the test, the results are as follows:

[0131]

[0132]

[0133] The vanadium sulfate electrolyte in the above stack assembly test was replaced by the electrolyte in the all-iron flow battery disclosed in Chinese Patent Document CN112467179B, and the graphite felt obtained in Examples 1-9 and Comparative Examples 1-2 was subjected to stack assembly test, and the direct current side energy conversion efficiency based on pump consumption, the flow resistance when the length of flow was 220mm, and the unit area flow rate were measured at a current density of 100mA / c㎡, and the specific surface area of the graphite felt of Examples 5-9 was measured.

[0134] Through the test, the results are as follows:

[0135]

[0136] According to the results of Examples 1-9 and Comparative Examples 1-2, the graphite felt with flow channel described in the present application has a higher specific surface area, can provide more reaction sites, and has a lower flow resistance, which can reduce the resistivity, and when applied as an electrode material in a flow battery energy storage system, can greatly improve the performance of the stack and the energy conversion efficiency based on pump consumption.

[0137] According to the results of examples 1-4 and comparative examples 1-2, the flow resistance of comparative example 1 without macroscopic flow channel is significantly higher than that of examples 1-4 and comparative example 2, resulting in lower energy conversion efficiency of the direct current side based on pump consumption. The specific surface area of comparative example 2 without soaking in liquid nitrogen to form a micro flow channel is significantly lower than that of examples 1-4 and comparative example 1, resulting in fewer reaction sites and lower energy conversion efficiency of the direct current side based on pump consumption.

[0138] According to the results of examples 1-4 and examples 5-9, examples 5-7 soaked in iron naphthenate before heat treatment have slightly improved specific surface area, and when applied to a full iron flow battery, the energy conversion efficiency of the direct current side based on pump consumption is significantly improved at the same current density. Although example 8 soaked in iron oleate before heat treatment can increase the active sites, it will increase the flow resistance, and thus cannot improve the energy conversion efficiency of the direct current side based on pump consumption. Therefore, soaking in iron oleate alone cannot effectively improve the energy conversion efficiency of the direct current side based on pump consumption. When soaking in a mixture of iron naphthenate and iron oleate, the specific surface area increases, the flow resistance does not increase significantly, and the energy conversion efficiency of the direct current side based on pump consumption is significantly improved. Therefore, when the two are used together, the comprehensive performance of the graphite felt obtained is optimal.

[0139] From the common general knowledge, the present application can be realized by other embodiments without departing from the spirit or essential characteristics thereof. Therefore, the above disclosed embodiments are merely illustrative, and not the only ones. All changes within the scope of the present application or within the scope equivalent to the present application are embraced by the present application.

Claims

1. A method for producing a graphite felt having a flow channel, characterized by, The method comprises the following steps: (1) fixing a fiber felt, constructing macroscopic flow channels on the fiber felt and shaping to obtain a preform; (2) performing carbonization treatment on the preform obtained in step (1) under inert gas protection, taking out the fiber felt to obtain a carbonized fiber felt; (3) soaking the carbonized fiber felt obtained in step (2) in liquid nitrogen to obtain a fiber felt with microscopic flow channels; (4) performing heat treatment on the fiber felt with microscopic flow channels obtained in step (3) and then performing activation wetting treatment to obtain a graphite felt with flow channels.

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

3. The method for producing a graphite felt having flow channels according to claim 2, characterized by, In step (1), the method for constructing macroscopic flow channels on the fiber felt and shaping is as follows: inserting needle arrays into both sides of the fiber felt along a direction parallel to the plane on which the fiber felt lies, the needle arrays on both sides form staggered flow channels in the fiber felt, and the needle arrays are fixed in the fiber felt.

4. The method for producing a graphite felt having flow channels according to claim 3, characterized by, The needle array is composed of a plurality of needles arranged at equal intervals; Optionally, the distance between two adjacent needles of the needle array is 10-40 mm; Optionally, the diameter of the needle of the needle array is 0.15 mm-7 mm; Optionally, the depth of insertion of the needle of the needle array into the fiber felt is 50-680 mm; Optionally, the material of the needle array is one of a metal alloy, a ceramic and graphite; Optionally, the metal alloy is a molybdenum-based alloy; the ceramic is one of an oxide ceramic, a carbide ceramic and a nitride ceramic; and the graphite is sintered graphite; Optionally, the nitride ceramic is one of silicon carbide and boron carbide; the oxide ceramic is one of zirconia and alumina; and the nitride ceramic is one of silicon nitride, aluminum nitride and boron nitride.

5. The method for preparing graphite felt with flow channels according to claim 1, characterized in that, In step (2), the carbonization temperature is 300-800℃, and the time is 5-30 min; Optionally, the carbonization is performed by using a microwave oven or a carbonization furnace.

6. The method of claim 1, wherein the graphite felt having flow channels is prepared by the steps of: In step (3), the soaking time in the liquid nitrogen is 10-20 s.

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

8. The method for producing a graphite felt having flow channels according to claim 7, characterized by, The high-temperature carbonization temperature is 1000-1400℃, and the time is 0.08-6 h; Optionally, the high-temperature graphitization temperature is 1800-3000℃, and the time is 0.08-3 h.

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

10. A graphite felt with flow channels prepared by the method of any one of claims 1-9.

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