CN110838592A - Preparation method of flow battery electrolyte - Google Patents
Preparation method of flow battery electrolyte Download PDFInfo
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- CN110838592A CN110838592A CN201810932747.9A CN201810932747A CN110838592A CN 110838592 A CN110838592 A CN 110838592A CN 201810932747 A CN201810932747 A CN 201810932747A CN 110838592 A CN110838592 A CN 110838592A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
- H01M8/184—Regeneration by electrochemical means
- H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
The invention relates to a preparation method of a flow battery electrolyte, which comprises the following steps: a. a step of providing an oxide of vanadium consisting of the following general formula (1): vxOy… … (1), wherein the average valence of V is +3.2 to + 3.7; b. and (2) a step of dissolving the vanadium oxide having the composition of the above general formula (1) in a hydrochloric acid solution, and obtaining a hydrochloric acid-based vanadium electrolyte, which further includes one or more ions selected from the group consisting of Mo, Mn, Pb, and Bi, after the reaction is completed.
Description
Technical Field
The invention belongs to the production field of flow batteries, and particularly belongs to a preparation method of an all-vanadium flow battery electrolyte.
Background
The flow battery technology has natural advantages of large-scale energy storage: the size of the electric storage quantity is linearly proportional to the volume of the electrolyte, and the charging and discharging power is determined by the size and the quantity of the galvanic pile, so that the flow battery with different charging and discharging powers from kW to MW level and different energy storage quantities from 1 hour to several days of sustainable discharging can be designed according to the requirements. The electrolyte based on common inorganic acid and inorganic salt has stable chemical components, convenient storage, small influence on environment, extremely low self-discharge coefficient and suitability for long-term electric energy storage. The reaction temperature of the battery is normal temperature and normal pressure, the flowing process of the electrolyte is a natural water-based circulating heat dissipation system, the safety performance is extremely high, and the accident influence is far lower than that of other large-scale energy storage schemes. There is no upper limit to the theoretical number of charge and discharge cycles due to its stable and reliable charge and discharge cycles.
In flow batteries, the electrolyte serves as an important component of the electrical energy storage, and its stability and lifetime directly determine the capacity of the overall battery system. At present, most of the products of flow battery enterprises worldwide are still in an exemplary project for grid-level energy storage, and the requirements of commercial products on reliability and stability are far from being met. The battery system that has reached the scale of the demonstration project uses mostly a pure sulfuric acid-based electrolyte containing vanadium ions, and a small part of a sulfuric acid-based/hydrochloric acid-based mixed electrolyte containing vanadium ions.
In the current all-vanadium flow battery, the electrolyte is prepared by taking high-valence vanadium oxide as a starting material, and adding a reducing agent or low-valence vanadium oxide into a diluted acid solution to finally gradually reduce the high-valence vanadium ions into the electrolyte in an equilibrium state. As for the acidic solution, a solution of sulfuric acid is conventional, and there has been a report of using hydrochloric acid as the acidic solution in recent years.
Citation 3 discloses a system and method for producing a 3.5-valent high-purity vanadium electrolyte. The method comprises the steps of hydrolyzing high-purity vanadium oxychloride into vanadium pentoxide by adopting fluidized bed gas-phase hydrolysis, accurately controlling and reducing the vanadium pentoxide into a low-valence vanadium oxide with the average vanadium valence of 3.5 in a reduction fluidized bed, adding water and a sulfuric acid solution under an external microwave field, dissolving at low temperature to obtain a 3.5-valence high-purity vanadium electrolyte, and directly using the electrolyte in a new pile of the all-vanadium redox flow battery. The special chemical effect of the microwave field promotes the dissolution of vanadium oxide and activates vanadium ions, so that the electrolyte is dissolved and prepared in a low-temperature range, and the activity of the electrolyte is greatly improved.
Similar to citation 3, citation 4 discloses a system and a method for preparing a high-purity electrolyte of a vanadium redox battery, wherein vanadium oxychloride is used as a raw material, a low-valence vanadium oxide with the average valence of vanadium of 3.5 is prepared by liquid-phase hydrolysis and fluidized reduction, clean water and sulfuric acid are added for dissolution, and the vanadium electrolyte is further obtained by ultraviolet activation, and can be directly used for a new galvanic pile of an all-vanadium redox flow battery.
Citation 5 provides a system and method for preparing a high-activity high-purity vanadium electrolyte having a specific valence state. Converting industrial-grade vanadium oxide into vanadium oxychloride by adopting fluidized chlorination, and removing dust and leaching to obtain crude vanadium oxychloride; rectifying, catalytic oxidizing and precisely controlling reduction to obtain high-purity low-valence vanadium oxide, wherein the average valence state of vanadium can be any value within 3.0-4.0; under the action of an activation device, pure water and a pure sulfuric acid solution are added to be dissolved at low temperature to obtain the high-activity high-purity specific valence vanadium electrolyte which can be directly used for the all-vanadium redox flow battery.
Citation 6 discloses a preparation method of an all-vanadium redox flow battery electrolyte, and V is2O5Preparation of V by reduction of the powder in hydrogen2O4Powder and V2O3And (3) powder. The resulting V is then treated with a sulfuric acid solution2O4And V2O3And respectively dissolving to obtain the electrolyte for the all-vanadium redox flow battery.
In the cited document 1, expensive vanadium pentoxide is used as a starting material and reacts with hydrochloric acid, and since the expensive vanadium ion has strong oxidizing property, it is easy to cause oxidation of chlorine ion and generate toxic chlorine gas. In addition, when the electrolyte of the positive electrode or the negative electrode is formed by using vanadium pentoxide or vanadium trioxide, an additional reducing agent or an oxidizing agent is needed, and the electrode liquid for the flow battery in the equilibrium state can be obtained through complicated adjustment, so that the preparation process is not simple.
After citation 2 obtains a low-valence vanadium oxide having an average valence of 3.0 to 4.5, water and sulfuric acid are added to dissolve the low-valence vanadium oxide, and the electrolyte is obtained through subsequent activation. Cited documents 3 to 5 each relate to the use of high-purity vanadium oxychloride as a starting material to obtain high-purity vanadium pentoxide, and the incorporation of a separate activation device to obtain a final electrolyte. Therefore, the preparation process of the electrolyte is not simple, and the sulfuric acid-based electrolyte obtained by using sulfuric acid as an acidic solution has room for further improvement in corrosion resistance and long life of the flow battery.
In the cited document 6, V is produced by reduction in hydrogen gas using vanadium pentoxide as a raw material2O4Powder, but the process requires precise control of the amount of reducing gas to ensure that over-reduction does not occur or that the reduction is insufficient.
Therefore, although various methods for preparing electrolytes for all-vanadium flow batteries have been attempted in the art, there is still room for further improvement in the convenience of preparation and the use properties of the electrolytes.
Citations
Cited document 1: US 2015/0050570 a1
Cited document 2: CN106257725B
Cited document 3: CN106257728B
Cited document 4: CN106257727A
Cited document 5: CN107565153A
Cited document 6: CN 103401010A
Disclosure of Invention
Problems to be solved by the invention
In order to solve the technical problems existing in the prior art, the invention provides a method for preparing an all-vanadium redox flow battery electrolyte, which takes vanadium oxide composed of the following general formula (1) as a direct starting material, takes hydrochloric acid as an acidic solution, and prepares the electrolyte in the presence of an activated catalyst.
VxOy……..(1)
Wherein, the valence of V is +3.2 to +3.7, x is 1: (1.6-1.85).
The method has low requirement on the purity of the raw materials and has stronger raw material applicability. The use of the oxide having the composition of the general formula (1) as a raw material enables a desired electrolyte to be obtained directly without the necessity of compounding an additional oxidizing agent or reducing agent. In addition, the activation catalyst present in the electrolyte enables activation of the electrolyte to be accomplished during the formation of the electrolyte without a separate activation process.
In addition, the hydrochloric acid is used as the acid solution, so that the use performance of the electrolyte is further improved compared with a sulfuric acid-based electrolyte, damage to components of the flow battery is avoided, and the service life is prolonged.
Means for solving the problems
Through detailed research and practice of the invention, the following technical scheme is found to be used for solving the problems:
the invention firstly provides a preparation method of a flow battery electrolyte, which comprises the following steps:
a. a step of providing an oxide of vanadium consisting of the following general formula (1):
VxOy……..(1)
wherein, the valence of V is +3.2 to +3.7, x is 1: (1.6-1.85);
b. a step of dissolving the vanadium oxide of the general formula (1) in a hydrochloric acid solution to obtain a hydrochloric acid-based vanadium electrolyte after the reaction is completed,
the electrolyte also comprises one or more ions selected from Mo, Mn, Pb and Bi.
According to the above-described process, in a preferred embodiment, the average valence of V is between +3.3 and + 3.5.
According to the above-described method, in a preferred embodiment, the concentration of the hydrochloric acid solution is 10 to 38% by mass.
According to the method described above, in a preferred embodiment, before the step a, the method further comprises the following steps:
a step of subjecting the high oxidation number vanadium oxide, preferably including V, to a reduction reaction to obtain the vanadium oxide composed of the general formula (1)2O5。
According to the above-mentioned method, in a preferred embodiment, the reduction reaction of the vanadium oxide with a high oxidation number is carried out in the presence of a reducing gas, preferably H2CO, hydrogen sulfide, methane, sulfur dioxide, ethylene or NH3One or any combination thereof.
Further, the present invention also provides a method for producing a flow battery, which includes the method for producing an electrolyte according to any one of the above.
ADVANTAGEOUS EFFECTS OF INVENTION
Through the implementation of the technical scheme, the method for preparing the electrolyte has the following effects:
compared with the method for preparing the electrolyte by using the high-valence vanadium oxide and the hydrochloric acid, the method disclosed by the invention does not need to use the high-valence vanadium oxide as a raw material to directly react with the hydrochloric acid, so that the possibility of oxidizing chloride ions into chlorine is reduced;
in the preparation method of the electrolyte, the purity of the raw materials has no special requirement on purity, and the applicability in actual production is strong;
according to the invention, hydrochloric acid is used as an acid solution to prepare the electrolyte, so that damage to a galvanic pile component in the use process of the flow battery can be avoided, and the service life can be prolonged.
In addition, the acidity of the electrolyte is required, and the electrolyte needs to be adjusted back to the specified range as soon as the acidity of the electrolyte deviates during the operation of the battery. When pure hydrochloric acid base electrolyte is used, HCl gas is used for supplementing acidity, and the volume of the electrolyte is not changed. When pure sulfuric acid base or hydrochloric acid/sulfuric acid mixed electrolyte is used, the volume of the electrolyte can be changed due to the fact that liquid is supplemented, and limitation can be caused under the condition that the size of the electrolyte tank is fixed.
The preparation method of the electrolyte does not need an independent electrolyte activation process, can complete the activation of the electrolyte while preparing the electrolyte, and can obviously improve the battery performance when the activation catalyst is used in the pure hydrochloric acid-based electrolyte.
Preparation of the electrolyte according to the invention, according to VxOyThe average composition of x and y in (a) can directly produce electrolyte of a balanced or unbalanced flow battery;
on the whole, the electrolyte preparation process is simple, and the preparation efficiency and performance of the electrolyte are improved obviously in industry.
Drawings
FIG. 1: preparation flow chart of electrolyte of the invention
FIG. 2: 4M HCl and 3M H were used2SO4Comparison as an electrolyte to simulate overcharge conditions
FIG. 3: FIG. 2 comparison of corrosion conditions of bipolar plate materials by different electrolytes
FIG. 4: 3M H2SO4Corrosion of electrolyte to graphite bipolar plate under different polarization voltages
FIG. 5: corrosion condition of 4M HCl electrolyte on graphite bipolar plate under different polarization voltages
FIG. 6: example 1 polarization curve of electrolyte
FIG. 7: comparative example 1 polarization curve of electrolyte
Detailed Description
The method for preparing the electrolyte for the all-vanadium redox flow battery of the invention will be described in detail below. It is to be noted that, unless otherwise specified, the unit names used in the present invention are all international unit names commonly used in the art. Furthermore, the recitation of numerical values or ranges of values herein below is understood to include industry-accepted errors.
< first embodiment >
In a first embodiment of the invention, a preparation method of an all-vanadium redox flow battery electrolyte is provided.
Direct feedstock
In the present invention, the oxide of vanadium that reacts directly with the acidic solution is referred to as "direct raw material" or "starting material", and the industrial raw material or mineral raw material from which these "direct raw material" or "starting material" are obtained is referred to as "raw material" or "raw source".
In the present invention, an oxide of vanadium having the following general formula (1) is used as a direct raw material for preparing an electrolyte for an all-vanadium battery:
VxOy……..(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 V2O5The oxide of (2) is directly reduced, or in other industrial production, other compounds of +5 vanadium can be mixed and dissolved with an acid solution, reduction reaction is carried out in the presence of a reducing agent, and then precipitates are obtained through adding alkaline substances, and then the precipitates are washed and dried to obtain the low-valence oxide.
The reduction method used in the above process 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, H2CO, hydrogen sulfide, methane, sulfur dioxide, ethylene or NH3One or any combination thereof.
As mentioned above, the oxide of the general formula (1) is used as the direct raw material for preparing the electrolyte in the invention, and the oxide is used as V in the prior art for preparing the electrolyte of the all-vanadium redox flow battery2O5The vanadium oxide with the valence state of 3.0-4.0 is used as a direct raw material or the vanadium oxide with the valence state of 3.0-4.0 is used as a direct raw material (usually, the direct raw materials are required to have higher purity, and in some cases, the vanadium oxide with the valence state of 3.0-4.0 is also based on high-purity V2O5Reduced as a raw material), the purity of the oxide having the composition of the general formula (1) in the present invention is not limited or required to be relatively pure in the past, and the purity of the oxide of vanadium having an average valence of +3.2 to +3.7 among the oxides of vanadium of the general formula (1) 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.
The main factor affecting the purity of the above vanadium oxide comes from the presence of other metal ions or oxides thereof, such as ions or oxides of Fe, Na, K, Ca, or noble metal ions or oxides such as Au, Ag, or Pt. Unlike a pure sulfuric acid-based electrolyte, the presence of these impurities described above has less effect on the performance of the electrolyte in a flow battery using a pure hydrochloric acid-based electrolyte according to the present invention, and therefore, as a pure hydrochloric acid electrolyte, the presence of these impurities can be allowed within a certain range without removal. In addition, from the viewpoint of further reducing the influence of impurities, with respect to some impurities derived from noble metals, in a preferred embodiment of the present invention, the content thereof contained in the oxide of vanadium having a composition of the general formula (1) is 100ppm or less, preferably 50ppm or less, more preferably 30ppm or less.
In the present invention, it is very advantageous for the industrial production of electrolytes to use the vanadium oxides of the general formula (1) as the direct starting material for the preparation of electrolytes, on the one hand, for the manufacturers of the oxides providing such vanadium, in the reduction of V2O5The oxidation state of vanadium is controlled within a certain range in the process of (2). Therefore, it is not necessary to control the reducing agent and V in the reduction reaction with particular accuracy2O5The addition amount of (A) reduces the risk of insufficient reduction or excessive reduction, is beneficial to reducing the cost, and transmits the effect to downstream industrial production. In addition, as described above, there is no excessive limit on the purity of the vanadium oxide having the composition of the general formula (1), and therefore, the source of the raw materials for preparing the electrolyte of the all-vanadium flow battery can be substantially expanded in the present invention, which is advantageous for further cost reduction.
With respect to the vanadium oxide represented by the general formula (1), in some preferred embodiments of the present invention, the average valence of vanadium therein is preferably +3.3 to +3.6, and in other preferred embodiments, the average valence of vanadium is preferably +3.3 to +3.5, and more preferably +3.4 to + 3.5.
The average valences mentioned above are understood to be statistical data, i.e. the oxides of vanadium are mixed oxide systems of vanadium in the lower valences, for example vanadium in the valences +3 and below, and vanadium in the valences +4 and above.
Acidic solution
In the present invention, the oxide of vanadium having the composition of the above general formula (1) is dissolved in an acidic solution to prepare an electrolytic solution.
The acidic solution used in the present invention is a hydrochloric acid solution, and in some preferred embodiments such a hydrochloric acid solution has a concentration of 10 to 38% by mass, and in other preferred embodiments such a hydrochloric acid solution has a concentration of 10 to 35% by mass.
In the present invention, the use of a hydrochloric acid solution instead of sulfuric acid as the acidic solution is considered to be relatively more excellent in solubility to vanadium oxide, and on the other hand, it is considered that although hydrochloric acid is used as the acidic solution, since vanadium has a valence between +3.2 and +3.7 in the oxide used, it is possible to prevent oxidation of chloride ions due to an excessively high oxidation valence of vanadium, and thus to avoid the generation of undesirable chlorine gas.
Further, the use of hydrochloric acid as the acidic solution avoids the use of conventional sulfuric acid, since, according to the present invention, a pure hydrochloric acid based electrolyte has the following advantages over sulfuric acid based electrolytes: the formed electrolyte has lower viscosity and better fluidity; the formed electrolyte has better conductivity and is beneficial to improving the efficiency of the battery. In addition, under the condition that local overcharge occurs inside the galvanic pile, the corrosion of the sulfuric-acid-based electrolyte on the graphite bipolar plate is irreversible, and under the same condition, the hydrochloric-acid-based electrolyte can generate chlorine, and the generated chlorine can be discharged out of the system or collected through the exhaust design of an additional electrolyte tank, so that irreversible influence cannot be caused on the galvanic pile and the whole system.
Preparation of electrolyte
In the present invention, the vanadium oxide of the general formula (1) is mixed and dissolved with hydrochloric acid. There is no particular requirement for the equipment used for mixing, and mixing equipment common in the art, such as a reaction tank equipped with an inlet, may be used. In some preferred embodiments of the invention, these apparatuses have, in addition to the feed device, a stirring device. The reaction temperature is preferably room temperature or lower, more preferably 20 ℃ or lower.
In some preferred embodiments, the vanadium oxide is dispersed in a hydrochloric acid solution for dissolution, and the following reaction is carried out:
VxOy+HCl→VClx+H2O
in the electrolyte formed by the above reaction, there are actually a plurality of valence states of vanadium chloride, and in some cases, if there are also high valence vanadium (+5 valence) ions and low valence vanadium (+2 valence) ions in the obtained electrolyte, the redox reaction will be immediately performed between such ions, so as to obtain an electrolyte composed of +3 valence and +4 valence vanadium ions in total.
Taking the case that the average valence of vanadium in the oxide is +3.5 as an example:
V2O3.5+7HCl→2VCl3.5+3.5H2O
here VCl3.5Is a statistically averaged number, and in some cases such a composition can be viewed as consisting essentially of VCl3With VOCl2Mixing according to the proportion of 1: 1. Thus, it can be understood that when V is used2O3.5(the average valence of V is +3.5) and hydrochloric acid, so as to directly obtain the electrolyte formed by + 3-valent vanadium ions and + 4-valent vanadium ions, and the electrolyte can be called as equilibrium electrolyte.
In other embodiments of the present invention, an oxide of vanadium having an average valence of less than +3.5 and above +3.2 may be used as a starting material to react with hydrochloric acid. In the obtained electrolyte, an electrolyte composed entirely of + 3-valent vanadium ions and + 4-valent vanadium ions was obtained in the same manner as in the case of V2O3.5In such a system, the content of the + 3-valent vanadium ions is more than that of the + 4-valent vanadium ions, and the electrolyte can be called a negative non-equilibrium electrolyte.
In other embodiments of the present invention, vanadium oxides having an average valence state higher than +3.5 and lower than +3.7 may be used as a raw material to react with hydrochloric acid. In the obtained electrolyte, the electrolyte is composed of all of the +3 valent vanadium ions and the +4 valent vanadium ions, and the same as the above V2O3.5In such a system, the +3 valent vanadium ion is differentIs lower than the content of +4 vanadium ions, and for such electrolytes, it can be referred to as positive non-equilibrium electrolytes.
Therefore, it can be seen that, in the production of an electrolyte using the vanadium oxide of the general formula (1) as a direct raw material, an equilibrium state electrolyte, a negative non-equilibrium state electrolyte, and a positive non-equilibrium state electrolyte can be directly obtained depending on the composition of the actual raw material.
The electrolyte in an equilibrium state can be used directly in the presence of a metal ion having catalytic activity as described below. In other embodiments of the invention, a negative non-equilibrium electrolyte may be used, and in particular, when a higher degree of charge is preferred, a negative non-equilibrium electrolyte may be suitably used, or an equilibrium electrolyte may be mixed with a negative non-equilibrium electrolyte in a certain ratio. In other embodiments of the present invention, under the condition of obtaining the positive non-equilibrium state electrolyte, the high valence vanadium ions may also be subjected to a reduction treatment by using a suitable reducing agent as required to obtain an equilibrium state electrolyte or a negative non-equilibrium state electrolyte. As the method of reduction, there is no limitation, and reduction means conventional in the art may be used, for example, a reducing gas or other reducing compound may be used. Mention may be made, as reducing gases, of hydrogen, CO, hydrogen sulphide, methane, sulphur dioxide, ethylene or NH3One or any combination thereof; as other reducing compounds, aldehydes, alcohols or reducing organic acids, typically oxalic acid, etc. may be used, and in other embodiments, oxides of vanadium may be added, such as V2O3To increase the content of the + 3-valent vanadium ions.
In the present invention, it is necessary to determine the average valence state of vanadium in the oxide of the general formula (1) to be +3.2 to +3.7 as a direct raw material for preparing the electrolyte of the all-vanadium flow battery. On the one hand, it can be seen from the above description that such raw materials are readily available, have a low cost, and have excellent suitability for the process of the present invention; on the other hand, if the oxidation state of vanadium in the oxide is too high or too low, the use of the formed non-equilibrium electrolyte will be significantly limited, and additional production costs will be required for the subsequent use of such an electrolyte.
In addition, when the reaction is carried out using the vanadium oxide represented by the general formula (1) and hydrochloric acid, the reaction solution may be diluted as necessary. In order to allow the reaction to proceed quickly at the beginning of the reaction, a hydrochloric acid solution having a high concentration and a large amount of vanadium oxide are generally used. The electrolyte thus obtained has a high vanadium ion concentration. However, such an electrolyte solution is usually used after further dilution. Therefore, without being limited thereto, in the method of the present invention, the dilution with water may be performed in any step of forming the electrolytic solution, preferably, the dilution is performed after the acidic solution is contacted with the oxide, and more preferably, the dilution is performed after the acidic solution is reacted with the oxide. In some preferred embodiments of the present invention, the water is deionized or distilled water.
Activating catalyst
In the method of the present invention, the preparation of the electrolyte by mixing the vanadium oxide having the composition of the general formula (1) with an acidic solution is carried out in the presence of an activated catalyst.
For the activating catalyst, there may be metal ions which can promote the interconversion of vanadium +3 with vanadium + 2. In the present invention, the metal ion as the activation catalyst may be one or more ions derived from Mo, Mn, Pb, Bi. In some preferred embodiments, the metal ions are used in an amount of 0.1ppm or more, or 0.3ppm or more, or 0.5ppm or more, or 0.7ppm or more, or 1.0ppm or more, or 3.0ppm or more, or 10ppm or more, or 30ppm or more, or 50ppm or more, and may be 800ppm or less, or 500ppm or less, or 300ppm or less, or 100ppm or less.
The addition time of the activated catalyst in the present invention is not particularly limited, and in some embodiments, the activated catalyst ions may be previously added to an acidic solution, and then the acidic solution may be mixed with the oxide of vanadium having a composition of the general formula (1) to obtain an electrolyte.
In other embodiments, the vanadium oxide of formula (1) may be mixed with the acidic solution prior to adding the activated catalyst to obtain the electrolyte.
In the present invention, by using the above catalyst activator in a pure hydrochloric acid based electrolyte, the electrolyte can be normally used without the presence of a separate external activation step.
Other aspects
Other aspects of the technical solution of the present invention may be implemented, and although not essential, auxiliary means existing in the art may be adopted as long as the technical effects of the present invention are not affected.
In some embodiments, although the present invention does not impose a high requirement on the purity of the vanadium oxide represented by formula (1), the present invention does not exclude the use of high purity vanadium oxide. The high purity vanadium oxide represented by the general formula (1) can be obtained by a method generally used in the art. For example, high-purity vanadium pentoxide can be obtained from high-purity vanadyl chloride, and further high-purity vanadium oxide represented by the general formula (1) can be obtained by reduction.
In the present invention, when the oxide of vanadium containing metal impurities is used as a raw material, the oxide of vanadium as a raw material may be dissolved in an acidic substance and then the resulting electrolyte solution may be further purified. For the purification step, it is preferable to carry out without adding the above-mentioned activating catalyst. The purification step is not particularly limited, and a chemical purification method and a chemical-electrochemical purification method which are generally used in the art can be used, and typically, for example, an electrolytic method or an ion exchange method is used.
Furthermore, although as noted above, achieving the technical effects of the present invention is not dependent on a separate external activation device, in some embodiments, external activation may also be performed using a separate activation step after obtaining an electrolyte with or without the above-described activation catalyst. The activation method may be any activation method known in the art, for example, ultraviolet activation, microwave activation, or the like may be used.
In the electrolytic solution obtained by the method according to the present invention, various additives such as complexing agents, stabilizers and the like, which are conventional in the art, may be used without limitation.
< second embodiment >
A second embodiment of the present invention provides a method for producing a flow battery, such a method including the method for producing an electrolyte according to < first embodiment >.
Without limitation, in the second embodiment of the present invention, other steps than the preparation step of the electrolyte may be performed using methods known in the art.
Examples
Specific examples of the present invention will be described below, and it should be noted that the following examples are only specific examples of the embodiments of the present invention and should not be construed as limiting the scope of the present invention.
Reference example 1(polarization comparison of pure hydrochloric acid with pure sulfuric acid electrolyte):
a) use of 4M HCl and 3M H2SO4And (3) as an electrolyte to simulate the corrosion comparison of the electrolyte on the graphite bipolar plate under the overcharge condition.
As can be seen from fig. 2 and 3, in the case of the pure sulfuric acid electrolyte, the current density has a tendency to increase at the same voltage, and the pure sulfuric acid electrolyte has a greater tendency to damage the battery element.
b) Use of 4M HCl and 3M H2SO4The corrosion of the electrolyte on the graphite bipolar plate under the overcharge condition was compared as the electrolyte solution, and the test results are shown in table 1, table 2 and fig. 4-5.
The experimental conditions are as follows:
electrolyte: 4M HCl and 3M H2SO4
Bipolar plate: graphite bipolar plate
Bipolar plate polarization zone: 2cmx2cm
Stirring speed: 400rpm
Temperature: room temperature 25 deg.C
Polarization voltage: 2/2.5/3/3.5/4V
Table 1: using 3M H2SO4The case (Current Density and electrode potential are data after 10 minutes of holding at polarizing voltage)
Table 2: case of using 4M HCl (Current Density and electrode potential are data after 10 minutes of holding at polarizing voltage)
From tables 1 and 2 above, and from the description accompanying figures 4 and 5, it can be seen that the use of pure sulphuric acid electrolyte has a greater tendency to damage the stack equipment components (10 minutes at each polarisation voltage) than the use of pure hydrochloric acid.
The polarization experiment of reference example 1 was used as a simulation experiment under an extreme overcharge condition, and the influence of different electrolyte environments on the corrosion of the graphite bipolar plate under a local overcharge condition inside the stack was simulated.
Example 1：
Using an average composition of V2O3.53.1L of industrial concentrated hydrochloric acid (38 mass%) is poured into the powder in batches, stirred at a constant speed in the process, the temperature is kept at 85 ℃ by utilizing a heating device, and 6.2L of deionized water is added after the powder is completely dissolved in the hydrochloric acid. Filtering, and adding Mo6+And Mn2+The total amount of the mixed ions was 50 ppm. The final 1.15mol/L V is obtained3.5+4mol/L HCl to obtain an equilibrium state electrolyte. Fig. 6 below is a polarization curve for a flow battery using the prepared electrolyte. Wherein the unit of the y-axis is voltage V and the unit of the x-axis is electricityFlow density A/cm2. And respectively carrying out charging and discharging polarization on the battery, carrying out straight line fitting on the obtained data points, and obtaining the slope of the fitted straight line, namely the equivalent resistance in the battery during charging and discharging. As can be seen from FIG. 6, the equivalent internal resistance of the cell using the electrolyte with the catalyst added thereto was 1.0735/-1.0956Ohm cm2。
The battery was subjected to charge and discharge cycles, and table 3 below shows charge and discharge efficiency data of the battery.
TABLE 3
Comparative example 1
The same operation as in example 1 was performed except that the activated catalyst was not added, and fig. 7 below is a polarization curve of the prepared catalyst-free electrolyte for a flow battery. Wherein the unit of y-axis is voltage V, and the unit of x-axis is current density A/cm2. And respectively carrying out charging and discharging polarization on the battery, carrying out straight line fitting on the obtained data points, and obtaining the slope of the fitted straight line, namely the equivalent resistance in the battery during charging and discharging. As can be seen from FIG. 7, the equivalent internal resistance of the cell without any catalyst of the electrolyte was 2.504/-2.7811Ohm cm2Significantly higher than the equivalent internal resistance of the cell with the catalyst added in example 1.
The battery was subjected to charge and discharge cycles, and table 4 below shows charge and discharge efficiency data of the battery. As can be seen from the comparison of the equivalent resistances, the internal resistance of the battery is high, and the voltage efficiency thereof is reduced, resulting in a reduction in the overall energy efficiency. Comparing the cell efficiencies in table 4 below with those in table 3 of example 1, it is apparent that the addition of the catalyst can greatly improve the cell performance.
TABLE 4
Example 2 and comparative example 2(comparison of Performance of pure sulfuric acid based electrolyte with pure hydrochloric acid based electrolyte)
Wherein example 2 is rootAn electrolyte having a composition of 0.75M V was obtained in a similar manner to example 14+And 0.75M of V3+And 4M HCl.
Comparative example 2 an electrolyte was prepared at room temperature (with the same addition of activating catalytic ions as in example 1) using vanadium pentoxide in a reaction with sulfuric acid, using a method known in the art, and having a composition of 0.75M V4+And 0.75M of V3+And 3M of H2SO4。
Pure hydrochloric acid-based and pure sulfuric acid-based electrolytes were simulated and tested using the above-described example 2 and comparative example 2, respectively, and the test results are shown in the table.
Table 5 shows the electrolyte test of example 2, and table 6 shows the electrolyte test of comparative example 2.
Table 5:
table 6:
(Note: the 3M sulfuric acid solution and the 4M hydrochloric acid solution are used here because these two concentrations are the most common acid solution concentrations for each of the sulfuric acid-based and hydrochloric acid-based electrolytes)
The comparison of current efficiency/voltage efficiency/energy efficiency shows that the voltage efficiency and the overall energy efficiency of the hydrochloric acid-based electrolyte are significantly higher than those of sulfuric acid-based electrolyte.
Reference example 2
The same preparation process as in comparative example 2 was conducted except that the activating catalyst was not used in the electrolyte.
The resulting electrolyte was tested as follows in table 7:
table 7:
example 1 was compared with comparative example 1, and comparative example 2 was compared with reference example 2. It can be seen that under the same conditions, the use of the activated catalyst, whether a hydrochloric acid-based or sulfuric acid-based electrolyte, provides a significant improvement in both voltage efficiency and overall energy efficiency, but the improvement is more pronounced with the use of the activated catalyst for a hydrochloric acid-based electrolyte. The active catalyst used in the hydrochloric acid-based electrolyte has higher use value.
Industrial applicability
The method provided by the invention can be used for simply and efficiently preparing the electrolyte for the all-vanadium redox flow battery in industry and preparing the all-vanadium redox flow battery.
Claims (6)
1. A method for preparing a flow battery electrolyte, comprising the steps of:
a. a step of providing an oxide of vanadium consisting of the following general formula (1):
VxOy……..(1)
wherein the average valence of V is +3.2 to +3.7, x: y is 1: (1.6-1.85);
b. a step of dissolving the vanadium oxide composed of the general formula (1) in a hydrochloric acid solution to obtain a hydrochloric acid-based vanadium electrolyte after the reaction is completed,
the electrolyte also comprises one or more ions selected from Mo, Mn, Pb and Bi.
2. The method of claim 1, wherein the average valence of V is +3.3 to + 3.5.
3. The method according to claim 1 or 2, wherein the concentration of the hydrochloric acid solution is 10 to 38 mass%.
4. The method according to claim 1 or 2, characterized by, before step a, further comprising the steps of:
vanadium with high oxidation numberPreferably the high oxidation valence vanadium oxide comprises V2O5。
5. The method according to claim 3, characterized in that the reduction of the vanadium oxide with a high oxidation number is carried out in the presence of a reducing gas, preferably H2CO, hydrogen sulfide, methane, sulfur dioxide, ethylene or NH3One or any combination thereof.
6. A method for producing a flow battery, characterized by comprising the method for producing an electrolyte according to any one of claims 1 to 5.
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