GB1597033A

GB1597033A - Electrodes for lead storage battery and cells and batteries containing them

Info

Publication number: GB1597033A
Application number: GB3097/78A
Authority: GB
Original assignee: Solargen Electronics Ltd
Current assignee: Solargen Electronics Ltd
Priority date: 1977-02-15
Filing date: 1978-01-25
Publication date: 1981-09-03
Also published as: NL182266B; IL53476A; SE7713522L; MX148202A; ES473868A1; DE2750596A1; NO155318B; AT368323B; IE46174B1; NL7713836A; NL182266C; AU3120677A; ATA24478A; NO155318C; NO774065L; BR7708182A; IT1114690B; CA1090878A; FR2380645B1; DE2750596C3

Abstract

The active substance of the positive electrode of an accumulator cell consists of crystalline and polycrystalline lead superoxide in which the lead has its maximum valency of 4. The polycrystalline lead superoxide is an aggregation of individual crystalline substances which are in different growth and development phases. The active substance is located, as an adhering and permanent coating layer, on a carrier plate consisting of Pb, a Pb-Sb alloy or an inert non-conductor which is coated with a Pb or Pb-Sb alloy. An accumulator cell having such an electrode has reduced internal resistance and higher capacity, and it can be recharged quicker.

Description

(54) ELECTRODES FOR LEAD STORAGE BATTERY AND CELLS AND BATTERIES CONTAINING THEM (71) We, SOLARGEN ELEC TRONICS LTD., a Company organised and existing under the laws of the State of New York, of 562 Fifth Avenue, New York, N.Y. 10036, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates generally to improved storage cells and to devices, including storage batteries, which incorporate such cells in their construction.

The construction and operation of a cell is generally well known. A cell, whether primary or secondary, is an electrochemical device which consists of two plates of conducting material immersed in an electrolyte. A primary cell is designed to develop an electric potential and to convert chemical energy into electrical energy irreversibly. A secondary cell, however, is reversible in its function and can transform chemical energy into electrical energy, or vice versa. Secondary cells are more commonly called "storage cells".

When a storage cell is supplying electric energy, the cell is said to be "discharging" and chemical energy is being converted to electrical energy, and when the storage cell is supplied with electrical energy, the process is reversed and the cell is said to be "charging".

Two or more cells connected together, in series or in parallel, constitute a battery and a battery made from connecting several storage cells is known as a storage battery.

There are two common types of storage batteries; the lead-acid type battery, or as it is simply called, the lead battery, and the nickel-alkaline or Edison type battery, popularly called the alkaline battery. It is with the former type battery that the present invention is concerned.

The cells in the lead-acid battery consist of a positive plate of lead oxide and a negative plate of spongy lead which are immersed in a diluted solution of sulphuric acid (electrolyte). The active mass or material of each plate is that part which undergoes a chemical change when electricity flows through the battery. This active mass is supported by a frame or grid of pure lead or lead alloy, e.g., an alloy of lead and antimony, which serves the dual function of carrying the active mass and conducting the electric current. It is with a novel, unique and improved active mass that the present invention is more specifically concerned.

The charging and discharging cycles of a typical lead-acid type battery may be represented by the following reversible reaction: Charge Discharge

+ plate -plate

The active material of the positive plate is brown, porous lead oxide, while the active mass on the negative plate is gray, spongy and porous lead, in pure form.

The lead-acid batteries which are currently available on the marketplace exhibit limited performance capabilities, and numerous attempts and suggestions have heretofore been made to improve them. Thus, improvements in charging and discharging characteristics of these batteries, increasing their current discharge rate and reduction in the internal resistance of the battery cells are but few of the numerous properties which have received considerable attention of the prior art workers in this field. Some have focused their attention on the electrodes while others have suggested a variety of electrolytes in order to improve the overall performance of the cells, and the devices which incorporate such cells.

Thus, U.S. 2,933,547 describes a battery made from a plurality of solid state electric cells consisting of silver and zinc electrodes and a solid, solvated cation-exchange resin membrane which is sandwiched between the electrodes.

U.S. 3,468,719 discloses a solid state ionic conductor made of a polycrystalline material in which the structural lattice is composed of ions of aluminium and oxygen in combination, and sodium ions which migrate in relation to the crystal lattice under the influence of an electric field. This material is employed as a half-cell separator in the construction of batteries as more fully described in example 3 of said patent.

U.S. 3,499,796 discloses a ceramic sandwich between a pair of electrochemically and cationicallyconductive crystalline objects which are in cation exchange relationship and separated by a cationically-conductive, electronically nonconductive crystalline object, and to storage devices comprising the same.

U.S. 3,709,820 discloses an organic solid electrolyte which is a crystalline electron donor-acceptor complex comprising ionic crystals of 7,7,8,8-tetracyanoquinodimethane, an aromatic amine, and a liquid impregnated in the ionic crystal lattice. The electrolyte described in this patent is employed in capacitors to lower their resistivity.

U.S. 3,765,915 describes the uses of Betaalumina polycrystalline ceramics for use as electrolyte in the construction of cells or batteries of the sodium/sulphur type.

The foregoing patents are but a few of the plethora of patents which represent the research and activities which have been expended in this art. Nevertheless, however, the basic construction of the lead-acid battery and its constituent cells remain essentially unchanged. Today, as it was made several decades ago, lead-acid batteries are made by serial connection of a plurality of cells (usually 3 or 6) wherein porous lead oxide is the active mass on the positive plate and spongy, porous lead is the negative plate, and dilute sulphuric acid is the electrolyte of choice.

According to the invention a conductor suitable for use in a storage cell comprises a carrier plate which carries a uniform and adherent layer of an active mass comprising polycrystalline lead superoxide as defined below A storage cell according to the invention is one in which the anode or anodes are formed of such conductor, the electrolyte is dilute sulphuric acid and the cathode or cathodes are of lead.

According to the invention a conductor suitable for use as a cathode in a storage cell is obtained by electrolytic reduction of a novel conductor as defined above, and such a cathode is preferably used in a storage cell according to the invention Storage cells according to the invention may comprise a plurality of anodes connected in parallel and a plurality of cathodes connected in parallel. Storage batteries according to the invention may comprise a plurality of cells as defined above connected in series.

In referring herein to lead superoxide we intend to refer to the lead oxide in which lead is at its maximum valence of four, and which conveniently can be expressed as PhO2.

The active mass of the invention is normally a dark brown to black material that is hard, homogeneous, highly porous and that has remarkably low internal resistance. It comprises crystalline and polycrystalline lead superoxide.

The term polycrystalline as used herein denotes an aggregation of single crystallinelike masses of lead superoxide that are at varying stages of growth and development and which, presumably as a result of being incompletely grown, do not have the characteristic tetragonal lattice structure of normal crystalline lead superoxide.

Generally the active mass of the invention is a mixture of single crystalline masses of lead superoxide together with the defined polycrystalline material.

Determination of whether or not a product is a polycrystalline superoxide can be made by, for example, X-ray diffraction tests. Additionally, a simple test to determine whether a test material comprises polycrystalline lead superoxide as defined, and especially whether or not it is a mixture of single crystals of lead superoxide and polycrystalline lead superoxide, can include comparison of that test material with a comparison material that has been made by any of the processes exemplified below and, in general, that has been made by a process comprising forming on a carrier plate a uniform and adherent coating comprising lead and cadmium and electrolytically oxidising this, the coating and the electrolysis conditions being such that substantially all the cadmium is removed into the electrolyte and the coating comprising the resultant active mass is formed on the plate. If the test material has similar essential physical properties of the comparison material then this is confirmation that the test material does comprise polycrystalline lead superoxide as defined.

It can be considered that the polycrystalline form of lead superoxide is a polymeric crystal form with the result that the active mass in the invention comprises crsytals of lead superoxide at various degrees of polymerisation.

The active mass preferably consists substantially only of the crystalline and polycrystalline lead superoxide although it may include trace amounts of other materials.

Any method that results in the formation of an active mass as defined above can be used in the invention but preferably the active mass is made from a mixture of lead and cadmium. Although most at least of the cadmium is preferably removed during the formation of the crystalline and polycrystalline lead superoxide the resultant active mass may contain trace amounts of cadmium in some form.

Preferably the conductors according to the invention are made by a method comprising forming on the carrier plate a uniform and adherent coating comprising lead and cadmium and electrolytically oxidising this, the coating and the electrolytic conditions being such that substantially all the cadmium is removed into the electrolyte and a coating comprising the said active mass is formed on the plate.

The ratio of lead to cadmium in the initial uniform and adherent coating usually is from 30 to 70 weight per cent and preferably from 45 to 55 weight per cent; however, optimum results are obtained when an approximately equal weight ratio of the two components are used. If the mixture is predominantly lead, say 70 weight per cent, the Pb-Cd layer will be softer and less porous, whereas if the cadmium component predominates, say, it constitutes 70 weight per cent of the mixture, the resulting Pb-Cd layer will be harder and more porous. Optimum hardness and porosity of the Pb-Cd layer are attained when the mixture is approximately a 1:1 ratio by weight.

The carrier plate should have an outer layer at least comprising lead. Preferably this outer layer at least is of lead, or an alloy of lead with antimony. The carrier plate may consist of lead or the lead alloy or may comprise a coating of lead or the lead alloy on an inert non-conductive substance.

Suitable non-conductive supports for the carrier plate used in the invention include plates made from a suitable plastic such as polypropylene or cellulosic material on which lead or a mixture of lead with antimony is deposited. The resultant plates are considerably lighter than plates according to the invention in which the carrier consists of lead or lead antimony mixture or alloy.

In one method for making the conductors of the invention a hot melt mixture of lead and cadmium is sprayed onto the carrier plate under a reducing atmosphere and the mixture is sinterised onto the carrier substantially without the formation of a lead cadmium alloy. In another method the coating is formed by depositing a paste of a mixture of particular lead and particulate cadmium in a reducing organic solvent and evaporating the solvent and sinterising the particulate mixture onto the carrier substantially without formation of a lead cadmium alloy. In another method cadmium is deposited on the carrier plate by electroplating in a fluoroborate bath, the electroplating preferably conducted in such a bath containing metallic lead and metallic cadmium, with the carrier plate serving as the cathode and an alloy of lead and cadmium serving as the anode, the deposited coating then often being in the form of an alloy of lead and cadmium.

After forming the uniform and adherent coating comprising lead and cadmium the plate is preferably then immersed in a container containing a dilute solution of sulphuric acid (as electrolyte) and a lead plate or sheet which serves as the cathode.

The carrier plate is then connected to the positive terminal of an emf source and the lead sheet is connected to the negative terminal of said source. The passage of electric current through the plates causes the oxidation of lead (in the lead-cadmium layer) to lead superoxide, in the form of crystalline and polycrystalline mass, while the cadmium reacts with sulphuric acid to form cadmium sulphate which is deposited on the lead sheet as a spongy material. The carrier plate is then removed from the solution, rinsed clean with water and dried.

To make a cell, preferably three such plates are then immersed in a second container containing a dilute solution of sulphuric acid. The middle carrier plate is connected to the positive terminal of an emf source while the other two carrier plates are jointly connected to the negative terminal of said emf source. Upon the passage of electric current, the middle carrier plate will be positively charged and the lead superoxide will remain unchanged while the lead oxide on the other two carrier plates is reduced to lead and becomes negatively charged.

After a few minutes, the emf source is removed and the emf within the cell drops, generally from 2.9 volts to approximately 2.4 volts, and remains essentially constant at this level. The cell is now charged and is storing energy for subsequent release.

Three or more such cells may be connected in series to form a battery. For convenience such batteries are called herein lead-crystal batteries, so as to distinquish from the conventional lead-acid batteries of the prior art.

The layer of active mass on the conductors of the invention must be uniform and adherent, and it is naturally necessary that these properties should include the requirement that the layer should be durable in order that the conductor has a satisfactory life in practice.

Lead-crystal batteries of the invention have many advantages. Included amongst these are the fact that it is usually from about 15% to about 30% lighter in weight than a lead-acid battery of comparable size and capacity, and exhibits greater capacity often 2530% greater capacity, as compared to a lead-acid battery of comparable size and weight. The ability to draw substantially larger amounts of power in a considerably shorter period of time due to its significantly lower internal resistance and higher activity makes is particularly useful in vehicles which require fast acceleration, e.g., electric vehicles and cars, and other electrically motivated power sources. The batteries can have faster charging rates and higher emf per cell than conventional lead acid batteries.

Also, the lead-crystal batteries which are made in accordance with this invention suffer from reduced, and often exhibit little or no, sulphatization. This means that, as a practical matter, these batteries often can discharge to a point approaching zero emf.

In contrast, sulphatization is a rather common phenomenon in the lead-acid batteries, and, consequently, the lead-acid batteries cannot discharge beyond about 1.5 to 1.8 volts emf, or almost irreversible sulphatization will take place in the lead grids which hold the paste of the active mass.

Preferred methods and products according to the invention are now described in more detail with reference to the accompanying drawings in which: Figure 1 is a schematic representation illustrating the method of formation of the active mass, i.e., the crystalline and polycrystalline lead oxide, Figure 2 is another schematic diagram illustrating the formation of the positive and negative plates and the cell comprising such plates; and Figure 3 shows two curves which compare the discharge characteristics of a lead-crystal cell made in accordance with this invention with a conventional lead-acid type cell.

In accordance with one embodiment of this invention, and with particular reference first to Fig. 1, a carrier plate 1 which is typically made of pure lead (Pb) or an alloy of lead with antimony (PbSb), coated with a layer of Pb-Cd as hereinafter described, is immersed in a dilute solution of sulphuric acid (electrolyte) in a container 3. The carrier plate used herein is conveniently a foil of approximately 0.2 mm thickness and is made of an alloy of lead and antimony.

The thickness of the carrier plate, however, may vary somewhat depending on the particular construction and intended use of the storage device.

Prior to immersing the carrier plate 1 in the sulphuric acid solution, a hot melt of lead and cadmium is sprayed on the surface of the foil by means of a conventional spray gun, or some other suitable spraying device, to deposit a uniform and adherent layer of lead and cadmium on both surfaces of the foil. A reducing gas such as, for example, hydrogen is used in conjunction with the spraying of the hot melt on the foil's surface, and spraying is discontinued when the thickness of the deposited layer reaches approximately 0.5 mm on each surface.

Again, this thickness may vary somewhat depending on the particular construction, the required resistivity and the intended use of the device. Generally, the thickness of Pb-Cd layer on each surface may vary from about 0.1 to 2 mm, preferably from about 0.5 to about 1.2 mm and is most preferably about I mm.

The PbCd melt is prepared by coating a cadmium wire of approximately 1 mm thickness electrolytically or by plating to obtain an approximately 1:1 ratio by weight of lead to cadmium, and the resulting wire is then melted, sprayed onto the surface of the foil as hereinbefore described at a temperature which is higher than the melting points of lead and cadmium, but lower than the temperature which will cause significant melting of the particular alloy of lead and antimony from which the carrier plate is made, thus causing sinterisation of the Pb-Cd on the surface of the carrier plate.

In order to improve the adhesion of the Pb-Cd layer to the surface of the carrier plate 1, the carrier plate (foil) may first be sandblasted for several minutes to create a roughened surface so that the sinterised PIHCd mixture will be better bonded to the foil's surface. It must be understood that the terms "foil", "carrier plate" and "collector plate" are used interchangeably throughout this application to refer to the Pb-Sb carrier plate.

Referring again to Fig. 1, there is shown the container 3 made from a nonconductive material (e.g., glass, plastic, etc.) and containing a dilute solution of sulphuric acid (electrolyte) having approximately the same specific gravity as the sulphuric acid solutions employed in ordinary lead-acid type storage batteries. The container 3 is also provided with a lead plate or lead sheet 5 which serves as the negative electrode (cathode). The collector or carrier plate 1 which has been made as aforesaid is immersed in the electrolyte as shown in Fig.

1 and is connected to the positive terminal of a 3 volt emf source 7 (e.g. a battery) while the lead sheet 5 is connected to the negative terminal of said 3 volt emf source. Although more than one carrier plate may be immersed in the electrolyte and suitably connected to the emf source, the invention will be described and illustrated with reference to the preparation of one positive plate only for the sake of simplicity of illustration.

When the circuit is closed as hereinbefore described, the cadmium from the Pb-Cd layer on the carrier plate will react with sulphuric acid to form cadmium sulphate which is deposited as a porous, spongy mass on the lead sheet 5. Water is dissociated into hydrogen (H2) and oxygen (02). Hydrogen appears as gas bubbles on the surface on the negative electrode while oxygen combines with lead, rapidly and continuously, to form lead superoxide (PbO2) in the form of crystalline and polycrystalline mass. The formation of the active mass in thus completed within minutes and the carrier plate is removed, rinsed clean and dried. It is now ready to be used in the construction of the lead-crystal battery or cell of this invention.

The lead superoxide crystalline and polycrystalline active mass is a dark brown to black material. It is hard, homogeneous highly porous and has remarkably low internal resistance.

In preparing the carrier plate having crystalline and polycrystalline lead superoxide as the active mass, the spraying and sintering should be so conducted as to avoid the formation of Pb-Cd alloy. The presence of Cd in the sinterisation mass is also importing since it aids or promotes the formation of PbO2 crystals and polycrystals.

Additionally, it must be noted that even though cadmium reacts with the sulphuric acid in container 3 to form cadmium sulphate and it is removed from this container, trace amounts of cadmium nevertheless remain in the active mass.

In order to construct a lead crystal cell in accordance with this invention as shown in Fig. 2 three identical carrier plates la, lb and l c which have been made by the aforedescribed procedure are immersed in a container 9. Container 9 is similar in structure to the cell of a lead-acid battery and contains a dilute solution of sulphuric acid which is conventionally employed in such batteries. Carrier plates la and ic are joined together by conductor 11 and connected by conductor 13 to the negative terminal of a 3 volt emf source 15 (e.g., a battery, a battery charger, etc.) while carrier plate lb is connected to the positive terminal of the emf source 15 via conductor 17. When the circuit is thus closed, the PbO2 on the carrier plates la and lc is reduced to Pb and the plates become negatively charged, whereas the PbO2 on the carrier plate ib remains chemically unchanged and will become positively charged. Thus, the lead plates will serve as the negative electrodes (cathode) and the lead superoxide plate will serve as the positive electrode (anode).

After a few minutes when the cell has been fully charged, the emf source 15 is removed and the emf within the cell thus drops from 2.9 volts to approximately 2.4 volts, and remains essentially constant at this level. The cell is now charged and is storing energy for later release.

When a cell made as hereinbefore described is connected in series with other cells (e.g., 3 cells in all), each containing several plates (usually 17 or 19) connected in parallel, a lead-crystal battery is formed which may contain 51 or 57 plates depending on the number of cells and the number of plates in each cell. It is obvious, however, that more than 3 cells (e.g., 6 cells, etc.) may be connected in series, if desired.

Lead crystal batteries incorporating the unique features of this invention exhibit superior performance characteristics as compared with lead-acid batteries. Thus, because of its lower internal resistance, a lead crystal battery comprising 51 or 57 plates can accept about 10 to about 15 times as much electric current as the lead-acid battery. Consequently, the lead-crystal battery can be charged at much faster rates than the lead-acid battery. Similarly, the discharge rate of the lead-crystal battery is considerably improved since it can supply electric current at a considerably more accelerated rate than the lead-acid battery.

The discharge curve of a lead-crystal cell made in accordance with this invention is compared in Fig. 3 with the discharge curve for a typical lead-acid cell. The solid curve in this figure represents the discharge curve for the lead-crystal cell and the dotted curve represents the discharge curve for the leadacid cell. A comparison of these two curves indicates that during the first 16 minutes (i.e. during approximately 80% of the discharge cycle), the emf of the lead-crystal cell remains constant, then dropping very slightly from 2.32 to approximately 2.3 volts, whereas the emf of the lead-acid cell decreases steadily and constantly during the same period, dropping from 2.1 to approximately 2.0 volts. This difference is particularly significant in batteries made from such cells, and indicates that the leadcrystal battery can maintain a higher emf level than the lead-acid battery, and, therefore, exhibits superior performance characteristics.

Additionally, the lead-crystal batteries of this invention exhibit from about 25 to about 30 per cent higher capacity than the conventional lead-acid batteries. Moreover, the lead-crystal cell is capable of a far more complete charge and discharge, with no after-reaction or self-charge, as compared with a lead-acid cell; consequently, the lead-crystal battery exhibits far greater storage capacity than a lead-acid battery of comparable weight and volume. Cells made in accordance with the principles set forth herein are capable of developing from about 0.1 to about 0.2 volt higher emf than conventional storage cells from which the lead-acid batteries are made.

In the foregoing description, sinterised lead and cadmium was applied to the surface of the collector plates by hot spraying to deposit a homogeneous, uniform and adherent layer of Pb--Cd thereon. Two additional methods will now be described for depositing such layer of Pb-Cd on the surface of the Pb-Sb carrier plate.

One of these methods the coating is deposited by powder metallurgy. For instance a soft, granular, 1:1 mixture of lead and cadmium, wherein the size of the granules is from about 100 to almost 500 microns, is dispersed in a suitable organic liquid such as, for example, methanol (or ethanol) to prepare a paste which is then deposited on the surface of the carrier plate by a suitable sieve. The methanol is thereafter evaporated; the plate is dried, and the Pb-Cd is sinterised in a press at a temperature of from about 3000C. to about 400"C. for approximately 3 seconds. Once again, the temperature and pressure during sinterisation should be carefully controlled so as to prevent the formation of the PtHCd alloy.

The thickness of the Pb-Cd layer on the carrier plate may be controlled by the selection of the proper sieve and by depositing the appropriate amount of paste uniformly on the surface of the plate. Thus, a PbCd layer of approximately 0.5 mm thickness may be deposited on both sides of the carrier plates.

After depositing the desired coating thickness, the carrier plate is immersed in a container comprising a dilute solution of sulphuric acid and a lead plate as hereinbefore described in connection with Fig. 1 and crystalline and polycrystalline lead superoxide (PbO2) is once again formed on the surface of the carrier plate in the same manner. The cadmium from the Pb-Cd layer reacts with sulphuric acid and is deposited in the form of CdSO4 from which the cadmium can be recovered and reused, and the carrier plate or plates then used to construct a lead-crystal cell as heretofore described in connection with Fig. 2.

In another embodiment of the invention a hard, compact alloy of lead and cadmium is deposited on the carrier plate by electroplating in a fluoroborate bath. Thus, two electrodes, one made from an alloy of lead with antimony (cathode) and the other from a 1:1 alloy of lead and cadmium (anode) may be immersed in a fluoroborate bath having the following composition: Lead Fluoroborate, Pb (by4)2 119 oz.

Metallic Lead, Pb 65 oz.

Fluoroboric Acid HBF4 1.0 oz.

Boric Acid 8.0 oz.

Cadmium Fluoroborate Cd(BF4) 32.5 oz.

Cadmium Metal, Cd 12.0 oz Ammonium Fluoroborate 8.0 oz.

Water 1 gallon The electrodes may then be connected to the positive and negative terminals of a 5 volt emf source for 1 hour until a uniform layer of cadmium and lead of approximately 0.1 mm thickness is deposited on each surface of the cathode. The emf source is then disconnected, the cathode removed from the bath, rinsed, clean with water and dried.

In order to produce three carrier plates with crystalline and polycrystalline lead superoxide on their surfaces, three cathodic carrier plates made by this procedure are immersed in a dilute sulphuric acid electrolyte and subjected to the same operation as hereinabove described in connection with Fig. 1. The resulting carrier plates are then used to construct a leadcrystal cell as hereinbefore described in connection with Fig. 2.

WHAT WE CLAIM IS: 1. A conductor suitable for use in a storage cell and comprising a carrier plate which carries a uniform and adherent layer of an active mass comprising polycrystalline lead superoxides as herein defined.

2. A conductor according to claim 1 in which the active mass consists substantially only of crystalline

Claims

**WARNING** start of CLMS field may overlap end of DESC **. slightly from 2.32 to approximately 2.3 volts, whereas the emf of the lead-acid cell decreases steadily and constantly during the same period, dropping from 2.1 to approximately 2.0 volts. This difference is particularly significant in batteries made from such cells, and indicates that the leadcrystal battery can maintain a higher emf level than the lead-acid battery, and, therefore, exhibits superior performance characteristics. Additionally, the lead-crystal batteries of this invention exhibit from about 25 to about 30 per cent higher capacity than the conventional lead-acid batteries. Moreover, the lead-crystal cell is capable of a far more complete charge and discharge, with no after-reaction or self-charge, as compared with a lead-acid cell; consequently, the lead-crystal battery exhibits far greater storage capacity than a lead-acid battery of comparable weight and volume. Cells made in accordance with the principles set forth herein are capable of developing from about 0.1 to about 0.2 volt higher emf than conventional storage cells from which the lead-acid batteries are made. In the foregoing description, sinterised lead and cadmium was applied to the surface of the collector plates by hot spraying to deposit a homogeneous, uniform and adherent layer of Pb--Cd thereon. Two additional methods will now be described for depositing such layer of Pb-Cd on the surface of the Pb-Sb carrier plate. One of these methods the coating is deposited by powder metallurgy. For instance a soft, granular, 1:1 mixture of lead and cadmium, wherein the size of the granules is from about 100 to almost 500 microns, is dispersed in a suitable organic liquid such as, for example, methanol (or ethanol) to prepare a paste which is then deposited on the surface of the carrier plate by a suitable sieve. The methanol is thereafter evaporated; the plate is dried, and the Pb-Cd is sinterised in a press at a temperature of from about 3000C. to about 400"C. for approximately 3 seconds. Once again, the temperature and pressure during sinterisation should be carefully controlled so as to prevent the formation of the PtHCd alloy. The thickness of the Pb-Cd layer on the carrier plate may be controlled by the selection of the proper sieve and by depositing the appropriate amount of paste uniformly on the surface of the plate. Thus, a PbCd layer of approximately 0.5 mm thickness may be deposited on both sides of the carrier plates. After depositing the desired coating thickness, the carrier plate is immersed in a container comprising a dilute solution of sulphuric acid and a lead plate as hereinbefore described in connection with Fig. 1 and crystalline and polycrystalline lead superoxide (PbO2) is once again formed on the surface of the carrier plate in the same manner. The cadmium from the Pb-Cd layer reacts with sulphuric acid and is deposited in the form of CdSO4 from which the cadmium can be recovered and reused, and the carrier plate or plates then used to construct a lead-crystal cell as heretofore described in connection with Fig. 2. In another embodiment of the invention a hard, compact alloy of lead and cadmium is deposited on the carrier plate by electroplating in a fluoroborate bath. Thus, two electrodes, one made from an alloy of lead with antimony (cathode) and the other from a 1:1 alloy of lead and cadmium (anode) may be immersed in a fluoroborate bath having the following composition: Lead Fluoroborate, Pb (by4)2 119 oz. Metallic Lead, Pb 65 oz. Fluoroboric Acid HBF4 1.0 oz. Boric Acid 8.0 oz. Cadmium Fluoroborate Cd(BF4) 32.5 oz. Cadmium Metal, Cd 12.0 oz Ammonium Fluoroborate 8.0 oz. Water 1 gallon The electrodes may then be connected to the positive and negative terminals of a 5 volt emf source for 1 hour until a uniform layer of cadmium and lead of approximately 0.1 mm thickness is deposited on each surface of the cathode. The emf source is then disconnected, the cathode removed from the bath, rinsed, clean with water and dried. In order to produce three carrier plates with crystalline and polycrystalline lead superoxide on their surfaces, three cathodic carrier plates made by this procedure are immersed in a dilute sulphuric acid electrolyte and subjected to the same operation as hereinabove described in connection with Fig. 1. The resulting carrier plates are then used to construct a leadcrystal cell as hereinbefore described in connection with Fig. 2. WHAT WE CLAIM IS:

1. A conductor suitable for use in a storage cell and comprising a carrier plate which carries a uniform and adherent layer of an active mass comprising polycrystalline lead superoxides as herein defined.

2. A conductor according to claim 1 in which the active mass consists substantially only of crystalline lead superoxide and the polycrystalline lead superoxide.

3. A conductor according to claim 2 in

which the active mass includes a trace amount of cadmium.

4. A conductor according to any preceding claim in which the carrier plate is a plate of lead or an alloy of lead and antimony or is a plate of non-conductive material coated with lead or an alloy of lead and antimony.

5. A method for making a conductor according to any of claims 1 to 4 comprising forming on the carrier plate a uniform and adherent coating comprising lead and cadmium and electrolytically oxidising this, the coating and the electrolysis conditions being such that substantially all the cadmium is removed into the electrolyte and the coating comprising the said active mass is formed on the plate.

6. A method according to claim 5 in which the electrolysis is conducted in dilute sulphuric acid using the said coated carrier plate as the anode and a lead plate as the cathode.

7. A method according to claim 4 or claim 5 in which the lead cadmium mixture in the coating contains 30 to 70% by weight lead and 70 to 30% by weight cadmium.

8. A method according to claim 7 in which the mixture contains 45 to 55% by weight lead and 55 to 45% by weight cadmium.

9. A method according to claim 7 in which the mixture contains substantially equal amounts by weight of lead and cadmium.

10. A method according to any of claims 5 to 9 in which the coating of lead and cadmium is formed by spraying a hot melt mixture of lead and cadmium onto the carrier plate under a reducing atmosphere and sinterising the mixture onto the carrier substantially without formation of a lead cadmium alloy.

11. A method according to any of claims 4 to 9 in which the lead cadmium coating is formed by depositing a paste of a mixture of particular lead and particulate cadmium in a reducing organic liquid and evaporating the solvent and sintering the particular mixture onto the carrier substantially without formation of a lead cadmium alloy.

12. A method according to claim 11 in which the particles are 100 to 500 microns in size, the liquid is methanol and the sinterising is conducted at 300 to 4000C for 3 seconds.

13. A method according to any of claims 5 to 9 in which the lead cadmium coating is deposited on the carrier plate by electroplating in a fluoroborate bath.

14. A method according to claim 13 in which the electroplating is conducted in a fluoroborate bath containing metallic lead and metallic cadmium and in which the carrier plate is the cathode and an alloy of lead and cadmium is the anode.

15. A method according to any of claims 5 to 14 in which the coating of lead and cadmium is 0.1 to 2 mm thick.

16. A method according to claim 15 in which the coating is 0.5 to 1.2 mm thick.

17. A method according to claim 5 substantially as herein described.

18. A conductor made by a method according to any of claims 5 to 17.

19. A conductor suitable for use as a cathode in a storage cell and obtained by electrolytic reduction of a conductor according to any of claims 1 to 4 or claim 18.

20. A conductor according to claim 1 or claim 19 substantially as herein described.

21. A storage cell in which the cathode or cathodes are of lead, the electrolyte is dilute sulphuric acid and the anode or anodes are formed of a conductor according to any of claims 1 to 4 or 18.

22. A storage cell in which the cathode or cathodes are formed of a conductor according to claim 19, the anode or anodes are formed of a conductor according to any of claims I to 4 or 18 and the electrolyte is dilute sulphuric acid.

23. A storage cell according to claim 21 or claim 22 comprising a plurality of anodes connected in parallel and a plurality of cathodes connected in parallel.

24. A storage battery comprising a plurality of cells according to any of claims 21 to 23 connected in series.