System for Convenient Introduction and Removal of Electrolyte in Mechanically Rechargeable Metal Air Cells by William Morris and Julio Solorzano BACKGROUND Metal air electrochemical cells are desirable energy sources, particularly for features such as relatively high specific energy (W-H/kg). In general, metal electrode materials (anodes) are oxidized by hydroxide ions formed at an air diffusion electrode (cathode).

One particularly desirable configuration for metal air electrochemical cells is mechanically rechargeable. Typically, an anode is inserted into a cathode structure, discharged, removed, and replaced with a fresh anode structure. However, oftentimes the removed anode card still contains a substantial amount of energy of electrochemical <BR> energy therein (i. e. , unconverted metal). Access to this energy is limited due to reaction of the electrolyte and depositing of metal oxide from the anode into the electrolyte.

Therefore, it is desirable to provide a system that allows for greater consumption of the electrochemical energy within metal fuel anodes.

SUMMARY The above-discussed and other problems and deficiencies of the prior art are overcome or alleviated by the several methods and apparatus of the present invention allowing for electrolyte replenishment without removal of metal fuel. A refuelable metal air electrochemical cell system is provided, generally comprising one or more cells for holding electrolyte. Note that in preferred embodiments where several cells are used, electrolyte is maintained at the same level. A leveling channel, created from plural baffles at or above the desired electrolyte height, is provided. An inlet is also provided at or above the desired electrolyte height when the system is in upright configuration, wherein the inlet includes an associated removable plug.

The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a general schematic of a metal air cell system showing a set of anodes supported in an anode holder and a corresponding base unit; Figure 2 is a general schematic of a metal air cell system showing the anodes inserted in the corresponding cathode base unit; Figure 3 shows schematically the action of tilting of the cell and filling of electrolyte therein; Figure 4 shows how crossover channels evenly distribute the electrolyte; Figure 5 shows dumping of liquid from the system; and Figures 6A and 6B show hydrogen vent tubes for allowing escape of gas evolved, e. g. , hydrogen gas in a magnesium air system.

DESCRIPTION A refuelable metal air electrochemical cell system is provided that allows for electrolyte replenishment without removal of metal fuel. Such a system generally includes one or more cells for holding electrolyte.

In preferred embodiments where several cells are used, electrolyte is maintained at the same level. An inlet is also provided at or above the desired electrolyte height (when the system is in an upright configuration), wherein the inlet includes an associated removable plug. A leveling channel, created from plural baffles at or above the desired electrolyte height, may also be provided.

Referring to Figures 1-2, a metal air cell system 100 is shown, whereby Figure 1 depicts system 100 having metal fuel cards 120 removed therefrom and Figure 2 depicted system 100 having metal fuel cards inserted therein. The system 100 generally includes a base unit or structure 110 generally containing anode receiving structures (suitable for holding electrolyte) and air diffusion electrodes, and associated metal fuel cards.

Embodiments of metal air electrochemical cell systems that may incorporate the features of the present disclosure is described in greater detail in PCT Application Serial No.

US/03/xxxxx, entitled"Liquid Seal and Electrical Connection Structure"filed on October 23,2003 (which claims priority to US Provisional Patent Application Serial Number 60/420,542 file don October 23,2002) and PCT Application Serial No. US/02/305585 entitled"Rechargeable and Refuelable Electrochemical Cell"field on September 26, 2002, both of which are incorporated by reference herein.

As is known in the art of metal air electrochemical cells, the metal anode may comprise suitable oxidizable metals such as magnesium, zinc, aluminum, calcium, lithium, ferrous metals, and combinations and alloys comprising at least one of the foregoing metals. During conversion in the electrochemical process, the metal is generally converted to a metal oxide. The anode may be in the form of a solid metal plate, or a structure of metal particles formed contiguously with suitable binders and the like.

The electrolyte generally comprises ion conducting liquid media. In a preferred embodiment, wherein the cell system is a magnesium air electrochemical cell, a neutral electrolyte such as salt water is used. However, caustic electrolytes may be used, e. g., potassium hydroxide, in zinc air or aluminum air system.

The air cathode may be a conventional air diffusion cathode, for example generally comprising an active constituent and a carbon substrate, along with suitable connecting structures, such as a current collector. The carbon used is preferably chemically inert to the electrochemical cell environment and may be provided in various forms including, but not limited to, carbon flake, graphite, other high surface area carbon materials, or combinations comprising at least one of the foregoing carbon forms. A binder is also typically used in the cathode, which may be any material that adheres substrate materials, the current collector, and the catalyst to form a suitable structure. An exemplary air cathode is disclosed in U. S. Patent No. 6, 368, 751, entitled "Electrochemical Electrode For Fuel Cell", to Wayne Yao and Tsepin Tsai, which is incorporated herein by reference in its entirety. Other air cathodes may instead be used, however, depending on the performance capabilities thereof, as will be obvious to those of skill in the art.

To electrically isolate the anode from the cathode, a separator is generally provided between the electrodes. The separator may be disposed in physical and ionic contact with at least a portion of at least one major surface of the anode, or all major surfaces of the anode, to form an anode assembly. In still further embodiments, the separator is disposed in physical and ionic contact with substantially the surface (s) of the cathode that will be proximate the anode. The physical and ionic contact between the separator and the anode may be accomplished by: direct application of the separator on one or more major surfaces of the anode; enveloping the anode with the separator; use of a frame or other structure for structural support of the anode, wherein the separator is attached to the anode within the frame or other structure; or the separator may be attached to a frame or other structure, wherein the anode is disposed within the frame or other structure.

The separator may be any commercially available separator capable of electrically isolating the anode and the cathode, while allowing sufficient ionic transport between the anode and the cathode, and maintaining mechanical integrity in the cell environment.

Preferably, the separator is flexible, to accommodate electrochemical expansion and contraction of the cell components, and chemically inert to the cell chemicals. Suitable separators are provided in forms including, but not limited to, woven, non-woven, porous (such as microporous or nanoporous), cellular, polymer sheets, and the like. Materials for the separator include, but are not limited to, polyolefin (e. g., GelgardS) commercially available from Dow Chemical Company), polyvinyl alcohol (PVA), cellulose (e. g., <BR> <BR> nitrocellulose, cellulose acetate, and the like), polyethylene, polyamide (e. g. , nylon),<BR> fluorocarbon-type resins (e. g. , the Nafion@ family of resins which have sulfonic acid group functionality, commercially available from du Pont), cellophane, filter paper, and combinations comprising at least one of the foregoing materials. The separator may also comprise additives and/or coatings such as acrylic compounds and the like to make them more wettable and permeable to the electrolyte.

Referring to Figure 3, liquid electrolyte, which, in the case of a magnesium air electrochemical cell, may comprise salt water or other neutral solutions, is added into a cell system 100 having an inlet 150. The inlet 150 is a single common inlet associated with plural sub-inlets for each anode receiving structure (as can be seen in Figure 1). The inlet 150 is positioned at the top of one side of the base structure 110, at a height which is at least above the contemplated height of electrolyte within each anode receiving structure. Each anode receiving structure is partially separated from an adjacent anode receiving structure by a baffle 152. The baffle 152 includes a notch 154, serving as an electrolyte crossover channel in direct communication with the electrolyte for"self leveling"and allowing fluid communication between adjacent anode receiving structures.

The notch 154 as shown is proximate the side of the base 110 opposite the inlet 150, however, it is understood that the notch 154 may be positioned slightly away from that edge, but preferably remains as close as possible to the interior of the side opposite the inlet. When liquid is introduced into the common inlet 150, and the cell is tilted such that the inlet is facing shown up as shown in Figure 3, the presence of the notches 154 allows electrolyte to be distributed evenly among the several anode receiving structures when the cell is placed upright as shown in Figure 4. The notches 154 provide crossover channels above the electrolyte level to limit crossover-shorting between cells. The notches 154 are generally positioned higher than the contemplated height of electrolyte.

After the electrolyte has been filled, even if excess electrolyte (i. e. above the contemplated electrolyte level) has been introduced, when the system 100 is placed in upright position (as shown in Figure 4), any excess electrolyte will spill out of the inlet 150. The inlet 150 may be then covered with a plug 156 during discharging operations.

After a system 100 is filled with electrolyte, and the output of the system drops below a certain level generally due to depletion of electrolyte (as opposed to depletion of electrochemical capacity of the anode itself) the electrolyte may be emptied (Figure 5) and replaced with fresh electrolyte. To remove electrolyte a user need only remove the plug 156, dump the electrolyte, and the capability exists to refill the system with new electrolyte-without removing the anodes from the system. This is particularly desirable to obtain maximum energy from the anodes while maintaining user convenience.

In certain types of metal air electrochemical cells, such as magnesium air electrochemical cells, the portions of discharged anode leave behind reaction products, generally magnesium oxide in the form of solid material. It is desirable to wash away as much of this solid material as possible before continuing discharge of the system, since this material may block access to fresh anode material. Therefore, with the inlet system of the present invention, a user may fill the cell through the inlet with fresh water, or in the event of a cell using salt water, salt water, and shake the system 100 to remove lose particles, and then dump the material out as shown in Figure 5.

This system provides manual electrolyte and reaction product management.

Optionally, and referring now to Figures 6A and 6B, a system may be provided for managing gases that may generate an electrochemical reaction such as hydrogen gas during reaction of a magnesium air cell. Such a system preferably minimizes or eliminates the possibility of electrolyte leaking form the system 100. As seen in Figures 6A and 6B, one or more tubes 160 are included at the top of the base 110. These tubes are in communication with ambient at the side of the base opposite the side having the inlet 150, and the tube extends across the width of the base 110 to an open end 162 that is proximate the wall of base 110 having inlet 150. Note that end 162 must be above the contemplated electrolyte level. Alternatively, the end 162 may be submersed in electrolyte, however, electrolyte will leak out from the hydrogen exhaust end 163 such that the level of electrolyte will be below the height of the ends of 162.

In this configuration the tubes 160 allow for generated gases to escape while preventing liquid from escaping (when the tubes are positioned above the contemplated electrolyte level), or allowing liquid to escape to reduce the electrolyte level to a desired level, regardless of the physical orientation of the cell (e. g. after plug is inserted the cell may be tilted such that inlet 150 is facing down or up and liquid will not escape).

Various materials may be used for the cell frame components of metal air electrochemical cells, spacers, and other support structures described herein, which are preferably inert to the system chemicals. Such materials include, but not limited to, thermoset, thermoplastic, and rubber materials such as polycarbonate, polypropylene, polyetherimide, polysulfonate, polyethersulfonate, polyarylether ketone, Viton@ <BR> <BR> (commercially available from EI DuPont de Nemours &amp; Co. , Wilmington Delaware),<BR> Delrin (E) (commercially available from EI DuPont de Nemours &amp; Co. , Wilmington Delaware), ethylenepropylenediene monomer, ethylenepropylene rubber, and mixtures comprising at least one of the foregoing materials.

Techniques for assembling plural cells to form a multiple cell system are described in PCT Application Serial No. US03/00473 entitled"Reserve Battery"filed on January 8,2003 and PCT Application Serial No. US03/17356 entitled"Method Of Manufacturing Metal Air Cell System"filed on June 2,2003, both of which are incorporated by reference herein.

Although the above referenced drawings and description refer to a system having a novel electrical/mechanical connect top cover, as detailed in the above referenced application (PCT Application Serial No. US/03/xxxxx, entitled"Liquid Seal and Electrical Connection Structure"filed on October 23,2003 and PCT Application Serial No. US/02/305585 entitled"Rechargeable and Refuelable Electrochemical Cell"field on September 26,2002), it is understood that the self-leveling features may be equally employed in the configuration of a conventional refuelable electrochemical cell system.

The features for the self-leveling system are common to various types of cells and they are not limited to how the anode is inserted, how mechanical connection between the anode and anode receiving structure is established, or how the electrical connection between the anode and cathode is established.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.