WO2017171289A1 - Bipolar plate and redox flow cell comprising same - Google Patents

Abstract

The present invention relates to a bipolar plate having a fiber-type conductive material inserted into a flow path, and a redox flow cell comprising the same. The fiber-type conductive material prolongs a residence time of an electrolyte solution in the flow path and increases the chance of a reaction with an electrode layer, whereby it is possible to implement a redox flow cell having improved charging/discharging capacity and efficiency while having excellent energy efficiency regardless of the flow rate of the electrolyte solution.

Description

Bipolar Plates and Redox Flow Cells Comprising the Same

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0038848 filed March 31, 2016 and Korean Patent Application No. 10-2017-0032353 filed March 15, 2017. All content disclosed in the literature is included as part of this specification.

The present invention relates to a bipolar plate suitable for a cell having a high flow rate and a high current density and a redox flow cell comprising the same.

Redox flow battery is an electrochemical power storage device that stores the chemical energy of the electrolyte directly as electrical energy as a system in which the active material in the electrolyte is redoxed and charged and discharged, unlike the existing secondary battery. Such batteries have the advantage of being easy for large capacity power storage, having high energy density and efficiency, and having a long life and safety. In addition, the battery does not require frequent replacement, low maintenance costs, operating at room temperature, and in particular have the advantage that can be designed in a variety of capacity and output, it is in the spotlight as the next generation mass storage device.

The basic structure of the redox flow battery includes a stack including a structure of a bipolar plate / electrode / ion exchange membrane / electrode / bipolar plate, an electrolyte tank containing active materials having different oxidation states, and a pump for circulating the same. .

The actual electrochemical reaction takes place in the stack and works by continuously circulating the electrolyte inside the stack using a pump. Redox pairs used as active materials in the electrolyte include V / V, Zn / Br, Fe / Cr, and Zn / air. Among them, V / V and Zn / Br redox pairs are most widely used.

The electrochemical reaction is determined by the interaction between the electrode and the electrolyte flowing along the bipolar plate in the stack.

1 is a cross-sectional view showing a contact between a bipolar plate and the electrode according to the prior art, the bipolar plate 11 / electrode 12 / ion exchange membrane 13 / electrode 14 / bipolar plate 15 is stacked from above Has a structure. This structure is a method of flowing the electrolyte solution directly to the bipolar plates (11, 15), there is an advantage that the structure is simple. However, when charging / discharging at high power conditions or increasing the size of the battery, the electrolyte is accompanied by a high flow rate, thereby causing a high differential pressure between the electrolyte inlet and the outlet, thereby causing a large energy loss.

In an attempt to solve the above problem, a structure in which a flow path through which an electrolyte can flow is provided in a bipolar plate has been proposed.

US Patent Publication No. 2012-0244395 proposes a configuration of a bipolar plate in which an interdigitated type or interdigitated flow path is formed.

2 is a cross-sectional view showing the contact between the bipolar plate and the electrode shown in US Patent Publication No. 2012-0244395, bipolar plate 21 / electrode 22 / ion exchange membrane 23 / electrode 24 / bipolar plate from above 25 has a stacked structure, and flow paths 27 and 29 are formed in the bipolar plates 21 and 25, respectively. In the case of using the bipolar plate having such a structure, the pressure difference between the inlet and the outlet applied to the battery module is reduced to some extent.

However, in the battery of FIG. 2, a problem arises in that the contact area between the electrode and the electrolyte is reduced due to the flow path structure of the battery of FIG. 1. As a result, the electrochemical reaction for generating electricity does not occur sufficiently, thereby causing a problem that the charge / discharge capacity and speed of the battery are reduced.

In addition, even if the flow path structure to reduce the internal differential pressure, there is a limit to the stable control of the flow rate of the electrolyte in all ranges, and the problem of not having sufficient reaction time due to the short residence time of the electrolyte in the flow path Occurred.

Therefore, there is an increasing demand for a redox flow battery capable of securing sufficient reaction time and improving charge / discharge capacity and efficiency while minimizing energy loss regardless of flow rate when the electrolyte passes through the flow path.

[Preceding technical literature]

[Patent Documents]

United States Patent Publication No. 2012-0244395 (2012.09.27), FLOW BATTERY WITH INTERDIGITATED FLOW FIELD

The present inventors extend the residence time of the electrolyte flowing through the flow path of the bipolar plate to increase the contact between the electrolyte and the electrode, thereby increasing the chance of the electrochemical reaction, while reducing the pressure difference between the inlet and the outlet of the electrolyte in the bipolar plate. A new bipolar plate with a conductive material was designed and applied to the redox flow battery, and it was confirmed that the resistance value per unit area was lowered while increasing the charge / discharge capacity and energy efficiency.

Accordingly, an object of the present invention is to provide a bipolar plate having a novel structure.

Another object of the present invention is to provide a unit cell for a redox flow battery having the bipolar plate.

In addition, another object of the present invention is to provide a redox flow battery having a plurality of the unit cells to target a high flow rate and a high current density.

The present invention to achieve the above object is a plate-shaped body; And a flow path formed to move the electrolyte in the center of the body, wherein the bipolar plate for a redox flow battery is characterized in that a fibrous conductive material is inserted into the flow path.

At this time, the parallel (parallel), serpentine (serpentine), semi-serpentine (semi-serpentine), zigzag (zigzag), interdigitated (interdigitated) and pin (pin) pattern is formed by including one or more types It is done.

The fibrous conductive material is characterized in that at least one type of fabric selected from the group consisting of carbon felt, graphite felt, carbon cloth, carbon paper, metal cloth, metal felt and foamed metal.

In addition, the present invention is an ion exchange membrane; Electrode layers disposed on both sides of the ion exchange membrane; And a bipolar plate disposed on one side of the electrode layer, wherein the bipolar plate provides a unit cell for a redox flow battery, which is the bipolar plate described above.

In addition, the present invention is a battery module formed by electrically connecting a unit module including a unit stack for generating a current to the side of each other; An electrolyte tank for supplying an electrolyte solution to the battery module and storing an electrolyte solution flowing out of the module; And an electrolyte pump for circulating the electrolyte between the module and the electrolyte tank, wherein the unit stack provides a redox flow battery in which a plurality of unit cells for the redox flow battery are connected.

The redox flow battery according to the present invention includes a bipolar plate in which a fibrous conductive material is inserted in the flow path, thereby extending the residence time in the electrolyte flow path, thereby increasing the chance of the electrochemical reaction between the electrode and the electrolyte, thereby charging and discharging the redox flow battery. The capacity and energy efficiency increase, while reducing the overvoltage, which lowers the resistance value per unit area.

Such a battery can be applied to various industrial fields as a redox flow battery targeting high flow rate and high current density.

1 is a cross-sectional view showing a contact between a bipolar plate and the electrode according to the prior art.

FIG. 2 is a cross-sectional view showing contact between a bipolar plate and an electrode disclosed in US Patent Publication No. 2012-0244395.

3 is a schematic diagram showing the structure of a redox flow battery according to the present invention.

4 is a three-dimensional perspective view showing a unit stack according to the present invention.

5 is a front view showing a bipolar plate according to the present invention.

6 is a three-dimensional perspective view showing the insertion of a fibrous conductive material into the flow path of the bipolar plate according to the present invention.

7 is a schematic diagram showing various types of flow paths according to an embodiment of the present invention.

8 is a photograph of a bipolar plate manufactured in Example 1. FIG.

9 is a photograph of a bipolar plate prepared in Comparative Example 1.

10 is a graph showing charge and discharge capacities of batteries manufactured in Example 1 and Comparative Example 1. FIG.

11 is a graph showing the energy efficiency of the batteries produced in Example 1 and Comparative Example 1.

The present invention proposes a redox flow battery having excellent energy efficiency and high charge / discharge capacity.

Hereinafter will be described in more detail with reference to the drawings.

3 is a schematic view showing a redox flow battery according to an embodiment of the present invention, Figure 4 is a three-dimensional perspective view showing a unit stack.

Referring to FIG. 3, the redox flow battery 1000 is formed by arranging and electrically connecting unit modules 101, 102, 103, and 104 including unit stacks that generate current to each other. ; An electrolyte tank (202, 204) for supplying an electrolyte solution to the battery module (100) and storing an electrolyte solution flowing out of the battery module (100); Electrolyte pumps 302 and 304 for circulating the electrolyte between the battery module 100 and the electrolyte tanks 202 and 204 are included.

In this case, the unit stack is formed by stacking a plurality of unit cells 130. For convenience, FIG. 4 illustrates a unit stack formed by stacking one unit cell 130.

Referring to FIG. 4, an ion exchange membrane plate 123 is disposed at the center of the unit cell 130, and electrode plates 120 and 121 and bipolar plates 118 and 119 are symmetrically disposed on both sides thereof, respectively.

 The unit cell 130 has a structure in which a plurality of unit cells 130 are stacked, and current collector plates 115 and 117 and end plates 111 and 113 are stacked to contact the bipolar plates 118 and 119.

Each of the above components is provided with unit cells 130 by joining each other using a connecting member (eg, bolt / nut) through a through hole after drilling each side, and arranging a plurality of unit cells 130. The unit stack is then formed through electrical connections.

Spacers (not shown) may be interposed between the ion exchange membrane plates 123, the electrode plates 120 and 121, the bipolar plates 118 and 119, the current collector plates 115 and 117, and the end plates 111 and 113 for the flow or coupling of the electrolyte. For example, it is preferable to arrange the ion exchange membrane plate 123 between the electrode plates 120 and 121.

A plurality of unit cells 130 has a structure connected in series or in parallel as shown in FIG. 3, and configured to generate a current in the circulation of the electrolyte. The unit stack is electrically connected to another neighboring unit stack through a bus bar (not shown). The unit modules 101, 102, 103, 104 and the battery module 100 discharge current generated inside the unit stacks or are connected to an external power source.

In the structure of the unit cell 130, the ion exchange membrane plate 123 has a plate-shaped body and a structure in which an ion exchange membrane is mounted at the center thereof. In addition, the electrode plates 120 and 121 have a plate-shaped body and a structure in which an electrode layer is mounted at the center thereof. The bipolar plates 118 and 119 have a plate-shaped body and a structure in which a flow path is mounted at the center thereof.

In the present invention, the configuration of the bipolar plates 118 and 119 constituting the unit cell is changed to improve the battery characteristics of the redox flow battery 1000.

The bipolar plates 118 and 119 in contact with the electrode plates 120 and 121 are supplied with electrolyte from the electrolyte tanks 202 and 204 for the electrochemical reaction, and are supplied to the electrode plates 120 and 121 in a uniform pressure and amount.

5 is a front view showing a bipolar plate.

In detail, the bipolar plates 118 and 119 include a plate-shaped body 152 and a flow path F formed to move the electrolyte in the electrolyte reaction part R, which is an area where the electrode layer and the electrolyte contact.

The body 152 of the bipolar plates 118 and 119 may be made of a conductive or nonconductive material and is not particularly limited in the present invention. The conductive material can be coated with a carbon material such as metal or graphite, or a conductive polymer, and the non-conductive material can be ethylene-tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), or fluorinated FEP (non-conductive material). Fluorine resins such as ethyleneepropylene polymer, ECTFE (Ethylene ChloroTriFluoroEthylene), and PVDF (Polyvinylidene fluoride) may be coated.

The bipolar plates 118 and 119 may have an inlet 161 for introducing the electrolyte to supply the electrolyte to the electrode plates 120 and 121 on one side of the body 152, an outlet 162 for discharging the electrolyte to the bottom of one side, and an electrode. Electrolyte reaction part (R) in contact with the plate (120, 121), the supply port 171 for equal distribution of the electrolyte is located between the outlet 161 and the electrolyte reaction part (R), and the outlet 162 and the electrolyte solution Located between the reaction unit (R) includes a discharge passage 172 for equal distribution of the electrolyte.

Connection members 181, 182, 183 and 184 are disposed at one end of the body 162 to be physically bonded to the electrode plate.

In addition, the supply passage 171 and the discharge passage 172 may have various forms so as to distribute or evenly distribute the flow rate of the electrolyte, and may have a distribution passage form having a plurality of branches, for example.

The flow of electrolyte in the redox flow battery 1000 is very important. The electrolyte transferred through the electrolyte pumps 302 and 304 is moved to the bipolar plates 118 and 119 having the flow path F, and then contacted with the electrode plates 120 and 121 having the electrode layers causing redox. At this time, if the flow rate characteristics of the electrolyte is not uniform, the difference in speed in the electrode layer, or overvoltage due to the portion that cannot react. When an overvoltage occurs, the temperature inside the stack rises, and when vanadium-based electrolyte is used, precipitation occurs to block the flow path. V ₂ O ₅ precipitated in solid state  (Vanadium oxide) reduces the flow path of the electrolyte passage, or reduces the reaction site with the electrolyte, thereby lowering battery efficiency. In addition, clogging due to precipitation causes leakage by increasing the internal pressure to expand the gasket portion of the unit stack connected in series. As a result, these problems can lead to malfunctions and shutdowns that can cause problems for the entire system.

Accordingly, it can be seen that the redox flow battery 1000 has a performance and lifespan of the unit stack depending on the flow rate characteristics of the electrolyte solution. Although it was used, there was a disadvantage that the installation is not easy due to the increase in peripheral equipment and volume accordingly.

In the present invention, the fibrous conductive material 151 is inserted into the flow path in the bipolar plates 118 and 119.

5A and 5B, the partition wall 154 is disposed on the bodies 151 of the bipolar plates 118 and 119 to form a flow path F, and the fibrous conductive material ( 3D is a perspective view showing the insertion of 151.

By inserting the fibrous conductive material 151 as shown in FIG. 5 (b), the residence time of the electrolyte passing through the flow path F is increased, thereby sufficiently securing the electrode reaction time, and thus the redox flow battery 1000 has a charge / discharge capacity. In addition, the differential pressure of the electrolyte solution at the inlet / outlet of the bipolar plates 118 and 119 can be dramatically reduced.

When the fibrous conductive material 151 is installed in the supply passage 171 or the discharge passage 172, the fibrous conductive material 151 may affect the fluid flow of the electrolyte, thereby increasing the pressure difference between the inlet 161 and the outlet 162. It is installed in electrolyte solution part R which contact | connects a plate.

The fibrous conductive material 151 or conductive fiber refers to a plurality of fiber structures forming a three-dimensional porous network structure. The material of the fibrous conductive material 151 inserted into the flow path F may have any porosity and may be any material as long as it is conductive. Preferably, the same or similar material used in the electrode layers of the electrode plates 120 and 121 may be used to increase the reaction between the electrolyte and the electrode layers of the electrode plates 120 and 121 without blocking the flow of the electrolyte.

More preferably, the fibrous conductive material 151 of the present invention means having a structure in which carbon fibers or metal fibers are stacked to form an aggregate.

The fibrous conductive material 151 is characterized in that at least one type of fabric selected from the group consisting of carbon felt, graphite felt, carbon cloth, carbon paper, metal cloth, metal felt and foamed metal.

The 'carbon felt or graphite felt' means that the fiber produced by spinning the carbon or graphite material to form an irregular aggregate (mat shape) in the form of a plate.

The 'carbon cloth' means that the carbon fibers produced through the spinning process to form a three-dimensional regular aggregate through the weaving.

The 'carbon paper' means that the carbon fibers are aggregated to form a paper-like aggregate.

The 'metal cloth' means that the metal fibers produced through spinning and the like form a three-dimensionally regular aggregate through weaving.

The 'foam metal' refers to a three-dimensional structure in which a metal material has a large number of air bubble gratings therein through a foaming process.

The metal cloth and the foamed metal may include Na, Al, Mg, Li, Ti, Zr, Cr, Mn, Co, Cu, Zn, Ru, Pd, Rd, Pt, Ag, Au, W, Ni, and Fe. It can be used including one or more metals selected from the group.

The fibrous conductive material 151 has a high rigidity by having a three-dimensional mesh structure in which fibers are regularly or irregularly bonded in the case of felt, and has a large number of pores without being easily deformed, thereby allowing the electrolyte to move smoothly. have. The fibrous conductive material 151 has a complex micropores, mesopores, macropores, etc. in the structure, the control of these pores may vary depending on the manufacturing method.

In the case of conductive particles such as carbon black, it is difficult to fix in the flow path (F), and even if fixed, movement occurs easily during operation of the battery, and thus it is difficult to control the flow rate of the electrolyte. In addition, in the case of the metal mesh, there is a fear that turbulence may occur during the flow of the electrolyte, thereby causing a problem that the pressure difference in the battery increases. Therefore, the use of the fibrous conductive material 151 may be most preferable.

In order to prevent the fibrous conductive material 151 from disturbing the flowability of the electrolyte, it is necessary to control the parameters for physical properties. As a parameter related to the flowability of the electrolyte, various factors may be considered. First, the porosity of the fibrous conductive material 151 and the bulk density associated with it may be mentioned.

If the porosity is too low or too high, the flow of the electrolyte is delayed by the filling of the fibrous conductive material 151, thereby increasing the differential pressure measured at the inlet 161 and the outlet 162 of the electrolyte, and the load on the battery due to the overvoltage. It may cause a drop in battery performance. The porosity (or porosity) is a parameter related to the fabric density, and when the bulk density is too high, it can prevent the fluid flow of the electrolyte and increase the differential pressure in the battery. ) The residence time of the electrolyte in the interior cannot be sufficiently increased.

Preferably, the porosity of the fibrous conductive material 151 is preferably 10 to 99%, preferably 50 to 95%, and the bulk density is 0.05 to 0.2 g / cm ³ , preferably ³ mm thick. To 0.1 to 0.15 g / cm ³ is used.

At this time, the diameter of each fiber constituting the fibrous conductive material 151 may have a 0.5 to 50㎛, preferably 0.1 to 30㎛, the average diameter of the fibrous conductive material 151 is 0.01 to 900㎛, Preferably it may have a range of 0.05 to 500㎛.

As the material of the fibrous conductive material 151 of the present invention, a material including a carbon material, a metal material, or a combination thereof may be used, and preferably, carbon felt is used. The carbon felt and the graphite felt have characteristics of chemical resistance, stability over a wide voltage range, and high strength. The metal cloth or the foamed metal may increase the electrochemical reaction rate due to high conductivity.

The fibrous conductive material 151 may be manufactured directly or be manufactured by customizing a commercially available product suitable for the flow path F of the bipolar plates 118 and 119.

In one example, the carbon felt may be prepared by carbonizing the carbon fiber precursor felt. The carbon fiber precursor felt can be made of rayon fiber, polyacrylonitrile fiber, or the like, and carbonization and graphitization are carried out in a nitrogen atmosphere or a vacuum atmosphere. The carbon fiber precursor felt is decomposed and removed except for carbon by carbonization and graphitization processes, and only carbon remains to produce carbon felt.

The fibrous conductive material 151 of the present invention may perform surface treatment or further add an additional material to the fibrous conductive material 151 in order to increase conductivity or promote a redox reaction to the felt material.

Since the surface of the carbon felt is hydrophobic, it may be very important to remove the surface polymer, introduce oxygen functional groups, and improve hydrophilicity so that the electrolyte solution and the electrode can easily react. The carbon material has different electrochemical performance when other anions are introduced, and in particular, nitrogen element increases electrochemical properties such as oxidation / reduction reaction.

In one example, the surface treatment is a heat treatment of about 1 to 15 hours at about 300 to 450 ℃ or in an ozone or air atmosphere to produce a functional group on the surface to improve the affinity with the electrolyte solution, 140 to 600 ℃ Heat treatment at temperature for 4 minutes to 7 hours to introduce oxygen functional groups such as carboxyl group, carbonyl group, or hydroxyl group on the surface, or nitrogen precursor under an inert gas atmosphere and heat treatment for 10 to 60 minutes at a temperature of 800 to 1000 ° C. It can be used by introducing a nitrogen functional group on the surface.

In addition, the addition of the additional material may consist of carbon-based conductive material and / or metal particles.

The carbon-based conductive material may be carbon paper, carbon fiber, carbon black, acetylene black, activated carbon, fullerene, carbon nanotubes, carbon nanowires, carbon nano-horns, and carbon nano rings. one or more selected from the group consisting of rings).

The metal particles are at least one selected from the group consisting of Na, Al, Mg, Li, Ti, Zr, Cr, Mn, Co, Cu, Zn, Ru, Pd, Rd, Pt, Ag, Au, W, Ni and Fe This is possible. They may use particles of several nanometers to several hundred microns for the catalytic effect of the electrochemical reaction, preferably those having a nanoscale particle size.

The additional material may be used at a level that does not prevent the flow of the electrolyte, and may be used in an amount of 10 wt% or less in the fibrous conductive material 151.

These surface treatments or additional materials can be used individually or in combination, which results in smoother redox reactions, increased electron transfer rates and redox reversibility by redox, and consequently redox flow cells (1000). Improve performance).

The flow path F is formed through the partition wall 154, and the width and thickness of the partition wall 154 may be appropriately adjusted according to the sizes of the bipolar plates 118 and 119. Referring to FIG. 5, the distance between the partition walls 154 is defined as the flow channel width, and the thickness of the partition walls 154 is defined as the depth of the flow channel.

The cross section of the partition wall 154 may have various shapes such as a rectangle, a square, a triangle, a trench structure, a hemisphere, a polygon, and the like, and generally have a rectangular shape for the flow of the electrolyte.

Generally, when the bipolar plates 118 and 119 having a width * length (5 to 10 cm ² ) are manufactured, the partition wall 154 has a width of 3.0 to 8.0 mm, a thickness of 1 to 3.5 mm, a flow channel width of 3.0 to 8.0 mm, The depth of the flow channel is between 1 and 3.5 mm.

In this case, the filling of the fibrous conductive material 151 may be filled at a volume of 10 to 100%, preferably 50 to 95%, based on the flow volume (flow channel width * flow channel depth * length of the partition wall).

In addition, when the filling thickness is adjusted, the depth (X) of the flow channel is compared with the thickness (Y) of the fibrous conductive material 151 such that 1 <Y / X≤2.5, preferably 1 <Y / X≤1.5. After the fibrous conductive material 151 is inserted and disposed, a predetermined pressure is applied to fix the fibrous conductive material 151 inside the flow path (F). At this time, the fibrous conductive material 151 finally fixed after the application of pressure has a thickness (Y) equal to the maximum flow channel depth (X) to be horizontal or formed slightly higher or lower than this (0.8≤Y / X≤ 1.2), taking into account the flow of the electrolyte, it can be formed to satisfy the formula 0.8≤Y / X≤1.0.

At this time, in order to increase the flowability of the battery in the flow path (F) it is necessary to adjust the interval between the flow path (F) and the inner width of the flow path (F).

When the width in the horizontal direction of the electrolyte reaction unit R is W1 and the width in the horizontal direction of the flow channel is W2, W1: W2 has a ratio of 1:10 to 10: 1. In more detail, when the number of flow paths is the same, when the spacing between the flow paths F is too dense and the flow channel width W2 is wide, there is almost no effect difference with the flow path-free bipolar plates 118 and 119. It is difficult to control the generated internal differential pressure. On the contrary, when the width W1 is too wide and the flow channel channel width W2 is narrow, a sufficient amount of electrolyte is difficult to flow into the flow path F, resulting in low battery efficiency.

If the filling volume and the filling thickness are not controlled, the fluid flow of the electrolyte may be affected, and the differential pressure may occur or the resistance value per unit area may be increased, thereby reducing the charge / discharge current density. It is preferable to manufacture the bipolar plates (118, 119) by adjusting the filling degree of (151).

Meanwhile, the flow paths F of the bipolar plates 118 and 119 of the present invention may include various flow path shapes, as illustrated in FIG. 6.

The shape of the flow path (F) can be used in various forms known in the art related to the fluid flow, for example, various forms are possible as shown in FIG.

Referring to Figure 7, the flow path (F) is (a) parallel (parallel), (b) serpentine, (c) ~ (d) semi-serpentine, (e) interlocking type ( Various forms such as interdigitated, (f) zigzag, and (h) to (i) pins are possible, and the start and end of the flow path may be open or closed.

According to a preferred embodiment of the present invention, the flow paths F of the bipolar plates 118 and 119 may have an interdigitated or pod shaped shape.

The interlocking flow path structure refers to a structure in which flow paths F engaged with each other are continuously disposed, and each flow path F has a closed surface, and the inlet or outlet of the flow path F is alternately opened. . In the interlocking flow channel structure, not only the electrolyte flows along the flow path but also flows through the flow path F, thereby increasing the chance of the electrode reaction, thereby increasing the charge / discharge capacity of the redox flow battery 1000.

However, in such an interlocking flow channel structure, only a part of the electrolyte flowing into the flow path F reacts with the electrode layers 32a and 32b, and thus there is a limit in obtaining the maximum reaction efficiency compared to the unit amount of the electrolyte. In particular, even when the electrolyte is provided at a high flow rate due to the high output or high density of the battery, it is difficult to sufficiently secure the residence time in the flow path F of the electrolyte.

As shown in the present invention, when the fibrous conductive material 151 is filled in the flow path F, the electrolyte does not flow along the flow path, but contacts the fibrous conductive material 151 inserted in the flow path and the bipolar plate ( Through the electrode layers in contact with the 118 and 119, it is transferred to the next adjacent flow path F beyond one flow path F. That is, the electrolyte solution does not simply flow, but stays in the flow path F, and sufficiently reacts with the fibrous conductive material 151, and reacts with the electrode layers in contact with the bipolar plates 118 and 119, while slowly reacting with one flow path F. ) Is transported through the process of passing over to another adjacent flow path (F) several times.

In this structure, the fibrous conductive material 151 inserted into the flow path F may cause an efficient electrode reaction even with the same amount of electrolyte and control the transport speed (flowability) of the electrolyte. This is because the electrolyte does not pass through the flow path (F), but contacts the fibrous conductive material 151 and stays for a predetermined time and diffuses in multiple directions, and the residence time of the electrolyte is long and the reaction surface area is widened, thereby increasing the chance of electrode reaction. Because it will increase.

In addition, an increase in the reaction area leads to a decrease in the overvoltage applied to the electrolyte reaction, resulting in an effect of increasing the efficiency of the battery. In such a structure, the pressure difference generated at the electrolyte inlet / outlet of the bipolar plates 118 and 119 can be reduced in the case of the flow battery in which the electrolyte is transferred at a high flow rate.

As a result, when the bipolar plates 118 and 119 having the interlocking flow path structure in which the fibrous conductive material 151 is inserted according to the embodiment of the present invention, the area of the electrochemical reaction is reduced by the fluid flow of the electrolyte. This can increase the resistance value per unit area. Therefore, even if a large capacity battery is implemented, it is possible to implement a battery having improved energy efficiency with high charge and discharge capacity and current efficiency.

The bipolar plates 118 and 119 having the above-described configuration are bonded to the electrode plates 120 and 121 and the ion exchange membrane plate 123 to form a unit cell.

The ion exchange membrane plate 123 has a plate-shaped body and an ion exchange membrane is inserted in the center thereof, and the electrode plates 120 and 121 have a structure in which an electrode layer is inserted in the center thereof together with the plate-shaped body.

The ion exchange membrane of the ion exchange membrane plate 123 is called an ion permeable membrane or a separator, and is configured to pass ions in the electrolyte, and conducts electricity through an electrochemical reaction of the electrode layers of the electrode plates 120 and 121 located at both sides through the electrolyte. Occurs. At this time, the material, thickness and each component of the ion exchange membrane is not particularly limited in the present invention, a known one can be used.

In addition, the electrode plates 120 and 121 positioned between the ion exchange membrane plate 123 and the bipolar plates 118 and 119 function as one of the electrode plates 120 and 121 as the anode and the other as the cathode according to the composition of the electrolyte. The electrode plates 120 and 121 are provided with an electrode layer (or electrode layer) for electrochemical reaction in the body, and a material having conductivity as known in the electrode layer is used. For example, the electrode layer may be one kind of conductive material selected from the group consisting of carbon felt, graphite felt, carbon cloth, carbon paper, metal cloth, metal felt, and foamed metal.

The electrode layer may be the same as or similar to the fibrous conductive material 151 described in the bipolar plates 118 and 119. That is, according to the composition and physical properties (eg, porosity, bulk density) as referred to as the fibrous conductive material 151.

Preferably, for the electrochemical reaction, the same materials as the fibrous conductive material 151 and the electrode layer filled in the bipolar plates 118 and 119 are used, and more preferably both sides use carbon felt.

In addition, the fibrous conductive material 151 and the electrode layer may have the same or similar porosity. Preferably, the porosity of the electrode layer is controlled to be larger than that of the fibrous conductive material 151 in the bipolar plates 118 and 119. Can be used. In this case, a maximum contact area for the reaction may be provided to sufficiently infiltrate the electrolyte into the fibrous conductive material 151 having many voids and remain in the flow path F, and the electrolyte in the flow path F until the reaction proceeds sufficiently. It may include, it is possible to finer pressure differential adjustment.

In addition, the electrode layer of this invention can use what has a gradient form as needed. Such a gradient may solve the nonuniformity of the reaction due to the pressure gradient inevitably occurring at the inlet 161 and the outlet 162 of the bipolar plates 118 and 119, a decrease in the current density, and an increase in the local resistance in the flow path F. .

According to one embodiment, the coating or impregnation to have a concentration gradient when using a material formed to have a porosity gradient or a pore size gradient in consideration of the fluid flow of the electrolyte, or when using additional materials such as metal particles Can be used.

The gradient may be made in the same direction with respect to the vertical direction of the inlet 161 and the outlet 162 of the bipolar plates 118 and 119 or in a direction orthogonal to or perpendicular to this direction. Preferably it may be made in a direction perpendicular to the inlet 161.

In addition, the gradient may be made in the same direction with respect to the longitudinal direction of the flow path (F) of the bipolar plates (118, 119) or in a direction orthogonal or a predetermined angle thereof. Preferably it may be made in the same direction with respect to the longitudinal direction of the flow path (F).

According to another embodiment of the present invention, while maintaining the porosity of the electrode layer on the side in contact with the inlet 161 and the outlet 162 of the bipolar plates (118,119) to have a lower porosity toward the center, the residence time of the electrolyte solution Can increase.

According to another embodiment of the present invention, the outlet 162 side is designed to have a step or progressively higher porosity than the inlet 161 of the bipolar plates 118 and 119 to enable relatively fast diffusion and electrolyte movement in various directions. As a result, the electrolyte solution can be flow balanced without excessively stagnating in the flow path (F).

According to another embodiment of the present invention, while lowering the content of the metal catalyst present in the electrode layer on the side in contact with the inlet 161 and the outlet 162 of the bipolar plates (118,119), the electrochemical in the electrode layer is increased to the center portion The reaction can be further promoted.

According to another embodiment of the present invention, while increasing the porosity of the electrode layer on the side in contact with the outlet 162 than the inlet 161 of the bipolar plates (118,119) while increasing the content of the metal catalyst to control the flow rate of the electrolyte It may further promote the electrochemical reaction.

Along with the concentration gradient, the electrode layer of the present invention may be composed of a single layer of one material or a combination of different materials. For example, after distributing the electrode layer into a plurality of areas, materials of the electrode layer corresponding to each area may be used differently.

In addition, the electrode layer of the present invention may be formed of a single layer or may be formed of two or more layers using one material or different materials. In the case of forming the plural layers, the materials, the porosity, and the content of additional materials such as metal catalysts may be formed by the same or different.

The choice of these configurations and materials. The present invention is not particularly limited and may vary depending on a required charge / discharge capacity of the battery and purpose of use.

In addition, the area of the electrode layer of the present invention may be the same as or different from the area of the electrolyte reaction portion (A) of the bipolar plates (118, 119), so as to sufficiently react with the electrolyte.

In the redox flow battery unit cell according to the preferred embodiment of the present invention, the bipolar plates 118 and 119 have an interlocking flow path F filled with carbon felt therein, and the carbon chemical reaction part of the electrode plate has carbon felt or Use carbon paper.

In this case, the carbon felt filled in the bipolar plates 118 and 119 and the carbon felt of the electrode plate are preferably made of the same material, and in this case, each carbon felt may be selected to have a different porosity.

More preferably, the porosity of the carbon felt of the electrode plate may be adjusted to be larger than that of the carbon felt in the bipolar plates 118 and 119. In this case, a maximum contact area for the reaction may be provided to sufficiently infiltrate the electrolyte into the fibrous conductive material 151 having many voids and remain in the flow path F, and the electrolyte in the flow path F until the reaction proceeds sufficiently. It may include, it is possible to finer pressure differential adjustment.

According to another embodiment of the present invention, the carbon felt may be filled by setting the porosity from the top to the bottom or from the left to the right with respect to the vertical direction of the body of the bipolar plates 118 and 119. . That is, by designing the upper side to have a lower porosity than the lower side and these porosities are gradually or gradually higher porosity toward the lower portion of the vertical direction to enable relatively fast diffusion and movement of electrolyte in multiple directions, It is possible to balance the flow of the electrolyte without excessive stagnation in the flow path (F).

On the other hand, other components constituting the redox flow battery 1000 according to the present invention, in particular, the various components for constituting the battery module 100, components such as the electrolyte tank 202,204, and the electrolyte pump 302,304 It does not specifically limit in this invention, It follows the content of well-known.

The electrolyte stored in the electrolyte tanks 202 and 204 is not particularly limited in the present invention, and electrolytes known in the art may be used.

The electrolytic solution includes an active material and a solvent, wherein the active material includes a 'redox' coupler organic material that reacts electrochemically stably, and the solvent may be an aqueous solvent, an organic solvent, or a mixture thereof.

The electrolyte may be an anode electrolyte for the function of the anode or a cathode electrolyte for the function of the cathode, which includes a redox pair configuration. That is, in the case of the positive electrode active material, it refers to a redox pair dissolved in the positive electrolyte, and means that the redox pair is charged when the redox pair is changed to a higher one of two oxidation states, that is, oxidation occurs. In the case of the negative electrode active material, it refers to a redox pair dissolved in the negative electrode electrolyte solution, which means that it is charged to the lower side of two oxidation states of the redox pair, that is, when reduced.

The active material used in the present invention is not particularly limited, and an active material commonly used in the art may be used. For example, V, Fe, Cr, Cu, Ti, Sn, Zn, Br, etc. are mentioned. Such active materials can be obtained by a variety of redox pairs such as V / V, Zn / Br, Fe / Cr by a combination of oxidation and reduction differences. In the present invention, redox pairs made of V / V are used. Thus, using the same type of redox pair in the positive electrode and the negative electrode has the advantage of overcoming irreversible contamination due to the mixing phenomenon between the two electrodes, for example, the positive electrode electrolyte is V ^{4 +} / V ^{5 +} used, and the negative electrolyte can be used for V ²⁺ / V3 ⁺ as the redox pair.

The aqueous solvent is one or a mixture of two or more selected from sulfuric acid, hydrochloric acid or phosphoric acid, and the organic solvent is acetonitrile, dimethyl carbonate, diethyl carbonate, dimethyl sulfoxide, dimethylformamide, propylene carbonate, ethylene carbonate, N-methyl-2-pyrrolidone, fluoroethylene carbonate, ethanol, methanol and gamma-butyrolactone may be one or a mixture of two or more thereof.

In addition, the electrolyte may further include a supporting electrolyte.

The supporting electrolyte may be selected from the group consisting of alkylammonium salts, lithium salts and sodium salts. In the redox flow battery electrolyte according to the present invention, the alkyl ammonium _{^{salt, PF 6 -, BF 4 -}} , AsF 6 -, ClO 4 -, CF 3 SO 3 -, CF 3 SO 3 -, C (SO ₂ CF ₃ ) ₃ , N (CF ₃ SO ₂ ) ₂ and CH (CF ₃ SO ₂ ) _{2 A combination} of an anion selected from a tetraalkylammonium cation, wherein alkyl is methyl, ethyl, butyl or propyl in the tetraalkylammonium cation Can be made. In the redox flow battery electrolyte according to the present invention, the lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN ( It may be at least one selected from CF ₃ SO ₂ ) ₂ and LiCH (CF ₃ SO ₂ ) ₂ . In the redox flow battery electrolyte according to the present invention, the sodium salt is NaPF ₆ , NaBF ₄ , NaAsF ₆ , NaClO ₄ , NaCF ₃ SO ₃ , NaCF ₃ SO ₃ , NaC (SO ₂ CF ₃ ) ₃ , NaN ( It may be at least one selected from CF ₃ SO ₂ ) ₂ and NaCH (CF ₃ SO ₂ ) ₂ .

The electrolyte pumps 302 and 304 are not specifically mentioned in the present invention, and those known in the art may be used.

The redox flow battery 1000 according to the present invention having the above-described configuration includes the bipolar plates 118 and 119 as described above as components of the unit cell, thereby providing substantial charge / discharge opportunities for the electrolyte in the flow path F. FIG. To increase. In addition, it is possible to stay in the time flow path (F) sufficient for the reaction, and in particular, it is possible to reduce the internal differential pressure more effectively than conventionally with respect to the electrolyte flowing into the high flow rate. In addition, it is possible to increase the reaction area to reduce the overvoltage applied to the reaction of the electrolyte, resulting in an effect of increasing the battery efficiency.

The redox flow battery 1000 is capable of maximizing charge / discharge capacity and efficiency while minimizing energy loss regardless of the flow rate of the electrolyte and the battery output, and thus, the redox flow battery 1000 that targets a high flow rate and a high current density. Is preferably applied. For this reason, it can be usefully used in various fields of various industries such as various industrial facilities, electronic products and automobiles.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example  One

(One) Bipolar  Plate making

As shown in FIG. 8, a bipolar plate having a fibrous conductive material inserted therein was produced.

Referring to FIG. 8, the bipolar plate formed a body having a width of 82 * 82 mm and an engaging flow path therein. At this time, the width of the partition wall for forming the flow path is 5.0 mm, the flow channel channel width is 4.0 mm, the depth of the flow channel has a 2.5 mm.

As a fibrous conductive material, a carbon felt (95 mm thick) having a porosity of 95% was purchased and used to cut it to fit the flow channel channel width.

Subsequently, the fibrous conductive material was mounted in the flow path and then inserted into the flow path by applying pressure. At this time, pressure was applied until the thickness of the fibrous conductive material was equal to the depth of the flow channel.

(2) Unit cell  making

The bipolar plate produced in the above (1) was configured to produce a unit cell.

After placing the electrode layers (900 µm) formed by stacking three sheets of carbon paper (300 µm each) on both sides with an ion exchange membrane ( Nafion 115, 75 µm) in between, and placing a bipolar plate on each outside Using a 0.5 g gasket, these were fastened to produce a redox flow battery.

An electrolyte was injected into each of the inlet and the outlet of the bipolar plate. At this time, 50 ml of 1.6M VOSO ₄ (3M H ₂ SO ₄ ) was used as the electrolyte, and the flow rate was 25 cc / min.

Comparative example  One

As shown in FIG. 9, a bipolar plate having no fibrous conductive material inserted therein was manufactured, and the same procedure as in Example 1 was performed to prepare a redox flow battery.

Experimental Example  One

Charge and discharge capacity and energy efficiency were measured using the unit cells produced in Example 1 and Comparative Example 1, respectively, and the results obtained are shown in FIGS. 10 and 11. The charging and discharging conditions were performed in 10 cycles at 2.5A, 10 cycles at 3.75A, 10 cycles at 2.5A, and 5 cycles at 2.5A.

10 is a graph showing the charge and discharge capacity of Example 1 and Comparative Example 1, it can be seen that the battery capacity of Example 1 is lower than the battery of Comparative Example 1 capacity decrease as the number of cycles.

Looking at the charge and discharge capacity shown in FIG. 10 showed a slightly better tendency in Example 1. This difference can be clearly seen through the energy efficiency comparison graph of Table 1 and FIG. 11. 11 is a graph showing the energy efficiency of Example 1 and Comparative Example 1.

2 to 10 times average energy efficiency		EE (%)
50 mA / cm 2	Comparative Example 1	79.0
	Example 1	87.0
100 mA / cm 2	Comparative Example 1	69.3
	Example 1	80.2
150 mA / cm 2	Comparative Example 1	56.5
	Example 1	67.1

Referring to Table 1 and FIG. 11, it can be clearly seen that the reaction area increases due to the insertion of the carbon felt as the fibrous conductive material, thereby decreasing the resistance value per unit area.

Therefore, it can be seen that it is very advantageous to introduce the structure of the present invention to a redox flow battery targeting high flow rate and high current density.

The redox flow battery of the present invention is preferably applicable as a high performance battery having a high flow rate and high current density.

[Description of the code]

11,15,21,25: bipolar plate

12,14,22,24: electrode layer

13,23: ion exchange membrane

27: Euro

1000: redox flow battery

100: battery module

101: unit module

111,113: end plate

115,117: current collector plate

118,119 bipolar plate

120,121: electrode plate

123: ion exchange membrane plate

130: unit cell

151: fibrous conductive material

152: body

154: bulkhead

161: outlet

162: outlet

171: supply euro

172: discharge passage

181,182,183,184: connecting member

202,204: electrolyte tank

302,304: electrolyte pump

F: Euro

A: electrolyte solution part

Claims (15)

1. Plate-shaped body; And

   In the bipolar plate comprising a flow path formed to move the electrolyte in the center of the body,

   A bipolar plate for a redox flow battery in which a fibrous conductive material is inserted into the flow path.
2. The method of claim 1,

   The fibrous conductive material is a carbon felt, graphite felt, carbon cloth, carbon paper, metal cloth, metal felt, and at least one type of fabric selected from the group consisting of foamed metal bipolar plate for redox flow battery.
3. The method of claim 1,

   The fibrous conductive material has a porosity of 10 to 99% and a bulk density of 0.05 to 0.2 g / cm ³ bipolar plate for a redox flow battery.
4. The method of claim 1,

   The fibrous conductive material is a bipolar plate for redox flow battery further comprises at least one selected from the group consisting of carbon-based conductive material and metal particles.
5. The method of claim 4, wherein

   The carbon-based conductive material is redox including at least one selected from the group consisting of carbon paper, carbon fiber, carbon black, acetylene black, activated carbon, fullerene, carbon nanotubes, carbon nanowires, carbon nanohorns, and carbon nanorings. Bipolar plate for flow cells.
6. The method of claim 4, wherein

   The metal particles are Na, Al, Mg, Li, Ti, Zr, Cr, Mn, Co, Cu, Zn, Ru, Pd, Rd, Pt, Ag, Au, W, Ni and Fe selected from the group consisting of The bipolar plate for redox flow batteries containing the above.
7. The method of claim 1,

   The fibrous conductive material is a bipolar plate for a redox flow battery is filled in a volume ratio of 10 to 100% with respect to the flow volume (flow channel width * flow channel depth * length of the bulkhead).
8. The method of claim 1,

   The bipolar plate for a redox flow battery for filling the fibrous conductive material in the flow path so that the depth (X) of the flow channel to the thickness (Y) of the fibrous conductive material satisfies the formula 1 <Y / X ≤ 2.5.
9. The method of claim 1,

   The bipolar plate has an outlet for inflow of the electrolyte on one side of the body;

   An outlet for discharging the electrolyte passing through the flow path;

   An electrode layer having a flow path formed therein to move the electrolyte and contact the electrode plate;

   A supply flow path positioned between the outlet and the electrode layer to distribute the electrolyte evenly; And

   And a discharge flow path disposed between the discharge port and the electrode layer to distribute the electrolyte evenly.
10. The method of claim 1,

    The flow path includes at least one pattern selected from the group consisting of parallel, serpentine, semi-serpentine, zigzag, interdigitated and pin shapes. Bipolar plate for redox flow batteries.
11. Ion exchange membrane;

    Electrode layers disposed on both sides of the ion exchange membrane; And

    A bipolar plate disposed on one side of the electrode layer,

    The bipolar plate is a unit cell for a redox flow battery is a bipolar plate according to any one of claims 1 to 10.
12. The method of claim 11,

    The electrode layer is a unit cell for a redox flow battery comprising at least one material selected from the group consisting of carbon felt, graphite felt, carbon cloth, carbon paper, metal cloth, metal felt and foamed metal.
13. The method of claim 11,

    The electrode layer is a unit cell for a redox flow battery formed by laminating one or two or more carbon materials.
14. The method of claim 11,

    The electrode layer is a unit cell for a redox flow battery having a form in which one or two or more carbon materials are laminated.
15. A battery module formed by arranging and electrically connecting unit modules including unit stacks for generating current to each other;

    An electrolyte tank for supplying an electrolyte solution to the battery module and storing an electrolyte solution flowing out of the module; And

    An electrolyte pump for circulating the electrolyte between the module and the electrolyte tank,

    The unit stack is a redox flow battery in which a plurality of unit cells for redox flow battery of claim 11 are connected.

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