KR20220020665A - Electrode for vanadium redox flow battery and vanadium redox flow battery including the same - Google Patents

Abstract

Disclosed are an electrode for a vanadium redox flow battery in which redox reaction sites of vanadium ions increase sufficiently and electrical resistance decreases so that a sufficient redox reaction time can be increased, and an ion adsorption layer including two or more types of hydrophilic functional groups is introduced on a carbon fiber support, and a vanadium redox flow battery which has improved reaction efficiency, charge/discharge capacity and cell efficiency by using the electrode for a vanadium redox flow battery.

Description

Electrode for vanadium redox flow battery and vanadium redox flow battery including same {Electrode for vanadium redox flow battery and vanadium redox flow battery including the same}

The present invention relates to an electrode for a vanadium redox flow battery and a vanadium redox flow battery comprising the same. More specifically, the present invention is an electrode for a vanadium redox flow battery capable of sufficiently increasing redox reaction sites of vanadium ions and decreasing electrical resistance, thereby increasing sufficient redox reaction time. Two or more types of hydrophilic functional groups on a carbon fiber support An electrode for a vanadium redox flow battery into which an ion adsorption layer comprising a; and to a vanadium redox flow battery having improved reaction efficiency, charge/discharge capacity and battery efficiency by employing the same.

The present invention is "Development of graphite felt electrode technology including an ion adsorption layer having a charge/discharge voltage efficiency of vanadium ions of 87% or more" of the technology innovation development project for small and medium enterprises supervised by the Small and Medium Business Technology Development Project of the Ministry of SMEs and Startups (task unique number S2629638) based on the research results of

Research and development of redox flow batteries as large-capacity secondary batteries for energy storage devices are being actively conducted. A redox flow battery is an electrochemical storage device that directly stores the chemical energy of an electrolyte in a system in which an electroactive species in an electrolyte is charged and discharged by oxidation-reduction. Carbon felt, for example, graphite felt, is mainly used as an electrode of a vanadium redox flow battery.

In order to increase the efficiency of the vanadium redox flow battery, surface oxidation treatment is performed through the carbon felt surface treatment technology to increase the surface area of the carbon felt and increase the wettability to the electrolyte, as well as the redox reaction site of the vanadium ion electroactive species. It is possible to improve the efficiency and performance of the redox flow battery by providing

Most of the surface-treated graphite felts applied to the existing vanadium redox flow batteries are made of long-fiber carbon precursors, and then undergo oxidation-carbonization-graphitization processes to make graphite felts, which are then heated to steam, By supplying carbon dioxide and/or ozone, a functional group containing oxygen is introduced on the surface of the graphite felt, but when only a functional group containing oxygen is included, the performance, output density and durability of the redox flow battery are limited due to limitations in high current density. It is difficult to have charging/discharging and high durability performance.

However, when the carbon felt electrode is manufactured according to the existing surface treatment method, it is very difficult to activate the graphitized carbon fiber, so that a functional group can be generated on the surface of the carbon fiber constituting the carbon felt or pores (pores) capable of adsorbing reactive ion species. ) is very difficult to form. As a result, reactive ionic species such as vanadium have lowered electrolyte adsorption properties and electrochemical reactivity on the electrode surface, and improvement is required. In addition, in order to increase the performance and output density of the flow battery, an electrode capable of realizing a high current per unit area is required, and the selective adsorption and reactivity of vanadium ions are limited by the conventional surface treatment method to obtain an electrode with high current performance. is difficult

Accordingly, the technical problem to be achieved by the present invention is to sufficiently increase the redox reaction sites of vanadium ions while sufficiently providing electrochemical durability in the strongly acidic electrolyte-supported electrolyte to solve the above-mentioned problems, and to reduce the electrical resistance, the electrolyte adsorption property, To provide an electrode for a vanadium redox flow battery in which an ion adsorption layer including two or more types of hydrophilic functional groups is introduced into a carbon fiber support as an electrode for a vanadium redox flow battery capable of increasing electrochemical reactivity and redox reaction time.

Another technical problem to be achieved by the present invention is to provide a vanadium redox flow battery having improved reaction efficiency, charge/discharge capacity and battery efficiency by employing the above electrode.

In order to achieve the above technical problem, one aspect of the present invention is

A carbon support electrode for a vanadium redox flow battery, the carbon support electrode comprising: a porous plate-like carbon fiber support having first and second surfaces opposite to each other; and an ion adsorption layer disposed on at least one surface of the first surface and the second surface of the carbon fiber support, or the carbon fiber support between the first surface and the second surface of the carbon fiber support. Including an ion adsorption layer distributed inside the

The ion adsorption layer includes conductive carbon and a binder resin carbide,

On the carbon fiber surface constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer, a hydrophilic functional group containing oxygen (hereinafter sometimes referred to as an 'oxygen functional group') and a hydrophilic functional group containing nitrogen (hereinafter sometimes referred to as 'nitrogen') A functional group (referred to as ') is provided with a carbon support electrode bonded thereto.

In one embodiment, the carbon support is composed of carbon fibers, and may be in the form of carbon fiber felt, carbon fiber nonwoven fabric, carbon fiber paper, carbon fiber knitted fabric, and carbon fiber woven fabric.

In one embodiment, the hydrophilic functional group containing oxygen includes at least one selected from a hydroxyl group, a ketone group, an aldehyde group, and a carboxyl group, and the hydrophilic functional group including nitrogen is a primary amino group, a secondary amino group, a tertiary amino group, and a pyrrole. It may include at least one selected from a (-C-NH-C-) group and a pyridine (-C=NC-) group.

In one embodiment, the binder resin is a phenol resin, an epoxy resin, polyester, polyvinyl acetate, polyimide, polystyrene, polyacrylonitrile (PAN), pitch (pitch), polyvinyl alcohol (PVA), cellulose, At least one selected from nanocellulose fibers and acrylic resins,

The conductive carbon has a spherical or needle-like shape with a specific surface area of 40 to 1,600 m ² /g, and when the conductive carbon is a spherical particle, the diameter of the spherical particle is 20 to 50 nm, and when the conductive carbon is a needle-like particle, the The needle-shaped particles may have a diameter of 30 to 100 nm and a length of 2 to 25 μm.

In one embodiment, the conductive carbon is activated carbon, carbon black, acetylene black, Ketjen Black, Denka black, carbon whisker, vapor grown carbon fiber (VGCF: Vapor Grown Carbon Fiber), carbon aerosol, carbon nano It may be at least one selected from the group consisting of tubes, carbon nanofibers, carbon nanohorns, graphene, natural graphite powder, synthetic graphite powder, and thermally expanded graphite powder.

In one embodiment, the content of the binder resin carbide is preferably 3 to 30 parts by weight based on 100 parts by weight of the total weight of the ion adsorption layer.

In one embodiment, the ratio (O:N) of the atomic percentage (atomic %) of oxygen derived from the oxygen-containing functional group to the nitrogen derived from the nitrogen-containing functional group on the surface of the carbon support electrode is 3 :1 to 10:1, and the content of nitrogen derived from the functional group containing nitrogen is preferably 1 atomic% or more.

In one embodiment, the total content of the ion adsorption layer is preferably 2 to 30 parts by weight based on 100 parts by weight of the total weight of the carbon support electrode.

In order to achieve the above other technical object, another aspect of the present invention provides a vanadium redox flow battery including the carbon support electrode according to an aspect of the present invention.

In the carbon support electrode for a vanadium redox flow battery according to the present invention, an ion adsorption layer containing conductive carbon and a binder resin carbide is introduced into the carbon fiber support, and the ion adsorption layer adsorbs reactive ionic species on the carbon fiber surface. It contains two types of hydrophilic functional groups capable of increasing hyperdiffusion, namely, oxygen functional groups and nitrogen functional groups. At this time, an oxygen functional group and a nitrogen functional group are bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer. The carbon support electrode of the present invention having such a structure can sufficiently provide a site for redox reaction of vanadium ion reactive species having various oxidation states contained in the electrolyte. Specifically, the carbon support electrode of the present invention has electrochemical durability in a strongly acidic electrolyte-supported electrolyte, while the oxidation-reduction reaction site of vanadium ions is sufficiently increased and electrical resistance is lowered, so that electrolyte adsorption, electrochemical reactivity, and redox reaction time can be increased sufficiently. Therefore, the carbon support electrode of the present invention is i) sufficient for the redox reaction of reactive species to occur, ii) has fast reactivity, and iii) has electrochemical durability in a strongly acidic supporting electrolyte to the electrode for a redox flow battery. It is possible to efficiently satisfy the required conditions.

The vanadium redox flow battery of the present invention including the electrode according to the present invention may exhibit improved reaction efficiency, charge/discharge capacity and battery efficiency.

1A is an exemplary configuration diagram showing the configuration of a vanadium redox flow battery according to an embodiment of the present invention.
Figure 1b shows the configuration of a vanadium redox flow battery according to another embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the configuration of the unit cell in FIG. 1 .

Hereinafter, the present invention will be described in more detail with respect to a carbon support electrode for a vanadium redox flow battery according to an exemplary embodiment of the present invention, and a vanadium redox flow battery including the same. However, the description below is for illustrative purposes only. Therefore, it is apparent to those of ordinary skill in the art to which the present invention pertains that they can be variously modified and modified.

A carbon support electrode for a vanadium redox flow battery according to an aspect of the present invention includes a porous plate-shaped carbon fiber support having a first surface and a second surface facing each other; and an ion adsorption layer disposed on at least one surface of the first surface and the second surface of the carbon fiber support, or ion adsorption distributed in the interior of the carbon fiber support between the first and second surfaces of the carbon fiber support include layers. The ion adsorption layer includes conductive carbon and a binder resin carbide. An oxygen functional group and a nitrogen functional group are bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer.

The carbon support structure composed of carbon fibers may be used for manufacturing the electrode of the present invention, and may be, for example, in the form of carbon fiber felt, carbon fiber nonwoven fabric, carbon fiber paper, carbon fiber knitted fabric, and carbon fiber woven fabric. Carbon fiber felt can be considered as an example of carbon fiber nonwoven fabric.

The hydrophilic functional group containing oxygen includes at least one selected from a hydroxyl group, a ketone group, an aldehyde group, and a carboxyl group, and the hydrophilic functional group containing nitrogen is a primary amino group, a secondary amino group, a tertiary amino group, a pyrrole group (-C-NH -C-), and a pyridine (-C=NC-) group may include at least one selected from the group.

Binder resin is phenol resin, epoxy resin, polyester, polyvinyl acetate, polyimide, polystyrene, polyacrylonitrile (PAN), pitch, polyvinyl alcohol (PVA), cellulose, nanocellulose fiber and acrylic resin. It may be at least one selected. The binder resin is not limited to the above, and is not particularly limited as long as it can be carbonized and activated in the carbonization and activation process performed during the electrode manufacturing process.

This binder resin can serve to bind conductive carbons in the network between carbon fibers and bond between conductive carbons, and after carbonization, it is stable at low pH and wet well with water by the introduction of oxygen functional groups and nitrogen functional groups. It can also help the reactive ion species to adsorb to the electrode by using its properties. If an ion adsorption layer containing electrically conductive carbon that adsorbs water and ions well is formed on the surface of the hydrophobic carbon support, the reactivity between the carbon support electrode and the electrolyte solution can be increased.

The conductive carbon is even more advantageous if the surface has pores or contains a functional group or has a structure advantageous to contain a functional group on the surface. The conductive carbon has a spherical or needle-like shape with a specific surface area of 40 to 1,600 m ² /g, such as 60 to 1,600 m ² /g, 70 to 1,500 m ² /g, or 60 to 1,400 m ² /g, and conductive When carbon is a spherical particle, the diameter of the spherical particle is 20 to 50 nm, for example, 25 to 50 nm, or 30 to 50 nm, and when the conductive carbon is an acicular particle, the diameter of the acicular particle is 30 to 100 nm, for example 32 to 100 nm, 34 to 100 nm, 36 to 95 nm, or 38 to 90 nm, and may have a length of 2 to 25 μm, for example 3 to 25 μm, 4 to 25 μm, or 5 to 25 μm.

Conductive carbon includes activated carbon, carbon black, acetylene black, furnace black, thermal black, Ketjen Black, denka black, carbon whisker, vapor grown carbon fiber (VGCF) ), carbon aerosol, carbon nanotube (CNT), carbon nanofiber, carbon nanohorn, graphene, natural graphite powder, synthetic graphite powder, and may be at least one selected from the group consisting of thermally expandable graphite powder. Single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs), and vapor-grown carbon fibers can be applied as needle-like carbon nanotubes. When formed on the same carbon support surface, a carbon support electrode with further improved electrical conductivity can be obtained.

As described above, the carbon support electrode of the present invention comprises i) an ion adsorption layer disposed on at least one of the first and second surfaces of the carbon fiber support, for example, on one or both surfaces, or ii) carbon and an ion adsorption layer distributed in the interior of the carbon fiber support between the first surface and the second surface of the fiber support. The ion adsorption layer includes conductive carbon and a binder resin carbide. An oxygen functional group and a nitrogen functional group are bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer.

The binder resin carbide, which attaches the ion adsorption layer to the carbon support and binds the conductive carbon particles, is phenol resin, epoxy resin, polyester, polyvinyl acetate, polyimide, polystyrene, polyacrylonitrile (PAN), polyvinyl. It may be a carbide of alcohol (PVA), cellulose, nanocellulose fiber, or an acrylic resin, for example, it may be a pitch.

The binder resin and the carbide formed by carbonizing it increases bonding between the conductive carbon and the conductive carbon, and between the conductive carbon and the carbon fibers constituting the carbon support. The content of the binder resin carbide is 3 to 30 parts by weight, for example, 3 to 20 parts by weight or 5 to 15 parts by weight, based on 100 parts by weight of the total weight of the ion adsorption layer. When the content of the binder resin carbide is within the above range, the resistance of the electrode is not increased and the wettability of the electrolyte is not deteriorated, and the ion adsorption layer of the carbon support has excellent bonding strength to the carbon fibers.

The total content of the ion adsorption layer is preferably 1 to 15 parts by weight, preferably 3 to 10 parts by weight, and more preferably 3 to 7 parts by weight based on 100 parts by weight of the total weight of the carbon support electrode. When the content of the ion adsorption layer, that is, the total content of the conductive carbon and the binder resin carbide is within the above range, the reactive ion species in the electrolyte have high wettability to the carbon support electrode, and the concentration of the reactive ion species adsorbed on the electrode surface is increased. As a result, the redox reaction efficiency is increased. The ion adsorption layer not only has the property of adsorbing ions, but also simply connects the carbon fibers in physical contact with electrically conductive carbon, so it can also play a role in increasing electrical conductivity. Graphite felt without an ion adsorption layer has a very smooth carbon fiber surface and weak contact between the carbon fibers, so the electrical conductivity is low, making electron transfer difficult in the high current region. Therefore, the electrode according to the present invention is advantageous in exhibiting improved electrode performance by increasing the time the reactive ion species stays at the reaction site, that is, the redox reaction time. Since the graphite felt with the ion adsorption layer formed in VRB has increased wettability to water, it is easily wetted uniformly and easily by the electrolyte composed of vanadium ions and strong acids, so reactivity and efficiency can be increased.

The ratio (O:N) of the atomic percentage (atomic %) of oxygen derived from oxygen functional groups to nitrogen derived from nitrogen functional groups on the carbon support electrode surface is 3:1 to 10:1, for example 3.5:1 to It is 4.5:1. The content of nitrogen derived from a functional group containing nitrogen is 1 atomic % or more, for example, 1.0 to 7 atomic %, 1.3 to 6 atomic %, 1.5 to 5.5 atomic %, 2.0 to 5.0 atomic %, or 2.1 to 4.9 atomic %. It is preferable to be

The atomic percentage (atomic %) of oxygen derived from an oxygen functional group and nitrogen derived from a nitrogen functional group on the surface of the carbon support electrode of the present invention is X-ray photoelectron spectroscopy (X-ray photoelectron spectroscopy: XPS) by analyzing the electrode surface. can be obtained Since the carbon support and the ion adsorption layer of the present invention are substantially all made of carbon except for other materials that may be included at the impurity level, respectively, the atomic % of oxygen and nitrogen obtained through XPS analysis is the above-described oxygen functional group and the above It can be considered to be derived from the nitrogen function.

The ratio (O:N) of the atomic percentage (atomic %) of oxygen derived from oxygen functional groups on the carbon support electrode surface to nitrogen derived from nitrogen functional groups is 3:1 to 10:1, derived from functional groups containing nitrogen. The content of nitrogen to be used is preferably 1 atomic% or more.

The oxygen functional group is a phenol resin, epoxy resin, polyester, polyvinyl acetate, polyimide, polyvinyl alcohol (PVA), cellulose, nanocellulose fiber or acryl containing a hydroxyl group, a ketone group, an aldehyde group and/or a carboxyl group. profit; And it can be produced using a low molecular weight substance such as glycerin, maleic acid, fumaric acid and / or glutaric acid added thereto. The above-mentioned nitrogen-containing functional group is obtained by adding urea, creatine, etc. having a nitrogen-containing functional group such as an amino group, a pyrrole (-C-NH-C-) group, and a pyridine (-C=NC-) group to the above-mentioned resin. It can be obtained, and it can be obtained by adding aspartic acid, serine, etc. which have an oxygen functional group and a nitrogen functional group simultaneously to the above-mentioned binder resin.

Most of the surface-treated graphite felt electrodes applied to the existing vanadium redox flow batteries introduce oxygen functional groups through thermal oxidation. It is difficult to have high-current-density charge/discharge and high-durability performance. In the present invention, this problem is solved by introducing not only an oxygen functional group but also a nitrogen functional group.

When the content of the oxygen functional group and the nitrogen functional group is increased too much, too much oxygen and nitrogen are introduced into the carbon fiber, so that the mechanical strength of the carbon support is lowered, the electrode resistance is increased, and the durability is also reduced. On the other hand, if the oxygen and nitrogen contents are too low, the electrolyte and reactive ionic species do not get wet properly on the carbon fiber surface. It becomes difficult to show discharge capacity and efficiency. In previous studies, when the surface treatment time is increased to increase the reaction site on the carbon fiber surface or when a large amount of reaction gas is injected at a high temperature, the carbon fiber itself is oxidized to increase the resistance of the electrode and increase the resistance of the carbon support. Since the mechanical strength is significantly lowered, there is a disadvantage in that the carbon support such as carbon felt is easily broken when the stack is manufactured in VRB. In the present invention, most reactive vanadium ion species have a structure in which they can easily migrate to the carbon fiber surface, and the reactive ionic species that migrated to the surface are very easily adsorbed to the carbon fiber surface and the ion adsorption layer. The adsorbed reactive ionic species may react in the ion adsorption layer or may move toward the functional group of the carbon fiber for a redox reaction. In terms of the total amount, the oxygen functional groups and the nitrogen functional groups are increased and the reaction sites are increased, but the structure of the carbon support becomes more rigid and the electrode resistance is lowered, and as a result, the energy density of the stack is increased.

The specific surface area of the carbon support electrode may be 1 to 100 m 2 /g, for example 1.5 to 30 m 2 /g or 2.0 to 15 m 2 /g.

In the present invention, one or both sides of a carbon fiber support to improve the low wettability of reactive species ions on the electrode surface and increase reactivity; Alternatively, it provides a carbon felt electrode having an ion adsorption layer formed on the inside of the carbon fiber support. To this end, conductive carbon, a binder resin capable of carbonization and activation, and a precursor containing an oxygen functional group and a precursor containing a nitrogen functional group are applied and/or impregnated and dried on the carbon fiber support, for example, a carbon felt precursor surface during carbon felt production. By surface treatment, an ion adsorption layer containing conductive carbon and carbide of a binder resin is formed on the surface of the carbon felt. Thereby, it is possible to obtain a carbon support electrode in which the above-described oxygen functional group and nitrogen functional group are bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer.

As used herein, the term "functional group containing oxygen" refers to a hydroxyl group (-OH), a ketone group (-C=O), an aldehyde group or a carboxyl group (-COOH), and "a functional group containing nitrogen" is a primary amino group, secondary amino group, tertiary amino group, pyrrole (-C-NH-C-) group, or pyridine (-C=NC-) group. When these two types of hydrophilic functional groups are held together, hydrophilicity is sufficiently imparted to the hydrophobic carbon fiber support electrode, thereby increasing the reactivity between the electrode and the electrolyte solution, thereby manufacturing a vanadium redox flow battery with improved charge and discharge characteristics.

When introducing the above-described oxygen functional group and nitrogen functional group to the carbon fiber support electrode, any method commonly used in the art is applicable. For example, a carbon fiber support electrode coated with and/or impregnated with a composition for forming an ion adsorption layer is heated in an oxygen atmosphere in an electric furnace of 200 to 800°C, for example 300 to 700°C or 400 to 600°C, specifically about 500°C. , for example, it can be carried out using a method of heat treatment by injecting steam in a state of steam. When a carboxyl group as an oxygen functional group is introduced into the carbon fiber support electrode, a mixed gas of oxygen and nitrogen may be injected into the reactor.

Hereinafter, a method for manufacturing a carbon felt electrode for a vanadium redox flow battery of the present invention will be described in more detail.

First, for example, a carbon felt precursor is prepared through a conventional nonwoven fabric manufacturing process using a crimped carbon fiber precursor staple having an average fiber length of 30 to 120 mm and an average fiber diameter of 5 to 20 μm. The carbon fiber precursor may be, for example, rayon fiber, polyacrylonitrile fiber, cellulose fiber, or the like. By subjecting the thus obtained carbon felt precursor to an oxidation process, an oxidized carbon felt precursor is obtained. The process of oxidizing the carbon felt precursor is carried out at 150 to 450 °C, for example, 250 to 350 °C, specifically about 300 °C in an atmosphere of air or oxygen gas. Through this oxidation process, the carbon fiber precursor is changed to a structure having a more benzene structure, and the carbon content increases to 60% or more. Alternatively, it is also possible to manufacture the oxidized carbon felt through a non-woven fabric process using oxidized staple carbon fiber without using a process for oxidizing the carbon felt precursor.

Then, the carbon felt is graphitized (which may be simply referred to as graphite felt) by performing carbonization and graphitization processes in which the oxidized carbon felt is heat-treated in an inert gas atmosphere. Here, the inert gas atmosphere is formed using, for example, a gas atmosphere such as nitrogen, argon, or helium. And the heat treatment temperature for carbonization and graphitization may be 1300 to 2200 ℃. When the heat treatment is carried out in the above temperature range, carbonization and graphitization of the oxidized carbon felt are smoothly performed. The carbon fiber diameter contained in the graphite felt produced in this way may be 8 to 10 μm, and the density of the graphite felt may be 0.09 to 0.13 g/cm 3 .

Subsequently, a composition for forming an ion adsorption layer including a conductive carbon powder, a carbonizable binder resin, a precursor including an oxygen functional group, a precursor including a nitrogen functional group, and a solvent is prepared. For the conductive carbon powder, the binder resin, and the precursor, those described above may be used. For example, as the binder resin, polyvinyl alcohol, polyvinyl acetate, polystyrene, phenol resin, acrylic resin, cellulose, and nanocellulose fiber can be used, and as a precursor including an oxygen functional group, glycerin, maleic acid, Fumaric acid and/or glutaric acid can be used as a precursor containing a functional group containing nitrogen, urea, creatine, etc., and aspartic acid, serine, etc. can be used as a precursor containing both an oxygen functional group and a nitrogen functional group. The content of the binder resin may be 0.5 to 10% by weight based on the total weight of the composition, and the precursor containing an oxygen functional group and the precursor containing a functional group containing nitrogen are 0.05 to 10% by weight, respectively, based on the total weight of the composition may be, and the conductive carbon powder may be 1 to 20% by weight based on the total weight of the composition, and the solvent may be, for example, 10 to 98% by weight, such as 20 to 95% by weight, 25 to 90% by weight, based on the total weight of the composition. % can be adjusted. As the solvent, alcohols such as ethanol, methanol, and isopropanol, water, or higher alcohols such as glycerin may be used. When the solvent content is within the above range, each component constituting the composition for forming an ion adsorption layer may be uniformly dispersed to form an ion adsorption layer uniformly on and/or inside the carbon felt.

The prepared composition for forming an ion adsorption layer (slurry) is applied to and/or impregnated with graphite felt and dried to form an ion adsorption layer on at least one or both surfaces of the graphite felt or inside the graphite felt. A method of applying and/or impregnating the composition for forming the ion adsorption layer on the graphite felt is not particularly limited, but, for example, a method of supplying using a spray nozzle or an impregnation method may be used.

Drying is carried out at, for example, 80 to 150°C, for example about 120°C.

Subsequently, the graphite felt with the ion adsorption layer disposed at 200 to 800 ° C, for example 300 to 700 ° C or 400 to 600 ° C, specifically, in an electric furnace of about 500 ° C. in an oxygen atmosphere (for example, the mixing ratio of oxygen and nitrogen A surface treatment step of heat treatment is performed under an adjusted mixed gas atmosphere). In the surface treatment step, thermal oxidation and chemical oxidation proceed simultaneously, so that the oxygen functional group-containing precursor and the nitrogen functional group-containing precursor are decomposed by heating, radicals derived from the decomposed precursor on the carbon fiber surface of the support and/or the conductive carbon powder surface, and / or ionic species are combined to form an oxygen functional group and a nitrogen functional group. When a carboxyl group as an oxygen functional group is introduced into the carbon fiber support electrode, a mixed gas of oxygen and nitrogen may be introduced into the reactor. The oxygen functional group and the nitrogen functional group introduced in this way can provide a reaction site capable of inducing an oxidation reaction by adsorbing and desorbing vanadium ions in various oxidation states.

When the carbonization and graphitization processes are performed through the above-described heat treatment, the binder resin, which is an organic material, is carbonized and mostly converted to carbon, and the remainder is discharged as a gas. After this process, the carbon felt is composed of an ion adsorption layer containing carbon fibers, conductive carbons widely distributed between the skeletons of carbon fibers, and carbides (carbon-based materials) of the binder resin. A surface-treated carbon felt in which an oxygen functional group and a nitrogen functional group are bonded is obtained on the surface of the carbon fibers constituting the carbon felt with the ion adsorption layer, the surface of the conductive carbon in the ion adsorption layer, and the surface of the carbide.

At this time, the binder resin for bonding the conductive carbon powders can provide more reaction sites for vanadium ions while being carbonized, and since it is composed of pure carbon, more ion adsorption sites are distributed. In addition, by introducing an oxygen functional group and a nitrogen functional group to the surface of the carbon felt on which the ion adsorption layer is formed, it is easier to introduce an increased amount of the hydrophilic functional group compared to introducing only the oxygen functional group. Therefore, it is possible to manufacture a carbon felt electrode having a high ion adsorption capacity and high electrical conductivity characteristics compared to the conventional case of introducing only oxygen functionalities. In the carbon felt that has undergone the above-described carbonization and graphitization, wettability to water may be reduced as a portion of the carbon fibers are changed to a crystal structure, but in the present invention, ion adsorption on the surface and/or inside of the carbon fiber support (carbon felt) Compared with carbon felt without forming an ion adsorption layer by forming a layer, adsorption and wettability for reactive ionic species such as vanadium ions are improved, as well as when only an oxygen functional group is introduced by introducing an oxygen functional group and a nitrogen functional group together Compared to that, while having electrochemical durability in a strongly acidic electrolyte supporting electrolyte, the oxidation-reduction reaction site of vanadium ions is sufficiently increased and the electrical resistance is lowered, so that the electrolyte adsorption property, electrochemical reactivity, and redox reaction time can be sufficiently increased. .

In the manufacturing method of the carbon fiber support electrode of the present invention, in the step of preparing a surface-treated carbon fiber support by introducing an oxygen functional group and a nitrogen functional group to the surface of the carbon fiber support, the oxygen content of the oxygen functional group and the nitrogen content of the nitrogen functional group are carbon fibers The surface of the support electrode was analyzed by XPS, and the ratio (O:N) of the atomic percentage (atomic %) of oxygen derived from the oxygen functional group to the nitrogen derived from the nitrogen functional group based on the total content of carbon, oxygen and nitrogen was 3 :1 to 10:1, for example, adjusted to be 3.5:1 to 4.5:1. The content of nitrogen derived from the nitrogen functional group is 1 atomic% or more, for example, 1.3 to 4.9 atomic%, and the content of oxygen derived from the oxygen functional group is 10 atomic% or more, for example 12 to 20 atomic%, or 12 to 19 atomic %. When the oxygen content and the nitrogen content are adjusted within the above ranges, the adsorption of reactive ion species on the electrode surface is further increased, so that the reactivity between the electrode and the electrolyte solution is greatly improved, thereby improving the current density characteristics.

When the carbon support electrode of the present invention is used, the affinity between the electrolyte and the carbon fiber support (eg, graphite felt) electrode is improved, and the adsorption and diffusion of reactive ionic species on the carbon fiber surface is increased. Therefore, the use of such a carbon support electrode improves the reversibility of the redox reaction and the current density. Therefore, by using the carbon support electrode of the present invention, it is possible to manufacture a vanadium redox flow battery with improved charge/discharge capacity and voltage efficiency. For example, when the carbon support electrode of the present invention is used, the oxidation and reduction of vanadium is promoted, so that the charging/discharging efficiency is increased by 20% or more; And it is possible to obtain a vanadium redox flow battery having greatly improved current and voltage efficiency due to the increase of the reaction site. The carbon felt electrode has a porous structure and has a porosity of 70 to 98%.

1 shows the structure of a vanadium redox flow battery having a carbon felt electrode according to an embodiment.

1, the vanadium redox flow battery 10 includes a stack 30 in which the unit cells 20 are stacked in series; Tanks 40 and 50 in which active materials having different oxidation states are stored; and pumps 42 and 52 for circulating the active material during charging and discharging. An acidic aqueous solution in which an active material such as vanadium (V), iron (Fe), and chromium (Cr) and a transition metal such as tin (Sn) are dissolved in a strong acid solution may be used as the electrolyte for the negative electrode and the positive electrode. The stack 30 is composed of unit cells 20 and two end plates 60 and 62 . The unit cells 20 and the end plates 60 and 62 are fastened by a plurality of tie rods 64 .

2, the unit cells 20 are basically a pair of electrodes 24 consisting of a membrane 22, an anode and a cathode disposed on both sides of the membrane; and a pair of separator plates 26 disposed on both sides of the electrodes 24 .

These electrodes are in direct contact with the electrolyte flowing through the redox flow battery 10 to provide an active site where the electroactive species dissolved in the electrolyte react during charging and discharging, and serve to provide an electron movement path. Therefore, the material used for the electrode has high electrical conductivity, has excellent durability in a strongly acidic solution of the supporting electrolyte used, and must provide a reaction site where the redox reaction of the electroactive species can occur. In addition, in order to lower the cell resistance, it is necessary to have an electrode structure capable of reducing the interface resistance between the electrode and the graphite separator and the interface between the electrode and the film.

The formation of oxygen functional groups and nitrogen functional groups on the surface of the carbon felt electrode can be confirmed using Fourier transform infrared spectroscopy (FT-IR) technique.

The average fiber diameter of the carbon fibers constituting the carbon felt electrode of the present invention is 5 to 20 μm, and the average length is 30 to 120 mm in average fiber length, for example 50 to 100 mm.

When an additional ion adsorption layer other than carbon fiber is included in the electrode of the vanadium oxide flow battery, the oxygen content on the surface of the graphite felt increases from 0.5 to 20 parts by weight of the total weight of functional groups compared to the conventional carbon electrode made of only carbon fibers, The specific surface area increases from less than 1 m 2 /g to 100 m 2 /g. As a result, the amount of vanadium redox ion species adsorbed to the graphite felt surface increases, and through this, the reaction site increases and the amount of ions participating in the oxidation-reduction reaction increases. Therefore, it is possible to see the effect of increasing the charging and discharging capacity and increasing the efficiency of charging and discharging. If the conventional graphite felt was a reaction by mass transfer of reactive ion species, the reaction of the present invention is higher because diffusion on the surface of the graphite felt increases.

The vanadium redox flow battery according to another aspect of the present invention uses the above-described electrode of the present invention as a cathode or an anode of the battery.

Figure 1b is a diagram schematically showing a redox flow battery according to an embodiment of the present invention.

Referring to Figure 1b, the redox flow battery according to an embodiment of the present invention is a cathode cell (1), an anode cell (2), an ion exchange membrane 100 separating the two cells (1,2) and the cells and tanks 21 and 22 in communication with (1, 2), respectively. The cathode cell 1 includes a cathode 13 and a cathode electrolyte 11 . The anode cell 2 includes an anode 14 and an anode electrolyte 12 . Charging and discharging occur according to the redox reaction occurring at the cathode (13) and the anode (14). The cathode 13 and the anode 14 may each comprise a carbon felt electrode of the present invention. In Fig. 1B, reference numerals 41 and 420 denote tubes or pipes, and 31 and 32 denote pumps.

The operating principle of the redox flow battery is disclosed in Korean Patent Publication No. 2011-0088881. Korea Patent Publication No. 2011-0088881 is incorporated herein in its entirety.

The redox flow battery can be used in all applications requiring high output and high voltage, and is particularly suitable for energy storage devices (ESS). In other words, it can replace a Li-ion battery that stores electricity generated by sunlight or wind power, and the amount of energy stored can be increased by adjusting the capacity of the electrolyte. It can be used as a generator.

Hereinafter, the present invention will be described in more detail using the following examples. This is illustrative and the present invention is not limited to the following examples.

comparative example One: carbon felt Preparation of electrodes

An oxidized PAN felt having a basis weight of about 900 g/m ² was produced in a nonwoven production process using oxidized PAN (polyacrylonitrile) fiber. The produced oxidized PAN was carbonized in an electric furnace in a nitrogen gas atmosphere having a temperature gradient of 900 to 2,200 ° C. - Through the graphitization process, graphite felt was produced in the form of a roll. The obtained graphite felt had a basis weight of about 400 g/m ² , and shrinkage occurs during the graphitization process, and as a part of the carbon fibers change into a crystal structure, it does not wet well with water. It was not suitable for direct use as an electrode due to low adsorption and wettability.

Separately, a composition for forming an ion adsorption layer was prepared by mixing 2 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 20 g of a phenol resin (product name: TD-2493D, manufacturer: Gangnam Chemical), and 2,000 g of water. .

The upper and lower surfaces of the graphite felt by impregnating the composition for forming an ion adsorption layer on the upper surface of the graphite felt obtained above, drying in an oven at about 120° C. for about 20 minutes, and surface treatment in an oven at about 500° C. for about 30 minutes, and An ion adsorption layer was formed over the entire interior to obtain a carbon felt electrode. At this time, the ion adsorption layer is evenly impregnated into the graphite felt so that it is applied to the network between the carbon fibers and bonded to the fiber surface. The application amount of the composition for forming the ion adsorption layer was adjusted to be about 5 parts by weight based on 100 parts by weight of the graphite felt.

During the surface treatment process, the phenolic resin in the ion adsorption layer applied to the graphite felt serves to maintain the bond between the carbon fibers and the carbon powder, and during the carbonization process, the phenolic resin is converted into a carbide made of amorphous carbon and some shrinkage. sometimes this happens

Graphite felt with functional groups such as hydroxyl and ketone groups introduced on the carbon fiber surface and the surface of the ion adsorption layer by putting graphite felt with an ion adsorption layer into an electric furnace at about 500°C and injecting steam in the form of water vapor into the electric furnace at a constant rate was obtained to prepare an electrode. The basis weight of the finally obtained graphite felt was adjusted to be about 400 g/m ² to 500 g/m ² .

Comparative Example 2: Preparation of carbon felt electrode

An oxidized PAN felt having a basis weight of about 900 g/m ² was produced in a nonwoven production process using oxidized PAN (polyacrylonitrile) fiber. The produced oxidized PAN was carbonized in an electric furnace in a nitrogen gas atmosphere having a temperature gradient of 900 to 2,200 ° C. - Through the graphitization process, graphite felt was produced in the form of a roll. The obtained graphite felt had a basis weight of about 400 g/m ² , and shrinkage occurs during the graphitization process, and as a part of the carbon fibers change into a crystal structure, it does not wet well with water. It was not suitable for direct use as an electrode due to low adsorption and wettability.

Separately, 10 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 20 g of phenolic resin (product name: TD-2493D, manufacturer: Gangnam Chemical), 50 g of glycerin as an oxygen functional group precursor, 50 g of urea as a nitrogen functional group precursor g and 2,000 g of water were mixed and uniformly mixed to prepare a composition for forming an ion adsorption layer.

Graphite felt by applying the composition for forming an ion adsorption layer on the upper surface of the graphite felt obtained above using a spray nozzle, drying in an oven at about 120° C. for about 2 hours, and surface treatment in an oven at about 500° C. for about 1 hour A carbon felt electrode was obtained by forming an ion adsorption layer over the upper and lower surfaces and the entire interior. At this time, the ion adsorption layer is evenly impregnated into the graphite felt so that it is applied to the network between the carbon fibers and bonded to the fiber surface. The application amount of the composition for forming the ion adsorption layer was adjusted to be about 5 parts by weight based on 100 parts by weight of the graphite felt.

During the surface treatment process, the phenolic resin in the ion adsorption layer applied to the graphite felt serves to maintain the bond between the carbon fibers and the carbon powder, and during the carbonization process, the phenolic resin is converted into a carbide made of amorphous carbon and some shrinkage. sometimes this happens

Graphite felt with functional groups such as hydroxyl and ketone groups introduced on the carbon fiber surface and the surface of the ion adsorption layer by putting graphite felt with an ion adsorption layer into an electric furnace at about 500°C and injecting steam in the form of water vapor into the electric furnace at a constant rate was obtained to prepare an electrode. The basis weight of the finally obtained graphite felt was adjusted to be about 400 g/m ² to 500 g/m ² .

Example 1: Preparation of carbon felt electrode

When preparing the composition for forming an ion adsorption layer, 2 g of carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech Co., Ltd.) were further added and the content of some components was changed as indicated below. A carbon felt electrode was obtained in the same manner and under the same conditions as in Comparative Example 2. That is, the composition of the composition for forming the ion adsorption layer was as follows: 3 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 2 g of carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech), 20 g of a phenolic resin (product name: TD-2493D, manufacturer: Gangnam Hwaseong), 50 g of glycerin as an oxygen functional group precursor, 20 g of urea as a nitrogen functional group precursor, and 2,000 g of water.

Example 2: Preparation of Carbon Felt Electrodes

When forming the ion adsorption layer on the graphite felt, first, 5 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 20 g of phenolic resin (product name: TD-2493D, manufacturer: Gangnam Chemical), glycerin as an oxygen functional group precursor Composition 1 obtained by mixing 50 g, 20 g of urea as a nitrogen functional group precursor, and 2,000 g of water and mixing uniformly was first impregnated on the upper surface of graphite felt and dried in an oven at about 120° C. for about 20 minutes, and in an oven at about 500° C. An intermediate ion adsorption layer using the composition 1 was first formed over the upper and lower surfaces and the entire interior of the graphite felt by surface treatment for about 1 hour.

Then, 5 g of surface-treated carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech), 20 g of phenolic resin (product name: TD-2493D, manufacturer: Gangnam Hwaseong), and 2,000 g of water are mixed and uniformly The composition 2 obtained by mixing is impregnated on the upper surface of the graphite felt on which the intermediate ion adsorption layer is formed, dried in an oven at about 120 ° C. for about 30 minutes, and surface treated in an oven at about 500 ° C. for about 1 hour. An ion adsorption layer using the composition 2 was further formed over the lower surface and the entire interior to complete the formation of the ion adsorption layer, thereby obtaining a carbon felt electrode. At this time, the ion adsorption layer is evenly impregnated into the graphite felt so that it is applied to the network between the carbon fibers and bonded to the fiber surface. The total coating amount of the compositions 1 and 2 for forming the ion adsorption layer was adjusted to be about 3 parts by weight based on 100 parts by weight of the graphite felt.

Example 3: Preparation of Carbon Felt Electrodes

When forming the ion adsorption layer on the graphite felt, first, 5 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 20 g of phenolic resin (product name: TD-2493D, manufacturer: Gangnam Chemical), glycerin as an oxygen functional group precursor 30 g, 10 g of urea as a nitrogen functional group precursor, and 2,000 g of water were mixed and uniformly mixed. Composition 1 was first applied on the upper surface of graphite felt using a spray nozzle and dried in an oven at about 120° C. for about 30 minutes. Thus, an intermediate ion adsorption layer using the composition 1 was first formed over the upper and lower surfaces and the entire interior of the graphite felt.

Subsequently, 10 g of carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech), 50 g of phenol resin (product name: TD-2493D, manufacturer: Gangnam Hwaseong), and 2,000 g of water were mixed and uniformly mixed to obtain Composition 2 was applied using a coating machine on the upper surface of the graphite felt on which the intermediate ion adsorption layer was formed, dried in an oven at about 120 ° C. for about 20 minutes, and surface treated in an oven at about 500 ° C. for about 2 hours. The upper surface of the graphite felt Although the ion adsorption layer material using the composition 1 is present over the upper and lower surfaces and the entire interior, the carbon nanotube component completed the formation of the ion adsorption layer existing only on the upper surface of the graphite felt to obtain a carbon felt electrode. The total coating amount of the compositions 1 and 2 for forming the ion adsorption layer was adjusted to be about 10 parts by weight based on 100 parts by weight of the graphite felt.

Example 4: Preparation of Carbon Felt Electrodes

By applying Composition 2 on both surfaces of the upper and lower surfaces of the graphite felt with the intermediate ion adsorption layer formed thereon using a coating machine and surface treatment, the material using the composition 1 is present over the upper and lower surfaces and the entire interior of the graphite felt, but carbon The nanotube component completed the formation of an ion adsorption layer existing only on both surfaces of the upper and lower surfaces of the graphite felt to obtain a carbon felt electrode. The total coating amount of the compositions 1 and 2 for forming the ion adsorption layer was adjusted to be about 15 parts by weight based on 100 parts by weight of the graphite felt.

Example 5: Preparation of Carbon Felt Electrodes

On the graphite felt obtained in Comparative Example 2, 0.1 g of conductive carbon black (VULCAN® XC-72, Carbot Corp.), 1 g of carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech Co., Ltd.), phenol resin (product name: TD-2493D, manufacturer: Gangnam Hwaseong) 20 g, glycerin 50 g as an oxygen functional group precursor, 20 g urea as a nitrogen functional group precursor, and 2,000 g of water were mixed and uniformly mixed to obtain Composition 1 for forming an ion adsorption layer using graphite felt first. An intermediate ion adsorption layer using the composition 1 was first formed on the upper surface of the graphite felt by using a spray nozzle and dried in an oven at about 120° C. for about 20 minutes over the upper and lower surfaces of the graphite felt and the entire interior.

Then, 5 g of carbon nanotubes (product name: CNT MR99, manufacturer: Carbon Nanotech), 50 g of phenol resin (product name: TD-2493D, manufacturer: Gangnam Hwaseong), and 2,000 g of water were mixed and uniformly mixed to obtain Composition 2 was applied using a coater on the upper and lower surfaces of the graphite felt on which the intermediate ion adsorption layer was formed, dried in an oven at about 120 ° C. for about 20 minutes, and surface treated in an oven at about 500 ° C. for about 2 hours. The ion adsorption layer material using the composition 1 is present over the upper and lower surfaces and the entire inside of the carbon nanotube component, the ion adsorption layer is present only on both surfaces of the upper and lower surfaces of the graphite felt to obtain a carbon felt electrode. . The total coating amount of the compositions 1 and 2 for forming the ion adsorption layer was adjusted to be about 15 parts by weight based on 100 parts by weight of the graphite felt.

Fabrication of Vanadium Redox Flow Cells

Nafion 117 was used as an ion exchange membrane, and the electrode prepared according to Comparative Example 1 was inserted into a flow frame made of polypropylene. As the current collector plate, gold was plated on the surface of the copper plate, and a carbon composite plate and an anodized aluminum plate were placed at both ends and fastened.

As the electrolyte solution, a mixed aqueous solution of VOSO ₄ and H ₂ SO ₄ was used, and the temperature of the mixed state was VOSO ₄ 1.5MH ₂ SO ₄ 3M to prepare a vanadium redox flow battery.

A vanadium redox flow battery was manufactured in the same manner as above, except that the electrode of Comparative Example 2 was used instead of the electrode of Comparative Example 1.

A vanadium redox flow battery was manufactured in the same manner as above, except that the electrodes prepared in Examples 1 to 5 were used instead of the electrode of Comparative Example 1.

Table 1 summarizes the physical properties of the electrodes or batteries measured for the electrodes of Comparative Examples 1-2 and Examples 1-5 and the vanadium redox flow battery equipped therewith.

Metrics unit comparative example
One comparative example
2 Example
One Example
2 Example
3 Example 4 Example
5 dry electricity
resistance mΩ 2.76 2.66 1.38 1.35 1.46 1.41 1.35 oxygen content atom% 10.4 12.4 17.6 18.5 15.2 12.4 12.6 nitrogen content atom% - 1.3 5.2 4.6 3.7 2.1 2.5 charging capacity Ah 2.23 2.47 2.86 2.69 2.59 2.51 2.54 discharge capacity Ah 2.12 2.37 2.79 2.60 2.47 2.40 2.42 Current Efficiency (Columb Efficiency) % 95.38 96.04 97.55 96.28 95.49 95.61 95.27 Voltage Efficiency % 82.77 84.06 86.67 86.92 85.32 84.21 85.05

Various physical properties shown in Table 1 were evaluated as follows.

Evaluation Example 1: Measurement of Dry Electrical Resistance of Electrodes

The electrodes prepared according to Examples 1-5 and Comparative Examples 1-2 were cut to a certain size, put into an electrical conductivity measuring jig of a universal tester, and under the condition of applying a current of 1.0A/cm2 under a pressure of 20N/cm2, dry the electrode Dry electrical resistance was measured.

Referring to Table 1, a hydrophilic functional group containing oxygen and a hydrophilic functional group containing nitrogen are bonded to the surface of the conductive carbon in the ion adsorption layer and the surface of the carbon fiber constituting the carbon fiber support and including the ion adsorption layer. It can be seen that in the case of the carbon support electrode (Example 1-5), the dry electrical resistance was reduced by 50% or more compared to the electrode of Comparative Example 1-2. The lower the resistance of the electrode, the smaller the charge transfer resistance in the charge/discharge reaction, so that the current may flow more smoothly. The electrons generated at the ion adsorption reaction site flow along the electrode, and since the electrical conductivity is low, it may appear as a leakage of some current during charging and discharging and may cause low voltage efficiency.

Evaluation Example 2: Measurement of content of oxygen functional groups and nitrogen functional groups

In order to measure the content of oxygen functional groups and nitrogen functional groups on the electrode surface in the graphite felt electrodes prepared according to Examples 1-5 and Comparative Examples 1-2, the atomic % of oxygen and nitrogen was evaluated using XPS.

The atomic ratio of C and O and the atomic ratio of C and N in each case were measured using XPS. As a result of the evaluation, it can be seen that the graphite felt electrode of Examples 1-5 has an increased content of oxygen functional groups and nitrogen functional groups compared to Comparative Examples 1-2. In the case of the electrode of Example 1-5, both oxygen and nitrogen contents were high, so it could be confirmed that two types of hydrophilic functional groups were sufficiently introduced, which covered the carbon fiber surface and conductive carbon as well as the carbonized polymer resin surface over the entire area. This is because an oxygen functional group and a nitrogen functional group were formed on the surface.

Evaluation Example 3: Evaluation of charge/discharge capacity, current efficiency and voltage efficiency of a vanadium redox flow battery

Charge and discharge at a current density of 80 mA/cm ² at a flow rate of 1.5 ml/min/cm ² of an electrolyte for a vanadium redox flow battery equipped with a graphite felt electrode prepared according to Examples 1-5 and Comparative Example 1-2 to evaluate the charge/discharge capacity, current efficiency, and voltage efficiency for each electrode.

The current efficiency (charge/discharge efficiency) and voltage efficiency of each battery were calculated by the following Equations 1 and 2, respectively.

[Equation 1]

Current efficiency (%) = (discharge capacity/charge capacity) X 100.

[Equation 2]

Voltage efficiency (%) = (Average discharge voltage/Average charge voltage) X 100.

Referring to Table 1, a hydrophilic functional group containing oxygen and a hydrophilic functional group containing nitrogen are sufficiently bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer including the ion adsorption layer. In the case of a carbon support electrode (Example 1-5) having an ion adsorption layer, Comparative Example 1 and an ion adsorption layer comprising only a hydrophilic functional group containing oxygen and a hydrophilic functional group containing oxygen and nitrogen Compared to the electrode of Comparative Example 2, which contains all hydrophilic functional groups but has insufficient nitrogen functional group content, the dry electrical resistance was significantly reduced, so the current flow became smoother, and thus the charge/discharge capacity, current efficiency, and voltage efficiency were all improved can check that

10: vanadium redox flow battery 20, 40: unit cell
24: electrode 26: separator
30: stack 42, 53: tank
42, 52: pump 60, 62: end plate

Claims (9)

A carbon support electrode for a vanadium redox flow battery, the carbon support electrode comprising:
a porous plate-like carbon fiber support having a first surface and a second surface opposite to each other; and
an ion adsorption layer disposed on at least one surface of the first surface and the second surface of the carbon fiber support, or between the first surface and the second surface of the carbon fiber support. It includes an ion adsorption layer distributed therein,
The ion adsorption layer includes conductive carbon and a binder resin carbide,
A carbon support electrode in which a hydrophilic functional group containing oxygen and a hydrophilic functional group containing nitrogen are bonded to the surface of the carbon fiber constituting the carbon fiber support and the surface of the conductive carbon in the ion adsorption layer. The carbon support electrode according to claim 1, wherein the carbon support is composed of carbon fibers, and is in the form of carbon fiber felt, carbon fiber nonwoven fabric, carbon fiber paper, carbon fiber knitted fabric, and carbon fiber woven fabric. According to claim 1, wherein the oxygen-containing hydrophilic functional group comprises at least one selected from a hydroxyl group, a ketone group, an aldehyde group, and a carboxyl group, and the hydrophilic functional group including nitrogen is a primary amino group, a secondary amino group, a tertiary amino group, A carbon support electrode comprising at least one selected from a pyrrole (-C-NH-C-) group and a pyridine (-C=NC-) group. According to claim 1, wherein the binder resin is phenol resin, epoxy resin, polyester, polyvinyl acetate, polyimide, polystyrene, polyacrylonitrile (PAN), pitch (pitch), polyvinyl alcohol (PVA), cellulose, At least one selected from nanocellulose fibers and acrylic resins,
The conductive carbon has a spherical or needle-like shape with a specific surface area of 40 to 1,600 m ² /g, and when the conductive carbon is a spherical particle, the diameter of the spherical particle is 20 to 50 nm, and when the conductive carbon is a needle-like particle, the A carbon support electrode having a needle-like particle diameter of 30 to 100 nm and a length of 2 to 25 μm. According to claim 4, wherein the conductive carbon is activated carbon, carbon black, acetylene black, Ketjen Black, Denka black, carbon whisker, vapor grown carbon fiber (VGCF: Vapor Grown Carbon Fiber), carbon aerosol, carbon nano A carbon support electrode which is at least one selected from the group consisting of a tube, carbon nanofibers, carbon nanohorn, graphene, natural graphite powder, synthetic graphite powder, and thermally expanded graphite powder. The carbon support electrode according to claim 1, wherein the content of the binder resin carbide is 3 to 30 parts by weight based on 100 parts by weight of the total weight of the ion adsorption layer. The method according to claim 1, wherein the ratio (O:N) of the atomic percentage (atomic %) of oxygen derived from the oxygen-containing functional group to the nitrogen derived from the nitrogen-containing functional group on the surface of the carbon support electrode is 3 :1 to 10:1, and the content of nitrogen derived from the functional group containing nitrogen is 1 atomic% or more. The carbon support electrode according to claim 1, wherein the total content of the ion adsorption layer is 2 to 30 parts by weight based on 100 parts by weight of the total weight of the carbon support electrode. A vanadium redox flow battery comprising a carbon support electrode according to any one of claims 1 to 8.

Images