CN115133081A

CN115133081A - Method for testing positive electrode charging state and total vanadium ion concentration in all-vanadium redox flow battery

Info

Publication number: CN115133081A
Application number: CN202211037031.5A
Authority: CN
Inventors: 王瑾; 祖革; 郑晓昊
Original assignee: Liquid Flow Energy Storage Technology Co ltd
Current assignee: Liquid Flow Energy Storage Technology Co ltd
Priority date: 2022-08-29
Filing date: 2022-08-29
Publication date: 2022-09-30
Anticipated expiration: 2042-08-29
Also published as: CN115133081B

Abstract

The invention relates to a method for testing the charging state of a positive electrode and the total concentration of vanadium ions in an all-vanadium redox flow battery. The method for testing the positive electrode charging state and the total concentration of vanadium ions in the positive electrode electrolyte in the all-vanadium redox flow battery system comprises the following steps: v ⁴⁺ And (3) concentration testing: sampling the anolyte and testing V in the anolyte at a first specified wavelength ⁴⁺ Concentration Cv of ⁴⁺ ₁ ；V ⁵⁺ And (3) concentration testing: testing V in the positive electrolyte at a second specified wavelength ⁵⁺ Concentration Cv of ⁵⁺ ₁ (ii) a Or adding a first reducing agent into the positive electrode electrolyte to obtain a mixed solution, and testing V in the mixed solution at the first specified wavelength at intervals of unit time by taking the time when the first reducing agent starts to be added as a starting point ⁴⁺ To obtain V in the mixed solution ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ V in the positive electrode electrolyte ⁵⁺ Concentration of Cv ⁵⁺ ₁ =Cv ⁴⁺ ₂ ‑Cv ⁴⁺ ₁ 。

Description

Method for testing positive electrode charging state and vanadium ion total concentration in all-vanadium redox flow battery

Technical Field

The invention relates to a method for testing the charging state of a positive electrode and the total concentration of vanadium ions of an all-vanadium redox flow battery, in particular to a method for obtaining the charging state of the positive electrode, the total concentration data of the vanadium ions in positive electrolyte and the total concentration data of the vanadium ions in the electrolyte preparation process through simple and convenient operation detection, and belongs to the technical field of detection of the electrolyte of the redox flow battery.

Background

In order to realize sustainable development and improve energy environment, human beings begin to utilize new energy such as wind energy and solar energy on a large scale, however, due to instability of new energy power generation, the impact on a power grid is large during grid connection. Therefore, a large-scale energy storage system capable of smoothing power fluctuation and maintaining power balance is developed, wherein the all-vanadium redox flow battery has the advantages of high efficiency, long service life, large capacity, deep charging and discharging and the like, and is one of the main existing large-scale energy storage devices.

The vanadium redox flow battery adopts V: (V:)

）/V（

) And V: (

）/V（

) As a redox couple, the vanadium ion interconversion of different valence states and the storage and release of electric energy are completed in the charging/discharging process. In order to ensure the maximum capacity of the all-vanadium redox flow battery, the positive and negative electrolytes need to maintain a balanced state, that is, the amounts of vanadium ions in the positive and negative electrolytes for oxidation reaction and reduction reaction are the same, for example, when the charge capacity (SOC) of the battery system is 0, VO in the positive electrolyte is present ²⁺ And V in the negative electrode electrolyte ³⁺ The amount needs to be consistent or close, VO in the positive electrolyte when the battery system charge (SOC) is 100% ²⁺ And V in the negative electrode electrolyte ²⁺ The number needs to be uniform or close. Anode and cathode electrolysis of all-vanadium redox flow battery under ideal conditionsThe charge states of the electrolyte are consistent, however, due to transmembrane migration of vanadium ions and water molecules, hydrogen evolution reaction and oxidation reaction of the cathode electrolyte and the like, the charge states of the anode electrolyte and the cathode electrolyte are inconsistent in long-term operation, and the total concentration of the vanadium ions of the anode electrolyte and the vanadium ions of the cathode electrolyte are inconsistent in many cases. If the proportion of vanadium ions in the positive electrolyte and the negative electrolyte is unbalanced or the total concentration of vanadium ions is inconsistent, the electric capacity of the battery system is reduced, so that the stored energy of the battery is reduced, more importantly, the unbalanced electrolyte inevitably causes other side reactions, such as generation of harmful gases, corrosion of electrodes and the like, and finally the whole battery system is possibly scrapped. Therefore, real-time monitoring of the balance state of the positive electrolyte and the negative electrolyte of the all-vanadium redox flow battery can provide a guiding function for maintenance and management work of the electrolyte of the vanadium galvanic pile running for a long time, and safe and stable running of the galvanic pile is ensured.

At present, electrolyte balance test methods of all-vanadium redox flow batteries are mainly divided into two types: (1) respectively measuring the relative potentials of positive and negative electrolytes, namely OCV values, by using a standard electrode; obtaining SOC values corresponding to the positive electrolyte and the negative electrolyte according to the SOC-OCV curves of the positive electrolyte and the negative electrolyte respectively; by comparing the SOC values of the two, equilibrium data of the whole electrolyte can be obtained [ cited documents 1-2](ii) a (2) Drawing a standard working curve of absorbance-vanadium ion concentration; respectively carrying out spectrum scanning on the diluted positive and negative electrolytes by utilizing an ultraviolet visible spectrophotometer to obtain V ³⁺ And VO ²⁺ The absorbance of the characteristic absorption peak is matched with a standard working curve to obtain V ³⁺ And VO ²⁺ The concentration of (c); according to V ³⁺ And VO ²⁺ The concentration calculation of (2) to obtain equilibrium data of the entire electrolyte solution [ cited document 3]. Both the two technologies can rapidly and accurately measure the balance data of the electrolyte, but both the technologies need to utilize perfect laboratory equipment to test in a laboratory environment.

In addition, methods have been reported to calculate other ion content and overall balance of the flow battery by determining the partial ion content.

Reference 4 discloses a vanadium redox battery defined to have a negative half cell and a positive half cellBy first determining V by absorption at a defined wavelength ²⁺ And V ³⁺ Further mixing a specified volume of the negative electrode electrolyte and the positive electrode electrolyte, and then determining V by absorption at a specified wavelength in the mixture of the negative electrode electrolyte and the positive electrode electrolyte ²⁺ And V ³⁺ Or V ³⁺ And V ⁴⁺ And finally calculating V from the concentrations determined in the above steps ⁴⁺ And V ⁵⁺ To determine the state of charge of the positive electrolyte.

Citation 5 develops a portable electrolyte balance testing method for an all-vanadium redox flow battery, which simultaneously samples a positive electrolyte and a negative electrolyte respectively, mixes the positive electrolyte and the negative electrolyte in equal volumes, and measures V in the mixed solution ³⁺ Further, a reducing agent was dropped, and tested for V ³⁺ Maximum concentration of ions, and thus indirectly calculating V ⁴⁺ The degree of non-equilibrium K of the entire electrolyte can be further calculated.

It can be seen that, in the prior art, although a certain research is made on monitoring the balance problem of the positive and negative electrolytes of the all-vanadium redox flow battery, V in the positive electrolyte is ⁵⁺ The convenience or accuracy of the concentration measurement is not sufficient.

Cited document 1: CN 104345278A

Cited document 2: CN 107422267A

Citation 3: CN 102621085A

Cited document 4: CN 109716572A

Cited document 5: CN 110857911A.

Disclosure of Invention

Problems to be solved by the invention

In the production preparation and operation of all-vanadium flow battery systems, the need to determine V is often encountered ⁴⁺ /V ⁵⁺ The total concentration or the proportion of ions in the mixed solution to determine the charging state of the positive electrode. In many different processes for large scale production of electrolytes, the first step of many of the production processes is to use a solution containing V ₂ O ₅ In an acid solution (e.g. hydrochloric acid or hydrochloric acid)Sulfuric acid or sulfuric acid mixture) with a reducing agent (e.g., hydrazine dihydrochloride, oxalic acid, ethylene glycol, etc.) to obtain a solution containing V ⁴⁺ The solution of (1). At the end of the reaction, V in the liquid needs to be adjusted ⁴⁺ And V ⁵⁺ Is tested and the test concentration is compared with the theoretical concentration to determine whether the reaction can be stopped. However, it has been found that there is no disclosure in the prior art that the state of charge of the positive electrode and the V in the positive electrolyte and in the electrolyte during preparation can be easily, quickly and accurately determined ⁴⁺ And V ⁵⁺ The total concentration of vanadium ions.

In addition, the present inventors found that V was measured in the positive electrode electrolyte using an ultraviolet-visible spectrophotometer ⁵⁺ When the absorbance of (1) is higher than that of (B), due to V ⁵⁺ The ultraviolet-visible absorption spectrum of the V-shaped optical fiber does not have a regular complete waveform, so that the V can be accurately determined in practical application ⁵⁺ There are great difficulties with the concentration of (b).

Accordingly, it is an object of the present invention to provide a method for measuring V simply, quickly and accurately ⁵⁺ Concentration of vanadium ions in the positive electrode electrolyte, total concentration of vanadium ions in the positive electrode electrolyte, and state of charge of the positive electrode. For the condition that the concentrations of ions in positive and negative electrolytes in some all-vanadium redox flow battery systems fluctuate dynamically, the method can obtain accurate data of the total concentration of vanadium ions in the positive electrolyte and the electrolyte during preparation at any time, and has important significance for ensuring the balance state of the positive and negative electrolytes and the preparation of the electrolytes.

Means for solving the problems

Through long-term research by the inventor of the present invention, it is found that the technical problems can be solved through implementation of the following technical scheme:

the invention provides a method for testing the charging state of a positive electrode in an all-vanadium redox flow battery system and the total concentration of vanadium ions in positive electrolyte, which is characterized by comprising the following steps:

V ⁴⁺ and (3) concentration testing: sampling the anolyte and testing V in the anolyte at a first specified wavelength ⁴⁺ Concentration Cv of ⁴⁺ ₁ ；

V ⁵⁺ And (3) concentration testing: testing V in the positive electrolyte at a second specified wavelength ⁵⁺ Concentration Cv of ⁵⁺ ₁ (ii) a Or adding a first reducing agent into the positive electrode electrolyte to obtain a mixed solution, and testing V in the mixed solution at the first specified wavelength at intervals of unit time by taking the time when the first reducing agent starts to be added as a starting point ⁴⁺ To obtain V in the mixed solution ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ The maximum concentration Cv ⁴⁺ ₂ I.e. the total concentration of vanadium ions in the positive electrolyte, V in the positive electrolyte ⁵⁺ Concentration Cv of ⁵⁺ ₁ =Cv ⁴⁺ ₂ -Cv ⁴⁺ ₁ 。

The test method according to the above, characterized in that the sampling is performed at any state of charge SOC, preferably at a state of charge SOC of 0.

The test method as described above, wherein the first predetermined wavelength is in a range of 700 to 830 nm.

The test method as described above, wherein the second predetermined wavelength is in a range of 200 to 300 nm.

The method according to the above, wherein the positive electrode charge state determining step includes at least calculating Cv ⁵⁺ ₁ /Cv ⁴⁺ ₂ To evaluate the positive electrode state of charge.

The invention also provides a method for testing the total concentration of vanadium, which is characterized by comprising the following steps:

the preparation step of the solution A comprises the following steps: will contain V ₂ O ₅ Dissolving the powder in an acid solution to obtain a solution containing V ⁵⁺ Solution A of (1);

a reducing agent adding step: adding a second reducing agent to the solution A to obtain a solution containing V ⁴⁺ And V ⁵⁺ Solution B of (4);

V ⁴⁺ and (3) concentration testing: sampling said solution B and measuring V in said solution B at a first defined wavelength ⁴⁺ Concentration of Cv ⁴⁺ ₁ ^’ ；

V ⁵⁺ Concentration and total vanadium concentration test: testing V in the sampled solution B at a second prescribed wavelength ⁵⁺ Concentration Cv of ⁵⁺ ₁ ^’ Then the total concentration of vanadium is Cv ⁴⁺ ₁ ^’ +Cv ⁵⁺ ₁ ^’ (ii) a Or alternatively

Adding a first reducing agent into the sampled solution B to obtain a mixed solution C, and testing V in the mixed solution C at the first specified wavelength at intervals of unit time by taking the starting time of adding the first reducing agent as a starting point ⁴⁺ To obtain V in the mixed solution C ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ ^’ The maximum concentration Cv ⁴⁺ ₂ ^’ I.e. the total concentration of vanadium ions in the solution B, V in the solution B ⁵⁺ Concentration Cv of ⁵⁺ ₁ ^’ =Cv ⁴⁺ ₂ ^’ -Cv ⁴⁺ ₁ ^’ 。

The test method as described above, characterized in that at V ⁴⁺ And in the concentration testing step, the positive electrolyte and the solution B are diluted and then tested.

Test method according to the above, characterized in that the test Cv is ⁴⁺ ₁ 、Cv ⁴⁺ ₂ 、Cv ⁴⁺ ₁ ^’ And Cv ⁴⁺ ₂ ^’ The test was carried out using an optical instrument in which V obtained on the basis of absorptiometry was stored ⁴⁺ At the first prescribed wavelength.

Test method according to the above, characterized in that the test Cv is ⁵⁺ ₁ And Cv ⁵⁺ ₁ ^’ The test was carried out using an optical instrument in which V obtained on the basis of absorptiometry was stored ⁵⁺ At the second prescribed wavelength.

The test method as described above, characterized in that the first reducing agent and the second reducing agent are the same or different and each comprises an inorganic reducing agent and an organic reducing agent.

The test method as described above, wherein the unit time is 3s to 5min, preferably 5s to 3min, and more preferably 30s to 2 min.

ADVANTAGEOUS EFFECTS OF INVENTION

Through the implementation of the technical scheme, the invention can obtain the following technical effects:

1) the method for testing the charging state of the anode in the all-vanadium redox flow battery and the total concentration of vanadium ions in the preparation of the anode electrolyte and the electrolyte is convenient and quick to operate, has low requirements on detection equipment, and has wider applicability;

2) in the detection process of the invention, V can be directly tested ⁴⁺ And V ⁵⁺ Or only detecting V ⁴⁺ The convenience of the detection method is further improved.

3) The method of the invention can be used for V with any concentration and proportion ⁴⁺ /V ⁵⁺ And (4) mixing the solution.

Detailed Description

The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

in the present specification, the numerical range represented by "a value a to B value" means a range including the end point value A, B.

In the present specification, the numerical ranges indicated by "above" or "below" mean the numerical ranges including the numbers.

In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

As used herein, the term "optional" or "optional" is used to indicate that certain substances, components, performance steps, application conditions, and the like are used or not used.

In the present specification, "normal temperature" used means an operating environment temperature of "25 ℃.

In the present specification, the unit names used are all international standard unit names, and the "%" used means weight or mass% content, if not specifically stated.

In the present specification, the term "substantially" is used to indicate that the standard deviation from the theoretical model or theoretical data is within a range of 2%, preferably 1%, and more preferably 0.5%.

In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

All-vanadium redox flow battery

The all-vanadium redox flow battery refers to a redox flow battery taking an acid solution of vanadium oxide as an electrolyte. The flow cell device is generally composed of a (stacked) stack, a positive electrode reservoir, a negative electrode reservoir, and other components such as a separator, a connecting device, and a control device.

The source or preparation method of the electrolyte for the all-vanadium flow battery is not particularly limited. Generally, the preparation can be carried out using an oxide of vanadium or a mixture of oxides of vanadium mixed with an acidic solution (e.g., sulfuric acid, hydrochloric acid, etc.).

In some embodiments of the invention, V may be used with a degree of purity ₂ O ₅ (vanadyl sulfate) is mixed with an acidic solution (including but not limited to hydrochloric acid, sulfuric acid, hydrochloric acid sulfate solution, etc.) to prepare an electrolyte containing pentavalent vanadium ions, which is then reduced as needed to obtain an electrolyte containing tetravalent vanadium ions. For high purity V ₂ O ₅ The method of preparation of (A) is not particularly limited, and for example, the solution is added to a solution in which a vanadium oxide is dissolvedAnalytically pure aluminum salt, sodium salt, calcium salt and the like are added, a series of processes such as vanadium precipitation, filtration, impurity removal and the like are carried out, and elements such as Fe, Al, Si, Na, K and the like with relatively high content are removed, so that the high-purity vanadium pentoxide raw material is prepared.

In other embodiments of the present invention, a mixture of vanadium oxides consisting of the following general formula (1) may also be used as a direct raw material for preparing an all-vanadium battery electrolyte:

V _x O _y (1)

wherein, the valence of V is +3.2 to +3.7, x is 1: (1.6-1.85);

the process for industrially obtaining the oxide composed of the above general formula (1) or the original source of the oxide is not particularly limited in the present invention and may be obtained in a conventional manner, for example, by reducing the oxide of vanadium in a high valence state.

The original raw material of the vanadium oxide in the high oxidation state is not particularly limited, and can be obtained by various methods known in the art, for example, a vanadium solution obtained by dissolving a leached vanadium solution or a vanadium-rich material (such as industrial grade ammonium polyvanadate, ammonium metavanadate, industrial grade vanadium pentoxide, etc.) is used as a raw material, and the raw material is purified by chemical precipitation purification or (and) solvent extraction/ion resin exchange, etc. to obtain a pure vanadium solution, and then ammonium salt precipitation is performed to obtain a pure ammonium polyvanadate or ammonium metavanadate precipitate, or the raw material is calcined and decomposed to obtain a high-purity vanadium pentoxide powder. Or a chlorination method is used for preparing high-purity vanadium pentoxide by taking vanadium-containing substances such as vanadium titano-magnetite, vanadium slag, vanadium-containing catalyst and the like as raw materials.

The resulting higher vanadium oxide is reduced, for example, with a reducing agent for V ₂ O ₅ Or, in other industrial production, other compounds of vanadium with the valence of 5 can be mixed and dissolved with an acidic solution, reduction reaction is carried out in the presence of a reducing agent, and then precipitates are obtained by adding alkaline substances, and then the precipitates are washed and dried to obtain oxides with low valence states.

Reduction used for the above procedureThe method is not particularly limited, and for example, a general reducing compound such as a reducing acid, a reducing alcohol, an aldehyde compound, typically, oxalic acid or the like; or a reducing gas or the like, typically, for example, H ₂ CO, hydrogen sulfide, methane, sulfur dioxide, ethylene or NH ₃ Or any combination thereof.

The purity of the vanadium oxide of the general formula (1) is not strictly limited or required, and the purity of the vanadium oxide of the general formula (1) having an average valence of +3.2 to +3.7 may be 90 mass% or more. In some preferred embodiments, the purity of the above-mentioned oxide is 95% by mass or more, and in other preferred embodiments, the purity of the above-mentioned oxide is 98% by mass or more.

In general, the average valence of the vanadium ion in the electrolyte injected into the negative electrode of the flow battery may be controlled to be +3.3 to +3.6, for example +3.5, and the average valence of the vanadium ion in the electrolyte injected into the positive electrode of the flow battery may be controlled to be +4.3 to +4.6, for example + 4.5. After the initial electrolyte is added, the average valence of vanadium ions in the negative electrode is controlled to be about +3 through the initial operation and adjustment of the flow battery, the average valence of vanadium ions in the positive electrode is controlled to be about +4, namely the SOC is 0%, the flow battery can be formally charged and used, after the flow battery is fully charged, the average valence of vanadium ions in the negative electrode is controlled to be about +2, the average valence of vanadium ions in the positive electrode is controlled to be about +5, namely the SOC is 100%.

[ first aspect ]

The invention relates to a method for testing the charging state of a positive electrode and the total concentration of vanadium ions in a positive electrode electrolyte in an all-vanadium redox flow battery system.

Electrolyte sampling

In the invention, the positive electrolyte can be sampled from any SOC state when the flow battery runs.

From the viewpoint of convenience and safety of sampling, it is preferable that sampling from the electrode is possible when the SOC state is 0%.

When the positive electrode electrolyte is sampled in the positive electrode system, the positive electrode system comprises any position of the positive electrode and any position of the positive electrode electrolyte storage tank.

The volume of the sample taken from the positive electrode system is not particularly limited, and may be, for example, 0.1 to 100mL, preferably 0.5 to 80mL, and more preferably 1 to 60 mL.

⁴⁺ Step of measuring concentration of V in electrolyte

After the anode electrolyte is sampled, the concentration Cv of the tetravalent vanadium ions in the anode electrolyte can be measured ⁴⁺ ₁ And (6) testing. In some preferred embodiments of the present invention, the positive electrode electrolyte may be diluted and then tested, from the viewpoint of convenience of the test. As the diluent, dilute hydrochloric acid, dilute sulfuric acid or a mixture of both of them may be used.

In the present invention, the above test is carried out by measuring absorbance under irradiation of a light source of a first predetermined wavelength. Specifically, the tetravalent vanadium ion can be tested at a first predetermined wavelength of 700 to 830nm, preferably at a wavelength of 720 to 800nm, more preferably at a wavelength of 740 to 780 nm. The determination of the above-specified wavelength is related to the characteristic absorption of the tetravalent vanadium ion.

The present invention is not particularly limited to an optical instrument used in the test, as long as it can emit light of the above-specified wavelength. In some specific embodiments, the optical instrument may have an emission spectrum in the wavelength range of 200 to 1000 nm.

Further, after the absorbance of the tetravalent vanadium ions is obtained through the test, the absorbance can be compared with a standard absorption curve of the tetravalent vanadium ions at the first specified wavelength obtained based on an absorption photometry, and therefore the V in the positive electrolyte is determined ⁴⁺ Concentration Cv of ⁴⁺ ₁ 。

In some preferred embodiments, the standard absorption curve can be stored in the optical instrument, and the concentration Cv is measured by the optical instrument when the electrolyte is measured ⁴⁺ ₁ Value is followed byAnd directly obtaining the result after the detection is finished.

⁵⁺ Step of measuring the concentration of V in the electrolyte

In a particular embodiment of the invention, V ⁵⁺ The concentration can be measured by a direct method or an indirect method.

In the direct test method, after sampling the positive electrode electrolyte, V can be tested under irradiation of a light source of a second prescribed wavelength ⁵⁺ Absorbance of (b). Specifically, the vanadium ion in the pentavalent state can be measured at a second predetermined wavelength of 200 to 300nm, preferably, the absorbance can be measured at a wavelength of 250 to 300nm, more preferably, at a wavelength of 260 to 280 nm. The determination of the above-specified wavelength is related to the characteristic absorption of the pentavalent vanadium ion.

In some preferred embodiments of the invention, with V ⁴⁺ The concentration test is similar, and the positive electrolyte can be diluted by the same times and then tested. As the diluent, dilute hydrochloric acid, dilute sulfuric acid or a mixture of both of them can be used.

The optical instrument used in the test is not particularly limited as long as it can emit light of the second prescribed wavelength. In a preferred embodiment, the test V described above can be used ⁴⁺ The same optical instrument used for the concentration of (a).

In the invention, after the absorbance of the pentavalent vanadium ions is obtained through the test, the absorbance can be compared with the standard absorption curve of the pentavalent vanadium ions under the second specified wavelength obtained based on the absorptiometry method, so that the V in the positive electrode electrolyte is determined ⁵⁺ Concentration Cv of ⁵⁺ ₁ 。

In some preferred embodiments, a standard absorption curve of pentavalent vanadium ions at the second prescribed wavelength can be stored in an optical instrument, and the concentration value Cv is detected using the optical instrument on electrolyte ⁵⁺ ₁ Directly obtaining the result along with the completion of the detection.

Although V ⁵⁺ Does not have a regular complete waveform, but due to standard absorptionThe curve is obtained by measuring V at different concentrations at the same wavelength ⁵⁺ The absorbance-concentration curve is prepared by the absorbance of the positive electrode, and the V in the positive electrode electrolyte is tested under the same wavelength ⁵⁺ The absorbance of the test result is accurate, and therefore errors or deviations caused by incomplete waveforms can be eliminated.

At V ⁵⁺ In the indirect concentration test method, a first reducing agent is added into the sampled positive electrolyte to obtain a mixed solution. The amount of the first reducing agent is an amount sufficient to reduce all pentavalent vanadium ions in the mixed solution to tetravalent vanadium. Generally, the reducing agent is added in excess without affecting the test, so that the test result is more accurate. After the addition of the reducing agent to the mixed solution, the first reducing agent first reduces all the pentavalent vanadium ions in the mixed solution to tetravalent vanadium ions, after which the tetravalent vanadium ions further start to be reduced to trivalent vanadium ions in small amounts due to the presence of an excess of the reducing agent.

The excess amount of the reducing agent is used here to ensure that the pentavalent vanadium ions can be completely reduced to give V ⁴⁺ The highest concentration. Monitoring V during the time after addition of the reducing agent ⁴⁺ Once V is ⁴⁺ The concentration of (2) begins to decrease, meaning that V in the mixed solution is decreased ³⁺ Generation is started. At this point, the recording of V can be stopped ⁴⁺ With the previously recorded V ⁴⁺ The highest value of the concentration is taken as V ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ 。

Therefore, the mixed solution was tested for V at the above-mentioned first prescribed wavelength every unit time with the start timing of the addition of the first reducing agent as the starting point ⁴⁺ Until V in the mixed solution is measured ⁴⁺ The maximum absorbance of (c). Similarly to the above, after obtaining the maximum absorbance of the tetravalent vanadium ion through the above test, the maximum absorbance can be compared with the standard absorption curve of the tetravalent vanadium ion at the first prescribed wavelength obtained based on absorptiometry, thereby obtaining V in the mixed solution ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ . The maximum concentration Cv ⁴⁺ ₂ Namely, the anode electrolysisIn liquid V ⁴⁺ And V ⁵⁺ Of vanadium ions (c).

From the measured V in the positive electrode electrolyte ⁴⁺ Concentration Cv of ⁴⁺ ₁ And V in the mixed solution ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ V in the positive electrode electrolyte can be obtained ⁵⁺ Concentration of Cv ⁵⁺ ₁ ，Cv ⁵⁺ ₁ =Cv ⁴⁺ ₂ -Cv ⁴⁺ ₁ 。

In some embodiments of the present invention, examples of the first reducing agent may include inorganic reducing agents and organic reducing agents. Among them, examples of the inorganic reducing agent may include Zn, Sn, Mn ²⁺ 、Fe ²⁺ 、SO ₂ And the like. Examples of organic reducing agents may include CH ₄ N ₂ S、CH ₃ CSNH ₂ 、N ₂ H ₄ ·H ₂ O, ethylene glycol, NH ₂ NH ₂ 2HCl, oxalic acid, glycerol, and the like. From the viewpoint of rapidly reducing pentavalent vanadium ions to tetravalent vanadium ions, it is preferable to use an inorganic reducing agent and a strongly reducing organic reducing agent such as N ₂ H ₄ ·H ₂ And O. The unit time may be 3s-5min, preferably 5s-3min, and more preferably 30s-2 min.

By adopting the indirect test method of the invention, the direct test V can be avoided ⁵⁺ The method only needs to test the absorbance of one ion of the tetravalent vanadium ions.

In addition, the invention is more favorable for the use of portable detection instruments because the requirements of the optical instrument on the spectral range basically fall in the ultraviolet-visible light spectral range. Furthermore, the portable detection instrument can be more favorable for meeting the requirement of detecting tetravalent vanadium ions and pentavalent vanadium ions in the positive electrolyte in a shorter time.

Evaluation and calculation of the state of charge of a positive electrode

In the present invention, Cv is obtained by the above test ⁴⁺ ₁ And Cv ⁵⁺ ₁ After the value, the liquid can be treatedAnd evaluating the charging condition of the positive electrode at the flow battery testing time point.

The calculation method for evaluation is not particularly limited, and may be, for example, Cv ⁵⁺ ₁ And Cv ⁴⁺ ₂ Is performed according to the ratio of (a). Theoretically, if the positive electrode is in the A% SOC operating state at the test time point, then Cv ⁵⁺ ₁ /Cv ⁴⁺ ₂ The value for 100% should be A%. Thus, can pass through Cv ⁵⁺ ₁ And Cv ⁴⁺ ₂ To evaluate the positive state of charge of the flow battery.

When it is estimated by the above method of the present invention that the actual detected data of the positive electrode state of charge of the flow battery at the detected time point does not coincide with the system state of charge SOC, the adjustment may be made by a conventional means in the art, such as adding a reducing agent or an oxidizing agent at the corresponding position or supplementing the required vanadium ions at the corresponding position.

[ second aspect ]

A second aspect of the invention relates to a method for measuring the total vanadium concentration in the electrolyte preparation.

The test method can be used for testing the total vanadium concentration in other solutions containing tetravalent vanadium ions and pentavalent vanadium ions besides the total vanadium concentration in the positive electrolyte. One important application is for testing the total vanadium concentration during electrolyte preparation.

As mentioned above, in many different processes for large scale production of electrolytes, the first step in many production processes is to use a solution containing V ₂ O ₅ Adding a reducing agent to the vanadium powder in an acid solution (e.g., sulfuric acid, hydrochloric acid, or a mixed solution of sulfuric acid and hydrochloric acid), thereby obtaining a vanadium-containing vanadium powder containing V ⁴⁺ The solution of (1). At the end of the reaction, V in the liquid is required to be adjusted ⁴⁺ And V ⁵⁺ The total concentration of (a) is tested and the test concentration is compared with the theoretical concentration to determine whether the reaction can be stopped. For example, if the measured total concentration is 1.5M and the target concentration is 1.6M, then there is also V at 6.25% of the total (0.1/1.6/2 × 100% =) ₂ O ₅ The vanadium powder does not react, and the vanadium powder needs to continuously wait for the reaction to proceed or be addedAnd (4) preparing a raw agent.

In practical applications, if the measured total concentration is not less than 99% of the target concentration, it can be judged that the reaction is substantially completed. In addition, by calculating V ⁵⁺ /(V ⁴⁺ +V ⁵⁺ ) In a ratio of (A) to (B) to obtain V in solution ⁵⁺ The content of (b) provides necessary raw data for the next subsequent balancing treatment of the electrolyte.

The method for testing the total vanadium concentration in the electrolyte preparation comprises the following steps: solution A preparation step, reducing agent addition step, V ⁴⁺ Concentration test procedure and V ⁵⁺ Concentration and vanadium total concentration test procedure.

In the preparation step of the solution A, V is to be contained ₂ O ₅ Dissolving the powder in an acid solution to obtain a solution containing V ⁵⁺ Solution A of (4). In the reducing agent addition step, a second reducing agent is added to the solution A to obtain a solution containing V ⁴⁺ And V ⁵⁺ Solution B of (1).

The second reducing agent herein includes inorganic reducing agents and organic reducing agents. Among them, examples of the inorganic reducing agent may include Zn, Sn, Mn ²⁺ 、Fe ²⁺ 、SO ₂ And the like. Examples of organic reducing agents may include CH ₄ N ₂ S、CH ₃ CSNH ₂ 、N ₂ H ₄ ·H ₂ O、NH ₂ NH ₂ 2HCl, ethylene glycol, oxalic acid, etc. Also, the second reducing agent can be used as described above [ first aspect ]]The first reducing agent in (a) is the same or different reducing agent. In a preferred embodiment, the second reducing agent is an organic reducing agent, which may be, for example, CH ₄ N ₂ S、CH ₃ CSNH ₂ 、N ₂ H ₄ ·H ₂ O、NH ₂ NH ₂ 2HCl, ethylene glycol, oxalic acid, etc. Among them, oxalic acid is preferable.

At V ⁴⁺ In the concentration measuring step, the solution B is sampled, and V in the solution B is measured at a first prescribed wavelength ⁴⁺ Concentration of Cv ⁴⁺ ₁ ^’ 。

At V ⁵⁺ Step of measuring concentration and total concentration of vanadiumIn step, two methods can be employed for testing. One method is as follows: testing V in the sampled solution B at a second prescribed wavelength ⁵⁺ Concentration of Cv ⁵⁺ ₁ ^’ Then the total concentration of vanadium is Cv ⁴⁺ ₁ ^’ +Cv ⁵⁺ ₁ ^’ 。

The other method comprises the following steps: adding a first reducing agent into the sampled solution B to obtain a mixed solution C, and testing V in the mixed solution C at the first specified wavelength at intervals of unit time by taking the moment of starting adding the first reducing agent as a starting point ⁴⁺ To obtain V in the mixed solution C ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ ^’ The maximum concentration Cv ⁴⁺ ₂ ^’ I.e. the total concentration of vanadium ions in the solution B, V in the solution B ⁵⁺ Concentration Cv of ⁵⁺ ₁ ^’ =Cv ⁴⁺ ₂ ^’ -Cv ⁴⁺ ₁ ^’ 。

The first reducing agent herein is the same as the above [ first aspect ]]The first reducing agent in (a) is the same reducing agent, and may be the same as or different from the second reducing agent described above. In a preferred embodiment, the first reducing agent is an inorganic reducing agent and a strongly reducing organic reducing agent such as hydrazine hydrate N ₂ H ₄ ·H ₂ And (O). This is because, generally, the reduction process of organic reducing agents with weak reducibility such as oxalic acid is very slow, and the reduction speed is greatly increased by using appropriate inorganic reducing agents or organic reducing agents with strong reducibility, so that V can be rapidly reduced ⁵⁺ Reduction to V ⁴⁺ To obtain V ⁴⁺ And V ⁵⁺ Total concentration sum V ⁵⁺ The concentration of (c).

The first predetermined wavelength and the second predetermined wavelength are the same as in the above-mentioned [ first aspect ]]And the absorbance test can be performed using the same optical instrument. In some preferred embodiments, the optical instrument has stored therein V obtained based on absorptiometry ⁴⁺ And V at the first prescribed wavelength ⁵⁺ At the second prescribed wavelength.

In some preferred embodiments, the absorbance test may be performed after the solution a is diluted. The unit time may be 3s to 5min, preferably 5s to 3min, and more preferably 30s to 2 min.

The testing method of the invention not only can be used for testing the charging state and the total concentration of the positive electrolyte, but also can be used for testing V in the industrial preparation engineering of the vanadium electrolyte ₂ O ₅ And (4) quickly judging the completion degree of the reaction reduction.

Examples

Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are commercially available, and are not indicated by manufacturers.

When a battery detection system of a certain system displays that the system is charged to 32% SOC, 50ml of sample is taken from a positive electrolyte barrel for detecting and verifying the actual charging state of the positive electrolyte. 10ml of the sample was taken out of the 50ml sample, diluted and then UV-measured at a wavelength of 758nm to determine the V content in the sample ⁴⁺ 1.23M. Then, 30ml of the sample was taken out of the original positive electrode sample, and the sample was mixed with a reducing agent N ₂ H ₄ ·H ₂ Mixing O in a volume ratio of 1:1, and adding V in the positive solution ⁵⁺ Is instantaneously reduced into V by a reducing agent ⁴⁺ . Diluting the reduced liquid by the same time, measuring UV at 758nm, and measuring V content in the sample ⁴⁺ 1.67M. The actual state of charge of the positive electrolyte sample is (1.67-1.23)/1.67 × 100% =26.3%, and the difference from the SOC data of the system by 32% is about 6%, and at this time, the state of charge of the negative electrolyte needs to be detected, and the balance of the electrolyte in the whole system needs to be detected. To ensure that the entire electrolyte system is in equilibrium. If the difference between the charging state of the positive electrolyte and the charging state of the system is two percentage points, the charging states are basically considered to be consistent, and the electrolyte system is considered to be in a normal state.

The foregoing description of the embodiments of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or improvements to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Industrial applicability

The detection method can be industrially used for testing the positive electrode charging state and the total vanadium concentration of the electrolyte of the flow battery.

Claims

1. A method for testing the charging state of a positive electrode and the total concentration of vanadium ions in a positive electrode electrolyte in an all-vanadium flow battery system is characterized by comprising the following steps:

V ⁵⁺ And (3) concentration testing: testing V in the positive electrolyte at a second specified wavelength ⁵⁺ Concentration of Cv ⁵⁺ ₁ (ii) a Or adding a first reducing agent into the positive electrode electrolyte to obtain a mixed solution, and testing V in the mixed solution at the first specified wavelength at intervals of unit time by taking the time when the first reducing agent starts to be added as a starting point ⁴⁺ To obtain V in the mixed solution ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ The maximum concentration Cv ⁴⁺ ₂ I.e. the total concentration of vanadium ions in the positive electrolyte, V in said positive electrolyte ⁵⁺ Concentration Cv of ⁵⁺ ₁ =Cv ⁴⁺ ₂ -Cv ⁴⁺ ₁ 。

2. The test method of claim 1, wherein sampling is at any state of charge (SOC).

3. The testing method according to claim 1 or 2, wherein the positive electrode state of charge determining step includes at least calculating Cv ⁵⁺ ₁ /Cv ⁴⁺ ₂ To evaluate the positive electrode state of charge.

4. The test method according to claim 1 or 2, characterized in that at V ⁴⁺ The concentration testing step comprises the step of testing after the positive electrolyte is diluted.

5. The test method according to claim 1 or 2, wherein the first reducing agent comprises an inorganic reducing agent and an organic reducing agent.

6. A method for testing the total concentration of vanadium is characterized by comprising the following steps:

a reducing agent adding step: adding a second reducing agent to the solution A to obtain a solution containing V ⁴⁺ And V ⁵⁺ Solution B of (1);

V ⁴⁺ and (3) concentration testing: sampling said solution B and measuring V in said solution B at a first defined wavelength ⁴⁺ Concentration Cv of ⁴ ⁺ ₁ ^’ ；

V ⁵⁺ And (3) testing the concentration and the total vanadium concentration: testing V in the sampled solution B at a second prescribed wavelength ⁵⁺ Concentration Cv of ⁵ ⁺ ₁ ^’ Then the total concentration of vanadium is Cv ⁴⁺ ₁ ^’ +Cv ⁵⁺ ₁ ^’ (ii) a Or

Adding a first reducing agent into the sampled solution B to obtain a mixed solution C, and testing the mixed solution C at the first specified wavelength at intervals of unit time by taking the starting time of adding the first reducing agent as a starting pointV in solution C ⁴⁺ To obtain V in the mixed solution C ⁴⁺ Maximum concentration of Cv ⁴⁺ ₂ ^’ The maximum concentration Cv ⁴⁺ ₂ ^’ I.e. the total concentration of vanadium ions in the solution B, V in the solution B ⁵⁺ Concentration of Cv ⁵⁺ ₁ ^’ =Cv ⁴⁺ ₂ ^’ -Cv ⁴⁺ ₁ ^’ 。

7. The test method according to claim 1 or 6, wherein the first prescribed wavelength is in a range of 700 to 830nm, and the second prescribed wavelength is in a range of 200 to 300 nm.

8. The test method of claim 6, wherein at V ⁴⁺ The concentration testing step comprises the step of testing after the solution B is diluted.

9. Test method according to claim 1 or 6, characterized in that the test Cv ⁴⁺ ₁ 、Cv ⁴⁺ ₂ 、Cv ⁴⁺ ₁ ^’ And Cv ⁴⁺ ₂ ^’ The test was carried out using an optical instrument in which V obtained on the basis of absorptiometry was stored ⁴⁺ At the first prescribed wavelength.

10. Test method according to claim 1 or 6, characterized in that the test Cv ⁵⁺ ₁ And Cv ⁵⁺ ₁ ^’ The test was carried out using an optical instrument in which V obtained on the basis of absorptiometry was stored ⁵⁺ At the second prescribed wavelength.

11. The test method according to claim 6, wherein the first reducing agent and the second reducing agent are the same or different and each comprises an inorganic reducing agent and an organic reducing agent.

12. The test method according to claim 1 or 6, wherein the unit time is 3s-5 min.