GB2129195A - Manufacturing electric storage batteries - Google Patents

Abstract

A method of manufacturing a recombination electric storage battery includes forming two or more cell packs comprising one or more positive electrodes 2 alternating with one or more negative electrodes 4 interleaved with separator material 6. Each electrode has an upstanding lug 10 and each cell pack is placed into a respective plastics bag 12 which extends up above the upstanding lugs. The cell packs are placed side by side and one or more intercell connectors are formed connecting together the or each lug of one polarity in one cell pack to the or each lug of the other polarity in an adjacent cell pack by placing a reaction member 16 into contact with the lug, or the lug furthest from the said adjacent cell pack, of the one polarity and placing a piercing member 18 into contact with the lug, or the lug furthest from the said one cell pack, of the other polarity. A force is applied to the piercing member to penetrate the or each lug of the said other polarity and the walls of the two plastics bags and an electric current is passed between the reaction and piercing members to fuse all the lugs together. <IMAGE>

Description

SPECIFICATION Manufacturing electric storage batteries The present invention relates to a method of manufacturing electric storage batteries of the type containing substantially no mobile electrolyte, e.g. batteries of recombination type, in particular such batteries of lead acid type, and is concerned with the formation of intercell connectors in such batteries.

Recombination batteries are those which contain substantially no free electrolyte and in which the gas evolved within them during operation or charging is not normally vented to the atmosphere but is induced to recombine within the battery.

Conventional lead acid batteries include a plurality of cells each containing alternating positive and negative plates each of which has an upstanding plate plug. The cells are electrically connected but electrolytically isolated so as to prevent the flow of intercell ionic leakage currents which degrade the battery's performance and reduce its service life. The plates of each polarity in each cell are conventionally connected together by a respective plate strap and plate straps of opposite polarity in adjacent cells are connected together by an intercell connector. The container conventionally has integral intercell partitions to seal adjacent cells from one another and each intercell connector passes over or through the respective intercell partition and is sealed thereto to prevent the flow of leakage currents.

However, in that type of battery which includes substantially no mobile electrolyte, e.g. batteries of recombination type, it is believed that there is a substantially diminished risk of intercell ionic leakage currents occurring because there is no electrolyte available for the conduction of such currents. This presents the possibility of providing a battery containing substantially no mobile electrolyte in which adjacent cells are not electrolytically sealed from each other which results in a substantial economy since the battery container need not be provided with integral intercell partitions and whilst intercell partitions are required it is not necessary for the intercell connectors to be sealed to them.British Patent Specification No. 2062945 of the present applicants discloses a recombination electric storage battery including a plurality of cell packs, each of which is accommodated in a respective open plastics bag, within a common uncompartmented outer container. Adjacent cells are separated only by two thicknesses of plastics film and communicate with the common head space beneath the lid. The plate straps and intercell connectors are constituted by straight bars of lead or lead alloy which connect together the plate lugs of one polarity in one cell and pass straight over the respective intercell partition and connect together also the plate lugs of the opposite polarity in the adjacent cell.Despite the fact that adjacent cells are not sealed from each other and that the intercell connectors pass over the intercell partitions and are not sealed thereto there is believed to be no substantial risk of degradation of the battery performance by intercell ionic leakage currents.

The formation of the plate straps and intercell connectors in the battery disclosed in the prior specification referred to above is a relatively time consuming process and requires a substantial amount of lead or lead alloy and is thus relatively expensive. It is an object of the present invention to provide a method of manufacturing an electric storage battery of the type containing substantially no mobile electrolyte in which the formation of plate straps is substantially simplified or eliminated altogether and the formation of intercell connectors is also substantially simplified.

According to the present invention a method of manufacturing an electric storage battery of the type containing substantially no mobile electrolyte includes forming two or more cell packs, each comprising one or more positive electrodes alternating with one or more negative electrodes interleaved with separator material, each electrode of each polarity in each cell pack having an upstanding lug, placing each cell pack into a respective plastics bag, the walls of which extend up above the upstanding lugs, placing the cell packs side by side and forming one or more intercell connectors connecting together the or each lug of one polarity in one cell pack to the or each lug of the other polarity in an adjacent cell pack by placing a reaction member into contact with the lug, or the lug furthest from the said adjacent cell pack, of the one polarity and placing a piercing member into contact with the lug or the lug furthest from the said one cell pack, of the other polarity, applying a force to the piercing member to penetrate the or each lug of the said other polarity and the walls of the two plastics bags and passing an electric current between the reaction and piercing members to fuse all the said lugs together.

Thus in the method of the present invention the or each electrode of one polarity in one cell pack is connected to the or each electrode of the other polarity in an adjacent cell pack by applying sufficient pressure to them to rupture the two walls of the plastics bags between them subsequent to which a substantial electric current, e.g. thousands of amps, is passed through them for a short time, e.g. a small fraction of a second, to fuse or weld all the lugs together. The connection of the lugs through the hole formed in the plastics bags constitutes an intercell connection and it will be appreciated that in the case in which there are two or more lugs of each polarity the fact that these lugs also are fused together means that the separate formation or moulding of plate straps is unnecessary.The hole in the plastics bags is of course filled with the metal of the lugs, i.e. lead or lead alloy in the case of a lead acid battery, which has been fused and subsequently solidified and in practice the edges of the aperture are found to be embedded in the solidified metal with the result that the aperture in the plastics bags is effectively sealed.

Thus in the battery disclosed in the prior specification referred to above, the plastics bags do not extend up as far as the top of the plate lugs or, if they do, they are depressed during the formation of the plate straps and the intercell connectors with the result that the intercell connectors simply pass over the tops of the plastics bags constituting the intercell partitions.

By contrast, however, in the method of the present invention the plastics bags extend up above the upstanding lugs and the intercell connections are formed through apertures in the bags which are formed during the process with the result that the plastics bags extend above and all the way round the intercell connectors and, in practice, are sealed thereto.The use of plastics bags which extend up somewhat higher than those disclosed in the prior specification referred to above is desirable firstly because in a method of adding electrolyte to a battery which forms no part of the present invention the plastics bags are used to define the volume of electrolyte added to the cells and it is desirable that these should extend an appreciable distance above the top of the cell packs so as to permit an excess of electrolyte to be added to the cells and retained therein whilst the cells are subjected to their initial formation.In addition, whilst there is a substantially reduced risk of intercell ionic leakage currents occurring in batteries of the type containing substantially no mobile electrolyte, it is believed that the intercell connectors may in time become pitted and porous with the result that their surface may be permanently wet with electrolyte due to capillarity effects and may thus constitute a path for intercell ionic leakage currents. For this reason it is believed that it may be desirable to provide a so called electrolyte creepage barrier around the or each intercell connector and the method of the present invention achieves this in a simple and reliable manner as a by-product of the simple method of forming the intercell connections.

It might be thought that it would be preferable to provide each plastics bag with a preformed aperture through which the upstanding lugs could be connected by fusion. However, quite apart from the fact that if the plastics bags are to be used to determine the amount of electrolyte in each cell pack these preformed apertures would permit at least a proportion of the electrolyte to run out of the cells, it is found in practice to be impossible satisfactorily to align pairs of such apertures. The formation of the apertures in the plastics bags immediately prior to fusing the lugs together inherently ensures that these apertures are in the correct positions and are aligned with each other.

If each cell contains two or more electrodes of each polarity the lugs associated with them will be connected together in the fusion step and it will be appreciated that this will mean that those lugs which are not immediately adjacent the associated intercell partition constituted by two thicknesses of plastics film will be bent towards that intercell partition. This means in practice that the more lugs there are in each cell the higher these lugs have to be to permit them to extend to a point adjacent the associated intercell partition and this is undesirable in that the higher the upstanding lugs are the greater will be the volume of the empty space in the battery above the cell packs. For this reason, it is preferred that each cell pack comprises only a single electrode of each polarity.This will mean that in each case one lug of one polarity has to be connected to only one lug of the opposite polarity in the adjacent cell with the result that the upstanding lugs can be relatively small. A battery which has only a single plate of each polarity per cell will of necessity have only a small capacity, and it is therefore preferred that the single electrode of each polarity has one or more folds in it dividing it into two or more integral plates.

It is preferred that the reaction member has a substantially planar engagement surface which is placed into contact with the lug or the lug furthest from the respective intercell partition and that the piercing member includes a conical portion, the apex of which is placed into contact with the associated lug. Thus the apex of the conical portion is applied against the lug or the lug furthest from the respective intercell partition and sufficient force is applied to it to rupture the or each lug on that side of the intercell partition and also the two plastics films constituting the intercell partition, each of which is preferably less than 0.25 mm or less than 0.1 mm thick. The engagement surface of the reaction member merely provides a reactive force to the force exerted on the piercing member.Once the plastics films have been pierced the electric current is passed between the piercing member and the reaction member and this current is sufficiently large to ensure that the heat evolved by reason of the resistance of the material of the lugs through which the current passes is sufficient to melt those lugs. The force applied to the piercing member is sufficient to force molten metal to flow through the apertures formed in the plastics films which subsequently solidifies in position to form an intercell connector. It is preferred that the axial length of the conical portion is less than the thickness of the lugs to be fused together so as to ensure that the piercing member and the reaction member do not contact one another directly for if this were to happen a short circuit current would pass which would produce little or no heating effect in the lugs.

Further features and details of the invention will be apparent from the following description of one specific embodiment which is a three cell six volt lead acid standby battery of recombination type which is given by way of example only with reference to the accompanying diagrammatic drawings, in which:~ Figure 1 is a perspective view of a single cell pack; Figure 2 is a perspective view of the cell pack of Figure 1 within an open-topped plastics bag; Figure 3 is a perspective view of three cell packs within a battery container prior to formation of the intercell connectors; Figure 4 is a side elevation of the piercing and reaction members of the fusion apparatus; and Figure 5 is a scrap sectional side elevation of two lugs after they have been fused together.

The cell pack shown in Figure 1 comprises a single positive electrode member 2 separated from a single negative electrode member 4 by a single sheet of compressible fibrous absorbent separator material 6, in this case of microfine glass fibre material. Each electrode member comprises a substantially rectangular sheet like grid or mesh of lead or lead alloy bearing positive and negative active electrode material respectively and folded once substantially half way along their length to divide them into two integral plates of the same polarity which are intercalated with the plates of opposite polarity.Each grid or mesh may be formed in any desired manner, e.g. by casting, but in this embodiment they are formed by expanding a strip of lead or lead alloy inwardly from its edges to leave an unexpanded central land and the resulting strip is then cut in a manner which will be apparent from Figure 1 which leaves no waste. Thus each electrode has a central elongate unexpanded area 8 which projects upwardly above the upper edge of the electrode and there constitutes an upstanding lug 10. It will be appreciated that to optimise the current flows in each electrode, the associated lug should be as close to the fold as possible but since it would be difficult to fold the electrode if the lug 10 and unexpanded area 8 were situated at the fold these are preferably situated between 5 and 15 mm from the fold.

Three cell packs of the type illustrated in Figure 1 are assembled and then each is placed in a respective open-topped plastics bag 12, as shown in Figure 2. The bags are so dimensioned that they extend slightly above the tops of the lugs 10. The three cell packs are then inserted into an uncompartmented rectangular section battery container 14 of polypropylene or the like, as shown in Figure 3. The container 14 is so dimensioned with respect to the cell packs that each cell pack is constrained to occupy a volume in the container less than its natural volume, e.g.

between 60 and 80% of its natural volume.

As may be seen in Figure 3, the total of six upstanding lugs are disposed as two spaced pairs of lugs, the two lugs of each pair being situated back to back and separated only by the walls of the two plastics bags, the remaining two lugs being situated adjacent opposite corners of the container 14. The two pairs of adjacent lugs are then connected together using a fusion machine incorporating a reaction member 16 and a piercing member 18 which is relatively movable thereto, both of which are illustrated in Figure 4.

The reaction member 16 affords a planar engagement surface 20 and the piercing member 18 carries a removable hard metal insert 22 of which one end 24 is conical and projects towards the engagement surface 20. The apex angle of the conical portion 24 is preferably between 60 and 1200 and in this embodiment is 900. The base of the conical portion is surrounded by an annular collar 26 connected to the main body of the piercing member. In use, the engagement surface of the reaction member is placed against one of a pair of lugs to be connected together and the apex of the conical portion 24 is placed against the other of the lugs of the pair. A substantial force is applied between the reaction and piercing members which results in the apex of the conical portion penetrating the lug which it contacts and the two thicknesses of plastic film separating that lug from the other lug of the pair.A substantial current is then passed between the engagement and piercing members by means of electrical leads (not shown) and this current, which may be of several thousand amps for about a tenth of a second, produces a sufficient resistive heating effect in the material of the lugs that they soften and partially melt. This softening in combination with the substantial force applied between the reaction and piercing members results in molten lead alloy being squeezed through the hole in the plastics films formed by the conical portion 24 thereby connecting the two lugs together and embedding the edges of the apertures in the plastics films in metal which subsequently solidifies. Both pairs of adjacent lugs are connected in a similar manner thereby providing the battery with intercell connectors in which the edges of the plastics films defining the apertures in them are embedded.

At some stage in the manufacturing process electrolyte must be added to each cell pack and the cell packs formed, and whilst this may be done subsequent to the formation of the intercell connectors described above it is preferred that this is effected prior to inserting the cell packs into the container and prior to formation of the intercell connectors. In this connection it will be appreciated that the intercell connectors may be formed either whilst the cell packs are in their final outer container, as described above, or alternatively within a jig either prior to or after electrical formation of the cell packs.

Subsequently, a lid with a single vent is sealed to the container and the battery is then ready for use. The material of the plastics bags separates adjacent cell packs and thus acts as intercell partitions but adjacent cells are not sealed from each other and thus all communicate with a common head space beneath the lid which is vented, if the pressure in the battery should rise to a predetermined superatmospheric pressure, by the single vent. Despite the fact that adjacent cells are not electrolytically sealed from each other intercell ionic leakage currents do not occur because there is substantially no mobile electrolyte in the cells available for the conduction of such currents. In this connection it will be noted that the only pathway for such currents is over the tops of the plastics bags which are of e.g.

polyethylene which is hydrophobic. The leakage path which might potentially be present along the intercell connectors after they have become pitted and porous due to the action of the sulphuric acid electrolyte on them is effectively blocked by the material of the plastics bags which, by virtue of the fusion process described above, is embedded in the metal of the intercell connectors and thus constitutes electrolyte creepage barriers around the intercell connectors. This latter feature may be of importance when the battery is first put into service since it is conventional for the cell packs to be provided with excess electrolyte for their electrical formation and whilst some of this is gassed off during formation the battery may contain a small volume of free electrolyte initially.

This will be progressively gassed off when the battery is charged in service and thus the amount of electrolyte will progressively decrease until it has reached an amount insufficient to saturate the pores in the electrodes and separator material whereafter substantially only oxygen will be evolved on charging which will be recombined at the negative plate and the battery then operates effectively in a recombination mode.

Claims (9)

1. A method of manufacturing an electric storage battery of the type containing substantially no mobile electrolyte including forming two or more cell packs, each comprising one or more positive electrodes alternating with one or more negative electrodes interleaved with separator material, each electrode of each polarity in each cell pack having an upstanding lug, placing each cell pack into a respective plastics bag, the walls of which extend up above the upstanding lugs, placing the cell packs side by side and forming one or more intercell connectors connecting together the or each lug of one polarity in one cell pack to the or each lug of the other polarity in an adjacent cell pack by placing a reaction member into contact with the lug, or the lug furthest from the said adjacent cell pack, of the one polarity and placing a piercing member into contact with the lug, or the lug furthest from the said one cell pack, of the other polarity, applying a force to the piercing member to penetrate the or each lug of the said other polarity and the walls of the two plastics bags and passing an electric current between the reaction and piercing members to fuse all the said lugs together.

2. A method as claimed in Claim 1 in which the battery is of recombination type and the separator material is compressible, fibrous and absorbent.

3. A method as claimed in Claim 1 or Claim 2 in which each cell pack comprises a single electrode of each polarity.

4. A method as claimed in Claim 3 in which each electrode has one or more folds in it dividing it into two or more integral plates.

5. A method as claimed in any one of the preceding claims in which the reaction member has a substantially planar engagement surface which is placed into contact with the associated lug.

6. A method as claimed in any one of the preceding claims in which the piercing member includes a conical portion, the apex of which is placed into contact with the associated lug.

7. A method as claimed in Claim 6 in which the apex angle of the conical portion is between 60 and 1200.

8. A method as claimed in Claim 6 or Claim 7 in which the axial length of the conical portion is less than the thickness of the lugs to be fused together.

9. A method of manufacturing an electric storage battery of recombination type substantially as specifically herein described with reference to the accompanying drawings.