KR20220139206A - Method for producing vanadium electrolyte and battery comprising vanadium electrolyte - Google Patents

Abstract

The present invention relates to a method for manufacturing a vanadium electrolyte and a battery including the vanadium electrolyte. According to the present invention, provided are a method for manufacturing a vanadium electrolyte and a battery including the vanadium electrolyte, wherein the reduction reaction rate of a vanadium compound can be controlled, separation and recovery processes can be omitted because by-products are not generated, and reproducibility of a single manufacturing process can be provided.

Description

Method for producing a vanadium electrolyte and a battery comprising a vanadium electrolyte

The present invention relates to a method for producing a vanadium electrolyte and a battery including a vanadium electrolyte, and more particularly, it is possible to control the reduction reaction rate of a vanadium compound, and it does not produce by-products, so the separation and recovery process can be omitted, and chemical reduction It relates to a method for producing a vanadium electrolyte capable of reproducibly providing a single process, and to a battery including the vanadium electrolyte.

Energy Storage System (hereinafter referred to as 'ESS') is a technology that provides efficient power management by converting the conventional power production/use system into a production/storage/use system, and various methods are being studied, Specific examples include pumped-water power generation, compressed air storage, and physical storage methods including flywheels; electromagnetic methods including superconducting energy storage, supercapacitors; chemical methods including flow batteries and lithium-ion batteries; and the like.

Among them, flow batteries have advantages such as low cost, large capacity, long lifespan, and stability. In particular, the demonstration has been completed in power plants, new and renewable energy ESS linkage systems, and smart grid ESS construction, and is evaluated as commercially advantageous in the relevant field.

An example of the electrolyte constituting the flow battery is a vanadium electrolyte.

Conventional vanadium electrolyte solution is manufactured in multiple steps of a reducing agent use method and an electrolysis method, but in this case, more than 1/3 of the commercially unnecessary electrolyte solution is manufactured, and multi-steps are required, and the limited cell size is considered in the electrolysis step. When mass production is not easy, there is a problem that consumables such as electrodes and separators for electrolysis are continuously generated.

At this time, the method of using the reducing agent is to dissolve the raw material V ₂ O ₅ in a sulfuric acid solution to make a vanadium pentavalent ion, and then reduce it with the vanadium tetravalent ion VO ²⁺ to prepare a tetravalent electrolyte using oxalic acid, methanol, etc. do.

Taking oxalic acid as an example, when preparing 1 L of a tetravalent electrolyte of 1.6 M of vanadium / 4.0 M of sulfuric acid, in consideration of heat generation, vanadium, sulfuric acid, and water are mixed, and then oxalic acid is added to conduct a stirring reaction. For reference, when the temperature of the reactor is maintained at 90° C., it takes 4 hours, and methanol takes a longer time because the reaction rate is slower than that of oxalic acid.

However, the above-described reducing agent only advances the reaction of vanadium pentavalent to vanadium tetravalent, but does not participate in the reaction of vanadium tetravalent to vanadium trivalent, and side-reactants generated by the oxidation reaction of unreacted reducing agent and reducing agent seriously deteriorate the properties of the electrolyte. There is a downside to lowering it.

Therefore, research using the same vanadium 3.3 to 3.7 electrolyte solution for anode and cathode is continued in addition to research on reducing agents that do not cause side reactions or easy removal of side reactants.

As a representative example, when reducing vanadium tetravalent to trivalent, it is added to vanadium tetravalent ions and reacted with catalytic reaction using noble metal catalysts such as Ru, Pd, and Pt to an organic reducing agent, including formic acid, which can produce a 3.3 to 3.7 valence electrolyte. 3.3 to 3.7 prepare electrolytes. Here, the 3.3 to 3.7 vanadium electrolyte refers to an electrolyte containing vanadium tetravalent and trivalent ions in the same molar ratio, unless otherwise specified.

However, some of the carbon component and the noble metal catalyst in the organic reducing agent may remain in the electrolyte to deteriorate battery performance, and since most catalysts are rare metals, the manufacturing cost is greatly increased.

Therefore, there is a need for research on manufacturing technology to improve the productivity, reproducibility, stability and high quality of the vanadium electrolyte.

Korean Registered Patent No. 1415538

In order to solve the problems of the prior art as described above, the present invention can control the reduction reaction rate of the vanadium compound in the production of a vanadium electrolyte, omit the separation and recovery process of by-products, and improve the reproducibility of the manufacturing process by chemical reduction. An object of the present invention is to provide a method for preparing a vanadium electrolyte solution provided in a single process and a battery including the vanadium electrolyte solution.

The above and other objects of the present invention can all be achieved by the present invention described below.

In order to achieve the above object, the present invention

A first step of reducing a pentavalent vanadium compound to a tetravalent vanadium compound as a vanadium compound; and a second step of reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound,

adding a redox additive to at least one of the first step and the second step,

The redox additive provides a method for producing a vanadium electrolyte, characterized in that the reducing power is lower than that of the nitrogen-based reducing agent used to reduce the vanadium compound in the first step.

The first step may include sequentially i) adding a pentavalent vanadium compound and water, ii) adding a nitrogen-based reducing agent, and iii) adding sulfuric acid.

The redox additive may dehydrate the sulfuric acid in the first step to form an aqueous solution and then oxidize the nitrogen-based reducing agent while reducing itself to generate nitrogen gas.

The redox additive may be used to reduce the tetravalent vanadium compound in the second step in a dehydrated aqueous solution state with sulfuric acid.

The redox additive is molybdenum metal, molybdenum oxide (MoxOy), molybdenum nitride (MoxNy), molybdenum chloride (MoxCly), molybdenum sulfide (MoxSy), molybdenum phosphide (MoxPy), Molybdenum Carbide (MoxCy), Molybdenum Metal Oxide (MoxMyOz), Molybdenum Metal Nitride (MoxMyNz), Molybdenum Metal Chloride (MoxMyClz), Molybdenum Metal Sulfide (MoxMySz), Molybdenum Metal Phosphide ( MoxMyPz) and molybdenum metal carbide (MoxMyCz) may be at least one selected from the group consisting of.

The metal of the redox additive is Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Mg, Mn, Na, Ni, Pb, Si, Sn, Ti, Zn, Au, Ag , Pt, Ru, Pd, Li, Ir, W, Nb, Zr, Ta, Ge, and a species or a plurality of species selected from In may be a metal forming an alloy, wherein x and y (x / y) or x, y and z (x/y/z) may independently be integers from 0 to 1.

The redox additive may be included in an amount of 0.1 to 1.6 parts by weight based on 100 parts by weight of the pentavalent vanadium compound.

The nitrogen-based reducing agent may be included in an amount of 10 to 35 parts by weight based on 100 parts by weight of the vanadium compound.

A ratio of the molar concentration (M; mol/L) of the pentavalent vanadium compound and the nitrogen-based reducing agent may be 1:0.1 to 1.6.

The second step may be performed at 70 to 120 °C.

The pentavalent vanadium compound may be a low-grade compound having a purity of 90% or more and less than 99.9%, or a high-grade compound having a purity of 99.9% or more.

It may include the step of filtering after the first step or after the second step.

Also, the present invention

(A) preparing a reaction mixture by adding a pentavalent vanadium compound to a solvent and then adding a nitrogen-based reducing agent;

(B) reducing the pentavalent vanadium compound to a tetravalent vanadium compound while performing a dehydration reaction by adding sulfuric acid and a redox additive to the reaction mixture;

(C) generating a self-reduced product while the dehydration reactant oxidizes the nitrogen-based reducing agent to generate nitrogen gas; and

(D) reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound while the self-reduced product is oxidized by heating the reactant; includes,

The nitrogen-based reducing agent provides a method for producing a vanadium electrolyte, characterized in that the total amount is added to the step (A) or divided into steps (A) and (D).

The redox additive participates in the reaction in the form of an aqueous solution by dehydration reaction with sulfuric acid, so that by-products derived from the redox additive are not generated.

The step (D) may be performed by applying the reduction reaction time of the vanadium compound calculated by substituting the reaction temperature of 70 to 120° C. and the amount of the redox additive into Equation 1 below.

[Equation 1]

t _R = Aln(Ma/Mv)+B

(Where t _R is the reaction time (min), A is the rate constant, B is the concentration constant, Ma is the input amount of the redox additive (g), and Mv is the input amount (g) of the vanadium compound)

In addition, the present invention provides a vanadium electrolyte prepared by the above-described method.

In addition, the present invention provides a redox flow battery comprising the above-described vanadium electrolyte.

The vanadium electrolyte may be included in the anode and the cathode.

According to the method for producing a vanadium electrolyte of the present invention, there is an effect of shortening the production time of the electrolyte, eliminating the need for a purification process for separating and recovering reaction by-products, and producing a vanadium electrolyte with improved charging and discharging performance of the product.

In addition, a single process of a chemical reduction method is possible without an electrolysis method, thereby simplifying the process.

In addition, there is an effect of reproducibly manufacturing a large amount of high-quality electrolyte while fundamentally blocking the residual carbon component and noble metal catalyst component in the vanadium electrolyte.

That is, by manufacturing an economical, high-efficiency, high-quality, and high-performance vanadium electrolyte according to the present invention, the battery containing the vanadium electrolyte can be applied to all fields in which the vanadium redox flow battery is used, such as renewable energy, smart grid, and power plants. It works.

1 is a graph showing the temperature change for each reduction reaction time period at the sulfuric acid flow rate of 240 ml/hr and 480 ml/hr of Example.
2 is a graph showing the correlation between the input amount of the redox additive of Example and the reduction reaction rate of the vanadium compound, and it can be seen that the Arrhenius approximation is followed.
3 is a graph showing the reduction reaction rate of the vanadium compound as the oxidation number of the vanadium ion for each input amount of the redox additive in Examples and Comparative Examples, thereby confirming the effect of the redox additive on the reduction reaction rate and reduction amount.
4 is a graph showing the charge capacity per cycle of the redox flow battery using the vanadium electrolyte for the positive electrode and the negative electrode according to the input amount of the redox additive of Examples and Comparative Examples.
5 is a graph showing the discharge capacity per cycle of the redox flow battery using the vanadium electrolyte for the positive electrode and the negative electrode according to the input amount of the redox additive of Examples and Comparative Examples.
6 is a graph showing the energy efficiency of a battery including a vanadium electrolyte for each input amount of the redox additive of Examples and Comparative Examples.

Hereinafter, a method for manufacturing a vanadium electrolyte solution according to the present invention and a battery including the vanadium electrolyte solution will be described in detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and considering that the inventor may appropriately define the concept of the term in order to best describe the invention. Therefore, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In the present description, the meaning of "consisting of" may be defined as "including polymerization prepared", "polymerized including", or "including as a derived unit" unless otherwise defined.

Unless otherwise specified, all numbers, values and/or expressions expressing quantities of ingredients, reaction conditions, polymer compositions and formulations used in this disclosure are, among other things, the measurements such numbers essentially result in obtaining such values. Since they are approximations reflecting various uncertainties of Also, where numerical ranges are disclosed in the present description, such ranges are continuous and inclusive of all values from the minimum to the maximum inclusive of the range, unless otherwise indicated. Furthermore, when such ranges refer to integers, all integers inclusive from the minimum to the maximum inclusive are included, unless otherwise specified.

In this description, when a range is recited for a variable, the variable will be understood to include all values within the recited range, including the recited endpoints of the range. For example, a range of “5 to 10” includes the values of 5,6,7,8,9 and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc. and any value between integers that are appropriate for the scope of the recited ranges, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9, and the like. Also, ranges from 10 to 30% include values of 10%, 11%, 12%, 13%, etc. and all integers up to and including 30%, as well as within the range of stated ranges such as 10.5%, 15.5%, 25.5%, etc. It will be understood to include any value between valid integers.

When the present inventors use an additive (hereinafter, referred to as a 'redox additive') having a lower reducing power than a reducing agent (hereinafter, referred to as a 'nitrogen-based reducing agent') used for the reduction of a vanadium raw material, an electrolysis process is required In addition to producing an electrolyte solution through a single process of chemical reduction, the reaction time is shortened by controlling the reduction reaction rate of the vanadium compound according to the input amount of the redox additive, and the reproducibility of the manufacturing process is provided. By confirming that the performance of the dox flow battery is improved, based on this, further research was devoted to complete the present invention.

A vanadium redox flow battery is an energy conversion device, a tank containing an electrolyte, a flow and electric field control system, and a vanadium electrolyte that moves cells and tanks by operating the flow and electric field systems and causes energy conversion through oxidation-reduction. The most important factor influencing cost and battery performance is the vanadium electrolyte, and manufacturing an economical, high-quality vanadium electrolyte is important for commercialization of the vanadium flow battery.

The vanadium electrolyte may be used without any particular limitation as long as it is a compound capable of providing vanadium ions used in a vanadium redox flow battery, and may be an aqueous electrolyte or a non-aqueous electrolyte including vanadium acetylacetone.

Unless otherwise specified, the term "redox additive" used in the present description provides reproducibility in the manufacturing process because it assists the vanadium ion reducing power of the nitrogen-based reducing agent and does not participate in the reduction amount, and secures the selectivity of the vanadium raw material as well as the electrolyte solution. It is preferable to select a type that is included in the battery to improve battery performance.

Unless otherwise specified, the vanadium raw material selectivity means that even a vanadium compound of the same purity is not limited by a fine quality difference that may occur depending on the vanadium origin or purification method.

The reducing power refers to the rate of a reduction reaction unless otherwise specified. Specifically, since reductions are sequentially performed in the order of increasing reducing power, reduction first means that the reduction reaction rate is fast. If it is first reduced and has a potential value of self-oxidation upon reduction of a subsequent material, the input amount of the first reduced material may affect the control of the reduction reaction rate of the subsequently reduced material.

Specifically, the redox additive of the present disclosure has an electrochemical/mechanical potential range in which the reduction reaction rate is faster than that of the vanadium compound and is reduced first, and then self-oxidized while reducing the vanadium compound. Therefore, the electrolysis process is omitted and the chemical process In addition to being able to be performed alone, the reduction reaction rate of the vanadium compound can be controlled because the amount of the redox additive directly affects the reducing power of the vanadium compound.

The redox additive of the present disclosure may satisfy the correlation between the input amount M _a of the redox additive and the reduction reaction rate t _R of the vanadium compound expressed by Equation 1 below.

[Equation 1]

t _R = Aln(Ma/Mv) + B

t _R is the reaction time (min), A is the rate constant, B is the concentration constant, Ma is the input amount (g) of the redox additive, Mv is the input amount (g) of the vanadium compound.

Equation 1 can be obtained as a statistical approximation of a regression analysis technique for experimental data. Here, the constants do not have any special physical meaning, but the constant A is closely related to the reduction rate, and the constant B is closely related to the concentration of vanadium/sulfuric acid/solvent/redox additive, so they are named as rate constants and concentration constants, respectively. do.

Equation 1 can be obtained as a statistical approximation of a regression analysis technique for experimental data. Here, the above description does not contain any special physical meaning, but the constant A is closely related to the reduction rate, so it is called a rate constant, and may be, for example, -2.233.

In addition, the constant B is closely related to the concentration of vanadium, sulfate solvent, and redox additive, so it is named as a concentration constant and may be, for example - 3.8086.

According to Equation 1, it is possible to control the process by predicting the reduction reaction rate of vanadium according to the input amount of the redox additive, thereby providing reproducibility of the manufacturing process and securing the vanadium raw material selectivity, thereby improving battery performance. .

Equation 1 above shows that when the reaction temperature and the vanadium compound (raw material)/sulfuric acid/water (solvent) concentration are constant, the reaction rate (t _R ) and the input amount (Ma) of the redox additive are proportionally negative, It can be seen in FIG. 2 below that the Renius equation is followed.

By satisfying Equation 1 above, the reduction reaction rate of the vanadium compound can be predicted according to the amount of the redox additive added, so process control is possible, and the reproducibility of the manufacturing process and the selectivity of the vanadium raw material can be secured, resulting in improved battery performance. will make it

The redox additive may be an ionic metal having solubility in a vanadium electrolyte, or a compound derived from the ionic metal.

The ionic metal may be a reversible transition metal capable of repeatedly serving as an intermediate mediator of the redox reaction between the reducing agent and vanadium.

The redox additive is characterized in that 1) the reduction rate is faster than that of vanadium ions, so that the reduced component has an electrochemical/mechanical potential to be oxidized by itself while reducing vanadium ions, and 2) redox between a nitrogen-based reducing agent and a vanadium compound. It has reversibility to repeatedly perform the role of an intermediate mediator of the reaction, and 3) The reduction reaction rate of the vanadium compound is shortened by adjusting the input amount of the redox additive according to the main component (metal) content of the redox additive contained in the vanadium compound. and control the reaction time. For example, when the ionic metal component, which is the main component of the redox additive, is contained in the electrolyte at an amount of 280 ppm or less, the battery performance can be maximized, but the reaction time can be shortened to within 8 hours. The ionic metal component may be selected from transition metals or salts thereof having a solubility of 0.1 ppm or more in a vanadium electrolyte.

In the present description, the raw material for vanadium may be a vanadium compound having a valence of 2.0 to 5.0, and at least a portion of the electrolyte may be a vanadium compound having a valence of 3.3 to 3.7.

In the present description, unless otherwise specified, the vanadium raw material may be a low-grade compound having a purity of 90% or more and less than 99.9%, or a high-grade compound having a purity of 99.9% or more.

The vanadium raw material may be, for example, a pentavalent vanadium compound or a tetravalent vanadium compound, the pentavalent vanadium compound may be at least one selected from V ₂ O ₅ , NH ₄ VO ₃ and NaVO ₃ , and the tetravalent vanadium compound may be VOSO ₄ • xH ₂ O (where x is an integer from 1 to 6).

Specifically, the starting material for preparing the vanadium electrolyte includes a pentavalent or tetravalent vanadium compound, sulfuric acid, and a solvent, and the pentavalent or tetravalent vanadium compound is dehydrated with sulfuric acid by a nitrogen-based reducing agent to reduce the vanadium compound. At the same time, nitrogen gas is produced, and the redox additive reacts by dehydration with sulfuric acid and is reduced to an aqueous solution by a nitrogen-based reducing agent to produce nitrogen gas and sulfuric acid, which is then oxidized by itself while further reducing the reduced vanadium compound In this case, mass production is possible with a single reaction of chemical reduction without electrolysis reaction, the reduction process can be shortened, the reaction efficiency can be maximized, and the performance of a battery containing the electrolyte can be improved by manufacturing a high-quality electrolyte. can have an effect.

In the present description, the vanadium electrolyte may include a 3.3 to 3.7 vanadium compound. In this case, the 3.3 to 3.7 vanadium compound may be reduced from the vanadium compound using sulfuric acid, a reducing agent, and a solvent.

As described above, the reduction reaction of the vanadium compound may be performed in an acidic solution containing sulfuric acid.

For example, the reduction reaction of the vanadium compound V ₂ O ₅ , the acidic solution H ₂ SO ₄ , and the nitrogen-based reducing agent N ₂ H ₄ ·H ₂ O may proceed as shown in Scheme 1 below.

[Scheme 1]

4V ₂ O ₅ + 10H ₂ SO ₄ + 3N ₂ H ₄ H ₂ O → 4VO(SO ₄ ) + 2V ₂ (SO ₄ ) ₃ + 19H ₂ O + 3N ₂

The vanadium compound having an oxidation number of 4.0 prepared through the reduction process according to Scheme 1 can form a specific compound with an acidic solution (hereinafter, also referred to as “acid”) and a reducing solvent (hereinafter also referred to as “solvent”), For example, when the solvent is water, it may be a compound containing VO ²⁺ , [VO(H ₂ O) ₅ ] ²⁺ or [VO(OH) ₂ (H ₂ O) ₄ ] ⁺ ions.

In addition, a vanadium compound having an oxidation number of 2.0 prepared through a reduction process can form a specific compound with an acid and a solvent. For example, when the solvent is water, V ²⁺ , [V(H ₂ O) ₆ ] ²⁺ ions It may be a compound containing this.

A vanadium compound having an oxidation number of 3.0 produced through a reduction process can form a specific compound with an acid and a solvent. For example, when the solvent is water, V ³⁺ , [V(H ₂ O) ₆ ] ³⁺ , [V (OH)(H ₂ O) ₅ ] ²⁺ or [V(OH) ₂ (H ₂ O) ₄ ] ⁺ ions may be included.

A vanadium compound having an oxidation number of 5.0 prepared through a reduction process can form a specific compound with an acid and a solvent. For example, when the solvent is water, VO ₂ ⁺ , V ₂ O ₃ ⁴⁺ , [VO ₂ (H ₂ O) ) ₃ ] ⁺ or [V ₂ O ₃ (H ₂ O) ₈ ] ⁴⁺ ions may be included.

The vanadium compound having an oxidation number of greater than 3.0 to less than 4.0 produced through a reduction process may consist of a mixture of a vanadium compound having an oxidation number of 3.0 and 4.0. For example, when the solvent is water, V ³⁺ , [ V(H ₂ O) ₆ ] ³⁺ , [V(OH)(H ₂ O) ₅ ] ²⁺ and [V(OH) ₂ (H ₂ O) ₄ ] ⁺ , and VO ^{2 +} , [VO(H ₂ O) ₅ ] ²⁺ or [VO(OH) ₂ (H ₂ O) ₄ ] ⁺ may be a compound composed of a mixture of ions.

When the above-described acid is a sulfate-based material and the solvent is water, the prepared vanadium compound having an oxidation number of 3.3 is VOSO ₄ and V ₂ (SO ₄ ) ₃ may be in a molar ratio of 6:5.5 to 6.5, and 3.5 is an oxidation number The vanadium compound having VOSO ₄ and V ₂ (SO ₄ ) ₃ may have a molar ratio of 2:0.5 to 1.5, and the vanadium compound having an oxidation number of 3.7 has a VOSO ₄ and V ₂ (SO ₄ ) ₃ ratio of 14:2.5. a molar ratio of ˜3.5.

In the present description, in order to represent V3.3, V3.5, and V3.7 as molar ratios of tetravalent and trivalent ions, the description of nH ₂ O is omitted, but does not mean that it does not include them.

In the present description, the redox additive may serve to promote the reduction reaction of the vanadium compound, and specifically, control the reduction reaction rate of the vanadium compound by the nitrogen-based reducing agent according to the input amount in the electrolyte of the vanadium redox flow battery. , and the correlation corresponding to Equation 1 described above is satisfied.

Another embodiment of the present invention provides information on a vanadium electrolyte derived from a pentavalent vanadium compound. In this case, the pentavalent vanadium compound may be a low-grade or high-grade compound.

The vanadium electrolyte may include 15 to 35 parts by weight of a nitrogen-based reducing agent along with sulfuric acid and a solvent of an appropriate weight based on 100 parts by weight of the vanadium contained in the pentavalent vanadium compound.

When the amount of the redox additive is adjusted according to the content of the ionic metal component, which is the main component of the redox additive, the vanadium electrolyte can shorten the reduction reaction rate and secure reproducibility through control of the reaction time.

In the present description, the redox additive may or may not contain 0.1 ppm or more of the main metal component of the redox additive specifically.

For example, when the ionic metal component, which is the main component of the redox additive, is included in the electrolyte at 280 ppm, the process can be performed within 8 hours while maximizing the battery performance.

The vanadium electrolyte may include a vanadium compound having a valence of 2.0 to 5.0, and particularly, at least a portion of the electrolyte solution may include a vanadium compound having a valence of 3.3 to 3.7.

In this case, the 3.3 to 3.7 vanadium compounds may be reduced from the vanadium raw material using sulfuric acid, a reducing agent, ultrapure water, and the redox additive.

The vanadium electrolyte may contain 15 to 35 parts by weight of the pentavalent hydrazine compound based on 100 parts by weight of the vanadium raw material. As a specific example, 16 parts by weight or more of N ₂ H ₄ are required based on 100 parts by weight of the vanadium raw material to reduce the pentavalent vanadium compound to tetravalent vanadium, and to reduce the pentavalent vanadium to 3.5 valent vanadium, based on 100 parts by weight of the vanadium raw material. N ₂ H ₄ needs 24 parts by weight or more.

The redox additive is preferably adjusted so that Mo per 1 L of the electrolyte is around 270 ppm, and the amount of the redox additive can be adjusted according to the presence or absence of an ionic metal component, which is a main component of the redox additive, in the vanadium raw material. For example, in the case where Mo is not present as an ionic metal component, it is preferable to add 4 mM Mo per 1 L of the electrolyte, and a content of about 70 ppm is dissolved in the electrolyte every time 1 mM Mo is added.

Acid and solvent can be appropriately adjusted according to the type and purpose of the electrolyte.

In another embodiment of the present invention, when pentavalent vanadium is reduced to tetravalent vanadium, 17.5 parts by weight of N ₂ H ₄ ·H ₂ O compared to 100 parts by weight of V ₂ O ₅ raw material, H ₂ SO ₄ based on 98% concentration It may include 108 parts by weight or more, and 100 parts by weight or more of DIW.

In another embodiment of the present invention, when pentavalent vanadium is reduced to 3.5 vanadium, 26 parts by weight or more, H ₂ SO ₄ 135 parts by weight or more, relative to 100 parts by weight of V ₂ O ₅ raw material, N ₂ H ₄ ·H ₂ O 26 parts by weight or more , DIW may be included in an amount of 110 parts by weight or more.

The vanadium electrolyte of the present invention may be, for example, V ₂ O ₅ of the pentavalent vanadium compound, based on 100 parts by weight of V ₂ O ₅ , 400 parts by weight or less of an acid, 38 parts by weight or less of a nitrogen-based reducing agent, and 700 parts by weight of a solvent It can be prepared by using not more than 1 part and 0.1 to 1.6 parts by weight of the redox additive, specifically, 100 to 400 parts by weight of an acid, 14 to 38 parts by weight of a nitrogen-based reducing agent, 300 to 700 parts by weight of a solvent, and 0.1 to 1.6 parts by weight of a redox additive. It can be prepared using parts.

In this case, the nitrogen-based reducing agent may be, for example, hydrazine hydrate, specifically, hydrazine monohydrate, but is not limited thereto.

The vanadium electrolyte may be prepared using 200 to 400 parts by weight of an acid, 14 to 30 parts by weight of a nitrogen-based reducing agent, 500 to 700 parts by weight of a solvent, and 0.2 to 1.6 parts by weight of a redox additive, more preferably 200 to 300 parts by weight of an acid, 20 to 30 parts by weight of a nitrogen-based reducing agent, 500 to 600 parts by weight of a solvent, and 0.2 to 1.2 parts by weight of a redox additive, and more preferably 250 to 300 parts by weight of an acid; It may be prepared by using 24 to 28 parts by weight of a nitrogen-based reducing agent, 500 to 550 parts by weight of a solvent, and 0.2 to 0.8 parts by weight of a redox additive. Within these ranges, the reaction time is shortened, the reaction efficiency is excellent, and a high-purity, high-quality vanadium electrolyte is prepared, and the charge/discharge capacity of the battery including the electrolyte is also improved.

In the above embodiments, the redox additive may be included in an amount of 0.1 to 1.6 parts by weight based on 100 parts by weight of the V ₂ O ₅ raw material.

For example, when using 1.6 parts by weight of MoO ₃ as a redox additive, the Mo content in the electrolyte is 1120 ppm, the amount of MoO ₃ added per 1L is 2.4 g, and the Mol% compared to the electrolyte may be 0.016 Mol%.

In the present description, the reaction time may be, for example, 3 to 13 hours.

The ratio of the pentavalent vanadium compound (V ₂ O ₅ ) to the molar concentration (M; mol/L) of the nitrogen-based reducing agent may be 1:0.1 to 1.6 or 1:0.2 to 0.4, and in this range, acid, solvent, By forming an appropriate molar concentration ratio with the redox additive, there is an advantage that the desired effect of the present invention is easily achieved.

The ratio of molar concentrations (M; mol/L) of the pentavalent vanadium compound (V ₂ O ₅ ), acid, nitrogen-based reducing agent and redox additive is, for example, 1: 2 to 3: 0.2 to 0.4: 0.001 or more 0.25 Less than, specifically, 1: 2 to 3: 0.3 to 0.4: 0.001 or more and less than 0.05, more preferably 1: 2.3 to 2.7: 0.36 to 0.39: 1.002 or more and less than 0.02, even more preferably 1: 2.4 to 2.6: 0.37 to 0.38: 0.003 to 0.01, within this range, the reaction time is shortened, the reaction efficiency is excellent, and a high-purity and high-quality vanadium electrolyte is prepared, and the charge/discharge capacity of the battery including the electrolyte is also improved.

The redox additive is, for example, 1 to 6000 ppm, preferably 10 to 3000 ppm, more preferably 50 to 1500 ppm, still more preferably 100 to 1000 ppm, most preferably 200 to 800 ppm in the vanadium electrolyte solution. can be included as

The main component of the redox additive may be included in an amount of 1 ppm or more and less than 1500 ppm in the vanadium electrolyte after the production process of the vanadium electrolyte solution, such as a reaction and filtration process, is completed.

Although the redox additive includes other additives for improving electrolyte performance, the nitrogen-based reducing agent provides the reducing power of vanadium ions and at the same time does not participate in the reduction amount but is involved in the reduction rate. For example, even if 20 parts by weight or less of H ₃ PO ₄ known as a thermal stability additive is added to 100 parts by weight of the V ₂ O ₅ raw material when preparing the vanadium electrolyte, the reducing effect of the redox additive is not affected.

Including the aforementioned H ₃ PO ₄ (NH ₄ )H ₂ PO ₄ , (NH ₄ ) ₃ PO ₄ such as PO ₄ series materials, HCl, MgCl ₂ , CaCl ₂ chlorine-based materials, such as cationic surfactants, Even if 20 parts by weight or less of additives such as anionic surfactants, amphoteric surfactants, and nonionic surfactants are added to 100 parts by weight of V ₂ O ₅ raw material, the reducing effect of the redox additive is not affected, and the unique functions of various additives are not affected. Redox additives have no effect.

According to another embodiment of the present invention, there is provided information on a vanadium electrolyte derived from a tetravalent vanadium compound. In this case, the tetravalent vanadium compound may also be a low-grade or high-grade compound.

The vanadium electrolyte may be prepared by using 10 to 20 parts by weight of a nitrogen-based reducing agent together with an appropriate amount of an acid and a solvent based on 100 parts by weight of vanadium contained in the tetravalent vanadium compound, and a redox additive to the tetravalent vanadium compound. It may be included while adjusting the amount of the redox additive input according to the content of the ionic metal component.

The main component of the redox additive may be included in an amount of 1 ppm or more and less than 1500 ppm in the vanadium electrolyte.

In the present description, the vanadium electrolyte is, for example, in the case of VOSO ₄ among the tetravalent vanadium compounds, based on 100 parts by weight of VOSO ₄ , 400 parts by weight or less of an acid, 25 parts by weight or less of a nitrogen-based reducing agent, 700 parts by weight or less of a solvent, and redox It can be prepared using 0.1 to 1.6 parts by weight of the additive, specifically 100 to 400 parts by weight of an acid, 1 to 25 parts by weight of a nitrogen-based reducing agent, 300 to 700 parts by weight of a solvent, and 0.1 to 1.6 parts by weight of a redox additive. and preferably 200 to 400 parts by weight of an acid, 2 to 20 parts by weight of a nitrogen-based reducing agent, 500 to 700 parts by weight of a solvent, and 0.2 to 1.6 parts by weight of a redox additive, and more preferably an acid 200 to 300 parts by weight, 4 to 15 parts by weight of a nitrogen-based additive, 500 to 600 parts by weight of a solvent, and 0.2 to 1.2 parts by weight of a redox additive, more preferably 250 to 300 parts by weight of an acid, a nitrogen-based additive It can be prepared using 6 to 10 parts by weight of a reducing agent, 500 to 550 parts by weight of a solvent, and 0.2 to 0.8 parts by weight of a redox additive. Within these ranges, the reaction time is shortened, the reaction efficiency is excellent, and a high-purity, high-quality vanadium electrolyte is prepared, and the charge/discharge capacity of the battery including the electrolyte is also improved.

The redox additive is, for example, 1 to 6000 ppm, preferably 10 to 3000 ppm, more preferably 50 to 1500 ppm, still more preferably 100 to 1000 ppm, most preferably 200 to 800 ppm in the vanadium electrolyte solution. can be included as

Although the redox additive includes other additives for improving electrolyte performance, it provides a reducing power of vanadium ions, thereby contributing to the reduction rate without being involved in the reduction amount. For example, even if 20 parts by weight or less of H ₃ PO ₄ , which is known as a representative additive for improving temperature stability, is added relative to 100 parts by weight of V ₂ O ₅ raw material when preparing a vanadium electrolyte, the reducing effect of the redox additive is not affected. . Including H ₃ PO ₄ as an example, (NH ₄ )H ₂ PO ₄ , (NH ₄ ) ₃ PO ₄ such as PO ₄ material, Cl-based material such as HCl, MgCl ₂ , CaCl ₂ , cationic interface Even if 20 parts by weight or less of substances such as activators, anionic surfactants, amphoteric surfactants, and nonionic surfactants are added relative to 100 parts by weight of V ₂ O ₅ raw material, the effect of the redox additive on the reducing agent is not affected, and at the same time The additive function of various additives is also not violated by redox additives.

In another embodiment of the present disclosure, more detailed information is provided for a method for preparing a vanadium electrolyte.

The method for preparing the above-described vanadium electrolyte includes, for example, a first step of reducing a pentavalent vanadium compound to a tetravalent vanadium compound as a vanadium compound; and a second step of reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound, wherein a redox additive is added to at least one of the first step and the second step, and the redox additive is the second step. It may be composed of a material having a lower reducing power than the nitrogen-based reducing agent used to reduce the vanadium compound in the first step.

Preferably, the first step may include sequentially i) adding a pentavalent vanadium compound and water, ii) adding a nitrogen-based reducing agent, and iii) adding sulfuric acid. In this case, the process There are advantages in that the time is shortened, the reaction efficiency is excellent, and the decomposition of the reducing agent is minimized to prepare a tetravalent vanadium electrolyte.

The nitrogen-based compound may be a hydrazine compound as a specific example.

The hydrazine compound may be preferably added in the form of a hydrate or an aqueous solution, and it may be preferable when the hydrazine compound is at least 95 weight ratio by weight relative to 100 weight ratio of the hydrazine compound.

In Examples to be described later, the hydrazine compound was diluted to about 200 to 500 weight ratio of water relative to 100 weight ratio, and there is no specific ratio, but the total amount of water required for preparing the electrolyte should be the same. When the hydrazine compound in the form of a hydrate is used as described above, the rapid reaction rate can be gently controlled and the reaction can be carried out more stably, so that the reaction efficiency is excellent and a high-purity, high-quality vanadium electrolyte can be prepared.

The hydrazine hydrate is preferably hydrazine monohydrate, and the hydrazine salt is preferably hydrazine sulfate.

The nitrogen-based reducing agent may be added in the entire amount in the first step, or may be partially added to the first step and then dividedly added to the second step. As an example of divided input, 60 to 80% by weight of the total amount may be added in the first step, and 20 to 40% by weight may be added in the second step, and preferably 60 to 70% by weight in the first step and the second 30 to 40 wt% may be added in the step. The input method of the nitrogen-based reducing agent may be appropriately used among the input methods commonly used in the technical field to which the present invention pertains depending on the purpose or process condition of the vanadium electrolyte solution.

The redox additive may dehydrate the sulfuric acid in the first step to form an aqueous solution and then oxidize the nitrogen-based reducing agent while reducing itself to generate nitrogen gas.

The redox additive is molybdenum metal, molybdenum oxide (MoxOy), molybdenum nitride (MoxNy), molybdenum chloride (MoxCly), molybdenum sulfide (MoxSy), molybdenum phosphide (MoxPy), Molybdenum Carbide (MoxCy), Molybdenum Metal Oxide (MoxMyOz), Molybdenum Metal Nitride (MoxMyNz), Molybdenum Metal Chloride (MoxMyClz), Molybdenum Metal Sulfide (MoxMySz), Molybdenum Metal Phosphide ( MoxMyPz) and molybdenum metal carbide (MoxMyCz) may be at least one selected from the group consisting of.

The metal of the redox additive is Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Mg, Mn, Na, Ni, Pb, Si, Sn, Ti, Zn, Au, Ag , Pt, Ru, Pd, Li, Ir, W, Nb, Zr, Ta, Ge, and a species or a plurality of species selected from In may be a metal forming an alloy, wherein x and y (x / y) or x, y and z (x/y/z) may independently be integers from 0 to 1.

The redox additive may be used to reduce the tetravalent vanadium compound in the second step in a dehydrated aqueous solution state with sulfuric acid.

Specifically, the redox additive converts the tetravalent vanadium compound into a 3.3 to 3.7 vanadium compound, preferably a 3.4 to 3.6 vanadium compound, and most preferably a tetravalent vanadium compound while self-oxidizing to an aqueous solution formed through a dehydration reaction with sulfuric acid. 3.5 is reduced to a vanadium compound, and in this case, there is an advantage in that a high-purity, high-quality vanadium electrolyte is prepared.

The second step may preferably be heated to 70 to 120 ° C, more preferably 80 to 115 ° C, more preferably 90 to 110 ° C, even more preferably 100 to 110 ° C, In this case, the reaction time is shortened and the reaction efficiency is excellent, but there is an advantage in that a high-purity, high-quality vanadium electrolyte is prepared.

In the second step, the heating time may be 12 hours or less, preferably 1 hour to 10 hours, more preferably 2 hours to 8 hours, still more preferably 3 to 8 hours, most preferably 4 to 8 hours time, and in this case, there is an advantage in that a high-purity, high-quality vanadium electrolyte solution is prepared while having excellent reaction efficiency.

The first step and the second step may be performed under atmospheric pressure, for example, but may be pressurized or reduced as necessary within a range satisfying the above-described reaction conditions.

The electrolyte preparation method may include a process of filtration after the first step or after the second step, more preferably, the first step after the first filtration and the second step after the second filtration. can In this case, there is an advantage in that a high-purity, high-quality vanadium electrolyte can be prepared without significantly extending the process time.

The filtration may be performed by gravity filtration using gravity, pressure filtration operated by applying pressure to the upper layer of the filtration means, and reduced pressure filtration operated by applying reduced pressure to the lower layer of the filtration means. In addition, the filtration can use a hydrophilic filtration means while having acid resistance having a pore size of 0.2 to 10 μm. In particular, when the pore size is less than 0.2 μm, the process time or pressure load increases, so that competitiveness compared to quality may be lowered. , when it exceeds 10 μm, the filtration effect may be insignificant.

When a filter aid such as diatomaceous earth is used together with the filtering means, impurities are primarily removed by the filter agent before the filtrate reaches the filtering means, thereby reducing the filtration load applied to the filtering means.

In this case, impurities that can deteriorate the properties of the electrolyte in the electrolyte are physically filtered through filtration and filtration means without significantly affecting the overall process time, while the electrolyte passes through the filtration and filtration means in a completely high-purity, high-quality vanadium. There is an advantage that an electrolyte solution is prepared.

The pentavalent vanadium compound is preferably V ₂ O ₅ , the tetravalent vanadium compound is preferably VOSO ₄ , and the 3.3 to 3.7 vanadium compound is preferably VOSO ₄ and V ₂ (SO ₄ ) ₃ Mixing may be performed, and in this case, there is an advantage in that a high-purity, high-quality vanadium electrolyte is prepared.

The electrolyte preparation method may include a catalyst together with a redox additive in the first step or the second step, if necessary, and promote the reduction reaction.

The catalyst serves as a catalyst in the first step, particularly in the second step, and is followed by a separation process from the electrolyte after performing the catalyst role. After the catalyst is added to the first step and filtered in the second step after the reaction is completed, the catalyst is added to the second step after the first step filtration and then filtered again in the second step after the reaction is completed, or the reactant is introduced into the catalyst facility It can be introduced and used in a way that a reduction reaction is possible.

In the present description, the main component of the catalyst may be a metal such as Pt, Pd, Ru, or the like, and may be a typical Pt catalyst. The Pt catalyst is not particularly limited if it is a Pt catalyst commonly used in the technical field to which the present invention pertains.

In the present disclosure, the method for preparing a vanadium electrolyte includes: (A) preparing a reaction mixture by adding a pentavalent vanadium compound to a solvent and then adding a nitrogen-based reducing agent; (B) reducing the pentavalent vanadium compound to a tetravalent vanadium compound while performing a dehydration reaction by adding sulfuric acid and a redox additive to the reaction mixture; (C) generating a self-reduced product while the dehydration reactant oxidizes the nitrogen-based reducing agent to generate nitrogen gas; and (D) reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound while the self-reduced product is oxidized by heating the reactant; Including, the nitrogen-based reducing agent may be added to the whole amount in step (A) or divided into steps (A) and (D).

The redox additive includes an aqueous vanadium redox flow electrolyte or an electrolyte for a non-aqueous vanadium redox flow such as vanadium acetylacetone, and the preparation and use of the same As long as the vanadium redox flow battery is mechanically and electromagnetically driven, it can be used without any particular limitation.

The vanadium electrolyte may be included in both the anode and the cathode.

When the redox additive is added to the electrolytic solution manufacturing process, the reaction rate can be shortened by promoting the reduction reaction, and the energy transfer material of the additive material between vanadium ions that can be activated by electric field energy when the vanadium redox flow battery is operating It is estimated that by contributing to the electron mobility of vanadium ions, it will contribute to the improvement of the charge/discharge capacity and energy efficiency of the battery. The redox additive needs to be added at a certain concentration or higher to improve the reaction rate, but when it is added in excess of a certain concentration, the force that interferes with the diffusion of vanadium ions increases due to an increase in viscosity due to excessive mutual attraction between the vanadium ions and the redox additives. This may negatively affect the charge/discharge capacity and energy efficiency.

The redox additive is preferably included in a concentration of about 0.2 to 2 mol% in the electrolyte when considering the improvement of the reaction rate and the improvement of the battery performance. When the concentration of the redox additive is contained in 0.2 mol% or more, there is a substantial effect on the reaction rate and performance improvement, and when it exceeds 2 mol%, the above-mentioned negative effects may occur. Considering the reaction rate and performance of the electrolyte, the redox additive may be included in the electrolyte in an amount of preferably 0.2 to 1.0 mol%, more preferably 0.2 to 0.8 mol%.

As described above, since the redox additive participates in the reaction in an aqueous solution state by dehydration reaction with sulfuric acid, a byproduct derived from the redox additive is not generated.

Step (D) may be performed by applying the reduction reaction time of the vanadium compound calculated by substituting the reaction temperature of 70 to 120° C. and the amount of the redox additive into Equation 1 above.

[Equation 1]

t _R = Aln(Ma/Mv)+B

(Where t _R is the reaction time (min), A is the rate constant, B is the concentration constant, Ma is the input amount of the redox additive (g), and Mv is the input amount (g) of the vanadium compound)

The vanadium electrolyte prepared with the redox additive of the present invention had a current density of 100 mA/cm ² , a discharge cut-off voltage of 0.8 V, a charge cut-off voltage of 1.6 V, and a flow rate of 180 ml/min. The charging capacity and the charging/discharging capacity within the system can be improved by an average of 5% or more, preferably by 6.5% or more per cycle compared to the absence of the corresponding redox additive. In addition, energy efficiency may be improved by 0.5% or more, preferably by 1% or more.

In the present description, the charge capacity means a state in which charges are accumulated up to the charge cut-off voltage, the charge/discharge capacity means a state in which the charge is emptied up to the discharge cut-off voltage, and energy efficiency means the charge capacity compared to the charge/discharge capacity. The three factors can be provided as indicators for judging the lifespan and performance of the electrolyte.

The redox additive of the present invention can provide an electrolyte having improved battery capacity and energy efficiency.

By economically manufacturing high-efficiency, high-quality, and high-performance vanadium electrolytes by adding redox additives in this base material, the effect that can be applied/applied to all fields where vanadium redox flow batteries are used, such as new and renewable energy, smart grids, and power plants have.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

[Example]

The composition of the vanadium electrolyte solution, which will be described as an example below, is 1.6 moles of a vanadium compound and 4.0 moles of sulfuric acid. The vanadium electrolyte has an ionic value of 3.5 and is a vanadium electrolyte in which vanadium tetravalent ions and vanadium trivalent ions are mixed in a molar ratio of 1:1.

Materials required to prepare the electrolyte solution of the embodiment are as follows.

Low grade vanadium compound 146 g (99% low grade), 98% sulfuric acid solution 400 g, water 775 g, nitrogen-based reducing agent (hydrazine monohydrate) 80% by weight aqueous solution 38.0 g, redox additive (molybdenum trioxide) 0.15 g.

Here, hydrazine monohydrate is required as much as the number of moles corresponding to the value obtained by multiplying the number of moles of vanadium by 0.375, and about 0.6 M is required with respect to 1.6 moles of the vanadium compound. In the case of hydrazine, an 80 wt% aqueous solution of hydrazine monohydrate was used, and molybdenum trioxide was used as a redox additive. In this description, M means the number of moles (mol/L) of the solute dissolved in 1 L of the solution.

In the present description, % means % by weight unless otherwise defined.

The apparatus required for preparing the electrolyte solution of the embodiment is as follows.

It is composed of a reaction tank (hereinafter referred to as 'reactor') that can react 1 L or more, a stirrer, a heater and thermometer capable of temperature control, and a filtration system (pump, tube, filter, etc.) The facing surface should be made of a material with acid resistance and chemical resistance such as glass, PTFE, PE, Teflon, etc.

Vanadium compound (V ₂ O ₅ ), sulfuric acid (H ₂ SO ₄ ), deionized water (DIW), and hydrazine monohydrate (N ₂ H ₄ ·H ₂ O) were added to the reaction tank through the raw material input port, and the reaction was introduced The raw material was stirred with a stirrer to start the first-step reduction reaction.

When the first-step reduction reaction is completed, the reactant is passed through a circulation pipe equipped with a filtration means (Filtration) to remove impurities, and then molybdenum trioxide (MoO ₃ ) is put into the reactor, and then jacketed heat exchange surrounding the reaction tank A two-step reduction reaction was carried out by heating the reactants with a heater (heater).

Water vapor generated during the reduction reaction and water vapor in nitrogen gas can be cooled and recovered to the reactor, and nitrogen gas can be discharged to the outside. When the two-step reduction reaction was completed, impurities were again removed through a discharge pipe equipped with filtration, and a final electrolyte product (V ^3.5+ electrolyte product) was obtained.

Hereinafter, the electrolyte preparation step of Example 1 will be described in detail by dividing the steps.

<Example 1: Three-step manufacturing process experiment>

Step 1: Input step of vanadium raw material and nitrogen-based reducing agent

In step 1, the input flow rate of raw materials is not considered much, but the order of raw material input needs to be considered.

As for the order of raw material input, it is most preferable to administer to the reaction tank (reactor) in the order of water → vanadium → hydrazine monohydrate under the operation of the stirrer. A certain amount of water may be added in this process. For example, it is possible to dilute a portion of water with hydrazine monohydrate and administer it. Also, after adding water and a vanadium compound, to treat the vanadium compound attached to the inside of the raw material inlet, a method of flushing it into the reactor by flowing water is also possible However, if there is water in the reactor before adding the vanadium compound, it may be more advantageous in dispersing the vanadium compound in the reactor. When water is added after adding the vanadium compound, the vanadium compound is more easily isolated between the reactor bottom and the vanadium compound-water interface, and the isolated and aggregated vanadium compound may generate unnecessary load.

The most undesirable mixing method in step 1 is a method of directly mixing the vanadium compound and hydrazine monohydrate. When a vanadium compound and hydrazine monohydrate are mixed and water is added, and sulfuric acid is administered in step 2 to be described later to make an electrolyte, a part of the vanadium compound, a raw material, is not dissolved in the sulfuric acid, and precipitation occurs. When the two raw materials are mixed without water, smoke and heat are generated under a vigorous reaction, and the vanadium compound turns black.

Inferred from such a phenomenon, it is estimated that a part of the hydrazine compound is decomposed by the instantaneous heat of reaction, and thus the reduction function is not performed after the sulfuric acid is added, resulting in precipitation of the vanadium compound. In this step, 25.2 g of hydrazine monohydrate was first added out of the total 38.0 g. During this input process, the temperature in the reactor may be slightly increased to within 10 °C.

Step 2: Addition of sulfuric acid

In step 2, the sulfuric acid input flow rate may be determined in consideration of exotherm in the reaction solution formulated in step 1. Sulfuric acid is introduced slowly to prevent the reaction solution from splashing on the wall of the container as much as possible, and it is preferable that the exothermic temperature does not exceed 110 °C. In this process, gas evacuation and collection devices such as open reflux condensers are required, and additional heating devices such as cooling devices or heaters (heat exchangers) may be required.

1 is a graph showing the change in temperature according to time during which a reduction reaction using a reducing agent is performed under a sulfuric acid flow rate of 240 ml/hr or 480 ml/hr.

1, in the first half of the sulfuric acid input, the temperature rise shows a steep slope, at a time point of about 25 minutes in the case of a flow rate of 240 ml/hr, and at a time point of about 13 minutes in the case of a flow rate of 480 ml/hr Each temperature drop was observed. The temperature rise in the first half occurs when 1.6M of vanadium is dissolved in 1.6M of sulfuric acid (about 100ml) and reduced to vanadium pentavalent ions, while the reduced vanadium pentavalent ions are converted to tetravalent ions by hydrazine monohydrate. Fever is the biggest factor. On the other hand, the temperature after a specific time point was observed to decrease slightly in the case of 240ml/hr and to be maintained in the case of 480ml/hr. Therefore, it is desirable to design the flow rate control of sulfuric acid in consideration of the reactor size, reactant amount and composition as well as the reaction point.

In this embodiment, the first half is 200 to 300 ml/h, preferably 220 to 260 ml/h, more preferably 235 to 245 ml/h, and the second half is 430 to 530 ml/h, preferably 460 to 500 ml/h, more preferably 475 to 485 ml/h, and the redox reaction was performed. The flow rate in this embodiment is a range value in experimental conditions such as equipment for implementing this embodiment, and it will be most preferable when the flow rate control in the two sections is performed under the target temperature.

The process of step 1 and 2 tested in this example (water → vanadium compound → hydrazine monohydrate → sulfuric acid, hereinafter referred to as the 'flow example') was introduced in the order of water → vanadium compound → sulfuric acid → hydrazine monohydrate. It has two advantages over the method (hereinafter referred to as 'flow rate comparative example').

First, the reaction time is short, and secondly, the reduction efficiency of the reducing agent is high.

If, as in the flow rate comparative example, sulfuric acid was administered to water + vanadium compound prior to hydrazine monohydrate at a rate of 240 ml/hr for 50 to 70 minutes, specifically 60 minutes, the temperature was increased from 26 ° C to 81 ° C. will rise Then, when 25.2 g of hydrazine monohydrate is diluted in 100 g of water and the inflow rate is 250 ml/hr, it takes about 30 minutes, and the final temperature was 105 °C. Here, hydrazine monohydrate is preferably used by diluting 20 to 30 parts by weight of 100 parts by weight of water.

Hydrazine has a reducing power capable of instantaneously reducing pentavalent ions to tetravalent ions even at room temperature, and considering that hydrazine has a boiling point of 114°C, hydrazine input at high temperature is never used in process control even if diluted with water. Inappropriate. In addition, it is difficult to have a positive effect on quality influence by increasing the possibility of hydrazine disappearance. For reference, if input at a high temperature is required, a method of compounding a diluted hydrazine raw material through flow control as in the flow rate comparative example may be used.

On the other hand, when hydrazine monohydrate is added first and sulfuric acid is added later, since the reduction of hydrazine starts from a low temperature, there are relatively few side effects on temperature increase and the overall process time can be shortened. That is, if the flow rate control material is one type of sulfuric acid according to the flow rate example, there are two types of flow rate control material according to the flow rate comparative example, so processing time or processing may be difficult.

Apart from the boiling point of 114 ℃, hydrazine decomposes into NH ₃ + NH when the temperature is 180 ℃ or higher, and N ₂ + 2H ₂ when the temperature is 350 ℃ or more. The possibility of decomposition of hydrazine without acting as a reducing agent increases due to the heat generated in Theoretically, even gaseous hydrazine above 114° C. may have a normal reaction if there is no loss, but there is a lot of room for loss in the actual process. Due to these side reactions and disappearance, experimentally, an amount of about 4 to 7% of the stoichiometric ratio must be added to achieve 3.5 value in the flow rate comparative example. On the other hand, since it is sufficient to consume a content of about 0 to 3% in the flow rate example, it is extremely superior from the problems of loss and side reactions compared to the flow rate comparative example.

The end time of step 2 may be the time when sulfuric acid input is completed, or additional stirring may be performed at 110° C. or less within 2 hours.

In step 2, the gas by-product (N ₂ ) from the reduction process of pentavalent vanadium ions is discharged out of the vessel, and the vaporized H ₂ O and H ₂ SO ₄ are condensed and cooled to stay in the reactor to maintain a high temperature (around 110 ℃). This has the advantage of maximizing the reaction efficiency and preventing a change in the composition in the reactor.

Step 3: Preparation of the 3.5-valent electrolyte solution

Next, 0.15 g of molybdenum trioxide (0.1 parts by weight relative to 100 parts by weight of V ₂ O ₅ ) was added to the reactor as a redox additive, and the reactor temperature was adjusted to 110° C. using a heater or a heat exchanger.

Then, 12.8 g of the remaining amount of hydrazine monohydrate was added to the reactor. Although hydrazine monohydrate can be added even if the reactor temperature does not reach 110 °C, when hydrazine monohydrate is added to the tetravalent electrolyte solution at 80 °C or less, particularly 60 °C or less, sulfuric acid-hydrazine salt is formed and the reducing function of hydrazine is reduced. may be lowered.

In step 3, the gas by-product (N ₂ ) from the reduction process of tetravalent vanadium ions is discharged out of the vessel, and the vaporized H ₂ O and H ₂ SO ₄ are condensed and cooled to stay in the reactor to maintain a high temperature (around 110 ℃). This has the advantage of maximizing the reaction efficiency and preventing a change in the composition in the reactor. The time required for the three-step process is less than 12 hours.

The division of Example 1 into three steps is for illustrative purposes only, and as a whole is a single process carried out in the same reactor. In this embodiment, although the redox additive is added in step 3, it may be added together when the vanadium is added in step 1 before adding hydrazine or sulfuric acid.

1 shows the effect of the redox additive on the sulfuric acid flow rate, and there is no significant difference depending on the presence or absence of the redox additive at a flow rate of 240 ml/hr. This means that the reducing power of hydrazine to vanadium pentavalent is too strong, so that the redox additive does not particularly play a role as a catalyst, or does not have a significant level of influence even if it does. The input time of the redox additive may be added to the above-described 3 step, but is not limited thereto, and may be added in the 1st or 2nd step.

<Examples 2 to 5: Redox additive content change experiment>

0.15 g of molybdenum trioxide (0.1 parts by weight relative to 100 parts by weight of V ₂ O ₅ ) used in Example 1 was added to 0.30 g (0.2 parts by weight: Example 2), 0.60 g (0.4 parts by weight: Example 3), The same experiment as in Example 1 was repeated except that 1.2 g (0.8 parts by weight: Example 4) and 2.4 g (1.6 parts by weight: Example 5) were respectively changed.

<Example 6: Manufacturing process using high quality raw materials>

The same experiment as in Example 4 was repeated except that the low-grade vanadium compound (purity 99%) used in step 1 of Example 4 was replaced with a high-grade vanadium compound (purity 99.9%).

<Comparative Example 1: No redox additive-electrolysis manufacturing process>

Materials required for preparing the vanadium tetravalent electrolyte for electrolysis of Comparative Example 1 are as follows.

146 g of vanadium compound, 400 g of 98% sulfuric acid, 775 g of water, 72.0 g of oxalic anhydride (organic reducing agent replacing nitrogen-based reducing agent)

A vanadium compound, oxalic anhydride, and water were added to the reactor, and sulfuric acid was added in consideration of exotherm as described in Example 1.

From the time the sulfuric acid was added, additional stirring was performed at 105° C. for about 3 hours. When the reduction reaction was completed, impurities were removed through a discharge pipe equipped with a filtration means, and approximately 1 L of an electrolysis target electrolyte product (V ⁴⁺ electrolyte product) was obtained.

330 ml each of the obtained vanadium tetravalent compound was placed in a positive electrode tank and a negative electrode tank, and electrolysis was performed while leaving 330 ml of the obtained vanadium tetravalent compound. Electrolysis was carried out in a constant current mode to reach a voltage of 1.8V under 150 mA/cm ² conditions to obtain 300 ml or more of a pentavalent vanadium compound from the anode tank.

300 ml of the pentavalent vanadium compound obtained by electrolysis and 300 ml of 330 ml of the 330 ml of the vanadium tetravalent compound remaining without electrolysis are combined to obtain 600 ml of a vanadium 3.5-valent electrolyte solution, and impurities are removed again using filtration means did. In this process, if some oxidized water deviate, it can be adjusted with the remaining excess amount.

<Comparative Example 2: Excessive use of redox additives>

The same experiment as in Example 1 was repeated except that 0.29 g of molybdenum trioxide (0.2 parts by weight relative to 100 parts by weight of V ₂ O ₅ ) used in Example 1 was changed to 15 g (10 parts by weight). .

<Test Example 1: Battery performance evaluation test>

In order to evaluate the performance of each electrolyte prepared in Examples 1 to 6 and Comparative Examples 1 to 2, the performance was measured in the following manner.

A constant current was charged with a current of 100 mA/cm ² until the voltage reached 1.60 V, and then discharged with a reverse constant current of 100 mA/cm ² until the voltage reached 0.8 V during discharging. After repeating the above cycle 30 times, the results are summarized and shown in Table 1 below.

In Table 1 below, the redox additive content represents ₃ parts by weight of MoO relative to 100 parts by weight of V ₂ O ₅ , and the reaction time is the time taken from the time when sulfuric acid input is completed to the time it is determined that the reaction is complete because the oxidation number hardly does not occur. , charge capacity, discharge capacity, and energy efficiency are the values of the 30th cycle, respectively, and the content (ppm) represents the content of Mo, the main component of the redox additive MoO ₃ in the electrolyte.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Redox additive
(parts by weight) 0.1 0.2 0.4 0.8 1.6 0.8 - 10 Raw material purity low quality low quality low quality low quality low quality high quality low quality low quality reaction required
time (hr) 12 10 8 6.5 5.5 6.5 - 1.5 final
oxidation number 3.503 3.498 3.500 3.501 3.500 3.499 3.501 3.501 Charge capacity (Ah) 2.30 2.31 2.24 2.31 2.16 2.34 2.16 1.71 Discharge capacity (Ah) 2.22 2.22 2.15 2.21 2.08 2.25 2.08 1.64 Energy efficiency (%) 80.72 81.08 80.74 80.57 78.55 80.72 79.56 79.81 Content (ppm) 71.0 134.2 271.6 538.5 1118.4 532.2 - 5974.2

As shown in Table 1 and FIG. 3 below, it was confirmed that the amount of the redox additive input did not affect the final oxidation number during the preparation of the electrolyte, and only affected the reaction rate without being involved in the reduction amount.

As shown in Table 1 and FIG. 2 below, it was confirmed that the time required for the reduction reaction showed a proportional negative correlation with the redox additive content as shown in Equation 1-1 above.

As shown in Examples 4 and 6 in Table 1, it can be seen that the performance difference between the electrolyte prepared with the low-grade vanadium compound and the electrolyte prepared with the high-grade vanadium compound is not clearly distinguished.

As shown in Examples 1 to 6 and Comparative Example 1 in Table 1, it can be seen that the performance of the electrolyte prepared according to the process of the present invention is superior to that of the electrolyte prepared by electrolysis, which is shown in FIGS. 4 to 6 was confirmed in

As shown in Example 5 and Comparative Example 2 in Table 1, when the redox additive is added in excess of an appropriate amount, the reaction rate may be slightly improved, but it can be seen that the electrolyte performance is reduced. According to the present examples, it can be confirmed that the redox additive has excellent performance degradation at the level of 10 parts by weight, which was confirmed in FIGS. 4 to 6 .

As shown in Table 1, it was confirmed that the change in energy efficiency according to the amount of the redox additive, including the results of Comparative Example 1, was relatively insignificant.

<Test Example 2: Equation 1 confirmation test for Examples 1 to 6>

In the present description, Equation 1 can be embodied as Equation 1-1 below by substituting the values of Examples 1 to 6.

[Equation 1-1] t _R = -2.233ln(Ma/Mv) - 3.8086, (R ² =0.9925)

In Equation 1-1, the relationship between the redox additive and the reaction rate in Example 1 is a proportional negative correlation, and it follows the Arrhenius equation, and is confirmed in FIG. 2 . That is, the process time can be controlled by determining the amount of the redox additive from the variables of the raw material, composition, and process condition using Equation 1-1.

<Test Example 3: Redox additive and other additive combination test>

In Test Example 3, H ₃ PO ₄ known to be added for electrolyte temperature stability was added, and the mutual influence with the redox additive was confirmed.

Specifically, electrolyte samples using redox additives were prepared in the same manner as in Example 3, and then electrolyzed to prepare pentavalent electrolytes of Reference Examples 1a to 4a.

By preparing an electrolyte sample in the same manner as in Comparative Example 1, the pentavalent electrolyte of Reference Examples 1b to 4b was prepared.

Precipitation of vanadium ions was observed at 50° C. in the obtained 8 electrolyte solutions of Reference Examples 1a to 4b, and the results are shown in Table 2 below.

division Reference Example 1a Reference Example 1b Reference Example 2a Reference Example 2b Reference Example 3a Reference example 3b Reference Example 4a Reference Example 4b additive H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ H ₃ PO ₄ V ₂ O ₅ contrast
additive amount 3 parts by weight 3 parts by weight 6 parts by weight 6 parts by weight 9 parts by weight 9 parts by weight 12 parts by weight 12 parts by weight oxidation number 3.501 3.500 3.500 3.502 3.501 3.499 3.499 3.500 Redox additive amount 0.4 parts by weight electrolysis 0.4 parts by weight electrolysis 0.4 parts by weight electrolysis 0.4 parts by weight electrolysis reaction time 8h electrolysis 8h electrolysis 8h electrolysis 8h electrolysis pentaion
precipitation time
(50℃) ~110h ~110h ~180h ~180h ~250h ~250h ~320h ~320h

As can be seen in Reference Examples 1a to 4b of Table 2, it can be seen that the redox additive and the H ₃ PO ₄ additive do not affect each other. This correlation is not limited to the H ₃ PO ₄ additive.

Therefore, the redox additive according to the embodiments of the present invention, and the electrolyte containing the same, react under a shortened reaction time to provide high-quality performance, so that a vanadium redox flow battery such as a new renewable energy, a smart grid, or a power plant is used. It can be applied in all fields.

Claims (17)

A first step of reducing a pentavalent vanadium compound to a tetravalent vanadium compound as a vanadium compound; and a second step of reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound,
adding a redox additive to at least one of the first step and the second step,
The redox additive is a vanadium electrolyte manufacturing method, characterized in that the reducing power is lower than the nitrogen-based reducing agent used to reduce the vanadium compound in the first step. According to claim 1,
The first step comprises sequentially i) adding a pentavalent vanadium compound and water, ii) adding a nitrogen-based reducing agent, and iii) adding sulfuric acid. 3. The method of claim 2,
The redox additive is a method for producing a vanadium electrolyte, characterized in that the dehydration reaction with the sulfuric acid in the first step to form an aqueous solution and then oxidize the nitrogen-based reducing agent while reducing itself to generate nitrogen gas. 4. The method of claim 3,
The redox additive is used to reduce the tetravalent vanadium compound in the second step in a dehydrated aqueous solution state with sulfuric acid. According to claim 1,
The redox additive is molybdenum metal, molybdenum oxide (MoxOy), molybdenum nitride (MoxNy), molybdenum chloride (MoxCly), molybdenum sulfide (MoxSy), molybdenum phosphide (MoxPy), Molybdenum Carbide (MoxCy), Molybdenum Metal Oxide (MoxMyOz), Molybdenum Metal Nitride (MoxMyNz), Molybdenum Metal Chloride (MoxMyClz), Molybdenum Metal Sulfide (MoxMySz), Molybdenum Metal Phosphide ( MoxMyPz) and molybdenum metal carbide (MoxMyCz) vanadium electrolyte manufacturing method, characterized in that at least one selected from the group consisting of. 6. The method of claim 5,
The metal of the redox additive is Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Mg, Mn, Na, Ni, Pb, Si, Sn, Ti, Zn, Au, Ag , Pt, Ru, Pd, Li, Ir, W, Nb, Zr, Ta, Ge, and a species or a plurality of species selected from In may be a metal forming an alloy, wherein x and y (x / y) or x, y and z (x/y/z) are each independently an integer of 0 to 1. According to claim 1,
The redox additive is a vanadium electrolyte preparation method, characterized in that it comprises 0.1 to 1.6 parts by weight based on 100 parts by weight of the pentavalent vanadium compound. According to claim 1,
The nitrogen-based reducing agent is a method for producing a vanadium electrolyte, characterized in that it comprises 10 to 35 parts by weight based on 100 parts by weight of the vanadium compound. According to claim 1,
A method for producing a vanadium electrolyte, characterized in that the ratio of the molar concentration (M; mol/L) of the pentavalent vanadium compound and the nitrogen-based reducing agent is 1:0.1 to 1.6. According to claim 1,
The second step is a method for producing a vanadium electrolyte, characterized in that it is carried out at 70 to 120 ℃. According to claim 1,
The pentavalent vanadium compound is a low-grade compound having a purity of 90% or more and less than 99.9%, or a high-grade compound having a purity of 99.9% or more. According to claim 1,
Method for producing a vanadium electrolyte, characterized in that it comprises the step of filtering after the first step or after the second step. (A) preparing a reaction mixture by adding a pentavalent vanadium compound to a solvent and then adding a nitrogen-based reducing agent;
(B) reducing the pentavalent vanadium compound to a tetravalent vanadium compound while performing a dehydration reaction by adding sulfuric acid and a redox additive to the reaction mixture;
(C) generating a self-reduced product while the dehydration reactant oxidizes the nitrogen-based reducing agent to generate nitrogen gas; and
(D) reducing the tetravalent vanadium compound to a 3.3 to 3.7 vanadium compound while the self-reduced product is oxidized by heating the reactant; includes,
The nitrogen-based reducing agent is a method for producing a vanadium electrolyte, characterized in that the total amount is added to the step (A) or divided into steps (A) and (D). 14. The method of claim 13,
The redox additive participates in the reaction in an aqueous solution state by dehydration reaction with sulfuric acid, so that by-products derived from the redox additive are not produced. 14. The method of claim 13,
Step (D) is performed by applying the reduction reaction time of the vanadium compound calculated by substituting the reaction temperature of 70 to 120° C. and the input amount of the redox additive into Equation 1 below.
[Equation 1]
t _R = Aln(Ma/Mv)+B
(Where t _R is the reaction time (min), A is the rate constant, B is the concentration constant, Ma is the input amount of the redox additive (g), and Mv is the input amount (g) of the vanadium compound) A vanadium electrolyte solution prepared by the method of any one of claims 1 to 15. A redox flow battery comprising the vanadium electrolyte of claim 16 .

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