Method for monitoring capacity of all-vanadium redox flow battery on line

Abstract

The invention relates to the technical field of battery capacity monitoring, in particular to an all-vanadium redox flow battery capacity on-line monitoring method which comprises the following steps: firstly, detecting the valence state composition of positive and negative electrode ions of an all-vanadium redox flow battery, and calculating the number of available electrons of the positive and negative electrodes through an available electron number calculation formula; and substituting the concentration and volume of one side with less available electrons into a theoretical capacity formula to calculate the theoretical capacity of the current all-vanadium redox flow battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery capacity monitoring, and particularly relates to a method for online monitoring of the capacity of a vanadium redox flow battery. Background Art

[0002] Due to its excellent scalability, long life, and environmental adaptability, the vanadium redox flow battery is playing an increasingly important role in the energy storage field, especially in large-scale energy storage systems. However, after long-term operation, the vanadium redox flow battery will inevitably experience capacity decay, which will reduce battery performance and increase maintenance costs. In order to achieve real-time monitoring of the battery state, timely detect performance changes, and prevent potential failures, it is particularly crucial to research and develop a method for online monitoring of the capacity of the vanadium redox flow battery.

[0003] The traditional method for monitoring battery capacity is to take samples from the positive and negative electrolyte tanks respectively, detect the concentrations of vanadium ions in various valence states in the positive and negative electrolytes by potentiometric titration, analyze the concentration changes, and then evaluate the state of the battery capacity. However, this method of sampling the electrolyte will expose the electrolyte to the air, affecting the determination of the concentration, and has a poorer effect compared with the online monitoring method. Patent (CN118263484A) proposes a method for detecting the stable state of the electrolyte of a vanadium redox flow battery, and judges whether the electrolyte is in a stable state according to the values of the volume change rate, concentration change rate, and average valence state. However, due to the presence of various sensors, primary batteries, and secondary batteries, its monitoring system is relatively complex and costly. Therefore, there is still a need to research and develop a new method for online monitoring of the capacity of the vanadium redox flow battery in engineering. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for online monitoring of the capacity of a vanadium redox flow battery, and solve the technical problem that the online monitoring system of the capacity of the vanadium redox flow battery in the prior art is relatively complex and costly.

[0005] The present invention discloses a method for online monitoring of the capacity of a vanadium redox flow battery, including the following steps:

[0006] First, detect the valence state composition of the positive and negative ions of the vanadium redox flow battery, calculate the available electron numbers of the positive and negative electrodes through the available electron number calculation formula, and substitute the concentration and volume of the side with fewer available electron numbers into the theoretical capacity formula to calculate the current theoretical capacity of the vanadium redox flow battery.

[0007] Further, according to the theoretical capacity Q of the vanadium redox flow battery, construct the available electron number calculation formula for vanadium ions in the positive and negative electrolytes.

[0008] Further, the theoretical capacity Q of the vanadium redox flow battery is given by the following formula:

[0009] Q = n·F·C·V

[0010] Where n is the number of electron transfers in each reaction process (n=1 in all-vanadium flow battery), F is the Faraday constant, F=96485C / mol, C: substance concentration of vanadium electrolyte (unit: mol / L), V: volume of vanadium electrolyte (unit: L).

[0011] Furthermore, through the VO2 in the positive and negative electrolytes + and V 2+ The total amount of electrons available at the positive and negative electrodes is obtained.

[0012] Furthermore, the number of electrons available at the positive and negative electrodes can be calculated as follows:

[0013] z 正 =1·V 正 ·C 5+

[0014] z 负 =1·V 负 ·C 2+

[0015] Where z is the number of available electrons in the positive and negative electrolytes, V is the volume of the positive and negative electrolytes (unit: L), C i+ : Substance concentration of vanadium electrolyte (unit: mol / L).

[0016] Furthermore, the valence composition of the positive and negative ions of the all-vanadium redox flow battery was detected by ultraviolet-visible photometer.

[0017] Furthermore, the capacity of the solution is restored according to the test results.

[0018] Furthermore, the capacity recovery is to transport the electrolyte on the side with more available electrons to the other side until the available electron numbers on both sides are balanced, thereby completing the capacity recovery of the electrolyte.

[0019] Furthermore, the volume formula required for capacity recovery is as follows:

[0020] V=|z 正 -z 负 | / (2C i+ )

[0021] Where V is the transfer volume of capacity recovery (unit: L), z is the number of available electrons at the positive and negative electrodes, and C i+ VO2 on the side with fewer available electrons + or V 2+ Concentration (unit: Mol / L).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention directly detects the comprehensive valence information of vanadium electrolyte, achieving real-time online monitoring of electrolyte concentration and valence, and providing accurate and timely data support for the control strategy of all-vanadium redox flow battery system;

[0024] 2. The invention combines the valence state composition of vanadium electrolyte with battery capacity, allowing direct analysis of capacity through comprehensive valence state information without the need to fully charge and discharge the battery;

[0025] 3. The present invention can adjust the flow of the positive electrode electrolyte to the negative electrode electrolyte, or adjust the flow of the negative electrode electrolyte to the positive electrode electrolyte according to the capacity displayed by the comprehensive valence state, so as to achieve the purpose of restoring the capacity. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0027] Unless otherwise specified, the examples of this application use carbon felt as the reaction electrode and Nafion 115 ion exchange membrane produced by DuPont as the separator to assemble the experimental battery. The positive and negative electrolytes are 1.7 mol / L VOSO4 + 4.78 mol / L H2SO4, respectively, and the electrode effective area is 25 cm 2 .

[0028] Example 1

[0029] The method for online monitoring of the capacity of an all-vanadium redox flow battery using the above-mentioned device in this embodiment includes the following steps:

[0030] (1) First, construct the theoretical capacity formula of all-vanadium redox flow battery:

[0031] According to Faraday's law, the theoretical capacity Q of the all-vanadium flow battery is given by the following formula:

[0032] Q=n·F·C·V

[0033] Where n is the number of electrons transferred during each reaction (n = 1 in an all-vanadium flow battery). F is the Faraday constant, F = 96485 C / mol. C is the concentration of the vanadium electrolyte (mol / L). V is the volume of the vanadium electrolyte (L).

[0034] It should be noted that the total vanadium ion concentration (C 总 ): is the total concentration of all vanadium ions in the electrolyte, usually expressed in mol / L.

[0035] Effective substance concentration (C 有效): is the concentration of vanadium ions that can participate in the electrochemical reaction.

[0036] Based on this, in an ideal situation, C 有效 is equal to C 总 , that is, all vanadium ions can participate in the reaction. However, in practice, due to problems such as ion migration or side reactions, there is always an asymmetric phenomenon in the positive and negative electrode electrolytes of the all-vanadium redox flow battery, resulting in some vanadium ions being unable to participate in the reaction and the electrochemical reaction not being fully carried out. At this time, the side where vanadium ions fully participate in the reaction ("limiting electrolyte") determines the capacity of the all-vanadium redox flow battery.

[0037] (2) Construct the calculation formula for the available number of electrons of vanadium ions in the positive and negative electrode electrolytes

[0038] During the operation of the all-vanadium redox flow battery, due to the existence of oxidation side reactions and vanadium migration and water migration, the valence state of the negative electrode of the vanadium electrolyte increases and the total vanadium amount decreases. However, at this time, it is impossible to judge which of the positive and negative electrode electrolytes becomes the "limiting electrolyte" simply from the concentration or volume (total vanadium amount). The available number of electrons of the all-vanadium redox flow battery refers to the total number of electrons transferred by vanadium ions participating in the oxidation-reduction reaction in the electrolyte. During discharge, VO2 + in the positive electrode electrolyte is reduced to VO 2+ , and V 2+ in the negative electrode electrolyte is oxidized to V 3+ , and both reactions transfer one electron. By comparing the total amounts of VO2 + and V 2+ in the positive and negative electrode electrolytes, the available number of electrons of the positive and negative electrodes can be obtained. The calculation of the available number of electrons of the positive and negative electrodes is as follows:

[0039] z 正 = 1·V 正 ·C 5+

[0040] z 负 = 1·V 负 ·C 2+

[0041] where z: the available number of electrons of the positive and negative electrode electrolytes, V: the volume of the positive and negative electrode electrolytes (unit: L), C i+ : the molar concentration of the vanadium electrolyte (unit: mol / L).

[0042] (3) Test the valence composition of the vanadium electrolyte by an ultraviolet-visible spectrophotometer, calculate the available number of electrons of the positive and negative electrodes through the available number of electrons calculation formula, and substitute the concentration and volume of the side with fewer available number of electrons into the theoretical capacity formula to calculate the current theoretical capacity of the all-vanadium redox flow battery.

[0043] Install liquid level gauges in the positive and negative electrolyte storage tanks and export the positive and negative electrolytes to an ultraviolet-visible spectrophotometer through pipelines. The liquid level gauges can calculate the volumes of the positive and negative electrolytes respectively, while the ultraviolet-visible spectrophotometer can test the valence state compositions of the positive and negative ions. Then, the available electron numbers of vanadium ions in the positive and negative electrolyte storage tanks can be obtained through calculation. Take the concentration and volume of the electrolyte on the side with fewer total available electrons (the side with fewer transferable electrons limits the capacity) in the positive and negative electrodes as the effective concentration and effective volume, and the theoretical capacity at this time can be calculated as:

[0044] Q = n·F·C 有效 ·V 有效

[0045] where n is the number of electrons transferred in each reaction process (n = 1 in a vanadium redox flow battery). F is the Faraday constant, F = 96485 C / mol, and C 有效 : the effective substance concentration of the vanadium electrolyte (unit: mol / L). V 有效 : the effective volume of the vanadium electrolyte (unit: L).

[0046] By using the method of this embodiment, online capacity monitoring is carried out on three vanadium redox flow batteries with different attenuation degrees, and their actual capacities are tested for comparison, which are named Battery 1#, Battery 2#, and Battery 3# respectively.

[0047] Table 1

[0048]

[0049] According to the data in Table 1, it can be seen that by using the method of this embodiment to carry out online monitoring of the capacity of a vanadium redox flow battery, the capacity of the vanadium redox flow battery can be monitored without complete charge and discharge, and the error compared with the actual capacity is within 8%. Compared with the patents currently found that focus on judging the state of charge (SOC) through information such as concentration and valence state, the theoretical capacity can be calculated through the available electron numbers (reaction available electron numbers), and there is no need to obtain capacity data through complete charge and discharge.

[0050] Example 2

[0051] This embodiment relates to a method for restoring the capacity of a vanadium redox flow battery, including the following steps:

[0052] (1) Calculate the available electron numbers of the positive and negative electrodes as described in steps 2 and 3, calculate the amount of electrolyte that needs to be transferred when the available electron numbers of the positive and negative electrodes are balanced, and pump the calculated amount of electrolyte to be transferred from the side with more available electrons to the other side through a two-way pump, and monitor it in real time through a liquid level gauge.

[0053] (2) When the difference between the ion concentration in the negative electrolyte storage tank and the available electron number in the positive electrolyte storage tank does not exceed 10%, stop the reverse transportation.

[0054] Preferably, in step (2), when the difference in the available electrons between the negative electrode liquid storage tank and the positive electrode liquid storage tank does not exceed 5%, the reverse transportation is stopped.

[0055] By using the method of this embodiment, charge-discharge tests are carried out on 5 all-vanadium redox flow batteries with different degrees of attenuation, which are respectively named Battery 1#, Battery 2#, Battery 3#, Battery 4# and Battery 5#, and the initial capacity, the capacity after recovery and the capacity recovery rate of the above five different batteries are recorded. The specific data are shown in Table 2 below:

[0056] Table 2

[0057]

[0058] According to the data in Table 2, it can be seen that by using the method of this embodiment to rebalance the available electrons of the attenuated all-vanadium redox flow battery, the reverse recovery of the capacity can be realized, the process of battery capacity attenuation can be reversed, turning waste into treasure, so as to achieve the purpose of extending the battery service life. The battery capacity recovery rate is above 89%, and the highest can reach above 97%.

[0059] The above are the implementation manners listed in this embodiment. However, this embodiment is not limited to the above optional implementation manners. Those skilled in the art can obtain many other implementation manners by arbitrarily combining the above manners. Anyone can obtain other various forms of implementation manners under the inspiration of this embodiment. The above specific implementation manners should not be construed as limiting the protection scope of this embodiment. The protection scope of this embodiment should be defined by the claims, and the description can be used to interpret the claims.

Claims

1. A method for on-line monitoring of the capacity of a vanadium redox flow battery, characterized in that: It includes the following steps: First, detect the ion valence state composition of the positive and negative electrodes of the all-vanadium redox flow battery, calculate the available electron numbers of the positive and negative electrodes through the available electron number calculation formula, and substitute the concentration and volume of the side with fewer available electrons into the theoretical capacity formula to calculate the current theoretical capacity of the all-vanadium redox flow battery.

2. The method for online monitoring of the capacity of an all-vanadium redox flow battery according to claim 1, characterized in that: According to the theoretical capacity Q of the all-vanadium redox flow battery, construct the available electron number calculation formula for vanadium ions in the positive and negative electrode electrolytes.

3. A method for online monitoring of the capacity of a vanadium redox flow battery according to claim 2, characterized in that: The theoretical capacity Q of the all-vanadium redox flow battery is given by the following formula: Q = n·F·C·V Where n is the number of electron transfers in each reaction process, and n = 1 in the all-vanadium redox flow battery; F is the Faraday constant, F = 96485 C / mol; C is the molar concentration of the vanadium electrolyte, unit: mol / L; V is the volume of the vanadium electrolyte, unit: L.

4. A method for online monitoring of the capacity of a vanadium redox flow battery according to claim 1, characterized in that: Through VO2 in the positive and negative electrolytes + and V 2+ The total amount of electrons available at the positive and negative electrodes is obtained.

5. A method for online monitoring of the capacity of a vanadium redox flow battery according to claim 4, characterized in that: The available electron numbers of the positive and negative electrodes are calculated as follows: z 正 = 1·V 正 ·C 5+ z 负 = 1·V 负 ·C 2+ where z: the number of available electrons of vanadium electrolyte in the positive and negative electrolytes, V: the volume of the positive and negative electrolytes, unit: L, C i+ : the molar concentration of vanadium electrolyte, unit: mol / L.

6. A method for online monitoring of the capacity of a vanadium redox flow battery according to claim 1, characterized in that: Detect the ion valence state composition of the positive and negative electrodes of the all-vanadium redox flow battery by an ultraviolet-visible spectrophotometer.

7. A method for restoring the capacity of an all-vanadium redox flow battery according to claim 1, characterized in that: Obtain the electron number detection result by the method for on-line monitoring of the capacity of an all-vanadium redox flow battery according to any one of claims 1-6.

8. A method for restoring the capacity of an all-vanadium redox flow battery according to claim 7, characterized in that: Perform capacity restoration on the solution according to the electron number detection result.

9. A method for restoring the capacity of a vanadium redox flow battery according to claim 8, characterized in that: The capacity restoration is to transport the electrolyte on the side with more available electrons to the other side until the available electron numbers on both sides are balanced, thereby completing the capacity restoration of the electrolyte.

10. A method for restoring the capacity of a vanadium redox flow battery according to claim 9, characterized in that: The volume formula required for the capacity restoration is as follows: V = |z 正 -z 负 | / (2C i+ ) Among them, V is the transfer volume unit of capacity recovery: L, z is the number of available electrons at the positive and negative electrodes, C i+ is VO2 on the side with fewer available electrons + or V 2+ concentration unit: Mol / L.

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