WO2001039312A1

WO2001039312A1 - Electrochemical energy storing cell

Info

Publication number: WO2001039312A1
Application number: PCT/DE2000/001218
Authority: WO
Inventors: Werner Henze
Original assignee: Werner Henze
Priority date: 1999-11-19
Filing date: 2000-04-14
Publication date: 2001-05-31
Also published as: DE10083651D2; AU5670800A; EP1230707A1

Abstract

The invention relates to an electrochemical energy storing cell comprising a cathode (K) and an anode (A). Said cell is divided into partial cells. A hydrogen electrode (E1) is situated between the partial cells. The partial cell facing the cathode comprises a metal storage device and an electrolyte (EL1) and the partial cell facing the anode comprises a gas accumulator (GSP) and an electrolyte (EL2).

Description

Electrochemical energy storage cell

The invention relates to an electrochemical energy-storing cell according to the preamble of claim 1 and an energy storage system according to claim 33.

Electrochemical energy stores should generally meet the following requirements:

high nominal voltage of the entire cell, high energy density per mass unit, high energy density per volume unit, low self-discharge at working temperature (generally -20 ° C to + 50 ° C),

Rechargeability, good reversibility, long service life, low material costs, sufficient environmental compatibility,

Ability to work without external material supply and no waste products.

In practice, it is difficult to meet all of these requirements simultaneously to a sufficient extent. Known cells and accumulators are often too large, too heavy and sometimes too expensive for their energy output. Their shelf life is limited by the occurrence of irreversible processes which, even if they occur on a small scale, lead to significant performance losses in the long run.

Known electrochemical cells are e.g. in the book "Batteries and Accumulators", Springerverlag 1998 by Lucien F. Trueb and Paul Rüetschi and in the journal Funkschau 15/96, pages 37 to 41.

The object of the invention is to provide an electrochemically operating cell in which reversible electrical energy can be converted into chemical energy and which meets the requirements mentioned above much better than conventional rechargeable batteries and accumulators.

The achievement of the object is characterized in claim 1, further advantageous embodiments and developments of the invention are given in the subclaims.

The cell according to the invention consists of a partial cell on the cathode side and an anode side. There is a hydrogen electrode between the two cell parts.

The cathode forms the negative electrode (negative pole). When charging with direct current, the positively charged ions migrate to the cathode, pick up the missing electrons there and become electrically neutral. The process is reversed when unloading.

The anode forms the positive electrode (positive pole). When charging with direct current, the negatively charged ions migrate to the anode and give off their excess electrons there. The process is reversed when unloading.

The cathode-side sub-cell consists of a cathode-side electrolyte and a memory which contains a base metal in crystalline or dissolved form.

This memory is referred to below as a metal memory.

If the metal storage consists of a crystalline metal, the metal itself forms the cathode.

In the case of a dissolved metal, preferably an alkali metal dissolved in anhydrous ammonia, the solution and an adjoining intermediate electrode form the metal store. The solution is delimited by the cathode on the opposite side of the intermediate electrode. Such a solution of anhydrous ammonia and an alkali metal has a very high electrical conductivity. The effective part of the intermediate electrode consists of at least one graphite layer. A graphite electrode can also be used as the cathode.

The electrolyte on the cathode side, which is arranged between the hydrogen electrode and the metal store, has a different composition depending on the type of metal store. If a crystalline metal is used as the metal store, the cathode-side electrolyte contains, in addition to the solvent, for example water, at least one additive which increases the conductivity, preferably potassium hydroxide or ammonia. This enables the electrolytic processes.

If, on the other hand, a dissolved alkali metal and an adjoining intermediate electrode are used as the metal store, the cathode-side electrolyte consists of an anhydrous solvent, preferably ammonia, and an additive which increases the conductivity, for example an alkali metal amide, which can be both electrolytically formed and decomposed ,

The anode-side sub-cell consists of an anode-side electrolyte and a memory which is able to store halogens, for example fluorine.

This storage will be referred to as gas storage in the following.

There is a graphite electrode between the anode-side electrolyte and the gas storage device, which encloses the gas storage device with a further opposite graphite electrode that forms the anode.

The anode-side electrolyte consists of a halogen-containing water-free solvent, for example hydrogen fluoride, in which to increase the conductivity and to accelerated course of the electrolytic processes at least one salt, for example ammonium fluoride or potassium fluoride, is dissolved.

Free halogens are known to be very aggressive and toxic. With the exception of bromine and iodine, they can only be stored as gas under great pressure, for example in steel bottles.

However, the gas storage device according to the invention is capable of chemically binding halogens and storing them in graphite. The gas storage therefore consists of a mixture of graphite particles and at least one halogen compound which can easily add and release further halogen atoms, the value of the binding partner atom changing. These compounds include, for example, manganese (III) fluoride, manganese (IV) fluoride, bromine fluoride or bromine trifluoride. Halogen atoms are stored in the crystal lattice of the graphite particles during charging and released again when discharging. The embedded halogens are partly ionically bound in the crystal lattice of the graphite and partly exist atomically or molecularly. In this way it is possible to store larger quantities of an otherwise gaseous halogen.

The halogen fluorine is preferably used, which has a very high normal potential E ₀ = 2.71 V compared to the normal hydrogen potential (0.0 V) in anhydrous hydrogen fluoride. Otherwise, the remaining processes in the entire cell only take place with elements that are relatively minor Have atomic weight, whereby a high energy density / mass unit can be achieved.

Also on the cathode side, for example, with the alkali metal sodium, which has a high normal potential (-2.71 V), a large potential difference voltage compared to the hydrogen electrode in basic ammonia solution (-0.83 V) can be achieved, whereby the energy density / mass unit again can be increased significantly.

Another point to consider is the liquid state of aggregation of the cathode-side and anode-side electrolytes in the operating temperature range, e.g. -20 ° C to + 50 ° C. The melting point of the saline solution can be lowered sufficiently by a sufficient proportion of the halogen solvent in the anode-side electrolyte. In the case of the use of the solvent ammonia in the cathode-side alkali metal storage and electrolytes, the boiling point of the cathode-side sub-cell is increased by adding, for example, an alkali amide and by setting an atmospheric pressure above the liquid. In addition, the alkali amide ensures the ionic conductivity of the respective solution.

The electrodes between the cathode and anode are intermediate electrodes and must have the following properties:

Ionic conductivity, (metal storage / electrolyte for alkali metal ions), (Hydrogen electrode, if possible only for hydrogen ions),

(Electrolyte / gas storage for halogen ions), good conductivity for electrons, closed crystalline structure to prevent physical mixing, chemical resistance to acids, alkalis and free halogens and mechanical stability.

All properties can be met by using at least one graphite layer, preferably retort graphite, on a carrier material, for example silicon carbide or Teflon. In the case of the hydrogen electrode, however, a platinum or palladium layer is more suitable.

The invention is explained below on the basis of exemplary embodiments. In detail show:

Fig. 1 shows the basic structure of a cell that a metal memory made of crystalline metal, e.g. made of zinc Zn,

Fig. 2 shows the basic structure of a cell that a metal memory made of dissolved alkali metal, e.g. Sodium, has,

3 the loading of a Zn / F cell, cathode-side sub-cell, 4 the discharge of a Zn / F cell, cathode-side sub-cell,

5 the loading of a Na / F cell, cathode-side metal storage,

6 the discharge of a Na / F cell, cathode-side metal storage,

7 charging a Na / F cell, cathode-side electrolyte,

8 the discharge of a Na / F cell, cathode-side electrolyte,

9 the charging of a Na / F or Zn / F cell, anode-side electrolyte,

10 the discharge of a Na / F or Zn / F cell, anode-side electrolyte,

11 shows the ion transport through a graphite layer,

Fig. 12 the ion charge exchange and transport in a graphite layer and

13 shows the schematic representation of the electrochemical energy-storing cell according to the invention. Fig. 1 shows the basic structure of the cell according to the invention, which has a metal storage made of crystalline base metal.

2 shows the basic structure of the cell according to the invention, in which the metal storage contains an alkali metal dissolved in anhydrous ammonia NH ₃ .

The electrochemical processes when charging and discharging the cells are shown in FIGS. 3 to 10. The chemical reactions between two electrodes for charging or discharging the cell are considered separately. The quantitative changes occurring between the substances between the electrodes are shown in a table. The numerical values given in the tables correspond to the chemical reaction equations given between the electrodes and represent the number of atoms or molecules added or formed and those withdrawn or entered into the reaction.

1, the cathode K consists of zinc Zn. In order to avoid short circuits between the cathode K and the hydrogen electrode El, it is necessary that the cathode K has a very large surface area and this is advantageous in part when charging the cell and is used successively. This can be achieved by electrically connecting parts in the form of layers via external resistors and only the furthest when charging the cell the layer removed from the hydrogen electrode El, serves as a cathode connection.

The electrolyte ELI consists of water H ₂ 0 as solvent, potassium hydroxide KOH and the complex salt K [Zn (OH) ₃ (H ₂ 0)].

The hydrogen electrode E1 consists, for example, of at least one graphite, palladium or platinum layer.

The hydrogen electrode El must be able to absorb electrochemically generated hydrogen H, ionically bind it and also release it again. In addition, the hydrogen electrode El must be conductive, i.e. electrons must be able to flow in the conduction band.

The conditions are met by the materials mentioned above, with palladium Pd and platinum Pt additionally having the advantage that they only take up hydrogen H and thus have an advantageous filter property compared to other substances.

In addition, the precious metals themselves are not attacked by hydrogen fluoride HF and by fluorine F in the operating temperature range of the cell (approx. -20 ° C to + 50 ° C).

If the hydrogen electrode E1 consists of a graphite layer, it is necessary, at least when charging and discharging the cell, to ensure that a sufficient amount of hydrogen H is previously in the crystal lattice of the hydrogen electrode El was stored. In addition to the possibility that externally generated hydrogen H can be supplied to the hydrogen electrode, it is possible for a limited time before charging the cell to load the half element K / EL1 / El via an external resistor and to E1 / EL2 / A a charging voltage to apply. When unloading, the half element K / ELl / El can also be loaded for a sufficient time and the recovered electrical energy can be supplied after conversion of the half cell E1 / EL2 / A.

During the actual charging and discharging process, the hydrogen concentration in the hydrogen electrode El no longer changes, because when charging on the anode-side surface of the hydrogen electrode El the same amount of hydrogen is generated as is consumed on its cathode-side surface, and when discharging only the assignment of generation and consumption to those Electrode surfaces change.

Porous silicon carbide SiC, which is not attacked by acids and alkalis, can be used as the carrier material for the graphite, palladium or platinum layers.

3 shows the electrochemical processes taking place in the electrolyte ELI during charging and in FIG. 4 when the Zn / F cell is discharged. As can be seen from the chemical reaction equations and Tables 1 and 2, Z Zn is deposited on the cathode during charging. The concentration of the complex salt K ⁺ [Zn (OH) ₃ H ₂ 0] ^" decreases because complexed zinc ions reduce Zn ²⁺ and the ligands water H ₂ 0 and hydroxide ions OH ^{" are released} again. The reverse process takes place when unloading. Zinc Zn goes into solution from the cathode K and again forms the complex salt K ⁺ [Zn (OH) ₃ H ₂ 0] ^" with water H ₂ 0 and the hydroxide ions OH ^" and the potassium ions K ⁺ .

As already described above, the hydrogen electrode El supplies the hydrogen H necessary for the chemical reaction during charging. When discharged, this is generated on the cathode-side surface of the hydrogen electrode El and from there is stored in the graphite grid of the hydrogen electrode El.

Since the anode-side area of the Zn / F cell shown in FIG. 1 is identical to that of the Na / F cell in FIG. 2, the cathode-side area of the Na / F cell in FIG. 2 is first described below.

Elemental sodium Na is deposited on the cathode K shown in FIG. 2, as illustrated in FIG. 5, which is then dissolved in the electrolyte EL0.

A particular advantage here is that no short circuits between cathode K and hydrogen electrode El can occur during charging. In addition, there is another advantage that the physical nature of the cathode K no longer changes, and thus all related electrodes, including cathode K and anode A, are not energy sources. As can be seen from the electrochemical reaction equations in FIGS. 5 and 6 and Tables 3 and 4, the sodium amide content in the electrolyte EL0 does not change during charging and discharging.

The intermediate electrode E0 is practically a sodium electrode.

The electrolyte EL0 also has a very high electrical conductivity due to the sodium Na dissolved in it, this applies to a greater extent to the charged state of the cell.

In Fig.2 is between the hydrogen electrode E1 and the sodium electrode E0 the electrolyte ELI, which is comparable in terms of cell structure with that in Fig.l.

It consists of the solvent ammonia NH ₃ and dissolved sodium amide NaNH ₂ .

As can be seen from the reaction equations in FIGS. 7 and 8 and Tables 5 and 6, the concentration of sodium amide NaNH _{2 is} reduced when the cell is charged and increases again when it is discharged, ie the concentration of sodium ion Na ⁺ is in the electrolyte ELI lower in the charged state than in the discharged state of the cell.

In addition, the proportion of the ammonia NH ₃ solvent increases during charging and decreases during unloading. During charging, sodium ions Na ^{+ are} discharged on the anode-side surface of the electrode E0 and taken up by the crystal lattice of the graphite.

During discharge, the sodium Na supplied via electrode E0 combines with the discharged NH ₂ ^" ions [NH ₂ ] to form sodium amide NaNH _2. The behavior of the NH ₂ ^" ions dissolved in ammonia NH _{3 is} comparable to that of the hydroxide ions OH ^" in water H ₂ 0.

During charging, discharged NH ₂ ^" ions [NH ₂ ] combine with hydrogen H, which is removed from the hydrogen electrode El, to form ammonia NH ₃ on the cathode-side surface of the hydrogen electrode El, as shown in FIG. 7.

When discharging, sodium ions Na ^{+ are} discharged on the cathode-side surface of the hydrogen electrode El, as shown in FIG. In order to achieve a reaction of the elemental sodium Na produced here with the ammonia NH ₃ solvent on the cathode-side surface of the hydrogen electrode El, it is necessary to use a catalyst.

For this purpose, iron Fe or, for example, a platinum or palladium layer can be used in the graphite crystal lattice of the hydrogen electrode El. These latter two metals also have the desired property of only absorbing hydrogen H and thus act as a filter against other substances. The catalytically active metals do not form a permanent chemical compound with the solvent ammonia NH ₃ and the dissolved sodium amide NaNH ₂ .

7, the reaction of the discharged NH ₂ ^" ions [NH ₂ ] with the hydrogen atoms H supplied by the hydrogen electrode E ₁ to ammonia NH _{3 is} favored by the catalytic effect.

In Fig.l and Fig.2 is between the hydrogen electrode El and the intermediate electrode E2, the anode-side electrolyte EL2. The effective part of the intermediate electrode E2 also consists of a graphite layer, which also applies to the anode A. The electrolyte EL2 is composed of the anhydrous hydrogen fluoride solvent HF and a salt, preferably ammonium fluoride NH ₄ F or potassium fluoride KF. A salt mixture can also be used.

In order to ensure the operating temperature range of the cell, it is necessary to achieve the lowest possible melting point of the electrolyte. Since the decomposition point of ammonium niumfluorid NH ₄ F to about 300 ° C are considerably lower than the melting point of the potassium fluoride KF (856 ° C), ammonium fluoride NH ₄ F is best suited to achieve the electrolyte EL2 a low melting point ,

The following values can be used for comparison:

KF. 3 HF mp 60 ° C

KF • 8..13 HF Smp. = Room temperature As can be seen from FIG. 9, ammonium ions NH ₄ ^{+ are} discharged at the anode-side surface of the hydrogen electrode El, which subsequently do not exist and decompose into ammonia NH ₃ and hydrogen H, which is taken up by the hydrogen electrode El.

The ammonia NH _{3 that forms} combines with hydrogen fluoride HF to form ammonium fluoride NH ₄ F.

Fluorine F is formed on the cathode-side surface of the intermediate electrode E2 and is taken up by the intermediate electrode E2.

As shown in FIG. 10, when discharging on the anode-side surface of the hydrogen electrode El fluoride ions F ^"are discharged, but these immediately combine with the hydrogen H supplied by the hydrogen electrode El to form hydrogen fluoride HF.

The property of the hydrogen fluoride HF to accumulate in a chain has an advantageous effect. This ensures that each RF molecule formed on an electrode surface is deposited in the EL2 electrolyte.

When discharging, the intermediate electrode E2 fluorine F is withdrawn, which again forms ammonium fluoride NH ₄ F with the discharged NH ₄ ⁺ ion [NH ₄ ] or with the hydrogen H formed therefrom. As can be seen from Tables 7 and 8, the concentration of the dissolved salt does not change. However, hydrogen fluoride HF is decomposed during the charging process and is formed again during the discharging process.

When charging the cell, it is possible that fluorine F reacts on the cathode-side surface of the intermediate electrode E2 with ammonium fluoride NH ₄ F to form nitrogen trifluoride NF ₃ in the following manner.

NH ₄ F + 6 F -> NF ₃ + 4 HF

However, this requires large electrode surfaces, such as those used in electrofluorination. In addition, in order to form nitrogen trifluoride NF _3, fluorine F must be present in excess, which is prevented during charging by the absorption of fluorine F by the intermediate electrode E2.

The gas storage GSP in Fig.l and Fig. 2 between the graphite anode A and the intermediate electrode E2 consists of a mixture of very small graphite particles and a fluorinating agent.

The chemical compounds manganese (III) fluoride MnF ₃ and manganese (IV) fluoride MnF ₄ as well as bromine fluoride BrF and bromine trifluoride BrF _{3 are} particularly suitable for taking up fluorine F during loading and releasing fluorine F during unloading. In the other possible valence levels, manganese (II) fluoride MnF ₂ and bromopentafluoride BrF ₅ are also suitable. On the one hand there is an excess of fluorine atoms F when charging on the anode-side surface of the intermediate electrode E2 and on the other hand there is a deficiency of these atoms when discharging.

This means that an ion flow of fluorine atoms F occurs in the gas storage GSP during charging and discharging, which results in a state of equilibrium between the fluorine atoms F absorbed by the fluorinating agent and the fluorine atoms embedded in graphite. The high energy density / mass unit associated with the use of fluorine F is given both by the high normal potential and by the large proportion of fluorine which can be stored in the graphite lattice.

The proportion can be increased further by occasionally reacting fluorine atoms F to carbon monofluoride CF during the production in the crystal lattice of the graphite particles, whereby the lattice spacing of the graphite layers is increased.

In the event that a mixture of bromofluoride BrF and bromotrifluoride BrF _{3 is used} as the fluorinating agent and an alkali metal dissolved in ammonia NH ₃ , for example sodium Na, in the gas storage unit GSP, it is possible to use the liquid substances EL0, ELI, EL2 and in the case of Gas storage GSP to store the solid liquid in tanks and to circulate through the cells of the cell according to the structure in Fig. 2.

The circulation can e.g. thermally.

Since the fluorinating agent bromofluoride BrF and bromotrifluoride BrF _{3 are} in the liquid state in this case the liquid temperature ranges of these compounds are given below.

Melting point boiling point

BrF approx. -33 ° C approx. + 20 ° C

BrF ₃ + 8.77 ° C + 125.75 ° C

Due to the solid, liquid state of the mixture of the smallest graphite particles and the interhalogens bromofluoride BrF and bromotrifluoride BrF ₃ , the circulation effect enables the interior of the gas storage unit GSP to be detected.

In addition, the mixture conducts the electrical current very well, because on the one hand graphite belongs to the first class conductors and on the other hand the fluorinating agent has electrical conductivity.

This means that the gas storage device GSP is comparable in terms of its electrical conductivity to the electrolyte EL0 in FIG. 2.

The heat losses due to the low ohmic resistance in the gas storage GSP are therefore low when charging and discharging the cell. In addition, the mixture of bromofluoride BrF and bromotrifluoride BrF _{3 has} a lower atomic weight than the manganese fluorides, which is associated with a greater energy density / mass unit. However, it is also possible to use the fluorinating agents manganese (III) fluoride MnF ₃ and manganese (IV) fluoride MnF ₄ . In this case, the gas storage GSP forms a solid gas storage.

The advantage of the liquid fluorinating agent compared to the solid gas storage is that even in connection with very large liquid tanks, in extreme cases only one cell according to the construction in FIG. 2 can be used.

It is also possible to extract the contents from one or more cell chambers, which can greatly reduce self-discharge in the idle state.

A further development provides that a metallic conductor connected to the graphite anode A does not corrode. Since the anode A consisting of graphite shown in FIG. 1 and FIG. 2 stores fluorine F in the graphite grid, it is in principle possible that, for example, the copper contact of the anode A corrodes by reaction with fluorine F.

With a longer graphite connection between the anode and a copper connection, the formation of copper fluoride can be avoided because the depth of the penetration of fluorine F into graphite depends on the ion transport, which becomes increasingly less inward. The good electron conductivity of graphite is making it increasingly difficult to transport fluoride ions F ^~ , because there must be sufficiently large electrical potential differences locally for ion transport. FIG. 11 shows how, during charging, fluoride ions F ^"of the electrolyte EL2 are discharged on the cathode-side surface of the intermediate electrode E2 and are transported ionically through them into the gas store GSP.

For reasons of drawing technology, only a very thin graphite layer is shown, but with which the transport principle can be explained. Carbon atoms C on the surface of the intermediate electrode E2, which face the electrolyte EL2, are positively charged by electron withdrawal via the anode A. A charge exchange takes place between positively charged carbon atoms C ⁺ and neighboring fluoride ions F ^" . The charge exchange is associated with a transport of the fluorine atom F into the graphite lattice because atoms or molecules of different polarity attract each other.

This process is shown in Fig. 11 in successive sections.

For better detection of the migration of the fluorine atoms F, these are numbered consecutively. The symbols of the carbon atoms C, which are drawn more strongly, represent carbon atoms C which are positively charged by electron withdrawal via the anode A.

The arrows indicated symbolize the emission of electrons e of the fluoride ions F ^" to the positively charged carbon atoms C ⁺ . How the fluorine transport takes place is shown in Examples A and B in FIG.

The same symbols are used there as in FIG. 11.

In addition, the polarity of the carbon atoms C and fluorine atoms F is entered in the case that the right side of the following reaction applies.

^" ^ C ⁺

Because the ion transport always has to start from the right side of the reaction equation, only (C ⁺ + F ^" ) pairs are shown in FIGS. 11 and 12.

Only when the fluorine atom F is negatively charged can a charge exchange with a positively charged carbon atom C ⁺ take place and thus a transport of the fluorine atom F can be achieved.

In order to better illustrate the processes, negatively charged fluorine atoms F ^″ and positively charged carbon atoms C ⁺ that belong together are identified by dashes in accordance with the above reaction.

In example A, the positive charge passes from anode A to a (C ⁺ + F ^" ) pair.

Since negative ions can only move in the direction of anode A during charging, the negatively charged fluorine atom F ^" migrates the positively charged carbon atom C ⁺ , which was created by electron withdrawal via anode A. The positively charged carbon atom C ^{+ of} the original (C ⁺ + F ^" ) pair discharges with the closest fluoride ion F ^{" of} the electrolyte EL2, as a result of which the fluorine atom F is embedded in the graphite lattice.

Example B shows how the process described in Example A can also be carried out with many fluorine atoms F or fluoride ions F ^" .

On the surface of the intermediate electrode E2, which faces the gas storage device GSP, discharge of fluoridions F ^" results in fluorine atoms F which leave the intermediate electrode E2 and are taken up by the gas storage device GSP. The fluorine atoms F can again be used as fluoride ions F ^" in the gas storage device GSP. occur because, for example, manganese (III) fluoride MnF _{3 can be converted} into manganese (IV) fluoride MnF ₄ and the graphite particles in the gas storage GSP can absorb fluorine atoms F. The electrons e extracted from the intermediate electrode E2 serve to transport the fluoride ions in the gas storage unit GSP.

The process is reversed when unloading.

Analogous to the fluoride ion migration described, the hydrogen is also transported through the intermediate electrode E1 and the sodium is transported through the intermediate electrode E0. A prerequisite for storing fluorine F in the gas storage unit GSP is that unhindered fluoride ion transport can take place in the entire storage unit.

The gas storage unit GSP must therefore not consist entirely of graphite. This means that the transport must not be increasingly hampered by the fact that the left part of the above Equation prevails.

In extreme cases, free fluorine F ₂ would then form and escape.

This effect can be avoided by

by mixing the smallest graphite particles with a fluorinating agent and the associated increase in specific resistance, a greater electrical energy is available for the fluoride ion transport, the fluorinating agent can release fluorine F during loading of the cell on graphite particles as well as when discharging and that the fluorinating agent can resume and that Graphite particles form a very large surface in their entirety, which allow the storage of fluoride ions F ^" .

When designing the intermediate electrodes E0, E1 and E2, it is also necessary to choose a sufficiently thin layer of graphite so that ion transport is still ensured in both directions, ie the above-mentioned reaction equation must be sufficiently valid on the right side in the area of the graphite layer.

Due to the mixture present in the gas storage unit GSP, there are cases where graphite particles are in electrical contact with one another or only touch with, for example, manganese (III) fluoride MnF ₃ or manganese (IV) fluoride MnF ₄ .

As an example, the transport of the fluorine atoms F in the gas storage GSP during charging at an arbitrarily selected location is given below.

The removal of electrons on the anode side produces positively charged atoms or molecules, the geometrical position of which is denoted by x below and which faces the anode A. The electrons supplied via the cathode K result in atoms or molecules which have been negatively charged with respect to the location x and which have already taken up fluorine atoms F, in the position designated x + 1.

anode

Anode anode

T t

C - e → C ⁺ or MnF ₃ - e -> Mn 4 + τF ₃

x + 1 C + F + e → C + F ^" or Mn, 4 ^* + F ₄ + e → MnF ₃ + F ^" t T

E2 cathode cathode Depending on the case of contact, the charges will balance as the fluorine atom F is transported. There are four possible cases.

anode

C ⁺ gives C ⁺ + F ^ C + F

T x + 1 C + F ^" results

E2

anode

returns C ⁺ + F ^" ^ C + F

x + 1 MnF + F ^" results in MnF

E2 anode

Mn ⁴⁺ F ₃ gives MnF ₄ tx + 1 F ^" gives

E2

anode

x Mn ⁴⁺ F ₃ gives MnF ₄ tx + 1 MnF ₃ + F ^" gives MnF

E2

If no electrons e flow, ie the outer circuit is interrupted, the fluorine atoms F will be spatially balanced. Fluorine atoms F on the surface of the graphite particles, which are currently in the atomic state, react with manganese (III) fluoride MnF ₃ to form manganese (IV) fluoride MnF ₄ and fluoride ions F ^" , which result from the decay of manganese (IV) - fluoride MnF ₄ to manganese (III) fluoride MnF ₃ + F ^" emerge, are taken up by graphite particles. Ultimately, a state of equilibrium will occur which corresponds to the state of charge of the gas storage unit GSP.

The structure of the electrochemical energy-storing cell is shown schematically in FIG. The cell comprises a cathode (K) and an anode (A) and is divided into sub-cells, between which there is a hydrogen electrode (El). The partial cell on the cathode side comprises a metal storage and an electrolyte (ELI). The anode-side sub-cell comprises a gas storage (GSP) and an electrolyte (EL2).

The voltage of the Zn / F cell shown in Fig.l between cathode K and anode A in the unloaded state is based on the normal potentials:

Half element K / ELl / El in basic solution on the cathode side (KOH and H ₂ 0)

Zn = -1.22 V and H = -0.83 V - ΔU _K / _EI = 0.39 V

anode-side half element E1 / EL2 / A in acid solution (fluoride salt in HF)

H = 0.0 V and F = 2.71 V ΔU _E ι _{/ A} = 2.71 V

The total voltage is:

U _K / _A = ΔUK / EI + ΔU _{E1 / A} U _K / _A = 0, 3 9 V + 2, 71 VU _{κ / A} = 3, 10 V The voltage of the Na / F cell shown in Fig. 2 between cathode K and anode A in the unloaded state is based on the normal potentials:

Half element K / EL0 / E0 / EL1 / E1 in basic solution (NaNH ₂ and NH ₃ )

Na = -2.71 V and H = -0.83 V ΔU _{κ / E} ι = 1.88 V

anode-side half element E1 / EL2 / A in acid solution (fluoride salt in HF)

H = 0.0 V and F = 2.71 V ΔU _E ι _{/ A} = 2.71 V

The total voltage is:

UK / _A = ΔU _K / EI + ΔU _{E1 / A} UK / A = 1.88 V + 2.71 VU _{κ A} = 4.59 V

In the Zn / F cell shown in Fig.l, the cell chambers in which the electrolyte EL2 and the gas storage GSP are located must be sealed gas-tight.

The same also applies to the Na / F cell shown in FIG.

Silicon carbide SiC or Bι ₃ C ₂ as well as Teflon (CF ₂ ) _n and carbon monographite (CFι _{, ι2} ) can be used as materials for the production of housings and containers in the gas storage unit GSP. In addition, hydrogen fluoride-resistant plastics are suitable for holding the EL2 electrolyte.

Porous silicon carbide SiC or Teflon is suitable as a carrier material for the graphite electrodes El, E2 and A in Fig.l and K, E0, E2 and A in Fig.2.

If the Zn / F cell shown in FIG. 1 is destroyed, it can be assumed that the intermediate electrodes El and E2 will also be destroyed with certainty, so that all substances, ie the electrolytes ELI and EL2 and the mixture contained in the gas storage GSP, can react with each other. In this case, the following reactions will essentially take place:

KOH + HF -> KF + H ₂ 0

Zn + 2 HF → ZnF ₂ + H ₂

Zn + F ₂ - »ZnF ₂

2 F ₂ + 2 H ₂ 0 → 4 HF + o ₂

The resulting end products are therefore potassium fluoride KF, zinc fluoride ZnF ₂ , free hydrogen H ₂ and free oxygen 0 ₂ , with zinc fluoride ZnF ₂ being difficult to dissolve in water H ₂ 0. In the case of the Na / F cell shown in FIG. 2, the electrolytes EL0, ELI and EL2 and the GSP will react with one another mainly when the electrodes E0, El and E2 are destroyed and form the following connections:

NH ₃ + HF -> NH ₄ F

2 Na + 2 HF → 2 NaF H ₂ 2 Na + F ₂ - »2 NaF

NaNH ₂ + HF - »NaF + NH ₃

In addition, sodium Na would react with external water H ₂ 0

2 Na + 2 H ₂ 0 _> 2 NaOH + H ₂

and then

NaOH + HF __ _> NaF + H ₂ 0

form.

Fluorine would also react with water

2 FH ₂ 0 → 2 HF O

Reactions with the complex salt in the electrolyte ELI according to Fig.l and the fluorinating agents in the gas storage GSP (Fig.l and Fig.2) also do not expect extremely toxic substances, so that the environmental compatibility in the event of destruction of the cell or tanks is manageable.

Finally, it is possible to form an energy storage system consisting of a number of electrochemical cells according to the invention.

Claims

Patent claims

1. Electrochemical energy-storing cell, which comprises a cathode (K) and an anode (A), characterized in that the cell is divided into sub-cells, between which there is a hydrogen electrode (El), the sub-cell on the cathode side being a metal store and an electrolyte (ELI) and the anode-side sub-cell comprises a gas storage (GSP) and an electrolyte (EL2).

2. Electrochemical cell according to claim 1, characterized in that the metal storage contains a crystalline, base metal, preferably zinc (Zn).

3. Electrochemical cell according to claim 2, characterized in that the metal storage forms the cathode (K).

4. Electrochemical cell according to claim 3, characterized in that the cathode (K) has a large surface.

5. Electrochemical cell according to one of claims 2 to 4, characterized in that the cathode-side electrolyte (ELI) is limited by the cathode (K).

6. Electrochemical cell according to one of claims 2 to 5, characterized in that the cathode-side electrolyte (EL1) contains water (H ₂ 0) as an electrically conductive liquid.

7. Electrochemical cell according to claim 6, characterized in that the cathode-side electrolyte (ELI) contains at least one compound which increases the ionic conductivity, preferably potassium hydroxide (KOH) or ammonia (NH3).

8. Electrochemical cell according to one of claims 2 to 7, characterized in that the cathode-side electrolyte

(ELI) contains at least one complex salt which comprises ions of the base metal acting as cathode (K).

9. Electrochemical cell according to claim 8, characterized in that when using zinc (Zn) as the cathode (K) the complex salt is a potassium zincate, preferably

K [Zn (OH) ₃ (H ₂ 0)].

10. Electrochemical cell according to claim 1, characterized in that the metal storage contains an alkali metal (EL0), preferably sodium (Na), dissolved in a solvent.

11. Electrochemical cell according to claim 10, characterized in that the solvent is anhydrous.

12. Electrochemical cell according to claim 11, characterized in that the solvent is ammonia (NH ₃ ).

13. Electrochemical cell according to one of claims 10 to

12, characterized in that the metal store (EL0) is limited by the cathode (K).

14. Electrochemical cell according to one of claims 10 to

13, characterized in that an intermediate electrode (E0) is arranged between the metal reservoir (EL0) and the cathode-side electrolyte (ELI).

15. Electrochemical cell according to one of claims 10 to

14, characterized in that the metal reservoir (EL0) and / or the cathode-side electrolyte (ELI) contains at least one dissolved alkali amide, preferably sodium amide (NaNH ₂ ), which increases the ionic conductivity of the solution.

16. Electrochemical cell according to one of claims 10 to

15, characterized in that the cathode-side electrolyte (ELI) contains the same solvent as the metal reservoir (EL0), preferably ammonia (NH ₃ ).

17. Electrochemical cell according to one of claims 1 to

16, characterized in that an intermediate electrode (E2) is arranged between the anode-side electrolyte (EL2) and the gas reservoir (GSP).

18. Electrochemical cell according to one of claims 1 to

17, characterized in that the hydrogen electrode (El) consists of graphite, platinum (Pt) or palladium (Pd).

19. Electrochemical cell according to one of claims 1 to

18, characterized in that the hydrogen electrode (El) on the cathode side has a metal-containing catalyst which preferably comprises iron (Fe), platinum (Pt) or palladium (Pd).

20. Electrochemical cell according to one of claims 1 to

19, characterized in that the hydrogen electrode (El) is designed such that it can be supplied with hydrogen externally at least before the cell is charged or discharged.

21. Electrochemical cell according to one of claims 1 to

20, characterized in that the anode-side electrolyte (EL2) as solvent at least one hydrogen halide

Contains connection.

22. Electrochemical cell according to one of claim 21, characterized in that the solvent is anhydrous.

23. Electrochemical cell according to one of claims 1 to 22, characterized in that the anode-side electrolyte (EL2) contains at least one salt which increases the conductivity of the solution.

24. Electrochemical cell according to claim 23, characterized in that the salt contains the same halogen as the solvent, preferably fluorine.

25. Electrochemical cell according to claim 23 or 24, characterized in that the salt is ammonium fluoride (NH ₄ F) and / or potassium fluoride (KF).

26. Electrochemical cell according to one of claims 1 to 25, characterized in that the gas storage (GSP) comprises a mixture of graphite particles and at least one metal-containing halogen compound or at least one interhalogen.

27. Electrochemical cell according to claim 26, characterized in that the gas storage (GSP) is delimited on one side by an anode (A), the anode not being attackable by the halogen used in the gas storage (GSP).

28. Electrochemical cell according to claim 26 or 27, characterized in that the halogen compound comprises a mixture of manganese fluorides with different valence levels of the manganese, for example manganese (III) fluoride (MnF ₃ ) or manganese (IV) fluoride (MnF ₄ ).

29. Electrochemical cell according to claim 26 or 27, characterized in that the halogen compound comprises a mixture of bromofluorides with different valence levels of bromine, for example bromofluoride (BrF) or bromotrifluoride (BrF ₃ ).

30. Electrochemical cell according to one of claims 1 to 28, characterized in that the electrodes (K, A, E0, El, E2) comprise graphite layers, preferably retort graphite.

31. Electrochemical cell according to claim 30, characterized in that the graphite layers of the graphite electrodes are applied to a carrier material, for example on porous silicon carbide (SiC) or polytetrafluoroethylene (PTFE / TefIon).

32. Electrochemical cell according to one of claims 1 to 31, characterized in that the electrolytes (EL0, ELI, EL2) forming liquid energy carriers and / or the storage (GSP, E0) forming solid-liquid energy carriers with separate tanks for the Storage of these energy sources are connected and can be fed to and removed from the tanks.

33. Energy storage system consisting of a number of electrochemical cells according to one of claims 1 to 32 and a number of tanks connected to these cells.