Abstract:
A battery comprising a consumable anode; a gas-diffusion cathode; a non passivated surface-destroying aqueous medium in contact with the anode and cathode; a housing enclosing the anode, cathode and medium; an additive contained within a medium-impermeable chamber separated from but receivable by the medium upon activation to effect mixing of the additive with the medium to provide an electrolytic mixture to effect electrical contact between the anode and cathode; and activation means to effect said activation. The battery provides an extended shelf-life prior to activation by reason that the anode is not corroded by the electrolyte. The battery is of particular use in portable cell-phones, computers, video cameras and players.

Description:
FIELD OF THE INVENTION 
     This invention relates to metal-air electrochemical batteries and fuel cells particularly aluminum-air batteries suitable for electronic devices, including radio-telephones, portable audio and video players, video cameras, and personal computers. 
     BACKGROUND OF THE INVENTION 
     There are known electrical rechargeable batteries comprising a housing with a pack of solid state cells, with a converter (controller) for stabilization of the output operating voltage when during the discharge cycle the voltage dips almost to one-half. In U.S. Pat. No. 5,656,876, a battery pack of lithium of NI—Cd solid-state cells is shown, where a DC/DC converter provides a stable operating voltage, possibly also different voltages upon request. U.S. Pat. No. 5,286,578 shows a flexible electrochemical cell having an air cathode, a metallic anode and an electrolyte chamber. The electrolyte chamber is collapsed when the battery is shipped (without electrolyte) to save space. U.S. Pat. No. 5,554,918 shows a mechanically rechargeable battery of a cylindrical shape having a replaceable zinc anode, an air electrode (one option) and housing. A non-spillable electrolyte is contained in the housing. When necessary, the anode can be removed and replaced with a new anode. 
     Batteries generally degrade during storage due to corrosion of the anode material. The corrosion results in one or more of the following, viz, loss of available energy in the cell, loss of cell voltage, and production of unwanted byproducts. 
     In order to decrease the corrosion of the anode material, a number of technologies are employed. 
     In one method, the addition of corrosion control inhibitors to the electrolyte is practiced. U.S. Pat. No. 5,378,559 teaches the addition of phosphate ester to the electrolyte of alkaline cells to reduce unwanted gas production at the anode. However, the addition of corrosion reducing chemicals adds to the cost of the cell and may adversely affect the power output of the cell. 
     A second approach known as water activation has been to keep the electrolyte separate from the cell until power is needed. U.S. Pat. No. 5,340,662 teaches an emergency battery with an infinite shelf life, wherein the primary battery is kept free of water until needed. U.S. Pat. No. 5,424,147 teaches a water activated battery with an aperture for aqueous liquid addition. U.S. Pat. No. 4,605,604 teaches a nickel-aluminum battery which has active components, but which has electrolyte stored separately. When power is needed the electrolyte must be transferred to the cell for activation. A disadvantage of these methods is that a liquid must be added to the cells before power can be produced. In all cases, additional external space and liquid handling capability must be available. Further, there is added complexity to the cell in order to allow transfer of the electrolyte to the cell and there is also the possibility of leakage due to the external connections for the filling of the electrolyte. Filling of a cell is usually difficult unless a second exit aperture is available to allow escape of the air displaced from the cell cavity. 
     A third approach has been to keep the electrolyte separate from one or both electrodes but within the cell compartment. The advantage is that no external electrolyte supply is needed. The key factor is that the ionic pathway is kept incomplete and the electrode(s) is kept isolated from the electrolyte. U.S. Pat. No. 3,653,972 teaches a cell in which the electrolyte is housed in a multiplicity of small capsules which keeps the electrolyte separate from the electrodes until the capsules are ruptured. However, the disadvantage of this arrangement is that multiple capsules must be broken and without breaking all of the capsules there will be loss of power due to unused electrolyte. There are also casings of the capsules that interfere with the ionic flow of chemical species in the cell and reduce the power output of the cell. 
     All of the above batteries suffer from a delay time before becoming active due to electrolyte filling and electrolyte wetting of the anode, cathode and membrane, if present. U.S. Pat. No. 6,136,468 teaches a similar concept of keeping the electrolyte separate from the electrodes by delaying full assembly of the cell until needed, while the electrolyte is immobilized in an adhesive protected by a release agent. Final assembly of the cell allows contact of the electrolyte with the electrodes. While this approach has application with electrolytes that can be immobilized in a gel type state, aqueous electrolytes would be difficult to handle. U.S. Pat. No. 4,059,717 teaches the use of a mask to inactivate a portion of the electrode and reduce corrosion of that masked area. Although battery life may be extended, there is still corrosion loss of the unprotected areas and a need to compensate for the loss in electrochemical activity caused by the mask. U.S. Pat. No. 5,314,502 teaches a electrically driven iontophoretic gate which when activated delivers ions to the cell and allows current to flow in the battery. The complexity of the cell, the electronics needed and the limited range of ions that can be delivered are limitations for this approach. 
     There is therefore a need for a metal-air battery which does not suffer from the aforesaid prior art disadvantages in providing extended shelf-storage life. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a metal-air battery having an extended pre-use shelf-storage life. 
     It is a further object of the present invention to provide such a battery for use, particularly, as a replaceable cartridge, within portable, hand-held cell phones, portable audio and visual players, cameras and the like, and personal computers. 
     The invention provides a metal-air battery having an extended shelf life by reason that the electrodes are not stored in contact with an electrolytic mixture, which mixture encourages corrosion of the anode until initial activation is desired, whereby the electrolyte is generated in situ to provide electrical contact between the anode and cathode. The battery is constituted in its simplest form as a self-contained cartridge adapted to be received by in electrical communication with, for example, a prior art DC/DC converter in the power receiving unit. 
     The cartridge is inexpensive and simple to manufacture. The battery with single or multiple anode, cathode and aqueous medium is constructed and sealed ready for use. The anode and cathode are pre-wetted ready for use and activates quickly. A surprising feature is that the battery shelf life is long in this wet state where anode and cathode are in contact with an anode non passivated surface-destroying aqueous medium. The prevention of corrosion is achieved by keeping the non passive film disrupting and film passive disrupting chemical species separated until desired by activation. The passive film disrupting species are contained in one embodiment in a rupturable device until needed in the cell for power production. A substantial reduction in cell complexity is achieved relative to the prior art. The passive disrupting species can be in dry form or concentrated aqueous form so that their in situ storage volume is minimal. The small quantity of passive film disrupting species allows for a small activating means and minimal interface with the operation of the cell. Unlike the cells which contain the electrolyte and have non conductive membranes or containment systems at least equal to the electrolyte volume and which are still present in the cell after rupture, the present invention has only a very small additive-containing chamber, which does not significantly interfere with power generation. 
     Accordingly, in one aspect the invention provides a battery comprising: 
     a consumable anode; 
     a gas-diffusion cathode; 
     a non passivated surface—destroying aqueous medium in contact with the anode and cathode; 
     a housing enclosing the anode, cathode and medium; 
     an additive contained within a medium-impermeable chamber separated from but receivable by the medium upon activation to effect release from said chamber and mixing of the additive with the medium to provide an electrolytic mixture to effect electrical contact between the anode and cathode; and 
     activation means to effect said activation. 
     In one embodiment, the chamber is defined in part by a chamber wall formed of a puncturable material and the activation means comprises puncture means to effect puncture of the material upon activation. The puncturable material preferably is formed of a puncturable plastics material or metal in the form of a foil, skin or membrane. 
     In an alternative embodiment, the chamber is defined in part by a displaceable end wall sealing member and the activation means comprises displacing means to effect displacement of the sealing member to effect mixing of the additive and medium upon activation. 
     The displacing means further comprises biasing means to effect retraction of the sealing member after activation to effect sealing of the housing. 
     The anode is preferably formed of aluminum, zinc, magnesium or an alloy thereof. 
     Preferably, but not limiting, the gas-diffusion cathode comprises copper, more preferably, nickel-free copper i.e., for example, non-nickel-plated copper, in the form of a grid, screen mesh or the like, or bar, rod or plate. Copper alloys, such as for example, brass, may also be used. 
     A preferred additive comprises an alkali metal hydroxide, most preferably, potassium hydroxide, in the form of a powder, pellet or aqueous solution, which upon activation results in a potassium hydroxide concentration, preferably, of about 4 moles/litre. 
     By the term “non-passivated surface-destroying aqueous medium” in this specification and claims is meant a medium that, essentially, in the absence of the additive does not affect, i.e. corrode or de-passivate, the anode surface which is passivated by the presence of a metal oxide layer produced by contact with air or oxygen-containing aqueous media. 
     The preferred aqueous medium in the practice of the invention is de-ionized or distilled ion free-water. However anions, for example, stannate in association with potassium cations may be present, at say a concentration of 0.1-2% w/w. 
     The aqueous medium preferably has a pH within the range 4-12, most preferably, 5-9. 
     The medium may further comprise ingredients which cause the medium to be constituted as an aqueous, paste, or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be better understood, preferred embodiments will now be described by way of example only with reference to the accompanying drawings wherein: 
     FIG. 1 is a diagrammatic perspective view of a battery cartridge according to the invention in association with a converter; 
     FIG. 2 is a diagrammatic plan view of the cartridge and converter of FIG. 1; 
     FIG. 3 is an end view of the cartridge shown in FIG. 1; 
     FIG. 4 is a diagrammatic side view of the cartridge and converter assembly within a retaining casing; 
     FIG. 5 is a diagrammatic perspective view of a hand-held portable cell phone according to the invention; 
     FIG. 6 is a diagrammatic perspective view of an alternative embodiment of a portable cell phone according to the invention; 
     FIGS. 7A and 7B are diagrammatic longitudal sectional views of an embodiment of an activation means of use in the practice of the invention; 
     FIG. 8 is a perspective view, in part, of an embodiment having an alternatively located activation means; and 
     wherein the same numerals denote like parts. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIG. 1, this shows generally as  10  a battery cartridge as a perspective, two halved exploded view. Cartridge  10  has an air-tight plastic housing  12  having side walls  14  and end portions  16 ,  18  which define an electrolyte chamber  20 . Chamber  20  contains a rectangularly-shaped aluminum anode plate  22 , flanked by a pair of rectangularly-shaped copper mesh cathodes  24  and an aqueous medium  26 . Medium  26  in the pre-activated storage mode is water, but after activation, as hereinafter described, is an aqueous electrolytic medium for example, potassium hydroxide solution at a concentration of about 4M in this embodiment. 
     End portion  16  consists of a body portion  28  defining a central chamber  30  containing the potassium hydroxide additive  32 . Portion  28  defines cylindrical cavity  30 , which embraces a centrally located piston-type push rod  31 , and has a resiliently flexible plastic outer wall  33  and puncturable inner sealing chamber wall  34  formed as a plastics material membrane. Push rod  31  is operably moveable in continuous sealing engagement with flexible outer wall  33  within cavity  30  to effect rupture of membrane  34  to operably permit contact of additive  32  with medium  26  and, in consequence, produce electrolytic medium. Retraction of rod  31  under the biasing means of flexible material wall  33  maintains waterproof sealing of electrolyte chamber  20 . Thus, in this specification, the term “activation” means the in situ production of the electrolytic medium within cartridge  10 , as hereinbefore exemplified. 
     FIG. 2 represents a diagrammatic plan view of cartridge  10  embodiment shown in FIG. 1, whereas FIG. 3 represents a diagrammatic end view at end portion  16  of cartridge  10 . 
     End portion  18  consists of a body  42  having a pair of metallic electrode prongs constituting an anode connector  44  and cathode connector  46  extending therethrough to the, respective, anode plate  22  and cathode mesh  24 . Connectors  44  and  46  extend from body  42  and are adapted to be received by an anode terminal socket  48  and a cathode terminal socket  50  extending from a complementary rectangularly-shaped body  52  of a DC/DC converter shown generally as  54 . Converter  54  has a pair of metallic electrical contact plates  56  at a face portion  58  distal of sockets  48 ,  50 , which plates  56  are in electrical contact with cell phone power receiver shown generally as  58  in FIGS. 4 and 5. 
     In an alternative embodiment showing alternative activation means, reference is made to FIG. 6, FIGS. 7A and 7B. 
     Portable cell phone, shown generally as  258 , comprises a plastics housing shown generally as  100  within which is received cartridge  220  and converter  230 , in close engagement. Housing  100  has a front wall member  60 , a back wall member  62 , a pair of side members  64 , top end member  66  and battery cover bottom end member  68 . Front wall  60  is so shaped as to provide suitable apatures to allow of visual display of features  70 . 
     With reference also to FIGS. 7A and 7B, bottom end member  68  is hinged to an edge  71  of side member  64 . Centrally disposed on the inner face  72  of end member  68  is an integrally formed button  74  receivable within a complimentary chamber  76  defined by a central portion of cartridge  110 . Within chamber  76  is an H-shaped, in vertical section, rupture member  80  of alkaline resistant flexible material having a metallic cutting portion  82  embedded therein as hereinbefore described with reference to FIGS. 1-3. Member  80  is retained within chamber  76  by integrally formed terminal clip portions  84  of member  80 , held within inner and outer recesses of cartridge end portion  222 . FIG. 7A shows the cell phone assembly with cartridge  110  within housing  100  prior to rupture and release of potassium hydroxide pellets  132  into aqueous medium  126 . FIG. 7B shows the post-rupture and operational mode of the recharged cell phone. Only inner membrane of foil type sealing member  134  has been ruptured, whereas member  80  still provides full sealing engagement within chamber to prevent escape or seepage of electrolyte out of the cartridge chamber. 
     FIG. 8 shows converter  200  having a piston-heated type plunger  202  adapted to be received within a cartridge chamber  204  to effect rupture of a sealing membrane  206  at the inner face of aqueous medium chamber  208  by the cutting means of H-shaped sealing member  210  in an analogous manner as hereinbefore described. 
     EXAMPLE 
     The following example illustrates that a non-passivated surface-destroying aqueous medium in contact with an anode and cathode can be stored with no anode corrosion until an electrolytic mixture is allowed to effect electrical contact between the anode and cathode. 
     An aluminum anode of mass 12.45 g was inserted into a cartridge as described with reference generally to aforesaid FIGS. 1-3 having two metal-air cathodes. The free volume of the cartridge chamber of the cartridge was 32.4 mL. With the aluminum anode present. The free volume of the cartridge chamber was filled with an aqueous medium consisting of 0.06 molar sodium stannate and water at pH 8.0. The time immediately after insertion of the anode was defined as time 0. A small Teflon™ (polytetrafluoroethylene) tube connected to the top of the cartridge was directed to a gas collecting water filled manometer. Evidence of corrosion of the anode would be demonstrated by the formation of gas in the cartridge and delivery of the gas to the water filled manometer. The water level in the manometer at time zero was 45.0 mL. No gas bubbles were observed and subsequent liquid readings as recorded in the Table below shows that no gas was produced by the anode in contact with the aqueous medium. At the end of this part of the experiment, the anode was carefully removed from the cartridge and reweighed. There was no mass loss of the anode plate confirming that there was no corrosion of the anode in contact with the aqueous medium. 
     A small quantity of electrolyte contained in a polyethylene thin film bag was inserted into the aqueous medium. The electrolyte was 7.29 g of KOH sufficient to give a 4 M KOH concentration in the cartridge when fully mixed. The plastic film was punctured with a hypodermic needle allowing the electrolyte to contact the aqueous medium and cathode. The anode was quickly reinserted into the cartridge to thereby reseal the cartridge. The time and liquid level measurements were restarted. 
     Gas evolution was immediately seen in the form of bubbles from the end of the Teflon™ tube. The drop in manometer liquid level is clearly seen from the readings in the Table. When the manometer was almost empty, the experiment was terminated and the anode carefully removed from the cartridge and reweighed. The mass loss of the anode was 0.0209 g to show that corrosion had occurred. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Time after electrolyte 
                 Manometer 
               
               
                 Time 
                 Manometer volume 
                 Container punctured (s) 
                 volume 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   0 
                 0 
                 0 
                 0 
               
               
                  300 s 
                 0 
                 480 
                  2.90 ml 
               
               
                  600 s 
                 0 
                 660 
                  4.55 ml 
               
               
                  900 s 
                 0 
                 1260 
                  7.15 ml 
               
               
                 1500 s 
                 0 
                 2880 
                  16.4 ml 
               
               
                 3780 
                 0 
                 4200 
                 24.10 ml 
               
               
                   
                   
                 6960 
                 41.25 ml 
               
               
                   
               
             
          
         
       
     
     The results show that the corrosion of the aluminum in 4 M KOH +0.06 M sodium stannate was appreciable. The reaction produced hydrogen gas which was measured by volume in a water filled manometer. The results also show that the aqueous media, water plus activating salts, can be allowed to contact the anode and cathode provided that anode passive film-destroying species, such as potassium hydroxide are kept from mixing with the aqueous media. 
     Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.