Preparation of vanadium electrolyte with aid of asymmetric vanadium-reducing electrolyzer and use of asymmetric vanadium-reducing electrolyzer for reducing electrolyte charge state balance in operating reduction-oxidation vanadium battery

FIELD: renewable electrochemical devices for energy storage in reduction-oxidation batteries.

SUBSTANCE: novelty is that acid vanadium electrolyte liquor that has in its composition V⁺³ and V⁺⁴ in desired concentration ratio introduced in electrolyte solution is produced from solid vanadium pentoxide by electrochemical method while at least partially reducing dissolved vanadium in acid electrolyte liquor; for the purpose electrolyte liquor is circulated through plurality of cascaded electrolyzers at least partially to V⁺³ degree; in this way reduced vanadium incorporating electrolyte liquor leaving the last of mentioned electrolyzers enters in reaction with stoichiometric amount of vanadium pentoxide to produce electrolyte liquor incorporating in effect vanadium in the V⁺³ form; acid and water are introduced to ensure definite molarity of liquor and the latter is continuously circulated through cascaded electrolyzers; stream of electrolyte liquor produced in the process that incorporates V⁺³ and V⁺⁴ in desired concentrations is discharged at outlet of one of electrolyzers of mentioned cascade. Each electrolyzer is distinguished by high degree of asymmetry and has cathode and anode of relevant surface morphology, geometry, and relative arrangement for setting current density on anode surface exceeding by 5 to 20 times that on projected cathode surface, oxygen being emitted from anode surface. Asymmetric electrolyzer of this type can be used in one of electrolyte circuits, positive or negative, of operating battery (cell) for reducing balance of respective oxidation degrees of their vanadium content.

EFFECT: facilitated procedure and reduced coast of vanadium electrolyte preparation.

10 cl, 4 dwg, 1 ex

The level of technology

The invention in General relates to renewable electrochemical device for energy storage systems redox flow battery (battery) and, in particular, to the so-called fully vanadium redox secondary batteries (rechargeable batteries).

Vanadium redox flow battery, also called a fully vanadium redox element or just - vanadium redox cell or battery, uses V(II)/V(III) and V(IV)/V(V) as the two redox couples in the negative (sometimes referred to as the analyte) and positive (sometimes called Catolica) polysemantic solutions of the electrolyte, respectively.

Normal electrolyte used in the vanadium battery consists of 50% of vanadium ions with oxidation state +3 and 50% of vanadium ions with oxidation state +4.

The electrolyte is usually divided into two equal parts, which are respectively placed in the positive and negative chambers battery, and more precisely to the respective circulation paths. In this initial state, the battery has an open circuit voltage, is practically zero.

The current passing through the battery by an external source with high enough, you are the one voltage V ⁺⁴(50%) in the negative electrolyte restored to V^+3,and at the same time, V⁺³(50%) in the positive electrolyte is oxidized to V⁺⁴.

At certain times the negative electrolyte is constantly circulating through the respective electrode chambers of the battery due to the circulation pump negative electrolyte will contain only V⁺³and the positive electrolyte circulating through the respective electrode chambers of the battery by using the circulation pump of the positive electrolyte will contain only V⁺⁴.

In this state, the battery is considered to have zero state of charge (Sz), and the open circuit voltage for this battery would be roughly 1,1 Century

If you continue to feed the “charging” current through the battery at the negative electrode V⁺³restored to V⁺²and on the positive electrode V⁺⁴oxidized to V⁺⁵. Upon completion of this transformation (after charging) the battery will have a voltage open circuit about 1,58 In and the battery will be considered as having Sz equal to 100%.

Vanadium is issued by the industry in the form of vanadium pentoxide (or also ammonium Vanadate). In any case, it is usually implemented in oxidation state +5.

The charging capacity of the installation is fully vanadium recovery-ocil the positive of the battery is determined by the amount of vanadium, dissolved in the acidic electrolyte. For this polyarnosti solutions of electrolytes charge capacity is directly proportional to the volume of the two electrolytes.

There is an obvious need for acidic solutions of vanadium, suitable as electrolyte for the first filling of the two circuits redox battery and/or to increase the charge capacity of the existing battery using commercially available vanadium pentoxide or ammonium Vanadate) as the source material (raw material).

The method of preparation of the vanadium electrolyte is therefore the way in which dissolved V₂O₅in sulfuric acid (or other acid) and restore it to the desired mixture V⁺³(about 50%) and V⁺⁴(about 50%).

Finely ground (powdered) solid vanadium pentoxide only marginally soluble in water or acid, such as sulfuric acid; therefore, a simple method for preparation of the electrolyte by dissolving V₂About₅the acid is impossible.

For dissolution of V₂About₅you must first restore it to a lower (easier soluble) oxidation state.

For dissolution and recovery V⁺⁵it was suggested different ways, mainly through the use of reducing compounds, or offered the ü complicated electrolytic or chemical processing methods.

The document EP-A-0566019 discloses a method of obtaining vanadium electrolyte solution through the chemical recovery of vanadium pentoxide or ammonium Vanadate in concentrated sulfuric acid, and thereafter heat treatment sludge.

Documents WO 95/12219 and WO 96/35239 disclose electrochemical-chemical method of preparation of vanadium electrolyte solution from the solid vanadium pentoxide, as well as how it stabilizirovannye. Vanadium pentoxide is dissolved at a special gills the cathode of the ion-exchange membrane electrolytic cell by passing the suspension pjatiokisi vanadium in contact with the gills cathode.

Currently developed methods and methods for the preparation of the corresponding vanadium acid electrolyte are quite complicated and expensive. On the other hand, for the total profitability of the system is completely vanadium flow redox battery having vanadium electrolyte solution with relatively low cost is an important factor in assessing the profitability of a vanadium redox battery compared with other systems of energy storage.

To meet these requirements, it is first necessary to use relatively inexpensive solid vanadium pentoxide as raw materials.

Purpose and somnos the ü inventions

Identified a very simple and inexpensive way of easy dissolution and recovery of vanadium pentoxide in an acidic electrolyte.

The invention is particularly suitable for the preparation of vanadium electrolyte from raw materials in the form of vanadium pentoxide or ammonium Vanadate), and it is carried out by using a very simple and inexpensive electrolytic cells while minimizing auxiliary processing solution.

However, the method according to this invention is quite effective from the point of view of energy consumption.

The method according to this invention is essentially continuous, and according to him a certain amount of circulating vanadium electrolyte solution is continuously injected solid vanadium pentoxide (V₂O₅in a fine-grained or powder form, the acid and water to maintain a certain polyarnosti solution; continuously divert an equivalent volume of electrolyte solution containing V⁺³and V⁺⁴in substantially similar or other desired concentration.

Exhaust flow of the electrolyte solution is a measure of the productivity of the method.

Basically, the method of the present invention is that:

skip the electrolyte solution in contact with the cathodes of many located in the hydraulic cascade electrolysis is the moat with the in order to consistently recover part or all V⁺⁴contained in the solution flowing in the first cell, to V⁺³and sometimes in a small amount even before V⁺²in the electrolyte solution at the outlet of the electrolyte solution from the last cell of the multiple cells in the cascade;

- implement the response recovered thus vanadium contained in the electrolyte solution at the output of the last cell, with the stoichiometric quantity of vanadium pentoxide (V₂O₅in the capacity of dissolution, provided with means for stirring, thus obtaining the electrolyte solution containing the appropriate amount of dissolved vanadium, which can almost entirely be in the condition V⁺⁴;

administered, the acid - sulfur or other equivalent acid and water in vanadium electrolyte solution (e.g., close to V⁺⁴), in order to maintain a certain both molarity;

- carry out the recycling of the electrolyte solution through a cascade of cells, while keeping the flow of the electrolyte solution containing V⁺³and V⁺⁴, preferably in similar concentrations at the outlet of one cell of the multiple cells in the cascade.

The essential feature of the electrolytic cells is that their cathode and anode imeadiately surface morphology, the geometry and relative position to establish on the anode surface current density from 5 to 20 times higher than the current density on the cathode surface and the anode surface oxygen is liberated.

In practice, the cathode may be a carbon felt or activated carbon felt, or similar material providing a relatively large surface area, and may have a tubular or even zheloboobraznogo shape, and the anode may be made in the form of a thin rod that is installed along the geometric axis of the tubular or zheloboobraznogo cathode.

A relatively large share of the active area of the cathode compared with specific active area of the electrode, and the ratio of the projected area such that define the current density at the active anode surface, from 5 to 20 times higher than the current density on the geometrically projected cathode surface.

When working with a cathode current density of the order of one to several hundred a/m²the projected area and by selection of the diameter of the anode rod, “concentrically” located relative to the tubular or equivalent at least partially covering the cathode, it is possible to create an anode current density of more than 1000 a/m²or higher.

In these conditions significantly disproportionate value is the current density and relatively high density anode current, when applied to the electrolytic current regulate to ensure that the cathode recovery V⁺⁴to V⁺³remained almost completely single cathode polysemantic reaction (i.e. limiting the maximum current density in order to eliminate such adverse reactions as hydrogen gas), the anode palvelimelta reaction begins first and foremost ensured by the oxygen evolution reaction (electrolysis of water).

In fact, thermodynamically preferred anode palvelimelta the oxidation reaction V⁺³to V⁺⁴practically and effectively restrained by being slow migration and, ultimately, the diffusion of ions V⁺³from the main volume of electrolyte that fills the gap between the anode and cathode spaces, to the anode surface of the cell.

Another significant obstacle to migration and/or diffusion of vanadium ions to the anode surface is the presence of bubbles of gaseous oxygen, which intensively allocated on the anode surface at such relatively high current densities.

The current flowing sequentially through the set in the hydraulic cascade of cells, can be adjusted depending on the flow rate of electrolyte through the cascade of cells that is advised to obtain almost complete restoration of all V ⁺⁴to V⁺³in the electrolyte, leaving the last cell in the cascade.

Of course, this is the ideal condition, as the minimum (residual) number V⁺⁴may be present in the case of a fault current flowing through the electrolytic cells, or, on the contrary, in the case of excess current may occur rudimentary recovery V⁺³to V⁺², resulting in the electrolyte leaving the last cell may be a small number V⁺²together with V⁺³.

The anode has an electrocatalytic surface low overvoltage of oxygen to promote the release of oxygen, and, most importantly, he is resistant to the acidic electrolyte under conditions of anodic polarization and oxygen release.

For example, the anode may be a rod of a valve metal, resistant to anodic destruction, such as titanium, tantalum or their alloys, with depassivation active coating electrocatalytic oxygen release.

The coating can be a mixed oxide or mixture of oxides, consisting at least of such a noble metal, such as iridium, rhodium or ruthenium, and at least from a valve metal such as titanium, tantalum and zirconium. The active coating may also consist of a coating of a noble metal, such ka is platinum, iridium or rhodium, or of the same metals dispersed in the conductive oxide matrix.

In the vessel of the dissolution, equipped with mechanical stirring means, the electrolyte solution leaving the last cell, in contact with the stoichiometric amount (specified as a number V⁺³(V⁺²)contained in the recovered electrolyte solution) solid vanadium pentoxide in micronized powder form, prepared by grinding and/or sieving of solid vanadium pentoxide way to introduce particles with a maximum size of not more than 100 microns.

Merged (decanted or filtered extract solution in the tank, and undissolved particles of vanadium pentoxide can be referred back to the capacity of dissolution.

Enriched the solution thus contains vanadium in fact, the condition V⁺⁴although relatively small amount of dissolved vanadium may be present in the form V⁺⁵.

Acid, which most often and is preferably sulfuric acid, and water is injected in vanadium enriched and filtered electrolyte solution, in order to maintain some both molarity of the electrolyte solution. Of course, the higher the molar vanadium content, the higher will be the ratio of the energy to total Electrol is the but the problem of stability of the solution in terms of the critical temperature can occur at relatively high molar concentrations. Most preferably, in the case of sulfuric acid to the molar content of vanadium was in the range from 1 to 5, and still more preferably 2 to 5 moles (moles/liter).

The solution is pumped back into the input of the first cell of the cascade of cells to carry out electrochemical recovery V⁺⁴(or any residual V⁺⁵) to V⁺³and sometimes to V⁺².

The product of such installations for the production of the electrolyte is a solution containing nearly the same number V⁺³and V⁺⁴that is diverted from the main stream of recirculating solution at the outlet of one of the cells of the cascade of cells.

A disproportionately large current density on the anode surface, which causes significant release of oxygen, and thus a slight oxidation of V⁺³to V⁺⁴is a condition that is very effective for ensuring the overall efficiency of the method to more than acceptable levels, while taking into consideration the relatively small proportion that the cost of electricity is in General economic performance of any method of preparation of the vanadium acid solution.

EF is aktivnosti can even improve, in an alternative embodiment, through the use of screen grid or even a microporous separator between the anode rod and the surrounding cylindrical cathode.

A shielding grid or microporous separator give effective “hold” oxygen bubbles rising due to buoyancy in the electrolyte as they continually grow and become detached from the anode surface, thus minimizing convective motion in the bulk of the electrolyte contained in the space between the screen grid and cathode, and also reducing the ability of the restored ions (V⁺³) vanadium migration and, ultimately, to achieve the anode.

The most effective microporous separator may be made of glass mittavinda tube, closed at its lower end and covering the anode rod (in this case a part of the cell from the top), resulting in bubbles of oxygen that is separated from the surface of the electrolyte, can break out of the cell through the outlet. Or the respective microporous separator can be felt from polypropylene fibers with a thickness of about 1 mm.

Brief description of drawings

Figure 1 illustrates the installation for the preparation of vanadium electrolyte solution from the solid source V₂O₅the agreement is but this invention.

Figure 2 - cross section of the electrolytic cell for recovery of vanadium according to this invention.

Figure 3 - cross section of an alternative implementation of the electrolytic cell for recovery of vanadium.

4 is a schematic diagram of the system is completely vanadium flow redox battery containing an electrolytic cell for recovery of vanadium according to the invention in the circuit of the positive electrolyte to implement rebalancing.

Description of the preferred embodiments of the invention

Referring to the block diagram in figure 1, the installation for the preparation of vanadium electrolyte according to this invention consists of a set of cells C1, C2, C3, ... C6 recovery of vanadium, hydraulically connected in cascade and sequentially fed to the appropriate source R1 DC.

The solution leaving the last cell C6 cascade, is collected in tanks T1 dissolution having means S1 mixing.

Vanadium pentoxide (V₂O₅) is injected into the tank T1 dissolved in an appropriate amount by using, for example, a typical raw material hopper and motor driven driven feed mechanism.

Vanadium enriched solution containing residual solids undissolved pentoxide is Anadia, it follows from the tank T1 dissolution through the outlet and is discharged into the settling tank T2.

Pump P2 supplies back into the tank T1 dissolving the separated residual solids vanadium pentoxide, which then collects in the bottom of the tank T2.

Vanadium enriched and filtered the solution ultimately is collected in the tank T3.

The vanadium contained in the enriched solution, which is collected in tank T3, will represent the vanadium in the condition V⁺⁴. Its content corresponds to the sum of the quantities V⁺³and sometimes V⁺²present in the electrochemically recovered solution resulting from the last cell recovery (C6) cascade, and is equivalent to the recovered amount of dissolved and recovered V⁺⁵. Residual unreacted number V⁺⁵can also be present together with V⁺⁴in enriched so the solution is going to T3.

The solution is continuously circulated by a pump P1 through a cascade of electrolytic recovery of vanadium after the introduction of acid, typically H₂SO₄and water in relative amounts corresponding provision of the necessary polyarnosti vanadium electrolyte solution.

Therefore, vanadium electrolyte solution flowing in the first cell C1 recovery is about being contain V ⁺⁴and possibly the residual quantity V⁺⁵.

On the negative electrodes (cathodes) of the cells C1, C2, C3,..., C6 recovery is the following basic reaction:

V⁺⁴+e^-==V⁺³(or more precisely VO⁺²+e^-+2N⁺==V⁺³+H₂O)

another reaction, if present vanadium in oxidation state +5:

V⁺⁵+e^-==V⁺⁴(or more precisely VO

On the negative electrode no other reactions do not occur. Hydrogen gas (thermodynamically favorable palvelimelta reaction) does not occur, since the electrode of a carbon felt has a relatively high hydrogen overvoltage, and the effective current density on the cathode surface is maintained at a sufficiently low level.

On the positive main electrode reaction should theoretically be any oxidation present ion vanadium with a low oxidation state (+4, +3 and +2) to pentavalent vanadium (V⁺⁵) (thermodynamically favorable palvelimelta reaction).

Of course, ions of vanadium, which is closer to the anode surface will be oxidized directly to V⁺⁵and any ion of vanadium in low the first degree of oxidation, which will migrate to the anode and to diffuse to the anode. But as vanadium ions near the positive electrode into V⁺⁵(absorbed), anode palvelimelta reaction will increasingly be supported by the only other possible polysemantic reaction, i.e. the formation and subsequent release of gaseous oxygen in accordance with the following reaction:

H₂O==O₂+2N⁺+2E^-

In asymmetric cell according to this invention the oxidation of vanadium is not practically excluded, as in the systems of the prior art that uses ion-exchange membrane electrolyzer and individual circuits containing vanadium Catolica and auxiliary acidic anolyte. In practice, any ion vanadium able to reach the surface of the anode of the electrolyzer, is easily oxidized to V⁺⁵.

But the special imbalance that is created in the densities of the electrode current, causes the anode to operate at relatively high current densities, which are orders of magnitude higher than those that can be provided by the processes of migration and diffusion of vanadium ions in the electrolyte solution and on the surface of the anode. This contributes to a significant release of oxygen at the anode surface, and the presence of intense emission of gaseous bubbles is ikorodu creates a mechanical barrier to the migration of ions V ⁺³to the anode.

This hindrance to diffusion cathode recovered vanadium ions in the anode can be greatly enhanced through the use of a shielding mesh or permeable (porous) membrane to hold the formed bubbles of oxygen near the anode and, thus, to exclude the guidance of a strong convective motions in the bulk electrolyte in the space between the retaining gas shielding grid and cathode surface, restored and enriched with ions of vanadium.

The application of the anode with low overvoltage of oxygen increases the release of oxygen.

Overall the Faraday current output increases significantly when using relatively thick microporous separator instead of the more permeable screen grid or aperture, but the voltage of the cell also increases. Therefore, it is possible to find the best compromise given the fact that the power consumption is proportional to the product of voltage and current.

Found that the Faraday current output above 40% can be easily provided at a density of cathode/anode current, equal to about 5; and with the increase of this ratio over 20 efficiency can reach 80% and above. Significant gains can be achieved through the use of separating g the C screen grid and even more, with a relatively dense microporous separator.

In the tank T1 dissolution V⁺³contained in the electrolyte solution from the electrolytic recovered vanadium reacts with solid vanadium pentoxide V₂About₅(or ammonium Vanadate)to dissolve it and restore to V⁺⁴according to the following reactions:

(V⁺⁵+V⁺³==2V⁺⁴or more precisely:

and (if V⁺²also present)

(2V⁺⁵+V⁺²===3V⁺⁴), or more precisely:

V₂O₅+V⁺²+4H⁺==3VO⁺²+2H₂About

The cross section of the asymmetric cell according to this invention used in the installation for the preparation of vanadium electrolyte according to this invention, is presented in figure 2.

Laboratory test cell, depicted in figure 2, consists of a cylindrical tubular body 1, usually made of metal, is chemically resistant to the electrolyte, acid-resistant non-conductive plastic, such as PVC, closed at the lower end of the cover 2 and having an inlet opening 3 at the lower part of the tubular housing 1 and the upper overflow hole 4.

A cylindrical cathode, which may consist of carbon felt 5 thickness of several millimeters, can be what is installed on the inner cylindrical surface of the tube 1 and suitably fastened thereto. The cathode of carbon felt may have a corresponding output 6 for electrical connection of the cell to the power circuit DC.

In a laboratory test cell, depicted in figure 2, the surface of the inner cylindrical surface of the cathode has a diameter of about 50 mm and height in contact with the electrolyte solution of about 250 mm.

The anode 7 is a titanium rod with a diameter of 6.3 mm, coated with a mixed oxide of iridium and tantalum, and the length of its immersion in the electrolyte is approximately 250 mm

The anode 7, which is a titanium rod coated, installed along the axis of the cylindrical cathode made of carbon felt.

In the specified laboratory test cell projected area of the cathode carbon felt is approximately 353 cm²and the surface of the anode, which is the titanium core, is about 47 cm².

When applying an electric current force 7A through electrolysis, the current density on the surface of the titanium anode is approximately 0,1485 A/cm²=1500 a/m²; the current density on the projected area of the carbon felt 0.022 A/cm²=220 A/cm². But due to the open and permeable morphology of the cathode in the form of a felt of carbon fibers valid or effective densely who be current on the cathode carbon may, estimated to be two to ten times smaller than the current density calculated by geometrically projected cylindrical cathode area, which is the carbon felt.

Figure 3 shows the cross section of the electrolyzer recovery of vanadium according to the alternative implementation of the present invention.

The only difference is represented by the presence of permeable for the fluid screen grid or diaphragm, or microporous separator 8, is installed between the cylindrical surface of the cathode and coaxially located anode rod, defining a cylindrical space around the anode rod 7, which essentially held a pop-up bubbles of oxygen that occurs on the anode surface and separated from it into the surrounding electrolyte.

The screen aperture 8 is essentially eliminates the hover strong convective motions in the bulk of the electrolyte near the cathode surface, which is the desired recovery V⁺⁴to V⁺³and then to V⁺².

Plastic tube with a small densely and uniformly distributed holes can serve as a satisfactory shielding mesh retention of gas bubbles, but a shielding grid 8 retention of bubbles of gaseous oxygen can be either a fine-meshed grid stakeho resistant material, as, for example, mesh, titanium wire, or woven material of the plastic fiber. More preferably, a shielding grid 8 retention of gas can be porous or microporous tube, for example of pittulongu glass, or of particles resistant metal such as sintered titanium.

EXAMPLE

Glass chemical glass with a capacity of 1/2 liter with an inner diameter of 8 mm was used to test the efficacy of the methods according to this invention.

Carbon felt with a thickness of about 6 mm was placed around the inner walls of the chemical glass and electrically connected to the negative pole of the source of DC power.

Titanium rod with a coating of mixed oxide IrO_x-ZrO_ywith an outer diameter of about 6 mm was mounted vertically along the geometric axis of the Cup and electrically connected with the positive pole of the source of DC power.

The ratio of the projected cathode space and an anode area was about 10.7.

Polypropylene fabric thickness of about 1 mm was made in the form of a round tube, a closed bottom, an inner diameter of about 12 mm and placed in a chemical glass concentrically around the coated anode in the form of a titanium rod.

The glass was filled 473 ml solution of 5-molar sulfuric to the slots and 90.9 g (0.5 mole) of vanadium pentoxide powder. Total volume of the mixture was 0.5 L.

Theoretically, for the recovery of 1 mole of vanadium from oxidation state +5 oxidation state +4 is required 26,8 A/h

The mixture was stirred electromagnetic stirrer, and yellow vanadium pentoxide powder remained essentially insoluble in a few days.

After power-DC and regulate its output voltage constant current power 8 And passed through the electrolyzer. The current density of the positive electrode (anode) was approximately USD 5,013 a/m²and the current density of the negative electrode (cathode) on the projected area of the carbon felt was approximately 468 a/m².

The voltage of the cell remained almost constant value of about 3.8 to 4.0 Century

Suspension nointention was stirred with a magnetic stirrer, and after passing current for 5,26 hours yellow powder, apparently, is completely dissolved.

Thus obtained blue solution was analyzed and found that it contains 2 mol of vanadium (2-molar solution), and the oxidation state of vanadium was +3,55.

The Faraday current output of the method was estimated 92,28%.

The test was repeated at reduced current of 5 amps, and the amount of time required was 9,87 hours. The Faraday current output decreased to approximately 78,74%, and also e.g. the position of the cell is about to 2.8 Century

After replacing the felt on thin woven polypropylene material of the Faraday current is reduced to approximately 47%, and without permeable hold approximately 20-25%.

Even under these sub-optimal conditions laboratory tests (in a glass beaker with stirring) the power consumption of the order of 0.2-0.5 kW·h/l obtained vanadium electrolyte gives a fairly low value from the point of view of General economic indicators obtain vanadium electrolyte.

The ability of asymmetric cell recovery of vanadium electrolyte in accordance with this invention effectively and inexpensively modify the oxidation state of dissolved vanadium content of the acid electrolyte solution makes a relatively simple and inexpensive, being undivided, asymmetric cell of the present invention is ideally suitable for rebalancing (restore equilibrium) state of charge of the positive and negative electrolytes vanadium in the current the battery (the battery) without having to perform costly and time-consuming processing, extracted from the state, redox battery installation whenever the battery reaches more invalid offset.

For poasm is of the nature of the difficulties, which can occur when the vanadium battery system for energy storage, a brief description of the main mechanisms that determine the emergence of an increasingly visible offset.

If theoretically to assume that the only process occurring during charging and discharging of the vanadium redox battery is electrochemical oxidation and reduction of the vanadium, and any other adverse reactions do not occur, the process of charging and discharging of the vanadium battery is a symmetric process.

While charging the electric current passing through the battery will oxidize V⁺⁴to V⁺⁵in the positive cells of the electrolyte and at the same time and with the same speed will restore V⁺³to V⁺²in negative cells of the electrolyte. The opposite reactions of oxidation and reduction occur in the positive and negative chambers of the electrolyte during discharge.

In practical terms, the situation is different.

Electrochemical oxidation and reduction of vanadium are not only occurring process. There is a probability that in critical conditions will be made following adverse reactions:

1) electrochemical separation of gaseous hydrogen on the negative the electrode

2) electrochemical oxygen at the positive electrode (*)

3) chemical oxidation V⁺²to V⁺³

4) chemical recovery V⁺⁵to V⁺⁴

(*) if the positive electrode is made of carbon, the oxygen is partially or completely replaced by carbon dioxide.

Reactions 1) and 2) become the only reactions on reaching 100 percent state of charge. In practice, after oxidation of all present in the positive electrolyte chamber V⁺⁴to V⁺⁵the only reaction on the positive electrode capable of providing current, is the release of oxygen (or carbon dioxide). Similarly, after the restoration of all things present in the positive electrolyte chamber V⁺³to V⁺²the only reaction on the negative electrode, capable of providing current, is the release of hydrogen. These reactions will begin during recharging batteries, although in relatively small volume, when the state of charge exceeds 90%.

The voltage at which the vanadium is oxidized or restored, proportionally increases with the ratio between the received object and expenditure object (Nernst equation), and therefore at high state of charge voltage of the cell rises to a voltage of hydrogen and to the of Sloboda (electrolysis of water), approximately 1.5 Century Reactions 1) and 2) will also occur in a relatively small space during battery discharge, if discharge is too fast pace (current).

When the current density reaches a limiting current, then the release of hydrogen and oxygen begins as spurious (unnecessary) reaction.

The limiting current is the electric current, at which the rate of oxidation or recovery of vanadium on the surface of the electrode is equal to the speed at which the vanadium ions diffuse from the main volume of electrolyte in the electrode surface through the depletion layer.

Reaction 3), the oxidation of V⁺²to V⁺³that is the most recurring adverse reaction during operation of the vanadium battery. V⁺²easily oxidized to V⁺³in the presence of air. Therefore, if the intake of atmospheric air into contact with the negative electrolyte is not strictly excluded (due to the fact that the surface of the electrolyte will be closed with a layer of nitrogen gas or covered with wax, for example), this adverse reaction can easily occur.

Due to the above adverse reactions, after many cycles of the battery, it is possible that the symmetry will essentially disappear.

Another reason because of which the electrolytes become unbalanced: applied membranes are not occur is different delimiters. Through the anionic membrane inevitably penetrates a small fraction of positive ions (H⁺and V⁺ⁿ).

As a rule, as battery separators preferred cationic membranes because of their higher mechanical and chemical resistance compared with anionic membranes.

Indeed, cationic membranes are mainly permeable to hydrogen ions (diffusion of N⁺much higher than the speed at ions of vanadium).

During recharging batteries hydrogen ions formed in the chamber by the reaction:

VO²⁺+H₂O===VO

easily migrate to the negative chamber through the membrane together with smaller amounts of the less mobile ions of vanadium.

Migratory vanadium ions will oxidize the appropriate amount recovered vanadium ions present in the negative chamber (V⁺³and V⁺³), but the process is not completely reversible, since ions of vanadium other oxidation States are coordinated differently with the solvent molecules (water, sulfuric acid), and have a different mobility in cation-exchange resin membrane. Of course, during the subsequent phase of the discharge, the number of ions of vanadium, passing the through the membrane in the opposite direction, will not be exactly the number that was carried out during the phase of charging.

The growing imbalance between electrolytes causes numerous problems, including:

1) battery capacity (in units of kW·h/l electrolyte) are reduced proportionally;

2) while charging one of the two electrolytes can be fully recharged, while the other will remain partially nezaryazhennymi.

In practice, especially in the case of a small battery, in which the removal of air from the negative chamber is often incomplete, ions of vanadium in the positive chamber can be completely oxidized to V⁺⁵and in the negative chamber will remain a significant volume V⁺³. This situation is very critical, because if the degree of oxidation carefully not to regulate in different electrolytes, but only to measure the open circuit voltage, the charging will continue until achieving complete oxidation of V⁺⁴to V⁺⁵. Under these conditions, a significant release of oxygen in the carbon electrode to oxidize and destroy the electrode.

In accordance with standard procedure, after a certain number of cycles of charging and discharging of the two electrolyte (negative and positive) are mixed, measure the degree of oxidation and, if it is not +3.5, then its chemicals regulate the to +3.5.

In practice, when the battery is stopped, and the electrolytes are mixed, the oxidation state of vanadium always exceeds +3,5 (mainly because of the influence of the dominant effects adverse reactions 3)).

The electrolyte to regulate the degree of oxidation of vanadium is +3,5, by introducing restorative substances (oxalic acid, sulfite, and others).

Then a significant amount of energy must be expended to bring the system back to its zero state of charge (V⁺³in a negative electrolyte, and V⁺⁴in the positive electrolyte).

It periodically takes the amount of energy represents a net loss of accumulation of energy.

This non-negligible, the energy loss can be substantially reduced in accordance with a feature of this invention, i.e. by installing a relatively small asymmetric cell recovery of vanadium in accordance with this invention in the negative, or more preferably, a positive circuit of the electrolyte according to Figure 4.

According to this picture the positive circulation of the electrolyte can be done fully or partially (in the latter case, by using, for example, an adjustable three-way valve or other means) through a relatively small asymmetric Electrol is grain recovery of vanadium (Reset).

Electrolyzer (Reset) may act in accordance with the need either continuously or periodically in order to keep the symmetric oxidation state of vanadium.

Thanks to the opportunities provided by the presence of this auxiliary cell recovery (Reset) can eliminate the need for mixing of the two electrolytes, regulation of oxidation to approximately +3.5 and pre-charge the battery to restore the zero state of charge, or you can perform them in cases of extreme necessity.

1. The method of obtaining acidic vanadium electrolyte solution containing V⁺³and V⁺⁴in the desired concentration of solid vanadium pentoxide, fed to the electrolyte solution, which consists in the fact that carry out electrochemical reduction at least partially dissolved vanadium in an acidic electrolyte solution by circulating the electrolyte solution through many cells in cascade at least to the degree of oxidation of V⁺³or to a lower oxidation state; carry out the reaction restored thus vanadium contained in the electrolyte solution, leaving the last of these cells, with the stoichiometric quantity of vanadium pentoxide, while receiving the solution e is carolita, containing vanadium, essentially, in oxidation state V⁺⁴; enter acid and water to maintain a certain polyarnosti solution; continuously recycling the electrolyte solution through a cascade of cells, while keeping the flow of the obtained electrolyte solution containing V⁺³and V⁺⁴in the right concentrations, the output of one of the cells specified cascade; each cell has a cathode and anode with the relevant morfologiya surface geometry and relative position to establish on the anode surface current density from 5 to 20 times higher than the current density in the projected cathode surface, and oxygen evolution at the anode.

2. The method according to claim 1, characterized in that the electrolyte solution is a sulfuric acid solution, and the molar content of vanadium is from 1 to 5.

3. The method according to claim 1, characterized in that the current density in the projected cathode surface is from 100 to 300 a/m²and the current density on the anode surface is from 1000 to 8000 a/m².

4. The method according to claim 1, wherein the vanadium oxide is in powder form and has a particle size less than 100 microns.

5. The method according to claim 1, characterized in that after the reaction recovered vanadium electrolyte solution with a specified degree is yoneticisi amount of vanadium pentoxide solution is separated from any residual undissolved particles of vanadium pentoxide.

6. Installation for the preparation of vanadium electrolyte solution containing V⁺³and V⁺⁴in the desired concentration of solid materials in the form of vanadium pentoxide, consisting of a number of electrolytic cells for recovery of vanadium, hydraulically connected in cascade and electrically fed sequentially from a regulated DC source; capacity dissolution collecting the recovered electrolyte solution leaving the last cell of the specified cascade of cells, and having a mechanical means of mixing and feeding mechanism for an adjustable amount of vanadium pentoxide in the form of a powder; a means of separating vanadium enriched solution coming out of the listed capacity of dissolution, the residual solids vanadium pentoxide; means for introducing sulfuric acid and water enriched with vanadium solution to maintain certain polyarnosti solution; pumping means for recirculatory of the electrolyte solution through a cascade of electrolytic cells for recovery of vanadium; an exhaust means for the discharge flow of the resulting electrolyte solution containing V⁺³and V⁺⁴in the right concentration ratio, the output of one of the cells specified cascade of cells; each cell has a cathode and the nod with the relevant morfologiya surface, the geometry and relative position to establish on the anode surface current density from 5 to 20 times higher than the current density in the projected cathode surface, and oxygen evolution at the anode.

7. An electrolytic cell for recovery of ions V⁺⁴and/or V⁺⁵in acidic vanadium aqueous electrolyte solution to V⁺³and/or V⁺²having cathode and anode with the relevant morfologiya surface geometry and relative position to establish on the anode surface current density from 5 to 20 times higher than the current density in the projected cathode surface, and oxygen evolution at the anode.

8. The electrolyzer according to claim 7, comprising a cylindrical tubular housing made of acid resistant electroconductive material having the inlet opening 3 and the overflow hole; a cathode made of carbon felt, located on the inner cylindrical surface of the tubular housing with output for electrical connection of the cell; rod anode of valve metal coated with depassivation electrocatalytic coating and installed along the axis of the cylindrical cathode made of carbon felt.

9. The electrolyzer according to claim 7, characterized in that it contains permeable to electrolyte means of retaining the floating bubbles of oxygen, rising in e is ektralite around or near the anode.

10. The electrolyzer according to claim 9, characterized in that the permeable means of retaining selected from the group consisting of a mesh screen, woven materials, felts, porous and microporous glass Frits and agglomerated bodies, which are all made of a material having chemical resistance to the electrolyte solution.

11. The electrolyzer according to claim 7, characterized in that the anode made of a valve metal coated with a mixed oxide of iridium and tantalum or zirconium.

12. The method of restoring the balance condition of the relative degree of oxidation of two separate vanadium electrolyte circulating in the system is completely vanadium flow redox battery without removing it from service, according to which the exercise circulation part one of two different electrolytes in the electrolytic cell for recovery of vanadium, which is external to the battery in accordance with any of claims 7-11, and serves the current through the cell during the time needed to restore the balance of the oxidation state of the vanadium contained in the two electrolytes system flow redox battery.

13. The method according to item 12, characterized in that the electrolyte is a positive electrolyte circulating in the chambers polojitelnogo the electrode of the battery.