KR20230007137A - Vanadium redox flow battery charge/discharge monitoring device and real-time measuring method - Google Patents

Abstract

The present invention relates to a real-time charge/discharge monitoring device and real-time measurement method for a vanadium redox flow battery, comprising: a sampling unit which samples the electrolyte, an electrolyte dilution unit which dilutes the electrolyte to prepare a diluted solution, and an absorbance measuring unit which measures the absorbance of the diluted solution in real time, wherein the concentration obtained using the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of divalent, trivalent, tetravalent, and pentavalent vanadium ions is applied to the following calculation formula 1 or calculation formula 2 to determine the state of charge (SOC) of the electrolyte. Accordingly, the present invention is helpful in determining the state of the electrolyte.

Description

Vanadium redox flow battery charge/discharge monitoring device and real-time measuring method

The present invention relates to a charging/reversing monitoring device and a real-time measuring method of a vanadium redox flow battery.

Recently, as the use of energy due to depletion of fossil fuels and environmental pollution is limited, the proportion of new and renewable energies is increasing. However, since the power generated from renewable energy sources is not constant, an energy storage system (ESS; Energy Storage System) for stable power supply and a power storage device capable of high capacity and excellent operation stability are redox flow batteries (RFB, Redox Flow Battery) is being studied.

Vanadium Redox Flow Battery (VRFB), which uses a vanadium electrolyte among redox flow batteries (RFB), oxidizes vanadium tetravalent to pentavalent at the anode and vanadium 3 at the cathode when charging occurs. Vanadium is reduced to divalent, and conversely, when discharge occurs, Vanadium 5 is converted to tetravalent at the anode and Vanadium divalent to trivalent at the cathode.

At this time, when charging or discharging proceeds, the state of the electrolyte (SOC, State of Charge) of each pole changes over time, and the vanadium ion has a characteristic that the color changes according to the number of electrons. Vanadium 5-valent color is yellow, 4-valent color is blue, 3-valent color is green, and 2-valent color is purple. As shown in FIG. 1, the color of the electrolyte that has changed through charging and discharging returns to the electrolyte container and the colors are mixed. When the charge is completed, the positive electrode shows a pentavalent yellow color, and when discharging starts, a tetravalent blue color is gradually generated. They are mixed with each other and turn blue at the discharge end point. In the negative electrode, purple at the time of charge completion and green at the time of discharge completion, and in between, when the two colors are mixed, if there is a lot of divalent, the color is closer to purple, and if there are more trivalent, the color is closer to green.

On the other hand, the separator separating the electrolytes of the positive and negative electrodes of the vanadium redox flow battery should serve to pass hydrogen ions and separate the electrolytes of the positive and negative electrodes, but cause side effects of passing some vanadium ions. also do As the vanadium ions pass through the separator to the other pole, the water molecules covalently bonded to the vanadium ions also move, and as the electrolyte initially filled in the anode and cathode in the same amount continues to operate, the electrolyte tends to move toward the anode , and the charge/discharge capacity gradually decreases according to the movement of vanadium ions.

Therefore, after checking the concentration of vanadium ions at both poles and checking the amount of electrolyte, the amount of electrolyte is rebalanced to recover the reduced charge / discharge capacity. It is necessary to periodically check the change of vanadium ions that have moved to the poles.

UV-Visible spectrophotometry is used as a device for measuring the ionic value of the vanadium redox flow battery electrolyte. This analysis equipment is characterized by absorbing and spectroscopying visible light wavelengths representing colors, and analyzing them using characteristics proportional to concentrations. The concentration of the electrolyte of the vanadium redox flow battery varies depending on the state of charging and discharging, and the concentration of vanadium ions of different colors varies, and the size of the wavelength absorbed accordingly varies, so the concentration can be measured.

However, the concentration of vanadium ions that emit visible light wavelengths that can be measured by an ultraviolet-visible spectrometer is less than 0.15M, but the actual electrolyte concentration of a vanadium redox flow battery is about 1.5M, which needs to be diluted by about 10 times or more. Accordingly, in order to measure in real time, an electrolyte sample may be taken in the field, a part of it may be transferred to a flask, diluted to a required concentration, and then measured. However, it is necessary to quickly analyze an electrolyte sample in the field to obtain a value, and it is necessary to easily clean the line even during operation so that it can be reused.

Therefore, the present invention is to provide a device and method for measuring the electrolyte concentration in the field in real time in order to improve the above problems.

An object of the present invention is to provide a charging/reversing monitoring device and a real-time measuring method for a vanadium redox flow battery.

In addition, the purpose is to predict the degree of charge and discharge by checking the state of electrolyte ions in real time.

In addition, the purpose of the present invention is to determine the degree of permeation of one electrolyte to the other through the separator and to check the state of the electrolyte according to the degree of permeation.

However, these tasks are illustrative, and the scope of the present invention is not limited thereby.

According to one aspect of the present invention for achieving the above object, a sampling unit for sampling an electrolyte, an electrolyte dilution unit for preparing a diluted solution by diluting the electrolyte, and an absorbance measuring unit for measuring absorbance of the diluted solution in real time; By applying the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of divalent, trivalent, tetravalent, and pentavalent vanadium ions to Equation 1 or Equation 2 below, the state of charge of the electrolyte (SOC, state of It provides a real-time charging/reversing monitoring device for a vanadium redox flow battery that determines charge).

Calculation 1

SOC =

Calculation 2

SOC =

According to one example of the present invention, the sampling unit includes a first sampling unit for sampling the anode electrolyte moving to the cathode and a second sampling unit for sampling the anode electrolyte moving to the anode, wherein the sampling unit has a 3-way valve (3 way valve).

According to an example of the present invention, the inside of the 3-way valve may be sealed with an EPDM material.

According to an example of the present invention, the electrolyte dilution unit may include a dilution cylinder for diluting the sampled electrolyte and an ultrapure water supply unit for supplying ultrapure water to the dilution cylinder.

According to another aspect of the present invention, a sampling step of sampling the electrolyte includes an electrolyte dilution step of diluting the electrolyte to prepare a diluted solution and an absorbance measurement step of measuring the absorbance of the diluted solution in real time, the diluted solution The absorbance value of and the absorbance value according to the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions are applied to the following formula 1 or formula 2 to determine the state of charge (SOC) of the electrolyte Provides a real-time charge/discharge monitoring method for vanadium redox flow batteries.

According to an example of the present invention, the sampling step may include a first sampling step of sampling the anode electrolyte moving to the cathode or a second sampling step of sampling the anode electrolyte moving to the anode.

According to one embodiment of the present invention, the step of measuring the absorbance may be to measure the absorbance value of the diluted solution using a UV-Visible spectrophotometry.

According to an example of the present invention, the divalent vanadium ion has absorbance values measured at wavelengths of 846.7 nm, 604.3 nm, and 396.8 nm, the natural wavelength of the divalent vanadium ion is 846.7 nm, and the wavelength range of 604.3 nm represents an absorbance value 2.12 times the absorbance value measured at the natural wavelength of the divalent vanadium ion, and exhibits an absorbance value 2.11 times the absorbance value measured at the natural wavelength in the 396.8 nm wavelength range.

According to an example of the present invention, the trivalent vanadium ion has absorbance values measured at wavelengths of 396.8 nm and 604.3 nm, the natural wavelength of the trivalent vanadium ion is 604.3 nm, and the 3 It may represent an absorbance value of 1.58 times the absorbance measured at the natural wavelength of the vanadium ion.

According to an example of the present invention, the absorbance values of the tetravalent vanadium ion are measured at wavelengths of 767.9 nm and 604.3 nm, the natural wavelength of the tetravalent vanadium ion is 767.9 nm, and the 4 It may represent an absorbance value of 0.36 times the absorbance measured at the natural wavelength of the vanadium ion.

According to an example of the present invention, the pentavalent vanadium ion has absorbance values measured at wavelengths of 396.8 nm and 767.9 nm, the natural wavelength of the pentavalent vanadium ion is 396.8 nm, and the 5 It may be to produce an absorbance value 0.03 times the absorbance measured at the natural wavelength of the vanadium ion.

In the present invention, UV-Visible spectroscopy measurement is the most accurate way to know the state of charge (SOC) of VRFB. By periodically checking the ion state of the electrolyte coming out of each electrolyte tank in the middle of the transition from charge to discharge and discharge to charge, to what extent the charge has progressed and to predict when the discharge point will be, in parallel with the voltage value of the battery can be used

In addition, about 5% of the electrolyte on one side is transmitted through the separator that separates the positive and negative electrodes of the battery.

Since vanadium 2, 3, 4, and 5 ions are mixed, it was found through analysis that the ratio in which the wavelength emitted from one ion affects the wavelength of another ion is constant, and the wavelength for each ion is reflected by reflecting the ratio The absorbance value according to is obtained, and the concentration can also be obtained from the value.

In addition, conventionally, analysis could be performed after manual work of sampling, transferring to a cylinder, and diluting for SOC measurement.

1 is a schematic diagram showing the color change according to the vanadium ion value of the electrolyte of a vanadium redox flow battery.
2 is a schematic diagram showing a device for monitoring charge and discharge in real time of a vanadium redox flow battery according to an embodiment.
3 is a schematic diagram showing the opening and neutrality of a 3-way valve according to an embodiment.
4 is an absorbance graph of divalent vanadium ions according to an embodiment.
5 is an absorbance graph of pentavalent vanadium ions according to an embodiment.
6 is an absorbance graph of tetravalent vanadium ions according to an embodiment.
7 is an absorbance graph of trivalent vanadium ions according to an embodiment.
8 is a schematic diagram showing a method of manually collecting samples and diluting them to analyze absorbance.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. These examples are only illustratively indicated to explain the present invention in more detail, and it is obvious to those skilled in the art that the scope of the present invention is not limited by these examples. something to do.

In addition, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art to which the present invention belongs, and in case of conflict, this specification including definitions of will take precedence.

In order to clearly explain the proposed invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification. And when it is said that a certain component "includes", it means that it may further include other components, not excluding other components unless otherwise stated. In addition, a “unit” described in the specification means one unit or block that performs a specific function.

In each step, the identification code (first, second, etc.) is used for convenience of description, and the identification code does not describe the order of each step, and each step does not clearly describe a specific order in context. It may be performed differently from the order specified above.

That is, each step may be performed in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

2 is a schematic diagram showing an apparatus 100 for monitoring charge and discharge in real time of a vanadium redox flow battery according to an embodiment.

Referring to FIG. 2 , the real-time charge/discharge monitoring device 100 of the vanadium redox flow battery includes a sampling unit 110, an electrolyte dilution unit 130, and an absorbance measuring unit 150, and the vanadium redox flow The real-time charge/discharge monitoring device 100 of the battery measures the absorbance value of the diluted solution, and the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of divalent, trivalent, tetravalent, and pentavalent vanadium ions It is characterized in that the state of charge (SOC) of the electrolyte is determined by applying the following formula 1 or formula 2.

Calculation 1

SOC =

Calculation 2

SOC =

The sampling unit samples the electrolyte and includes a first sampling unit 110 for sampling the anode electrolyte moving to the cathode and a second sampling unit 120 for sampling the anode electrolyte.

In detail, the first sampling unit 110 has a first sampling point 111 branched from an electrolyte line injected from the cathode electrolyte tank to the cathode of the vanadium redox flow battery and a 3-way valve , 112). In addition, the second sampling unit 120 includes a second sampling point 121 and a 3-way valve (not shown) formed by branching from an electrolyte line injected from the anode electrolyte tank to the anode of the vanadium redox flow battery. do.

The electrolyte dilution unit 130 dilutes the electrolyte sampled from the sampling unit to prepare a dilution solution, and supplies ultrapure water to the dilution cylinder 132 and the dilution cylinder 132 for diluting the sampled electrolyte. It is characterized in that it comprises an ultrapure water supply unit 131 to.

In detail, the dilution cylinder 132 has a protrusion so that a pipe can be connected to the lower part of the dilution cylinder 132 so that the sampled electrolyte can be transferred, and the dilution solution is the electrolyte measuring unit ( 150), it is characterized in that a protrusion to which a pipe can be connected is formed on the upper part of the dilution cylinder 132 so that it can be transferred.

At this time, the pipe may be a Teflon tube, etc., and the diameter of the pipe connected to the upper part of the dilution cylinder 132 is preferably 1/8 inch, and the length of the pipe is the lower part of the dilution cylinder 132. It is desirable to be able to reach up to

In addition, the ultrapure water supply unit 131 is characterized in that it is located above the dilution cylinder 132. As the ultrapure water supply unit 131 is positioned above the dilution cylinder 132 , the ultrapure water may be injected into the dilution cylinder 132 using a head difference.

Furthermore, the dilution cylinder 132 and the ultrapure water supply unit 131 are characterized in that they are connected to the 3-way valve 112. That is, the first sampling point 111, the dilution cylinder 132, and the ultrapure water supply unit 131 are connected by the 3-way valve 112, and the first sampling point 111 and the 3-way valve (112) and the distance between the dilution cylinder (132) and the three-way valve (112) is minimized.

This is to minimize the retention amount of the sampled electrolyte, and as the retention amount is minimized, the concentration error of the diluted solution can be reduced.

That is, in order to improve the accuracy of the concentration measurement, the accuracy of the concentration measurement is improved only when the amount of electrolyte and ultrapure water injected into the cylinder is accurately injected.

At this time, if the distance between the first sampling point 111 and the 3-way valve 112 and the distance between the dilution cylinder 132 and the 3-way valve 112 are long, the electrolyte or Since the amount of ultrapure water may increase, it is necessary to measure the amount contained in this pipe in advance and correct it by the amount.

Accordingly, by minimizing the distance between the first sampling point 111 and the 3-way valve 112 and the distance between the dilution cylinder 132 and the 3-way valve 112, the electrolyte or If the amount of ultrapure water is reduced and the amount is insignificant, the correction step may not be performed, and contamination of the pipe through which the electrolyte moves may be prevented.

On the other hand, the inside of the 3-way valve (3-way valve) is characterized in that it is sealed with EPDM material. The EPDM material is a material with high acid resistance, and by sealing the inside of the 3-way valve (3-way valve) with EPDM material, it is possible to improve durability by preventing corrosion caused by acid, and has an effect of preventing leakage when the valve direction is changed. there is.

The absorbance measuring unit 150 measures the absorbance of the diluted solution in real time, and includes an auto sampler 151 and an ultraviolet-visible spectrometer 152.

The auto sampler 151 is connected to the dilution cylinder 132, and collects a certain amount of the dilution solution and injects it into the ultraviolet-visible spectrometer 152. Accordingly, it is preferable to further include a pump between the dilution cylinder 132 and the ultraviolet-visible spectrometer 152 to collect a predetermined amount of the dilution solution with the auto sampler 151 .

Hereinafter, a real-time monitoring method using the real-time charge/discharge monitoring device 100 of the vanadium redox flow battery will be described.

The real-time monitoring method using the real-time charging and discharging monitoring device 100 of the vanadium redox flow battery includes a sampling step of sampling an electrolyte, an electrolyte dilution step of diluting the electrolyte to prepare a diluted solution, and measuring the absorbance of the diluted solution in real time. It is characterized in that it comprises an absorbance measurement step of measuring with.

The sampling step includes a first sampling step of sampling the anode electrolyte moving to the cathode or a second sampling step of sampling the anode electrolyte moving to the anode. In detail, it is characterized in that the sampling is performed by controlling the 3-way valve (3way, 112) in order to sample the cathode electrolyte or the anode electrolyte.

In the electrolyte dilution step, the sampled negative electrolyte or the positive electrolyte is transferred to the dilution cylinder 132, and ultrapure water is supplied to the dilution cylinder to dilute the negative electrolyte or the positive electrolyte to prepare a diluted solution. to be characterized

In this case, a stirring process may be further included to uniformly dilute the negative electrolyte or the positive electrolyte. That is, a stirrer is disposed under the dilution cylinder 132, and a magnet is added to the dilution cylinder 132 containing the cathode electrolyte or the anode electrolyte and the ultrapure water to perform stirring, thereby removing the anode electrolyte or the anode electrolyte. It can be diluted evenly.

The absorbance measuring step is characterized by measuring the absorbance value of the diluted solution using a UV-Visible spectrophotometry (152).

Specifically, it is preferable to collect a diluted solution using the auto sampler 151, and inject the diluted solution into the ultraviolet-visible spectrophotometer (UV-Visible spectrophotometry, 152) to measure absorbance.

On the other hand, in order to sample the electrolyte and prepare a diluted solution using the sampled electrolyte, the 3-way valve 112 is characterized in that it operates as disclosed in FIG. 3. Hereinafter, a method for diluting the cathode electrolyte or the anode electrolyte with reference to FIG. 3 will be described with reference to the three-way valve 112.

At the time of sampling, the electrolyte in the electrolyte state at the time of sampling is filled from the sampling point (111 or 121) to the 3-way valve 112 before. At this time, the electrolyte needs to be discarded. Accordingly, the pipe connected to the 3-way valve at the bottom of the dilution cylinder is released and the 3-way valve is opened for electrolyte sampling, from the sampling point (111 or 121) to the 3-way valve 112 and from the 3-way valve 112 to the discharge port ( 140), it is preferable to discard the solution filled in the pipe to the tray.

That is, since the ultrapure water flowed from the 3-way valve 112 to the outlet 140 during the previous analysis, a clear solution comes out first, and then a thick electrolyte solution comes out.

Furthermore, for accurate measurement, it is preferable to start sampling after the electrolyte solution flowing out at the beginning of sampling is discharged for a certain period of time.

As shown in FIG. 3, a 3-way valve 112 connected to the first sampling point 111 and the dilution cylinder 132 or a 3-way valve 112 connected to the second sampling point 121 and the dilution cylinder 132 The way valve 112 is opened, and the 3-way valve 112 connected to the ultrapure water supply unit 131 is not opened so that the cathode electrolyte or the anode electrolyte is sampled and transferred to the dilution cylinder 132.

Then, the opening degree of the 3-way valve is changed so that the ultrapure water is injected, and the ultrapure water is entered.

The diluted diluted solution is to measure the absorbance value using the ultraviolet-visible spectrophotometry (UV-Visible spectrophotometry, 152), put the 3-way valve 112 in neutral so that the diluted solution does not flow in any direction, , It is characterized in that the diluted solution is collected using the autosampler 151. Thereafter, the absorbance of the anode electrolyte or cathode electrolyte may be measured by injecting the diluted solution into the ultraviolet-visible spectrophotometer (UV-Visible spectrophotometry, 152).

Thereafter, the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions are applied to the following formula 1 or formula 2 to determine the state of charge (SOC) of the electrolyte It is characterized by judging.

Calculation 1

SOC =

Calculation 2

SOC =

Hereinafter, the present invention will be described in detail through Examples and Experimental Examples. However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the present invention is not limited by the following Examples and Experimental Examples.

Experimental Example 1. Preparation of tetravalent vanadium and measurement of absorbance.

VOSO ₄ 99.9% powder exists as a hydrate, and after quantifying the amount of moisture through ICP analysis, an appropriate amount was taken to prepare 1.5M vanadium tetravalent ions.

At this time, the VOSO ₄ powder was prepared by dissolving in 3M sulfuric acid.

At this time. A sample of the tetravalent vanadium ion was analyzed with an ultraviolet-visible spectrometer to obtain a graph having absorbance values of 767.9 nm and 604.3 nm wavelengths according to the dilution ratio as shown in FIG. 6 and Table 1.

At this time, according to Beer's law, the concentration of the substance (0.15M or less) and the absorbance are proportional to the following equation, and the absorbance of this wavelength appears in proportion to the concentration, and a proportional relationship is formed between the wavelengths and the absorbance.

Equation 1.

A = εbC (where A is the absorbance, ε is the molar absorptivity (slope of the calibration curve), b is the length of the cell through which light passes (1 cm, the value is 1), and C is the concentration.)

In the case of a single component, Equation 1 is applied, and it indicates that the concentration vs. absorbance calibration curve passes the 0 point.

Eq 2.

A = εbC + d

Wavelength (nm) 12.5-fold dilution
absorbance 15.6-fold dilution
absorbance 20.8-fold dilution
absorbance 31.2 fold dilution
absorbance 62.5 fold dilution
absorbance Average absorbance vs. 767.9nm absorbance 767.9 2.07136 1.6483 1.22884 0.82815 0.40475 One 604.3 0.74725 0.59608 0.44697 0.2966 0.144 0.360001

Referring to FIG. 6 and Table 1, the tetravalent vanadium ion has absorbance values measured at wavelengths of 767.9 nm and 604.3 nm, and the natural wavelength of the tetravalent vanadium ion is 767.9 nm, and in the 604.3 nm wavelength range. It is characterized in that it exhibits an absorbance value of 0.36 times the absorbance measured at the natural wavelength of the 4-valent vanadium ion.

In addition, the calibration curve relational expression for each concentration of the absorbance of the tetravalent vanadium ion at a wavelength of 767.9 nm is the same as the calibration curve relational expression 1 below.

Calibration curve relational expression 1.

y = 17.306x - 0.0098

Experimental Example 2 and Experimental Example 3. Preparation of trivalent vanadium ions and pentavalent vanadium ions and measurement of absorbance.

The tetravalent vanadium ions prepared in Experimental Example 1 were placed on the positive electrode and the negative electrode, and through an electrochemical reaction, trivalent vanadium ions were produced at the negative electrode and pentavalent vanadium ions were produced at the positive electrode.

At this time, the trivalent vanadium ion sample was analyzed with an ultraviolet-visible spectrometer to obtain a graph having absorbance values of 604.3 nm and 396.8 nm wavelengths according to the dilution ratio as shown in FIG. 7 and Table 2.

In addition, the pentavalent vanadium ion sample was analyzed with an ultraviolet-visible spectrometer to obtain a graph having absorbance values of 396.8 nm and 767.9 nm wavelengths according to the dilution ratio as shown in FIG. 5 and Table 3.

Wavelength (nm) 8.33 fold dilution
absorbance 10x dilution
absorbance 12.5-fold dilution
absorbance 16.67 fold dilution
absorbance Average absorbance versus absorbance at 604.3 nm 604.3 1.27915 1.08766 0.8597 0.65839 One 396.8 2.03615 1.70521 1.35662 1.04732 1.58208

Referring to FIG. 7 and Table 2, the trivalent vanadium ion has absorbance values measured at wavelengths of 604.3 nm and 396.8 nm, the natural wavelength of the trivalent vanadium ion is 604.3 nm, and in the 396.8 nm wavelength range Characterized in that it exhibits an absorbance value of 1.58 times the absorbance measured at the natural wavelength of trivalent vanadium ion.

In addition, the calibration curve relational expression for each concentration of the absorbance of the trivalent vanadium ion at a wavelength of 604.3 nm is the same as the calibration curve relational expression 2 below.

Calibration curve relational expression 2.

y = 6.3335x + 0.0314.

wavelength
(nm) 16.67 fold dilution
absorbance 20x dilution
absorbance 25-fold dilution
absorbance 33.33 fold dilution
absorption copper 50-fold dilution
absorbance Average absorbance versus absorbance at 396.8 nm 396.8 1.05876 0.85243 0.68985 0.50916 0.35918 One 767.9 0.03393 0.02701 0.02557 0.01459 0.00932 0.03056

5 and Table 3, the pentavalent vanadium ion has absorbance values measured at wavelengths of 396.8 nm and 767.9 nm, the natural wavelength of the pentavalent vanadium ion is 396.8 nm, and in the 767.9 nm wavelength range It is characterized in that it exhibits an absorbance value of 0.03 times the absorbance measured at the natural wavelength of 5-valent vanadium ion.

In addition, the calibration curve relational expression for each concentration of the absorbance of the pentavalent vanadium ion at a wavelength of 396.8 nm is shown in the following calibration curve relational expression 3.

Calibration curve relational expression 3.

y = 12.191x - 0.0032

Experimental Example 4. Preparation of divalent vanadium ions and measurement of absorbance.

The tetravalent vanadium ions prepared in Experimental Example 1 were put into the positive electrode electrolyte bath, and the trivalent vanadium ions prepared in Experimental Example 2 were put into the negative electrode electrolyte bath, followed by a charging reaction to produce divalent vanadium ions at the negative electrode.

At this time. The divalent vanadium ion sample was analyzed with an ultraviolet-visible spectrometer to obtain a graph having absorbance values of 846.7 nm, 604.3 nm, and 396.8 nm wavelengths according to the dilution ratio as shown in FIG. 4 and Table 4.

wavelength
(nm) 5-fold dilution
absorbance 10x dilution
absorbance 12.5 times dilution
absorbance 16.67 fold dilution
absorbance 846.7nm absorbance contrast
average absorbance 846.7 0.62262 0.29094 0.2396.84 0.16708 One 604.3 1.20121 0.62136 0.4732 0.37378 2.11747 396.8 1.1199 0.61976 0.45158 0.38807 2.114

Referring to FIG. 4 and Table 4, it can be seen that the wavelength appearing only in divalent vanadium ions is around 846.7 nm. In detail, when the absorbance of divalent vanadium ions is measured, a peak is basically observed at a wavelength of 846.7 nm, and it can be confirmed that 604.3 nm and 396.8 nm wavelengths appear together with this wavelength.

That is, the divalent vanadium ion has absorbance values measured at wavelengths of 846.7 nm, 604.3 nm, and 396.8 nm, the natural wavelength of the divalent vanadium ion is 846.7 nm, and the divalent vanadium ion in the wavelength range of 604.3 nm It can be seen that the absorbance value is 2.12 times the absorbance value measured at the natural wavelength of , and the absorbance value is 2.11 times the absorbance value measured at the natural wavelength in the 396.8 nm wavelength range.

In addition, the calibration curve relational expression for each concentration of the absorbance of the divalent vanadium ion at a wavelength of 846.7 nm is shown in the following calibration curve relational expression 4.

Calibration curve relational expression 4.

y = 1.9534x - 0.0266

Comparative Example 1. Manual sample collection (during filling), dilution and absorbance measurement

(A) Cathode (divalent, trivalent vanadium ion) sampling from the VRFB system (manual)

As shown in the sequence of FIG. 8, the valve of the sampling point of the VRFB system is opened and the cathode electrolyte is received in the beaker.

(B) 20-fold dilution

2.5ml of the anode electrolyte collected from the beaker (A) is put in a 50ml flask, diluted 20 times with ultrapure water according to the 50ml scale, and then stirred.

(C) Absorbance measurement

In order to measure the absorbance with the UV-Visible spectrometer, the sample in (B) is flowed through the UV-Visible spectrometer with an autosampler without bubbles in the cell of the spectrometer. And absorbance is measured. The result is obtained by measuring the absorbance of all wavelengths.

(D) Results

The absorbance values measured by a UV-Visible spectrometer were as follows.

Wavelength (nm) 20 times
dilution absorbance 2-valent absorbance trivalent absorbance tetravalent absorbance Pentavalent absorbance 846.7 nm 0.01354 0.01354 604.3 nm 0.41574 0.02867 a d 767.9 nm 0.02362 b e 396.8 nm 0.66597 0.02862 f c

The basis of divalent vanadium is 846.7 nm, and along with this wavelength, wavelengths around 604.3 nm and 396.8 nm also appear. Absorbance of 2.11747 times the absorbance of 846.7nm wavelength appears around 604.3nm, and the absorbance at 604.3nm becomes 0.02867 by divalent.

In addition, 2.114 times the absorbance at 846.7 nm appears around 396.8 nm, so the absorbance becomes 0.02862.

The basis of trivalent vanadium is 604.3 nm, and along with this wavelength, a wavelength appears around 396.8 nm. An absorbance of 1.582081 times the wavelength of 604.3 nm appears around 396.8 nm.

Therefore, the relationship between a and f in Table 5 is f = 1.582081*a. And a is obtained by subtracting the absorbance derived from divalent vanadium and the absorbance derived from tetravalent vanadium from the measured absorbance. That is, a relationship of a = 0.41574-0.02867-d arises.

The basis of tetravalent vanadium is 767.9 nm, and along with this wavelength, a wavelength around 604.3 nm appears. 0.360009 times the absorbance of the 767.9 nm wavelength appears around 604.3 nm. Therefore, it has a relationship of d = 0.360009*b. In addition, b is obtained by subtracting the absorbance derived from pentavalent vanadium from the measured absorbance. That is, the relationship of b = 0.02362-e arises.

The base of pentavalent vanadium is 396.8 nm, and a wavelength around 767.9 nm appears along with this wavelength.

An absorbance of about 0.030556 times the wavelength of 396.8 nm appears around 767.9 nm. Therefore, it has a relationship of e = 0.030556*c. In addition, c is obtained by subtracting the absorbance derived from divalent vanadium and the absorbance derived from trivalent vanadium from the measured absorbance. That is, the relationship of c = 0.66597-0.02862-f arises.

If these are simply represented, they can be simplified as shown in Table 6.

Wavelength (nm) 20-fold dilution absorbance 2-valent absorbance trivalent absorbance tetravalent absorbance Pentavalent absorbance 846.7 nm 0.01354 0.01354 604.3 nm 0.41574 0.02867 0.38707-d d 767.9 nm 0.02362 d/0.360009 c×0.030556 396.8 nm 0.66597 0.02862 1.582081×
(0.38707-d) c

c=0.66597-0.02862-(1.582081×(0.038707-d))=0.02497+1.582081×d

Here, the tetravalent absorbance value at 767.9 nm is equal to the value obtained by subtracting the pentavalent absorbance from the measured absorbance. That is, d / 0.360009 = 0.02362 - (0.02497 + 1.582081 × d) × 0.030556 = 0.02286 - 0.04834 × d, where d = 0.00809 is calculated. Therefore, Table 6 is organized as Table 7 below.

Wavelength (nm) 20 times
dilution absorbance 2-valent absorbance trivalent absorbance tetravalent absorbance Pentavalent absorbance measured concentration actual concentration
(20x) 846.7 0.01354 0.01354 0.02055 0.41098 604.3 0.41574 0.02867 0.37898 0.00809 0.05488 1.0976 767.9 0.02362 0.02247 0.00115 0.00186 0.03729 396.8 0.66597 0.02862 0.59958 0.03777 0.00336 0.06721

That is, SOC is defined as in Equation 1 below.

Calculation 1

SOC =

The SOC of the negative electrolyte sampled manually is as follows.

SOC = (0.41098)/(0.41098+1.0976) = 0.27243

The cathode electrolyte is composed mostly of divalent and trivalent vanadium ions. This is the point at which trivalent vanadium becomes the main and divalent vanadium is generated according to sampling 5 minutes after the end of discharge and the start of charging. However, the amount of tetravalent and pentavalent vanadium ions moved through the separator that separates the anode and cathode of the battery, and the amount corresponds to about 6.5% of the total.

When charging, the positive electrolyte tends to move to the negative electrode, and when discharging, the negative electrolyte tends to move to the positive electrode. It can be seen that this sample is a charging sample and a negative electrode sample, so that about 6.5% of the electrolyte in the positive electrode migrates to the negative electrode.

Example 1. Automated sampling line configuration (during charging) Dilution of cathode electrolyte and measurement of absorbance

(A) Taking a sample from the VRFB system (semi-automated)

As shown in FIG. 2, a certain amount (eg, 5 ml) of cathode electrolyte is transferred to the cylinder for dilution by opening the 3-way valve so that the sample moves from the sampling point of the VRFB system to the analyzer. Before that, measure the volume of the tube between the cylinders in the 3-way valve.

(B) 20-fold dilution

Open the 3-way valve so that the cathode electrolyte is contained in the cylinder for dilution, and receive 5 ml into the cylinder. Then, turn the 3-way valve to allow pure water to flow so that the total volume is 100 ml in the dilution cylinder. Then, insert a magnet for stirring and stir.

(C) Absorbance measurement

To measure the absorbance with the UV-Visible spectrometer, pump the sample from the dilution cylinder to the UV-Visible spectrometer through the auto sampler pump for the absorbance meter. And absorbance is measured. The result is obtained by measuring the absorbance of all wavelengths.

(D) Results

Table 8 shows the absorbance analysis value and the relationship between the values.

Wavelength (nm) 20 times
dilution absorbance 2-valent absorbance trivalent absorbance tetravalent absorbance Pentavalent absorbance measured concentration actual concentration
(20x) 846.7 0.00474 0.00474 0.01604 0.32088 604.3 0.38287 0.01004 0.36774 0.00509 0.05311 1.0621 767.9 0.01627 0.01414 0.00213 0.00138 0.02767 396.8 0.66146 0.01002 0.5818 0.06964 0.00597 0.1195

Calculated as in Equation 1 above according to the concentration of the negative electrolyte sampled semi-automatically, SOC was obtained as 0.23202. In other words, as a result of analysis of the system composed of a semi-automated sampling line in which the system electrolyte was collected by opening the 3-way valve directly in the dilution cylinder and the pure water was added by opening the 3-way valve again, the result of SOC was 23.2%. .

After the manual sample of Comparative Example was taken, the semi-automated sample was taken, resulting in a slight difference in concentration due to a time difference and a corresponding difference in SOC. In addition, it can be seen that about 9.6% of the total vanadium ions of 4 and 5 have migrated.

Example 2. Configuration of semi-automated sampling line (during charging), dilution of anode electrolyte and measurement of absorbance

(A) Taking a sample from the VRFB system (semi-automated)

Open the 3-way valve to move the sample from the sampling point of the VRFB system to the analyzer, and transfer a certain amount (eg, 2.5ml) of the anode electrolyte to the dilution cylinder. That is, sampling is performed through the second sampling point and the 3-way valve connected thereto, and the volume of the tube between the cylinders is measured in the 3-way valve beforehand.

(B) 40-fold dilution

Open the 3-way valve so that the positive electrolyte is contained in the cylinder for dilution, and receive 2.5 ml into the cylinder. Then, turn the 3-way valve to allow pure water to flow so that the total volume of 100 ml is poured into the cylinder for dilution. Then, insert a magnet for stirring and stir.

(C) Absorbance measurement

To measure the absorbance with the UV-Visible spectrometer, pump the sample from the dilution cylinder to the UV-Visible spectrometer through the auto sampler pump for the spectrometer. And absorbance is measured. The result is obtained by measuring the absorbance of the relevant wavelength.

(D) Results

The following absorbance values and the relationship between the values are shown in the following table, and the SOC of the anode electrolyte is calculated by the following formula 2.

Calculation 2

SOC =

Wavelength (nm) 40 times
dilution absorbance 2-valent absorbance trivalent absorbance tetravalent absorbance Pentavalent absorbance measured concentration actual concentration
(40 times) 846.7 0 0 0 0 604.3 0.19924 0 (-0.00367) 0.20097 (-0.0055) 0 767.9 0.56415 0.55823 0.00592 0.03282 1.31291 396.8 0.19374 0 0.19374 0.01615 0.64618

When the concentration was converted into the trivalent absorbance value at 604.3 nm, the measured concentration was -0.00367, and this value was treated as 0. The SOC according to the concentration of the positive electrolyte collected semi-automatically obtained a result of 0.32984, which was calculated using the above formula 1.

Samples of the anode electrolyte of Example 1 were taken and samples of the cathode electrolyte of Example 2 were taken, and a difference in SOC occurred according to the time difference.

At the time of charging, since the electrolyte of the positive electrode tends to slightly permeate through the separator to the negative electrode, negative ions were not detected from the positive electrode. That is, it is believed that the analysis value measured in this way can obtain a reliable result and analyze the electrolyte in real time by a semi-automated sampling method.

In this specification, only a few examples of various embodiments performed by the present inventors are described, but the technical idea of the present invention is not limited or limited thereto, and can be modified and implemented in various ways by those skilled in the art, of course.

Claims (14)

Sampling unit for sampling the electrolyte;
An electrolyte dilution unit for diluting the electrolyte to prepare a diluted solution; and
To include; absorbance measurement unit for measuring the absorbance of the diluted solution in real time,
Determine the state of charge (SOC) of the electrolyte by applying the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions to Equation 1 or Equation 2 below to do,
Real-time charge/discharge monitoring device for vanadium redox flow battery.
Calculation 1
SOC =

Calculation 2
SOC =

According to claim 1,
The sampling unit includes a first sampling unit for sampling the cathode electrolyte moving to the cathode; and
To include; a second sampling unit for sampling the anode electrolyte moving to the anode,
The sampling unit is to include a 3-way valve (3 way valve),
Real-time charge/reversal monitoring device for vanadium redox flow battery. According to claim 2,
The inside of the 3-way valve (3-way valve) is sealed with EPDM material,
Real-time charge/reversal monitoring device for vanadium redox flow battery. According to claim 1,
The electrolyte dilution unit dilution cylinder for diluting the sampled electrolyte; and
To include; ultrapure water supply unit for supplying ultrapure water to the dilution cylinder,
Real-time charge/reversal monitoring device for vanadium redox flow battery. A sampling step of sampling the electrolyte;
An electrolyte dilution step of diluting the electrolyte to prepare a diluted solution; and
Absorbance measurement step of measuring the absorbance of the diluted solution in real time; comprising,
Determine the state of charge (SOC) of the electrolyte by applying the absorbance value of the diluted solution and the absorbance value according to the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions to Equation 1 or Equation 2 below to do,
Real-time charging and discharging monitoring method of vanadium redox flow battery.
Calculation 1
SOC =

Calculation 2
SOC =

According to claim 5,
The sampling step includes a first sampling step of sampling the anode electrolyte moving to the cathode or a second sampling step of sampling the anode electrolyte moving to the anode,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The electrolyte dilution step transfers the electrolyte to a dilution cylinder,
To dilute by supplying ultrapure water to the dilution cylinder,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The absorbance measurement step is to measure the absorbance value of the diluted solution using a UV-Visible spectrophotometry,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The divalent vanadium ion has absorbance values measured at wavelengths of 846.7 nm, 604.3 nm and 396.8 nm,
The natural wavelength of the divalent vanadium ion is 846.7 nm,
Represents an absorbance value of 2.12 times the absorbance measured at the natural wavelength of the divalent vanadium ion in the 604.3 nm wavelength range,
In the 396.8 nm wavelength range, which represents an absorbance value of 2.11 times the absorbance value measured at the natural wavelength,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The trivalent vanadium ion has absorbance values measured at wavelengths of 604.3 nm and 396.8 nm,
The natural wavelength of the trivalent vanadium ion is 604.3 nm,
In the 396.8 nm wavelength range, exhibiting an absorbance value 1.58 times the absorbance measured at the natural wavelength of the trivalent vanadium ion,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The tetravalent vanadium ion has absorbance values measured at wavelengths of 767.9 nm and 604.3 nm,
The natural wavelength of the tetravalent vanadium ion is 767.9 nm,
In the 604.3 nm wavelength range, exhibiting an absorbance value of 0.36 times the absorbance measured at the natural wavelength of the tetravalent vanadium ion,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
The pentavalent vanadium ion has absorbance values measured at wavelengths of 396.8 nm and 767.9 nm,
The natural wavelength of the pentavalent vanadium ion is 396.8 nm,
To produce an absorbance value 0.03 times the absorbance measured at the natural wavelength of the 5-valent vanadium ion in the 767.9 nm wavelength range,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 5,
A calibration curve graph is prepared through the absorbance values for each concentration at the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions,
Measuring the concentration of an unknown sample using the calibration curve,
Real-time charging and discharging monitoring method of vanadium redox flow battery. According to claim 13,
The calibration curve at the natural wavelength of the divalent, trivalent, tetravalent, and pentavalent vanadium ions is
To create a calibration curve graph by subtracting the absorbance values of other ions affecting each ion from the absorbance values of the natural wavelengths of the divalent, trivalent, tetravalent, and pentavalent vanadium ions,
Real-time charging and discharging monitoring method of vanadium redox flow battery.

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