GB2211017A

GB2211017A - Fibre structure electrode frame

Info

Publication number: GB2211017A
Application number: GB8823615A
Authority: GB
Inventors: R Guenter Gutmann; Rainer Klink
Original assignee: Deutsche Automobil GmbH
Current assignee: Deutsche Automobil GmbH
Priority date: 1987-10-09
Filing date: 1988-10-07
Publication date: 1989-06-21
Anticipated expiration: 2008-10-07
Also published as: DE3734131C1; FR2621740B1; FR2621740A1; GB8823615D0; GB2211017B

Description

1 ' 1 221101" Fibre structure electrode frame The invention relates to a

fibre structure electrode frame with a weldedon or soldered-on current diverter tab of sheet metal for a fibre frame electrode for alkaline secondary cells, and particularly but not exclusively for nickel-hydrogen cells.

For joining fibre structure electrode frames to current diverter tabs, it is known to slit the edge of the electrode frame, to insert the current tab into this slit and then weld the electrode frame to the current tab. However, such a possibility is.very expensive and is feasible only for small quantities. With larger quantities, the current tab is placed on the edge of the fibre structure electrode frame and welded thereto under pressure. To achieve adequate durability, it is thereby generally necessary galvanically to strengthen the rim of the electrode frame as is described, for example, in DE-PS 31 42 091. The durability of such joints can be further improved in that on the wide which bears on the fibre frame, the current diverter tab is provided with steps of diminishing thickness or with a steplessly tapering off chamfer such as is described in German Patents Nos. 36 32 351 and 36 32 352. For long connecting zones on rectangular plates of prismatic batteries having relatively thick tabs, the said measures are also adequate for large-area electrodes, since their connection between tab and frame is subject to a traction loading only in the direction of the plate surface. For a small connecting zone, particularly at the central hole or at the edge of round electrodes for nickel/hydrogen cells, the said measu'res are either inadequate or by reason of the shape of the electrode or by reason of the large number of connections required by the small surface of the electrode and conditioned by the capacitance, they are too expensive.

Therefore, the present invention seeks to provide the most stable, simple, easily produced connection possible between the fibre structure electrode frame and the current diverter tab which requires no galvanic strengthening of the plate and in which the current diverter can consist of relatively thin sheet.

2 According to the present invention there is provided a fibre structure electrode frame with a current diverting tab of sheet metal for a fibre structure electrode for alkaline secondary cells, wherein on the side facing the fibre frame, the current diverting tab is sub-divided by cuts or cut-outs into at least three tongues, of which at least every second tongue is formed out of the tab plane so that together with the other tongues, viewed in the direction of the row of tongues' and in the tab plane, it forms a mouth-like opening in which the fibre structure electrode frame is held.

In the case of a fibre structure electrode frame with a weldedon or soldere-on current diverter tab of sheet metal for a fibre frame electrode for alkaline secondary cells, particularly for nickel/hydrogen cells, this problem is resolved in that the current diverter tab is on the side facing the fibre frame. sub-divided by cuts or cut-outs into at least three tongues, of which at least every second tongue is bent or cranked out of the tab plane so that, together with the other tongues, viewed in the mouth-like opening in which the fibre frame is held.

Preferably the length of the tongues should be about 3 to 20 mm. If the tongue length is shorter than 3 mm, then the fibre structure electrode frame fan quite frequently be no longer correctly held between the tongues. If a tongue length of 20 mm is exceeded, then in general there is no improvement in the joint between current diverter tab and fibre structure electrode frame. Instead, only the usable are.a of the fibre structure electrode frame is reduced. In the case of very thin structure electrode frames, short tongues are recommended while longer tongues should be used in the case of thick fibre structure electrode frames. The width of the tongues can fluctuate within wide limits and generally good results are achieved if the width of the tongues is likewise in the range from 3 to 20 mm. The tongues are bent out of the tab plane alternately on one or on both sides and viewed in the direction of the row of tongues and in the tab plane they form a mouthlike opening into which the edge of the fibre structure electrode frame is pushed. The tongues are then connected to 3 the edge of the fibre structure electrode frame by welding, e.g, spot welding, laser welding, etc.

Particularly good connections are obtained if the fibre structure electrode frame is compressed in the region of the cont:act zone by a pressing process. It is recommended to compact the fibre structure electrode frame down to about 20 to 35% of the original sheet thickness. In the case of the particularly preferred fibre structure electrode frames which consist of metallised, particularly nickel plated textile substrates, such a degree of compaction produces a residual porosity in th e compacted contact zone of about 50% or less.

Preferably the compacting of the fibre structure electrode frame should be carried out in the region of the contact zone in such a way that the compacted area is slightly larger than the area used for the contact face of the tongues. The result is a particularly even and reliable contact establishment. The transition from the thickened area of the fibre structure electrode frame is preferably such that there are no sharply edge transitions between compacted and non-compacted areas, since such sharp-edge transitions encourage crack formation in the fibre structure electrode frame.

The angle to which the individual tongues are bent out of the tab plane is expediently so chosen that the edge of the fibre structure electrode frame can be pushed conveniently between the two rows of tongues. Too large an angle is disadvantageous since when the tongues are welded to the two sides of the fibre structure electrode frame, the tongues bend back again in the direction of the tab plane. It has been found to be particularly favourable if the tongues form an angle of about 50 to 200 with one another. At the indicated tongue lengths and conventional plate thicknesses very good joints are achieved with these angles.

It is preferable, particularly for fibre structure electrode frames having an edge thickness of about 1 mm or more, for the tongues not to be simply bent out of the tab plane but to be cranked, in fact to a reciprocal extent of cranking as corresponds to the thickness of the fibre frame in the contact zone.

4 The invention will now be described by way of example with reference to the accompanying drawings, in which:- Figs. 1 to 4 show a cross-section through various current diverter tabs viewed in the direction of the row 6f tongues and in the tab plane; Fig. 5 is an elevation showing a fibre structure electrode frame contacted at the outer radius, and Figs 6 to 8 show in elevation and in section a fibre structure electrode frame which is contacted on the inner radius.

Fig. 1 shows a view of a current diverter tab, seen in the direction of the row 'of tongues and in the tab plane. The tongues are bent out of the plate plane on both sides to an angle of about 5 to 100. Thus they form a mouth-like opening into which the edge of the fibre structure electrode frame can be pushed for welding. Fig. 2 shows a current diverter-tab in which a row of tongues remains in the tab plane, only the other row of tongues being bent out of the tab plane. In this case, the angle to which the row of tongues is bent out of the tab plane is expediently larger. Fig. 3 shows a current diverter tab in which the tongues are alternately cranked out of the tab plane on both sides. The angle which the tongues form with the tab plane amounts in each case to about 5 to 100. The degree of reciprocal cranking corresponds to the thickness of the fibre frame which has to be fixed between the tongues. Fig. 4 shows an embodiment similar to that in Fig. 2 but in which the row of tongues projecting from the tab plane is so cranked that there is a step of a width which corresponds to the thickness of the compacted zone of the fibre structure electrode frame. The tongues bent out of the tab plane by 50 to 100 facilitate fitment of the tab on the compacted zone of the plate.

Fig. 2 shows a circular fibre structure electrode frame 21 which is contacted on its outer radius. The frame 21 is provided with a compacted zone 22. In the region of the compacted zone 22, a part of the circle is out away'to form a straight edge for fitting the current diverter tab 23. The current diverter tab 23 is provided with contact tongues 24P 24' and 24" which contact the compacted zone 22 above and with 4 contact tongues 25, 25', 25" which contact the compacted zone below the plane of the plate. The long end of the contact tab 23 is bent over downwardly at a right-angle from the plate plane and cannot therefore be seen, while the individual contact tongues are in each case connected to the compacted zone 22 by a spot welding process. In Fig. 5, the current diverter tab comprises altogether six tongues. The number of tongues depends upon the length of the contact zone, but the number of tongues ought not be fewer than three tongues since with only two tongues there is a marked impairment of the durability of the connection. The number of tongues can be increased by making the tongues narrower. Too many excessively narrow tongues do, however, make manufacturing the current divert tab more expensive and can lead to difficulties when joining the fibre structure electrode frame to the current diverter tab if, for example, one of the excessively thin tongues happens to be accidentally misshapen during transmit or storage of the current diverter tab.

Figs. 6 to 8 shows a disc-shaped fibre structure electrode frame 31 with a central hole in which contacting takes place on the inner radius of the fibre structure electrode frame. The current diverter tab 33 consists of two welded-together parts, a short auxiliary tab 35 which also carries the contact tongues, and the longer end 36 which is welded to it. The contact tongues 34, 37 and 37' are fixed in the compacted zone 32 of the fibre structure electrode frame 31 by a spot welding process. The contact tongue 34 is thereby on one side while the contact tongues 37 and 37' are on the other side of the compacted zone 32. Fig. 7 shows a cross section on the line AA in Fig. 6. The drawing clearly shows the compacted zone 32 within which the fibre structure electrode frame is contacted by the contact tongues 34 and 37 of the tab 33. The tongue 34 is so cranked out of the tab plane that the degree of cranking corresponds to the thickness of the compacted zone 32.

Where manufacture of the fibre-structure electrode frame is concerned, it is expedient to proceed in such a way that firstly the auxiliary tab 35 with contact tongues 34 and 37 is fixed to the compacted zone 32 by spot welding, soldering or 6 the like and in that the tab portion 36 is then connected to the auxiliary tab 35. The position of the tab 33 after connecting the auxiliary tab 35 to the tab portion 36 is shown by dash-dotted lines. In a battery cell, the current diverter tab 33 is in the position indicated by the continuous lines which can be achieved by an appropriate bending out of the position shown by dash-dotted lines. Fig. 8 shows an enlarged section taken on the line B-B through the contact zone. it will be seen that the compacted zone 32 of the fibre structure electrode frame 31 is further-compacted in the region of the contact tongues 34, 37.and 37' because during the spot welding process, due to the ction of pressure and heat, the tongues further compress the fibre structure which is compacted in the contact zone 32 by having been pressed. A particularly pronounced compression occurs during welding, particularly in the region 38 of the tongue edges which are adjacent one another.

Example:

Centrally contacted circular fibre structure electrode frames of 86.5 mm outside diameter and having a central hole of 20 mm diameter, a plate thickness of 2.3 mm and a porosity of 83% were contact by means of differently configured connections with electrode tabs and the strength of the joint was measured.

The tab used was in each case a 0.2 mm wide and 150 mm long.

The textile plate substrate consisted of polyolefin fibres carrying a nickel overlay of 0.15 g per sq.cm. The geometry of the arrangement of tab and plate corresponded substantially to Fig. 6. The following different connections were made between tab and plate:

a) parallel with the surfaces of the plate, a substantially 5 mm wide, 5 mm deep slot was cut into the plate on one side of the central hole, one end of the tab was pushed into it about 5 mm and then secured by spot welding; b) an area of 7 x 12 sq.mm was compacted around the edge of the interior hole from 2.3 down to 0.8 mm by means of dies having rounded edges, so that the residual porosity of the frame was still about 50% at this point. One end of the tab 1 7 was placed on the compacted surface with an overlap of 5 mm and fixed by spot welding.

c) into the tab end, two parallel cuts 5 mm deep were made in each case 3 mm away from the edge of the tab so that the result was a central tongue of 4 x 5 sq.mm on either side of which there were two tongues measuring 3 x 5 sq.mm. The'middle tongue was cranked out of the tab plane as indicated in Fig, 4 and the tab was fitted onto a compacted zone of the plate produced as under b). The tongues were secured by spot welding.

The tabs attached according to a),b) and c) were then, as shown in Fig. 7, bent at an angle of 900 to the surface of the plate, through a radius of 5 mm. By means of a tensile testing machine, the tear-out strength of the tabs was determined. For this purpose, the edges of the plates were clamped horizontally and traction was applied to the end of the vertical tabs. The following tear-out forces were measured:

fitment according to a): 28 N disposition b): 87 N disposition c): 105 N The result clearly shows the greatly improved strength of the configuration according to the invention, as indicated in c).

1 8

Claims

CLAIMS: 1. A fibre structure electrode frame with a current diverting tab of sheet metal for a fibre structure electrode for alkaline secondary cells, wherein on the side facing the fibre frame, the current diverting tab is sub-divided by cuts or cut-outs into at least three tongues, of which at least every second tongue is formed out of the tab plane so that together with the other tongues, viewed in the direction of the row of tongues and in the tab plane, it forms a mouth-like opening in which the fibre structure electrode frame is held.

1

2. A fibre structure electrode according to claim 1, wherein the alkaline secondary cell is a nickel/hydrogen cell.

3. A fibre structure electrode frame according to claim 1 or 2, wherein in the region of contact with the current diverting tab, the frame is pressed to 20 to 35% of its original thickness.

4. A fibre structure electrode frame according to claim 1, 2 or 3, wherein the tongues are 3 to 20 mm long.

5. A fibre structure electrode frame according to any one of claims 1 to 4, wherein said tongue, out of the tab plane, is formed, so that the width of said mouth-like opening corresponds to the thickness of the fibre structure electrode frame in said region of contact with the current diverting tab.

6. A fibre structure electrode substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

-CM The Paten- Ofice.

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