GB2088119A - Improvements in or relating to electric batteries - Google Patents

Abstract

A plate assembly (6) for use in a cell compartment (4) of an electric storage battery (2) comprising a stack of first plates (10) of one polarity alternating with second plates (12) of the opposite polarity is made by assembling a conducting strip (8) with a sheet or sheets of separator material (14), folding the assembly back and forth to form, as a single unit, a stack of first plates (10) and interleaving the second plates (12) with the first plates (10). <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric batteries The present method relates to electric batteries and to a method of making a plate assembly for use in a cell compartment of an electric storage battery and to a plate assembly made by such a method.

In one convention method, electrode plates for a storage battery have been produced by casting a metal grid, which is then pasted and the pasted grid parted into two separate plates. For instance, for a lead-acid battery the grid would be made of lead or a lead alloy.

A more recent method of plate production is the so-called "continuous plate production" method. In this method, a continuous ribbon grid is produced by any convenient method such as weaving, punching a strip to form a fresh, or expanding a continuously cast or rolled strip. The ribbon grid is then pasted, and the pasted grid sandwiched between two paper strips, which reduce paste loss from the grid during subsequent handling. Individual battery plates are then cut from the pasted continuous ribbon grid, and the plates dried, cured and assembled to form a battery.

Although continuous plate production provides improvements, such as increased production rates, over the previous methods, it still suffers certain disadvantages. Handling individual pasted plates cut from the ribbon grid is expensive and time consuming. Damage to the plates occurs frequently. After the ribbon grid is divided into individual plates, the plates are reconnected electrically, at a later stage during assembly of a battery and some problems are associated with making good electrical interconnections between the plates.

An object of the present invention is to provide an improved method of making a plate assembly for a cell compartment of an electric storage battery, an improved plate assembly made by such a method and an improved electric storage battery comprising such a plate assembly.

According to one aspect of the invention there is provided a method of making a plate assembly for use in a cell compartment of an electric storage battery and comprising a stack of first plate members of one polarity alternating with, and electrically separated from, second plate members of the other polarity, which method comprises forming an elongate electrically conducting element which provides, as a single unit, a plurality of first plate members side-by-side, assembling said conducting element with an adjacent sheet or sheets of separator material which extends along and is face to face with the conducting element while both separator material and conducting element are flat, and subsequently making one or more folds in the assembly substantially perpendicular to the length of the assembly, so as to form said plurality of first plate members into a unitary stack in which said first plate members are disposed face to face and at least one face of each said first plate member is covered with separator material, second plate members being interleaved between the first plate members with separator material between the first and second plate members.

Suitably, separator material is positioned adjacent both faces of the conducting element prior to folding whereby, when the assembly is folded, both faces of each first plate member are covered with separator material, and the separator material may comprise a single sheet which is folded about a longitudinal edge of the conducting element, so that the single sheet is face to face with both faces of the element.

Advantageously, a plurality of said folds are made in the assembly perpendicular to its length, the folds being substantially equispaced, with alternate folds made in opposite senses, whereby the unitary stack of first plate members has a zigzag configuration.

The second plate members may be formed as a single unit from a one-piece conducting element.

In an alternative embodiment, a plurality of said folds in the assembly perpendicular to its length are made, all the folds being made in the same sense, whereby the unitary stack of first plate members has a flattened spiral configuration, and the second plate members may be formed as a single unit from a further elongate electrically conducting element which is assembled face to face with the element forming said first plate covered on both its faces with separator material, the assembly being folded into a flattened spiral configuration.

In any of these methods, preferably the conducting element, for forming the first plate members, and the separator sheet material are fed through a continuous supply system and cut into lengths as required for each plate assembly.

According to a further aspect of the invention, there is provided a plate assembly for use in a cell compartment of an electric storage battery comprising a stack of first plate members of one polarity alternating with, and electrically separated from, second plate members of the other polarity, made by the method according to the said one aspect of the invention.

According to a yet further aspect of the invention, there is provided an electric storage battery comprising a plate assembly according to the said one aspect of the invention.

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:~ Figure 1 shows a plan view of a battery casing having three cell compartments each containing a plate assembly according to the invention; Figure 2 shows a perspective view of a strip of battery plates which form part of a battery plate assembly according to the invention; Figure 3 illustrates a first stage in a method of making a battery plate assembly according to the invention: Figures 4 to 7 illustrate subsequent stages in the method of making the plate assembly, Figure 7 showing, in plan view, the plate assembly made by that method; and Figure 8 shows a plate assembly according to the invention, but in a different embodiment to that of Figure 7.

Referring to Figure 1 of the drawings there is shown a battery casing 2 comprising three cell compartments 4 each of which contains a plate assembly 6. The plate assembly 6 generally comprises a one-piece electrically conducting strip 8 of interconnected battery plates 10, the strip being arranged in a zig-zag configuration and with plates 10 substantially parallel to one another.

Plates 10 are interleaved with individual battery plates 12, which are of opposite polarity to plates 10. Separator material 14 is disposed so as to electrically insulate plates 10 from plates 12.

Figure 2 shows a strip 8 of interconnected battery plates 10. The strip 8 is in a zig-zag configuration but is shown before being compressed in the direction of arrows C until the plates 10 are substantially parallel. Each plate 10 comprises a grid region 16 made of a dilute Pb-Ca alloy or other suitable material, the interstices of the grid being filled with paste. Along the top edge of the grid region 1 6 is an integral solid edge region 1 8 also made of dilute Pb-Ca alloy, the edge region being provided with a lug 20.

The plates 10 are interconnected, being joined to each other along their side edges 22, except for one side edge 22' of each of the two end plates in the strip 8, these edges being free.

One possible method of making a plate assembly for a cell compartment of an electric storage battery is now described, with reference to Figures 3 to 7. A strip of a suitable material, i.e.

a metal which is not too brittle, and an example for use in a lead-acid battery would be a dilute Pb-Ca alloy, is formed by continuous casting, extrusion, rolling from an ingot or any other suitable method.

Unless already rolled during its formation, the strip may be rolled at this stage to induce an elongate grain structure which enhances malleability, so long as subsequent deformation of the strip takes place relatively soon after this rolling, before any appreciable age-hardening can occur. If making plates approximately 30 cm high, a strip about 5 cm wide is desirable. | The strip is fed into an expander, continuous feed to the expander being ensured by soldering several strips end to end. The expander forms a ribbon 24 having a width A (Figure 3), A being approximately 60 cm, and comprises two expanded edge regions 26, in the form of a mesh, and a central, unexpanded solid region 28 of width B. The central region is cut along its length to part the ribbon 24 of width A into two continuous half-width ribbons 30.

Cutting is effected by stamping to remove portions 32 from central region 28 leaving a solid edge portion 18 along each ribbon 30, with lugs 20 protruding from the edge portion 18. For plates having a height other than about 30 cm, a suitable initial strip width is selected as either greater or smaller than 5 cm. Plates can be from about 5 cm to 100 cm or more in height.

The mesh region 26 of the ribbon 30 is pasted in the usual way, the paste filling the interstices in the mesh.

The pasted, continuous ribbon 30 is then cut transversely along lines denoted by the broken lines 34 (Figure 4) into strips 8 of finite length suitable to form the desired number of plate widths. The strip can be formed into two or more plates up, to any number, but in the case illustrated in Figure 4, the length of each strip 8 is four plate widths.

A strip 8 is formed according to the method described above, with reference to Figures 3 and 4, or formed by any other suitable method such as weaving metal strand or punching sheet to form the mesh which is pasted and then assembled with separator material. The separator material must be flexible and able to fold sharply without cracking and a suitable material is microporous polyethylene. In this embodiment, the strip 8 is placed over one half 36 of a one-piece elongate sheet of separator material 14 (Figure 5). The sheet may be precreased along its longitudinal axis 38 and the strip 8 disposed on the sheet 14 so that the free edge of its pasted mesh region 16 is adjacent the axis 38 of the sheet. It is to be noted that the sheet 14 extends beyond either end of the strip 8.The other half 40 of the separator sheet 14 is folded over the strip 8, which is thus sandwiched between two layers of separator material (Figure 6).

The sandwich is folded back and forth about substantially parallel and equispaced lines 42 which are perpendicular to the longitudinal axis 36, the separator material and conducting strip 8 being bent together about these lines 42, which are also shown in Figure 4 as the intended bend lines, and the strip 8 may be scored or precreased along these lines to facilitate the bending operation as well as making the position of the bend lines 42 more accurate. Thus, plates 10 are formed between successive bend lines 42, though the plates remain joined to one another. The strip 8 of interconnected plates 10 now has a zig-zag configuration and is wrapped in the sheet 14 of separator material itself constrained by the strip into a double-layered zig-zag configuration. The plates 10 are not yet parallel to each other.

Individual plates 12, each provided with a pasted mesh region 16 and lugs 20 are disposed on alternate sides of the wrapped zig-zag sheet 8, and inserted one between two plates 10 so as to interleave the plates 10. The strip 8 is then compressed in the directions of arrows C so as to form a stack of substantially parallel plates 10, 12, plates 10 alternating with plates 12, as shown in Figure 1. Clearly, plates 10 will all be of the same polarity. Plates 12 are of the opposite polarity, and are electrically insulated from plates 10 by the sheet 14 of separator material. It will now be apparent why the sheet 14 must extend beyond the ends of the strip 8; it is so as to ensure separation of the end plates 10 of the strip from adjacent plates 12.

The past in the mesh region of the plates 10, 12 must be cured. Curing could be carried out on all plates after inserting plates 12 and compressing the strip 8. However, in one method the positive plates are cured at a higher temperature than are the negative plates, and the higher temperature may adversely affect the separator material. Accordingly, plates 10 within the separator material are conveniently the negative plates and these are cured in their wrapping of separator material, curing of the individual positive plates 12 being carried out separately. The strip 8 of negative plates may be carried out after bending into the zig-zag configuration, but before insertion of plates 12 end compression. In another method, however, the negative plates are cured at a higher temperature, and so the plates 10 are then conveniently the positive plates.Alternatively, the separator material may be made of heat-resistant material, when the plates 10 could be used as positive or negative plates.

Although the separator material is described above as comprising a single sheet 14, folded over the strip 8 to cover both faces of the strip, clearly the separator material could instead comprise two sheets, one covering each face of the strip 8.

Although the embodiments described hitherto involve using individual plates 12, these plates could be joined to one antoher, in the same way as plates 10.

Figure 8 illustrates an alternative form of plate assembly. This assembly still comprises a zig-zag strip 8 of interconnected plates 10 of one polarity interleaved with individual plates 12', 12" of the opposite polarity, but the arrangement of the separator material electrically insulating plates 10 from plates 12' or 12" is different from that in the embodiment illustrated in Figures 1 and 3 to 7.

Instead of a double-layered sheet 14 of separator material, each layer covering one surface of the strip 8, there is provided a separator sheet 14' facing only one of the surfaces of the strip 8. This separates the strip 8 of plates 10 from plates 12' arranged to one side of the strip, but not plates 12" disposed on the other side, each of which may be separated from the strip 8 by inserting it in a pocket-shaped separator 44. The pocket-shaped separators each comprise two superimposed layers of separator material, the same shape as, but slightly bigger than the plate 12" it contains, the layers being joined along three of their sides, with the top open.

In a further alternative embodiment, not illustrated, the plate assembly may be made by bending the strip 8 about the lines 42, but instead of being bent in alternately opposite directions, all bends are made in the same sense to wrap the strip 8 so that it forms a flattened spiral of plates 10. Before making these bends, the strip 8 is assembled with either a single sheet of separator material folded over to cover both its surfaces, as shown in Figures 5 and 6, or each of its surfaces is covered with a respective sheet of separator material. Plates 12, which are either individual, or which are themselves in a strip of connected plates, are placed over the strip 8 of plates 10, already covered either side with separator material, and the whole assembly folded about lines 42, thus forming a plate assembly, in the shape of a flattened spiral.

The methods of making the plate assembly described so far involve assembling a conducting element, in the form of a strip cut from a ribbon, face to face with one or more sheets of separator material in pre-cut lengths. However, for increased production speed, it is advantageous if the conducting element and separator material are both still in continuous lengths while they are assembled, the assembly then being cut into desired lengths for a predetermined number of plates 10.

The above examples have been described with specific reference to lead acid storage batteries but it will be understood that the invention is applicable to other types of electric storage batteries.

Claims (12)

1. A method of making a plate assembly for use in a cell compartment of an electric storage battery and comprising a stack of first plate members of one polarity alternating with, and electrically separated from, second plate members of the other polarity, which method comprises forming an elongate electrically conducting element which provides, as a single unit, a plurality of first plate members side-by-side, assembling said conducting element with an adjacent sheet or sheets of separator material which extends along and is face to face with the conducting element while both separator material and conducting element are flat, and subsequently making one or more folds in the assembly substantially perpendicular to the length of the assembly, so as to form said plurality of first plate members into a unitary stack in which said first plate members are disposed face to face and at least one face of each said first plate member is covered with separator material, second plate members being interleaved between the first plate members with separator material between the first and second plate members.

2. A method as claimed in claim 1, in which separator material is positioned adjacent both faces of the conducting element prior to folding whereby, when the assembly is folded, both faces of each first plate member are covered with separator material.

3. A method as claimed in claim 2, in which the conducting element is assembled with a single sheet of separator material which is folded about a longitudinal edge of the conducting element, so that the single sheet is face to face with both faces of the element.

4. A method as claimed in any preceding claim, in which a plurality of said folds are made in the assembly perpendicular to its length, the folds being substantially equispaced, with alternate folds made in opposite senses, whereby the unitary stack of first plate members has a zig-zag configuration.

5. A method as claimed in any preceding claim, in which the second plate members are formed as a single unit from a one-piece conducting element.

6. A method as claimed in any of claims 1 to 3, in which a plurality of said folds in the assembly perpendicular to its length are made, all the folds being made in the same sense, whereby the unitary stack of first plate members has a flattened spiral configuration.

7. A method as claimed in claim 6, in which said second plate members are formed as a single unit from a further elongate electrically conducting element which is assembled face to face with the element forming said first plate covered on both its faces with separator material, the assembly being folded into a flattened spiral configuration.

8. A method as claimed in any preceding claim, in which the conducting element, for forming the first plate members, and the separator sheet material are fed through a continuous supply system and cut into lengths as required for each plate assembly.

9. A plate assembly for use in a cell compartment of an electric storage battery comprising a stack of first plate members of one polarity alternating with, and electrically separated from, second plate members of the other polarity, made by the method as claimed in any of the preceding claims.

10. A method of making a plate assembly for use in a cell compartment of an electric storage battery substantially as hereinbefore described with reference to the accompanying drawings.

1 A plate assembly for use in a cell compartment of an electric storage battery substantially as hereinbefore described with reference to the accompanying drawings.

12. An electric storage battery comprising a plate assembly as claimed in claim 9 or claim 11.