Abstract:
Air managers for metal-air batteries are described, utilizing a diaphragm or bellows to move air in and out of one or more air openings or to move air from an inlet to an outlet. The diaphragm or bellows may be reciprocated by a linear actuator, such as an electromagnetic oscillator, or a shape memory alloy wire. Micromachines such as microrelays may be used as actuators. The battery may include one or more air passageways preferably including an isolating passageway such as a thin elongate tube shaped to impede air flow to the air electrode when the air moving device is not operative, even while the tube remains unsealed. The result is an improved air moving device for metal-air cells that occupies a minimal amount of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal air cell, and is capable of developing high pressure for high velocity air movement at a relatively low rate of power consumption. Prismatic and cylindrical batteries incorporating the invention are described.

Description:
RELATED APPLICATIONS 
     The following patent applications for related subject matter, 
     “CYLINDRICAL METAL-AIR BATTERY WITH A CYLINDRICAL PERIPHERAL AIR CATHODE” Ser. No. 09/215,020; 
     “AIR MOVER FOR A METAL-AIR BATTERY UTILIZING A VARIABLE VOLUME ENCLOSURE” Ser. No. 09/216,113; 
     “DIFFUSION CONTROLLED AIR VENT WITH AN INTERIOR FAN” Ser. No. 09/215,879; 
     “UNIFORM SHELL FOR A METAL-AIR BATTERY” Ser. No. 09/216,114; 
     “LOAD RESPONSIVE AIR DOOR FOR A METAL-AIR CELL” Ser. No. 09/216,115; 
     “Geometry Change Diffusion Tube For Metal-Air Batteries” Ser. No. 09/216,273; 
     “AIR-MANAGING SYSTEM FOR METAL-AIR BATTERY USING RESEALABLE SEPTUM” Ser. No. 09/216,343; and 
     “AIR DELIVERY SYSTEM WITH VOLUME-CHANGEABLE PLENUM OF METAL-AIR BATTERY” Ser. No. 09/216,660; all of which are incorporated herein by reference, have been filed concurrently with the present application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to metal-air batteries of the type that are supplied with reactive gas by an active air moving device, and more particularly relates to an air mover mechanism that utilizes a diaphragm or bellows to move air in and out of one or more air openings or to move air from an inlet to an outlet. 
     BACKGROUND OF THE INVENTION 
     Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power. 
     Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical “button cell” was not practical because it would lead to premature failure as a result of flooding or drying out. 
     In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983, 5,356,729, and 5,691,074. 
     A disadvantage of most air managers, however, is that they utilize an air moving device, typically a fan or an air pump, that occupies space that could otherwise be used for battery chemistry to prolong the life of the battery. This loss of space presents a particular challenge in attempts to provide a practical metal-air cell in small enclosures such as the “AA” cylindrical size now used as a standard in many electronic devices. 
     In addition to being bulky, air moving devices used in metal-air batteries also consume energy stored in the metal-air cells that might otherwise be delivered as power output to a load. Complicated electronics for controlling an air manager can increase this use of stored energy. Also, as most air moving devices used in metal-air cells distribute air to a cathode plenum at low pressure, a flow path must be defined passing over all regions of the cathode surface to evenly distribute air to the entire cathode surface. Thus, the function of bringing in make up air and the function of mixing and distributing air within the battery have been separate. A further disadvantage of fans used as air moving devices in metal-air cells is that they may create noise at a level disruptive to users of devices such as cellular telephones. 
     As a result, while a key advantage of metal-air cells is their high energy density resulting from the low weight of the air electrode, this advantage is compromised by the space and power required for an effective air manager, and the noise it may produce. 
     Therefore, there has been a need in the art for an air manager incorporating an air moving device that occupies less of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal-air cell, is quiet, does not require a complex baffle system in the cathode air plenum to distribute the air, needs relatively simple controls, and consumes power at a relatively low rate. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved air moving device for metal-air cells that occupies a minimal amount of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal air cell, and is capable of developing high velocity air movement at a relatively low rate of power consumption. 
     In accordance with one aspect of the invention, this object is accomplished by providing an air-moving device for supplying ambient air to the air electrodes of a metal-air cell by moving the air alternately in through and out of a passageway extending from the air electrodes to an outside air environment. 
     In a preferred embodiment, the air moving device is a diaphragm or bellows reciprocated by a linear actuator, such as an electromagnetic oscillator, or a shape memory alloy wire. There may be one or more passageways preferably including an isolating passageway such as a thin elongate tube shaped to impede air flow to the air electrode when the air moving device is not operative, even while the tube remains unsealed. In this embodiment, the function of bringing in make up air is combined with the function of circulating and mixing the air for the metal-air cell or cells by giving the make up air stream sufficient pressure and velocity to provide mixing and circulation. Make up air entry points can be located to make use of the inertial force of the air stream along with diffusion and thermal forces to perform the circulation and mixing function. Furthermore, the air movers of this embodiment can have simplified controls and power requirements that use up less than 5% of the energy stored in the battery. In particular, when the actuator is a shape memory wire or electromagnetic oscillator, controls needed to supply a fixed voltage and the attendant voltage conversion and regulation needed to run fans and blowers may be eliminated. 
     According to another of its aspects, the present invention provides a reciprocating partition for moving air and one or more ventilation passageways extending through the partition and operable for providing outside air to a metal-air cell as the partition reciprocates. The ventilation passageway may be a tube attached at one end to an opening in the partition, the tube reciprocating with the partition. In a preferred form, the partition is a rolling diaphragm. 
     According to another of its aspects, the present invention provides a ventilation system for a metal-air power supply, having one or more cells each including an air electrode, and at least one air passageway passing between facing surfaces. Each surface defines an opening therethrough and the openings through the surfaces are spaced apart from one another. The passageway is capable of passing sufficient air to operate the cell when associated with an operating air moving device, and the passageway is further operative, while unsealed and not under the influence of an operating air moving device, to restrict air flow through the passageway to protect the cells. Preferably, one of the facing surfaces is a movable diaphragm, and the air moving device includes the diaphragm and an actuator for reciprocating the diaphragm. When the air moving device is not reciprocating the diaphragm, the diaphragm is positioned in a rest position closely adjacent to the other facing surface. In the rest position, the surfaces preferably are, for practical purposes, touching in the region between their respective openings, the centers of which preferably are spaced apart along the surfaces by at least about 1.5 times the diameter of the openings. The surfaces need not, however, be touching, as long as the openings are separated far enough apart, depending on the size of the gap between the surfaces, to retard passage of air between the openings in a manner similar to that provided by the isolation passageways described herein. 
     According to another of its aspects, the present invention provides in a metal-air battery including a cylindrical housing containing a pair of metal-air cells and a pair of facing air cathodes separated by a generally rectangular cathode air plenum, an air manager comprising an air pathway defined within the housing by the cathode air plenum connected at one end of the housing to a return plenum defined between a chordal wall and a cylindrical wall of the housing. An air moving device is operable to move a flow of air axially through the cathode air plenum and axially in the opposite direction through the return plenum. The housing may further include an air inlet, preferably an isolating tube, providing outside air to the air moving device and an air outlet, also preferably an isolating tube, directing at least a portion of air moving through the return plenum to the exterior of the battery. The air moving device may be a diaphragm reciprocating within a peripheral guide aligned with the cathode plenum. 
     According to another of its aspects, the present invention provides in a metal-air battery including a housing containing one or more metal-air cells each having an air electrode, an air manager comprising an air pathway defined within the housing and extending adjacent to an air electrode of a metal-air cell; an inlet and an outlet each extending between the air pathway and an environment outside the housing; a micro-oscillator mounted in the air pathway; and a diaphragm air pump connected to the micro-oscillator, the micro-oscillator vibrating the diaphragm to move air along the air pathway between the inlet and the outlet. The micro-oscillator may oscillate the diaphragm at a frequency of 20,000 hertz or greater so that the frequency will be above those normally audible to the human ear. The battery may also define a recirculation path positioned to cause a portion of the air flowing in the air pathway to bypass the outlet. 
     In a preferred form of this embodiment, the battery includes a pair of metal-air cells and a pair of facing air cathodes separated by a generally rectangular air plenum that includes a central axis of a cylindrical housing. The air pathway is a U-shaped space defined by a cathode current collector extending to divide the air plenum for a portion of the distance across the air plenum. 
     According to another of its aspects, the present invention provides an air moving device for a metal-air battery including one or more metal-air cells, comprising a flexible membrane, a leaf spring extending across at least a portion of the membrane and attached thereto, a shape memory wire attached at its ends to the leaf spring so as to lie loosely along the leaf spring when the wire is in a relaxed condition; and a circuit selectively connecting the ends of the wire to the cell to direct a current through the wire, causing the wire to shrink, thereby bending the leaf spring, and deforming the membrane to move air within the battery. 
     The air moving devices and air pathways of the various embodiments of the present invention provide improved air managers for metal-air batteries including one or more metal-air cells. As may be understood from the foregoing, most aspects of the present invention are applicable to individual metal-air cells or to batteries of cells, and to both prismatic and cylindrical cells and batteries. 
     Other objects, features and advantages of the present invention will become apparent upon reviewing the following detailed description of preferred embodiments of the invention, when taken in conjunction with the drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded pictorial view of a cylindrical metal-air battery embodying the present invention. 
     FIG. 2 is an axial cross sectional view taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is a radial cross sectional view taken along line  3 — 3  of FIG.  2 . 
     FIG. 4 is a bottom view of the interior of the cell of FIGS. 1-3, with the case bottom removed. 
     FIG. 5 is diagrammatic axial cross sectional view of a second embodiment of a metal-air cell according to the present invention. 
     FIG. 6 is a diagrammatic partial cross sectional view of the cell of FIG. 4, showing the diaphragm in an inactive position. 
     FIG. 7 is diagrammatic partial axial cross sectional view of a third embodiment of a metal-air cell according to the present invention. 
     FIG. 8 is diagrammatic top view of the interior of a prismatic metal-air cell according to a fourth embodiment of the present invention. 
     FIG. 9 is diagrammatic partial axial cross sectional view of a fifth embodiment of a cylindrical metal-air battery according to the present invention, taken along line  9 — 9  of FIG.  10 . 
     FIG. 10 is a top cross sectional view taken along line  10 — 10  of FIG.  9 . 
     FIG. 11 is a diagrammatic view of an alternative drive mechanism for a bellows of the type shown in FIG. 9, according to a sixth embodiment of the present invention. 
     FIG. 12 is a diagrammatic side cross sectional view of a diaphragm drive mechanism according to a seventh embodiment of the present invention. 
     FIG. 13 is a diagrammatic plan view of the drive mechanism of FIG.  12 . 
     FIG. 14 is a diagrammatic axial cross sectional view of an eighth embodiment of a metal-air battery according to the present invention. 
     FIG. 15 is a pictorial view of the interior of an upper portion of the cell of FIG.  14 . 
     FIG. 16 is an exploded pictorial view of a microrelay device used in the battery of FIGS. 14 and 15. 
     FIG. 17 is a diagrammatic side plan view of a ninth embodiment of a metal-air battery according to the present invention. 
     FIG. 18 is an axial cross sectional view taken along line  18 — 18  of FIG.  20 . 
     FIG. 19 is an axial cross sectional view taken along line  19 — 19  of FIG.  20 . 
     FIG. 20 is a radial cross sectional view taken along line  20 — 20  of FIG.  18 . 
    
    
     DETAILED DESCRIPTION 
     Referring now in more detail to the drawings, in which like numerals refer to like parts throughout the several views, FIG. 1 shows an exploded view of the components of a cylindrical metal-air battery  10 . The assembled battery is shown in FIGS. 2 and 3. The battery  10  is assembled within a conductive cylindrical case  12 , containing a dual-cathode metal-air cell  20 . A cap  30  encloses the top of the case  12  and defines a terminal  14  that is electrically insulated from the case  12 . 
     The cell  20  includes two rectangular air cathodes  22   a  and  22   b  supported between carrier frame members  25 . The air cathodes face each other at the center of the case  12  and are spaced apart to define a central cathode plenum that intersects the central axis of the case  12 . Anode material  26 , preferably zinc particles suspended in an electrolyte paste or gel, fills volumes defined within each of the cathodes  22   a  and  22   b,  the case  12 , and the frame members  25 . A conventional separator (not shown) separates each cathode from the anode material. Potting material  27  holds the anode material in place. As best shown in FIGS. 3 and 4, the spaces between the frame members  25  and the case  12  provide a pair of side plenums  28  for air recirculation as described below. 
     The anode material  26  is confined at the bottom of the case by a support plate  33  that spans the cross section of the case  12  a short distance from the bottom of the case, except for openings communicating with the cathode plenum  24  and the side plenums  28 , as shown in FIG. 4. A lower plenum  36  below the support plate  33  includes an isolating tube  34  of the type described in detail below. The isolating tube communicates with outside air through an opening  37  in the case  12 . The case  12  acts as the anode current collector, defining an anode terminal  39  in the bottom of the case. The cylindrical surface of the case may be wrapped in an insulating film (not shown). A cathode current collector  38  extends downwardly from the terminal  14  along the central axis of the battery into the cathode plenum, where it is electrically connected to current collector screens (not shown) embedded in the air cathodes  22   a  and  22   b.    
     At the top end of the case  12  an air mover assembly  40  is positioned. A printed circuit board (PCB)  42  carries a control circuit which controls the operation of an electromagnetic oscillator including a coil  44  and a magnet  46 . The coil  44  is attached to the bottom of the PCB  42 , and the magnet  46  fits around the current collector  38  and within a cylindrical opening in the coil  44 . The magnet also is attached to a diaphragm  48 , which may be adhered to the case around the periphery of the diaphragm, or may allow air to pass around the periphery of the diaphragm on an upward stroke. In the alternative, the diaphragm may include a pressure equalization opening (not shown). Current supplied from the cells to the coil under control of the control circuit causes the magnet to reciprocate, which reciprocates or vibrates the diaphragm. 
     Air may pass freely between the space immediately above the diaphragm  48  to an upper space above the PCB  42 . Within the upper space, another isolating tube  32  extends from a case opening (not shown) into the interior of the battery. The interior end of the tube  32  may optionally be fitted with a flap valve  35 , preferably made of mylar or another flexible material that will move away to open the tube when air is forced through the tube toward the valve, and subsequently return to an unstressed position over the end of the tube  34  when the flow of air ends. The flap fits fairly closely over the end of the tube, but need not seal the tube. 
     In operation, current is passed through the coil  44  in a manner required to reciprocate the diaphragm  48 . If the diaphragm is solid and sealed around its edge, and the optional flap valve  35  is not present, each stroke in one direction will push air out of a first one of the isolating tubes  32 ,  34 , and pull air in through the other tube. The subsequent stroke will push air out of the other isolating tube, and pull air in through the first tube. On each stroke, the diaphragm sucks air in through one of the isolating tubes at high velocity, and this new air mixes with the air within the cathode plenum. 
     In the alternative, the diaphragm may be mounted to allow air to bypass the diaphragm on the upward stroke, and the flap valve  35  is installed. In this mode a flow of air is established in through the tube  32 , which provides an inlet, continuing through the cathode plenum and into the lower plenum  36 , and out through the tube  34 , which provides an outlet 
     The diaphragm may be made of various flexible materials including a thermoplastic elastomer (TPE) such as SANTOPRENE® thermoplastic rubber available from Advanced Elastomer Systems. The timing of pulses of air created by the diaphragm may be varied according to the demand for output from the cell  50 . If noise is a concern, a frequency of vibration normally below that audible to the human ear will provide sufficient air to operate the cells  20 . For example, a diaphragm 2 cm in diameter reciprocated through a 1 mm stroke will move about 0.3 cc per stroke; at 15 Hz, this diaphragm will create a flow of air at about 300 cc per minute. The frequency can be adjusted electrically, or by adjusting the mass moving with the magnet  46 . 
     When the diaphragm air mover is inactive, the isolating tubes  32  and  34  limit the exchange of oxygen and water vapor with the outside air to protect the cell. Characteristics of the isolating tubes are described in detail below. 
     A single cylindrical metal-air cell  50 , constructed according to a second embodiment of the present invention, is shown in FIGS. 5 and 6. Within a conductive cell case  52 , a circular air cathode  54  is positioned radially across the case. Anode material of the type described above fills the case below the cathode  54  and a separator (not shown), down to an elastic member  59 , such as a non-reactive foam, in the bottom of the case  52 . The elastic member  59  has a spring function to press the anode material against the separator and cathode. An anode current collector spike  57  extends from the conductive case into the anode material along the central axis of the case  52 . 
     Spaced a short distance above the air cathode  54 , a circular support partition  60  perforated with air openings  62  extends across the case  52 . An air cathode plenum  61  is defined between the cathode  54  and the partition  60 . An electromagnetic coil  63  is mounted on the partition  60 , preferably centered at the case axis. A rolling diaphragm  64  spans the case spaced above the partition  60 . The diaphragm  64  includes a central section  65 , which preferably is a relatively rigid planar member occupying most of the cross section of the case  52 , and an annular hinge  66  having a U-shaped cross section. The hinge  66 , and preferably also the central section  65 , are formed from an elastomeric polymer or rubber, and the outer periphery of the hinge  66  is adhered to the case  52 . At the center of the diaphragm, a magnet  68  is attached and extends down into an axial opening in the coil  63  for axial relative movement with respect to the coil. Together, the coil  63  and the magnet  68  form an electromagnetic oscillator that drives the rolling diaphragm  64  in a reciprocating manner. Current to cause this action is supplied to the coil  63  from the cell  50  via a control circuit mounted on a PCB  69  that spans the case above the diaphragm  64 . 
     An opening  67  is formed in the central section  65  of the diaphragm  64 , spaced radially from the axis of the cell. An elastomeric coating  71  is applied to the underside of the PCB  69 , and an opening  73  is formed in the coating, aligned with an opening  74  in the PCB. The opening  73  preferably has a size similar to that of the opening  67 , and its center is positioned at a location spaced in a radial plane from the center of the opening  67 , preferably by at least 1.5 times the diameter of the openings. It should be noted that more than one opening  67  or  73  or both may be provided. The size of the openings  67  and  73  may be varied depending on the amount of air exchange desired. One of more exterior air openings  75  are provided in the case  52  above the PCB  69 . A cathode terminal  76  is provided at the top of the case. The terminal  76  is electrically connected to the cathode  54  and insulated from the remainder of the case  52 . 
     In operation of the cell  50  of FIGS. 5 and 6, current is passed through the coil  63  in a manner required to reciprocate the diaphragm  64 . The length of travel of the central section  65  from its uppermost to its lowermost position is preferably 1 mm or more, and more preferably falls in a range from about 2 mm to about 3 mm in a cell  50  of “AA” size. As the magnet  68  pulls the diaphragm downward, air is compressed in the cathode plenum  61  and therefore exits through the opening  67 . This action also pulls air from above the PCB  69  into the space between the PCB and the diaphragm, where it mixes with the air exiting the plenum  61 , and tends to pull air into the cell from the outside through air openings  75 . When the diaphragm moves up, air from above the diaphragm is sucked into the cathode plenum  61 , and air above the diaphragm is pumped out into the space above the PCB  69 . In this way, air from the outside containing fresh oxygen gradually makes its way to the cathode plenum  61 , and spent air gradually makes its way out of the cell. At each stage, incoming and exiting air masses mix together. The large area of the diaphragm  64  builds a pressure within the cathode plenum, which causes a rapid flow of air through the opening  67 , tending to evenly mix the oxygen within the plenum for optimal consumption by the air cathode  54 . 
     On its upward stroke, the diaphragm section  65  preferably engages or moves very close to the coating  71 , as shown in FIG.  6 . During pumping of air, this results in efficient replacement of air in the space above the diaphragm. When the air moving function is inactive, the diaphragm preferably is stopped in this upward position, so that air attempting to move between the openings  67  and  73  is effectively inhibited from flowing therebetween. It is not critical that the diaphragm and the coating completely seal the path between the openings. For example, when the gap between the surfaces is about 0.2 mm or less and the distance between the openings  67  and  73  is about 2 mm or more, the gap will act to inhibit diffusion of air molecules, including oxygen and water vapor, in a manner similar to the protective function of the isolating tubes  32  and  34  described above. 
     An alternative embodiment of a metal-air cell  80 , similar to the cell  50 , is shown in FIG.  7 . In this embodiment, a mask  81  is shown over the air cathode  54 . The mask has small openings to control air flow to the cathode in a known manner, and can be used with any of the air cathodes disclosed in this application. A rolling diaphragm  85  spans the cell case above the air cahode  54 , with a magnet  87  attached to its upper surface. An isolating tube  89  is attached to the diaphragm and extends upwardly from an opening in the diaphragm. Above the diaphragm  85 , a PCB  91  contains a control circuit and supports a coil  92  that extends down to receive the magnet  87 . The PCB  92  defines an opening  93  through which the isolating tube  89  freely passes. 
     In operation of the cell  80 , current is passed through the coil  63  in a manner required to reciprocate the diaphragm  85 . The isolating tube  89  moves with the diaphragm. On its downward stroke, the diaphragm forces air out through the tube  89  by compressing the air in a cathode plenum  84  between the diaphragm and the mask  81 . On its upward stroke, the diaphragm sucks air into the cathode plenum through the tube  89  at a high velocity. The air above the diaphragm mixes with new oxygen from the outside as a result of exchange of air through the air openings  75 . Therefore, make-up oxygen is fed into the cathode plenum with the air pulled in through the tube  89 . When the diaphragm air mover is inactive, the isolating tube  89  limits the exchange of oxygen and water vapor with the outside air to protect the cell. The components of the cell  80  not particularly described are constructed and operate in a manner similar to their counterpart elements in the cell  50 . 
     FIG. 8 shows diagrammatically a prismatic battery  100  constructed according to another embodiment of the present invention. The battery  100  includes a prismatic housing  102  in which are positioned a plurality of prismatic metal-air cells (not shown). A bellows  104  is mounted on an exterior wall  103  of the housing  102  to communicate with the interior of the housing through an opening  105 . The bellows preferably is an electroformed metal bellows an accordion fold side wall  119  surrounding a planar member  120 . A shape memory alloy wire  107  is connected to the planar member  120  of the bellows  104 , extends through the opening  105 , across the cell housing  102 , and is attached to an opposite housing wall  106  at a connector  108 . A pair of inlet isolating and distributing tubes  110  extend into the housing and branch to distribute air to the various cells. The tubes  110  branch into a plurality of air inlets  111  that are positioned in an array laid out so that high pressure air entering through the inlets  111  will cause mixing and circulation of air to all the air electrode surfaces in the housing  102 . Near the location at which the tubes  110  enter the housing  102 , each includes an interior mylar flap valve  112  mounted to inhibit air from exiting the housing through the tube  110 . Air exits the housing through an outlet isolating tube  114  extending into the housing from the wall  106 . Power is supplied to the shape memory wire  107  by a timing circuit  116  connected to the ends of the wire  107  by leads  117  and  118 . 
     By shape memory alloy wire, we mean a wire, for example, nitinol alloy, with nearly equal atomic amounts of nickel and titanium, that is made to “remember” a particular shape. Such a shape memory alloy wire is formed at low temperatures to the desired shape, clamped, and then heated past its transformation temperature to its annealed temperature. When cooled, the shape memory alloy wire can be easily deformed. Thereafter, the wire will return to its annealed shape when heated. After the heat source is removed, the wire can be forced back to its deformed shape and the cycle can be repeated. A shape memory alloy wire can thus provide mechanical movement without the use of a traditional motor, solenoid, or other actuator. A preferred shape memory alloy is sold by Dynalloy, Inc. or Erin. California under the trademark “Flexinol” actuator wires. 
     When current is applied across the wire  107 , it heats and shrinks in a known manner from the configuration shown in dashed lines to the configuration shown in fill lines in FIG.  8 . This causes the bellows to compress the air within the housing  102  and expel some air through the outlet tube  114 . The flap valves  112  limit expulsion of air through the inlet tubes  110 . When the wire  107  cools, the spring action of the bellows  104  stretches the wire  107 , returning the bellows to its expanded configuration. This action reduces the pressure within the housing, drawing air in through the tubes  110 . When the bellows is not being cycled by the wire  107 , the isolating tubes  110  and  114  limit the exchange of oxygen and water vapor with the outside air to protect the cell. 
     Referring to the shape memory alloy wire  107  (and the wires  136  and  163  described below), the gage of the wire should be reduced as much as possible to minimize thermal mass, while still providing the tensile strength needed to move the load to which the wire is attached in the various embodiments of the present invention. Multiple parallel wires may be used. A gage of 0.025 inch (0.6 mm) may be used for air movers in individual cells and battery packs for portable electronic devices. 
     A battery  125  constructed according to a further embodiment of the present invention is shown in FIGS. 9 and 10. The battery  125  includes a dual-cathode cell  20  rwithin a case  127 , in the same basic configuration as the first embodiment of FIG.  1 . When the reference numerals used are those used for corresponding elements in the embodiment of FIG. 1, their construction or composition is similar to the earlier embodiment. In the battery  125 , however, the cathodes  22   a  and  22   b  extend to a position adjacent to the interior walls of the case  127 , from which they are insulated. A rectangular cathode plenum  129  is formed between the facing cathodes. From an opening in the bottom of the case  127 , an isolating tube  130  extends up into the plenum  129 , preferably to end at a position near the center of the plenum, and radially near the cathode current collector spike  38 . 
     A circular support plate  132  spans the case  127  above the anode and cathode components, and defines a slot  133  over the cathode plenum  129  to allow free air flow. A bellows  134  is adhered to the plate  132  near the periphery of the case  127 , sealing around the slot  133 . The bellows is compressed and expanded by a shape memory alloy wire  136  that extends from a connector  143  near the center of the bellows down through the cathode plenum  129  to a connector  140  insulated from the case bottom. Electric current to operate the wire  136  is provided from a control circuit mounted on a PCB  145  through a lead  139  attached to the connector  140 , and a lead  141  attached to the connector  143 . 
     In operation of the battery  125 , current is applied across the wire  136 , it heats and shrinks in a known manner, causing the bellows  134  to compress the air within the cathode plenum  129  and expel some air through the isolating tube  130 . When the wire  136  cools, the spring action of the bellows  134  stretches the wire  136 , returning the bellows to its expanded configuration. This action reduces the pressure within the plenum  129 , drawing air in through the tube  130  at high velocity. Elevated pressure can be used to impart velocity to the air stream to perform enough mixing to achieve the needed level of oxygen concentration throughout the cathode plenum. High pressure also can allow a highly restrictive isolating tube  130 , in which case it may be possible to eliminate a cathode mask of the type shown in FIG. 7, which can result in improvement of the rate capability and the energy density of the battery. When the bellows is not being moved, the isolating tube  130  limits the exchange of oxygen and water vapor with the outside air to protect the cells  20 . More than one isolating tube can be installed for better air distribution. Such tubes can be of varying lengths, and each tube can perform alternating inlet and outlet functions as the bellows expands and contracts. 
     An alternative system for reciprocating a bellows  148  of the type that may be used in the embodiments of FIGS. 8 and 9 is shown in FIG.  11 . The bellows  148  fills the cross section of a tubular case  147 . A pair of controllable electromagnets  150  and  152  are provided, one inside and one outside of the bellows. The electromagnets can be energized in a sequential fashion to pull the planar member of the bellows in one direction and then the other with respect to the case  147 . 
     A modified diaphragm air mover  158  is shown diagrammatically in FIGS. 12 and 13. The air mover  158  can be used in a battery of the type shown in FIG. 1 or FIG. 9 as well as in a cell of the type shown in FIG.  5 . Positioned to span a cell case  155  above a cathode plenum, the air mover assembly  158  includes an elastic membrane  160  made of an elastic polymer, such as SANTOPRENE® thermoplastic rubber. A flat leaf spring  162  made of metal or plastic is laminated across a width, or diameter, of the membrane  160 . A shape memory alloy wire  163  is attached at its ends to opposite ends of the leaf spring  162 . In its relaxed state, the wire lies loosely against the leaf spring, which then has the dashed line configuration shown in FIG. 12. A timing circuit  165  configured to supply current from the cells of the metal-air battery is connected by leads  166  to the ends of the wire  163  so that the current is directed through the wire  163  for time periods determined by the circuit  165 . The wire  163  shrinks when heated by the current, and, as it shortens, it buckles the leaf spring  162 , causing the membrane  160  to bow as shown in the solid line configuration of FIG.  12 . Then, when the wire  163  cools, the resiliency of the spring  162  stretches the wire back to its original length and draws the membrane  160  back to a flat configuration. Such reciprocating motion of the membrane moves air in one of the above-described cells or batteries along the same paths as the air is moved by a bellows or rolling diaphragm. 
     The buckling motion created by the shrinking of the shape memory alloy wire can also be provided by a piezoelectric acutator. 
     A battery  170  constructed according to a further embodiment of the present invention utilizing an micromachine air mover is shown in FIGS. 14,  15 , and  16 . The battery  170  includes a dual-cathode cell within a case  172 , in the same basic configuration as the embodiment of FIG.  9 . However, a cathode current collector  174  extending down from the terminal  14  terminates above the bottom of the case  172  and fills the entire width of the cathode plenum between the cathodes  22   a  and  22   b.  A support plate  176 , through which the current collector spike  174  passes, closes off the cells from an upper plenum  182  except for a microrelay driven air pump  178  positioned over one side of the cathode plenum, and a ventilation opening  180  allowing air flow from the other side of the cathode plenum to the upper plenum. 
     An isolating tube  185  extends from an opening  186  in the case  172  into the upper plenum  182  on one side of the cathode current collector  174 . A second isolating tube  188  extends from an opening  189  in the case  172  into the upper plenum  182  on the other side of the cathode current collector  174 . Between the two isolating tubes, the upper plenum is divided by a pair of baffles as shown in FIG.  15 . One baffle  192  extends from the case wall to the collector  174  between the air pump  178  and the tube  185 . The other baffle  194  (shown in dashed lines) extends from the case wall to the collector  174  between the ventilation opening  180  and the tube  188 . 
     FIG. 16 shows a microrelay drive  198  of a type known to those skilled in the micromachine art, suitable for use in the air mover  178 . A suitable microrelay is shown in U.S. Pat. No. 5,778,513. In the microrelay drive  198 , a main frame  200  supports planar copper coils  202  and gold contact pads  204 . Within an upper frame  206 , a gold shunt pad  208 , movable permalloy pole pieces  210 , and a movable silicon platform  212  overlay the coils and contact pads. A diaphragm  214  (shown only in part to reveal internal detail) is physically connected to vibrate with the silicon platform  212 . The diaphragm and the microrelay together form the micro-oscillator air mover  178 . 
     The diaphragm  214  is constructed with an air bypass (not shown) so that the air mover pumps air in one direction into the cathode plenum. It thus will be seen that a flow-through air path is defined for air entering through the isolating tube  188 , being pumped in a U-shaped path down one side of the cathode plenum and back up the other side, through the opening  180 , and out of the battery through the isolating tube  185 . The microrelay of the drive  198  can oscillate at a rate above the frequency normally audible to the human ear, such as 20,000 Hz or higher. At such a high rate of pumping, even though the volume of air moved per stroke is small, the flow rate is high and the pressure differential across the air mover is high. The pressure differential across the isolating tube  188  may be 1 psi or higher, which makes it possible to reduce the cross sectional area of the isolating tubes to 0.1 square mm or smaller, while still pulling in enough air to operate the cells of the battery. 
     The baffles  192  and  194  are shown fully dividing the upper plenum  182 . However, it should be understood that the baffle  194  can be perforated to allow a portion of the air pumped by the air mover to be recirculated. 
     A battery  220  constructed according to a further embodiment of the present invention is shown in FIGS. 17 through 20. The battery  220  includes a dual-cathode cell within a case  224 , in the same basic configuration as the first embodiment of FIG.  1 . When the reference numerals used are those used for corresponding elements in the embodiment of FIG. 1, their construction or composition is similar to the earlier embodiment. As shown in FIG. 17, the case  224  is cup shaped, and defines an annular crimp  225  at its upper end to hold interior components in place, as described below. An insulator layer  227  closes the top of the case and separates the case from a conductive cap  229  that serves as the cathode terminal. An insulating wrapper  230  preferably is laminated to the outer cylindrical wall of the case  224 . The case  224  serves as the anode current collector, and at its bottom end forms an anode terminal  226 . 
     Referring to FIGS. 18-20, a U-shaped holder  236  having a bottom support disc  237  and upstanding walls  238  retains the anode material  26  and the cathodes  22   a  and  22   b  of the cell  20 . A separator  242  is shown between the anode and cathode of each cell. A cathode air plenum  24  is formed between the cathodes  22   a  and  22   b,  and a cathode current collector  38  extends from the cathode terminal  229 , through the insulator layer  227  and down the length of the plenum  24 . 
     The walls  238  of the cell holder  236  span a chord of the cross section of the case  224  to define two side return plenums  28 . In the bottom support disc  237 , a slot  239  is formed corresponding to the cathode plenum  24  to allow air to move from the cathode plenum into the return plenums  28  between the chordal walls  238  and the arcuate cell case  224 . 
     At the top end of the case  224  an air mover assembly  250  is positioned. A PCB  252 , shown diagrammatically, provides a structural member across the top of the case  224 , and is held in position by the crimp  225  that is formed with the PCB in place. The PCB carries a control circuit which controls the operation of an electromagnetic oscillator including a coil  255  and a magnet  257 . The coil  255  is attached to the bottom of the PCB  252 , and the magnet  257  fits around the current collector  38  and within a cylindrical opening in the coil  255 . The magnet also is attached to a diaphragm  260 , which moves within a diaphragm guide  262 . The guide  262  is an annular member attached to the case  224  above potting material  27 , and defines a pair of air openings  266  above each of the return plenums  28 . The guide  262  also provides a cylindrical peripheral guide wall  263  within which the diaphragm  260  moves. The diaphragm  260  allows air to pass around the periphery of the diaphragm on an upward stroke, or may include a pressure equalization opening (not shown) for the same purpose. Current supplied from the cells to the coil under control of the control circuit causes the magnet to reciprocate, which reciprocates or vibrates the diaphragm within the guide wall  263 . 
     An inlet isolating tube  270  extends from an opening  269  in the cap  229  through the insulator  227  and the PCB  252  diagonally to a point over the diaphragm  260 . An outlet isolating tube  274  extends from an opening  273  in the cap  229  through the insulator  227  and the PCB  252  to a point outside the guide wall  263 . Thus, it will be understood that when current pulses are supplied in a known manner to the coil  255 , the diaphragm operates as an air pump to draw air in through the tube  270 , and pump the air across the air cathodes  22  on both sides of the current collector  38 , through the slot  239 , up through the return plenums  28  and the openings  266 , and out of the cell through the tube  274 . The diaphragm builds a pressure within the cathode plenum in this mode. The timing of pulses of air created by the diaphragm may be varied according to the demand for output from the battery  220 . When the diaphragm air mover is inactive, the isolating tubes limit the exchange of oxygen and water vapor with the outside air to protect the cell. The more powerful the diaphragm air pump, the more restrictive and protective the isolating tubes  270  and  274  can be. 
     It should be understood that the actuators for driving reciprocating motions described above in connection with particular embodiments can be utilized in the other embodiments described. Furthermore, the reciprocating motions provided by the actuators described above in connection with the various embodiments could also be performed by a motor, piezoelectric element, or fluid operated cylinders or chambers. 
     Referring in detail to the isolating passageways described above, these isolating passageways are preferably constructed and arranged to allow a sufficient amount of airflow therethrough while the air moving device is operating so that a sufficient output current, typically at least 50 ma, and preferably at least 130 ma can be obtained from the metal-air cells. In addition, the isolating passageways are preferably constructed to limit the airflow and diffusion therethrough such that the drain current that the metal-air cells are capable of providing to a load while the air moving device is not forcing airflow through the isolating passageways is smaller than the output current by a factor of about 50 or greater. In addition, the isolating passageways are preferably constructed to provide an “isolation ratio” of more than 50 to 1. 
     The “isolation ratio” is the ratio of the rate of water loss or gain by a cell while its oxygen electrodes are fully exposed to the ambient air, as compared to the rate of the water loss or gain of the cell while its oxygen electrodes are isolated from the ambient air, except through one or more limited openings. For example, given identical metal-air cells having electrolyte solutions of approximately thirty-five percent (35%) KOH in water, an internal relative humidity of approximately fifty percent (50%), the ambient air having a relative humidity of approximately ten percent (10%), and no fan-forced circulation, the water loss from a cell having an oxygen electrode fully exposed to the ambient air should be more than  100  times greater than the water loss from a cell having an oxygen electrode that is isolated from the ambient air, except through one or more isolating passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained. 
     More specifically, each of the isolating passageways preferably has a width that is generally perpendicular to the direction of flow therethrough, and a length that is generally parallel to the direction of flow therethrough. The length and the width are selected to substantially eliminate airflow and diffusion through the isolating passageways while the air moving device is not forcing airflow through the isolating passageways. The length is greater than the width, and more preferably the length is greater than about twice the width. The use of larger ratios between length and width are preferred. Depending upon the nature of the metal-air cells, the ratio can be more than 200 to 1. However, the preferred ratio of length to width is about 10 to 1. 
     The isolating passageways could form only a portion of the path air must take between the ambient environment and the oxygen electrodes. Each of the isolating passageways may be defined through the thickness of the battery housing or cell case, but preferably they are in the form of tubes as described above. In either case, the isolating passageways may be cylindrical, and for some applications each can have a length of about 0.3 to 2.5 inches or longer, with about 0.88 to 1.0 inches preferred, and an inside diameter of about 0.03 to 0.3 inches, with about 0.09 to 0.19 inches preferred. The total open area of each isolating passageway for such applications, measured perpendicular to the direction of flow therethrough, is therefore about 0.0007 to 0.5 square inches. In other applications, such as small cylindrical cells, the isolating passageways each can have a length of about 0.1 to 0.3 inches or longer, with about 0.1 to 0.2 inches preferred, and an inside diameter of about 0.01 to 0.05 inches, with about 0.015 inches preferred. The preferred dimensions for a particular application will be related to the geometry of the passageways and the cathode plenums, the particular air mover utilized, and the volume or air needed to operate the cells at a desired level. 
     The isolating passageways are not necessarily cylindrical, as any cross-sectional shape that provides the desired isolation is suitable. The isolating passageways need not be uniform along their length, so long as at least a portion of each isolating passageway is operative to provided the desired isolation. Further, the isolating passageways may be straight or curved along their length. 
     Other exemplary isolating passageways and systems are disclosed in U.S. Pat. No. 5,691,074 and U.S. application Ser. No. 08/556,613, and the entire disclosure of each of those documents is incorporated herein by reference. 
     While this invention has been described in detail with particular reference to a preferred embodiment thereof, it will be understood that modifications and variations may be made without departing from the scope of the invention as defined in the appended claims.