Zinc air battery and its uses

[00002] This application is a continuation of U.S. patent application Ser. No. 09/200,398, filed Nov. 24, 1998, now abandoned, which claims benefit of Provisional Ser. No. 60/105,415, filed Oct. 23, 1998.

[00003] The invention relates to the fields of portable high-density energy sources and small batteries capable of high power rates. It also relates to cochlear implant systems and to functional electric stimulation (FES), electric stimulators and to muscle and nerve stimulators (neuromuscular stimulators).

[00004] Certain types of biological tissue stimulators, such as heart pacemakers, have a low duty cycle, and draw relatively little power over the course of some time frame, say, an hour. On the other hand, other biological stimulator types have a higher duty cycle, and may thus draw relatively higher power. Such higher power stimulators include, for example, a class of cochlear implants, as well as electrical stimulators for muscles and for nerves, such as in the case of stimulators for muscles which have their nerves inoperative because of trauma or degenerative illnesses, or, for nerves which may not be receiving normal synaptic input from the other ordinarily incoming other nerves, because of loss or disconnection (i.e., severing of those other nerves). For example, the spinal column nerves may be severed at some point, and the restoration of function below the cut area may be enabled with high-powered electric stimulators. These functions may include lower gastrointestinal (GI) function, urinary functions, sexual functions, and walking and limb movement functions, all of which may be served by functional electrical stimulators (FES) or other neuromuscular stimulators.

[00005] Today's primary battery sources tend to be of not high enough energy density, or if high enough energy density, too expensive and too large for any real use as a primary battery for any of the uses and systems above. Consequently, there is a real, unmet need for such systems, and such a power unit. A high amount of energy stored in a small space is a high energy density apparatus. Such an apparatus can potentially supply a high amount of energy per unit time (power) before it is exhausted. The current teaching of the art is away from this high energy density, relatively cheap, primary battery and systems which utilize it, and toward small, relatively low energy density, rechargeable batteries.

[00006] The present invention addresses the above and other needs by providing a primary battery for use in the systems above that is prismatic in shape, small in size, and inexpensive to make.

[00007] In accordance with one aspect, the invention provides a method for increasing the airflow to a zinc-air battery such that the energy density is 500 mwh/cc to 1000 mwh/cc. This thereby allows the battery to be used for approximately 8 to 16 hours as a primary (throwaway) battery, with, for example, high-duty cycle, high-drain cochlear implants, and neuromuscular stimulators for nerves, muscles, and for nerves and muscles together.

[00008] In accordance with another aspect of the invention, there are provided medical stimulation systems and methods incorporating a high energy density source, e.g., a zinc-air battery having increased airflow. Therefore, advantageously, due to the small prismatic shape and small size of the power source, such systems can be housed in a much more compact and useful space than has heretofore been possible. Moreover, due to the cost of the power source, it represents an inexpensive, i.e., a $1.00 per day, throw-away primary battery that may be used in systems directed toward helping people hear again, walk again, and regain body functionality which they may have otherwise lost permanently.

[00009] One embodiment of the invention may be characterized as a small high energy density battery having a rectangular solid shape with dimensions of approximately 8 mm thick by 20 mm long by 17 mm wide. Such a small prismatic shape allows it to fit slidingly into a behind-the-ear external speech-processing component of a cochlear implant system. Hence, while existing cochlear implants systems use belt-mounted batteries and speech processors, the system of the present invention with its new high-density energy source allows the belt-mounted batteries and speech processor to be dispensed with and to be replaced by a lightweight behind-the-ear (BTE) unit.

[00010] The casing of the high energy density source includes a non-reactive plastic or other non-reactive material, which contains small holes in it. Or it is in part, or, whole, permeable to air allowing a sufficient flow of air to enter so that the air may react with the zinc in the zinc-air battery configuration to produce the desired power. A characteristic feature of a zinc-air battery is that the energy produced by the battery results from a reaction between the oxygen in the air and zinc. Moreover the amount of energy produced is, in large part, a function of how much air is flowing to the air electrode part of the battery.

[00011] Smaller “button” batteries of the zinc-air type disadvantageously have high series equivalent impedance. In order to get a higher current and power and lower impedance from this battery type, a larger size is needed. Prior teaching is toward a small size because the amount of air required for a smaller battery is more easily accomplished, while the casing of a larger battery makes it impossible to supply the required air. The present invention advantageously overcomes these difficulties and provides a lower impedance battery in a small prismatic package having higher energy density than has been heretofore achieved.

[00012] Thus, with the invention herein, a whole new area is opened up for neuromuscular electric stimulation, as well as for cochlear implants, requiring a small, high energy-density source.

[00030] The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is merely made for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.

[00031] As in FIG. 1a, the zinc-air battery (11) may be slid into a battery receptacle (13), for example, as in FIG. 1b, of a behind-the-ear unit of a cochlear implant system (12). As shown in FIG. 1c, in another embodiment, the zinc-air battery (111) slides into the battery holder of the BTE (112) part of the cochlear implant system, as in FIG. 1d. The electrical contacts (113) of the BTE (112) unit mate by simple spring pressure to the corresponding contact points on the zinc-air battery (111), which are not shown. A third embodiment is shown in FIG. 1e, with the zinc-air battery (1111) slidingly mating with the BTE battery holding case (1114) as shown in FIG. 1f. The battery case (1114) has large air openings (1112) as well as spring loaded electrical contacts (113) which contact corresponding electrical contacts on the battery (1111).

[00032] The zinc-air battery uses the oxygen from the air as one electrode and a consumable metal, zinc, as the other electrode. The electrochemical reaction is mediated by a suitable electrolyte. A principal advantage of the zinc-air battery is that the weight and volume of the battery are cut way down, because one electrode is consumable, ambient air, and an amount of a second metal corresponding to that of the first electrode need not be included. However, to get the air to the electrochemical reaction, provision for the air to come into the battery, e.g., holes, permeable membranes, and airways or such, need to be provided.

[00033] In the range of zinc-air battery weight, size, and power considered for the present invention, more provision for air entry is required than in a simple button battery. That is, a simple hole will not suffice to provide the necessary air transport. On the other hand, an air management system with fans, and possibly coolers and heaters and active desiccator(s) and/or humidifier(s), would be prohibitive in expense, size, and weight for the batteries in the present invention, but would be suitable for the ease of some larger zinc-air batteries.

[00034] An embodiment shown in FIG. 2a uses small holes (21) in a rigid case (22) to enable and facilitate the diffusive transport of air to the zinc-air battery unit in sufficient quantity. The sufficient quantity is such that a zinc-air battery of the sizes (32), (36), shown in FIGS. 3a and 3b, operates in the required power flow range. The quantitative sizes are discussed in the third paragraph below, in conjunction with FIG. 3a and FIG. 3b.

[00035] Another embodiment (FIG. 2b) uses a permeable membrane (24) supported by a rigid frame or case with a case with areas cut out (23). Another embodiment (FIG. 2c) shows small pipes (25) connected through the case (26) to the outside air. These small pipes (25) have small holes (27) where the pipes are internal to the battery in order to enable the air to diffuse to more places internal to the battery case (26). Another embodiment (FIG. 2d) uses permeable membrane(s) (28) over open areas in the small pipes (25) to enable the air transport.

[00036] In all embodiments of this invention, care is taken to prevent the electrolyte, typically corrosive, such as ammonium chloride, potassium hydroxide, or neutral manganese chloride, from leaking out. Any leakage of the corrosive electrolyte could potentially harm the patient. Therefore, typically, many small, laser-drilled holes are used, which acting together with the surface tension of the electrolyte and a hydrophobic coating material such as carbon black is used to prevent electrolyte escape. Another embodiment utilizes a membrane such as tetrafluoroethylene (DuPont TEFLON) to allow the entry of air, but prevent the escape of the electrolyte.

[00037] One embodiment (FIG. 3b) of the invention is a rectangular solid shape with dimensions 6 mm (±20%) thick (38) by 25 mm (±20%) long (36) by 17 mm (±20%) wide (37), such that it can fit slidingly into a behind-the-ear (BTE) external speech-processing component of a cochlear implant. An example of an implantable cochlear stimulator is described in U.S. Pat. No. 5,603,726, which is hereby incorporated by reference. An example of a type of BTE is described in U.S. Pat. No. 5,824,022, that is hereby incorporated by reference. The positive (39) and negative (399) terminals are shown. Another embodiment (FIG. 3a) of the invention is a rectangular solid shape with dimensions 6 mm (±20%) (31) thick by 20 mm (±20%) long (32) by 10 mm (±20%) wide (33). The positive (34) and negative (35) terminals are shown. Many cochlear implants use belt-mounted batteries and speech processors. The new high-density energy source allows these latter to be dispensed with and replaced by a lightweight behind-the-ear (BTE) unit.

[00038] FIG. 5a shows details of how the battery and its case are situated in the BTE cochlear implant system battery receptacle. The BTE battery holder (51) uses stand-offs (52) to allow the zinc-air battery (53) to be surrounded by air spaces (54). These air spaces allow the permeable surface (55) of the zinc-air battery (53) to have a sufficient air supply. A similar case is shown in FIG. 5b, except that here one or more standoffs (56) are keyed so as to place the positive and negative terminals of the zinc-air battery (53) correctly. FIG. 5c shows another embodiment of the BTE battery receiving housing (51) for providing air access to the zinc-air battery (53). Different surface structures such as (57) with perforations on the inner and outer layer of the BTE battery receiving housing, with a baffle unit (578), structure (58) with perforation (577) and baffle unit (578), structure (59) with perforation (577), and structure (599) with perforation (577) and permeable membrane (5999).

[00039] The zinc-air batteries typically have, in the uses cited, a flat electrode geometry. In that case, the air holes and air tube ducts are arranged so as to lead oxygen (in the air) to the air electrode and to return the air which is slightly depleted in oxygen after reacting with the zinc via the battery electrolyte. In another embodiment, the electrode pairs may be cylindrical or piecewise planar. In these cases, the air holes and/or ducts are arranged to maximize the transport of air to and from the air electrode.

[00040] A further embodiment utilizes the small tubes and tubules as mechanical elements to help prevent the desiccation in a dry ambient condition (approximately, below 40% relative humidity).

[00041] Similarly the same mechanical structure is used to help prevent “flooding” of the electrolyte, too much water in the electrolyte when the ambient conditions have high humidity (approximately, above 60% relative humidity).

[00042] The permeable membrane embodiments also may act to prevent desiccation and flooding, as well as to prevent carbon dioxide and other contaminants, such as tobacco smoke from entering the battery and decreasing its efficiency.

[00043] The invention is a method as well as an apparatus for increasing the air flow to a zinc-air battery such that the energy density, approximately, is from 500 mwh/cc to 1000 mwh/cc allowing about 8 to 16 hours use as a primary (throw-away) battery. It is designed for and is particularly good for use with, for example high-duty cycle, high-drain cochlear implants, and neuromuscular stimulators for nerves, muscles, and both nerves and muscles together. FIG. 4 shows various uses of the present invention. Zinc-air battery (ies) (41) may enable limb movement and locomotion via neuromuscular stimulators (42), spinal column stimulators (43), and may allow more effective use of the BTE component of cochlear implant systems (44).

[00044] The systems incorporating the high energy density energy source are also part of the invention, as well as the resulting apparatus of the method. The uses of this inexpensive, (i.e., approximately a cost of one dollar per day), throw-away primary battery are new uses of the modified zinc-air battery and are directed toward helping people hear again, walk again, and regain body functionality which they have otherwise lost permanently.

[00045] It is noted that while zinc-air batteries may be obtained commercially from numerous sources, e.g., Electric Fuel, Ltd., Har Hotzvina Science Park, P.O.B. 23073, Jerusalem, 91230, Israel, the present invention is not directed to zinc-air batteries per se. Rather, the invention is directed to zinc-air systems that include a zinc-air battery in a small, prismatic shaped case that allows sufficient air to enter the battery case so that a high power output is achieved, at low cost.

[00046] While the invention herein disclosed has been described by means of specific embodiments and applications thereof numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.