Patent Application
20070015021
1. Field of the Invention
The present invention relates to electrochemical cells. More particularly, the invention provides a planar, metal-air canless bi-cell and a battery containing a multitude of said cells. The word “can” in the context of electrochemical cells is a recognized term in the art and the term “canless” as used herein refers to a cell using its active components as an outer casing.
2. Related Art of the Invention
The important desired properties of electrochemical cells are high energy and power per cell weight, and per cell volume, a flat discharge curve, and reasonable shelf life. Energy density, per weight or per volume of a defined cell is not a fixed value, as much depends on the rate of discharge being near the design discharge. For example, a cell of the type used in a wristwatch is required to supply a very low current over a period of about 5 years, while a cell used in a torpedo needs to supply a high current for a few minutes only. Furthermore, some cells operate best, or only at all at temperatures far removed from room temperature, and also there are applications where cost is, or is not an important consideration. To accommodate such varied requirements, many different types of primary and secondary batteries apart from the original lead-acid have been developed, for example the nickel-cadmium, silver zinc, zinc-nickel zinc-oxygen and zinc air, the latter being the subject of the present invention.
Battery cells are usually supplied with an outer casing which takes no part in chemical reactions taking place. The casing does however add both weight and volume, which is an important consideration in vehicles, particularly in aerospace applications. An important application for batteries of the type relating to the present invention is for powering unmanned aerial vehicles and running auxiliary equipment, such as cameras, navigation instruments, radio controls etc. of unmanned aerial vehicles (drones.)
The present inventors have previously disclosed new designs of zinc-anode cells.
In U.S. Pat. No. 5,366,822 we disclosed a zinc-air cell of a type which is suitable for use in an electrically-propelled road vehicle. The improvements detailed include improved air flow across the air electrodes, loss-free electric terminals and arrangements for rapid exchange of exhausted anodes.
Further, in U.S. Pat. No. 5,445,901 we disclosed a Zinc-oxygen battery which is also intended for vehicular use, particularly sea-craft, and is sufficiently compact for use in torpedoes. The primary improvement of this patent was the addition of thin plastic sheets or films between adjacent cathodes. One of the functions of said sheets was to divert water droplets formed by condensation away from the cell and into dead space of the battery casing.
While the designs described in the above-mentioned patents were satisfactory for their intended use, the acute demand for weight reduction, and to a lesser extent also volume reduction posed by aerospace applications are difficult to satisfy with the cells referred to which are provided with a frame.
It is therefore one of the objects of the present invention to obviate the disadvantages of prior art zinc-air cells and to provide a thin, flat, canless cell having high W-hr/kg and W-hr/dm3 ratios, typically both ratios being above 150 as measured when used in a practical battery.
It is a further object of the present invention to provide a thin, flat, canless zinc-air cell having high W/kg and W/dm3 ratios, typically both ratios being above 100 as measured over a continuous discharge in a practical battery.
It is a further object of the present invention to provide a compact cell suitable for use in unmanned aerial vehicles.
The present invention achieves the above objects by providing a substantially flat, planar, metal-air canless bi-cell having two major surfaces formed of oppositely-disposed spaced-apart gas-permeable liquid-impermeable air-electrode cathodic material, defining therebetween a space containing a fluid anodic material comprising anodic metal particles and electrolyte.
In a preferred embodiment of the present invention there is provided a planar metal-air canless bi-cell wherein said two major surfaces are formed of a single air-electrode cathodic material folded upon itself.
In a most preferred embodiment of the present invention there is provided a planar metal-air canless bi-cell having a thickness of about 2 to 15 mm and a length and a width exceeding said thickness.
Also, the invention includes a battery formed from a plurality of planar metal-air canless bi-cells as described.
Yet further embodiments of the invention will be described hereinafter.
It will thus be realized that the novel bi-cell of the present invention in its thinner embodiment can be bent, formed or shaped to satisfy the space restrictions met in unmanned vehicles, such as drones and torpedoes.
In preferred embodiments of the present invention, said fluid anodic material is a pumpable material which is added after the formation of the electrochemical cell just before the sealing thereof.
In other preferred embodiments, the anodic metal particles can be first introduced after which the electrolyte, usually dilute aqueous KOH, is added in the factory, or added immediately prior to use.
With regard to a battery comprising such cells, the cells will be interconnected through their terminals in a manner similar to other batteries. The series-parallel connection is arranged according to the voltage and current which the battery is intended to deliver.
As will be realized, the present invention also is directed to the technology of sealing a prismatic primary metal air bi-cell. The seal of a prismatic cell is by far more complicated than the seal of a rounded cell in that in a round cell, the seal is carried out in one plane and can be achieved by application of central forces while heretofore, in a prismatic cell, the seal has to be on each edge of the cell, and has to overcome the discontinuity of the seal in the cell corners.
The present invention obviates this problem by providing a sealed cell without the use of any metal cans. Thus, the parasitic weight of the assembled cell is substantially reduced.
The present seal design also allows the building of a cell having a footprint which is very high compared to its thickness, where in cell length and width are at least twice the cell thickness, and theoretically has no upper limit and thus allows the cell to deliver high power.
Furthermore, the seal design allows the building of a cell without any footprint geometry to fit any application geometry.
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In the drawings:
There is seen in
The cathodic material is typically composed of a catalyzed carbon and a metallic current collector. The cathodic material is preferably covered externally by a gas permeable hydrophobic film such as Teflon, and internally by a separator such as a non-conductive ion-permeable film (not shown).
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Any joining method that is resistant to a mild alkali may be used.
In reference to the following Figures, similar number will be used to designate similar features referred to in the previous Figures.
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The components discussed above can be made of any suitable material known per se in the art and the rivets are preferably made of stainless steel while the plastic cup-like element 48, the support plug 56, the internal frame 14, and plug member 46 are all preferably made of a plastic such as Plastic Noryl®.
As is known per se in the art oxygen reaches the active area of the cell by either diffusion or forced means e.g. a fan or RAM air of a moving vehicle.
The finished cell 2 has a thickness usually in the range of 2-15 mm. The length and width of the cell, which determine the cell W-hr capacity and W power, exceed the thickness thereof, typically by at least a factor of 3.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
