Abstract:
Lithium metal anode protection, and various semi-fuel cell constructions for use in deep, high pressure seawater or air media are provided. The described lithium semi-fuel cells achieve record high energy densities, due to the high energy density of lithium anode and the use of the cathode reactant from the surrounding media, which is not part of the cell weight, and the use of ultralight and flexible packaging materials. These features make the described semi-fuel cells the ideal choice for powering underwater and air vehicles.

Description:
CROSS REFERENCE TO RELATED DOCUMENTS 
     The subject matter of the invention is shown and described in the Disclosure Document of Ian Kowalczyk et al., Ser. No. 603,189 filed on Jul. 7, 2006 and entitled “Lithium Metal Anode Construction for Seawater or Air Semi-Fuel Cells Having Flexible Pouch Packaging.” 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains mostly to a lithium metal anode and cell construction having suitable multi-layer protection for use in high pressure lithium-seawater or lithium-air semi-fuel cells, while providing a very high energy density. 
     2. Description of the Prior Art 
     Lithium-water and lithium-air primary batteries are the batteries of choice for various military applications, like unmanned underwater vehicles and unmanned air vehicles, due to their record high practical energy densities (1000 Wh/kg). However, the prior art underwater lithium batteries suffer from limitations of their use in relatively shallow depths, due to their low resistance to the high water pressure. Prior art lithium-air batteries do not utilize their full potential in energy density, due to their relatively heavy packaging structures. The prior art cell sizes are also limited by available ceramic layer, which can not be made in large sheets due to the brittleness of this material. Examples of the prior art batteries are described in U.S. Patents of Abraham et al. U.S. Pat. No. 5,510,209 and Visco et al. U.S. Pat. No. 6,432,584 B1. Therefore, it is desirable to provide a better protective structure of the cells and their anodes, which structures can withstand higher water pressure and also be very lightweight, and of a modular design. 
     The lithium anode and cell construction of the present invention does not suffer from prior art problems and provides many positive advantages. 
     SUMMARY OF THE INVENTION 
     It has now been found, that an underwater cell with a lithium anode, which can withstand higher water pressure than prior art cells, can be made by packaging the anode in a multilayer flexible metal foil pouch, which is coated with a plastic layer and heat sealed, and which hermetically encapsulates the lithium metal electrode. Because this packaging is flexible and compliant, it can withstand much higher water pressure than any hard structures of the prior art packaging. The lithium anode is preferably of a flat metal foil, additionally protected from the surrounding media on the active side by a flexible electro-spun polyimide-based porous membrane, soaked with a non-aqueous lithium-ion conducting electrolyte, which is stable against lithium. On top of this membrane and in contact is a water impermeable, solid-state lithium-ion conducting glass-ceramic layer facing the seawater or air cathode, through an opening in the flexible pouch packaging. Resulting frame of the flexible pouch around the solid state ceramic layer is also heat sealed to the solid state ceramic layer. It is a major discovery, that the flexible metal pouch packaging is heat sealable to the solid state ceramic layer, and also that the electro-spun membrane can be electro-spun directly onto the lithium anode foil. 
     In case of lithium metal-seawater semi-fuel cells, preferably porous carbon or a metal flat cathode is facing the solid state ceramic layer in its proximity or in contact with said ceramic layer, and is also submerged into the seawater. 
     Both electrodes have metal terminals electrically connected to the electrodes and insulated from the surrounding water. 
     In case of lithium-air semi-fuel cells, an identical anode structure as described is used, but the cathode electrode structure is of well known fuel cell porous carbon type, in contact with said ceramic layer and attached to the ceramic insulating separator layer by another frame, preferably of the same flexible pouch material, which is heat welded to the anode frame. The outer opposite side of the cathode is facing an air flow and permits the oxygen in the air to enter the cathode. The inner porous carbon side of the cathode is preferably wetted by an aqueous H 2 SO 4 , or KOH based electrolyte, which is in contact with the ceramic separator layer, as described in our prior patent application Ser. No. 11/418,629 now abandoned. 
     The underwater cells may be identically constructed except the aqueous H 2 SO 4  or KOH electrolyte is replaced with seawater soaked into the cell cathode. In both applications, the cells may be constructed with a large area cathode, facing a plurality of several smaller anodes, electro-spun membranes, and ceramic separators, due to the size limitation of the ceramic separators, thus making a production of large lithium-seawater and lithium-air semi-fuel cells possible. 
     Another variant of this construction may have one large anode plate with one large flexible electrospun membrane, with a plurality of smaller glass-ceramic separators facing one large area cathode. 
     In case of lithium-air semi-fuel cells only, the cells may be also constructed differently, having the ceramic separator and the aqueous electrolyte removed and a polymeric, oxygen selective, hydrophobic gel or hydrophobic solid-state membrane added onto the outer side of the cathode. This membrane prevents evaporation of the non-aqueous electrolyte in the electro-spun membrane and in the inner side of the cathode, and permits oxygen to selectively enter the cathode. It also prevents any moisture in the air to enter the cell. 
     The principal object of this invention is to provide high water pressure resistant lithium anodes and larger lithium seawater semi-fuel cells, which can operate in greater depths of the ocean over the prior art. 
     Another object of this invention is to provide larger and more lightweight lithium-air semi-fuel cells, having higher capacity and energy density over the prior art. 
     Other objects and advantages of the invention will be apparent from the description and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of lithium-seawater or air anode packaging. 
         FIG. 2  is a vertical sectional schematic view, on the line  2 - 2  of  FIG. 1 , illustrating lithium anode construction for lithium-seawater and lithium-air semi-fuel cells, said anode being protected by a flexible polymer coated metal foil pouch, and electrospun membrane with a non-aqueous electrolyte, and a ceramic, lithium-ion conducting and water impermeable layer, facing the water or an aqueous electrolyte. 
         FIG. 3  is a sectional schematic view, illustrating lithium-seawater pouch single cell with an integrated porous carbon or metal cathode, facing the seawater. 
         FIG. 4  is a sectional schematic view, illustrating lithium-air pouch single cell with an integrated porous carbon cathode, facing the air. 
         FIG. 5  is a sectional schematic view, illustrating lithium-seawater pouch bi-cell having integrated two porous carbon cathodes facing the seawater, and the protected lithium anode in the middle. 
         FIG. 6  is a sectional schematic view, illustrating lithium-air pouch bi-cell having integrated two porous carbon cathodes facing the air, and protected lithium anode in the middle. 
         FIG. 7  is a top view of large lithium-seawater or air anode having multiple small ceramic separators, porous spun membranes and lithium foils sealed in one large flexible pouch, which positions and holds them in place together. 
         FIG. 8  is a top view of a large lithium-seawater or air semi-fuel cell. 
         FIG. 9  is a vertical sectional schematic view, on line  9 - 9  of  FIG. 8 , illustrating large lithium-seawater or air single semi-fuel cell with one integrated porous carbon or metal cathode, facing the seawater or air, and all parts are held together by a flexible pouch material. 
         FIG. 10  is a sectional schematic view, illustrating a large lithium-seawater or lithium-air bi-cell, having multiple protected anodes integrated with two porous carbon or metal cathodes facing the medium, and all parts are held together by a flexible pouch material. 
         FIG. 11  is a sectional schematic view, illustrating a large lithium-seawater or lithium-air anode packaging having multiple small ceramic membranes on one large anode. 
         FIG. 12  is a top view of another large lithium-seawater or lithium-air single semi-fuel cell. 
         FIG. 13  is a sectional schematic view on the line  13 - 13  of  FIG. 12 , illustrating large lithium-seawater or lithium-air single semi-fuel cell with one integrated cathode facing multiple small ceramic membranes of the anode packaging. 
         FIG. 14  is a sectional schematic view illustrating a large lithium-seawater, or lithium-air bi-cell, having multiple small ceramic membranes facing two integrated cathodes. 
         FIG. 15  is a sectional schematic view illustrating a single lithium-air semi-fuel cell having an oxygen selective hydrophobic membrane laminated to the outer surface of the cathode. 
     
    
    
     Like parts have the same numbers through several views and Figures. 
     It should, of course, be understood that the description and the drawings herein are merely illustrative, and it will be apparent that various modifications, combinations, and changes can be made of the structures and the systems disclosed without departing from the spirit of the invention and from the scope of the appended claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When referring to the preferred embodiments, certain terminology will be utilized for the sake of clarity. Use of such terminology is intended to encompass not only the described embodiment, but also all technical equivalents which operate and function in substantially the same way to bring about the same results. 
     Lithium-seawater and lithium-air anodes usually comprise a lithium foil protected by a hard, moisture impermeable and sealed structure, which has on the active side ion conductive layers facing the cathode. The surrounding medium, such as seawater, or oxygen in air enters the porous cathode layer and results in an open circuit potential slightly higher than 3 volts against lithium. 
     Present invention employs new and novel anode packaging structure, which utilizes a compliant, flexible pouch enclosure heat welded to a glass-ceramic ion conductive layer facing the cathode, which provides for cell operation in greater depth of the ocean and also results in higher energy density of lithium-air cells, due to the lightweight, flexible packaging. 
     Referring now in more detail to the drawings of this patent, one embodiment of this invention can be understood by reference to  FIGS. 1 and 2 . The lithium anode packaging structure  1  for lithium-seawater or lithium-air cells comprises: lithium anode foil  2 ; at least one outer water-impervious, lithium-ion conducting solid state glass-ceramic layer  3 ; at least one inert, electrospun porous polyimide membrane  4 , saturated with a lithium compatible and lithium-ion conductive electrolyte solution  5 ; at least one flat metal collector tab  6 , which is press-joined with the anode  2  at the joint area  7 ; at least one base layer of flexible pouch  8 , having a flexible metal foil, such as aluminum coated with a heat sealable insulating and flexible plastic layer  8 A facing and in contact with the anode  2 ; and at least one flexible top frame  9 , preferably of the same material as the bottom layer  8 , having the plastic layer  8 A facing the layer  3 . The frame  9  is heat sealed to the ceramic layer  3  all around, as shown in the shaded area  10 , and also to the bottom layer  8 , as shown in the shaded area  11 , preferably under vacuum. Preferred flexible material of 8 and 9 parts is manufactured by Pliant Corp., Chippewa Falls, Wis. The bottom layer  8  and frame  9  are also heat sealed to the tab  6 , under vacuum. 
     It is a major discovery and finding, that the flexible pouch top frame  9  is heat sealable to the glass-ceramic layer  3 , which glass-ceramic layer is preferably manufactured by OHARA, INC., Sagamihara-Shi, Japan, or Somerville, N.J., as LIC-GC product. This is another embodiment of the invention. The inert electro-spun membrane  4  is preferably electro-spun directly onto the lithium foil anode  2 , and adheres to it, which is another embodiment of the invention and may be referred to as lithium spun membrane (LSM). The membrane  4  may be also a commercially available polyolefin micro-porous separator, such as manufactured by Celgard LLC, and others. 
     The described protected lithium anodes structures  1  can be incorporated into lithium-seawater single semi-fuel cell  12  as shown in  FIG. 3 , and lithium-air single semi-fuel cell  13  as shown in  FIG. 4 , which is another embodiment of the invention. The lithium-seawater cell  12  comprises: 
     The lithium anode  2  with its terminal tab  6  (−), protected as described above by the plastic coated flexible metal pouch parts  8  and  9 , and ceramic layer  3  with membrane  4  saturated with the electrolyte  5 ; and porous carbon and/or metal cathode  14 , preferably coated or laminated onto a porous metal grid or mesh current collector  14 A, electrically connected to metal terminal tab  14 B (+), such as a metal foil. 
     When this cell is submerged into the seawater, the seawater enters the pores of the cathode  14  and is ionically conductive. The cathode material must be hydrophilic to permit the water to soak inside and be in contact with the ceramic layer  3 : The cathode  14  may be held in place by also flexible material frame  15 , similar to the frame  9 . The frame  15  may be heat sealed or welded to the cathode  14  and to the frame  9 , and over the terminal  14 B. The frame  15  has an electrically insulating plastic material facing the terminal tab  14 A (+). The cathode  14  may also be just a metal piece submerged in the seawater in a proximity if the anode structure  1 . 
     The lithium-air single semi-fuel cell  13  in  FIG. 4  comprises: 
     All identical components as described for the cell  12 , except the cathode  14  is replaced with fuel cell type cathode  16 . The cathode  16  has porous carbon coated on the porous grid  14 A, but carbon outer layer  16 C is made hydrophobic by polytetrafluoroethylene coating. The inner carbon cathode layer  16 D, facing the ceramic layer  3  is hydrophilic and is saturated by an electrolyte  17 , such as aqueous H 2 SO 4 , or KOH based electrolyte, for example, as described in our prior patent application Ser. No. 11/428,629, which is herein incorporated by reference. The electrolyte  17  is in contact with ceramic layer  3 . The cell  13  may also have an adhesive, removable tape covering the cathode  16  before use, to prevent evaporation of the electrolyte  17  (not shown). 
     Referring now to  FIGS. 5 and 6  illustrating lithium-seawater and lithium-air bi-cells  18  and  19  respectively, which are another embodiment of the invention. 
     The bi-cell  18  as shown in  FIG. 5  is a lithium-seawater semi-fuel cell and comprises: 
     Lithium anode  2 A in the middle, protected on both sides by the layers  3  and  4  and by two flexible frames  9 , (the membrane layers  4  are saturated with non-aqueous inert electrolytes  5 ); anode terminal tab  6  (−); two porous carbon cathodes  14  on the outside, facing the seawater, and having porous metal grids  14 A embedded therein; two cathode terminal tabs  14 B attached to the grids  14 A and welded together at area  20  and to the final terminal tab  14 C (+); and two outside frames  15  heat sealed (welded) to the frames  9 . This configuration doubles the capacity of the prior single cell  12 . The bi-cell  19 , as shown in  FIG. 6  is lithium-air semi-fuel cell and comprises: 
     All identical components as described for the cell  18 , except the cathodes  14  are replaced with cathodes  16  having the outer layers  16 C and the inner layers  16 D, which inner layers  16 D are saturated by the electrolyte  17 , as described above. Both cathodes  16  may be also covered by the removable tape before use (not shown), to prevent evaporation of the electrolyte  17 . 
     Referring now to  FIGS. 7 and 9 , showing packaging of a large anode  21  in a form of planar array, which is another embodiment of invention, and which comprises for example, nine smaller lithium anodes  2 , nine ceramic layer  3 , nine electrospun membranes  4 , saturated with electrolyte  5 , all held together in place by a flexible top frame  9 A, heat sealed (welded) to the ceramic layers  3  in areas  10 A and to bottom flexible layer  8 C under vacuum, in area  11 A as shown in  FIG. 9 , and as is similarly described for the cell  1  (area  10  and  11 ). Terminal tabs  6  (−) are attached to anodes  2  and sealed identically as described for the cell  1 . Additionally, the anodes  2  are connected together by flat metal connectors  6 A, which connectors are sandwiched and sealed between parts  8 C and  9 A identically as terminal tabs  6 . This provides for electrical current flow from all anodes  2  to the terminal tabs  6  (−), which tabs maybe connected together (not shown). It should be noted, that any desired quantity of small anodes  2  may be similarly protected and connected together to create one large anode, facing a one piece large cathode. This is necessary, due to the limited size of ceramic layers  3  available. 
     Referring now to  FIGS. 8 and 9 , showing large single lithium-seawater or lithium-air semi-fuel cell  22 , which is another embodiment of the invention, and which comprises: Anode assembly  21 , with terminal tabs  6  (−), as described above in  FIG. 7 ; cathode  23  for lithium-seawater cell, or cathode  24  for lithium-air cell, coated on a porous metal grid  23 A, electrically connected to cathode terminal  25  (+); and cathode flexible top frame  26  welded to the anode assembly  21 . The difference in construction between cathodes  23  and  24  is the same as described for cathode  14  and  16 . The top frame  26  may also be heat sealed (welded) to the anode top frame  9 A. 
     The above described construction makes large lithium-seawater and lithium-air single semi-fuel cells possible. 
     Another embodiment of the invention is shown in  FIG. 10 , showing large Lithium-seawater, or lithium-air bi-cell  27 , which comprises: 
     Large anode assembly  28  of a plurality of smaller lithium anodes  2 , electrically connected by metal connectors  6 A, and protected by ceramic layers  3 , electrospun membranes  4  with electrolyte  5 , and having terminal tab  6  (−), all sandwiched and heat sealed between two flexible frames  9 A; two cathodes  23  for lithium-seawater bi-cell, or two cathodes  24  for lithium-air bi-cells connected to two terminal tabs  25  (+); and two flexible frames  26 , heat sealed to the frames  9 A. Two cathode tabs  25  (+) may be ultrasonically welded together, or otherwise electrically connected. 
     This cell construction doubles the energy capacity of the single cell  22 , and also makes large lithium-seawater and lithium-air bi-cells possible. 
     Another large anode packaging construction for lithium-seawater and lithium-air semi-fuel cells is shown in  FIG. 11 , which is another embodiment of the invention, and which illustrates large anode assembly  29  having lithium-sheet  2 C with terminal tab  6  (−) hermetically heat sealed under vacuum between at least one flexible base layer  8 C and at least one top layer  9 A, protected by at least one flexible porous inert membrane  4 A and by a plurality of smaller glass-ceramic membranes  3 , heat sealed to the flexible layer  9 A, within the foot print of the anode  2 A. Membrane  4 A is in contact with the lithium-anode sheet  2 A and is saturated with the described electrolyte  5 . Membranes  3  are in contact with membrane  4 A due to the vacuum packing. For each membrane  3  there is opening  3 A in the layer  9 A for lithium-ions flow to a cathode (not shown). 
     Another embodiment of the invention is shown in  FIGS. 12 and 13 , illustrating large single lithium-seawater or lithium-air semi-fuel cell  30  comprising the anode assembly  29 , with terminal tab  6  (−); cathode  23  for lithium-seawater cell, or cathode  24  for lithium-air cell, electrically connected to terminal  25  (+); and cathode flexible top frame  26 , welded to the anode assembly  29 . This construction results in fewer components than in the cell  22 , having the same performance. Cathodes  23  and  24  have the same construction as cathodes  14  and  16  respectively. 
     Referring now to  FIG. 14 , another embodiment of the invention is illustrated, showing lithium-seawater or lithium-air large bi-cells  32 , comprising: 
     Large flat lithium anode assembly  31  which includes lithium sheet  2 B with at least one terminal tab  6  (−) sandwiched between at least two flexible inert membranes  4 A, saturated with lithium ion conductive electrolyte  5 , and at least two flexible layers  9 A, having a plurality of glass-ceramic membranes  3  hermetically heat sealed at openings  3 A, to the layers  9 A, within the footprint of the anode  2 B; and two cathodes  23  or  24  facing the membranes  3  on the outside, and attached to the anode assembly  31  by at least two flexible frames  26 . The anode assembly  31  is hermetically sealed under vacuum first by welding the two flexible layers  9 A together, and to the terminal tab  6 , as shown and is described for cells  18  and  19 . 
     This configuration results in fewer components than in the bi-cell  27 , having the same performance. Cathodes  23  and  24  have the same construction as cathodes  14  and  16  respectively. 
     It is apparent that two opposite hand single cells  12  or  13  or  22 , or  30 , can also be assembled preferably by an adhesive with the cathodes facing outside, which results in similar performances as bi-cells  18 , or  19 , or  27  or  32 , respectively, but they will be thicker and heavier, due to the packing layers  8  and  8 C (not shown). 
     It is apparent to a person skilled in the art, that the entire negative terminal tabs  6  (−) as shown in all FIGURES, must be insulated from the surrounding media, like water etc. (not shown). 
     It should be noted that all described components above are compliant and flexible, except the glass-ceramic membranes  3 . This flexibility and the packing under vacuum provides for pressure equalization and thus high resistance to rupture under water. 
     It is also apparent from the description, that the anodes and cells can be made into virtually any desired shape and size, and that the cells can be connected in parallel and/or series to create multi-celled high voltage semi-fuel cells. 
     Described hermetic sealing of anodes also permits the lithium-seawater type cells to function when submerged into various other media, such as aqueous acids, bases, and neutrals; and the lithium-air type cells will function also in other media gases, such as oxygen. 
     Lithium-air semi-fuel cells shown in  FIGS. 4 and 13  may be also constructed differently, as shown in  FIG. 15 , illustrating a lithium-air single semi-fuel cell  33 , which is another embodiment of the invention, and in which the glass-ceramic membrane  3  is removed and replaced with at least one thin polymeric, water impermeable, oxygen selective membrane  34 , which membrane is laminated onto the outer layer  16 C of the fuel cell type cathode  16 . The flexible frame  9  or  9 A may be also removed, as shown. The non-aqueous electrolyte  5  is soaked into the membrane  4  and into the inner layer  16 D of the cathode  16 . The aqueous electrolyte  17  is omitted. 
     The oxygen selective, hydrophobic membrane  34  permits the oxygen from the surrounding air to enter the cathode, but it does not permit the electrolyte to evaporate, and does not permit water moisture in air into the cell. 
     Therefore, this membrane makes the masking tape over the cathode, and its removal before use unnecessary. The cell is ready for use as is, and will provide electric current, when an electric load is applied to the cell. 
     The flexible frame  15  is hermetically heat sealed to the membrane  34  and holds the membrane in place and also encapsulates the cell by being heat sealed all around to the flexible base layer  8 . The terminal tabs  6  and  14 B are also heat sealed between the base  8  and the frame  15 . 
     It is apparent that this construction can be similarly applied to create similar bi-cells and large cells as described above. 
     Primary applications of the described semi-fuel cells are for powering deep seawater sensors, underwater vehicles (manned or unmanned), and aerial vehicles, such as electric airplanes and UAV&#39;s. 
     It should, of course be understood, that the description and the drawings herein are merely illustrative and it will be apparent, that various modifications, combinations and changes can be made of the structures and the systems disclosed without departing from the spirit of the invention and from the scope of the appended claims. 
     It will thus be seen, that novel and improved cells&#39; structures have been provided with which the objects of the invention are achieved.