DE2927868A1 - METHOD FOR STORING AND RELEASING ELECTRICAL ENERGY AND A BATTERY SUITABLE FOR THIS - Google Patents

Description

■■ .. £ ■ "■■

PATKNTANWÄLTE g 9 2 7 8 6 §

J. RBITSTÖTTER W. KINZBBACH

PROF. DR. DR. DIPL. ING; DR. PHIL. DIPL. CHBM.

W. BUNTE (1958-1976) K. P. HÖLLER

DR. INO. X) R. RER. NAT. DIPL. CHEM.

TELEPHONE: (08Θ) 37 85 83 j

TELBXi E2I6208 ISAR D}

BAUKRSTRASSE 22. βΟΟΟ MUNICH ΛΟ ,

Munich, July 10, 1979 M / 20 199

ORONZIO DE NORA IMPIANTI
ELETTROCHIMICI SpA
Via Bistolfi 35

20134 Milan
Italy

Process for storing and releasing electrical energy and more suitable for it accumulator

POSTAL ADDRESS ι POSTKACH 7BO, D -8000 MUNICH 43

ORIGINAL INSPECTED

M / 20 199 - 8 - 2327868

The present invention relates to a method for storing and releasing electrical energy in an electrochemical Cell and an accumulator suitable for this process.

It is known that an accumulator can be produced using electrochemical reduction and oxide i tion processes that essentially take place in the liquid phase * using soluble salts of metals that have different oxidation states. For example, works! a chromium-redox-accumulator according to the following electro-chemisehen Reaction:

Charge level:

4Cr ₂ (SO ₄ ) ₃ + 7H ₂ O ^ -> 6 CrSO ₄ + H ₂ Cr ₂ O ₇ + 6 H ₂ SO ₄

Discharge level:

6CrSO ₄ + H ₂ Cr ₂ O ₇ + 6 H ₂ SO ₄ ^ -> 4 Cr ₂ (SO ₄ J ₃ + 7 H ₂ O

with an electromotive force of about 1.74 volts.

An iron-titanium redox secondary battery operates according to the following electrochemical reaction:

Charge level: FeCl ₂ + TiCl ₃ —— >> FeCl ₃ + TiCl ₂

Discharge level: FeCl ₃ + TiCl ₂ —— > FeCl ₂ + TiCl ₃

with an electromotive force of about 1.14 volts.

The redox accumulators have the fundamental advantage that the reaction proceeds completely in solution and during

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ORIGINAL INSPECTED

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no chemical compounds in the charge and discharge stages deposit on the electrodes or be detached from them. In addition, no gases are released from the electrodes. Therefore problems that are common with other types of accumulators occurred, such as the morphology of metallic deposits on electrodes, gas development on the electrodes with the accompanying bubble effect, as well as the removal of the gas and storage, avoided.

Unfortunately, the redox accumulators are according to today. Considered rather bulky and unsuitable for the manufacture of accumulators with high specific power. About that also require the presence of a separator or a membrane that delimits the two cell compartments and - because of the mass transport - to avoid the need for a rapid flow of electrolyte over the electrodes of secondary electrode reactions, such as development of hydrogen at the anode or the evolution of chlorine and oxygen at the cathode, such electrode and electrode gap dimensions, that the cells become very bulky. In addition, the ohmic voltage drop in the electrolyte is considerable and contributes to a large extent to lowering the Capacity of the accumulator.

In known accumulators, the unit cell consists of _; essentially of two compartments which are separated by a microporous, inert separating device or preferably an ion exchange membrane. In general, the electrodes in the compartments are spaced from the separator or membrane surface so that the electralytes can circulate in the spaces between the electrode surface and the membrane surface. Porous electrodes are also often used, with the electrolyte flowing through the electrode. The electrode gap is therefore necessary

ORIGINAL INSPECTED

large and consequently of a high ohmic voltage drop accompanied in the electrolyte.

The object of the present invention is therefore to provide a new, improved redox accumulator with a high current density and to create low ohmic losses and in which the electrodes are in contact with the membrane or, preferably, are bound to it.

Another object on which the present invention is based is to provide a new, improved method for To store and / or release energy in an electrochemical cell.

Further objects and advantages of the invention can be found in the description below.

The present invention relates to a method for storing and releasing energy, in which the storage takes place in that the anode compartment of an electrochemical cell, which consists of an anode compartment and a Cathode compartment consists, which are separated from one another by a semi-permeable ion exchange membrane and has a solution-permeable anode, which consists of a thin, porous There is a layer of an electrically conductive, corrosion-resistant powder and is applied to the anode side of the membrane, with an anolyte solution of an oxidizable compound which is essentially dissolved in the anolyte solvent remains and can be reduced from its oxidized form,

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ORIGINAL INSPECTED

charged, an electric one to oxidize the anolyte solution Potential applied between the anode and the cathode, the oxidized anolyte solution removed from the anolyte compartment and stored, the catholyte compartment with a catholyte solution reducible compound, which is essentially in the catholyte solvent remains dissolved and can be oxidized from its reduced form, and the reduced catholyte solution removed from the catholyte compartment and stored, and in which the energy is subsequently released by being the oxidized anolyte through the anolyte compartment and the reduced one Circulating catholytes through the cathode compartment, while that is between the anode and the cathode forming potential allows a current to flow through an external power consumer.

The electrodes are in direct contact with the surfaces the ion exchange membrane and they consist of a thin, porous, permeable layer of a fine, powdery, electrically conductive, corrosion-resistant material that adheres to the membrane surface.

The devices with the help of which a direct electrical current Is applied to the electrodes, grids are preferably the electrode surfaces at a plurality of uniformly Touch points distributed over the entire surface of the electrodes, these grids preferably being electrically connected to the back plates of the electrode compartments.

The electrolyte flows continuously over the surface of the porous and permeable electrode resting on the surface the cell separator, i.e. the semi-permeable membrane is embedded.

The supply of the areas in which the electrode reactions expire, with the polyvalent metal ions is due to the porosity

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ORIGINAL INSPECTED

m / 20 199 -12 - 2927888

sity of the extremely thin layer of the particular material from which the electrode is made, and the electrode reaction takes place essentially at the interface between these particles and the ion exchange resin that makes up the membrane and on which it is embedded. the end For this reason, a voltage drop in the electrolyte can practically be ruled out.

The cathode and the anode preferably consist in the same way of a thin layer of an electrically conductive, powdery material. * that of the opposite Sides of the ion exchange resin membrane is bonded, although only one of the two electrodes is constructed in this way must be, while the other corresponding electrode is a conventional, holey, self-supporting Can be metal or graphite electrode, which is pressed against the other side of the membrane, or is arranged at a distance from the same.

The redox accumulator according to the invention consists of a housing with at least one cell that has a cathode compartment and an anode compartment, separated by an ion exchange membrane, contains porous, permeable layers of an electrically conductive, corrosion-resistant material on the two Sides of the membrane are applied and represent the anode and cathode surface, devices for uniform Distribution of a direct current on the anode and cathode surface, devices for the circulation of anolyte solutions through the anode compartment and devices for the circulation of catholyte solutions through the cathode compartment, the Anolyte and the catholyte metal ions in different oxidation states included.

In a preferred embodiment of the invention

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ORIGINAL INSPECTED

M / 20 199-13-2527868

Accumulators are a number of unit cells arranged in series and separated from each other by bipolar separating inserts, which consist of an electrically conductive wall, 'which on beden Sides are provided with protrusions which are in contact with the anode and the cathode through a series of points, wherein the anode is on the membrane surface of the one unit cell while the cathode is attached to the membrane surface of the adjacent cell.

The anolyte and catholyte solutions can be in two corresponding Containers stored and are circulated with two circulation pumps through the anode and cathode compartment. the Electrolyte solutions are applied over the surfaces of the porous, permeable and on the surface of the membrane Electrodes flow so that the electrodic oxidation and reduction reactions essentially take place at the interface of the Electrode particles and the ion exchange membrane take place. In this way, the ohmic voltage drop is practically prevented both in the anolyte and in the catholyte solution. In addition, the high specific surface supports the electrodes, which are formed by the thin layers of powdery material bound to the membrane, in terms of apparent surface area, effectively reducing polarization and allowing use high current densities.

While the new features that made the invention of particular Meaning are described in the claims, the invention will be both in essence and practical Implementation as described in detail below, the understanding is facilitated by reference to the attached figures.

809885/0734

ORIGINAL INSPECTED

The preferred redox couples in a Storage batteries that can be used are chrome-chrome, titanium-iron, vanadium-vanadium and vanadium-iron.

FIG. 1 shows a schematic representation of a complete arrangement of a redox accumulator according to the invention.

FIG. 2 shows an enlarged partial longitudinal section of a unit cell of the accumulator from FIG. 1 to explain the reactions taking place.

Figure 3a shows an exploded view of a typical

Embodiment of an accumulator according to the invention and

FIG. 3b shows a longitudinal section of the assembled accumulator from FIG. 3a.

With reference to FIG. 1, the complete system of a redox accumulator consists of at least one unit cell 10 which contains an ion exchange membrane 11 on its Surface the electrodes made of electrically conductive, chemically corrosion-resistant, powdery materials are appropriate. Examples of suitable materials are metals of the platinum group, their alloys or intermetallic compounds, their conductive oxides, platinum black, Palladium black, oxides of tin, lead, antimony, bismuth, cobalt and Manganese, conductive oxides such as spinel-type oxides, perovskites and delafossite, graphite and acetylene black.

The anode 12 is bound to the membrane surface, while the cathode 13 is bonded to the opposite ¹ membrane surface. The metallic lattice-shaped electricity

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ORIGINAL INSPECTED

m / 20 199-15-2927861

Pickups 14 and 15 are electrically connected to walls 16 and 17, which act as negative and positive end plates, respectively and the current collectors are pressed against the electrodes. The two cell coils 16 and 17 are electrically isolated from one another by an insulating seal 18. When commissioning of the system, the anolyte solution contained in the container 19 is continuously passed through the circulation pump 110 through the anode compartment pumped, while the catholyte solution contained in the container 111 through the circulation pump 112 continuously the cathode compartment is circulated.

The cell electrodes are chemically inert, they act as electron acceptors and donors and thereby build a potential that depends on the concentration of the ions in the solutions with which they are in contact. For example is a previously charged chromium accumulator discharged by the fact that the catholyte solution contained in the container 111 with the hexavalent chromium circulates in the cathode compartment and the anolyte solution contained in container 19 with the divalent Circulating chromium in the anode compartment. The hexavalent chromium is reduced to trivalent chromium at the cathode Chromium, whereby SO, - ions are released and migrate through the anionic membrane and reach the anode, where the bivalent chromium is oxidized to trivalent chromium. Therefore the concentrations of the anolyte and catholyte solutions will be different ultimately balance and the cell potential drops to zero.

To charge the accumulator, the anode and the cathode are connected to the negative or positive pole of an electrical direct current source connected and the reactions "proceed in the opposite direction, with in relation to the trivalent chromium in the catholyte solution has a high concentration of hexavalent Chromium is achieved again and vice versa in terms of that

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ORiGlNAL INSPECTED

M / 20 199 - 16 -

trivalent chromium has a high concentration in the anolyte solution is obtained on divalent chromium.

Figure 2 is a schematic representation of a longitudinal section the accumulator unit cell, consisting of an ion exchange resin membrane 21 to which the anode 22 and the cathode 23 are bonded. The two metallic, reticulated j Current collectors touch the electrodes at a large number of I evenly over the entire surface of the electrodes ver j shared posts. This figure is used in particular to understand the invention and the operation of the invention Accumulator. A storage system based on chromium compounds is shown, with the specified reactions describe the discharge of the accumulator. The membrane 21 is of the anionic type and it is opposed to sulfuric acid solutions resistant and is preferably made of fluorinated resin containing quaternary ammonium groups.

The electrodes 22 and 23 are preferably made of a powdery mixture of graphite and platinum black, which is an the membrane surface is bound, and form a porous layer, which is well permeable to the membrane. The current collectors 24 and 25 are nets, preferably made of a valve metal (valve metal), such as niobium, tantalum, titanium, zirconium and hafnium, these being galvanically coated with platinum or a platinum-iridium alloy in a particularly preferred embodiment are. The current collectors 24 and 25 are pressed against the electrodes 22 and 23 and are connected to the electrical connections be connected to the battery.

The catholyte solution containing hexavalent chromium becomes so circulates into the cathode compartment, the solution flows along the porous cathode surface, the current collector 25 is so wide that the flow of the solution along the cathode surface 23 is not hindered. This is

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COPY ^ ORIGINAL INSPECTED

m / 20 199 - "■ -, .- 17 - 2927860

favors a good mass transport away from the electrode surface and towards it and at the same time prevents a Depletion of reactive ionic species on the electrode. The divalent chromium containing anolyte solution is on is circulated into the anode compartment in the same manner and brought into contact with the porous anode surface 22. Form thereby the two electrodes from their respective potentials, which are dependent on the ratio of the concentration of hexavalent and divalent chromium ions in the corresponding solutions.

While the battery is discharging, an electrical current flows through the electrical connections that connect to the cell terminals connected, with the following reactions occurring:

at the cathode (positive pole):

Cr ₂ O ₇ ² ^ + 14H® + 6e®-) 2 Cr ³ ® + 7H ₂ O

[Ion transport through the membrane (from the cathode side to the Anodes page):

12 SO ₄ ²⁰ -> 12 SO ₄ ²⁰
at the anode (negative pole):

6 Cr '
Overall reaction:

H ₂ Cr ₂ O ₇ + 6CrSO ₄ + 6H ₂ SO ₄ ■ ^ 4Cr ₂ (SO ₄ J ₃ + 7H

The opposite happens when the battery is charged, as follows the reactions:

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ORIGINAL INSPECTED COPY }

M / 20 199-18-2927869

at the cathode: 6Cr ⁺⁺⁺ + 6e ~> 6Cr ⁺⁺

Ion transport through the membrane (from the anode side to the cathode side):

12 SO ""

at the anode: 2Cr ⁺⁺⁺ + 7 H ₂ O> ^Cr 2 ° 7 ~~ ^{+ 14 H + + 6e}

Overall reaction:

7 H ₂ O + 4Cr ₂ (S0 ₄ ) ₃ - ^ -> 6CrSO ₄ + H ₂ Cr ₂ O ₇ + 6H ₂ SO ₄

The anodic and cathodic reactions take place practically at the interfaces between the particles that make up the electrodes and the ion exchange resin membrane, i.e. the catalytic areas in the electrodes are in direct contact with the ion-exchanging residues of the resin membrane. Ion conduction in the solution is practically excluded and the ionic conduction occurs only through the thickness of the membrane, which causes the ohmic voltage drop in the cell is significantly reduced. At the same time, the porosity and the thin layer properties of the electrodes facilitate the renewal of the Electrolyte on the entire electrode surface, thereby avoiding polarization effects, while the multitude the electrical contact points with the pantographs have a low ohmic voltage drop in the electrically conductive ones Areas of the cell, i.e. in the porous particulate electrodes attached to the membrane.

FIGS. 3a and 3b serve to explain a practical embodiment of the accumulator according to the invention. Figure 3b

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COPY, ORIGINAL INSPECTED

292786a

M / 20 199 - 19 -

shows a longitudinal section of the accumulator shown in FIG. 3a, with identical parts of the accumulator J in both figures are provided with the same reference numbers. ί

The accumulator consists of an anode end plate 31, one Cathode end plate 32, a bipolar separator insert 33 and two membranes 34a and 34b, on the surfaces of which the electrodes are bonded. The accumulator thus consists of two in Series arranged unit cells and it is obvious that a practically unlimited number of similarly arranged Unit cells can be inserted between the two end plates by making an appropriate number of bipolar Separator inserts and membranes that carry the electrodes are inserted between the plates. The anode end plates are preferably made 31 and the cathode end plate 32 made of the same material as the bipolar separator insert 33. The anode end plate 31 has one in the center on its inner surface corrugated area, the channels forming corrugations 35 hydraulically with the anolyte in cup 36 and the Anolyte outlet 37 are connected.

The cathode end plate 32 similarly has on its inner surface in the center a corrugated area 38, the Corrugations 39 hydraulically via the inflow and outflow channels 310 with the catholyte inlet 311 and the catholyte outlet 312 are connected. Both end plates are provided with devices 313 for the electrical connection of the battery. The bipolar Separation insert 33 has on both sides a corrugated area in the middle, the channels of which forming corrugations 314 on the cathode side with two bores 315 and 316, which are coaxial with the inlet 311 and the Outlet 312 of the cathode end plate are arranged, while the corrugations 317 on the anode side of the bipolar separating insert with the two bores 318 (not

COPY I ORIGINAL INSPECTED

m / 20 199 - 20 - 29278 §8

shown) and 319 coaxial with the anolyte inlet 36 and Anolyte outlet 37 of the anode end plate are arranged, connected are.

The bipolar separating insert and the two end plates are preferably composed of a conductive mass of powdery Graphite and a chemically inert resin. The membrane 34a of the first unit cell consists of an ion exchange resin plate, on the middle area of which, corresponding to the corrugated areas on the anode end plate and the cathode side of the bipolar separator insert 33, the electrodes are attached, ie the anode 320a on the side opposite the anode end plate and the cathode 321a on the side, which is opposite the cathode side of the bipolar separator insert 33, with both electrodes made of an electrically conductive, corrosion-resistant, powdery material have been produced. The membrane 34b of the second unit cell also exists from a ion exchange resin plate, on the middle area, corresponding to the corrugated areas on the anode side of the bipolar separator insert 33 and the cathode end plate 32, the anode 320b and the cathode 321b are attached.

Suitable materials for the anodes 320a and 320b and the cathodes 321a and 321b are powders of graphite, precious metals, such as platinum, ruthenium, rhodium, palladium, iridium, osmium, their alloys and intermetallic compounds, oxides these metals and oxides of tin, lead, antimony, bismuth, cobalt and manganese, conductive oxides such as oxides of the spinel type, Perovskites, delafossite, palladium black, platinum black and acetylene black. Both membranes 34a and 34b each have four bores (6a) 37a, 311a, 312a and (6b) 37b, 311b, 312b, which are coaxial with the bores 36, 37, 311 and 312 of the anode end plate 31 or cathode end plate 32 are arranged. The bores (6a) and (6b), which are not shown in the figures, are coaxial to the bores 36 of the anode end plate 31 and the

909885/0734

ORIGINAL INSPECTED

Bores 3ί8 of the bipolar separation insert arranged.

The anode end plate 31, the cathode end plate 32, the membranes 34a and 34b as well as the bipolar separating insert 33 have a number of bores 322 for the connecting rods 323 on. Said connecting rods 323 can be made of an insulating material such as Teflon, nylon etc. or a Made of metal »whereby in the latter case an insulating plastic cover and washers must be provided, around the connecting rods, the endplates and the bipolar Isolate separating insert electrically from each other and so on To prevent short circuits within the cell »The connection Bars are secured with nuts 324 and washers 325 and when the cell is assembled, shown in Figure 3b, the peripheral portions of the end plates are 31 and 32 and the bipolar separator 33 opposite the peripheral areas of the membranes 34a and 34b hydraulically sealed.

All surfaces of the bipolar separator and the two end plates, with the exception of the surfaces that correspond to the Electrodes in contact are preferably powdered with a thick resin layer that is not electrically conductive Has material, isolated. This prevents electrode reactions on the surface - those with the electrolyte solution or are in contact with the ion exchange resin caused by ion migration through the membrane resin, for example "-. on the sealing surface.

The projections of the "central corrugated area" of the anode endplate .31 are in electrical contact with the anode. 32Qa is mounted the mn der.Membrane 34a "while the Vorspringe of the central corrugated portion of the bipolar TirenneiEtsatzes 33.auf the Katfeode-nseits in electrical contact. RiIt-the cathode 32, Ia ₃ , -die Sii tier ifesfttorane 34a angs

ORIGINAL INSPECTED

M / 20 199-22-2927869

Make contact and the projections located on the anode side of the separating insert 33 with the anode 320b and the projections of the cathode end plate 32 with the cathode 321b in Be in contact. In this way a series of bipolar unit cells is formed and their number can be determined by insertion several bipolar elements can be increased in this series arrangement.

When the accumulator is in operation, the anolyte solution pumped into the cell through inlet 36 of the anode end plate and the electrolyte is distributed in the first anode compartment, which is formed by the corrugations of the central area of the anode end plate 31 and the electrolyte then flows through the passage through the bore 36a in the membrane 34a and through the bore 318 in the bipolar separation insert 33 is formed, with both bores arranged coaxially with the inlet 36, in the second anode compartment, which is through the Corrugation of the central area of the anode side of the bipolar separator 33 is formed. The electrolyte then leaves the cell through the outlet 37 which passes through the bore 37a in the membrane 34a and the bore 319 in the bipolar separator insert is connected to the second anode compartment. The catholyte solution is in the same way through the cathode compartments circulated through inlet 311 and outlet 312 of cathode end plate 32.

To attach the electrode to the membrane surface you can different procedures can be used. According to a known method, the powder of the electrically conductive material mixed with powdered polytetrafluoroethylene »its proportion in the mixture can be about 15 to 60% by weight, preferably about 15 to 20% by weight. A powder that turns out to be more satisfactory Way, is marketed by DuPont under the name Teflon-T-30! Instead of polytetrafluoroethylene (PTFE), however, j

COPY ^ ORIGINAL INSPECTED

other resins can be used in the battery, provided they are
are resistant to the electrolytes. The mixture of powders is placed in a mold and made into a sintered one
Film heated, which is then applied to the membrane surface and pressed hot on this.

Another method is described in U.S. Application No. 878,906, filed February 17, 1978, wherein the electrodes are formed by applying a liquid suspension of the electrically conductive powder in an ion exchange resin solution to the membrane surface, the resin with the
the membrane-forming resin is compatible. The suspension is then dried and heated, whereby the powder containing resin is deposited on the membrane surface and bound to it. Preferably the binder is an ion exchange resin similar to that from which the membrane is made.

The electrically conductive powders have a particle diameter between 0.5 and 30 μm, preferably between 10 and 20 μm. The charge with electrically conductive material is
0.5 to 10 mg / cm ² , preferably 1 to 5 mg / cm ^{2 of} the electrode surface. The thickness of the electrodes bonded to the membrane surface is less than 0.1 mm and is preferably 0.01 to 0.06 mm.

The poor strength of the electrodes is along with theirs
Porosity is of great concern as it has in fact been found that side reactions are effective in the
Electrodes can be prevented if the strength of the electrode is reduced. This can be understood by considering that the transport of the ions that support the main electrode reaction from the electrolyte to the catalytic sites in the contact areas between the electrode

9095887073 *

ORiGiNAL INSPECTED ^C0PY

particles and the ion exchange resin of the membrane, the easier the thinner and the more permeable the electrodes are. on this way, the diffusion of the ions supporting the main electrode reaction through the so-called electric double layer becomes supported and this leads in practice to a lower polarization of the electrodes and thus to a better current-voltage curve during the discharge of the accumulator and thus ultimately to a higher energy yield. The lower electrical planar conductivity of the electrodes, which are extremely thin for the reasons mentioned above, can effectively compensated for by increasing the density of the contact points with the current collectors, which can be achieved by using, for example, very fine-meshed nets. Another reduction in Ohmic voltage losses can be achieved by coating the contact areas of the current conductors with platinum.

The membrane can be either anionic or cationic, depending on the nature of the redox couple in the solutions and thus depending on the type of ions which pass through the membrane. Indeed, the ionic conduction through the membrane is due to the transport of anions, such as SO. or Cl "or cations, typically H ⁺ .

Particularly suitable cationic membranes consist of a fluorocarbon polymer which has been formed into thin sheets and which contains acid residues such as sulfonic acid or carboxylic acid residues. In the membranes containing the sulfonic or carboxylic acid residues, the ion-exchanging groups are formed by the hydrated acid residues SOg ^- H '«0, which have been incorporated into the polymeric structure by sulfonation. The ion exchange groups are immobile in the membrane because they are chemically attached to the polymer

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ORIGINAL INSPECTED

Are chain linked so that their concentration is constant remain.

A specific class of such cationic membranes that are particularly resistant to acids and oxidizing reagents are stable, is marketed by DuPont under the name Nafion, these membranes of hydrated copolymers of polytetrafluoroethylene and sulfonated polyfluorovinyl ethers that contain sulfonic acid groups exist. Other suitable cationic membranes can be made from sulfonated styrene-divinylbenzene copolymers, preferably on an inert and porous carrier material such as asbestos paper or made of sulfonated tetrafluoroethylene / acrylic acid copolymers are produced.

Particularly suitable anionic membranes consist of one thin film of a fluorocarbon polymer or a styrene-divinyibenzene copolymer, the basic radicals, such as, for example, quaternary ammonium groups, pyridine or substituted Contains pyridine groups. Such membranes are made by Ionics manufactured.

The membrane must be able to be traversed on the one hand by the special ions (Cl "or SO." Or H ⁺ ), while on the other hand they effectively prevent the passage and mixing of other ionic species through the membrane or on a The thickness of the membrane is generally on the order of a few tenths of a millimeter In the case of thermoset crosslinked resins, such as styrene-divinylbenzene copolymers, which have been copolymerized on an inert support such as asbestos paper, the thickness of the membrane can be any or be several millimeters.

90988 5/0734

The charging or discharging process of the accumulator, which is connected to an external electrical circuit or connected to a direct current source, is carried out by introducing the catholyte solution into the cathode compartment and the anolyte solution into the anode compartment and circulating these solutions through the corresponding containers and cell compartments leaves. The flow rate is preferably 100 to 5000 cm ³ per minute per 1000 cm ^{2 of} electrode surface at 0.08 A / cm ² measured as the current drawn from the battery by the circuit.

In the following example, the invention is described on the basis of a preferred embodiment. The invention is but not limited to these.

example

Sample accumulators were produced according to FIGS. 3a and 3b and arranged as shown in FIG. The electrodes consisted of a powdery mixture of graphite and platinum black in a weight ratio of 9: 1, and were bound to the surface of an anionic membrane (IONAC 3475 M). The electrodes were about 0.05 mm thick, which corresponds to a powder load of 2 to 3 mg / cm ² . The powders had an average particle diameter of 20 μ.

The accumulators operated using a Cr / Cr redox couple. The two containers were charged with a 1 M chromium sulfate solution / Cr ₂ (SO ₄ ) ^ in 10% sulfuric acid. The accumulators were charged by connecting the cathode and the anode to the positive or negative pole of a direct current source and the two solutions in their corresponding

909885/0734

ORIGINAL INSPECTED

The corresponding cell compartments were allowed to circulate at a flow rate of 1000 cm ³ per minute per 1000 cm ^{2 of the} electrode surface. The current density during the charging stage was 0.1 A / cm ² and the charging was prolonged corresponding to 40 Mhr per kg of chromium in the system.

At this point, the battery terminals were connected to an external circuit and the battery was discharged ^{at a current density of 0.1 A / cm 2.} The flow rate of the solution through the accumulator was kept at 1000 cm ³ / minute per 1000 cm ^{2 of} electrode surface. The accumulator had an electromotive force of 1.7 volts and an operating voltage of 1.5 volts,

The power density was 5.8 k Wh / m ² and the energy yield was during an entire cycle

Obviously, various modifications of the Accumulator according to the invention are possible without the frame to leave the present invention.

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ORIGINAL INSPECTED

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Claims (17)

M / 20 t99 ■. ".-- :. ---. 292-7368" Pa ten ta η s ρ r Ii c he Process for storing and releasing electrical energy in an electrochemical cell with an anode and a cathode compartment, which are separated from one another by a semi-permeable ion exchange membrane, characterized in that one cell with a solution-permeable anode made of a thin porous layer; an electrically conductive, corrosion-resistant powder, which is applied to the anode side of the membrane and a solution-permeable cathode made of a thin porous Layer of an electrically conductive corrosion-resistant Powder that is applied to the cathode side of the membrane, the anode compartment with an anolyte solution an oxidizable compound which remains essentially dissolved in the anolyte solution and out of its oxidized form can be reduced again, charged, an electrical potential applied between the anode and the cathode in order to to oxidize the anolyte solution, the oxidized anolyte solution removed from the anolyte compartment and stores the oxidized anolyte solution, and at the same time the catholyte compartment with a catholyte solution of a reducible compound, those essentially in the catholyte solvent remains dissolved and oxidizes again from its reduced form can be charged, the reduced catholyte removed from the catholyte compartment and the reduced catholyte solution stores and that one then releases the electrical energy by the fact that one oxidized Circulating anolyte through the anolyte compartment and the reduced catholyte through the catholyte compartment, wherein the potential that develops between the anode and cathode generates a current through an external circuit lets flow. 909885/073 * ORIGINAL INSPECTED H / 20 199 - / - 2927888 2. The method according to claim 1, characterized in that the supply and discharge of the electrical current to the electrodes and away from the electrodes over a plurality of evenly across the surface of said Electrode distributed points takes place. 3. The method according to claim 2, characterized in that the oxidizable anolyte solution obtained during the energy storage cycle circulates is a solution of a soluble salt of a metal that has more than one valence state has, wherein the salt of said metal ^ is in a lower valence state and that the catholyte solution is a solution of a soluble salt of a Is metal that has more than one valence state, whereby the salt of this metal is in a higher valence state of affairs. 4. The method according to claim 3, characterized in that the j metals are selected from the group chromium, titanium, Iron and vanadium. Process according to claim 1, characterized in that the electrically conductive and corrosion-resistant powder is made from at least one of the materials selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium, osmium, i their alloys and intermetallic compounds _s their oxides, Platinum black, palladium black, graphite, acetylene black, oxides of tin, lead, antimony, bismuth, cobalt and manganese, electrically conductive oxides of the spinel type, perovskite and delafossite. 6. The method according to claim 1, characterized in that the thin porous layer electrodes on the membrane surfaces | 909885/0734 ORIGINAL INSPECTED m / 20 199 - ■ /-._ ■ '. - 2927888 ■■ "■ ^: " ν .-: U ■. ■. · ³ ' ^: · ■.'. ■■ are applied, have a thickness of 0.010 to 0.06 mm and the powder has an average particle diameter of 0.5 to 30 µm. 7. A process for the electrolytic oxidation of metal ions from a lower valency state to a higher valency state in an anolyte solution, characterized in that the anolyte solution with the metal ions in the lower valency state is passed over an anode surface made of a thin, porous anolyte-resistant layer of a finely powdered, electrically conductive and corrosion-resistant Resistant material _r which is applied to the surface of a semipermeable membrane that separates the anolyte compartment from the catholyte compartment, allows it to flow and at the same time applies an electrical potential between said anode surface and the corresponding cathode, which is sufficient to bring the metal ions into the higher Hertig state oxidize, and then the oxidized anolyte solution from-de.nv AnoTytab-part ^: wins. 8. The method according to claim 7, characterized in that the finely powdered, electrically conductive and corrosion-resistant material is selected from the group of platinum, Palladium, iridium, ruthenium, rhodium, osmium, their alloys and intermetallic compounds, their oxides, platinum black, pail adium black, graphite, acetylene black, oxides of tin. Lead, antimony, bismuth, cobalt and manganese, electrically conductive oxides of the spinel type, perovskite and Delafossite. ~ 9. The method according to claim 7, characterized in that the thin, porous, electrolyte-permeable, on the membrane surface applied layers have a thickness of 0.01 to 0.06 mm and the powder has an average particle diameter of 0.5 to 30 μm. 909885/0734 ORIGINAL INSPECTED 10. Process for the electrolytic reduction of metal ions from their higher valence state to a lower one Valence state in a catholyte solution, characterized in that that the catholyte solution with the metal ions in the higher valence state over a cathode surface made of a thin, porous, catholyte-permeable layer of a finely powdered, electrically conductive and corrosion-resistant material, which is applied to the surface of a semipermeable Membrane is applied, which the cathode; part separates from the anode compartment, allows it to flow and equal- j a timely electrical potential is applied between said j cathode surface and the corresponding anode, j which is sufficient to reduce the metal ions in their lower valence state and the reduced Catholyte solution from the said catholyte abbey new i η η t. 11. The method according to claim 10, characterized in that the electrically conductive and corrosion-resistant fine powdered material is selected from the group of platinum, palladium, iridium, ruthenium, rhodium, osmium, their alloys and intermetallic compounds, their oxides, Platinum black, palladium black, graphite, acetylene black, oxides of tin, lead, antimony, bismuth, cobalt and manganese, electric conductive oxides of the spinel type, perovskites and delafosites. 12. The method according to claim 10, characterized in that the thin, porous, electrolyte-permeable, on the Membrane surface applied layers a thickness of 0.01 to 0.06 mm and the powder has an average particle diameter of 0.5 to 30 μm. 13. Redox accumulator consisting of a housing with at least a cell consisting of a cathode compartment and an ano- 909885/073 * ORIGINAL INSPECTED M / 20 199 -V- 1927869 the compartment, which is separated by an exchange membrane are, porous permeable layers of an electrically conductive, corrosion resistant material on each side of the Membranes as anode and cathode surfaces, devices for the even distribution of a direct current on the; Anode and cathode surface, devices for the circulation of the anolyte solutions through the anode compartment as well as pre- directions for the circulation of catholyte solution through the Cathode compartment, said anolyte and catholyte Contains metal ions in various states of oxidation. 14. Accumulator according to claim 13, characterized in that the electrically conductive and corrosion-resistant material from which the electrodes are made is selected from the ■ '- ..' group platinum, palladium, iridium, ruthenium, rhodium, Osmium, its alloys and intermetallic compounds, their oxides, platinum black, palladium black, graphite, acetylene black oxides of tin, lead, antimony, bismuth, cobalt and manganese, j electrically conductive oxides of the spinel type, perovskites and Delafossite. j 15. Accumulator according to claim 13, characterized in that , using the electrically conductive powdery material ; a resin binder that is opposite to the cathodic and anodic solutions is resistant to the surface of the ι membrane is bound. 16. Accumulator according to Claim 15, characterized in that the porous, permeable, applied to the surface of the membrane Layer of the electrically conductive material has a thickness of 0.01 to 0.06 mm and the powder has a has an average particle diameter of 0.5 to 30 μm. 909885/0734 ORIGINAL INSPECTED 17. Accumulator according to claim 13, characterized in that Cr ⁺ , Cr ³⁺ and Cr are used as metal ions of different oxidation states. 909885/0731 ORIGINAL INSPECTED