Patent Application
20250087709
The present disclosure relates to an electrode, a battery cell, a cell stack, and a redox-flow battery system.
The present application claims the benefit of priority to Japanese Patent Application No. 2022-000990 filed on Jan. 6, 2022, the entire contents of which are incorporated herein by reference.
Redox-flow batteries are one type of rechargeable batteries in which the electrolyte is supplied to the electrode to cause battery reactions. For example, in the redox-flow battery disclosed by PTL 1, a carbon paper sheet is used as an electrode.
An electrode according to the present disclosure is
Development of an electrode that is excellent in electrolyte flowability is demanded.
An object of the present disclosure is to provide an electrode that is excellent in electrolyte flowability.
An electrode according to the present disclosure is excellent in electrolyte flowability.
First, aspects of the present disclosure will be described below.
(1) An electrode according to an aspect of the present disclosure is
In an electrode in which the median diameter is at least 1.025 times the modal diameter, as compared to an electrode in which the median diameter is less than 1.025 times the modal diameter, the number of large voids is high. In the above-mentioned configuration in which the median diameter is at least 1.025 times the modal diameter, electrolyte flowability is excellent. As a result, in the above-mentioned configuration, diffusive resistance tends to be low.
(2) In the electrode according to (1) above,
An electrode in which the modal diameter is 80 μm or less has excellent battery reactivity.
(3) In the electrode according to (1) above or (2) above,
An electrode in which the median diameter is 80 μm or less has excellent battery reactivity.
(4) In the electrode according to any one of (1) above to (3) above, on Log differential pore volume distribution of the electrode determined by mercury porosimetry, a symmetry factor S0.1h of a curve of a highest peak may be 1.5 or more.
As described below in detail referring to
In an electrode in which the symmetry factor S0.1h is 1.5 or more, as compared to an electrode in which the symmetry factor S0.1h is less than 1.5, the number of large voids is high. In the above-mentioned configuration in which the symmetry factor S0.1h is 1.5 or more, electrolyte flowability is excellent.
(5) In the electrode according to any one of (1) above to (4) above,
An electrode in which the porosity is 60% or more has more voids, as compared to an electrode in which the porosity is less than 60%. In the above-mentioned configuration in which the porosity is 60% or more, electrolyte flowability is excellent.
(6) In the electrode according to any one of (1) above to (5) above,
When the average diameter of the plurality of carbon fibers is 2 μm or more, the strength of the electrode is high. When the average diameter of the plurality of carbon fibers is 30 μm or less, the surface area of the carbon fibers per unit weight is large. This allows for sufficient battery reactions to occur in the electrode.
(7) A battery cell according to an aspect of the present disclosure is a battery cell for use in a redox-flow battery system, and comprises the electrode according to any one of (1) above to (6) above.
In the above-mentioned configuration which comprises an electrode that is excellent in electrolyte flowability, diffusive resistance tends to be low.
(8) A cell stack according to an aspect of the present disclosure is a cell stack for use in a redox-flow battery system, and comprises a plurality of the battery cells according to (7) above.
In the above-mentioned configuration which comprises a plurality of the above-mentioned battery cells, electrolyte flowability is excellent. As a result, in the above-mentioned configuration, diffusive resistance tends to be low.
(9) A redox-flow battery system according to an aspect of the present disclosure comprises the battery cell according to (7) above or the cell stack according to (8) above.
In the above-mentioned configuration which comprises the above-mentioned battery cell or the above-mentioned cell stack, electrolyte flowability is excellent. As a result, in the above-mentioned configuration, diffusive resistance tends to be low.
(10) The redox-flow battery system according to (9) above may comprise a positive electrolyte and a negative electrolyte that are supplied to the battery cell,
The above-mentioned configuration has a high electromotive force.
In the following, a redox-flow battery system according to an embodiment of the present disclosure is described in detail. Hereinafter, a redox-flow battery system may also be expressed as an RF battery system. In the drawings, members that have the same name are given the same reference numeral.
Referring to
RF battery system 100 illustrated in
Battery cell 4 in RF battery system 100 is divided by membrane 4M into a positive electrode cell and a negative electrode cell. Membrane 4M is an ion-exchange membrane that does not allow transmission of electrons but allows transmission of, for example, hydrogen ions. The positive electrode cell internally includes positive electrode 4P. The negative electrode cell internally includes negative electrode 4N. Circulation mechanism 6 in RF battery system 100 comprises a positive electrode circulation mechanism 6P and a negative electrode circulation mechanism 6N. Positive electrode circulation mechanism 6P circulates the positive electrolyte to the positive electrode cell. Negative electrode circulation mechanism 6N circulates the negative electrolyte to the negative electrode cell.
As described above, electrode 1 according to the present embodiment illustrated in
As illustrated in
The median diameter based on pore volume is obtained from a cumulative pore volume curve of cumulative pore distribution based on mercury porosimetry. In the cumulative pore distribution, the X axis represents pore diameter and the Y axis represents pore volume. The median diameter based on pore volume is a pore diameter that corresponds to the midpoint between the smallest value and the largest value of the pore volume on the cumulative pore volume curve.
The measurement range of the pore diameter on the X axis is defined by the upper limit and the lower limit measureable by mercury porosimetry. The upper limit corresponds to the smallest value of the pore volume on the Y axis. The lower limit corresponds to the largest value of the pore volume on the Y axis. The upper limit is usually about 500 μm. The lower limit is usually about 0.003 μm. The smallest value of the pore volume on the Y axis is usually 0 (zero). Herein, a median diameter based on pore volume may be simply referred to as a median diameter. The modal diameter is a pore diameter for the highest derivative value on the differential pore distribution based on mercury porosimetry.
In electrode 1 in which the median diameter is at least 1.025 times the modal diameter, as compared to an electrode in which the median diameter is less than 1.025 times the modal diameter, the number of large voids 25 is high. A large electrode 1 in which the median diameter is at least 1.025 times the modal diameter is excellent in electrolyte flowability.
Further, the median diameter may be at least 1.03 times the modal diameter, particularly at least 1.05 times the modal diameter. The median diameter is at most 1.5 times the modal diameter, further at most 1.3 times the modal diameter, particularly at most 1.2 times the modal diameter, for example. In other words, the median diameter is from 1.025 times to 1.5 times the modal diameter, further from 1.03 times to 1.3 times the modal diameter, particularly from 1.05 times to 1.2 times the modal diameter. Further, the difference between the median diameter and the modal diameter may be at least 3% of the modal diameter, particularly at least 5% of the modal diameter. The difference between the median diameter and the modal diameter is at most 50% of the modal diameter, further at most 30% of the modal diameter, particularly at most 20% of the modal diameter, for example. In other words, the difference between the median diameter and the modal diameter is from 2.5% to 50% of the modal diameter, further from 3% to 30% of the modal diameter, particularly from 5% to 20% of the modal diameter.
The median diameter is 80 μm or less, for example. Electrode 1 in which the median diameter is 80 μm or less has excellent battery reactivity. Further, the median diameter is 75 μm or less, or 60 μm or less, or 55 μm or less, or particularly 50 μm or less. The lower limit to the median diameter is 3 μm, for example. In other words, the median diameter is from 3 μm to 80 μm, further from 10 μm to 75 μm, particularly from 20 μm to 60 μm.
The modal diameter is 80 μm or less, for example. Electrode 1 in which the modal diameter is 80 μm or less has excellent battery reactivity. Further, the modal diameter is 75 μm or less, or 60 μm or less, or 55 μm or less, or particularly 50 μm or less. The lower limit to the modal diameter is 2 μm, for example. In other words, the modal diameter is from 2 μm to 80 μm, further from 10 μm to 75 μm, particularly from 20 μm to 60 μm.
The symmetry factor S0.1h of the curve is 1.5 or more, for example. Referring to
The symmetry factor S0.1h is determined by “(width W0.1h)/(2×(width f0.1h))”. Width W0.1h is the difference between a first pore diameter D11 and a second pore diameter D12. Width f0.1h is the difference between first pore diameter D11 and a third pore diameter D13. First pore diameter D11 is the smaller of the pore diameters corresponding to 10% of the height of the highest peak on curve C1. Second pore diameter D12 is the larger of the pore diameters corresponding to 10% of the height of the highest peak on curve C1. Third pore diameter D13 is the pore diameter for the highest peak on curve C1.
In electrode 1 in which the symmetry factor S0.1h is 1.5 or more, as compared to an electrode in which the symmetry factor S0.1h is less than 1.5, the number of large voids 25 is high. Electrode 1 in which the symmetry factor S0.1h is 1.5 or more is excellent in electrolyte flowability. Further, the symmetry factor S0.1h is 1.6 or more, particularly 1.7 or more. The symmetry factor S0.1h is 15 or less, or further 10 or less, for example. In other words, the symmetry factor S0.1h is from 1.5 to 15, further from 1.6 to 10, particularly from 1.7 to 10.
The average diameter of the plurality of carbon fibers 21 is from 2 μm to 30 μm, for example. When the average diameter of the plurality of carbon fibers 21 is 2 μm or more, the strength of electrode 1 is high. When the average diameter of the plurality of carbon fibers 21 is m or less, the surface area of carbon fibers 21 per unit weight is large. This allows for sufficient battery reactions to occur in electrode 1. Further, the average diameter of the plurality of carbon fibers 21 is from 5 μm to 25 μm, particularly from 7 μm to 20 μm.
The average diameter of the plurality of carbon fibers 21 is the average of the diameters of circles that have the same area as the cross-sectional area of respective carbon fibers 21, and is determined in the below-described manner. Electrode 1 is cut in the thickness direction, to expose cross sections of the plurality of carbon fibers 21. In the cross section of electrode 1, five or more fields of view are selected under a microscope. As the microscope, a scanning electron microscope (SEM) is used. The magnification is from 500 times to 3000 times. For three or more carbon fibers 21 per one examination field of view, the diameter of a circle that has the same area as the cross-sectional area thereof is determined. The diameters of the circles determined in all the examination fields of view are averaged.
The mass per unit area of electrode 1 is from 20 g/m2 to 400 g/m2, for example. Electrode 1 in which the mass per unit area is 20 g/m2 or more tends to have many contact points between carbon fibers 21. Therefore, electrode 1 tends to have an enhanced conductivity. In electrode 1 in which the mass per unit area is 400 g/m2 or less, voids 25 tend to be ensured. Therefore, electrode 1 is excellent in electrolyte flowability. Further, the mass per unit area of electrode 1 is from 25 g/m2 to 300 g/m2, particularly from 30 g/m2 to 200 g/m2. The mass per unit area is determined by measuring the weight per unit area.
The porosity of electrode 1 is 60% or more, for example. The porosity is determined by mercury porosimetry. The porosity refers to the proportion of the volume of the pores to the volume of electrode 1 including the pores. Electrode 1 in which the porosity is 60% or more has more voids 25, as compared to an electrode in which the porosity is less than 60%. This electrode 1 is excellent in electrolyte flowability. The upper limit to the porosity of electrode 1 is 99%, for example. Electrode 1 in which the porosity is 99% or less has excellent battery reactivity. The porosity of electrode 1 is from 60% to 99%, or from 60% to 95%, further from 65% to 93%, particularly from 75% to 90%.
Electrode 1 is one selected from the group consisting of nonwoven fabric, woven fabric, and paper. The nonwoven fabric is formed of independent carbon fibers 21 entangled together. The woven fabric is formed of the warp and the weft of carbon fibers 21 woven alternately. The paper has the plurality of carbon fibers 21 and a binder for securing the carbon fibers 21.
Electrode 1 according to the present embodiment is a nonwoven fabric. For example, electrode 1 according to the present embodiment is formed of carbon fibers 21 entangled together by needle-punching, water punching, and/or stitch bonding. For example, electrode 1 according to the present embodiment is obtained by adjusting, as appropriate, the average diameter of carbon fibers 21, the average length of carbon fibers 21, the mass per unit area, and the entangling conditions.
Battery cell 4 is usually formed inside a structure called a cell stack 200, as illustrated in
As illustrated in
As illustrated in
Negative electrode circulation mechanism 6N comprises a negative electrolyte tank 62, supply tube 64, discharge tube 66, and a pump 68. Negative electrolyte tank 62 stores the negative electrolyte. Through supply tube 64 and discharge tube 66, the negative electrolyte flows. Supply tube 64 connects negative electrolyte tank 62 with the negative electrode cell. Discharge tube 66 connects the negative electrode cell with negative electrolyte tank 62. Pump 68 pressure feeds the negative electrolyte from negative electrolyte tank 62. Pump 68 is provided at some midpoint on the supply tube 64.
During charging or discharging operation, the positive electrolyte and the negative electrolyte flow in the manner described below. By pump 67, the positive electrolyte flows from positive electrolyte tank 61 through supply tube 63, and is supplied to the positive electrode cell. The positive electrolyte flows from liquid supply manifold 53 through liquid supply slit 53s illustrated in the upper drawing of
A positive electrode active material included in the positive electrolyte is one or more types selected from the group consisting of manganese ions, vanadium ions, iron ions, polyacids, quinone derivatives, and amines. A negative electrode active material included in the negative electrolyte is one or more types selected from the group consisting of titanium ions, vanadium ions, chromium ions, polyacids, quinone derivatives, and amines. When the positive electrolyte includes manganese ions and the negative electrolyte includes titanium ions, RF battery system 100 tends to have a high electromotive force. In
RF battery system 100 according to the present embodiment comprises electrode 1 that is excellent in electrolyte flowability, and therefore tends to have a low diffusive resistance.
A plurality of electrodes were prepared, and battery reactivity and electrolyte flowability were evaluated.
The electrode of the battery cell of Sample No. 1 to Sample No. 6 each was a single electrode that included a plurality of carbon fibers and voids. The average diameter of the carbon fibers of each sample is within the range of 2 μm to 30 μm. The average diameter of the carbon fibers was determined by the method described in the embodiment section. The mass per unit area of the electrode of Sample No. 1 is 110 g/m2. The mass per unit area of the electrode of Sample No. 2 is 120 g/m2. The mass per unit area of the electrode of Sample No. 3 is 80 g/m2. The mass per unit area of the electrode of Sample No. 4 is 90 g/m2. The mass per unit area of the electrode of Sample No. 5 is 90 g/m2. The mass per unit area of the electrode of Sample No. 6 is 100 g/m2. The mass per unit area was determined by the method described in the embodiment section.
The median diameter based on pore volume, the modal diameter, the symmetry factor, and the porosity of the electrode of each sample are shown in Table 1. These values were measured by mercury porosimetry. For the measurement, a pore distribution measurement apparatus AutoPore IV 9520 manufactured by Shimadzu Corporation-Micromeritics Instrument Corporation was used. In Table 1, the value of the modal diameter of the electrode of each sample multiplied by 1.025 is also given. The value of the modal diameter multiplied by 1.025 has been rounded to three decimal place.
Each electrode was cut into a strip having a size of about 12.5 mm×25 mm, which was used as a measurement sample. The weight of the measurement sample was approximately from 0.03 g to 0.24 g. The measurement sample was placed in a 5-cc cell that was specifically designed for powder. The volume of the stem of the powder cell is 0.4 cc. The measurement was carried out under the conditions of an initial pressure of about 3.7 kPa. “About 3.7 kPa” corresponds to about 0.5 psia (pound-force per square inch absolute), and corresponds to a pore diameter of about 340 μm. The mercury parameters were set at the default of the apparatus, namely a mercury contact angle of 130 degrees and a mercury surface tension of 485 dynes/cm (485 mN/m).
The electrode of the battery cell of Sample No. 101 was a single electrode. The electrode of Sample No. 101 includes carbon fibers. The median diameter based on pore volume, the modal diameter, the symmetry factor, and the porosity of the electrode of Sample No. 101 are shown in Table 1. In Table 1, the value of the modal diameter of the electrode of Sample No. 101 multiplied by 1.025 is also given. The value of the modal diameter multiplied by 1.025 has been rounded to three decimal place.
The battery cell of each sample was used to produce a single-cell battery, and various resistivities described below were measured. The single-cell battery is a battery that comprises a single positive electrode, a single membrane, and a single negative electrode. The single-cell battery was formed by stacking a first cell frame, a positive electrode, a membrane, a negative electrode, and a second cell frame in this order. The membrane is sandwiched between the positive electrode and the negative electrode. The first cell frame is placed so that a bipolar plate of the first cell frame comes into contact with the positive electrode. The second cell frame is placed so that a bipolar plate of the second cell frame comes into contact with the negative electrode. As the positive electrode, a carbon paper sheet was used. As the negative electrode, the electrode of each sample was used. As the positive electrolyte, a manganese sulfate solution that included manganese ions as an active material was used. As the negative electrolyte, a titanium sulfate solution that included titanium ions as an active material was used.
The battery cell of each sample was subjected to constant-current charging and discharging at a current density of 100 mA/cm2. In this test, three cycles of charging and discharging were carried out. In this test, charging was switched to discharging when a previously defined switching voltage was reached, and discharging was switched to charging when a previously defined switching voltage was reached. The switching voltage for switching from charging to discharging was 1.62 V. The switching voltage for switching from discharging to charging was 1.0 V. In this manner, charging and discharging of the RF battery of each sample were accomplished.
After the constant-current charging and discharging, another charging was carried out in the manner described below, and the conductive resistivity (Ω·cm2), the charge-transfer resistivity (Ω·cm2), and the diffusive resistivity (Ω·cm2) of each sample were determined by the methods described below. Results are given in Table 2, together with the cell resistivity (Q·cm2). Cell resistivity is the sum of conductive resistivity, charge-transfer resistivity, and diffusive resistivity. The charging here was carried out to reach a midpoint SOC. The midpoint SOC is an average value of the sum of the highest SOC value and the lowest SOC value during the constant-current charging and discharging.
The conductive resistivity was an impedance at the time when the measurement frequency in the alternating-current impedance method was 1 kHz.
The charge-transfer resistivity was measured by an alternating-current impedance method. For the measurement of the charge-transfer resistivity, a commercially-available measurement apparatus was used, under a bias at a value around the open circuit voltage, at a voltage amplitude of 10 mV, at a measurement frequency within the range of 10 kHz to 10 mHz.
In the same manner as for the charge-transfer resistivity, the diffusive resistivity was measured by an alternating-current impedance method.
With the use of a measuring system 600 illustrated in
Measurement cell 610 is a single-cell battery that has the same structure as the single-cell battery used in the above-described measurement of various resistivities. Fluid tank 620 stores a fluid 622 that is to be supplied to the electrode inside the measurement cell 610. Fluid 622 is water, for example. Pipe 630 connects fluid tank 620 with measurement cell 610. Pump 640 is provided to pipe 630, and pressure feeds fluid 622 from fluid tank 620 to measurement cell 610. Fluid 622 discharged from measurement cell 610 flows through pipe 630 back to fluid tank 620. In this manner, by pump 640 and pipe 630, fluid 622 inside the fluid tank 620 is circulated and supplied to measurement cell 610. The dash-dot arrows in
Differential pressure gauge 660 measures the difference (P0−P1) between a pressure P0 of fluid 622 supplied to measurement cell 610 and a pressure P1 of fluid 622 discharged from measurement cell 610. Pressure loss ΔP is the difference between these pressures, (P0−P1). The lower the pressure loss ΔP is, the more excellent in electrolyte flowability the measurement cell 610 is considered to be. Results of the pressure loss of each sample are shown in Table 2. The result of the pressure loss in Table 2 is expressed as a value relative to the pressure loss ΔP of Sample No. 1, which is regarded as 1.0.
Referring to Table 2, Sample No. 1 to Sample No. 6 had low diffusive resistivity as compared to Sample No. 101. The difference between the diffusive resistivity of each of Sample No. 1 to Sample No. 6 and the diffusive resistivity of Sample No. 101 was greater than the difference between the conductive resistivity of each of Sample No. 1 to Sample No. 6 and the conductive resistivity of Sample No. 101. The difference between the diffusive resistivity of each of Sample No. 1 to Sample No. 6 and the diffusive resistivity of Sample No. 101 was greater than the difference between the charge-transfer resistivity of each of Sample No. 1 to Sample No. 6 and the charge-transfer resistivity of Sample No. 101. This indicates that the diffusive resistivity lowering effect of Sample No. 1 to Sample No. 6 was greater than that of Sample No. 101. The pressure loss of each of Sample No. 1 to Sample No. 6 was smaller than that of Sample No. 101. Due to the great diffusive resistivity lowering effect and the small pressure loss as compared to Sample No. 101, Sample No. 1 to Sample No. 6 were found to be particularly excellent in electrolyte flowability.
Sample No. 1 to Sample No. 6 had low cell resistivity as compared to Sample No. 101. This indicates that Sample No. 1 to Sample No. 6 are also excellent in battery reactivity as compared to Sample No. 101.
It is intended that the scope of the present invention is defined by claims, not by these examples, and encompasses all modifications and variations equivalent in meaning and scope to the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-000990 | Jan 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/043803 | 11/28/2022 | WO |
