GB2129191A - Electric storage batteries - Google Patents

Abstract

A recombination electric storage battery comprises a container 14 sealed by a lid 16 and containing two or more cells connected in series. Each cell is separated from the or each adjacent cell by a planar intercell partition constituted by the walls of two plastics bags 22 and contains a single positive electrode member 6 separated from a single negative electrode member 6 by separator material 10. Each electrode member is of sheet form with n folds in it dividing it into n+1 electrodes extending parallel to the or each intercell partition. The electrodes in each cell are of alternating polarity and each electrode member has a projecting connector member 8 or 12 situated adjacent the fold closest the longitudinal centre point of that electrode member. The connector member 12 of one electrode member in each end cell constitutes a terminal connector and is connected to a respective battery terminal 18 and each remaining connector member 8 is integral with a connector member of an electrode member of opposite polarity in an adjacent cell, each integral pair of connector members 8 constituting an intercell connector member which extends over the respective intercell partition. <IMAGE>

Description

SPECIFICATION Electric storage batteries The present invention relates to electric storage batteries, particularly of the type including substantially no mobile electrolyte, e.g. of recombination type, and particularly though not exclusively such batteries of lead acid type.

Recombination batteries are those batteries in which the amount of electrolyte present is restricted so that there is substantially no free unabsorbed electrolyte in the cells and the gases evolved during operation or charging are induced to recombine within the battery.

Conventionally, when assembling batteries of either recombination or flooded electrolyte type, it is necessary either before or after placing the plates in the battery container to form both plate straps connecting together plates of the same polarity within each cell and also intercell connectors connecting together the plate straps of opposite polarity in adjacent cells. These two steps are frequently combined, but nevertheless the formation of plate straps and intercell connectors is a time consuming and thus expensive procedure which utilises a substantial amount of metal, i.e. lead or lead alloy in a lead acid battery, and the metal of the plate straps and intercell connectors has a certain resistivity which contributes to the total internal resistance of the battery.

When assembling conventional batteries of flooded electrolyte type one of the problems is to ensure that the intercell connectors form an electrolytic seal with the intercell partitions over or through which they pass so as to prevent intercell ionic leakage currents. However, in recombination batteries in which there is substantially no free unabsorbed electrolyte it is found that there is a substantially diminished risk of such leakage currents occurring and this enables the electrolyte seal between the intercell connectors and intercell partitions to be dispensed with.

British Patent Specification No. 2070844 of the present applicants proposes a construction of recombination battery which eliminates the need for the formation of plate straps and intercell connectors since each plate, with the exception of every alternate plate in the two end cells, is one half of a bipolar plate which is integrally connected to a plate of opposite polarity in an adjacent cell by a bridge piece. Since each plate is directly connected to a plate of opposite polarity in an adjacent cell, the need for plate straps is eliminated completely and the bridge pieces fulfil the function of the conventional intercell connectors.However, the construction proposed in this prior specification is somewhat complex to assemble and it is therefore an object of the present invention to propose a battery construction in which the separate formation of plate straps and intercell connectors is not necessary and which is both simple and economical to assemble.

According to the present invention an electric storage battery comprises a container sealed by a lid and containing two or more cells connected in series, each cell being separated from the or each adjacent cell by a substantially planar intercell partition and containing a single positive electrode member separated from a single negative electrode member by separator material, each electrode member being of substantially sheet form with n folds in it thereby dividing each electrode member into n+1 electrodes extending substantially parallel to the or each intercell partition, the electrodes in each cell being of alternating polarity, each electrode member having a projecting connector member situated adjacent the fold closest the longitudinal centre point of that electrode member, the connector member of one electrode member in each end cell constituting a terminal connector and being connected to a respective battery terminal and each remaining connector member being integral with a connector member of an electrode member of opposite polarity in an adjacent cell, the or each integral pair of connector members constituting an intercell connector member which extends over the respective intercell partition.

Thus in the battery in accordance with the present invention each cell contains only one electrode member of each polarity. Each electrode member has one or more folds in it to define two or more substantially parallel extending electrodes of the same polarity which alternate with electrodes of opposite polarity and are separated therefrom by separator material. One electrode member in each end cell is connected to the battery terminals whilst each remaining electrode member is integrally connected to an electrode member of opposite polarity in an adjacent cell by an integral intercell connector member. The intercell connector members extend over the associated intercell partition, preferably in a substantially U-shaped configuration.

By reason of the fact that all the electrodes of each polarity in each cell are integral, no plate straps are required and the separate formation of intercell connectors is also unnecessary since their function is fulfilled by the integral intercell connector members.

If the battery is of flooded electrolyte type it will be appreciated that it is essential that adjacent cells be completely sealed from one another to prevent intercell ionic leakage currents.

In this event it is preferred that the battery container is provided with integral intercell partitions over which or through a notch in which the integral intercell connector members pass.

The intercell connector members must then be sealed to the intercell partitions and this may be conveniently effected in the case in which they pass through a notch in the intercell partitions by hot melt adhesive or like settable material or by moulding a plastics material, e.g. polypropylene, around the intercell connector members. When the lid is sealed to the container it will then be sealed to the intercell partitions also thereby sealing the cells from each other.

The sealing of adjacent cells from each other is a time consuming and expensive operation and the invention therefore finds greater application in those batteries in which there is substantially no mobile electrolyte available for the conduction of intercell ionic leakage currents since in such batteries it is not necessary for adjacent cells to be sealed from each other. It is therefore preferred that the battery is of recombination type containing substantially no free unabsorbed electrolyte, the separator material comprising compressible fibrous absorbent material, e.g.

microfine glass fibre material, each cell being accommodated within a respective open-topped plastics bag, the adjacent walls of the or each pair of adjacent plastics bags constituting an intercell partition. Thus in this embodiment the container does not require integral intercell partitions and the function of these partitions is fulfilled by the material of the plastics bags. By virtue of the fact that there is substantially no free unabsorbed electrolyte it is not necessary for adjacent cells to be sealed from each other and the intercell connector members can therefore simply pass over the tops of the plastics bags.

The capacity of the battery is of course determined by the number of electrodes in each cell. In the simplest form of the invention in which the battery is of relatively low capacity n=1 and each cell thus includes only two electrodes of each polarity. Thus in this construction each electrode member is simply folded half way along its length and its folds intercalated with those of an electrode member of opposite polarity.

If a battery of larger capacity is required each cell will contain more than two electrodes of each polarity and it will be appreciated that this may constitute a problem in that if each electrode member is given a large number of folds in the manner of a concertina and its folds then intercalated with those of an electrode member of opposite polarity the resultant structure will comprise two electrodes of one polarity adjacent to one another alternating with two electrodes of the opposite polarity. It might be thought that a larger capacity battery could be manufactured by simply spirally winding two elongate electrode members of opposite polarity separated by separator material and then squashing the resultant structure flat to give it a shape suitable for accommodation in a battery container.

However, it is highly desirable that the connector member on each electrode member should be disposed substantially half way along its length so as to minimise the length of current paths within that electrode member. However, if the connector members are so situated and a cell is spirally wound it will be appreciated that the connector members would not be situated on the outer peripheral edge of the wound structure and thus it would be a physical impossibility for such a spirally wound cell to be integrally connected to an adjacent cell in accordance with the present invention.

Thus in a further embodiment of the present invention n=2 or more and each electrode member has n/2, when n is an even number, or (n+1)/2, when n is an odd number, of consecutive folds of one sense, the remaining folds being consecutive and of the opposite sense, the associated connector member being situated adjacent the central fold when n is an odd number or adjacent the n/2th fold from one or the other end of the electrode member when n is an even number. Thus in this embodiment the electrode members can be considered effectively to be spirally wound in one sense for substantially half their length and then spirally wound in the opposite sense for the remainder of their length.

Such a configuration results in the connector members, which are situated substantially half way along the length of the electrode members, being situated on the outer edge of the associated cell and thus permits these to be integral with a similar connector member in an adjacent cell.

For mechanical ease of folding it is preferable that the connector members are not situated precisely on a fold since this would necessitate folding them also and they are therefore preferably spaced somewhat from the fold to which they are adjacent, e.g. between 5 and 15 mm away from the fold. in the case in which each electrode member has one fold only the connector member for that electrode is of course adjacent the single fold. In the case in which each electrode member has a higher but odd number of folds, e.g. three folds, the associated connector member is situated adjacent the central fold, that is to say adjacent the second fold. When each electrode member has an even number of folds, e.g. four folds, the associated connector member will be situated adjacent either the second fold or third fold when starting from one end of the electrode member.It will be appreciated that if the electrode member has four folds the third fold from one end is the second fold from the other end and thus the connector member is adjacent the n/2th fold, that is to say the second fold, starting from one or the other end of the electrode member. It will be appreciated also that it is not convenient for the connector members to be situated precisely half way along the length of their associated electrode members but that it is convenient to position them adjacent the fold or one of the two folds closest to this centre point.

The end electrode members may be formed by casting or by expanding a metallic strip, e.g. a strip of lead or lead alloy in the case of a lead acid battery. Similarly, each integral pair of electrode members may be formed by casting or by expanding a metallic strip, and in the latter connection it is convenient to expand a metallic strip inwardly from its two edges leaving a central unexpanded land and then to remove portions from the central land and subsequently to cut the strip into expanded grid pairs connected by an unexpanded or solid strip which will constitute an intercell connector member in the finished battery. Either prior to or subsequent to cutting the strip the two expanded meshes are pasted with positive and negative active material respectively or alternatively they are both pasted with the same universal active electrode material.

Alternatively, each integral pair of electrode members may be made by continuously expanding a metallic strip over substantially its entire area and then removing spaced portions along its longitudinal centre line and subsequently cutting the strip into electrode pairs connected by an expanded metal area which will constitute an intercell connector member in the finished battery. If the intercell connector member is of expanded metal it is desirable for it to be longer than when it is of solid and unexpanded metal so that it may have the desired conductivity, and it will be appreciated that it is possible for the intercell connector member in the finished battery to extend over the intercell partition over the entire length of the latter.

Each integral pair of electrode members preferably comprises a substantially H-shaped member of which the two uprights are the two electrode members and the cross-piece is an intercell connector member which is offset from the central portion of the electrode members.

Further features and details of the present invention will be apparent from the following description of one specific embodiment of recombination battery in accordance with the invention which is given by way of example with reference to the accompanying drawings of which Figures 1 to 13 are diagrammatic views illustrating successive stages in the method of assembly of a three cell lead acid battery.

Figure 14 is a perspective view of the battery assembled as shown in Figures 1 to 13, with the lid shown to one side for the sake of clarity; and Figure 1 5 is a diagrammatic view of the electrodes for a modified construction of two cell battery in accordance with the invention.

The battery of the present invention includes two different types of electrode member, the first being an intermediate electrode member, generally designated 2 in Figure 1, and the other being an end electrode member generally designated 4 in Figure 2. Each intermediate electrode member is of generally planar construction comprising two rectangular electrodes 6 extending side by side and spaced apart and connected by an integral connector strip 8 which is slightly offset from the longitudinal centre of the electrodes 6. The intermediate electrode members may be formed by casting or by expanding a strip of lead or lead alloy. When assembling a battery having n cells, n-i intermediate electrodes 2 are required.

Regardless of the number of cells in the battery, two end electrodes 4 will be required and these may be considered as consisting of one half of an intermediate electrode 2, that is to say when severed along the centre of its connector strip 8.

The two end electrodes 4 bear positive and negative active electrode material respectively and the two halves of each intermediate electrode 4 also bear positive and negative active electrode material respectively. Alternatively, it would be possible for all the electrodes to be pasted with the same universal active electrode material.

The method of assembly commences by placing two elongate strips of microfine glass separator material 10 side by side on a work surface. These are then overlaid by an intermediate electrode member 2, as shown in Figure 1. The width of the strips of separator material is substantially the same as that of each electrode 6 of the intermediate electrode member whilst their length is approximately two and a half times that of the intermediate electrode member.

One of the sheets of separator material is then folded through 1800 so as to overlie its associated electrode 6 and extend beyond it, at the right-hand end as seen in Figure 2, by a distance equal to about half the length of the intermediate member. An end electrode member, whose length and width correspond to that of an electrode 6, is then placed on top of the folded sheet of separator material so that one half of its length overlies one half of the length of the electrode 6 beneath it, as shown in Figure 2. The other half of the electrode 6, that is to say the lefthand half as seen in Figure 2, is then folded through 1800 to overlie the left-hand half of the end electrode 4 and the right-hand half of the end electrode 4 is then folded through 1 800 to overlie the upper layer of the electrode 6, thus forming an end cell whose structure is seen in Figure 3.This end cell has two integral positive electrodes alternating with two integral negative electrodes and interleaved by the sheet of separator material.

Projecting from the end cell is a terminal connector 12 which is integral with the end electrode member 4.

The end cell is then placed within an opentopped plastics bag 22 (seen in Figure 14) and the connector strip 8 is then folded through 1800 so that the unfolded electrode 6 and the associated strip of separator material overlies the end cell, as shown in Figure 4. A further strip of separator material 10 is then placed on the work surface adjacent to the electrode stack, as seen in Figure 5, and the strip of separator material projecting from the electrode stack is then folded through 1 800 in a similar manner to the previous strip of separator material so as to overlie the associated electrodes, as seen in Figure 6.The further intermediate electrode is then provided and placed in contact with the strip of separator material which has just been folded so that one half of the length of one of its electrodes~8 overlies one half of the length of the electrodes stack, as seen in Figure 7. The electrode 6 which is contacted on both sides by separator material and projects from the stack is then folded through 1 800 so as to contact the upper surface of the second intermediate electrode member, as seen in Figure 8. The electrode 6 of the second intermediate electrode member which projects from the electrode stack is then folded through 1800, thereby forming the second cell of the battery, as seen in Figure 9 (it will be appreciated that the structure shown in Figure 8 has been turned upside down in Figure 9).The second cell is then placed in an open-topped plastics bag and the connector strip connecting the electrode stack to the unfolded electrode 6 is then folded through 1 800 so that the latter overlies the former, as seen in Figure 10.

The projecting strip of separator material is then folded through 1800, the second end electrode placed on top of it and the third or second end cell is then formed in a manner similar to the first end cell thereby producing the completed electrode stack seen in Figure 11.

The completed electrode stack is then placed in a battery container 14 (seen in Figure 14) and either before or after this step electrolyte is added to each cell in an amount which is preferably insufficient to saturate all the pores in the electrodes and separator material. The container is then sealed by a lid 16 and the terminal connectors 12 are connected to the battery terminals 18 projecting from the lid in any conventional manner. The lid carries a single vent 20 adapted to open at a superatmospheric pressure to vent all the cells.

It will be appreciated that many of the steps in the method of assembling the battery may be performed in a different order to that described above. Thus the precise stage at which the strips of separator material are placed in contact with their associated electrodes, the stage at which the completed cells are placed into a plastics bag and the stage at which the connector strips are folded may be varied to suit operational requirements.

Similarly, the electrolyte may be added to the cells either before or after they are placed in the battery container.

Figure 15 illustrates the electrodes for a modified construction which, in this embodiment, includes only two cells. There is thus one intermediate electrode member 2 and two end electrode members 4 and the microfine glass fibre separator material has been omitted for the sake of clarity. In this embodiment the two halves of the intermediate electrode member and the two intermediate electrodes each have three folds in them, in each case two of one sense adjacent to one another followed by the remainder, i.e. one fold, of the opposite sense.The intermediate electrode member has an integral bridge piece 8 connecting its two halves at points adjacent their longitudinal centres, that is to say adjacent the second or central fold in each half, whilst the two end electrode members each has a terminal connector 12 adjacent its longitudinal centre, that is to say adjacent the second or centre fold in each case.

It will be apparent from the description of the preceding embodiment that the battery illustrated in Figure 15, which may of course be extended to have as many cells as desired by the incoporation of additional intermediate electrode members, is assembled by appropriate folding and regardless of the precise sequence of folding and superposition that is utilised the method may be effectively summarised as forming each cell by spirally winding one half of it in one sense followed by spirally winding the remainder in the opposite sense and pressing the resultant structure flat, though the two winding operations may be performed whilst maintaining the individual areas of the electrodes substantially planar thereby removing the necessity of subsequently flattening the resultant structure. Of importance, however, is that the terminal connectors and bridge pieces are substantially adjacent the centre of each end electrode member and each half of each intermediate electrode member respectively so that there are positioned optimally as regards the length of the current paths within each electrode member and positioned so that they are always on an exterior surface of a cell so that they can readily be connected to a battery terminal or connect that cell to an adjacent cell.

Claims (6)

Claims

1. An electric storage battery comprising a container sealed by a lid and containing two or more cells connected in series, each cell being separated from the or each adjacent cell by a substantially planar intercell partition and containing a single positive electrode member separated from a single negative electrode member by separator material, each electrode member being of substantially sheet form with n folds in it thereby dividing each electrode member into n+ 1 electrodes extending substantially parallel to the or each intercell partition, the electrodes in each cell being of alternating polarity, each electrode member having a projecting connector member situated adjacent the fold closest the longitudinal centre point of that electrode member, the connector member of one electrode member in each end cell constituting a terminal connector and being connected to a respective battery terminal and each remaining connector member being integral with a connector member of an electrode member of opposite polarity in an adjacent cell, the or each integral pair of connector members constituting an intercell connector member which extends over the respective intercell partition.

2. A battery as claimed in Claim 1 which is or recombination type containing substantially no free unabsorbed electrolyte, the separator material comprising compressible fibrous absorbent material, each cell being accommodated within a respective open topped plastics bag, the adjacent walls of the or each pair of adjacent plastics bags constituting an intercell partition.

3. A battery as claimed in Claim 1 in which n is equal to one and each cell thus includes only two electrodes of each polarity.

4. A battery as claimed in Claim 1 in which n is equal to two or more and each electrode member has n/2, when n is an even number, or (n+1 )/2, when n is an odd number, of consecutive folds of one sense, the remaining folds being consecutive and of the opposite sense, the associated connector member being situated adjacent the central fold when n is an odd number or adjacent the n/2th fold from one or the other end of the electrode member when n is an even number.

5. A battery as claimed in any one of the preceding claims in which the or each integral pair of electrode members comprises a substantially H-shaped member of which the two uprights are the two electrode members and the cross-piece is an intercell connector member which is offset from the central portion of the electrode members.

6. An electric storage battery of recombination type substantially as specifically herein described with reference to Figures 1 to 14 or Figure 15 of the accompanying drawings.