CN117397075A

CN117397075A - Preparation method of vanadium electrolyte and battery containing vanadium electrolyte

Info

Publication number: CN117397075A
Application number: CN202180098869.2A
Authority: CN
Inventors: 河钟郁; 黄德炫
Original assignee: Soulbrain Co Ltd
Current assignee: Soulbrain Co Ltd
Priority date: 2021-04-07
Filing date: 2021-11-22
Publication date: 2024-01-12
Also published as: KR20230016791A

Abstract

The present invention relates to a method for preparing a vanadium electrolyte and a battery including the same, according to which a reduction reaction rate of a vanadium compound can be adjusted, and separation and recovery processes can be omitted since byproducts are not generated, and reproducibility of a single preparation process can be provided.

Description

Preparation method of vanadium electrolyte and battery containing vanadium electrolyte

Technical Field

The present invention relates to a method for preparing a vanadium electrolyte and a battery including the same, and more particularly, to a method for preparing a vanadium electrolyte, which is capable of adjusting a reduction reaction rate of a vanadium compound, omitting or reducing separation and recovery processes due to no by-products, and providing a single process of chemical reduction with reproducibility, and a battery including the same.

Background

The power storage technology (Energy Storage System; hereinafter, referred to as "ESS") is a technology for converting an existing power generation/use system into a production/storage/use system to provide efficient power application, and various modes of power storage technology are being studied.

Representative power storage technologies include, for example, physical storage modes including, for example, power generation by pumping, compressed air storage, flywheel (fly wheel); electromagnetic modes including superconducting energy storage and supercapacitors; including flow batteries, lithium ion batteries, and the like.

Among them, all-vanadium redox flow batteries have advantages of low cost, large capacity, long life, stability, etc., and in particular, have been examined in power plants, novel renewable energy ESS connection systems, smart grid ESS construction, etc., and thus have been evaluated as commercially advantageous in the art.

The electrolyte constituting the flow battery is, for example, a vanadium electrolyte. The most used vanadium electrolyte is a 3.5-valent vanadium electrolyte containing the same content of 4-valent vanadium ions and 3-valent vanadium ions. Therefore, a preparation process of the 3.5-valence vanadium electrolyte, which is simple, low in cost, high in quality and easy to produce in mass, needs to be developed.

The existing electrolyte preparation process is mainly a multi-step process using a chemical reaction mode and an electrolysis mode simultaneously.

The prior method for preparing the 4-valent vanadium electrolyte by using the reducing agent mainly comprises the following steps of ₂ O ₅ Dissolved in sulfuric acid solutionTo obtain 5-valent vanadium ion, and reducing the vanadium ion to 4-valent vanadium ion (VO) with reducing agent ²⁺ ) Thereby preparing a 4-valent electrolyte. The types of reducing agents proposed by the existing technology include oxalic acid, ethanol and the like.

The oxalic acid (C) ₂ H ₂ O ₄ ) Is a representative reducing agent used, and when preparing a 1L 4-valent electrolyte of 1.6M vanadium/4.0M sulfuric acid, oxalic acid is added and a stirring reaction is performed after mixing vanadium, sulfuric acid, and water in consideration of heat release. When the temperature of the reactor was kept at 90 ℃, about 4 hours was required, and the reaction formula was as follows.

V ₂ O _s +C ₂ H ₂ O ₄ +2H ₂ SO ₄ →2VOSO ₄ +3H ₂ O+2CO ₂

The reaction rate of methanol is significantly slower than that of oxalic acid, and thus, the use is limited.

The reducing agent only reacts from 5 to 4 valences. Furthermore, unreacted reducing agent or CO generated by oxidation of the reducing agent ₂ Some of the gases may dissolve in the electrolyte, and these unreacted/side reaction products are responsible for severely degrading the characteristics of the electrolyte.

Existing use of sulfur dioxide (SO ₂ ) The preparation process of (2) prepares the vanadium ion with the valence of 4 by the following reaction formula.

V ₂ O ₅ +SO ₂ +H ₂ SO ₄ →2VOSO ₄ +H ₂ O

Sulfur dioxide is a gas at normal temperature and pressure, so that the absorption rate in the electrolyte is low, and thus, the sulfur dioxide is excessively used, and thus, the preparation process is severe and inefficient. In addition, since the electrolyte is toxic, an additional step of making the remaining sulfur dioxide harmless is required after the electrolyte is prepared, and thus the process cost increases.

After the first preparation of the 4-valent vanadium electrolyte as described above, 1/3 of them are charged into the anode cell, 1/3 are charged into the cathode cell, and electrolysis is performed to obtain 5-valent and 3-valent electrolytes, respectively, and the 4-valent electrolyte of 1/3 remaining after the first preparation is combined with the 3-valent vanadium electrolyte of 1/3 generated by the second preparation (electrolysis), thereby preparing the 3.5-valent vanadium electrolyte.

Thus, disadvantages of the prior art include: first, through a multi-step process, second, the performance of the electrolyte in the first preparation is reduced, and third, 33% of the electrolyte is necessarily lost. Further, since electrolysis is accompanied by continuous consumable cost such as electrodes and separators in addition to initial investment cost of the electrolysis facility, and there is no significant advantage in constructing a mass production facility, it is difficult to provide a competitive unit cost even if it has high quality in producing a vanadium electrolyte.

In order to improve the disadvantages of the above processes, a vanadium preparation process using a catalyst and an organic reducing agent has been developed. Vanadium 3.3-3.7 valence electrolyte is prepared by using organic reducing agents including formic acid and noble metal catalysts such as Ru, pd, pt and the like in a mode of not carrying out electrolysis. Wherein, unless otherwise defined, the vanadium 3.3 to 3.7 valent electrolyte means an electrolyte containing 4 valent vanadium and 3 valent vanadium ions in the same molar ratio.

However, this method still uses an organic acid-based reducing agent, and there is a risk that a part of noble metal catalyst which reduces the battery performance in the electrolyte remains, and the catalyst used is mostly rare metal, and thus, the process is still to be improved.

Accordingly, a technology for preparing a 3.5-valent vanadium electrolyte using a single reactor using a catalyst-free chemical reaction scheme of a hydrazine compound is being recently developed. Specifically, when the 5-valent vanadium compound is reduced by using the hydrazine compound in the vicinity of the boiling point of the electrolyte without additional catalyst and various step processes, a high-purity vanadium electrolyte free of byproducts can be produced.

Although a more advanced production process, there is a disadvantage in that it is difficult to adjust the reduction reaction rate only by the hydrazine compound.

Therefore, research into a preparation technology capable of improving productivity, reproducibility, stability, and providing high quality of the vanadium electrolyte is still required.

Prior art literature

Patent literature

Korean patent No. 1415538

Japanese laid-open patent No. 2002-175831

Disclosure of Invention

Technical problem

In order to solve the problems in the prior art as described above, an object of the present invention is to provide a method for preparing a vanadium electrolyte, which is capable of adjusting a reduction reaction rate of a vanadium compound at the time of preparing a vanadium electrolyte, omitting separation and recovery processes of byproducts, and maximizing reaction efficiency.

In addition, the present invention has an object to provide a method for producing a vanadium electrolyte, which can provide reproducibility of a production process in a single process manner of chemical reduction, and can produce a high-yield and high-quality electrolyte.

In addition, it is an object of the present invention to provide a battery including the vanadium electrolyte prepared by the method of preparing the vanadium electrolyte.

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

Technical proposal

In order to achieve the above object, the present invention provides a method for preparing a vanadium electrolyte, comprising the steps of:

firstly, after adding a 5-valent vanadium compound and water, adding a nitrogen reducing agent and an acid in sequence, and carrying out a reduction reaction to generate a 4-valent vanadium compound; and

and a second step of reducing the 4-valent vanadium compound to produce a 3.3 to 3.7-valent vanadium compound, wherein the reaction rate of one or more reduction reactions selected from the reduction reaction in the first step and the reduction reaction in the second step is reduced.

Redox additives having a lower reducing power than the nitrogen-based reducing agent may be used to reduce the reaction rate of the reduction reaction.

The redox additive is capable of self-reducing and oxidizing the nitrogen-based reducing agent after dehydration reaction with the acid to form an aqueous solution, thereby producing nitrogen gas.

The redox additive may be selected from molybdenum metals, molybdenum oxides Mo _x O _y Molybdenum nitride Mo _x N _y Molybdenum chloride Mo _x Cl _y Molybdenum sulfide Mo _x S _y Molybdenum phosphide Mo _x P _y Molybdenum carbide Mo _x C _y Metallic molybdenum oxide Mo _x M _y O _z Metallic molybdenum nitride Mo _x M _y N _z Metallic molybdenum chloride Mo _x M _y Cl _z Metallic molybdenum sulfide Mo _x M _y S _z Molybdenum phosphide Mo _x M _y P _z Metallic molybdenum carbide Mo _x M _y C _z More than one of them.

The metal of the redox additive may be one metal selected from 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 In or a plurality of metals forming an alloy, and the x and y (x/y) or the x, y and z (x/y/z) may be integers of 0 to 1 independently of each other.

The content of the redox additive may be 0.1 to 1.6 parts by weight based on 100 parts by weight of the 5-valent vanadium compound.

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

The molar concentration (M; mol/L) ratio of the 5-valent vanadium compound to the nitrogen-based reducing agent may be 1:0.1-1.6.

The acid may be one or more selected from sulfuric acid, hydrochloric acid, nitric acid and acetic acid, and the concentration of proton ions derived from the acid may be 1 to 20 moles per 1 mole of the vanadium compound.

The second step may be carried out at 70 to 120 ℃.

The 5-valent 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.

The method may comprise the step of filtering after said first step or after a second step: .

In the first step, 5 to 15 moles of water may be used per 1 mole of the vanadium compound, and in the second step, after the generated vanadium compound is cooled to a room temperature or lower, an excess amount of water exceeding the previously charged water may be charged, and the reaction solution may be filtered to reduce the reaction rate of the reduction reaction.

The water content added in excess may be in the range of 42 to 44 moles with respect to the composition of 1.6 moles of vanadium and 4.0 moles of sulfuric acid.

In the first step, 5 to 15 moles of water are used per 1 mole of the vanadium compound, and after the reaction is performed at 100 ℃ or higher to produce the vanadium compound, an excess amount of water exceeding the previously charged water is charged, and after the reduced vanadium compound is cooled to-25 to 20 ℃, the reaction solution is subjected to cyclic filtration at-25 to 40 ℃ to reduce the reaction rate of the reduction reaction.

In the first step, after a reaction is performed at 100 ℃ or higher to produce a vanadium compound using 5 to 15 moles of water per 1 mole of the vanadium compound, the reduced vanadium compound is cooled to-25 to 20 ℃, excess water exceeding the content of the previously charged water is charged, and the reaction solution is subjected to cyclic filtration at-25 to 40 ℃ to reduce the reaction rate of the reduction reaction.

In addition, the invention provides a preparation method of the vanadium electrolyte, which comprises the following steps:

step A, after adding a 5-valent vanadium compound into a solvent, adding a nitrogen-based reducing agent to prepare a reaction mixture;

step B, adding acid and redox additive into the reaction mixture to carry out dehydration reaction, and reducing the 5-valent vanadium compound into 4-valent vanadium compound;

step C, oxidizing the nitrogen reducing agent by the dehydration reaction product to generate nitrogen and a self-reduction product; and

step D, heating the reactant to oxidize the self-reduction product and reduce the 4-valent vanadium compound into 3.3-3.7-valent vanadium compound,

wherein the nitrogen-based reducing agent is entirely added in the step A or is added in steps A and D in divided portions.

The redox additive participates in the reaction in the state of an aqueous solution through a dehydration reaction with an acid, so that byproducts derived from the redox additive are not generated.

In the implementation of the step D, the reaction temperature of 70 to 120℃may be used, and the reduction reaction time of the vanadium compound calculated by substituting the input amount of the redox additive into the formula 1 may be used.

Mathematical formula 1:

t _R ＝Aln(Ma/Mv)+B

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

a first step of reacting a vanadium compound, a reducing agent and an acid at 100 ℃ or higher under conditions having 5 to 15 moles of a pre-solvent per 1 mole of the vanadium compound to form a reduced vanadium compound;

a second step of cooling the reduced vanadium compound to-25 to 20 ℃ after the reaction is completed; and

and thirdly, circularly filtering the cooled vanadium electrolyte at the temperature of between 25 ℃ below zero and 40 ℃.

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

In addition, the invention provides a redox flow battery comprising the vanadium electrolyte.

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

Advantageous effects

According to the method for preparing the vanadium electrolyte, the preparation time of the electrolyte can be shortened, a purification process for separating and recovering reaction byproducts is not needed, and the vanadium electrolyte with improved charge and discharge performance of the product can be prepared.

In addition, a separate process of the chemical reduction system can be realized without an electrolytic system, and thus, the process can be simplified.

In addition, the carbon component and the noble metal catalyst component can be blocked from the source to remain in the vanadium electrolyte, and a large amount of high-quality electrolyte can be prepared in a reproducible manner.

Further, impurities can be effectively reduced, and therefore, a high-purity vanadium electrolyte can be provided.

That is, by preparing a vanadium electrolyte having economical efficiency, high quality, and high performance according to the present invention, a battery including the vanadium electrolyte can be applied to all fields using an all-vanadium redox flow battery, such as a novel renewable energy source, a smart grid, a power station, and the like.

Drawings

FIG. 1 is a graph showing temperature changes for different reduction reaction time periods at sulfuric acid flows of 240mL/hr and 480mL/hr for the examples.

Fig. 2 is a graph showing a correlation between the input amount of the redox additive and the reduction reaction rate of the vanadium compound of the example, and it is known that the arrhenius approximation is followed.

Fig. 3 is a graph showing the reduction reaction rate of the vanadium compound in terms of the oxidation number of vanadium ions according to the amounts of the redox additive charged in the examples and comparative examples, so that the influence of the redox additive on the reduction reaction rate and the reduction amount can be confirmed.

Fig. 4 is a graph showing charge capacities per cycle of redox flow batteries using vanadium electrolytes for anodes and cathodes according to different input amounts of redox additives of examples and comparative examples.

Fig. 5 is a graph showing discharge capacities per cycle of redox flow batteries using vanadium electrolytes for anodes and cathodes according to different input amounts of redox additives of examples and comparative examples.

Fig. 6 is a graph showing energy efficiency of a battery including a vanadium electrolyte according to different input amounts of a redox additive of examples and comparative examples.

Fig. 7 is a graph showing the result of the reaction rate depending on the content ratio of the front solvent to the rear solvent in the first step of carrying out the reduction reaction as an example of the present invention.

Fig. 8 is a graph of charge capacity as a function of the content ratio of the front solvent to the rear solvent in fig. 7.

Fig. 9 is a graph of discharge capacity according to the content ratio of the front solvent to the rear solvent in fig. 7.

Fig. 10 is an energy efficiency graph according to the content ratio of the front solvent to the rear solvent in fig. 7.

Fig. 11 is an image showing the reaction result when the number of moles of the pre-solvent in fig. 7 used is less than five times the number of moles of vanadium.

Fig. 12 is a device diagram schematically showing the structure of a device and a process flow chart for preparing the electrolyte of the embodiment.

Detailed Description

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

The terms and words used in the present specification and claims should not be construed as being limited to the usual meaning or meaning in a dictionary, and the inventor can appropriately define the concept of terms in order to explain the invention by an optimal method, and in view of this, should be construed as meaning and concept conforming to the technical idea of the present invention.

In the present invention, "comprising … …" may be defined as "comprising … … polymerized", "comprising … … polymerized" or "comprising in units derived from … …" unless otherwise defined.

Unless otherwise defined, all numbers, values, and/or expressions in the present invention indicating the amounts of components, reaction conditions, polymer compositions, and complexes used are to be understood in any case as modified by the term "about" because these numbers are approximations reflecting the various uncertainties in the measurement that occur when these values are obtained from essentially different numbers. In addition, where a range of values is disclosed in the present invention, the range is continuous and includes all values from the minimum value of the range to the maximum value including the maximum value unless otherwise defined. Further, when such a range refers to an integer, all integers from the minimum value to the maximum value inclusive of the maximum value are included unless otherwise defined.

In the present invention, when a range recites a variable, the variable should be understood to include all values within the recited range, including the endpoints of the range. For example, a range of "5 to 10" should be understood to include not only values of 5, 6, 7, 8, 9, and 10, but also any lower ranges of 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, and also any values between a plurality of appropriate integers such as ranges recited as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9, and the like. It should be noted that a range of 10 to 30% is understood to include not only all integers equivalent to 10%, 11%, 12%, 13% and up to 30%, but also any value between a plurality of appropriate integers such as those in the ranges described as 10.5%, 15.5%, 25.5%, etc.

The inventors of the present invention confirmed that the method includes the steps of:

and a second step of subjecting the 4-valent vanadium compound to a reduction reaction to produce a 3.3 to 3.7-valent vanadium compound, wherein the reaction rate of one or more reduction reactions selected from the reduction reaction of the first step and the reduction reaction of the second step is reduced, reproducibility of the production process can be provided, and performance of the all-vanadium redox flow battery including the electrolyte can be improved, and further studies have been made based on this, thereby completing the present invention.

According to an embodiment of the present invention, it can be confirmed that, when an additive having a lower reducing power than the reducing agent (hereinafter, referred to as "redox additive") is used in a reduction reaction using the reducing agent for reduction of a vanadium raw material (hereinafter, referred to as "nitrogen-based reducing agent"), since an electrolytic process is not required, an electrolyte can be prepared by a single process of chemical reduction, and furthermore, the reduction reaction rate of a vanadium compound can be controlled according to the amount of the redox additive added, thereby shortening the reaction time, enabling reproducibility of the preparation process, and enabling improvement of performance of an all-vanadium redox flow battery including the electrolyte.

Preferably, unless otherwise defined, the term "redox additive" used in the present invention is to assist the reducing ability of vanadium ions of a nitrogen-based reducing agent without affecting the amount of reduction, thereby providing reproducibility of the preparation process and ensuring selectivity of vanadium raw materials, and further to improve battery performance due to inclusion in an electrolyte.

The selectivity of the vanadium raw material is meant to be not limited by a minute quality difference of the same purity of the vanadium compound according to the origin of vanadium or the purification method, etc., unless otherwise defined.

The reducing ability refers to the speed of the reduction reaction unless otherwise defined. Specifically, since the reduction is performed sequentially from the beginning of the strong reducing power, the reduction is performed first, which means that the reduction reaction speed is high. When the potential energy value is set so that oxidation proceeds first and autooxidation occurs at the time of subsequent reduction of the substance, the amount of the substance to be reduced first affects the adjustment of the reduction reaction rate of the substance to be reduced later.

Specifically, the redox additive of the present invention has an electrochemical/mechanical potential range in which autoxidation occurs at the time of reducing a vanadium compound after it is reduced faster than the vanadium compound because of its reduction reaction rate, and therefore, not only can an electrolytic process be omitted and a chemical process be separately performed, but also the amount of the redox additive added directly affects the reduction ability of the vanadium compound, and thus, the reduction reaction rate of the vanadium compound can be adjusted.

The input M of the redox additive of the invention _a And the reduction reaction rate t of the vanadium compound _R The correlation represented by the expression 1 can be satisfied.

Mathematical formula 1:

t _R ＝Aln(Ma/Mv)+B

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

The equation 1 can be obtained by statistical approximation of regression analysis method for experimental data. Among them, the plurality of constants have no particular physical meaning, and 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, and thus are named as a rate constant and a concentration constant, respectively.

The equation 1 can be obtained by statistical approximation of regression analysis method for experimental data. Among them, the plurality of constants have no particular physical meaning, and the constant a is closely related to the reduction rate, and thus is named as a rate constant, and may be, for example, -2.233.

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

According to the above equation 1, the process can be controlled by predicting the reduction reaction rate of vanadium according to the amount of the redox additive added, and thus, the selectivity of the vanadium raw material can be ensured while providing the reproducibility of the preparation process, thereby improving the battery performance.

As can be confirmed from fig. 2, in the above equation 1, when the reaction temperature, the concentration of vanadium compound (raw material)/sulfuric acid/water (solvent) is constant, the reaction rate (t _R ) It appears to be proportional negative to the amount of redox additive (Ma) charged, following the alennis Wu Sigong formula.

By satisfying the above equation 1, the reduction reaction rate of the vanadium compound can be predicted according to the input amount of the redox additive, so that the process can be controlled, and the reproducibility of the preparation process and the selectivity of the vanadium raw material can be ensured, with the result that the battery performance can be improved.

The redox additive may be selected from an ionic metal capable of dissolving in the vanadium electrolyte or a compound derived from the ionic metal.

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

The redox additive (1) has electrochemical/mechanical potential energy in which the vanadium ions are reduced and autoxidized by the reduced components having a faster reduction rate than the vanadium ions, (2) has reversibility capable of repeatedly functioning as an intermediate agent for the redox reaction between the nitrogen-based reducing agent and the vanadium compound, and (3) can control the reduction reaction rate of the vanadium compound and shorten the reaction time by adjusting the amount of the redox additive to be added according to the content of the main component (metal) of the redox additive contained in the vanadium compound. For example, when the content of the ionic metal component as the main component of the redox additive in the electrolyte is 280ppm or less, it is possible to maximize the battery performance and shorten the reaction time to within 8 hours. The ionic metal component may be selected from a transition metal or a salt thereof having a solubility in the vanadium electrolyte of 0.1ppm or more.

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

In the present invention, unless otherwise defined, 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.

As an example, the vanadium source may be a 5-valent vanadium compound or a 4-valent vanadium compound, and the 5-valent vanadium compound may be selected from V ₂ O ₅ ，NH ₄ VO ₃ NaVO ₃ More than one of the 4-valent vanadium compounds can be VOSO ₄ ·xH ₂ O, wherein x is an integer of 1 to 6.

Specifically, the starting materials for preparing the vanadium electrolyte include a 5-valent or 4-valent vanadium compound, sulfuric acid, and a solvent, the 5-valent or 4-valent vanadium compound generating nitrogen gas while undergoing a dehydration reaction with sulfuric acid and reducing the vanadium compound due to a nitrogen-based reducing agent, the redox additive undergoing a dehydration reaction with sulfuric acid to be reduced by the nitrogen-based reducing agent in an aqueous state and generating nitrogen gas and sulfuric acid, and then, the reduced vanadium compound being further reduced and autoxidized, at this time, mass production can be achieved through a separate reaction of chemical reduction without electrolytic reaction, and the reduction process can be simplified, the reaction efficiency can be maximized, and a high-quality electrolyte can be prepared, thereby improving the performance of a battery including the electrolyte.

In the present invention, the vanadium electrolyte may contain a 3.3 to 3.7 valent vanadium compound. In this case, the 3.3 to 3.7 valent vanadium compound may be reduced from a 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.

As an example, vanadium Compound V ₂ O ₅ Acidic solution H ₂ SO ₄ N as nitrogen-based reducing agent ₂ H ₄ ·H ₂ The reduction reaction of O can be performed as shown in reaction formula 1.

Reaction formula 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, which is prepared by the reduction process based on the reaction formula 1, may constitute a specific compound with an acidic solution (hereinafter, referred to as "acid") and a reducing solvent (hereinafter, referred to as "solvent"), for example, may be VO-containing when the solvent is water ²⁺ 、[VO(H ₂ O) ₅ ] ²⁺ Or [ VO (OH) ₂ (H ₂ O) ₄ ] ⁺ An ionic compound.

In addition, the vanadium compound having an oxidation number of 2.0 prepared by the reduction process may form a specific compound with an acid and a solvent, for example, may be a compound containing V when the solvent is water ²⁺ 、[V(H ₂ O) ₆ ] ²⁺ An ionic compound.

The vanadium compound having an oxidation number of 3.0 prepared by the reduction process may form a specific compound with an acid and a solvent, for example, may be a compound containing V when the solvent is water ³⁺ 、[V(H ₂ O) ₆ ] ³⁺ 、[V(OH)(H ₂ O) ₅ ] ²⁺ Or [ V (OH) ₂ (H ₂ O) ₄ ] ⁺ An ionic compound.

The vanadium compound having an oxidation number of 5.0 prepared by the reduction process may form a specific compound with an acid and a solvent, for example, may be VO-containing when the solvent is water ₂ ⁺ 、V ₂ O ₃ ⁴⁺ 、[VO ₂ (H ₂ O) ₃ ] ⁺ Or [ V ] ₂ O ₃ (H ₂ O) ₈ ] ⁴⁺ An ionic compound.

The vanadium compound having an oxidation number of more than 3.0 and less than 4.0 prepared by the reduction process may be mixed with a vanadium compound having an oxidation number of 3.0 and a vanadium compound having an oxidation number of 4.O, and may be selected from V when the solvent is water ³⁺ 、[V(H ₂ O) ₆ ] ³⁺ 、[V(OH)(H ₂ O) ₅ ] ²⁺ [ V (OH) ₂ (H ₂ O) ₄ ] ⁺ More than one ion and VO ²⁺ 、[VO(H ₂ O) ₅ ] ²⁺ Or [ VO (OH) ₂ (H ₂ O) ₄ ] ⁺ And (3) a compound formed by mixing ions.

When the acid is a sulfate-based material and the solvent is water, VOSO in the vanadium compound having an oxidation number of 3.3 is produced ₄ And V is equal to ₂ (SO ₄ ) ₃ The molar ratio of (2) can be 6:5.5-6.5, oxygenVOSO in vanadium compound having valence of 3.5 ₄ And V is equal to ₂ (S0 ₄ ) ₃ The molar ratio of (C) may be 2:0.5-1.5, and the oxidation number is 3.7 ₄ And V is equal to ₂ (SO ₄ ) ₃ The molar ratio of (2) to (3) can be 14:2.5-3.5.

In the present invention, the reference to nH is omitted in order to represent V3.3, V3.5, V3.7 by the molar ratio of the 4-valent ion to the 3-valent ion ₂ O is described as not including nH ₂ O。

In the present invention, the redox additive can play a role in promoting the reduction reaction of the vanadium compound, and specifically, can 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 all-vanadium redox flow battery, and satisfy the correlation corresponding to the above-described equation 1.

Another embodiment of the invention provides the context with respect to a vanadium electrolyte derived from a 5-valent vanadium compound. In this case, the 5-valent vanadium compound may be a low-grade or high-grade compound.

The vanadium electrolyte may contain sulfuric acid and a solvent in an appropriate amount and 15 to 35 parts by weight of a nitrogen-based reducing agent based on 100 parts by weight of vanadium contained in the 5-valent vanadium compound.

In the vanadium electrolyte, when the input amount of the redox additive is adjusted according to the content of the ionic metal component as the main component of the redox additive, it is possible to control the reduction reaction rate and to secure reproducibility by shortening the reaction time.

In the present invention, in particular, the content of the main metal component in the redox additive may be 0.1ppm or more, or the redox additive does not contain the main metal component.

As an example, when the content of the ionic metal component as a main component of the redox additive in the electrolyte is 280ppm, the battery performance can be maximized and the process can be shortened to within 8 hours.

The vanadium electrolyte may contain a 2.0 to 5.0 valent vanadium compound, and in particular, at least a part of the electrolyte may contain a 3.3 to 3.7 valent vanadium compound.

In this case, the 3.3 to 3.7 valent vanadium compound may be reduced from a 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 a 5-valent hydrazine compound based on 100 parts by weight of a vanadium raw material. Specifically, it is required to use 16 parts by weight or more of N based on 100 parts by weight of the vanadium raw material ₂ H ₄ Based on 100 parts by weight of vanadium raw material, more than 24 parts by weight of N is required by reducing a 5-valent vanadium compound into 4-valent vanadium ₂ H ₄ To reduce vanadium at 5 to vanadium at 3.5.

The redox additive is preferably adjusted so that the amount of Mo in the electrolyte is about 270ppm per 1L, and the amount of the redox additive to be added can be adjusted depending on whether or not the vanadium raw material contains an ionic metal component as a main component of the redox additive. Taking Mo as the ionic metal component, for example, it is preferable to add 4mM of Mo to 1L of the electrolyte, and about 70ppm of Mo per 1mM of added Mo is dissolved in the electrolyte.

The acid and the solvent may be appropriately adjusted depending on the kind and purpose of the electrolyte.

In another embodiment of the present invention, when reducing vanadium at 5 to vanadium at 4, V is added in 100 parts by weight ₂ O ₅ The raw materials can comprise 17.5 parts by weight of N ₂ H ₄ ·H ₂ O, more than 108 parts by weight of H ₂ SO ₄ (based on 98% concentration), 100 parts by weight or more of DIW.

In another embodiment of the present invention, when reducing vanadium at 5 to vanadium at 3.5, V is added in 100 parts by weight ₂ O ₅ The raw materials may contain 26 parts by weight or more of N ₂ H ₄ ·H ₂ O, more than 135 parts by weight of H ₂ SO ₄ 110 parts by weight or more of DIW.

As an example, V in the 5-valent vanadium compound ₂ O ₅ For example, 100 parts by weight of V ₂ O ₅ For reference, 4 can be used00 parts by weight or less of an acid, 38 parts by weight or less of a nitrogen-based reducing agent, 700 parts by weight or less of a solvent, and 0.1 to 1.6 parts by weight of a redox additive to prepare the vanadium electrolyte of the present invention, 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 may be used to prepare the vanadium electrolyte of the present invention.

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

It is preferable to use 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 to prepare the vanadium electrolyte, 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 to prepare the vanadium electrolyte, still more preferably 250 to 300 parts by weight of an acid, 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. In these ranges, the reaction time can be shortened, the reaction efficiency is excellent, and the high-purity and high-quality vanadium electrolyte can be prepared, and not only can the charge-discharge capacity of the battery including the electrolyte be improved.

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

For example, when 1.6 parts by weight of MoO is used ₃ As redox additive, the Mo content in the electrolyte may be 1120ppm, moO per 1L ₃ The amount of (2) added may be 2.4g, and Mol% based on the electrolyte may be 0.016Mol%.

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

The 5-valent vanadium compound (V ₂ O ₅ ) Molar concentration with nitrogen-based reducing agent (M; mol/L) may be 1In the range of 0.1 to 1.6 or 1:0.2 to 0.4, an appropriate molar concentration ratio can be formed with the acid, the solvent and the redox additive, thereby easily achieving the objective effect of the present invention.

As an example, the 5-valent vanadium compound (V ₂ O ₅ ) The molar concentration of the acid, nitrogen-based reducing agent, and redox additive (M; mol/L) may be 1:2 to 3:0.2 to 0.4:0.001 or more and less than 0.25, and as a specific example, 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, still more preferably 1:2.4 to 2.6:0.37 to 0.38:0.003 to 0.01, in this range, the reaction time can be shortened, the reaction efficiency is excellent, and a high-purity and high-quality vanadium electrolyte can be produced, and not only this can be improved, but also the charge/discharge capacity of a battery containing the electrolyte can be improved.

As an example, the content of the redox additive in the vanadium electrolyte may be 1 to 6000ppm, preferably 10 to 3000ppm, more preferably 50 to 1500ppm, still more preferably 100 to 1000ppm, and most preferably 200 to 800ppm.

After the vanadium electrolyte preparation process such as the reaction and filtration process is completed, the content of the main component of the redox additive in the vanadium electrolyte may be 1ppm or more and less than 1500ppm.

Even if other additives for improving the performance of the electrolyte are contained, the redox additive can provide the reducing ability of vanadium ions of the nitrogen-based reducing agent while not affecting the amount of reduction but affecting the reduction rate. For example, even when preparing a vanadium electrolyte, V is used for 100 parts by weight ₂ O ₅ Raw materials, 20 parts by weight or less of H known as a heat stability additive is charged ₃ PO ₄ The reducing effect of the redox additive is not affected.

Even at 100 parts by weight of V ₂ O ₅ Adding 20 parts by weight or less of the above H ₃ PO ₄ Such as (NH) ₄ )H ₂ PO ₄ 、(NH ₄ ) ₃ PO ₄ Equal PO (Point of sale) ₄ Classes of substances, e.g. HCl, mgCl ₂ 、CaCl ₂ And other chlorine-based substances, additives such as cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants and the like, the reducing effect of the redox additive is not affected, and the redox additive does not affect the inherent functions of various additives.

According to another embodiment of the present invention, the content is provided with respect to a vanadium electrolyte derived from a 4-valent vanadium compound. In this case, the 4-valent vanadium compound may be a low-grade or high-grade compound.

The vanadium electrolyte may be prepared using an appropriate amount of acid and solvent and 10 to 20 parts by weight of nitrogen-based reducing agent based on 100 parts by weight of vanadium contained in the 4-valent vanadium compound, and the input amount of the redox additive to the 4-valent vanadium compound may be adjusted according to the content of the ionic metal component of the redox additive.

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

In the present invention, as an example, VOSO in the 4-valent vanadium compound ₄ For example, 100 parts by weight of VOSO ₄ For the purpose of preparing the vanadium electrolyte of the present invention, 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 0.1 to 1.6 parts by weight of a redox additive may be used, 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 may be used to prepare the vanadium electrolyte of the present invention, 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 may be used to prepare the vanadium electrolyte of the present invention, more preferably 200 to 300 parts by weight of an acid, 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 may be used to prepare the vanadium electrolyte of the present invention, and still more preferably 200 to 300 parts by weight to 250 parts by weight of an acid, 6 to 10 parts by weight of an acid The vanadium electrolyte is prepared from nitrogen reducing agent in parts by weight, solvent in parts by weight of 500-550 parts by weight and redox additive in parts by weight of 0.2-0.8 part by weight. In this range, the reaction time can be shortened, the reaction efficiency is excellent, and a high-purity and high-quality vanadium electrolyte can be prepared, and not only can the charge/discharge capacity of a battery including the electrolyte be improved.

The redox additive can provide the reducing ability of vanadium ions even if other additives for improving the performance of the electrolyte are included, so that the reducing amount is not affected but the reducing speed is affected. For example, even when preparing a vanadium electrolyte, V is used in an amount of 100 parts by weight ₂ O ₅ The raw materials are added with 20 parts by weight or less of H known as a typical additive for improving temperature stability ₃ PO ₄ The reducing effect of the redox additive is not affected. Even at 100 parts by weight of V ₂ O ₅ Adding 20 parts by weight or less of H as exemplified below based on the raw materials ₃ PO ₄ Such as (NH) ₄ )H ₂ PO ₄ 、(NH ₄ ) ₃ PO ₄ Equal PO (Point of sale) ₄ Classes of substances, e.g. HCl, mgCl ₂ 、CaCl ₂ The effect of the reducing agent of the redox additive is not affected by Cl-based substances, such as cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, and the like, and the redox additive does not affect the additive functions of various additives.

An embodiment of the present invention provides more details about the preparation method of the vanadium electrolyte.

As an example, the preparation method of the vanadium electrolyte comprises the following steps: a first step of reducing a 5-valent vanadium compound as a vanadium compound to a 4-valent vanadium compound; and a second step of reducing the 4-valent vanadium compound to a 3.3-3.7-valent vanadium compound, wherein a redox additive is added to at least one of the first step and the second step, the redox additive being composed of a substance having a lower reducing power than the nitrogen-based reducing agent used for reducing the vanadium compound in the first step.

Preferably, the first step may sequentially include the steps of: step i, adding a 5-valent vanadium compound and water; step ii, adding a nitrogen reducing agent; and step iii, sulfuric acid is added, at this time, the process time can be shortened, the reaction efficiency is excellent, and the decomposition of the reducing agent can be minimized, and there is an advantage in that a 4-valent vanadium electrolyte is prepared.

As a specific example, the nitrogen-based compound may be a hydrazine compound.

Preferably, the hydrazine compound may be added in the form of a hydrate or an aqueous solution, and preferably, water is at least 95 parts by weight based on 100 parts by weight of the hydrazine compound.

In the examples described later, the electrolyte is diluted with 200 to 500 parts by weight of water based on 100 parts by weight of the hydrazine compound, and the total amount of water required for preparing the electrolyte is the same although the specific ratio is not specified. When the hydrazine compound in the form of a hydrate is used as described above, the reaction rate can be controlled to be relatively low and the reaction can be performed more stably, and therefore, the reaction efficiency is excellent and there is an advantage that a high-purity and high-quality vanadium electrolyte can be produced.

The hydrazine hydrate is preferably a hydrazine monohydrate, and the hydrazine salt is preferably a hydrazine sulfate, and in this case, there is no residue of by-products that degrade the quality of the electrolyte, and thus there is an advantage in that a high-purity high-quality vanadium electrolyte can be produced.

The nitrogen-based reducing agent may be entirely charged in the first step, or may be charged in the second step after being charged in part in the first step. As an example of the fractional addition, 60 to 80% by weight of the total amount may be added in the first step, 20 to 40% by weight may be added in the second step, preferably 60 to 70% by weight may be added in the first step, and 30 to 40% by weight may be added in the second step. The method for adding the nitrogen reducing agent can properly utilize the method for adding the nitrogen reducing agent which is conventionally used in the technical field of the invention according to the preparation purpose or the process condition of the vanadium electrolyte.

The redox additive is capable of undergoing self-reduction and oxidation of the nitrogen-based reducing agent to produce nitrogen gas after dehydration reaction with the sulfuric acid to form an aqueous solution in the first step.

The redox additive may be used to reduce the 4-valent vanadium compound in the second step in the form of an aqueous solution that is dehydrated with sulfuric acid.

Specifically, the redox additive undergoes autoxidation in the form of an aqueous solution formed by dehydration reaction with sulfuric acid and reduces the 4-valent vanadium compound to 3.3 to 3.7-valent vanadium compound, preferably to 3.4 to 3.6-valent vanadium compound, and most preferably to 3.5-valent vanadium compound, and at this time, has an advantage of producing a high-purity and high-quality vanadium electrolyte.

In the second step, the temperature is preferably raised to 70 to 120 ℃, more preferably to 80 to 115 ℃, still more preferably to 90 to 110 ℃, and even more preferably to 100 to 110 ℃, and at this time, the reaction time can be shortened, the reaction efficiency is excellent, and the method has the advantage of preparing the high-purity and high-quality vanadium electrolyte.

In the second step, the heating time may be 12 hours or less, preferably 1 to 10 hours, more preferably 2 to 8 hours, still more preferably 3 to 8 hours, and most preferably 4 to 8 hours, and in this case, the reaction efficiency is excellent and the advantage of producing a high purity and high quality vanadium electrolyte is obtained.

As an example, the first step and the second step may be performed under atmospheric pressure, and may be pressurized or depressurized as needed within a range satisfying the above-mentioned reaction conditions.

Preferably, the method of preparing the electrolyte may include a process of performing filtration after the first step or after the second step, and more preferably, may include a process of performing the first filtration after the first step and performing the second filtration after the second step. At this time, the process time is not greatly prolonged, and the method has the advantage of preparing the high-purity and high-quality vanadium electrolyte.

The filtration may be performed by gravity filtration using gravity, pressure filtration in which the upper layer of the filtration unit is pressurized and operated, or pressure reduction filtration in which the lower layer of the filtration unit is depressurized and operated. In addition, as the filtration, a filtration unit having an acid resistance and a hydrophilic material having a pore diameter of 0.2 to 10 μm can be used, and in particular, when the pore diameter is smaller than 0.2 μm, the process time or the pressure load increases, and when the pore diameter is larger than 10 μm, the competitive power is lowered as compared with the quality, and the filtration effect is not remarkable.

When the filter unit is used together with a filter aid such as diatomaceous earth, the filter aid removes impurities for the first time before the filtrate reaches the filter unit, so that the filtration load to which the filter unit is subjected can be reduced.

At this time, there is no great influence on the total process time, and a plurality of impurities that may degrade the characteristics of the electrolyte are physically screened out in the electrolyte by the filter aid and the filter unit, and at the same time, the electrolyte stably passes through the filter aid and the filter unit, thus having an advantage of preparing a high purity and high quality vanadium electrolyte.

The 5-valent vanadium compound is preferably V ₂ O ₅ The 4-valent vanadium compound is preferably VOSO ₄ The 3.3-3.7-valent vanadium compound is preferably composed of VOSO ₄ And V ₂ (SO ₄ ) ₃ The method has the advantage of preparing the vanadium electrolyte with high purity and high quality.

The method of preparing the electrolyte may include a redox additive and a catalyst in the first step or the second step as needed to promote the reduction reaction.

The catalyst is catalytically active in a first step, in particular in a second step, and accompanies the process of separation from the electrolyte after catalytic action. The catalyst may be charged in the first step and then filtered in the second step after the end of the reaction, or the catalyst may be charged in the second step and then filtered again in the second step after the end of the reaction, or may be used in such a manner that the reactants can be introduced into the catalytic device to perform the reduction reaction.

In the present invention, the main component of the catalyst may be a metal such as Pt, pd, ru, etc., and typically may be a Pt catalyst. The Pt catalyst is not particularly limited as long as it is a Pt catalyst conventionally used in the art to which the present invention pertains.

In the present invention, the preparation method of the vanadium electrolyte may include the steps of: step A, after adding a 5-valent vanadium compound into a solvent, adding a nitrogen-based reducing agent to prepare a reaction mixture; step B, sulfuric acid and a redox additive are added into the reaction mixture to carry out dehydration reaction, and the 5-valent vanadium compound is reduced into a 4-valent vanadium compound; step C, oxidizing the nitrogen reducing agent by the dehydration reaction product to generate nitrogen and a self-reduction product; and step D, heating the reactant to oxidize the self-reduction product and reduce the 4-valent vanadium compound into 3-3 to 3.7-valent vanadium compound, wherein the nitrogen reducing agent can be completely added in the step A or added in the step A and the step D in a divided manner.

The redox additive may be used without limitation in the manufacture of vanadium electrolytes, including aqueous all-vanadium redox flow electrolytes or non-aqueous all-vanadium redox flow electrolytes such as vanadium acetylacetonate, capable of providing vanadium ions for all-vanadium redox flow batteries, and mechanical, electronic drives of all-vanadium redox flow batteries utilizing the same.

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

When the redox additive is charged during the preparation of the electrolyte, the reduction reaction can be promoted to control the reaction rate, and when the all-vanadium redox flow battery is operated, the energy transfer substrate of the additive material among a plurality of vanadium ions which can be activated to electric field energy contributes to the electron mobility of the vanadium ions, thereby contributing to the improvement of the charge-discharge capacity and energy efficiency of the battery. The redox additive is preferably added at a prescribed concentration or more to improve the reaction rate, but when it is excessively added as compared with a specific concentration, excessive mutual attraction between vanadium ions and the redox additive causes an increase in viscosity, and therefore, the force of preventing the diffusivity of the vanadium ions is further increased, thereby adversely affecting the charge-discharge capacity and energy efficiency.

When both improvement of the reaction rate and improvement of the battery performance are considered, the concentration of the redox additive in the electrolyte is preferably 0.2 to 2mol%. Only when the concentration of the redox additive is 0.2mol% or more, it has a substantial effect of improving the reaction rate and performance, and when it is more than 2mol%, the above-mentioned negative effects are generated. When the reaction rate and the performance of the electrolyte are taken into consideration, the content of the redox additive in the electrolyte is preferably 0.2 to 1.0mol%, more preferably 0.2 to 0.8mol%.

As described above, the redox additive participates in the reaction in the state of an aqueous solution through the dehydration reaction with sulfuric acid, and thus, by-products derived from the redox additive are not generated.

In the implementation of the step D, the reaction temperature of 70 to 120℃may be used, and the reduction reaction time of the vanadium compound calculated by substituting the amount of the redox additive into the above formula 1 may be used.

Mathematical formula 1:

t _R ＝Aln(Ma/Mv)+B

When the temperature is 100mA/cm ² When the vanadium electrolyte prepared by using the redox additive of the present invention is measured at a current density, a discharge cut-off voltage of 0.8V, a charge cut-off voltage of 1.6V, and a flow rate of 180mL/min, the charge capacity and charge/discharge capacity can be improved by 5% or more, preferably 6.5% or more on average, per cycle, in the first 30 cycles (cycle) as compared with those without the redox additive. The energy efficiency can be improved by 0.5% or more, preferably by 1% or more.

In the present invention, the charge capacity means a state of charge accumulation up to a charge cutoff voltage, the charge/discharge capacity means a state of charge exhaustion up to a discharge cutoff voltage, and the energy efficiency means a ratio of the charge capacity to the charge/discharge capacity, and the above three elements can be used as an index for judging the life and performance of an electrolyte.

The redox additive of the present invention is capable of providing an electrolyte with improved battery capacity and energy efficiency.

In the invention, the redox additive is input to economically prepare the vanadium electrolyte with high efficiency, high quality and high performance, so that the method can be applied to all fields of novel renewable energy sources, smart grids, power stations and the like using all-vanadium redox flow batteries.

As an example, the above-described method for producing a vanadium electrolyte confirms that, when a solvent is added in several steps and the addition amount and the addition time are adjusted, an optimized process having the effect of improving the reaction rate and reducing the impurity can be provided.

The solvent used in the present invention is used to reduce the vanadium compound to a 3.3 to 3.7 valent vanadium compound by a reduction reaction of the vanadium compound, and may be purified water, preferably deionized water or ultra-pure distilled water, unless otherwise defined.

The preparation method of the vanadium electrolyte comprises the following steps: a first step of reacting the vanadium compound, a reducing agent, and an acid under conditions having 5 to 15 moles of a pre-solvent per 1 mole of the vanadium compound to form a reduced vanadium compound; a second step of cooling the reduced vanadium compound after the reaction is completed; a third step of adding a post-solvent after the cooling step; and a fourth step of filtering the reaction solution after the post-solvent introduction step, capable of shortening the total reaction time while securing reproducibility of the preparation process and improving the reaction efficiency to reduce impurities, at which time the electrolyte can be mass-produced by a chemical reaction process in a single reactor and not only shortening the reduction process time, maximizing the reaction efficiency, preparing an electrolyte of high yield and high quality, but also improving the battery performance of a battery including the electrolyte.

In the present invention, unless otherwise defined, the solvent used for the reduction reaction of vanadium in the first step is referred to as a "pre-solvent", and the solvent charged for adjusting the composition of vanadium obtained by the above-described reduction reaction in the third step, which is a subsequent step, is referred to as a "post-solvent".

In the first step, the vanadium compound, a reducing agent and an acid are reacted under conditions having 5 to 15 moles of a pre-solvent per 1 mole of the vanadium compound to form a reduced vanadium compound.

In the present invention, when the vanadium compound, the reducing agent, sulfuric acid and the pre-solvent are not simultaneously charged, but the reducing agent is charged after the reaction of the vanadium compound and the solvent and then the acid is charged, it is possible to prevent the formation of by-products such as hydrazine salt, thereby having an effect of preparing the high purity vanadium compound in high yield.

As an example, the pre-solvent may be deionized water, ultra-pure distilled water, or a mixture thereof.

The smaller the amount of the pre-solvent used, the more improved the reaction rate and reduced impurities are preferred.

Specifically, the smaller the amount of the pre-solvent used, the more the interaction between reactants including the vanadium compound, the reducing agent, and the reaction promoter increases, so that the reduction reaction can be performed more rapidly.

In addition, the smaller the amount of the pre-solvent used, the higher the ionic ratio of the acid compared to the vanadium compound, so that the ionization of the vanadium compound can be significantly accelerated.

In addition, the smaller the amount of the pre-solvent used, the more capable of reducing impurities such as Al, si, etc., which reduce the active surface of the electrode and interfere with hole mobility on the separator in the charge-discharge operation of the electrolyte, and therefore, the performance of the battery using the electrolyte can be maximized while controlling the speed of the manufacturing process.

In the present invention, when a 5-valent vanadium compound is used as a raw material, its reduction reaction is a 4-valent compound in which a 5-valent vanadium ion is converted into a solid phase in the form of an octahedral coordination bond based on the normal magnetism of the vanadium ion and a strong metal polarization force when at least 5 moles of moisture are present per 1 mole of vanadium compound.

When 1 mole of water is contained in the solid phase of the 4-valent compound per 1 mole of the solid phase of the 4-valent compound, the solid phase of the 4-valent compound can be converted into 1 mole of the liquid phase of the 3-valent vanadium compound, and therefore, if the solid phase of the 4-valent vanadium compound is reduced to 3.3 to 3.7-valent compound, at least 5.5 moles of the solvent are required, which is a theoretical value that does not consider the viscosity of the vanadium compound, the uniform reaction of the reducing agent, and the like, but in the actual reaction process, additional solvent is required, and therefore, when 6 moles or more (an amount of more than 5.5 moles) of the precursor solvent per 1 mole of the vanadium compound is charged, the 3.5-valent vanadium compound in the liquid phase or in the slurry form can be obtained.

When the above-described slurry-type 3.5-valent vanadium compound is used to obtain a 3.5-valent vanadium compound, even if a post-solvent described later is put into the slurry, the 4-valent vanadium and impurities thereof existing in a solid phase state cannot be removed, but remain in the 3.5-valent vanadium compound, and temporarily affect the surfaces of the electrode and the separator, so that an abnormal phenomenon such as noise occurs at the start of initial charge and discharge.

For this reason, it is preferable to use 8 mol or more or 8 to 15 mol of a pre-solvent to perform the reaction under the liquid phase condition of slurry or more, thereby achieving an optimal vanadium electrolyte preparation process.

In the present invention, the post-solvent plays a role of a combination of the above-mentioned 3.3 to 3.7-valent electrolytes which are finally prepared in the liquid phase, and the amount of the post-solvent to be added depends on the composition ratio of vanadium to sulfuric acid to be added as a raw material.

Specifically, unless otherwise defined, an electrolyte having a composition of 1.6 moles of vanadium, 4.0 moles of sulfuric acid requires 42 to 44 moles of solvent. When a mole of water is used as the pre-solvent, the post-solvent may be added only in an amount to remove the amount of the pre-solvent (a mole).

The above-described pre-and post-solvents, as shown in examples described later, achieve an optimized vanadium electrolyte preparation process by maintaining the content of the pre-solvent and the content of the post-solvent within a specific ratio range.

In the present invention, the vanadium electrolyte contains 2.0 to 5.0 valence vanadium compounds, and at least a part of the electrolyte may be 3.3 to 3.7 valence vanadium compounds.

In this case, the 3.3 to 3.7 valent vanadium compound may be reduced from a vanadium compound using an acid, a reducing agent and a solvent.

In the present invention, the vanadium compound may be a low-grade or high-grade compound.

The low-grade vanadium compound is a vanadium compound having a purity of 99% or more, specifically 99% or more and less than 99.9% and a relatively large impurity content.

The high-grade vanadium compound is a vanadium compound having a purity of 99.9% or more and a relatively small content of impurities.

According to the definition in the present invention, the low-grade vanadium compound or the high-grade vanadium compound may be used as a commercially available product, and when the low-grade vanadium compound is used, the manufacturing cost and the like are facilitated, and when the high-grade vanadium compound is used, the performance and the like are facilitated.

In addition, in the present invention, the vanadium compound used for preparing the vanadium electrolyte may be a 5-valent vanadium compound or a 4-valent vanadium compound. In this case, the 5-valent vanadium compound may be, for example, V ₂ O ₅ The 4-valent vanadium compound may be VOSO, for example ₄ ·xH ₂ O. In addition, unless otherwise defined, the 3.3 to 3.7 valent vanadium compound may be a compound derived from VOSO ₄ And V ₂ (SO ₄ ) ₃ Mixing.

The vanadium electrolyte having an oxidation number of 2.0 obtained by the reduction reaction may form a specific compound with an acid and a solvent, for example, may be a solution containing V when the solvent is water ²⁺ 、[V(H ₂ O) ₆ ] ²⁺ An ionic compound.

The vanadium electrolyte having an oxidation number of 3.0 obtained by the reduction reaction may form a specific compound with an acid and a solvent, for example, may be a solution containing V when the solvent is water ²⁺ 、[V(H ₂ O) ₆ ] ³⁺ 、[V(H ₂ O) ₅ ] ²⁺ Or [ V (OH) ₂ (H ₂ O) ₄ ] ⁺ An ionic compound.

The vanadium electrolyte having an oxidation number of 4.0 obtained by the reduction reaction may form a specific compound with an acid and a solvent, for example, may be a solution containing V when the solvent is water ²⁺ 、[V(H ₂ O) ₅ ] ²⁺ Or [ V (OH) ₂ (H ₂ O) ₄ ] ⁺ An ionic compound.

The vanadium electrolyte having an oxidation number of 5.0 obtained by the reduction reaction may form a specific compound with an acid and a solvent, for example, may be a solution containing VO when the solvent is water ²⁺ 、[VO ₂ (H ₂ O) ₄ ] ⁺ An ionic compound.

The vanadium electrolyte having an oxidation number of more than 3.0 and less than 4.0 obtained by the reduction reaction may be formed by mixing a vanadium compound having an oxidation number of 3.0 and a vanadium compound having an oxidation number of 4.0, for example, may be VO when the solvent is water ²⁺ 、[VO(H ₂ O) ₅ ] ²⁺ Or [ VO (OH) (H ₂ O) ₄ ] ⁺ Ions and VO ²⁺ 、[VO ₂ (H ₂ O) ₄ ] ⁺ And (3) a compound formed by mixing ions.

Specifically, when the acid is sulfuric acid and the solvent is water, the oxidation number of the resulting VOSO in the vanadium electrolyte having a valence of 3.3 is obtained by the reduction reaction ₄ And V is equal to ₂ (SO ₄ ) ₃ The molar ratio of (C) can be 6:6-9 or 6:6-8, and the oxidation number is 3.5 VOSO in the vanadium electrolyte ₄ And V is equal to ₂ (SO ₄ ) ₃ The ratio can be 2:0.5-1.5 mole ratio or 2:0.8-1.2 mole ratio, and the oxidation number is 3.7 VOSO in the vanadium electrolyte ₄ And V is equal to ₂ (SO ₄ ) ₃ The ratio may be a molar ratio of 14:1 to 5 or a molar ratio of 14:2 to 4.

In particular, when the acid is sulfuric acid and the solvent is water, VOSO in the vanadium electrolyte having an oxidation number of 3.3 obtained by the reduction reaction ₄ And V is equal to ₂ (SO ₄ ) ₃ May be about 6:7, and the oxidation number is 3.5 ₄ And V is equal to ₂ (SO ₄ ) ₃ May be about 2:1, and the oxidation number is 3.7 ₄ And V is equal to ₂ (SO ₄ ) ₃ May be about 14:3. In the present invention, unless otherwise defined, the term "about" means a value including an error range of ±0.5 on the basis of a reference value.

The reducing agent may be one or more hydrazine compounds selected from anhydrous hydrazine, a hydrate thereof, and a salt thereof.

The reducing agent may contain 15 to 35 parts by weight of a hydrazine compound based on 100 parts by weight of the vanadium compound. For example, when reducing vanadium at 5 to vanadium at 4, 16 parts by weight or more of a hydrazine compound is required based on 100 parts by weight of vanadium, and when reducing vanadium at 5 to vanadium at 3.5, 24 parts by weight or more of a hydrazine compound is required. Within this range, the reaction time can be shortened, the reaction efficiency is excellent, and not only a high-purity high-quality vanadium electrolyte can be prepared, but also the discharge capacity of a battery including the electrolyte can be improved.

Deionized water or ultrapure distilled water may be used as the pre-solvent and the post-solvent, and 5 to 15 moles of the pre-solvent may be charged per 1 mole of the vanadium compound, and as a specific example, 8 to 15 moles of the pre-solvent may be charged.

For example, when the electrolyte has a composition of 1.6 moles of vanadium, 4.0 moles of sulfuric acid, and 43 moles of water, 10 to 24 moles of the front solvent, preferably 13 to 24 moles of the front solvent, and 19 to 33 moles of the rear solvent, preferably 19 to 30 moles of the rear solvent may be charged. In this range, the reaction time can be shortened, the reaction efficiency is excellent, and impurities can be reduced, so that not only a high-purity high-quality vanadium electrolyte can be prepared, but also the discharge capacity of a battery including the electrolyte can be improved.

The mixing order of the reactants may be varied, and the method of adding the solvent, the vanadium compound, the hydrazine compound and the acid to the reactor in this order is most preferable under the operation of the stirrer. In this process, the solvent before the addition may be divided into a predetermined amount. For example, a part of the solvent in the pre-solvent may be mixed with the hydrazine compound to be diluted and then introduced, or a method may be employed in which the solvent is introduced after the solvent and the vanadium compound are introduced so as to flush the vanadium compound attached to the inlet into the reactor.

In addition, when a small amount of solvent is present inside the reactor before the vanadium compound is charged, it is advantageous to disperse the vanadium compound. This is because isolation of the vanadium compound is likely to occur between the bottom of the reactor and the vanadium compound-solvent interface when the solvent is charged after the vanadium compound is charged, and the isolated and condensed vanadium compound may cause unnecessary load on a stirring system such as a stirring screw or a motor.

For reference, the least preferable mixing method is a method of directly mixing the vanadium compound with the hydrazine compound. When an acid is added in the second step after mixing a vanadium compound with a hydrazine compound and adding a solvent to prepare an electrolyte, a part of the raw material is not dissolved by the acid but precipitated. In addition, when mixed without using a solvent, smoke is generated and heat is released under severe reaction, and the vanadium compound is blackened. Based on this phenomenon, it was determined that the transient heat of reaction decomposed a part of the hydrazine compound, and the reduction function was not achieved after the acid was charged, thereby causing precipitation of the vanadium compound.

The hydrazine compound may be a hydrate or a salt, and when a hydrazine hydrate, may be a hydrazine monohydrate, and the hydrazine salt may be a hydrazine sulfate.

Preferably, the hydrazine compound may be added in the form of a hydrate or an aqueous solution, and as a preferred example, the total amount of water required for preparing the electrolyte should be the same, for example, by diluting with 200 to 500 parts by weight of water, based on 100 parts by weight of the hydrazine compound, to at least 95 parts by weight of water. When the hydrazine compound in the form of a hydrate is used in an appropriate ratio as described above, the reaction rate can be controlled to be relatively slow, and the process can be performed more stably, and therefore, the reaction efficiency is excellent and there is an advantage that a high-purity and high-quality vanadium electrolyte can be prepared.

In the mixing of the reactants, the acid needs to be fed from the time of feeding the acid, and the flow rate needs to be taken into consideration. The size of the reactor and the exotherm of the mixed reaction solution, which is determined by the content of the reactants, should be taken into account when determining the input flow of acid.

For example, when 1L of an electrolyte having a composition of 1.6 mol of vanadium and 4.0 mol of sulfuric acid is prepared in a 2L flask, the acid input flow rate may be 200 to 300mL/h, preferably 220 to 260mL/h, and more preferably 230 to 250mL/h.

Specifically, the increase in the severe heat release caused by the addition of the acid is stopped until the time when the same number of moles of acid as the number of moles of vanadium is added, and then, when a phenomenon in which the temperature is gradually increased or decreased occurs, it is preferable to further increase the addition flow rate of the acid or to keep the temperature around the reaction target temperature by a heating device.

The acid is preferably slowly fed in order to avoid splashing of the reaction solution to the walls of the container as much as possible and it is important that the water in the electrolyte is prevented from being lost due to the exothermic temperature during the feeding of the acid, and therefore, a thermal regulating means such as a cooling means or a heater (heat exchanger) may be used, preferably, as little as 120 c is exceeded.

The acid may be appropriately adjusted in the range of dissolving at least the vanadium compound according to the kind of the vanadium compound and the purpose of the electrolyte.

The acid may be one or more selected from sulfuric acid, hydrochloric acid, nitric acid, and acetic acid.

As an example, the sulfuric acid may be contained in an amount of 1000 parts by weight or less based on 100 parts by weight of the vanadium compound, and as a specific example, the sulfuric acid may be contained in an amount of 100 to 400 parts by weight.

The above-described order of addition (solvent→vanadium compound→hydrazine compound→sulfuric acid) has two advantages over the order of addition (solvent→vanadium compound→sulfuric acid→hydrazine compound) in the comparative example. First, the reaction time is short, and second, the reducing efficiency of the reducing agent is high.

For example, when 1L of an electrolyte having a composition of 1.6 mol of vanadium and 4.0 mol of sulfuric acid is prepared in a 2L flask, the temperature is raised from 26 ℃ to 81 ℃ when sulfuric acid is added for 50 to 70 minutes, specifically 55 to 65 minutes, before adding a hydrazine compound to a mixed solution of a solvent and a vanadium compound. Then, when the hydrazine compound aqueous solution was added at 240 to 260mL/hr, it took about 30 minutes to confirm that the final temperature was 105 ℃.

When the hydrazine compound is added after this, if no additional cooling process is performed, the reaction is performed at a high temperature where sulfuric acid is added and the flow rate has to be adjusted because the hydrazine compound can instantaneously reduce 5-valent ions to 4-valent ions even at normal temperature and a severe reaction is caused under a relatively high temperature condition.

When the hydrazine compound is added first and then sulfuric acid is added, the reduction of the hydrazine monohydrate starts from a lower temperature, and therefore, the side effects caused by the temperature rise are relatively small, whereby the total process time can be shortened. That is, when the order of the charging is followed in the present invention, the component that needs to be adjusted in flow rate is one component of sulfuric acid, and when the order of the charging is changed, the component that needs to be adjusted in flow rate is two components of sulfuric acid and a hydrazine compound, and therefore, there are difficulties in terms of process time and handling.

In addition, hydrazine compounds decompose to NH when the temperature reaches 180 ℃ or higher ₃ +NH, which decomposes to N when the temperature reaches 350 ℃ or higher ₂ +2H ₂ When the hydrazine compound is charged at a relatively high temperature, the heat generated locally increases the possibility that the hydrazine is decomposed without being reduced. Since a part of hydrazine is consumed without participating in the reduction reaction, the amount of hydrazine can be adjusted to 3.5 price only by about 4 to 7% more than the amount of hydrazine in the experiment, unlike the actual amount. In contrast, when the hydrazine compound is added first and then sulfuric acid is added, the possibility of occurrence of the above-mentioned side reaction is low, and the cost can be adjusted to 3.5 price by adding about 3% or less in the experiment, which is economical.

In the first step, the reaction can be promoted by further using a catalyst or an additive. In this case, the catalyst which can be used is, for example, pt, ru, pd, etc., and the additive is, for example, mo, moO ₃ 、(MoO ₂ )SO ₄ Etc. The catalyst can be recovered and reused.

In the first step, a gaseous by-product (N ₂ ) To the outside of the container, for gasified H ₂ O and H ₂ SO ₄ Condensation is performed so as to remain in the reactor and maintain a high temperature, so that the reaction efficiency can be maximized and the composition change in the reactor can be prevented.

That is, the reaction in the first step is performed in a reflux manner within the reaction temperature range, whereby the reaction participation of the reactants can be improved, and the productivity can be further improved.

In the present invention, the reflux is not particularly limited as long as it is a reflux process which is conventional in the art to which the present invention pertains, and as a specific example, a cooler or condenser is connected to an upper inlet/outlet of the reactor, the solvent evaporated during the reaction is condensed, and the condensed solvent is recycled to the reactor to continuously perform the reaction.

Unless there is a special pressure means in the reactor, the reaction of the first step may be carried out, for example, at 70 to 120 ℃, preferably at 80 to 120 ℃, more preferably at 90 to 120 ℃, still more preferably at 100 to 110 ℃, at which time the reaction participation rate of the reactants can be further improved, and there is an advantage that the reaction can be produced in a shorter time to improve productivity.

The reaction in the first step may be carried out for, for example, 13 hours or less, preferably 1 to 13 hours, more preferably 2 to 8 hours, and when the amount of the solvent is a larger number of moles which is 6 times larger than the number of moles of vanadium and is closer to 6 times, the shorter the reaction time, the more excellent the impurity removing effect. However, 6 times is only a theoretical value, and when the amount of the current solvent is about 6 times in practice, it may be difficult to prepare an electrolyte due to slurrying, solidifing, etc. of the reactants, and this varies depending on the characteristics of the vanadium raw material.

Therefore, the number of moles of the pre-solvent to be charged is preferably 8.0 times or more the number of moles of vanadium.

In addition, when the front solvent is more than 15 times the mole number of vanadium, there is no advantage in that the solvent is fed in stages through two steps of the before-feed solvent and the after-feed solvent, and therefore, when the front solvent having 8 to 15 times the mole number of vanadium is used, the reaction participation rate of the reactants can be further improved, and there is an advantage in that it is prepared in a shorter time to improve productivity.

The reaction is preferably carried out under a non-reactive atmosphere such as nitrogen.

The reaction may be carried out under atmospheric pressure, or may be carried out under pressure or reduced pressure as required within the range satisfying the above-mentioned reaction conditions.

The weight of the solvent may be 20 to 80% by weight, preferably 30 to 70% by weight, among the vanadium compound, the reducing agent, sulfuric acid and the solvent in total of 100% by weight, and at this time, the concentration of the reaction tank is high, the reaction efficiency is excellent, and there is an advantage that the purity is further improved.

In the second step, the reduced vanadium compound formed in the first step is cooled.

The reaction of the second step may be carried out, for example, under natural cooling conditions, preferably using a temperature adjustment device to cool more rapidly than natural cooling. The cooling temperature change and the time required for cooling may vary depending on the scale of the reaction, the temperature at the end of the reaction, the ambient temperature, and the scale of the temperature adjusting means, but are preferably carried out under stirring.

As an example, if the reaction is completed at 110 ℃ in the first step by using a 2L flask at normal temperature with 1L of the target electrolyte having a composition of 1.6 mol of vanadium, 4.0 mol of sulfuric acid, and 20M of the pre-solvent, the natural cooling reaction in the second step may be performed for 4 to 7 hours. In this case, when a temperature adjusting device for cooling is added, the cooling time can be shortened according to the cooling scale, and therefore, there is an advantage that the production yield is further improved when a cooling device of an appropriate scale is used.

In the third step, a post-solvent is added to the electrolyte solution obtained in the second step and filtered. When the post-solvent is mixed in such a manner that natural cooling is performed or the post-solvent is kept at normal temperature by suppressing the heat generated when the post-solvent is put into the apparatus using an adjusting means such as a cooler, a phenomenon that a part of filterable impurities is dissolved in the electrolyte can be further suppressed by the filtering means.

The filtration may be a gravity filtration method using only gravity, or may be a pressure filtration method in which an upstream layer of the filtration unit is pressurized and operated, or a pressure reduction filtration method in which a downstream layer of the filtration unit is depressurized and operated. In addition, as the filtration, a filtration unit having an acid resistance and a hydrophilic material having a pore diameter of 0.2 to 10 μm can be used, and in particular, when the pore diameter is smaller than 0.2 μm, the process time or the pressure load increases, and when the pore diameter is larger than 10 μm, the competitive power is lowered as compared with the quality, and the filtration effect is not remarkable.

The content of impurities remaining in the vanadium electrolyte may be 30ppm or less. Wherein, the components contained in the residual impurities can represent Si and Al. The content of the remaining impurities is preferably 20ppm or less, whereby it is possible to prevent unnecessary impurities from remaining in the vanadium electrolyte and causing degradation of the battery performance.

The invention provides a vanadium electrolyte prepared by the preparation method of the vanadium electrolyte.

The vanadium electrolyte comprises 2.0 to 5.0 vanadium compounds, and at least a portion of the electrolyte may comprise 3.3 to 3.7 vanadium compounds.

At 100mA/cm ² The vanadium electrolyte prepared by the preparation method of the present invention was evaluated during the first 30 cycles (cycle) of the current density, the discharge cut-off voltage of 0.8V, the charge cut-off voltage of 1.6V, and the flow rate of 160 mL/min.

In the present invention, the charge capacity means a state where charge is accumulated up to the charge cutoff voltage, the discharge capacity means a state where charge is emptied up to the discharge cutoff voltage, and the energy efficiency means a ratio of the charge capacity to the discharge capacity, and the above three variables can be used as an index for judging the life and performance of the electrolyte.

The vanadium electrolyte is not particularly limited as long as it is a compound capable of providing vanadium ions for use in an all-vanadium redox flow battery, and an aqueous all-vanadium redox flow electrolyte and a non-aqueous all-vanadium redox flow electrolyte such as vanadium acetylacetonate may be used.

As an example, in the above-described method for producing a vanadium electrolyte, when cooling is performed before filtering the produced vanadium electrolyte and the cooling conditions and filtering conditions are adjusted, an optimized process for improving the reaction rate and minimizing impurities is provided.

Specifically, in the first step described above, 5 to 15 moles of water per 1 mole of the vanadium compound may be used, and after the reaction is performed at 100 ℃ or higher to produce the vanadium compound, an excess amount of water exceeding the previously charged water may be charged, and after the reduced vanadium compound is cooled to-25 to 20 ℃, the reaction solution may be subjected to cyclic filtration at-25 to 40 ℃ to reduce the reaction rate of the reduction reaction.

In the first step, after the reaction is performed at 100 ℃ or higher to produce a vanadium compound using 5 to 15 moles of water per 1 mole of the vanadium compound, the reduced vanadium compound may be cooled to-25 to 20 ℃, excess water exceeding the content of the previously charged water may be charged, and the reaction solution may be subjected to cyclic filtration at-25 to 40 ℃ to reduce the reaction rate of the reduction reaction.

The weight of the solvent among the vanadium compound, the reducing agent, sulfuric acid and the solvent may be 20 to 80 wt%, preferably 30 to 70 wt% in total 100 wt%, and at this time, the concentration of the reaction tank is high, the reaction efficiency is excellent, and there is an advantage that the purity is further improved.

Specifically, unless there is a special pressure means in the reactor, the reaction of the first step may be performed, for example, at 70 to 120 ℃ (equal to or lower than the first temperature), preferably at 80 to 120 ℃, more preferably at 90 to 120 ℃, still more preferably at 100 to 110 ℃, at which time the reaction participation rate of the reactants can be further improved, and there is an advantage that the preparation can be performed in a shorter time to improve productivity.

The reaction may be carried out for, for example, 13 hours or less, preferably 1 to 13 hours, more preferably 2 to 8 hours, and when the amount of the solvent is a larger number of moles larger than 6 times the number of moles of vanadium and is closer to 6 times, the effect of removing impurities is more excellent as the reaction time is shorter. However, 6 times is only a theoretical value, and when the amount of the current solvent is about 6 times in practice, it may be difficult to prepare an electrolyte due to slurrying, solidifing, etc. of the reactants, and this varies depending on the characteristics of the vanadium raw material. Therefore, the pre-solvent is preferably added in a molar amount of 8.0 times or more the molar amount of vanadium.

In addition, when the front solvent is more than 15 times the mole number of vanadium, there is no advantage in that the solvent is fed in stages through two steps of the before-feed solvent and the after-feed solvent, and therefore, when the front solvent in the mole number range of 8 to 15 times the mole number of vanadium is used, the reaction participation rate of the reactants can be further improved, and there is an advantage in that it is prepared in a shorter time to improve productivity.

Thereafter, the reduced vanadium compound formed in the first step is cooled to a temperature at least 80 ℃ lower than the first temperature.

The cooling reaction may be carried out, for example, under natural cooling conditions, preferably using a temperature adjustment device to cool more rapidly than natural cooling. The cooling temperature change and the time required for cooling may vary depending on the scale of the reaction, the temperature at the end of the reaction, the ambient temperature, and the scale of the temperature adjusting means, but are preferably carried out under stirring.

As an example, when the reaction is ended at 110 ℃ in 1L of the target electrolyte having a composition of 1.6 mol of vanadium, 4.0 mol of sulfuric acid, 20M of the pre-solvent in a 2L flask at normal temperature in the first step described above, the cooling reaction (corresponding to the second temperature) may be performed at-25 to 20 ℃ for 4 to 7 hours. At this time, when a temperature adjusting device for cooling is added, the cooling time can be shortened according to the cooling scale, and therefore, there is an advantage that the production yield is further improved when a cooling device of an appropriate scale is used.

The second temperature corresponds to a lower temperature node (precipitation temperature) at which the vanadium electrolyte does not precipitate within 48 hours, and it is confirmed that although the vanadium electrolyte does not precipitate, impurities precipitate with a decrease in temperature, and the present invention has been completed, and the second temperature is preferably-25 to 20 ℃, more preferably-10 to 10 ℃, even more preferably-5 to 5 ℃, and is most preferably in the vicinity of 0 ℃ to reduce the impurities compared to the cooling temperature.

The resulting cooled electrolyte is then filtered at a third temperature at least 40 ℃ lower than the first temperature.

The third temperature is preferably-25 to 40 ℃, more preferably-10 to 30 ℃, still more preferably-5 to 30 ℃, and the vicinity of 0 ℃ is most preferable for reducing impurities as compared with the cooling temperature.

In the present invention, filtration may be performed either with or without recycling.

As an example, when the circulation is not performed, the third temperature is the same as the second temperature, preferably-25 to 20 ℃, more preferably-10 to 10 ℃, still more preferably-5 to 5 ℃, and most preferably around 0 ℃ to reduce impurities.

However, in the case of performing the cyclic filtration, the third temperature is preferably slightly higher than that in the case of not performing the cyclic filtration in view of the reaction efficiency, and as an example, it is preferably 20 to 40 ℃, more preferably 25 to 35 ℃, still more preferably 25 to 30 ℃ similar to the second temperature described above, and most preferably for reducing impurities.

The post-solvent may be introduced between the first step and the second step or between the second step and the third step. A small amount of heat is generated during the addition of the post-solvent, and when the post-solvent is mixed in such a manner that natural cooling is performed or the heat generated during the addition of the post-solvent is suppressed by using an adjusting means such as a cooler to maintain the third temperature, a phenomenon in which a part of filterable impurities is dissolved in the electrolyte can be further suppressed by using a filtering means.

The content of impurities remaining in the vanadium electrolyte may be 30ppm or less. Wherein the component contained in the residual impurity may represent Si, al, ca, fe. The content of the remaining impurities is preferably 20ppm or less, whereby it is possible to prevent unnecessary impurities from remaining in the vanadium electrolyte and causing degradation of the battery performance.

As shown in examples described later, it was confirmed that when the cyclic filtration was performed and the post-addition solvent was added after the second temperature was used at-25 to 20℃and the third temperature was used at 20 to 40℃in total, al was 4.6ppm, ca was 8.2ppm, fe was 3.3ppm, si was 4.0ppm, and the total was 20ppm or less.

Further, it was confirmed that when the post-solvent was fed in such a manner as to perform the cyclic filtration and the-25 to 20 ℃ was used as the second temperature and then the-25 to 20 ℃ was used as the third temperature, al was 2.1ppm, ca was 7.4ppm, fe was 2.5ppm, si was 2.2ppm and 15ppm or less in total, and that, in particular, al and Si were significantly reduced.

On the other hand, it was confirmed that when the post-solvent was fed in a non-circulating manner and 20 to 40℃was used as the third temperature after-25 to 20℃was used as the second temperature, al was 4.5ppm, ca was 9.9ppm, fe was 8.8ppm, si was 4.1ppm, and the total was more than 20ppm.

Further, it was confirmed that when the circulation was not performed and the post-addition solvent was added after the second temperature of-25 to 20℃was used and then the third temperature of-25 to 20℃was used, al was 2.3ppm, ca was 7.4ppm, fe was 6.2ppm, si was 2.4ppm and less than 20ppm in total, and it was confirmed that especially Al and Si were reduced.

Further, it was confirmed that when the second temperature of-25 to 20℃and the third temperature of-25 to 20℃were used after the addition of the post-solvent without recycling, al was 2.2ppm, ca was 7.3ppm, fe was 7.3ppm, si was 1.8ppm and less than 20ppm in total, and it was confirmed that especially Al and Si were reduced.

In the present invention, as an example, the circulation filtration may include an electrolyte discharge pipe connected to an electrolyte discharge port of the vanadium electrolyte preparation apparatus and a circulation pipe selectively extending from one side of the discharge pipe and connected to an upper portion of the reaction tank, and a filtration apparatus may be provided at the electrolyte discharge pipe or the circulation pipe, in which case a filtration step is naturally inserted in a single process, thereby having an advantage of being able to prepare a high-purity and high-quality electrolyte without greatly extending a process time.

In the present invention, as an example, the vanadium electrolyte preparation apparatus includes: a single reaction tank; a raw material inlet for inputting a reaction raw material into the single reaction tank; an electrolyte discharge port for discharging the prepared vanadium electrolyte; a stirrer for stirring the input reaction raw materials; an open reflux condenser connected to an upper portion of the single reaction tank for cooling water gasified in the reaction to recover and discharge nitrogen gas; and a temperature adjusting means for adjusting the reaction temperature, at this time, the manufacturing cost is low and the process is simple, the facility investment cost is low and the maintenance and the management are easy, the mass production can be performed by the catalyst-free chemical reaction process, and the predetermined reaction conditions can be applied, thereby achieving the effects of shortening the reaction time, maximizing the reaction efficiency, and preparing the high-quality electrolyte.

Preferably, the reaction tank is coated with at least one selected from the group consisting of glass, PE and polytetrafluoroethylene resin, more preferably with at least one selected from the group consisting of PE and polytetrafluoroethylene resin, and most preferably with polytetrafluoroethylene resin, and at this time, there is an advantage in that the maintenance and management of the reactor are easy and the reaction efficiency is excellent.

More preferably, the vanadium electrolyte preparation apparatus may be provided with a filtering apparatus at the electrolyte discharge pipe, and even more preferably, a filtering apparatus may be provided at both the electrolyte discharge pipe and the circulation pipe configured as needed, in which case a filtering step is naturally inserted in a single process, thereby having an advantage of being able to prepare high-purity and high-quality electrolyte without greatly extending a process time.

Preferably, the number of the filtering means provided in the circulation pipe may be one or more, more preferably one or two, and still more preferably one, within which the filtering step is naturally inserted in a single process, thereby having an advantage of being able to prepare a high purity and high quality electrolyte without greatly extending the process time.

Preferably, the filtering means provided in the discharge pipe may be one or more, more preferably one to three, and still more preferably one or two, within which a filtering step is naturally inserted in a single process, thereby having an advantage of being able to prepare a high purity and high quality electrolyte without greatly extending a process time.

Preferably, the total number of the filtering devices provided to the vanadium electrolyte preparation apparatus may be two or more, more preferably two or three, and still more preferably two, within which a filtering step is naturally inserted in a single process, thereby having an advantage of being able to prepare a high-purity and high-quality electrolyte without greatly extending a process time.

The temperature adjusting device is preferably a heat exchanger, more preferably a jacket (jacket) heat exchanger, in which case the reaction temperature is easily adjusted, and thus, the reaction efficiency is excellent and there is an advantage in that a high-purity high-quality vanadium electrolyte is prepared.

In the present invention, the jacket type heat exchanger (jack) is not particularly limited as long as it is a jacket type heat exchanger conventionally used in the art to which the present invention pertains, and may be, for example, a jacket that surrounds a reaction tank and includes a heat transfer medium.

In the present invention, the structure of the apparatus for preparing an electrolyte by cyclic filtration and the process flow chart are shown in fig. 16. Referring to fig. 16, hydrazine monohydrate (N) is charged into a single reaction tank through a raw material charging port ₂ H ₄ ·H ₂ O), vanadium compound (V) ₂ O ₅ ) Sulfuric acid (H) ₂ SO ₄ ) And deionized water (DIW), stirring the charged reaction raw materials by a stirrer and starting the reduction reaction of the first step. When the reduction reaction of the first step is completed, the reactant is passed through a circulation pipe provided with a Filtration unit (Filtration) to remove impurities, and then heated by a jacket type heat exchanger (heater) surrounding the reaction tank to perform the reduction reaction of the second step. Steam, nitrogen (N) generated in the reduction reaction ₂ ) The water vapor in (a) was cooled by an open reflux condenser and recovered into the reactor, nitrogen (N) ₂ ) Then discharged to the outside through the open reflux condenser. When the reduction reaction of the second step is completed, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Thus, unlike available vanadium electrolyte preparing apparatus and process, the present invention can prepare 3.5-valent electrolyte with only one reactor, and is favorable to technological equipment, maintenance and management.

The following preferred embodiments are set forth to aid in understanding the present invention, and are merely illustrative of the present invention, and those skilled in the art can make various changes and modifications within the scope and spirit of the present invention, and these changes and modifications fall within the scope of the appended claims.

Examples (example)

First embodiment

In the following, in the composition of the vanadium electrolyte described as the first example, the vanadium compound was 1.6 mol, sulfuric acid was 4.0 mol, and the ionic valence of the vanadium electrolyte was 3.5, which is a vanadium electrolyte in which 4 valence vanadium ions and 3 valence vanadium ions were mixed at a molar ratio of 1:1.

The materials required for preparing the electrolyte of the first embodiment are as follows.

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

Among them, hydrazine monohydrate having a molar number corresponding to the value obtained by multiplying the molar number of vanadium by 0.375 is required, and about 0.6M based on 1.6 mol of the vanadium compound is required. The hydrazine adopts a hydrazine monohydrate aqueous solution containing 80 weight percent, and the oxidation-reduction additive is molybdenum trioxide.

In the present invention, M represents the number of moles (mol/L) of solute dissolved in 1L of solution. In the present invention,% is expressed as% by weight unless otherwise defined.

Referring to fig. 12, the apparatus required for preparing the electrolyte of the first embodiment is as follows.

The reaction vessel is composed of a reaction tank (hereinafter, referred to as "reactor") capable of carrying out a reaction of 1L or more, a stirrer, a heater capable of adjusting a temperature, a thermometer, a filtration system (pump, pipe, filter, etc.), and a surface in contact with the electrolyte in the apparatus should be a material having acid resistance and chemical resistance such as glass, PTFE, PE, polytetrafluoroethylene (Teflon), etc.

The vanadium compound (V) is introduced into the reaction tank through a raw material inlet ₂ O ₅ ) Sulfuric acid (H) ₂ SO ₄ ) Deionized water (DIW) and hydrazine monohydrate (N) ₂ H ₄ ·H ₂ O) the charged reaction raw materials are stirred by a stirrer and the reduction reaction of the first step is started.

When the reduction reaction of the first step is completed, the reactant is passed through a circulation pipe provided with a Filtration unit (Filtration) to remove impurities, and then molybdenum trioxide (MoO) is introduced into the reactor ₃ ) And then heating the reactant by using a jacketed heat exchanger (heater) wrapping the reaction tank so as to carry out the reduction reaction of the step two.

The water vapor generated in the reduction reaction and the water vapor in the nitrogen gas are cooled and recovered in the reactor, and the nitrogen gas is discharged to the outside. When the reduction reaction of the second step is completed, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Hereinafter, the electrolyte preparation step of example 1 is divided into different steps to be described in detail.

< example 1: three-step preparation Process experiment ]

Step one: the step of adding vanadium raw material and nitrogen reducing agent

In the first step, the flow rate of the raw materials is not emphasized, but the order of the raw materials to be fed needs to be considered.

The most preferable order of charging the raw materials is a method of charging water, vanadium and hydrazine monohydrate into the reaction tank (reactor) in this order under the operation of a stirrer. In this process, water may be added in portions in a prescribed amount. For example, a method of mixing a part of water with hydrazine monohydrate to dilute and charge it, or a method of introducing water to flush it into a reactor after charging water and a vanadium compound in order to treat the vanadium compound adhering to the inside of a raw material charging port, may be employed. When water is present in the reactor prior to the addition of the vanadium compound, it is advantageous to disperse the vanadium compound in the reactor. When water is added after the addition of the vanadium compound, isolation of the vanadium compound tends to occur between the bottom of the reactor and the vanadium compound-water interface, and the isolated and aggregated vanadium compound tends to generate unnecessary load.

In step one, the least preferred method of mixing is a method of directly mixing the vanadium compound with the hydrazine monohydrate. When sulfuric acid is added in the step two described later to prepare an electrolyte after mixing the vanadium compound with hydrazine monohydrate and adding water, a part of the vanadium compound as a raw material is not dissolved by sulfuric acid but precipitated. When the two raw materials are mixed without using water, smoke is generated and heat is released under severe reaction, and the vanadium compound is blackened.

Based on this phenomenon, it is inferred that the transient heat of reaction decomposes a part of the hydrazine compound, and the reduction function cannot be achieved after sulfuric acid is charged, thereby causing precipitation of the vanadium compound. In this step, 25.2g of hydrazine monohydrate was charged first, in total of 38.0 g. During this charging, the temperature in the reactor may rise to a small extent within 10 ℃.

Step two: sulfuric acid feeding step

In the second step, the flow rate of sulfuric acid to be charged may be determined in consideration of the heat released from the reaction solution mixed in the first step. The sulfuric acid is preferably slowly fed in order to avoid as much as possible that the reaction solution splashes onto the walls of the vessel, in which case the exothermic temperature preferably does not exceed 110 ℃. In this process, a gas discharge and trapping device such as an open reflux condenser is required, and a cooling device or a heating device such as a heater (heat exchanger) may be further required.

FIG. 1 shows a graph of temperature as a function of time for a reduction reaction using a reducing agent at a sulfuric acid flow rate of 240mL/hr or 480 mL/hr.

Referring to FIG. 1, in the first half of the sulfuric acid injection, the temperature rise shows a steep slope, and at about 25 minutes at a flow rate of 240mL/hr, the temperature drop occurs at about 13 minutes at a flow rate of 480 mL/hr. In the first half, the main reason for the temperature rise is that heat is generated during the reduction of the reduced 5-valent vanadium ion by hydrazine monohydrate to 4-valent ion while 1.6M vanadium is dissolved in 1.6M (about 100 mL) sulfuric acid and reduced to 5-valent vanadium ion. Conversely, after a particular time, the temperature was slightly decreased at 240mL/hr and maintained at 480 mL/hr. Therefore, the size of the reactor, the amount and composition of the reactants, and the reaction site are preferably taken into consideration when adjusting the flow rate of sulfuric acid.

In this embodiment, the first half may be set to 200 to 300mL/h, preferably 220 to 260mL/h, more preferably 235 to 245mL/h, and the second half may be set to 430 to 530mL/h, preferably 460 to 500mL/h, more preferably 475 to 485mL/h, to perform the redox reaction. The flow rate in this embodiment is a range of values for achieving experimental conditions such as the equipment of this embodiment, and it is most preferable to control the flow rates in two sections at the target temperature.

The process of step one-step two (water→vanadium compound→hydrazine monohydrate→sulfuric acid, hereinafter referred to as "flow rate example") of the experiment performed in this example has two advantages compared with the method of feeding in the order of water→vanadium compound→sulfuric acid→hydrazine monohydrate (hereinafter referred to as "flow rate comparative example").

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

When sulfuric acid is added to the water+vanadium compound at a rate of 240mL/hr for 50 to 70 minutes, specifically 60 minutes, before the hydrazine monohydrate as in the flow rate comparative example, the temperature is increased from 26℃to 81 ℃. Next, when 25.2g of hydrazine monohydrate was diluted with 100g of water and fed at an inflow rate of 250mL/hr, a time of about 30 minutes was required, and the final temperature was shown to be 105 ℃. Among them, it is preferable to mix 20 to 30 parts by weight of hydrazine monohydrate in 100 parts by weight of water.

Hydrazine has a reducing ability to instantaneously reduce 5-valent ions to 4-valent ions even at normal temperature, and is unsuitable for controlling a process even if it is diluted in water and then added thereto at high temperature, considering that the boiling point of hydrazine is 114 ℃. Furthermore, the possibility of hydrazine loss is increased, and therefore, it is difficult to provide a positive effect on quality influence. For reference, when it is necessary to perform the injection at a high temperature, a method of mixing and diluting the hydrazine raw material by controlling the flow rate as in the flow rate comparative example may be used.

On the other hand, when hydrazine monohydrate is charged first and sulfuric acid is then charged, since reduction of hydrazine starts from a lower temperature, side effects caused by a temperature rise are relatively small, and thus the total process time can be shortened. That is, when the order of the flow rate of the raw materials is followed, the flow rate-adjusted raw material is one of sulfuric acid, and when the order of the flow rate of the raw materials is followed, the flow rate-adjusted raw material is two raw materials, and therefore, there are difficulties in terms of process time and handling.

In addition to hydrazine having a boiling point of 114 ℃, hydrazine decomposes to NH when the temperature reaches 180 ℃ or higher ₃ +NH, when the temperature reaches above 350 ℃, it is decomposed into N ₂ +2H ₂ When hydrazine monohydrate is put into the reactor at a high temperature, the heat generated locally increases the possibility that hydrazine is decomposed without functioning as a reducing agent. Theoretically, if there is no loss, the reaction can be performed normally even in the gas phase of 114 ℃ or higher, but in the actual process, there is a high possibility of loss. Because of such side reactions and losses, in the experiment, the flow rate of the comparative example was adjusted to 3.5 price only by adding about 4 to 7% more than the metering ratio. In the flow rate example, only about 0 to 3% of the content is consumed, so that the flow rate is extremely advantageous in terms of problems such as loss and side reaction as compared with the flow rate comparative example.

The end time in the second step may be the time when the sulfuric acid is charged, or may be stirring at 110 ℃ or lower for 2 hours or less.

In the second step, the gas by-product (N ₂ ) To the outside of the container, for gasified H ₂ O and H ₂ SO ₄ Condensation is performed so as to remain in the reactor and a high temperature (around 110 c) is maintained, so that the reaction efficiency can be maximized and the composition change in the reactor can be prevented.

Step three: 3.5 preparation step of the electrolyte

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

Next, the remaining 12.8g of hydrazine monohydrate was charged into the reactor. Hydrazine monohydrate can be added even if the temperature of the reactor does not reach 110 ℃, but when hydrazine monohydrate is added to the 4-valent electrolyte at 80 ℃ or lower, particularly at 60 ℃ or lower, sulfuric acid-hydrazine salt is formed, thereby reducing the reducing function of hydrazine.

In step three, the gas by-product (N ₂ ) Is discharged outside the container to gasify H ₂ O and H ₂ SO ₄ Condensation is performed so as to remain in the reactor and a high temperature (around 110 c) is maintained, so that the reaction efficiency can be maximized and the composition change in the reactor can be prevented. The time required for the process of step three is within 12 hours.

The division of example 1 into three steps is made for illustration only and is a single process carried out in the same reactor as a whole. Although the redox additive is added in the third step in this example, it may be added together with vanadium in the first step in which hydrazine is added before sulfuric acid is added.

FIG. 1 shows the influence of the flow of the redox additive and sulfuric acid together, with no significant difference in the presence or absence of the redox additive at a flow rate of 240 mL/hr. This means that hydrazine has a very strong reducing power for 5-valent vanadium, and therefore, the redox additive does not function as a catalyst and has no significant influence even if it does. The redox additive may be added in the third step, but is not limited thereto, and may be added in the first or second step.

< examples 2 to 5: experiment for changing the content of Redox additive ]

Except that 0.15g (V in 100 parts by weight) of the catalyst used in the example 1 ₂ O ₅ For the reference, 0.1 part by weight) of molybdenum trioxide was changed to 0.30g (0.2 part by weight: example 2), 0.60g (0.4 part by weight: example 3), 1.2g (0.8 part by weight: example 4), 2.4g (1.6 parts by weight: the same experiment as in example 1 was repeated except for example 5).

< example 6: preparation process using high-grade raw materials

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

Comparative example 1: non-use of Redox additive-electrolytic preparation Process)

The materials required for preparing the 4-valent vanadium electrolyte for electrolysis of comparative example 1 are as follows.

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

The reactor was charged with vanadium compound, oxalic anhydride, water and sulfuric acid taking into account the exotherm as described in example 1.

At 105℃the mixture was stirred for about 3 hours from the time the sulfuric acid was added. When the reduction reaction was completed, impurities were removed through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining about 1L of an electrolyte product (V) ⁴⁺ electrolyte product)。

The electrolysis was performed in a state where 330mL of the obtained 4-valent vanadium compound was added to each of the anode cell and the cathode cell, and the remaining 330mL was retained. Electrolysis in constant current mode at 150mA/cm ² To a voltage of 1.8V, thereby obtaining 300mL or more of the 5-valent vanadium compound from the anode cell.

300mL of the 5-valent vanadium compound obtained by electrolysis was mixed with 300mL of the 4-valent vanadium compound remaining without electrolysis of 330mL, thereby obtaining 600mL of 3.5-valent vanadium electrolyte, and then impurities were removed again using a filtration unit. When the oxidation number is somewhat detached in the process, the remaining amount can be used for adjustment.

Comparative example 2: excessive use of Redox additive ]

Except that 0.29g (in 100 parts by weight of V ₂ O ₅ The same experiment as in example 1 was repeated except that 0.2 parts by weight of molybdenum trioxide was changed to 15g (10 parts by weight) based on the standard.

< experimental example 1: battery Performance evaluation experiment ]

The properties were measured by the following methods to evaluate the properties of the respective electrolytes prepared in the examples 1 to 6 and comparative examples 1 to 2.

At 100mA/cm ² Constant current charging is carried out until the voltage reaches 1.60V, and then 100mA/cm is used in discharging ² Is discharged until the voltage reaches 0.8V. After repeating the above cycle 30 times, the results are collated and shown in table 1.

In Table 1, the content of the redox additive is expressed as V in 100 parts by weight ₂ O ₅ MoO based on ₃ The time required for the reaction is the time required from the time when the sulfuric acid is charged to the time when the oxidation number is hardly changed and the time when the reaction is judged to be completed, the charge capacity, the discharge capacity and the energy efficiency are respectively 30 th cycle (cycle) values, and the content (ppm) represents MoO as a redox additive in the electrolyte ₃ The content of Mo as a main component of the steel.

Table 1:

as shown in table 1 and fig. 3, the amount of the redox additive added did not affect the final oxidation number during the preparation of the electrolyte, and it was confirmed that it did not affect the amount of reduction but only the reaction rate.

As shown in table 1 and fig. 2, it can be confirmed that the time required for the reduction reaction and the content of the redox additive exhibit a proportional negative correlation as shown in the above-mentioned mathematical formula 1-1.

As shown in examples 4 and 6 in table 1, it is found that there is no significant difference in performance between the electrolyte prepared using the low-grade vanadium compound and the electrolyte prepared using the high-grade vanadium compound.

As shown in examples 1 to 6 and comparative example 1 in table 1, the electrolyte prepared according to the process of the present invention was superior in performance to the electrolyte prepared by electrolysis, as confirmed from fig. 4 to 6.

As shown in example 5 and comparative example 2 in table 1, it was confirmed that when the redox additive was added in an amount larger than a proper amount, the reaction rate could be slightly improved, but the performance of the electrolyte was lowered. According to a plurality of the present examples, it can be confirmed that the performance is significantly reduced when the redox additive is 10 parts by weight, as is confirmed from fig. 4 to 6.

As shown in table 1, the energy efficiency was less varied with the amount of the redox additive added, including the result of comparative example 1.

In the present invention, the values of the embodiments 1 to 6 are substituted in the equation 1, and thus can be embodied as the equation 1-1.

Mathematical formula 1-1: t is t _R ＝-2.233ln(Ma/Mv)-3.8086，R ² ＝0.9925。

It can be confirmed from fig. 2 that in the above-described mathematical formula 1-1, the redox additive in example 1 exhibits a proportional negative correlation with the reaction rate, following the arrhenius Wu Sigong formula. That is, the amount of the redox additive can be determined from the variables of the raw materials, the composition, and the process conditions using the above-mentioned mathematical formula 1-1 to control the process time.

In Experimental example 3, H was added ₃ PO ₄ And confirming the interaction force with the redox additive, wherein H is added for the temperature stability of the electrolyte ₃ PO ₄ Are well known.

Specifically, after preparing a sample of the electrolyte solution using the redox additive by the same method as in example 3, electrolysis was performed to prepare the 5-valent electrolyte solutions of reference examples 1a to 4 a.

A sample of the electrolyte was prepared by the same method as in comparative example 1 to prepare 5-valent electrolytes of reference examples 1b to 4 b.

The process of precipitating vanadium ions from the eight electrolytes of reference examples 1a to 4b obtained at 50℃was observed, and the results thereof are shown in Table 2.

Table 2:

/>

from reference example 1a to reference example 4b in Table 2, it can be confirmed that the redox additive and H ₃ PO ₄ The additives do not affect each other. This relationship is not limited to H ₃ PO ₄ An additive.

In the composition of the vanadium electrolyte described as the second example, the vanadium compound was 1.7 mol, sulfuric acid was 4.3 mol, and the density of the electrolyte was 1.35g/cm ³ The ionic valence of the vanadium electrolyte is 3.5, and the vanadium electrolyte is an electrolyte formed by mixing 4-valence vanadium ions and 3-valence vanadium ions according to the ratio of 1:1.

The materials required for preparing the electrolyte of the second embodiment are as follows.

154.5g of a vanadium compound having a purity of 99.5%, 432g of 98% sulfuric acid, deionized water (DIW) for a pre-solvent for Ag, 720-A) g of deionized water (DIW) for a post-solvent, and 40.4g of an aqueous solution containing 80% by weight of hydrazine monohydrate, wherein A is as described in examples 7 to 9 and comparative examples 3 to 4 described below.

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

The reaction vessel is composed of a reaction tank (hereinafter, referred to as "reactor") capable of carrying out a reaction of 1L or more, a stirrer, a heater capable of adjusting a temperature, a thermometer, a reflux, a filtration system (pump, pipe, filter, etc.), and the surface in contact with the electrolyte in the apparatus should be a material having acid resistance and chemical resistance such as glass, PTFE, PE, polytetrafluoroethylene (Teflon), etc.

The vanadium compound (V) is introduced into the reaction tank through the raw material inlet ₂ O ₅ ) Pre-solvent and hydrazine monohydrate (N) ₂ H ₄ ·H ₂ After O), sulfuric acid is added.

During the sulfuric acid injection, the reactants were heated by a jacketed heat exchanger (heater) surrounding the reaction tank to maintain the reaction temperature at 110 c, and the reaction of the first step was performed.

When the reaction of the first step is completed, cooling is performed to cool water vapor, nitrogen (N) ₂ ) The water vapor in (a) was recovered into the reactor, and nitrogen (N) ₂ ) Is discharged to the outside.

Then, after the solvent was added and adjusted to be kept at normal temperature, impurities were removed through a drain pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ³⁵⁺ electrolyte product)。

In example 7, the amount of the front solvent A was 540g, which was about 75% of the total solvent, the amount of the rear solvent was 180g, and the front solvent was 30M and the rear solvent was 10M, which was about 3.2 times as much as the minimum 9.35M water required for 1.7M vanadium, and the molar number was 17.6 times as much as that of 1.7M vanadium, respectively, converted to the molar number.

Hereinafter, the electrolyte preparation step of example 7 is divided into different steps to be described in detail.

The reaction of the first step proposed in the preparation example was carried out.

Vanadium compound and pre-solvent feeding step

Firstly, deionized water (DIW) and a vanadium compound (V) are charged into a reactor under the operation of a stirrer ₂ O ₅ ). At this time, 440g of the pre-solvent was charged with 540 g.

Step of charging hydrazine Compound

Next, 40.4g of hydrazine monohydrate (N) was mixed with the remaining 100g of the precursor solvent ₂ H ₄ ·H ₂ O) and then charged into the reactor. During the plunging, the temperature in the reactor may rise within 10 ℃.

Sulfuric acid feeding step

In the above-described step, sulfuric acid is charged in accordance with the charging flow rate of sulfuric acid in consideration of heat release.

Specifically, sulfuric acid is slowly charged, and the flow rate is adjusted so as to avoid the reaction solution from splashing to the wall surface of the container as much as possible, and the exothermic temperature in the reactor is not more than 110 ℃.

Wherein the gas by-product (N) generated during the reduction of the vanadium ion of valence 5 is recovered by reflux ₂ ) To the outside of the container, for gasified H ₂ O and H ₂ SO ₄ Condensation is performed so as to remain in the reactor to maintain a high temperature of around 110 c and to prevent composition change in the reactor.

Reduction step

The temperature of the reactor was maintained at 110 c by a heater or a heat exchanger and reduced. After a part (0.5 mL or less) of a sample of the reactant was collected and diluted, UV measurement was performed, and the extent of progress of reduction was confirmed.

Wherein the gas by-product (N) generated during the reduction of the vanadium ion of valence 5 is recovered by reflux ₂ ) To the outside of the container, for gasified H ₂ O and H ₂ SO ₄ Proceed toCondensed so as to be left in the reactor to maintain a high temperature of around 110 c and to prevent composition changes in the reactor.

A cooling step

When the reduction reaction is completed, the operation of the heater or the heat exchanger is stopped, and the mixture is cooled to normal temperature by the cooler.

Post solvent input and filtration step

180g of the post-solvent was charged into the reactor and stirred with the above-mentioned cooled electrolyte. In this process, a small amount of heat is generated, and the temperature is lowered to normal temperature by cooling. Thereafter, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

< example 8: 1> change in the amount of the pre-solvent/post-solvent added

Example 8 the same procedure as in example 7 was repeated except that the amount of the front solvent/rear solvent charged in example 7 was changed.

Specifically, the a of the front solvent used in said example 7 was 360g, and the rear solvent was 360g, i.e., equivalent to about 50% of the total solvents. This corresponds to a molar content of about 2.1 times the minimum content of pre-solvent and to 11.8 times the vanadium of 1.7 moles.

< example 9: 2> change in the amount of the pre-solvent/post-solvent added

Example 9 the same procedure as in example 7 was repeated except that the amount of the front solvent/rear solvent charged in example 7 was changed.

Specifically, the a of the front solvent used in the above example 7 was 180g, and the rear solvent was 540g, that is, approximately 25% of the total solvent was used as the front solvent, and 75% was used as the rear solvent. This corresponds to a molar content of about 1.1 times the minimum content of pre-solvent and to 5.9 times the vanadium of 1.7 moles.

Comparative example 3: unused post-solvent ]

Comparative example 3 the same procedure as in example 7 was repeated for comparison with the plurality of examples except that 720g of the total amount of the front solvent+the rear solvent was entirely charged in the front solvent charging step of example 7, but not in the rear solvent charging step. The amounts of the front solvent/rear solvent used in examples 7 to 9 and comparative example 3 are specifically shown in table 2.

Comparative example 4: modification of the amount of the front solvent/rear solvent input 3-

Comparative example 4 the same procedure as in example 7 was repeated except that the amount of the pre-solvent/post-solvent charged in example 7 was changed. Specifically, comparative example 4 used 95g of the pre-solvent described in the present invention (whose mol was 3.1 times that of 1.7mol of vanadium).

Experimental example 3 ]

The performance was measured by the following method to evaluate the performance of each of the electrolytes and secondary batteries prepared in examples 7 to 9 and comparative example 3.

[ measurement of oxidation number ]

According to each reaction step in the electrolyte preparation process, the oxidation number of vanadium was measured using a UV spectrometer, and the reaction time is shown in table 3.

[ measurement of impurities ]

The content of Si and the content of Al as impurities in the electrolyte were measured using an ICP-OES apparatus, respectively, and the results thereof are shown in Table 2.

[ evaluation of battery capacity (Ah) and energy efficiency (%) ]

At normal temperature, the secondary battery is charged at 100mA/cm ² Constant current charging is carried out until the voltage reaches 1.60V, and then 100mA/cm is used in discharging ² Is discharged until the voltage reaches 0.8V. The above cycle was repeated 30 times, and the average value thereof was calculated, and the results thereof are shown in table 3, respectively.

Table 3:

as shown in Table 3, according to the production method of the present invention, the content of impurities in the electrolytic solution was reduced by at most 82.8% for Si, 45.2% or more for Al, and 85.7% for reaction time, as compared with the comparative example. In addition, it was confirmed that in examples 7 to 9, 600 minutes were required at most for the reduction of the oxidation number of the vanadium compound to 3.5, and 840 minutes were required at least for comparative example 3, whereby the effect of shortening the reaction time of the production method of the present invention was confirmed.

As shown in table 3, the electrolyte using the process of the present invention had a minimum charge capacity of 2.51Ah or more, and the comparative example had a minimum charge capacity of 2.42Ah or more, at least 0.09Ah or less, and the electrolyte using the process of the present invention had a minimum discharge capacity of 2.43Ah or more, and the comparative example 3 had a minimum charge capacity of 2.33Ah, at least 0.10Ah or more.

As shown in table 3, the energy efficiency of the electrolyte using the process of the present invention was at least 83.84%, which is at least 0.74% lower than that of the electrolyte using the comparative example 83.10%. This means that the quality and battery performance of the electrolyte using the process proposed in the present invention are improved.

In particular, in examples 7 to 9, the reaction time shortening effect and the impurity reducing effect were significantly improved in example 7 in which the amount of the rear solvent was larger than that of the front solvent as compared with example 9 in which the amount of the front solvent was larger than that of the rear solvent.

Further, it can be confirmed that example 8 is most excellent in battery performance such as charge capacity, discharge capacity, and energy efficiency. This example illustrates that even the theoretical minimum amount of the aforementioned precursor solvent does not necessarily optimize the battery performance.

On the other hand, as shown in fig. 11, it was confirmed that the electrolyte solution could not be prepared in comparative example 4. From this, it was confirmed that the process of the present invention can be effectively carried out only by using the minimum number of moles of water per mole of vanadium as described above.

Third embodiment

In the following, in the composition of the vanadium electrolyte described as the third example, the vanadium compound was 1.7 molSulfuric acid of 4.3 mol and electrolyte density of 1.35g/cm ³ The ionic valence of the vanadium electrolyte is 3.5, and the vanadium electrolyte is an electrolyte formed by mixing 4-valence vanadium ions and 3-valence vanadium ions according to the ratio of 1:1.

The materials required for preparing the electrolyte of the third embodiment are as follows.

154.5g of a vanadium compound having a purity of 99.5%, 432g of 98% sulfuric acid, deionized water (DIW) for a pre-solvent for Ag, 720-A) g of deionized water (DIW) for a post-solvent, and 40.4g of an aqueous solution containing 80% by weight of hydrazine monohydrate, wherein A is as described in examples 10 to 13 and comparative examples 5 to 6 described below.

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

During the sulfuric acid injection, the reactants were heated by a jacketed heat exchanger (heater) surrounding the reaction tank to maintain the reaction temperature at 110 c (first temperature), and the reaction of the first step was performed.

Then, the mixture was cooled to-25 to 20℃and the post-solvent was added (example 1), or the mixture was cooled to-25 to 20℃after the post-solvent was added (example 2), and the cooling condition was maintained, and at the same time, impurities were removed through a discharge tube provided with a Filtration unit (Filtration), thereby obtaining a final electrolyteProduct (V) ^3.5+ electrolyte product)。

On the other hand, after cooling to 20 to 40 ℃ and adding the post-solvent, filtration was performed while maintaining the cooling condition (comparative example 1), or Filtration was performed at 40 to 100 ℃ without cooling step after adding the post-solvent (comparative example 2) by removing impurities through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V) ^3.5 ⁺ electrolyte product)。

Specifically, the pre-solvent used in examples 10, 11, 5 and 6 had a concentration of 540g, accounting for about 75% of the total solvent, the post-solvent was 180g, the pre-solvent was 30M and the post-solvent was 10M in terms of mole numbers, respectively, wherein the pre-solvent was about 3.2 times as much as the minimum 9.35M water required for 1.7M vanadium, and the mole number was 17.6 times as much as that of 1.7M vanadium.

The electrolyte preparation steps of example 10, example 11, comparative example 5, and comparative example 6 were the same except for the above-described post-solvent addition procedure and the application of cooling conditions, and thus, the following description was divided into different steps to be described in detail.

Vanadium compound and pre-solvent feeding step

Step of charging hydrazine Compound

Sulfuric acid feeding step

In the above-described step, sulfuric acid is charged at a charging flow rate of sulfuric acid in consideration of heat release.

Reduction step

A cooling step

When the reduction reaction is finished, the operation of the heater or the heat exchanger is stopped, and the temperature is cooled to-25-20 ℃ by a cooler.

Post solvent input step

180g of the post-solvent was charged into the reactor and stirred with the above-mentioned cooled electrolyte. During this process, a small amount of heat is generated, and the temperature is reduced to-25 to 20 ℃ by cooling.

Filtration step

Thereafter, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), and the cooling temperature is maintained, thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

< example 11: changing the cooling and post-solvent feeding step)

Example 11 repeated the same process as in example 10, except that the order of the cooling step and the post-solvent feeding step in example 1 was changed.

Specifically, when the reduction step of example 10 was completed, 180g of the post-solvent was charged into the reactor and stirred with the electrolyte. During this process, a small amount of heat is generated, and the temperature is reduced to-25 to 20 ℃ by cooling.

Maintaining the cooling temperature or cooling to-25 to 20 ℃ and maintaining the temperature, and at the same time, removing impurities through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Comparative example 5: changing the cooling conditions ]

Comparative example 5 the same process as in example 10 was repeated except that the cooling conditions in example 10 were changed.

Specifically, the temperature in example 10 was reduced to-25 to 20℃and cooled to 20 to 40℃and then 180g of the post-solvent was charged into the reactor and stirred with the electrolyte.

Thereafter, the cooling temperature (20 to 40 ℃) is maintained, and at the same time, impurities are removed through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V) ^3.5+ electrolyte product)。

Comparative example 6: unused cooling step and modified filtration conditions >

Comparative example 6 the same procedure as in example 10 was repeated except that the cooling step was not used and the filtration conditions were changed in example 10.

Specifically, the step of lowering the temperature to-25 to 20℃in example 10 was omitted, 180g of the post-solvent was charged into the reactor and stirred with the electrolyte, and then, a Filtration unit (Filtration) was provided under cooling conditions of 40 to 100℃obtained by natural coolingRemoving impurities from the electrolyte to obtain a final electrolyte product (V ^3.5+ electrolyte product)。

< example 12: 1> change in the amount of the pre-solvent/post-solvent added

Example 12 the same procedure as in example 10 was repeated except that the amount of the front solvent/rear solvent charged in example 10 was changed.

Specifically, 360g (i.e., A) of the front solvent and 360g of the rear solvent were used in the example 10, i.e., equivalent to about 50% of the total solvents. This corresponds to a molar content of about 2.1 times the minimum content of pre-solvent and to 11.8 times the vanadium of 1.7 moles.

< example 13: 2> change in the amount of the pre-solvent/post-solvent added

Example 13 the same procedure as in example 10 was repeated except that the amount of the front solvent/rear solvent charged in example 10 was changed.

Specifically, 180g (i.e., a) of the front solvent and 540g of the rear solvent were used in the example 10, that is, approximately 25% of the total solvent was used as the front solvent and 75% was used as the rear solvent. This corresponds to a molar content of about 1.1 times the minimum content of pre-solvent and to 5.9 times the vanadium of 1.7 moles.

Comparative example 7: unused post-solvent ]

Comparative example 7 the same procedure as in example 10 was repeated for comparison with the plurality of examples except that 720g of the total amount of the front solvent+the rear solvent was entirely charged in the front solvent charging step of example 10, but not in the rear solvent charging step. The amounts of the front solvent/rear solvent used in examples 10 to 13 and comparative example 7 are specifically shown in table 4.

Comparative example 8: modification of the amount of the front solvent/rear solvent input 3-

The same procedure as in example 10 was repeated except that the amount of the pre-solvent/post-solvent charged in example 10 was changed. Specifically, comparative example 2 used 95g of the pre-solvent described in the present invention (whose mol was 3.1 times that of 1.7mol of vanadium).

< example 14: cyclic filtration, low-temperature cooling and solvent after input)

The cyclic filtration (filtration) process is an operation of filtering an electrolyte in a reactor by using a cyclic system to remove impurities. The cyclic filtration process may be performed immediately after the sulfuric acid is charged in the second step, or may be performed between "the time when the same molar amount as that of vanadium is charged" and "the time when about 2 hours elapses from the time when the entire sulfuric acid flows in". The filter used in the cyclic filtration process may be hydrophilic or hydrophobic or amphiphilic or amphiphobic in nature, its material should be one or more selected from PTFE, PE, PET having acid resistance and PP, and the pore size may be between 0.2 and 5 μm. Wherein the time required for filtration can be adjusted by the size of the filter, i.e. diameter and pore size, etc.

That is, example 14 repeated the same process as that of example 10, except that the filtration was performed in a circulating filtration manner in the apparatus shown in fig. 16 provided with a circulating filtration pipe in example 10.

Specifically, the apparatus structure and process flow diagram for preparing the electrolyte of example 14 are shown in fig. 16. As shown in fig. 16, hydrazine monohydrate (N) was charged into a single reaction tank through a raw material charging port ₂ H ₄ ·H ₂ O), vanadium compound (V) ₂ O ₅ ) Sulfuric acid (H) ₂ SO ₄ ) And deionized water (DIW), stirring the charged reaction raw materials by a stirrer, and starting the reduction reaction of the first step. When the reduction reaction of the first step was completed, 180g of the post-solvent was charged into the reactor after cooling the reactant to-25 to 20℃and stirred with the electrolyte. During this process, a small amount of heat is generated, and the temperature is reduced to-25 to 20 ℃ by cooling.

Maintaining the cooling temperature or further cooling to-25-20 ℃, removing impurities through a circulating pipe provided with a filtering unit (Filtration), and heating the reactant by a jacket type heat exchanger (heater) wrapping the reaction tank to perform the reduction reaction of the second step. Steam, nitrogen (N) generated in the reduction reaction ₂ ) In (a)Is cooled by an open reflux condenser and is recycled to the reactor, nitrogen (N) ₂ ) Then discharged to the outside through the open reflux condenser. When the reduction reaction of the second step is completed, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Comparative example 9: circulation filtration, normal temperature cooling and solvent after input-

That is, comparative example 9 was repeated by the same process as comparative example 5 except that in comparative example 5, filtration was performed by the circulation filtration method in the apparatus shown in fig. 5 provided with the circulation filtration pipe.

Specifically, the apparatus structure and process flow chart for preparing the electrolyte of comparative example 9 are shown in fig. 16. As shown in fig. 16, hydrazine monohydrate (N) was charged into a single reaction tank through a raw material charging port ₂ H ₄ ·H ₂ O), vanadium compound (V) ₂ O ₅ ) Sulfuric acid (H) ₂ SO ₄ ) And deionized water (DIW), stirring the charged reaction raw materials by a stirrer, and starting the reduction reaction of the first step. When the reduction reaction of the first step is completed, 180g of the post-solvent is charged into the reactor after cooling the reactant to 20 to 40 ℃ and stirred with the electrolyte.

Thereafter, the cooling temperature (20 to 40 ℃) is maintained and the filter unit is arrangedFiltration) to remove impurities, and then heating the reactant by a jacketed heat exchanger (heater) surrounding the reaction tank to perform the reduction reaction of the second step. Steam, nitrogen (N) generated in the reduction reaction ₂ ) The water vapor in (a) was cooled by an open reflux condenser and recovered into the reactor, nitrogen (N) ₂ ) Then discharged to the outside through the open reflux condenser. When the reduction reaction of the second step is completed, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Comparative example 10: cyclic filtration, low-temperature cooling and solvent after no input)

Comparative example 10 the same procedure as in example 14 was repeated except that the post-addition solvent was not added in example 14.

Specifically, the apparatus structure and process flow chart for preparing the electrolyte of comparative example 10 are shown in fig. 16. As shown in fig. 16, hydrazine monohydrate (N) was charged into a single reaction tank through a raw material charging port ₂ H ₄ ·H ₂ O), vanadium compound (V) ₂ O ₅ ) Sulfuric acid (H) ₂ SO ₄ ) And deionized water (DIW), stirring the charged reaction raw materials by a stirrer, and starting the reduction reaction of the first step. After the reaction is cooled to-25-20 deg.c, the solvent is passed through a circulating pipe with filtering unit to eliminate impurity, and the reaction is heated with a jacket heat exchanger to complete the reduction reaction. Steam, nitrogen (N) generated in the reduction reaction ₂ ) The water vapor in (a) was cooled by an open reflux condenser and recovered into the reactor, nitrogen (N) ₂ ) Then discharged to the outside through the open reflux condenser. When the reduction reaction of the second step is completed, impurities are removed again through a discharge pipe provided with a Filtration unit (Filtration), thereby obtaining a final electrolyte product (V ^3.5+ electrolyte product)。

Experimental example 4 ]

The performance was measured by the following method to evaluate the performance of each of the electrolytes and secondary batteries prepared in examples 10 to 14 and comparative examples 5 to 10.

[ measurement of oxidation number ]

According to each reaction step in the electrolyte preparation process, the oxidation number of vanadium was measured using a UV spectrometer, respectively, and the reaction time is shown in table 4 and fig. 7.

[ measurement of impurities ]

The content of Si and the content of Al as impurities in the electrolyte were measured using an ICP-OES apparatus, respectively, and the results thereof are shown in Table 4.

[ evaluation of battery capacity (Ah) and energy efficiency (%) ]

At normal temperature, the secondary battery is charged at 100mA/cm ² Constant current charging is carried out until the voltage reaches 1.60V, and then 100mA/cm is used in discharging ² Is discharged until the voltage reaches 0.8V. The above cycle was repeated 30 times, the average value thereof was calculated, and the results thereof are shown in table 4 and fig. 8 to 10, respectively.

Table 4:

as shown in Table 4, according to the production method of the present invention, the content of impurities in the electrolytic solution was reduced by at most 82.8% for Si, 45.2% or more for Al, and 85.7% for reaction time, as compared with the comparative example. As shown in fig. 8, in examples 10, 12 to 13, the reduction of the oxidation number of the vanadium compound to 3.5 took 600 minutes at the most, whereas comparative example 3 took 840 minutes at the least, whereby the effect of shortening the reaction time of the production method of the present invention was confirmed.

Further, as shown in table 4 and fig. 8 to 9, the electrolyte employing the process of the present invention had a minimum charge capacity of 2.51Ah or more, and the comparative example was 2.42Ah or more, at least 0.09Ah or less, and the electrolyte employing the process of the present invention had a minimum discharge capacity of 2.43Ah or more, and the comparative example 5 was 2.33Ah, at least 0.10Ah or more.

As shown in table 4 and fig. 10, the energy efficiency of the electrolyte using the process of the present invention was at least 83.84%, which is at least 0.74% lower than that of the electrolyte using the comparative example 83.10%. This means that the quality and battery performance of the electrolyte using the process proposed in the present invention are improved.

In particular, in examples 10, 12 to 13, the reaction time shortening effect and the impurity reducing effect were significantly improved in example 10 in which the amount of the rear solvent was larger than that of the front solvent, as compared with example 13 in which the amount of the front solvent was larger than that of the rear solvent.

Further, it can be confirmed that example 12 is most excellent in battery performance such as charge capacity, discharge capacity, and energy efficiency. This means that not only the theoretical minimum amount of the above-mentioned amount of the precursor solvent is the most excellent battery performance.

Experimental example 5 ]

The impurities of the electrolytes prepared in examples 10 to 14 and comparative examples 5 to 10 were measured using an ICP instrument, respectively. The measured results are shown in table 5, respectively.

Table 5:

as shown in Table 5, according to the production method of the present invention, the content of impurities in the electrolytic solution was reduced by at most 87.4% for Al, 26.2% for Ca, 71.2% for Fe and 89.0% or more for Si, as compared with the comparative example. First, as shown in examples 10 and 11 in which only the order of the cooling step and the post-solvent feeding step was changed, it was confirmed that the purification effect of Fe was more remarkable in example 10 in which the cooling step was previously performed, and the purification effect of Si was more remarkable in example 11 in which the post-solvent feeding step was previously performed.

On the other hand, it was confirmed that example 10, which was cooled at low temperature, showed good effects on all of the four kinds of Al, ca, fe, si impurities when cooled at low temperature, compared with comparative example 5, which was cooled at normal temperature, and comparative example 6, which was cooled at high temperature.

In addition, when the post-addition solvent was not added, it was found that it was difficult to reduce the impurities as shown in comparative example 7.

In addition, it was confirmed that in example 14 in which the cooling step was performed before and the circulating cooling was performed, fe impurities were significantly reduced, and good effects were exhibited for all four impurities of Al, ca, fe, si.

In particular, it was confirmed that the removal effect of four kinds of Al, ca, fe, si impurities was maximized when the solvent was cooled at low temperature and added and the solvent was again subjected to the cyclic filtration, by comparing example 14 in which the solvent was cooled at low temperature and added, and example 9 in which the solvent was cooled at normal temperature and subjected to the cyclic filtration, and example 10 in which the solvent was cooled at low temperature and was not added and then subjected to the cyclic filtration.

Therefore, considering the results of the various embodiments of the present invention and the various comparative examples in combination, the process of the present invention can greatly shorten the reaction time and is excellent in impurity improvement effect, and at the same time, the prepared electrolyte has excellent secondary battery performance, and can reduce impurities under the shortened reaction time to provide high-quality performance, thereby being applicable to all fields of novel renewable energy sources, smart grids, power stations, etc. using all vanadium redox flow batteries.

Claims

1. The preparation method of the vanadium electrolyte is characterized by comprising the following steps of:

A second step of reducing the 4-valent vanadium compound to produce a 3.3 to 3.7-valent vanadium compound,

wherein the reaction rate of one or more reduction reactions selected from the reduction reaction of the first step and the reduction reaction of the second step is reduced.

2. The method for preparing a vanadium electrolyte according to claim 1, wherein,

redox additives having a lower reducing power than the nitrogen-based reducing agent are used to reduce the reaction rate of the reduction reaction.

3. The method for preparing a vanadium electrolyte according to claim 2, wherein,

the redox additive undergoes self-reduction and oxidation of the nitrogen-based reducing agent after dehydration reaction with the acid to form an aqueous solution, thereby producing nitrogen gas.

4. The method for preparing a vanadium electrolyte according to claim 3, wherein,

the redox additive is selected from molybdenum metal and molybdenum oxide Mo _x O _y Molybdenum nitride Mo _x N _y Molybdenum chloride Mo _x Cl _y Molybdenum sulfide Mo _x S _y Molybdenum phosphide Mo _x P _y Molybdenum carbide Mo _x C _y Metallic molybdenum oxide Mo _x M _y O _z Metallic molybdenum nitride Mo _x M _y N _z Metallic molybdenum chloride Mo _x M _y Cl _z Metallic molybdenum sulfide Mo _x M _y S _z Molybdenum phosphide Mo _x M _y P _z Metallic molybdenum carbide Mo _x M _y C _z More than one of them.

5. The method for preparing a vanadium electrolyte according to claim 4, wherein,

the metal of the redox additive is one metal or more alloy-forming metals selected from 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 In,

the x and y or the x, y and z are independently integers from 0 to 1.

6. The method for preparing a vanadium electrolyte according to claim 5, wherein,

the content of the redox additive is 0.1 to 1.6 parts by weight based on 100 parts by weight of the 5-valent vanadium compound.

7. The method for preparing a vanadium electrolyte according to claim 1, wherein,

the content of the nitrogen-based reducing agent is 10-35 parts by weight based on 100 parts by weight of the vanadium compound.

8. The method for preparing a vanadium electrolyte according to claim 1, wherein,

the molar concentration ratio of the 5-valent vanadium compound to the nitrogen reducing agent is 1:0.1-1.6.

9. The method for preparing a vanadium electrolyte according to claim 1, wherein,

the acid is one or more selected from sulfuric acid, hydrochloric acid, nitric acid and acetic acid, and the concentration of proton ions derived from the acid is 1 to 20 moles per 1 mole of the vanadium compound.

10. The method for preparing a vanadium electrolyte according to claim 1, wherein,

the second step is carried out at 70-120 ℃.

11. The method for preparing a vanadium electrolyte according to claim 1, wherein,

the 5-valent 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.

12. The method for preparing a vanadium electrolyte according to claim 1, wherein,

comprising a step of filtering after said first step or after a second step.

13. The method for producing a vanadium electrolyte according to claim 1 or 2, characterized in that,

in the first step, 5 to 15 moles of water are used per 1 mole of the vanadium compound, and in the second step, after the produced vanadium compound is cooled to a room temperature or lower, an excess amount of water exceeding the content of the water previously added is added, and the reaction solution is filtered to reduce the reaction rate of the reduction reaction.

14. The method for preparing a vanadium electrolyte according to claim 13, wherein,

the water content added in excess is in the range of 42 to 44 moles with respect to the composition of 1.6 moles of vanadium and 4.0 moles of sulfuric acid.

15. The method for preparing a vanadium electrolyte according to claim 13, wherein,

16. The method for preparing a vanadium electrolyte according to claim 13, wherein,

17. The preparation method of the vanadium electrolyte is characterized by comprising the following steps of:

18. The method for preparing a vanadium electrolyte according to claim 17, wherein,

19. The method for preparing a vanadium electrolyte according to claim 17, wherein,

in the implementation of the step D, the reaction temperature of 70-120 ℃ is adopted, the addition amount of the redox additive is substituted into the formula 1 to calculate the reduction reaction time of the vanadium compound,

mathematical formula 1:

t _R ＝Aln(Ma/Mv)+B

20. The preparation method of the vanadium electrolyte is characterized by comprising the following steps of:

21. A vanadium electrolyte is characterized in that,

prepared by the method of any one of claims 1 to 20.

22. A redox flow battery is characterized in that,

comprising the vanadium electrolyte as set forth in claim 21.

23. The redox flow battery of claim 22, wherein,

the vanadium electrolyte is contained in the anode and the cathode.