AU653862B2

AU653862B2 - Support matrix for negative electrodes of lead storage batteries

Info

Publication number: AU653862B2
Application number: AU26392/92A
Authority: AU
Inventors: Wieland Rusch; Dieter Sziksnus
Original assignee: VARTA Batterie AG
Current assignee: VHB INDUSTRIEBATTERIEN GmbH
Priority date: 1991-10-23
Filing date: 1992-10-14
Publication date: 1994-10-13
Anticipated expiration: 2012-10-14
Also published as: ES2072678T3; DE59201903D1; EP0538645B1; DE4134978A1; AU2639292A; RU2078391C1; EP0538645A1; KR930009153A

Description

Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

I

S.

Application Number: Lodged: *5 S S *5 5l Invention Title: SUPPORT MATRIX FOR NEGATIVE ELECTRODES OF LEAD STORAGE

BATTERIES

The following statement Is a full description of this Invention, Including the best method of performing It known to :-US 2 Support matrix for negative electrodes of lead storage batteries The invention relates to a support matrix for negative electrodes of lead storage batteries in the form of a rectangular grid plate composed of lead-coated expanded copper metal and having a lead current-carrying lug cast onto the grid plate.

Such grid plates have already been disclosed as supports for the active mass in, for example, German Patent Specification 22 41 368 or German Patent Specification 33 12 550. They exploit the considerably higher conductivity of copper compared with lead grid structures, the copper being cathodically protected by e S the lead material.

15 In these known grid plates, the expanded metal is expanded in a direction parallel to the plate side on which the current collector is situated. The shape and orientation of the grid meshes resulting from this imparts a larger conduction cross section in the vertical direction of the grid plate to the support matrix, which benefits electrodes with large overall height because the internal resistance of lead storage batteries increases predominantly with the electron resistance in the longitudinal direction of the grid (cf. J. Euler and 25 W. Nonnenmacher, Electrochimica Acta, 1960, vol. 2, pages 268-286).

In the known grid plates, the cuirrent collector is formed by a lead strip which takes up the entire top edge of the copper grid and by a cast-on terminal lug.

The purpose of the lead strip is to collect the current at the top edge of the plate and conduct it to the current-carrying lug, to terminate the pasted area at the top, i.e. to avoid shedding, and to absorb the mechanical forces which originate from the weight of the plate and its inertial forces during acceleration processes.

In this connection, it is precisely with regard to the mechanical stress just m, tioned that the junction 3 region between the solid lead strip and the expanded metal represents a critical point because, on the one hand, it must ensure a good current transfer and, on the other hand, it must not be susceptible either to fracture or to corrosion.

According to German Patent Specification 33 12 550, account is best taken of this problem by flattening the upper edge, to be joined to the lead strip, of the grid plate in the plane of the grid plate and then sheathing it with lead by injection moulding so that the expanded metal is anchored in the lead strip by a flat border of mutually crossing webs which are, in the beneficial case, cut off on the other side of the cross- •ing point.

e• However, such a support matrix is left with the following defects as a minimum: S"when the led strip is cast on, those interstices of the grid meshes which already project from the bottom edge of the strip are also unavoidably filled with lead. During 20 pasting, these meshes and their neighbours do not absorb any paste. One edge strip of the lead-coateu expandedmetal grid is consequently not protected by the paste; it •r is endangered by heavy discharge loading and may under •coo•: certain circumstances dissolve.

25 Furthermore, the lead strip represents a load for the storage battery simply because of its weight, because it extends over the entire width of the negative electrode plate.

The object of the invention is therefore to provide a support matrix for negative electrodes of lead storage batteries which ensures an optimum paste utilisation by good current distribution without a disproportionately high apportionment of weight to current-conducting dead material and, in addition, is matched to the high strength requirements both in relation to handling during the electrode manufacture and also when used in a battery.

4 The object is achieved, according to the invention, by a support matrix as defined in Patent Claim 1.

In the novel negative grid, only one lead lug which is directly cast onto the grid plate at the connection point with the expanded-metal grid being left in its original state is provided for current supply and current removal. A flattened region of the expanded-metal grid surrounds the casting-on point at the bottom and at the sides and is screened by means of a plastic coating.

The advantage of the cast-on lug according to the invention at the edge of the grid plate, which edge is not flattened but left in its original state, is that the ""webs of the expanded copper metal are left in their inclined position in the lead lug and improve the S" 15 mechanical strength as a result of cramping.

Sa bl For such a casting-on to be successful, a suit- S"able casting mould must complete its closure outside the casting-on, but around the region provided for the latter, for which region a suitable zone of the grid plate, which is subsequently situated in the sealing plane of the casting-mould halves, is flattened. The rubbery-elastic profiled sections in the casting mould prevent grid meshes situated below the lug from being filled with lead.

25 A grid having only a cast-on lug does not have adequate mechanical strength, in particular when the plate is being handled during pasting. The webs of the expanded copper metal grid below the lead lug readily crack and, under these circumstances the electrochemical stability of the copper grid is endangered. The sheathing of the flattened grid zone by injection moulding in accordance with the invention hnparts a high degree of mechanical stability to the support matrix. This protects the particularly critical region of the lead/copper junction against corrosion during the operation of the battery.

These and other advantages of the novel support matrix are explained in still greater detail by reference 5 to the figures.

Figure 1 shows a support matrix in a preferred embodiment in accordance with the invention.

Figure 2 shows a cross section of the support matrix according to Figure 1 in the region of the caston lug.

Figure 3 shows a portion of a modified support matrix in accordance with the invention.

According to Figure 1, the grid plate 1, which is composed of lead-coated expanded copper metal 2, has a protective copper frame composed of injection-moulded sheaths 3, 4 of the upper and lower grid edges and of plastic profiled sections 5 which are pushed onto the side edges. The edges, covered by the plastic frame, of S• 15 the expanded grid are advantageously flattened. An all-round frame can also be produced by a single injection-moulding operation.

As a further protection against the mechanical 2 loading of the lead-coating layer in the lug region, a 20 handling projection 6 is provided on the upper injectionmoulded sheath 3, while the lower injection-moulded sheath 4 has feet 7 composed of the same, and consequently insulating, plastic. A suitable plastic is, S"for example, polypropylene or, if the grid has to withstand elevated temperature, polycarbonate.

Particularly important is that section of the S"injection-moulded sheath 3 which surrourds the foot of the lead lug 8 and which screens a grid zone (not visible here) of flattened expanded metal. This zone, over which the two mould halves 9, 10 of the casting tool close while the lug is being cast on, can be seen in Figure 2, which shows a cross section of the expanded grid 2 after placing in the casting mould, with the casting slit to be filled by the lead lug 8. 11 denotes rubber profiled sections which are placed in the mould and which prevent the lead itself from flowing into the interstices of the grid which are in this case flattened. The upper edge 12, projecting into the casting slit, of the expanded grid 2 6 is not flattened, with the result that the inclined webs are securely embedded in the solidified lead.

The plastic frame of the novel grid plate also results in advantages in regard to pasting. During pasting, the grids slide under the pasting funnel on a conveyor belt, during which process the pasting funnel normally rests on the grid. This fixes the plate thickness. As a departure from this, the pasting funnel rests on the plastic frame in the case of the grid plates in accordance with the invention, as a result of which plate thicknesses can be achieved which exceed the grid thickness. At the same time, as a result of resting on the plastic frame, a uniform plate thickness is ensured.

':As shown by a portion in Figure 3, a particularly S• 15 advantageous embodiment of the novel grid plate is r' distinguished by the fact that the web width of the expanded copper metal 2 in the region under the current,carrying lug 8 is increased compared with its normal web Swidth. In addition to the chosen expansion of the grid in 20 the direction parallel to the plate side provided with the current-carrying lug, such a measure improves the conduction cross section in the vertical direction because of the greater density of material and is parr ticularly beneficial in electrodes with large overall height.

Expanded metal grids in this design can be produced by a metal expanding machine which is capable of altering the web width during the expansion.

The choice of a larger web width is, however, not arbitrary since different thicknesses of the expanded grid within a plate generally present difficulties during pasting. The plastic frame of the plate according to the invention offers an aid, however, by evening out small differences in thickness.

A reasonable merging of the two web widths to one another is, however, possible and must take place in such a way that no undesirable deformations are produced during the production of the grid with subsequent 7 calendering.

This treatment results in an expanded metal with uniform web width with a certain (as a rule, maximum) grid thickness. Experience has shown that both an increase and a reduction in the original web width result in a reduction in the grid thickness. This means that there are pairs of webs of larger and smaller width, which have, however, to be found empirically, to which grids of approximately equal final thickness correspond.

For example, a grid having a thickness of 4 mm has the following parameters: S. Material thickness 0.4 to 0.6 mm, preferably 0.5 mm Web width 2.8 to 3.2 mm, preferably 3.0 mm Mesh length 20 to 30 mm, preferably 26 mm 15 Mesh width 8 to 15 mm, preferably 12.5 mm A web width of approximately 2.4 mm is suitable j. for the main part of a grid according to the invention and a web width of approximately 3.8 mm is suitable for "the lug region. These values make it possible to produce the expanded metal without difficulties.

This embodiment is advantageous, in particular, in the case of long (length 0.5 m) and, consequently, also heavy grids. Not only is the conductivity consequently improved, but the shock and vibration capability of the entire cell is also markedly increased.

Claims

1. Support matrix for negative electrodes of lead storage batteries in the form of a rectangular grid plate composed of lead-coated expanded copper metal and having a lead current-carrying lug cast onto the grid plate, characterised in that the expanded metal is flattened in the region of the grid plate surrounding the cast-on lug and is sheathed in plastic by injection moulding.

2. Support matrix according to Claim 1, charac- terised in that the expanded-metal grid is additionally pressed flat at the corners and along the free edges of the grid plate and is sheathed in plastic by injection 15 moulding or is screened by means of plastic profiled strips.

3. Support matrix according to Claim 2, charac- terised in that handling projections are formed onto the profiled strips. 20

4. Support matri, according to any of Claims 1 to 3, characterised in that the expanded-metal grid has webs of greater width in the region situated under the current- carrying lug than in the remaining region of the grid. DATED this 13th day of October 1992. VARTA BATTERIE AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS "THE ATRIUM" 290 BURWOOD ROAD HAWTHORN. VIC. 3122. V Abstract Support matrix for negative electrodes of lead storage batteries In a grid plate 1 based on lead-coated expanded copper metal 2, which grid plate has a lead current- carrying lug 8 directly cast on, the region, screened by the plastic injection-moulded sheath 3, of the expanded grid is flattened around the casting-on point in order to make it possible for the mould halves to close over the grid for the purpose of casting the lead lug and to prevent lead flowing into the grid meshes not covered by the lug. In an expanded-grid design which is particularly e beneficial for the current distribution in high electrodes, the grid webs under the lug are widened, but in a ratio to a normal width which is such that no different thicknesses are as a whole produced across the grid plate. Publication with Figure 1