CA1173899A - Reduced maintenance explosion damage resistant storage battery - Google Patents

Abstract

REDUCED MAINTENANCE EXPLOSION DAMAGE RESISTANT
STORAGE BATTERY

ABSTRACT OF THE DISCLOSURE
A reduced maintenance, explosion damage resistant storage battery (10), having internal means for both recombining evolved gases and for protecting the bat-tery against damage due to evolved gas ignition whether from external or internal sources is disclosed. In a first embodiment of the invention, a honeycomb-like member (60) of electrolyte-resistant material substan-tially fills the space within the battery above the battery electrodes, dividing this volume into a plural-ity of small volumes (76), surrounded by cooling sur-faces, so that ignition of one small volume (76) by an external spark or by failure of an internal battery.
component will not cause damage. A small space (20) is left above the honeycomb member (60), and a planar catalytic recombination element (78) is provided, substantially filling this space. In a second embodi-ment, the honeycomb member (60) itself is the catalytic recombination element, being formed of a hydrophobic material such as polytetrafluoroethylene impregnated with platinum or palladium, or of an inert material plated with platinum or palladium.

Description

:~'7~ 3 REDUCED MAINTENANCE EXPLOSION DAMAGE RESISTANT
STORAGE BATTERY

BACKGROUND OF THE INVENTION

This application relates to the field of storage batteries. In particular, this application relates to structure integral with a storage battery rendering it 5 explosion damage resistant, and providing gas recom-bination means to reduce or eliminate the need for maintenace in the form of water addition.
Conventional lead-acid storage batteries, such as used for heavy duty charge-discharge applications, 10 including such uses as powering industrial trucks, industrial street vehicles and mine locomotives, require frequent replacement of water. Water is iost from such batteries due to the electrolysis of the water in the electrolyte into hydrogen and oxygen, as 15 well as through evaporation. This electrolysis occurs to a slight extent during operation of the battery, but primarily during overcharge, when at least some cells of the battery have accepted substantially full charge, and additional energy supplied is expended in 20 electrolysis.
This problem is particularly severe when batteries are built for extended life, by the addition of anti-mony to the lead grids to increase the tensile strengthand retard the degradation of the positive active material. This addition also causes undesirable side effects, which increase the internal losses of the bat-5 tery, resulting in a decrease in overall battery effi-ciency, and an increased need for water additions.
This problem has largely been overcome by substituting calcium as the hardening agent for the grids, resulting in a reduced amount of required overcharge.
The gases evolved from a battery, primarily oxygen and hydrogen, combine explosively when ignited. If ignited external to the battery, the flame enters the volume of gas confined within the battery, causing an explosion of the battery. There have been numerous 15 attempts to solve this problem by keeping the advancing flame front from entering the battery by the use of porous membranes, which cooi the gases below their ignition temperature. However, in industrial applica-tions, it may occur that a severe overload may cause a 20 portion of the internal structure of the battery to melt explosively, in turn igniting the gas within the battery, and causing the battery to explode. Since the source of ignition is internal to the battery, devices which cool a flame front advancing towards the battery 25 are of no effect.
Batteries may also be provided with catalytic recombination devices containing platinum or palladium, to recombine the oxygen and hydrogen generated by the disassociation of water during the overcharge. Such 30 devices are well-known and readily availabie in the form of replacement vent caps, which fit onto the top of the battery. Unfortunately, such units require con-siderable extra space over the top of the battery and, in most cases, this additional height is not available.

~7~3~9 In batteries for electric industrial trucks, the height of the cell is at a maximum, in order to provide the maximum number of kilowatt hours of energy for a given size truck. The same consideratlons apply in railroad 5 applications, and, to a lesser extent, to automotive applications. However, in automotive applications, the addition of calcium instead of antimony as the har-dening agent for grids reduces the quantity of explo-sive gases generated and results in a battery which 10 does not require maintenance, since the life is five years or less, and sufficient additional electrolyte is initially provided to allow for losses due to disasso-ciation of the water. Obviously, this approach is not useful for batteries intended for industrial use or 15 long life.
The instant invention overcomes these and other disadvantages and problems of the prior art.

SUMMARY OF THE INVENTION
_ The invention provides a battery which is explosion 20 damage resistant whether the source of ignition is exterior or interior to the battery, and which reduces or eliminates the need for maintenance in the form of adding water to the battery by providing means for catalytic recombination of the evolved gases by struc-25 ture within the battery itself. In accordance with theinvention, the battery is rendered explosion resistant by a honeycomb structure which is fitted over the top of the plates, to separate the evolved gases into smaii pockets, which will withstand the force of the 30 resultant smaller explosions without breakage in surrounding pockets. To reduce the need for addition of water by catalytic recombination of evolved gases, a ~7~ 3 hattery according to the inven-tion is provided with a catalyst such as pa~ladium or platinum, either as a gas recombining element in the form of a flat plate containing a catalyst in a non-5 wetting material resting on the honeycomb struc-ture, or, the honeycomb structure may be made from a suitable non-wetting sintered material including small amounts of platinum or palladium, so that a single structure provides both damage-preventing 10 and catalytic recombination features.
Therefore, it is a primary object of the invention to provide a reduced maintenance, explo-sion damage resistant storage battery. It is an advantage of the invention that such a storage 15 battery does not require additional heiqht for the provision of features which render it an explosion damage resistant and reduced maintenance battery.
It is a further advantage of the invention that such a battery is explosion damage resistant 20 whether the ignition of evolved gases is external to the battery, or internal to the battery. It is a feature of the invention that a honeycomb struc-ture is disposed within the battery, resting either on top of the plates, or slightly above the 25 plates, substantially filling the space above the battery electgrolyte, and that the means for cata-lytic combination of evolved gases is located entirely within the battery.
Accordingly, the invention provides an explo-30 sion damage resistance reduced maintenance storagebattery, including a case, a plurality oE negative and positive plates and a quantity of electrolyte, and defining a first chamber between the negative and positive plates and an uppermost chamber of 35 the case. First and second strap members respec-tively interconnect the positive and negative pla-~7~
-4a-tes, and respectively include first and second post members connected to the strap members and passing through the chamber and the uppermost sur-face of the case. An explosion suppressing member 5 is disposed in the first c~amber and around both the first post member and the second post member, and defines a substantially smaller second chamher between itself and the uppermost surface, and divides the first chamber into a plurality of 10 separated gas chambers having lower ends helow the surface of the electrolyte and upper ends com-municating with the second chamber, the explosion suppressing member being a catalyst member for catalyzing the recombination of the valved gases 15 of the storage battery. The case defines a vent opening through the uppermost surface and in com-munication with the second chamber.

BRIEF DESCRIPTION OF THE DRAWI~G

FIG. 1 is a top view of a storage battery 20 according to the invention.
FIG. 2 is a side elevational sectional view taken along line 2-2 in FIG. l, showing an integral means for resisting explosion damage and recombining evolved ~'7 gases.
FIG. 3 is a side elevational sectional view, taken along line 2-2 in FIG. 1 showing a second embodiment of a battery provided with separate means for resisting 5 explosion damage and recombining evolved gases.
~ IG. 4 is a top elevational view of the means for resisting explosion damage as shown in FIGS. 2 and 3.
FIG. 5 is a top elevational view of the means for recombining evolved gases shown in FIG. 3.
FIG. 6 is a side elevational view, taken along line 6-6 in FIG. 5.

DESCRIPTION OF THE PREFE~RED EMBODIMENTS

Referring to FIG. 1, a top elevational view of a battery incorporating the invention, shows a battery 10, having a case 12. In the illustrated embodiment case 12 is made of polypropylene or polyethylene. The upper end of case 12 is covered by cover member 14. It should be noted that directional references are used for description only, and not intended as limits on the 20 scope of the invention. As illustrated, cover member 14 is joined to case 12 by sealing material 16. Cover member 14 has raised areas 18 surrounding positive posts 20 and negative posts 22. Positive posts 20 and negative posts 22 are fused to conductive inserts 24, 25 molded in the insulating material of cover member 14, thus forming a seal around posts 20 and 22.
Preferably, inserts 24 and posts 20 and 22 are made of pure lead or lead alloy. Cover member 14 also includes, as iliustrated, a central raised area 26 30 surrounding a filling opening 28 which is provided with interrupted threads 30 for retaining a conventional battery cap or vent plug, not shown.

~'7~ 9 FIG. 2 shows a side eievational sectional view of a battery 10 according to the invention, where the means for resisting explosion damage due to ignition of gases evolved from the active elements of battery 10, par-S ticularly during the overcharge portion of a chargingcycle, and the means for catalytically recombining the evolved gases, oxygen and hydrogen, is a single member. As shown, battery 10 includes a plurality of negative plates 32 and positive plates 34. To p~event loss of active material from the positive plates 34 as the battery is used, a prefabricated mat 36 of finely-divided strands of a suitable material such as glass are used. Mats 36 are held firmly against the surfaces of a positive plate 34, by mats shown as mats 38 and 15 40. Mat 36 is bonded to mat 38, which is wrapped around the faces and bottom of a pl,ate 34, and mat 40 is wrapped around the faces and sides of a plate 34, over mats 36 and 38. Thin retaining and separating assemblies 44 hold mats 36, 38 and 40 firmly in place.
Assemblies 44 include retainers which are perforated adjacent the central portion of the surfaces of plates 34, and imperforate along their bottom and side edges to prevent mossing, the growth of free lead particles at the edges of negative plates, such as plates 32, from forming a conductive bridge between plates 32 and 34. Assemblies 44 also include microporous separators extending beyond the edges of negative plates 32, nega-tive plates 32 being smaller than positive plates 34, further separating and insulating a plate 32 from a plate 34. Negative plates 32 are supported upon bridge member 46 by tabs 47 so that separators 44 extend beyond the edges of negative plates 32, further reducing the possibility of electrical shorts forming between positive plates 34 and negatives plates 32.

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Bridge member 46 is supported above the floor 48 of case 12 by support members 50, so that whatever sedi-ment does form will not build unduly high in any area of floor 48. In the view shown, tabs 52 of positive 5 plates 34 pass through perforated moss shield 54 and are joined t~ positive strap 56, made of pure lead or a lead alloy. Moss shield 54 reduces the opportunity for interplate shorts forming at the tops of the plates.
Positive strap 56 is joined to positive posts 20; and lO the connection between positive s~rap 56 and positive post 20 is reinforced by support members 58.
Explosion damage to battery 10, due to either internal or external ignition of evolved gases 5 iS pre-vented by means of flash or e~plosion suppressing means 15 here shown as a honeycomb structure 60, disposed within battery 10. hs illustrated, honeycomb member 60 rests upon positive strap 56, and on a corresponding negative strap, not shown in FIG. 2, thus having a lower edge 62 below electrolyte level 64 and an upper edge 66 which 20 is above electrolyte level 64 in battery 10. As illustrated, member 60 fills the majority of the volume of a first chamber 59 between moss shield 54 and cover member 14. As shown, a small space or second chamber 68 may be left above honeycomb member 60, to allow the 25 escape of any gases which may be evolved and not pre-viously recombined. As shown, member 60 is formed to fit closely around battery posts, such as positive post 20 and negative post 22, support members 58, and wall 70, which defines filling opening 28. ~s shown, member 30 60 has a reduced-diameter opening 72 adjacent filling opening 28, between moss shield 54 and lower edge 74 of wall 70, adequate to receive a hydrometer or ther-mometer, while reducing the amount of gas which may be contained in filling opening 28 to the smallest ~L~'73 possible amount. Evolved gas which may escape, escapes through vent openings 75 in wall 70. As can be seen, member 60 thus divides the majority of the space within battery 10 above electrolyte level 64 into a plurality 5 of individual pockets or chambers 76, each so small that ignition of gas within one such pocket will not result in any damage to battery ~0, and isolates the gas in one pocket from gases in other such pockets, to minimize and localize the explosive results of ignition lO of evolved gases. Although there is some communication between pockets 76 through space 68, it will be apparent that, due to the presence of member 60, and its thermal mass, the majority of the evolved gases within battery 10 may be held below combustion tem-15 perature even if a small volume of evolved gases israised above combustion temperature by some means of ignition, either within or without battery 10.
~ oneycomb member 60 must be made of a material which is inert to the electrolyte used, and may be made 20 of any appropriate material. For instance, it may be made of lead, to further improve its heat-absorption capability and explosion reduction capability, or, as illustrated, may include a material which catalyzes the recombination of evoived gases such as hydrogen and 25 oxygen. Platinum and palladium are well-known materials for this purpose. If member 60 is made of lead, it must be electrically insulated from po~itive and negative straps such as strap 56 by a layer of a suitable plastic material, not shown.
As illustrated, member 60 is made of a powdered material, preferably a hydrophobic material which resists flooding, and small pellets 77 of a catalyst material such as platinum or palladium mixed and molded in the form of member 60. Among the materials useful ~'o ~ 3~
g to support the peilets of catalyst material is poly-tetrafluoroethylene resin, such as is sold under the registered trademark Teflon. Other suitable moiding materials which are resistant to the electrolyte used 5 will be apparent, and may also be used.
Member 60 may also be formed of an inert material, and subsequently plated with platinum or palladium. A
member 60 plated with a catalyst, such as by flash-plating, will serve to recombine much of the evo~ved lO gas, reducing the loss of water from the electrolyte, and reducing the need for maintenance, while simulta-neously reducing the magnitude of any explosion that may result from ignition of evolved gases to a magni-tude which will not cause bursting of the battery and 15 throwing about of acid electrolyte.
FIG. 3 is a partial view of a battery 10, showing a second preferred embodiment of means for resisting explosion and reducing water loss due to evolved gases.
As in the embodiment shown in FIG. 2, a flash or explo-20 sion suppressing means here shown as honeycomb member60a is disposed within battery 10, extending both above and below electrolyte level 64. In the embodiment illustrated, honeycomb member 60a does not perform a catalytic recombination function, but mere'y protects 25 battery 10 against the results of ignition of evolved gases. A means for recombining the evolved gases is shown disposed in a space or chamber identified with the referene number 68 in FIG. 2, between the top edge 66 of the honeycomb member 60a and cover member 14.
As shown in FIG. 3, a catalyst member f~8 iS substan-tially planar, and includes a catalytic mixture 80 including catalyst pellets 82 in a hydrophcbic powder 84. Preferably, pellets 82 are of platinum or palla-dium, and hydrophobic or non wetting powder 84 is silica carbor or graphite powder treated with a hydrophobic material such as silicon or powdered Teflon. Thus, pellets 82 are supported, and protected against an uncontrolled rate of contact with evolved 5 gases. Mixture 82 is constrained between a first plate member 86 and a second plate member 88. Both first and second plate member 86 and 88 are perforated, to allow the entrance of evolved gases, the perforations being small enough to prevent the escape of catalytic mixture 10 80. Preferably, plate members 86 and 88 are made of lead, to assist in dissipation of the heat of recom-bination of the evolved gases, but can also be made of any suitable plastic.
Referring now to FIG. 4~ a top plan view of a pre-15 ferred embodiment of a member such as 60 or 60a is shown. As shown, member 60, 60a defines a plurality of honeycomb-shaped chambers or pockets 76, thus dividing the gases within battery 10 into small individual pockets. Honeycomb member 60, 60a is provided with 20 opening 90 to clear positive and negative battery posts 20 and 22, and with recesses 92 to clear support members 58, if used, and with a recess 94 to clear wall 70 of filling opening 28, as well as a reduced-diameter filling opening 72, here shown centrally disposed as 25 appropriate for the battery shown in FIGS. 1-3.
Referring now to FIG. 5 and 6, a catalyst member 78, as shown in FIG. 3, is depicted. First plate me~ber 86 and second plate member 88 are joined together at edges 96, catalyst member 78 defining a 30 plurality of openings 98, to provide for the passage of battery posts such as post 20, 24 therethrough, and a filling opening 100, here shown as a centrally-disposed filling opening. In the embodiment illustrated, first and second plate members 86, 88 are perforated by .

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shearing a portion of the periphery of a plurality of areas 102. As shown in FIG. 6, edges 104 of areas 102 are deflected inwardly, defining openings 106 which are too small to allow the escape of catalytic mixture 80.
As will be apparent, numerous variations and modi-fications of the catalytic recombination means and explosion resistant means disclosed herein will be obvious to one skilled in the relevant art, and may be easily made without further invention and without lO departing from the spirit and scope of this invention.

Claims (4)

CLAIMS:

1. An explosion damage resistant reduced main-tenance storage battery, comprising:
a case containing a plurality of negative plates and positive plates and a quantity of electrolyte;
said case defining a first chamber between said negative and positive plates and an uppermost surface of said case;
a first strap member electrically connected to said plurality of positive plates, and a second strap member electrically connected to said plurality of negative plates;
a first post member electrically connected to said first strap member and passing through said chamber and said uppermost surface, and a second post member electrically connected to said second strap member and passing through said chamber and said uppermost surface;
an explosion suppressing member disposed in said first chamber and around said first post member and around said second post member and defining a substan-tially smaller second chamber between said suppressing member and said uppermost surface;
said explosion suppressing member dividing said first chamber into a plurality of separated gas cham-bers having lower ends below the surface of said electrolyte and having upper ends communicating with said second chamber;
said explosion suppressing member being a catalyst member for catalyzing the recombination of evolved gases of said storage battery;
said case defining a vent opening through said uppermost surface communicating with said second chamber.

2. An explosion damage resistant reduced main-tenance storage battery according to claim 1, wherein:
said explosion suppressing member is formed of a plastic material coated with a catalyst material selected from the group consisting of platinum and palladium.

3. An explosion damage resistant reduced main-tenance storage battery according to claim 1, wherein:
said explosion suppressing member is made of a material which resists flooding impregnated with a multitude of bodies of a catalyst.

4. An explosion damage resistant reduced main-tenance storage battery according to claim 3, wherein:
said material which resists flooding is a poly-tetrafluoroethylene material and said catalyst is selected from the group consisting of platinum and palladium.