DE2211233A1 - Electrodes for primary or secondary electrochemical cells - Google Patents

Description

Patent attorney ** '

Dipl. Phys, Gsrhard Lipdl

Munich 2:.!, Sieinsdorfstr. 21-22 Eck * Zwe «idi« nstr.,. Tel. 2f 64S2

ACCUMULATOR SHARE BOMGEiD JUHGNEH Oskarshamn / Sweden

Electrodes for electrochemical primary or secondary cells «

The present invention relates to electrodes for primary or secondary electrochemical cells, preferably on electrodes of this type, which consist of an electrode skeleton made of metal wire mesh or metal foil, the one or is coated on both sides with an electrochemically active compound, wherein the layer extends outwards to one or more edges of the electrode skeleton. To derive from Electricity from the electrodes is the electrode skeleton with a or several current arresters.

One type of electrode frequently used in electrochemical cells is the so-called pocket electrode. In this is

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an electrochemically active mass in relatively thin Bags or containers included, made up of paired, perforated strips are composed of electrically conductive material. The electrode in turn ' by joining a number of such pockets to form a coherent one Electrode plate formed. Such electrodes have a robust design and can be relatively to manufacture cheaply.

Purely electrochemical cells, with which one has high discharge currents and low weight in relation to cell capacity, one often uses a type of electrode instead that consists of a flexible electrode skeleton made of metal wire mesh or metal foil with one or both sides provided, preferably porous and cohesive layer electrochemically active mass exists. The electrode skeleton can possibly consist of a perforated or perforated and expanded Consist of metal foil. !

The active material present in the electrochemically active mass, the positive or negative character or catalytic Can have an effect is often mixed with an electrically conductive material, sometimes with an organic j or inorganic binder "The present invention is" refers to an improved design of this type of electrode. i

These electrodes can be manufactured by various methods. You can do this electrochemically, for example or catalytically active material with possible additives in the form of a dry powder mixture on the electrode skeleton; attach and then fasten by pressing or rolling on one or preferably both sides of the skeleton. Afterward a heat treatment for sintering the powder mixture or melting a possibly added binder can sometimes follow.

One can also cold weld the active material with a Mix the binding agent and cold-press or roll it onto the electrode skeleton, for example onto the one in the Swedish interpretation document 323 118 described type and V / eise.

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. - Furthermore you can use the active material together with eventual Mix the binder and electrically conductive material with a liquid to form a paste that is applied to the skeleton is, after which the liquid evaporates and the electrode is pressed or rolled and optionally sintered will.

In all of these manufacturing processes, the electrodes are often made in large, coherent patties and • cut to the desired electrode formats. In other In some cases, the electrodes are made in the form of long, contiguous strips of the desired width or length corresponding bandwidth of the electrode, which is then assigned suitable electrodes. Furthermore, the electrode skeleton the desired dimensions of the finished electrode in terms of length and width or diameter prior to attachment of the active material.

A recurring problem in the manufacture of electrodes by the above method is that they are sufficiently uniform and to achieve durable electrode edges.

When using metal wire meshes for the electrode skeleton and for the production of electrodes in large coherent patties one tries, as far as possible, to use electrodes cut parallel to the wires of the chase. Piping wires However, they are seldom completely straight and parallel, and after cutting, certain edges can run along the cutting edges Wires sticking out of the hand. These wires must be removed by manually cleaning the electrode edges. T / earth not removing them can cause short circuits in the electrochemical cell in which the electrode is used will.

Regardless of whether it is a metal wire mesh or a metal foil is used as the starting material for the electrical skeleton, "There is always the risk of cracks forming in the hate layer at the electrode edges when the electrodes are cut Using such electrodes in electrochemical primary or secondary cells then runs the risk of becoming active haters

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becomes detached from the electrode and interferes with the puncture of the cell.

When pressing or rolling electrodes, starting from a dry powder mixture, there is the problem of the powder mixture Distribute evenly over the surface of the electrode. The bulk density is often in the peripheral areas less than at other places on the electrode. In particular, this can be done in the manufacture of electrodes in the form of observe long contiguous bands. A minor one Mass density means a lower strength and there is also the risk that material will come off the electrode replaces.

It has already been proposed to use flat electrodes with a skeleton made of, for example, metal wire mesh the coating to provide the edges of the electrodes with a U-shaped bent metal strip. However, this makes the Making the electrodes and making them unnecessarily thick. Particularly in the case of high-performance cells, one strives for very thin ones Electrodes. This type of edge reinforcement is also included Curved or spiral-wound electrodes are not appropriate.

It has also been suggested earlier that an electrode skeleton with a large number of perforated recesses to fill it with a layer of active material and then the active material coated on both sides Bend skeleton together. Then you bend or weld the outer edges of the electrode together, the none for this purpose Have depressions or active material. So you get an electrode in which the active mass is like a pocket electrode is enclosed between two parts of the skeleton.

The present invention relates to an electrode that has tangible advantages compared to previously known electrodes of the corresponding type. By having one or more edges of the electrode skeleton that are electrochemically active Mass are covered, are bent inwards to the middle of the electrode skeleton, one obtains an electrode with solid stable'en

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Edges where the active mass is reliably on the electrode skeleton adheres.

Palis or the active mass rolled onto the skeleton is pressed firmly, each of the inwardly bent edges forms an angle of approximately 180 ° to the electrode skeleton. In the rest Cases, the angle can be a little smaller, if the ge «? desired electrode thickness allows this. With flat electrodes in particular, additional rigidity of the edges can be achieved in this way. However, the angle should be around 155 ° not fall below.

The invention is particularly suitable for strip electrodes. It is advantageous to use a band made of skeleton mate-i for this rial, with one or both side edges of the tape through a; simple rolling or pressing process inwards to the center of the Tape must be bent before putting the active mass on the; Attaching skeleton. The bandwidth after bending the long sides should correspond approximately to the width of the finished strip electrodes. Such strip electrodes can, for example used for cylindrical cells where the electrode after being inserted into the cell, it is in the form of a spiral wound ribbon. The ribbon electrode can also are folded together with one or more electrodes of opposite polarity and separators in between so that that the finished and used ?! Electrode the shape of a ■ Has zigzag band. i 4

Flat electrodes with a rectangular or any other flat shape can conveniently be compression molded, using an electrode skeleton, all of its edges by mechanical bending or pressing prior to coating be bent with active mass inwards towards the middle of the skeleton. This also applies to circular electrodes. Man thus obtains electrodes that have the shape of a mainly flat rectangle or any other flat shape, all of which edges of the electrode skeleton covered by the electrochemically active material are bent inwards towards the center. The end" -circular flat electrode skeletons are obtained in a corresponding manner and V / eise electrodes that take the form of a mainly

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ORIGINAL INSPECTED.

t ■ *

have a circular plate in which the edge zone of the electrode skeleton is bent inwards towards the center of the circle. ■ ^:

The width of each inwardly folded electrode The edge of the skeleton should be between 1 and 10 mm if possible. "" ' Within these limits, it is adapted to the dimensions of the electrodes to be produced. In principle, however, can the fold can be both wider and narrower as the electrode cuts require this. .

Electrodes generally have one or more am inwardly bent edge of the electrode skeleton attached Current arrester. This gives you a «! very good stroine drainage, because the area of the skeleton gives double the conductivity. This is of particular importance when using metal mesh; Skeletons, as the current mainly flows through the; individual wires to the edge of the electrode and from there through! the edge wires to the Stromable4.tern flows. In certain In cases, only an edge fold of the skeleton can serve as a current conductor. This should then not be covered by the mass.

The more stable electrode edges, di ^ one in the invention-j according to the electrodes, should there be? come that angry electrochemically active Hasse aÄ a bent Edge fold of the electrode skeleton is tied more tightly than to a non-bent edge, due to the increased thickness of the electrode skeleton at the edge fold the perforations or net meshes on the bent edge zones of the electrode skeleton with a high degree of probability to lie on top of each other irregularly and one can therefore expect that the pressed; active electrode mass at the edge fold there is a large number of attachment points on the electrode skeleton. In the first place one does not strive for an increased one Stiffness of the electrode, although this is an advantage with flat electrodes, but the greatest advantage of the invention Rather, electrodes lies in the good and uniform Binding of the active mass of the electrode. This avoids the dangerous formation of cracks on the electrode edge.

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ORIGINAL INSPECTED

The invention will now be described in more detail in connection with "the accompanying drawings
1 shows a partially sectioned side view of an electrode according to the invention,

Fig. 2 is a vertical section through the Pig electrode. 1, Pig. 2a shows an enlarged edge zone of the Pig section. 2, Pig. Fig. 3 is a partially sectioned flat electrode in a modified version,

Fig. 4 is a partially sectioned flat circular Electrode according to the invention, FIG. 5 shows a helically wound strip electrode according to the invention and

Pig. 6 schematically shows the splitting of an electrode according to the invention. In the drawing figures, 10 denotes an electrode skeleton, which is shown in Pig. 1 and 4 is shown as a metal wire mesh. The net can for example be made of ITiekel, or nickel-plated iron Consist of copper, silver or other electrically conductive material that is resistant to the electrolyte of the cell, in which the electrode is to be used. The network can consist of woven wires or by electrolytic precipitation '

ρ must be established. The number of net meshes per cm can be between 4 and approx. 150, but is generally chosen between 10 and 100. The wire thickness can be between approximately 0.03 and 0.5 mm, preferably between 0.10 and 0.25 mm.

In Pig. 3 is the electrode skeleton 12 as a perforated one Metal foil shown, which can be made from the same electrically conductive material as the metal mesh 10. That The electrode skeleton can also consist of a perforated and expanded metal foil or a metal foil without perforation getting produced. The thickness of the poles can be between approx. 0.04 and 0.4 mm, mostly between approx. 0.05 and 0.2 mm. at perforated film, the hole area can be up to about 90 # of the poly area.

In the drawing figures, 14 is also an electrochemical one active mass, which is attached to the electrode skeleton 10, 11, 12. The electrochemically active mass exists

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primarily from either an electrochemically active one Material in the form of metals, oxides or hydroxides such as nickel, cobalt »silver, manganese, lead, cadmium, Zinc or iron or from a catalytically active material, for example in the form of activated carbon or a catalytically active material effective metal. In addition, an electrically conductive material in powder or fiber form can be added to the mass be like nickel, silver, iron or graphite etc. The Bulk sometimes also contains a binder, which can often be cellulose-based, for example carboxymethyl cellulose or from polymers such as polyethylene, polytetrafluoroethylene, polyvinyl acetate, polyvinyl chloride and the like. The mass 14 can be provided on both or only on one side of the electrode skeleton 10, 12. The thickness of the The finished electrode is generally between about 0.4 and about 1 mm, but both thinner and thicker electrodes can be carried out according to the invention.

The electrode skeleton 10 according to FIGS. 1 and 2 or Pig. 6th has an edge zone 16 on the top and a corresponding one Randaone 18 at the bottom, both inwards towards the center of the metal electrode skeleton are bent over. The active mass it spreads outwards over the folded hand zones 16, 18 and covers them. The one in Pig. 2a, the inwardly folded edge 16 is bent over 180 ° to form the electrode skeleton 10.

With the Pig. 3 are both an edge zone 20 on the upper side of the skeleton as well as an edge zone 22 on the lower side of the same and the two side zones 24 the same bent inwards towards the center and covered with electrochemically active compound 14 ". The corners 26 of the folded Edge zones are cut at an angle of 45 ° so that they can ^ do not overlap at the corners of the electrode skeleton.

[In the Pig. 4 is the edge 28 of the electrode skeleton 10 bent over the entire circumference of the same inwardly towards the center of the flat, circular electrode and covered with electrochemically active mass 14.

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In the figures, 30 denotes current conductors which are attached to the electrode skeletons 10, 12 in an electrically conductive manner are. The current arresters 30 consist of strips of sheet metal or foil of the same type as the conductive material in the electrode skeleton 10, 12. ' The current conductors 30 are on the electrode skeleton 10, 12 expediently attached by spot welding and at least one spot weld is to be made in such a way that that there is good contact between the current conductor 30 and the folded edge zone 16 or 20, 24 of the electrode skeleton. Before the spot welding of the current arrester 30 is the active mass removed from the skeletal sites where the current collector 30 is to be attached.

■ The one in Pig. 5 schematically illustrated electrode 32 is Sunk into a cylindrical cell vessel 34 and is wound in a spiral shape for this purpose. For the sake of clarity, there is only one Electrode 32 and only one current collector 30 is shown. The electrode can, however, have several current collectors and is wound in a spiral together with an electrode of opposite polarity and with separators in between, before it is introduced into the cell vessel 34. Then the cell is given a suitable amount Electrolyte matched to the active material present in the electrode and seals the cell.

Pig ... 6 shows schematically an example such as one according to the invention Electrode can be folded in a zigzag. The slektrode skeleton has a folded top edge 16 and a - Folded bottom edge 18, both of which are covered with electrochemically active mass 14. The ribbon-shaped electrode is longitudinal of lines 36, 38 alternately folded forwards and backwards, so that there are mainly cohesive, coherent Form electrode sections 40. The electrodes ground together with one or more electrodes of opposite polarity combined, which are attached on both sides of each electrode section 40 with separators in between, then jointly compressed into a mainly flat electrode packet and introduced into a cell vessel in a known manner ν ^ rden.

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The electrodes according to the invention are not based on the one here. types described in more detail, but can be based on the Porm and execution within the scope of the invention \ lying idea can be modified.

- patent claims -

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Claims (9)

! Patent claims . fly electrode for electrochemical primary and secondary ■ cells, "consisting of an electrode skeleton made of metal wire mesh or metal foil which is coated on one or both sides with an electrochemically active material, the Layer extends outwards Ms to one or more edges of the electrode skeleton, characterized in that one or more edges of the electrode skeleton, which are covered with electrochemically active material, bent inwards towards the center of the electrode skeleton are. 2. Electrode according to claim 1, characterized in that that the bent edges have an angle of Form about 180 ° to the electrode skeleton. 3. Electrode according to claim 1 or 2, characterized in that the electrode has the shape of a tape, as well as that one or both long sides of the electrode strip are bent inwards towards the longitudinal center line of the strip. 4- electrode according to claim 1 or 2, characterized characterized in that the electrode has the shape of a mainly, flat rectangles or any other flat shape and that all with an electrochemically active mass covered hands of the electrode skeleton are bent inwards towards the center. 5. Electrode according to claim 1 or 2, characterized g ekenη draws that the electrode is a Porm mainly circular plate and that the outer edge of the electrode skeleton is bent inwards to the center of the circle. 209840/1002 6. Electrode according to claim 3, characterized in that that it has the shape of a spiral wound ribbon. • 7 · Electrode according to claim 3, characterized · - draws that it is folded in the shape of a zig-zag: teten tape has. 8. Electrode according to one or more of the preceding claims, characterized in that the fold width of the bent electrode skeleton edges between 1 and 10 mm. 9. Electrode according to one or more of claims 1-7, characterized in that one or several current conductors are attached to one of the inwardly bent edges of the electrode skeleton. 209840/1002 Blank page