NO165264B - DEVICE FOR FITTING A LAMP ON A SURFACE. - Google Patents

Abstract

A device for fastening a lamp on a surface, whereby a frame (1) of the lamp is provided with a round opening, a fastening plate (9) being turnably secured on said opening. In order to enable turning of angular lamps in particular into a desired position before the final fastening, the frame of known devices is provided with elongated holes for fastening screws. A disadvantage of such holes is that water easily gets inside the lamp through said holes. The possibility of turning the lamp can be retained without losing the waterproofing, if the frame is provided with a conical projection (7) and the fastening plate (9) with a sealing surface (15) roughly following said projection, whereby the coning angle of said sealing surface differs from that of the projection (7), said surface being of a resilient material.

Description

Secondary battery.

The invention relates to a secondary battery for generating electrical energy and comprising a molten alkali metal anode reactant, a liquid cathodic reactant electrolyte in contact with a cathode and heating means capable of maintaining the anode reactant and the cathodic reactant electrolyte in a molten state, and characterized in that between and in contact with the anode reactant and the cathodic reactant electrolyte, a solid half-cell separator is placed which separates the anode reactant and the anodic half-cell reactions from the cathodic reactant electrolyte and the cathodic half-cell reactions, and which consists of a solid electrolyte which is selectively ion-conductive with regard to cations of the alkali metal when an electrical voltage difference is provided between the anode reactant and the cathode, and that the cathodic reactant electrolyte consists of a substance capable of reacting reversibly electrochemically with cations of the alkali metal at a temperature above its melting point.

The anode reactant and the cathode are electrically connected by means of a conductor which forms part of the electrical circuit and provides opportunities for an electron flow between the anode reactant and the cathode, this electrical circuit being terminated by ionic conduction between the anode reactant and the cathode through the cathodic reactant electrolyte and the solid electrolyte , as both the anode reactant and the cathodic reactant electrolyte are kept at a temperature sufficient to keep them in a molten state and for the half-cell reactions to proceed.

The use of solid electrolytes in energy conversion devices for the production of electrical energy is well known. See e.g. "Galvanic Cells with Solid Electro-lytes Involving Ionic and Electronic Conduction", C. Wagner, Department of Metallurgy, Massachusetts Institute of Technology, pages 361 - 377 in "International Committee of Electrochemical Thermodynamics and Kinetics, Proceedings of the Seventh Meeting at Lindau 1955", Butterworth Scientific Publications, London, England, 1957, and in "Solid Electrolyte Fuel Cells", J. Weissbart and R. Ruka, Fuel Cells, G.J. Young Editor, Reinhold Publishing Corporation, New York, New York, 1963.

The use of molten alkali metal as anode reactants in energy conversion cells is well known. Reference may be made to the U.S. patent No. 3,245,836, which uses a

porous separator impregnated with a liquid electrolyte, e.g. porous aluminum oxide, impregnated with sodium chloride, U.S. patent No. 3,031,518 which describes a galvanic cell with two consumable electrodes which form ions which combine to form a compound which is decomposed by heat at a temperature above the operating temperature of the cell during regeneration of the electrode materials, and U.S. Pat. patent no. 2,102,701 which describes a cell in which a porous filter is used, e.g. porous cement, which acts as a filter for the flow of alkali metal into contact with the liquid electrolyte. This cell is chemically regenerated. A primary cell in which an alkali metal reactant is contained in a sealed glass container is described in U.S. Pat. Patent No. 2. 631,180.

In the latter patent, it is stated that the wall of the glass container is a barrier electrolyte in the cell, and that due to the relatively high resistance of the glass, the cell only delivers small currents, even in the event of a short circuit. According to the above, this primary cell must be used either as a dry cell or the cathode material can be moistened with water or a suitable aqueous solution.

From the U.S. patent no. 3,057,945 it is known to use lead as one electrode, lead monoxide as the solid electrolyte and oxygen as the other electrode.

From French patent no. 1,280,511 it is known to use molten metal both as the positive and the negative electrode, and porous separators are used there.

It is an object of the invention to provide a new anodic half-cell unit in a rechargeable cell. This new anodic half-cell unit according to the invention can be made in an unlimited number of different designs, whereby the possibilities for constructive designs of the entire cell are significantly increased so that the possibilities exist for designing new battery units comprising two or more such cells that are connected electrically in series or parallel or both.

Another object of the invention is to provide for use in a rechargeable cell

a new anodic half-cell, whose interfaces have a constant shape and essentially constant structural strength during repeated electrochemical cycles, during which both charging and discharging reactions occur. Thereby, it is achieved that the electrode deterioration during recharging is reduced, whereby the utilization of a larger percentage of the anodic reactant during the discharge is made possible.

A further object of the invention is to provide a rechargeable cell which gives a high power per unit of weight, i.e. W/kg, at the same time as it has a high capacity for energy storage per weight unit.

A further object of the invention is to provide a rechargeable electric cell comprising a molten alkali metal anode, a cathode, a molten sulphurous electrolyte which can be reduced by means of alkali metal ions, and which can react reversibly electrochemically with the alkali metal ions, and which is in contact with the cathode, and a cation-conducting, solid electrolyte placed between and in contact with the anode and the liquid electrolyte, the solid electrolyte being characterized by the fact that it is conductive to cations of said alkali metal, and by the fact that it has a high resistance to physical and chemical attack by molten alkali metals, which is shown by the preservation of the high ionic conductivity.

Further advantages of the present secondary battery are the separator's low resistance to alkali metal ions, the separator's excellent thermal and chemical resistance which allows the use of molten alkali reactant which has not previously been used together with a solid electrolyte, a calculated high energy yield of the alkali metal-sulfur system, and that the solid electrolyte sits in a fixed position, which gives a constant configuration of the anode space even when the anode reactant is consumed.

In the following, the invention is described in more detail with reference to the drawing where: . fig, 1 schematically shows a vertical section of a single cell according to the invention comprising an anodic unit consisting of a cation-conducting tube containing a molten anodic reactant which is essentially surrounded by molten cathodic reactant,

fig. 2 is a schematic vertical section through a more complicated cell according to the invention comprising a multi-tube anodic unit which is supplied with anodic reactant from a common reservoir,

fig". 3 is a horizontal section through another embodiment of a cell according to the invention to illustrate the variation possibilities with regard to the design and placement of the containers for the molten anode, and fig. 4 shows a schematic vertical section through a cell according to the invention

corresponding to another embodiment, in which the molten reactants are separated by a plate-like separator and thus face each other along a single plane.

When operating the secondary, rechargeable batteries according to the present invention, a high electrical yield is achieved by keeping the alkali metal anode in a molten state and the molten anode is kept separated from the molten electrolyte by relatively thin half-cell separators, i.e. solid electrolytes, which have such a physio-chemical composition that they are resistant to attack by liquid alkali metal and thus that they are characterized by a low resistance to ion conduction for the cations of the alkali metal.

According to the invention, the anodic reactant or reducing agent is an alkali metal, the temperature of which is maintained above the melting point when the cell is in operation. The anodic reactant is heated in any known manner, e.g. by induction heating via electricity, by indirect heat exchange with a suitable heated heat exchange medium or by direct heating. The anodic reactant can also be considered to be the anode itself or a conductor, through which the electron current is led to the external circuit. A cell component of this type is often called a sacrificial electrode, because at the same time as it serves as a conductor, it also undergoes an electrochemical reaction.

A preferred design of the cells described below to illustrate the invention uses molten sodium as the anodic reactant. Potassium, lithium and other alkali metals or mixtures of alkali metals can be used, if the cathodic reactant and the separator, described below, are chosen corresponding to the selected alkali metal.

In all embodiments of the apparatus according to the invention, the cathodic reactant is a material capable of reacting reversibly electrochemically with the anodic reactant. The cathodic reactant or oxidant is likewise used in a molten state and is preferably a material which will undergo all phases of the above reversible reaction in such a way that all occurring components remain in a liquid state, i.e. without evolution of gas. The cathodic reactant can suitably be a metal salt and preferably a sulphide of the metal used as anodic reactant. If the anodic reactant is e.g. sodium, the cathodic . reactant thus preferably contain sodium and sulphur. The operation of such a cell can possibly be started without sodium in the cathodic reactant if the sulfur is thoroughly treated with a suitable conductive material, such as finely divided carbon powder. In a particularly preferred embodiment, the discharge is started with a concentration of approx. 5 equivalents of sulfur for every 2 equivalents of sodium, and the discharge ends when the atomic ratio between sodium and sulfur is approx. 2:3. The relative concentrations of sodium and sulfur determine the melting point of the cathodic reactant. This ratio must therefore be considered in relation to the cells' operating temperature and vice versa. If other metal salts are used, such as metal dioxides, nitrates, etc., care must be taken to ensure that gas evolution is either completely avoided or controlled both during charging and discharging.

The term "sodium and sulfur-containing cathodic reactant" is not limited to any theory with respect to ionization and additions, and a reactant so designated may therefore contain ions, compounds, and electrically saturated elements.

The anodic reactant is separated from the cathodic reactant by a solid wall, which acts as a barrier to fluid mass transfer, i.e. a solid-electrolyte half-cell separator, which is selectively conductive to the cations of the anodic reactant and essentially impermeable to other ions which may be formed in the cationic reactant. Thus, the separator is a material that will allow transfer of the ions from the anionic reactant through the separator into the cationic reactant during the discharge reaction and allow their selective return when an electric current is passed through upon recharging. Together with this separator, the cathodic reactant constitutes a sufficient barrier for the free flow of electrons in the inner part of the electrical circuit to allow an electrical potential difference to occur at the respective electrodes when the cell is in operation. It is preferred that the separator be as thin as possible, without undue reduction in its mechanical strength. As the separator's optimal thickness will vary with the intended application, it should be mentioned that the separator with a thickness in the range from approx. 20 to approx. 2,000 microns, preferably from approx. 100 to 1,000 microns have been found to be effective. The transfer of anodic material begins when the external circuit is closed.

The described cells were first kept in operation with a sodium oxide-aluminum oxide-silicon dioxide glass in which the ratio of AlgO^ to NagO was practically 1:1, i.e. pp. from approx. 80 - 100 parts Na20 to approx. 80 - 100 parts AlgOg, and where the molar ratio between NagO, AlgOg and SiOg was essentially 1:1:3-6. Glass of this type is described

in detail in the U.S. Patent No. 2,829,090 and by Isard, J.O. in "Electrical Condition in the Aluminosilicate Glasses, 43 Journal of the Society of Glass Technology, 113T (1959)". Such glasses can be used for this purpose, but exhibit a relatively high resistance to conduction when they are started. Such glasses have a short service life in contact with molten sodium before they break apart mechanically. It was subsequently discovered that certain other glass compositions, described in more detail below, exhibit a surprisingly high resistance to molten alkali metal as well as a remarkably low resistance to ion penetration.

While glass materials have certain advantages with regard to the shaping characteristic of glass, other materials have been found which exhibit a higher resistance to oyer. chemical and physical attacks from cell reactants, and which exhibit lower electrical resistance to cation conduction.

~ "; ■ -. For this purpose, there are some cation-conducting materials, which are crystalline

or ceramic or both, and which exhibit exceptional resistance to molten alkali metal, and which at the same time exhibit extremely low specific resistance. Examples of such crystalline materials are given below.

A glass which can be used in cells according to the invention, and which exhibits an exceptionally high resistance to attack by molten alkali metal, contains 47 - 58 mol% Na2O, from 0 to 15, preferably from 3 to 12 mol% ^ 2°2 and 34 " 50 mo1^ SiQ2.

Other glasses which can be used in cells according to the invention, and which exhibit high resistance to attack by molten alkali metal, contain 35 - 65, preferably from 47 to 58 mol% Na2O, and from 0 to 30, preferably from 20 to 30 mol% Al2O3 and from 20 to 50, preferably from 20 to 30 mol%

The glasses described in the last two paragraphs can be produced by conventional glass-making methods using the aforementioned components in the listed concentrations and by heating them to temperatures of approx. 1480°C.

In the present invention, the above-mentioned glass, which is resistant to attack by molten alkali metals, can be used in combination with the above crystalline separators.

The anodic reactant, and in most designs also the cathodic reactant, should be kept in an oxygen-free atmosphere. An inert gas, such as helium, argon or nitrogen, can be suitably used in the respective containers for this purpose.

Although the anodic reactant and the cathodic reactant may be connected electrically only by means of filamentary conductors connected through an external circuit, in a preferred embodiment the cathodic reactant may be held in contact with a non-sacrificial cathode of substantially greater surface area. This electrode should be a good conductor and be made of a material capable of withstanding sustained contact with the molten cathodic reactant. Conventional carbon electrodes, which generally consist of a mixture of graphite and amorphous carbon, are suitable. Such electrodes are conventionally produced by mixing fine particles from graphite, coke, etc., with a suitable binder, such as pitch, after which the mixture is subjected to high temperatures and pressure for a longer time. Electrodes consisting mainly of graphite have also proven to be suitable in these cells.

When using the cells, these are kept at temperatures above the melting point of both the anodic reactant and the cationic reactant and below the temperature at which significant softening of the separator takes place when the latter is made of glass. Crystalline separators are suitable to withstand even higher temperatures. Such cells will generally be held at temperatures between 200°C and 600°C, most often in the range from 250 to 450°C. The temperature of the reactants can be maintained with the help of external heating devices as mentioned above, and possibly the internal resistance of the cells can be utilized for heating.

The discharge period can optionally be terminated automatically by placing the conductor which provides the connection to the molten electrode so that the electrical connection is automatically interrupted when a predetermined amount of the anode material has been converted, whereby the level of unreacted anode material is lowered. Moreover, changes in the melting point or electrical resistivity of the cathodic reactant can possibly be used to indicate a desired degree of discharge in conjunction with other more conventional means.

In accordance with the usual nomenclature, the terms "anode" and "cathode" are used here to denote the electrodes at which the electrochemical reaction that takes place in the cell develops negative and positive potential, respectively. Fig. 1 shows a cell container 11, which can be made of any suitable material or materials, which provide both thermal and electrical insulation, e.g. burnt stone, certain thermally and chemically resistant polymers, ceramic materials, crystalline materials or suitable glasses, etc. Inside the container 11 is placed a graphite cylinder 12, which is closed at the lower end. The cylinder 12 forms a container for the cathodic reactant 13, which can be a metal-containing oxidizing agent, e.g. Na„S , and a cation-conducting separator 14, which also acts as a container for the anodic reactant 15, which e.g. may be molten sodium. The upper part of the separator and container 14 is in this design funnel-shaped to provide extra volume for the molten anodic reactant. The purpose of this is to prevent the surface of the molten sodium from falling below the upper level of the cathode reactant during discharge of the cell. Wire conductors 16 and 17 constitute organs for closing the circuit, and when these are connected, the reaction in the cell is initiated. The space above the molten anodic reactant 15 in the separator or container 14 is filled with an inert gas 19, e.g. argon. Fig. 2 shows a modification of the cell shown in fig. 1. In this embodiment, the cell comprises a number of glass tubes 24, which are closed at one end, and which have relatively smooth sides. These glass tubes contain a molten anodic reactant 25, which may optionally be the same as that shown in fig. 1. Each of the tubes 24 consists of a sodium-aluminium-silicon glass containing approx. 47 to approx. 58 mol% Na2O, approx. 3 to approx. 12 mol% AlgOg and approx. 34 to approx. 50 mol% SiOg, or a boron oxide glass containing approx. 47 - 58 mol% Na2O, approx. 20 - 30 mol% AlgOg pg approx. 20-30 mol% 52^3' Each of the tubes 24 is fed from a common supply container 28, which is partially filled with molten anodic reactant 25, i.e. an alkali metal, which may possibly be the same as that assumed to be used in the one in fig. . 1 shown embodiment, or different from this, e.g. potassium. The supply container 28 can be made of the same glass as that used in the pipes 24, but other suitable materials can also be used. A conductor 22 forms a container for the cathodic reactant 23. JBoth 22 and 23 can be the same materials as the corresponding components in the cell

len which is shown in fig. 1, or they may differ from this, e.g. aluminum for the container and a mixture of potassium and sulfur as the cathodic reactant. The insulator 21 forms a container for the entire cell. Conductors 26 and 27 connect the cell to an external circuit.

Fig. 3 shows a particular design of the cell according to the invention seen from above.

In this design, the glass separators or anode containers 34 used are of varying size and design, and they are assembled in the cell in a specific pattern. The tubes 34 can again contain a molten alkali metal 35 and are separated from the carbon cathode 32, which acts as a cell container, by means of a cathodic reactant 33 consisting of a metal salt. Electrical connections are not shown in this figure, and the container 32 is not covered. This is for the sake of contact connections with other cells to build up a multi-cell battery.

The one in fig. The design shown in 4 differs from the preceding cells in that the anodic reactant 45 is not substantially enclosed by the separator 44. In this design, a box-shaped anode space is limited by the cell container 41 and the separator 44. The glass container 41 can be isolated from the separator 44 if the glass 41 is sufficiently conductive at the operating temperatures to short-circuit the cell. The glass container 41 is here protected with a metal cover 48. A cathode compartment is likewise limited by the cell container 41 and the separator 44, and contains the molten cathodic reactant 43 and the carbon cathode 42. The conductors 46 and 47 have the same function as the corresponding conductors in the cells described above. In this cell, the anodic and cathodic reactants are thus located on opposite sides of a glass which extends substantially in a plane. Although a large part of the volume efficiency achieved in the other designs is lost, this design finds application where the duration of the discharge operation is more important than the effect per weight unit.

It will be seen that in relation to the variation possibilities for the construction of the anode unit in question, i.e. the molten anode reactant and its container, the above examples are merely descriptions of a few simplified designs of a practically unlimited number of possible cell designs, all of which would fall within the scope of the invention.

During normal operation, both the glass separator and the cathodic reactant will exhibit ionic conductivity, this being a normal function of an electrolyte, but the present invention is not limited by any theory as to which functions of these materials are the decisive function, and therefore the composition of each of

these described in connection with the description of the operating conditions for the component.

In the following, the invention is described in more detail with the help of a number of design examples.

Example 1

A cell was constructed in accordance with the invention comprising a glass tube containing sodium and a graphite rod spaced apart from it and immersed in NagSg. An external circuit provided electrical connection between the sodium and the graphite rod. The external circuit included a voltmeter, an ammeter and a variable resistor. The cell was placed in an electrically heated oven in an argon atmosphere, the oven being heated to a temperature above the melting point of both sodium and Na2S5-

The glass in the tube containing the sodium anode was prepared by mixing chemical equivalents of silicon dioxide, aluminum oxide and sodium carbonate in the ratio 4:1:1 and heating the resulting mixture in a platinum crucible at 1650°C. The glass tube used was closed at one end and had an average external diameter of approx. 2 mm. The average wall thickness of the pipe was approx. 0.1 mm or 100 microns. The applied NagS,. was produced by heating Na2S. 9H20, until the material was practically water-free. Hydrogen sulphide was bubbled through this sodium sulphide during the formation of NaHS. This was weighed and sulfur was added in the amount necessary to achieve conversion to Na2S5< The mixture was heated in nitrogen to drive off hydrogen sulphide and leave Na2S,_. The immersion depth in the molten Na2Sg was approx. 6 cm. This was also equal to the operating length or utilized length of the tube as the tube was filled with sodium to a level that was above the surface of the Na 2 Sg in which it was immersed. The tube containing the anode was placed approx. 1-2 cm from the graphite cathode element. The graphite rod had an average diameter of 6.35 mm and was immersed in Na 2 S 5 to a depth of 6 cm.

When only a single anode tube and a graphite rod were used, the effective space utilization shown in the drawings was not achieved. This means that a larger amount of Na2S,., must be used than would be used in the more efficient designs of the cell shown in the drawing, and an increased internal resistance. A tungsten wire immersed in the sodium and a platinum wire connected to the graphite rod were connected by a copper wire to complete the external circuit. The threads used were 24 gauge.

By means of an automatic contact, the cell was connected to a charging current source in such a way that the cell was continuously alternately charged and discharged for a period of approx. 48 hours without significant change in the electromotive force of the cell. The appearance of the cell's individual components was unchanged at the end of this period. The time interval for each discharge period was 10 minutes. The charging period was the same.

The operation of the cell was controlled at varying temperatures above the melting point of the reactants. The following data illustrate this: At the temperatures of 310, 340 and 387°C, the electromotive force of the cell was essentially unchanged, namely 2-2.1 volts. When the anode and cathode conductors were directly connected to each other by only the resistance of the wire and a low-resistance ammeter in the outer circuit, the current varied greatly with temperature, e.g. 175 mA at 310°C, 240 mA at 340°C and 430 mA at 387°C.

When the current was passed through the cell during both the charge and discharge periods, the cell potential was different from the thermal potential, the difference being essentially equal to the calculated drop in potential due to ohmic resistance, which means that there is no significant polarization. at some of the electrodes. The measured ohmic voltage drop across the glass membrane at 300°C was 0.2 V, when the current density through the glass was 5.0 mA per cm 2.

Experiments were carried out using a platinum cathode instead of the graphite rod. The results obtained were essentially unchanged.

Example 2

Soda-alumina-silicon dioxide glass separators with the following concentrations of the individual components were tested with regard to attack by molten sodium and electrical resistance. The results are reproduced in the following table:

When heated in contact with liquid sodium to 350°C, the above glass increased less than 0.1 mg/cm 2 , 1000 h, and showed none of the characteristic brown discoloration, scaling or other visible signs of sodium attack.

Example 3

The following glasses containing B203 were tested for attack by molten sodium and for electrical resistance within a certain temperature range with the following results:

These glasses showed no visible deterioration as a result of attack by molten sodium at 350°C after exposure to this for over 2 months.

The term "glass" is used here in the sense given by the definition of this term in A. S. T. M. designation C-162-45T. See also J. E. Stanworth: Physical Properties of Glass, pp 1-8, Oxford University Press London, 1950, and Glass Industry 26, 417 (1945).

Example 4

A secondary battery comprising a single cell is constructed so that the interior of a first glass tube and the interior of a second glass tube are separated from each other by means of a disc of sodium-beta-aluminum oxide attached to these glasses by means of glass gaskets, so that there a tight seal is achieved. The tubes have an inner diameter of approx. 12 mm. These tubes and glass seals are made from a glass whose coefficient of expansion is close to the coefficient of expansion of beta aluminum oxide, e.g. "Corning 7052, Kovar". The first tube forming the anode compartment is filled with molten sodium, and the second tube is partially filled with a molten reactant containing sodium and sulphur,

e.g. sodium pentasulfide (Na2S,.). The sodium and sodium pentasulphide are kept in a molten state by heating in a known manner. The air in the pipes can optionally be essentially evacuated and the pipes sealed, or the cell can work in an inert atmosphere, e.g. argon. The beta aluminum oxide disc has a diameter of approx. 12 mm and is approx. 2 mm thick with a surface area in contact with the reactants in each of the tubes of o approx. 1.13 cm 2 measured as flat surface.

In this cell, the molten sodium serves both as an anodic reactant and as an electrode, while the sodium and sulfur-containing reactant acts both as a cathodic reactant and as a liquid electrolyte. In general, the reaction is initiated with a sodium to sulfur ratio in the cathodic reactant of approx. 2:5, and the cell's discharge ends when this ratio is at least 2:3. A copper wire conductor protrudes into the sodium electrode (anode), and a stainless steel electrode (cathode) protrudes into the sodium pentasulphide. These conductors are electrically connected via an external circuit, which may include a voltmeter, an ammeter, etc. During the discharge period of the cell, sodium is attracted to the sulfur on the opposite side of the beta-aluminum oxide membrane, the above-mentioned disc, emits an electron and passes through the membrane in the form of a sodium ion and unites with the Bulfidion, which is formed at the cathode during the absorption of an electron, whereby an electric current is caused to flow through the aforementioned circuit. Recharging is carried out by applying an external electrical power source to the circuit with the opposite current direction in relation to the discharge period.

The cell described above has an electromotive voltage of approx. 2 V. At a temperature of approx. At 312°C, the cell exhibits the following charging and discharging characteristics:

A cell constructed as described is subjected to lifetime tests in which the cell is exposed to alternating charges and discharges with a period of 1/2 hour at a temperature of approx. 312°C. In this cell, the sodium beta-alumina disc was prepared as follows: Commercially available beta-alumina refractory rocks were crushed or ground, or both, to a powder with a particle size of less than about 1 micron, preferably not significantly above approx. 1/3 micron as largest diameter. Sodium carbonate or aluminum oxide powder of a similar size is added to the powder obtained if this is necessary to bring concentrations of Na,,0 into the range approx. 5 to approx. 6% by weight of the weight of the mixture, and thus close to the stoichiometric composition for Na20. 11 Al^O^. The powder is pressed into tablets at approx. 633 kg/cm 2, e.g. tablets of approx. 19 mm diameter, 12.7 mm length and a density of approx. 1.98 g/cm<2>. The sintering of the tablets was carried out in a closed platinum-rhodium crucible in the presence of a coarse powder of beta aluminum oxide, i.e. particles of more than 1 micron in diameter at a temperature in the range of approx. 1593 to approx. 1815°C for a period of time from approx. 5 minutes to approx. 1 hour. The sintered tablet had a density of approx. 3.0 g/cm and was cut into thin slices for use as a solid electrolyte in the cells described above.

A cell of the same type used in the above-mentioned experiments was tested at 294°C to determine its charge-discharge characteristics. In this cell, the beta-aluminum oxide disc was prepared as follows:

The powder of sodium carbonate and aluminum oxide was mixed in such a ratio

that a mixture equivalent to 60% by weight NaAlOg and 40% by weight Na2Og was obtained. This mixture was heated to approx. 1316°C and forms a molten eutectic, which on cooling to room temperature gives a product consisting of particles of sodium beta aluminum oxide embedded in NaAlOg. This compound NaAlC*2 is dissolved in water leaving the powdered sodium beta aluminum oxide, which is then crushed or ground or both.

The particle size before sintering is approx. 0.16 microns. The fresh tablets are sintered at 1788°C for 5 minutes in a closed container in the presence of a coarse powder of sodium beta aluminum oxide. The disc used in this cell is approx. 2.8 mm thick and presents a surface area of 1.5 cm 2 to each reactant. The Na20 content in the finished disc is approx. 5.75% by weight (approx. 9.1 mol%). The content of SiOg is approx. 0.05% by weight. The charge-discharge characteristics of this cell were measured as follows:

Sodium-beta-aluminum oxide discs are produced from the aforementioned eutectic

as described above. Before sintering, the beta aluminum oxide powder had an average particle size of approx. 0.16 microns. The sintering is carried out at approx. 1797°C for approx. 1/2 hour. The tablet obtained had a density of approx. 3.05 g/cm, and contained approx. 5.75% by weight (approx. 9.1 mol%) Na2O and approx. 0.05% by weight SiOg, with a residue consisting mainly of Al^O^,

Beta aluminum oxide electrolytes prepared in this way were tested for measuring the electrical resistance of the wafers at different temperatures. The following results were obtained:

Example 5

Lithium-substituted beta-alumina discs, in which lithium is substituted for sodium, were prepared by first preparing sodium-beta-alumina discs as described above, The sodium-beta-alumina discs were immersed overnight in liquid silver nitrate under an argon blanket and then removed from the bath. The resulting silver-substituted sodium-beta-alumina wafers were immersed overnight in liquid lithium chloride under an argon blanket and then removed from the bath.

A cell that was constructed in the same way as the one in fig. 1 shown cell, was used with a lithium-substituted beta-aluminum oxide solid electrolyte. This cell

The anodic reactant is molten lithium and the cathodic reactant is sulfur and graphite.

A cell constructed in the same manner as those in fig. 1 and 2 shown cells, were kept in operation with a eutectic mixture of two alkali metals, e.g. sodium and potassium, as the anodic reactant. At the beginning of the experiment, the cathodic reactant is molten sulfur and graphite powder.

Example 6

Another test cell comprised a glass tube mounted inside a heated shell.

The glass tube contained liquid sodium pentasulphide. A smaller glass tube is placed inside

in the former tube and contains molten sodium. The lower end of the smaller tube is closed by a plate cut from a cylinder prepared in the manner described below: Crystalline cylinders, which measured approx. 1 cm in length and approx. 1.2 cm in diameter, was produced in the following way: 1. Magnesium oxide was produced by calcining basic magnesium carbonate at a temperature of approx. 816°C. 2. The magnesium oxide was mixed with finely divided ("Linde B") AlgOg as a benzene slurry.

3. The benzene was removed by evaporation.

4. The magnesium oxide-aluminium oxide mixture was then heated to approx.

1427°C for approx. 30 minutes:

5. The product obtained from step 4 was mixed with sodium carbonate as a

benzene slurry.

6. The benzene was removed by evaporation.

7. The magnesium oxide-aluminum oxide-sodium carbonate mixture was then added

heated to approx. 1427°C!for 30 minutes.

8. The powdered product from step 7 was then mixed with a conventional, non-wax lubricant and pressed into cylinders at a hydrostatic pressure of 7030 kg/cm o. 9. The wax lubricant was removed by heating the cylinders in air as the temperature was raised within 2 hours to approx. 600°C and then held constant for further

1 hour.

10. The cylinders were then sintered by packing them in MgO in crucibles with packing powder of the same composition, i.e. the powdered product from step 7, and heating to 1900°C in air for 15 minutes.

The composition of these cylinders was found to be 6.3 wt% NagO, 2.18 wt% MgO and 91.52 wt% AlgOg. The composition was determined by conventional chemical analysis, i.e. sodium by flame photometry, magnesium by titration using "eriochrome black T" as indicator, while aluminum was determined as the difference.

An electrical connection is established via an external circuit between the sodium and the sodium pentasulphide. An electrical connection is established with a charging circuit. This connection begins a charging period in which sodium from the compartment that originally contained Na„S is passed through the plate into the smaller tube. By regulating the supplied electrical energy, e.g. the charging voltage, on recharging, and the variable resistance on discharging, the cell was kept in operation under such conditions that the difference between the charge taken out of the cell, and the charge introduced into the cell, became zero over a complete cycle comprising discharge and charging.

The electromotive force of the cell was measured to be 2 V. The cell was alternately charged and discharged at 30 minute intervals. The charge-discharge current was kept at approx. 10mA.

Crystalline cylinders were also prepared by this method using LigO instead of MgO. Lower sintering temperatures were used here.

Using this method, crystalline cylinders were produced that measured approx.

1 cm in length and approx. 1.2 cm in diameter. The relative amounts of the components were changed as described below. In cases where the sintering temperatures were changed, this is also stated.

In this way, cylinders were produced from components which, immediately before sintering, had the following composition:

The cylinders were sintered at approx. 1850 C for 30 minutes. Representative cylinders were then analyzed chemically and the composition was found to be as follows, after sintering:

Measurement of the specific electrical resistance (direct current) was carried out on these cylinders as in the above examples. The measured specific resistance fell in the range from approx. 318 to approx. 500 ohm-cm.

Another group of cylinders was produced in a similar manner with an exception

that the relative quantities of the constituents had changed. Chemical analysis of representative cylinders after sintering showed that these cylinders contained approx. 3.94 wt% MgO, 8.45 wt% NagO and the rest AlgO^. Eleven of these cylinders were stacked vertically during sintering with the furnace's hottest point in the area around cylinder no. 4. The temperature at this point was 1900°C. Weight and specific electrical resistance were measured for these cylinders with the following result:

Another group of cylinders was prepared in a similar manner and compression molded at 281 kg/cm 2 and hydrostatically pressed at 7734 kg/cm 2. Representative samples were analyzed with the following results:

These cylinders were heated to 1950°C and tested for electrical specific resistance

condition (direct current) as in the above examples. The results obtained were as follows-

is:

Representative cylinders of aluminum oxide-sodium oxide-magnesium oxide from

Example 8 was subjected to X-ray spectral analysis to investigate the crystalline structure, and a pattern was thereby repeatedly obtained, which was similar to, but distinguishable from, the pattern reported by Thery and Briancon, Comptes Rendu 254 2782, 1962, which they attribute a compound with the formula NaAlcO0. This

connection that they describe is not stable over approx. 1500 - 1600 oC.

The crystal structure of representative cylinders of aluminum oxide-sodium oxide-

magnesium oxide from example 1 gives an X-ray spectral pattern that is completely

different from this. This pattern is of the same type as that obtained from the compound Na20. 11 A1203.

Claims (11)

1. Secondary battery for generating electrical energy and comprising a molten alkali metal anode reactant, a liquid cathodic reactant electrolyte in contact with a cathode and heating means, capable of maintaining the anode reactant and the cathodic reactant electrolyte in a molten state, characterized in that between and in contact with the anode reactant and the cathodic reactant electrolyte is placed a solid half-cell separator which separates the anode reactant and the anodic half-cell reactions from the cathodic reactant electrolyte and the cathodic half-cell reactions, and which consists of a solid electrolyte which is selectively ion-conductive with respect to cations of the alkali metal when a electrical voltage difference between the anode reactant and the cathode, and that the cathodic reactant electrolyte consists of a substance capable of reacting reversibly electrochemically with cations of the alkali metal at a temperature above its melting point. 2. Battery according to claim 1, characterized in that the anode reactant and the cathodic reactant electrolyte are kept at a temperature in the range from 200°C to 600°C. 3. Battery according to claim 1 or 2, characterized in that the alkali metal is sodium. 4. Battery according to claims 1 - 3, characterized in that the cathodic reactant electrolyte comprises a molten sulphide of the alkali metal. 5. Battery according to claims 1-4, characterized in that the cathodic reactant electrolyte is an oxidizing agent containing sulfur ions and sodium ions, in which the ratio between sulfur and sodium is greater than the stoichiometric ratio corresponding to the compound Na2S3> 6. Battery according to claims 1 - 5, characterized in that the solid electrolyte has a specific electrical resistance at 350°C of not significantly more than 1000 ohm-cm. 7. Battery according to claim 6, characterized in that the alkali metal and the cathodic reactant electrolyte are kept at a temperature in the range from 250°C to 450°C. 8. Battery according to claim 1, characterized in that the alkali metal is sodium, and that the solid electrolyte is a glass which is conductive to sodium ions. 9. Battery according to claim 8, characterized in that the solid electrolyte is a glass object consisting essentially of 47 - 58 mol% Na2O, 0 - 15 mol% AlgOg and 34 - 50 mol% SiOg. 10. Battery according to claim 8, characterized in that the solid electrolyte is a glass object consisting essentially of 47-58 mol% Na2O, 3-12 mol% AlgOg and 34-50 mol% SiOg. 11. Battery according to claim 8, characterized in that the solid electrolyte is made of a glass, consisting essentially of 35 - 65 mol% NagO, 10 - 30 mol% AlgOg and 20 - 50 mol% BgOg.