ELECTRIC STORAGE BATTERIES

TECHNICAL FIELD

The present invention relates to electric storage batteries and provides a novel multicell structure as well as a novel form of intercell separation and 5. interconnection of plates between different cells. BACKGROUND ART

Spirally wound single cells are known, see for example British Patent Specification No. 1531225.

The present invention has as an object the 10. provision of a multicell spirally wound lead acid battery.

Whilst developed particularly for so called sealed cell applications for the lead acid electro¬ chemical system it is applicable also to flooded cell 15. systems and is not excluded from applicability to other electrochemical couples such as alkaline systems e.g.using nickel cadmium active materials. DISCLOSURE OF THE INVENTION

According to the present invention there is 20. provided a multicell spirally wound electric storage battery in which the cells are coaxial and are divided from each other by partitions disposed transverse to the said . axis and the cells are interconnected by portions of the plates which pass through the said 25. partitions.

In a preferred form of the invention the cells are of annular form and are arranged around a central former. The battery may further include a seal between each partition and the former, outer container 30. means enclosing the outer circumference of the annular

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cells, a seal being provided between the said outer container means and the outer peripheral edge of each partition.

The battery may further include a seal between

5. each partition and the former, outer container means enclosing the outer circumference of the annular cells, a seal being provided between the said outer container means and the outer peripheral edge of each partition. In a preferred embodiment electrolyte

10. access and venting means are provided in the former for each cell.

Each current conducting element in one cell is preferably integral with a current conducting element of opposite polarity in an adjacent cell.

15. The plates may comprise current conducting elements of expanded metal and preferably the majority of the mesh elements extend transverse to the length of the strip so as to shorten the current pathways between adjacent cells.

20. The portion of the plates which extends through the partition is preferably apertured and the apertures are filled with the material of the partitions.

In this form of the invention each plate has a pair of active material carrying portions extending along

25. its length with an intercell connector portion located therebetween, the intercell connector portions having a greater cross sectional area of metal per unit length than the active material carrying portions.

A preferred form of the invention provides a

30. battery with two or more cells in which each cell

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comprises first and second layers of conducting mesh carrying active material, separated by a separator, the cells being disposed edge to edge with an intercell connector between one layer of each cell,

5. provided by a gap part of the mesh not carrying active material, and integral with the layers on either side of it carrying active material, and each constituting a plate of a respective cell.

The electrolyte impervious partition between

10. adjacent cells can pass through the intercell connector in the perforations in the mesh not carrying the active material.

Preferably each cell is in the form of a coil with the first and second layers constituting the cell plates

15. being annular, or part annular and concentric with each other. The cells are disposed side by side along the axis of the coil with the plates of adjacent cells disposed edge to edge with one another.

The invention also extends to a novel method of

20. making a battery in accordance with the invention which comprises providing a number of longitudinally extending electrode affording members with a positive active material strip along one side and a negative active material strip along the other side, direct electrical

25. interconnection being provided between the strips of opposite polarity along the full length of the electrode member, either continuously or discontinuously, a partition region free of active material being disposed between the two active material strips, and providing

30. one positive terminal strip having a continuous current

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take off band along one edge and a negative active material strip electrically connected thereto along the other edge, a partition region free of active material being disposed between the take off band and the active

5. material strip, and one negative terminal strip having a continuous current take off band along one edge and a positive active material strip electrically -connected thereto along the other edge, a partition region free of active material being disposed between the take off

10. band and the active material strip, overlapping positive active material strips with negative active material strips, with interleaved separator material and covering the free face of at least all the negative strips or at least all the positive strips with separator material,

15. presenting one end of the overlapped strips to the surface of a former and winding the assembly around the former into a pack, with separator material between contacting faces of active material, the partition region being supplied with partition polymer material

20. compatible with the material of the former and effective to produce an electrolyte impervious seal therewith, the partition polymer material being supplied in such condition and or shape as to form a continuous electrolyte impervious seal with its own juxtaposed 25. surface between each turn of the spirally wound pack whereby an annular electrolyte impervious partition between adjacent cells is formed in the fully wound cell, the partition polymer material being supplied to the partition region either before the assembly

30. is wound round the former, or whilst it is being wound round the former and providing an outer

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container forming a electrolyte impervious seal with the outer peripheral edge of each partition between the cells.

Thus, in one form of the method, the partition 5. region is provided continuously with hot melt adhesive in a hot adhesive state immediately prior to the moment when the portion of the region which is being supplied with hot melt adhesive is pressed against the outer surface of the hot melt adhesive in 10. the barrier region previously supplied and already wound.

The former is preferably provided with electrolyte access and venting means disposed opposite each cell. The access and venting means may be a single hole 15. for each cell which is occluded by a resilient lining tube.

Alternatively separate electrolyte access and venting means may be provided for each cell.

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BEST MODE OF CARRYING OUT THE INVENTION "

The invention may be put into practice in various ways and a number of specific embodiments will be described to illustrate the invention with reference to the accompanying drawings in which: 5. Figure 1 is a perspective view of an individual grid element;

Figure 2 is a cross-section of an array of two terminal grids and two intermediate grid elements prior to winding; 10. Figure 3 is- a perspective view of the arrangement shown in Figure 2 showing the central perforated • former around which the element assembly is wound, Figure - is a view in the same sense on a reduced scaie showing the finally wound construction 15. wrapped in εn encapsulating plastic εheeτ;;

Figure 5 is a longitudinal cross section of a former for use in the invention and shows a flexible liner which provides the seal for the vents to ^* individual cells; 20. Figure 6 is a cross section of the wound path showing a stepped former;

Figure 7 shows an alternative arrangement of stepped former;

Figure 8 shows in diagrammatic cross section 25. a modified form of sealing arrangement between cells in which the intercell conductor is provided with a channel section in which the sealant is located;

Figure 9 is an enlarged cross section to scale of the arrangement shown in Figure 2; 30. Figure 10 is a vertical cross section of a fully

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wound and encased battery in accordance with the invention; and

Figure 11 is a diagrammatic longitudinal section of apparatus for carrying out the winding of the battery.

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Referring now to Figure 1 , the grid strip comprises a perforated strip grid,preferably a slit expanded mesh grid, having a plastic member 20 extending down its length along its centre, this 5. being the basic form of the grid element referred to as an intermediate grid element above. Terminal elements are similar except that one half of the expanded mesh is replaced by a longitudinal selvedge of solid metal to which the current take-off 10. tabs or members are connected. The end element thus has a central continuous plastic member 20 which will eventually constitute the cell partition.

The positive half of the expanded grid ^" strip is labell

21 and the negative half of the expanded grid strip 22. 15. It should be noted the expanded grid strip 21,

22 extends right through the partition element 20 providing continuous electrical inter-connection between the positive and negative elements of each grid element and thus minimising intercell connector

20. resistance. Referring again to Figure 2, the multi¬ element assembly is made up by overlapping the positive strip 21 of one individual grid element with the negative strip 22 of another individual grid element, the elements having their members 20 running

25. parallel to each other. A separator 25 is placed between the juxtaposed positive and negative elements and separator material is also provided on one or other of the back or front faces of the whole assembly so that when wound the elements are also 30. separated from other in the wound assembly. In the

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Figure 2, arrangement this is done by providing an envelope of separator material around each of the negative elements 22. This envelope extends up to the edge of each member 20 and if desired can either 5. be left open at its ends or sealed at its ends by an appropriate adhesive, or in the case of a thermoplastic separator element, by welding. If the separator material is thermoplastic then it may also extend across the intercell elements 20 and

10. be sealed to it so as not to interfere with the integrity of the intercell seal. Clearly the polymer used in the separator must be compatible with that used in the member 20 so that an effective seal is formed. There may be some

15- advantages also in enveloping the positive plate so that in arrangements where the plates are orientated in the battery in use in a vertical plane the bottom of the envelope around the positive will act to retain any active material shed from the

^' 20. positive and thus minimise bridging of the plates in the individual cells. Referring now to Figure 3, the assembly shown in Figure 2 is shown in position prior to winding around a central former 30. This is made of a tube of a resin compatible with and

25. effective to form a seal with the resin of the member 20. For example the members 20 may be a polyolefin e.g. a polyethylene based hot melt composition and then the tube 30 will be made of a compatible polyolefin based composition. The tube 30 is provided

30. with holes 31 extending through its wall and positioned

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so as to be juxi-aposeα to the overlapped grid elements 21 and 22. Grid elements 21 and 22 are preferably- perforated prior to assembly into the configuration shown in Figure 2 and the perforations 42 are spaced from the

5. end at which the winding has started in such a way as to be essentially juxtaposed to each other although exact overlap is not needed. Logarithmic spacing of the holes would therefore -be appropriate. Clearly the separator must not be punched since otherwise treeing

10. through between the positive and negative plate could very readilj- occur.

The punching of the grid strips is done after pasting. These holes 42 provide a duct 43 through which electrolyte entering the cell through the holes 31 in

15. the former 30 can more readily gain access to the intεrio: of each cell. The tube jp is preferably provided with a step as shown in the cross-section in Figure 5 since this assists in the location of the multi-element assembly shown in Figure 2 at the beginning of the

20. winding operation. Indeed it night be that a _# slit would be formed or a notch formed in the former 30 so as to positively grip the ends of the multi-element assembly and further assist automatic winding of the array. Figure 6 identifies the step by the reference

25. ^-0. .An alternative stepped arrangement is shown in Figure 7 in which the thickness cf the tube is built up on its external diameter so that its internal profile is circular. This is of advantage in connection with the sealing arrangement which is

30. shown in Figure 5 and can conveniently be used to provide a sealed form of battery using this inventive concept. The arrangement shown in Figure , Figure 5 and Figure 7 can have its electrolyte

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content added to it after winding and this permits dry winding which is advantageous from the point of view of retaining the strength of the separator material and ease of handling. The electrolyte 5. may be added to the battery by injecting a measured quantity of electrolyte into the central tube 32 of the former 30 and then either allowing the electrolyte to percolate outwardly or preferably rotating the assembly around the longitudinal axis

10. of the tube 30 so as to force the electrolyte out under centrifugal force into the individual cells. After this measured volume of electrolyte has been taken up, or if preferred after decanting any surplus not absorbed by the assembly, the central

15. tube 32 of the tube 30 can have a close fitting rubber sleeve 35 pushed into place and this will then act as a pressure release valve during any gassing which may occur during high overcharge conditions during use of the cell but at the same

20. time will prevent electrolyte leakage of any substantial extent between the individual cells. In an alternative arrangement the assembly is wound with the paste wet.

It should be explained that a variety of tech-

25. niques are available with regard to the sequence of operations in making up and wάnάing the cell elements. One possibility is to paste the strips leaving an open region between the positive and negative strips, then apply the hot melt adhesive to

30. the strip between the positive and negative pastes

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and then wind the assembly with the paste wet. Another alternative is to dry the paste prior to applying*the hot melt adhesive. A further alternative is that instead of hot melt adhesive one could 5. use some other form of activatable resin composition capable of forming a seal with the resin of the tube 30. It should be appreciated that the portion of the mesh between the positive and negative paste strips will be fully inter-penetrated by the members 20 so

10. as to form an effective seal between the positive and negative halves of the individual cell element.

In a further alternative the region around which the member 20 is formed could be an unperforated, unexpended strip extending down the centre of the the

15. mesh element. Two other possibilities for forming the member 20 are to form a basic strip of polymer whic may or may not be sealable to the polymer of the element 30 down the central portion of the element before pasting, achieve the pasting and

20. then clean the surface of the member 20 ready for attachment to the tube 30. An alternative to this possibility is to apply a masking film e.g. a masking tape or some polymer film which will adhere to the polymer of the member 20 in this form, paste

25. the element, remove the masking film and then achieve the sealing. A further modification to this alternative is to apply a bead of hot melt adhesive or other resin of improved compatability and sealing properties with the polymer of the member 30 after

30. pasting has been carried out. Figure 9 shows a cross-

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section to scale of the arrangements shown schematically in Figure 2. The members 20 here are shown as being formed either of hot melt adhesive or of epoxy resin. The structure when using hot melt adhesive utilises 5. its good sealing properties with lead when held under compression. In a further arrangement shown in Figure 8 the sealing of successive turns of members 20 is facilitated by the forming of the conductor in the region of the member 20 with a V or other duct

10. section and filling this section with the hot melt ad esive immediately prior to the moment of the members 20 being juxtaposed to each other so that the resin in one duct is pressed into the back of the preceding duct. Apparatus appropriate for carrying

15. out this aspect of the invention will be described below.

Figure 10 shows a vertical cross-section of a fully wound and encased battery assembly. It will be seen that the cell elements are wound around

20. central former 30 with positive and negative plate elements being juxtaposed and separated by separator sheets 25. The positive tabs 23 are connected to a radial terminal bar 37 which has an axially extending positive take off tab 36 positioned

25. adjacent one end of the tube 30. The negative take off tabs 24 are similarly connected to a terminal bar 8 affording a tab 39. The regions 20 are fused both to the tube 30 and to each other to form an integral intercell partition between adjacent cells,

30. there being three cells stacked one above the other

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in disc form in the battery. The tube 30 has electro¬ lyte introduction holes 31 and it will be seen that these are juxtaposed to perforations formed in the pasted positive and negative plates which form more 5- or less continuous radially extending channels 40 shown in dotted lines in the right hand half of the drawing. The wound assembly is encapsulated in an appropriate sheet 41 which may be of a polymer compatible with the resin 20 so as to be heat sealed

10. thereto or could merely be a shrink wrapped can. In addition a further shrink wrapping could be provided outside. In a further alternative the member 41 is both shrink wrapped and heat sealed simultaneously to the outer ring of the members 20 and the

15- material 41 may be of the order of .005" τhick. The wrapped assembly would then be placed within an appropriately dimensioned outer canister and appropriate end seals provided, for example by • potting in hot melt adhesive or epoxy resin or

20. forming a close fitting dish nesting over the terminals and take off lugs and then potting in an appropriate resin. It should be appreciated that the central core of the former 30 may be provided with appropriate venting means for example the rubber

25. tube 35 described above with reference to Figure 5. The cell can then be provided with a small aperture at one or both ends rather than needing a separate venting arrangement to be incorporated within the end closure. Of course additional venting provisions at

30. the ends of the cell are not υrecluded and in

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environments where flame proofing is required these venting arrangements can be provided. Indeed, if overally dimensions are critical this venting or additional venting could be located within the ends 5. of the tube 30.

The method of assembly of the battery described above is as follows:

Referring to Figure 3 four strips of lead sheet are expanded, preferably the expansion method being

10. such as to ensure that the majority of the strands run transverse to the length of the strip rather than along the length of the strip. For the Figure 3 arrangement two strips will be terminal strips having one expanded portion and one solid edge

15. portion and the other two strips will be expanded on both sides. The negative terminal stπp is then pasted with positive active material on its left hand side and the two intermediate strips with • negative active material on the right hand side and

20. positive active material on the left-hand side and then the left-hand edge strip is pasted v/ith negative active material on the right hand side. Alternatively a universal paste can be used. The first strip is then fed to a conveyor belt and separator material

25. folded round the positive strip from a feed coil.

The second strip is then overlapped onto the enveloped positive, its positive enveloped v/ith separator material and the third strip laid down with its negative strip over-lapping the previous enveloped

30. positive strip. The positive strip of this cell

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element is then enveloped in separator and left-hand edge strip laid down with its negative laid over the positive of the previous cell element. The multi-element assembly is then fed along a conveyor 5. 100 as shown in Figure 11 beneath a multihead hot melt adhesive supplying station 111 positioned closely before the location of the core 30 in a winding mechanism having a belt 110. Four ribbons of hot melt adhesive composition are laid down on the

10. unpasted regions between the positive and negative paste strips of the multi-element assembly. Figure 11 shov.'s the winding mechanism which we prefer to use. The core 30 is of the form shown in Figure 7 having an external step against which the

15. input end of the multi-element assembly is butted. The hot melt adhesive is squeezed between the outside surface of the former 30 and the multi¬ element assembly by the tensioning force of the'wind¬ ing mechanism. Thus the winding mechanism has an

20. upper front roller 105 and a lower front roller 106 the upper one of which is mounted on springs, as may be the lower one if desired, so that variable tension can be applied to the belt as it passes round the major proportion of the circumference of

25. the former 30. The tensioning of these rollers also permits them to move apart as the radius of the wound pack increases as the winding progresses. The belt then passes round tv/o rear rollers, upper 107 and lower 108, and around a tensioning idler roller

30. 109 as well. It will be appreciated that the ribbon

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of hot melt adhesive is carefully juxtaposed to the unpasted area of the multi-element assembly.

Once the pack has been wound to its specified dimensions it is ejected from the winding mechanism

5. and secured in place by either an adhesive wrapper or by the adhesive effect of the ribbon of hot melt adhesive. If an adhesive wrapper is used this can merely be attached to the end of the multi-element assembly and then the winding mechanism will

10. automatically wind this round the pack. The secured pack is then ejected and may be shrink wrapped prior to placing into the protective canister.

Whilst the cell has been described as being cylindrical, thus having a circular cross section,

15. it will be appreciated that the advantages of ease of assembly and reduced intercell connector lengths can still be obtained even when other cross sections are used.

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The cells may be filled by immersion in electro¬ lyte and evacuation of air from the assembly. Alternatively the electrolyte could be injected into the cells, e.g. , under pressure. It is desirable for each cell to have at least two vents, one through which the electrolyte could be introduced and one through which the air could escape. If necessary, one or both of the vents can be sealed after introduction of the electrolyte and charging. Reference has been made above to expanded lead material, whilst this is preferred the electrode pairs could be made from thin cast grid form or wrought form or from fibrous supports provided with electrically conductive coatings or deposited conductors such as are dis- closed in the present applicants British applications Nos. 9876/76 and 15664/76. The grids are preferably 0.1 to 1.0 rams thick especially 0.5 to 0.8 mm thick. The preferred alloy is a lead calcium tin alloy prefer¬ ably containing 0.075 to 0.13 e.g., 0.08 to 0.09% calcium and 0.34% to 0.79% tin e.g., 0.4 to 0.8 of tin.

Alternative alloys include 99.9% lead and antimonial alloys such as those disclosed in United States patents Nos. 3879217 and 3912537.

As mentioned above, the individual electrode element or electrode pairs are preferably pasted with a universal paste composition since half of the electrode pair has to be converted to positive active material in one cell and the other half of the electrode pair has to be converted to negative active material in the adjacent cell. The mid point of the strip is left unpasted right

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across its width for a few rams e.g., 0.5 to 10 rams or is cleaned after pasting, since this is the region at which it will pass from one cell to the other and the region where it it wished for the barrier or potting compound to form a seal.

One suitable universal paste composition comprises;

60lbs of Hardinge grey oxide

12 grams of fibre

82 grams of Vanisperse CB (a lignosulphonate material)

3.47 litres of water

1.93 litres of 1.400 sp. gravity sulphuric acid.

This is readily converted electrochemically in the cell either to positive or negative active form. Details of Vanisperse C.B. are given in British patent specification No. 1396308.

Any desired separator material may be used such as a dense fibrous material e.g. fibreglass or a microporous polymer sheet e.g. , PVC but thin separator materials are preferred.

Especially for (so called) sealed cells, the separator is selected to have a good moisture retention, a good rate of wicking i.e., it picks up and permits liquids to wick rapidly through it by capillary action and a good gas (especially 0_) permeability so as to retain electrolyte within its pores readily and also permit rapid passage of gas through it even when contain¬ ing electrolyte. Dense glass fibre mats are especially satisfactory in these respects, for example, non-woven mats of very fine short staple glass fibres e.g, 0.2 to

10 microns in diameter and having surface areas of 0.1 to 20 square metres per gram of silica are very suitable. Dense mats made from such fibres, whilst being flexible and having high electrolyte absorption properties, also can have porosities as high as 85 to 95%.

Alternatively the separator material 25 may be about 0.2 rams thick a'nd have a tensile strength in the

2 2 machine direction of 150 Kgs/cm and 130 Kgs/cm in the transverse direction an average pore size of 1 micron and an elongation at break of 100% in the machine direction. Such a material is madeby biaxially stretch¬ ing a chill roll cast film of high density polyethylene and is sold by the Sekisui Chemical Co. as PCM separator film.

The separator material may thus have a thickness in the range 0.1 to 0.3 rams, a tensile strength of 15 to 200 preferably 50 to 160 Kgs/cm 2 , an elongation at break of 50 to 150%, a Gurley stiffness of 1 to 50 mg preferably 5 to 20 mg and a pore size of 0.1 to 10 microns preferably 0.5 to 5 microns.

Any potting material which has an adequate resistance to attack by acid and can ^' form an electrolyte resistant seal with lead may be used for the partitions between cells and for the seals, but epoxy resins and polyolefin based hot melt adhesives are satisfactory.

Suitable polyolefin hot melt adhesives include those comprising: A. A high molecular weight polyolefin component

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e.g., polyethylene or polypropylene providing viscocity to the melt and cohesive strength to the solid,

B. as a tackifying agent, a synthetic or natural resin, e.g., a wood resin or a derivative thereof to add tack and fluidity and premote wetting action,

C. a plasticizer, e.g., a paraffin wax to lower the viscocity of the mixture for easier application, and

D. a small amount of an a tioxidant.

One suitable proprietory hot melt adhesive is that sold by Eastman Kodak as EASTOBOND A381S which is a polyolefin based material. Aς3.2_ As an alternative to universal paste the positive expanded mesh may be made and pasted separately from the negative expanded mesh of each electrode pair and they may be joined by a continuous seam weld 1 - 5 rams wide by means of overlapped perforated solid selvedges 2 to 10 rams wide. The selvedge can have 1 circular perforation 1 - 5 mms in diameter each 1 cms.

Each positive mesh before pasting preferably has more lead e.g., 5 to 20% more lead, than the negative mesh. The positive electrodes may be pasted with the following paste composition:

1000 kgs Activematerial comprising 40% lead and 60% lead monoxide, 297.9 litres water, 156.1 litres sulphuric acid (1.4 sp.gr.) and 4.5 kgs of amorphous silica (Gasil 23) .

The negative electrodes may be pasted with the following paste composition:

1091 Kgs. leady oxide, 302 kgs. of Vanisperse CB lignosulphonate, 5.5 kgs. of Barium sulphate,

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0.23 kgs. of Fibre, 0.57 kgs. of antioxidant (stearic acid), 1.8 kgs. of carbon black, 122 litres of water and 70 litres of sulphuric acid (1.4 sp.gr.).

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INDUSTRIAL APPLICABILITY

The battery system of the _. present invention may be used for conventional sealed cell applications such as in hand held powered tools where the ability to function in any orientation is required. It may also be used when appropriately dimensioned as a car starter battery and may be either sealed or flooded for this application. It-may also be used for floating charge standby applications.

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