GB2160704A

GB2160704A - Electrode for a primary or secondary battery

Info

Publication number: GB2160704A
Application number: GB08514954A
Authority: GB
Inventors: Johannes Jensen
Original assignee: ENERGIFORSKNING LAB
Current assignee: ENERGIFORSKNING LAB
Priority date: 1984-06-20
Filing date: 1985-06-13
Publication date: 1985-12-24
Also published as: DE3521734A1; DK156859C; GB8514954D0; DK156859B; DK302184D0; DK302184A; GB2160704B

Abstract

An electrode for primary or secondary electric battery comprises an electrically conducting substrate 5,6 supporting an active mass 2,3 which is covered by an electrolyte permeable separator 1. An electrode suitable for automatic production and bearing the active mass 2,3 retained effectively against the support is obtained by providing the active mass in the form of a plurality of strips 2,3 which are retained under pressure by the separator layer 1 said layer being effectively secured to the substrate between the strips of active mass. The electrode may be bipolar having positive and negative masses 2,3 on its respective faces. In a battery carried out of such electrodes the strips 2,3 of active mass are parallel and have an approximately triangular cross section and on adjacent electrodes of opposite polarity the strips of active mass are displaced a half pitch with respect to one another. The electrodes are mutually sealed around the periphery by means of a sealing packing. in the method for producing the electrode the active mass is placed as a plurality of parallel strips on a ribbon of the substrate whereafter the separator is placed upon the strips and secured to the substrate whereupon the ribbon is cut into individual electrodes. <IMAGE>

Description

SPECIFICATION Primary or secondary electric battery and electrode therefor The present invention relates to an electrode for a primary or secondary electric battery comprising an electrochemically active mass located on one or both surfaces of a supporting sheet-like, electrically conductive substrate and covered by an electrolyte permeable separator. Furthermore, the invention relates to an electric battery comprising at least two electrodes provided with positive and negative active mass, respectively. Moreover, the invention relates to a method of producing the said electrode.

The positive electrochemically active mass may consist for example of metal oxide, such as MnO2, PbO2, NiOOH, HgO and Ag2O, which is reduced when the battery is discharged while the negative active mass may consist of a metal, such as Zn, Cd, Pb and Sn, which is oxidized during discharge. However, the invention is in no way limited to the said well known electrode materials but comprises all such solid materials which can operate electrochemically in reduced as well as oxidized condition.

All solid electrode materials have in common that they change their volume to a higher or smaller degree during discharging and charging of the battery whereby the active mass of the electrode tends to lose its cohesive force which results in that the capacity and ability of the battery to endure repeated charges and discharges deminishes.

This circumstance is often limiting for the practical applicability of the battery and is sought to be met by various structural shapes of the electrodes.

The problems caused by the volumetric changes are particularly pronounced in the well known lead acid battery in which the material for the negative electrode consists of lead sponge and for the positive electrode of lead dioxide PbO2 while the electrolyte consists of diluted sulphuric acid. In the following the invention will mainly be described in relation to this type of battery but the fields of application of the invention should in no way be limited thereto.

The electrodes for prior lead acid batteries are often formed as grids or plates of a lead alloy wherein the positive and negative electrode masses, respectively, are deposited in the form of a paste which is matured and formated in a manner known per se, cf. for instance: Hand Bode: "Lead Acid Batteries", John Wiley and Sons, 1977, pp 2-5. Batteries in which this electrode type is used are called grid plate or flat plate batteries and are extensively used as starting batteries for automobiles.

In the use of this type of battery for the propulsion of trucks or electric automobiles it has proved, however, that the active mass loses its electrochemical activity after a few hundreds of charge-discharge cycles because the grains of which the mass consists lose their contact to each other and to the lead grid which serves to conduct the electric current to and from the plate. As a result a great area of active mass cannot be retained intact by the porous layers of web or perforated plastics material located over the active mass.

The result is that in particular the positive mass gets loose and thereafter no longer participates in the electrochemical process.

The lifetime of the battery measured in numbers of charge-discharge cycles and the output or capacity of the battery therefore depend on how well in particular the positive active mass can be retained.

Another type of electrode for lead batteries is the so-called tubular cell electrode which is described e.g. in Danish patent specification No. 141.977 and which consists of a plurality of relatively narrow tubes of separator material filled with powdered or pasted active material and in which a current conducting electrode is centrally located in the form of a lead spine.

These lead spines are mutually connected so that the electrode consists of a plurality of parallel disposed tubes. Batteries manufactured of such electrodes can be charged and discharged more than a thousand times before the capacity of the battery diminishes, they do not suffer from the other above mentioned deficiencies in flat plate batteries, they present a large area of the active mass, so that they are suitable for deep discharges, and they can resist vibrations so that all things considered they are suitable i.a. for the above mentioned traction applications.However, they suffer from other serious drawbacks, for example a very high production price of the electrodes, because the manufacture of them is rather complicated and especially the filling of the tubes with active mass is a troublesome and costly process and the design implies a relatively high amount of inactive lead which increases the weight of the battery. Also the inner resistance of the battery is considerably higher than in the grid plate battery in which the electrodes are placed closely adjacent.

Similar conditions apply to the tubular cell electrodes for other types of batteries, e.g. the iron-nickel battery.

A usual battery plate disclosed in US patent No. 2.318.498 consists of metallic grid divided by longitudinal slots into a plurality of columns which are interconnected by conducting end pieces. After being pasted each column is covered by upper and lower telescoping flanged strips of perforate sheet paste retaining material. Adhesive on the the flanges holds the retaining strips together.

Alternatively, the plate may be covered with two interlocking perforate half envelopes se cured by anchoring rubber strips inserted into the slots in the plate. This prior electrode consisting of several single parts to be assembled is rather complex resulting in a timeconsuming and expensive process of manufacture and assembly.

The object of the present invention is to provide an electrode of the type defined initially which combines the advantageous production price and properties of the grid plate electrode with the long life of the tubular cell electrode and which eliminates the above mentioned deficiencies of both electrodes.

In order to achieve this object of the invention the substrate is a continuous sheet on which the active mass is located on the substrate in strips and the mass is maintained by a pressure against the substrate by means of the separator, said separator being anchored to the free portion of the substrate between the strips of active mass.

Hereby is obtained that the active mass like in the tubular cell electrode is prevented from expanding and accordingly is retained effectively against the substrate so that the chemically determined change of volume only takes place in the interstices between the grains of which the mass consists. Thereby the mutual contact and the contact to the substrate is maintained during discharge and charge.

Compared to the tubular cell battery a much higher contact surface is achieved and with a suitable cross-section of the strips of active mass a small distance between the positive and negative masses is obtainable. Both effects contribute to provide batteries produced with such electrodes with a low inner resistance and therefore an increased current density or power density which is advantageous for traction purposes especially during acceleration of the vehicle. With the electrode according to the invention the expensive filling of the tubes required with tubular cell electrodes is avoided, the active mass being simply placed on the substrate whereupon the separator is located on the active mass and secu red to the substrate.

It is to be understood that the conducting plate acting as substrate for the active mass must be in possession of good electrical as well as mechanical properties and be chemically resistant against the applied electrode masses and the applied electrolyte. These requirements are fulfilled for example in case of lead acid batteries by certain lead alloys e.g. with 2-9% antimone, while in the case of alkalic batteries, nickel or iron can be used as substrate.

In order to achieve particularly good mechanical or electrical properties i.a. a low weight it may in certain cases be advantageous to use other metals, such as copper or aluminum alloys for example, which are not chemically resistant. They may then be provided with a tight chemically resistant electrically conducting covering consisting for example of a resistant metal, such as titanium, lead or gold or of an electrically conducting polymere, such as polyacetylene or polyisobutylene with the addition of a conducting material, such as graphite, carbon black or metal powder. Dependent on the application of the electrodes both faces may be provided with a protecting covering or one face of the substrate may remain unprotected while the other face being provided with the protecting covering.

In an embodiment of the invention the metal sheet is constituted of a perforate sheet or metal network which is completely surrounded by the electrically conductive coating.

Since the coating material hereby may extend through the perforations or openings in the sheet a particularly efficient binding between the metal sheet and the coating is achieved.

In order to obtain a very efficient anchoring of the separator to the substrate when the latter is provided with a conducting coating the separator according to the invention may consist of a perforate sheet of plastics material which may be supplemented with a reinforcement layer e.g. of fiber glass, impregnated paper or the like, which beyond providing strength to the separator also may absorb electrolyte and furthermore operate to prevent electrophoretic migration of conductive particles of active mass between the electrodes.

The anchoring of the separator to the free portion of the substrate between the strips of active mass may according to the invention dependent on the material of the substrate and separator take place by adhering, vulcanization or welding or in the form of a mechanical anchoring such as by a compressed bead of the substrate or by a combination of these anchoring methods.

Although the essential is that the active mass is placed on the substrate in strips which may take different cross-sections, the strips according to the invention may advantageously be parallel and have approximately triangular cross-section whereby a short distance between similarly produced positive and negative electrodes can be simply provided.

Electrode mass of the same type may be placed on both faces of the substrate. A battery cell having such electrodes accordingly consists of a number of electrodes with negative mass and a number of electrodes with positive mass disposed alternately with electrolyte in a space in a battery box which may contain several cells. Electrodes of similar polarity are connected in well known manner and the individual cells of the battery may be connected in series connection.

In another embodiment each electrode may be provided with positive mass on one face and negative mass on the other face of the substrate. By the combination of such bipolar electrodes the cells will be series connected in well known manner without the use of particular connection members. This particular advantage cannot be obtained with the initially mentioned prior tubular cell electrodes.

In an electric battery comprising at least two electrodes provided with positive and negative active masses, respectively, parallel strips of active mass having approximately triangular cross-section on adjacent electrodes of opposite polarity are displaced a half pitch with respect to one another. Thereby a particularly compact construction is obtained with maximum interface between the electrolyte and the surface of the active mass which is particularly favourable for the progress of the transportation processes determined by diffusion which processes otherwise often limit the efficiency of the battery. The minimum distance between the positive and negative active masses determines the above mentioned low inner resistance and consequently the high current density of the battery. This embodiment can be used with single as well as bipolar electrodes.

In an embodiment of the battery according to the invention the substrate sheets are kept free of active mass along their periphery and upon assembling of the electrodes to a battery each pair of electrodes with added electrolyte is provided with a circumferential sealing e.g.

of rubber or similar material, which both seals and isolates the separate cells so that the electrolyte cannot run out and fixes the mutual distance of the plates. This seal may advantageously be provided with a plurality of parallel sealing lips engaging the electrodes and providing a high sealing security. At its ends the battery is provided with singly coated additional heavy substrate plates with positive and negative active masses, respectively. These end plates have a somewhat higher area than the intermediate electrodes and upon assembling and tightning e.g. by stay bolts or tieing with bands of metal or plastics material a complete seal is obtained.

In order to achieve further security the electrodes may along their periphery be sealed with an elastic sealing mass based on rubber or silicone which for example may be selfvulcanizing. By using well known art the battery may besides be formed in such a manner that no substantial amounts of gas developes during surcharge so that the complete arrangement may be hermetically sealed, however, with the use of a safety valve in each individual cell. This embodiment using heavy end plates makes it unnecessary to place the battery in a special battery box but it is obviously also possible to place the battery in such box whereby the total weight inevitably increases.

Furthermore, the invention relates to a method of producing an electrode for an electric battery, said electrode comprising an electrochemically active mass located on one or both faces of a supporting sheet-like, electrically conductive substrate and covered by an electrolyte permeabie separator, said method being characterized by passing the substrate in ribbon form through a first station in which the active mass in paste form is applied onto the substrate in a plurality of parallel strips having a length adapted to the corresponding dimension of each electrode to be produced, applying separator material in ribbon form at a second station upon the strips of active mass and anchoring said separator material to the substrate at least between the strips of active mass and cutting the resulting plate ribbon to provide separate electrodes.This method is advantageous because it can be carried out as a continuous process which is easily automized so that the manufacture costs become low.

An embodiment of the method according to the invention is characterized by securing the separator material to the substrate by pressure applying means compressing the separator and substrate between the strips of active mass. The securing is preferably done by welding while weld mass and heat being supplied. The pressure means may be vibrated e.g. by ultrasound. The securing may also be provided e.g. by a pressure sensitive adhesive, by wedging of the separator in a bead in the substrate or by a combination of these methods.

The invention will hereinafter be illustrated in more detail with reference to the drawings, in which: Figure 1 shows a cross-section of a part of an embodiment of a single electrode according to the invention, Figure 2 shows a similar cross-section of another embodiment of an electrode according to the invention in the form of a bipolar electrode, Figure 3 shows a cross-section in another embodiment of a bipolar electrode according to the invention, Figure 4 shows a cut ribbon of substrate where strips of active mass are placed transverse to the longitudinal direction of the ribbon, Figure 5 shows a similar cut ribbon of substrate where the strips of active mass are placed parallel to the longitudinal direction of the ribbon, Figure 6 shows a section along the line VI VI in figure 4 and figure 5, respectively, Figure 7 shows a cross-section of a part of a single pole electrode where the active mass is placed on both faces of the substrate, Figure 8 shows a section in a part of a battery including single pole electrodes according to figure 7 assembled in a battery box, Figure 9 shows a section in a part of a battery according to the invention including bipolar electrodes and provided with a seal for each pair of electrodes, and Figure 10 shows a view of a plurality of interconnected batteries according to figure 9.

Figure 1 of the drawings shows an electrode for use in an electric element or battery.

The electrode consists of a substrate comprising a metal sheet 5 which for example may be of aluminum to make the structure of light weight and low costs. The sheet 5 has a tight conductive coating 8 for the protection of the sheet against the electrolyte and the active mass. The active mass is in figure 1 designated by 3 and is in a lead-acid battery lead dioxide and porous lead, respectively, and is placed as shown as a plurality of parallel strips (see also figures 4 and 5). Upon the strips of active mass 3 an acid resistant separator layer 1 is disposed, said layer being of an electrolyte permeable material, such as a woven fabric or perforate plastics material 17 and a porous reinforcing layer 18 of glass fiber impregnated paper or the like which is able to absorb electrolyte during the application of the electrode in a battery.Between the strips 3 the separator 1 is secured to the substrate, that is to the coating 6 in the illustrated embodiment such as shown at 4.

The separator is secured to the substrate such as to apply a pressure to the active mass, which in the manner shown is divided into subregions having a relatively small area so that loose fragments of the mass are avoided in the cause of time. Although it is not absolutely necessary the separator is usually also secured to the substrate at the ends of the strips of active mass, see also figure 6.

The bipolar electrode shown in figure 2 has negative and positive active masses 2 and 3, respectively, on a respective face of the electrode and consists also of a thin metal foil 5 provided on both faces with an eletrolyte resistant coating 6 of plastics material or metal as in figure 1, and the active mass on both faces are likewise covered by an electrolyte resistant separator layer 1, which also like in figure 1 is maintained to the substrate by welding the separator layer and the coating 6 together. The strips 2 and 3 of active mass have a substantially triangular cross section and are displaced a half pitch with respect to one another in preparation for the assembling of the electrodes to a battery.

The embodiment of a bipolar electrode shown in figure 3 is similar to the electrode shown in figure 2 with the exception that the separator 1 in figure 3 is secured to the substrate by being fixed in a compressed bead 19 formed in the substrate between the strips of active mass viz. in the coating 6 on the substrate in the embodiment shown. For achieving a still better securing in the bead it may in addition be provided with adhesive (not shown).

Figures 4 and 5 show a respective ribbon of electrodes cut into single electrodes. This ribbon can be manufactured continuously. The substrate i.e. the metal sheet 5 provided with the protecting coating 6, if necessary, is passed through an apparatus in which the strips 2 and/or 3 of active masses in the form a paste are deposited for example by extrusion through a plurality of juxtaposed nozzles onto the substrate on one or both faces thereof.

The strips are deposited with the desired length transverse to the ribbon as in figure 4 or longitudinally to the ribbon as in figure 5.

Thereafter a ribbon of separator material is pulled over the active masses and secured at the juntions 4 between the strips of active mass by means of cam rolls or other pressure applying means. The separator and the substrate are welded together while weld mass is supplied, said weld mass being placed on the separator in the form of a band or wire. The rolls or pressure applying means may advantageously be heated by ultrasound. The junctions may also be provided by a pressure sensitive binding agent by securing in the beads 19 shown in figure 3 or by other well known methods for securing layers of plastics material and/or metal.

Figure 6 shows in a cross section of a bipolar electrode how the edge 8 at the ends of the strips 2,3 are closed by sealing of the separators 1 to the coating 6 by being welded to them and to an additional applied closure strip 20, e.g. of plastics material.

While the substrate can be made of a metal which is chemically resistant to the applied electrode masses and the applied electrolyt it may be advantageous to use other metals, which are not chemically resistant and in that case it is necessary to provide the metal sheet 5 with the above mentioned chemically resistant coating 6. Figure 7 shows a cross section of an electrode, which is provided of active mass of the same type on both faces of the substrate and the strips 3 of active mass are placed opposite one another. However, the substrate consists here of a perforate metal sheet or a metal network 21, which is completely surrounded by a protective coating 6.

The application of such a perforate sheet or a metal network 21 results in the fact that an efficient securing of the coating 6 to the sheet or network 21 is provided in a simple manner and by welding the separator 1 and the coating 6 together a particularly efficient anchoring of the separator is achieved.

Figure 8 shows a cross section in a part of a battery consisting of the a battery box 15, which is divided into cells 16 by partitions 22. Each cell 16 contains a plurality of double-sided single pole electrodes 23, e.g. of the same kind as the electrode shown in figure 7, and a single-sided electrode 24 at each side of the cell. The electrodes are displaced in respect to one another so that the approximately triangular strips of active mass engage completely into one another. The separate electrodes and the separate cells are interconnected in a well known but not shown manner.

In the part sectional view of a battery shown in figure 9 a plurality of bipolar electrodes of the type shown in figure 2 are provided and the strips 2,3 of active mass covered by the separator layers are placed closely adjacent as in figure 2 which contributes to prevent the active masses from loosening from the supporting substrate. Although an approximately triangular cross section of the strips of active mass has been shown other cross sections are obviously also applicable but in order to make the battery as compact as possible the electrode sides facing each other are preferably carried out such that the space between them is substantially completely utilized.In order to obtain an optimum efficiency of the battery the cross section of the electrolyte space should be of the same order as the cross section of the active masses said electrode space being constituted mainly of the separator layers 1 in which the electrolyte is absorbed in the embodiment shown.

The outermost single-sided electrode shown in figure 9 has a particularly heavy electrode plate 5' which like the other electrode plates is provided with a protective coating 6 on which the strips of active mass are placed and retained by a separator 1. The heavy electrode plate 5' along the edges thereof is provided with bolt holes 12 as mentioned more detailed below.

Between every two electrodes the outer edges of which have not been coated a seal 10 of rubber or other suitable material has been provided which seal for achieving a good engagement against the electrode and accordingly a good sealing security is provided with two or more parallel sealing lips 13. These seals simultaneously fix the mutual distance of the plates. In order to achieve further safety of the sealing and to keep the electrodes together an elastic sealing compound on rubber or silicone basis may be provided over the circumferential packings 1 0 said sealing compound adhering well to the substrates of the electrodes and the packings 10. The sealing compound may have a sufficient elasticity to permit the active masses to work during charges and discharges and at the same time it must be able to withstand an internal pressure in the electrolyte chambers in the separate cells.

A battery built in this way with particularly heavy substrate plates may be used without a separate battery box. The battery may also by tied up with band of metal or plastics material or the battery may be bolted together by staybolts 14 as shown in figure 10 which bolts are passed through the bolt holes 12 disposed in the flanges of the outer electrodes. These bolts may also be used for bolting a plurality of such batteries together as will appear from,figure 10 and also connection leads may be secured by the bolts.

Claims

1. An electrode for a primary or secondary electric battery comprising an electrochemically active mass located on one or both surfaces of a supporting sheet-like, electrically conductive substrate and covered by an electrolyte permeable separator characterized in that the substrate is a continuous sheet on which the active mass is located on the substrate in strips and that the mass is maintained by a pressure against the substrate by means of the separator said separator being anchored to the free portion of the substrate between the strips of active mass.

2. Electrode according to claim 1, characterized in that the substrate consists of a supporting metal sheet, at least one surface thereof being provided with a tight protective, chemically resistant, electrically conductive coating.

3. Electrode according to claim 2, characterized in that the metal sheet is constituted of a perforate sheet or metal network which is completely surrounded by the electrically conductive coating.

4. Electrode according to any of the preceding claims, characterized in that the separator consists of a perforate sheet of plastics material having a porous reinforcement layer e.g.

of fibre glass or impregnated paper.

5. Electrode according to any of the preceding claims, characterized in that the separator is anchored to the substrate by positive or non-positive locking connection such as adhering, vulcanization, welding, bead securing or riveting.

6. Electrode according to any of the preceding claims, characterized in that the strips of active mass are parallel and of approximately triangular cross section.

7. An electric battery comprising at least two electrodes according to any of the preceding claims and provided with positive and negative active masses, respectively, characterized in that parallel strips of active mass having approximately triangular cross section on adjacent electrodes of opposite polarity are displaced a half pitch with respect to one another.

8. Electric battery according to claim 7, characterized in that each pair of electrodes with added electrolyte has a circumferential seal packing.

9. A method of producing an electrode for an electric battery, said electrode comprising an electro-chemically active mass located on one or both surfaces of a supporting sheetlike, electrically conductive substrate and covered by an electrolyte permeable separator characterized by passing the substrate in ribbon form through a first station in which the active mass in paste form is applied onto the substrate in a plurality of parallel strips having a length adapted to the corresponding dimension of each electrode to be produced, applying separator material in ribbon form at a second station upon the strips of active mass and anchoring said separator material to the substrate at least between the strips of active mass and cutting the resulting plate ribbon to provide separate electrodes.

10. Method according to claim 9, characterized by securing the separator material to the substrate by pressure applying means compressing the separator and substrate between the strips of active mass.

11. An electrode for a primary or secondary electric battery, substantially as described herein with reference to the accompanying drawings.

12. An electric battery, substantially as described herein with reference to the accompanying drawings.

13. A method of producing an electrode for an electric battery, substantially as described herein with reference to the accompanying drawings.