Electrochemical cell and anode structure

The invention relates to a composite anode structure comprising a micromolecular silver support, in which electrochemically active anode material in the form of an electronically conductive, electropositive substance is sorbed and retained in dispersed form, which anode structure is intended to be used in an electrochemical cell together with a combined electrolyte cathode and in this is intended to separate the combined electrolyte cathode from the electrochemically active anode material in the molten state.

In recent years, interest has increased in the development of energy storage systems. However, these efforts have been counteracted to varying degrees by the difficulties in effectively controlling and regulating the mobile, electrochemically active substances and by the difficulties with the high operating temperatures, which in many cases are necessary for the efficient operation of electrochemical cells.

SE-B-430 447 discloses a sodium sulfur cell in which the sulfur is immobilized by sorption in the molecular sieve support comprising crystals of a dehydrated zeolite, the sodium being immobilized in the porous stainless steel matrix. DE-A-2 928 863 discloses sodium as the anode substance for an electrochemical cell, in which the sodium is immobilized by sorption in a zeolite molecular sieve carrier. Both publications state the necessity of electronic conductivity in

448 797 the carrier for primarily power collection reasons.

According to the invention, there is provided a composite anode structure of the kind mentioned at the outset, characterized in that the micromolecular screen carrier is substantially non-electronically conductive and has surface pores of a size not exceeding 50 Å, and in that a reservoir of the electropositive substance is in contact with the carrier.

Without being bound by any theory, it is likely that the electropositive substance may form electronically conductive pathways that run along at least one portion of the channels and / or pores in the carrier and thus place at least a portion of the openings in the carrier surface in electronic contact with each other. via the wearer's interior.

Thus, in use, these pathways, when doped with the electropositive substance, are electronically conductive as a whole, via these pathways, so that electrons can be conducted along the pathways from the interface between the support and the electrolyte to the interface between the support and the electropositive substance. in the anode.

It is likely that the electropositive substance is sorbed in elemental form and retained in the support in dispersed form and may move in the form of an atom or base element along the channels and / or pores of the support, thereby occupying suitable sites which have become free after other atoms in the electropositive substance, so that in use it can move through the support from the anode to the electrolyte.

When there is a risk that, as is the case when the electrolyte is in liquid form at the operating temperature of the cell, the electropositive substance may react chemically in an undesired manner with the electrolyte, e.g. with the anions of the electrolyte, the carrier, when containing the sorbed electropositive substance, can be selected or modified so that the openings in its surface towards its microporous interior prevent e.g. the anions of the electrolyte to gain access to the interior of the support and thereby cause undesirable reactions. Similarly, when, as described in more detail below, the selected electrolyte is an aqueous solution, the carrier when it contains the sorbed electropositive substance can be selected or modified so that the openings or pores in its surface do not allow access to its interior by water molecules.

The electropositive substance is present in the molten state at the operating temperature of the cell and may comprise an alkali metal or alkaline earth metal, a combination or alloy of two or more alkali metals or alkaline earth metals or a combination or alloy of one or more alkali metals or alkaline earth metals with one or more other substances. In other words, the alkali metal or alkaline earth metal or metals may be used alone or in combination with two or more thereof or one, two or more thereof may be used in a composition or alloy with one or more compatible other substances provided that they are such that the electropositive substance is present in the molten state at the operating temperature of the cell.

The alkali metal or metals in the electropositive substance may be present in any suitable combination containing e.g. lithium, sodium and / or potassium. The alkaline earth metals can likewise be present in any JO combination of alkaline earth metals, such as calcium or magnesium. As mentioned above, the electropositive substance is present in the molten state at the operating temperature of the cell. For use at atmospheric pressures, certain alloys of sodium and potassium are particularly suitable as they have melting points below 100 ° C and potassium and in particular sodium may be considered for use alone due to their readily available at competitive prices.

448 797

By micromolecular sieve carrier is meant a molecular sieve carrier with contacting cavities and / or channels in its interior and openings and / or pores in its surface leading into the cavities and channels, the openings, pores, cavities and / or channels having a size not exceeding 5 Å and preferably less than 20 Å or when used with an electrolyte which is an aqueous solution, such that water molecules cannot be sorbed into the interior of the carrier regardless of whether other sorbed substances are found in the cavity of the carrier.

Suitable micromolecular sieves are mineral micromolecular sieve carriers, ie inorganic grid or space network structures, although certain substantially organic micromolecular sieve carriers, such as climbers, may be suitable in some cases.

Suitable mineral micromolecular silica carriers can be selected from substances which build up the tectosilicates, ie the class of substances which are also referred to as space network silicates, which may be naturally occurring or synthetically produced, crystalline or non-crystalline / amorphous and which include silicates, e.g. silica gel, zeolites, feldspars and fatty spathoids, which are silicates of a structural type, in which all four oxygen atoms. in the silicate tetrahedron is divided by adjacent tetrahedra The space network in the tectosilicate is made up of silicon atoms with in some cases aluminum atoms together with other atoms. Mineral micromolecular sieves also include mixtures of or analogues to tectosilicates, in which the silicon and / or aluminum atoms in the space network may be exchanged for other atoms selected from one or more of iron, beryllium, boron, phosphorus, carbon, germanium and gallium in smaller or larger proportions and wherein the micromolecular properties are unaffected by this substitution. As long as their properties relevant to the present invention are substantially unaffected, these analogs are considered tectosilicates in the context of the present invention.

448 797

For molten salt electrolytes the micromolecular sieve carrier is suitably a zeolite and when the electrolyte is to be aqueous the carrier may be a tectosilicate which cannot sorb water, e.g. a feldspar or a feldspar.

Zeolites, feldspars and feldspar are a class of crystalline or amorphous, naturally occurring or synthetically produced materials, containing aluminum and silicon in fairly specific proportions, and analogues thereof. For a more detailed description of zeolites, see the January 1975 publication of the International Union of Pure and Applied Chemistry entitled Chemical Nomenclature and Formulation of Compositions of Synthetic and Natural Zeolites.

Zeolites contain sorbed water molecules, which can be removed, usually reversibly, by heating and / or evacuation. Although zeolite molecular sieve carriers, which are at least partially dehydrated and usually fully dehydrated, can be expected to be commonly used, the presence of water in the zeolite may in some cases be beneficial in improving the ionic conductivity associated with the cell reaction mechanism discussed below.

Zeolites, feldspars and feldsparoids usually have a reasonably ordered internal structure, have a high internal surface area and are characterized by the presence of a variety of regular collections of molecular cavities, ie channels and / or cavities with openings to the surface of the zeolite via windows and / or pores. Other tectosilicates, especially if they are amorphous or non-crystalline, have a substantially less ordered or substantially disordered internal structure but still exhibit suitable areas of molecular voids.

The zeolites in their hydrated form can, as far as is known, be represented by the following structural formula

448 797 ^M2 / n ° *^A12°3 * ^xsi02·^YH2 ° in which M is a cation with the valence n and X and Y are independent variables, which is a function of the composition of the starting mixture and the mode of formation.

It has been found that suitable tectosilicate crystals can have a sufficiently high physical strength for efficient use in the cell of the invention. When tectosilicate is a powder, it can be compressed and supported,

for example in a porous container for use.)

In addition, it has been found that tectosilicate crystals doped with an electropositive substance can be sufficiently resistant to electrochemical and thermal action during repeated use in a cell according to the invention.

Thus, when crystalline tectosilicates are used, physical or electrochemical deficiencies of tectosilicates doped with the electropositive substances need not constitute factors which decisively or at all contribute to a failure of the cells of the invention.

According to the invention, the micromolecular sieve carrier has a three-dimensional skeletal structure which remains physically and electrochemically stable, so that it does not in any decisive way collapse as a result of the electrochemical reactions occurring during normal use, and continues to function as a sieve which allows diffusion of the electropositive substance but prevents access to the electropositive substance in its interior by anions from the electrolyte, in which case the anions would react undesirably with the electropositive substance in the anode and prevent access to water when the electrolyte is an aqueous solution.

448 797

Thus, said aspects should be considered in the selection of molecular sieve carriers for use with the selected electropositive substances and electrolytes in the practice of the invention.

It should be noted, however, that when certain carriers are doped with extremely electropositive substances, such as lithium metal alone or in combination with other metals, this can lead to significant modification of the carrier's space network. However, it has been found that such modified space networks still possess the necessary properties in that they can act as carriers and / or strainers for the electropositive substance, are sufficiently electrochemically inert or relatively electrochemically inert during use in a cell and can prevent access to it. electropositive substance of undesirable chemical substances or, when present, water from the electrolyte.

Such carriers, e.g. tectosilicates such as zeolites, which have been physically and / or chemically modified during doping with the selected electropositive substances but which still possess the necessary properties can thus be used as micromolecular silicate carriers in the anodes of the invention and for the purposes of the invention these modified tectosilicates, zeolites etc. are nevertheless considered , zeolites etc.

It should further be noted that in some tectosilicates, cation exchange can sometimes occur during the use of the anodes of the invention in certain electrochemical cells. Such reactions are well known and only change the size of the windows and pores present in the carrier's space network and also this aspect should be considered in the choice of electropositive sub35 punch and carrier to ensure that the pores or windows in the carrier have the desired size to allow passage. thereby of the electropositive substances but

448 797 exclude water in the electrolyte when an aqueous electrolyte is used in the cells, and undesirable anions in the electrolyte in cases where these anions are chemically unstable in relation to the electropositive substance.

Again, these are considered as tectosilicates of the type in question.

Thus, it should be noted that although the tectosilicate molecular sieve carriers of the invention in some cases, namely after doping or after being subjected to several charge / discharge cycles in a cell, no longer strictly exist in the form of tectosilicates as such in the ordinary sense, they can still be considered such or at least as mineral micromolecular sieve carriers in the present invention provided that they exhibit the necessary properties.

Thus, when the tectosilicate molecular sieve carriers in the electrodes of the invention are in the form of modified tectosilicates, they are such that although physically or chemically modified they still possess the necessary molecular cavities or pores to capture the electropositive substance, they still possess the channels or pores to the cavities and still has windows of suitable size.

Thus, when the molecular sieve carriers of the invention are in the form of modified substances, they are those which have windows, channels, pores and cavities in order to be able to receive the electropositive substances and allow passage therethrough of the electropositive substances but exclude water and / or undesirable electrolyte anions. .

By considering such factors as pore or channel size, cavity size and window size and the ability to sorb electropositive substances in effective quantities and still allow high mobility or passage of the electropositive substances and exclude water and / or such

448 797 anions in the electrolyte, which are unstable in relation to the electropositive substances, one can get a rough guide in the selection of suitable micromolecular sieve carriers for use in connection with the invention.

.. 5

Other factors that may serve as a guide may be the degree of porosity, the density, the availability and the mechanical strength, the stability and the electronic conductivity or the absence thereof of the doped micro10 molecular sieve carriers.

By way of example, natrolite has the proper structural properties to allow its function in the manner described herein as a micromolecular carrier for the purposes of the invention. Such aluminosilicates or the like, which exhibit acceptable structural properties to function as required by the invention, may be suitable tectosilil cat molecular sieve carriers.

Thus, the micromolecular sieve carrier should preferably be such that the electropositive substance when sorbed therein is retained in finely dispersed elemental form e.g. optionally in atomic form, molecular form, atomic lump form or molecular lump form to show its greatest availability for electrochemical activity during use.

Furthermore, the carrier should preferably be such that it retains an effective amount of the electropositive substance for efficient electron conduction and, if necessary, ionic conduction for the electropositive substance, so that effective quantities can move therethrough.

_s According to the invention, it is probable that the carriers can in fact act as sieves, which allow diffusion of the electropositive substances in elemental, atomic or ionic form from the anode to the electrolyte during discharge of the cell but at the same time prevent access to those therein.

448 797 ίο constituent electropositive substances of water and / or the anions in the electrolyte if they are unstable with respect to the electropositive substances. The function of the carriers is thus to prevent reduction of the electrolyte of electropositive substances contained in the anode and to prevent these electropositive substances from reacting with any water in the electrolyte. The intention is that the cell according to the invention, if desired, can be used as a secondary cell or rechargeable cell, whereby during the charging the electropositive substances diffuse over from the electrolyte to the anode.

The anode structures according to the invention have particular utility in electrochemical cells, in which electrolytes are used in the form of liquid molten salts or aqueous solutions and which are intended to operate at relatively low temperatures, e.g. between room temperature and up to about 360 ° C.

In such cells, the cathodes may comprise an oxide of one or more transition metals selected e.g. from the group consisting of manganese, iron and nickel or an intermediate refractory cemented carbide compound of at least one metal selected from the group consisting of chromium, manganese, iron, cobalt and nickel with at least one non-metal selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorus, which is activated by halogenation. Thus, the cathode can e.g. comprise a refractory cemented carbide compound, which is an activated carbide of iron, chromium or manganese.

Instead, the cathode may comprise sulfur and / or selenium and a micromolecular sieve carrier, e.g. a tectosilicate in which the sulfur and / or selenium is sorbed and retained during use of the cathode in the cell. The sulfur and / or selenium can e.g. be sorbed in a dehydrated zeolite molecular sieve support, which may be selected from the group consisting of erionite, faujasite, synthetic zeolite 3Å, zeolite 4ä and

448 797 zeolite 13X. The zeolite support material is made electron conducting by the addition of a suitable electron conducting material, such as graphite.

For such low temperature cells, the electrolyte may be an aqueous acid or base, e.g. an aqueous solution of sodium hydroxide or potassium hydroxide or may be a molten inorganic salt such as an iodine-based inorganic salt electrolyte. To investigate this possibility, a eutectic mixture of lithium iodide and potassium iodide was prepared in the ratio proposed by DB Leiser and AJ Whittemore Jr. J Amer. Ceram. Soc. 50 (1961), 60. This mixture was doped with 99.5% pure strontium iodide obtained from Cerac Inc. The components were mixed and ground into a fine powder and melted in glass tubes under an argon gas stream.

The temperatures at which the mixtures melted and solidified were recorded. The homogeneous solid mixtures were then ground and accurate melting point determinations were performed. The added strontium iodide accounted for between about 25 - 50% of the mass of the mixture. Melting points were found to be in the range 220 - 240 ° C while the eutectic mixture of lithium iodide and potassium iodide could be confirmed to melt at about 260 ° C.

The electrolyte may instead be a molten inorganic salt of the general formula

M Al Halji in which M comprises one or more alkali or alkaline earth metal cations and Hal comprises one or more halides, the proportions between the alkali or alkaline earth metal cations and the halide anions being such that the above stoichiometric product is maintained and the alkali metal cations and halide anions are selected

448 797 so that the electrolyte has a sufficiently low melting point to allow use in the molten state at the desired operating temperature of the cell.

When such electrolyte is used together with a tectosilicate-based support and the electropositive substance of the anode (eg one or more alkali metals) is able to reduce aluminum in the electrolyte and cause its precipitation on the anode and / or separation from the electrolyte e.g. for precipitation, the molecular sieve support material in the anode should have the size of windows or pores such that the windows exclude the Al Hal When these halide ions are AlC atoms or ions of lithium, sodium and / or potassium.

In this way, Al Hal 2 is prevented^1-the anions from coming into direct contact with the electropositive material in its elemental or atomic / molecular form, so that reduction and separation of aluminum by reaction can not take place directly and easily.

Tectosilicate molecular sieve carriers which are suitable for use with molten salt electrolytes of formula M Al Al

In the case of aqueous electrolytes, tests of electrolytes in cells of the invention with sodium / potassium anodes and the cathode comprising manganese dioxide have been found to give excellent electrochemical properties at operating temperatures below 100 ° C.

When such electrolytes are used together with a tecto

448 797 silicate-based support, the electropositive substance in the anode (eg one or more alkali metals) is able to react with the water in the electrolyte, so the window or pore size of the molecular sieve support must be such that the windows exclude the water in the electrolyte from entering the anode . The window or pore size of the tectosilicate should be such that the water is further excluded, while the electropositive material, e.g. atoms or ions of sodium, lithium and / or potassium can easily gain access to the windows or pores in the interior of the anode.

In this way, water is prevented from coming into direct contact with the electropositive material in its elemental or atomic / molecular form so that undesired reaction can not take place.

Without being locked into any explanation, it is likely that in micromolecular sieve carriers having cavities in the form of capillary or tubular channels, which may have a dimension approximately the same as the pore or window size, the electropositive substance may move along the channels for discharge from the source of electropositive material to the interface between the support and the electrolyte and in some cases the electropositive substance in the channels may maintain electronic contact with the electropositive substance reservoir in the support body. In other words, the carrier will in this way be electronically conductive via the electropositive substance in the channels between the reservoir or the source of electropositive substance and the electrolyte. It should be emphasized here that the source of electropositive charge is not in direct contact with the electrolyte other than via the doped micromolecular sieve carrier.

In case the doped molecular sieve carrier is an electron conductor, a possible mechanism may be that during discharge of

448 797 cell atoms in the electropositive substance are ionized at the interface between the electrolyte and the molecular sieve carrier and the ions pass into the electrolyte, the electrons from the ionization pass via the electropositive substance in the carrier's interior to the source of electropositive material which acts as or can only be connected to a current collector . At the same time, atoms from the electropositive substance pass from the source of anode material into the molecular sieve support material and replace those ionized, with rapid diffusion of electropositive material taking place via the channels in the molecular sieve support from the anode to the electrolyte.

According to the above-mentioned mechanism, the electropositive substance may then be present in the form of electronically conductive wires or chains in the channels. However, it is possible that instead of the electropositive substance present in the form of electrically conductive chains or wires in the channels, the electrochemically active, sorbed, electronically conductive substance may form lumps with suitable cations forming part of the space network or matrix of molecular sieve material. These lumps can thus separate electrons from the sorbed electropositive substance. Such electrons may be sufficiently mobile to be able to move through the molecular sieve carrier from its interface with the electrolyte where the ionization takes place to the anode reservoir and from there to the collector.

If the mechanism proposed above, according to which ionization takes place at the interface between the molecular sieve carrier and the electrolyte, is faulty and the ionization takes place at the interface between the molecular sieve carrier and the anode or source of electropositive substance or a hybrid mechanism, whereby ionization at the source is predominant, then For example, the molecular sieve carrier with the electropositive substance sorbed therein can not in a strict sense function as a sieve but instead as a solid electrolyte. Ions instead of atoms diffuse

448 797 then rapidly passes through the molecular sieve carrier. This process can be accelerated by the presence of sorbed atoms in the form of lumps, the solid electrolyte being rich in metal, 3+

for example Na 2 lumps in natrolite. Regardless of whether the carrier impregnated with the electropositive substance is considered as a screen or a solid electrolyte, this does not affect its usefulness and function, in the manner described above in the cells and anode structures according to the invention.

To prepare a carrier according to the invention, a tectosilicate, e.g. a suitable feldspar or feldsparoid or a zeolite which is completely or partially dehydrated by being subjected to vacuum and heat, for the action of a vapor phase of the electropositive substance sorbed therein, optionally under pressure and after being subjected to vacuum. Although it may not be necessary to saturate all the vacancies in the zeolite molecular sieve carrier with the electropositive substance and only a desired proportion of vacancies need to be occupied, in practice as much of the electropositive material as possible should be sorbed in the zeolite molecular sieve carrier.

The pore size of the zeolite molecule carrier may optionally be modified by the sorption of the electropositive material and the zeolite molecule carrier is selected so that its channel and pore sizes, in particular its window sizes, after doping function effectively to exclude any anion unstable to the alkali metal in the anode or possibly water from the electrolyte from reacting with electropositive substance in the channels. In other words, if such modification takes place, the micromolecular sieve carrier and the metals may be selected so that the finally obtained micromolecular sieve carrier has suitable channel, pore and window sizes.

448 797

Thus, lithium, sodium or potassium may be used alone or such alkali metals may be used together or they may be used in conjunction with other metals such as aluminum. When an electropositive substance, such as sodium or lithium, is used in conjunction with another metal, such as aluminum, both the alkali metal and the second metal, such as aluminum, may be sorbed in the support, the other metal modifying the zeolite molecular sieve support by reducing the effective channel the pore and / or window sizes to the desired size suitable for the intended use of the anode. Starting from a molecular sieve carrier with channels, pores and in particular windows which are too large to exclude unwanted electrolyte ions, after sorption of the other metal these channels, pores and / or. windows are reduced in size by the presence of atoms in the other metal - so that they are the right size to exclude any water or unwanted electrolyte ions but allow the passage or entry of the electropositive alkali metal atoms / ions, such as sodium, potassium and / or lithium.

It is also possible that when the pore size of the support is large enough molecules of the electrolyte in the initial stage of cell function may penetrate into the support body a certain piece, at which point a reaction takes place with the electropositive substance with the result that the product produced can reduce the cavity size and thereby prevent additional electrolyte from penetrating and reacting and the cell functioning in the manner described above, such as when sodium is the electropositive material and sodium aluminum chloride is the liquid electrolyte, the reaction leads to the precipitation of aluminum metal, which clogs the cavities to the desired extent.

Accordingly, it is possible to choose either a suitable molecular sieve carrier which initially has windows, pores and channels of the correct size or to choose a carrier with openings which are too large but which can be modified during the initial sorption process so that the pores, channels and the window is the right size. In this case, the second metal, such as aluminum or even nickel, which is used together with the electrochemically active, electropositive alkali metal, can form an effective coating in the channels and remain there and electrochemically behave relatively inertly in the cell, having a reducing effect on the channels. the size of the pores and / or windows and also have the function of increasing the electron conductivity along the paths formed by the channels containing the electrochemically active, the electropositive substance. Thus, some substances in the sorbed material may have a modifying effect on the molecular sieve carrier and stabilize it but still increase its electron conductivity along the pathways provided by the channels while other substances may act as an electropositive material. The electron-conducting properties of the molecular sieve carrier can thus probably be limited to the channels, while the main mass of the molecular sieve-carrier material or at least the part thereof which is in direct contact with the liquid electrolyte appears non- or negligibly electronically conductive to prevent deposition of cations from the electrolyte thereon. surface. of the anode, which is exposed to the electrolyte during charging.

Said condition helps to prevent dendritic formation, which in many cases is a reason for a cell to fall out, since a coating of the electropositive material can only take place inside the cavity structure of the carrier, thereby preventing it from leaving the anode structure and / or causing internal short circuits.

According to preferred embodiments of the invention, when the support is a zeolite, the anode may comprise natrolite with sodium sorbed therein, mordenite with suitable amounts of

448 797 potassium and sodium or mordenite sorbed therein with appropriate proportions of potassium and lithium sorbed therein.

According to another preferred embodiment of the invention, when the material in the molecular sieve carrier is a non-negligible electronically conductive zeolite, it may be possible to dispense with a particular liquid electrolyte and leave the zeolite molecular sieve carrier in direct and intimate contact with a suitable compatible cathode, such as sulfur sorbed in 10 graphite coated zeolite 4ä. In this case, the sulfur (in the form of polysulfide) can act as an electrolyte and the zeolite with sulfur sorbed therein can be considered as a catholyte. In this case, the zeolite-sulfur catholyte is thus considered as a combined electrolyte / cathode and the cells according to the invention contain this possibility, whereby the electrolyte and the cathode must be constructed accordingly. However, if the zeolite material in the anode exhibits too strong electronic conductivity to allow this, it may be necessary to have a porous insulating layer between the support and the cathode impregnated with a suitable liquid electrolyte.

This porous insulating layer may be a suitable insulating, doped dehydrated zeolite material. This embodiment has the advantage that, apart from the anode or the electropositive material, which is usually in the molten state, the cell is substantially in the solid state and zeolite-based.

When the cell can operate at a sufficiently low temperature, clathrate micromolecule sieve carriers can be used in the same manner as the above-mentioned mineral micromolecule sieve carriers. They must not, when used with aqueous electrolytes for the same reason as above, sorb water and should have a similar channel-like structure and in the same way non-tectosilicate oxide micromolecular sieve carriers can be used.

The invention will now be further elucidated with reference to the accompanying schematic drawing figures, of which

448 Fig. 797 schematically shows a device used as a cell for conductivity tests performed on a zeolite support for a device according to the invention, Fig. 2 shows a similar device according to the invention and Figs. 3 and 4 graphically represent the results of tests performed with the device according to Fig. 1. .

In Figs. 1 and 2, the same reference numerals are used for the same parts.

In Fig. 1, a conductivity cell designated by the numeral 10 comprises a pair of stainless steel bowls 12 held together by insulated locking screws 14. In the bowls 12 are found the electrodes 16 of molten alkali metal and they are separated by a carrier 18 for a cell. The carrier is clamped between the edges 12.1 of the cups 12 and separates the electrodes

16 from eachother.

Fig. 2 shows essentially the same arrangement with the difference that one of the electrodes 16 is replaced with a liquid electrolyte / cathode mixture 20, so that the electrode 16 is the anode and the cups 12 function as current collectors.

The invention is described in more detail below with some non-limiting examples made with the device according to Fig. 1 and

2.

Example 1

Referring to Fig. 1, the support 18 was made in the form of a briquette containing zeolite 4Å and kaolin. A mixture of equal parts by weight of zeolite 4A and kaolin was ground in a ball mill for 24 hours and a briquette was pressed on a line press at a pressure of 2 x 10 kPa. The briquette was heated at 650 ° C for 3 hours. After cooling was placed

448 797 the product in a freshly made gel of zeolite 4a, in which the kaolin was converted to zeolite 4a, and the briquette was further compressed by squeezing fresh gel from the zeolite 4a.

The reconstituted briquette was removed from the gel after 10 days, washed with distilled water and dehydrated at 360 ° C and 10 kPa for 6 hours. The briquette was then impregnated with sodium metal from the gas phase under vacuum at 350 ° C for 2-3 hours.

The briquette with sodium sorbed therein was then handled in a glove box containing dry argon and the device of Fig. 1 was mounted and electrically connected to form a conductive cell. This procedure was repeated several times and a number of such cells were constructed doped with potassium and lithium.

The AC resistance R was measured against the temperature T of the briquettes. A representative graphical representation of the conductivity of the briquette as logO .^T

A summary of comparative test results is given in the following Table 1, where a sodium-impregnated briquette is compared with briquettes impregnated with lithium and potassium, respectively.

448 797

Table 1

<td>Metal</td><td>(.Ω. Cm) 1</td><td>T ° C</td>

<td>Li</td><td> 0,006</td><td> 350</td>

<td>Na</td><td> 0,050</td><td> 350</td>

<td>K</td><td> 0,010</td><td> 350</td>

Example 2

Additional briquettes were made containing zeolite 4a.

The briquettes in this Example 2 were then dehydrated and treated with sodium as described in Example 1 and tested at different temperatures.

Fig. 4 shows a representative graphical representation of logC / T versus 10 6 using the cell of Fig. 1.

T

The experimental results are summarized in the subsequent take bell 2 for sodium.

Table 2

<td>(-CLcm)¹</td><td>T ° C</td>

<td></td><td></td>

<td> 0,006</td><td> 200</td>

<td> 0,020</td><td> 250</td>

<td> 0,060</td><td> • 300</td>

Example 3

Small electrochemical test cells were made in accordance with Fig. 2, comprising an alkali metal anode 16, a zeolite having alkali metal sorbed therein as briquette 18 and a suitable compatible liquid electrolyte and cathode 20. An experiment was performed using a sodium anode, a zeolite

448 797

4th impregnated with sodium as briquette and an electrolyte of molten salt of potassium iodide and lithium iodide mixed with cathode material comprising zeolite IJX crystals doped with sorbed sulfur and containing graphite for electron conduction purposes. In this case, an open current voltage of 1.9 V was achieved along with a short-circuit current of 35 mA with an effective surface area of ​​1 cm² at 300 ° C.

Another cell was constructed using potassium for the anode, a zeolite 4A for a briquette impregnated with potassium, a lithium-aluminum chloride electrolyte and a zeolite 4a containing impregnated sulfur as the cathode. In this case, an open current voltage of 2.0 V was achieved with a short-circuit current of 5 mA at a temperature of 200 ° C and an ef. · 2 effective surface area of ​​about 1 cm.

Finally, a cell was constructed using sodium c anode, sodium impregnated in a zeolite support, a sodium aluminum chloride electrolyte and as cathode sulfur sorbed in zeolite 4A. From this cell an open current voltage of 1.9 V was obtained with a short-circuit current of about 10 mA at 200 ° C and an effective surface area of ​​about 1 cm.

In all cells, the zeolite in the support was prepared by mixing kaolin as described in Example 1.

All of the cells described above ceased to function after varying lengths of time for reasons which were essentially not related to the electrochemical conditions, but were due to sealing problems, cracking, etc. Continued experiments can be expected to eliminate these problems. While some of these cells stopped working after a few hours, others worked for up to 7 days.

An advantage of the present invention is that it provides a cell in which the electrolyte is separated from the anode by a carrier having a conductivity which is largely

448 797 order of play is several times greater than in undoped tectosilicates, e.g. the zeolites reported in Breck, Donald W. Zeolite Molecular Sieves, published by John Wiley &amp; Sons, 1974, p. 397 - 410.

It can be pointed out that the tested carrier, as shown in Figs. 3 and 4, has a conductivity which increases with the operating temperature, i.e. it exhibits a conducting coefficient positive with increasing temperature, which indicates that the conductivity may be ionic or hybrid rather than purely metallic or electronic.

As far as the construction of the carrier according to the invention is concerned, the intention is that it should be in the main case liquid-tight during use. For this reason, every effort should be made to make it completely tight without any macroporous spaces, channels, etc. As for its function, it should further be noted that after such an initial stabilization or conditioning period as may be necessary, there is in fact no change in the average composition of the carrier during charging and discharging and no change in the average oxidation state of the electropositive substance.