GB2158285A - Multicell electric storage batteries - Google Patents

Abstract

A multicell electric storage battery of the type containing no mobile electrolyte includes a container 2 and a plurality of plates of which every alternate plate in the two end cells comprises a unipolar plate 6 and all the remaining plates constitute one half of a bipolar pair of plates 8 which is connected to its other half in an adjacent cell by one or more integral bridge pieces 10 whereby adjacent cells are separated and spaced apart only by the said bridge pieces. Each bipolar pair of plates 8 has a recess 14 engaging a corresponding projection 20 formed on one of two opposed side walls of the container thereby restraining movement of the bipolar pair of plates. <IMAGE>

Description

SPECIFICATION Multicell electric storage batteries The present invention relates to multicell electric storage batteries of the type containing substantially no mobile electrolyte, e.g. batteries in which the electrolyte is in gel form or recombination batteries in which substantially all the electrolyte is absorbed in the plates and separators. The invention is concerned in particular with such batteries of lead acid type. Recombination batteries are those which contain a reduced amount of electrolyte such that substantially all the electrolyte is absorbed in the plates and separators 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.

The invention is concerned with that type of battery in which every alternate plate in the two electrical end cells constitutes a unipolar plate and all the remaining plates constitute one half of a bipolar pair of plates which is connected to its other half in an adjacent cell by one or more integral bridge pieces. Such batteries have the advantage that the material and labour costs relating to the provision of plate straps connecting the plates of the same polarity in each cell and of intercell connectors connecting the plates of opposite polarity in adjacent cells are eliminated.

It has been discovered that with batteries containing no mobile electrolyte, in particular recombination batteries, there is a reduced risk of intercell ionic leakage occurring, primarily because there is no free electrolyte available for the conduction of leakage currents. As a consequence, a gas-tight seal between adjacent cells is not necessary. It has, however, always been believed that an intercell partition, though not necessarily a continous, sealed partition is necessary between adjacent cells in order to avoid premature failure of the battery.

British patent specification No. 2070844 discloses a lead acid recombination battery of the type referred to above in which all the plates with the exception of every alternate plate in the two end cell constitutes one half of a bipolar pair of plates. The constructions disclosed in this prior specification include a container which is divided into compartments by integral intercell positions which terminate short of one or both of two opposed side walls of the container and the bipolar pairs of plates are connected either by a single integral bridge piece which passes around one end of the intervening intercell partition or by two integral bridge pieces which pass around respective ends of the intervening intercell partition.Adjacent cells are therefore not sealed from one another but they are separated from one another over the majority of their length by an intercell partition to minimise the risk of intercell leakage currents degrading the battery's performance.

The construction of the container in this prior specification is somewhat complex since the bridge pieces must be able to pass around one or both ends of the intercell partitions and this means that the tooling and moulding process for the container are relatively complex and in many cases that the container must be moulded with two walls missing which in turn further complicates the subsequent assembly procedure. In addition, the insertion of the plates into the container is difficult in that the gaps between the halves of the bipolar pairs of plates must be aligned precisely with the correct intercell partition.

The adjacent partitions and the walls of the container can not materially assist in this alignment process without making the compartments of the container almost exactly the same size as the plates in which event sliding the plates into the compartments would be problematic.

Accordingly it is an object of the present invention to provide a battery of the type referred to above whose container may be simply manufactured and which may be simply assembled.

According to the present invention there is provided a multicell electric storage battery of the type containing substantially no mobile electrolyte, every alternate plate in the two ends cells comprising a unipolar plate and all the remaining plates constitutuing one half of a bipolar pair of plates which is connected to its other half in an adjacent cell by one or more integral bridge pieces whereby adjacent cells are separated and spaced apart substantially only by the said bridge pieces, each bipolar pair of plates having at each end a projection or a recess which engages a corresponding recess or projection formed in one of two opposed side walls defining the space accommodating the plates. The fit between the projections and recesses is preferably such as substantially to restrain movement of the bipolar pairs of plates in their plane.In the preferred embodiment a plurality of ribs is formed on the two side walls of the battery container which engage in recesses formed in the bipolar pairs of plates.

Thus in the battery in accordance with the present invention the cells are not spaced apart by intercell partitions, as is conventional, but merely by the bridge pieces which connect the two halves of bipolar pairs of plates.

It is however found that intercell ionic leakage does not occur since there is substantially no mobile electrolyte available for the conduction of leakage currents. Each bipolar pair of plates, which preferably constitutes a substantially planar unit, is restrained against movement and thus any risk of short circuits by virtue of any movement of the plates is elimi nated. In the preferred embodiment in which the recesses or projections on the side walls of the battery container extend over substantially the full height of the container, these recesses or projections enable the bipolar pairs of plates to be correctly located when the battery is assembled and thus permit the battery container to act as an assembly jig.The moulding of a container with shallow ribs on its interior walls is, however, a simple operation which requires relatively simple tooling and a reduced amount of e.g. plastics material as compared with a conventional compart mented battery container.

In practice, there-is unlikely to be any real risk of movement of the unipolar plates since these will generally be connected by a terminal post which is connected to a terminal of the battery and passes through a wall of the battery and thus locates the unipolar plates in position. However, in the preferred embodiment each unipolar plate has at each end a projection or a recess which engages a recess or projection formed on one of the two opposed side walls of the battery container since this enables the unipolar plates to be readily correctly positioned during assembly of the battery. Each unipolar plate is preferably provided with a selvedge extending along one edge thereof, which selvedge may act as a current collecting bar.In the preferred embodiment the unipolar plates are formed with recesses which are engaged by ribs on the side walls of the battery container and these recesses may be formed in the selvedges and the unipolar plates in each end cell of the battery may be connected by means of their respective selvedges.

It has previously been thought that even in a battery of the type containing substantially no mobile electrolyte there is a risk of intercell ionic leakage currents flowing along a layer of electrolyte extending ver the bridge pieces or intercell connectors and to prevent such currents occurring it has been proposed that each intercell connector (and it will appreciated that in the battery of the present invention all the bridge pieces extending between pair of adjacent cells constitute an intercell connector) be provided with an electrolyte creepage barrier.

It is now thought that such an electrolyte creepage barrier may in fact not in general be necessary but there is a somewhat greater risk of such intercell ionic leakage currents occurring in a battery of the type with which the present invention is primarily concerned, that is to say a motive power battery, than an automotive battery since a motive power battery tends to be more deeply discharged and when discharged a small amount of free liquid may in fact be present in a recombination battery. Accordingly, it may be desirable to provide each bridge piece with an electrolyte creepage barrier by providing a layer or line of hot melt adhesive or other plastics material extending around the bridge pieces or by dipping or coating the bridge pieces in a laquer or plastics material.

Further features and details of the present invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a scrap perspective exploded view of a recombination lead acid motive power battery in accordance with the present invention in which only two layers of plates and separator material are shown and the lid is omitted; Figure 2 is a scrap plan view of the battery of Figure 1 in which only one separator is shown; and Figuge 3 is a plan view of a single bipolar pair of plates.

The battery, which may comprise any desired number of cells in a line, e.g. 6 cells, includes a substantially cuboidal uncompartmented container 2 of polypropylene or the like which is sealed by a lid (not shown). Each cell comprises a stack of plates of alternating polarity separated by sheets of separator material 4. Each plate is substantailly planar and lies in the same plane as one plate in every other cell, each of which planes is substantially parallel to the plane of the open side of the container, i.e. the plane of the lid. Every alternate plate in the two end cells of the battery constitutes a unipolar plate 6 and all the remaining plates constitute one half of a bipolar pair of plates 8 which is connected to its other half in an adjacent cell by an integral bridge piece 10 of lead or lead alloy in which a plurality of spaced apertures 12 is formed.

Referring now to Figure 3, each bipolar pair of plates comprises two spaced rectangular grids of lead or lead alloy which bear positive and negative active material respectively and which are mechanically and elctrically connected by the bridge piece 10. The apertures 12 are provided primarily to reduce the amount of lead used since the bridge piece can fulfil its function adequately with the residual cross sectional area that remains. At each end of the bridge piece is an open recess or aperture 14 whose function will be described below. The bipolar pair of plates may be produced by casting and subsequent application of the active material or alternatively a strip of lead or lead alloy may be expanded inwardly from its outer edge to leave a central land in which the apertures 12 are stamped.

After application of the active open sided apertures 14 are provided by ensuring that each cut passes through an aperture 12.

The unipolar plates may be considered as constituting one half of a bipolar pair of plates with one half of the associated bridge piece acting as a current-collecting selvedge 16.

The apertures 12 are omitted in this case but an open ended and sided recess 18 corresponding to one half of a recess 14 is provided at each end of each selvedge 16.

Referring now to Figures 1 and 2, the two opposed longitudinal side walls of the container are provided with integral shallow, equispaced, vertical ribs 20 extending over their full height whose width is substantially equal to that of the open recesses 14. The side walls are also provided with similar ribs 22 of reduced width at each end, that is to say in the corners of the container. Each recess 14 in a bipolar pair of plates is engaged by a rib 20 thereby locating each such pair of plates positively in position and preventing its movement within the container.

Each recess 18 in a unipolar plate is engaged by a rib 22 thereby preventing the unipolar plates from moving towards the end walls of the container. The width of each plate between the transverse edge of its recess 18 or 14 and its free edge is somewhat less than the distance between the opposed surfaces of adjacent ribs 20 and 22 but nevertheless each bipolar pair of plates is positively restrained against movement by the ribs 20 whilst each unipolar plate can at most move a limited distance in the horizontal direction, which distance is insufficient to permit internal short circuits to occur.

It will however be noted that there are no intercell partitions between adjacent cells but due to the absence of mobile electrolyte intercell ionic leakage currents do not flow. The only components between adjacent cells are the bridge pieces and it is these which maintain adjacent cells spaced apart. The ribs 20 and 22 have a locating function and prevent movement of bipolar pairs of plates and they do not have an intercell ionic separation function since they extend only over a minor proportion of the width of the battery, preferably over 10% or 5% or less of the width of the battery i.e. the height of the plates. When assembling the battery, a strip of microfine glass fibre separator material 4 is placed between each pair of ribs 20 and 20 or 20 and 22, the size of each strip being substantially the same as that of the area defined by the four ribs in question.Bipolar pairs of plates, three pairs in the case of a six cell battery, are then inserted into the container by engaging their recesses 14 with a respective opposed pair of ribs 20 and then sliding them down into the container. After inserting six further strips of separator material a unipolar plate 11 then slid in at each end of the container with its selvedge facing the adjacent end wall and with the ribs 22 engaging the recesses 18.

The second layer of plates is completed by the addition of two further bipolar pairs of plates which are of course offset from those of the first layer. More separator material is added and then three further bipolar plates and the sequence continues until the required number of layers of plates have been inserted, which number determines the capacity of the finished battery. It will be appreciated that the ribs on the container thus not only serve to locate the plates but also permit the container to act as an assembly jig.

The plates and separators are then subjected to a compressive force transverse to their planes and vertical bars 24 of lead or lead alloy are then cast by any conventional means adjacent the two end walls of the container which connect together the selvedges 16 of the unipolar plates and act as terminal pillars. Electrolyte is then added to the battery and either before or after electrolytic formation the lid is sealed to the container whilst maintaining a compressive force on the plates and separators which is necessary in recombination batteries if the plates are to have sufficient electrolyte available for their electrochemical requirements.

In the battery in accordance with the present invention the two opposed walls defining the space accommodating the plates are formed with projections or recesses which cooperate with recesses or projections on the bipolar plates and in the specific embodiment the battery container is ribbed. It is, however, possible for the battery container to have completely plane walls and for the recesses or projections which co-operate with the bipolar plates to be provided on separate side plates of e.g. plastics material which engage opposed side walls of the container. This not only further simplifies the moulding of the container but enables the side plates carrying the recesses or projections to be produced in long lengths and then cut to size. The thickness of these plates may also be varied over a wide range enabling them to act as "adaptors" to adapt a standard sized container to varying capacities of battery. The plates may be positively secured in position or merely retained in position by virture of their size and their engagement by the plates.

Claims (10)

1. A multicell electric storage battery of the type containing substantially no mobile electrolyte, every alternate plate in the two end cells comprising a unipolar plate and all the remaining plates constituting one half of a bipolar pair of plates which is connected to its other half in an adjacent cell by one or more integral bridge pieces whereby adjacent cells are separated and spaced apart substantially only by the said bridge pieces, each bipolar pair of plates having at each end a projection or a recess which engages a corresponding recess or projection formed on one of two opposed side walls of the battery container thereby restraining movement of the bipolar pairs of plates.

2. A battery as claimed in Claim 1 in which a plurality of ribs is formed on the two side walls of the battery container which engage in recesses formed in the bipolar pairs of plates.

3. A battery as claimed in Claim 2 in which the bridge pieces extend over substantially the full length of the bipolar pairs of plates and the recesses in the bipolar pairs of plates are formed at each end of each bridge piece.

4. A battery as claimed in Claim 3 in which there is a plurality of spaced apertures formed in each bridge piece.

5. A battery as claimed in any one of the preceding claims in which each unipolar plate has at each end a projection or recess which engages a recess or projection formed on one of the two opposed side walls of the battery container.

6. A battery as claimed in Claim 5 in which ribs are formed on the two side walls of the battery container which engage in recesses formed in the unipolar plates.

7. A battery as claimed in Claim 6 in which each unipolar plate is provided with a selvedge extending along one edge thereof in which the recesses are formed.

8. A battery as claimed in any one of the preceding claims in which all the plates are planar and each bipolar pair of plates constitutes a planar unit.

9. A battery as claimed in any one of the preceding claims which is of recombination type and adjacent plates in each cell are separated by microfine glass fibre separator material.

10. A multicell recombination electric storage battery substantially as specifically herein described with reference to the accompany drawings.