阅读说明：本技术 便携式全钒液流电池电解液平衡度的测试方法 (Method for testing electrolyte balance degree of portable all-vanadium redox flow battery ) 是由 祖革 王瑾 郑晓昊 于 2018-08-24 设计创作，主要内容包括：本发明公开了一种便携式全钒液流电池电解液平衡度的测试方法。所述方法包括如下步骤：步骤1：绘制吸光度-浓度标准工作曲线；步骤2：分别同时取样正极电解液和负极电解液,等体积混合,氧化还原反应结束后得到混合溶液A；步骤3：采用便携式紫外可见分光光度计,得到所述混合溶液A中三价钒离子的浓度C<Sub>V</Sub><Sup>3+</Sup>；步骤4：向所述混合溶液A中加入还原剂,得到混合溶液B,采用便携式紫外可见分光光度计,得到测试时间内所述混合溶液B中三价钒离子的最大浓度C<Sub>m</Sub>,所述混合溶液A中四价钒离子的浓度为C<Sub>VO</Sub><Sup>2+</Sup>,C<Sub>VO</Sub><Sup>2+</Sup>＝C<Sub>m</Sub>-C<Sub>V</Sub><Sup>3+</Sup>；步骤5：计算整体电解液的非平衡程度K,K＝(C<Sub>VO</Sub><Sup>2+</Sup>-C<Sub>V</Sub><Sup>3+</Sup>)/(C<Sub>VO</Sub><Sup>2+</Sup>+C<Sub>V</Sub><Sup>3+</Sup>)。所述方法操作方便、简单快捷,便于携带,检测准确,适用于液流电池实际运行场所的实地检测。(The invention discloses a method for testing electrolyte balance degree of a portable all-vanadium redox flow battery. The method comprises the following steps: step 1: drawing an absorbance-concentration standard working curve; step 2: respectively and simultaneously sampling the positive electrolyte and the negative electrolyte, mixing the positive electrolyte and the negative electrolyte in equal volume, and obtaining a mixed solution A after the oxidation-reduction reaction is finished; and step 3: obtaining the concentration C of trivalent vanadium ions in the mixed solution A by adopting a portable ultraviolet-visible spectrophotometer V 3+ (ii) a And 4, step 4: adding a reducing agent into the mixed solution A to obtain a mixed solution B, and obtaining the maximum concentration C of trivalent vanadium ions in the mixed solution B within the testing time by adopting a portable ultraviolet-visible spectrophotometer m The concentration of tetravalent vanadium ions in the mixed solution A is C VO 2+ ，C VO 2+ ＝C m ‑C V 3+ (ii) a And 5: calculating the degree of unbalance K, K ═ C of the whole electrolyte VO 2+ ‑C V 3+ )/(C VO 2+ +C V 3+ ). The method is convenient, simple and rapid to operate, convenient to carry, accurate in detection and suitable for field detection of the actual running place of the flow battery.)

1. A method for testing electrolyte balance degree of a portable all-vanadium redox flow battery is characterized by comprising the following steps:

step 1: preparing a series of trivalent vanadium ion standard solutions with known concentrations, and obtaining an absorbance-concentration standard working curve by adopting an ultraviolet-visible spectrophotometry;

step 2: respectively and simultaneously sampling the positive electrolyte and the negative electrolyte, mixing the positive electrolyte and the negative electrolyte in equal volume, and obtaining a mixed solution A after the oxidation-reduction reaction is finished;

and step 3: adopting a portable ultraviolet-visible spectrophotometer to carry out wavelength scanning on the mixed solution A, and matching with the standard working curve to obtain the concentration C of trivalent vanadium ions in the mixed solution A_V ³⁺；

And 4, step 4: adding a reducing agent into the mixed solution A to obtain a mixed solution B, wherein the amount of the reducing agent is enough to reduce all tetravalent vanadium ions in the mixed solution B,

taking the moment when the reducing agent begins to be added as a starting point, scanning the wavelength of the mixed solution B by adopting a portable ultraviolet-visible spectrophotometer at intervals, and matching with the standard working curve to obtain the maximum concentration C of the trivalent vanadium ions in the mixed solution B in the testing time_mThe concentration of tetravalent vanadium ions in the mixed solution A is C_VO ²⁺，C_VO ²⁺＝C_m-C_V ³⁺；

And 5: calculating the degree of unbalance K, K ═ C of the whole electrolyte_VO ²⁺-C_V ³⁺)/(C_VO ²⁺+C_V ³⁺)。

2. The method according to claim 1, wherein in step 2, sampling is performed at any state of charge SOC, preferably at 0.

3. The method according to claim 1 or 2, wherein in the step 2, the mixed solution a is a mixed solution of trivalent vanadium ions and tetravalent vanadium ions.

4. The method as set forth in any one of claims 1 to 3, wherein in the step 3, the operating wavelength of the portable UV-visible spectrophotometer is 350-500 nm.

5. The method according to any one of claims 1-4, further comprising: diluting the mixed solution A between the step 2 and the step 3.

6. The method according to any one of claims 1 to 5, wherein in step 4, the reducing agent is a metal reducing agent, preferably zinc.

7. The method according to any one of claims 1 to 6, wherein in step 4, the unit time is from 30s to 90s, preferably from 40s to 70 s.

Technical Field

The invention relates to a portable all-vanadium redox flow battery electrolyte balance testing method, in particular to a method for detecting by using a portable device so as to obtain electrolyte balance data, and belongs to the technical field of redox flow battery electrolyte detection.

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 (II)/V (III) and V (IV)/V (V) as redox couples to complete the interconversion of vanadium ions with different valence states and the storage and release of electric energy 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 present²⁺And V in the negative electrode electrolyte³⁺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 electrolyte²⁺The number needs to be uniform or close. Under an ideal condition, the charge states of positive and negative electrolytes of the all-vanadium redox flow battery are consistent, but due to transmembrane migration of vanadium ions and water molecules, hydrogen evolution reaction and oxidation reaction of the negative electrolyte and the like, the charge states of the positive and negative electrolytes are inconsistent in long-term operation. If the proportion of vanadium ions in the positive electrolyte and the negative electrolyte is out of balance, 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, the balance state of the positive electrolyte and the negative electrolyte of the all-vanadium redox flow battery can be monitored in real timeThe method provides a guiding function for the maintenance and management work of the electrolyte of the vanadium galvanic pile running for a long time, and ensures the safe and stable running of the galvanic pile.

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 V³⁺And VO²⁺The absorbance of the characteristic absorption peak is matched with a standard working curve to obtain V³⁺And VO²⁺The concentration of (c); according to V³⁺And VO²⁺The concentration calculation of (2) to obtain equilibrium data of the whole 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.

However, for all-vanadium redox flow battery systems constructed for matching with electric energy storage of photovoltaic power generation and wind power generation, because actual operation sites of the all-vanadium redox flow battery systems are generally in remote areas, necessary experimental test equipment is probably lacked around the all-vanadium redox flow battery systems, and the two test methods are often not practical to operate.

It can be seen that, although some research has been conducted on monitoring the balance problem of the positive and negative electrolytes of the all-vanadium redox flow battery in the prior art, the research on the convenience of the detection method or the portability of the detection device is not sufficient.

Cited document 1: CN 104345278A

Cited document 2: CN 107422267A

Cited document 3: CN 102621085A

Disclosure of Invention

Problems to be solved by the invention

In the process, a certain time is actually consumed from sampling to detection, and the condition of the continuously-operated flow battery actually changes in the period. After the detection result is obtained, the conclusion that the flow battery is different from the actual condition of the flow battery at the moment is often obtained. Further, the evaluation or intervention of the operating condition of the flow battery according to the data of the laboratory test often misses the optimal time window, and may also result in that although the manpower and material resources are consumed, the improvement of the actual condition of the flow battery operation is still insufficient. Thus, the timeliness, accuracy and convenience of current tests are inadequate.

The invention provides a portable electrolyte balance testing method for an all-vanadium redox flow battery, and a detection device and medicines involved in the method are convenient to carry, so that the method is suitable for being carried out in the actual operation place of the redox flow battery, and the obtained result can timely and accurately feed back the real condition of the redox flow battery in operation.

Means for solving the problems

The invention solves the technical problems by adopting the following technical scheme:

the invention firstly provides a method for testing the balance of electrolyte of an all-vanadium redox flow battery, which comprises the following steps:

step 1: preparing a series of trivalent vanadium ion standard solutions with known concentrations (in a laboratory environment), and obtaining an absorbance-concentration standard working curve by adopting an ultraviolet-visible spectrophotometry, wherein the curve can be used as a standard curve in future detection and used for calculating the concentration of the trivalent vanadium ions and the total balance degree of the electrolyte;

step 2: respectively and simultaneously sampling the positive electrolyte and the negative electrolyte, mixing the positive electrolyte and the negative electrolyte in equal volume, and obtaining a mixed solution A after the oxidation-reduction reaction is finished;

and step 3: adopting a portable ultraviolet-visible spectrophotometer to carry out wavelength scanning on the mixed solution A, and matching with the standard working curve in the step 1 to obtain the concentration C of trivalent vanadium ions in the mixed solution A_V ³⁺；

And 4, step 4: adding a reducing agent into the mixed solution A to obtain a mixed solution B, wherein the amount of the reducing agent is enough to reduce all tetravalent vanadium ions in the mixed solution B, and after the reducing agent is added, the reducing agent reduces all tetravalent vanadium ions in the mixed solution B into trivalent vanadium ions. The electrolyte obtained finally is V³⁺/V²⁺The solution was mixed.

Taking the moment when the reducing agent begins to be added as a starting point, scanning the wavelength of the mixed solution B by using a portable ultraviolet-visible spectrophotometer at intervals of unit time, and matching with the standard working curve in the step 1 to obtain the maximum concentration C of trivalent vanadium ions in the mixed solution B in the testing time_mThe concentration of tetravalent vanadium ions in the mixed solution A is C_VO ²⁺，C_VO ²⁺＝C_m-C_V ³⁺；

And 5: calculating the degree of unbalance K, K ═ C of the whole electrolyte_VO ²⁺-C_V ³⁺)/(C_VO ²⁺+C_V ³⁺)。

According to the method described above, in step 2, sampling is performed at any state of charge SOC, preferably at a state of charge SOC of 0.

According to the method, in the step 2, the mixed solution A is a mixed solution of trivalent vanadium ions and tetravalent vanadium ions.

According to the method, in the step 3, the operating wavelength of the portable ultraviolet-visible spectrophotometer is 350-500 nm.

The method according to the above, the method further comprising: diluting the mixed solution A between the step 2 and the step 3.

According to the above method, in the step 4, the reducing agent is a metal reducing agent, preferably metallic zinc.

According to the method described above, in step 4, the unit time is 30s to 90s, preferably 40s to 70 s.

Invention ofEffect

The method for testing the balance of the electrolyte of the all-vanadium redox flow battery has the following excellent effects:

(1) the test method provided by the invention is simple to operate, is rapid and convenient, can realize the test of the electrolyte balance data of the all-vanadium redox flow battery under the condition of lacking complete laboratory conditions, and has the advantages of field property, timeliness and accuracy.

(2) The used detection device and the medicine are convenient to carry, and the on-site detection can be conveniently carried out at any time under the non-laboratory condition.

(3) The detection method provided by the invention is beneficial to accurately detecting the running condition of the flow battery for a long time, and can shorten the processing time when the electrolyte of the flow battery is unbalanced, so that the countermeasures are more targeted.

Detailed Description

Hereinafter, a mode for carrying out the present invention will be described in detail.

The invention provides a method for testing electrolyte balance degree of a portable all-vanadium redox flow battery. The method comprises the following steps:

step 1: preparing a series of trivalent vanadium ion standard solutions with known concentrations, and obtaining an absorbance-concentration standard working curve by adopting an ultraviolet-visible spectrophotometry. The curve can be prepared in advance under the laboratory condition, can be used as a standard curve in future detection and is used for calculating the concentration of trivalent vanadium ions and the total balance degree of electrolyte;

step 2: respectively and simultaneously sampling the positive electrolyte and the negative electrolyte, mixing the positive electrolyte and the negative electrolyte in equal volume, and obtaining a mixed solution A after the oxidation-reduction reaction is finished; the sampling mode is not particularly limited, and the sampling mode can be directly taken out from the positive electrode or negative electrode liquid storage device of the flow battery as long as the requirement of safe operation is met.

And step 3: adopting a portable ultraviolet-visible spectrophotometer to carry out wavelength scanning on the mixed solution A, and matching with the standard working curve to obtain the concentration C of trivalent vanadium ions in the mixed solution A_V ³⁺；

And 4, step 4: and adding a reducing agent into the mixed solution A to obtain a mixed solution B, wherein the amount of the reducing agent is enough to reduce all tetravalent vanadium ions in the mixed solution B. In general, in field operation, the reducing agent is added in excess under the condition of not influencing the test, so that the test result is more accurate. After the reducing agent is added to the mixed solution B, the reducing agent first reduces all tetravalent vanadium ions in the mixed solution B to trivalent vanadium ions, and further, the trivalent vanadium ions further start to be reduced to divalent vanadium ions in a small amount due to the presence of an excessive amount of the reducing agent, forming V^{3 +}/V²⁺The solution was mixed.

The excess amount of the reducing agent is used here to ensure that V is obtained³⁺Concentration maximum, in the following time, once V^{3 +}The concentration of (2) begins to decrease, meaning that V in the mixed solution²⁺Generation is started. At this point, the recording of V can be stopped³⁺With the previously recorded V³⁺The highest concentration value is used as V in the original mixed electrolyte³⁺/V⁴⁺And V measured when no reducing agent was initially added³⁺And (4) calculating the balance degree of the original electrolyte.

Therefore, at every unit time, the wavelength of the mixed solution B is scanned by a portable ultraviolet-visible spectrophotometer, and the maximum concentration C of the trivalent vanadium ions in the mixed solution B in the testing time is obtained by matching with the standard working curve_mThe concentration of tetravalent vanadium ions in the mixed solution A is C_VO ²⁺，C_VO ²⁺＝C_m-C_V ³⁺；

And 5: calculating the degree of unbalance K, K ═ C of the whole electrolyte_VO ²⁺-C_V ³⁺)/(C_VO ²⁺+C_V ³⁺). The composition of the positive electrode/negative electrode solution of the flow battery can be rapidly adjusted according to the obtained unbalance value.

The method for preparing the standard solution in step 1 is not particularly limited, and may be performed according to a method generally used in the art. Meanwhile, the number of samples of the standard solution should be appropriate, and it is understood that the number of samples of the standard is important for the accuracy of drawing the standard working curve, and thus, standard solutions of different concentrations can be obtained more frequently as conditions allow.

The concentration range of the standard working curve obtained in step 1 should also be appropriate, and in some cases, it is required that the concentration range is as wide as possible and the intervals between different concentrations are as small as possible so as to obtain the final absorption peak intensity-C_V ^{3 +}A curve with good continuity of ion concentration. In the present invention, such a concentration range should include at least the trivalent vanadium ion concentration C in the mixed solution A described below_V ³⁺And the maximum concentration C of trivalent vanadium ions in the mixed solution B_m。

Step 1 can be completed in a laboratory in advance, in order to ensure the detection accuracy, in some preferred embodiments of the present invention, a portable uv-vis spectrophotometer identical to that used in steps 3 and 4 is required for detection, and since the instruments used in the whole detection method are identical, the subsequent detection steps 3 and 4 are not affected by the detection environment or time.

The step 2 relates to a process of sampling from the flow battery. In the invention, the sampling is required to be respectively carried out from the positive and negative liquid storage tanks of the redox flow battery. The sampling method is not limited, and may be determined according to the actual equipment. With respect to the working state of the flow battery during sampling, the method provided by the invention can be used for sampling during the working period of the flow battery and also can be used for sampling during the non-working period, as long as the safe operation condition is met.

Specifically, in some embodiments of the present invention, sampling test can be selected at any state of charge SOC of the all-vanadium redox flow battery, and therefore, the electrolyte balance test method provided by the present invention can monitor the balance problem of the positive and negative electrolytes of the all-vanadium redox flow battery at any time. Preferably, the sampling is performed when the state of charge SOC is 0, and at this time, when the positive electrolyte contains only tetravalent vanadium ions and the negative electrolyte contains only trivalent vanadium ions, the accuracy of the test method can be further increased.

In the positive electrode liquid tank of the flow battery, vanadium ions are expressed as V⁵⁺/V⁴⁺In the negative electrode liquid tank of the flow battery, the vanadium ions are V²⁺/V³⁺The form of (A) is stored. In the step 2, after the positive electrolyte sample obtained from the positive electrode and the negative electrolyte sample obtained from the negative electrode are mixed in equal volume, the pentavalent vanadium ions contained in the positive electrolyte and the divalent vanadium ions contained in the negative electrolyte undergo redox reaction to generate corresponding tetravalent vanadium ions and trivalent vanadium ions. In the state where the electrolytes of the positive and negative electrodes are not balanced, substantially all of V is present in the mixed solution⁵⁺Or V²⁺Will also generate V⁴⁺And V³⁺Because of whether it is V⁵⁺Or V²⁺Excessive, will continue to react with V³⁺Or V⁴⁺Reaction, therefore, the mixed solution a finally obtained is usually a mixed solution of tetravalent vanadium ions and trivalent vanadium ions. As such, the operating state of the flow battery can be determined by the degree of imbalance K described below.

In the step 3, the working wavelength of the portable ultraviolet visible spectrophotometer is 350-500 nm. Since the maximum absorption wavelength of the trivalent vanadium ions is 400-410nm, strong absorption is generated in the working wavelength, while the maximum absorption wavelength of the tetravalent vanadium ions is 760-770nm, no absorption is generated in the working wavelength, therefore, the concentration C of the trivalent vanadium ions in the mixed solution A is measured_V ³⁺And the interference of the absorption peak of the tetravalent vanadium ion is avoided. The portable ultraviolet-visible spectrophotometer is small in size and convenient to carry, so that the testing method provided by the invention is suitable for being carried out under the non-laboratory condition lacking large-scale detection equipment, such as the place where the all-vanadium redox flow battery operates, the non-equilibrium degree of the electrolyte can be detected immediately, and the method is simple, convenient and quick.

Further, in some embodiments of the invention, the method further comprises: diluting the mixed solution A between the step 2 and the step 3. When the sampling amount is small, the mixed solution A can be properly diluted with deionized water, and such a method can make sampling difficult to reduce and increase the convenience of detection. In some embodiments of the invention, the dilution may be performed using an acidic solution, such as a hydrochloric acid solution or a sulfuric acid solution compatible with the electrolyte, and the like.

In the step 4, in the process of reducing high-valence vanadium ions by the reducing agent, it can be observed that the absorbance of trivalent vanadium ions gradually increases and then gradually decreases, because after all tetravalent vanadium ions are reduced to trivalent vanadium ions, the trivalent vanadium ions are further reduced to divalent vanadium ions, and therefore, when the absorbance of the trivalent vanadium ions reaches the highest value, that is, when the concentration of the trivalent vanadium ions is the highest, all tetravalent vanadium ions contained in the mixed solution a are converted to trivalent vanadium ions. From the maximum concentration C of trivalent vanadium ions in the mixed solution B_mAnd the concentration C of trivalent vanadium ions in the mixed solution A_V ³⁺The concentration C of the tetravalent vanadium ions in the mixed solution A can be calculated_VO ²⁺，C_VO ²⁺＝C_m-C_V ³⁺。

The reducing agent used in step 4 is preferably a metal reducing agent from the viewpoint of convenience in use, provided that the maximum absorption wavelength range of the metal ions formed by the metal does not overlap with the maximum absorption wavelength range of the trivalent vanadium ions. In the present invention, the reducing agent is further preferably metallic zinc, and in some preferred embodiments, metallic zinc in a granular or powder form, which is oxidized into divalent zinc ions in an oxidation-reduction reaction with higher vanadium ions or hydrogen ions, and the maximum absorption wavelength of the divalent zinc ions is about 520nm, without interfering with the detection of the concentration of trivalent vanadium ions, may be used. The addition mode of the reducing agent is not limited, and the reducing agent can be added under a relatively rapid condition or added in portions.

In the step 4, the time when the reducing agent starts to be added into the mixed solution a is taken as a timing starting point, the absorbance test is performed in a unit time, the unit time is preferably 30s to 90s, preferably 40s to 70s, in some embodiments of the present invention, the unit time is preferably 1min, and it is observed that the maximum concentration of the trivalent vanadium ions in the mixed solution B is reached at 5 to 7 min.

When the concentration of tetravalent vanadium ions C in the mixed solution A is higher_VO ²⁺And a concentration of trivalent vanadium ions C_V ³⁺When the electrolyte is equal or close to the positive electrolyte and the negative electrolyte, the positive electrolyte and the negative electrolyte reach a balanced state, and the running condition of the battery is good; on the contrary, the positive and negative electrolytes are in a non-equilibrium state, and the larger the non-equilibrium degree K value of the electrolytes is, the larger the degree of deviation of the positive and negative electrolytes of the flow battery from the equilibrium state is, and certain measures need to be adopted to maintain and manage the electrolytes of the flow battery.

The electrolyte balance testing method is reasonable in design, convenient to operate, accurate in detection and small in error, can provide a guiding function for maintenance and management work of the electrolyte of the all-vanadium redox flow battery running for a long time, and ensures safe and stable running of a galvanic pile.